Water Quality Program

Permit Writer’s Manual

Revised December 2011

Publication no. 92-109
Publication and Contact Information

This report is available on the Department of Ecology’s website at 

www.ecy.wa.gov/biblio/92109.html

For more information contact:

Water Quality Program

P.O. Box 47696

Program Development Services Section 

Olympia, WA 98504-7696

Phone: 360-407-6600

Washington State Department of Ecology - www.ecy.wa.gov

o Headquarters, Olympia 360-407-6000

o Northwest Regional Office, Bellevue 425-649-7000

o Southwest Regional Office, Olympia 360-407-6300

o Central Regional Office, Yakima 509-575-2490

o Eastern Regional Office, Spokane 509-329-3400

If you need this document in a format for the visually impaired, call the Water Quality Program

at 360-407-6600. Persons with hearing loss can call 711 for Washington Relay Service. Persons 

with a speech disability can call 877-833-6341.
Water Quality Program

Permit Writer’s Manual

Prepared by:

Gary Bailey

Water Quality Program

Washington State Department of Ecology

Olympia, Washington

TABLE OF CONTENTS (December 2011)

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TABLE OF CONTENTS

TABLE OF CONTENTS................................................................................................. III

ACKNOWLEDGEMENTS.............................................................................................XII

NOTE TO PERMIT WRITERS .....................................................................................XIII

NOTE TO OTHER READERS .....................................................................................XIII

GLOSSARY................................................................................................................ G-1

CHAPTER I. INTRODUCTION ....................................................................................I-1

1. OBJECTIVES AND FUNCTIONS ..............................................................................................................1

2. FORMAT FOLLOWS PROCESS ...............................................................................................................2

2.1 Other References...................................................................................................................................2

3. SCOPE............................................................................................................................................................3

4. INSPECTIONS AND ENFORCEMENT.....................................................................................................3

5. NOT REGULATION.....................................................................................................................................3

6. A SHORT HISTORY LESSON....................................................................................................................4

7. THE CLEAN WATER ACT.........................................................................................................................5

8. TECHNOLOGY-BASED CONTROL.........................................................................................................6

9. WATER QUALITY BASED CONTROL....................................................................................................7

10. PERMIT WRITERS IMPLEMENT THESE LAWS AND REGULATIONS .......................................7

11. PERMIT TOOLS.........................................................................................................................................8

CHAPTER II. AN OVERVIEW OF THE PERMITTING PROCESS.............................II-1

1. WHAT TYPE OF WASTEWATER DISCHARGE PERMIT?..................................................................1

1.1 State Wastewater Discharge Permit........................................................................................................1

1.2 NPDES Wastewater Discharge Permit...................................................................................................1

1.3 General Wastewater Discharge Permit...................................................................................................2

1.4 Hydraulic Continuity ..............................................................................................................................2

2. WHAT IS A WASTEWATER DISCHARGE PERMIT? ...........................................................................2

3. THE PERMITTING PROCESS....................................................................................................................3

4. MODIFICATION OF PERMITS..................................................................................................................8

5. GENERAL PERMITS - NEW AND RENEWAL........................................................................................9

6. THE GENERAL PERMIT DEVELOPMENT PROCESS ......................................................................10

7. QA/QC PROCESS .......................................................................................................................................17

8. PERMITTEE REVIEW (also see Chapter XV, Section 4).......................................................................20

9. PUBLIC REVIEW.......................................................................................................................................20

10. EPA REVIEW............................................................................................................................................21

11. AN EXAMPLE PERMIT..........................................................................................................................21

12. PERMIT SHIELD POLICY .....................................................................................................................21
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13. CWA JURISDICTION ON TRIBAL LANDS ........................................................................................22

14. STATE AUTHORITY ON FOREST SERVICE LAND ........................................................................22

15. ANTIBACKSLIDING ...............................................................................................................................23

CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW.........................III-1

1. WHO NEEDS PERMITS..............................................................................................................................1

1.1 NPDES Permit Requirements for Non-discharging Facilities Which Have Zero Discharge 

Limitations in Effluent Limitation Guidelines.....................................................................................3

1.2 Independent Leaking Underground Storage Tank (LUST) Cleanup Sites ............................................4

1.3. Vehicle And Equipment Washing ........................................................................................................8

1.4. Petroleum Bulk Plants, SIC 5171 ..........................................................................................................8

2. APPLICATION FORMS FOR INDIVIDUAL PERMITS ........................................................................8

3. APPLICATION PROCESS ........................................................................................................................12

3.1 Analytical Requirements ......................................................................................................................16

3.2 Reviewing an Application ....................................................................................................................17

4. APPLICATION AND EXPIRED PERMITS ............................................................................................18

4.1 NPDES .................................................................................................................................................18

4.2 State......................................................................................................................................................19

5. APPLICATION FOR NEW PERMITS.....................................................................................................22

5.1 NPDES .................................................................................................................................................22

5.2 STATE..................................................................................................................................................22

6. TIME OF REAPPLICATION ....................................................................................................................22

7. CONFIDENTIALITY OF INFORMATION ............................................................................................22

8. DOMESTIC SEWAGE EXCLUSION.......................................................................................................23

9. OWNER/OPERATOR AGREEMENTS ...................................................................................................26

9.1. Ecology Must Review Agreements.....................................................................................................26

9.2 NPDES Permittee under Owner/Operator Agreement .........................................................................26

9.3 State Permittee under Owner/Operator Agreement ..............................................................................29

CHAPTER IV. DERIVING TECHNOLOGY-BASED EFFLUENT LIMITS..................IV-1

1. EFFLUENT LIMITATION GUIDELINES ................................................................................................2

1.1 A Summary of Some Treatment Standards as Currently Defined .........................................................3

1.2 Steps for Using Effluent Guidelines.......................................................................................................4

1.3 Multiple Processes..................................................................................................................................6

1.4 Mass vs. Concentration ..........................................................................................................................7

1.5 Some Solutions.......................................................................................................................................7

1.6 Outdated Effluent Guidelines.................................................................................................................8

1.7 Integrated Facilities..............................................................................................................................17

1.8 Converting Performance to Limits .......................................................................................................17

2. CASE-BY-CASE DERIVATION OF TECHNOLOGY-BASED EFFLUENT LIMITS.......................21

3. ALL KNOWN, AVAILABLE, AND REASONABLE METHODS OF TREATMENT (AKART)......26

3.1. A Summary of AKART......................................................................................................................26

3.2. AKART As Given In Law..................................................................................................................27

3.3. AKART As Given In Regulation .......................................................................................................28

3.4. AKART as State Treatment Standards...............................................................................................32

3.5. AKART As Defined By the Pollution Control Hearings Board (PCHB) And Other Courts .............32

3.6. Direct Definitions of AKART ............................................................................................................35

3.7. AKART Defined In Individual Permits..............................................................................................35
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3.8. AKART Versus Case-by-Case ...........................................................................................................36

3.9. Zero Discharge ...................................................................................................................................37

3.10. AKART For Pretreatment ................................................................................................................37

3.11. Engineering Analysis for All Known and Available ........................................................................37

3.12. Economic Tests Define Reasonable .................................................................................................38

4. ADJUSTMENT OF EFFLUENT LIMITS FOR AUTOCORRELATION ............................................72

CHAPTER V. MUNICIPAL EFFLUENT LIMITATIONS AND OTHER

REQUIREMENTS ...........................................................................................V-1

1. INTRODUCTION..........................................................................................................................................1

2. TECHNOLOGY-BASED WASTEWATER DISCHARGE STANDARDS .............................................3

3. ALTERNATIVE WASTEWATER DISCHARGE STANDARDS............................................................5

3.1 Conditions for Receiving Alternative Effluent Limitations....................................................................5

3.2 Trickling Filters.....................................................................................................................................6

3.3 Waste Stabilization Ponds.....................................................................................................................9

3.4 Facilities with Combined Sewers ........................................................................................................14

3.5 Facilities with Less Concentrated Influent Wastewater.......................................................................25

3.6 Substitution of CBOD5 For BOD5.......................................................................................................28

3.7 Defining Compliance with 85% Removal...........................................................................................30

3.8 Operation and Maintenance (O & M) Manual.....................................................................................32

3.9 Maintaining Adequate Capacity ...........................................................................................................34

3.10 Operator Certification.........................................................................................................................35

3.11 Loading Calculation for intermittent discharges.................................................................................36

4.1 The State Program...............................................................................................................................37

4.2 The Federal Program............................................................................................................................39

4.3 Delegation ............................................................................................................................................39

4.4 Overlap With Wastewater Permits .......................................................................................................39

CHAPTER VI. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE 

WATERS........................................................................................................VI-1

1. WATER QUALITY CRITERIA AND STANDARDS ...............................................................................1

1.1 The Water Quality Standards Define the Designated Uses and Incorporate Criteria ............................3

1.2 Conversion Factors and Translators for Metal Criteria .........................................................................5

1.3 Site-Specific Water Effect Ratio ...........................................................................................................6

2. THE POINT OF COMPLIANCE OF THE WATER QUALITY STANDARDS ................................6

2.1 General Considerations for Authorizing Mixing Zones .........................................................................7

3. PREDICTING IMPACTS AND DEFINING EFFLUENT LIMITS FOR NUMERIC CRITERIA ....16

3.1 The Water Quality Impact Of BOD And Nutrients.............................................................................16

3.2 Other Specific Pollutants - Conventional and Nonconventional .........................................................18

3.3 Deriving Effluent Limits for Toxic Pollutants, as Seasonal Limits and for Impaired Waters.............25

4. ANALYTICAL LEVELS ............................................................................................................................49

4.1 Introduction ..........................................................................................................................................49

4.2 Background Information.......................................................................................................................50

4.3 Implementation - NPDES and State Permits........................................................................................52

4.4 Choosing a Quantitation Level.............................................................................................................52

5. WHOLE EFFLUENT TOXICITY (WET)................................................................................................61

5.1 Permit Writer's Task Summary.............................................................................................................61

5.2 Introduction ..........................................................................................................................................61

5.3 The Purpose of Effluent Characterization ............................................................................................66
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5.4 Determining the Need for Effluent Characterization............................................................................66

5.5 Determining Compliance with WET Limits.........................................................................................67

5.6 Noncompliance, Transient Toxicity Reports, and TI/RE Plans............................................................69

5.7 Removal of WET Limits ......................................................................................................................71

5.8 Determining the Need for Rapid Screening Tests ................................................................................71

5.9 Technology-Based WET Limits...........................................................................................................72

5.10 Options for Permittees........................................................................................................................73

5.11 Species Selection for WET Testing....................................................................................................74

5.12 Rapid Screening Test Selection..........................................................................................................77

5.13 Samples for WET Testing ..................................................................................................................78

5.14 Managing Effluent Characterization Results......................................................................................80

CHAPTER VII. DERIVING WATER QUALITY-BASED EFFLUENT LIMITS FOR 

PROTECTION OF HUMAN HEALTH ...........................................................VII-1

1. WATER QUALITY CRITERIA - BACKGROUND..................................................................................1

2. IMPLEMENTATION - OVERVIEW..........................................................................................................6

3. SCREENING AND PRIORITIZATION .....................................................................................................7

4. THE REASONABLE POTENTIAL DETERMINATION ........................................................................8

4.1 Which Criteria? ......................................................................................................................................8

4.2 Effluent and Background Concentration ................................................................................................8

4.3 Mixing Zones .........................................................................................................................................8

4.4 Plant Design Flows...............................................................................................................................10

4.5 Critical Flow Conditions ......................................................................................................................10

4.6 Coefficient of Variation of Effluent Concentration.............................................................................11

4.7 Dilution Factor .....................................................................................................................................11

4.8 Statistical Confidence Level.................................................................................................................11

4.9 Background Data on Chemical Concentrations....................................................................................11

5. RESULTS OF THE REASONABLE POTENTIAL DETERMINATION.............................................15

5.1 Yes, a Reasonable Potential Exists to Exceed Water Quality Standards.............................................15

5.2 No, a Reasonable Potential Does Not Exist to Exceed Water Quality Standards................................16

5.3 The Result of the Reasonable Potential Determination is Ambiguous, or, "Can't Determine"............17

6. ANALYTICAL METHODS .......................................................................................................................17

CHAPTER VIII. DERIVING WATER QUALITY-BASED EFFLUENT LIMITATIONS 

FOR THE PROTECTION OF GROUND WATER QUALITY........................VIII-1

1. GROUND WATER CRITERIA AND STANDARDS ................................................................................1

1.1 Numeric Criteria.....................................................................................................................................1

2. De MINIMIS APPLICATION OF FOOD PROCESS WASTEWATER .................................................1

CHAPTER IX. DERIVING EFFLUENT LIMITS FOR THE PROTECTION OF 

AQUATIC SEDIMENTS .................................................................................IX-1

1. PERMIT WRITER'S TASKS.......................................................................................................................1

For permits to Puget Sound ..........................................................................................................................1

For permits to other marine waters...............................................................................................................2

For permits to low saline waters...................................................................................................................2

For permits to fresh water.............................................................................................................................2

2. THE SEDIMENT MANAGEMENT STANDARDS...................................................................................2

3. OVERVIEW OF THE PROCESS................................................................................................................7

3.1 Evaluation of the Potential for a Discharge to Impact Receiving Sediments (WAC 173-204-
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400(1)(a)).............................................................................................................................................8

3.2 Application for a SIZ (WAC 173-204-400(1)(b))................................................................................11

3.3 SIZ Eligibility Requirements (WAC 173-204-400(1)(c) and (f))........................................................11

3.4 Development of SIZ Specifications (WAC 173-204-400(1)(d),(e), and (g)) .....................................12

3.5 SIZ Monitoring and Maintenance Requirements (WAC 173-204-400(1)(i))......................................13

3.6 Public Notice and Landowner Notification Procedures (WAC 173-204-400(1)(h))...........................13

3.7 Renewal, Modification, and Elimination of Authorized SIZs Over Time (WAC 173-204-400(1)(j)) 14

3.8 Closure and Restoration of SIZs (WAC 173-204-400(1)(I))................................................................15

4. SCREENING-LEVEL EVALUATION OF POTENTIAL FOR SEDIMENT IMPACTS....................15

4.1 Initiation of Activities......................................................................................................................15

4.2 Narrative Evaluation of the Potential for Sediment Impacts ...............................................................20

4.3. Technical Evaluation of the Potential for Sediment Impacts.............................................................20

4.4 Alternative Procedures for the Technical Evaluation of the Potential for Sediment Impacts in 

Freshwater, low Salinity, and Non-Puget Sound Marine Environments............................................38

CHAPTER X. PRETREATMENT PROGRAM ............................................................X-1

1. OVERVIEW ...............................................................................................................................................1

1.1. Federal Pretreatment Rules..................................................................................................................1

1.2. Washington State’s rules for non-domestic wastewater ......................................................................2

1.3. Philosophy of Washington State’s Pretreatment Program ...................................................................3

2. NPDES PERMITS FOR POTWS: ...............................................................................................................4

2.1. Requiring a POTW to Develop a Pretreatment Program: ....................................................................5

2.2. NPDES Permit Conditions for Delegated Programs..........................................................................10

2.3. Requiring and Recognizing changes to Delegated Programs ............................................................10

2.4. NPDES Permit Conditions for Non-Delegated Programs..................................................................11

2.5. Pretreatment Related NPDES Permit Fact Sheet Language for POTWs...........................................12

3. STATE WASTE DISCHARGE PERMITS FOR NON-DOMESTIC WASTE......................................13

3.1. Overview of the Permitting Process...................................................................................................13

3.2. Pretreatment Standards ......................................................................................................................14

3.3. Other Pretreatment Requirements......................................................................................................16

3.4. State Waste Discharge Permit Fact Sheet Contents...........................................................................18

4. REGIONAL PRETREATMENT ENGINEER STAFF EXPERTISE AREAS......................................19

4.1. Conducting Industrial User Surveys..................................................................................................20

4.2. Developing “Technically Based” Local Limits .................................................................................21

4.3. Providing Model Pretreatment Ordinance Language.........................................................................22

4.4. Inspecting and Auditing Delegated Programs....................................................................................23

4.5. Reviewing Pretreatment Related Submittals from POTWs...............................................................24

4.6. Reviewing Pretreatment Permits........................................................................................................24

4.7. Providing Organized Pretreatment Related Training Events.............................................................24

CHAPTER XI. RECLAIMED WATER USE................................................................XI-1

1. LEARNING THE LANGUAGE...................................................................................................................1

1.1 Working Definitions:..............................................................................................................................1

1.2 Abbreviations and Acronyms.................................................................................................................4

2. STATUTORY REQUIREMENTS ...........................................................................................................4

2.1 Reclaimed Water Standards....................................................................................................................5

2.2 Industrial Process Reuse Water..............................................................................................................5

2.3 Water Resources Permitting ...................................................................................................................5

2.4Guidance for Coordinated Permits ..........................................................................................................6

2.5 Wetlands.................................................................................................................................................9
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2.6 Stormwater ...........................................................................................................................................10

2.7. Department of Health Provisions........................................................................................................10

3. THE PERMITTING PROCESS .............................................................................................................10

3.1. Ecology Water Quality Program Role ................................................................................................11

3.2. Department of Health Role.................................................................................................................12

3.3. Ecology Water Resources Program Role ...........................................................................................13

3.4 Fact Sheets and Documentation ...........................................................................................................19

3.5 Public Involvement...............................................................................................................................20

4. TREATMENT TECHNOLOGY REQUIREMENTS ..............................................................................20

4.1 Source Control and Pre-treatment ........................................................................................................20

4.2 Four Basic Classes................................................................................................................................20

4. 3 Distribution Line Chlorine Residual....................................................................................................22

4.4 Advanced Treatment Techniques.........................................................................................................22

4.5 Water Quality Technology Limits........................................................................................................23

4.6 Monitoring Requirements.....................................................................................................................27

5. DISTRIBUTION AND USE........................................................................................................................31

5.1 Use-Based Water Quality Limits..........................................................................................................31

5.2 Discharges from Distribution Maintenance..........................................................................................31

6. IRRIGATION...............................................................................................................................................32

6.1. Class of Reclaimed Water Required for Use. .....................................................................................32

6.2 Other Considerations for Irrigation Water Quality...............................................................................33

6.3 Incidental Site Runoff...........................................................................................................................36

6.4 Incidental Percolation and Ground Water Monitoring .........................................................................37

7. IMPOUNDMENTS......................................................................................................................................38

7.1. Class of Reclaimed Water Required for Use. .....................................................................................38

7.2 Relationship to Stormwater Ponds........................................................................................................38

7.3 Incidental Runoff from Impoundments ................................................................................................38

7.4 Releases from Reclaimed Water Ponds................................................................................................39

8. COMMERCIAL AND INDUSTRIAL USES ............................................................................................40

8.1. Class of Reclaimed Water Required for Use. ......................................................................................40

9. GROUND WATER RECHARGE BY SURFACE PERCOLATION .....................................................41

9.1 Water Quality Limitations....................................................................................................................42

9.2 Ground Water Recharge Criteria..........................................................................................................43

9.3 Additional Contaminants of Concern ...................................................................................................48

9.4 Ground Water Monitoring....................................................................................................................50

9.5 Blended Flows for Groundwater Recharge ..........................................................................................51

CHAPTER XII. ALTERNATIVES AND ADDITIONS TO NUMERICAL EFFLUENT 

LIMITS...........................................................................................................XII-1

1. GENERAL CONDITIONS ...........................................................................................................................1

1.1 The General Conditions for NPDES Permits ........................................................................................1

1.2 The General Conditions for State Permits...........................................................................................16

2. SPECIAL CONDITIONS............................................................................................................................19

3. POLLUTION PREVENTION AND BEST MANAGEMENT PRACTICES (BMPs)...........................20

3.1 Pollution Prevention .............................................................................................................................20

3.2 Best Management Practices..................................................................................................................21

3.3 Scope of BMPs....................................................................................................................................21

3.4 Minimum Requirements for the BMP Plan .........................................................................................23
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4. CERTIFIED OPERATORS AT INDUSTRIAL SITES WITH DOMESTIC WASTEWATER 

TREATMENT FACILITIES ..................................................................................................................36

XIII. MONITORING GUIDELINES............................................................................XIII-1

1. GENERAL CONSIDERATIONS OF A SELF-MONITORING PROGRAM.........................................4

1.1 Establish Monitoring Objectives ...........................................................................................................4

1.2 Parameters to Monitor ...........................................................................................................................5

1.3 Monitoring Frequency ...........................................................................................................................9

1.4. Baseline Monitoring Frequencies.......................................................................................................16

1.5 Special Monitoring Strategies ..............................................................................................................17

1.6 Sampling and Testing Methods............................................................................................................18

1.7 Determining the Sampling Location.....................................................................................................21

1.8 Quality Assurance/Quality Control ......................................................................................................22

1.9 Data Management.................................................................................................................................25

2. POTW MONITORING................................................................................................................................26

2.1 Influent and Effluent Monitoring of POTWs .......................................................................................27

2.2 Process Control Monitoring..................................................................................................................42

2.3 POTW Sludge Monitoring and Special Conditions.............................................................................69

2.4 Combined Sewer Overflows................................................................................................................70

2.5 Monitoring Bypasses............................................................................................................................71

3. INDUSTRIAL AND COMMERCIAL FACILITY MONITORING .......................................................71

3.1 Influent Monitoring .............................................................................................................................72

3.2 Effluent Monitoring..............................................................................................................................73

4. WET TESTING MONITORING ................................................................................................................74

4.1 Recommended Test Frequency for Characterization...........................................................................74

4.2 Sampling..............................................................................................................................................79

5. STORM WATER MONITORING..............................................................................................................79

5.1 Types of Storm Water Permits .............................................................................................................80

5.2 Wastewater Characterization for Industrial Storm Water.....................................................................82

5.3 Compliance Monitoring........................................................................................................................84

6. RECEIVING ENVIRONMENT MONITORING......................................................................................89

6.1 General Considerations for Monitoring Receiving Environments .......................................................90

6.2 Surface Water Monitoring ..................................................................................................................106

6.3 Sediment Monitoring..........................................................................................................................112

6.4 Crop/Soil/Vadose Monitoring ............................................................................................................112

6.5 Groundwater Monitoring....................................................................................................................113

6.6 Biological Surveys..............................................................................................................................113

6.7 Data Compatibility .............................................................................................................................113

7. SEDIMENT MONITORING....................................................................................................................113

7.1. General Types of Monitoring in the Sediment Source Control Process...........................................114

7.2 Monitoring Objectives........................................................................................................................115

7.3. Types of Monitoring Data .................................................................................................................116

7.4. Methods for Collecting Monitoring Data .........................................................................................120

7.5. Development of Appropriate Monitoring Requirements...................................................................130

7.6. Interpretation of Monitoring Results................................................................................................133

8. SUMMARY CHECKLIST........................................................................................................................135

CHAPTER XIV. FACT SHEETS AND DOCUMENTATION.................................... XIV-1

1. FEDERALLY REQUIRED FOR SELECTED PERMITS........................................................................1
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2. STATE REQUIREMENTS FOR ALL PERMITS .....................................................................................1

3. PUGET SOUND PLAN REQUIREMENTS ...............................................................................................2

4. FEDERALLY REQUIRED DETAILS ........................................................................................................3

5. FACT SHEET CONSIDERATIONS ...........................................................................................................3

6. FACT SHEET FORMATS............................................................................................................................4

CHAPTER XV. PUBLIC INVOLVEMENT................................................................ XV-1

1. SEPA ...............................................................................................................................................................1

2. PUBLIC NOTICE OF PERMIT ACTIONS ...............................................................................................2

3. PUBLIC NOTICE OF APPLICATION (PNOA)........................................................................................2

4. PERMITTEE REVIEW................................................................................................................................3

5. PUBLIC NOTICE OF DRAFT PERMIT (PNOD).....................................................................................4

6. DISTRIBUTION OF DRAFT AND FINAL PERMIT MATERIALS ......................................................4

7. PUBLIC INFORMATIONAL MEETINGS AND WORKSHOPS ...........................................................5

7.1. Informational Meetings Preceding Hearings.........................................................................................5

7.2. Public Notice of Informational Meetings ..............................................................................................6

8. HEARINGS ....................................................................................................................................................6

8.1. Public Notice of Hearing .......................................................................................................................6

8.2. Hearing Officer......................................................................................................................................7

9. PUBLIC NOTICE OF PERMIT ISSUANCE .............................................................................................7

10. PUBLIC NOTICES OF OTHER ACTIONS.............................................................................................7

11. WHEN TO GO BACK TO PUBLIC NOTICE WITH A REVISED DRAFT PERMIT.......................8

CHAPTER XVI. APPEALS AND VARIANCES ...................................................... XVI-1

1. APPEAL OF THE FINAL PERMIT TO THE POLLUTION CONTROL HEARINGS BOARD 

(PCHB)........................................................................................................................................................1

1.1 The PCHB .............................................................................................................................................1

1.2 Appeal Process......................................................................................................................................1

2. VARIANCES..................................................................................................................................................3

2.1 The Federal Variances...........................................................................................................................3

2.2 The State Requirements..........................................................................................................................5

REFERENCES................................................................................................................ 1

CHAPTER I. .......................................................................................................................................................1

CHAPTER II.......................................................................................................................................................1

CHAPTER IV......................................................................................................................................................1

CHAPTER V .......................................................................................................................................................1

CHAPTER VI......................................................................................................................................................2

CHAPTER VIII ..................................................................................................................................................3

CHAPTER IX......................................................................................................................................................4

CHAPTER XIII. .................................................................................................................................................7

APPENDIX 1.........................................................................................................APP1-1

1. INDEX TO NPDES REGULATIONS..........................................................................................................1

APPENDIX 4.........................................................................................................APP4-1
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I. AUTOCORRELATION ................................................................................................................................1

II. NEW SOURCE ...........................................................................................................................................10

APPENDIX 6.........................................................................................................APP6-1

1. GUIDANCE FOR CONDUCTING MIXING ZONE ANALYSES...........................................................1

1.1 SELECTING VALUES FOR MODEL INPUT PARAMETERS.........................................................1

1.2 UNDERSTANDING INITIAL DILUTION THEORY ........................................................................9

1.3 CHOOSING AN INITIAL DILUTION MODEL...............................................................................13

1.4 UNDERSTANDING FARFIELD THEORY......................................................................................21

1.5 CHOOSING A FARFIELD MODEL .................................................................................................22

1.6 CONDUCTING A DYE STUDY .......................................................................................................25

1.7 REFERENCES....................................................................................................................................32

2.0 SPREADSHEETS FOR WATER QUALITY-BASED NPDES PERMIT CALCULATIONS..........37

2.1. DETAILED DESCRIPTIONS AND USER INSTRUCTIONS..........................................................38

2.2 GUIDELINES FOR USING TSDCALC.XLW ..................................................................................49

3. AN ALTERNATE METHOD FOR ESTIMATING UPPER QUANTILES ..........................................54

4. GUIDANCE ON THE APPROPRIATE SIZE MIXING ZONE FOR A UNIQUE OUTFALL 

CONFIGURATION .................................................................................................................................56

5. DERIVING THE 7Q10 HIGH FLOW (HF) AND THE DESIGN SPILL..............................................57

5.1. Guidelines for Deriving the 7QHF .....................................................................................................57

5.2. Determining Design Spill for Gas Abatement....................................................................................58

APPENDIX 13.....................................................................................................APP13-1

1. SUPPORTING STATISTICAL STUDY FOR PERFORMANCE-BASED REDUCTION OF 

MONITORING (from EPA, April 96)......................................................................................................1

2. DETERMINING THE NUMBER OF SAMPLES REQUIRED FOR COMPLIANCE 

MONITORING ..........................................................................................................................................9
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Acknowledgements

This manual represents an effort by the Water Quality Program to improve its point source 

pollution control program. Numerous people have contributed to the manual.

Mike Herold, Dewey Weaver, Ed O'Brien, Ray Henneke, Randy Marshall, Cheryl Neimi, 

Carl Tonge, Foroozan Labib, Kathy Cupps, and Norm Glenn have contributed directly by writing 

parts of the manual. 

Many of the regional and industrial section permit staff were involved in a manual workgroup 

that formulated direction and processes in the manual.

An advisory group representing those with an active interest in the permit program helped to 

provide direction for the first edition of this manual. The members of this group are:

Roger Von Gohren, Association of Washington Business, 

Mike Meeuwsen, Texaco 

Andre Caron, National Council for Air and Stream Improvement

Vallana Piccolo, Puget Sound Water Quality Authority

Lincoln Loehr, NW Pulp and Paper Association

Dan Cheney, Bay Center Mariculture

Dan Curry, City of Wenatchee

Diane Lefevre, SEH America

Jack Lilja, DSHS Shellfish Program

John Magill, City of Stanwood

Jim Matsuyama, Northeast Tri-County Health District

Mary Lou Mills, Department of Fisheries

Pat Romberg, METRO

M. Pat Wennekens, Sierra Club

Kerrie Schurr, EPA

Miles Beach, City of Ocean Shores

Paul Schissler, Swinomish Tribal Community

Darrell Turner, Washington Farm Bureau

Stephen Vincent, Columbia Analytical Services

Many support staff in the Program Development Services Section have assisted with typing and 

composition.

Everyone's efforts are appreciated.

Gary C. Bailey

Project Leader
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Note to Permit Writers

There are visuals of a computer throughout the text of the manual. This indicates that there is 

some computer-related assistance available such as model permit language, model fact sheet 

language or spreadsheets to assist in calculations. The model language 

and spreadsheets are available on the network or from the Program 

Development Services Section.

The manual is designed to be used in a binder and is formatted to 

accommodate revisions. The current version of the manual will be 

noted as the version date on the cover page and the Table of Contents 

header. 

Please direct any comments or requests for the manual to the Program Development Services 

Section.

Note to Other Readers

This manual is a working document for people in the Department of Ecology who write 

wastewater discharge permits. It is available to the public on the Ecology Web site. The manual 

will be updated periodically.

Appendices numbers reflect the related chapter. For example, Appendix 6 covers mixing zones 

and other topics which supplement the information in Chapter VI. Water Quality-Based Effluent 

Limits For Surface Waters.

The Department of Ecology is interested in your comments on this manual. Please address your 

comments to PERMIT WRITERS MANUAL, DEPT OF ECOLOGY, PO BOX 47696, 

OLYMPIA WA 98504-7696.

Comments may also be posted at www.ecy.wa.gov/programs/wq/comments.html
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GLOSSARY

DEFINING THE TERMS OF WASTEWATER PERMITS

401(a) CERTIFICATION - A requirement of Section 401(a) of the Clean Water Act that 

all federally issued permits be certified by the state in which the permit is issued. The 

state certifies that the proposed permit will comply with state water quality standards.

ACEC (ACUTE CRITICAL EFFLUENT CONCENTRATION) - The maximum 

concentration of effluent during critical conditions at the boundary of the zone of 

acute criteria exceedance assigned in the permit. If no zone of acute criteria 

exceedance is specified the acute critical effluent concentration shall be one hundred 

percent effluent.

ACUTE TOXICITY - The lethal effect of a compound on an organism that occurs in a 

short period of time, usually 48 to 96 hours.

ACUTE TOXICITY TEST - A toxicity test with the death of test organisms as the 

measured response.

AET (APPARENT EFFECTS THRESHOLD) - For a given quality-assured data set 

approved by the department, the highest sediment concentration of an individual 

chemical contaminant which is not associated with statistically significant biological 

effects (proposed WAC 173-204-020).

AKART - Acronym for "all known available and reasonable methods"..."to prevent and 

control"..."pollution" (RCW 90.48.010, RCW 90.48.520). (see Chapter IV)

ANTI-BACKSLIDING - A provision in the Federal Regulations (40 CFR 122.44) which 

says a reissued permit must be as stringent as the previous permit with some exceptions.

AVERAGE MONTHLY DISCHARGE LIMITATION - The highest allowable average 

of "daily discharges" over a calendar month. Calculated as the sum of all daily 

discharges measured during a calendar month divided by the number of daily 

discharges measured during that month (40 CFR 122.2).
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AVERAGE WEEKLY DISCHARGE LIMITATION - The highest allowable average of 

"daily discharges" over a calendar week. Calculated as the sum of all daily 

discharges measured during a calendar week divided by the number of daily 

discharges measured during that week (40 CFR 122.2). Applicable only to 

municipal discharges.

BAT (BEST AVAILABLE TECHNOLOGY ECONOMICALLY ACHIEVABLE) - The 

wastewater treatment technology required to control toxic pollutants. Required to be 

in place by July 1, 1984, however, EPA has not completed the guidelines for all 

industries.

BCT (BEST CONVENTIONAL POLLUTANT CONTROL TECHNOLOGY) - This 

was the second step in defining treatment technology for conventional pollutants. A 

candidate technology must pass 2 cost tests which compare industrial costs to 

municipal costs of treatment. BCT was to be in place by July 1, 1984, but EPA did 

not complete guidelines for all industries.

BIOSOLIDS - Biosolids is municipal sewage sludge that meets standards for application 

to the land.

BOILER PLATE LANGUAGE - See GENERAL CONDITIONS.

BMP (BEST MANAGEMENT PRACTICE) - Permit condition used in place of or in 

conjunction with effluent limits to prevent the discharge of pollutants. BMPs may 

include schedules of activities, prohibitions of practices, maintenance procedures, 

treatment requirements, operating procedures and practices.

BOD (BIOCHEMICAL OXYGEN DEMAND) - The quantity of substances present in a 

water or wastewater that utilizes oxygen to decompose. The test for BOD is to put a 

sample of water or wastewater in a sealed bottle with sewage bacteria and measure 

how much oxygen is used in 5 days.

BPJ (BEST PROFESSIONAL JUDGMENT) - The highest quality technical opinion 

developed by permit writer after consideration of all reasonably available and 

pertinent data or information which forms the basis for the terms and conditions of 

an NPDES permit. BPJ may also be called BEJ (Best Engineering Judgment). 

Authorized by Section 402(a)(1)(B) of the Clean Water Act. 
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BPT (BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY 

AVAILABLE) - The first step of treatment technology identified by EPA for 52 

categorical industries. The technology was identified by surveying the treatment 

technology in use and defining the best average performance. See section 

301(b)(1)(A) of CWA.

BYPASS - The intentional diversion of waste streams from any portion of a treatment 

facility.

CCEC (CHRONIC CRITICAL EFFLUENT CONCENTRATION) - The maximum 

concentration of effluent during critical conditions at the boundary of the mixing 

zone assigned in the permit. Where no mixing zone is specified, the chronic critical 

effluent is one hundred percent effluent.

CERTIFICATION, 401(a) - See 401(a) CERTIFICATION.

CFR (CODE OF FEDERAL REGULATIONS) - A codification of the general and 

permanent rules published in the Federal Register by the Executive departments and 

agencies of the Federal Government. Environmental regulations are found in Title 40.

CHRONIC TOXICITY TEST - A toxicity test which measures a sublethal effect such as 

failed fertilization, development, growth, or reproduction. Organism survival is also 

a measured endpoint in some chronic toxicity tests.

COD (CHEMICAL OXYGEN DEMAND) - A measure of the decomposable substances 

in water or wastewater which uses a chemical oxidant instead of bacteria as in the 

BOD test.

COMBINED SEWER OVERFLOW (CSO) - The event during which excess combined 

sewage flow caused by inflow is discharged from a combined sewer, rather than 

conveyed to the sewage treatment plant because either the capacity of the treatment 

plant or the combined sewer is exceeded.

COMPLIANCE SCHEDULE - A schedule of remedial measures included in a permit or 

an enforcement order, including an enforceable sequence of actions or operations 

leading to compliance with an effluent limitation, other limitation, prohibition, or 

standard (CWA 502, 40 CFR 122.47).
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CONVENTIONAL POLLUTANTS - Pollutants typical of municipal sewage and defined 

by Federal Regulation (40 CFR 401.16) as BOD, total suspended solids, fecal 

coliform, pH, and oil/grease.

CRITERIA - The numeric values and the narrative standards that represent contaminant 

concentrations which are not to be exceeded in the receiving environmental media 

(surface water, ground water, sediment) to protect beneficial uses.

CRITICAL CONDITION - The time during which the combination of receiving water 

and waste discharge conditions have the highest potential for causing toxicity in the 

receiving water environment. This situation usually occurs when the flow within a 

water body is low, thus, its ability to dilute effluent is reduced.

DAILY DISCHARGE - The discharge of a pollutant measured during any 24-hour period 

that reasonably represents a calendar day for purposes of sampling. For pollutants 

with limitations expressed in units of mass, the daily discharge is calculated as the 

total mass of the pollutant discharged during the day. For pollutants with limitations 

expressed in other units of measurement, the daily discharge is calculated as the 

average measurement of the pollutant throughout the day (40 CFR 122.2).

DEVELOPMENT DOCUMENT - A document prepared during the development of 

effluent guidelines by EPA which explains the methodology and data which was 

used to develop the guidelines.

DETECTION LIMIT (DL) - See METHOD DETECTION LIMIT.

DILUTION FACTOR - A measure of the amount of mixing of effluent and receiving 

water that occurs at the boundary of the mixing zone. Expressed as the inverse of the 

effluent fraction e.g., a dilution factor of 16 means the effluent comprises 6.25% by 

volume and the receiving water 93.75% at the compliance boundary or volume 

restriction (DF = 1/.0625). The applicable dilution factor is the minimum of 

volume/volume fraction or effluent concentration at the distance boundary.

DILUTION ZONE - See MIXING ZONE.

DISCRETE SAMPLE - A single sample of wastewater taken at neither set time nor flow. 

Also known as a grab sample or single sample.
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DMR (DISCHARGE MONITORING REPORT) - A report submitted by a permittee, 

(usually monthly or quarterly) which gives the results of the effluent monitoring tests 

performed.

Do. or do. - Within the effluent limits sections of 40 CFR means ditto or the same as 

above.

DRAFT PERMIT - A document which indicates a decision to issue, deny, modify, 

revoke and reissue, terminate or reissue a permit. Usually is in the form of a permit 

and indicates a decision to issue, reissue, or modify a permit.

EARLY WARNING VALUES - Act as a trigger in the groundwater standards to detect 

increasing contaminant concentrations prior to the degradation of a beneficial use.

EFFLUENT LIMITATION - Any restriction established by a permitting authority on 

quantities, rates, and concentrations of chemical, physical, biological pollutants 

discharged to waters of the state.

ENFORCEMENT LIMITS - The values assigned by the groundwater standards to a 

contaminant for the purposes of regulation. This limit assures that a criterion will 

not be exceeded.

EPA EFFLUENT GUIDELINES - (see Chapter IV of this Manual).

EXCURSIONS - Violations of effluent limits or water quality standards.

FACT SHEET - A document prepared and issued with every permit which summarizes 

the activities and decisions on the permit and tells how the public may comment (40 

CFR 124.8, 124.56).

FR (FEDERAL REGISTER) - The periodical of the U.S. government in which draft and 

final regulations are published.

GENERAL PERMIT - A permit to regulate storm water point sources or other category 

of point sources. A general permit is developed for a category of dischargers and is 

not specifically tailored for an individual discharger (40 CFR 122.28).

INDIRECT DISCHARGER or INDUSTRIAL USER - A discharger of wastewater to the 

sanitary sewer which is not sanitary wastewater or is not equivalent to sanitary 

wastewater in character.
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INDUSTRIAL WASTEWATER - Water or liquid-carried waste from industrial or 

commercial processes, as distinct from domestic wastewater. These wastes may 

result from any process or activity of industry, manufacture, trade or business, from 

the development of any natural resource, or from animal operations such as feed lots, 

poultry houses, or dairies. The term includes contaminated storm water and, also, 

leachate from solid waste facilities.

INSPECTION, COMPLIANCE - WITHOUT SAMPLING - A site visit for the purpose 

of determining the compliance of a facility with the terms and conditions of its 

permit or with applicable statutes or regulations. The minimum requirements are 

specified in the Compliance Inspection Checklist (August 15, 1996).

INSPECTION, COMPLIANCE - WITH SAMPLING - Similar to INSPECTION, 

COMPLIANCE - WITHOUT SAMPLING but includes as a minimum sampling and 

analysis for all parameters with permit limits for the purpose of ascertaining 

compliance with those limits. For municipal facilities this includes sampling of the 

influent to determine compliance with the 85% removal requirement. Additional 

sampling for other parameters may also be conducted.

INSPECTION, COMPLIANCE FOLLOW-UP - An inspection for the main purpose of 

verifying that a compliance issue required by a previous action (inspection, NOC, 

order) has been completed or initiated.

INSPECTION, COVERAGE - An inspection of an unpermitted facility for the purpose 

of determining if a permit is required or an inspection of a permitted facility to 

determine whether permit termination is appropriate.

INSPECTION, MULTIMEDIA COMPLIANCE - An INSPECTION, COMPLIANCE -

WITHOUT SAMPLING or an INSPECTION, COMPLIANCE - WITH SAMPLING 

which is conducted on a metals mining facility that includes an assessment of dam 

safety and air permit compliance in accordance with the multimedia inspection 

checklist.

INSPECTION, OPERATOR OUTREACH - An inspection for the purpose of providing 

assistance to municipal treatment plant operators conducted by a Technical 

Assistance Officer designated under RCW 43.21A.085.
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INSPECTION, OPERATION AND MAINTENANCE - A scheduled on-site visit to a 

sewage treatment plant to review operations, record keeping, personnel information 

and to make visual observations on the condition of a plant and its discharge. Any 

documented operations deficiencies will be noted and used to provide a basis for 

making recommendations for future operation and maintenance programs and 

activities at the plant.

INSPECTION, PRETREATMENT AUDIT - An audit of a municipal treatment facility 

and system for municipalities that have been delegated pretreatment program 

responsibilities. Conducted at least once every five years. The primary purposes are 

to determine compliance with the requirements of the municipalities’ approved 

program and to assess the need for program improvements. Audits are conducted 

using EPA’s “Control Authority Pretreatment Audit Checklist and Instruction.”

INSPECTION, PRETREATMENT COMPLIANCE - An annual inspection of a 

municipal treatment facility and system for municipalities that have been delegated 

pretreatment program responsibilities. The primary purpose is to determine 

compliance with the requirements of the municipalities’ approved pretreatment 

program. Inspections are conducted using the PCT Checklist and EPA’s “Guidance 

for Conducting a Pretreatment Compliance Inspection.”

INSPECTION, TECHNICAL ASSISTANCE VISIT - An inspection on a permitted 

facility for the sole purpose of providing compliance assistance to the permittee and 

where the permittee and the inspector have agreed to this purpose prior to or at the 

initiation of the inspection.

INTERFERENCE - A discharge which, alone or in conjunction with a discharge or 

discharges from other sources, both:

Inhibits or disrupts the POTW, its treatment processes or operations, or its sludge 

processes, use or disposal; and,

Therefore is a cause of a violation of any requirement of the POTW's NPDES permit 

(including an increase in the magnitude or duration of a violation) or of the 

prevention of sewage sludge use or disposal in compliance with the following 

statutory provisions and regulations or permits issued there under (or more stringent 

State or local regulations): Section 405 of the Clean Water Act, the Solid Waste 

Disposal Act (SWDA) (including title II, more commonly referred to as the Resource 

Conservation and Recovery Act (RCRA), and including State regulations contained 

in any State sludge management plan prepared pursuant to subtitle D of the SWDA), 

sludge regulations appearing in 40 CFR Part 507, the Clean Air Act, the Toxic 

Substances Control Act, and the Marine Protection, Research and Sanctuaries Act.
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INTEGRATED FACILITY - A primary industry with operations covered by more than 

one subcategory of operation.

LOAD ALLOCATION (LA) - Within a TMDL, the allocation for the nonpoint sources 

of a pollutant.

LOCAL LIMITS - Conditional discharge limits imposed by municipalities upon 

dischargers to their sewage treatment system.

MAJOR FACILITY (PERMIT) - A facility discharging to surface water with an EPA 

rating score of > 80 points based on such factors as flow volume, toxic pollutant 

potential, and public health impact. EPA reviews these major NPDES permits 

during issuance and tracks compliance with the permits.

MAXIMUM DAILY DISCHARGE LIMITATION - The highest allowable daily 

discharge of a pollutant measured during a calendar day or any 24-hour period that 

reasonably represents the calendar day for purposes of sampling. The daily 

discharge is calculated as the average measurement of the pollutant over the day (40 

CFR 122.2).

MCL (MAXIMUM CONTAMINANT LEVEL) - are federally promulgated by the 

Environmental Protection Agency. These are enforceable health-based standards,

which means the maximum permissible level for a contaminant in ground water. 

These values reflect the effect of certain risk management factors such as laboratory 

confidence limits and economics.

MCLG (MAXIMUM CONTAMINANT LEVEL GOAL) - are health goals for drinking 

water which are set at a level at which no known or anticipated adverse effects on the 

health of persons should occur and which allows for an adequate margin of safety. 

These limits do not take into account treatment technology and economics as the 

MCL's do.

MDL (METHOD DETECTION LIMIT) - The minimum concentration of a substance 

that can be measured and reported with 99% confidence that the analyte 

concentration is greater than zero and is determined from analysis of a sample in a 

given matrix containing the analyte. (40 CFR Part 136, Appendix B)

ALSO GIVEN AS:

Detection Limit (DL): Smallest measured amount or concentration of

analyte in a sample that gives rise to a Type I error tolerance of alpha under
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the null hypothesis that the true amount or concentration of analyte in the

sample is equal to that of a blank. (The alternative hypothesis is that the

true amount or concentration of analyte is greater than that of a blank).

Detection Limit (DL): The minimum observed result such that the lower

100 (1- α) % confidence limit on the result is greater than the mean of the

method blanks. (Report of the Federal Advisory Committee on Detection and 

Quantitation Approaches and Uses in Clean Water Act Programs Submitted to the

US Environmental Protection Agency December 2007)

MGD (MILLION GALLONS PER DAY) - A unit of flow commonly used for 

wastewater discharges. One MGD is equivalent to 1.547 cubic feet/second.

MINIMUM LEVEL OF QUANTITATION (ML) – See QUANTITATION LEVEL

MINOR PERMIT - Any NPDES individual permit which is not a MAJOR PERMIT.

MIXING ZONE - An area or a volume fraction of the receiving water, specified in a 

permit, which surrounds an effluent discharge point. This area is not required to 

meet numeric water quality criteria but must allow passage of aquatic organisms and 

not upset the ecological balance of the receiving water. The mixing zone 

specifications and conditions for authorization are given in WAC 173-201A.

NEW DISCHARGER – See 40 CFR 122.2

NEW SOURCE - Any building, structure, facility, or installation from which there is or 

may be a discharge of pollutants, the construction of which commenced:

(a) After promulgation of standards of performance under section 306 of CWA 

which are applicable to such source, or

(b) After proposal of standards of performance in accordance with section 306 of 

CWA which are applicable to such source, but only if the standards are 

promulgated in accordance with section 306 within 120 days of their proposal 

(40 CFR 122.2).

NOEC (NO OBSERVED EFFECT CONCENTRATION) - The highest measured 

continuous concentration of an effluent or a toxicant that causes no observed effect 

on a test organism.

NONCONVENTIONAL POLLUTANTS - Any pollutants which are not defined as 

CONVENTIONAL POLLUTANTS or TOXIC POLLUTANTS. Includes pollutants 

such as COD, nitrogen, phosphorus, and fluoride.
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NPDES - National Pollutant Discharge Elimination System (Section 402 of the Clean 

Water Act). Permits issued under Section 402 of the Clean Water Act. The federal 

wastewater permitting system for discharges to navigable waters. The authority for 

issuing these permits has been delegated to the State. NPDES permits issued by 

Washington permit writers are NPDES/state permits issued under both federal and 

state law.

NSPS (NEW SOURCE PERFORMANCE STANDARDS) - Effluent limitations that

apply to those dischargers that qualify as new sources under 40 CFR 122.2 and 

122.29.

PARTIES OF RECORD - People who have indicated an interest in a particular permit 

during the public notice of application (PNOA) or public notice of draft (PNOD) and 

are kept informed of progress of the permit and future permit actions.

PASS THROUGH - A discharge which exits the POTW into waters of the State in 

quantities or concentrations which, alone or in conjunction with a discharge or 

discharges from other sources, is a cause of a violation of any requirement of the 

POTW's NPDES permit (including an increase in the magnitude or duration of a 

violation), or which is a cause of a violation of State water quality standards.

PCHB (POLLUTION CONTROL HEARINGS BOARD) - A 3-member board appointed 

by the governor to hear and decide appeals of Ecology's permits and orders. See 

Chapter XVI of this manual and Chapter 371-08 WAC.

PERMIT - An authorization, license, or equivalent control document issued by EPA or an 

approved state to implement the requirements of 40 CFR 122.2 and Parts 123 and 

124. Permit includes any NPDES GENERAL permit. Permit does not include any 

proposed or draft permit which has not yet been the subject of public comment or 

EPA review, if necessary.

PERMIT, WASTEWATER DISCHARGE - A document prepared by a permitting 

authority (Federal Government, State Government, Local Government) which limits 

the pollutants to be discharged by the holder of the permit (Permittee).

pH - A measure of the acidity of water or wastewater. A pH of 7 is neutral, a pH less 

than 7 is acidic, and a pH greater than 7 is basic.
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POINT SOURCE - Any discernible, confined, and discrete conveyance, including but not 

limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fixture, container, 

rolling stock, concentrated animal feeding operation, vessel, or other floating craft 

from which pollutants are or may be discharged. This term does not include 

agricultural stormwater discharges and return flows from irrigated agriculture. (See 

40 CFR 122.3 for exclusions)

POLLUTANT - Dredged soil, solid waste, incinerator residue, sewage, garbage, sewage 

sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, 

wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal and 

agricultural waste discharged into water.

POLLUTANT, NON-CONSERVATIVE - Pollutants that are mitigated by natural 

biodegradation or other environmental decay or removal processes in the receiving 

stream after in-stream mixing and dilution have occurred.

POLLUTION - Contamination, or other alteration of the physical, chemical or biological 

properties, of any waters of the state, including change in temperature, taste, color, 

turbidity, or odor of the waters, or such discharge of any liquid, gaseous, solid, 

radioactive, or other substance into any waters of the state as will or is likely to 

create a nuisance or render such waters harmful, detrimental or injurious to the 

public health, safety or welfare, or to domestic, commercial, industrial, recreational, 

or other legitimate beneficial uses, or to livestock, wild animals, birds, fish or other 

aquatic life.

POLLUTION PREVENTION - Source reduction; or protection of natural resources by 

conservation; or increased efficiency in the use of raw materials, energy, water or 

other resources.

POTENTIAL SIGNIFICANT INDUSTRIAL USER--A potential significant industrial 

user is defined as an Industrial User which does not meet the criteria for a Significant 

Industrial User, but which discharges wastewater meeting one or more of the 

following criteria:

a. Exceeds 0.5 % of treatment plant design capacity criteria and discharges <25,000 

gallons per day or;

b. Is a member of a group of similar industrial users which, taken together, have the 

potential to cause pass through or interference at the POTW (e.g., facilities which 

develop photographic film or paper, and car washes).
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The Department may determine that a discharger initially classified as a potential 

significant industrial user should be managed as a significant industrial user.

POTW (PUBLICLY OWNED TREATMENT WORKS) - A sewage treatment plant and 

the collection system (40 CFR 122.2).

PQL (PRACTICAL QUANTIFICATION LIMIT) - is the lowest level that can be 

reliably achieved within specified limits of precision and accuracy during routine 

laboratory operating conditions.

PRECURSOR - A substance present in effluent that is not toxic in its present form (not 

listed). However, a precursor could change into or react to form a toxic compound.

PRETREATMENT - The treatment of wastewater to remove or reduce the concentration 

of pollutants prior to discharge to a municipal sewage system. Pretreatment may 

denote a formal program (PRETREATMENT PROGRAM) which allows a 

municipality to issue permits for discharges to its system under Federal and State 

authority.

PRIMARY INDUSTRY CATEGORIES - A group of 34 industry groups for which EPA 

has or will develop effluent guidelines (40 CFR Part 122 Appendix A).

PRIORITY POLLUTANT (TOXIC POLLUTANT) - A group of chemicals specifically 

listed in Federal Regulations and with priority for regulatory control (40 CFR 

401.15).

PROCESS CONTROL MONITORING - An internal program whereby the permittee 

performs intermediate checks on the plant's operations to assess the efficiency of the 

process.

PROCESS WASTEWATER - Any water which, during manufacturing or processing, 

comes into direct contact with, or results from, the production or use of any raw 

material, intermediate product, finished product, byproduct, or waste product.

PROPOSED PERMIT - A State NPDES permit prepared after the close of the public 

comment period (and, when applicable, any public hearing and administrative 

appeals) which is sent to EPA for review before final issuance by the State.

A PROPOSED permit is not a DRAFT permit (40 CFR 122.2).
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PSES (PRETREATMENT STANDARDS EXISTING SOURCE) - Effluent limitations 

that apply to existing pretreatment dischargers.

PSNS (PRETREATMENT STANDARDS NEW SOURCE) - Effluent limitations that 

apply to pretreatment dischargers qualifying as new sources under 40 CFR 122.2. 

and 122.29.

QUANTITATION LEVEL (QL) also known as Minimum Level of Quantitation (ML) -

The lowest level at which the entire analytical system must give a recognizable 

signal and acceptable calibration point for the analyte. It is equivalent to the 

concentration of the lowest calibration standard, assuming that all method-specified 

sample weights, volumes, and cleanup procedures have been employed. The QL is 

calculated by multiplying the MDL by 3.18 and rounding the result to the number 

nearest to (1, 2, or 5) x 10n

, where n is an integer. (64 FR 30417).

ALSO GIVEN AS: 

The smallest detectable concentration of analyte greater than the Detection Limit 

(DL) where the accuracy (precision & bias) achieves the objectives of the intended 

purpose. (Report of the Federal Advisory Committee on Detection and Quantitation 

Approaches and Uses in Clean Water Act Programs Submitted to the US 

Environmental Protection Agency December 2007)

SCHEDULE OF COMPLIANCE - See COMPLIANCE SCHEDULE.

SECONDARY STANDARDS - are numeric criteria within the groundwater standards 

designed to protect the public welfare. Limits established for those constituents will 

not adversely affect human health, but may affect the taste or odor of the water or 

cause discoloration of laundry or plumbing fixtures. Secondary standards are 

established for: chloride, color, copper, corrosivity, fluoride, foaming agents, iron, 

manganese, odor, pH, sulfate, total dissolved solids (TDS) and zinc.

SEDIMENT QUALITY STANDARDS - These standards identify sediment chemical 

concentration criteria, and biological toxicity criteria which correspond to no 

observable acute or chronic adverse effects on biological resources, and which do not 

pose a significant health threat to humans. The standards are used as a basis for 

identification of surface sediments that exceed these standards, and for limiting toxic 

discharges to waters of the state (WAC 173-204-010).

SELF-MONITORING PROGRAM - A program whereby a permittee is required through 

the NPDES permit system to maintain records and to report periodically on the 
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amount and nature of the waste components in the effluent. The required 

information obtained by the Permittee’s self-monitoring program is reported to the 

permitting agency using a DISCHARGE MONITORING REPORT (DMR) on a 

regular schedule delineated in the permit.

SEPA (STATE ENVIRONMENTAL POLICY ACT) - A state law which requires an 

examination of the environmental effects of development projects. (RCW 43.21, 

Chapter 197-10 WAC)

SIGNIFICANT INDUSTRIAL USER (SIU) - 1) All industrial users subject to 

Categorical Pretreatment Standards under 40 CFR 403.6 and 40 CFR Chapter I, 

Subchapter N; and;

2) Any other industrial user that: discharges an average of 25,000 gallons per day or 

more of process wastewater to the POTW (excluding sanitary, noncontact cooling, 

and boiler blow-down wastewater); contributes a process wastestream that makes up 

five percent or more of the average dry weather hydraulic or organic capacity of the 

POTW treatment plant; or is designated as such by the Control Authority on the 

basis that the industrial user has a reasonable potential for adversely affecting the 

POTW's operation or for violating any pretreatment standard or requirement (in 

accordance with 40 CFR 403.8(f)(6)).

Upon finding that the industrial user meeting the criteria in paragraph 2, above, has 

no reasonable potential for adversely affecting the POTW's operation or for violating 

any pretreatment standard or requirement, the Control Authority may at any time, on 

its own initiative or in response to a petition received from an industrial user or 

POTW, and in accordance with 40 CFR 403.8(f)(6), determine that such industrial 

user is not a significant industrial user.

SINGLE SAMPLE - (See DISCRETE SAMPLE).

SLUDGE – Solids produced during wastewater treatment.

SOURCE REDUCTION - Any practice which eliminates or reduces the amount or use of 

hazardous substances, pollutants or contaminants that enter a waste stream or are 

released into the environment, including fugitive emissions, prior to recycling, 

treatment or disposal, and thereby reduces adverse public health and environmental 

effects associated with the release of such substances, pollutants or contaminants.
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SANITARY SEWER OVERFLOW (SSO) - Discharge of untreated sewage from a 

separate sanitary sewer collection system prior to the headworks of a sewage 

treatment plant.

STATE WASTE DISCHARGE PERMIT - A wastewater discharge permit issued under 

State authority (Chapter 90.48 RCW) to control the discharge of pollutants to waters 

of the State. Generally issued for discharges to ground water and for industrial 

discharges to a municipal sewage system when that municipal system does not have 

a delegated pretreatment program.

STATE WATERS - Lakes, rivers, ponds, streams, inland waters, underground waters, 

salt waters, and all other surface waters and watercourses within the jurisdiction of 

the state of Washington

STORMWATER - That portion of precipitation that does not naturally percolate into the 

ground or evaporate, but flows via overland flow, interflow, pipes, and other features 

of a storm water drainage system into a defined surface water body, or a constructed 

infiltration facility.

TDS - See TOTAL DISSOLVED SOLIDS

TECHNOLOGY-BASED EFFLUENT LIMIT - A permit limit for a pollutant which is 

based on the capability of a treatment method to reduce the pollutant to a certain 

concentration.

TI/RE (TOXICITY IDENTIFICATION/REDUCTION EVALUATION) - A set of 

procedures to identify the specific chemicals responsible for whole effluent toxicity.

TIERED TESTING - Any of a series of tests that are conducted as a result of a previous 

test's findings.

TOTAL DISSOLVED SOLIDS (TDS) - The material in water or wastewater that passes 

through a glass fiber filter. TDS is measured by Method 2540 C in Standard 

Methods.

TOTAL MAXIMUM DAILY LOAD (TMDL) - A determination of the amount of 

pollutant that a water body can receive and still meet water quality standards.
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TOXIC - Causing death, disease, behavioral abnormalities, cancer, genetic mutations, 

physiological malfunctions (including malfunctions in reproduction), or physical 

deformations in any organism or its offspring upon exposure, ingestion, inhalation, 

or assimilation.

TOXIC POLLUTANT - Those pollutants, or combinations of pollutants, including 

disease-causing agents, which after discharge and upon exposure, ingestion, 

inhalation or assimilation into any organism, either directly from the environment or 

indirectly by ingestion through food chains, will, on the basis of information 

available to the Administrator, cause death, disease, behavioral abnormalities, 

cancer, genetic mutations, physiological malfunctions (including malfunctions in 

reproduction) or physical deformations, in such organisms or their offspring. (listed 

at 40 CFR 401.15).

TOXIC SUBSTANCE (TOXICANT or TOXICS) - Poison or substance, which if present 

in sufficient quantity or concentration, is capable of producing a toxic response in a 

native or test organism.

TOXICITY - The quality or state of being TOXIC.

TOXICITY TEST - A procedure to determine the toxicity of a chemical or an effluent 

using living organisms. A toxicity test measures the degree of effect a specific 

chemical or effluent has on exposed test organisms.

TRE (TOXICITY REDUCTION EVALUATION) - A site-specific study conducted in a 

stepwise process designed to identify the causative agents of effluent toxicity, isolate 

the sources of toxicity, evaluate the effectiveness of toxicity control options, and 

then confirm the reduction in effluent toxicity.

TSD - Abbreviation for Technical Support Document for water quality-based toxics 

control (EPA/505/2-90-001), or

An abbreviation for a facility which recycles, reuses, reclaims, transfers, stores, 

treats, or disposes of dangerous wastes as defined in WAC 173-303.

TSS (TOTAL SUSPENDED SOLIDS) - Particulates in water or wastewater retained by a 

glass fiber filter. TSS is measured by tests as given in 40 CFR Part 136 and 

referenced as Residue - nonfilterable (TSS) or as given in Standard Methods (17th 

ed.) method 2540 D.
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TTO (TOTAL TOXIC ORGANICS) - Organic chemicals listed within a specific 

category of discharge (such as electroplating Part 413). TTO is the summation of all 

quantifiable values of the organic chemicals greater than 0.01 milligrams per liter.

UPSET - An exceptional incident in which there is unintentional and temporary 

noncompliance with technology-based permit effluent limitations because of factors 

beyond the reasonable control of the Permittee. An upset does not include 

noncompliance to the extent caused by operational error, improperly designed treatment 

facilities, lack of preventative maintenance, or careless or improper operation.

WASTELOAD ALLOCATION (WLA) - Within a TMDL, the allocation for point 

sources of a pollutant. For an individual water quality-based effluent limit, the WLA 

is the numeric water quality criteria times the dilution factor.

WATER QUALITY-BASED EFFLUENT LIMIT - A permit limit for a pollutant which 

limits the concentration such that it will not cause a violation of water quality 

standards. The limit may include a dilution factor if AKART has been determined 

and other restrictions are met.

WATER QUALITY STANDARDS - Numerical and narrative criteria to protect the 

beneficial uses of the States' waters. Includes conventional and toxic pollutants. 

(Chapter 173-201A WAC) 

WET (WHOLE EFFLUENT TOXICITY) - The total toxic effect of an effluent measured 

directly with a toxicity test so that the interaction of all toxicants present in the 

effluent are assessed.
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CHAPTER I. INTRODUCTION (JULY 2011)

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CHAPTER I. INTRODUCTION

This manual is a technical guidance and policy manual for permit writers who develop 

wastewater discharge permits in Washington State. Developing this manual was specified as 

task element P5 in the 1987 Puget Sound Water Quality Management plan and subsequent 

amendments. Maintenance and improvement of the manual is recommended in the final report 

of the Commission for Efficiency and Accountability in Government (1990).

The first version of this manual was issued in June, 1989. A 23-member advisory committee 

assisted the Department of Ecology (Ecology) for one year on policy issues identified in the 

manual. The advisory committee represented those interested in wastewater permits. An 

internal work group also assisted in the development of this manual.

The primary purposes of this manual are to enhance the quality and consistency of the 

wastewater discharge permits issued by Ecology and to improve the efficiency of the permitting 

process.

1. OBJECTIVES AND FUNCTIONS

The specific objectives and functions of this permit writer's manual are to:

Briefly review the legal history of wastewater permitting to provide permit writers with a 

perspective on their role.

Define the requirements for permits in Washington. This manual integrates state and federal 

law, state and federal regulation and Ecology implementation policies. Permits reviewed for 

401(a) certification must be consistent with procedures in this manual.

Ensure statewide consistency in permitting, especially for permits which require best 

professional judgment (BPJ) determinations.

Identify state and federal laws, regulations and policies relating to permitting.

Identify legal opinions of the Attorney General's Offices, rulings of the Pollution Control 

Hearing Board and rulings of other courts on permitting and permit related issues.

Gather collective knowledge of Ecology on permit writing.

Provide a central document to place new information, guidance, and requirements related to 

permitting.
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Serve as a reference for experienced permit writers.

Train new permit writers. This manual is identified in the Permit Writers Training Strategy as a 

component of training for new permit writers. The manual will reduce the training time for new 

permit writers and the demand on experienced permit writers to train new permit writers.

Demonstrate to the regulated community and other interested public what the agency does in 

permitting a wastewater discharge.

This manual is a technical and philosophical compendium of the experienced permit writers in 

Ecology.

The manual is expected to be revised annually and therefore has been placed in a loose leaf 

format to facilitate revision. Revisions or additions to the manual may occasionally be made 

between annual revisions. These revisions and additions will be sent with a transmittal cover 

memo from the Program Manager explaining the need for revision and where the text is to be 

placed in the manual.

2. FORMAT FOLLOWS PROCESS

The manual's format follows the process of developing a wastewater discharge permit. Because 

of the complexity of the permitting process it is impossible to completely separate functions 

chronologically. For example, the public involvement chapter is one of the later chapters in the 

manual because historically public involvement occurred after the permit conditions were 

drafted. Public involvement now begins upon permit application.

In preparing the manual, we borrowed materials freely from EPA and from other states when 

appropriate. These materials are cited in the reference section. They are available from the 

Ecology library and on the Internet.

2.1 Other References

The new permit writer should read and have on hand some reference documents related to 

permitting. Specifically, the permit writer should have access to water pollution laws and 

regulations, the Code of Federal Regulations dealing with environmental regulation (40 CFR 

Parts 100-149 and 400-471), and a current copy of the Clean Water Act. The permit writer 

should read Chapters 173-220, 173-216 WAC and study Chapter 90.48 RCW. The Technical 

Support Document for Water Quality-based Toxics Control (EPA 505/2-90-001) is required 

background reading for Chapters VI and VII.
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3. SCOPE

The scope of this manual includes:

• Joint State/NPDES permits as issued under Chapter 90.48 RCW and the Federal Water 

Pollution Control Act.

• Municipal wastewater treatment plants

• Industrial/Commercial Facilities

• General Permits

• State waste discharge permits as issued under 90.48 RCW.

• Discharges to groundwater

• Discharges to municipal sanitary sewer systems as part of the state wide (undelegated) 

pretreatment program.

4. INSPECTIONS AND ENFORCEMENT

The issuance of a wastewater discharge permit leads to subsequent regulatory activities 

including inspections and enforcement. Guidance for those functions is provided in the 

Inspection Manual (Ecology 92-76) and the Compliance Assurance Manual (posted on the 

Intranet, under the Resources tab, Investigations, Compliance, and Docket Numbers).

5. NOT REGULATION

This manual is not regulation and should not be cited as regulatory authority for any permit 

condition. This manual describes law and regulation pertaining to permitting. These laws 

and regulations must be followed to issue a legal permit. Where those laws and regulations 

are not explicit on implementation the manual describes a process for implementation. This 

process is a program decision (policy) for implementing the laws and regulations and 

typically has been subject to debate by permit writers and management. If the process does 

not fit a permitting circumstance, the permit writer can explore alternative processes as long 

as the law and regulation are met. Alternative processes require section supervisor approval 

prior to implementation.
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6. A SHORT HISTORY LESSON

The point source water pollution control program in this state is based on both Federal and 

State law which evolved concurrently. The state of Washington began a formal pollution 

control program in 1945 with the creation of the Pollution Control Commission and 

enactment of RCW 90.48. The law did not allow strong enforcement. Pollution control was 

a negotiation process and required the state to demonstrate a water pollution problem and 

assign the cause of that problem to a specific discharger.

In 1948 the federal government passed the Water Pollution Control Act (PL 80-845). This 

law provided some funds for the design of municipal wastewater treatment plants and for 

study of water pollution problems. This law also required the U.S. Surgeon General, in 

cooperation with the states, to develop water pollution control programs for interstate 

waters. The Federal Water Pollution Control Act of 1956 (PL 84-660) and its 1961 

amendments (PL 87-88) established federal grants for construction of municipal treatment 

plants.

The Water Quality Act of 1965 (PL 89-234) required states to adopt water quality standards 

for interstate waters and created a small agency, the Federal Water Pollution Control 

Administration (FWPCA). These federal laws generally required the states or federal 

government to demonstrate that a water quality problem had implications for human health 

or violated water quality standards. Enforcement was minimal because the burden of proof 

lay with the agencies: they had to demonstrate a direct link between a discharge and a water 

quality problem before enforcing on a discharger.

Meanwhile, Washington had adopted a waste water discharge permit system in 1955 

(Chapter 90.48 RCW). This permit system was apparently not very effective in controlling 

pollution problems because in 1961 Washington requested assistance of the FWPCA in 

solving the problems with pulp mill discharges.

Increasing water pollution became apparent in the mid-1960's. Existing laws were not 

solving the problems. Two examples that reinforced this impression were Lake Erie, which 

suffered from severe eutrophication and toxic discharges, and the Cuyahoga River, which 

caught fire on several occasions. The Federal Government responded in 1970 by instituting 

a discharge permit system based on the authority of the Rivers and Harbors Act of 1899. 

This system was ineffective because it rapidly got tied up in litigation but it indicated 

increased Federal interest in controlling wastewater discharges by means of a permit system.

In 1971, the State of Washington enacted legislation which required dischargers to use, "all 

known, available, and reasonable methods of treatment prior to", discharge regardless of the 

quality of the water to which the wastes are discharged. This law, the Pollution Disclosure 

Act of 1971 (Chapter 90.52 RCW), signaled a change of philosophy in water pollution law. 
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Instead of trying to assign responsibility for water pollution problems to particular 

dischargers, the state would require that all dischargers provide a high level of wastewater 

treatment regardless of the quality of water to which they discharged (technology-based 

control).

7. THE CLEAN WATER ACT

The Federal Government, in 1972, also adopted this philosophy of technology based

pollution control when it enacted the Federal Water Pollution Control Act Amendments of 

1972 (PL 92-500). Despite the name of the law, it was essentially a new law. Since 1977, 

the law and its revisions have been popularly called the Clean Water Act (CWA or the Act). 

This law, in conjunction with our state laws, forms the basis and framework for our water 

quality regulatory program today. The objective of the law was, "to restore and maintain the 

chemical, physical, and biological integrity of the Nation's waters."

The Clean Water Act lists several goals and policies in Section 101 which show the 

Congressional intent for the Act. The best known is the goal that, "discharge of pollutants 

into navigable waters be eliminated by 1985." This goal wasn't reached, of course, but it 

still should be used as a principle for permitting. The Act had an interim goal for July 1, 

1983: "water quality which provides for the protection and propagation of fish, shellfish, 

and wildlife and provides for recreation in and on the water". This is known as the, 

"fishable, swimmable" goal.

Congress also recognized the issue of toxics and declared it "national policy that discharge 

of toxic pollutants in toxic amounts be prohibited".

Other policies in the Act addressed Federal financial assistance, area wide waste 

management plans, research and demonstration projects.

The Act also contains 4 important principles:

• Discharge of pollutants to navigable waters is not a right. A permit is required to use 

public resources for wastewater disposal.

• The discharge permit limits the amount of pollutants to be discharged.

• Wastewater must be treated with the best treatment technology which is economically 

achievable--regardless of the condition of the receiving water.

• Effluent limits are based on treatment technology but more stringent limits may be 

imposed if the technology-based limits do not prevent violations of water quality 

standards in the receiving water.
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More specifically, the Act created a system for permitting wastewater discharges (Section

402). This system is known as the National Pollutant Discharge Elimination System 

(NPDES). The objective of this system is to implement the goals and policies of the Act.

Section 306 provided for the creation of federal standards of performance for wastewater 

treatment. This eventually resulted in effluent guidelines for major categories of industries.

Enforcement is provided in Section 309 of the Act. Both procedures and penalty amounts 

were explicitly stated. This strong enforcement language was also a major departure from 

previous legislation.

In 1973, Washington State's water pollution control law (Chapter 90.48 RCW) was amended 

to enable the state to apply to EPA for authority to administer the NPDES program. In 

November of 1973, Washington became one of the first states to be delegated the NPDES 

program.

Congress amended the Clean Water Act in 1977, 1981, and 1987. In 1977 the construction 

grants program was reauthorized, and Congress clarified its intent and focus for toxic 

pollutants. The categories of conventional and toxic pollutants were defined. The 1987 

amendments created a schedule to end the federal commitment to the construction grant 

program, addressed storm water permits, water quality problems due to toxics, and sludge 

management. The major philosophical change in these latest amendments is a greater 

emphasis on water quality based permitting for toxic pollutants. This assumed that all 

permits now comply with technology based requirements.

8. TECHNOLOGY-BASED CONTROL

The permit writer should recognize that the environmental gains in point source pollution in 

this country in the 1970's and 1980's were largely due to the imposition of technology based 

control and it remains the basis for both Federal and State law. There has been some 

discussion recently about utilizing the assimilative capacity of receiving waters to reduce the 

cost of wastewater treatment. This contradicts the legislative principles in the Clean Water 

Act and Chapter 90.48 RCW. Legislative and Congressional Policy recognizes that a 

manageable and equitable clean water program requires a technology based program even 

though the treatment might be greater than required to meet water quality standards. Our 

stated public policy is to maintain the highest possible purity of public waters by minimizing 

pollutant discharges to the extent practicable--as opposed to allowing the maximum 

tolerable level of pollutant discharge.

Federal legislators also adopted a goal of total elimination of the discharge of process 
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pollutants. The time stated for achieving the goal has passed but the language remained 

through several major amendments to the Act. This "zero discharge" goal obviously 

requires treatment in excess of that necessary to meet water quality standards.

There is no regulatory mechanism in this state for limiting the number of dischargers on a 

water body until the cumulative effect of the pollutants cause an interference with a 

designated use of that water, in other words, a violation of water quality standards. 

Requiring technology based treatment, even though the treatment exceeds the requirements 

necessary to meet the water quality standards, may continually reduce the pollutant load 

from any source and postpone the necessity of allocating the waste load from each discharge 

to assure meeting water quality standards.

The technology based approach also functions as a buffer for our incomplete understanding 

of the fate and effects of pollutants.

For further discussion of the legal and regulatory background of the permit program see 

Bellingham v. Ecology PCHB No. 84-211, and the Clean Water Act of 1987 published by 

the Water Pollution Control Federation in 1987.

9. WATER QUALITY BASED CONTROL

The 1987 CWA and subsequent regulation clarified an earlier principle of the CWA. The 

principle is that when there is determined, by scientifically valid methods, to be a potential 

for the violation of the water quality standards from a discharge, then that discharge must 

receive effluent limits. The effluent limits are to assure the effluent does not cause a 

violation of the water quality standards. The law does not require 100% certainty but 

requires a judgment of reasonable potential based on a rational process in order to impose 

limitations.

10. PERMIT WRITERS IMPLEMENT THESE LAWS 

AND REGULATIONS

The permit writers in the Department of Ecology are primarily located in the four regional 

offices, the Industrial Section and the Program Development Section. Permit writers are 

engineers or environmental scientists. The regional staff is responsible for both industrial 

and municipal permits. The Industrial Section writes permits for the largest industrial 

dischargers such as pulp mills, petroleum refineries and aluminum smelters. The Program 

Development Section primarily develops general permits.

Permit writers are actually point source pollution control managers with multiple 
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responsibilities, therefore the terms permit writer and permit manager are used 

interchangeably in this manual.

Permit writers represent the people of the state and the country in limiting the amount of 

pollutants discharged from point source discharges. They must exercise a considerable 

amount of discretional authority.

Permit writers should expect to receive criticism from all groups interested in the permit 

program. Environmental groups often charge Ecology permit writers with not writing 

strong enough permits, for not keeping permits current and for not enforcing on permits. 

The regulated community often charges that permit requirements are unnecessary, overly 

stringent, and expensive.

Permit writers have a large amount of authority and responsibility, and this demands the 

exercise of good judgment. A good permit writer needs some things that are not in this 

manual, such as a strong commitment to the Department's mission, an internal sense of self 

worth and self satisfaction, confidence, and a good sense of humor to make it through the 

white water of the Water Quality permit program.

11. PERMIT TOOLS

The Water Quality Program and the Environmental Assessment Program have developed 

several tools to assist permit writers. These tools include model permit language, model fact 

sheet language and spreadsheets for doing the calculations for water quality-based 

permitting. These tools are available for permit writers from the Program Development 

Services Section and are available in Outlook. The spreadsheets and permit shells are 

located at Outlook/Public Folders/All Public Folders/ECY/Water Quality Shells/. The 

spreadsheets are also available to the public through the Ecology home page on the Internet 

at www.ecy.wa.gov/programs/eap/pwspread/pwspread.html.
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CHAPTER II. AN OVERVIEW OF THE 

PERMITTING PROCESS

This chapter presents an overview of the several kinds of wastewater permits required in 

Washington State, the permitting process, and permit modification. The regulatory view of a 

permit and the components of a permit are described. The process of writing a permit is 

described briefly in text and illustrated by the use of flow charts. The tasks identified within the 

flow charts are described in detail in subsequent chapters.

1. WHAT TYPE OF WASTEWATER DISCHARGE 

PERMIT?

In Washington State anyone discharging wastewater (including contaminated stormwater) must 

have a wastewater discharge permit. There are 3 types of wastewater discharge permits:

1) State Waste Discharge Permit; 2) NPDES/State Wastewater Discharge Permit; and

3) General Permit.

1.1 State Wastewater Discharge Permit

A State Waste Discharge Permit is required for a discharge of wastewater to waters of the state 

which includes groundwater. A state waste discharge permit is also required for any industrial or 

commercial operators discharging solid or liquid waste material into sewerage systems operated 

by municipalities or public entities which in turn discharge to waters of the state. This permit is 

issued under authority of Chapter 90.48 RCW. A State Waste Discharge Permit is valid for a 

maximum of 5 years. An applicant for a State Waste Discharge Permit may receive a Temporary 

State Waste Discharge Permit if Ecology fails to act upon a complete application for a period of 

sixty days. A temporary state waste discharge permit is valid for 5 years or until Ecology issues 

a state waste discharge permit. A temporary state waste discharge permit authorizes discharge as 

requested in the permit application. A facility covered under a temporary state waste discharge 

permit must reapply at least 60 days prior to expiration of the temporary permit.

1.2 NPDES Wastewater Discharge Permit

An NPDES Permit is required for a discharge of wastewater to waters of the U.S (surface 

waters). This permit is issued by Ecology by delegated authority of the Clean Water Act. Since 

waters of the U.S. are also waters of the state, NPDES permits are actually NPDES/State permits 

issued under dual authorities. NPDES permits are issued for a maximum of 5 years. Temporary

permits are not allowed under the Clean Water Act.
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1.3 General Wastewater Discharge Permit

General permits are wastewater discharge permits that are developed for a category of discharger 

instead of an individual facility. General permits may be issued under federal (NPDES) or State 

authority. General permits are issued for 5 years. Facilities which are eligible for coverage 

under the permit apply for coverage and then are covered for the remaining length of the permit.

1.4 Hydraulic Continuity

Permit writers, in some cases, must decide if the discharge of a pollutant onto the ground near a 

surface water is subject to an NPDES permit or State Waste discharge permit. Ecology believes 

the best guidance on this issue comes from the United States District Court Eastern District of 

Washington (Washington Wilderness Coalition v. Hecla Mining, 870 F. Supp 983, 990). The 

court held that “since the goal of the CWA is to protect the quality of surface waters, any 

pollutant which enters such waters, whether directly or through groundwater, is subject to 

regulation by NPDES permit.” The court went on to hold, “[I]t is not sufficient to allege 

groundwater pollution, and then to assert a general hydrological connection between all waters. 

Rather, pollutants must be traced from their source to surface waters, in order to come within the 

purview of the CWA.”

The decision on hydraulic continuity is dependent upon the pollutant (type and mobility in soils), 

the pollutant loading, the soils at the site, and the hydrology of the site. At sites where it is 

difficult to make a determination, a permit writer should require, by order, a discharger to do 

appropriate monitoring and analysis to determine whether pollutants discharged to the ground

(water) can be traced to surface water. Ground water monitoring or other monitoring that will 

substantiate the analysis should be required.

2. WHAT IS A WASTEWATER DISCHARGE PERMIT?

In its simplest conceptual meaning a wastewater discharge permit is a legal document issued by a 

regulatory body that allows some entity to discharge wastewater. In reality, a wastewater 

discharge permit represents a complex regulatory program that incorporates hundreds of legal, 

engineering, and scientific decisions. A simple permit may be just a few pages long but a 

complex permit may be dozens of pages. A permit package which would give a reviewer a 

complete picture of the discharge consists of the application, the permit, and the fact sheet. The 

permit application documentation gives the permit writer most of the information necessary to 

produce the permit. The application requirements and detailed process are given in Chapter III.

The body of the permit has 3 distinct components:

• The cover page gives the name and location of the facility;

• The effluent limitations, monitoring requirements and other special conditions are in the 

main body of the permit and are derived for each individual permit or general permit;
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• The general conditions are the last several pages of the permit.

Derivation of effluent limits, monitoring requirements and special conditions in permits is 

covered in detail in Chapters IV through XIII.

The general conditions, sometimes called standard conditions, are exactly the same within each 

category of permit. General conditions come directly from federal or state law or regulation or 

court interpretations of those laws and regulations. They are not subject to change by the permit 

writer. Some general conditions may not be applicable to some Permittees because of the 

circumstance of their discharge but they are not removed from the permit. State wastewater 

discharge permits for discharge to ground water have different general conditions from

wastewater discharge permits for discharge to surface water.

The fact sheet describes the discharge, the regulatory basis of the permit, and the decisions made 

on the permit. The requirements of the fact sheet and a fact sheet check list are given in Chapter 

XIV.

Permits are generally issued for the regulatory maximum period of 5 years. The permit writer 

may have occasion to issue a permit for less than 5 years and nothing prohibits this although 

dischargers generally prefer a 5-year permit. Permits may be administratively extended past 

their expiration date for a period of five years if an application for renewal has been properly 

submitted. The conditions of an extended permit remain in effect and are enforceable. An

extended permit may not be modified.

3. THE PERMITTING PROCESS

The major components of wastewater discharge permitting are illustrated in Figure II-1. After 

receiving the application and making a decision to proceed on a permit, the permit writer reviews 

the application for completeness and accuracy. When the application is complete the permit 

writer derives the technology-based effluent limits. This is the core of the permit writer's task. 

Permit writers must always calculate technology-based effluent limits because they may be more 

stringent than water quality-based limits. The technology-based effluent limits are compared 

with effluent limits which are protective of surface or ground water or sediment quality standards 

(water quality-based limits). The more stringent of the two is placed in the permit. The effluent 

monitoring requirements and other conditions are placed in the permit. This proposed permit 

and fact sheet are reviewed internally, by the permittee and the public, and the permit is 

subsequently issued as a final permit.

The permitting process is illustrated in more detail in Figure II-2. This flow chart illustrates that 

the major steps of Figure II-1 are actually multistep processes. For example, the task of deriving 

technology-based effluent limits is separated into BCT, BAT, BPJ and AKART. Figure II-2 also 
CHAPTER II. AN OVERVIEW OF THE PERMITTING PROCESS (JULY 2011)

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functions as an index to later chapters because the sidebars list later chapters where the processes 

are discussed.
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Figure II-1. Overview of the major components of the permitting process for all dischargers.

Receive Application

Review Application for Completeness and Accuracy

Derive Technology-based Effluent Limits

Will Effluent Cause

Violation of Water Quality

Standards with

Technology-based Limits?

Derive Effluent Limits

Necessary to Meet Water

Quality Standards

Derive Monitoring Requirements

and Other Special Conditions

Conduct Review Process for Draft or

Proposed Permit

Issue Final Permit

yes

no
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Figure II-2. The permitting process for industrial dischargers.

IS APPLICANT A

NEW SOURCE?

REQUIRE ENGINEERING REPORT OR SUPPLEMENTAL

INFORMATION THROUGH SEPA

REVIEW PERMIT

APPLICATION

IS REPORT

COMPLETE?

IS APPLICATION

COMPLETE?

REQUEST NEW APPLICATION OR SUPPLEMENTAL

INFORMATION

START PUBLIC

NOTICE

REVIEW BACKGROUND

INFORMATION

INSPECT EXISTING

SOURCE

ARE COMPILED DATA

ADEQUATE TO BEGIN PERMIT?

REQUEST SUPPLEMENTAL

INFORMATION

ARE

CONVENTIONAL

POLLUTANTS

PRESENT?

ARE BCT EFFLUENT

GUIDELINES AVAILABLE?

DO BCT

GUIDELINES MEET

AKART?

DEVELOP BCT

LIMITS BY BPJ

USE BCT

GUIDELINES

DOES THE FACILITY HAVE

KNOWN, PROBABLE, OR POTENTIAL

PROBLEMS WITH SURFACE RUNOFF, SPILLS,

OR LEAKS OF POLLUTANTS OR ARE

HAZARDOUS WASTES STORED OR

DISPOSED ON SITE?

ARE TOXIC

POLLUTANTS

PRESENT IN THE

EFFLUENT?

REQUIRE A

POLLUTION

PREVENTION PLAN

OR DEVELOP

SPECIFIC BMPs

GO TO A

GO TO B

YES

NO

NO

YES

NO

YES

NO

YES

YES

NO

YES NO

YES

NO

YES

NO

CHAPTERS II AND III

CHAPTER IV

CHAPTER XII
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Figure II-2. (Continued)

A

SELECT TOXIC

POLLUTANTS TO

BE LIMITED

ARE BAT

GUIDELINES

AVAILABLE FOR

TOXICS?

DEVELOP BAT

LIMITS BY

BPJ/AKART

DO THE BAT

GUIDELINES MEET

AKART?

USE THE BAT

GUIDELINES

ARE NONCONVENTIONAL

POLLUTANTS PRESENT IN THE

EFFLUENT?

ARE BAT GUIDELINES

AVAILABLE FOR

NONCONVENTIONALS?

DO THE BAT

GUIDELINES MEET

AKART?

DEVELOP BAT

LIMITS BY

BPJ/AKART

PERFORM WATER QUALITY MODELING AND REASONABLE POTENTIAL DETERMINATION WITH

BCT/BAT/AKART LIMITS AND WET DATA

USE BAT

GUIDELINES

ARE ALL WATER

QUALITY

STANDARDS MET?

DEVELOP SPECIAL

CONDITIONS

DEVELOP

MONITORING

REQUIREMENTS

PREPARE FACT

SHEET AND

SUPPORTING

DOCUMENTATION

DRAFT PERMIT

COMPLETE

COMPLETE

REVIEW AND

ISSUANCE

PROCESS

DEVELOP WATER

QUALITY-BASED

LIMITS

YES

NO

YES

NO

YES

NO

YES NO

CHAPTERS XIVXVI

CHAPTER XIII

CHAPTER XII

 CHAPTERS VI - VII

CHAPTER IV YES NO

NO

YES

B
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4. MODIFICATION OF PERMITS

A permit modification may involve many of the same processes as developing a new permit. A 

term that has become synonymous with permit modification is “reopening the permit”. Permit 

modifications may be initiated by Ecology, by the permittee, by the Pollution Control Hearings 

Board (PCHB), or by the public. Ecology may modify the permit for any of the causes listed in 

40 CFR 122.62. Typically, Ecology modifies permits because of alterations of the facility 

(122.62 (a)(1)) or because of new information (122.62 (a)(2)) such as the effluent causing a 

violation of water quality standards. Other causes for modification are listed in 122.62.

If the permittee or the public wants the permit modified, they submit a letter to Ecology requesting 

the modification and the reason for the request. Ecology may proceed with the modification as 

requested, or not act on the request. When a permit is modified by Ecology, those portions of the 

permit that are modified are subject to appeal to the PCHB.

When the PCHB requests a permit modification, it is the result of a permit appeal and the PCHB 

remands the permit back to Ecology for change.

A permit modification may be minor or major. The definition of minor modification is found in 

40 CFR 122.63. A permit modification is minor if it:

• Corrects typographical errors;

• Requires more frequent monitoring or reporting;

• Changes an interim compliance date in a compliance schedule, provided the new date is 

no more than 120 days later and it doesn't affect the final compliance date;

• Allows for a change of ownership or control of a facility;

• Changes the construction schedule for a new source discharger;

• Deletes a point source outfall when the discharge from that outfall stops, provided it 

doesn't cause a change at the other outfall(s); or,

• Incorporates conditions of a POTW pretreatment program if the pretreatment program 

has been subject to public hearing.
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Minor modifications do not require public notice but the modifications should be sent to the 

parties of record. Any permit modification which goes beyond the above circumstances is a 

major modification and has the same requirements as a permit renewal including the public 

notice requirements. Modification does not change the expiration date of the permit.

A permit writer should consider revocation and reissuance of a permit when a major 

modification is required in order to extend the time until renewal. Anytime a permit is modified 

it may be revoked and reissued if the permittee agrees. Regulations (40 CFR 122.64) allow a 

permit to be revoked and reissued without permittee agreement for any of the following causes:

• Noncompliance with the permit

• Misrepresentation or failure to disclose facts during application of the permit,

• Discovery that the discharge is endangering human health or the environment,

• A change in any condition that requires either a temporary or permanent reduction or 

elimination of any discharge or sludge use or disposal practice controlled by the permit 

(for example, plant closure or termination of discharge by connection to a POTW).

When a permit is revoked and reissued the whole of the permit may be appealed.

5. GENERAL PERMITS - NEW AND RENEWAL

General permits are NPDES/state or state wastewater discharge permits that are developed for a 

category of discharger instead of an individual facility. General permits may be cost effective 

because of the large numbers of facilities that can be covered rapidly with a general permit. 

When deciding whether to do a general permit, consider the following:

• Are there a large number of facilities to be covered?

• Do they have similar production processes?

• Do they have similar process pollutants?

• Does only a small percentage have a potential for water quality standards violations?

The decision to develop or reissue a general permit is made after section or program deliberation 
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and a program management decision.

6. THE GENERAL PERMIT DEVELOPMENT PROCESS

The regulation covering general permits is Chapter 173-226 WAC. Many of the federal 

regulations in 40 CFR 122 and 125 are also applicable to NPDES general permits. The 

following is the step-by-step process for developing a general permit.

For a New general permit

• Identify a category of dischargers for the development of a general permit. The permitting 

section and the Water Quality Program must concur on the development of the permit.

• Post a public notice of the department's intent to develop a general permit.

The scope of this public notice is largely left up to the permit manager, but must be done so 

as to inform interested and potentially affected persons.

All persons who express an interest in the permit may request to be placed on a mailing list 

to receive notices of the draft and final permit.

Start another mailing list. The list could be the same as the permit list above, or it could be 

composed of the existing regional "interested persons" mailing lists, or a new list specific to 

each general permit. The list will consist of people who want to know who is being covered 

under the general permit.

If Ecology decides not to develop a general permit after the public notice of intent to issue a 

general permit, then Ecology will publish a notice to that effect.

For New and Reissued General Permits

• Characterize the wastewater – This may require EAP participation or issuance of 

administrative orders if components of the wastewater are unknown.

• Assemble the internal workgroup and, if necessary, a stakeholder advisory group.

• Start a web page for the permit if there isn’t an existing page. This page should be started 

shortly after the formation of the external advisory group. This page should tell people the 

process for renewal has started and if people want to be on a mail list for information to 

contact us. The people on this mail list must be notified when a draft permit is available.

• Draft the application for coverage (if necessary), the general permit, and the fact sheet.

The application for coverage becomes a problem when a permit is being renewed and it is 

determined that additional information is needed from existing Permittees (the existing 

application form is inadequate). Existing Permittees must submit a renewal application prior 
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to expiration of the existing general permit and the recommendation is to send out a renewal 

notice 12 months prior to expiration of the existing general permit. Applications must be 

received by Ecology at least 180 days prior to expiration of the general permit. If the permit 

is not re-issued before expiration, only those Permittees who have submitted timely 

application will be covered in the interim and be deemed “existing discharger” for 

regulatory purposes. At the time the reapplication notice is sent, the permit development 

may be still formative and the information requirements not known. The recommendation, 

in this case, is to continue development of the new application with development of the 

permit and request the new information as an order to existing Permittees at the time of 

issuance of coverage.

The terms and conditions of a general permit are similar to those in an individual permit, and 

are developed in manner similar to the terms and conditions contained in an individual 

permit. The process includes, at a minimum, characterization of pollutants in the 

wastewater and the development of technology-based effluent limitations. Technologybased limitations in general permits may be the requirement for best management practices 

(BMPs). The Antidegradation Plan must be addressed in the fact sheet.

A fact sheet is drafted on the general permit only, fact sheets will not be written for the 

facilities requesting coverage under a general permit. Antidegradation analysis is not 

required for individual coverages under a general permit.

• Prepare a small business economic impact analysis (SBEIS) on the general permit if 

required. Contact the Rules Unit early in permit development for assistance with the SBEIS.

• A separate application for coverage will be developed for each new general permit. For 

renewal of general permits the existing application should be reviewed for suitability and 

revised if necessary.

• For NPDES and combined NPDES/state waste discharge general permits only, the draft 

general permit, fact sheet and application for coverage must be submitted to EPA for a 90-

day review. EPA does not review general permits issued solely under State authority.

• Complete a public notice, fact sheet, and the revised application for coverage (if necessary). 

The public notice of the draft general permit includes:

- Publication of a short summary of the permit and the small business economic impact 

statement in the state register.

- For new type of general permit with state-wide coverage, publish in the state register 

and on the appropriate Ecology web page and consider publication of a notice in, at 

least, five local newspapers. If the new general permit covers a category of dischargers 
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which is highly localized, publication of notice in the major newspapers of one region 

may be sufficient. For renewals, place notice in the state register and on the Internet.

- Send individual notices of draft to the “interested persons” mailing list and “required” 

governmental agencies and all tribes. This mailing list and newspaper receipts must be 

saved as part of the permit record.

• Hold a minimum of one public hearing on the proposed general permit within the area 

covered by the general permit. Although only one public hearing is required, three or four 

hearings are recommended for a new type of state-wide general permit.

• After the close of the public comment period, prepare a response to comments and make any 

required changes to the permit as a result of comments received on the general permit. The 

response to comments documentation must note where significant changes were made in the 

draft permit as a result of comments. This may be done as a separate summary section or by 

highlighting the response that notes a change in the draft permit. The response to comments 

becomes an attachment to the fact sheet. The response to comments may also be published 

as a separate document.

• A public notice must be completed for the issuance of all general permits. A general permit 

is issued when signed by the program manager or appropriate regional water quality section 

head. Public notice of the issuance of a general permit must be done in a manner similar to 

the public notice of the draft permit, including publication in the state register.

• A general permit may become effective 31 days after a notice of the issuance of the general 

permit is published in the state register. The effective date should be set with consideration 

of the monitoring requirements of the permit and the Ecology permit data system.

• If the reissued permit is significantly different than the previous permit then consider 

conducting state-wide workshops on the permit.

• Applications for new coverage under a general permit:

May be submitted any time following the public notice of the draft general permit, or at a 

later date as specified by the department.

Generally, do not require public notice from facilities previously covered under the 

permit unless the facility has an increase in volume or a change in the character of the 

effluent. A new application form may require that existing facilities may have to reapply 

or provide additional information.
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• Coverage under a general permit is automatic on the latter of the following:

The effective date of the permit;

31 days following the end of any public notice and public comment period on an 

application for coverage under the general permit;

31 days after receipt of a completed application for coverage; or,

A date specified in the general permit.

• Periodically, a list of facilities which have requested coverage under the general permit must 

be mailed out to people who have expressed an interest in who is being covered under the 

general permit. Alternatively, the list may be posted on the web site for the general permit. 

The frequency for listing these facilities should be proportional to the number of applicants

but should not be less than once a year. This listing is not required when the public gains 

access to our permit data system.

All of the requirements above must be documented and placed in the permit file. This includes 

documentation of mail outs, public notices and transmittal letters to EPA and other required 

government agencies.
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Figure II-3. General Permit Process

GENERAL PERMITS PROCESS 

(REISSUE)

Form Internal Team and 

Stakeholder Advisory Group.

 Post reissue notice on web 

site.

18 Months before 

expiration

Identify problem areas of current permit. 

Review expected water quality impacts, 

AKART and DMR data if available. Write 

summary issue paper. Identify expected 

direction of renewed permit. Draft revised 

application form if necessary.

First meeting of Internal Team –

Discuss ground rules, issues and 

problems. 

Send renewal notice to all 

existing permittees 12 Months before permit expiration

First meeting of stakeholders. Introductions, history of 

permit, and presentation of summary issues. Document 

issues as presented by stakeholders.(Invite the internal 

team). Start the permit web page

Meeting of Internal Permit Team to review 

stakeholder views and concerns

Permit writer prepares draft permit and 

fact sheet -transmit to Internal 

Workgroup for review

Internal Workgroup meeting(s)-

 allow for 10 meetings

Present PMT 

Unresolved Issues 

for Decision 

Stakeholder Review and 

Meeting (Entity Review)

Reconcile Stakeholder Review Comments with Internal 

Workgroup, Management and AAG as necessary. Revise 

as Directed (Draft Permit) – No Formal Reponse to 

Comments Required Here. 

- Are you interested? Let 

us know

- If selected you are 

expected to be a 

representative of your 

interest group

- There will be a limited 

number of meetings (2-3)

- Come to the first meeting 

prepared to discuss 

problems with the current 

permit

Letter to Potential 

Stakeholder Group 

Member

NEXT 

PAGE 30 days

Regional visits to discuss current permit or data collection if necessary

20 weeks

4 weeks

2 weeks

2 weeks

2 weeks

2 weeks

2 weeks

2 weeks

1 year
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PUBLIC NOTICE OF DRAFT AND HEARING(S)

(SEE NOTICE TEMPLATE)

- Publish notice of draft permit and hearing(s) in the 

State Register*

- Place notice of hearings on agency calendar and 

sharepoint

- Send notice of draft by email to advisory group

serving the area covered by the general permit

 - Place the notice of draft, draft permit, and draft fact 

sheet, draft application form and economic analysis 

on the specific Internet site

 - Issue news release, focus sheet, or newsletter

 - Notify by letter everyone on the Program mailing lists or 

listserve wishing to be notified of draft permits and the 

required governmental agencies and tribes

- Send draft permit, fact sheet and application to EPA for 

90 day review (This review may be waived by EPA)

* The Notice is 

delivered to the 

Code Revisors 

Office on or 

before the 1st or 

3rd Wednesday 

of the month. 

Publication in 

the Register is 2 

weeks later. The 

Governmental 

Relations 

Section, Rules 

Unit can assist 

you. Deliver to 

the rules unit on 

Monday or 

Tuesday. The draft comment period begins upon publication of Notice in the 

Register and extends a minimum of 30 days but must extend several 

days past the date of last public hearing/workshop. Allow about 45 

days from time of publication to close of comment period. During this 

period conduct one (minimum) to four workshops/hearings on the 

draft permit.

Prepare response to comment and revised permit. The 

response to comments is attached as an appendix to the fact 

sheet and as a stand alone document. Circulate to permit 

team for review/comment. Send to AAG review if 

recommended by Section Head.

Post the Combined Comment 

Letters on the Website

FROM PREVIOUS 

PAGE

The Comment Letters 

received as paper can 

be scanned to create an 

electronic file.

Program Manager signs the permit (3 weeks 

minimum before expiration of current permit). 

Schedule Program Manager appt. 6 weeks before 

signing.

Next Page

Organize comments in 

preparation of response 

(allow 1 to 3 weeks). Similar 

comments may be 

consolidated

120 days

Comments received by email should be 

consolidated into a separate folder for 

future notice of issuance.
CHAPTER II. AN OVERVIEW OF THE PERMITTING PROCESS (JULY 2011)

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From previous page

PUBLIC NOTICE OF ISSUANCE

(SEE NOTICE TEMPLATE)

- Publish notice of issuance in the State Register*

- Send Tribal letter when notice goes to register.

- Send permit and coverage letter to permittees 

- Place the notice of issuance on the Internet site.

- Issue news release, focus sheet, newsletter, or FAQ

- Issue coverages with the permit to existing coverages on the 

issuance date. The transmittal letter should inform of available 

fact sheet and any workshops.

- Send copy of final permit, fact sheet and application form to 

EPA 

- Send a letter of issuance to all who commented by letter and 

those on the program mailing list wishing to be notified of 

issuance. The letter includes links to web site with permit, fact 

sheet and response to comments as separate documents. The 

letter offers hard copies to be sent upon request. Response to 

any requests as a result of this letter must be made within 3 

days.

- Send an email on the day of issuance to all who commented 

by email. The email contains links to the web site containing the 

permit, fact sheet and response to comments.

- Notify other governmental agencies on the date of issuance

- Email advisory group one or two days before publication

Consolidate the permit file of record in preparation of 

appeal 

Present workshops to 

explain requirements of the 

permit

WAC 173-220 has some 

mandatory notification 

parties

Required Governmental Agencies include:

State of Idaho, State of Oregon, applicable Indian Tribes, District Engineer Army Corp of Engineers, 

US Fish and Wildlife, National Marine Fisheries Service, WA Dept. Fish and Wildlife, WA Dept. of 

Health, WA Dept. of Social and Health Services, and WA Dept of Archaeology and Historic 

Preservation.

2 weeks from time of delivery to register 

to publication (issuance) 

The effective 

date of the 

permit is a 

minimum of 

30 days after 

publication in 

the register
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7. QA/QC PROCESS

The originating section and the Water Quality Program (WQP) Development Services Section 

(PDS Section) will conduct a consistency check for all proposed and draft permits through a 

combination of pre-issuance reviews.

The Water Quality Program Manager originally established the following procedure for 

centralized quality control associated with permit issuance by a memorandum dated April 8, 

1994. Each issuing office must establish the implementation details of the required procedures 

for in-office internal quality assurance. All Ecology programs that issue wastewater permits 

under the authority of RCW 90.48 will adhere to the centralized quality control process for all 

NPDES and state waste discharge permits and major permit modifications issued. These 

programs typically include the Water Quality Program, Toxic Cleanup Program, Nuclear and 

Mixed Waste Management Program, Hazardous Waste and Toxics Reduction Program, and the 

Solid Waste and Financial Assistance Program (Industrial Section). The regions and Ecology 

Programs identified above will also submit administrative orders establishing interim effluent 

limits issued under the authority of RCW 90.48 to the PDS Section for a quality control check. 

Actions initiated as "substantive requirements" of water quality permit requirements under 

CERCLA or MTCA will also undergo centralized quality control. The signatory authority must 

approve any variations to this procedure and must convey the reason or cause for the variation to 

the WQP Manager prior to adopting the specific procedure and issuing of the permit.

• Responsibility for Quality Permits

The ultimate responsibility for the content and quality of a permit rests with the supervisor 

signing the permit. The unit supervisor and the permit writer are responsible for briefing the 

supervisor signing the permit on all significant issues raised from central QA/QC review, any 

EPA review, written review, and from an oral presentation. The unit supervisor and the permit 

writer will explain the resolution of these issues.

• Resolution of Disagreements

Disagreements on significant issues may occur between the PDS Section Permit QA/QC 

Coordinator and the permit writer. The relevant unit supervisor, permit writer, and the QA/QC 

Coordinator will meet either directly or via a conference call as the first step towards resolution. 

If resolution does not occur, the relevant section supervisor and the PDS Section supervisor will 

discuss the issue. The final decision rests with the permit signature authority. The supervisor 

with signature authority and the PDS Section supervisor will determine the need for further 

management involvement in the decision.
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Pre-Issuance Review

Internal peer review of all Water Quality Program draft permits, modifications, and 

relevant orders must take place within the section or regional office. Each issuing office 

must establish the implementation details of the required procedures for in-office internal 

quality assurance. The WQ Program encourages cross-region and cross-program review. 

The paragraphs below describe two in-office internal approaches used by some of the 

regional WQ sections as well as the required PDS Section Permit QA/QC review and EPA 

review.

Peer Review through Document Distribution: The unit supervisor may assign the draft 

permit and fact sheet to one or more other permit managers for comments, suggested 

changes and additions.

Peer Review through Oral Presentations: Peer review of industrial and municipal 

permits through an oral presentation may occur at the local regional office, at a permit 

writer training session, or other suitable forum prior to issuance of the permit.

PDS Section Central Permit QA/QC Review: This PDS Section central review should 

occur after regional peer and unit supervisor review. The permit coordinators must submit 

the draft permit, any associated compliance order, fact sheet and appendices to the PDS 

Section Permit QA/QC Coordinator for Central Permit QA/QC Review prior to entity 

review and the Public Notice of Draft (PNOD). Permit writers can expect that the Permit 

QA/QC coordinator will complete the quality control check of minors and state permits 

within ten days (two weeks) and within three weeks for major permits.

EPA Review: Permit writers must send all major and general permits to EPA Region 10 

for review concurrent with public review. If the PDS Section Permit QA/QC reviewer 

believes that EPA may have concerns with a permit he/she will recommend that the region 

forward the permit to EPA during entity review so that Ecology and EPA have an 

opportunity to work out any issues prior to public review. Permit writers may contact the 

EPA reviewer at any time while drafting a permit to discuss issues if they foresee an 

objection by EPA of the permit terms and conditions.

The Permit QA/QC Coordinator will review as many permits as possible for consistency and 

fulfillment of policy, procedural, and legal requirements. The Permit QA/QC Coordinator will 

provide assistance to the permit writer in the form of constructive suggestions and advice on 

addressing relevant policy issues. The Permit QA/QC Coordinator will identify areas of 

inconsistency requiring new or revised policies, procedures, and guidance and will identify areas 

where lack of policies, procedures, and guidance cause permit issuance inefficiencies. The PDS 

Section supervisor will relay these issues to the Permit Writer’s Workgroup (PWG) and/or as 

necessary to the Program Management Team for discussion and resolution.
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The originating region/Program may publish the PNOD after consideration of comments 

received from the peer reviews, central QC check, any EPA review peer reviews and compliance 

with the pre-issuance review procedures.

Post Issuance PDS Section Central Review

The Permit QA/QC Coordinator will randomly review final permits after issuance for 

consistency, use of common guidelines, and incorporation of internal and external 

comments. The Permit QA/QC Coordinator will give special attention to review of permit 

elements driven by new requirements.

Communication of Findings

When issues emerge that are of interest to permit managers, the Permit QA/QC Coordinator 

will communicate the issues to permit managers through emails, newsletters, PWG 

discussions, videoconferences, training sessions, and other appropriate methods.

The Permit QA/QC Coordinator will route recommendations for changes to the permit 

shells to the chair of the PWG for inclusion in the shell update process.

The Permit QA/QC Coordinator will discuss issues that require supervisory attention first 

with the appropriate unit supervisor and, when necessary, elevate issues to the PDS Section 

supervisor for resolution.

The PDS Section Supervisor will elevate issues involving the efficiency of permit writing 

and issues needing policy determinations or procedural guidance to program management.

The Permit QA/QC Coordinator will, as necessary, prepare and distribute a summary of 

issues prior to each permit writer training session for discussion at the session.

PDS Central Permit QA/QC Review: Submittal of draft permit, any associated compliance 

order, fact sheet, and the permit application for PDS Section Central Permit QA/QC Review to 

the QA Coordinator in the PDS Section will occur prior to the Public Notice of Draft (PNOD). 

Ten days (two weeks) will be allowed for the quality control check of minor permits and three 

weeks will be allowed for major permits. The EPA review and PDS quality control check period 

should take place concurrently and before entity review for majors and general permits. Central 

quality control review will take place during, or prior to, any entity review period for state and 

minor permits.

The permit QA Coordinator will be reviewing as many permits as possible for consistency and 

fulfillment of policy, procedural, and legal requirements. The permit QA Coordinator will 

provide assistance to the permit writer in the form of constructive suggestions and advice on 

addressing relevant policy issues. A key role of the QA Coordinator will be to identify areas of 

inconsistency requiring new or revised policies, procedures, and guidance. Areas where lack of 
CHAPTER II. AN OVERVIEW OF THE PERMITTING PROCESS (JULY 2011)

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policies, procedures, and guidance are causing inefficiencies in permit issuance will be identified 

for management attention.

The PNOD may proceed after consideration of comments received from the peer reviews, central 

QC check, any EPA review peer reviews and compliance with the pre-issuance review 

procedures.

8. PERMITTEE REVIEW (also see Chapter XV, Section 4)

Procedures

1. Permit writers shall inform Permittees of significant changes to their renewed permits as 

early as possible in the permitting process.

2. The proposed fact sheet, permit, or permit and fact sheet should be forwarded to the 

Permittee for comment on factual content 30 days prior to the beginning of the formal 

public review period. A shorter review period may be used when acceptable to the 

Permittee or if permit deadlines require a shorter review period.

3. The Permittee shall be made aware that the proposed permit conditions could be changed 

during the public review process.

4. The draft permit transmittal letter shall specify a date certain by which comments are due, 

and be clear that the permit issuance process will not be delayed if the date is not met.

5. For permit renewals with significant changes, the permit writer may offer the Permittee an 

opportunity to meet two weeks or more after forwarding the proposed permit or fact sheet. 

The purpose of the meeting is to explain new or changed requirements, receive comments 

on factual content, and to discuss the practicality of compliance schedules.

Waste discharge permits are now very complex documents, and new more complex requirements 

in reissued permits have become the norm. It is extremely important that Ecology informs

Permittees of significant changes proposed in their permit as soon as possible. It is also 

important that the proposed permit and fact sheet be factually correct with respect to facility 

information such as discharge locations, and process description before the public review.

The Permittee needs to know what the new permit requirements are and the basis for the 

requirements. The practicality of any proposed compliance schedules also needs to be discussed 

with the Permittee prior to setting a proposed schedule in the public review draft.

9. PUBLIC REVIEW

Ecology is committed to implementing a more effective public involvement program and 

strongly supports public involvement in the review of and input on permit conditions during the 
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public review.

If, during the public review period, members of the public wish to meet with Ecology staff to 

discuss new permit requirements and their basis, such a request should be granted. Early 

Permittee involvement ensures a correct draft permit for public review and avoids unnecessary 

delays in the public issuance process. It also ensures that Permittees are informed of the 

proposed permit requirements in a timely manner. It’s also important that the public has full 

access and opportunity to participate in the permit process during the public notice process.

10. EPA REVIEW

Draft individual NPDES permits for major dischargers should be sent to the EPA Region 10 for 

review during the public review process.

11. AN EXAMPLE PERMIT

New permit writers who are not familiar with permits should review several recent permits from 

their section files or posted on the Internet. The permit writer may contact the QA/QC person for 

some exemplary permits.

12. PERMIT SHIELD POLICY

Permittees are afforded some protection of liability from enforcement and citizen suit by having 

a discharge permit. This protection comes from language in Section 402(k) of the Clean Water 

Act. This section of the CWA says “Compliance with a permit issued pursuant to this section, 

shall be deemed compliance, for purposes of sections 309 and 505, with sections 301, 302, 306, 

307, and 403, except any standard imposed under section 307 for a toxic pollutant injurious to 

human health.” EPA has adopted a policy (EPA 1995) to clarify the circumstances of protection 

afforded by this policy. The policy states that if the pollutants in the discharge, the suspected 

pollutants in discharge and the manufacturing processes are fully disclosed during application, 

the Permittee is shielded from enforcement if it’s subsequently discovered the discharge is 

causing a violation of water quality standards. Several courts have agreed with EPA on the legal 

interpretation of Section 402(k).

Occasionally, permit writers receive requests to place some explicit permit shield language in a 

permit. Ecology permit writers should not put permit shield language in permits. This is a 

protection afforded Permittees by the fact of receiving a permit and the circumstances 

surrounding the permit application and issuance. Nothing in the Clean Water Act or federal 

regulation or policy directs permit writers to place this language in permits. The language often 

suggested by Permittees grants far broader immunity than that afforded by Section 402(k). 
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Permit writers who want to assure 402(k) protection for Permittees should require extensive 

analysis of the effluent for the permit application and be very explicit in the fact sheet about how 

each pollutant in the effluent was considered. Permittees who want the protection of 402(k) only 

have to make sure they disclose all relevant information on their discharge in their permit 

application.

13. CWA JURISDICTION ON TRIBAL LANDS

Jurisdiction within Indian Reservations is very mixed and is based on complex case law. Also 

terminology can be confusing. County-issued permits are not evidence of state NPDES 

jurisdiction.

The State does not have jurisdiction for any of the EPA delegated/approved programs on any 

lands (fee/trust, Indian owned/non-Indian owned) within any Indian Reservation, except the 

Puyallup Reservation where we have received specific authorization.

EPA believes that it can only delegate/approve state programs within Indian Reservations if it 

makes a specific finding of state authority on those lands. On the Puyallup Reservation the tribe 

agreed and Congress approved a land claims settlement that provided that the state would have 

jurisdiction on fee lands within the Reservation. On this basis, EPA has approved Ecology’s 

CWA, RCRA, and CAA programs on fee lands within the Puyallup Reservation.

On all of the other 25 reservations within the state, EPA has retained CWA jurisdiction or has 

delegated specific programs to tribes under its “Treatment as a State” (TAS) process. This is due 

to EPA’s read of its authority and EPA’s interpretation that tribes have inherent authority, for the 

purposes of the federal environmental programs, over all tribal members and their land and all 

non-member residents and their land within reservations.

A county may have taxing jurisdiction on fee land within a reservation and may have (or assert) 

zoning and building code authority on fee land. Ecology would still not have NPDES authority 

on fee land within the reservation unless EPA has specifically delegated CWA programs to the 

state within the reservation as it did on the Puyallup Reservation.

14. STATE AUTHORITY ON FOREST SERVICE LAND

Washington has concurrent jurisdiction with the US regarding both civil and criminal processes 

on national forest lands within the state (RCW 37.08.220). This means that the state has the 

authority to enforce our statutes and regulations on national forest lands in the state. However, 

Ecology’s ability to take enforcement action against the federal government is limited. 

Consequently, if the federal government is the operator of the treatment plant discharging to 

land, Ecology can issue a state waste discharge permit for the facility, but Ecology’s ability to 
CHAPTER II. AN OVERVIEW OF THE PERMITTING PROCESS (JULY 2011)

Permit Writer’s Manual

II-23

enforce the permit may require a federal court action. If the plant is operated on USFS land by a 

private entity, Ecology can issue a permit to that entity and use all the usual enforcement tools 

(orders, penalties, etc) to enforce the permit.

15. ANTIBACKSLIDING

In general, Ecology may not renew, reissue or modify an existing NPDES with effluent limits 

that are less stringent. The requirements and exceptions are found in CWA 402(o), CWA 

303(d)(4), and 40 CFR 122.44(l). The requirements are relatively straight forward but the 

exceptions are confusing.

Regardless of the exceptions given below, Ecology may not propose a less stringent effluent 

limit if any of the following apply:

1) It is less stringent than required by federal effluent guidelines.

2) It violates applicable water quality standards (including antidegradation requirements).

3) It violates State technology-based treatment requirements that are more stringent than federal 

requirements (see discussion below).

State law is silent on antibacksliding so the following does not apply to limits in State permits;

however, the groundwater standards do have an antidegradation requirement which would apply 

for increased limits.

Ecology may propose less stringent water quality-based effluent limits if any of the following 

apply:

1) Material and substantial alterations to the permitted facility occurred after permit issuance 

justifying application of a less stringent effluent limit.

2) Information, not available at the time of permit issuance (other than revised regulations, 

guidance, or test methods), would have justified applying a less stringent effluent limit at the 

time of permit issuance. (This is available for listed waters only if the cumulative effect of 

these revisions assures attainment and the increase meets antidegradation requirements. This 

assumes that if limits for some dischargers to the impaired waters go up, others will go down 

to assure attainment of standards.)

3) Ecology made a mistake when it calculated limits or when it interpreted law or regulation 

when it issued the permit (available for listed waters only if the cumulative effect of these 

revisions assures attainment and increase meets antidegradation requirements).

4) When Ecology revises a TMDL and transfers a WLA to increases the limits after it had based 

limits on a TMDL in listed waters. Ecology must still ensure the water body attains water 

quality standards.

5) When Ecology changes the use designation so the criteria are less stringent after it had based 

limits on a TMDL in listed waters.
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Ecology believes that situations 2 and 3 would most commonly occur. It’s not clear how 

situation 1 would apply to water quality-based limits unless the material and substantial 

alterations changed the character of the effluent.

EPA also stated in its guidance memo (Elder 1993) that exceptions 1 through 5 also apply to 

“any other State treatment requirements more stringent than required by the CWA (e.g., 

technology-based State treatment requirements).

Ecology may increase technology-based limits based on applicable EPA effluent guidelines if:

1) Material and substantial alterations to the permitted facility occurred after permit issuance 

justifying the application of a less stringent effluent limitation.

Ecology may increase technology-based limits determined on a case-by-case (BPJ) basis [40 

CFR 125.3(d)] if any of the following apply:

1) Material and substantial alterations to the permitted facility occurred after permit issuance 

justifying the application of a less stringent effluent limitation.

2) Information, not available at the time of permit issuance (other than revised regulations, 

guidance, or test methods), would have justified applying a less stringent effluent limit at the 

time of permit issuance. (This is available for listed waters only if the cumulative effect of 

these revisions assures attainment and the increase meets antidegradation requirements.

3) Ecology made a mistake when it calculated limits or when it interpreted law or regulation 

when it issued the permit (available for listed waters only if the cumulative effect of these 

revisions assures attainment and increase meets antidegradation requirements).

4) Ecology determines a less stringent effluent limitation is necessary because of events over 

which the permittee has no control and for which there is no reasonably available remedy.

5) The permittee has received a variance or exception under CWA sections 316(a) or 301(c), 

301(g), 301(h), 301(i), 301(k), 301(m) and 301(n). These variances or exceptions are: 316(a) 

– Thermal discharge, 301(c) – Demonstration of maximum use of treatment technology, 

301(g) – Modification for certain nonconventional pollutants, 301(h) – Marine waiver for 

secondary treatment, 301(i) – Municipal time extension, 301(k) – Innovative technology, 

301(m) – Deep sea industrial discharge of BOD and pH, and 301(n) – Fundamentally different 

factors.

6) The permittee has installed the treatment facilities required to meet the BPJ limits and has 

properly operated and maintained the facilities but has, nevertheless, been unable to achieve 

the effluent limit, in which case, Ecology may revise the limits to reflect the level of pollutant 

control actually achieved.
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Ecology believes antibacksliding applies to effluent limits developed on a case-by-case basis 

under authority of 90.48 (AKART) and placed in an NPDES permit. For example, Ecology 

develops a performance-based limit for an industrial discharger with obsolete effluent guidelines. 

The permit writer determines the treatment technology and the operation of that technology is 

AKART and develops appropriate technology-based effluent limits based on the monitoring data 

from the facility. EPA then revises the effluent guidelines for the industrial discharger. The 

guidelines are less stringent than the AKART limit. Even if antibacksliding did not apply, 

Ecology would still have an independent duty under state law to impose the more stringent 

AKART limit rather than the less stringent limit based on federal effluent guidelines.
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Figure II-4. Antibacksliding

IS THE LIMIT BASED 

ON WATER QUALITY 

CRITERIA?

ANTIBACKSLIDING 

FOR TECHNOLOGY 

BASED LIMITS IS 

DISCUSSED ABOVE 

[SEE 40 CFR 

122.44(l)]

ARE WQ STANDARDS 

ATTAINED?

402(o)(1)/303(d)(4)

IS REVISION 

CONSISTENT WITH 

ANTIDEGRADATION?

303(d)(4)(B)

IS LIMIT BASED ON 

A TMDL?

303(d)(4)(A)

IS ATTAINMENT OF 

WATER QUALITY 

STANDARDS ASSURED 

(INCLUDING 

ANTIDEGRADATION)

IS A LISTED 

EXCEPTION MET?

402(o)(2)

REVISION NOT 

ALLOWED

DOES REVISION COMPLY 

WITH EFFLUENT 

GUIDELINES AND WATER 

QUALITY STANDARDS?

402(o)(3)

REVISION 

ALLOWED

NO

YES

YES

YES

YES

YES

NO NO

NO YES

NO

YES NO

REFERENCES

Elder, James 1989. Draft Interim Guidance on Implementation of Section 402(o) Antibacksliding Rules For Water Quality-Based Permits (Draft).
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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CHAPTER III. THE APPLICATION AND 

BACKGROUND REVIEW

This chapter covers the process of permit application and background review including 

categories of application, forms, and time frames for application. A flow chart showing the tasks 

for permit writers is included at the end of the chapter. The objective of permit application and 

background review is for the permit writer to become as knowledgeable as possible about the 

circumstances of discharge and the characteristics of the proposed effluent discharge.

1. WHO NEEDS PERMITS

Anyone who owns or operates a facility discharging or proposing to discharge wastewater 

(including some stormwaters) to the state waters must apply for an individual wastewater 

discharge permit. State and Federal regulations require a facility to apply for an individual 

permit to discharge to surface waters at least 180 days prior to the initial discharge. Ecology 

may allow a shorter time period by letter, however, 180 days is not enough time to work through 

engineering reports for new dischargers or complex issues for existing dischargers. Permit 

writers should alert their permit applicants to the realistic schedules for permit issuance and 

renewal. Major Permittees should be sent applications at the beginning of the fiscal year in 

which their permit expires. Permits should require reapplication one year prior to expiration.

Application for an individual state waste discharge permit must be made 60 days prior to the date 

on which it is desired to begin discharge but for complex discharge situations 60 days is 

insufficient time to develop a permit. State permits should also require reapplication one year 

prior to expiration.

Application times for coverage under a general permit are developed for the specific general 

permit.

Anyone who discharges wastewater or has a significant potential to discharge wastewater to the 

surface waters of the state must obtain a joint NPDES/state wastewater discharge permit (40 

CFR 122.3). Ecology issues joint federal/state permits because the state’s water pollution law 

requiring wastewater discharge permits preceded federal law.

Those exempted from obtaining an NPDES individual permit include:

• Anyone discharging domestic sewage only to a POTW,
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• Anyone who is covered by a general permit (see Section 5 of Chapter II and Section 9 

of this chapter),

• Anyone discharging industrial and commercial wastewater to a POTW,

• Discharges of pollutants from nonpoint source agricultural and silvicultural activities,

• Return flows from irrigated agriculture,

• Any discharge in compliance with the instructions of an On Scene Coordinator, and

• Any discharge occurring under CERCLA (but these discharges must meet substantive 

requirements)

State wastewater discharge permits are required by:

• Anyone who discharges waste materials from a commercial or industrial operation to 

the waters of the state or to a municipal sewage system (RCW 90.48.160); and,

• Any county or any municipal or public corporation operating or proposing to operate a 

sewage system which results in the disposal of waste material into the waters of the 

state (RCW 90.48.162).

• All lagoons containing wastewater, lined and unlined, require state waste discharge 

permits.

The exemptions for the requirement for state waste discharge permits include:

• Discharges to municipal sewerage systems of domestic wastewater (sanitary 

wastewater) from residential, commercial, or industrial structures.

• Any discharge to a municipal system which is already permitted (subject to review and 

limitation) by the local authority.

• Any discharge to a municipal system which is already permitted under a local 

pretreatment program (FWPCA section 307).

• Discharges to municipal sewerage systems from commercial or industrial operations if 
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the waste strength and characteristics are the same as domestic wastewater (if it's not 

easily degradable or if its high strength, then the permit writer should examine it in the 

permit process to assure the waste will not cause an upset at the treatment plant).

• Discharges which have an NPDES/state individual or general discharge permit for 

discharge to surface water.

• Discharges from small domestic on-site septic systems (design capacity less than or 

equal to 14,500 gallons per day) which discharge to the ground.

• Discharges from small (less than or equal to 3,500 gallons per day) aerobic, domestic 

treatment plants which discharge to the ground.

• Discharges during oil spill cleanup which have received prior authorization from 

Ecology.

• Discharges under the State of Washington Model Toxics Control Act.

• Discharges from LUST sites and vehicle and equipment washing under some 

circumstances (see below).

1.1 NPDES Permit Requirements for Non-discharging Facilities 

Which Have Zero Discharge Limitations in Effluent Limitation 

Guidelines

Federal law is clear that any discharge of pollutants to surface waters of the United States 

requires an NPDES permit. Federal regulations [40 CFR § 122.21(a)] also impose on any 

facility that “discharges or proposes to discharge” a clear “duty to apply” for an NPDES permit. 

EPA has issued guidance interpreting these regulations to impose a further duty to apply on 

certain facilities (such as concentrated animal feeding operations) that have a “potential to 

discharge.” However, facilities that do not discharge, do not propose to discharge, and do not 

have the potential to discharge have no obligation to apply for or to obtain NPDES permits.

EPA has developed categorical effluent limitation guidelines for a number of industries. The 

purpose of these guidelines is to establish for these categories the minimum technology-based 

requirements in terms of effluent limits in NPDES permits. A number of these federal effluent 

limitation guidelines (such as those for the Wood Preserving – Boulton Subcategory [40 CFR 

Part 429, Subpart H] and the Sawmills and Planing Mills Subcategory [40 CFR Part 429, Subpart 

K]) establish “zero discharge” requirements for process wastewater pollutants. Federal 

regulations require permits and permit applications from these facilities if they propose to 
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discharge or have the potential to discharge to surface waters.

A facility subject to a “zero discharge” effluent limitation guideline may seek NPDES permit 

coverage to take advantage of the “unavoidable bypass” and “upset” defenses available to 

facilities with NPDES permit coverage. To the extent that the facility operator is “proposing to 

discharge” during these bypass and upset events, such a permit application is appropriate (and 

may in fact be required by 40 CFR § 122.21(a)).

However, some facilities subject to effluent limitation guidelines may (because of topography, 

process, etc.) have no potential to discharge pollutants to waters of the United States. For these 

facilities, Ecology has decided to follow the process demonstrated in practice by EPA Region 10. 

No permits will be issued solely because the facility falls within a zero discharge subcategory. If 

the determination is made that there is a substantial probability of process water discharge to 

surface waters, an individual NPDES permit may be issued.

1.2 Independent Leaking Underground Storage Tank

(LUST) Cleanup Sites

Sites that are classified as “non-independent cleanup sites” are those under which cleanup 

activities are being conducted under the MTCA formal process of an agreed order or consent 

decree.

Sites that are classified as “independent cleanup sites” are those under which cleanup activities 

are being conducted under MTCA’s Voluntary Cleanup Program by choice through Ecology 

Toxic Cleanup Program (TCP) involvement, and those cleanup activities being conducted 

voluntarily without involvement from TCP.

Both types, if they have a discharge resulting from their cleanup activities, must follow the 

guidance below or contact Ecology directly for case-specific exemptions that may apply.

Independent Leaking Underground Storage Tank (LUST) cleanup sites are allowed an 

exemption from permits for short term discharges that meet high treatment standards. The 

following conditions apply:

• The proponent must submit a letter to Ecology. If the discharge is to a POTW, a copy of 

the letter must be delivered to the POTW. The letter shall include the following items:

1. A project description, including treatment method, disposal method, rate of 

discharge (gpm), dates of discharges, and duration of discharge (days).

2. Analytical data from an accredited laboratory showing analysis of pollutants of 

concern (see Table C following) from the proposed treatment system.

3. A street map indicating the extent of the site, location of the treatment equipment, 
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address of the site, and point of discharge to the sewer or storm drain.

4. The name and telephone number of the project manager or person who should be 

contacted about the project.

• All discharges to ground water at LUST cleanup sites must also register with the state 

Underground Injection Control (UIC) program. The UIC coordinator will evaluate the 

registration and will refer the owner/operator to the regional permit coordinator if a permit is 

required.

• All long term discharges (>60 days) to surface waters must contact the regional office.

• All long term dischargers to ground water must submit an engineering report which 

includes a hydrogeological investigation.

• The facility must notify Ecology when the discharge stops or effluent quality meets Level 2 

and a permit is no longer required.

• For Independent LUST sites involving gasoline or diesel (only) go to Table A if there is a 

short-term discharge (<60 days), otherwise go to Table B for discharges longer than 60 days.

• A facility manager may require a permit in a situation that otherwise may be exempted if 

monitoring and reporting is required.
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Table A

Short Term <60 day Discharge

Discharge Location Conditions Permit Requirement

Surface Water Meet Table C level 1 

treatment

Local approval required if 

discharge is to municipal 

stormwater system

Generally no permit required. 

Permit writers should make 

determination based on 

circumstances (e.g., if hydraulic 

capacity is a concern).

POTW Meet Table C level 3 

treatment

Local approval required

Generally no permit required. 

Permit writers should make 

determination based on 

circumstances (e.g., if hydraulic 

capacity is a concern).

Ground Water by injection 

well or UIC, hydraulically 

contained* on-site

Meet Table C level 1 

treatment 

UIC registration only

No permit required

Ground Water, but not 

contained on-site Option A: If meet Table C 

level 2 treatment 

UIC registration only (if it meets 

UIC well definition)

No permit

Option B: Meet Table C 

level 1 treatment

Permit-By-Rule

Discharge to an injection well is 

not allowed

*Hydraulically contained means that the aquifer is recharged in such a manner as to prevent the injected water from 

leaving the site. 
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Table B

Long Term ≥60 day Discharge

Discharge Location Conditions Permit Type

Surface Water Meet Table C level 1 

treatment

Local approval required if 

discharge is to municipal 

stormwater system

NPDES Permit

POTW Meet Table C level 1 

treatment

Local approval required

State Industrial User (IU) Permit, 

or Permit-By-Rule

Ground Water by UCI, 

hydraulically contained onsite

Option A: Meet Table C level 

2 treatment

UIC Registration - No permit

Option B: Meet Table C level 

1 treatment

Permit-By-Rule

Ground Water by UCI, but 

not contained on-site

Meet Table C level 2 

treatment 

Temporary Permit-By-Rule

Table C

Discharge Quality Maximum Concentration Levels

Parameter Level 1 (discharge to 

surface water)a

Level 2 (discharge to 

groundwater)b

Level 3 (discharge to 

POTW)c

pH 6.0 -9.0 6.5 -8.5 6 to 9

TPH-G 1 ppm 1 ppm 2 ppm

TPH-D 5 ppm 1 ppm 10 ppm

Total Lead 15.0 ppb 15.0 ppb 20 ppb

BTEX 100 ppb N/A 200 ppb

Benzene 5.0 ppb 1.0 ppb 10 ppb

Toluene N/A (see BTEX) 40 ppb N/A

Ethylbenzene N/A (see BTEX) 30 ppb N/A

Xylene N/A (see BTEX) 20 ppb N/A

a. Level 1 limits are based on the groundwater standards or MTCA method A value, whichever 

is more stringent.

b. Level 2 limits are based on the ground water standards or MTCA method A value, whichever 

is more stringent. c Level 3 limits are based on King County pretreatment levels and best professional judgment to prevent explosives in the 

collection system and to prevent interference or upset at the wastewater treatment plant. Permit writers should confirm that these 

levels meet local pre-treatment levels before using in permit.
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1.3. Vehicle And Equipment Washing

Ecology will generally not require discharge permits for vehicle or equipment wash water to 

ground, to POTW’s, or if it is non-discharging or regulated by the hazardous waste program. 

Instead of a permit, Ecology relies on education and outreach for these types of discharges. This 

education and outreach approach relies on the business community’s cooperation in using Best 

Management Practices identified in Vehicle and Equipment Washwater Discharges (WQ-R-95-

56). Permit writers should observe the following:

• A state wastewater discharge permit will not be issued to cover vehicle/equipment washing 

operations described in Vehicle and Equipment Washwater Discharges (WQ-R-95-56) if 

they are using BMPs consistent with this document.

• A state wastewater discharge permit may be issued under exceptional circumstances, such 

as, for a discharge to the ground over a sole source aquifer where there is reason to believe 

that the discharge needs to be controlled to protect the ground water resource. Also, where 

there is an obvious non-compliance with the appropriate BMPs, Ecology may require a 

wastewater discharge permit to prevent and/or control pollution from the discharge.

• Discharges to surface waters or to storm sewers require individual NPDES permits, 

however, in order to avoid the resource intensive process for an NPDES permit, alternatives 

to surface water or storm sewer discharges should be strongly encouraged where 

appropriate. Permits should only be issued where absolutely necessary to control pollution.

1.4. Petroleum Bulk Plants, SIC 5171

Facilities with product storage over 100,000 gallons should be issued an individual NPDES or 

State wastewater discharge permit

Facilities with product storage under 100,000 gallons are usually covered by the industrial 

stormwater general permit with a companion order to cover any monitoring and reporting 

requirements. An individual permit may also be issued.

2. APPLICATION FORMS FOR INDIVIDUAL PERMITS

When it is determined that a facility needs a permit, the facility must make an application for a 

permit; however, the facility must be allowed 30 days to submit. Applications are made on 

forms which are specific to the type of discharge. Discharges to surface waters are usually made 

on federal NPDES forms as shown in Table III-1.
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There are also application forms for state waste discharge permits. These include:

• Application for POTW Discharges to Land,

• Application for Industrial Discharge to Land, and

• Application for Industrial Discharge to POTW (for POTWs without a delegated 

pretreatment program).

A general instruction page is used with each of these state application forms.

In the past an applicant could renew a permit by submitting a letter stating there had been no 

significant change at the facility during the term of the expiring permit. Federal Regulation 

changes in 1980 no longer allow the use of these letters for NPDES permits. An applicant must 

apply on a permit application form as given in Table III-1 or its equivalent.

There is nothing in regulation that prohibits alternative applications as long as the minimum 

amount of information submitted is equivalent to that required by the federal application form. 

This is sometimes an issue for new facilities that submit engineering reports. An engineering 

report prepared in compliance with WAC 173-240 and Ecology supplementary guidance will 

have all of the information in the body of the report that is required on the permit form. In this 

case it is allowable to have the facility make out Form 1, the first page of the application, sign it, 

and attach it to the engineering report.
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Table III-1. NPDES AND STATE PERMIT APPLICATION FORMS 

TYPE OF FACILITY FORM

Municipally Owned Wastewater Treatment

Plants Form 2A

Commercial Facilities

1. New Source Forms 1 and 2D

2. New source with discharge Forms 1 and 2E

 of non-process waste water only and 

follow-up data

Industrial Facilities

1. New Source Forms 1 and 2D

2. New Source with discharge Forms 1 and 2E

 of non-process waste water and

 only follow-up data

3. Existing Source Forms 1 and 2C

 4. Reapplication Forms 1 and 2C

Mining

1. New Source Forms 1 and 2D

and

mining plan

2. Reapplication Forms 1 and 2C

Feedlot Forms 1 and 2B

Federal Forms
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Table III-1. (Continued).

Fish Hatchery Forms 1 and 2B

Water Treatment Forms 1 and 2D

Storm Water Form 2F

Industrial Discharge to Land Ecology form 040-179

Industrial Discharge to a POTW Ecology form 040-177

POTW Discharge to Land Ecology form 040-178

Industry to Industry Ecology form 040-177

All of the wastewater discharge permit application forms are available as electronic fill-in forms 

at www.ecy.wa.gov/programs/wq/permits/guidance.html.

State Forms
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3. APPLICATION PROCESS

The process of applying for a wastewater discharge permit is often frustrating for both the 

applicant and the permit writer. The key to making it go as smoothly as possible is to 

communicate the requirements for application as early and as in as much detail as possible. 

Many large industries are very knowledgeable about the permit process and only need direction 

on their specific application process. Smaller dischargers may require some background 

information on application requirements. For example, many smaller dischargers may not be 

familiar with the objective and process of whole effluent toxicity testing. The NPDES 

requirements for permit application are given in 40 CFR 122.21. The processes of application 

and background review are illustrated in Figures III-1 and III-2.

The permit application is reviewed by the permit writer for completeness and accuracy. 

Reviewing an application for completeness is a fairly simple task but there's only one way to do 

it. Go over it item by item, making sure each blank is filled in. Each part of the form should 

have the requested information or an indication that it is not applicable. The instructions for both 

the EPA forms and the state forms instruct the applicant to place an "NA" in a blank to show it 

has been considered but the question is not applicable. Many times an application is incomplete 

and the question is how to deal with it. Do not fill in any information yourself unless it's 

information commonly available from public sources. Substantial time is saved by simply 

getting the information over the telephone and then writing in the answer. This information will 

not be certified as correct by the person who signed the application. Send the application back to 

the applicant for completion if there is any uncertainty. This is the legally correct procedure.
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Figure III-1. Permit Application Review

Review Permit Application

Is the application on

the correct form?

Require new application on

correct form

Does the

application include all

outfalls, priority pollutant,

sludge and toxicity data

when required?

Establish schedule for submittal of

required information

Does the application

have all of the information

necessary to adequately

characterize the nature and quantity

of pollutants in the effluent and

their impact on the receiving

water?

Establish schedule for the submittal of

the required information

Are all

calculations and flow

diagrams correct

Request recalculation and resubmittal

May begin public notice of

application now or after facility

inspection

Go to Figure III-2

yes

no

no

yes

no

yes

no

yes

Data Received

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Figure III-2. Background Information Review

CONTINUED

FROM

FIGURE III-1

IS THE

DISCHARGE A

NEW SOURCE

REVIEW THE CURRENT PERMIT AND FACT

SHEET FOR DOCUMENTATION OF CURRENT

PERMIT LIMITS 

REVIEW ENGINEERING REPORT AND

SUPPLEMENTAL INFORMATION

DETERMINE WHAT FACILITY CHANGES SUCH AS

PRODUCTION OR WASTEWATER TREATMENT

HAVE OCCURRED SINCE THE LAST PERMIT WAS

ISSUED 

REVIEW THE RECENT DISCHARGE MONITORING REPORTS TO

EVALUATE THE COMPLIANCE HISTORY AND OBVIOUS TREATMENT

DEFICIENCIES

REVIEW HAZARDOUS WASTE AND WATER RIGHTS FILES

REVIEW INSPECTION REPORTS FOR GENERAL

BACKGROUND AND COMPLIANCE PROBLEMS

REVIEW DEVELOPMENT DOCUMENTS,

VOLUME II OF THE TREATABILITY MANUAL,

AND APPROPRIATE REFERENCE TEXTBOOKS

TO DEFINE THE CHARACTERISTICS OF THE

INDUSTRY TYPE INVOLVED

ARE ADDITIONAL

DATA NEEDED FROM THE

APPLICANT TO COMPLETE THE

BACKGROUND

INFORMATION?

REQUEST

SUPPLEMENTAL

INFORMATION

DATA RECEIVED

INSPECT THE FACILITY BEGIN PUBLIC NOTICE OF

APPLICATION

DEFINE WHICH EFFLUENT GUIDELINES

HAVE BEEN PROMULGATED FOR THIS

FACILITY TYPE

REQUEST SUPPLEMENTAL INFORMATION

AND TECHNICAL ASSISTANCE FROM THE

EPA EFFLUENT GUIDELINES DIVISION, IF

NECESSARY

GO TO FIGURE

IV-1

NO

YES

YES

NO

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Some requirements that are often overlooked in applications are:

• Grab samples must be used for pH, temperature, cyanide, total phenols, residual chlorine, oil 

and grease, fecal coliform, and fecal streptococcus. All others are collected by 24-hour 

composite unless waived by Ecology. If the 24- hour composite sampling is waived, the 

applicant is then required to collect a minimum of 4 grab samples which are representative 

of the effluent. The 4 grab samples can be combined for analysis.

• Every applicant must submit data for BOD, COD, TOC, TSS, Temperature (winter and 

summer) and pH. Ecology may waive these test requirements if the applicant can 

demonstrate they are not necessary for characterizing the effluent.

• Primary industries have some mandatory testing requirements for toxic pollutants (40 CFR 

122.21 Appendix D, Table I and Table II; also listed in Application Form 2C). Primary 

industries that are also small businesses [122.21(g)(8)] may be exempted from these testing 

requirements. Existing dischargers who believe certain pollutants may be present in their 

effluent must test for those pollutants (122.21 Appendix D, Table IV, Table V).

• Municipalities also have some mandatory application requirements for whole effluent 

toxicity and sludge. POTW's larger than 1 MGD or those with pretreatment programs are 

required to submit valid whole effluent biological toxicity testing. This requirement may be 

satisfied if the expiring permit contains a requirement for effluent characterization of whole 

effluent toxicity (see Chapter VI, Part 5). The permit writer should note the use of this 

option in the fact sheet.

The following are application requirements for municipalities under the form 2A. Permits 

should contain the appropriate monitoring requirements to assure the data is available at time of 

reapplication.

NPDES Application Testing Requirements for municipalities with design flow< 0.1 MGD 

(a minimum of three values for each parameter collected within 4.5 years prior to 

submission of the application)

pH (min and max)

Flow rate

Temperature (winter and summer)

BOD (or CBOD)

Fecal Coliform

Total Suspended Solids
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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Additional NPDES Application Testing Requirements for municipalities with design flow 

≥ 0.1 MGD (a minimum of three values for each parameter collected within 4.5 years prior 

to submission of the application).

Ammonia

Total Residual Chlorine

Dissolved Oxygen

Total Kjeldahl Nitrogen

Nitrate plus Nitrite Nitrogen

Oil and Grease

Phosphorus (Total)

Total Dissolved Solids

NPDES Additional Application Requirements for municipalities with design flow ≥ 1.0 

MGD or with Pretreatment Program (a minimum of three values for each parameter 

collected within 4.5 years prior to submission)

Metals, Cyanide, Phenols, and Hardness

Volatile Organic Compounds

Acid-extractable Compounds

Base-neutral Compounds

Toxicity Testing:

quarterly testing in past year using two species;

or

results from four acute or chronic tests performed at least annually within the four and one 

half years prior to application.

Upon request the applicant must submit other information which may be needed in deciding 

whether to issue a permit. The requested information may include additional quantitative data on 

the effluent or receiving water.

3.1 Analytical Requirements

Ecology has defined the analytical requirements (detection and quantitation levels) for permit 

application and for compliance monitoring of effluent. The objective is to reduce the number of 

non-detects when effluent is analyzed. The current table is posted with the other permit writer’s 

materials in Outlook.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-17

3.2 Reviewing an Application

When a permit application is completed it must be reviewed for accuracy. The accuracy of the 

permit application can be assessed by checking the numbers on the application, and, for existing 

dischargers, by reviewing the files and inspecting the facility.

• Everybody makes mistakes in arithmetic. Review the concentrations of pollutants reported 

in the effluent to make sure they're reasonable. Then add the flows to ensure the total is 

correct, and then do the mass loading calculations.

• Check the files for information. If the application is for an existing facility there is probably 

a large amount of information in the files. A reporting facility will have a previous permit 

file, discharge monitoring reports, correspondence and inspection reports.

In addition to the water quality files, there may be some good information in other files such as 

the Dangerous Waste files. The Dangerous Waste Regulations (Chapter 173-303 WAC) require 

anyone who generates, transports or treats dangerous waste to have an EPA/state identification 

number and to report their activities annually. There may also be some inspection reports in this 

file. The information in this file may indicate some pollutants or problems that need attention in 

the permit process. (See Section 8, following, which discusses the domestic sewage exclusion 

for hazardous waste.)

• Check to see if the facility has a water right and if it corresponds to the water use in the 

application.

• If you're new to the office, check with the complaint inspectors to see if there is a 

history of complaints on the facility.

• Check any additional information available on similar types of discharges (EPA 

Development Documents) to see if the reported effluent concentrations seem 

reasonable.

• Check with other permit writers in the agency who have permitted this type of facility 

to see if there are any special considerations in the application process.

• Inspect the facility. An existing facility that is being permitted should be inspected at 

least once, except those being covered under a general permit. A facility inspection 

acquaints you with the facility, the people you'll be dealing with, and verifies the 

information in the permit application. If you're not an experienced inspector, review the 

Ecology Inspection Manual beforehand.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-18

The things you want to determine or verify during this inspection are:

• The application's accuracy in describing the production processes;

• The number and type of outfalls (storm drains are frequently omitted);

• The raw materials and chemicals used;

• The operation and maintenance of the treatment equipment;

• Production; and,

• The company attitude toward environmental compliance.

Go over the facility from roof to basement. Air pollution equipment may be discharging 

pollutants to the roof, which washes off in the rain. Piping in basement areas may be neglected 

and have a potential for leakage. Pay particular attention to those things (such as the need for 

spill prevention and housekeeping) that can be used as preventative mechanisms in permits but 

are not described very well in permit applications. Take photographs of key processing areas or 

problem areas.

For those permit managers who have been dealing with a facility for a long time, this is a good 

time to take a fresh look and ask all the questions that you would ask if you were seeing the 

facility for the first time.

You may wish to include a sit-down meeting at this time to discuss the general direction of the 

new permit and any new regulatory requirements that might be included in the permit. Avoid 

discussion of specific numbers at this time.

If you have discovered inaccuracies in the application, point out the need to get correct 

information. Remind them of the statement on the signature block of the application if 

necessary.

4. APPLICATION AND EXPIRED PERMITS

4.1 NPDES

If a permittee has made "timely and sufficient application" for permit renewal, an expiring permit 

remains in effect until Ecology has either denied the application or issued a new permit (WAC 
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-19

173-220-180(5)). Consequently, an expired NPDES permit remains in effect while Ecology 

reviews an application for a permit renewal, so long as the application is "timely and sufficient." 

Ecology must notify the permittee of the extension, by letter, that they have made timely and 

sufficient application and that the permit remains in effect until the permit is reissued or for 

another five years, whichever comes first.

4.2 State

A permittee must submit a satisfactory application at least 60 days prior expiration of an existing 

permit (RCW 90.48.170) (WAC 173-216-070) or as specified in the existing permit, unless the 

requirement is waived by Ecology. A satisfactory permit application consists of a completed 

form including the proper signature and any other information determined as necessary by the 

Department (WAC 173-216-070(4)). The existing permit remains in effect until the application 

has been finally determined by the Department (RCW 34.05.422(3)). In the event that Ecology 

takes no action on an application within 60 days, the applicant receives a temporary permit based 

on information in the application. The temporary permit is effective until Ecology acts on the 

application or for a period of five years. This process is illustrated for new and renewal state 

permits respectively in Figures III-3 and III-4.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-20

Figure III-3. Application process for a new state wastewater discharge permit.

SEND

APPLICATION AND

COVER LETTER

REVIEW BY

PERMIT

COORDINATOR

IS APPLICATION

COMPLETE?

SCREEN BY

PERMIT

MANAGER

IS APPLICATION

ACCEPTABLE?

1. REJECT APPLICATION OR

2. CALL FOR INFORMATION OR

3. ISSUE ORDER

FEES

PAID? 60 DAYS START*

NO PERMIT

POSSIBLE ENFORCEMENT

NEED

PERMIT?

ISSUE PUBLIC NOTICE OF

APPLICATION

WILL THIS PERMIT HAVE

RESTRICTIONS ON

DISCHARGE AND REQUIRE

MONITORING?

WILL THIS PERMIT HAVE

ONLY MONITORING

REQUIREMENTS?

ISSUE PERMIT

AND FACT SHEET

SEND LETTER OF

NOTIFICATION OF

TEMPORARY

PERMIT (RCW

90.48.200)

NO

SEND LETTER

SAYING NO

PERMIT

NECESSARY

YES

YES

NO

NO

STAPNEW2.ADS

IF PERMIT WILL TAKE

LONGER THAN 60

DAYS SEND LETTER

ESTIMATING TIME TO

ISSUANCE 

YES

1. REJECT APPLICATION OR

2. CALL FOR INFORMATION OR

3. ISSUE ORDER

NO

YES

NO

* SEPA PROCESS MUST BE COMPLETED

NO

YES

ISSUE PERMIT

DETERMINE FEE

CATEGORY AND

SEND LETTER

YES
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-21

Figure III-4. Application process for renewal of a state wastewater discharge permit.

SEND APPLICATION, COVER 

LETTER, AND CERTIFICATION 

DOCUMENT

RECEIVE 

APPLICATION 

AND 

CERTIFICATION

INITIAL REVIEW 

OF APPLICATION 

BY PERMIT 

COORDINATOR

IS 

APPLICATION 

COMPLETE?

1. RETURN APPLICATION 

FOR COMPLETION OR 2. 

CALL FOR MISSING INFO OR 

3. ISSUE ORDER FOR INFO

REVIEW BY 

PERMIT 

MANAGER

IS APPLICATION 

ACCEPTABLE?

60 DAY COUNT 

STARTS

IS THERE A CHANGE IN THE 

VOLUME OR CHARACTER OF 

THE WASTEWATER FROM THE 

PREVIOUS APPLICATION?

SEND A LETTER WHICH SAYS 

ECOLOGY IS ACTING ON THE 

APPLICATION AND THE 

PERMIT ACTION IS EXPECTED 

ON DATE. THE CURRENT 

PERMIT WILL REMAIN IN 

EFFECT UNTIL DATE 

(TEMPORARY PERMIT). THE 

LETTER MAY SAY AN 

UPDATED APPLICATION WILL 

BE REQUESTED.

CONDUCT OR 

REQUIRE PNOA

PREPARE AND 

ISSUE PERMIT

NO

NO

YES

YES

NO

YES
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-22

5. APPLICATION FOR NEW PERMITS

5.1 NPDES

Applicants must submit an application at least 180 days before the date they wish to begin 

discharging or, with Ecology’s agreement, in sufficient time prior to commencement of 

discharge to allow the Department to formulate technology-based and water quality-based 

limitations. No discharge is authorized until the effective date of the permit.

5.2 STATE

Applicants must submit a satisfactory permit application at least 60 days before the date of the 

proposed discharge. The applicant will receive a temporary permit if Ecology fails to act upon 

the application within 60 days. The temporary permit is conditional upon the applicant having 

completed SEPA process. Any action within the 60-day period from the time of filing also 

prevents the temporary permit from becoming effective. Typically, this action would be a 

notification to the applicant that the application was not satisfactory for Ecology to process the 

permit.

6. TIME OF REAPPLICATION

All Permittees must reapply for permits every five years (40 CFR 122.46(a)) (RCW 90.48.180). 

This includes temporary permits and permits extended during application if the application 

period extends for five years. An NPDES permit extended for 5 years during application must 

be reissued upon the second application.

7. CONFIDENTIALITY OF INFORMATION

A permit writer is occasionally requested to keep confidential the information obtained during 

the permit application process. A permit writer cannot grant confidentiality because the 

authority is vested only to the director or those delegated the authority by the director.

The federal regulations (40 CFR 122.7(c)) state that information required by NPDES application 

forms may not be claimed as confidential. Information not explicitly required on the NPDES 

forms and information required on forms for state waste discharge permits is subject to the state 

Public Disclosure Act codified in Chapter 42.17 RCW. Confidentiality is also addressed in 

Chapters 43.21A and 90.52 RCW.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-23

The Public Disclosure Act generally makes all information normally submitted to Ecology as 

part of the permit process subject to public disclosure except "Valuable formulae, designs, 

drawings, and research data obtained by (Ecology) within 5 years of the request for disclosure 

when disclosure would produce private gain and public loss."

RCW 43.21A.160 provides that upon request, the director of Ecology may treat certain 

information furnished as confidential if such information relates to processes unique to the 

person providing the information, or if such information might adversely affect the competitive 

position of that person if released to the public, provided that such action would not be 

detrimental to the public interest.

RCW 90.52.020 states that Ecology shall provide proper and adequate procedures to safeguard 

the confidentiality of manufacturing processes. The confidentiality shall not extend to waste 

products discharged into the waters or air of the state.

The request for confidentiality must accompany the information for which the request is made. 

If the information is a part of the NPDES application form then no confidentiality can be 

granted. Other information is considered by the appropriate section head, as a delegate of the 

Director, as to whether it may be deemed confidential. The AG's have not provided guidance as 

to the interpretation of "public loss" or "detrimental to the public interest". Determination of 

"public loss" or "detrimental to the public interest" will therefore be made on a case-by-case 

basis.

8. DOMESTIC SEWAGE EXCLUSION

In some instances industrial dischargers to POTW’s are allowed to discharge dangerous waste if 

the waste is treated in the POTW. The judgment on treatability is made by conferring with the 

regional hazardous waste and toxics reduction section.

Section E, question 8 of the state permit application for discharge to a POTW asks if the 

wastewater to be discharged designates as a dangerous waste according to procedures in Chapter 

173-303 WAC. The applicant may answer yes, no, or don’t know. If the applicant answers yes 

they complete the following question 8 on the application which asks for the details on how the 

waste designated. In some cases it will be immediately apparent that some dangerous wastes 

cannot be discharged. For example, any wastewater that designates because of characteristics 

(ignitable, reactive, corrosive, TCLP) would not be allowed to be discharged without treatment. 

In other cases, such as with dilute listed waste or state-only toxic waste (see Appendix 3.1), it 

will not be immediately apparent if the discharge is allowable. In these instances the permit 

writer should confer with the regional hazardous waste and toxics waste reduction section.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-24

If the applicant answers question 7 “no” or “don’t know” the permit writer must use information 

from other parts of the application and from experience to judge the presence of dangerous waste 

in the wastewater. If dangerous waste potential exists the permit writer should confer with the 

regional hazardous waste and toxics waste reduction section about the course of action on the 

permit.

Dangerous waste discharges are subject to source reduction (pollution prevention) measures 

under:

• HWTR interpretive policies for the Domestic Sewage Exclusion.

• 40 CFR Part 403.12(p)(4), referenced in WAC 173-208.

The permit writer should confer with Regional Hazardous Waste and Toxics Reduction staff for 

information on source reduction opportunities. In many cases, source reduction can offer the 

applicant a variety of attractive benefits.

Case study examples for some common pollutants:

1. Formaldehyde--treatable

Formaldehyde is an animal carcinogen, suspected human carcinogen, and mutagen which 

is a State toxic dangerous waste at 10% concentration. Fate modeling indicated that 

formaldehyde would probably be 84% biodegraded in an extended aeration activate sludge 

sewage treatment plant. King County has chosen to accept this waste based on its 

treatability (i.e., biodegradability) and low potential for interference.

2. Antifreeze--recyclable

Ethylene glycol antifreeze is a State toxic waste that can be economically recycled through onsite filtration or off-site re-refining. Rather than accept this high-BOD waste, King County has 

established recycling of antifreeze as a best management practice.

3. Dry Cleaner Separator Water--dilute listed waste

Dry cleaner separator water is saturated with perchlorethylene (tetrachlorethene), a listed waste. 

Because the concentration of the solvent can range from 300 to 3000 mg/l, it does not meet the 

HWTR policy criteria for "dilute listed wastes" mentioned in the regulatory language of the 

domestic sewage exclusion. The WQ and HWTR programs have agreed not to allow disposal of 

separator water to the sewer.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-25

WASTESTREAM IS IDENTIFIED BY INDUSTRIAL

USER SURVEY, SITE VISIT, OR STATE PERMIT

APPLICATION

Figure III-5. Interpreting the domestic sewage exclusion (DSE).

IS THE

DISCHARGE TO

A POTW?

THE DSE

DOES

NOT

APPLY

NO

DOES THE

PROPOSED

DISCHARGE/WASTESTREAM

DESIGNATE AS A DANGEROUS

WASTE?

YES

NO

DOES THE PROPOSED WASTE

EXHIBIT THE DANGEROUS WASTE

CHARACTERISTICS , SUCH AS

IGNITABILITY, CORROSIVITY,

REACTIVITY OR TCLP?

IS THE WASTE A PERSISTENT

DANGEROUS WASTE

(HALOGENATED HYDROCARBONS

>100 PPM) OR A PAH GENERATOR

GREATER THAN > 10,000 PPM OR A

SOLI D /CORROSIVE WASTE?

NO

THE WASTE IS A TREATED

WASTE, A DILUTE LISTED

WASTE OR A STATE ONLY DW

DUE TO ITS TOXICITY

NO

YES

YES

HAVE AKART AND P2

BEEN APPLIED TO THE

WASTE?

NO

YES

IS THE WASTE

SUITABLE FOR

DISCHARGE TO

A POTW?

NO

DOES THE

POTW AGREE

TO ACCEPT

THE WASTE?

YES

PROHIBIT

THE

DISCHARGE

ISSUE STATE

WASTEWATER

DISCHARGE

PERMIT WITH

APPROPRIATE

LIMITATIONS

NO

YES

YES

IS TREATMENT

AVAILABLE TO REDUCE

CHARACTERISTICS?

DISCHARGE IS

PROHIBITED

UNDER THE DSE

AND

PRETREATMENT

RULE. TALK TO

HWTR STAFF

ABOUT DISPOSAL

OPTIONS

APPLY

TREATMENT/P2

YES

NO
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-26

9. OWNER/OPERATOR AGREEMENTS

Municipalities frequently contract the operation and maintenance of the wastewater treatment 

plant. This requires some special consideration from Ecology.

9.1. Ecology Must Review Agreements

RCW 70.150 authorizes a public body to enter into service agreements to design, finance, 

construct, own, operate or maintain water pollution control facilities. Before a public body 

enters into a service agreement to provide any of these services, the agreement "shall be 

reviewed by the department of ecology to ensure consistency with the purposes of chapters 90.46 

and 90.48 RCW." RCW 70.150.040(9). Ecology does not have the resources to review all 

municipal agreements pertaining to water pollution control facilities; therefore, Ecology will 

only review contracts for operation of wastewater treatment facilities.

9.2 NPDES Permittee under Owner/Operator Agreement

Under section 301(a) of the Clean Water Act, 33 USC section 1311(a), "the discharge of any 

pollutant by any person shall be unlawful" unless the discharge is authorized by an NPDES 

permit. This prohibition suggests that both the public owner and the private operator need to be 

permitted since both the owner and operator are "persons" who will be discharging pollutants. 

However, under 40 CFR section 122.21(b), when a facility is owned by one person but operated 

by another, it is the operator's duty to obtain a permit. While this regulation suggests that only 

the private operator needs to be permitted, the regulation only says it is the operator’s duty to 

obtain a permit. It does not address who should be listed as permittee(s) on the permit.

In general, it is the Water Quality Program’s policy to identify contract operators as copermittees on individual municipal NPDES permits, to address both state and federal 

requirements for permittees. The policy is based on advice from the Attorney Generals’ Office 

and was accepted by the PCHB in its Hartstene Opinion (Order on Summary Judgment, PCHB 

No. 09-152, WSUD and Hartstene Pointe WSD v. Ecology).

However, in the Hartstene Opinion, the Board stopped short of stating that in every case, copermittee status for owners and operators is appropriate. As a result, Ecology must decide on a 

case-by-case basis if identifying the operator as a co-permittee is appropriate.

In reviewing any service agreement for wastewater operating services, Ecology staff should:

• Review the service agreement using the recommended contract provisions following 

Section 9.3 as a guide.

• Discuss with a supervisor any need for AG assistance, and if necessary, request that an 

AAG review the service agreement. An AG review may be helpful for complicated 

contracts.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-27

• Within 30 days of receipt of the agreement, respond in writing to the municipality.12

In deciding whether to identify a contract operator as a co-permittee, Ecology staff and managers 

should:

• Consider the extent of the operator’s control over the treatment system, as described in 

the service agreement.

• Consider the experience and record of the operator at other facilities.

• Consider the performance and enforcement provisions in the service agreement between 

the owner and the operator.

• Review the recommendations or comments from the Attorney General’s office.

• Make a reasoned decision based on the facts, Ecology guidance, and the manner in which

the entities’ service agreement defines the responsibilities each will have (see the 

Hartstene Opinion, pages 8 and 9).

The nature of these service agreements is commonly one of shared responsibility for the facility. 

As a result, Ecology may commonly identify the operator as a co-permittee. In the Hartstene 

decision (pages 7-8), the PCHB noted:

The undisputed facts establish that both Hartstene and West Sound are responsible for 

operation and maintenance of the plant.... Hartstene, as owner of the physical plant, is 

responsible for capital improvements and expenditures related to maintenance, and is 

“ultimately responsible for compliance” with permits issued by Ecology and other 

agencies. However, the Interlocal Agreement between Hartstene and West Sound for the 

operation of the Plant is premised on the fact that Hartstene lacks qualified employees to 

operate the plant, and therefore looks to West Sound to manage and operate the sewer 

system. Indeed, the very purpose of the agreement is to have West Sound provide its 

expertise and staff to Hartstene for Plant operation.... Both the owner and the operator 

have duties in relation to Plant operations, and those operations result in discharges to 

state waters. Discharges must be consistent with permit terms, and both parties must 

ensure compliance with the same. Given the facts, and Ecology’s broad authority under 

the NPDES program to control the discharges of pollutants to waters of the state, Ecology 

was well within its authority to require both entities to be named as permittees on the 

NPDES permit.

Ecology staff and managers should assume that co-permittee status will be necessary to ensure 

 

1 Ecology does not need to approve the contract. RCW 70.150.040 (9) reads in part: Before any service agreement is entered 

into by the public body, it shall be reviewed by the Department of Ecology to ensure consistency with the purposes of chapters 

90.46 and 90.48 RCW. The Department of Ecology has thirty days from receipt of the proposed service agreement to complete 

its review and provide the public body with comments.... 

2 The Attorney General may not be able to respond within Ecology’s 30-day statutory deadline. In such cases, Ecology staff 

should respond within the 30-day statutory deadline and if the agency has requested review by the AG, note that the agency may

forward additional comments or make a decision on co-permittee status once that review is complete.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-28

permit compliance when inspections or compliance reviews reveal un-resolved management, 

operation or maintenance issues, especially those that have caused permit violations. As with 

any “co-permittee” designation, the service agreement must support the co-permittee 

determination.

There are also facilities where Ecology staff and managers may consider issuing the permit to the 

owner only, including facilities where:

1. Listing the contractor as a co-permittee would create a disproportionate burden for a 

small community to attract an operator, due to location or other factor; or

2. The service agreement is for a limited duration; for example, to provide temporary 

service until the owner can hire a permanent contractor, or to train staff; or

3. The need for enforcement has been or is expected to be low; for example, at larger 

facilities where owner resources and planning have historically addressed capacity or 

operational problems before they arise.

4. The operator has a superior record of compliance at the facility or other facilities; and the 

service agreement allows the owner to enforce on permit requirements as a matter of 

service agreement compliance.

In cases were Ecology issues the permit to the owner only, the service agreement should address 

the recommended provisions that follow Section 9.3 (Recommended Service Agreement 

Provisions for Wastewater Treatment Plant Operations).

Naming a contract operator as a co-permittee is an important decision with ramifications for both 

the operator and the owner. Operators that are co-permittees:

• Are subject to Ecology enforcement and third party liability.

• Face potential capital expenditures (the contract should clearly identify the owner as 

responsible for capitol costs) that logically should fall on the owner.

• May turn down contracts that result in exposure, especially at small facilities where 

problems arise from a lack of resources.

Contract operators facing a greater risk may pass their risk-related costs (including insurance) 

onto the owner. While exposure can be handled via contract, there is a transactional cost

associated with contract enforcement. Co-permittee status complicates the owner-contractor 

relationship in a manner that Ecology staff may not appreciate.

Accordingly, when Ecology is proposing co-permittee status at a facility, Ecology staff and 

management (i.e. the Section or Field Office Manager) should consider meeting with the facility 

owner and the contract operator, to discuss concerns and consider alternatives.

In all cases, the decision to identify the operator as a co-permittee resides with the Section or 

Field Office Manager, as delegated by the Program Manager. 
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-29

Finally, it is critical that permit writers note the contractor’s responsibilities in the fact sheet 

(using the service agreement as a reference) and document the decision to identify (or not) the 

operator as co-permittee.

9.3 State Permittee under Owner/Operator Agreement

With respect to state waste discharge permits, under WAC 173-216-110(8), permits for domestic 

wastewater facilities shall be issued only to a public entity, however, if a domestic wastewater 

facility is owned by a nonpublic entity under contract to a public entity, a joint permit shall be 

issued to both the public and non-public entity.

----------------------------------------------------------------------------------------------------------

Recommended Service Agreement Provisions for Wastewater Treatment Plant Operations

The service agreement should define the facilities covered by the agreement (e.g., treatment 

plant, pump stations, collection system, pretreatment program), and include provisions 

addressing:

• Responsibility for management, operations, maintenance, and capital improvements

• Permit compliance

• Permit renewal process (application and entity review)

• Monitoring and reporting

• Record keeping 

• Solids handling

• Coverage including vacation coverage, emergency and non-routine operations.

• Ordering and payment for supplies and equipment

• Capital improvements

• Communication between the contractor and owner addressing the state of the facility

• Contractor transitions

• Penalty responsibilities

• Responsibility for implementing pretreatment requirements

• Compensation, insurance, indemnification, and Force Majeure.

Ecology recommends that the owner/operator write the service agreement in the “active voice” 

to make it clear which party is responsible for each activity.

The service agreement should ensure that the contractor will:

1. Manage and operate the plant to meet permit requirements and prevent nuisance 

conditions.

2. Notify Ecology as required by the permit reporting conditions, in particular reporting for 

non-compliance.

3. Calibrate, maintain and repair all equipment to manufacturers’ specifications, and to 

preserve warranties.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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III-30

4. Operate the facility according to the Ecology-approved operation and maintenance 

manual.

5. Repair equipment in an expeditious manner to ensure that it is serviceable at all times.

6. Staff the plant with certified operators, at the appropriate level.

7. Obtain and maintain laboratory certification for permit-required analysis, unless the 

facility uses a contract laboratory; and use the appropriate test methods as defined in the 

permit and as accredited.

8. Prepare monthly DMRs and any other DMRS at the required permit frequency. The 

owner may retain or delegate signature authority, and may take responsibility for other 

reporting.

9. Allow Ecology to inspect the facility, inspect and copy records, and sample any 

substances or parameters necessary to determine compliance with the permit, at 

reasonable times, with or without prior notification. Reasonable times include afterhours site visits during non-routine operations.

10. Cooperate with the owner on planning, design, construction and audits.

11. Keep permit-related records for three years or longer for records related to any 

unresolved litigation regarding the discharge of pollutants by the Permittee, or when 

requested by Ecology.

12. Provide for termination of the service agreement for cause or convenience.
CHAPTER III. THE APPLICATION AND BACKGROUND REVIEW (JULY 2011)

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CHAPTER IV. DERIVING TECHNOLOGY-BASED EFFLUENT LIMITS (JULY 2011)

Permit Writer’s Manual

IV-1

CHAPTER IV. DERIVING TECHNOLOGY-BASED 

EFFLUENT LIMITS

This chapter, chapter VI and chapter VII discuss the major task of writing a wastewater 

discharge permit - deriving the effluent limits. The effluent limits restrict the amount of 

pollutants that may be discharged. Effluent limits may be based on the technology which is 

available to treat the pollutants at a reasonable cost (technology-based) or they may be based on 

the effect of the pollutants in the receiving water (water quality-based), whichever is most 

stringent. Derivation of the effluent limits, whether they're based on technology, as discussed in 

this chapter or on water quality, as discussed in following chapters, is the core task of permit 

writing and often the most complex task.

Effluent limits are process control parameters or numbers which indicate that a process, which in 

this case is wastewater treatment, is functioning properly.

Not all of the pollutants in an effluent are limited with numeric limits. A pollutant may not 

require an effluent limitation if it meets all of the following:

• Its concentration is too low to be treated at a reasonable cost; and,

• It can’t be eliminated by production changes or best management practices; and,

• There is no potential for causing surface or ground water quality or sediment quality 

standards violations; and,

• It is not listed in regulations, such as effluent guidelines.

There are two general approaches to deriving technology-based effluent limits. A permit writer 

can use Federal effluent guidelines, if they are applicable and appropriate, or develop effluent 

limits specifically for an individual discharger or pollutant (case-by-case). In some cases a 

permit may contain both types of effluent limits.

This chapter discusses the derivation of technology-based effluent limits from the federal 

effluent guidelines, provides a step-by-step process on how they're used and details some 

problems with them. An example is provided to demonstrate the use of effluent guidelines.

This chapter also discusses the development of technology based effluent limits on a case-bycase basis under state (AKART) and federal authority.

Flow charts at the end of the chapter illustrate the process of developing technology-based 

effluent limits.

Adjustment of effluent limits to account for autocorrelation is discussed in Part 4 of this chapter.
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1. EFFLUENT LIMITATION GUIDELINES

The Federal Water Pollution Control Act of 1972 (Clean Water Act) directed EPA to develop 

standards of performance (effluent limitations) for industrial categories. Specifically, the law 

required existing industrial dischargers to achieve "effluent limitations requiring the application 

of the best practicable control technology currently available (BPT)" by July 1, 1977. The law 

also required dischargers to achieve "effluent limitations requiring the application of the best 

available technology economically achievable (BAT)" by July 1, 1983. Other performance 

standards to be developed were new source performance standards (NSPS) for new direct 

dischargers and pretreatment standards for indirect dischargers. The Administrator (of EPA) was 

given one year to develop and implement these performance standards.

EPA was unable to complete all effluent guidelines within the statutory deadline due to technical 

problems and pressure from various trade associations. In addition, EPA did not fully address 

toxic discharges in the guidelines it did promulgate. As a result, in 1976, EPA was sued by 

several environmental groups for failing to accomplish the promulgation of effluent guidelines as 

directed in the Clean Water Act. The EPA and the environmental groups reached a settlement 

agreement which required EPA to develop a program and adhere to a schedule for promulgating 

BAT effluent guidelines, pretreatment standards and new source performance standards for 65 

priority pollutants and classes of pollutants. This agreement was limited to a group of 21 major 

categories of industries which became known as the primary industries. These are listed in 40 

CFR 122 Appendix A. This settlement was incorporated into the 1977 amendments of the Clean 

Water Act. The 1977 amendments also redefined BAT to include only toxic and 

nonconventional pollutants. The deadline for meeting BAT limits was 3 years after their 

promulgation but no later than July 1, 1987 (The 1987 amendments to the Clean Water Act have 

moved this deadline to March 31, 1989). The 1977 amendments also redefined BAT for 

conventional pollutants to become "best conventional pollutant control technology (BCT)." The 

deadline for achieving BCT was July 1, 1984 but the date was amended to become March 31, 

1989.

When Congress enacted the 1977 amendments, they also required that a cost test be applied to 

any treatment that was proposed for BCT (more on the cost test later, in the case-by-case permits 

section). The EPA developed and published the regulations for BCT in 1979. At the same time 

the EPA published BCT limits for 41 industrial subcategories. This 1979 regulation was 

challenged and the final BCT methodology was not adopted until 1986.
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All of the proceeding is to show some of the gyrations on the way to achieving the intent of 

Congress to develop technology-based performance standards. It also helps to explain why some 

of the effluent guidelines, such as feedlots, contain BAT requirements for conventional 

pollutants or BCT limits that were never imposed. For more information on the history of the 

promulgation of effluent guidelines (see Miller, et al. 1990).Miller, L.A., R.S. Taylor, L.A. 

Monk. 1990. NPDES Permit Handbook. Government Institutes, Inc., Washington, D.C.

1.1 A Summary of Some Treatment Standards as Currently 

Defined

BPT - Best Practicable control Technology currently available - applicable to conventional 

pollutants - to be achieved by July 1, 1977

BCT - Best Conventional pollutant control Technology (BCT) - the level of treatment that 

succeeds BPT for conventional pollutants. The deadline for achieving BCT was July 1, 1984 but 

was changed in the 1987 amendments to March 31, 1989.

BAT - Best Available Technology economically achievable - applicable to toxic pollutants. The 

deadline for achieving BAT was July 1, 1983 but was changed by the 1987 amendments to 

March 31, 1989.

We now have performance standards (effluent limitation guidelines) for 52 groups or categories 

of industries and over 1,000 performance standards for all the subcategories. EPA typically 

developed these performance standards after completing the following tasks:

• Performing a literature search to obtain the latest information on treatment processes;

• Conversing with regional and state staff with experience pertaining to the industry;

• Reviewing any comparable industrial limitations;

• Conducting industrial plant surveys to collect statistical data on operations;

• Conducting site visits, sampling, and evaluation of selected industrial sites;

• Soliciting public comment from industrial representatives and the public at large;

• Conducting an economic analysis of the impact of the identified treatment technology 

on the industry.

EPA estimated that it required 2-5 years to develop each set of standards. The cost for each set 

of standards ranged from two million to 20 million dollars for technical contractors plus between 
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3 and 25 person-years of EPA staff effort. The list of industries for which EPA has developed 

effluent guidelines is given in 40 CFR 122 Appendix A. The information that EPA developed is 

available in several forms. The most informative are the development documents prepared by 

EPA. These documents contain the technical and economic information from which the effluent 

guidelines were developed. The effluent guidelines are summarized in 40 CFR Parts 400-471.

1.2 Steps for Using Effluent Guidelines

STEP 1. Categorize the discharger.

To be able to use the effluent guidelines it's necessary to know the processes at the facility you're 

permitting. Then if you're lucky, the facility will fit cleanly into a category and subcategory.

STEP 2. Learn about the category of discharger.

To be able to write an effective permit, the permit writer must know the pollutants that are being 

discharged or have the potential to be discharged. This usually requires an understanding of the 

manufacturing processes that take place at a facility. There are several sources of information 

available to a permit writer to learn about an industry.

• The EPA Development Documents that were discussed previously are an excellent 

source of information. More recent literature is sometimes available. Contact the 

Ecology library for a search.

• EPA has industry experts located in Washington, D.C. and in the regional offices. EPA 

lists these experts in the training manual for the permit writing course. Call the 

Program Development Services Section for assistance if you have difficulty finding or 

contacting these people.

• Trade associations for the category of discharger can be sources of information.

• The pre-permit inspection of the facility being permitted is informative. This inspection 

is most valuable if the permit writer has done some background work before the 

inspection.

STEP 3. Decide on category.

This is a decision point for the permit writer. The permit writer must decide after reading the 

development document, reviewing the application, and inspecting the facility whether the facility 

being permitted has essentially the same kind of manufacturing processes as described in the 

development document. If the manufacturing process and the pollutants which are generated 

have changed to the extent that it is no longer described in the development document, the permit 

writer must do case-by-case development of effluent limits. Outdated development documents 

may become more common as time goes by.
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STEP 4. Decide on treatment.

This is another decision point for the permit writer. The permit writer must decide if the 

treatment process described in the development document is currently the best available. If it is 

not then the permit writer must do a case-by-case determination of the effluent limits.

STEP 5. Decide on the production base.

Most of the EPA effluent guidelines are mass limits based on production as opposed to 

concentration limits (see the example at the end of the chapter). Production-based limits cause a 

problem for permit writers in verifying the production base. The company may want to claim as 

high a production as possible to get higher effluent limits and thus not have to worry about 

compliance problems. The permit writer wants the production estimate to represent, as 

accurately as possible the production during the life of the permit. The Federal permit 

application asks the applicant for the facility maximum production but what the permit writer 

needs is an estimate of future average annual production. The derivation of the effluent 

guidelines incorporates an allowance for the daily and monthly variations. The best estimate of 

future production is generally the production of the past year. In some cases the past year may 

have been a boomer for them and the next few are going to be bust. In that case, by basing the 

effluent limits on the past years production you would be allocating more pounds of discharge 

than necessary. You may wish to use the highest yearly production of the last five years as the 

production base. If the company knows that there will be a substantial (25%) increase in 

production sometime during the course of the new permit, you may offer them alternate limits to 

be effective at the time they begin increased production. The company should have committed 

the capital expenditure and completed the design before alternate limits are used, otherwise, 

modify the permit at the time of increased production.

Production levels may be verified by checking the previous year’s monitoring data. Assuming 

that water usage is proportional to production, you should be able to detect any changes. The 

development document for the industry may have some water use/production data. The 

production data that you receive on the application is certified by the signature of the responsible 

official to be correct and subject to criminal enforcement if deliberately false. This creates a 

strong incentive for not falsifying information. That person should understand that any 

information submitted subsequently during the permit process is also certified. If you have a 

basis to suspect that any production information is incorrect, you may ask to review their books 

or ask for some other verification.

STEP 6. Apply the effluent guidelines to derive limits.

The final calculations of the effluent limitations should be done from the effluent guideline 

summaries found in 40 CFR Parts 400-471. Although the effluent limits in the development 
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documents and the CFR are usually the same, the CFR's are the most current regulatory version.

In this state there is another decision to be made at this point. The decision is whether the 

effluent guidelines also constitute all known, available and reasonable methods of treatment 

(AKART). AKART is discussed in detail in Part 3 of this Chapter. As a general rule, if the 

effluent guidelines for a particular category are 5 years old or less they will be AKART and this 

will be immediately apparent in reviewing the development document. If the effluent guidelines 

are between 5 and 10 years old they are probably AKART but the permit writer should review 

the treatability data base for a determination. If the effluent guidelines are over 10 years old, the 

permit writer should, at the minimum, conduct an analysis of unit processes design and 

efficiencies at the facility to determine if the effluent guidelines constitute AKART.

1.3 Multiple Processes

For industries with only one process and relatively constant production, the production-based 

effluent limits are simple to calculate and monitor. Now consider the Seafood Processors as a 

good example of some problems with production-based effluent limits. In our state, many 

seafood processors work on a variety of seafood. A typical processor in the coastal area might 

work on shrimp, salmon, bottom fish, and crab. On any given day the processor might be 

working on one or all of these products depending on what's available and the market demand. 

Each of these products has production-based effluent limits within Part 408 - Canned and 

Preserved Seafood Processing Point Source Category for the pollutants TSS, oil/grease, and pH 

for existing sources. The treatment process identified as BPT treatment is screening of solids 

from the waste stream. Some product subcategories also include some management practices to 

reduce pollutants. To verify that the process is within the production-based effluent limits 

requires daily monitoring of effluent and a daily production report. The purpose of monitoring is 

to verify that the treatment process is working properly; therefore, some permit writers have 

simply placed requirements in the seafood permits for a daily check on the condition of the 

screen but with no effluent monitoring. This is contrary to regulations which require sampling at 

least once per year for those parameters in the effluent guidelines. This has also resulted in 

another problem because the permit writer has not built a data base to determine the potential for 

water quality standards violations from the discharges.

A similar difficulty exists with fruit and vegetable processors who run a mix of products and then 

treat the wastewater in a lagoon system with a 30-day detention. The effluent which is analyzed 

is not representative of the production process for that month.
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1.4 Mass vs. Concentration

Effluent limits expressed as mass (pounds or kilograms per day) create an opportunity for 

inefficient operation of a treatment process so a permit writer should consider using 

concentration limits (milligrams per liter) in addition to the mass limits.

An example would be a company that has effluent limits for pollutant X of 390 pounds/day daily 

maximum and 260 pounds/day monthly average. These limits are based on annual production of 

widgets. The annual average flow is 0.9 MGD and the maximum daily flow is 1.6 MGD.

During periods of reduced production and flow (0.5 MGD) the company is able to reduce the 

efficiency of their treatment apparatus and still meet the monthly average mass limit of 260 

pounds/day.

Under Average Production and Flow (0.9 MGD)

260 LBS/DAY /[(8.34)(0.9 MGD)] = 35 mg/L

Under Reduced Production and Flow (0.5 MGD)

260 LBS/DAY/[(8.34)(0.5 MGD)] = 62 mg/L

The number 8.34 in the formulas above is a conversion factor to get from pounds per million 

gallons to milligrams per liter. The first formula for Average Production and Flow with the units 

expressed as follows:

Unit cancellation results in mg/l. Note that MGD (millions of gallons per day), is expressed as 

MG divided by day(s) so day(s) will cancel correctly.

1.5 Some Solutions

The regulatory objective of effluent limits is to assure that the wastewater treatment process is 

being run as efficiently as possible and meeting the long term average (LTA). Some solutions to 

the problems identified above include the use of concentration limits, requiring a statement of 

production, specifying the efficiency of the treatment process and doing an annual balance.

260 lb

day

0.9 MG

day

x

1 MG mg

8.34 lb l

= 34.64 mg

l

•

•

• •

• •

•
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In the example above the permit writer could have specified an effluent limit of 35 mg/L in 

addition to the 260 lbs/day limit. This would have forced continued efficiency during periods of 

reduced production. Incorporating concentration limits might discourage a facility from 

practicing water conservation. By reducing water usage in a process while continuing to provide 

good waste treatment the mass discharge might be reduced but the concentrations exceed 

monthly and daily limits, therefore, a permit writer who places concentration limits in a permit in 

addition to the mass limits, should allow some exclusion from those concentration limits if there 

is a demonstration of water conservation.

Another option for the permit writer is to specify treatment efficiency by mass and concentration. 

This is already incorporated into the municipal effluent limits for secondary treatment. The 

percent removal efficiency could be based on the design efficiency of the plant as specified in the 

approved engineering report.

A third option that is especially suitable for mixed production such as the seafood processors 

above is to require a statement of monthly production. This is commonly required in the permits 

for pulp mills which have a mix of products.

A fourth option to assure the efficient operation of the treatment process is to place some type of 

operating parameter as the daily control mechanism and then to run the balance sheet at the year 

end. This might be appropriate for the food processor example above. This option would be 

consistent with the way effluent limits were derived. As noted earlier, the production based 

effluent limits may have been derived on an annual basis and the monthly and daily limits 

calculated with the use of variability factors. This annual balance sheet creates a great deal of 

uncertainty for both the regulator and the regulated.

1.6 Outdated Effluent Guidelines

Frequently, the permit writer will find that the effluent guidelines are outdated such that the 

industrial processes or process pollutants are no longer accurately described. In this case the 

permit writer must derive effluent limits on a case-by-case basis as described previously in this 

chapter.
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EXAMPLE IV-1 WOOL FINISHING EFFLUENT LIMITS 

This example is a company that receives cleaned wool, wool yarn, and wool fabric and produces 

finished wool yarn and fabric. This example is typical of the type of problems encountered 

when using effluent guidelines.

This company belongs to the category of industries called "textile mills". For this company the 

category is apparent. For some industries it's not so easy to determine the industrial group. For 

an industry that's not obvious, the permit writer may be able to use the SIC (Standard Industrial 

Classification) code information that the company supplies on the permit application form. The 

SIC numerical system was originally developed and used by the Federal government for tax and 

data gathering purposes. EPA adopted it as part of their categorization system.

The Ecology library contains the EPA documents relating to the development of effluent limits 

for textile mills.

For this industry there are several documents dated from 1974 to 1982. The earliest document is 

called "Development Document for Effluent Limitations Guidelines and New Source 

Performance Standards for the TEXTILE MILLS Point Source Category" (June 1974).

This 1974 document proposed BPT limits to be imposed by 1977, BAT limits to be imposed by 

1983 and New Source Performance Standards (NSPS). The BAT parameters included fecal 

coliform and color (remember the discussion from the earlier section that BAT was initially for 

conventional pollutants). The proposed BAT guidelines were rescinded as a result of a 

successful challenge in court by the industry.

The next two documents were released by EPA in 1979. They are the "Proposed Effluent 

Limitations Guidelines, New Source Performance Standards and Pretreatment Standards for 

TEXTILE MILLS Point Source Category" and "Economic Impact Analysis of Proposed 

Effluent Limitations Guidelines...". These guidelines redefined the industry and added some 

additional subcategories. BAT was now defined by the CWA as control of toxic pollutants. For 

textiles BAT is defined as the existing BPT. The NSPS is changed in this document and the 

pretreatment standards are given.

These early documents are interesting from a historical perspective but the most pertinent and 

current document is the one released in 1982. This final "Development Document for Effluent 

Limitations Guidelines and Standards for the Textile Mills Point Source Category" EPA 440/1-

82/022 contained very few changes from the 1979 proposed guidelines.
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The effluent limitations are summarized in 40 CFR Part 410 which are reproduced on the 

following two pages. These regulations also include definitions that sometimes become 

important criteria for application of the regulations. Occasionally a question will arise that 

cannot be answered by reviewing the development document or the regulations. In this case 

the permit writer should also review the Federal Register in which the effluent limits were 

promulgated. Many times, the EPA response to comments will clarify the regulatory intent. 

These effluent guidelines were published in 47 FR 38819 on September 2, 1982 as noted in 

the CFR's.

The current development document describes how the industry was categorized and 

subcategorized. In addition, there are sections on wastewater characteristics, the pollutants 

of concern, control and treatment technology, non-water quality aspects including costs, and 

recommendations for BPT, BAT, and NSPS effluent limits.

For more information about a particular aspect of the industry process, get the appropriate 

references listed in the development document and request a computer search from the 

department library for more recent papers. Contact the Program Development Services 

Section to see if there is someone there or elsewhere in Ecology knowledgeable about the 

industry.

The production processes at this example facility fit the subcategory called wool finishing. 

In this case, it's particularly easy to determine because there is a flow chart describing the 

process (Figure IV-1). The other subcategories that are described are wool scouring, low 

water use processing, woven fabric finishing, knit fabric finishing, carpet finishing, stock 

and yarn finishing, nonwoven manufacturing, and felted fabric processing.

The permit writer in this example reads the development document and inspects the facility. 

The permit writer decides that this particular woolen mill is adequately described by the 

development documents and the processes are essentially the same as described in the 

development document.

The company claims they are an integrated facility because in addition to being covered 

under wool finishing they are covered under the woven fabric finishing subcategory. A 

review of the development document reveals that wool and wool blends are not covered in 

the woven fabric finishing subcategory because fabric finishing was included as a process in 

the wool finishing subcategory. There is no additional discharge allowance on that basis. 
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EXAMPLE IV-1 (continued)

THIS PAGE CONTAINS A REPRODUCTION OF THE CFR
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EXAMPLE IV-1 (continued)
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EXAMPLE IV-1 (continued)

Figure IV-1 

Wool

Stock

& Top

Wool

Yarn

Wool

Fabric

CARBONIZE

AND

SCOUR

CARBONIZE

AND

SCOUR

FELT

AND

RINSE

BLEACH

AND

RINSE

LIGHT

SCOUR

DYE

WASH

FINAL

FINISH

BLEACH

AND

RINSE

LIGHT

SCOUR

DYE

WASH

SPIN

OIL AND

CARD

LIGHT

SCOUR

DYE

WASH

SIZE

(Warp Yarns)

KNIT OR

WEAVE

Wool

Yarn

Wool

Fabric

Finished

Fabric

Water

Liquid

Waste

Liquid

Waste

Liquid

Waste

Liquid

Waste

Liquid

Waste

Liquid

Waste

Liquid

Waste

H2SO4 and

Na2CO3

Detergent: Acid

and/or Alkali

H2O2

Scouring

Agents

Dyestuffs

and

Auxiliary

Chemicals

Detergents

Lubricants,

Sizing, and

Finishing Agents

(TOP) (YARN) (FABRIC)

(From Cleanup)
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EXAMPLE IV-1 (continued)

When industry requests to be included in a different category that would allow higher 

pollutant discharge and the permit writer determines that the request is not justified, the 

reasons should be explained in the fact sheet.

The effluent limits for the wool finishing subcategory are given as pounds of pollutant per 

1000 pounds of fiber processed (this type of limit is called a production-based effluent limit 

as opposed to a concentration limit). The regulated pollutants for BPT are BOD5, COD, 

TSS, Sulfide, Phenol, Total Chromium and pH. The regulated pollutants for BAT are COD, 

Sulfide, Phenols, and Total Chromium with the same effluent limits as for BPT. The limits 

for BCT haven't been promulgated. This is noted in 40 CFR 410.27 by the words 

"reserved".

A textile mill submits the following information on an application for permit renewal.
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EXAMPLE IV-1 (continued)

The company also indicates in their application that the maximum raw material usage at the 

facility is 19,500 pounds per day. The permit writer requests more information on the raw 

material usage, including some supporting data. The company replies that the 19,500 

pounds includes the maximum daily usage and a planned increase during the next 5 years. 

The permit writer requests detailed raw material usage and tells the company the permit will 

be based on current production with a permit modification later, if necessary to 

accommodate increased production. The typical materials taken in for processing in the 

wool finishing operation are washed and dried wool (stock), yarn, and fabric. The applicant, 

mill X, submits information showing they receive and process 12,627 pounds of stock, 

3,294 pounds of cloth, and 1,306 pounds of yarn per day. It receives the cloth and yarn from 

company mill Y located in another state. The applicant claims that the 3,294 pounds of 

cloth represent 3,765 pounds of original stock and the difference is wastage. Similarly they 

claim the 1,306 pounds of yarn represents 1,606 pounds of stock. The applicant claims 

17,998 pounds as the production base (12,627 + 3,765 + 1,606). The permit writer allows 

17,281 pounds as the production basis. The definition of fiber in 40 CFR 410.21 is wool 

and other fiber as received at the mill. The production base for facility X does not include 

material processed or partially processed at facility Y.

The effluent limits for the permit are calculated as:

22.4 X 17.281 = 387 pounds per day maximum BOD

11.2 X 17.281 = 193.5 pounds per day average BOD

and so on for the other parameters. Note that BAT limits are the same as BPT and that BCT 

limits have not been promulgated for this industry.
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1.7 Integrated Facilities

In the previous example, if the facility X above also produced nonwoven fabric by an adhesive 

process, the facility would be an integrated facility and receive an additional effluent allowance in 

the nonwoven subcategory.

In the nonwoven subcategory, the limitation is based on pounds of product produced. Therefore, 

the facility in the example would have to separately track that wool fiber used for nonwoven 

production so as not to get dual credit.

1.8 Converting Performance to Limits

EPA derived the BPT limits for wool finishing mills by determining the pollutants produced and the 

potential treatment methods available for treating those pollutants. EPA then examined the 

performance of two existing "exemplary" biological treatment plants at wool finishing mills (BPT = 

average of the best for conventional pollutants). The average effluent concentrations from the two 

treatment plants were then increased by 50% to derive the 30-day average maximum limit. This 30-

day limit was multiplied by 2 to derive the maximum daily limit.

Sometimes more sophisticated statistical methods were used for deriving effluent limits when the 

data were available. The first step was to determine if the data was normally distributed and if not 

then to do a transformation. The transformation if done correctly enabled the use of normal 

distribution statistical techniques. The data or transformed data were then used to calculate a mean 

and standard deviation. The effluent limits for daily maximum may be set at Z + 3s. The 

probability of any measurement randomly exceeding this limit is 0.00135, so any exceedance means 

the treatment process is not functioning properly.

Another method used to arrive at daily maximum limits was to derive a variability factor V = (Z + 

3s)/Z which was then multiplied by the annual average effluent concentration. The resultant 

number was the proposed daily maximum concentration. This variability factor may also be 

calculated by plotting the data on probit paper or using a computer program and finding the 50th 

and 99th percentile concentration. The variability factor V = 99th percentile concentration/50th 

percentile concentration.

Monthly or 30-day effluent limits may be set as Z + 2s or by determining variability factors on 

monthly data.

Performance-based effluent limits may be derived using the formulas in Appendix E of the TSD 

(EPA 1991) and the observed data for the long term average (LTA).
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EXAMPLE OF PERFORMANCE-BASED LIMITS

A permit writer proposes to issue a permit with water quality-based effluent limits for BOD and 

wants to derive performance-based limits as interim limits for a compliance schedule. The data 

base consists of 169 effluent values collected once per week. The summary statistics (calculated 

in Excel) are presented below.

UNTRANSFORMED LOGNORMAL(base e) 

TRANSFORMED

Mean 32.9941 Mean 3.2783

Standard Error 2.00885 Standard Error 0.0492

Median 26 Median 3.2581

Mode 22 Mode 3.091

Standard Deviation 26.115 Standard Deviation 0.6396

Sample Variance 681.994 Sample Variance 0.4091

Kurtosis 7.27301 Kurtosis 0.5068

Skewness 2.51836 Skewness 0.2898

Range 147 Range 3.2387

Minimum 6 Minimum 1.7918

Maximum 153 Maximum 5.0304

Sum 5576 Sum 554.03

Count 169 Count 169

Confidence Level 

(95.0%)

3.96584 Confidence Level 

(95.0%)

0.0971

95th percentile 98 95th percentile

99th percentile 141 99th percentile

Federal regulations require effluent limits be expressed as a maximum daily limit (MDL) and an 

average monthly limit (AML)(except municipal limits for conventional pollutants). The method 

for determining effluent limits from demonstrated performance is found in Appendix E of the 

TSD. The formulas have been incorporated into TSDCALC.
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tan log 0.6396

log 3.2783

( .99 ) exp 2.326

= =

= =

















= +

s dard deviation of transformed data

mean of transformeddata

where

MAXIMUM DAILY LIMIT X

y

y

y y

σ

μ

μ σ

Maximum Daily Limit (MDL) =exp(3.2783 + (2.326)(0.6396)) = 117.

The AVERAGE MONTHLY LIMIT (AML) depends on the number of samples that will be 

required per month for compliance monitoring. The following method is appropriate for 10 or 

fewer samples/month (Technical Support Document, Appendix E, Table E-2).

( ( ))

( )[ ( ) ] [ ]

( ) { }

( )

( )

exp(3.4235 1.645 0.3447) 54.08

ln ( ) 0.5 ln 32.5524 0.5 0.1188 3.4235

0.3447

ln 1.1262 0.1188

ln 1 ln 1

exp 2 3.2783 0.4091 exp 0.4091 1 exp(6.9657) .505 535.126

( ) exp 2 exp 1

( ) exp 0.5 exp 3.2783 0.5 0.4091 32.5524

variance of lognormal transformed data 0.4091

mean of lognormal transformed data 3.2783

( ) exp 1.645

2

4 32.5524

535.126

( )

( )

2

2 2

2

2

.95

2 2

= + ⋅ =

 − = − ⋅ = 

 



 =

=

=

= + =





















= +

⋅ + − = =

=















 −





























 = +

= + =





















= +

= =

= =





















= +

























 





AML

E X

V X

E X

where

AVERAGEMONTHLY LIMIT X

n n

n

n E X

V X n

y y y

y y

y

y

n n

μ σ

σ

σ

μ σ σ

μ σ

σ

μ

μ σ
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The average monthly limit (AML) when there are more than 10 samples per month for 

compliance is calculated as follows:

( ) ( )

( ) ( ) ( ( ))

( ) ( )

( ) 32.55 1.645(44.653) 43.5

1 /12 535.83/12 44.653 2exp 2 / exp 2

exp 3.2783 0.5 0.4091 32.55 2 exp 0.5

number of samples/month = 12

2 variance of lognormal transformed data 0.4091

mean of lognormal transformed data 3.2783

( ) 1.645

1/ 2

.95

1/ 2

.95

= + =

= =





















−





















































= = +

= + =





















= = +

=

= =

= =





 



 = +

AML X

y y y

V X V X n

E X E X y y

n

y

y

where

AML X X V X

n

n

n n

μ σ σ

μ σ

σ

μ

Effluent limits using these formulas can be calculated using TSDCALC.

In this example for effluent limits for BOD for a municipality the effluent limits would be as 

average monthly limits and average weekly limits instead of a daily maximum. The weekly average 

limit is the appropriate average monthly limit (44 or 54) times 1.5.
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2. CASE-BY-CASE DERIVATION OF TECHNOLOGYBASED EFFLUENT LIMITS

Technology-based effluent limits may be derived on an individual 

facility basis which is also called case-by-case or BPJ. Case-bycase limits may be developed under federal authority (40 CFR 

125.3) or they may be developed under authority of the state law 

RCW 90.48 (AKART).

Case-by-case derivation of effluent limits may be on a facility basis 

and cover all pollutants or may be on an individual pollutant basis.

Case-by-case development of effluent limits for an individual facility follows the same process as 

EPA used for developing effluent guidelines for categories of dischargers. The permit writer can 

review any development document to reinforce the process described in this Part. Case-by-case 

development of effluent limits is a 2-part determination. The first part is an engineering 

determination and the second part is an economic determination.

Case-by-case derivation of effluent limits is necessary in the following circumstances:

• The facility being permitted has an effluent guideline but the industrial processes have 

changed to the extent that the process and the pollutants produced are no longer 

accurately described in the development document.

• The facility type does not have federal effluent guidelines. Some of the kind of 

facilities in Washington that do not have effluent guidelines are hazardous waste 

treaters, some equipment manufacturers, waste oil reclaimers, industrial laundries, 

barrel reclaimers, transportation facilities, some mining operations, water treatment 

plants, petroleum industry (other than refineries), chitin manufacturers, and some 

metallurgical manufacturers.

• The facility being permitted has an effluent guideline that accurately describes the 

manufacturing processes but has a pollutant or pollutants in the effluent that were not 

described in the development document.

The authority to develop and impose case-by-case or BPJ limits is given in the Clean Water Act 

Section 402(a)(1). This section authorizes the EPA administrator to issue permits containing "such 

conditions as the Administrator determines are necessary to carry out the provisions of the Act".

Hap Thron - Former EPA Permit Writer

Expert
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The process of deriving case-by-case (BPJ) effluent limits is not described in federal regulations but 

the factors which must be considered are given in Section 304(b) of the CWA and 40 CFR 

125.3(c)(2) and 40 CFR 125.3(d).

The general factors to be considered for BPJ permit limits are:

• The appropriate technology for the category or class of point sources of which the 

applicant is a member, based upon all available information; and

• Any unique factors relating to the applicant.

The specific considerations are:

1. FOR BPT REQUIREMENTS (Conventional Pollutants)

i) The total cost of application of technology in relation to the effluent reduction benefits to be 

achieved from such application;

ii) The age of equipment and facilities involved;

iii) The process employed;

iv) The engineering aspects of the application of various types of control techniques;

v) Process changes; and

vi) Non-water quality environmental impact (including energy requirements).

2. FOR BCT REQUIREMENTS (Conventional Pollutants)

i) The reasonableness of the relationship between the costs of attaining a reduction in effluent and 

the effluent reduction benefits derived;

ii) The comparison of the cost and level of reduction of such pollutants from the discharge from 

publicly owned treatment works to the cost and level of reduction of such pollutants from a 

class or category of industrial sources;

iii) The age of equipment and facilities involved;
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iv) The process employed;

v) The engineering aspects of the application of various types of control techniques;

vi) Process changes; and

vii) Non-water quality environmental impact (including energy requirements).

3. FOR BAT REQUIREMENTS (Toxic Pollutants)

i) The age of equipment and facilities involved;

ii) The process employed;

iii) The engineering aspects of the application of various types of control techniques;

iv) Process changes; 

v) The cost of achieving such effluent reduction; and

vi) Non-water quality environmental impact (including energy requirements).

The BAT factors have been briefly defined in EPA guidance as:

AGE OF EQUIPMENT AND FACILITIES - Age of the plant including manufacturing lines, sewer 

lines and wastewater treatment system.

PROCESS EMPLOYED - The manufacturing process(es) used, and/or the wastewater treatment 

process employed.

ENGINEERING ASPECTS OF THE APPLICATION OF VARIOUS TYPES OF CONTROL 

TECHNIQUES - The design, construction, cost, performance, reliability, etc., of the wastewater 

treatment processes.

COST OF ACHIEVING THE EFFLUENT REDUCTION - The capital and operating cost of 

attaining a specified effluent quality.
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NON-WATER QUALITY ENVIRONMENTAL IMPACTS - The trade-offs associated with 

achieving a specified effluent quality including energy requirement; air pollution; hazardous waste 

generation; solid waste; etc.

There is no other federal guidance on case-by-case development of effluent limits. The EPA permit 

writers training course makes several points on case-by-case limits.

• These are best done with a team approach involving at least an engineer and an 

economist.

• Defensibility depends on a reasonable process and documentation of that process.

The permit writer has several useful tools for defining the appropriate treatment technology. 

These include engineering reports, the treatability manual, the abstracts of industrial permits, and 

a computerized literature review.

The permitting process for new facilities in Washington State includes a requirement of 

dischargers to produce an engineering report in conformance with Chapter 173-240 WAC. This 

regulation (173-240-130-q) requires, "a statement, expressing sound engineering justification 

through the use of pilot plant data, results from other similar installations, and/or scientific 

evidence from the literature, that the effluent from the proposed facility will meet applicable 

permit effluent limitations and/or pretreatment standards." This may seem like a catch-22

situation for those industries not covered by effluent guidelines. The permit writer can't tell the 

industry what the permit limits will be until an engineering analysis is completed and the applicant 

can't make a statement as required until those limits are known. In these cases the permit writer 

should explicitly instruct the applicant to review all possible treatment technologies, quantify the 

expected concentration of pollutants from each identified treatment, detail the cost of each identified 

treatment and list the other environmental factors associated with each treatment method. This data 

in the engineering report will form the technical basis for the permit writer's BPJ determination of 

effluent limits.

Another useful tool for determining the appropriate treatment technology or verifying an 

engineering report is the Treatability Manual (EPA-600/2-82-001). The Treatability Manual is in 5 

volumes. The individual volumes are; 

Volume I - Treatability Data 

Volume II - Industrial Descriptions 

Volume III -Technology for Control/Removal of Pollutants 

Volume IV - Cost Estimating 

Volume V - Summary
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Volume I provides physical data for 202 chemical compounds, their occurrence patterns, and 

methods of treatment and/or removal (with references to Volume III). Volume II is a summary of 

industrial descriptions from the development of effluent guidelines and describes only those 

industries for which there are guidelines. It describes manufacturing processes and the pollutants 

they produce. Volume III describes treatment technologies and their performance when treating 

industrial wastewater. The technologies include those which are widely used in treating industrial 

wastewater and those which are being used on a limited basis but have potential application in the 

removal of toxic pollutants from wastewater. The manual does not specify final effluent 

concentrations because those would be dependent upon individual wastewater characteristics and 

other factors.

The permit writer may request a computer search of the literature for any pollutants or process and 

treatment methods from the Ecology library. The primary journals included in the search which 

include new treatment process data are the Journal of the Water Pollution Control Federation (now 

called Water Environment and Technology), the Sanitary Engineering Division of the ASCE, and 

the Purdue Industrial Waste Conference.

Those permit writers who may need further technical assistance in developing BPJ permit limits 

may request it from the Water Quality Program Development Services Section. Although problems 

unique to a region will most likely be solved by that region, some, because of their complexity, 

political impact, etc. will be viewed as high enough state priority to require the Program 

Development Services Section involvement.

The second major part of BPJ permitting is the task of determining the cost of the proposed treatment 

method. The cost is then subjected to a test for reasonableness. Reasonable is an economic test. The 

reasonable test for BCT is defined by federal regulation and the reasonable test for BAT is defined by 

Federal guidelines. These economic tests are reviewed in the following Part 3.
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3. ALL KNOWN, AVAILABLE, AND REASONABLE 

METHODS OF TREATMENT (AKART)

This part discusses the phrase, "all known, available, and reasonable methods of treatment" or 

AKART, which occurs in state water quality law and regulation. This part clarifies the meaning 

of AKART as used by Ecology in the process of permitting wastewater discharges. Specifically, 

this part has sections which review law, regulation, PCHB decisions and individual permit 

instances in which AKART has been used or defined. Subsequent sections discuss engineering 

analysis and other tests for AKART. This part does not specify in detail the process of 

engineering analysis because it is assumed that any engineering analysis will be conducted by a 

qualified engineer.

3.1. A Summary of AKART

AKART is a statement of legislative intent directed toward the goal of clean water.

AKART has been interpreted as a technology-based approach to limiting pollutants from 

wastewater discharges which requires an engineering judgment and an economic judgment. 

Because AKART encompasses a complex process of engineering and economic decision-making 

there can be no simple definition.

AKART allows the state to be more stringent than federal effluent guidelines but actually parallels 

parts of the CWA.

AKART has been defined in state regulation for some categories of dischargers.

A determination of AKART may be the same process as case-by-case permitting as given in 40 

CFR 125.3 if a proposed permittee has no effluent guidelines.

Production increases greater than 10% should be treated as new source for defining effluent 

limitations for those dischargers with new source performance standards.

The discharge of pollutants already captured does not meet the intent of AKART.

AKART may be equivalent to the federal effluent guidelines or may be more stringent.

AKART means that effluent limits may be derived in consideration of the treatment performance of 

a similar facility.
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AKART may be a requirement to control pollutants at the source.

AKART may be zero discharge.

An industrial/commercial indirect discharger should not be required to treat for BOD and solids 

discharged to a POTW as long as the POTW has the capacity to treat the waste.

The general requirements of an engineering report are specified in WAC 173-240. The actual 

analysis must be done by an engineer who is trained and experienced in wastewater treatment. 

Other scientists may assist in determining whether the report meets the AKART criteria. Case-bycase decisions on technology-based effluent limits for existing facilities must be reviewed and 

approved by an engineer.

Ecology has adopted EPA's BCT and BAT economic tests for AKART analysis.

The BCT economic reasonableness tests imply that the minimum treatment for conventional 

pollutants on a BPJ basis is secondary treatment with 85% removal of BOD and solids. A candidate 

treatment technology would be advanced secondary treatment. A new industry producing 

conventional pollutants similar in nature and strength to municipal wastewater, but not covered by 

effluent guidelines, would be required at a minimum to treat with secondary treatment as BPT. A 

candidate BCT treatment would be advanced secondary treatment.

3.2. AKART As Given In Law

In the regulatory scheme of things legislative bodies express their intent through law. Laws are 

generally not explicit as to how they should be implemented. Therefore, regulations are 

promulgated to clarify the implementation of the law. In some cases regulatory authorities must 

also provide guidance as an additional tool to implement the regulations.

AKART has not been explicitly defined in law. AKART has been defined in certain regulations 

and has been ruled upon by the Pollution Control Hearings Board (PCHB). The following 

discussion reviews the law and regulation in which the phrase AKART is used.

The phrase AKART is found in 3 statutes dealing with water pollution and water resources in 

Washington. The context of these statutes in which the phrase AKART occurs gives some 

indication of the legislative intent.

The introduction to this manual reviewed some of the legislative history of Chapter 90.48 RCW, 

Water Pollution Control. Section 010 of 90.48 states, "It is declared to be the public policy of the 

state of Washington to maintain the highest possible standards to insure the purity of all waters of 

the state consistent with public health and public enjoyment thereof, the propagation and protection 

of wild life, birds, game, fish and other aquatic life, and the industrial development of the state, and 
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to that end require the use of all known available and reasonable methods by industries and 

others to prevent and control the pollution of the waters of the state of Washington." AKART 

in this section of the law relates to industries and others preventing pollution so as not to affect other 

water uses and intrinsic values.

Chapter 90.48 RCW, section 520 states, "In order to improve water quality by controlling toxicants 

in wastewater, the department of ecology shall in issuing and renewing state and federal wastewater 

discharge permits review the applicant's operations and incorporate permit conditions which require 

all known, available, and reasonable methods to control toxicants in the applicant's 

wastewater." This section ties AKART to the control of toxics, improvement of water quality, and 

the issuance of wastewater discharge permits.

In the Pollution Disclosure Act of 1971, Chapter 90.52 RCW, section 040 states "Except as 

provided in RCW 90.54.020(3)(b), in the administration of the provisions of chapter 90.48 RCW, 

the director of the department of ecology shall, regardless of the quality of the water of the state to 

which wastes are discharged or proposed for discharge, and regardless of the minimum water 

quality standards established by the director for said waters, require wastes to be provided with 

all known, available, and reasonable methods of treatment prior to their discharge or entry 

into waters of the state." This statute introduces the concept that AKART is required regardless of 

the quality of the receiving water.

In the Water Resources Act of 1971, Chapter 90.54 RCW, section 020 (3)(b) states, "Waters of the 

state shall be of high quality. Regardless of the quality of the waters of the state, all wastes and 

other materials and substances proposed for entry into said waters shall be provided with all 

known, available, and reasonable methods of treatment prior to entry. Notwithstanding that 

standards of quality established for the waters of the state would not be violated, wastes and 

other materials and substances shall not be allowed to enter such waters which will reduce the 

existing quality thereof, except in those situations where it is clear that overriding 

considerations of the public interest will be served." This section of 90.54 continues on with 

technology-based treatment exemptions for wastewater discharges from municipal water treatment 

plants on the Chehalis, Columbia, Cowlitz, Lewis, and Skagit Rivers. This law explicitly states that 

AKART is required even if it results in more stringent treatment than required to meet water quality 

standards. This is the basic philosophical approach found in the Clean Water Act. Chapter 90.54 

also contains the caveat not found in other statutes of an exemption for, "overriding consideration of 

the public interest."

3.3. AKART As Given In Regulation

The phrase AKART is also found in the regulations that implement the laws reviewed above. In

these regulations the phrase may be defined, simply repeated or may be changed to indicate 

implementation process. In some cases the context of the regulation also indicates implementation.

The state's surface water quality standards, Chapter 173-201A, define AKART as, "represent(ing) 
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the most current methodology that can be reasonably required for preventing, controlling, or abating 

the pollutants associated with a discharge." These water quality standards also require dischargers to 

achieve AKART before receiving a mixing zone and require AKART as a condition for exemption 

to the antidegradation condition.

The state wastewater discharge permit program is implemented by Chapter 173-216 WAC, State 

Waste Discharge Permit Program. WAC 173-216-020(1) states, "It shall be the policy of the 

department in carrying out the requirements of this chapter, to maintain the highest possible 

standards to ensure the purity of all waters of the state and to require the use of all known, 

available and reasonable methods to prevent and control the discharge of wastes into the 

waters of the state."

WAC 173-216-050(3): "These exemptions" (to the requirement to obtain a state discharge permit) 

"shall not relieve any discharger from the requirement to apply all known, available, and 

reasonable methods to prevent and control waste discharges to the waters of the state,"...

WAC 173-216-110(1): "Any permit issued by the department shall specify conditions necessary to 

prevent and control waste discharges into the waters of the state, including the following, whenever 

applicable:

(a) All known, available, and reasonable methods of prevention, control, and treatment:"...

This regulation reiterates the phrase as found in law. The regulation notes that a discharger may be 

exempted from getting a permit but they are not exempt from AKART.

The state's surface water discharge permit program is implemented through Chapter 173-220 WAC, 

National Pollutant Discharge Elimination System Permit Program. This regulation refers to the 

statutes covered above and the technology-based processes of the CWA.

WAC 173-220-130(1): "Any permit issued by the department shall apply and insure compliance 

with all of the following, whenever applicable:

(a) All known, available and reasonable methods of treatment required under RCW 

90.52.040, 90.54.020(3)(b), and 90.48.520; including effluent limitations established under 

sections 301, 302, 306, and 307 of the FWPCA."

The state dangerous waste regulations, Chapter 173-303 WAC, which allow a (dangerous waste) 

permit by rule. That permit by rule is conditioned upon meeting AKART. WAC 173-303-802 

(5)(a): "The owner or operator of a totally enclosed treatment facility or an elementary 

neutralization or wastewater treatment unit that treats dangerous wastes shall have a permit by rule, 

except as provided in (b) of this section, if he:

(i) Has a NPDES permit, state waste discharge permit, pretreatment permit (or written 

discharge authorization from the local sewerage authority) and the permit or authorization 
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provides for the use of all known, available, and reasonable methods of prevention, 

control, and treatment of pollution pursuant to chapter 90.48 RCW, prior to 

discharge;"...

The underground injection control program, Chapter 173-218 WAC sets forth the procedures and 

practices applicable to the injection of fluids through wells. This regulation specifies in 173-218-

100 that: (1) Any permit issued by the department shall specify conditions necessary to prevent and 

control injection of fluids into waters of the state, including the following, whenever applicable: (a) 

All known, available, and reasonable methods of prevention, control, and treatment;.

Other state standards are the ground water standards, Chapter 173-200, and Sediment 

Management Standards Chapter 173-204 WAC. These two regulations also use the phrase 

AKART.

The Water Quality Standards for Ground Waters of the State of Washington, Chapter 173-200 

WAC, implement Chapters 90.48 RCW and 90.54 RCW.

WAC 173-200-030 Antidegradation policy.

WAC 173-200-030(2)(c): "Whenever ground waters are of a higher quality than the criteria 

assigned for said waters, the existing water quality shall be protected, and contaminants that will 

reduce the existing quality thereof shall not be allowed to enter such waters, except in those instances where it can be demonstrated to the department's satisfaction that:

(i) An overriding consideration of the public interest will be served; and 

(ii) All contaminants proposed for entry into said ground waters shall be provided with all known, 

available, and reasonable methods of prevention, control, and treatment prior to entry."

WAC 173-200-050 Enforcement limit

WAC 173-200-050(3): "All enforcement limits shall, at a minimum, be based on all known, 

available, and reasonable methods of prevention, control, and treatment."

WAC 173-200-050(3)(b)(iv): "When naturally nonpotable ground water exceeds a secondary 

contaminant criterion, an enforcement limit for a secondary contaminant may exceed a criterion 

when it can be demonstrated to the department's satisfaction that:"..."(D) All known, available, and 

reasonable methods of prevention, control, and treatment will not result in concentrations less 

than the secondary contaminant criteria."

The Sediment Management Standards, Chapter 173-204 WAC expand the phrase to include best 

management practices.

WAC 173-204-120(c): "Whenever surface sediments are of a higher quality (i.e., lower chemical 

concentrations or adverse biological response) than the criteria assigned to said sediments, the 

existing surface sediment quality shall be protected and waste and other materials and substances 
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shall not be allowed to contaminate such sediments or reduce the existing sediment quality thereof, 

except in those instances where:"..."(ii) all wastes and other materials and substances proposed for 

discharge that may contaminate such sediments are provided with all known, available and 

reasonable methods of prevention, control, and treatment and/or best management practices;"

WAC 173-204-400(2): "Permits and other authorizations of wastewater, storm water, and nonpoint 

source discharges to surface waters of the state of Washington under authority of chapter 90.48 

RCW shall be conditioned so that the discharge receives all known, available and reasonable 

methods of prevention, control and treatment, and best management practices prior to 

discharge, as required by chapters 90.48, 90.52, and 90.54 RCW. The department shall provide 

consistent guidance on the collection, analysis, and evaluation of wastewater, receiving-water, and 

sediment samples to meet the intent of this section using consideration of the pertinent sections of 

the Department of Ecology Permit Writer’s Manual, as amended, and other guidance approved by 

the department."

WAC 173-204-410(3):"Except as identified in subsection (6)(d) of this section, any person may 

apply for a sediment impact zone under the following conditions: 

(a) The person's discharge is provided with all known, available and reasonable methods of 

prevention, control, and treatment, and meets best management practices as stipulated by the 

department;"...

WAC 173-204-410(6)(c): "Any person with a new or existing permitted storm water or nonpoint 

source discharge, which fully uses all known, available and reasonable methods of prevention, 

control, and treatment, and best management practices as stipulated by the department at the 

time of the person's application for a sediment impact zone, shall be required to meet the standards 

of WAC 173-204-400 through 173-204-420;"...

It is apparent from the language in both law and regulation that AKART is meant to be a 

technology-based requirement conditioned by a judgment of reasonableness. In this respect it 

shares the same characteristics of case-by-case or BPJ determinations specified in 40 CFR 125.3. 

This is discussed in more detail later.
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3.4. AKART as State Treatment Standards

AKART has been defined explicitly as effluent limitations in some Ecology regulations for some 

categories of dischargers and some pollutants.

For domestic wastewater facilities the discharge standards are given in Chapter 173-221 WAC, 

Discharge Standards and Effluent Limitations for Domestic Wastewater Facilities

WAC 173-221-010(1): "The purpose of this chapter is to implement RCW 43.21A-010, 90.48.010, 

and 90.52.040 by setting discharge standards which represent “all known, available, and reasonable 

methods of prevention, control, and treatment for domestic wastewater facilities which discharge to 

waters of the state.”

WAC 173-221 then defines treatment standards (effluent limits) for domestic wastewater treatment 

plants for the parameters of BOD, TSS, pH, and fecal coliform. This regulation was preceded by a 

PCHB decision regarding municipalities discharging to marine waters, which is discussed below.

Treatment standards are also defined in Chapter 173-221A WAC, Wastewater Discharge Standards 

and Effluent Limitations.

WAC 173-221A-010: "This chapter implements chapters 43.12A, 90.48, 90.52, and 90.54 RCW by 

setting minimum discharge standards which represent "known, available, and reasonable methods" 

of prevention, control, and treatment for industrial wastewater facilities that discharge to waters of 

the state."

This regulation currently defines treatment technology, treatment standards, and best management 

practices only for upland fin-fish facilities.

3.5. AKART As Defined By the Pollution Control Hearings Board 

(PCHB) And Other Courts

The PCHB has confirmed some of the individual permit determinations which were based on 

AKART. The board looks to these past decisions as guidance for future decisions. Discussed 

below are decisions made on marine discharging municipalities, New Source Performance 

Standards (NSPS) for production increases and the discharge of captured pollutants.
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3.5.1. Marine Discharging Municipalities

The Clean Water Act Section 301(h) allows marine-discharging municipalities to obtain a variance 

from the requirement of secondary treatment. The variance is conditional upon 7 factors primarily 

dealing with water quality and upon concurrence of the state in which the discharge is located. In 

anticipation of several Washington municipalities applying for marine waivers, Ecology requested a 

formal AG opinion to the question, "Under state law may a municipality discharge wastes from its 

sewerage system into Puget Sound, or other marine waters, without providing secondary 

treatment?" The response (AGO 1983 No. 23) reviewed the law as given previously in this section 

and then continued,

"Such statutory directions to the Department of Ecology, however, clearly do bring into play 

the expertise of the department as administrator of the state's water pollution control system. 

Accord, Weyerhaeuser v. Southwest Air Pollution Control Authority, 91 Wn.2d 77, 586 

p.2d 1163 (1978). The precise level of treatment required by those general standards 

involves, primarily, engineering determinations; i.e., as to what treatment methods are 

"known," what treatment methods are "available," and what treatment methods are 

"reasonable" with respect to the particular installation in light of the factual circumstances 

surrounding it.19 To make those determinations a review must be conducted by the 

department of existing engineering technologies in order to enable it to decide which 

methods of treatment--including but not limited to "secondary treatment" as above defined--

are suitable with respect to the waste situation involved in the particular case.

Cf., Weyerhaeuser , supra.

20

 -------------------------------------------------------

19. The use of the encompassing word "all" indicates to us that the existing "state of the 

art" or "best available" treatment technologies are required to be used.

Cf., Weyerhaeuser v. Southwest Air Pollution Control Authority, supra.

20. These determinations by the Department of Ecology are, of course, to be made in 

light of the foundation policy that "waters of the state" shall be of high quality and 

be maintained to the "highest possible standards to insure the purity of all waters of 

the state" consistent with various environmental and economic objectives.

RCW 90.54.020(3)(b) and RCW 90.48.010.

Ecology denied the marine waivers on the basis that secondary treatment constituted all known, 

available and reasonable treatment for municipal dischargers. Ecology determined reasonableness 

for each of the municipalities on 3 factors: (1) planning status, (2) environmental or siting 

constraints, and (3) economics. The economics factor was an analysis of resulting rate structure 

after meeting secondary treatment and a comparison to rates in other municipalities in the state and 

nation. The PCHB concurred with Ecology that secondary treatment for marine discharging 

municipal treatment plants was AKART. The decision for Bellingham v. Ecology (PCHB No. 84-

211) contains a good discussion on technology-based treatment.
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Footnote 20 above also mentions environmental objectives as a consideration of AKART. 

Environmental considerations are also a requirement given in federal regulations for case-by-case 

determinations. Unfortunately, there is no federal guidance on the process of making these 

environmental considerations. The environmental considerations required for BPT and BCT 

determinations were a consideration of the environmental effects of the pollutants in question.

3.5.2. New Source Performance Standards for Production Increases

Federal effluent guidelines allow a permit writer to grant an increase in pollutant discharge for 

production increases because the guidelines are production-based. The new source performance 

standards in federal regulations are more stringent than standards for existing source because 

new facilities can take advantage of new treatment methods and equipment and incorporate these 

into the design of the facility. In 1985 the Industrial Section issued a permit to Weyerhaeuser, 

Longview pulp mill complex which includes R-W Paper and NORPAC. The permit writer used 

new source performance standards to derive effluent limits for the 150 tons per day production 

increase at NORPAC and the 100 tons per day at R-W Paper and used AKART as the basis. 

Ecology argued that given the cost and planning required for anything except a marginal increase 

in production, a facility should also be planning and investing in its waste treatment to 

accommodate production increases. In this case the company did not have to make any capital 

investment to meet the new effluent limitations. The appellant Weyerhaeuser argued that the 

AKART standard was too uncertain. The PCHB found that the limits were "more stringent than 

federally required, but 'reasonable' as a matter of state law." As a general policy, wasteload 

increases greater than 10% at facilities with applicable effluent guidelines should be considered 

as new source loading when defining effluent limitations.

3.5.3. Discharge of Captured Pollutants

In the early 1980's, Ecology discovered that an ITT Rayonier pulp mill was discharging clarifier 

solids to come up to its permitted effluent limit for TSS. When Ecology reissued the permit, it 

contained a specific prohibition against discharge of sludge. The facility appealed this provision 

(PCHB No. 85-218), arguing that as long as they were meeting their technology-based effluent 

limits based on the federal effluent guidelines Ecology could not prohibit the discharge of sludge 

especially since Ecology could not prove water quality degradation. The mill also argued that 

the cost to deal with all their solids was excessive. Ecology argued that the discharge of 

pollutants already captured did not meet the intent of AKART. The PCHB ruled for Ecology.

3.5.4. Source Control of Pollutants

Ecology issued a permit in 1998 to Shell Oil (Tesoro) that contained numeric effluent limits 

based on the current EPA effluent guidelines and narrative effluent limits for source control 

(pollution prevention). The narrative limits were based on authority of 90.48 as AKART. The 

PCHB (98-50) and the Court of Appeals (No. 44762-9-1) affirmed the narrative limits. The 

Court of Appeals stated, “The Tesoro permit’s conditions, which directly address the refinery’s 

pollution control methods, may in fact better satisfy AKART than numeric limits alone...”
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3.6. Direct Definitions of AKART

Some legal rulings contain text that clarifies the definitions of AKART. In the footnote number 

19 of the marine discharge section above, for example, the Attorney General's office has defined 

"all" as indicating that the existing "state of the art" or "best available" treatment technologies are 

required to be used.

In PCHB 85-218 (ITT Rayonier v. Ecology), also discussed above, the board pointed to a decision 

by the Southwest Washington Air Pollution Control Authority (SWAPCA) for a definition of the 

terms "known" and "available":

" ...SWAPCA may not require an applicant to develop new technology to advance the art of 

emission control. The "advance" must be "known" in the sense that it has been tested and 

found to control emissions effectively and efficiently. Under this test SWAPCA may not 

insist that an emission source be utilized as a proving ground for as yet untried control 

technology. An applicant must, however, incorporate into its proposal those control systems 

previously developed and presently available. 99 Wn.2nd at 81,82."

The issue of reasonableness was addressed in PCHB 84-211 (Bellingham v. Ecology) dealing with 

the marine waivers. The results of this case are discussed in the following section 3.12.

3.7. AKART Defined In Individual Permits

In individual permitting situations AKART may be equivalent or more stringent than the federal 

effluent guidelines. A permit manager may examine a development document and available 

treatment technologies for a particular category of discharger and make a determination that the 

federal effluent limitations are AKART. This becomes more difficult as the effluent guidelines 

become dated and the manufacturing processes change. In some cases the manufacturing 

processes change to such an extent that they no longer fit those described in the development 

documents. As described in an earlier section, those effluent guidelines less than 5 years old will 

always be AKART for the pollutants described in the development document. For effluent 

guidelines between 5 and 10 years old, the permit manager should compare production 

processes, pollutants generated and treatment efficiencies at the facility with those in the 

development document and in the treatability data base. For effluent guidelines older than 10 

years, the permit writer should do the previous analysis and review unit processes design if time 

allows.

In some cases Ecology permit writers have determined that a category of discharger is capable of 

better performance than specified under effluent guidelines. An example is continuouslymonitored pH. Under federal regulations, if a pH limitation in a permit is technology-based and 

is continuously monitored, then a discharger may receive an exclusion from the permit limits for 

a period of 1 hour per excursion and a maximum monthly excursion period of 7 hours and 26 
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minutes (40 CFR 401.17). The federal regulations place no bounds on magnitude of the 

excursions. Ecology has issued permits which place outside limits on these excursions of 5.0-

10.0 units for petroleum refineries and 4.0-9.5 units for pulp mills. The justification for these 

excursion limits was that water quality standards may be violated at extreme pH ranges, that 

extreme ranges would be a violation of the state's dangerous waste laws, and that the facilities 

were capable of achieving a narrower range (AKART). This determination was appealed but a

settlement was reached on the issue.

An AKART determination may take into consideration the treatment performance at a similar 

manufacturing facility. In this situation the permit writer must assess the costs to the facility to 

achieve the increased treatment efficiency. Some of the factors to be analyzed are; 

Are the production processes equivalent?

Does this facility have some site specific constraints that would prohibit the increased 

treatment efficiency? 

And are the facilities of comparable age? 

3.8. AKART Versus Case-by-Case

In the cases above where proposed effluent limits are more stringent than those promulgated in 

the federal effluent guidelines, the effluent limits are based on the authority of RCW 90.48 

(AKART). Federal regulations are not explicit as to whether or not case-by-case determinations 

should be made in every permitting circumstance, whereas, the language in 90.48 clearly 

indicates that all discharges are to be treated with all known, available and reasonable methods. 

Technology-based limitations based on AKART may have a compliance schedule placed in the 

permit instead of in a compliance order.

In the case of a facility without effluent guidelines, a permit writer must make concurrent decisions 

on case-by-case under federal regulations (40 CFR 125.3) for BCT (conventional pollutants), BAT 

(toxics/nonconventional pollutants) and AKART. This process is covered in the previous section of 

this manual. In this situation because the permit writer will be using the same cost tests for 

economic achievability, case-by-case and AKART determinations are equivalent. In this situation 

the compliance schedule must be put in a companion enforcement order.
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3.9. Zero Discharge

The permit writer may determine that for some permits AKART is zero discharge. Although 

there is no explicit statement in RCW 90.48 equivalent to the "zero discharge" goal of the Clean 

Water Act, both of these laws have a technology-based principle which, when followed to the 

logical conclusion lead to zero discharge, when achievable and reasonable.

3.10. AKART For Pretreatment

The pretreatment program parallels the surface discharge program. Municipal treatment plants 

are designed to treat domestic sewage. The uses to be protected at the treatment plant are 

biological functioning of the biomass and uses of the biosolids (sludge). Local limits are 

designed in part to protect these uses and are equivalent to water quality-based limits for surface 

discharges to prevent violations of the water quality standards. The categorical (pretreatment) 

effluent limitations are equivalent to the technology-based effluent limitations in federal 

regulations for surface dischargers.

All indirect dischargers must be examined for AKART in the permitting process because there is no 

exemption in law for indirect dischargers. Determining AKART for indirect dischargers is the same 

process as described previously. If the discharger is a categorical discharger the permit writer must 

determine the applicability of the effluent guidelines. A permit writer may derive limits that are 

more stringent than the effluent guidelines on the basis of AKART. If the discharger is not a 

categorical discharger the permit writer must do an engineering and economic analysis to determine 

appropriate technology-based effluent limits on a case-by-case basis.

Since POTW's are designed to treat BOD and solids, an industrial/commercial discharger should not 

be required to treat for BOD and solids if the municipality has the capacity to treat the waste.

3.11. Engineering Analysis for All Known and Available

The general requirements for the engineering analysis for all known and available are specified in 

WAC 173-240 as requirements of an engineering report. The process of engineering analysis is not 

given in Chapter 173-240 WAC, however, one of the requirements of this regulation is that the 

engineering report be prepared under the supervision of a licensed engineer unless the requirement 

is waived by Ecology. The review and analysis of this report by Ecology must also be done by an 

engineer who is trained and experienced in wastewater treatment. Scientists in the permit unit may 

contribute to the determinations in an engineering report but an engineer must make the judgment

on the question of whether the treatment system proposed meets the AKART criteria. Case-by-case 

decisions on technology-based effluent limits for existing facilities must also be reviewed and 

approved by an engineer.
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One point made earlier is important to review here. The PCHB in its citation of the SWAPCA 

decision indicated that Ecology cannot require Permittees to develop new treatment technology. 

That does not mean that treatment methods must be demonstrated for each kind of discharger. For 

example, if a discharger has a process not described in the effluent guidelines or elsewhere and 

which produces the pollutant BOD, and if the BOD concentration and degradation rates are similar 

to domestic wastewater, then biological treatment process and secondary treatment efficiencies are 

applicable to that discharger.

3.12. Economic Tests Define Reasonable

The section describes how to conduct the economic evaluation for deriving effluent limits by 

case-by-case or by AKART.

Performing the economic reasonableness tests requires estimates of the costs of the proposed 

treatment technologies; estimates of pollutant removal levels; and profit, cost and revenue data. 

The permittee is responsible for providing any data needed by the permit writer to make a 

decision. For new dischargers the cost and pollutant removal estimates for the proposed 

treatment technologies should be included in the engineering report submitted under WAC 173-

240. This section covers the information permit writers need from dischargers before deciding 

on economic reasonableness.

Permit writers can use this section and the other reference documents to carry out economic 

reasonableness tests for BPJ permits.

As mentioned earlier, Ecology has adopted EPA's economic reasonableness tests. Ecology may 

develop its own tests in the future. There are 3 federal economic reasonableness tests 

corresponding to 3 levels of treatment: (1) BPT (2) BCT, and (3) BAT. The New Source and 

Pretreatment tests are identical to the BAT test.

For indirect dischargers, both AKART and federal pretreatment regulations define the effluent 

limits. The economic factors in setting pretreatment effluent limits are discussed later in this 

section.

For dischargers to ground water, AKART alone defines the effluent limits. No Federal law or 

regulation defines treatment standards for ground water dischargers.

BPT ECONOMIC REASONABLENESS TEST
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BPT was the first level of treatment identified in the CWA and is applicable only to conventional 

pollutants. BPT costs are also used in the economic achievability tests for BCT and BAT levels 

of treatment. BPT treatment for conventional pollutants is used as the base cost for BAT 

treatment for toxics and nonconventional pollutants because treatment for conventional 

pollutants is effective in varying degrees for removing toxic pollutants. The BPT economic 

reasonableness test is authorized by section 304(b)(1)(B) of the CWA. Among the factors that 

the permit writer must consider in setting BPT effluent limits is:

"...the total cost of application of technology in relation to the effluent 

reduction benefits to be achieved from such application..." (40 CFR 

125.3(d)(1).

The BPT economic reasonableness test is intended to be a cost-benefit test and benefits are 

measured in terms of amounts of pollutants removed.

EPA writes that:

"The cost-benefit inquiry for BPT is a limited balancing, committed to EPA's discretion, 

which does not require the Agency to quantify benefits in monetary terms....In balancing 

costs in relation to effluent reduction benefits, EPA considers the volume and nature of 

existing discharges, the volume and nature of discharges expected after application of 

BPT, the general environmental effects of the pollutants, and the cost and economic 

impact of the required pollution control level." (47 FR 23263).

Thus, there is no single, precisely-defined BPT economic reasonableness test. The economic 

factors considered in determining BPT can vary from industry to industry.

According to an EPA economist, in setting BPT effluent limitations, EPA weighed the cost per 

pound of pollutants removed by the treatment technology more heavily than the effect of the 

annual cost of the treatment technology on the profitability of the plant (although some weight is 

given to the effect on profitability). The cost per pound of pollutants removed is intended to be a 

cost-benefit measure. By considering cost per pound, total cost in relation to pollution reduction 

is considered.

The intent of the BPT cost-benefit requirement is to avoid requiring wastewater treatment "where 

the additional degree of effluent reduction is wholly out of proportion to the costs of achieving 

such marginal level of reduction..." Costs cannot be wholly disproportionate to benefits.

For at least a few industries EPA used the "inflection" or "knee of the curve" method as the 
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economic reasonableness test for BPT effluent limits. For each industry, "cost-effectiveness" 

diagrams were constructed which graphed the total cost of various treatment technologies against 

the percentage of pollutants removed by each technology. These graphs show that the marginal 

cost per percentage of pollutants removed rises as the total percentage of the pollutants removed 

rises. The BPT effluent limitations "were set at the point where the costs per percent (of) 

pollutant reduction took a sharp break upward toward higher costs per percent of pollutant 

removed". The cost per percent of pollutant reduction is called the marginal cost of pollutant 

removal.

However, the "knee of the curve" test is not the BPT economic reasonableness test. The U.S. 

Fifth Circuit Court of Appeals rejected the argument that the CWA required the use of the "knee 

of the curve" cost test in setting BPT effluent limits. The court wrote that:

"The CWA contains no specific statutory language establishing a BPT "knee of the 

curve" test or any other quantitative cost-benefit ratio test for BPT.... The courts of appeal 

have consistently held that Congress intended Section 304(b) to give the EPA broad 

discretion in considering the cost of pollution abatement in relation to its benefits and to 

preclude the EPA from giving the cost of compliance primary importance."

Section 304(b) of the CWA requires EPA to establish BPT effluent limits. The CWA does not 

require that the knee of the curve test be used. The knee of the curve test can be used in 

combination with other tests. EPA does have to consider costs in relation to benefits in some 

manner.

For each development document, an accompanying economic analysis is written. The economic 

analysis estimates the impact of the proposed effluent limits (BPT, BCT, BAT, NSPS, etc.) on 

the affected industry. The economic analysis includes estimates of the regulation's impact on 

prices, production, employment, profits, and the industry's ability to finance expansion. The 

ability of the industry to pass costs on to consumers through price increases is also considered. 

The economic analysis is one of the determinants of the effluent limits (for an example, see 47 

FR 23269).

For example, in setting BPT effluent limits, the development documents often make estimates of 

the impact of the cost of the BPT technology on product prices. The size of the price impact is 

one determinant of the BPT technology. Technologies with low price impacts are more 

economically achievable.

In conclusion, there is no single, precisely-defined BPT economic reasonableness test.

BCT ECONOMIC REASONABLENESS TEST

Best Conventional Technology (BCT) effluent limits only apply to the 5 conventional pollutants: 

BOD, TSS, pH, fecal coliform, and oil and grease.
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BCT always provides control of conventional pollutants at least as stringent as that provided by 

BPT. BCT effluent limits cannot be less stringent that BPT limits. If no BCT treatment 

technology exists or if it is economically unreasonable, then BCT is set equal to BPT.

The BCT economic reasonableness test is the only federal or state test that is precisely defined in 

regulations.

The BCT economic reasonableness test is described in 40 CFR 125.3(d)(2)(i) and (ii). In writing 

case-by-case or BPJ permits for BCT technology, among the factors that the permit writer must 

consider are:

1. “The reasonableness of the relationship between the costs of attaining a reduction in effluent 

and the effluent reduction benefits derived.

2. The comparison of the cost and level of reduction of such pollutants from the discharge from 

publicly owned treatment works (POTW) to the cost and level of reduction of such pollutants 

from a class or category of industrial sources.” Section 304(b)(4)(B) Clean Water Act.

The details of the BCT economic reasonableness test were published in 51 FR 24973-86 (July 9, 

1986). This includes the BCT economic reasonableness test methodology.

The BCT economic reasonableness test considers whether it is “cost-reasonable” for an industry 

to control conventional pollutants to a level more stringent than BPT effluent limitations. The 

test compares a permit holder’s cost of removing conventional pollutants beyond BPT to a 

POTW’s cost of removing conventional pollutants beyond secondary treatment. The test is a 

cost-benefit test because it compares costs and benefits (benefits are measured by the amount of 

pollutants removed).

The BCT economic reasonableness tests imply that the minimum treatment for conventional 

pollutants on a BPJ basis is secondary treatment with 85% removal of BOD and solids. A 

candidate treatment technology would be advanced secondary treatment. A new industry 

producing conventional pollutants but not covered by effluent guidelines would be required at a 

minimum to provide secondary treatment as BPT. A candidate BCT treatment would be 

advanced secondary treatment.

Conducting the BCT Test

The following BCT test was promulgated as regulation to define a cost test. EPA subsequently 

used the test to examine those industries that already had promulgated BPT effluent limits. This 

test requires that BPT technology and costs to have previously been calculated.

Conducting the BCT test as promulgated requires performing two tests:
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1. POTW cost-comparison test.

2. Industrial cost-effectiveness test.

Both of these tests are intended to be cost-reasonableness tests. They implement 40 CFR 

125.3(d)(2)(i) and (ii) and section 304(b)(4)(B) of the Clean Water Act. The tests are shown as 

flow charts in Figures IV-5, IV-6 and in Tables IV-1 and IV-2.

The proposed BCT technology must pass both tests for it to be economically reasonable. If it 

passes one test but fails the other, then it is not economically reasonable.

Performing the two BCT tests requires the calculation of two marginal costs:

1. The annual marginal cost of the existing or proposed BPT treatment technology (MBPT).

2. The annual marginal cost of the proposed BCT treatment technology (MBCT).

The marginal costs are in annual dollars per pound of BOD and TSS removed units (51 FR 

24975).

To calculate these two marginal costs requires two annual total cost estimates:

1. The annual total cost of the existing or proposed BPT treatment technology (TBPT).

2. The annual total cost of upgrading the BPT technology to the proposed BCT treatment 

technology (TBCT).

The two total costs are annual costs.

In addition, the two annual pollutant removal amounts are estimated:

1. The amount of BOD and TSS removed annually by the BPT treatment technology in pounds 

(PBPT).

2. The additional amount of BOD and TSS removed annually by upgrading the BPT technology 

to the proposed BCT technology in pounds (PBCT).

To calculate marginal costs, the annual pounds of BOD and TSS removed by the BPT and BCT 

treatment technologies must be estimated. Annual amounts of BOD and TSS removed by the 

BPT and BCT treatment technologies are measured in pounds per year units. The pounds of 

BOD and TSS are added together.

In general, only the amounts of BOD and TSS removed by the various treatment technologies are 

used in calculating annual amounts of pollutants removed. The amounts of the other three

conventional pollutants (oil and grease, pH, and fecal coliform) removed should not be included. 

They should not be included because when EPA calculated the cost benchmarks it only used the 
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amounts of BOD and TSS removed. The chief reason that EPA did not include fecal coliform 

and pH in the calculation is that these two pollutants cannot be measured in pounds.

However, EPA says that the pounds of oil and grease removed may also be included in the 

calculation of annual amounts pollutants removed when appropriate "in the context of the 

industry and technology" (51 FR 24973).

EPA calculated total annual amounts of BOD and TSS removed using the following method 

using actual data or the monthly maximum effluent limit.
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FIGURE IV-2. The BCT Cost Test.

BCT TWO PART ECONOMIC TEST

CALCULATE ANNUAL TOTAL COST OF EXISTING OR PROPOSED BPT

TREATMENT TECHNOLOGY (TBPT)

CALCULATE ANNUAL TOTAL COST OF PROPOSED BCT TREATMENT (TBCT)

CALCULATE POUNDS OF BOD AND TSS REMOVED ANNUALLY BY BPT (PBPT)

CALCULATE ADDITIONAL BOD AND TSS REMOVED BY PROPOSED BCT

TREATMENT (PBCT)

CALCULATE BPT MARGINAL COST (MBPT) AS TBPT/PBPT

CALCULATE BCT MARGINAL COST (MBCT) AS TBCT/PBCT

CONDUCT POTW TEST AND CONDUCT INDUSTRY TEST IF NECESSARY
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FIGURE IV-3. The POTW and Industrial Cost Tests for BCT.

THE POTW AND INDUSTRIAL TEST

COMPARE MBCT WITH BENCH MARK

COST OF $0.25 OR $0.14 (1976 BASIS)

FAILS COST

TEST

IS MBCT

LESS THAN

BENCH MARK

COST?

NO

PERFORM

INDUSTRIAL

COST TEST

YES

DIVIDE MBCT

BY MBPT

IS RATIO

LESS THAN 1.29

OR 0.68?

PROPOSED

TREATMENT

IS

ACHIEVABLE

YES NO
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Treatment processes for which long-term pollutant removal data is available (long-term means at 

least 12 months), actual long-term pollutant removal data (or data on pollutant concentrations in 

the effluent of the various treatment processes) should be used to calculate the amount of BOD 

and TSS removed annually.

For treatment processes for which long-term pollutant removal data is unavailable, the maximum 

30 day BPT effluent limits for BOD and TSS effluent limits should be used to calculate the 

amount of BOD and TSS removed annually.

For both types of processes (those with and those without long-term data) pollutant loadings of the 

raw wastewater should be estimated from actual data. (For more information on how to calculate 

amounts of pollutants removed by treatment processes, see 51 FR 24983 and 51 FR 24985-6.)

Marginal Costs

The marginal costs are in annual dollars per pound of BOD and TSS removed units.

To calculate the marginal cost of BPT treatment: divide the BPT annual costs by the BPT annual 

weight in pounds of conventional pollutants removed.

To calculate the marginal cost of BCT treatment, compute the following ratio:

1. Numerator: The annual total cost of upgrading the BPT technology to the proposed BCT 

technology.

2. Denominator: The additional amount of BOD and TSS removed annually by upgrading the 

BPT technology to the proposed BCT technology.

The POTW Cost-Comparison Test

The POTW cost-comparison test is the first part of the cost-reasonableness test. It compares the 

industry's cost of removing additional pounds of conventional pollutants (beyond BPT) to a 

POTW's cost of removing additional pounds of conventional pollutants (beyond secondary 

treatment).

The POTW benchmarks were calculated in 1986. They are expressed in 1976 prices. These 

benchmarks must be updated to the year in which the proposed BCT technology cost estimate is 

made. If old benchmarks were used, the benchmarks would be too low (because construction 

and operation costs are constantly rising) and too many proposed BCT treatment technologies 

would be rejected as economically not achievable.
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EPA published a table that updated the benchmarks through 1985 (51 FR 24985). EPA has not 

formally updated the benchmarks past 1985. However, it can give help in updating them (cost 

indices, etc.).
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TABLE IV-1. THE POTW COST-COMPARISON TEST

POTW COST-COMPARISON TEST

TO PERFORM THE POTW COST-COMPARISON TEST, COMPARE THE 

FOLLOWING 2 MARGINAL COSTS:

1. The permit holder's annual marginal cost per pound of pollutant removed when 

upgrading its treatment process from BPT to the proposed BCT treatment 

technology.

2. An average-size POTW's annual marginal cost per pound of pollutant removed 

when upgrading from secondary treatment to advanced secondary treatment. 

Secondary treatment is defined as 30 mg/L of BOD and TSS. Advanced secondary 

treatment is defined as 20 mg/L of BOD and TSS.

Use the following figures for the POTW's annual marginal cost (51 FR 24985-6): 

A. $.25 (in 1976 dollars) when the proposed BCT treatment process has 

long-term pollutant removal data (here, long term means at least 12 

months). This figure is referred to as the "first tier POTW benchmark."

B. $.14 (in 1976 dollars) when the proposed BCT treatment process does 

not have long-term pollutant removal data. This figure is referred to as 

the "second tier POTW benchmark."

If the permit holder's marginal cost exceeds the appropriate POTW marginal cost 

benchmark, then the proposed BCT treatment process is not economically reasonable. 

If the permit holder's marginal cost is less than or equal to the appropriate POTW 

marginal cost threshold, then the proposed BCT treatment process is economically 

reasonable.
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The Industrial Cost-Effectiveness Test

The industrial cost-effectiveness test is intended to be a test of the proposed BCT technology's 

cost-effectiveness. It compares the industry's costs of attaining a reduction in pollution with the 

pollution reduction benefits derived. See the following Table IV-2 for the test.

The POTW benchmarks were calculated in 1986. They are expressed in 1976 prices. They do 

not have to be updated to the year in which the proposed BCT technology's cost estimate is 

made. EPA (47 FR 49199) stated that the benchmarks for the industrial cost-effectiveness test 

would not be indexed for cost changes over time because any such changes would be small. The 

ratios are the ratios of the marginal cost of upgrading a secondary STP to advanced secondary to 

the marginal cost of building a secondary STP. It is unlikely that ratio will change much over 

time because the cost indices for secondary and advanced secondary STPs should be nearly 

identical.

The proposed BCT technology must pass both tests for it to be economically reasonable. If it 

passes one test but fails the other, then it is not economically reasonable.

If the proposed technology fails one or both tests, then BCT is set equal to BPT.
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Table IV-2. The Industrial Cost-Effectiveness Test.

INDUSTRIAL COST-EFFECTIVENESS TEST

TO PERFORM THE INDUSTRIAL COST-EFFECTIVENESS TEST, COMPARE THE FOLLOWING 

2 RATIOS OF MARGINAL COSTS:

1. The permit holder's ratio of marginal costs. This ratio is intended to be a measure of the 

candidate BCT treatment's cost-effectiveness. It is the ratio of the following 2 marginal costs:

A. Numerator: The permit holder's marginal cost per pound of additional pollutants removed 

when upgrading its treatment process from BPT to the proposed BCT treatment process.

B. Denominator: The permit holder's marginal cost per pound of pollutant removed when 

upgrading its treatment process from no treatment (raw waste) to BPT.

2. A POTW benchmark ratio of marginal costs. This ratio is referred to as the "industry cost 

benchmark." This is the ratio of the following two marginal costs:

A. Numerator: The marginal cost per pound of pollutant removed when a POTW upgrades 

from secondary treatment to advanced secondary treatment.

B. Denominator: The marginal cost per pound of pollutant removed when a POTW upgrades 

from no treatment (raw sewage) to secondary treatment.

Use the following figures for the POTW benchmark ratio (51 FR 24985-6):

A. 1.29 (calculated using 1976 dollars) when the proposed BCT treatment process has longterm pollutant removal data (here, long term means at least 12 months).

B. 0.68 (calculated using 1976 dollars) when the proposed BCT treatment process 

does not have long-term pollutant removal data.

If the permit holder's ratio exceeds the POTW benchmark ratio, then the proposed BCT treatment 

process is not economically reasonable. If the permit holder's ratio is less than or equal to the POTW 

benchmark ratio, then the proposed BCT treatment process is economically reasonable.
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BAT ECONOMIC REASONABLENESS TEST

BAT is Best Available Technology Economically Achievable and is applicable to toxics and 

non-conventional pollutants.

In setting BPJ effluent limits for BAT treatment technologies, 40 CFR 125.3(d)(3)(v) states that 

"the cost of achieving such effluent reduction" must be considered. This regulation repeats a 

portion of section 304(b)(2) of the Clean Water Act, which defines BAT. Even though the CWA 

does not list pollution reduction benefits among the factors that must be considered in 

determining BAT, they are considered by EPA when determining BAT. Therefore, the 

relationship between the cost of BAT and the pollution reduction achieved by the installation of 

BAT is also considered. An EPA permit writing expert has defined the cost of achieving the 

effluent reduction as the capital and operating cost of attaining a specified effluent quality.

The CWA does not require a comparison of costs and benefits. EPA writes:

"The statutory assessment of BAT "considers" cost, but does not require a balancing of costs 

against pollution reduction benefits...In developing the BAT limitations, however, EPA has 

given substantial weight to the reasonableness of costs. The Agency has considered the 

volume and nature of discharges, the volume and nature of discharges expected after 

application of BAT, the general environmental effects of the pollutants, and the costs and 

economic impact of the required pollution control levels" (47 FR 23263).

Costs and benefits do not have to be compared. However, EPA does consider the cost of the 

pollutant reduction achieved by BAT technology in setting BAT effluent limits. Thus, it does 

compare costs and benefits (as measured by pollutant reduction) in determining BAT. However, 

economic achievability is given more weight.

With regard to the BAT economic achievability test, the U.S. Fifth Circuit Court of Appeals 

wrote:

"Both Congress and the Supreme Court have made clear that in setting BAT, 

the EPA is not required to compare the costs against the benefits of pollution 

reduction in the same manner as the EPA is required to do in setting BPT 

standards". (page 250, Chemical Manufacturers Association vs. USEPA)

The court also wrote that section 301(b)(2)(A), which defines BAT, differs from section 

301(b)(1)(A), which defines BPT, in that it does not state that costs shall be considered in 

relation to effluent reduction. No cost-benefit test is required by the CWA (page 250, Chemical 

Manufacturers Association vs. USEPA). In setting BAT effluent limits, EPA must only consider 

their "economic achievability." 
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BAT Economic Achievability Tests

The BAT economic achievability tests are described in federal guidelines--not in federal or state 

regulations. EPA's Guidance Manual for Estimating the Economic Effects of Pollution Control 

Costs describes these tests. EPA emphasizes that this manual is not regulation or policy. 

Therefore, Ecology must determine the specific methods that it will use to evaluate economic 

achievability and to justify those methods. Ecology could use methods other than the federal 

tests if it has legitimate reasons for using them.

EPA's Guidance Manual defines a treatment technology to be economically achievable if its use 

would not cause the plant to shut down. That is, the technology is economically achievable if its 

annual cost is less than the plant's annual profits.

EPA's Guidance Manual uses a 3-stage approach to determining economic achievability:

1. First, perform a firm-level test.

2. If the control technology passes the firm-level test, but the permit holder protests that the 

technology is not economically achievable, then perform a plant-level test.

3. If the firm-level test is inconclusive, then a plant closure analysis must be conducted.

The BAT economic achievability test is shown in Figure IV-7.

Figure IV-4. Sequence of Analysis for Determining Economic Achievability for BAT.
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CONDUCT FIRM LEVEL ANALYSIS IF NECESSARY TO SUPPORT PLANT LEVEL ANALYSIS

DOES PROPOSED 

TREATMENT PASS 

FIRM LEVEL TEST?

TREATMENT IS 

NOT 

ECONOMICALLY 

ACHIEVABLE

DOES THE FIRM 

CONTEST DECISION AND 

PROVIDE PLANT 

FINANCIAL DATA?

PROPOSED 

TREATMENT IS 

ECONOMICALLY 

ACHIEVABLE

CONDUCT 

PLANT LEVEL 

ANALYSIS

DOES PLANT PASS 

PLANT LEVEL 

TEST?

PROPOSED TREATMENT IS ECONOMICALLY ACHIEVABLE

TREATMENT IS 

NOT 

ECONOMICALLY 

ACHIEVABLE

NO

NO

NO

NO

YES

YES
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The plant-level test makes the most sense economically. It is more precise than the firm-level 

test. However, plant-level tests are difficult to do because plant-level data is limited and 

confidential. Therefore, the Guidance Manual recommends doing the firm-level test first 

because, in some cases, it is possible to conduct it with publicly-available data on the firm's 

balance sheet, income statement, and stock prices.

However, in most cases it is either impossible or a waste of time to perform the firm-level test 

for two reasons:

1. For most permit holders, the firm-level test is difficult to do because few of them are 

publicly held corporations. Therefore, no publicly available balance sheet or stock market 

data exists. In many cases, because the firm is so small, the firm will equal the plant.

2. Any permit holder with any business sense will demand that the plant-level economic 

achievability test be performed in any case, because he/she, as a profit-maximizer, is 

interested in the profitability of the plant. A profit-maximizing firm owner has no interest in 

subsidizing the wastewater treatment costs of one plant with profits earned by the remainder 

of his/her firm.

The primary justification for conducting the firm-level test is that the data needed to perform the 

test is publicly available from sources such as Moody's Industrial Manual and from stock prices. 

However, very few Washington permit holders (especially small- and medium-sized companies) 

are publicly owned. Thus, few have stock that is publicly traded. Few permit holders are listed 

in Moody's and similar publications. There is no other publicly available data. Therefore, for 

these firms, permit holders must provide the data needed to conduct firm-level tests.

In cases where the firm is identical to the plant, a plant-level test is the same as a firm-level test, 

therefore, call it a plant-level test.

Even when there is publicly available data, a firm-level test will usually yield a meaningless 

answer that will be immediately disputed by the permit holder. There is little point in estimating 

the impact of the annual cost of a proposed BAT treatment system for a Weyerhaeuser plant on 

the total worldwide profits of the Weyerhaeuser Co. It is obvious that the impact will be tiny. It 

is also obvious that Weyerhaeuser will immediately point out that it is concerned with the 

profitability of each of its facilities and is not interested in subsidizing one plant with profits 

from its other plants. Therefore, it will want a plant-level test to be conducted.

Generally the firm-level test should not be conducted except in the situation discussed below 

where it is used to compliment the plant-level test.
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Firm-Level Test

The firm-level test examines whether the firm as a whole can afford the treatment technology. It 

is performed using publicly available balance sheet and stock market data.

There are 7 different firm-level tests. They all estimate the impact of the cost of pollution 

control equipment on a financial ratio. Among the tests are: the current ratio, which is the ratio 

of current assets to current liabilities; Beaver's ratio, which is the ratio of cash flow to total debt; 

the debt/equity ratio; and the market-to-book ratio.

The Guidance Manual suggests that if the firm-level test shows that the proposed BAT treatment 

technology is not economically achievable for the firm, then it is not economically achievable for 

the plant. This is not always true because the firm-level test may give misleading results. It is 

possible that the plant is making large profits, while the firm as a whole has low profits. Losses 

in some of the firm's plants offset profits in others. In such a situation, the firm-level test would 

indicate that the proposed BAT technology is economically unreasonable, when, in fact it was 

reasonable.

If the firm-level test shows that the proposed BAT treatment technology is economically 

achievable, the owner may contest this determination. The owner may contend that the BAT 

technology will make the plant unprofitable to operate. If the determination is contested, the 

owner must provide plant-level data for the plant-level test.

In some cases (especially when the permit holder has only one plant), the firm-level tests can be 

used to supplement the plant-level test. They can provide information that the plant-level test 

does not. In most cases the data needed to perform the firm-level tests will have to be provided 

by the permit holder. Because there are several firm-level tests and because performing them is 

complicated, instructions for conducting them are not included here. See the Guidance Manual

for instructions.

As explained earlier, in most cases the firm-level test is meaningless and will probably be 

disputed by the permit holder. In addition, for many firms, balance sheet and stock price data 

which is required to perform the firm-level test is not publicly available. Therefore, the firmlevel test should only be performed to compliment the plant-level test.

Plant-Level Test

There are three plant-level tests. All the plant-level tests ask the same question: would the plant's 

earnings before taxes be greater than zero if it installed the proposed BAT technology? That is, 

would the plant be driven out of business by the cost of the BAT technology?
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The three plant-level tests are:

1. Earnings test.

2. Gross margin test.

3. Revenue test.

According to EPA, only 1 of the plant-level tests needs to be done because the three tests are 

essentially the same, differing only in the amount of data that they require the firm to provide. 

The three tests require data from the plant's income statement and estimation of the annual cost 

of the proposed BAT treatment technology.

It is important to note that all three of the BAT plant-level economic achievability tests are 

conservative. They assume that the permit holder cannot pass any portion of the cost of the BAT 

treatment equipment on to its customers. The cost is assumed to come completely out of its 

profits. The tests assume that the cost of the pollution control equipment is an additional cost but 

that revenue is constant. Generally, this assumption is incorrect for many of the industries that 

hold permits because the permit holder will be able to pass along a portion or all of the cost, thus 

lowering the impact of the cost of the treatment equipment on its profits. The more that water 

pollution control regulations are consistent throughout the U.S., the easier it is for the permit 

holder to pass the costs on. Therefore, this economic achievability test is biased in favor of the 

permit holder.

The permit holders are responsible for providing the cost, earnings, and revenue data needed to 

perform the economic achievability test. If they refuse to supply the data, then it should be 

assumed that the treatment technology is economically achievable.

Plant Closure Analysis.

If the plant-level tests do not provide conclusive answers, then a detailed plant closure analysis 

must be conducted. This is a much more detailed and therefore, more valid and expensive--

examination of the impact of the cost of the treatment technology on the plant's economic 

viability. It is a job for a consultant.

The EPA Guidance Manual states:

The plant-level tests are intended and designed as screening tests rather than rigorous and 

definitive evaluations of a plant's ability to afford pollution control costs. If the test results 

indicate that pollution controls would impose severe economic impacts, then a more detailed 

plant closure analysis would be necessary. This would entail working closely with the plant 

and corporate accountants to gather information on a variety of costs, revenues, and 

accounting procedures. Information on salvage values of equipment as well as projections 

of future economic conditions may be desirable or required.
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Data Requirements for Plant-Level Test

If the owner does not think that a treatment technology proposed by Ecology is economically 

reasonable and wants a plant-level test conducted, he/she must provide the data needed to 

conduct the economic achievability tests.

The permit holders are responsible for providing all the data needed to perform the economic 

achievability tests. They must supply two types of data: 

1. Cost estimate for upgrading the treatment technology from BPT to the proposed BAT 

technology.

2. Data from its income statement.

Pollution Control Equipment Cost Estimate

All 3 BAT plant-level economic achievability tests require estimates of the annual cost of the 

proposed BAT treatment technology. This cost is the cost of upgrading from BPT to BAT 

treatment. For the BAT test, the total annual cost of upgrading from BPT or proposed BPT to 

the proposed BAT treatment technology is used. Marginal costs per unit of pollutant removed 

are not used in the BAT tests.

Ecology may propose a BAT treatment process based on the fact that a competitor of the 

permittee had a similar process. If the permittee disputes this type of comparison they must 

submit data to show why they are substantially different from their competitor.

The plant-level tests use before-tax annual costs.

Income Statement Data

The permit holder must provide plant-level income statement data—revenue, costs, and 

earnings—for the most recent three years (the EPA Guidance Manual only uses data from the 

most recent year’s income statement). If it does not collect this data at the plant level, it must do 

the best job it reasonably can in constructing accurate income statements for the plant.

The permit holder must provide the following income statement data:

1. Revenue.

2. Cost of Goods Sold.

A. Cost of materials.

B. Direct labor costs.

C. Production overhead costs (indirect labor, rent, energy, etc.).

D. Extraordinary costs should not be included.
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3. Corporate Overhead Costs Assigned to the Plant

A. Selling, general, and administrative expense.

B. Interest expense.

C Depreciation on common property.

D. Etc.

The permit holder must supply documentation to verify the data. For example, state excise tax 

returns, federal income tax returns, tax schedules, etc.

For plants that are owned by companies with several facilities, income tax returns and schedules 

will usually lump together the revenue, cost, and earnings data for all the facilities. In such 

cases, income tax forms will be worthless for verifying plant-level revenue and cost data. 

Ecology will then have to rely on accounting records. Such records might be biased by the 

permit holder. There is little Ecology can do about this, short of auditing the firm.

There are several problems that will be faced in obtaining accurate plant-level data:

• Plant-level data is usually confidential.

• Sometimes firms do not collect plant-level revenue and cost data. Many companies do 

not keep revenue data at the plant level. Instead, they maintain some cost records at the 

plant level but record revenues at the division or firm level.

• Corporate overhead costs are not usually allocated to individual plants. And when they 

are, biases may exist in the allocation method.

• Non-standard accounting procedures used internally by the firm can make it difficult to 

verify cost and revenue data.

• Firms may bias the plant's costs and revenues. It is essentially impossible to audit the 

cost and revenue data for accuracy.

• Transfer prices for inputs purchased by the plant from other parts of the firm can be 

biased upward in order to increase costs.

• Transfer prices for goods sold by the plant to other parts of the firm may be biased 

downward in order to reduce revenue.

The BAT plant-level economic achievability tests are performed using the following tests which 

are calculated using income statement data:
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• Earnings before taxes test (EBT) = revenues minus the costs of goods sold and 

corporate overhead

• Gross margin test = revenues minus costs of goods sold

• Revenue test

Performing the Plant-Level Tests

The earnings test is the most accurate plant-level BAT test. Therefore, if the data is available, it 

is the test that should be performed. The earnings test asks the question: would the plant's 

earnings before taxes be greater than zero if it installed the proposed BAT technology?

The earnings test analyzes a plant's earnings before taxes (EBT) and determines if the EBT 

would be positive after installation of pollution control equipment.

The earnings test requires data that may not normally be collected at the plant level. Therefore, 

its application may be limited. The gross margin test and the revenue test require less data and, 

therefore, can be used in more situations.
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Table IV-3. The BAT Earnings Test.

EARNINGS TEST

TO PERFORM THIS TEST CALCULATE:

Earnings before taxes minus the annual cost of proposed BAT technology

• If this number is greater than zero, the proposed BAT treatment technology is 

economically achievable.

• If this number is less than zero, the proposed BAT technology is not economically 

achievable.

• If this number is equal to zero (or near zero), then the test is inconclusive. A plant 

closure analysis must be carried out.

If the earnings test is inconclusive, the other two plant-level tests will not help to determine 

whether or not the proposed technology is economically achievable. All three tests are identical 

except that the gross margin and revenue test use less accurate data than the earnings test uses. 

Tests performed using less accurate data cannot help provide a conclusive answer when the test 

using the most accurate data (the earnings test) does not provide a conclusive answer.

Gross Margin Test

According to the EPA Guidance Manual, if the earnings test cannot be performed because cost 

data that allocates corporate overhead costs to individual plants is not available, then either the 

gross margin test or the revenue test should be performed. There is no need to perform both. As 

explained below the two tests are equivalent except for the data requirements.

Gross margin is equal to revenue minus the cost of goods sold. It is a measure of the plant's 

profit before deducting corporate overhead costs. The gross margin test avoids the problem of 

accurately allocating corporate overhead to the plant. This test is a less accurate test of economic 
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achievability than the earnings test because an estimate of the plant's corporate overhead is used 

instead of actual data.

The gross margin test assumes that the firm's EBT-to-gross margin ratio is equal to its industry's 

EBT-to-gross margin ratio. The test uses the firm's gross margin and the industry's EBT-to-gross 

margin ratio to estimate the firm's EBT (multiply the firm's gross margin by the industry's 

EBT/gross margin to yield the estimate of the firm's EBT). It then compares the cost of the BAT 

technology to the firm's estimated EBT. So, the gross margin test is an earnings test that uses 

estimated earnings rather than actual earnings.

Table IV-4. The Gross Margin Test for BAT.

GROSS MARGIN TEST

TO PERFORM THE GROSS MARGIN TEST CALCULATE:

1. Ratio of the annual cost of the proposed BAT technology to the firm's gross 

margin.

2. Ratio of the industry’s average EBT to the industry’s average gross margin.

The industry average EBT and gross margin are obtained from Robert Morris 

Associates’ Annual Statement Studies. They are available for 4-digit SIC 

codes.

• If the first ratio is less than the second ratio, then the proposed BAT 

treatment technology is economically achievable.

• If the first ratio is greater than the second ratio, then the proposed BAT 

treatment technology is not economically achievable.

• If the first ratio is equal (or approximately equal) to the second ratio, then 

the test is inconclusive. A plant closure analysis must be carried out.
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If the gross margin test is inconclusive, the revenue test will not help to determine whether or not 

the proposed technology is economically achievable. Both tests are essentially the same except 

that the revenue test uses less accurate data than the gross margin test does. A test performed 

using less accurate data cannot help provide a conclusive answer when the test using the more 

accurate data (the gross margin test) does not provide a conclusive answer. However, if not 

enough data is available for the BAT earnings test or the gross margin test, then the revenue test 

can be used.

Revenue Test

The EPA Guidance Manual suggests that if the earnings test cannot be performed because 

accurate cost data for the plant is not available, then the revenue test should be performed. This 

test has easy-to-meet data requirements.

The revenue test completely avoids the problem of collecting accurate cost data for the plant. It 

does not require any data on production or overhead costs. It only uses the plant’s revenue. The 

disadvantage of this is that the revenue test is a less accurate test of economic achievability than 

either the earnings test or the gross margin test.

The revenue test assumes that the firm’s EBT-to-revenue ratio is equal to its industry’s EBT-torevenue ratio. The test uses the firm’s revenue and the industry’s EBT-to-revenue ratio to 

estimate the firm’s EBT (multiply the firm’s revenue by the industry’s EBT/revenue to yield the 

estimate of the firm’s EBT). It then compares the cost of the BAT technology to the firm’s 

estimated EBT. So, the revenue test is an earnings test that uses estimated earnings rather than 

actual earnings.
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Table IV-5. The Revenue Test for BAT.

REVENUE TEST

TO PERFORM THE REVENUE TEST CALCULATE:

1. Ratio of the annual cost of the proposed BAT technology to the firm’s revenue.

2. Ratio of the industry's average EBT to the industry's average revenue.

The industry average EBT and revenue are obtained from Robert Morris 

Associates' Annual Statement Studies. They are available for 4-digit SIC 

codes.

• If the first ratio is less than the second ratio, then the proposed BAT 

treatment technology is economically achievable.

• If the first ratio is greater than the second ratio, then the proposed BAT 

treatment technology is not economically achievable.

• If the first ratio is equal (or approximately equal) to the second ratio, then 

the test is inconclusive. A plant closure analysis must be carried out.

NSPS ECONOMIC REASONABLENESS TEST

In setting New Source Performance Standards (NSPS), section 306(b)(1)(B) of the CWA 

requires that EPA "take into consideration the cost of achieving such effluent reduction." This 

language is identical to that which specifies how costs are to be considered in defining BAT.

In setting NSPS effluent limits for toxic and conventional pollutants discharged by chemical 

manufacturers, EPA used the BAT economic test. The U.S. Fifth Circuit Court of Appeals 

agreed with EPA that use of the BAT test in setting NSPS effluent limits was required by the 

CWA (page 262, Chemical Manufacturers Association vs. USEPA).
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Therefore, BAT economic achievability analysis is also applicable to NSPS.

The cost of installing a given level of treatment in a new plant (NSPS) should be less than the 

cost of installing it in an existing plant (BCT and BAT). Therefore, the economic reasonableness 

test for NSPS should be easier to pass than the test for BPT and BAT.

PRETREATMENT ECONOMIC REASONABLENESS TEST

In setting Pretreatment Standards for Existing Sources (PSES) and Pretreatment Standards for 

New Sources (PSNS), EPA stated:

"The legislative history of the 1977 Act (i.e., the CWA) indicates that 

pretreatment standards are to be technology-based and analogous to the best 

available technology for removal of toxic pollutants" (47 FR 23264).

That is, PSES and PSNS are analogous to BAT.

However, in setting PSES and PSNS effluent limits, EPA also considered:

The cost of application of technology in relation to the effluent reduction and other benefits 

achieved from such application (47 FR 23264).

This criterion is similar to that used in setting BPT effluent limits. It is a cost-benefit test.

The U.S. Fifth Circuit Court of Appeals wrote that the CWA requires that pretreatment standards 

be "based on BAT or more stringent criteria" (page 196, Chemical Manufacturers Association vs. 

USEPA). The court also wrote that the PSES pretreatment standards are:

..."technology-based and are analogous to the BAT effluent-limitation 

guidelines for the removal of toxic pollutants--that is, they are intended to 

represent the best available technology that is economically achievable by 

indirect dischargers" (page 244, Chemical Manufacturers Association vs. 

USEPA).

In addition, the court wrote that the PSES standards are equivalent to BAT standards and, 

therefore, are to be set in accordance with section 304(b)(2)(B) of the CWA, which lists the 

factors that must be considered in determining BAT (page 249, Chemical Manufacturers 

Association vs. USEPA).

Therefore, the BAT economic achievability test is applicable for pretreatment effluent limits.
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The cost of installing a given level of treatment in a new plant (PSNS) should be less than the 

cost of installing it in an existing plant (PSES). Therefore, the economic reasonableness test for 

PSNS should be easier to pass than the test for PSES.
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ECONOMIC REASONABLENESS TESTS FOR SEWAGE TREATMENT PLANTS 

REQUESTING MARINE WAIVERS 

In denying the municipal sewage treatment plants' (POTWs) applications for marine waivers 

discussed earlier, Ecology used the following criteria to determine "reasonable methods of 

treatment" for AKART for municipal POTWs' discharges to marine waters:

• Status of planning needed to proceed with the proposed method of treatment.

• Environmental or siting constraints.

• Economic factors.

The PCHB accepted Ecology's use of these 3 criteria to determine reasonableness. The PCHB 

also wrote:

"The economic aspect of the reasonableness criterion of the State Standard is, 

we conclude, defined by two propositions: (1) whether secondary treatment for 

the source would involve significantly greater costs than for others obliged to 

obtain the same levels of treatment, and (2) whether secondary treatment is 

within the economic ability of the source to meet the costs of treatment.

EPA's refusal to consider the second of these propositions in industrial variances was upheld in 

National Crushed Stone Association, supra. But, underlying this conclusion was the realization 

that a single plant unable to come up to industry-wide standards can simply cease operations. 

This is a luxury municipal sewage treatment facilities do not enjoy. The sewage must go 

someplace. Therefore, in interpreting the state law requirement for reasonableness as to 

municipalities, we think it is appropriate to include "ability to pay" factor. Cf. Weyerhaeuser v. 

Southwest Air Pollution Control Authority, 91 Wn.2nd 77, 586 P.2d 1163 (1978)."

Here the PCHB is defining a test for economic reasonableness.

The first proposition (1) applies to both industrial and municipal permit holders. A proposed 

treatment technology is economically reasonable if its cost is "similar" to the cost to other 

dischargers with the same level of treatment (the other dischargers may or may not be in the 

same industry). One measure of cost is cost per pound of pollutants removed. Another measure-

-which is applicable to STPs--is cost per user.

"Similar" is not precisely defined. It does not mean identical. Costs can be either above or 

below other dischargers' costs. If they are below, then they are definitely reasonable. And even 

if they are above other dischargers' costs they can still be reasonable as long as they are not too 

far above.
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The second of the PCHB's propositions (2) considers whether the cost of the treatment 

technology is within the permit holder's ability to pay. For an industrial discharger, the impact of 

the cost of the treatment technology on the discharger's profitability is examined. Impact on 

profitability may be considered in BAT analysis, but not in BCT or BPT analysis. The PCHB 

held that only the first proposition is relevant in determining economic reasonableness for 

industrial dischargers when the AKART level is the same as the BCT level. For municipalities, 

ability to pay is measured by the impact of the treatment technology's cost on user rates.

In setting AKART effluent limits, pollution reduction benefits (as measured by amounts of 

pollution reduction) are also to be considered. Greater amounts of pollution reduction make a 

given level of cost more reasonable.

Water Quality Financial Assistance

Ecology takes economic factors into account when dealing with municipal POTWs in the 

Centennial Clean Water Fund (CCWF) and the State Revolving Fund (SRF). Ecology's Water 

Quality Financial Assistance Program (WQFAP) administers both these funds.

The CCWF makes grants and loans to public bodies for water pollution control activities and 

facilities. Economic achievability or ability to pay is one of the determinants of the size of loan 

or grant that a municipality may receive.

Among the rating criteria for allocating CCWF grants and loans to marine dischargers (this 

includes POTWs, CSOs, and storm water dischargers) is the monthly residential user charge that 

would result from construction of the project without any state assistance (see Chapter IV of 

WQFAP's Centennial Clean Water Fund: Program Guidelines).

In addition, under the CCWF, public bodies may receive "supplemental financial hardship 

assistance" when project costs cause user charges to exceed 1.5% of the municipality's median 

household income. In some cases, other information--for example, unemployment rates--may be 

used to establish financial hardship. Chapter IV of the Centennial Clean Water Fund: Program 

Guidelines contains more detailed information on how economic factors determine loan and 

grant amounts.

The impact of project costs on rate payers is also a rating criterion for making loans from the 

State Revolving Fund. If project costs without financial assistance would cause a municipality's 

user charges to exceed 1.5% of its median household income, WQFAP will try to award 

sufficient funding to bring the user charge down to 1.5 %.

 
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EPA Affordability Guidelines. EPA's Construction Grants Program had several affordability 

guidelines for municipal sewer user charges. They ranged from 1.0% of median household 

income for low-income communities to 1.75% of median household income for high income 

communities. The guidelines were used to determine whether a project was a "high cost" 

project. The guidelines are the source of the 1.5% threshold used by WQFAP.
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Figure IV-5. Deriving BCT Limits for Conventional Pollutants.

CONTINUED FROM

FIGURE III-2

ARE CONVENTIONAL

POLLUTANTS PRESENT IN

THE EFFLUENT AT

TREATABLE

CONCENTRATIONS?

ARE BCT

GUIDELINES

AVAILABLE?

DOES BCT=BPT

FOR THIS

INDUSTRY TYPE?

DOES BCT=BAT

FOR THIS

INDUSTRY TYPE?

DEFINE THE LEVEL

OF BPT

TREATMENT FOR

THE FACILITY

ARE BCT

GUIDELINES

EQUIVALENT TO

AKART?

USE BCT

GUIDELINES

ARE BPT

GUIDELINES

EQUIVALENT TO

AKART?

USE BPT

GUIDELINES

ARE BAT

GUIDELINES

EQUIVALENT

TO AKART?

SELECT A CANDIDATE

BCT/AKART TREATMENT

SYSTEM

CONDUCT THE

BCT/AKART COST

TEST

IS THE COST OF THE

SELECTED BCT/AKART

SYSTEM REASONABLE?

IS BCT MORE

STRINGENT THAN

BPT?

SET BCT/AKART

LIMITS

USE BPT

GUIDELINES FOR

LIMITS

GO TO

FIGURE IV-6

USE BAT

GUIDELINES

NO

YES

YES

NO NO YES

YES

NO NO YES

YES

NO

NO YES

NO

YES

YES

NO
CHAPTER IV. DERIVING TECHNOLOGY-BASED EFFLUENT LIMITS (JULY 2011)

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Figure IV-6. Deriving BAT Limits for Toxic Pollutants.

CONTINUED

FROM FIGURE

IV-5

ARE THERE PRIORITY

POLLUTANTS IN THE

EFFLUENT?

DETERMINE

CONCENTRATIONS OF

PRIORITY POLLUTANTS IN

THE EFFLUENT

COMPARE WITH KNOWN

BAT LEVELS, AND

TREATABILITY MANUAL

DATA

SELECT POLLUTANTS TO BE

LIMITED

ARE BAT

GUIDELINES

AVAILABLE?

DO BAT

GUIDELINES

MEET AKART?

USE BAT

GUIDELINES

ARE THERE OTHER

TOXIC POLLUTANTS

PRESENT THAT NEED TO

BE LIMITED?

GO TO FIGURE

VI-4

IS BCT TREATMENT

SELECTED IN FIGURE IV-1

EQUIVALENT TO BAT FOR

TOXICS?

SELECT A CANDIDATE BAT

TREATMENT SYSTEM USING

BPJ

IS THE SELECTED BAT

SYSTEM ECONOMICALLY

ACHIEVABLE?

HAVE SEVERAL BAT

SYSTEMS BEEN

CONSIDERED?

CHOOSE THE MOST

PRACTICAL/ECONOMICAL

ALTERNATIVE WITH

ACCEPTABLE POLLUTANT

REMOVAL LEVELS

SELECT INDICATOR

PARAMETERS IF

APPROPRIATE

SELECT A NEW

CANDIDATE BAT

SYSTEM

GO TO IV-7

DEVELOP AKART

LIMITS

YES

NO

YES

NO NO

YES

YES

NO

NO

YES

YES

NO

YES

NO

DEVELOP

BPJ-BAT

LIMITS
CHAPTER IV. DERIVING TECHNOLOGY-BASED EFFLUENT LIMITS (JULY 2011)

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Figure IV-7. Deriving BAT Limits for Nonconventional Pollutants 

CONTINUED

FROM FIGURE

IV-6

ARE THERE

NONCONVENTIONAL

POLLUTANTS IN THE

EFFLUENT AT TREATABLE

CONCENTRATIONS?

SELECT POLLUTANTS TO BE

LIMITED

GO TO FIGURE VI-4

ARE BAT GUIDELINES

AVAILABLE FOR THE

NONCONVENTIONAL

POLLUTANTS?

USE BAT

GUIDELINES

ARE OTHER

NONCONVENTIONAL

POLLUTANTS PRESENT THAT

NEED TO BE LIMITED?

IS BCT SELECTED IN FIGURE

IV-2 EQUIVALENT TO BAT FOR

NONCONVENTIONALS?

SELECT A CANDIDATE BAT

TREATMENT SYSTEM USING

BPJ

IS THE SELECTED

BAT SYSTEM

ECONOMICALLY

ACHIEVABLE?

CHOOSE THE MOST

PRACTICAL/ECONOMICAL

ALTERNATIVE WITH

ACCEPTABLE POLLUTANT

REMOVAL LEVELS

SELECT

INDICATOR

PARAMETERS IF

APPROPRIATE

SELECT A NEW

CANDIDATE BAT

SYSTEM

YES NO

YES

NO

YES

GO TO FIGURE

VI-4

NO

HAVE SEVERAL

BAT SYSTEMS

BEEN

CONSIDERED?

YES

NO

NO

DEVELOP BPJ-BAT

LIMITS
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4. ADJUSTMENT OF EFFLUENT LIMITS FOR 

AUTOCORRELATION

This part discusses the process of adjustment to the monthly average effluent limit in cases 

where the effluent data is not independent. This part is based on two technical memoranda from 

Jeanette L. Kranacs, Mathematical Statistician, and Henry Kahn, Chief, Statistical Analysis 

Section of the Engineering and Analysis Division, U.S.E.P.A. (March 20, 1996, June 25, 1996). 

Background material is presented in Gilbert (1987) and Box and Jenkins (1976). The example in 

Appendix 4 is from a request to the Ecology Industrial Section.

Applicability - This adjustment is applicable only to water quality-based effluent limits and caseby-case technology-based effluent limits. It is not applicable to effluent limits derived from 

effluent guidelines. It is applicable only to the average monthly limitation.

Process - The permit writer may evaluate effluent data for autocorrelation in the course of 

developing effluent limits or a permittee may request an adjustment of an effluent limitation. 

The PDS Section will provide assistance in evaluating autocorrelation.

Background

The Technical Support Document for Water Quality-based Toxics Control (EPA 505/2-90-001, 

Appendix E) discusses the problem of correlated effluent data when deriving effluent limits and 

presents techniques for adjusting monthly average effluent limitations based upon an analysis of 

autocorrelation.

What is autocorrelation and why does it result in an increase in effluent limits 

When calculating statistics such as mean and variance from a data set there is a presumption of 

normal distribution and independence. If the data are not normally distributed they can be 

transformed to approximate a normal distribution so that statistics may be derived using 

techniques based on normal theory. If the data are not independent (i.e., each value is correlated 

to the value preceding and following) then the calculated mean will be lower than the true mean 

of the sample distribution. In wastewater treatment processes with hydraulic detention times of 

several days, the daily sample values are usually correlated. If sample values are correlated then 

a correction process must be used to derive the correct mean. Monthly average effluent limits 

developed on a case-by-case basis (water quality or technology based) are dependent on the 

mean so that an adjustment to the mean results in a different monthly average effluent limitation. 

Correction for autocorrelation results in a smaller effective sample size, a numerically higher 

mean and corresponding higher monthly effluent limitation.

When EPA develops effluent guidelines they conduct an analysis for autocorrelation and adjust 
CHAPTER IV. DERIVING TECHNOLOGY-BASED EFFLUENT LIMITS (JULY 2011)

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the effluent limitations accordingly.

Accurate Estimates of Autocorrelation

If x1. x2, ....., xn denotes a series of equally spaced measurements, Box and Jenkins (1976) 

indicate that the most satisfactory method of estimating the lth lag autocorrelation, ρl is

( )( )

∑( − )

∑ − −

=

=

+

−

=

n

t

t

t

n l

t

t

l

x x

x x x x

1

2

1

1 ρ

In practice, at least n=50 measurements are needed to obtain accurate estimates of the ρl for lags 

l = 1, 2, ...., K, where K should not exceed n/4 (Gilbert 1987). Therefore, a 30 day lag requires a 

data base (n) of 30 x 4 = 120. Because it’s difficult to predict what the maximum lag will be 

before data collection and because a 30 day autocorrelation may be allowed, the permit writer 

should specify a data requirement of 120 data points collected over a year. These should be 

collected as daily samples for a month and the 4 months should be seasonally representative. 

This will allow for an analysis of seasonally effected autocorrelation.

Most of the time we would expect significant autocorrelation to occur in biological treatment 

plants rather than physical/chemical treatment because of the longer hydraulic residence time. 

The significant autocorrelation should be within the range of one to three times the hydraulic 

residence time. Autocorrelation that occurs at lag periods longer than three times the hydraulic 

residence time should be suspect and may simply be a characteristic of the data set. Gilbert 

(1987) cautions that the analysis for autocorrelation assumes that the underlying process being 

measured does not cycle, does not have long-term trends, does not make sudden jumps in 

magnitude or change its autocorrelation coefficient over time. If the significant autocorrelation 

factors are not continuous (i.e., one day, two days, three days, and up to the maximum significant 

lag) the facility must provide some engineering explanation of why the autocorrelation is 

discontinuous, otherwise Ecology will not approve it. Discontinuous autocorrelation lags 

indicates some periodicity (cycling) that is process related.

Monitoring Frequency

The collection of data to assess autocorrelation and the autocorrelation coefficient allows the 

permit writer to derive a monitoring frequency which is characteristic of the discharge. The 

procedure is illustrated in the example in Appendix 4. The number of measurements, n, required 

to estimate the mean μ by the sample mean X with the prescribed accuracy, d, and 100(1-α)% 
CHAPTER IV. DERIVING TECHNOLOGY-BASED EFFLUENT LIMITS (JULY 2011)

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confidence is





 



 = + ∑

−

=

1

1

1 2

n

l

D l n ρ

where ρl includes only the significant autocorrelations

and 

2

2

1





















= −

d

z

D

ασ

with σ

2 estimated by

( )

2

1

2

1

1 ∑=

− − =

n

i

i x x

n

s and 



 



 = − 



 



 − 2

1

2

1

α α z percentile of the standard normal distribution.
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CHAPTER V. MUNICIPAL EFFLUENT 

LIMITATIONS AND OTHER REQUIREMENTS

1. INTRODUCTION

The largest category of discharger which has technology-based effluent limits is the municipal 

treatment plants. This chapter discusses the technology-based effluent limits for municipal 

plants and some other requirements for municipalities such as biosolids, and CSO control.

The Department of Ecology has quantitative discharge standards for domestic wastewater 

facilities (i.e., municipal sewage treatment plants) which discharge to surface waters. The 

standards are codified in chapter 173-221 WAC. Prior to this rule, Washington state generally 

used federal standards as published first on August 17, 1973 [38 FR 22298] and codified in 40 

CFR Part 133. The regulation was extensively revised in 1984, and amended again in 1985 and 

1989. See Table V-l for a history of the federal rule.

In 1984, when the federal government amended its secondary treatment requirements, individual 

states had the option of applying those regulations or establishing more stringent requirements. 

Ecology decided to establish an ad hoc committee to study the options and make 

recommendations.

After hearing committee recommendations, Ecology adopted a state regulation defining 

secondary treatment requirements.

This section explains how to determine technology-based permit limits for conventional 

pollutants (BOD5, TSS, pH, fecal coliform) discharged by domestic wastewater treatment 

facilities. When reviewing a permit application or renewal, the permit writer must first 

determine the proper technology-based limits. Then the writer must decide if these limits are 

stringent enough to ensure that water quality standards are not violated in the receiving water. If 

they are not, then water quality-based limits must be developed. Guidance for making that 

decision is provided in chapter VI.

Domestic Wastewater treatment facilities are also subject to other permitting requirements such 

as whole effluent toxicity testing and monitoring of receiving water and sediments. Please refer 

to other chapters for these topics.
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Table V-1. SECONDARY TREATMENT REGULATION - 40 CFR 133 

Date

(Federal Register)

Applicability Action Parameter Limit Citation

August 17, 1973

(38 FR 22298)

All secondary facilities initial definition BOD5 30 mg/L, 30-day avg

45 mg/L, 7-day avg

85% removal, 30 day avg

133.102(a)

SS 30 mg/L, 30-day avg,

45 mg/L, 7-day avg

85% removal, 7-day avg

133.102(b)

FC 200/100 ML, 30-day avg

400/100 ML, 7-day avg

133.102(c)

pH 6.0 to 9.0 133.102(d)

Secondary facilities with 

combined sewers, during 

wet weather

revise limits BOD5

SS

% removal discretionary

% removal discretionary

133.103(a)

133.103(a)

Secondary facilities with 

industrial wastes

revise limits BOD5 Proportional adjustment of 30-day and 7-

day concentration and load limits, but 

not % removal

133.103(b)

SS Proportional adjustment of 30-day and 7-

day concentration and load limits, but 

not % removal

133.103(b)

July 26, 1976

(41 FR 30788)

All secondary facilities delete FC --

revise definition pH --

October 7, 1977

(42 FR 54665)

WSP less than 2 mgd revise limit SS State-determined,

EPA-adopted

133.103(c)

September 20, 1984

(49 FR 36986)

TF, WSP revise limits BOD5 45 mg/L, 30-day avg

65 mg/L, 7-day avg

133.105(a)(1)&(2)

SS 45/mg/L, 30-day avg

65 mg/L, 7-day avg

133.105(b)(1)&(2)

September 20, 1984

(49 FR 36986)

allow ASR's BOD5 State-determined

EPA-approved

133.105(d)

SS State-determined

EPA-approved

133.105(d)

All WSP remove 2 mgd cap SS State-determined,

EPA-adopted

133.103(c)

All secondary facilities allow use of 

CBOD5 for BOD5

CBOD5 25 mg/L, 30-day avg

40 mg/L, 7-day avg

85% removal, 30-day avg

133.102(a)(4)

June 3, 1985

(50 FR 23382)

TF, WSP revise limits BOD5

SS

65% removal, 30-day avg

65% removal, 30-day avg

133.105(a)(3)

133.105(b)(3)

Secondary facilities with 

separate sewers, less 

concentrated influent 

during wet or dry weather

revise limits BOD5

SS

% removal discretionary

% removal discretionary

133.103(d)

133.103(d)

January 27, 1989

54 FR 4224)

Secondary facilities with 

combined sewers, less 

concentrated influent 

during dry weather

revise limits BOD5

SS

% removal discretionary

% removal discretionary

133.103(e)

133.103(e)

Before writing domestic wastewater permits, a permit writer should be familiar with WAC 173-

221 Sections 10-50.
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2. TECHNOLOGY-BASED WASTEWATER 

DISCHARGE STANDARDS

TASK OUTLINE FOR STANDARD TECHNOLOGY-BASED PERMIT LIMITS

(Following the rules in WAC 173-221-040.)

1. Unless a facility qualifies for an alternative discharge standard or effluent limitation, 

listed in Section 050, its discharge must meet the following standards.

 

 7- and 30-day

Pollutant 30-day Average 7-day Average Average

Parameter Concentration Concentration Daily Load Limits

Biological Oxygen

Demand (BOD5) 30 mg/L 45 mg/L NA* lbs/day

(see Step 3)

Total Suspended

Solids (TSS) 30 mg/L 45 mg/L NA lbs/day

(see Step 3)

Fecal Coliform

(geometric means) 200 organisms/ 400 organisms/ NA NA

 100 mL 100 mL

pH 6-9 standard NA

 units * Not applicable.

2. In addition, the 30-day average percent removal for BOD5 and TSS shall not be less than 

85%.

3. Determine the maximum allowable 30-day (monthly) average pounds per day of BOD5 and 

TSS as follows: 

Influent:

Refer to the Ecology approved plans and specifications. They should include a table which 

specifies the design, maximum month influent BOD5 and TSS loadings. Include those in the 

permit. If no record exists, consider requiring an engineering report to determine the design 

capacity of the plant. Alternatively, use the historical capacity listed in previous permits or set a 

capacity based on the historical discharge monitoring reports (DMRs).

Task outline (continued)
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• Effluent:

Specify the lower number obtained by one of these two methods:

a) Multiply 30 mg/L by 8.34 and by the design flow as expressed in million gallons per day 

(mgd) for the maximum flow month in the design year. The result is in lbs./day.

 

b) Multiply the Ecology approved, design maximum month influent loading (lbs/day) 

by .15 (fifteen/hundredths).

Method (b) results in a lower number when, for example, the influent BOD5 is below 200 

mg/L or CBOD5 is used in place of BOD5.

Permit writers may apply the less stringent method if the following factors apply:

• The facility designed its treatment facility based on weak influent strength (<200 mg/L 

TSS or BOD as noted in the engineering report).

• The actual influent concentrations are higher than the influent concentrations assumed in 

the design report (i.e., infiltration and inflow is not excessive).

• The facility consistently treats and achieves greater that 85% removal.

The permit writer must explain, in the fact sheet, the reason for the use of the less stringent 

method.

Refer to the most recent engineering report and plans and specifications which Ecology has 

approved for the maximum month design flow and loading. For permit compliance, remember 

that the permittee must still achieve 85% removal of every monthly average influent 

concentration and every monthly influent mass loading. Therefore a permittee may discharge 

less than the maximum allowable 30-day average lbs/day and still violate its permit.

4. Determine the 7-day (weekly) average load limits by multiplying the 30-day limits by 1.5. 

The result is expressed in lbs/day.

5. Finally, Permittees can qualify for pH effluent limits outside the allowable range of 6-9, if 

they can meet all 3 conditions listed in Subsection 040(3).

6. Determine whether the technology-based limits derived above (including pH) will cause 

water quality standards violations in the receiving water (Chapter VI).

Note: Federal and state regulations refer to 30-day and 7-day average limits, not monthly and 

weekly average limits. For ease of permit writing and compliance monitoring, permits are 

typically written in terms of monthly and weekly averages.
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3. ALTERNATIVE WASTEWATER DISCHARGE 

STANDARDS

The secondary treatment regulation (WAC 173-221-050) allows alternative effluent limitations 

in 5 cases: 

• Trickling filters

• Waste stabilization ponds

• Facilities with combined sewers

• Weak influent sewage

• CBOD5 in lieu of BOD5

The state rule also includes alternative discharge standards for the above, but adds additional 

restrictions in each case. The next page describes conditions a municipality must meet to qualify 

for any alternative limit. Following that are background and explanations for each alternative 

discharge standard and a task outline for determining the appropriate alternative effluent 

limitation. The permit writer should be familiar with the background section before using the 

corresponding task outline.

3.1 Conditions for Receiving Alternative Effluent Limitations

3.1.1 Discussion of Section 050(5)

In order to qualify for any of the alternative effluent limitations of WAC 173-221-050(1-4), a 

municipality must prove compliance with the 6 conditions in 050(5). Therefore, those 

conditions, a, b, and d are explicitly required by federal regulation. Condition a requires that the 

alternative limit not cause a water quality violation. For condition b, note that the phrase 

"effluent concentrations consistently achievable through proper operation and maintenance" is 

defined in Section 030 (Definition #11). For condition d, check the design criteria sheet of the 

facility's plans and specifications.

Ecology has added condition c to the list. This prevents issuing alternative limits to a facility 

which cannot achieve 30/30 mg/L BOD5/TSS because of interference by industrial wastewater. 

USEPA did not intend alternative limits for such cases. The federal industrial pretreatment 

regulation, 40 CFR Part 403, allows states to require a pretreatment program for any size facility 

if industrial wastewater interferes with attaining permit effluent limitations.

Condition e requires the permittee to analyze whether alternative limits should be seasonal rather 
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than year-round. Here are two examples.

• Facilities may have less concentrated influent wastewater only during certain winter 

months. Any reduced percent removal limit should be applied only to those months.

• Some ponds may have difficulty meeting the 30 mg/L BOD5 limit during certain 

months (e.g., winter time when biological activity is slow). If a review of the historical 

record shows a consistent pattern, consider alternative limits just for those months.

Finally, condition f requires a municipality to meet all other permit requirements and conditions.

3.2 Trickling Filters

3.2.1 Discussion of Section 050(1)

The trickling filters which were constructed and/or expanded prior to November 1984 can 

qualify for alternative effluent limitations. In this case, the effluent limitations for BOD and TSS 

are set on a case-by-case basis, according to past performance. However, effluent limitations 

must not exceed 45 mg/L BOD5 and 45 mg/L TSS on a 30-day average.

Rule 050(1) is more restrictive than the federal rule in two ways.

First, it applies only to trickling filters which meet definition #23 in Section 030. The definition 

excludes trickling filters which have a supplemental biological treatment system, other than 

waste stabilization ponds, for the principal wastewater stream.

In recent years, engineers have developed various ways of combining trickling filters with 

suspended growth; i.e., activated sludge systems. These systems have proven to be cost effective 

and reliable. When designed properly, they are capable of achieving 30/30 mg/L BOD5/TSS 

effluent and better. Ecology requires that such systems achieve those limits. Note that trickling 

filter/waste stabilization pond combinations (built before November 1984) can qualify for 

alternative effluent limitations allowed under Section 030. Any trickling filter may still qualify 

for alternative limits as allowed under Section 050(3), (4), and (6). These systems will still have 

periodic problems with algae in the effluent. The algae are reported as suspended solids.

Secondly, the rule does not allow alternative limits for trickling filters constructed and/or 

expanded after November 1984. That is the effective date of the 1984 federal secondary 

treatment rule revisions. Recent advances in trickling filter design and technology have made 

these systems more efficient pollutant removers. Synthetic media, and proper hydraulic and 

organic loading designs are examples of these advances. New trickling filters are capable of 

achieving 30/30 mg/L BOD5/TSS and thus should not be eligible for alternative discharge 

standards. This position is consistent with the USEPA Science Advisory Board.
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The November 1984 cutoff date is appropriate because it coincided with the effective date of 

USEPA's regulations. When Ecology was proposing its secondary treatment rule, no 

municipalities in the state had expanded or constructed trickling filters since November 1984.

Most of the existing trickling filters in the state were built between 1930 and 1960. Some of 

these qualify for alternative effluent limitations because they are not consistently achieving 30/30 

mg/L BOD5/TSS and 85% removal. However, most are achieving those limits the majority of 

the time and Ecology expects them to continue to do so. When these facilities need replacing 

because of population growth or age, the new systems should meet the 30/30 and 85% standards. 

The permit writer must use judgment when deciding whether a rehabilitation project at such a 

facility is sufficiently extensive that 30/30 and 85% should apply.

One reason for requiring new trickling filters to achieve 30/30 is the recent concern about 

toxicants in effluents. In general, the amount of toxicant removal by a conventional secondary 

treatment plant is proportional to its removal of conventional (BOD, TSS) pollutants. Trickling 

filters designed for 30/30 will be better suited to deal with toxicity-based limits.

3.2.2 TASK OUTLINE FOR DETERMINING TRICKLING FILTER 

BOD5/TSS EFFLUENT LIMITS

1. Does the facility meet definition #23 of Section 030?

Yes - Go to 2

No - Use Section 040. Sections 050(3), 050(4), and (6) may also apply if requested by the 

applicant.

2. Was the facility constructed or did it have its most recent significant rehabilitation before 

November 1984?

Yes - Go to 3.

No - Use Section 040. Sections 050(3), (4), and (6) may also apply if requested by the 

applicant.

3. Determine BOD5 and TSS "effluent concentrations consistently achievable.." per definition 

#11 of Section 030, then find the percent removal value.

Procedure:

Examine at least the last few years of discharge monitoring reports for average monthly effluent 

concentrations and percent removals. Do not use effluent data for months during which the 

facility had equipment failure, operator error, overloading, or other extenuating circumstances. 

Review the permit file for any information which may indicate that certain data are inaccurate. 

Do not use those data. Class I and II inspection reports, Roving Operator Trainer reports, and 

memos of conversations are examples of information sources.
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Determine the effluent concentration and percent removal that have been achieved 95% of the 

time. The following table indicates which data points represent the 95th percentile values.

Number of Acceptable 95th Percentile Values

Monthly Average Values Percent Removal Concentration

24-35 2nd lowest value 2nd highest value

36-59 3rd lowest value 3rd highest value

above 60 4th lowest value 4th highest value

4a. Is the 95th percentile value for TSS or BOD5 less than 45 mg/L?

Yes - Propose the 95th percentile value as the monthly effluent limit. Proceed to 4b.

No - Propose 45 mg/L as the limit. Proceed to 4b.

4b. Is the 95th percentile value for percent removal greater than 65%?

Yes - Use the percent removal value as the monthly effluent limit. Proceed to 5.

No - Use 65% as the monthly effluent limit. Proceed to 5.

Note: You can have different percent removal limits for BOD5 and TSS.

5. Does the facility meet all 6 requirements of Section 050(5)? (See above.)

Task outline (continued)

Yes - Use the limits obtained in 4. Proceed to 6.

No - Use Section 040 or Section 050(6)(a).

6. Determine maximum monthly average weight per day of BOD5 and TSS effluent loading by:

a) Multiplying the facility's approved design year maximum month flow as expressed in 

million gallons per day by the concentrations determined in 4, and by 8.34; or,

b) Multiplying the Ecology approved, design maximum month influent loading by the 

quantity (1 minus the % removal limit (from 4b and expressed as a decimal)). The result 

is expressed in lbs/day. Use the lower number (6a or 6b) as the effluent limit. Proceed
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to 7.

7. Determine the effluent weekly average concentration and loading limits by multiplying the 

monthly values by 1.5. However, the maximum acceptable weekly concentration limits are 

65/65 mg/L BOD5/TSS.

8. Determine whether the technology-based limits derived above will cause water quality 

standard violations in the receiving water. If they will, see Chapter VI on water quality-based 

effluent limits.

3.3 Waste Stabilization Ponds

3.3.1 Discussion of Section 050(2)

Waste stabilization ponds which have design capacity below 2 million gallons per day (mgd) or 

have received the Department of Ecology's approval for a greater design capacity, prior to the 

effective date of the regulation (11/12/87), can qualify for alternative limits. Permit writers 

should determine effluent limitations for individual waste stabilization ponds on a case-by-case 

basis according to past performance. However, effluent limitations shall not be set higher than 

45 mg/L BOD5 and 75 mg/L TSS on a 30-day average, and 65 mg/L BOD5 and 112 mg/L TSS 

on a 7-day average.

The USEPA secondary treatment regulation applies to all ponds. It does not include design 

capacity restrictions. Ecology added 4 conditions: 

a. In 1977, USEPA published a regulation (see Table V-1) which allowed ponds under 2 

million gallons per day (mgd) capacity to exceed the 30 mg/L TSS requirement. By that 

regulation, USEPA established the TSS requirement for such ponds on a state-by-state basis. 

For each state, USEPA made the TSS limit a concentration which 90% of the ponds in that 

state were achieving. In 1977, a survey of lagoon effluent quality set that concentration limit 

at 75 mg/L.

USEPA figured that ponds under 2 mgd probably served towns of under 10,000 population. 

Such towns, they reasoned, should not be required to operate and maintain a treatment 

system more complex than a simple pond system. However, those ponds could not always 

achieve 30 mg/L TSS. Rather than requiring each small town which had a pond treatment 

system to change to a different system, EPA allowed higher TSS limits for ponds.

Ecology agrees with this approach, and will continue to allow small municipalities the option 

of constructing and keeping ponds as their treatment system. Forcing these communities to 

more complex systems would be counterproductive. Such systems would require more 

intensive operation and maintenance (highly qualified operators working longer hours). In 

the short run, lack of qualified operators and funds would result in poor operation, 
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maintenance, and poor effluent quality. Ultimately it would mean a financial burden which 

USEPA and Ecology contend is not necessary or reasonable.

b. USEPA used similar arguments for justifying alternative BOD5 limits for ponds. Ecology 

concurs, and will continue to require engineers to design ponds using state of the art 

techniques to achieve 30 mg/L BOD5. However, if despite proper design a pond under 2 

mgd design capacity does not achieve 30 mg/L BOD5, the permit writer can change the 

effluent limits for that facility. The permit writer should require the facility to achieve that 

which it has proven it can achieve. No permit should have an average monthly discharge 

effluent limit above 45 mg/l BOD5.

c. USEPA now allows these higher effluent limits for all ponds regardless of size. They have 

done so because the Clean Water Act legislative history does not necessarily indicate that 

Congress intended to limit alternative standards to small communities.

Ecology is not constrained by the federal congressional record. Municipalities over 10,000 

population should have the ability and the financial wherewithal to construct and operate a 

facility which can achieve 30/30 mg/L BOD5/TSS. Therefore, any new ponds with design 

capacity equal to or greater than 2 mgd must meet those limits.

In addition, if a municipality with a pond system expands such that it exceeds the 2 mgd 

ceiling, it must treat that portion of the flow over 2 mgd to the 30/30 mg/L BOD5/TSS 

standard. However, if a municipality expands its total treatment capacity above 2 mgd by 

replacing the old pond system with a new pond system, it must treat all of the flow to the 

30/30 mg/L BOD5/TSS. These various permitting situations are described in steps 1 to 9 of 

the next section (3.3.2, Task outline for determining waste stabilization ponds BOD5/TSS 

effluent limits).

d. Municipalities which have Ecology-approved pond systems of greater than 2 mgd design 

capacity can also qualify for alternative effluent limitations. Again, Ecology wants to allow 

those municipalities which have invested in a pond treatment system to continue to use that 

investment. However, the provisions of state law which require all known available and 

reasonable technology (AKART) dictate that more complex treatment systems capable of 

achieving 30/30 mg/L BOD5/TSS are reasonable for larger municipalities. Therefore, any 

flows exceeding the pond system design capacity approved prior to December 12, 1987, must 

be treated to meet the 30/30 mg/L BOD5/TSS standard.
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3.3.2 TASK OUTLINE FOR DETERMINING WASTE STABILIZATION 

PONDS' BOD5/TSS EFFLUENT LIMITS

Permitting Situation Start at this Step

New Pond under 2 mgd, Step 1

Existing Pond under 2 mgd,

renewal application for same capacity Step 3

renewal application for greater capacity < 2 mgd Step 1

renewal application for greater capacity > 2 mgd Step 8

Pond > 2 mgd, capacity approval by Ecology after 12/87 Step 2

Existing Pond > 2 mgd, renewal application for capacity > 2 mgd Step 9

1. The first 5-year permit limits shall be 30 mg/L BOD5 and the TSS concentration which 

Ecology is using to satisfy definition #25. Until notified otherwise, use 75 mg/L TSS for the 

30-day average, and 112 mg/L TSS for the 7-day average. The applicant should submit a 

design based on achieving 30 mg/L BOD5 and minimizing TSS. The design review should 

use the Criteria for Sewage Works Design and nationally recognized design manuals as 

standards for proper design.

Percent removal limits for BOD5 or CBOD5 shall be 85% unless Section 050(3) and/or (4) 

apply. No percent removal applies to TSS.

2. Use Section 040 for this and all renewal permits. Section 050(3), (4), and (6) may also apply 

if requested by the applicant.

3. Determine BOD5 and TSS "effluent concentrations consistently achievable..." per definition 

#11 of Section 030.

Procedure:

Examine at least the last 2 years of discharge monitoring reports for average monthly effluent 

and percent removals. Do not use effluent data for months during which the facility had 

equipment failure, operator error, overloading, or other extenuating circumstances. Review the 

permit file for any information which may indicate that certain data are inaccurate. Do not use 

those data. Examples of information sources are Class I and II inspection reports, Roving 

Operator Trainer reports, and memos of conversations.

Determine the effluent concentration and percent removal that have been achieved 95% of the 

time. The table below indicates which data points represent the 95th percentile values.
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Task outline (continued)

Number of Acceptable 95th Percentile Values 

Monthly Average Values Percent Removal Concentration

24-35 2nd lowest value 2nd highest value

36-59 3rd lowest value 3rd highest value

above 60 4th lowest value 4th highest value

Alternatively, place the values in Excel and use the Data Analysis to calculate the 95th percentile.

4a. Is the BOD5 value less than 45 mg/L? 

Yes - Propose that value as the monthly effluent limit and proceed to 4b.

No - Propose 45 mg/L as the limit and proceed to step 4b.

4b. Is the TSS value less than 75 mg/L?

Yes - Propose it as the monthly effluent limit and proceed to 4c.

No - Propose 75 mg/L as the limit and proceed to step 4(c).

4c. Is the percent BOD5 removal determined in 5, greater than 65%?

Yes - Propose it as the monthly limit.

No - Propose 65%.

5. Does the facility meet all 6 requirements of Section 050(5)? (See review of that section.)

Yes - Use the limits obtained above in 4. Proceed to 6.

No - Use Section 040, or Section 050(6)(a) if requested by applicant.

Note: One of the conditions of Section 050(5) is the identification of effluent concentrations 

consistently achievable through proper operation and maintenance. The permit writer should 

have already checked the permit file, as explained in Step 3 above, for indications of inaccurate 

data. The permit writer should also check whether the facility is being operated in accordance 

with the Operation and Maintenance Manual.
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Task outline (continued)

For pond systems, the writer should particularly note whether the manual includes any 

recommendation for frequency of sludge removal from the ponds, or whether it indicates an 

acceptable sludge depth. Prior to considering any alternative limits, the permit writer should 

require the applicant to verify the extent of sludge accumulation. Significant accumulations can 

be the reason for declining performance.

If the Operation and Maintenance Manual is silent on sludge accumulation and dredging, the 

permit writer will have to use judgment in deciding when dredging of the pond is necessary. If 

the existing pond system has extensive accumulations in one or more ponds which are likely 

affecting the quality of the effluent, require dredging as soon as possible. Review the long term 

effluent quality records to note if a gradual decrease (corresponding to the sludge accumulation) 

in treatment efficiency has occurred. If so, give the pond system higher effluent limits (based on 

the last few years of data) for the time period up to the dredging, and lower limits (based on pond 

performance years when sludge accumulations were low) for the remaining time of the 5-year 

permit. Permit limits at the next renewal should be based on pond performance after the 

dredging.

Finally, the permit writer should include periodic sludge depth monitoring in the pond system as 

a condition of the permit. Such a condition is included in the recommended monitoring schedule 

for lagoons.

6. Determine maximum monthly average (lbs/day) of BOD5 and TSS effluent loading limits by: 

(a) Multiplying the facility's approved design year maximum month flow (as expressed in 

million gallons per day) by the concentrations determined in 4 above, and by 8.34; or,

(b) for BOD5 only, multiplying the Ecology approved, design maximum month influent 

loading by the quantity (1 minus the % removal limit [expressed as a decimal] determined 

in 4(c) above). The result is expressed in lbs./day. For BOD5, use the lower number 

obtained by method a or b.

7. Determine the weekly average concentration and loading limits by multiplying the monthly 

values by 1.5. However, the weekly average BOD5 concentration limits should not exceed 

65 mg/L; and the weekly average TSS concentration limits should not exceed 112 mg/L.

8. Case I: If all the flow is treated by the ponds, use Section 040. Sections 050(3), (4), and (6) 

may also apply, if requested by the applicant.

Case II: The applicant plans to use its existing ponds for its previously approved flow capacity. 

In this case, follow the instructions in Steps 3 through 7 to determine the permit limits. The
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Task outline (continued)

remaining flow must be treated in a separate facility which meets the requirements of Section 

040. Section 050(3), (4), and (6) may also apply if requested by the applicant.

Case III: The applicant plans to expand the existing pond capacity up to 2 mgd and take higher 

flows to a separate facility. Design the pond for 30 mg/L BOD5. The first 5-year permit limits 

should be a 30-day average of 30 mg/L BOD5, 75 mg/L TSS; and a 7-day average of 45 mg/L 

BOD5, 112 mg/L TSS for the pond. The separate facility shall have permit limits required under 

Section 040. Section 050(3), (4), or (6) may also apply if requested by the applicant. The pond 

may qualify for alternative effluent limitations in subsequent permits.

9. This step applies only to the following pond systems:

Everett

Longview

Montesano

Marysville

The applicant has the option of proposing a system(s) which meets limits under Case A or Case 

B.

Case A: If the proposal is to use the existing ponds within the previously approved design 

capacity, use the procedure outlined in Steps 3 through 7 above. Any additional flow over the 

previously approved capacity must be treated in a separate facility whose effluent limits shall be 

based upon Section 040. Section 050(3), (4), and (6) may also apply if requested by the 

applicant.

Case B: If the proposal is to expand the design capacity of the pond system, use Section 040. 

Section 050(3), (4), and (6) may also apply if requested by the applicant.

10. Determine whether the technology-based limits derived above will cause water quality 

standard violations in the receiving water. If they will, see Chapter VI on water qualitybased effluent limits.

3.4 Facilities with Combined Sewers

3.4.1 Discussion of Section 050(3)

Facilities which receive flow from combined sewers during wet weather can qualify for 

alternative monthly percent removal limits. During such wet weather conditions, the facility 

may be excused from achieving any predetermined percent removal requirement or may have a 

percent removal limit which is lower than otherwise allowed.
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During rainfall events, sewage treatment facilities which serve combined sewers can receive 

widely fluctuating influent flow rates and influent pollutant concentrations. These fluctuations 

are due to the intrusion of storm water to the sewer system. In some situations the influent 

concentrations are so dilute that achieving 85% or any other predetermined percent removal per 

Section 050(1) or (2) is not possible. The fluctuations can also cause inaccurate computation of 

the 85% removal requirement. In many cases, the wide fluctuations prevent the establishment of 

a minimum (below 85%) percent removal requirement which the treatment system would be 

expected to achieve regardless of any flow situation.

This section of the regulation differs from USEPA's rule because we define "wet weather" (See 

definition #30 in WAC 173-221-030). We want the option to restrict application of this waiver 

to the time period immediately surrounding rainfall events.

In all cases first verify whether the applicant has a significant combined sewer area in its 

collection system. Refer to the definition of combined sewers (#5). Verify that the sewers were 

originally designed to serve a storm water and sanitary sewage function; and that the combined 

sewer area is allowed by local ordinance. The following is an inclusive list of those which to 

have combined sewer systems as of December 1988. Please contact the Program Development 

Services Section if any municipalities request to be added to this list.

Seattle Port Angeles

METRO Mt. Vernon

Everett Bremerton

Spokane Olympia

Bellingham Anacortes

Snohomish

Note that municipalities should not build, nor should Ecology approve, any new combined 

sewers. All new construction must have separate sanitary and storm sewers. New building 

construction in a combined sewer area can place storm water into the combined system. 

However, all municipalities with combined sewers must comply with Chapter 173-245 WAC for 

reducing combined sewer overflows. Any new storm drainage from new construction must not 

delay achievement of compliance with Chapter 173-245 WAC. The municipality should have an 

Ecology approved CSO plan with a schedule for CSO control compliance.

For communities with secondary treatment, review the DMRs to see if a minimum percent 

removal requirement for wet weather months is identifiable. For municipalities still at primary 

treatment, consider no percent removal requirement for the traditional wet weather months until 

secondary treatment is on line for at least a couple years. This should give sufficient data to 

identify plant capabilities.
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A municipality may choose to comply with Chapter 173-245 WAC regarding CSO control by 

transporting and treating high wet weather flows at the central domestic wastewater treatment 

plant. For these situations in particular, the permit writer can grant relief from the monthly 

percent removal requirement. However, federal rules do not allow relief from the monthly and 

weekly concentration limits. If any municipality wishes to control their CSOs in this way, but is 

concerned about meeting their monthly concentration limits, please consult the Program 

Development Services Section about making inquiries to USEPA.

3.4.2 CSO Treatment Facilities (173-245-090) (1) (a) (ii))

If the municipality has chosen at-site treatment facilities (e.g., primary treatment and 

disinfection) for CSO control, the permit writer can choose to permit the facility under the same 

permit as that for the secondary treatment plant, or write a separate permit. In either case, the 

permit should include numerical limits for the discharge, flow capacity limits for the facility, and 

reporting requirements.

The numerical limits must at a minimum address the definition of "primary treatment” given in 

WAC 173-245-020; i.e., settleable solids not exceeding 0.3 ml/l/hr and not less than 50% 

removal of total suspended solids. The permit writer has some discretion in how to write the 

numerical permit limits. They can apply and be enforced on a yearly, monthly, or per event 

basis. That which is reasonable to achieve should be required. Refer to Chapter XII-2.4 for 

monitoring guidance.

The permit should also note that "the total treated and untreated annual discharge from an at-site 

treatment plant shall not increase above the baseline annual" level (WAC 173-245-090)(1)(a)(ii).

3.4.3 TASK OUTLINE FOR DETERMINING PERCENT REMOVAL 

LIMITS FOR COMBINED SEWER SYSTEMS

1. The applicant may request the alternative limit and submit supporting documentation for 

that request. The permit writer is not obliged to initiate any adjustment without a request.

2. Determine whether the applicant meets the requirements of Section 050(5) (discussed 

earlier in this chapter).

Yes - Proceed to 3.

No - Use Section 040, or Section 050(6)(a) if requested by the applicant.

3. Determine whether the facility is capable of 85% removal on a monthly basis in spite of 

the combined sewage flow.

Yes - Use 85%. Go to 6.
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No - Go to 4.

4. If 85% removal is not reasonable, determine whether a lower percent removal is 

consistently achievable.

Yes - Use the lower, consistent percent removal as the limit. Go to 5.

No - Delete the percent removal requirement during wet weather conditions. Go to 5.

5. Include a condition which lists the specific months for which a lower or no percent 

removal limit applies. For example, delete the requirement for November through April, 

the rainiest months.

Word the condition such that the percent removal requirement does apply for any 

month which does not receive significant rainfall or snow melt, (e.g., a dry December).

Also state that this condition does not relieve the permittee from operating the treatment 

facility as efficiently as possible. Cross reference the standard condition that requires 

this.

6. Determine whether the percent removal limit determined above will be sufficient to 

prevent water quality standard violations in the receiving water. If not, determine 

Task outline (continued)

what percent removal will achieve the standards. Chapter VI on water quality-based 

effluent limits may be helpful.

3.4.4. Definition of a CSO Event

RCW 90.48.480 requires “the greatest reasonable reduction of combined sewer overflows at 

the earliest possible date”. Chapter 173-245 WAC defines the greatest reasonable reduction as 

“the control of each CSO such that an average of one untreated discharge may occur per year”.

The process of CSO control is given in the Criteria for Sewage Works Design (Ecology 98-37 

WQ); however, that document does not define storm (event), overflow event or averaging period. 

A definition of event is necessary for large communities with numerous overflow sites and 

frequent overflows to design facilities for collection and treatment.

• A CSO event may be defined as the overflow or multiple overflows of a CSO outfall 

occurring within a 24 hour period (option 1 below).

• A CSO event may be defined by a 24 hour minimum inter-event time for a CSO outfall 

(option 5 below).
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• One rainfall storm event causes only one CSO event.

• The averaging period may be one year or the five year permit term.

Defining Some Terms

Combined Sewer Overflow (CSO) – an event during which excess combined sewage flow 

caused by inflow is discharged from a combined sewer, rather than conveyed to the sewage 

treatment plant because either the capacity of the treatment plant or the combined sewer is 

exceeded.

Inter-Event Time (IET) – The dry period or time steps between storm or CSO events.

Minimum Inter-Event Time (MIET)– The amount of dry time or non-overflow time required 

to indicate a storm event or CSO event is independent (CV ≈ 1).

Storm Duration – The time from the first wet time step at the beginning of the storm event to 

the last wet time step ending the event.

Storm Event – A period of rainfall separated from other wet time steps by a dry period equal to 

or greater than the minimum precipitation inter-event time.

Storm Inter-Arrival Time – The time from the beginning of one storm event to the beginning 

of the next storm event. (Equal to one storm duration and one inter-event time).

Threshold Rainfall – The amount of rainfall necessary to cause runoff. In the Portland Oregon 

area this varies from 0.05 to 0.1 inch, depending on length of the storm.

Wet Time Steps – A time increment in a precipitation record in which a measurable amount of 

precipitation occurs. The measurable amount may be defined as threshold rainfall.

Options Considered For Defining Event 

1. Any overflow or multiple overflows in a specific interval of time (e.g., 24 hours) is 

considered an event.

This is the simplest option and may be appropriate for small CSO communities with few 

overflows and that are close to compliance with the one per year requirement. This option 

may be applicable where the engineering analysis is relatively straight forward and the 

solution may be as simple as additional storage or I and I correction. The advantage of this 

option is that it does not require analysis of regional precipitation, CSO system response to 

storm events and derivation of a design storm.
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This option doesn’t provide the statistical tools to predict the return period (probability) of a 

storm event of a certain magnitude.

The current regulatory practice for larger sewer systems required to design to a certain return 

period is to link the definition of overflow event to the definition of storm event. Linking 

overflow events to storm events provides engineers with a mechanism for determining return 

periods of storm events and subsequent design of control structures. The following options 2 

through 5 (based on Nicholson and Adderley, 1994) are contingent upon linking the 

definition of a CSO event to the definition of a storm event.

2. Sewer System-Based Definition: 

Under this definition, a storm event is considered to end when the sewer system has 

processed or discharged the wet weather flows.

It is difficult to justify use of this definition for facilities planning because the system 

performance will change as controls are put in place. Systems with storage or systems 

affected by rain-induced infiltration also cause difficulties with using this system because the 

overflow may continue long past the end of the precipitation. This problem is discussed in 

more detail later.

3. Best Professional Judgment IET:

This definition relies heavily on the expertise, local knowledge, and preferences of the 

individual(s) developing the event definition. Typical values recommended for various 

projects include 1 hour, 3 hours, 6 hours, 12 hours, 24 hours, and 48 hours of dry time 

between storms (precipitation IET) or outfall discharges (CSO IET).

4. Duration-Volume Design Criteria:

An event is considered over when a specific amount of time has elapsed (6 hours to 3 days) 

since the rainfall stopped, or when a certain depth or volume of rainfall has occurred (0.5 

inch to 3 inches).

The problem with this definition is that design storms based on return periods developed 

from this storm definition may be misleading. A 10-year, 24-hour design storm may 

generate a 100-year CSO or a 1-year CSO depending on the soil moisture conditions and 

available storage in the system at the time the design storm occurred.

5. Statistical Independence: 

This definition is used when the probabilistic return frequency of events is important to the 

design, operation, or evaluation of the system. A frequency analysis has as its underlying 

assumption that the events (storms, CSO flows) are independent of one another; i.e., there is 

no joint probability linking one event to any other event. Such a definition helps prevent 

facilities from being undersized. The drawback of this definition is that the methods required 

to determine the statistical independence are somewhat difficult to use. This method has been 

used for the City of Portland (Nicholson and Adderley 1994) and for the EPA national model 
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(Woodward-Clyde Consultants 1989). This method has also been examined for use in Seattle 

(Lukas and Merrill, 1996) and Spokane (Mau, 1999). The method is based on a paper by 

Restrepo-Posada and Eagleson (1982).

Additional desirable criteria considered for selecting the most appropriate storm/CSO event 

definition are:

1. Incorporates the local hydrology patterns.

2. Provides results that are appropriate for use in frequency analysis.

3. Is objective and defensible.

4. Provides results that are reasonable and useful.

Why Not Use The EPA National Definition Of Storm Event?

An analysis of 40 years of rainfall data from 138 gages across the U.S. was conducted by 

Woodward-Clyde (1989). This analysis defined precipitation inter-event times required to define 

independent storm events. The IET for the Eastern US was six hours, 20 hours for the midcountry, and 300 hours for the arid southwest. This analysis did not specify an IET for the 

Pacific Northwest. Woodward-Clyde (1989) recommended that a uniform 6-hour minimum IET 

be used nationwide to assure a common basis throughout the country. Nicholson and Adderly 

(1994) say that a 6-hour IET may be used for the design of small-scale storm water facilities but 

should not be used for design of large-scale CSO control facilities in the Pacific Northwest.

Precipitation events in the Pacific Northwest have different characteristics than events in other 

parts of the country. Rainfall in the Pacific Northwest is characterized by long-duration, lowintensity storms and it may be difficult to identify individual storms. Several analysts have 

demonstrated a 6-hour IET is not applicable for defining a storm event in the Pacific Northwest.

Defining CSO Event by Defining Storm Event (Option 5 Statistical Independence)

The process as described in the paper by Restrepo-Posado and Eagleson (1982) utilizes longterm precipitation data, typically hourly records. The following description of the process is 

taken from Nicholson and Adderley (1994).

In rainfall frequency analysis, the return period of a storm of a given volume or peak intensity is 

based on the assumption that the volume or peak intensity of each storm is independent. A 

sufficient condition that assures independence between peak storm volumes and peak intensities 

is when the inter-event times (dry times) between storms is independent as well. Establishing 

independence between storm events is done by assuming the rainfall data represent continuous 

time (t) divided into a sequence (i = 1 to n) of discrete subintervals of duration (∆t, 1 hour if 

hourly record). The variable Xi (i = 1 to n) is defined as depth of rainfall occurring in each 

interval i. At each time interval, a test is made to determine if rain occurred (Xi > 0) or no rain 

occurred (Xi = 0). Then a second variable that characterizes the occurrence of rain or event 

function, Yi, is defined as:
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Yi = 1 for Xi > 0

Yi = 0 for Xi = 0

If the storm events as represented by Yi are independent of each other, then the series will fit a 

Poisson distribution, 

x!

P e

x

x

−λ λ = , and the dry periods between the events (the precipitation 

inter-event times) are exponentially distributed. One of the characteristics of a Poisson 

distribution is that the mean (m) and the standard deviation (s) are the same, and the coefficient 

of variation (CV = s/m) equals one. The test for independent storm events is conducted by 

calculating the coefficient of variation (CV) of the IETs and comparing it to one.

This simplified method is applicable up to the point where overlapping begins to occur. 

Overlapping means that the storm as modeled actually contains several storms grouped into one 

large event. Overlapping is prevented by keeping the ratio of the storm duration and the storm 

inter-arrival rate (time from the beginning of one storm to the beginning of the next storm) much 

less than 1.0:

(Storm Duration)/(Storm Duration + Inter-Event Time) << 1.0

An additional requirement is that the method must be applied to data that are homogenous or 

belong to the same seasonal weather patterns. The data must be analyzed by months and 

grouped into seasons with similar patterns.

The authors of this procedure noted that it was empirical and inexact but useful in many design 

situations.

The statistical independence technique for defining event resulted in a precipitation MIET for the 

Portland area of 18 hours for winter and 48 hours for summer. A combined precipitation MIET 

of 24 hours was recommended (Nicholson and Adderley, 1994) for the Portland area.

An analysis of rainfall from the SeaTac Airport resulted in a precipitation MIET of 15 hours for 

winter and 36 hours for summer. A combined precipitation MIET of 18 hours was 

recommended (Lukas and Merrill, 1996).

An analysis of the Spokane rainfall record showed independent events at a MIET of 24 hours 

(Mau, 1999).

The basic assumption of this procedure is that the definition of an independent storm event also 

defines a CSO event and that only one CSO event will occur during one storm event. Therefore, 

if the rainfall event is defined, then a CSO event is also defined. During a storm event, the 

rainfall intensity will vary over the duration of the storm. At certain times in the storm when the 

rain falls at an intense rate, CSO discharges may occur. A discharge may occur at the beginning 
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of the storm, stop, and then begin again at the end of the storm. The assumption that a rainfall 

event defines a CSO event means that these intermittent flows are considered one CSO event.

Defining Event by Overflows

The simplest method to define a CSO using the statistical-based procedure is to define a CSO by 

equating the CSO IET to the precipitation MIET so that any CSO’s that were separated by a 

period longer than the precipitation MIET would be deemed separate events (one storm event 

can only cause one CSO event). CSO communities would measure compliance by measuring the 

beginning and ending of each CSO.

Lucas and Merrill (1996) point out a potential problem with this approach as illustrated in the 

following figure of actual precipitation record and resulting computer simulated overflows at the 

Martin Luther King Way (MLK) CSO.

Figure 1. An illustration from Lucas and Merrill (1996) comparing rainfall and CSO inter-event 

periods.

This figure shows a series of precipitation events that have been classed as one event based on an 

18-hour precipitation MIET. The three CSO overflows are separated by more than 18 hours and 

would be classified as three overflow events if we simply used the precipitation MIET as the 

CSO MIET. Lucas and Merrill (1996) propose an alternative in which they use the simulation 

model to predict the number of overflows for the MLK overflow for the period of the 

precipitation record (Table V-2). The CSO IET is analyzed for varying periodicity (3 hours, 6 
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hours, etc.) and the resulting number of overflows. For the SeaTac precipitation data, an 18-hour 

precipitation MIET caused a simulated 3805 precipitation events (81.8/year) for the 46.5 period 

of record. Of these 3805 precipitation events, 802 (17.3/year) caused simulated overflow events. 

The analysis of the CSO IETs showed that a 40-hour (interpolated) CSO IET caused an 

equivalent number (802) overflow events for the period of record. They recommend, for the 

MLK overflow, the use of 48-hour CSO MIET for administrative convenience. A 48-hour CSO 

MIET results in an average of 17 CSO events/year at MLK. This CSO process and the interevent number were based on the assumptions that the Carkeek CSO permit had defined 

Ecology’s future processes for CSO’s. Specifically, that future CSO permits would be written to 

require reporting of CSO discharge without regard to the causative rainfall and Ecology would 

require reporting of CSO discharges on a calendar day basis.

Table V- 2. Inter-Event Analysis Results – Martin Luther King Way CSO and SeaTac

Airport Rainfall (from Lukas and Merrill, 1996).

Minim

um 

interevent , 

hr.

MLK Overflow SeaTac Rainfall Rainfall Events 

Causing 

Overflow 

(Simulated)

No. of 

Events 

in 46.5 

year 

record

Events 

per 

year

No. of 

Events 

in 46.5 

year 

record

Events 

per 

year

Summer 

interevent 

C.V.

Winter 

interevent 

C.V.

No. of 

Events 

in 46.5 

year 

record

Events 

per 

year

3 1196 25.72 9458 203.40 1.87 1.63 1048 22.54

6 1103 23.72 6668 143.40 1.57 1.32 961 20.67

9 1047 22.52 5448 117.16 1.42 1.17 900 19.35

12 999 21.48 4706 101.20 1.33 1.07 862 18.54

15 967 20.8 4202 90.37 1.26 1.00 836 17.98

18 943 20.28 3805 81.83 1.21 0.94 802 17.25

24 884 19.01 3216 69.16 1.12 0.85 742 15.96

30 849 18.26 2744 59.01 1.06 0.78 687 14.77

33 831 17.87 2555 54.95 1.02 0.75 660 14.19

36 821 17.66 2409 51.81 1.00 0.73 639 13.74

48 771 16.58 1904 40.95 0.92 0.63 571 12.28

60 725 15.59 1533 32.97 0.84 0.57 497 10.69

72 679 14.60 1311 28.19 0.79 0.52 450 9.68

84 633 13.61 1138 24.47 0.75 0.49 408 8.77

96 600 12.90 999 21.48 0.72 0.46 379 8.15

120 559 12.02 751 16.15 0.65 0.41 314 6.75

144 527 11.33 589 12.67 0.59 0.39 270 5.81

168 485 10.43 475 10.22 0.55 0.38 224 4.82
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Note that the precipitation IET of 18 hours contains 17 storm events/year but a predicted 20 CSO 

events/year. While this analysis may be valid for counting the number of overflows now, this 

analysis is not applicable to other systems and does not predict the probability of this problem 

when overflows approach the required one per year. Ecology believes this difference between 

events will become negligible as CSO frequency approaches one per year and therefore no 

adjustment on a policy basis is necessary for overflows into the inter-event period.

Definition of Event 

For smaller communities with few overflow points and infrequent overflows a CSO event may 

be counted as any 24-hour period when a CSO discharge or multiple discharges occur. This 

prevents having to do a regional precipitation analysis and modeling of the CSO system to derive 

a design storm.

For large communities with numerous overflow points and frequent overflows, a CSO event is 

defined as a 24 hour minimum inter-event time for a CSO outfall

Averaging Period and Compliance Options

(Reserved)
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3.5 Facilities with Less Concentrated Influent Wastewater

3.5.1 Discussion of Section 050(4)

The facilities which receive less concentrated influent wastewater than normally received by 

domestic wastewater facilities can qualify for alternative limits. The influent wastewater must 

have a BOD5 concentration less than 167 mg/L. In such cases, the facility may apply for a lower 

percent removal requirement than the 85% from Section 040 or the minimum 65% for trickling 

filters and waste stabilization ponds (BOD5 only).

The 85% removal requirement was originally established to achieve 2 basic objectives:

1. to encourage municipalities to remove high quantities of infiltration and inflow (I/I) from 

their sanitary sewer systems, and 

2. to prevent intentional dilution of influent wastewater. However, in facilities with dilute 

influent which is not attributable to high quantities of I/I or intentional dilution, the 

percent removal requirement will result in forcing "advanced treatment". Advanced 

treatment generally refers to additional treatment processes (e.g., filtration, chemical 

addition, or 2-stage biological treatment) which achieve significantly greater pollutant 

removals than secondary treatment processes alone. Ecology concurs with USEPA, that 

it is not reasonable or cost effective to require advanced treatment in these cases.

However, the USEPA regulation does not accomplish objective (1) above. Despite establishing 

3 conditions (see 40 CFR 133.103(d) and WAC 173-221-050(4)(b)(i-iii)) to qualify, a 

municipality could still qualify despite grossly high levels of I/I. The federal regulation would 

allow such a municipality to claim that it is more effective to transport and treat such flows--at a 

reduced percent removal--than to correct. This could result in increasing total weight of 

pollutants discharged and neglecting adequate sewer system maintenance. To prevent this 

situation, Ecology has added a fourth condition (See 050(4)(b)(iv). That condition requires a 

municipality to submit a program aimed at controlling I/I. Ecology has approval authority over 

the program. The permit writer should incorporate the program into the conditions of the 

NPDES permit.
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3.5.2 TASK OUTLINE FOR DETERMINING LOWER PERCENT 

REMOVAL LIMITS FOR LESS CONCENTRATED INFLUENT 

WASTEWATER

1. The permittee must request and submit supporting documentation for the permit writer's 

review. The documentation should include I/I analyses, and sewer system surveys, performed to 

meet federal requirements (as referred to in 2.c. below). The daily historical rainfall record and 

historical daily sewage flows should be provided with these studies.

2. Determine whether the permittee qualifies under Section 050(4)(b).

a. Does the facility meet its effluent concentration limits and the mass loading limits based on 

those effluent concentration limits for BOD5 (or CBOD5) and TSS as established in Section 

040 and 050(1) and (2)?

Yes. Proceed to b.

No. Does not qualify. The permit should include the requirements of Section 040 or section 

050(1) or (2). If the permittee cannot immediately comply, issue an administrative order 

requiring submission of a plan and schedule to achieve compliance (e.g., build more 

capacity).

b. Have the average influent concentrations of BOD5 and TSS generally been below 167 mg/L in 

the months for which the permittee has requested lower percent removal limits? (Review at 

least a few years worth of data.)

Yes. Proceed to c.

No. Does not qualify. Section 040, or Section 050(1) or (2) applies.

c. Is the less concentrated influent the result of "excessive" I/I?

The permit applicant must use the USEPA pamphlet document "I/I Analysis and Project 

Certification" for proposing what is "excessive" I/I. When computing the costs of transporting 

and treating the sewage, include the present cost (capital and operation and maintenance) of 

whatever technology would be necessary to achieve the limits allowed by Section 040, or 

Section 050(1), or (2), whichever is applicable. Any overflow of sewage is deemed excessive 

I/I.

If the answer to c. is Yes, the applicant does not qualify for a lower percent removal limit. Issue 

a permit with the standard percent removal requirement (Section 040 or Section 050(1) or (2)), 

and propose a sewer rehabilitation program and schedule as a condition of the permit or within 
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an administrative order. You will probably need additional guidance for determining reasonable 

rehabilitation schedules. The minimum goal of the rehabilitation program would be to eliminate 

"excessive" I/I.

When the "excessive" I/I is eliminated, the applicant can get lower percent removal limits in 

accordance with #4 below, if they agree to further sewer rehabilitation as outlined in #4.

If the answer to c. is No, proceed to 3.

3. Does the facility meet all the requirements of Section 050(5)? (See task outline for this earlier 

in this chapter.)

Yes, proceed to 4.

No, does not qualify.

4. Propose a lower percent removal effluent limitation which the applicant has demonstrated it 

can meet 95% of the time. This % removal limit can be less than 65% for certain lagoons and 

trickling filters. Use DMR data as explained in Step 3 of the task outline for determining 

trickling filler BOD5/TSS effluent limits. Make a note in the permit that whenever the 

monthly influent concentration exceeds 167 mg/L, 85% removal is the permit limit.

5. If the applicant ever exceeds the USEPA screening criteria of 120 gallons per capita per day 

(7-14 day average for sewage plus infiltration) or 275 gallons per day (highest daily flow 

recorded during a storm event--includes sewage flow plus I/I), propose a sewer rehabilitation 

program and schedule as conditions of the permit. Alternatively, keep the permit condition 

worded in general terms and place the specific schedule of activities in an administrative 

order.

The goal must be to eliminate sufficient I/I quantities such that the influent sewage BOD5 and 

TSS concentrations exceed 167 mg/L. Thereafter, the standard percent removal requirements 

of Sections 040 and 050(1) and (2) would once again apply and should be written into the next 

permit renewal.

If the permittee rehabilitates the sewer and gets flows below the USEPA screening criteria, yet 

the BOD5 and TSS concentrations do not exceed 167 mg/L on a monthly average, propose a 

lower percent removal effluent limitation.

For trickling filters (BOD5 and TSS) and waste stabilization ponds (BOD5) which also 

qualify for percent removal limitations between 85 and 65% under Sections 050(1) and (2), 

the sewer rehabilitation goal should be to reduce I/I below the USEPA screening criteria, or to 

raise the influent concentrations such that the facility no longer meets 050(4)(b)(ii); i.e., the 
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influent concentrations are above 167 mg/L and therefore Section 040 or Section 050(1) or (2) 

applies. If during the rehabilitation program, the flows are reduced below the USEPA 

screening criteria, yet the BOD5 and TSS concentrations do not rise above 167 mg/L, propose 

a lower percent removal limitation based on Section 050(1) or (2).

3.6 Substitution of CBOD5 For BOD5 

3.6.1 Discussion of Section 050(6)

The facility owner/operator can request and the Department can approve substitution of 

carbonaceous BOD5 (CBOD5) for the standard BOD5 limitation. In such cases, the Department 

may substitute a 25 mg/L CBOD5 limit for a 30 mg/L BOD5 limit.

USEPA has extensively studied the use of a CBOD5 limit in lieu of a BOD5 limit. They 

concluded that a 25 mg/L CBOD5 limit is effectively equivalent to a 30 mg/L BOD5 limit. We 

agree. A detailed explanation for this substitution is in the preamble to 40 CFR part 133 as 

published on September 20, 1984.

Using CBOD5, a municipality could discharge more oxygen-demanding nitrogenous material 

than when using BOD5. This is likely if a facility can't prevent partial nitrification.

Nitrification is the conversion of organic nitrogen and ammonia-nitrogen (nonoxidized) to nitrate 

(oxidized). It occurs by chemical action or by certain microorganisms which consume 

nonoxidized nitrogen getting into the water. These organisms use large amounts of oxygen when 

consuming organic nitrogen and ammonia-nitrogen (both unoxidized) and converting them to 

nitrate (oxidized). When this process is underway (partial nitrification), it creates a high BOD. 

Once nitrification is complete, there is very little oxygen-demanding nitrogenous material left.

Using the BOD5 test, facilities have to either keep nitrifying microorganisms out (prevent partial 

nitrification), or wait for them to completely nitrify the water before discharge. Using CBOD5 

however, facilities can discharge partially nitrified water, even with its high nitrogenous oxygendemand.

Notably, unless Ecology identified a problem in receiving water quality, a facility has no 

obligation to remove nitrogenous oxygen-demanding substances from its wastewater. USEPA's 

longstanding 30 mg/L BOD5 effluent limit was not intended to force removal of nitrogenous 

pollutants. It was intended for carbonaceous pollutants. The newer federal rule and Chapter 

173-221 WAC clarify that intent, and eliminate the need for facilities to remove these 

nitrogenous pollutants. This need exists at some facilities only because the nitrogenous 

pollutants gave a false indication of poor facility performance.
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3.6.2 TASK OUTLINE FOR DETERMINING CBOD5 LIMITS

1. The permittee must request the change.

2. Is the facility a waste stabilization pond or trickling filter as defined in Section 030, which has 

requested or received alternative BOD5 or CBOD5 limits? 

Yes - Go to 3.

No - Issue new permit limits of 25 mg/L CBOD5 for the monthly average; and 40 mg/L for 

the weekly average. Refer to the explanation (earlier in this chapter) of Section 040 to 

determine monthly and weekly load limits. Percent removals are based on CBOD in 

the influent and effluent.

The Average Monthly Mass Effluent Limit (CBOD) =

The maximum monthly design flow (MGD) x Concentration Limit (mg/L) x 8.34 =

_____MGD x 25 mg/L CBOD x 8.34 = lb/day CBOD

The Average Weekly Mass Effluent Limit (CBOD) = 1.5 x Average Monthly Mass Limit

3. Have the permittee submit at least one year's worth of influent and effluent data for CBOD5, 

BOD5, and ammonia nitrogen.

a. Try to establish a ratio between BOD5 and CBOD5, (for example, the BOD5/CBOD5 

could be 1.2/1) for months with low or moderate nitrification.

b. Determine the "effluent BOD5 concentration consistently achievable through proper 

operation and maintenance." See task outlines for Section 050(1) or (2).

c. Determine corresponding CBOD5 concentration for the BOD5 value determined above 

by using the ratio established in 3a.

d. Is the corresponding monthly average CBOD5 concentration limit less than 40 mg/L?

Yes - Use it as the new CBOD5 limit.

No - Use 40 mg/L as the new CBOD5 limit.

e. Determine the weekly average CBOD5 limit by multiplying the number obtained in d. by 

1.5.

f. Refer to the explanation in this chapter for Section 040 for guidance in determining 

influent and effluent load limits for CBOD5. Remember to use the CBOD5 influent and 

effluent concentrations determined above.

g. Determine percent removal requirements similarly to the procedures explained earlier for 
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trickling filters and waste stabilization ponds respectively.

NOTE: Whenever effluent CBOD5 limits are given, the permit must also be changed to require

influent CBOD5. The 85% removal requirement applies to the CBOD5 effluent as compared to 

the CBOD5 influent.

When designing biological aeration tanks, it's still appropriate to use BOD5, and in many cases, 

nitrification-demand requirements for determining aeration capacity.

3.7 Defining Compliance with 85% Removal

Compliance with the 85% removal standard of secondary treatment is defined as the 30-day 

average influent concentration (AIC) minus the 30-day average effluent concentration (AEC) 

divided by the 30-day influent concentration (AIC):

(AIC - AEC)/ AIC.

This method of calculation is consistent with the regulatory intent of the performance standard as 

a long-term average performance standard. This method gives a percentage that is a fraction of a 

percent higher than if calculated as the average of the daily percent removals.

This determination comes from federal regulations, 40 CFR Part 133 (definitions).

40 CFR 133.101(b) 30-day average. The arithmetic mean of pollutant parameter values of 

samples collected in a period of 30 consecutive days.

40 CFR 133.101(j) percent removal. A percentage expression of the removal efficiency across a 

treatment plant for a given pollutant parameter, as determined from the 30-day average values of 

the raw wastewater influent pollutant concentrations to the facility and the 30-day average values 

of the effluent pollutant concentrations for a given period of time.

40 CFR 133.102 Secondary treatment

(a) BOD5

(3) The 30-day average percent removal shall not be less than 85%

(b) SS

(3) The 30-day average percent removal shall not be less than 85%

3.7.1. STEP Systems

Section 2 of this chapter pointed out that federal and state regulations require POTW's to remove 

85% of BOD and solids of the influent wastewater. This removal requirement is difficult to 

assess in a STEP systems which utilize septic tanks as part of the treatment system. This part 

presents a process for dealing with STEP systems.
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RECOMMENDATIONS

A NPDES discharge permit and fact sheet for a POTW with a STEP system should include the 

following:

1. The permit should contain the appropriate effluent concentration limits and percent 

removal requirements from WAC 173-221-040 or 050 (1) or (2).

2. The 85% BOD5 removal requirement in the permit should be footnoted with the 

following: 

The permittee will be presumed to be in compliance with the percent removal 

requirement in the permit if the permit effluent concentration limit is met and there is no 

excessive inflow and infiltration (I/I). Infiltration is excessive when the highest 7-14 day 

average daily dry weather flow is greater than 120 gallons per capita per day. Inflow is 

excessive when the highest recorded daily flow during a storm event is greater than 275 

gallons per capita per day or when hydraulic overloading of the treatment plant occurs.

3. The permit should require monitoring and reporting of the influent BOD5 and the 

percent BOD5 removal accomplished at the central treatment plant.

4. The fact sheet should explain that as long as the permit effluent concentration is met and 

neither USEPA criteria (120 gallons per capita per day for the highest 7-14 day average, 

and 275 gallons per capita per day for the highest 24-hour average) are exceeded, the 

permittee will be presumed to be in compliance with the percent removal requirement in 

the permit.

5. The fact sheet should also explain that if either USEPA criteria are exceeded the 

permittee will be required to implement a rehabilitation program to reduce I/I. The 

program will be agreed upon between Ecology and the permittee and the details 

(schedule, work plan, financial commitment) will be incorporated into an administrative 

order.

6. The permit should require annual reporting of the highest 7-14 day average daily dry 

weather flow rate and the highest 24-hour per capita daily flow rate.

7. The permit should require the permittee to institute or continue an adequate operation and 

maintenance program for the entire sewage system including the septic tanks in the STEP 

system.

BACKGROUND

Septic tanks remove settleable solids and provide a limited amount of digestion of organic matter 

of domestic wastewater. When used as part of a STEP system, properly operated and maintained 

septic tanks can achieve some degree of BOD5 removal and thus reduce wastewater BOD5

loading to the sewage treatment plant downstream. The reported mean effluent BOD5

concentrations from domestic septic tanks range from 120 to 240 mg/l (USEPA 1980). Based on 
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limited data, the influent BOD5 concentration to the central sewage treatment plant of a Western 

Washington municipality (Montesano) with septic tank effluent pumps discharging to a pressure 

conveyance system was found to be around 180 mg/l.

For POTWs that receive domestic sewage after treatment in septic tanks (STEP system), the 

BOD5 removal in the septic tanks is considered an integral part of the treatment process for 

BOD5 removal. Since it is impractical to measure the actual influent BOD5 to the septic tanks, 

compliance with the 85 percent BOD5 removal requirement of the secondary treatment rule may 

be assumed if the effluent concentration meets 30 mg/l, and if there is no excessive inflow and 

infiltration (I/I). In this case excessive infiltration is defined as exceedance of the USEPA 

screening criterion of 120 gallons per capita per day (average daily dry weather flow - highest 

average daily flow recorded over 7-14 day period of seasonal high ground water); excessive 

inflow is exceedance of the USEPA criterion of 275 gallons per capita per day (highest daily 

flow recorded during a storm event for wastewater plus I/I); or any occurrence of treatment plant 

hydraulic overload. If the USEPA screening criteria for I/I are not exceeded, the presumption is 

that the raw sewage influent would be at least 200 mg/L if the septic tanks were not present. 

These screening criteria apply regardless of whether the I/I can be cost-effectively removed (see 

section 3.5 of this chapter).Therefore, complying with the 30 mg/L effluent BOD5 concentration 

limit means that the 85% removal requirement is also achieved.

Since the sewage conveyance system is under pressure, ground water intrusion (infiltration) into 

the public sewer should not be a factor for weak influent. However infiltration can occur 

through sewers connecting the buildings to the septic tanks and through possible cracks in the 

tanks. The report required under (6) above should be sufficient to allow the permit writer to 

make an assessment of excessive infiltration.

3.8 Operation and Maintenance (O & M) Manual

The NPDES permit special condition "Operation and Maintenance of Municipal Facilities" 

requires the permittee to keep an approved O & M manual at the treatment plant. The approved 

O & M manual must be updated as needed and a copy of the updated portions be submitted to 

the Department for review and approval. Failure to keep an approved and updated O & M 

manual at the treatment plant is a permit violation and subject to enforcement. The permit writer 

should talk with his/her supervisor concerning the appropriate enforcement measures needed.

3.8.1. O & M Requirements for Collection Systems

The collection system (that is the network of sewers and pumps or lift stations) is an integral part 

of the wastewater treatment works. For the most part these are buried and distant from the 

treatment facilities, so that small leaks often go unnoticed for long periods. Leaks of untreated 

sewage constitute a discharge of wastewater which is not allowed under the terms of the permit.

Small leaks, especially if numerous or under pressure, can result in significant impacts on the 
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environment. Leaks can adversely impact the treatment plant if they result in excessively dilute 

sewage (infiltration or inflow). For these reasons, maintenance of the collection system should 

be considered part of the Operations and Maintenance for the wastewater treatment system, even 

if they are managed by different departments of the municipality.

If the existing O&M manual for the facility does not include the collection system, the permit 

will require preparation and implementation of a section on the collection system. If the 

collection system is included in the O&M Manual for the facility, a periodic review will be 

required and an update for all modifications of the system (e.g., extensions) required.

Mechanical systems (lift stations and pumps)

• There needs to be a regular schedule for reviewing the performance of mechanical 

systems which are part of the collection system. This includes schedules for lubrication, 

testing pump and motor performance, testing the operation of level switches and alarms, 

call out systems and cleaning any screens, floating material and sediments. If there is 

excessive corrosion of the interior walls of wet wells, then leak testing may be warranted. 

Planning for power failures or unanticipated overflows needs to be implemented.

Gravity sewers 

• Sewer pipes which operate partly full have low internal pressures (nearly atmospheric), 

which allows ground water to enter the sewer through leaks whenever the water table is 

above the level of the sewage and the leak. This is called infiltration. The water table 

typically fluctuates seasonally (high during wet weather or irrigation season) so that leaks 

which result in infiltration during part of the year may result in exfiltration, leakage of

raw sewage out of the sewer, at another time during the year. Excessive infiltration 

dilutes the sewage, increases the costs of treatment and potentially interferes with the 

complete treatment of the sewage. Exfiltration is a discharge of pollutants to 

groundwater.

• Testing sewers designed to operate at atmospheric pressure is more difficult than testing 

piping systems intended for operation under pressure, since there are more openings to 

close and less strength for resisting leakage without failing. Although pressure testing of 

individual pipe segments is possible, testing sewers for infiltration (and by implication 

exfiltration) is usually done by measuring flows or other characters of the sewage such as 

temperature or conductivity. Temporal patterns of varying temperature and conductivity 

might be indicative of infiltration of groundwater into the sewer pipes. If the temperature 

or conductivity show values closer to groundwater during the low flow period in the early 

morning, infiltration is suspected and needs to be further characterized as to how much 

and where the leaks are occurring. Also, smoke testing of sewers can be an effective 

technique for detecting leaks.

• Sewers may also collect water such as stormwater through holes in the covers for the 

access points to the sewer, direct connection of downspouts to the sanitary sewer, etc. 
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This results in increased flows associated with storms and can cause some of the same 

problems as infiltration for treatment. This is referred to as inflow. Once inflow has 

been identified, it needs to be characterized for how much and where it enters; the 

techniques and tools used are often the same as those used for infiltration.

Pressurized sewers:

• These are sewers with pressures significantly greater than atmospheric pressure, in which 

case leaks will almost always result in exfiltration. Sewers which operate at greater than 

atmospheric pressure include force mains where the pressure is generated by a pump 

operating against gravity and friction, and inverted siphons where the pressure results 

from gravity acting on the column of water between the invert of the siphon and the free 

surface in the gravity sewer.

• Pressurized sewers can be tested, if they can be taken out of service, by closing all of the 

valves, pressurizing the system and measuring the loss of pressure with time.

Leaks can be especially problematic if the collection system contains segments which cross 

surface water or follow the low lying land along surface water (river, stream, or lake). A regular 

schedule of inspections and testing of the collection system on those segments in sensitive 

environments is required.

Once a leak has been determined to be present and its location narrowed down, (for instance 

between two manholes), confirmation of the type of leak and location can often be done by 

passing a television camera through the sewer.

3.9 Maintaining Adequate Capacity

Ecology has observed over the years that it takes municipalities several years to plan and fund 

expansions of the wastewater treatment plant. Permit writers should note the population growth 

of a municipality when redrafting their wastewater discharge permit. For those nearing capacity 

or with rapid population growth, the permit writer should put a requirement in the permit that 

causes the municipality to submit a report on capacity. The triggers for submitting a report are 

when the peak flows waste load exceeds 85% of the design criteria for three months in a row or 

if flows or loads are expected to reach design capacity during the life of the permit. The plan 

should include a schedule for continuing to maintain capacity. The capacity as outlined in the 

plan must be sufficient to achieve the effluent limitations and other conditions of this permit. 

This plan should address any of the following actions or any others necessary to meet the 

objective of maintaining capacity.

1. Analysis of the present design including the introduction of any process modifications 

that would establish the ability of the existing facility to achieve the effluent limits and 

other requirements of this permit at specific levels in excess of the existing design 

criteria.
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2. Reduction or elimination of excessive infiltration and inflow of uncontaminated ground 

and surface water into the sewer system.

3. Limitation on future sewer extensions or connections or additional waste loads.

4. Modification or expansion of facilities necessary to accommodate increased flow or 

waste load.

5. Reduction of industrial or commercial flows or waste loads to allow for increasing 

sanitary flow or waste load.

3.10 Operator Certification

Anyone operating a wastewater treatment plant in Washington State is required to be a certified 

operator. Certification requires a combination of training and experience as described below. A 

higher certification is required to operate higher discharge or more complex treatment plants. 

The complete requirements for Operator Certification are given in Chapter 173-230 WAC.

Table V-3 below gives the operator level required for various treatment processes and flow 

volumes.

Table V-3 Treatment Plant Classification Criteria

Treatment type Design flow MGD Operator Classification required

Primary

≤1 I

>1, ≤10 II

>10, ≤20 III

>20 IV

Lagoon (Nonaerated) All I

Lagoon (Aerated) ≤1 I

>1 II

Biofiltration

≤1 II

>1, ≤10 III

>10 IV

Extended aeration ≤5 II

>5 III

Activated sludge

≤1 II

>1, ≤10 III

>10 IV

Wetlands

≤1 I

>1, ≤5 II

>5 III

Tertiary

≤5 III

>5 IV
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Treatment type Design flow MGD Operator Classification required

Membrane bioreactora

(Operators of these facilities must 

have an expert on call when needed 

as determined by the department)

For any size facility discharging to a sensitive with effluent limits 

beyond secondary treatment, Ecology will decide on the certification 

level on a case-by-case basis using engineering judgment, the complexity 

of the operation, the record of permit compliance and the risk to humans 

and the environment.

≤1 II

≤1 Class A reuse III

≤1 with chemical addition 

for nutrient removal

III

>1, ≤10 III

>10 IV

Any size discharge with 

water quality-based limits 

with limits more stringent 

than technology-based 

secondary treatment

Determined on a case-by case 

basis using engineering 

judgment based on the 

complexity of the operation, 

the record of compliance, and 

the risk to humans and the 

environment.

a. Classification levels have been determined by policy

Plants may be classified in a group different than indicated in this section if:

1) They have characteristics that make operation less complex or more difficult than other 

similar plants of the same flow range; or

2) The conditions of flow or the use of the receiving waters require an unusually high degree of 

plant operational control; or

3) They use an approved method of wastewater treatment that is not included in this section.

3.11 Loading Calculation for intermittent discharges

The following method is recommended for calculating loading for intermittent discharges:

Multiply the month’s average daily flow (gpd) x average of sampled daily concentrations x

[0.00000834]. Days with zero flow are included in the average daily flow calculation.

The federal definition (40 CFR Part 122.2 is “Average monthly discharge limitation means the 

highest allowable average of ‘‘daily discharges’’ over a calendar month, calculated as the sum of 

all ‘‘daily discharges’’ measured during a calendar month divided by the number of ‘‘daily 

discharges’’ measured during that month. 

Ecology notes that if a facility discharges intermittently, this definition does not adequately 

represent the discharge loading particularly for discharges to land and for TMDL compliance. 

EPA’s definition was intended to apply to technology based limits and continuous discharges. 

We can direct facilities with intermittent discharges to calculate compliance with limits using a 
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different method specific to the situation.

4. BIOSOLIDS (SLUDGE)

Important points for permit writers

• The Waste 2 Resources Program has the lead for biosolids management, including 

permitting and regulation. There is a biosolids coordinator in each regional office 

and at headquarters.

• Treatment plant upgrades are a critical control point for effective biosolids 

management. When an upgrade or significant change in treatment technology is 

contemplated, it is essential to be sure the regional biosolids coordinator is in the 

loop. Rather than attempting to decipher the options for biosolids management 

available under the regulations, it is often more helpful for operators to ask 

themselves, “What do we want to do with our biosolids,” and then investigate the 

requirements and feasibility.

• Virtually all sewage treatment facilities (and some others) come under the state 

biosolids program, including lagoons. Lagoons often neglect biosolids management 

and find themselves with a very short time frame for decision making on costly 

projects. The recommended planning horizon for removing biosolids from a lagoon 

is two years.

• Biosolids are not a solid waste. State law says they are a valuable commodity and 

directs Ecology to implement a program maximizing beneficial use. The Waste 2 

Resources Program generally does not support management options that lead to 

disposal.

• Ecology does not have delegation of federal program authority. This does not 

affect state program implementation because we have independent statutory 

authority, however, Ecology’s program must meet federal program requirements.

Lack of federal delegation means that treatment works continue to have dual 

obligation of submitting permit applications and annual reports to both agencies. It 

also means that EPA can initiate unilateral permitting or enforcement actions, 

although this has not occurred. In some cases Ecology has delegated certain 

authorities to local health jurisdictions (LHJs). It can be helpful to know the extent 

of local delegation agreements.

4.1 The State Program

1992 Legislation directed the Department of Ecology to implement a program maximizing the 

beneficial use of biosolids, a valuable commodity (Chapter 70.95 J RCW). This Legislation was 

significant because it was the first in the nation to recognize “biosolids” in statute, it gave 

authority for program development and implementation to Ecology, and it removed biosolids 

from regulation as a solid waste, declaring instead the product was a valuable commodity. 
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Ecology adopted new rules for biosolids management in Chapter 173-308 WAC and issued a 

statewide general permit for biosolids management in the spring of 1998. New general permits 

were issued in 2005 and 2010, and a revised rule was adopted in 2007. The Waste 2 Resources 

Program is the regulatory authority responsible for authorizing and permitting the use of 

biosolids throughout the state. In some cases delegation agreements are in place with LHJs.

Ecology’s biosolids program is intended to meet or exceed federal program requirements of the 

Clean Water Act, 40 CFR Part 503, and various other federal regulations. There is a program 

coordinator in the headquarters office and a coordinator in each regional office.

The term biosolids was adopted by the state Legislature in 1992 in Chapter 70.95J RCW.

Biosolids is municipal sewage sludge that meets the quality standards allowing it to be 

beneficially used. The standards for quality are defined in Chapter 173-308- WAC. Biosolids 

which do not meet these standards may not be applied to the land (even under a solid waste 

permit). Disposal options include incineration and landfill disposal. Chapter 70.95J recognizes 

biosolids as a valuable commodity and directs Ecology to develop a program to maximize 

beneficial use. Landfill disposal is discouraged, but may be allowed in some cases on an 

emergency or short-term basis, or even as a long-term management option. Ecology does not 

support incineration but recognizes the importance of incineration to a few communities in the 

state who have incineration facilities in place. We have encouraged these communities to 

operate their incinerators as efficiently as they can for as long as they are serviceable. As these 

units need significant upgrades or replacements, Ecology will advocate strongly for 

abandonment and a shift to beneficial use.

The state rule includes a permitting program, the key to which is identification of a facility as a 

Treatment Works Treating Domestic Sewage (TWTDS). TWTDS is a term adopted from federal 

rules and essentially refers to any treatment facility which changes the quality of biosolids. The 

vast majority of TWTDS are publicly owned treatment works. Privately owned treatment works 

qualify only if there is no industrial influent component. Other facilities may also meet the 

definition of TWTDS. Biosolids compost facilities are TWTDS as are facilities which simply 

combine biosolids from two different sources, because they both change the quality of biosolids 

they receive. Certain land application sites, called Beneficial Use Facilities, are also TWTDS.

Facilities that treat or land apply septage are also TWTDS. Ecology can also use its authority to 

designate TWTDS and bring facilities under the permit program that would not typically require 

permitting.

The state biosolids rule is directly enforceable. All facilities and persons subject to the rule must 

comply with its requirements, regardless of their standing under the permit program. There are 

several steps to the permitting process which includes SEPA review, public notice, an 

application process and potentially public hearings. The first step involves submission of a 

Notice of Intent form at least 6 months before an existing general permit expires. The notice of 

intent acknowledges the facility’s intention of applying for coverage under the general permit.

In the second step of permitting, the facility submits a complete permit application. The permit 

application must be submitted within 180 days following the issuance of a new general permit.

Complete review by Ecology may not occur for some time. In the third step Ecology reviews the 

application and current practices. Once final conditions have been established, the facility is 

notified with a letter of final approval; this letter may include additional or more stringent 
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requirements if needed. The facility must then comply with all final plans and any additional or 

more stringent requirements stipulated in their final approval letter.

4.2 The Federal Program

The Environmental Protection Agency (EPA) has responsibility for implementing biosolids 

program requirements on Indian lands and in states which have not taken delegation of federal 

program authorities. EPA does not consider the federal program to be a high priority and in 

recent years has significantly disinvested from the biosolids program. This has left EPA Regions 

in a very difficult position to implement federal requirements. In Region X the primary focus 

has been on facilities in Alaska and Idaho which have fewer resources for implementing state 

programs. EPA has also worked with some facilities on Indian lands and federal facilities. EPA 

has chosen two approaches to implementing the biosolids program at the federal level. The 

initial focus was on inclusion of requirements in federal NPDES permits. This effort is 

continuing at some level in Region X. After a time, EPA began using a general permit approach 

in some regions. EPA’s expectations of Washington facilities appear to be fairly reasonable and 

minimal at this point in time. Facilities with NPDES permits should have complete (and 

updated) federal biosolids permit applications on file with Region X. Other Treatment Works 

Treating Domestic Sewage (mostly state waste discharge permitted treatment works) should 

have Part 1 of the federal application on file. All major facilities should submit annual reports to 

EPA. EPA does not have an annual report form and has stressed that content of the report is the 

critical issue. Washington’s form has been determined to be acceptable. Beyond these 

requirements, EPA has a fundamental expectation of compliance with the rules.

4.3 Delegation

Ecology originally intended to pursue delegation of federal program authority, but staff cannot 

set aside implementation activities in order to pursue federal delegation without compromising 

the state program. Consequently, the Waste 2 Resources Program has elected not to pursue 

delegation until adequate resources are available for the task. Ecology’s authority to implement 

the state program, however, is independent of federal delegation. A lack of federal delegation 

does not in any way invalidate the state program. The benefits of federal delegation are marginal 

for Ecology. Delegation would relieve the regulated community of certain duplicative processes, 

particularly permit applications and annual report submittals. It would also clarify the first line 

of authority for regulatory decisions. EPA, however, has not played an active role in biosolids 

management with Washington facilities to date, although they have been helpful to Ecology.

Nationwide only a handful of states have received delegation of federal authority.

Ecology may delegate certain responsibilities to LHJs. Typically this delegation will at a 

minimum include review of applications and site plans and routine inspections. A few LHJs 

around the state have delegation agreements in place with Ecology.

4.4 Overlap With Wastewater Permits

Generally, Water Quality Program permit writers and managers should consult with the 

biosolids permit managers in the Waste 2 Resources Program regularly, as there is the potential 

for significant overlap between permits.
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One of the most critical points of overlap with wastewater permits are biosolids sampling and 

analysis requirements. All TWTDS which apply biosolids or sell or give away biosolids for 

application must conduct a minimum amount of sampling on an annual basis. The pollutants and 

monitoring schedules are the same in the federal and state rules, although permit requirements 

may extend those requirements. Both rules have provisions that require representative sampling 

as well. Many times the minimum specified sampling frequency may be inadequate. This is an 

area where Ecology’s biosolids permit program must fill the gap. While sampling methods are 

specified in the rules, the specific vehicle directing them is not critical to the biosolids program.

For example, samples obtained in support of a pretreatment program may also be acceptable for 

biosolids program compliance. Water Quality permit managers should check with their 

counterparts in the Waste 2 Resources Program as monitoring requirements come under review.

Facility upgrades and new construction are areas of critical concern to both programs. Facilities 

should have a clear vision of future biosolids management practices when contemplating 

upgrades. For example, the biosolids treatment systems designed to produce Class A biosolids (a 

measure of pathogen reduction) are different than those which produce a Class B product. Both 

products are acceptable, but there are markedly different implications for permitting in the 

biosolids program as well as for end uses. Also, the Waste 2 Resources Program would likely 

oppose a proposed management system which would depend either on incineration or landfilling 

of biosolids.

Finally, a delegation agreement between Ecology and a LHJ may be important in terms of Water 

Quality Program permitting. Permit managers should specifically inquire about current 

delegation agreements in both the area where the biosolids are generated, and where they are 

used.
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CHAPTER VI. WATER QUALITY-BASED 

EFFLUENT LIMITS FOR SURFACE WATERS

Permit writers must consider the impact of every proposed discharge to surface waters on the 

quality of the receiving water and specifically consider how the discharge may affect the use of 

the receiving water. In some cases, this consideration may reveal that permit limits based on a 

treatment technology are not sufficiently stringent to protect water quality even with a mixing 

allowance. In these cases, additional permit limits must be developed, or alternative disposal 

methods or locations must be found. This chapter deals with conducting an analysis of 

reasonable potential and developing effluent limits for the protection of aquatic life for 

individual permits. Human health protection is covered in Chapter VII.

To evaluate the effect an effluent has on receiving water, a permit manager must use:

• the water quality criteria and standards described below in Section 1,

• the mixing zone criteria described below in Section 2, and

• a method for predicting impact and defining effluent limits for numeric criteria 

described below in Section 3.

The permit writer should keep in mind that the requirement for imposing effluent limitations for 

the protection of water quality does not require a demonstration of impact beyond any doubt but 

only that there is a determination of reasonable potential determined by a rational and scientific 

process.

Section 4 of this Chapter describes analytical levels for permit application and effluent limits.

Evaluating an effluent's effect on receiving water includes an evaluation of whole effluent 

toxicity (WET). Section 5 presents Ecology's approach for dealing with whole effluent toxicity.

Additional guidance on determining effluent mixing is presented in Appendix 6.

1. WATER QUALITY CRITERIA AND STANDARDS

Water quality criteria are estimated threshold concentrations for specific pollutants which are 

based on scientific data about adverse effects to aquatic life or human health. These criteria 

address human health effects, toxicity to aquatic organisms, bioaccumulation potential, or an 

adverse effect on some other beneficial water use. These criteria may be single numbers, a 

concentration range, or a narrative statement.
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The first water quality criteria developed by direction of the Water Quality Act of 1965 and the 

Federal Water Pollution Control Act (Clean Water Act) have since been revised several times.

The methods used for deriving the criteria have changed over the years. The different methods 

that EPA has used are published as appendices to the Gold Book EPA 440/5-86-001. EPA 

maintains a site dedicated to criteria development 

http://water.epa.gov/scitech/swguidance/standards/policy.cfm. The criteria have become 

increasingly complex as EPA tries to incorporate all the factors which affect toxicity including 

exposure patterns or characteristics. The Criteria sheet of TSDCALC contains the current 

criteria.

Many of the numeric criteria for aquatic life protection have 3 components:

 • magnitude or concentration, 

 • duration - averaging period for exposure to the chemical in question, and

 • frequency - the number of times that the criteria may be exceeded within a given time frame 

without permanently affecting the aquatic communities. Three years is used as the period of 

time for aquatic community reestablishment.

Each of these components is defined for short-term (acute) and long-term (chronic or sub-lethal) 

effects.

The current EPA aquatic life criteria for zinc, for example, are:

"freshwater aquatic organisms and their uses should not be affected unacceptably 

if the 4-day average (duration) concentration of zinc (in μg/L) does not exceed 

the numerical value given by (.986)(e(0.8473[ln(hardness)]+0.7614)) (concentration) more 

than once every three years on the average (frequency) and if the 1-hour average 

(duration) concentration (in μg/L) does not exceed the numerical value given by 

(.978)(e(0.8473[ln(hardness)]+0.8604)) (concentration) more than once every three years on 

the average (frequency). For example, at hardness of 50, 100, and 200 mg/L as 

CaCO3, the 4-day average concentrations of zinc are 32, 105, and 188 μg/L 

respectively, and the 1-hour average concentrations are 64, 114, and 206 μg/L. If 

the striped bass is as sensitive as some data indicate, it will not be protected by 

this criterion... Saltwater aquatic organisms and their uses should not be affected 

unacceptably if the four-day average concentration of zinc does not exceed 81 

μg/L more than once every 3 years on the average and if the 1-hour average 

concentration does not exceed 90 μg/L more than once every 3 years on the 

average."(Values are from FR Volume 60, No. 86, May 4, 1995)

The criteria for toxic pollutants, including zinc, have separate development documents which 

provide a detailed review of the data used to develop the criteria. These documents are available 

from the Department of Ecology Library, the Environmental Assessment Program, and from the 
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EPA Region 10 library in Seattle. New or revised criteria are published in the Federal Register.

The criteria for toxic pollutants are not static. EPA continues to refine these numbers to 

incorporate new research data and risk methods.

1.1 The Water Quality Standards Define the Designated Uses 

and Incorporate Criteria

Water quality standards for Washington's surface waters are codified in Chapter 173-201A 

WAC, Water Quality Standards for Surface Waters of the State of Washington, Amended 

November 20, 2006 (Water Quality Standards) and in 40 CFR Part 131 Water Quality Standards, 

Section 131.36, known as the National Toxics Rule. The National Toxics Rule does not apply to 

those substances which were already included in our Water Quality Standards at the time the 

Rule was adopted. The Water Quality Standards consist of 3 key parts.

Part I of the standards contains the purpose and definitions.

Part II of the standards defines the designated uses of surface waters and the in-stream criteria 

necessary to protect those designated uses. The four categories of uses are aquatic life, shellfish 

harvesting, recreational uses, and miscellaneous. Within these categories there are subcategories 

and the criteria necessary to support those uses. The criteria within a subcategory or 

classification are numerical values or narrative statements. The conventional and historical 

parameters are dissolved oxygen, fecal coliform, dissolved gas saturation, temperature, pH, and 

turbidity. A map application assists Ecology staff in identifying the designated uses on a water 

body and their associated numeric criteria. The application and instructions are found at: 

http://aww.ecology/programs/wq/swqs/index.html .

Toxic substances are addressed through both narratives statement and numerical criteria. Toxic

criteria apply to all uses of waters. Note that in this section footnotes aa and bb to Table 240(3) 

contain small typographical errors in the formulas as published, however, TSDCALC (discussed 

later) calculates the criteria correctly.

Many of the numerical values of the criteria are dependent on other water quality parameters 

such as pH, temperature and hardness. Some values have duration periods specified as 

instantaneous values, 1-hour averages, 24-hour averages or 4-day averages.

Silver is given in our standards as an instantaneous value not to be exceeded. Implementation of 

silver is the same as an acute one hour average exposure.

The chronic aquatic life criterion for mercury is based on accumulation of methylmercury in 

aquatic organisms. Permit writers should use the chronic criterion for mercury just like all other 

chronic criteria.
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In addition to the specific numerical criteria, the State Water Quality Standards state that the 

Gold Book may be used as a source of information for determining the toxicity of substances not 

specifically listed in the standards [(173-201A-240(4) and (5)].

The key narrative criteria of the Water Quality Standards are:

• Toxic, radioactive, or deleterious material concentrations must be below those which have 

the potential, either singularly or cumulatively, to adversely affect characteristic water uses, 

cause acute or chronic conditions to the most sensitive biota dependent upon those waters, or 

adversely affect public health (see WAC 173-201A-240, toxic substances, and 173-201A250, radioactive substances).

• Aesthetic values must not be impaired by the presence of materials or their effects, excluding those 

of natural origin, which offend the senses of sight, smell, touch, or taste (see WAC 173-201A-230 

for guidance on establishing lake nutrient standards to protect aesthetics).

Part III of the Water Quality Standards is the antidegradation policy and process. Three levels of 

protection are described. Tier 1 is a statement of policy that existing and designated uses will be 

protected. Tier 2 is most applicable to permit writers. Tier 2 is applicable to new dischargers or 

any discharger increasing pollutant loading which then causes a measurable degradation

(concentration exceeding detection levels) of the receiving water (boundary of the chronic zone 

for those pollutants with near field effects). Measurable degradation is defined in regulation for 

temperature, dissolved oxygen, bacteria, pH, and turbidity. The increase in pollutant loading 

must be shown to be necessary and in the overriding public interest. Generally, the tier II 

analysis should be conducted by the permittee as a companion to an engineering report. 

Implementation of antidegradation for general permits requires Ecology to describe in the fact 

sheet how new stormwater pollutant control technologies will be incorporated into the permit 

[(WAC 173-201A-320(6)]. The detailed guidance for antidegradation is posted in Outlook.

The Water Quality Standards also contain some specific directives for permit managers. These 

include the requirements that:

• Permits be conditioned such that the discharge will not cause a violation of the standards 

[WAC 173-201A-510(1)],

• Permits are subject to modification if a permitted discharge is discovered to be causing a 

violation of the standards [WAC 173-201A-510(1)(b)], and

• No waste discharge is allowed to: the Cedar River (RM 21.6 to headwaters), the Green River 

(RM 59.1 to headwaters), Mill Creek (RM 25.2 to headwaters), the Sultan River (RM 9.4 to 

headwaters), the Tolt River (RM 6.9 to the headwaters), the Union river and tributaries (RM 

6.9 to the headwaters), and the Wishkah River and tributaries (RM 32.0 to the headwaters) 

[WAC 173-201A-602]. These river sections are preserved as sources of drinking water.
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There are also many other special waterbody-specific special conditions listed in Sections 602 

and 612 concerning fecal coliform, temperature and dissolved oxygen.

EPA has promulgated criteria to protect human health for 91 substances. These criteria apply to 

the states waters and are found in 40 CFR Part 131.36 (see Chapter VII). These criteria are given 

in TSDCALC.

1.2 Conversion Factors and Translators for Metal Criteria

In the 1992 revision of the Washington Water Quality Standards, the metals criteria were 

changed from being expressed as total recoverable to expression as dissolved. The conversion 

was accomplished using the conversion factors recommended by EPA at the time. The 

conversion factors recommended by EPA were ratios observed in laboratory testing. The 

conversion did not make the criteria more or less stringent but simply expressed them in the form 

believed to be toxic. These conversion factors become part of the formula for calculating the 

criteria. The current criteria are given in permit tool TSDCALC.XLW.

Conversion of the metal criteria to the dissolved form created a problem for permit writers 

because federal regulation (40 CFR 122.45(c)) requires that effluent limitations for metals be in 

the form of total recoverable. The permit writer then needs a translator to conduct a 

determination of reasonable potential or derive effluent limits. The translator is used to predict 

the dissolved to total recoverable fraction that will occur in the receiving water from the total 

recoverable metal in the effluent.

Ecology permit writers should use one of the following as a translator, in the following order of 

priority depending on the circumstances: 1). Use the measured fraction of dissolved to total 

recoverable measured in the receiving water during critical condition. 2). If there is no data on 

the dissolved fraction in the receiving water but there is TSS data on the receiving water use the 

TSS-dissolved fraction relationship described in Table VI-1 below for copper and zinc. Use the 

appropriate fraction for Cd and Pb from Table VI-1. 3). If there is no receiving water data on 

ratios or data on TSS, use the appropriate dissolved fraction from Table VI-1 for cadmium, 

copper, lead and zinc. For other metals, use the conversion factor as the translator. 

TSDCALC.XLW will calculate the appropriate translator (see Appendix VI ). A 

facility/receiving water-specific translator may be used if the appropriate experimentation is 

conducted.

Table VI-1. Recommended estimates of the 90th and 95th percentiles of ambient dissolved 

fractions (fd) of Cd, Cu, Pb, and Zn based on data from rivers in Washington (regressions assume 

TSS in mg/l).(from Pelletier, 1996)
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90th percentile of fd* 95th percentile of fd

Cd 0.898 0.943

Cu if seasonal TSS<6.7 mg/L: 1

if seasonal TSS ≥ 6.7 mg/L: 1.91*TSS-0.341

if no TSS data: 0.968

if annual TSS<11.4 mg/L: 1

if annual TSS ≥ 11.4 mg/L: 2.29*TSS-0.341

if no TSS data: 0.996

Pb 0.340 0.466

Zn if seasonal TSS<4.9 mg/L: 1

if seasonal TSS ≥ 4.9 mg/L: 1.44*TSS-0.231

if no TSS data: 0.965

if annual TSS<12.5 mg/L: 1

if annual TSS ≥ 12.5 mg/L: 1.79*TSS-0.231

if no TSS data: 0.996

*The 90th percentile values are used if the TSS data is from the critical season. The 95th 

percentile values are used if the data are not stratified by season.

Waste-specific translator

The translators described above assume a near-instantaneous equilibrium of the metal in the 

receiving water. This may be a valid assumption for metals bound to the light floc discharging 

from secondary treatment. Other wastewaters, such as from physical chemical treatment may 

have metals tightly bound in the solids fraction and the conversion to dissolved form occurs 

slowly. A discharger may be allowed to develop a waste-specific translator if the permit writer 

agrees. An example QAPP and experimental design for a waste-specific translator is available.

1.3 Site-Specific Water Effect Ratio

Footnote dd to Table 240(3) mentions the use of the water effects ratio to adjust metal criteria on 

a site-specific basis. This adjustment currently requires an amendment to the Water Quality 

Standards and therefore can only be granted for exceptional circumstances. Permit writers 

should contact the Watershed Management Section for more information.

2. THE POINT OF COMPLIANCE OF THE WATER 

QUALITY STANDARDS

The Water Quality Standards allow the use of mixing zones for discharges that would otherwise 

exceed the water quality criteria for aquatic life. Mixing zones are areas where the water quality 

standards may be exceeded but the exceedances are small enough and short enough so as not to 

interfere with beneficial uses. Mixing zones are a regulatory recognition that the concentrations 

and effects of most pollutants diminishes rapidly after discharge due to dilution. They are 
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established in a manner which limits the duration of exposure for organisms passing through the 

effluent plume in order to minimize the risk from each discharge. The water quality standards 

for chronic protection must be met at the boundary of this zone and beyond. A smaller zone in 

which acute criteria may be exceeded can also be authorized. This zone must be small enough to 

limit exposure times and therefore not cause acute mortalities or interfere with passage of aquatic 

organisms in the water body.

An intermediate goal in point source pollution control which is consistent with the CWA goal of 

zero discharge is the elimination of the need for a mixing zone.

The water quality standards do not prohibit a permit writer from granting a mixing zone for a 

shore discharge, but shore areas are important biological areas. A permit writer should be sure 

that granting of the mixing zone on a shoreline will not cause biological effects as specified in 

the regulation. This may require a demonstration on the part of the permittee in some cases.

2.1 General Considerations for Authorizing Mixing Zones

The authorization of a mixing zone (chronic) is subject to some conditions, as given in the Water 

Quality Standards.

1. The allowable size and location shall be established in discharge permits or orders.

A discharger does not receive a mixing zone unless it is specifically authorized in a permit or 

order. Any discharger whose effluent exceeds the water quality criteria and has not been 

authorized a mixing zone is in violation of the water quality standards. For marine waters the 

permit writer should authorize, as necessary, some distance around the point of discharge and 

place this in the permit. The fact sheet should discuss the distance, the dilution factor that results 

from this distance and the method of deriving the dilution factor. A diagram of the mixing zone 

and a map of location are helpful for the fact sheet reader. For fresh water, the permit writer 

should authorize some distance or some volume fraction of the receiving water, whichever is 

more stringent, and discuss the selection in the fact sheet.

2. The discharger shall be required to fully apply AKART prior to being authorized a mixing 

zone.

This is the technology-based limit process described in Chapter IV. In some instances a 

pollutant may not have been addressed in the derivation of the technology-based limits for a 

discharger. For example, municipal discharges have technology-based limits for BOD, TSS, 

fecal coliform and pH in regulation and this has been determined to be AKART (Chapter 173-

221 WAC). This regulation does not address ammonia or chlorine and therefore ammonia and 

chlorine should be addressed on the design basis or on a water quality basis.

3. Consider critical discharge conditions.

The receiving water critical condition is generally defined in the Water Quality Standards. 
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Design conditions are discussed in more detail later in this section.

4. Not cause loss of sensitive or important habitat,

Generally, permit managers have little data on the physical and biological characteristics of the 

receiving water and must meet the intent of this section by limiting the size of the mixing zone 

and conditioning permits to meet water quality standards.

5. Not exceed criteria past the boundary of the mixing zone

The process of deriving effluent limits described later in this chapter will ensure the water 

quality standards are not exceeded past the mixing zone boundary or flow restriction.

6. The mixing zone size and the pollutant concentrations shall be minimized.

Mixing zones are minimized by the design factors given in Table VI-2.

A mixing zone is typically sized for the pollutant with the largest potential to violate water 

quality standards. Mixing zones may be authorized and sized for individual pollutants.

7. Maximum size specifications (Chronic)

In rivers and streams the maximum mixing zone boundary is 300 feet downstream plus water depth 

at critical condition. The dilution factor to use in calculating effluent limits for protection of the 

chronic criteria is the more restrictive of 1) twenty-five percent (25%) of the flow at critical 

condition or 2) the center line dilution factor occurring at the downstream boundary of the 

authorized mixing zone (Figure VI-1) as determined by use of a hydraulic mixing model.

In estuaries the maximum mixing zone boundary is 200 feet plus water depth at MLLW in any 

horizontal direction (Figure VI-2).

In oceanic waters the maximum mixing zone boundary is 300 feet plus water depth at MLLW in

any horizontal direction (Figure VI-3).

8. Zone of acute criteria exceedance.

This zone can only be authorized if it will not create a barrier to the migration or translocation of 

indigenous organisms to a degree that has the potential to cause damage to the ecosystem. If a 

permit is conditioned such that acute criteria are not exceeded past the boundary of this zone it 

can be assumed in the absence of information to the contrary that it will not cause a barrier.

In rivers and streams the maximum size of this zone is the more restrictive of the mixing 

occurring at 10% of the mixing zone distance (centerline) or 2.5% of the flow at critical 

condition.

In estuaries and oceanic waters the maximum size of this zone is 10% of the mixing zone 

horizontal distance. There is no vertical limitation on this zone.
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2.1.1 Determining Mixing

A mixing zone may be a boundary around a point of discharge and a permit writer must know or 

be able to estimate the amount of mixing which occurs inside that area to determine the potential 

for a violation of the water quality standards and to derive effluent limitations if necessary.

The permit writer has 3 basic options for determining the amount of mixing occurring within a 

mixing zone:

 1. Use a computer hydraulic simulation model to predict the amount of mixing. A permit 

writer has several models available for use if the input data is available or can be reasonably 

estimated. These models are discussed in Appendix 6 of this Manual and Section 4.4 of the 

TSD. The EA Program must be consulted before using these models unless the permit 

writer has a strong background in modeling.

 2. Require the mixing analysis to be done within the permit. A permit writer may run a model 

using the best available data for determination of reasonable potential but also require a 

permittee to do a mixing analysis as a requirement of a regulatory order or as a requirement 

in the permit.

 3. Require the mixing analysis as a part of the permit application. If a permit writer knows that 

a permit will be done in the next fiscal year, the mixing and other data necessary for making 

water quality determinations can be requested well in advance. The data that could be 

requested are mixing data, effluent data and ambient receiving water data. Producing this 

data may be beneficial to the discharger. For example, the multiplication factor for making 

a "reasonable potential" determination decreases with increasing number of data points.

Requiring the analysis as an order or permit application will slow the issuance of the permit. 

Requiring the analysis as a permit condition may mean the permit will have to be modified when 

the analysis is completed if it leads to a different conclusion than what the permit conditions are 

based.

Saltwater discharges are modeled using steady state analysis and hydraulic models. These 

models require data on discharge depth, effluent flow rates, density of effluent, density gradients 

in the receiving water, ambient current speed, ambient current direction and outfall 

characteristics such as port size, spacing and orientation. The model output includes the 

dimensions of the plume at each integration step, time of travel to points along the plume 

centerline, and the average dilution at each point.

Mixing models are changing rapidly. The currently recommended models for most situations is 

the EPA PLUMES, CORMIX, UDKHDEN and site specific analysis using the formulas in 

Chapter 5 of Fisher, et al (1979). Guidelines for the selection of the appropriate model are given 

in Appendix VI.
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In those permitting situations where input data is not available, the permit manager should 

require the permittee to develop the data and run the appropriate model. The requirements may 

be in an order, as a part of the permit application or within the permit. The EAP program can 

also do this as a requested project.

Where the hydraulic conditions at the discharge point are complex such as in the tidal reach of a 

river, a dye or tracer study should be used to confirm the model output at the chronic compliance 

boundary.

The mixing analysis should determine centerline or minimum mixing at the compliance zone 

boundaries for unidirectional flow situations and flux average for multidirectional flow situations 

such as tidal areas.

For flowing fresh water the water quality standards require, for chronic mixing, the more 

stringent of the dilution factor that results from the mixing at the boundary of the assigned 

mixing zone at critical condition (usually 7Q10 flow) or effluent mixing with 25% of the 7Q10 

flow. For acute mixing, the allowed mixing is the more stringent of the modeled mixing that 

occurs at the boundary of the acute compliance zone (10% of the chronic zone) at 7Q10 

condition or 2.5% of the 7Q10. Exceptions to the size criteria for mixing zones (including the 

percent flow limitation) may be made in those circumstances where:

 • the engineering report for the discharge was approved before November 24, 1992, or

 • where altering the size configuration would result in greater protection, or

 • where the effluent provides a greater benefit than removing it, if removing it is the only 

option, or 

 • where the exceedance is clearly necessary to accommodate important social or economic 

development.

Before an exception can be made, it must be demonstrated to Ecology that

 • AKART is applied

 • all other options that are economically achievable are being utilized and

 • granting the exception would not have the reasonable potential to cause a loss of sensitive 

or important habitat, substantially interfere with the existing or characteristic uses of the 

water body, result in damage to the ecosystem, or adversely affect public health.
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AKART is covered in Chapter IV, Part 3. A permit writer who makes a determination that a 

larger mixing zone is required or the percent of flow limitations are not applicable should 

discuss, in the fact sheet, the determinations of AKART, economically achievable options, and 

receiving water impacts. This determination should be discussed with the Watershed Planning 

Section.

2.1.2 Shellfish Protection

Ecology has a shellfish protection strategy in cooperation with the Department of Health 

(Ecology 1984). Permit writers for marine dischargers should consult with DOH Shellfish 

Program to determine if the outfall is located in the general vicinity of shellfish resources, to 

gather other information about the discharge site, and to discuss dilution modeling.

The Shellfish Program of the Department of Health (DOH) is responsible for establishing 

prohibited areas around the outfalls of wastewater dischargers in waters located near shellfish 

production areas. DOH utilizes many of the same assumptions used by Ecology in the selection 

of critical receiving water and effluent flow conditions. However, the area of interest to DOH 

for such discharges is far-field. Therefore, the results of modeling or field studies which stop at 

the edge of dilution zones are often inadequate in providing appropriate information to DOH in 

establishing shellfish prohibited areas in the far field. Where shellfish beds are in the area of the 

discharge, the results from computer models or field studies should be extended to the farther 

field (usually in terms of several hundreds of yards). This initial screening may indicate a need 

to require the permittee to obtain additional information on receiving water conditions beyond 

the boundary of the dilution zone.

The Department of Health is also concerned about the discharge of human viral pathogens to 

shellfish beds from municipal treatment plants. They have asked that Ecology permit writers 

consider the following in developing municipal wastewater discharge permits:

The efficiency of UV disinfection decreases with increasing tube age.

The standard UV dosage is 16 milliwatt-seconds per square centimeter, however, some 

reactivation of bacteria occurs with dosages less than 30 milliwatt-seconds per square centimeter.

The use of detention time in the discharge pipe may be considered when deriving effluent limits 

for chlorine.

2.1.3. Miscellaneous

Water Quality Standards in Tidal Rivers - In tidal rivers in which the salt water wedge reaches 

the discharge point, the permit manager may apply the salt water criteria.
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Alternatively the permit writer may apply the following process if the information is available:

Where 95 percent of the vertically averaged daily maximum salinity values are less than or 

equal to one part per thousand the freshwater criteria are applied. Exceptions to this include 

dissolved oxygen in which the marine criteria apply at any point where the salinity is one 

ppt or greater and fecal coliform in which the marine criteria apply where the salinity is 10 

ppt or greater.

Reflux in Tidal Rivers - In tidal rivers, some of the effluent that is discharged is carried back 

upstream during the flood tide (reflux). In conducting a mixing analysis for a tidal river, the 

permit manager should model as an outgoing current and then assume reflux reduces the dilution 

factor by 1/2. This is based on Ecology's studies of these situations. The permittee may supply 

information to show the factor is something else in their situation.
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Figure VI-1. Mixing zones in rivers.
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Figure VI-2. Mixing zones in estuaries.
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Figure VI-3. Mixing zones for oceanic discharges.
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3. PREDICTING IMPACTS AND DEFINING EFFLUENT 

LIMITS FOR NUMERIC CRITERIA

The permit manager must make several decisions when developing effluent limits for a permit. 

One decision, noted previously, is whether or not technology-based effluent limits for a pollutant 

will protect the quality of the receiving water.

Generally, 2 types of analyses are done by the permit manager to predict impacts. One type of 

analysis is for pollutants such as BOD or nutrients which may cause an impact some distance 

from the point of discharge and for which mixing zones are not applicable. The other type of 

analysis examines the concentrations of specific pollutants or effects of pollutants within or at 

the edge of the mixing zone or the assigned dilution factor. These pollutants may be specific 

conventional, non-conventional, or toxic compounds.

3.1 The Water Quality Impact Of BOD And Nutrients

3.1.1 BOD

Biochemical oxygen demand (BOD) causes a depletion of dissolved oxygen in receiving water 

and consequently causes negative impacts on aquatic life and water quality in general. Many of 

the existing municipal and industrial permit conditions in Washington are based upon 

consideration of the water quality impact of BOD. In these cases, the treated effluent met the 

technology-based limitations but the small volume of receiving water warranted additional 

consideration.

In some cases, the dischargers were required to install advanced treatment to 

produce a lower effluent concentration of BOD. In other cases, they were 

required to change their point of discharge to new outfall locations or to land 

application during low flow periods.

The model used to predict dissolved oxygen deficit from BOD is the Streeter-Phelps equation. 

The Streeter-Phelps equation has the basic form as follows:

 DOSAG
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The impact of BOD is determined at the critical condition. The critical condition (design flow) 

for flowing freshwater is usually the 7-day average low flow with a recurrence interval of 10 

years (7Q10). The critical period for marine waters is determined on a site-specific basis. The 

effluent design flow for industrial discharges is the highest monthly average flow for the past 

three years over the months when the 7Q10 is likely to occur. The effluent design flow for 

municipalities depends on how close to the design flow the facility is operating. For those 

municipalities that are operating within 15% of the design capacity or are experiencing a rapid 

population growth use the dry weather design flow. For those facilities that are operating well 

below design flow and are expected to have a stable population over the permit cycle, use a 

projected average dry weather flow for the five year period. The projected flow can be estimated 

from trend analysis or population projections from the engineering report.

This model is for a determination of reasonable potential for violation of the dissolved oxygen 

criteria. If the model indicates a probable violation of the dissolved oxygen criteria in the 

receiving water, the permit writer should contact the EA Program for assistance in verification of 

the model or confirmation with more sophisticated models.

3.1.2 Nutrients

Nutrients are another class of pollutants which would be examined for impacts at some point 

away from the discharge. The special concern is for those water bodies quiescent enough to 

produce strong algae blooms. The algae blooms create nuisance conditions, dissolved oxygen 

depletion, and toxicity problems (i.e., red tides or blue-green algae). High nutrient 

concentrations can also create nuisance conditions in flowing waters. The impact of nutrients is 

very difficult to predict and usually there are several point and nonpoint sources contributing to a 

Streeter-Phelps Equation:

Dt = DOsat - DOt

= [K2BODu ÷ (K1 - K2)](10-K2t- 10-K1t) + Do(10-K1t)

where:

Dt = dissolved oxygen deficit at any time t (days).

DOsat = the dissolved oxygen level at saturation 

DOt = the dissolved oxygen level at any time t (days)

BODu = ultimate carbonaceous BOD of the stream immediately after mixing.

K1 = reoxygenation rate constant (Kr).

K2 = deoxygenation rate constant (Kd).

Do = dissolved oxygen deficit immediately after mixing.
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nutrient problem. The Water Quality Standards contain recommendations for total phosphorus 

concentrations for lakes in several ecoregions of the state. The Gold Book also contains some 

guidelines for phosphorus loading to freshwater streams and reservoirs. A permit manager 

should point out any suspected nutrient problems to the unit and section supervisor. Suspected 

water quality problems due to nutrients are best handled by a TMDL process conducted by the 

EAP.

3.2 Other Specific Pollutants - Conventional and Nonconventional

This section addresses dissolved oxygen, fecal coliform, pH, turbidity, temperature, total 

dissolved gas and aesthetics. The design flow for dissolved oxygen, fecal coliform, pH, 

turbidity, and temperature is the maximum monthly flow which may be estimated for existing 

facilities by using the discharge data for a period of the last three years for the months in which 

the critical flow is likely to occur.

3.2.1 Dissolved Oxygen

An effluent may cause a violation of the dissolved oxygen criteria near 

the point of discharge from 2 components. If the effluent is low in 

dissolved oxygen it may cause a violation of the dissolved oxygen criteria 

near the point of discharge from mixing with receiving water. The 

effluent may also have chemical components which cause rapid oxygen 

depletion called Immediate Oxygen Demand (IDOD). For most 

discharges the IDOD is not significant relative to the effect of mixing of the effluent, containing 

a low concentration of dissolved oxygen, with the receiving water.

The process for calculating dissolved oxygen concentration following initial dilution is a simple 

mixing calculation found in TSDCALC. This process requires data on the dissolved oxygen 

concentration of the effluent, the receiving water at the critical period and the dilution factor. 

The point of compliance is the chronic mixing zone boundary and the receiving water design 

concentration is the 10th percentile dissolved oxygen concentration.

3.2.2 Pathogenic Bacteria

Ecology uses fecal coliform (fc) and enterococci bacteria (en) as indicator organisms for the 

control of pathogenic bacteria in wastewater effluent. Fecal coliform is limited on a technology 

basis in municipal permits to 200 colonies/100 ml as a monthly geometric mean and 400 as a 

weekly geometric mean. This limit is based on the performance of standard disinfection 

treatment processes. It is a promulgated performance standard in Chapter 173-221 WAC.

The water quality criteria for fecal coliform are quantified on a geometric mean of the number of 

colonies per 100 mL with an additional 10% or single sample limit (in parenthesis below). They 

are based on the probable exposure to pathogenic bacteria causing intestinal upset. These criteria 

are currently under review by EPA.

 IDOD
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The criteria are:

Extraordinary Primary Contact Recreation, freshwater- 50 (100)/100 mL fc

Shellfish and Primary Contact Recreation, marine- 14 (43)/100 mL fc

Primary Contact Recreation, freshwater- 100 (200)/100 mL fc

Secondary Contact Recreation, freshwater- 200 (400)/100 mL fc

marine- 70 (208)/100 mL en

 

The point of compliance for the fecal coliform standard is at the boundary of the chronic mixing 

zone if one is allowed. The design flow for application of the standard is the 7Q10 low flow for 

flowing freshwater and the 50th percentile current velocity for marine.

A municipal permittee meeting the technology-based limitations would require minimal dilution 

to be able to meet the water quality standards for fecal coliform. Permit writers must address any 

human exposure within the mixing zone. Alternatively, the permit writer may impose a limit of 

100 cfu/100mL as a daily maximum and then no mixing allowance is necessary.

3.2.3 pH

The pH in most permits in Washington is limited to a range of 6 to 9 unless pH has been defined 

by the federal effluent guidelines as a process pollutant. The range of pH 6 to 9 in permits for 

most dischargers is based on the demonstrated performance of simple equalization or 

neutralization. Unless pH is a process pollutant, the discharge of effluent 

outside this range generally indicates spills or treatment plant upset.

The criteria for pH in the water quality standards restrict the pH change caused 

by a source to 0.2 units for core summer salmonid habitat and within a range of 

6.5 to 8.5. The point of compliance with the pH standard is the boundary of the 

chronic dilution zone at 7Q10 or critical condition.

The resultant pH of a mixture of 2 flows is calculated by processes described in EPA (1988). A 

spreadsheet for the calculation in found in PWSPREAD.

Modeling of freshwater discharges is usually unnecessary unless the effluent pH is above 8 and 

the receiving water is poorly buffered or unless the volume of the discharge is very large.

Source-caused pH changes are seldom a problem in salt water because of the high buffering 

capacity of sea water. A spreadsheet in PWSPREAD is available to predict pH effects of a point 

source discharge.

 PHMIX2
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3.2.4 Turbidity

Turbidity is not a parameter generally considered in point source discharges except for water 

treatment back flush wastewater. Control of particulates as total suspended solids in an effluent 

usually results in low turbidity, however, depending on the size of the particulates and the pore 

size of the filter media used to determine TSS, some effluents may cause some turbidity in the 

receiving waters while meeting TSS limits. Turbidity does not have a linear response to dilution. 

Any data that indicates a violation of water quality standards should be verified in the receiving 

water.

3.2.5 Dissolved Gas Supersaturation

The Watershed Management Section monitors compliance with dissolved gas supersaturation. 

Dam operators can control dissolved gas by controlling the amount of spillage. The design 

condition for dissolved gas is the 7Q10 high flow (7Q10hf). During these very large natural 

runoff events, the resulting high flows make it impossible for dam operators to abate for 

dissolved gas. Guidelines for deriving the 7Q10 high flow are presented in Appendix 6.7.

3.2.6 Temperature

Temperature in the water quality standards has multiple criteria and requirements. These 

include:

1. Annual summer maximum threshold criteria.

2. Supplemental spawning-season criteria.

3. Incremental warming restrictions.

4. Protections against acute effects.

5. Antidegradation requirements.

1. Annual summer maximum threshold criteria. In freshwater, each of 8 categories has a 7 day 

average daily maximum (7-DADmax) upper temperature limit and a maximum allowable 

rise. See the table below from WAC 173-201A.
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Table 200 (1)(c)

Aquatic Life Temperature Criteria in Fresh Water

Category Highest 7-DADMax

Char Spawning 9°C (48.2°F)

Char Spawning and Rearing 12°C (53.6°F)

Salmon and Trout Spawning 13°C (55.4°F)

Core Summer Salmonid Habitat 16°C (60.8°F)

Salmonid Spawning, Rearing, 

and Migration

17.5°C (63.5°F)

Salmonid Rearing and Migration 

Only

17.5°C (63.5°F)

Non-anadromous Interior 

Redband Trout

18°C (64.4°F)

Indigenous Warm Water Species 20°C (68°F)

In marine water the categories have a 1 day maximum (1-DMax).

Aquatic Life Temperature Criteria in Marine Water

Category Highest 1-DMax

Extraordinary quality 13°C (55.4°F)

Excellent quality 16°C (60.8°F)

Good quality 19°C (66.2°F)

Fair quality 22°C (71.6°F)

2. Supplemental spawning-season criteria. In some waters, a second threshold criterion is 

assigned to protect the spawning and incubation of salmonids (9°C for char and 13°C for 

salmon and trout) [WAC 173-201A-200(1)(c)(iv)], and Ecology publication [06-10-038]. 

These criteria include explicit date-windows for application, and must be applied in addition 

to the annual summer maximum criteria discussed above. For fresh water bodies identified 

in Part VI of the standards the following are applicable:

- Maximum 7-DADMax temperatures of 9°C (48.2°F) at the initiation of spawning and at fry 

emergence for char; and,

- Maximum 7-DADMax temperatures of 13°C (55.4°F) at the initiation of spawning for 

salmon and at fry emergence for salmon and trout.

3. Incremental warming restrictions. In addition to the criteria discussed above, the water 

quality standards limit the amount of warming human sources can cause at any time water 

temperatures are cooler than the assigned threshold criteria. This criteria is designed to 

provide protection for the overall temperature regime [See WAC 173-201A-200(1)(c)(ii), 

210(1)(c)(ii)].
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At any time the background temperature is cooler than the assigned threshold 

criterion, point sources are permitted to warm the water by only a defined 

increment, t.

Calculate t as follows:

o t = 28/(Tambient + 7) in freshwaters, or

o t = 12/(Tambient – 2) in marine waters.

4. Protection against acute effects

A. Moderately acclimated (16-20°C, or 60.8-68°F) adult and juvenile salmonids will 

generally be protected from acute lethality resulting from discrete human actions by 

maintaining the 7-DADMax temperature at or below 22°C (71.6°F) and the 1-day 

maximum (1-DMax) temperature at or below 23°C (73.4°F).

B. Lethality to developing fish embryos can be expected to occur at a 1-DMax temperature 

greater than 17.5°C (63.5°F).

C. To protect aquatic organisms, discharge plume temperatures must be maintained such that 

fish could not be entrained (based on plume time of travel) for more than two seconds at 

temperatures above 33°C (91.4°F) to avoid creating areas that will cause near 

instantaneous lethality.

3.2.6.1 Determining Reasonable Potential for Temperature.

The process of determining reasonable potential is similar to other pollutants except no 

transformation or prediction of the 95th percentile is required. Figure VI-4 below illustrates 

the administrative process. TSDCALC contains spreadsheets for determining reasonable 

potential and effluent limits for temperature, when required. A companion document 

explaining temperature implementation is available on the Water Quality web site and is also 

posted in Outlook.

Guidance for permittees to conduct temperature sampling and a model QAPP are available.

Permit writers should realize that in cases where dilution factors are approximately 6 or less, 

an effluent limit derived for the critical mid-summer or supplemental period may cause a 

slight exceedance of the incremental allowance during the winter time. This probability of 

exceedance depends on changes in dilution factor and effluent temperature from summer to 

winter. The incremental restriction was formulated to prevent a change of temperature 

regime in situations where the ambient temperature was well below the criteria. An 

incremental rise of 1 or 2 degrees is well within the normal daily fluctuation in mid-winter 

and will not cause a change in the temperature regime.
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Table VI-2. Effluent and receiving water design conditions for temperature

Chronic criteria

Ambient background 

temperature1

90th percentile annual maximum 7DADMax, or 

90th percentile of annual maximum 1DMax; whichever matches the 

criterion.

Ambient flow 7Q10 for critical periods:

 July-Aug for summer criteria

 First month of any fall supplemental spawning criterion and last 

month of any spring supplemental spawning criterion.

Effluent temperature2 95th percentile (0.05 probability) of 7DADMax, or 

95th percentile of 1DMax; whichever matches the criterion.

Effluent flow Selected from Table VI-3 of the permit writer’s manual.

Acute criteria

Ambient background 

temperature1

90th percentile annual maximum 1DMax, or

90th percentile annual maximum 7DADMax; whichever matches criterion.

Ambient flow 7Q10 for critical periods:

 July-Aug for summer criteria

 First month of any fall supplemental spawning criterion and last 

month of any spring supplemental spawning criterion.

Effluent temperature2 99th percentile (0.01 probability) of 1DMax, or 

99th percentile of 7DADMax; whichever matches the criterion.

Effluent flow Selected from Table VI-3 of the permit writer’s manual.

Notes to Table VI-2:

1.The highest annual upstream ambient temperature (1-DMax or 7-DADMax, whichever 

matches the criterion) observed from 3 or more years of monitoring (1/2 hour measurement for 

the period) should be used to represent both the 95th and 99th percentile background receiving 

water temperature.

2.The highest annual effluent temperature (1-DMax or 7-DADMax, whichever matches the 

criterion) observed from 3 or more years of monitoring should be used to represent both the 

95th and 99th percentile effluent temperature.
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Figure VI- 4. Decision process for temperature

Is there adequate data to 

determine a reasonable potential 

to violate the temperature 

standards?

Is there a reasonable 

potential to exceed the 

standards?

Ensure adequate data to 

characterize effluent and 

background receiving 

water temperatures and 

the available dilution 

during the critical 

conditions.

The permit language 

requires an evaluation 

of reasonable potential 

in an engineering report

Next permit issuance

No Limit in 

Permit –

Consider 

continued 

monitoring

Place an effluent limit in 

the permit that meets the 

temperature standards

Can the Permittee 

immediately comply 

with the limit?

Require 

effluent 

monitoring to 

assure 

compliance 

with the liimit

Will the Permittee require two 

permit cycles to comply with 

the water quality-based limit?

Place the compliance schedule 

and a performance-based interim 

limit in the permit

Place the compliance schedule in 

an order and place a 

performance-based limit in the 

permit.

Permit condition to collect the 

necessary data during the 

permit

yes no

yes

no

yes

no

no

yes

3.2.7 Aesthetics

The Water Quality Standards require that aesthetic values shall not be impaired by the presence 

of materials or their effects, excluding those of natural origin, which offend the senses of sight, 
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smell, touch, or taste. These values will, of course, be mostly considered for new discharges or 

when a complaint has been received on an existing discharge. Examples of measures that could 

be required of a discharger to preserve aesthetic values include:

 • control of oil sheens,

 • submerged discharges, and

 • locating the discharge away from sensitive locations/persons.

3.3 Deriving Effluent Limits for Toxic Pollutants, as Seasonal 

Limits and for Impaired Waters

Defining water quality impacts and developing effluent limits is usually more complex for toxic 

pollutants than for the other pollutants. As noted in the earlier discussion on water quality 

criteria and standards, the toxic numerical criteria are given at 2 levels (acute and chronic) each 

of which contains 3 components (magnitude, duration, and frequency). The analysis to predict 

water quality impacts and thus to define effluent limits must be conducted for both acute and 

chronic criteria in order to define the most limiting criteria. Many of the criteria for toxic 

pollutants are variable and depend on receiving water conditions. This section covers these 

subjects and others and presents an example of how to develop effluent limits for toxic 

pollutants.

Whole effluent toxicity (WET) is evaluated separately and explained in Section 5 of this chapter.

After determining a technology-based limit for a toxic pollutant, the permit manager must decide 

if the limit will cause the discharge to meet the water quality standards. Federal regulations 

require the permit manager to determine whether a discharge has a reasonable potential to violate 

water quality standards and if so to place a water quality-based effluent limit in the permit (40 

CFR 122.44). To determine this, the permit manager must know the criteria, the background 

concentration, the point of compliance, design flows for the receiving water and effluent flow, 

how to deal with multiple pollutants and effluent variability and the process of developing an 

effluent limit.

The EPA document, Technical Support Document for Water Quality-based Toxics Control

EPA/505/2-90-001, is the basic reference document for the rest of this chapter and it is assumed 

that the permit manager has read it. The rest of this chapter will focus on Washington's process 

and will not review the background material which is presented in the Technical Support 

Document.

3.3.1 Points of Compliance

The points of compliance for toxic pollutants are the same as discussed previously in this 

chapter. A permit manager may authorize a mixing zone as necessary with the size and other 
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restrictions as specified in the water quality standards for acute and chronic criteria.

3.3.2 Design Flows

The design flows for effluent and receiving water has been discussed above for some pollutant 

parameters. They are summarized in Table VI-3.

The traditional receiving water design flow or critical condition for steady state modeling of 

pollutant discharge such as BOD to freshwater is the 7-day low flow period with a recurrence 

interval of 10 years (7Q10). This flow is typically when the least amount of mixing occurs, 

temperature is the highest, and dissolved oxygen is the lowest. Ecology will use the 7Q10 as the 

design flow for the acute and chronic toxic criteria also. The permit manager should use this 

design flow unless another design flow is more suitable because of the nature of a particular 

pollutant or receiving water.

For saltwater discharges the critical mixing condition is defined according to the characteristics 

of the receiving water such as tidal exchange, river inflow, stratification by temperature and 

salinity, the characteristics of the outfall location, and the characteristics of the effluent such as 

temperature and salinity. It may be necessary to run a computer simulation of the discharge and 

receiving water to determine critical condition.

3.3.3 Criteria Vary With Background Conditions

Some criteria vary with other chemical or physical parameters. For example, 

the aquatic life criteria for some metals in freshwater vary with hardness of 

the receiving water. The criterion for ammonia varies with temperature and 

pH. The critical period for ammonia is often difficult to calculate because 

the criterion varies on the 2 parameters. The EA Program or the Program Development Services 

Section can assist if the permit manager has difficulty.

3.3.4 Multiple Pollutants

Each toxic pollutant in a single discharge is considered independently. Many toxic pollutants are 

interactive but any additive or synergistic effects are difficult to predict. Interactive effects in a 

single effluent will be detected with whole effluent toxicity testing. The chance for interactive 

effects is reduced by not allowing overlap of acute compliance zones and by not allowing the 

overlap of mixing zones for the same parameters.

3.3.5 Effluent Variability (Coefficient of Variation)

A permit manager must have an estimate of variability to determine reasonable potential and to 

calculate a permit limit. The estimator of variability which is most commonly used is the 

coefficient of variation (CV). The CV is the ratio of the standard deviation to the mean. The 

best estimate of effluent variability can be derived from a set of results from random effluent 

samples for the toxic parameter. As a general rule of thumb, because the distribution of values 

from wastewater treatment is non-normally distributed, any number of samples less than 20 is 

AMMONIA

NH3SALT
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probably not valid as a predictor of distribution. The number of samples required depends on the 

true variance of the population being sampled which is usually not predictable except by 

sampling. For sample sizes less than 20 use the default CV of 0.6, which was derived by EPA on 

a large database of municipal effluent. The spreadsheet TSDCALC has a default CV of 0.6.

 

A permit writer may be able to obtain a value for variability from the development document for 

the category of discharger.

The permit writer may calculate an effluent CV if data is available. Non-detect concentrations in 

the data set may be estimated by using one half of the detection level or estimation techniques 

described by Gilbert (1987) or EPA (1991).

3.3.6 Background (Receiving Water) Data

Permit writers and watershed coordinators, during the watershed scoping process should identify 

the need for background water quality data for the basin waters. Information and data necessary 

to develop a water quality-based permit should be requested from the discharger by letter or 

order in year two of the basin cycle. This gives ample time to budget and hire a contractor, if 

necessary.
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Table VI-3. Applicable criteria/design conditions for determining the acute and chronic dilution factors for aquatic life.

Design Conditions for Mixing Zone/Ratio Analysis - Aquatic life Criteria

Parameter Mixing 

Zone

Critical Design Condition

Plant Effluent

Flow - Municipal

Acute

The critical plant effluent flow, for those plants operating at less than 85% of the dry 

weather design flow during the critical period, is defined as the highest daily maximum 

plant effluent flow for the past three years during the critical flow or when the critical 

condition is likely to occur. If the facility is operating between 85 and 100% of dry 

weather design flow during the critical period then use a peaking factor applied to dry 

weather design to determine acute design flow. The peaking factor is a ratio of daily 

maximum to monthly average flows derived from actual plant data during critical period. 

A peaking factor may also be available in the engineering report for the facility.

Chronic

The critical plant effluent flow is defined as the dry weather design flow if the facility is 

operating between 85 and 100% of design during the critical period. If the facility is 

operating at less than 85% of design flow during the critical period the critical plant 

effluent flow is defined as the highest monthly average plant effluent flow for the past 

three years during the critical flow or when the critical condition is likely to occur. 

Plant Effluent 

Flow - Industrial

Acute

The critical plant effluent flow is defined as the highest daily maximum plant effluent flow 

for the past three years during the critical flow or condition is likely to occur. If plant 

effluent flows are expected to increase during the life of the permit, the highest daily 

maximum flow must be estimated.

Chronic

The critical plant effluent flow is defined as the highest monthly average plant effluent 

flow for the past three years during the critical flow or condition is likely to occur. If plant 

effluent flows are expected to increase during the life of the permit, the highest average 

monthly flow must be estimated.

Receiving Water 

(Characteristics)

Acute and 

ChronicFreshwater

The critical receiving water current velocity is defined as the current velocity at both the 

7-day low flow and high flow periods with a recurrence interval of 10 years (7Q10 by the 

appropriate statistical method).

The diffuser depth is defined as the depth at the 7Q10 low flow period.

Acute -

Saltwater

The critical receiving water current velocity is defined as the critical 10th and 90th

percentile current velocities derived from a cumulative frequency distribution analysis. 

The current velocity frequency distribution analysis should be conducted, at minimum, 

over one neap and spring tide cycle.

The critical ambient density profile is defined as the density profile that results in the 

lowest mixing.

The diffuser depth is defined as the depth at MLLW. For estuaries, the diffuser depth is 

defined for low-water slack and low river flow conditions. 

Chronic -

Saltwater

The critical receiving water current velocity is defined as the 50th percentile current 

velocity derived from a cumulative frequency distribution analysis. The current velocity 

frequency distribution analysis should be conducted, at minimum, over one tidal cycle.

The critical ambient density profile is defined as the density profile that results in the 

lowest mixing.

The diffuser depth is defined as the depth at MLLW. 
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Miscellaneous Design Conditions for Mixing Zone/Ratio Analysis

Parameter No. of Data 

Points

Methodology

Maximum 

expected 

Receiving Water 

Concentration

(Analytical Data)

1 to 20

The geometric mean of the receiving water values at time of critical condition 

should be multiplied by a factor of 1.74 to estimate the 90th percentile. This 

value should then be used in conjunction with the plant effluent data to 

evaluate reasonable potential to cause an exceedance of the criteria for 

aquatic life protection and derive effluent limits. 

Over 20

The critical background receiving water value is defined as the 90th percentile 

value derived from a cumulative frequency distribution analysis of data from 

time of critical condition. This 90th percentile background value should be used 

in conjunction with the plant effluent data to evaluate reasonable potential to 

cause a violation of the criteria for aquatic life protection and derive effluent 

limits.

Maximum 

Expected Effluent 

Concentration 

(Analytical Data)

1 to 20

Use the highest single effluent concentration, assume a coefficient of variation 

(CV) of 0.6 and use the reasonable potential multiplying factors from Table 3-2 

of the TSD (page 57) to estimate the maximum expected effluent 

concentration (TSDCALC does this by formula). This value should then be 

used in conjunction with the background receiving water data to evaluate a 

reasonable potential to cause a violation of the criteria for aquatic life/human 

health protection and derive effluent limits.

Over 20

Calculate CV and use the reasonable potential multiplying factors from Table 

3-2 of the TSD to estimate the maximum expected effluent concentration. This 

derived effluent value should then be used in conjunction with the background 

receiving water data to evaluate a reasonable potential to cause a violation of 

the criteria for aquatic life/human health protection and derive effluent limits.

Dilution Factor

unidirectional 

flows

N/A Centerline for acute and chronic dilution.

Dilution Factor

marine and 

rotating direction

N/A Flux average for acute and chronic

Reflux N/A Assume reflux reduces the dilution factor by 1/2 in the absence of site-specific 

data.

Mixing Zone/Ratio Analysis - Point of Compliance

Parameter Point of Compliance

pH, DO, Fecal Coliform, Temperature Compliance at the edge of the chronic mixing zone.

Human Health Criteria Compliance at the edge of the chronic mixing zone.

Whole Effluent Toxicity and Numeric 

Criteria

Compliance at the edge of the acute dilution zone for acute WET/numeric 

criteria and at the edge of the mixing zone for chronic WET/numeric criteria.

Chronic design conditions are used for both the initial mixing and the far-field mixing calculations.
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3.3.7 Determining Reasonable Potential

Ecology has adopted EPA's (1991) process of determining reasonable 

potential including their statistical assumptions for estimating the 95th 

percentile effluent concentration from a limited data set of effluent data.

The current version of the TSD (1991) documents EPA's assumptions in 

determining the multipliers to derive the 95th percentile effluent concentration 

based on a limited sample.

An alternate method for estimating quantiles from limited data sets with an assumed log normal 

distribution is presented in Gilbert (1987). This method produces an estimate of an upper 

percentile value that is a maximum likelihood estimator which is proportional to the geometric 

mean. This estimator is lower for limited data sets than the EPA estimator and is used for 

estimating the 90th percentile receiving water concentration when making determinations of 

reasonable potential for aquatic life criteria. The details of this method are given in Appendix 6.

3.3.8 Calculating the Effluent Limits

Water quality-based effluent limits are calculated by the two-value wasteload 

allocation process as described on page 100 of the TSD (EPA, 1991) and shown 

below.

1. Calculate the acute wasteload allocation WLAa by multiplying the acute 

criteria by the acute dilution factor and subtracting the background concentration. Calculate 

the chronic wasteload allocation (WLAc) by multiplying the chronic criteria by the chronic 

dilution factor and subtracting the background concentration.

WLAa = (acute criteria × acute zone dilution factor) - (background concentration × (acute 

zone dilution factor - 1))

WLAc = (chronic criteria × chronic zone dilution factor) - (background concentration ×

(chronic zone dilution factor - 1))

2. Calculate the long term averages (LTAa and LTAc) which will comply with the wasteload 

allocations WLAa and WLAc.

LTAa = (WLAa)( e[0.5σ2 - zσ])

where:

σ2 = ln(CV2 + 1)

z = 2.326

TSDCALC

REASPOT

TSDCALC
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LTAc = (WLAc)( e(0.5σ2 - zσ))

where:

σ2 = ln[(CV2 + 4) + 1]

z = 2.326 

3. Use the smallest LTA of the LTAa or LTAc to calculate the maximum daily effluent limit 

and the monthly average effluent limit.

Maximum Daily Limit = MDL

where:

σ2 = ln[CV2 + 1]

z = 2.326 (99th percentile occurrence probability)

 LTAmin = smallest long term average (LTAa or LTAc) 

Average Monthly Limit = AML

where:

2 σ n = ln[(CV2 ÷ n) + 1]

n = number of samples/month 

z = 1.645 (95th percentile occurrence probability)

LTAmin = smallest long term average (LTAa or LTAc)

2 ( 0.5 )

min ( )( ) z MDL LTA e σ σ − =

2 ( 0.5 )

min ( )( ) n n z AML LTA e σ σ − =
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The numeric water quality standards and the dilution factors define wasteload allocations (WLA) 

for pollutants. The WLA's are numbers not to be exceeded in order to protect aquatic life. In the 

statistical world, however, there is no such thing as 100% certainty. Ecology uses an estimate of 

variability (coefficient of variation or CV) for these parameters in the effluent to define a 

distribution of values with a long term average (LTA) such that there is a one percent probability 

(0.01) of exceedance of the WLA. There are two long term averages defined for each parameter. 

One is for acute and one is for chronic. Effluent limits for each parameter are defined for the 

more limiting of the acute LTA or the chronic LTA. Effluent limits are control parameters to 

determine when a process is out of control. A process is deemed out of control when the 

extreme values are higher than expected (expressed as the daily maximum limit) or the average 

is higher than expected (expressed as the monthly average limit). The 95% percentile (0.05 

probability) used in calculating the average limit and the 99% percentile (0.01 probability) is 

used in calculating the daily maximum. These probabilities are the probability of determining 

the process is out of control when in fact the process is still in control.

The 95th percentile (0.05 probability) is used for calculating the average limit for the 

following reasons:

1. Exceedance of an average (average limit) indicates a more serious potential for 

environmental harm than exceedance of a daily maximum. Even so, the Department 

rarely enforces the occasional exceedance of monthly average limit. Typically, 

enforcement occurs after several consecutive violations of the monthly average limit or 

when both the daily maximum and the monthly average have been exceeded. This 

effectively reduces the probability of false noncompliance to something far less than 0.05.

2. The Department also uses the 95th percentile (0.05 probability) because this is a 

recommendation of EPA in the Technical Support Document.

3. The 95th percentile (0.05 probability) for monthly average was used for development of 

technology-based effluent limits when EPA developed the industrial effluent guidelines 

and secondary treatment standards.

The above formulas may also be used to derive performance-based limitations where the long 

term average (LTA) is the demonstrated performance and assuming the data is log normally 

distributed.
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3.3.9 Seasonal Effluent Limitations

The permit writer may elect to develop seasonal effluent limitations for a discharger, especially 

in those situations where meeting water quality-based effluent limitations has a high operational 

cost and there is a considerable difference of magnitude between the seasonal limits. Generally, 

seasonal effluent limitations are developed on a semi-annual or quarterly basis.

3.3.10 Dynamic Modeling

The use of dynamic modeling is an acceptable alternative to the static modeling discussed above 

in those situations where the discharger is willing to meet the data requirements and submit the 

analysis for approval. A discussion of the three main types of dynamic modeling techniques is 

given in the TSD (EPA 1991).

3.3.11 TMDL'S, WLA'S and 303(d) – Discharges to Impaired Waters

Discharges to impaired waters require additional consideration when issuing permits. The 

wasteload allocations (WLA's) which are used to derive effluent limits may be derived on an 

individual permit basis or they may be determined by a basin TMDL allocation.

In the absence of a basin TMDL and the resultant WLA, the permit writer must do an individual 

WLA.

The general principles of this section are:

1. A water body listed on the 303(d) list is not a presumption of impairment unless the listed 

section is the point of discharge.

2. A point source discharging to a water body with multiple sources (point and nonpoint) of 

impairment, which is a minor source of the impairment, and may gain relief from a 

TMDL is not required to have a final limitation as the numeric water quality criteria 

before a TMDL is completed.

No TMDL and No 303(d) Listing – Existing Discharge

Occasionally, the permit writer, in the course of renewing a permit, will have information that 

the receiving water concentration (background) at the point of discharge during critical condition 

does not meet the aquatic life or human health criteria and that the receiving water is not listed 

on the 303(d) list ( http://www.ecy.wa.gov/programs/wq/303d/index.html ).

The applicable federal regulations in this case are 40 CFR 122.44(d)(1)(i), (ii), (iii) and (vii).

In these cases, where the excursion is documented with data that meets the criteria for 303(d)

listing (see the 303(d) listing policy), the permit writer should develop interim effluent limits 

based on existing performance (no increase in loading) to be placed in the permit (see EPA 1991 

and Chapter IV of this Manual for development of limits based on existing performance). These 

interim limits are effective on the effective date of the permit. A final limit based on the water 
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quality criteria is calculated and placed in the permit (with a compliance schedule) if compliance 

is expected in the term of the permit. The compliance schedule must be as short as practicable 

and must include specified required actions that demonstrate reasonable progress toward 

attainment of the final limit or water quality criteria. The final limit is placed in the fact sheet if 

compliance with those limits is expected to exceed five years. If technology-based limits have 

not been established for the pollutant the permit must also cause the permittee to investigate the 

feasibility and reasonableness of meeting the final limit with technology and cost tests 

established for BCT or BAT. This is accomplished by requiring an engineering report completed 

in accordance with current Ecology guidance. In some cases, where the final limits are placed in 

the fact sheet, additional source control investigation may be productive and should be included 

in the permit.

At this point the permit writer should consider how the effluent pollutants would be permitted if 

the background was not exceeding the criteria. This analysis is for near-field pollutants. If an 

analysis of reasonable potential shows an exceedance of the numeric criteria with a background 

of zero (for human health pollutants), the effluent quality must be improved regardless of the 

outcome of the TMDL. For other chemical pollutants, use an expected reduction of 50% of 

observed background (this is probably more than can be achieved in a TMDL). A determination 

of reasonable potential in these cases requires a reduction of effluent pollutant concentration 

during the permit term. For temperature, the permit writer should target an effluent temperature 

that will meet a 0.3° C rise at the boundary of the chronic mixing zone. The two likely outcomes 

of a temperature TMDL are 1) that the natural condition exceeds the current numeric water 

quality criteria or 2) that with non-point controls in place there may be some small amount of 

dilution. In either case, a 0.3° C increase at the boundary of the mixing zone is a reasonable 

target. The permits in the situations described above should contain requirements for source 

control or evaluating treatment options to reduce the effluent pollutants regardless of the status of 

a TMDL.

Receiving water data received by the permit writer that meets the listing criteria should be given 

to the Watershed Management Section. This data must be in Storet or Ecology’s EIM format. 

The water body will subsequently then be listed on the 303(d) list and prioritized for a TMDL.

If the data on the excursion is likely to be valid but does not meet the 303(d) listing criteria, the 

permittee should be required, usually by compliance order, to investigate receiving water quality 

to determine if the receiving water exceeds water quality standards at the time of critical 

condition. A quality assurance plan (QAPP) must be prepared by the permittee and approved by 

Ecology. The final data must be suitable for entry into Storet or the Ecology EIM database. No 

interim limits are necessary in this situation, however, if technology-based limitations have not 

been explored for the pollutant, the order should also include the requirement for an engineering 

report on treatment options and costs (see Ecology engineering report guidance). If the receiving 

water study does show impairment, the decisions on final limits, interim limits and compliance 

schedules are the same as discussed above. Depending on the timing of the receipt of the data, 
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the permit may be modified or adjusted at the next renewal. If the data shows no impairment and 

dilution is available then reasonable potential analysis and effluent limits are developed as 

discussed elsewhere in this chapter. The data from the receiving water is given to the Watershed 

Section for 303(d) listing.

Figure VI-5. Discharges to water bodies not meeting standards but not yet listed on 303(d).

No TMDL – 303(d) Listed – Existing Discharge

It’s more likely that a permit writer will be renewing a permit and discover the receiving water 

body is on the 303(d) list. The applicable federal regulations in this case are the same as the 

previous case.

If the pollutant that caused the listing is not present in the discharge no limit is required.

If the pollutant is a far-field pollutant, is present in the discharge and is the subject of a TMDL in 

progress, the permit writer may defer any water quality-based limits on the pollutant until the 

TMDL is completed and a WLA is assigned. When the WLA is assigned the permit writer may 

modify the permit or incorporate the WLA at the next reissuance, depending on timing.
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If the pollutant is present in the discharge and the TMDL is not started the options are given 

below in Figure VI-6 and the text that follows.

IS LISTING DATA VALID (is 

water quality impaired) AT THE 

POINT AND TIME OF 

DISCHARGE?

REQUIRE 

RECEIVING WATER 

STUDY, MAY 

REQUIRE INTERIM 

LIMITS

DEVELOP 

EFFUENT LIMITS 

NORMALLY

CAN THE EFFLUENT BE TREATED OR 

CAN THE EFFLUENT OR POLLUTANT(S) 

BE REMOVED SEASONALLY AT A COST 

WHICH IS ECONOMICALLY ACHIEVABLE 

OR REASONABLE?

PERMIT HAS 

INTERIM LIMIT 

(NO ADDITIONAL 

LOADING) AND 

REQUIRES 

ENGINEERING 

REPORT ON 

OPTIONS AND 

COST

FINAL LIMITS AS 

THE WATER 

QUALITY 

CRITERIA OR 

LOWER, A 

COMPLIANCE 

SCHEDULE AS 

NECESSARY, AND 

INTERIM LIMITS 

BASED ON 

CURRENT 

DISCHARGE (NO 

ADDITIONAL LOADING)

ARE THERE OPTIONS FOR 

EFFLUENT TRADING OR 

MITIGATION BY TREATING 

UNCONTROLLED 

SOURCES?

PERMIT 

CONTAINS 

INTERIM LIMITS 

TO PREVENT 

INCREASE IN 

LOADING AND 

FINAL LIMITS IN 

FACT SHEET

PERMIT CONTAINS 

FINAL EFFLUENT 

LIMITS AS THE WATER 

QUALITY CRITERIA, A 

COMPLIANCE 

SCHEDULE TO 

ACCOMODATE 

TRADING AND 

MEETING FINAL 

LIMITS, AND INTERIM 

EFFLUENT LIMITS 

BASED ON CURRENT 

DISCHARGE

TMDL

COMPLETED

NO UNSURE

YES

DATA IS VALID 

(no dilution is 

available)

DATA NOT VALID 

(dilution is available)

YES

YES

NO

NO

UNSURE

Figure VI-6. Permitting discharges to a 303(d) listed waterbody with no TMDL. If an 

AKART analysis has not been completed for the pollutants at issue, decision boxes 1 

and 2 are conducted concurrently.

1

2

3
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Figure VI-6. (continued)

DOES THE TMDL PREDICT

ACHIEVEMENT OF THE WATER QUALITY

STANDARDS BY A SIGNIFICANT MARGIN

AFTER IMPLEMENTATION OF POINT

SOURCE AND NON-POINT SOURCE

CONTROLS AND/OR EFFLUENT

TRADING?

TMDL

COMPLETED

WASTELOAD

ALLOCATION

MAY INCLUDE

DILUTION

SEE WER, UAA, AND VARIANCE PROCESSES

YES

NO

Decision box 1 (Is Listing Data Valid?)– Non-conservative Pollutants.

The permit writer must make a judgment, based on the circumstances of the 303(d) data on how 

to proceed with the listed pollutant in the effluent. This judgment is influenced by the proximity 

of the listed section to the point of discharge. The judgment is also influenced by the type of 

pollutant and whether it is a conservative or non-conservative pollutant. Non-conservative 

pollutants are pollutants that degrade in the receiving water. Some typical non-conservative 

pollutants are BOD, ammonia nitrogen, and fecal coliform.

If the discharge is to a listed section, the receiving water is impaired. If the listing is for one 

station at some distance from the point of discharge then there may be some uncertainty about 

the water quality at the point of discharge for non-conservative pollutants. If there are station 

listings above and below the point of discharge or one station close to the point of discharge then 

there is more certainty that the water quality does not meet the criteria at the point of discharge. 

Another judgment must be made regarding the degradation rate of the pollutant in relation to the 

point of discharge and the listing station(s). Some volatile pollutants may degrade in a matter of 

hours in a turbulent river but others such as BOD may not reach full effect on dissolved oxygen 

until several days travel time down-river. A permit writer who is unsure of the dynamics of the 

water quality at the point of discharge may wish to consult with someone in the EA Program.
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Decision box 1 (Is Listing Data Valid?)– Conservative Pollutants

Conservative pollutants do not degrade in the receiving water, however, they may change form 

or their media association. Metals are a common conservative pollutant. They may be in a 

bound or dissolved form in the water column or go to the sediments. The decision-making 

process is much the same as for non-conservative pollutants except that if the listing station is 

downstream of the discharge, the effluent is assumed to be contributing to the impairment.

A factor of uncertainty with metals is the correctness of the data if the receiving water or effluent 

data wasn’t collected using ultra-clean sampling and analysis. In this case, the concentrations of 

metals in the receiving water and the effluent should be confirmed using clean sampling and 

analytical techniques.

Decision box 1 (Is Listing Data Valid?)– Human Health Pollutants

The listing for human health pollutants may be made on the basis of water column concentration 

or on the basis of fish tissue analysis. If the listing is on the basis of resident fish tissue 

concentration above or below the point of discharge assume the effluent is contributing to the 

impairment (assuming the pollutant is present in the effluent). If the listing is on the basis of 

water column concentration the decision criteria given above for other pollutants are applicable.

Decision box 1 (Is Listing Data Valid?) - Water Quality Studies

If there is some uncertainty about the conditions at the point of discharge and whether dilution is 

available, the permit writer may require a receiving water study. A water quality-based effluent 

limit is not always required in the permit that requires the study (see the following discussion on 

timing), but an effluent limit based on demonstrated performance should be placed in the permit. 

This limits the discharger to their current loading until the uncertainty about the receiving water 

condition is resolved.

Permit conditions which require receiving water studies should require that the study plan be 

submitted as a QAPP to be approved by Ecology before the study proceeds. The permit should 

require the data from the study be submitted in a Storet format. The permit should also require 

that the critical conditions be determined for the 10 year critical condition. This can be done for 

some parameters by correlating the site data to a long-term monitoring station. For other 

parameters where long-term data is not available, the techniques for estimating 90th (or 10th) 

percentile values from a small data set are given in appendix 6.

If receiving water data indicates there is no dilution available for part or all of the year, then 

other options can be explored as indicated on the flow chart. If no dilution is available, however, 

a final effluent limitation of the criteria concentration (amount) is placed in the permit if 

compliance is expected within five years. The final limit is placed in the fact sheet if compliance 

is longer than five years and an interim limit based on existing performance is placed in the 

permit. A compliance schedule may be authorized for meeting the final limit but it must be as 

short as possible and must require demonstration of reasonable progress toward meeting the 
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water quality criteria or final limit.

Decision box 2. Once the water quality impairment is confirmed or verified the following 

principle is in effect:

• There can be no additional loading or higher concentration allowed for the listed pollutants at 

times of impairment until the TMDL is completed and it shows dilution available at full 

implementation of the TMDL.

Ceasing discharge to surface waters may be an option for some small dischargers especially for 

summer discharges with high temperatures and low dilution. Other options include using the 

wastewater for irrigation or simply storing the wastewater. In some cases there may be 

opportunities for seasonal pollutant removal. These options are explored in an engineering 

report required as part of the compliance schedule if these options were not originally explored 

in the AKART analysis. If seasonal removal appears feasible for a facility, the final effluent 

limit should be either:

• the water quality criteria or 

• no discharge during critical period.

The final limit is placed in the permit, if achievable in five years, or in the fact sheet, if a longer 

period is required for compliance. If longer than five years, an interim limit, based on existing 

performance, is placed in the permit. For some pollutants, treatment may be available that is 

within the financial capability of the facility. If the treatment option is used the permit should 

contain a final effluent limitation of the criteria concentration (amount) and an interim limit 

based on existing performance or a compliance schedule to meet final limitations.

Decision box 3. For some limited number of pollutants and discharges there may be some 

options for pollutant trading in which a discharger would pay some upstream point source or 

non-point source for treatment in order to gain some allowable dilution at the dischargers 

location. If this option is used, the permit should contain a final effluent limitation of the criteria 

concentration (amount) and an interim limit based on existing performance or a compliance 

schedule to meet final limitations. If this option is considered, there must be available data on 

the upstream source that would be used for the trade. This option is administratively very time 

consuming.

Timing for Decision Boxes 1, 2, and 3. The permit language requiring examination of the 

options in boxes 1, 2, and 3 in Figure VI-6 may be sequential within one permit term depending 

on the size and priority of the discharge. For example, a permit for a large industrial source 

which is being required to do a water quality study in the initial years of the permit, should also 

require an engineering report for treatment options in the later years of the permit if the studies 

show violations of water quality standards. In other cases, such as small municipalities, which 

may require several years to fund a water quality study, the initial permit may only require the 

water quality study. The next permit would then require the engineering report.
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New Discharges To Listed Water Bodies

No TMDL

The applicable regulation is 122.4(i)

Section 122.4 Prohibitions. No permit may be issued: 

i) To a new source or a new discharger, if the discharge from its construction or operation will 

cause or contribute to the violation of water quality standards. ...

A new discharge to a listed water body can not be allowed (issuance of permit is prohibited) if 

the discharge will cause or contribute to a violation of water quality standards. A new discharge 

may be allowed to discharge at the water quality criteria (for those pollutants with criteria) or at 

the quantitation level for those pollutants without criteria, such as BOD.

A permit applicant may be allowed to demonstrate that the listed water body has the ability to 

accept additional loading at the proposed point of discharge without measurable impairment or 

measurable increased impairment to the water body.

In some cases a new discharger may be allowed to discharge listed pollutants by trading effluent 

reduction (effluent trading) or discharging seasonally. Effluent trading may entail treating a 

previously untreated but quantified pollutant source, such as a stormwater outfall such that the 

net effect of the new discharge is zero. Water reuse is encouraged by Ecology and it may be a 

good option for new dischargers to avoid discharge during the critical condition, typically the 

low flow period.

TMDL Completed

The applicable regulation is 122.4(i)

...The owner or operator of a new source or new discharger proposing to discharge into a water 

segment which does not meet applicable water quality standards or is not expected to meet those 

standards even after the application of the effluent limitations required by sections 301(b)(1)(A) 

(BPT) and 301(b)(1)(B) (Secondary treatment) of CWA, and for which the State or interstate 

agency has performed a pollutants load allocation for the pollutant to be discharged, must 

demonstrate, before the close of the public comment period, that: (1) There are sufficient 

remaining pollutant load allocations to allow for the discharge; and (2) The existing dischargers 

into that segment are subject to compliance schedules designed to bring the segment into 

compliance with applicable water quality standards. The Director may waive the submission of 

information by the new source or new discharger required by paragraph (i) of this section if the 

Director determines that the Director already has adequate information to evaluate the request. 

An explanation of the development of limitations to meet the criteria of this paragraph (i)(2) is to 

be included in the fact sheet to the permit under Section 124.56(b)(1) of this chapter.

A new source or new discharger proposing to discharge to a listed water body for which a 

TMDL has been completed and WLA’s assigned may obtain a permit for discharge into a water 
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segment which does not meet applicable water quality standards by submitting information 

demonstrating that there is sufficient loading capacity remaining in the waste load allocations for 

the stream segment to accommodate the new discharge and that existing dischargers to that 

segment are subject to compliance schedules designed to bring the segment into compliance with 

the applicable water quality standards.

General Permits

General permits are issued under the same laws and regulations as individual permits but 

Ecology is unable to invest the time necessary to make the site-specific decisions regarding the 

water quality at the point of discharge for the large number of permittees wanting coverage under 

general permits. Existing discharges to impaired waters will receive the same limitations as 

dischargers to non-impaired waters. The permit coverages should include monitoring for the 

impairment pollutant for use in the TMDL. The application for coverage under the General 

Permit for new facilities will ask if the discharge is to a listed water body and will provide 

information for the applicant to determine if they will be discharging to a listed water body. 

When possible, the pollutants specific to the type of discharge covered by the general permit will 

be identified in the permit application materials. If the permit applicant indicates they will be 

discharging a named pollutant to listed water body at or near the impaired section, the applicant 

may receive an individual permit or special limits in the permit coverage.

TMDL Completed

If the TMDL has been completed at the location, the steps for compliance may be similar to 

those given above especially when the WLA doesn’t allow for any significant dilution. The 

permit may contain a compliance schedule if necessary to meet a WLA.

Natural Conditions

A determination that natural conditions in a water body exceeded water quality standards can 

only be made from: 1) data from the water body prior to any human disturbance in the 

watershed, 2) correlation of the water body to a nearby undisturbed water body, or 3) a model of 

the water body and watershed.

In some cases the permittee or applicant may try to demonstrate that conditions in the water body

were not meeting standards before the addition of wastewater and therefore are natural 

conditions or natural background levels. Natural conditions are defined in the Water Quality 

Standards as the surface water quality that was present before any human-caused pollution 

(WAC 173-201A-020). Human-caused pollution includes non-point sources such as timber 

harvesting and farming. Therefore, unless data is available from the watershed before there was 

any human disturbance or from a nearby less disturbed watershed showing exceedance of 

standards, a determination of natural conditions should not be made by the permit writer. An 

estimate of natural conditions can be made by modeling. This may be developed as part of a 

TMDL or may be conducted by Permittees using methods approved by Ecology.
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3.3.12. EFFLUENT LIMITS

Derive effluent limits for those pollutants that are determined to have a reasonable potential (to 

violate the water quality standards). Effluent limits are also derived using the criteria as total 

recoverable. The process for deriving limits was described earlier and the calculations are 

available in spreadsheets. Figure VI-7 illustrates the process of compliance.

3.3.13. COMPLIANCE SCHEDULES

If an existing permittee can not immediately comply with the water quality-based effluent limits 

the permit writer may allow a compliance schedule with interim limits. The interim limits and 

compliance schedule are placed in the permit. The interim limits may be based on existing 

performance and calculated by using PERFORMLIM in TSDCALC.XLW.

If the schedule for permit issuance schedule allows, the permit writer may request the permittee 

to do the following analysis on a voluntary basis as a part of the permit application.

The compliance schedule will direct the permittee to do ultra-clean sampling and analysis of 

effluent and receiving water. The guidance for ultra-clean sampling and analysis is available 

from EPA (1995). The receiving water sampling is necessary because historic data on metals 

may be biased on the high side. For industrial dischargers and municipal dischargers that receive 

industrial wastewater, the compliance schedule should also require a determination of the source 

of the metals and opportunities for reduction.

The ultra-clean analysis of effluent and receiving water and any source reduction may result in 

lower concentrations of metals. If this results in a determination of no "reasonable potential", 

then the effluent limits and interim limits may be removed from the permit by permit 

modification. This will not violate the anti-backsliding provision of the Clean Water Act 

because this constitutes new information which if available at the time of permit issuance would 

have caused a different action (no limits).

3.3.15. LARGER MIXING ZONES

If the permittee cannot meet the final effluent limits then the permittee may request an exception 

to the mixing zone size as allowed and conditioned by WAC 173-201A-400(12),(13), and (14).

The permittee may also conduct a Use Attainability Analysis to demonstrate the classification for 

the water body is inappropriate. This option will require a set of studies to demonstrate the 

natural potential of the water body to support beneficial uses and the ability of the point and 

nonpoint source dischargers to control pollutants to those waters. It is unlikely that a single 

discharger would elect to conduct this type of analysis.
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3.3.16 INTERIM INTERPRETATION OF WATER QUALITY STANDARDS 

FOR EXISTING MUNICIPAL DISCHARGES (less than 0.5 MGD) TO 

INTERMITTENT STREAMS 

Section 1 of this chapter discussed the use-based water quality standards that were adopted in 

2006. Numeric criteria are associated with the designated uses for each water body. In most 

cases, waters receive the same designated uses as it is downstream receiving stream, regardless if 

it is shown on the map application. To view the designates uses and link to the numeric criteria 

use one of the applications available through this web site: 

http://aww.ecology/programs/wq/swqs/map-apps.html

At this time, the WQ Standards do not address the “permanency” of streams, such as perennial 

intermittent or ephemeral. If a stream is isolated (does not contribute water to another stream) it 

would receive a Salmonid Spawning and Rearing Use.

Facility managers should evaluate the impacts of a municipal effluent upon the characteristic 

uses of a stream and its water volume, including seasonal fluctuations. The impacts are 

compared to the beneficial effects of the effluent going to a stream reach that would otherwise be 

dry. In order to protect characteristic uses associated with streams during flow and non-flow 

periods, and to provide small municipal dischargers with options for treatment and disposal, the 

facility manager should require the facility to evaluate the following alternatives treatment 

options.

1. A treatment/disposal system that meets all numeric criteria and characteristic uses for the 

receiving water body. This may require removal of the discharge from the stream either 

seasonally or completely.

2. A treatment/disposal system that protects the characteristic uses in the stream during seasonal 

fluctuations, including nonflow periods. This option requires the evaluation of treatment 

technology commonly available which exceeds secondary treatment and which produces the 

following effluent quality (as monthly averages):

BOD and TSS - 15 mg/l

Total Ammonia - 1 mg/l

if costs for achieving 1 mg/l are disproportionate to costs for achieving BOD and TSS Ecology 

may allow total ammonia average of 2 mg/l.

If Chlorine is used for disinfection, dechlorination is required. The facility should evaluate other

disinfection methods.

If treatment option 2 is chosen, the discharge should be modeled or instream sampling required

of the facility to demonstrate that all numeric criteria are met at the point of perennial flow.
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EFFLUENT 

LIMITS

Figure VI-7. Compliance with water quality-based effluent limits

CAN PERMITTEE COMPLY 

WITH THE LIMITS?

ISSUE PERMIT WITH NO 

COMPLIANCE SCHEDULE

DOES BETTER DATA SHOW LOWER 

EFFLUENT CONCENTRATIONS OR 

RESULT IN A NO REASONABLE 

POTENTIAL DETERMINATION?

ISSUE PERMIT WITH COMPLIANCE 

SCHEDULE OR IF TIME PERMITS 

REQUIRE ADDITIONAL ANALYSIS 

BEFORE ISSUING THE PERMIT

PERMITTEE IS ABLE 

TO COMPLY WITH 

LIMITS OR PERMIT 

IS MODIFIED TO 

REMOVE LIMIT

PERMITTEE MAY REQUEST A LARGER MIXING ZONE

NO

YES

NO

YES

3.3.17. Flow Adjusted Effluent Limits

Typically, effluent limits are derived using a static model at the time of critical condition 

(discussed elsewhere in this Chapter). Critical condition is typically at time of low flow because 

of the reduced dilution. Many people have considered that limits derived from a static model 

were more conservative than those from a dynamic model or a Monte Carlo simulation. The 

static model was considered conservative because of the many probability factors or design 

conditions considered in deriving limits. These probabilities for an industrial discharge to 

freshwater are given in Table VI-4 below.
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Table VI-4. Statistical probabilities in static model effluent limits.

Design Parameter Design Condition

Probability of Occurrence 

or exceedance

Effluent Flow (Acute) Highest daily maximum effluent flow 

for past 3 years

1 day in 1080 days (assuming 

daily effluent monitoring)

Effluent Flow 

(Chronic)

Highest monthly average effluent 

flow for the past three years. 1 month in 36 months

Receiving Water Flow 

(Fresh Water)

Typically 7Q10 low flow.

(7 day average daily low flow with an 

expected return period of 10 years 

based on historical record)

1 year in 10 (as a 7 day 

average). Flows with a 

smaller averaging period will 

occur more frequently.

Acute Criteria 

(metals)

One hour exposure concentration not 

to be exceeded more than once in 

three years

Chronic Criteria 

(metals)

Four day exposure concentration not 

to be exceeded more than once in 

three years

Effluent 

Concentration 95th percentile 5% for period of data collection

Receiving Water 

Concentration 90th percentile 10% for period of data collection

Waste Load 

Allocation

Water Quality Criteria times the 

dilution factor or from TMDL

Long Term Averages 

(Acute and Chronic) Based on WLA and CV 1% exceedance of WLA (Water Quality Criteria)

Daily Maximum 

Effluent Limit Based on limiting LTA Type 1* error = 1%Type II error = ?

Monthly Average 

Effluent Limit Based on limiting LTA

Type I error = 5%

Type II error ≈ 20% with 

d=0.2 and CV = 0.6

* Type I error in this case is the probability that the facility will violate the limit but actually be in compliance with 

the expected long term average. Type II error is the probability that the facility will be meeting effluent limits but 

not meeting the expected long term average.

The derivation of effluent limits is typically done by static modeling for conditions existing at 

the time of critical condition. Critical condition is usually at times of low flow because the 

amount of dilution is lowest at that time.

Some elements of the process of deriving water quality-based effluent limits by the static process 

are conservative (cause effluent limits to go down) while other are liberal (cause effluent limits 

to increase) and some people have argued that the combination of extreme probabilities causes 
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unnecessary conservatism. On the other hand, many toxic water quality criteria are expressed as 

one hour or four day exposure and our typical definition of critical flow is a seven day average 

low flow. In addition, effluent monitoring for toxic pollutants is typically weekly or monthly 

and is rarely conducted on an hourly basis.

Alternates to the static model are the dynamic models as discussed in the TSD (1991). These 

models require large amounts of data to model properly. It had been assumed that dynamic 

models more accurately predicted water quality conditions and did not compound probabilities. 

It was also assumed that effluent limits derived from dynamic models would be higher than if 

derived from a static model, however, a paper (Dilks and Pendergast 2000) demonstrated that 

limits from static models are generally higher.

Some permittees have requested effluent limits which would vary based on the amount of flow 

and subsequent dilution occurring at the point of discharge. These permittees have the ability to 

modify their flow or pollutant loading within a short time period. There are two major 

difficulties with these types of flow-based limits. One problem is simply the administrative 

problem of trying to keep track of the effluent limits so as to assess compliance. Any flexible 

process for formulating effluent limits increases the difficulty of measuring compliance. 

Difficulty with measuring compliance means difficulty assuring compliance with the water 

quality standards and enforcing the provisions of the permit.

The second difficulty with flow based limits is maintaining the margin of safety. With the static 

model, it is assumed that the combination of probabilities described above would result in a 

probability of violating the water quality standards in any given year during the critical period to 

be 10% or less. When effluent limits are based on the existing receiving water flows (and 

resulting dilution factor) there is no margin of safety.

Options for Flow Based Limits

Case 1. Continuously Variable – Continuously variable limits, if allowed, would only be 

applicable for a very small group of dischargers who are able to vary production on a short term 

basis. In this case effluent limits would be fixed to the data produced by a nearby hydrograph on 

the receiving water. The margin of safety would have to be explicitly set at 10% by reducing the 

calculated limit or dilution factor by 10%. This case would be virtually impossible to track for 

compliance because effluent limits, calculated on a daily basis, would have to be entered 

individually into the data base. In consideration of the limited applicability of this case and the 

impossible data management, Ecology will not consider continuously variable effluent limits.

Case 2. Step Variable – In this case effluent limits are increased or decreased in a stepwise 

manner as actual river flows increase or decrease respectively. This option affords flexibility but 

reduces the administrative burden if the number of increments is limited. The margin of safety 

can be set explicitly at 10% or by introducing a one step lag. This option is not feasible on an 

individual basis because of the difficulty of developing limits that retain a margin of safety with 

a falling hydrograph (Figure VI-8).
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Case 3. Seasonally Variable Limits based on historical flows or predicted flows.- In this case (a 

variation of stepped limits) the seasonal effluent limits are based on a seasonal flow with a return 

frequency adjusted to give an annual probability of exceedance of 10%. For example, for two 

season limits the 7Q20 flows would be determined for each season and used for determining the 

effluent limits. For three season limits the 7Q38 flows would be determined for each season and 

for quarterly limits the 7Q114 flows would be determined for each season. Determining these 

flows requires a good historical record of flows for the water body to accurately predict these 

flows. In reviewing cases where seasonal effluent limits have been proposed, it’s apparent that 

there is little difference between 3-season limits and 4-season limits.

In some cases, the seasonal high and low flows are predicted from snow pack measurements. 

These are primarily for hydropower management, however, they could be used for determining 

seasonal effluent limits for the water year. The margin of safety is adjusted on the basis of the 

historical error rate of predicted flows to actual observed flows to an annual 10% probability of 

exceedance.

Case 4. Seasonal Removal of Effluent - In some cases there will not be any assimilative capacity 

in the receiving water at low flows. In this case the only option (other than administrative) is to 

remove the effluent by land applying, reusing or storing the effluent. The margin of safety is 

applied by selection of the dates of removing and re-discharging the effluent. The dates should 

be chosen such that the annual probability of exceeding the water quality standards is 10% or 

less.

Considerations for flow adjusted limits

Permit writers who are considering flow-adjusted limits need to take into account the fluctuation 

in other variables that affect the compliance with water quality standards. For example, the 

dilution factor and background pollutant concentration will typically change seasonally and may 

be higher or lower than low flow measurements depending upon the specific water body.
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TIME

TIME

TIME

MAGNITUDE

FLOW

EFFLUENT LIMIT

X

X

X

X

X SEASONAL

 EFFLUENT LIMIT

FLOW

X

X

X

X

X

X

FLOW

x EFFLUENT LIMIT

CASE 1

CASE 2

CASE 3

MAGNITUDE MAGNITUDE

Figure VI-8. Flow-based effluent limitations
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Hardness, pH, and temperature which affect the numeric criteria for some metals and ammonia 

will also vary seasonally and must be accounted for in setting limits. The information on these 

variables should be developed by the permittee. The permit writer should also consider the 

difficulty of accounting for upstream dischargers if there are multiple dischargers to a reach. 

Where conditions become too complex to authorize flow adjusted limitations, the permit writer

should consider doing static water quality-based limits and authorizing a compliance schedule to 

incorporate the time necessary to do the TMDL.

4. ANALYTICAL LEVELS

This part discusses detection and quantitation levels and outlines an approach to assess 

compliance with water quality standards and with effluent limits that are near or below the levels 

of quantitation. The approach is primarily for organic and metal pollutants where criteria and 

effluent limits may be very low. Chemical-specific concentration levels that can be used for 

compliance assessment are presented, as well as guidance on how to tailor those levels to fit 

regulatory concerns regarding the possible impacts of the discharge. Compliance levels are 

expected to change over time as analytical methods improve and as we gather more data on 

laboratory performance.

The permit writer should require EPA Methods as given in Part 136 and specify the specific 

method to achieve detection and quantitation levels for permit application or permit compliance 

monitoring.

4.1 Introduction

Effluent limits based on water quality criteria may be set at very low concentrations (in the range 

of parts per billion to parts per quadrillion). Laboratory analytical methods approved for use in 

the NPDES program are often not capable of measuring chemical concentrations at the 

concentrations of the permit limits. In many cases we are unable to determine if pollutants 

contained in discharges are at concentrations that merit concern, and when we set an effluent 

limit, we are often unable to determine if that limit is being exceeded.

Historically, the method detection limit (MDL) was used to determine compliance (all data at 

or above the MDL were considered adequate for assessing compliance and supporting 

enforcement actions). The MDL, however, is the level at which a chemical's presence or absence 

can be detected, and provides limited information with regard to actual concentration. The low 

concentrations of many of the aquatic life-based and human health-based criteria have made the 

issue of quantitation important to both the regulator and the discharger. This section uses the 

term “quantitation level” as equivalent to the term “minimum level of quantitation (ML)” 

which is used by EPA. The ML is defined by EPA as the lowest concentration of an analyte that 
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can be measured with a defined level of confidence (see further discussion below). This may 

also be called the reporting level by some laboratories.

Historically, analytical results of wastewater effluent testing were only used only to demonstrate 

compliance with effluent limits. The analytical results are now being used to determine loading 

of pollutants to receiving waters and compliance with human health criteria. This requires the 

use of lower detection and quantitation levels.

4.2 Background Information

Two types of analytical levels are in common use. The first type is the Method Detection Limit 

(MDL) or Detection Level which is defined as the minimum concentration of a substance that 

can be measured and reported with 99% confidence that the analyte concentration is greater than 

zero and is determined from analysis of a sample in a given matrix containing the analyte. This 

may be called the Instrument Detection Level (IDL) for some analyses. The Quantification 

Level (QL) or Minimum Level is defined as the practical quantitation level (PQL) in Ecology's 

groundwater quality standards. Another type of quantitation level commonly used is the 

Contract Required Quantitation Levels (CRQLs) listed in the EPA Contract Laboratory Program 

(CLP). The CRQLs are a list used historically in EPA's groundwater and waste programs for 

laboratory contracts, and have been routinely used to measure concentrations at waste sites. The 

advantage of these levels is that numerous laboratories throughout the country provide the 

services, but the levels specified are not always based on the use of the most sensitive analytical 

test methods that EPA has approved for the NPDES permitting program. Both quantitation types 

have advantages in a regulatory program. Using the Method Detection Limit times a safety 

factor is straight forward and easy to understand, and is widely used in many regulatory 

programs throughout the country. The CLP values are also well known to the regulatory 

community, and are attainable for most labs. However, with each quantitation type, certain 

regulatory issues can increase or decrease the cost of the compliance monitoring program for 

dischargers and regulators.

The minimum level of quantitation (ML) has not been formally defined except as a component 

of the specific analytical method. EPA has proposed adopting a definition and procedure for 

defining a ML (FR 3/12/2003). The text of the proposal is reprinted below. EPA also convened 

an advisory committee on this issue. A committee report is available (Report of the Federal 

Advisory Committee on Detection and Quantitation Approaches and Uses in Clean Water Act 

Programs, December 2007).
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The definition of ML as proposed by EPA in the text above is still controversial among chemists, 

including some chemists within Ecology.
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4.3 Implementation - NPDES and State Permits

An analytical result below the MDL means there can be no judgment regarding the presence of 

analyte in the sample. The actual concentration may fall from 0 to just below the detection level. 

Given this uncertainty, single analytical results below the MDL may be treated as 0. A few 

measurements below the MDL may be set equal to half of the detection level to calculate an

average if the data set also contains measurements above the QL.

An analytical result that falls between the MDL and the QL means there is a level of certainty

that the analyte is in the sample. The actual concentration may lie anywhere between the MDL 

and the QL. These values may be reported by the laboratory but are accompanied by a qualifier. 

Ecology’s Manchester Laboratory uses a J qualifier in this case. A value falling between the 

MDL and the QL may be used for calculating averages (daily maximum and monthly average) 

but should not be used for enforcing the daily maximum if the daily maximum value consists of 

a single daily analysis.

All analytical result above the QL may be used as valid single values for assessing compliance 

with the daily maximum and for use in the monthly averages.

The objective in wastewater characterization (permit application) is to quantify at or below 

criteria levels.

4.4 Choosing a Quantitation Level

Table VI-5 below lists the detection and quantitation levels recommended by Ecology for 

wastewater analysis in permitting. These should be used for application and permit requirements 

unless the Ecology laboratory advises differently for a particular pollutant.

Effluent matrices (interfering substances) may affect the MDL of an analysis. If a discharger 

cannot provide a required Method Detection Limit or quantitation level because the matrix of 

their particular effluent causes interferences with the analysis, the discharger also could face noncompliance because of inability to provide a quantitation level required in a permit. This 

situation can be addressed by allowing the discharger to develop a matrix-specific quantitation 

level. If a discharger suspects that the quantitation level cannot be attained in its effluent 

because of matrix effects (e.g., high salinity), the discharger could run a laboratory spike of their 

sample matrix along-side an unspiked sample. If the recovery in the laboratory spike is poor, the 

discharger may need to develop an effluent specific MDL and quantitation level. Based on data 

from Wisconsin and communication with the State of New York, matrix effects are not a 

common problem, however, dischargers should be allowed time schedules in permits to provide 

required quantitation levels if local labs cannot provide them, and should be allowed to develop 

matrix specific quantitation levels if their effluent matrices cause analytical interference. In 
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order to qualify for development of a matrix specific quantitation level, the discharger must show 

that it is matrix effects, and not lack of a laboratory's ability to perform a method, that is 

affecting the MDL. This demonstration can be made by providing laboratory performance data 

showing all information needed to calculate the needed MDL, as defined in 40 CFR 136. All 

sample measurements and supporting QA/QC data should be submitted to Ecology.

Metals. Method detection limits have not been developed for metals. Instead, instrument 

detection limits (IDLs) are available for each method. The method detection levels for metals 

listed in Table VI-5 are typically given as IDLs in 40 CFR Part 136. The quantitation levels for 

metals were estimated by multiplying the IDL by a factor of 4.

Organics - The quantitation levels recommended here should prove attainable by most 

dischargers, and protective of most surface waters. Those dischargers unable to attain the 

recommended QLs may be allowed to develop matrix specific quantitation levels or given time 

schedules to attain appropriate laboratory services.

The approach outlined above will (1) reduce the uncertainty dischargers are faced with if data 

below quantitation levels were used to assess compliance, (2) provide dischargers with schedules 

to provide laboratory services and the ability to determine matrix specific effects from their 

effluents, (3) promote high quality laboratory services in a reasonable time frame, (4) provide the 

agency with data reasonable to use in enforcement, and (5) provide receiving waters with 

protection by specifying the best approved methods for measuring compliance. 
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Table VI- 5. Methods, detection and quantitation levels recommended for effluent characterization and 

effluent monitoring. This list includes EPA-required pollutants (priority pollutants) and some ecology 

priority toxic chemicals (PBTs).

The following table with analytical levels is to be used as guidance for effluent characterization in NPDES 

new permit applications and applications for permit renewal. The table should also be used as a guide for 

routine effluent monitoring. This table contains values which have been shown to be consistent for 

wastewater analysis and may be slightly higher or lower than published values in 40 CFR Part 136. The 

objectives are to reduce the number of analytical “non-detects” in applications and monitoring reports and to 

measure effluent concentrations near or below criteria values where possible at a reasonable cost. If an 

applicant or Permittee knows that an alternate method from 40 CFR Part 136 is sufficient to produce 

measureable results in their effluent, that method may be used for analysis.

Chemical name in bold denotes a State of Washington priority pollutant. (Table October 2011)

Pollutant & CAS No. (if available)

Recommended 

Analytical 

Protocol

Detection 

(DL)1

μg/L unless 

specified

Quantitation

Level (QL) 2

μg/L unless 

specified

CONVENTIONALS

Biochemical Oxygen Demand SM5210-B 2 mg/L

Chemical Oxygen Demand SM5220-D 10 mg/L

Total Organic Carbon SM5310-B/C/D 1 mg/L

Total Suspended Solids SM2540-D 5 mg/L

Total Ammonia (as N) SM4500-NH3-

GH

0.3 mg/L

Flow Calibrated device

Dissolved oxygen 4500-OC/OG 0.2 mg/L

Temperature (max. 7-day avg.) Analog recorder 

or Use microrecording devices 

known as 

thermistors

0.2o C

pH SM4500-H+ B N/A N/A

NONCONVENTIONALS

Total Alkalinity SM2320-B 5 mg/L as 

CaCo3

Chlorine, Total Residual 4500 Cl G 50.0

Color SM2120 B/C/E 10 color unit

Fecal Coliform SM 

9221D/E,9222

N/A N/A

Fluoride (16984-48-8) SM4500-F E 25 100
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Pollutant & CAS No. (if available)

Recommended 

Analytical 

Protocol

Detection 

(DL)1

μg/L unless 

specified

Quantitation

Level (QL) 2

μg/L unless 

specified

Nitrate-Nitrite (as N) 4500-NO3- E/F/H 100

Nitrogen, Total Kjeldahl (as N) 4500-NH3-

C/E/FG

300

Soluble Reactive Phosphorus ( as P) 4500- PE/PF 3 10

Phosphorus, Total (as P) 4500-PE/PF and 

SM4500-PE/PF

3 10

Oil and Grease (HEM) 1664A 1,400 5,000

Salinity SM2520-B 3 PSS

Settleable Solids SM2540 -F 100

Sulfate (as mg/L SO4) SM4110-B 200

Sulfide (as mg/L S) 4500-S2F/D/E/G 200

Sulfite (as mg/L SO3) SM4500-SO3B 2000

Total dissolved solids SM2540 C 20 mg/L

Total Hardness 2340B 200 as CaCO3

Aluminum, Total (7429-90-5) 200.8 2.0 10

Barium Total (7440-39-3) 200.8 0.5 2.0

BTEX (benzene +toluene + 

ethylbenzene + m,o,p xylenes)

EPA SW 846 

8021/8260

1 2

Boron Total (7440-42-8) 200.8 2.0 10.0

Cobalt, Total (7440-48-4) 200.8 0.05 0.25

Iron, Total (7439-89-6) 200.7 12.5 50

Magnesium, Total (7439-95-4) 200.7 10 50

Molybdenum, Total (7439-98-7) 200.8 0.1 0.5

Manganese, Total (7439-96-5) 200.8 0.1 0.5

NWTPH Dx4 Ecology NWTPH 

Dx

250 250

NWTPH Gx5 Ecology NWTPH 

Gx

250 250

Tin, Total (7440-31-5) 200.8 0.3 1.5

METALS, CYANIDE & TOTAL PHENOLS

Antimony, Total (7440-36-0) 200.8 0.3 1.0

Arsenic, Total (7440-38-2) 200.8 0.1 0.5

Beryllium, Total (7440-41-7) 200.8 0.1 0.5

Cadmium, Total (7440-43-9) 200.8 0.05 0.25

Chromium (hex) dissolved (18540-

29-9)

SM3500-Cr EC 0.3 1.2

Chromium, Total (7440-47-3) 200.8 0.2 1.0

Copper, Total (7440-50-8) 200.8 0.4 2.0
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Pollutant & CAS No. (if available)

Recommended 

Analytical 

Protocol

Detection 

(DL)1

μg/L unless 

specified

Quantitation

Level (QL) 2

μg/L unless 

specified

Lead, Total (7439-92-1) 200.8 0.1 0.5

Mercury, Total (7439-97-6) 1631E 0.0002 0.0005

Nickel, Total (7440-02-0) 200.8 0.1 0.5

Selenium, Total (7782-49-2) 200.8 1.0 1.0

Silver, Total (7440-22-4) 200.8 0.04 0.2

Thallium, Total (7440-28-0) 200.8 0.09 0.36

Zinc, Total (7440-66-6) 200.8 0.5 2.5

Cyanide, Total (57-12-5) 335.4 2 10

Cyanide, Weak Acid Dissociable SM4500-CN I 2 10

Cyanide, Free Amenable to 

Chlorination (Available Cyanide)

SM4500-CN G 5 10

Phenols, Total EPA 420.1 50

DIOXIN

2,3,7,8-Tetra-Chlorodibenzo-P-Dioxin 

(176-40-16)

1613B 1.3 pg/L 5 pg/L

VOLATILE COMPOUNDS

Acrolein (107-02-8) 624 5 10

Acrylonitrile (107-13-1) 624 1.0 2.0

Benzene (71-43-2) 624 1.0 2.0

Bromoform (75-25-2) 624 1.0 2.0

Carbon tetrachloride (56-23-5) 624/601 or 

SM6230B

1.0 2.0

Chlorobenzene (108-90-7) 624 1.0 2.0

Chloroethane (75-00-3) 624/601 1.0 2.0

2-Chloroethylvinyl Ether (110-75-8) 624 1.0 2.0

Chloroform (67-66-3) 624 or SM6210B 1.0 2.0

Dibromochloromethane (124-48-1) 624 1.0 2.0

1,2-Dichlorobenzene (95-50-1) 624 1.9 7.6

1,3-Dichlorobenzene (541-73-1) 624 1.9 7.6

1,4-Dichlorobenzene (106-46-7) 624 4.4 17.6

Dichlorobromomethane (75-27-4) 624 1.0 2.0

1,1-Dichloroethane (75-34-3) 624 1.0 2.0

1,2-Dichloroethane (107-06-2) 624 1.0 2.0

1,1-Dichloroethylene (75-35-4) 624 1.0 2.0

1,2-Dichloropropane (78-87-5) 624 1.0 2.0

1,3-dichloropropylene (mixed isomers) 

(542-75-6)6

624 1.0 2.0

Ethylbenzene (100-41-4) 624 1.0 2.0
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Pollutant & CAS No. (if available)

Recommended 

Analytical 

Protocol

Detection 

(DL)1

μg/L unless 

specified

Quantitation

Level (QL) 2

μg/L unless 

specified

Methyl bromide (74-83-9) (Bromomethane) 624/601 5.0 10.0

Methyl chloride (74-87-3) (Chloromethane) 624 1.0 2.0

Methylene chloride (75-09-2) 624 5.0 10.0

1,1,2,2-Tetrachloroethane (79-34-5) 624 1.9 2.0

Tetrachloroethylene (127-18-4) 624 1.0 2.0

Toulene (108-88-3) 624 1.0 2.0

1,2-Trans-Dichloroethylene (156-60-5) 

(Ethylene dichloride)

624 1.0 2.0

1,1,1-Trichloroethane (71-55-6) 624 1.0 2.0

1,1,2-Trichloroethane (79-00-5) 624 1.0 2.0

Trichloroethylene (79-01-6) 624 1.0 2.0

Vinyl chloride (75-01-4) 624/SM6200B 1.0 2.0

ACID COMPOUNDS

2-Chlorophenol (95-57-8) 625 1.0 2.0

2,4-Dichlorophenol (120-83-2) 625 0.5 1.0

2,4-Dimethylphenol (105-67-9) 625 0.5 1.0

4,6-dinitro-o-cresol (534-52-1) 

(2-methyl-4,6,-dinitrophenol)

625/1625B 1.0 2.0

2,4 dinitrophenol (51-28-5) 625 1.0 2.0

2-Nitrophenol (88-75-5) 625 0.5 1.0

4-nitrophenol (100-02-7) 625 0.5 1.0

Parachlorometa cresol (59-50-7)

(4-chloro-3-methylphenol)

625 1.0 2.0

Pentachlorophenol (87-86-5) 625 0.5 1.0

Phenol (108-95-2) 625 2.0 4.0

2,4,6-Trichlorophenol (88-06-2) 625 2.0 4.0

BASE/NEUTRAL COMPOUNDS (compounds in bold are Ecology PBTs)

Acenaphthene (83-32-9) 625 0.2 0.4

Acenaphthylene (208-96-8) 625 0.3 0.6

Anthracene (120-12-7) 625 0.3 0.6

Benzidine (92-87-5) 625 12 24

Benzyl butyl phthalate (85-68-7) 625 0.3 0.6

Benzo(a)anthracene (56-55-3) 625 0.3 0.6

Benzo(b)fluoranthene (3,4-

benzofluoranthene) (205-99-2)7

610/625 0.8 1.6

Benzo(j)fluoranthene (205-82-3)7 625 0.5 1.0

Benzo(k)fluoranthene (11,12-

benzofluoranthene) (207-08-9)7

610/625 0.8 1.6

Benzo(r,s,t)pentaphene (189-55-9) 625 0.5 1.0
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Pollutant & CAS No. (if available)

Recommended 

Analytical 

Protocol

Detection 

(DL)1

μg/L unless 

specified

Quantitation

Level (QL) 2

μg/L unless 

specified

Benzo(a)pyrene (50-32-8) 610/625 0.5 1.0

Benzo(ghi)Perylene (191-24-2) 610/625 0.5 1.0

Bis(2-chloroethoxy)methane (111-91-

1)

625 5.3 21.2

Bis(2-chloroethyl)ether (111-44-4) 611/625 0.3 1.0

Bis(2-chloroisopropyl)ether (39638-32-

9)

625 0.3 0.6

Bis(2-ethylhexyl)phthalate (117-81-7) 625 0.1 0.5

4-Bromophenyl phenyl ether (101-55-

3)

625 0.2 0.4

2-Chloronaphthalene (91-58-7) 625 0.3 0.6

4-Chlorophenyl phenyl ether (7005-72-

3)

625 0.3 0.5

Chrysene (218-01-9) 610/625 0.3 0.6

Dibenzo (a,j)acridine (224-42-0) 610M/625M 2.5 10.0

Dibenzo (a,h)acridine (226-36-8) 610M/625M 2.5 10.0

Dibenzo(a-h)anthracene (53-70-

3)(1,2,5,6-dibenzanthracene)

625 0.8 1.6

Dibenzo(a,e)pyrene (192-65-4) 610M/625M 2.5 10.0

Dibenzo(a,h)pyrene (189-64-0) 625M 2.5 10.0

3,3-Dichlorobenzidine (91-94-1) 605/625 0.5 1.0

Diethyl phthalate (84-66-2) 625 1.9 7.6

Dimethyl phthalate (131-11-3) 625 1.6 6.4

Di-n-butyl phthalate (84-74-2) 625 0.5 1.0

2,4-dinitrotoluene (121-14-2) 609/625 0.2 0.4

2,6-dinitrotoluene (606-20-2) 609/625 0.2 0.4

Di-n-octyl phthalate (117-84-0) 625 0.3 0.6

1,2-Diphenylhydrazine (as Azobenzene) 

(103-33-3) 

1625B 5.0 20

Fluoranthene (206-44-0) 625 0.3 0.6

Fluorene (86-73-7) 625 0.3 0.6

Hexachlorobenzene (118-74-1) 612/625 0.3 0.6

Hexachlorobutadiene (87-68-3) 625 0.5 1.0

Hexachlorocyclopentadiene (77-47-4) 1625B/625 0.5 1.0

Hexachloroethane (67-72-1) 625 0.5 1.0

Indeno(1,2,3-cd)Pyrene (193-39-5) 610/625 0.5 1.0

Isophorone (78-59-1) 625 0.5 1.0

3-Methyl cholanthrene (56-49-5) 625 2.0 8.0
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Pollutant & CAS No. (if available)

Recommended 

Analytical 

Protocol

Detection 

(DL)1

μg/L unless 

specified

Quantitation

Level (QL) 2

μg/L unless 

specified

Naphthalene (91-20-3) 625 0.3 0.6

Nitrobenzene (98-95-3) 625 0.5 1.0

N-Nitrosodimethylamine (62-75-9) 607/625 2.0 4.0

N-Nitrosodi-n-propylamine (621-64-7) 607/625 0.5 1.0

N-Nitrosodiphenylamine (86-30-6) 625 0.5 1.0

Perylene (198-55-0) 625 1.9 7.6

Phenanthrene (85-01-8) 625 0.3 0.6

Pyrene (129-00-0) 625 0.3 0.6

1,2,4-Trichlorobenzene (120-82-1) 625 0.3 0.6

PESTICIDES/PCBs

Aldrin (309-00-2) 608 0.025 0.05

alpha-BHC (319-84-6) 608 0.025 0.05

beta-BHC (319-85-7) 608 0.025 0.05

gamma-BHC (58-89-9) 608 0.025 0.05

delta-BHC (319-86-8) 608 0.025 0.05

Chlordane (57-74-9)8 608 0.025 0.05

4,4’-DDT (50-29-3) 608 0.025 0.05

4,4’-DDE (72-55-9) 608 0.025 0.05

4,4’ DDD (72-54-8) 608 0.025 0.05

Dieldrin (60-57-1) 608 0.025 0.05

alpha-Endosulfan (959-98-8) 608 0.025 0.05

beta-Endosulfan (33213-65-9) 608 0.025 0.05

Endosulfan Sulfate (1031-07-8) 608 0.025 0.05

Endrin (72-20-8) 608 0.025 0.05

Endrin Aldehyde (7421-93-4) 608 0.025 0.05

Heptachlor (76-44-8) 608 0.025 0.05

Heptachlor Epoxide (1024-57-3) 608 0.025 0.05

PCB-1242 (53469-21-9)9 608 0.25 0.5

PCB-1254 (11097-69-1) 608 0.25 0.5

PCB-1221 (11104-28-2) 608 0.25 0.5

PCB-1232 (11141-16-5) 608 0.25 0.5

PCB-1248 (12672-29-6) 608 0.25 0.5

PCB-1260 (11096-82-5) 608 0.13 0.5

PCB-1016 (12674-11-2)9 608 0.13 0.5

Toxaphene (8001-35-2) 608 0.24 0.5
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1. Detection level (DL) or detection limit means the minimum concentration of an analyte (substance) that 

can be measured and reported with a 99% confidence that the analyte concentration is greater than zero 

as determined by the procedure given in 40 CFR part 136, Appendix B.

2. Quantitation Level (QL) also known as Minimum Level of Quantitation (ML) – The lowest level at which 

the entire analytical system must give a recognizable signal and acceptable calibration point for the 

analyte. It is equivalent to the concentration of the lowest calibration standard, assuming that all methodspecified sample weights, volumes, and cleanup procedures have been employed. The QL is calculated 

by multiplying the MDL by 3.18 and rounding the result to the number nearest to (1,2,or 5) x 10n

, where 

n is an integer. (64 FR 30417).

ALSO GIVEN AS: 

The smallest detectable concentration of analyte greater than the Detection Limit (DL) where the 

accuracy (precision & bias) achieves the objectives of the intended purpose. (Report of the Federal 

Advisory Committee on Detection and Quantitation Approaches and Uses in Clean Water Act Programs

Submitted to the US Environmental Protection Agency December 2007.
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5. WHOLE EFFLUENT TOXICITY (WET)

5.1 Permit Writer's Task Summary 

This Section is a summary of how permit writers implement Chapter 173-205 WAC, Whole Effluent 

Toxicity Testing and Limits for different permitting situations. The following subsections of 5.2 

through 5.14 describe the rule and implementation processes in more detail. Additional detail on test 

species, statistics, anomalous tests, and sampling is found in Ecology Publication WQ-R-95-80 

(Laboratory Guidance and Whole Effluent Toxicity Test Review Criteria) which is available from 

agency libraries or from http://www.ecy.wa.gov/programs/wq/wet.

New Permits 

Permit managers should: 

♦ Evaluate the discharge for need for effluent characterization (See subsection 5.4.).

♦ Decide on species to require in the permit (See subsection 5.11.).

♦ Decide on the monitoring frequency (See Chapter XIII, Section 4.).

♦ Decide on the use of rapid screening tests (See subsection 5.8.).

♦ Use model language in the permit.

♦ Contact the PDS Section for assistance with non-compliance or reviewing a TI/RE plan.

Permit Renewals with Previous Effluent Characterization 

Permit managers should: 

♦ Contact the PDS Section for the WET data record (See subsection 5.14.).

♦ Decide if additional characterization is required (See subsection 5.4.).

♦ Decide if a permittee with a WET limit no longer needs that limit (See subsection 5.7.).

♦Decide on species to require in the permit (See subsection 5.11.).

♦ Decide on the monitoring frequency (See Chapter XIII, Section 4.).

♦ Decide on the use of rapid screening tests (See subsection 5.8.).

♦ Use model language in the permit.

♦ Contact the PDS Section for assistance with non-compliance or reviewing a TI/RE plan.

5.2 Introduction 

Whole effluent toxicity is the total toxicity of an effluent measured directly with a toxicity test. WET 

testing is necessary because EPA cannot develop water quality criteria for every one of the thousands 

of toxic pollutants possibly found in wastewater discharges. WET testing is also the only method 

available to permit managers for assessing the toxic interaction of pollutants.

Chapter 173-205 WAC, Whole Effluent Toxicity Testing and Limits (the WET rule), became 

effective November 6, 1993. The goal of the WET rule is the eventual elimination of the discharge 

of toxics in toxic amounts. The WET rule establishes a procedure for deriving whole effluent 
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toxicity limits in accordance with RCW 90.48.520, 40 CFR 122.44(d), and 40 CFR 122.44(e) for 

inclusion into NPDES permits. The rule implements the requirement for all known, available, and 

reasonable methods of prevention, control, and treatment of toxicants and assures the attainment of 

state water quality standards.

This guidance explains WET requirements and helps readers locate WET rule sections pertinent to 

each issue. It will be helpful to refer to the text of the WET rule while using this Section of the 

Permit Writer's Manual. The WET rule contains the authoritative language on the WET 

requirements and should be consulted directly in order to make correct decisions. This guidance 

directs the reader to the section of the WET rule applicable to each subject discussed below.

WET testing is used in NPDES permits for the following purposes: 

♦ To serve as a broad spectrum indicator of increases in effluent toxicity. Analyzing effluents 

regularly for every possible toxic chemical would be expensive. WET tests provide an assessment of 

the overall toxicity of every toxicant and toxicant combination.

♦ To assess and limit WET to levels allowable under the state Water Quality Standards. The state's 

water quality standards prohibit ambient toxicity (WAC 173-201A-040(1), WAC 173-201A-030). 

The water quality standards also establish the point of compliance; there is no ambient toxicity 

allowed past the edge of an approved mixing zone (WAC 173-201A-100). The main purpose of 

Chapter 173-205 WAC is to characterize effluents for WET in order to establish whether a 

reasonable potential exists to violate this prohibition against ambient toxicity. If a reasonable 

potential exists, a permit limit is required on WET (WAC 173-205-050(2)(a)). The WET rule also 

describes how to monitor for WET limits based on the prohibition against ambient toxicity outside of 

approved mixing zones (WAC 173-205-070(1) and (2)).

♦ To assess and limit WET on a technology basis. Technology-based limits on acute WET may be 

placed into permits on a case-by-case basis (WAC 173-205-130). WAC 173-

205-130 does not provide for technology-based WET limits for categories of dischargers or for 

chronic WET. 

The regulatory process for WET in NPDES permits is shown in Figure VI-8 and Figure VI-9. Figure 

VI-10 illustrates the compliance process for WET. The steps in the process in Figure VI-8 are 

described below. 

1. The process begins with NPDES permit application. The application can be for a new NPDES 

permit or for renewal of an existing permit. If a previous permit required an effluent 

characterization, the permittee will either be at STEP 5 and STEP 6 will determine the new permit 

requirements or the permittee will be at STEP 7 and STEP 8 will determine the new permit 

requirements. 

2. Section 173-205-040 of the WET rule contains a list of circumstances under which a discharge is 

required to be characterized for WET. These circumstances define discharges with a risk for aquatic 

toxicity. The permits for a discharge which fits any of these circumstances will contain a 

requirement for WET characterization. Unless section 173-205-060 applies, effluent characterization 

will only happen once in the lifetime of a discharge. Permits for discharges which do not fit any of 

the circumstances will not require WET testing. If circumstances change so that a facility no longer 

has a risk for aquatic toxicity pursuant to WAC 173-205-040(1), a permit writer may make a 

determination in accordance with WAC 173-205-040(2)(h) to stop WET testing.
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3. An effluent characterization usually occurs during the first year of the permit term. Effluent 

characterization establishes the baseline toxicity level and determines the need for WET limits. Every 

sample during effluent characterization will be tested with all of the WET tests listed in the permit 

(multiple species testing). 

4. The permit will require that the permittee determines, at the end of effluent characterization,

whether the WET performance standards have been met for acute and chronic toxicity. The 

performance standard for acute toxicity is a median of at least 80% survival in 100% effluent with no 

single test showing less than 65% survival in 100% effluent. The performance standard for chronic 

toxicity is no toxicity in a concentration of effluent representing the edge of the acute mixing zone. 

Permittees meeting performance standards will get no WET limits or compliance monitoring and go 

straight to STEP 7 on the diagram. 

5. Those permittees not meeting a performance standard during effluent characterization will receive 

WET limits. The permit will require monitoring to determine compliance with the WET limit. 

Failing to comply with a WET limit will trigger additional WET testing and possibly other 

enforcement actions as described in subsection 5.6 and Figure VI-10 below. 

6. The WET rule does not intend that WET limits are permanent. If a permittee with a WET limit 

meets the performance standard during compliance monitoring for a permit term, then the WET limit 

will not be placed into subsequent permits. By controlling toxicity well enough to meet the 

performance standard, the permittee has allowed the limit and routine monitoring to be removed from 

the permit. The permittee's cost and liability are lower.

7. Permittees who have attained the performance standards can remain indefinitely without WET 

limits or compliance monitoring. The only requirement will be WET test results submitted with each 

permit application or rapid screening testing during the permit term. The results of the WET tests 

done for permit application or routine rapid screening testing will be used to determine if another 

effluent characterization is needed. (In addition, there is a requirement in 40 CFR 122.21(j) that 

POTWs with design influent flows greater than or equal to 1 mgd and POTWs required to develop 

pretreatment programs must submit WET test results with each permit application in Part E of the 2A 

permit application form.) 

8. If changes have occurred that might increase toxicity, then the next permit will require a new 

effluent characterization in accordance with WAC 173-205-060 and start the process over again at 

STEP 3. WET limits could result from a new effluent characterization or the permittee could go 

directly back to STEP 7 with no WET limits. If changes have occurred that decrease the chance for 

effluent toxicity, then the permit application should be reviewed as in STEP 2 to see if any of the 

risk criteria in WAC 173-205-040 still apply. If none of the risk criteria apply, WET testing 

requirements can be removed from the next permit. If any of the risk criteria still apply, the permit 

should keep the requirement to submit a set of WET test results with the next permit application as in 

STEP 7 even though there is a reduced risk.
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Figure VI-8. The WET implementation process.
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Figure VI-9. WET requirements for permits 

HAS THE

APPLICANT ALREADY 

CHARACTERIZED EFFLUENT

FOR WET?

CONTINUE LIMIT

AND COMPLIANCE

MONITORING OR

CONTINUE

APPLICATION

REQUIREMENT OR 

REMOVE

REQUIREMENTS

YES

DOES THE

APPLICANT MEET

CRITERIA FOR 

EXCLUSION?

NO

NO REQUIREMENT YES

CONDUCT EFFLUENT

CHARACTERIZATION

FOR ACUTE AND

CHRONIC TOXICITY

NO

MEET ACUTE

PERFORMANCE STANDARD

OF SURVIVAL MEDIAN OF

80% WITH NONE < 65% IN

100% EFFLUENT?

MEET

CHRONIC

PERFORMANCE OF

NO CHRONIC EFFECT

AT THE ACEC?

NO LIMIT, MONITORING AND

RECHARACTERIZATION IF

NECESSARY

YES YES

LIMIT OF NO

CHRONIC EFFECTS

AT THE CCEC

LIMIT OF NO

ACUTE EFFECTS

AT THE ACEC

MEET PERFORMANCE

STANDARD FOR ONE

TERM?

YES

NO

NO

NO NO

PERMIT APPLICATION

ACUTE CHRONIC
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5.3 The Purpose of Effluent Characterization 

Effluent characterization is used to establish whether a reasonable potential exists pursuant to 40 

CFR 122.44(d)(1)(v) which would require a WET limit. Acute and chronic WET are evaluated 

separately for a reasonable potential to violate the water quality standards. Permittees who cannot 

meet the WET performance standards have demonstrated a reasonable potential for ambient toxicity 

and need WET limits (WAC 173-205-020 and in WAC 173-205-050(2)(a)). Effluent 

characterization is also used to establish a baseline toxicity level (WAC 173-205-050(2)(b)). The 

effluent characterization process lasts for one year (WAC 173-205-020 and WAC 173-205-050(1)). 

During the year of effluent characterization, each effluent sample is tested with all WET test species 

listed in the permit. This multiple species testing provides an assessment of effluent toxicity in order 

to provide protection to as many different types of receiving water organisms as possible. See 

subsection 5.11 for guidance on WET test species selection. 

5.4 Determining the Need for Effluent Characterization 

Effluent characterizations for WET are required when: 

♦ A discharge has never before been characterized for WET and has one or more of the risk factors in 

WAC 173-205-040(1). These factors include the presence of hazardous substances (Table VI-3) at 

the facility which could be released to the wastewater system, the presence of toxic pollutants in the 

effluent for which there are no water quality criteria, being an industry listed in Table VI-4, or 

toxicity detected in past WET testing. 

♦ A discharge that has been previously characterized for WET experiences changes in process or 

discharge characteristics (WAC 173-205-060(1)) and has not made the demonstration pursuant to 

WAC 173-205-060(2) that the changes have not increased effluent toxicity. 

♦ Either a rapid screening test result during the permit term or a WET test result submitted with the 

permit application has shown toxicity at levels of regulatory concern (WAC 173-205-060(3)). 

♦ A new WET test has been approved pursuant to WAC 173-205-050(1)(d) that would measure 

effluent toxicity better than the WET tests used in the original effluent characterization. The 

discharge will then be characterized using only the new WET test (WAC 173-205-060(5) and (6)). 

Effluent characterizations for WET are not required when: 

♦ The discharge has none of the risk factors in WAC 173-205-040(1) and is excluded by WAC 173-

205-040(2).

♦ The discharge has none of the risk factors in WAC 173-205-040(1) and the permit manager has 

made a determination the effluent doesn't have the potential to contain toxic substances in toxic 

amounts (WAC 173-205-040(2)(h)). 

♦ If the effluent receives at least 1000:1 dilution at the edge of an approved mixing zone, the chronic 

testing is skipped but characterization for acute toxicity is still done. (WAC 173-205-040(3)) 

♦ If the permittee is monitoring for compliance with a WET limit using species rotation, additional 

characterizations for WET are not required (WAC 173-205-060(4)) for the type of toxicity (acute or 

chronic) covered by that WET limit. 

♦ No additional effluent characterization is required for a discharge that has experienced a change if 

the permittee has made a demonstration that the change has not increased toxicity (WAC 173-205-

060(2)). The demonstration might include toxicity testing, chemical analysis, or both. 
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Other effluent characterization requirements: 

♦ Characterization for WET may be delayed for existing facilities that are under a compliance 

schedule to implement technology-based controls or to achieve compliance with water quality-based 

effluent limits (WAC 173-205-030(4)). 

♦ Unless WAC 173-205-060 applies, effluent characterizations conducted in a previous permit need 

not be repeated as long as the information is adequate to make all determinations in WAC 173-205-

050(2) and meet the permitting requirement in WAC 173-205-030(5)(b). The determinations in 

WAC 173-205-050(2)(a) can be made as long as the results of the effluent characterization include 

the percent survival in 100% effluent for every acute test and the NOEC for every chronic test. 

WAC 173-205-050(2)(b) also requires that an effluent characterization generate point estimates 

(LC50, EC50, etc.) to use in establishing a baseline toxicity level. WET tests conducted for effluent 

characterization must be from EPA manuals (WAC 173-205-050(1)(d)) or listed in 40 CFR Part 136. 

♦ The determination in WAC 173-205-050(2)(a)(ii) can be complicated, or perhaps even 

inconclusive, if the acute critical effluent concentration (ACEC) is not specified in the permit and 

included in the concentration series of chronic WET tests conducted for effluent characterization.

♦ Effluent characterization may include WET tests conducted on ambient water collected 

downstream of the discharge or using ambient water collected upstream of the discharge as dilution 

water (WAC 173-205-030(6)). Testing downstream samples has already been done in one permit 

and has withstood challenge in front of the Pollution Control Hearings Board (PCHB). 

5.5 Determining Compliance with WET Limits 

SPECIES ROTATION. Because changes in an effluent can change the relative sensitivity of the WET 

test species listed in the permit, species will be rotated during compliance monitoring. The rotation 

schedule need not have an equal testing frequency for all of the species. If one species was clearly 

the most sensitive during effluent characterization, then the rotation schedule should use the most 

sensitive species for all monitoring. The model permit language allows Ecology to notify a permittee 

of the rotation schedule. If the rotation schedule is not specified by Ecology, then the permit 

language directs the permittee to test the species in the order listed in the permit. 

ACUTE WET LIMITS. Compliance with an acute WET limit requires a demonstration of no acute 

toxicity in a concentration of effluent equal to the acute critical effluent concentration (ACEC)(WAC 

173-205-070(1)). The ACEC is defined as the maximum concentration of effluent during critical 

conditions at the boundary of the zone of acute criteria exceedance (WAC 173-205-020). A 

demonstration of no acute toxicity at the ACEC means that the effluent is not at a concentration 

above acute toxicity thresholds outside of the zone of acute criteria exceedance. 

CHRONIC WET LIMITS. Compliance with a chronic WET limit requires a demonstration of no 

chronic toxicity in a concentration of effluent equal to the chronic critical effluent concentration 

(CCEC) (WAC 173-205-070(2)). The CCEC is defined as the maximum concentration of effluent 

during critical conditions at the boundary of the mixing zone (WAC 173-205-020). A demonstration 

of no chronic toxicity at the CCEC means that the effluent is not at a concentration above chronic 

toxicity thresholds outside of the mixing zone. 

STATISTICALLY SIGNIFICANT DIFFERENCES IN RESPONSE. The scientifically valid way to 

make a demonstration of no toxicity is to demonstrate that the ACEC or the CCEC in a WET test has 

no statistically significant difference in organism response from the control. The control is 
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laboratory water that is known to be nontoxic to test organisms. If there is a statistically significant

difference in response between the ACEC or CCEC and the control, then toxicity has been 

demonstrated. If there is no statistically significant difference in response, then it can be assumed 

that there is no toxicity at the ACEC or CCEC and that the permittee has complied with the 

performance standard or the WET limit. 

HYPOTHESIS TESTING. Statistical significance means that the difference in response between a 

control and the ACEC or CCEC is likely to be due to toxicity and not to test variability. The 

statistical technique for making this determination is a hypothesis test. A hypothesis test compares 

the average response of the replicates of the ACEC or CCEC to the average response of the control 

replicates in order to determine if there is a statistically significant difference in response at some 

level of confidence such as 95%. There is a 5% chance for some test results at the 95% level of 

confidence that a difference will be due to chance and not toxicity. There is a 1% chance for some 

test results at the 99% level of confidence that a difference will be due to chance and not toxicity. 

Differences due to chance are called false positives or Type I errors. 

FALSE POSITIVE TEST RESULTS. When a statistically significant difference in response is due to 

test variability and not to toxicity, the WET test has produced a false positive result. However, a 

confidence level of 95% does not mean that 1 in 20 (5%) of failed WET tests is a false positive. The 

confidence level only approximates the worst case false positive rate which exists when the two 

values being compared are relatively close together. The further apart these values are, the less likely 

are false positive results. In other words, if all of the organisms in the ACEC die and none die in the 

control, the probability that the statistically significant difference in response is a false positive is 

closer to 0 than 1 in 20. The overall false positive rate is less than 1 in 20 and is almost always less 

than the overall false negative rate. To prevent most false positive test results, the model permit 

language raises the confidence level to 99% when the differences in response are small. 

DEFINITION OF INVALID TESTS AND ANOMALOUS TEST RESULTS. Invalid WET tests occur 

when the lab does not follow the test method or when the results do not meet the validation criteria in 

the test method. Permittees are obligated to assure that all tests are valid because the permit requires 

that only the results of valid tests be submitted. The Program Development Services Section reviews 

WET test results to see that they are based on valid tests. 

Anomalous test results happen when the lab appears to have conducted the WET test in accordance 

with the test method, but the results are unreliable according to review criteria. There is no 

requirement for Permittees to attempt to identify anomalous WET test results. All valid WET test 

results must be submitted whether anomalous or not. See subsection 5.10.2 for a discussion of 

permittee identification of anomalous test results. 

The Program Development Services Section will be reviewing WET test results and screening out 

anomalous test results. Anomalous test results will not be used for compliance determinations (WAC 

173-205-070(5)(c)). Most anomalous test results will be identified by the lack of a good 

concentration-response relationship. If the toxic response does not increase as the concentration of 

effluent increases, then the test is considered to be anomalous in most cases. Permittees will usually 

be required to take another sample and repeat the WET test when results are anomalous. 

FALSE NEGATIVE TEST RESULTS AND THE POWER STANDARDS. Sometimes variability across 

replicates will prevent a large difference in response (in other words, a toxic effluent) from being 

detected as statistically significant. False negatives happen easily when the number of replicates is 
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low and the lab is not careful in conducting the WET test. Chapter 173-205 WAC handles false 

negatives through the establishment of power standards. Several parts of the WET rule require that 

toxicity tests meet the power standards (WAC 173-205-050(1)(f)(ii), WAC 173-205-

050(2)(a)(iii)(A), WAC 173-205-070(4), and WAC 173-205-120(2)(c)). The acute statistical power 

standard and the chronic statistical power standard are defined in WAC 173-205-020. The acute 

statistical power standard says that acute toxicity tests must be able to detect a minimum of a 30% 

difference in survival between the ACEC and a control as statistically significant. The chronic 

statistical power standard says that chronic toxicity tests must be able to detect a minimum of a 40% 

difference in response between the ACEC or CCEC and a control as statistically significant. If a 

WET test does not meet the appropriate statistical power standard, then the permittee will be required 

to immediately resample the effluent and repeat the toxicity test with the number of replicates 

increased in order to meet the statistical power standard. 

5.6 Noncompliance, Transient Toxicity Reports, and TI/RE Plans 

ADDITIONAL TESTING AND TRANSIENT TOXICITY REPORTS. (Figure VI-10). When a 

permittee fails a routine compliance test for a WET limit, then additional testing is immediately 

required to assess and confirm the continuing presence of toxicity (WAC 173-205-090(1)). WET 

testing of 4 additional weekly samples are required following noncompliance with an acute WET 

limit and 3 additional monthly samples following noncompliance with a chronic WET limit (WAC 

173-205-090(1)). If only the routine compliance test is failed, then the permittee is required to 

prepare a transient toxicity report on the possible causes and prevention of the toxicity. Compliance 

with the permit limit is restored with the first additional sample that passes the compliance test. 

Compliance with all WET testing provisions of the permit is accomplished by passing all of the 

additional testing following a routine compliance test failure and submitting an acceptable transient 

toxicity report. The contents of a transient toxicity report are described in WAC 173-205-100(1). 

TI/RE PLANS. If any toxicity test fails the compliance test during the additional monitoring, then the 

permittee must submit a TI/RE plan to Ecology within sixty days of the last additional sample (WAC 

173-205-100(2)). The TI/RE plan will be based on procedures in the latest versions of the EPA 

guidance documents for conducting toxicity reduction evaluations or toxicity identification 

evaluations (WAC 173-205-100(2)(b)). However, the TI/RE plan need not include any procedure 

from the EPA manuals that is not necessary to the goal of controlling the discharge of WET by the 

permittee (WAC 173-205-100(2)(b)(i)). Ecology may approve any modifications or additions to the 

EPA procedures that will improve the ability to identify or reduce toxicity (WAC 173-205-

100(2)(b)(ii)). The permittee is required to implement the TI/RE plan immediately upon notification 

by Ecology of plan approval (WAC 173-205-100(3)). Model permit language specifies an 

administrative order as the means to notify a permittee to implement a TI/RE. The Program 

Development Services Section will assist in reviewing TI/RE plans and in writing administrative 

orders to implement TI/RE plans.
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Figure VI-10 Compliance Process for WET 

Testing as specified in the permit for acute and chronic toxicity

Meet 

performance 

standards?

Meet 

effluent 

limits?

Consider removal of 

requirements after 

one permit term of 

compliance

Does permittee 

acknowledge 

effluent is toxic?

Increased WET 

testing to 4 

weekly acute 

and 3 monthly 

chronic

Prepare TI/RE 

plan and 

submit to 

Ecology

Does toxicity 

occur again?

Prepare transient 

toxicity report 

and submit to 

Ecology

Resume 

monitoring

Is reduction effort 

successful?

2 to 6 months 

to confirm and 

eliminate 

source of 

toxicity

Implement TI/RE 

plan

Is there an 

apparent source 

of toxicity?

yes

yes

yes

yes

yes

yes

no

no

no

no

no
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5.7 Removal of WET Limits 

A WET limit is eligible for removal upon permit renewal if the permittee has demonstrated 

compliance with the WET performance standard associated with that limit for at least the last three 

consecutive test years following effluent characterization or for an entire subsequent permit term, and 

has not made any changes within the last three years which would otherwise require additional 

effluent characterization (WAC 173-205-120(1)). 

Removing a WET limit under this provision of Chapter 173-205 WAC is a good idea for the 

following reasons: 

♦ It protects the environment. Concentration-response curves are steep and toxicity decreases rapidly 

with dilution. As a consequence, toxicity is often undetectable at the ACEC or CCEC. This means 

that WET limits will be easily met by most dischargers. However, when the concentration of toxic 

chemicals increases in the effluent, then toxicity increases quickly. Toxicity (especially acute 

toxicity) tends to behave as if there was a threshold where one side is safe and the other side is lethal 

to aquatic organisms. A larger margin of safety is a good idea under these circumstances. Offering 

to remove these WET limits provides a strong incentive to do more to control toxicity than is 

required to meet the water quality standards. The performance standards provide a margin of safety 

for the environment and move toward the goal of RCW 90.48.520. 

♦ It is fair. Other permittees conducted a similar or smaller amount of WET testing during effluent 

characterization and did not receive a WET limit in the first place. If a permittee can meet the same 

performance standard measured with at least as much WET testing over a longer period of time as 

other permittees who received no WET limits did, then that permittee also has no reasonable 

potential to violate the water quality standards. 

♦ It fits into the system for regulating WET in Chapter 173-205 WAC. Chapter 173-205 WAC 

recognizes that the evaluation of WET is an ongoing process that encompasses more than just 

dividing permittees into two groups: those with WET limits and those without WET limits. Chapter 

173-205 WAC also has provisions for rapid screening tests, for additional effluent characterizations, 

for permittee evaluations of facility changes, and for technology-based acute WET limits. All of 

these provisions are enhanced by or dependant on WET limit removal. 

5.8 Determining the Need for Rapid Screening Tests 

RAPID SCREENING TESTS. A rapid screening test is a screening toxicity test on one hundred 

percent effluent or some other high concentration of effluent in order to detect unanticipated 

increases in toxicity. Examples of rapid screening tests include twenty-four hour EPA acute tests, 

acute toxicity tests using rotifers produced from cysts, bacterial bioluminescence tests (Microtox®), 

and two-day life cycle tests with rotifers. See subsection 5.12 for guidance on rapid screening test 

selection. 

RAPID SCREENING TESTS WHEN WET LIMITS ARE NOT ASSIGNED OR ARE REMOVED. 

Permit managers may condition the nonassignment of a WET limit with a requirement for routine 

monitoring with a rapid screening test (WAC 173-205-120(2)). A permit manager must place rapid 

screening tests into a permit if there is the potential for an event at the facility which could result in a 

toxic discharge that would otherwise go unnoticed (WAC 173-205-120(2)(a)(ii)). The permit 

manager should consider the potential for treatment system upsets, control equipment failures, spills, 

accidental releases to the wastewater system, or any other event which could result in a toxic 

discharge. If a permittee refuses to accept rapid screening tests in the permit, leave the WET limit in 
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place. Chemical monitoring may also be required to assess increases in effluent toxicity when 

adequate for that purpose. 

RAPID SCREENING TESTS AND ADDITIONAL EFFLUENT CHARACTERIZATIONS. Rapid 

screening testing can be beneficial for the permit manager and the permittee. Toxicity caused by a 

facility change can be determined if a permittee is routinely doing rapid screening tests with a known 

sensitivity relative to the regular WET tests. Additional effluent characterizations are then 

unnecessary. 

THE RESULT OF RAPID SCREENING TESTING. Whenever a rapid screening test is failed, the 

permittee must immediately retest with all of the acute or chronic toxicity tests used in the last permit 

with WET (WAC 173-205-120(2)(d)). Toxicity detected by a rapid screening test must be confirmed 

by the traditional EPA WET tests. The results of these acute or chronic toxicity tests conducted in 

response to a rapid screening test will be evaluated to determine the need for a new WET 

characterization in the next permit or the need for immediate administrative orders to implement the 

regulatory process which begins in WAC 173-205-090. 

OTHER USES OF RAPID SCREENING TESTS. Rapid screening tests may be required of any 

permittee (WAC 173-205-030(5)). This means that, in addition to evaluating changes in the toxicity 

of discharges which have no WET limits, rapid screening tests can be used during effluent 

characterization to develop a correlation with the WET tests or in a permit with WET limits to raise 

the monitoring frequency. Compliance with WET limits is never measured with a rapid 

screening test. They can be required at a higher monitoring frequency than the WET tests and are 

used to trigger the WET tests when needed.

5.9 Technology-Based WET Limits 

PROCESS. A permit manager may place the WET performance standard for acute toxicity into 

permits as a limit on a case-by-case basis pursuant to 40 CFR 125.3(d)(3) (WAC 173-205-130(2)). 

40 CFR 125.3(d)(3) contains the list of factors which must be considered in setting case-by-case 

BAT limits. There are six of these site-specific factors. These include: the age of equipment, the 

process employed at the facility, changes to the process required to meet the performance-based 

limit, engineering aspects of the control techniques, and the cost of achieving the performance-based 

limit. These considerations require the assistance of the Program Development Services Section. 

TIMING. The performance-based acute toxicity limit in WAC 173-205-130(2) will not be 

automatically applied to all permittees in a category, but will only be imposed on a case-by-case 

basis after several years have passed during which permittees are encouraged to meet the 

performance standards solely through the incentive of offering to remove WET limits and 

compliance monitoring from the permit. The determination to impose a performance-based WET 

limit will not occur until after a water quality-based acute WET limit has been assigned, after at least 

one permit term of monitoring for compliance with the water quality-based WET limit, after a similar 

permittee has met the acute toxicity performance standard, and after consideration of the site-specific 

factors listed in 40 CFR 125.3(d)(3). Because these steps must occur before the determination is 

made to impose a performance-based limit, the delay will be at least five years before such a limit is 

placed in a permit unless such a limit was already in place before Chapter 173-205 WAC became 

effective. 
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5.10 Options for Permittees 

5.10.1 Conducting WET Tests 

There are three options for permittees: 

♦ Permittees may conduct toxicity tests using a full dilution series (WAC 173-205-030(9)). A full 

dilution series would protect the permittee by allowing anomalous test results to be identified by 

examining the concentration-response relationship. It also allows our database to contain a better 

record of baseline effluent toxicity, compare the toxicity of different discharges, and evaluate the 

response of different WET tests. 

♦ A permit manager may approve the request of a POTW discharging less than 0.5 mgd or a small 

business as defined in RCW 43.31.025(4) to conduct WET testing as effluent screening tests using 

100% effluent for the acute toxicity tests and the ACEC for the chronic toxicity tests (WAC 173-205-

050(1)(f)). A small business is defined as a business entity which is owned and operated 

independently from all other businesses, which has the purpose of making a profit, and which has 50 

or fewer employees (RCW 43.31.025). Effluent screening tests are WET tests that are conducted as 

a screen for toxicity in 100% effluent (acute tests) or the ACEC (chronic tests). No other effluent 

concentrations (except the control) are tested until toxicity has been detected in the effluent screening 

test. This saves the permittee money as long as the effluent is nontoxic. The effluent screening tests 

are about two-thirds to one-half the cost of a full dilution WET test. However, since the quality of 

the information is lower and repeating tests ends up being more expensive, it would be best to limit 

this option to dischargers that are likely to be nontoxic. 

♦ The WET rule requires that samples, dilution water, and test solutions be handled as specified in 

the test method or the permit (WAC 173-205-080(1). Permittees who received permit language 

which is not consistent with the test method, Ecology Publication WQ-R-95-80 (Laboratory 

Guidance and Whole Effluent Toxicity Test Review Criteria), or model permit language may request 

approval of alternative samples, dilution water, or test solutions (WAC 173-205-080(1)(c)). 

5.10.2 Notification of an Anomalous Test Result 

Ecology will be reviewing WET test results to see if these results are anomalous and should not be 

used for compliance determinations (WAC 173-205-070(5)(b)). Examples of anomalous WET test 

results include tests with a lower toxic response at higher effluent concentrations or a concentrationresponse which has no slope. A review for these kinds of WET test results will protect permittees 

from the consequences of noncompliance with a WET limit when the WET test itself was responsible 

for the appearance of noncompliance. 

If the permittee believes that a compliance test failure will be identified by Ecology as an anomalous 

test result, the permittee may send Ecology notification with the compliance test result that the 

compliance test result might be anomalous and that the permittee intends to take only one additional 

sample for toxicity testing and wait for notification from Ecology before completing the additional 

monitoring required in WAC 173-205-090(1). The notification must identify the reason for 

considering the compliance test result to be anomalous. Our definitions of anomalous tests are 

published in Ecology Publication WQ-R-95-80 (Laboratory Guidance and Whole Effluent Toxicity 

Test Review Criteria). The permittee must complete all of the additional monitoring required by 

WAC 173-205-090(1) as soon as possible after notification by Ecology that the compliance test 

result was not anomalous. Ecology will review all compliance test results to determine if they are 
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anomalous regardless of whether or not they are accompanied by permittee notification that they may 

be anomalous. 

5.10.3 Conducting a TI/RE 

There are three options for permittees: 

♦ A permittee may proceed directly to a TI/RE and not perform the additional testing (WAC 173-

205-090(4)). Permittees that choose this option save themselves the expense of the additional 

monitoring and lessen the time between first detecting WET in excess of a limit and taking action to 

achieve compliance. 

♦ If any WET test fails the compliance test during the additional monitoring conducted in accordance 

with WAC 173-205-090(1), then the permittee shall submit a plan for a TI/RE (WAC 173-205-

100(2)). As a part of this plan, the permittee may request that Ecology allow up to six months before 

beginning the TI/RE for facility personnel to attempt to control the most likely sources of toxicity 

through efforts such as changes in plant operation, replacement of a toxic material used in the 

facility, or improvement of best management practices (WAC 173-205-100(2)(a)). Ecology 

approves the request in writing, and if the attempt is successful, then the permittee and Ecology are 

saved the time and expense of TI/RE plan review and implementation. However, since time and 

effort will be wasted if the attempt is unsuccessful, requests should only be approved for attempts 

that have a good chance of success. 

♦ Ecology may approve the interruption of a TI/RE if toxicity has disappeared (WAC 173-205-

110(1)). The permittee then returns to the routine monitoring schedule and takes enough extra 

sample each time to begin a TI/RE if the effluent fails the compliance test. If toxicity testing shows 

compliance with WET limits for one year after interruption of the TI/RE, then the permittee may 

cease taking the extra sample (WAC 173-205-110(2)). The approval letter for the TI/RE interruption 

should inform the permittee of the option to cease taking the extra sample after one year of 

compliance. 

5.11 Species Selection for WET Testing 

5.11.1 Acute WET Test Species 

Selecting acute WET test species is fairly simple. Effluents with a risk for aquatic toxicity are tested 

at a minimum for toxicity to a fish, an invertebrate, and any appropriate plant (WAC 173-205-

050(1)(a)). Because EPA has not provided any test for acute toxicity to plants, effluents can only be 

tested for acute toxicity using a fish and an invertebrate. If the effluent itself is freshwater, 

freshwater species are generally used for acute WET testing. Freshwater WET tests are more readily 

available and more convenient for TI/REs. The saltwater and freshwater acute WET tests do not 

differ significantly in sensitivity. However, discharges to saltwater of low hardness (< 50 mg/L) 

freshwater might be best tested using acute tests with saltwater organisms. Contact the Program 

Development Services Section if you want permit language for using acute tests with saltwater 

organisms. 

CHOICE OF INVERTEBRATE. Daphnids are the standard freshwater invertebrate test organisms. 

The permittee or lab may choose the most convenient species (Daphnia pulex, Daphnia magna, or 

Ceriodaphnia dubia). The sensitivity to toxicity of these species is similar. WAC 173-205-050(1)(c) 

requires daphnid (or mysid) acute tests to be 48 hours in duration.
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CHOICE OF FISH. WAC 173-205-050(1)(c) requires fish acute tests to be 96 hours in duration. 

Fathead minnow are recommended for acute WET testing for several reasons. Fathead minnows are 

sensitive test organisms; they were more sensitive than rainbow trout tested using the DOE 80-12 

procedure. EPA has developed the freshwater WET testing program around the use of fathead 

minnows for fish testing. More labs around the country have experience with fathead minnow WET 

testing or fathead minnow toxicity identification/reduction evaluations (TI/REs) than any other fish. 

The national experience with fathead minnow TI/REs is much more extensive than with rainbow 

trout. 

TI/REs will be more difficult and expensive with rainbow trout. The volume of effluent that must be 

sampled, shipped, and fractionated is much larger for a rainbow trout WET test or TI/RE than it is for 

fathead minnow. EPA protocols require about 20 times the volume of effluent for rainbow trout 

testing than fathead minnow testing. For example, it might require 5 liters of effluent for a fathead 

minnow TI/RE and 100 liters for a rainbow trout TI/RE. Taking a representative sample of 100 liters 

of effluent, shipping it, and performing the chemical manipulations required in a TI/RE will be more 

difficult and expensive to accomplish than it would be with 5 liters of effluent. 

If you have decided to require acute WET testing with rainbow trout in order to provide direct 

protection of salmonids, it is recommended that you also require fathead minnow testing so that any 

TI/RE can be performed with fathead minnow. Each sample during effluent characterization will be 

tested using both of the fish and this information can be used to guide the fathead minnow TI/RE so 

that it also protects rainbow trout. 

ACUTE TESTING OF SALINE EFFLUENTS. If the effluent is too saline for freshwater organisms, 

contact the Program Development Services Section to discuss acute WET tests with saltwater 

organisms. 

5.11.2 Chronic WET Test Species 

Unlike the situation with acute WET testing, permits for discharges to freshwater should have 

requirements for freshwater chronic WET tests, and permits for discharges to saltwater or brackish 

water should have requirements for saltwater chronic WET tests. Exceptions to this recommendation 

are allowable but should be discussed with the Program Development Services Section. Ecology 

Publication WQ-R-95-80 (Laboratory Guidance and Whole Effluent Toxicity Test Review Criteria) 

has important extra detail on the chronic tests and their sublethal endpoints such as development, 

biomass, growth, reproduction, intrinsic rate of population increase, germination, etc. It also 

describes in detail the new supplemental chronic tests described below in subsection 5.11.3. 

FRESHWATER CHRONIC WET TEST SPECIES. Chronic WET test species selection is fairly simple 

for discharges to freshwater. EPA recommends testing with a fish, an invertebrate, and a plant and 

has provided only one of each for freshwater chronic WET testing (fathead minnow, Ceriodaphnia, 

and Selenastrum). The new species name for Selenastrum is Pseudokirchneriella subcapitata. 

Effluents with a risk for aquatic toxicity should be tested for toxicity to a fish, an invertebrate, and if 

appropriate, a plant (WAC 173-205-050(1)(a)). 

The WET Rule required testing with a plant only when deemed appropriate because the plant tests 

available in the early 1990s had deficiencies. Most of these deficiencies have now been resolved by 

improvements in the Selenastrum test and by inclusion in the EPA west coast manual of a good kelp 
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test. If you have the slightest suspicion that an effluent might be toxic to plants, use the model permit 

language that requires these plant tests. 

SALTWATER CHRONIC WET TEST SPECIES. The selection of chronic WET test species for 

discharges to saltwater is complex for two main reasons: 

♦ The reproduction of multicellular organisms in a marine environment usually begins with broadcast 

fertilization resulting in very small embryos and larvae which drift with the plankton. These early 

life stages of marine organisms are very sensitive to toxicity, and are part of the life cycle of most 

marine organisms including examples such as oysters, kelp, halibut, and crab. EPA has provided a 

larger list of chronic WET tests for protecting marine waters so effects on these sensitive early life 

stages could be assessed. 

♦ The transition to west coast organisms is complete except for the mysid. The mysid in the EPA 

west coast manual cannot be cultured and must be caught in the wild for use in toxicity testing. 

Wild-caught organisms are less readily available, more expensive, and have an uncertain history. 

The east coast mysid is one of the more reliable test organisms and has been retained in the model 

permit language. All other saltwater test species are from the west coast manual. 

Standard Fish and Invertebrate 

Topsmelt (Atherinops affinis) and east coast mysid (Americamysis bahia)

The chronic WET tests with these two species should be included in all permits for discharges to 

saltwater. The level of protection provided by these two tests is similar to the protection provided by 

the freshwater chronic tests. The mysid test is an excellent test. When EPA studied the toxicity of 

13 effluents from a wide variety of sources, they found the Americamysis bahia test to be the most 

sensitive of the tests in the marine chronic toxicity test manual 31% of the time. Another study found 

the Americamysis bahia test to be 42-times more sensitive than the average fish and crustacean in 

EPA's database of toxicity test results used in the development of the marine water quality criteria. 

When the minnow and mysid provide less than adequate protection, the permit should also contain a 

fertilization test, an embryo-larval development test, or the kelp germination and growth test. 

Permits containing WET testing requirements for only the fish and mysid meet the minimum 

requirement of WAC 173-205-050(1)(a). 

Bivalve Embryo-Larval Survival and Development Test 

Pacific oyster (Crassostrea gigas) or blue mussel (Mytilus sp.) 

The bivalve embryo-larval development test is recommended for discharges to ecosystems of special 

importance or fragility. Put this chronic WET test into a permit along with the standard fish and 

invertebrate test when there is a risk of toxicity to sensitive larval life-stages of marine organisms. 

This test is especially appropriate for discharges to areas where mollusks are being cultivated or for 

discharges to breeding grounds for important marine organisms. This chronic WET test is often the 

most sensitive of all the tests, except to polycyclic aromatic hydrocarbons (PAHs). 

Echinoderm Embryo-Larval Survival and Development Test 

Sea urchin (Strongylocentrotus purpuratus) or sand dollar (Dendraster excentricus) 

Put this chronic WET test into a permit along with the standard fish and invertebrate test when there 

is a risk of toxicity to sensitive larval life-stages of marine organisms. This chronic WET test is the 

most sensitive test to polycyclic aromatic hydrocarbons (PAHs). If an effluent contains PAHs and is 

discharged to a marine ecosystem of special importance or fragility, then the echinoderm 

development test should be required. 
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Echinoderm Fertilization Test 

Sea urchin (Strongylocentrotus purpuratus) or sand dollar (Dendraster excentricus)

The echinoderm fertilization test has some advantages over the other WET tests. The combination of 

high sensitivity and short duration (forty minutes) is unique to this test. Very small volumes of 

effluent can be tested successfully and one spawning yields enough material for many tests. TI/REs 

with the echinoderm fertilization test are likely to be more convenient and successful than with other 

WET tests because of these advantages. The echinoderm fertilization test is an excellent rapid 

screening test. It is recommended that permit managers require the echinoderm fertilization test 

when both high sensitivity and ease of use are important. 

Kelp Germination and Growth Test 

Giant kelp (Macrocystis pyrifera) 

If the discharge is to an area with kelp beds, water shallow enough to admit sunlight, or to a rocky 

area that should be capable of supporting kelp, then the kelp germination and growth test should be 

considered. This plant test is a sensitive and reliable test. 

5.11.3 Supplemental Chronic WET Test Species 

The Environment Canada Trout Embryo Viability and EPA Rainbow Trout 7-day Survival and 

Growth test methods are used in the evaluation of stormwater treatment chemicals and can be used in 

permits. The trout embryo test has withstood challenge in front of the PCHB. Because they do not 

qualify under WAC 173-205-050(1)(d), they cannot be used for effluent characterization or 

monitoring for compliance with any WET limit. They can be used in permits as monitoring tools for 

effluents or receiving waters and trigger TI/REs if needed. The TI/RE requirement has also 

withstood PCHB challenge. Contact the PDS Section if you want advice or permit language for 

these two trout tests. 

Three Pacific herring (Clupea pallasi) toxicity tests have been developed for us at the Shannon Point 

Marine Center (SPMC) of Western Washington University. The three tests are a 16-day (7-day 

toxicant exposure) embryo development test, a 4-day acute test with yolk sac larvae, and a 7-day 

larval survival and growth test. These methods do not meet the conditions in WAC 173-205-

050(1)(d) and cannot be used for compliance monitoring but have been put into several permits in 

order to assess the potential impacts of wastewater on the early life stages of Pacific herring. The 

herring tests are also used in the evaluation of ballast water biocides. Contact the PDS Section if you 

want advice or permit language for any of these herring tests. 

5.12 Rapid Screening Test Selection 

5.12.1 Acute Rapid Screening Tests 

Rotifer, Brachionus sp. (ASTM E 1440-91). This test is a 24-hr acute test using rotifers hatched 

from cysts. Tests with organisms hatched from cysts are less expensive because no time or materials 

are consumed by maintaining a culture. This rotifer test is common in Europe and is accepted by 

ASTM. The rotifer test is a sensitive test (except to insecticides) and can be used in freshwater or 

saltwater. 
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24-hr EPA screening tests. If the permittee is uncomfortable with the rotifer test, you might consider 

the EPA 24-hr screening tests instead of the rotifer. The 24-hr EPA acute tests are conducted using 

the same EPA manual and species that were used for effluent characterization. 

5.12.2 Chronic Rapid Screening Tests 

Bacterial bioluminescence test (Microtox® or approved alternate). 

Microtox® can screen more than one effluent sample at a time. The ability to test samples from 

several permittees at one time will lower the cost of Microtox®. Microtox® is a relatively 

inexpensive test and an economy of scale within any lab which tests frequent samples will bring the 

cost down even lower. This low cost will allow very high monitoring frequencies if necessary to 

catch episodes of effluent toxicity. 

Snell, Terry W. 1992. A 2-d Life Cycle Test With The Rotifer Brachionus calyciflorus. Environ. 

Toxicol. Chem. 11:1249-1257. 

The chronic rotifer test has good ecological relevance. The rotifer test measures the intrinsic rate of 

population increase. Measuring the intrinsic rate of population increase simultaneously assesses both 

mortality and reproduction. The chronic rotifer test is as ecologically relevant as any EPA chronic 

tests and about as sensitive as the Ceriodaphnia chronic test. Because it starts with rotifer cysts, uses 

small volumes of effluent, and only takes two days, it will be less expensive than EPA chronic tests. 

The rotifer test may not be sensitive to insecticides. 

Echinoderm Fertilization Test 

The combination of high sensitivity and short duration (40 minutes) is unique. Very small volumes 

of effluent can be tested successfully. Because the echinoderm fertilization test uses the same test 

protocol whether conducted for effluent characterization, compliance monitoring, or rapid screening, 

it is especially useful. It would be a very good rapid screening test.

5.13 Samples for WET Testing 

5.13.1 Advantages of Grab Samples 

The toxicity of an effluent sample begins changing at the time of sampling. Often the toxicity 

decreases, but it can also increase. These changes continue throughout the holding time. Composite 

sampling lengthens the holding time by 24 hours and allows more changes in toxicity to occur. In 

addition, composite samplers contain a large amount of surface area which enhances toxicant 

adsorption or reaction. Composite samplers must be cleaned frequently to prevent toxicant 

adsorption or reaction and the growth of bacteria which can infect the test organisms. The 

compositing process increases the opportunity for the escape of volatile toxicants. Changes in 

dissolved gases during compositing cause changes in pH which ultimately affect the chemistry and 

toxicity of the sample. 

Properly taken grab samples minimize changes in chemistry and provide the most accurate 

measurement of toxicity. Grab samples can be taken quickly with a minimum of equipment, sealed 

in a container with no void space, cooled to 4o C, and sent directly to the lab for testing. 
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5.13.2 Advantages of Composite Samples 

If toxicity varies unpredictably during a day, grab samples will not be representative unless the 

monitoring frequency is increased to compensate. (If toxicity varies over a time period longer than a 

day or produces a huge peak of toxicity for only a few hours out of twenty-four, then 24-hr 

composite sampling will also not be representative.) In addition, permittees can sometimes 

deliberately schedule grab sampling for times of day when the effluent is less likely to be toxic. 24-

hr composites usually provide a representative sample of effluent toxicity. The toxicity highs and 

lows over a day are all represented in the sample. Composite samples are sometimes more difficult 

for permittees to schedule for times predicted to have low toxicity. 

5.13.3 Recommended Sampling Technique 

If the effluent chemistry or toxicity is consistent over time, use grab samples. If sampling can be 

scheduled for times of typical or peak effluent toxicity, use grab samples. 

If grab samples will not be representative of effluent toxicity, use 24-hr composite sampling.

5.13.4 Sampling Chlorinated Effluents 

For all chlorinated effluents, review WAC 173-205-080 to determine whether to test unmodified 

final effluent, test dechlorinated final effluent, or test a sample taken just prior to the chlorinator. 

Samples for WET should be taken before the chlorinator for discharges which can meet water 

quality-based effluent limits for chlorine and have an ACEC below 25% effluent. If the ACEC is 

25% effluent or higher, the effluent is sampled after the chlorinator because extra control on chlorine 

is needed due to the effluent-dominated receiving water. If the treatment plant will begin 

dechlorination within two years, then the sample may be dechlorinated at the lab. 

5.13.5 Low Hardness Samples 

Model permit language now contains an option to allow dischargers of low hardness (< 50 mg/L) 

effluent to sample receiving water at the same time and instruct the lab to increase the hardness of the 

effluent sample to match the hardness of the receiving water sample prior to beginning the toxicity 

test. If hardness is significantly lower in a sample than in the receiving water, metals toxicity in the 

test will be significantly greater than in the environment. Low hardness by itself might reduce 

Ceriodaphnia reproduction or increase sporadic mortalities due to disease in fathead minnows. The 

use of a low hardness sample will produce a hardness gradient in the test concentrations with 

hardness declining as effluent concentration increases and make it difficult to screen for adverse 

effects due to low hardness. In other words, adverse effects due to the hardness gradient will mimic 

toxicity. 

If you are managing a permit that does not yet have the language allowing low hardness samples to 

have hardness increased to match the receiving water, the permit likely says to “test an unmodified 

sample of final effluent.” Keep in mind that effluent samples from discharges to saltwater have 

always had salinity increased to about 30‰ to avoid adverse effects due to a declining salinity 

gradient across test concentrations even though the permit said to test an unmodified effluent sample. 

Therefore, it is probably OK to allow any discharger of low hardness effluent to adjust the hardness 

to match the receiving water. This both makes sense for low hardness discharges to freshwater and 

provides consistency with the standard practice for saltwater testing. 
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5.14 Managing Effluent Characterization Results 

5.14.1 Whole Effluent Toxicity Information Assistance 

As a service to permit managers and permittees, the Water Quality Program purchased CETIS in 

order to be able to provide quality assurance of WET test results and maintain a database able to 

support permitting decisions. CETIS is computer software that creates a record in a database of each 

toxicity test and can automatically perform the statistical procedures in the EPA test manuals. 

CETIS also allows queries of the database to produce tables of the WET test results for each 

permittee. 

The step of the information management system is getting quality records of each permittee's WET 

test results into the database. Achieving quality records requires a review of each WET test, entry of 

the test into CETIS, and performance of the proper statistics. After the record of WET test results is 

completed for a permittee, then the database can be queried to produce a table of effluent 

characterization test results that will assist permittees and permit managers during permit renewal. 

The production of an accurate table of the numbers to be used for regulatory determinations for each 

permittee is the ultimate goal of the information management system.

Permit managers should utilize the services of the Program Development Services Section for 

information management of WET. The PDS Section evaluates every test before entering into the 

data base. Data entered into CETIS is assured of using the proper statistics. Only WET test results 

produced from CETIS should be considered accurate. 

The PDS Section will, upon request, provide summary data of their test results to permittees. 

Therefore, it is essential that all WET data be entered into CETIS and that permittees and permit 

managers receive the same summary information. 

5.14.2 Getting Complete Effluent Characterizations 

If an effluent characterization is not adequate for making regulatory determinations under the WET 

rule, there are several possible solutions. For example, every permittee who is regulated under the 

WET rule, has no WET limits, and conducts no rapid screening testing is required to submit a set of 

WET tests with each permit application [WAC 173-205-030(8)]. Most of the permittees currently fit 

this situation, and when they are informed of the requirement to submit a set of WET tests with the 

permit application, the WET tests could be chosen to complete any inadequate effluent 

characterization. The PDS Section can advise permit managers on how to use this requirement to 

supplement inadequate effluent characterizations with a minimum of extra effort by permittees. This 

assistance will be most valuable if permit managers contact the PDS Section six months prior to the 

application time.
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Table VI-6 . Chemical screening list for WET testing. (40 CFR 403, Appendix C) 

Acenaphthene

Acenaphthylene

Acetaldehyde

Acetic acid

Acetic acid (2,4-dichlorophenoxy)

Acetic acid, lead(2+) salt

Acetic acid, (2,4,5-trichlorophenoxy)

Acetic anhydride

Acetone cyanohydrin

Acetyl bromide

Acetyl chloride

Acrolein

Acrylonitrile

Aldrin

Allyl alcohol

Allyl chloride

Aluminum sulfate

Ammonia

Ammonium acetate

Ammonium benzoate

Ammonium bicarbonate

Ammonium bichromate

Ammonium bifluoride

Ammonium bisulfite

Ammonium carbamate

Ammonium carbonate

Ammonium chloride

Ammonium chromate

Ammonium citrate, dibasic

Ammonium fluoborate

Ammonium fluoride

Ammonium hydroxide

Ammonium oxalate

Ammonium silicofluoride

Ammonium sulfamate

Ammonium sulfide

Ammonium sulfite

Ammonium tartrate

Ammonium thiocyanate

Amyl acetate

Aniline

Antimony pentachloride

Antimony potassium tartrate

Antimony tribromide

Antimony trichloride

Antimony trifluoride

Antimony trioxide

Aroclor 1016

Aroclor 1221

Aroclor 1232

Aroclor 1242

Aroclor 1248

Aroclor 1254

Aroclor 1260

Arsenic 

Arsenic disulfide

Arsenic oxide As2O3

Arsenic oxide As2O5

Arsenic pentoxide

Arsenic trichloride

Arsenic trioxide

Arsenic trisulfide

Asbestos 

Barium cyanide

Benz[a]anthracene

1,2-Benzanthracene

Benzenamine

Benzene

Benzene, 1-bromo-4-phenoxyBenzene, chloroBenzene, chloromethyl1,2-Benzenedicarboxylic acid, 

 dioctyl ester

1,2-Benzenedicarboxylic acid,

 [bis(2-ethylhexyl)]-

1,2-Benzenedicarboxylic acid,

 dibutyl ester

1,2-Benzenedicarboxylic acid,

 diethyl ester

1,2-Benzenedicarboxylic acid,

 dimethyl ester

Benzene, 1,2-dichloroBenzene, 1,3-dichloroBenzene, 1,4-dichloroBenzene,

 1,1'-(2,2-dichloroethylidene)bis[4-chloroBenzene, dimethyl

1,3-Benzenediol

Benzene, hexachloroBenzene, hexahydroBenzene, hydroxyBenzene, methylBenzene, 2-methyl-1,3-dinitroBenzene, 1-methyl-2,4-dinitroBenzene, nitroBenzene, 

1,1'-(2,2,2-tri-chloroethylidene)bis[4-chloroBenzene, 
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1,1'-(2,2,2-trichloroethylidene) bis[4-methoxyBenzidine

Benzol[a]anthracene

Benzo[b]fluoranthene

Benzo(k)fluoranthene

Benzo[j,k]fluorene

Benzoic acid

Benzonitrile

Benzo[ghi]perylene

Benzo[a]pyrene

3,4-Benzopyrene

Benzoyl chloride

1,2-Benzphenanthrene

Benzyl chloride

Beryllium 

Beryllium chloride

Beryllium fluoride

Beryllium nitrate

alpha-BHC

beta-BHC

delta-BHC

gamma-BHC

(1,1'-Biphenyl)-4,4'diamine

[1,1'-Biphenyl]-4,4'diamine, 3,3'dichloroBis (2-chloroethyl) ether

Bis (2-ethylhexyl)phthalate

Bromoform

4-Bromphenyl phenyl ether

1,3-Butadiene, 1,1,2,3,4,4-hexachloro2-Butenal

Butyl acetate

Butylamine

Butyl benzyl phthalate

n-Butyl phthalate

Butyric acid

Cadmium 

Cadmium acetate

Cadmium bromide

Cadmium chloride

Calcium arsenate

Calcium arsenite

Calcium carbide

Calcium chromate

Calcium cyanide

Calcium cyanide Ca(CN)2

Calcium dodecylbenzenesulfonate

Calcium hypochlorite

Camphene, octachloroCarbaryl

Carbofuran

Carbon disulfide

Carbon tetrachloride

Carbonic dichloride

Chlordane

Chlordane, alpha & gamma isomers

Chlordane, technical

CHLORINATED BENZENES

CHLORINATED ETHANES

CHLORINATED NAPHTHALENE

CHLORINATED PHENOLS

Chlorine

CHLOROALKYL ETHERS

Chlorobenzene

4-Chloro-m-cresol

p-Chloro-m-cresol

Chlorodibromomethane

Chloroethane

2-Chloroethyl vinyl ether

Chloroform

beta-Chloronaphthalene

2-Chloronaphthalene

2-Chlorophenol

o-Chlorophenol

4-Chlorophenyl phenyl ether

Chlorosulfonic acid

Chlorpyrifos

Chromic acetate

Chromic acid

Chromic acid H2CrO4, calcium salt

Chromic sulfate

Chromium 

Chromous chloride

Chrysene

Cobaltous bromide

Cobaltous formate

Cobaltous sulfamate

Copper 

Coumaphos

Cresol(s)

Cresylic acid

Crotonaldehyde

Cupric acetate

Cupric acetoarsenite

Cupric chloride

Cupric nitrate

Cupric oxalate

Cupric sulfate

Cupric sulfate, ammoniated

Cupric tartrate

Cyanogen chloride
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Cyanogen chloride (CN)Cl

Cyclohexane

Cyclohexane, 1,2,3,4,5,6-hexachloro-,

 (1 alpha,2alpha,3beta,4alpha,5alpha,6beta)-

1,3-Cyclopentadiene, 1,2,3,4,5,5-hexachloro2,4-D Acid

2,4-D Ester

2,4-D, salts and esters

DDD

4,4' DDD

DDE

4,4' DDE

DDT

4,4'DDT

Diazinon

Dibenz[a,h]anthracene

1,2:5,6-Dibenzanthracene

Dibenzo[a,h]anthracene

Dibutyl phthalate

Di-n-butyl phthalate

Dicamba

Dichlobenil

Dichlone

Dichlorobenzene

1,2-Dichlorobenzene

1,3-Dichlorobenzene

1,4-Dichlorobenzene

m-Dichlorobenzene

o-Dichlorobenzene

p-Dichlorobenzene

3,3'-Dichlorobenzidine

Dichlorobromomethane

1,1-Dichloroethane

1,2-Dichloroethane

1,1-Dichloroethylene

1,2-Dichloroethylene

Dichloroethyl ether

Dichloroisopropyl ether

Dichloromethoxy ethane

2,4-Dichlorophenol

Dichloropropane

1,2-Dichloropropane

Dichloropropane-Dichloropropene (mixture)

Dichloropropene

1,3-Dichloropropene

2,2-Dichloropropionic acid

Dichlorvos

Dicofol

Dieldrin

Diethylamine

Diethylhexyl phthalate

Diethyl phthalate

Dimethylamine

2,4-Dimethylphenol

Dimethyl phthalate

Dinitrobenzene (mixed)

4,6-Dinitro-o-cresol and salts

Dinitrophenol

Dinitrotoluene

2,4-Dinitrotoluene

2,6-Dinitrotoluene

Di-n-octyl phthalate

1,2-Diphenylhydrazine

Diphosphoric acid, tetraethyl ester

Di-n-propylnitrosamine

Diquat

Diuron

Dodecylbenzenesulfonic acid

Endosulfan

alpha - Endosulfan

beta - Endosulfan

Endosulfan sulfate

Endrin

Endrin aldehyde

Endrin, & metabolites

Epichlorohydrin

Ethanal

Ethane, 1,2-dibromoEthane, 1,1-dichloroEthane, 1,2-dichloroEthane, 1,1'-oxybis[2-chloroEthane, 1,1,2,2-tetrachloroEthane, 1,1,1-trichloroEthane, 1,1,2-trichloroEthene, chloroEthene, 2-chloroethoxyEthene, 1,1-dichloroEthene, 1,2-dichloro- (E)

Ethene, tetrachloroEthene, trichloroEthion

Ethylbenzene

Ethylenediamine

Ethylenediamine-tetraacetic acid (EDTA)

Ethylene dibromide

Ethylene dichloride

Ethylidene dichloride

Ferric ammonium citrate

Ferric ammonium oxalate

Ferric chloride
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Ferric fluoride

Ferric nitrate

Ferric sulfate

Ferrous ammonium sulfate

Ferrous chloride

Ferrous sulfate

Fluoranthene

Fluorene

Formaldehyde

Formic acid

Fumaric acid

2-Furancarboxaldehyde

2,5-Furandione

Furtural

Guthion

Heptachlor

Heptachlor epoxide

Hexachlorobenzene

Hexachlorobutadiene

HEXACHLOROCYCLOHEXANE (all isomers)

Hexachlorocyclohexane (gamma isomer)

Hexachlorocyclopentadiene

Hexachloroethane

Hydrazine, 1,2-diphenylHydrochloric acid

Hydrocyanic acid

Hydrofluoric acid

Hydrogen chloride

Hydrogen cyanide

Hydrogen fluoride

Hydrogen sulfide

Hydrogen sulfide H2S

Indeno(1,2,3-cd)pyrene

Isophorone

Isoprene

Isopropanolamine dodecylbenzenesulfonate

Kepone

Lead 

Lead acetate

Lead arsenate

Lead chloride

Lead fluoborate

Lead fluoride

Lead iodide

Lead nitrate

Lead stearate

Lead sulfate

Lead sulfide

Lead thiocyanate

Lindane

Lithium chromate

Malathion

Maleic acid

Maleic anhydride

Mercaptodimethur

Mercuric cyanide

Mercuric nitrate

Mercuric sulfate

Mercuric thiocyanate

Mercurous nitrate

Mercury

Methanamine, N-methylMethanamine, N-methyl-N-nitrosoMethane, bromoMethane, chloroMethane, dichloroMethane, tetrachloroMethane, tribromoMethane, trichloroMethanethiol

Methoxychlor

Methyl bromide

Methyl chloride

Methyl chloroform

Methylene chloride

2-Methyllactonitrile

Methylmercaptan

Methyl methacrylate

Methyl parathion

Mevinphos

Mexacarbate

Monoethylamine

Naled

Naphthalene

Naphthalene, 2-chloroNaphthenic acid

Nickel 

Nickel ammonium sulfate

Nickel chloride

Nickel hydroxide

Nickel nitrate

Nickel sulfate

Nitric acid

Nitrobenzene

Nitrogen dioxide

Nitrogen oxide NO2

Nitrophenol (mixed)

o-Nitrophenol

p-Nitrophenol

2-Nitrophenol
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4-Nitrophenol

N-Nitrosodimethylamine

N-Nitrosodiphenylamine

Nitrotoluene

Oxirane, (chloromethyl)-

Paraformaldehyde

Parathion

Pentachlorophenol

Perchloroethylene

Phenanthrene

Phenol

Phenol, 2-chloroPhenol, 4-chloro-3-methylPhenol, 2,4-dichloroPhenol, 2,4-dimethylPhenol, 2,4-dinitroPhenol, methylPhenol, 2-methyl-4,6-dinitroPhenol, 4-nitroPhenol, pentachloroPhenol, 2,4,5-trichloroPhenol, 2,4,6-trichloroPhosgene

Phosphoric acid

Phosphorothioic acid, 

 O,O-dimethyl O-(4-nitrophenyl) ester

Phosphorus

Phosphorus oxycloride

Phosphorus pentasulfide

Phosphorus sulfide

Phosphorus trichloride

Plumbane, tetraethylPotassium arsenate

Potassium arsenite

Potassium bichromate

Potassium chromate

Potassium cyanide

Potassium cyanide (K(CN)

Potassium hydroxide

potassium permanganate

1-Propanamine, N-nitroso-N-propylPropane, 1,2-dichloroPropanenitrile, 2-hydroxy-2-methylPropane, 2,2'-oxybis[2-chloroPropargite

2-Propenal

1-Propene, 1,3-dichloro2-Propenenitrile

2-Propenoic acid, 2-methyl-, methyl ester

2-Propen-1-o1

Propionic acid

Propionic anhydride

Propylene dichloride

Propylene oxide

Pyrene

Pyrethrins

Quinoline

Resorcinol

Selenium 

Selenium dioxide

Selenium oxide

Silver 

Silver nitrate

Silvex (2,4,5-TP)

Sodium

Sodium arsenate

Sodium arsenite

Sodium bichromate

Sodium bifluoride

Sodium bisulfite

sodium chromate

Sodium cyanide

Sodium cyanide Na (CN)

Sodium dodecylbenzenesulfonate

Sodium fluoride

Sodium hydrosulfide

Sodium hydroxide

Sodium hypochlorite

Sodium methylate

Sodium nitrite

Sodium phosphate, dibasic

Sodium phosphate, tribasic

Sodium selenite

Strontium chromate

Strychnidin-10-one

Strychnine, & salts

Styrene

Sulfur monochloride

Sulfur phosphide

Sulfuric acid

Sulfuric acid, dithallium (1+) salt

2,4,5-T acid

2,4,5-T amines

2,4,5-T esters

2,4,5-T salts

2,4,5-T

TDE

Tetraethyl lead

Tetraethyl pyrophosphate

Thallium 
CHAPTER VI. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATERS (JULY 2011)

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Thallium (1) sulfate

Thiomethanol

Toluene

Toxaphene

2,4,5-TP acid

2,4,5-TP esters

Trichlorfon

1,2,4-Trichlorobenzene

1,1,1-Trichloroethane

1,1,2-Trichloroethane

Trichloroethene

Trichloroethylene

Trichlorophenol

2,4,5-Trichlorophenol

2,4,6-Trichlorophenol

2,4,5-Trichlorophenol

2,4,6-Trichlorophenol

Triethanolamine dodecylbenzenesulfonate

Triethylamine

Trimethylamine

Uranyl acetate

Uranyl nitrate

Vanadium oxide V205

Vanadium pentoxide

Vanadyl sulfate

Vinyl chloride

Vinyl acetate

Vinyl acetate monomer

Vinylidene chloride

Xylene (mixed)

Xylenol

Zinc 

Zinc acetate

Zinc ammonium chloride

Zinc borate

Zinc bromide

Zinc carbonate

Zinc chloride

Zinc cyanide

Zinc cyanide Zn(CN)2

Zinc fluoride

Zinc formate

Zinc hydrosulfite

Zinc nitrate

Zinc phenosulfonate

Zinc phosphide

Zinc silicofluoride

Zinc sulfate

Zirconium nitrate

Zirconium potassium fluoride

Zirconium sulfate

Zirconium tetrachloride
CHAPTER VI. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATERS (JULY 2011)

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Table VI-11. Industry Categories of 40 CFR Part 122, Appendix A.

Industrial Category 40 CFR part

Aluminum Forming 467

Asbestos Manufacturing 427

Battery Manufacturing 461

Builder’s Paper and Board Mills 431

Carbon Black Manufacturing 458

Centralized Waste Treatment 437

Coil Coating and Canmaking 465

Copper Forming 468

Electrical and Electronic Components 469

Electroplating 413

Feedlots 412

Ferroalloy Manufacturing 424

Fertilizer Manufacturing 418

Glass Manufacturing 426

Grain Mills 406

Ink Formulation 447

Industrial Laundries 441

Inorganic Chemicals 415

Iron and Steel Manufacturing 420

Landfills and Incinerators 437

Leather Tanning and Finishing 425

Metal Finishing 433

Metal Molding and Casting 464

Metal Products and Machinery Phase 1 438

Metal Products and Machinery Phase 2 438

Nonferrous Metal Forming and Metal Powders 471

Nonferrous Metals Manufacturing 421

Organic Chemicals, Plastics, and Synthetic Fibers 414

Paint Formulation 446

Paving and Roofing Material 443

Pesticide Formulation, Packaging and Repacking 455

Petroleum Refining 419

Pharmaceutical Manufacturing 439

Porcelain Enameling 466

Pulp, Paper and Paperboard 430/431

Rubber Manufacturing 428

Soap and Detergent Manufacturing 417

Steam Electric Power Generating 423

Sugar Processing 409

Timber Products Processing 429

Transportation Equipment Cleaning 442
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CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-1

CHAPTER VII. DERIVING WATER QUALITYBASED EFFLUENT LIMITS FOR PROTECTION 

OF HUMAN HEALTH

Our water quality standards now include 91 numeric human health-based criteria that permit 

writers must consider when drafting an NPDES permit. These criteria were promulgated for the 

state by the U.S.EPA in its' National Toxics Rule (40 CFR 131.36). Permit writers must 

consider whether a discharge has a reasonable potential to violate these criteria. The criteria are 

listed in TSDCALC. (NOTE: At the time of this publication Ecology is revising the fish 

consumption estimate. This will result in changes in the human health criteria and the 

implementation process.)

This section outlines the process of conducting an initial screening and conducting a reasonable 

potential determination for these chemicals, as well as how to determine monitoring 

requirements and compliance schedules. This guidance complies with the NTR. The process of 

determining a reasonable potential for human health-based criteria exceedances parallels the 

procedure currently used for aquatic life-based criteria (Chapter VI). The decision path for 

human health-based permitting is illustrated in Figure VII-1.

1. WATER QUALITY CRITERIA - BACKGROUND

The human health-based water quality criteria incorporate several exposure and risk 

assumptions. These include (1) a 70-year lifetime of daily exposures, (2) an ingestion rate for 

fish or shellfish in kg/day, (3) 2 liters/day ingestion rate for drinking water, and a one-in-onemillion excess cancer risk for carcinogenic chemicals. In general, these exposure assumptions 

will provide a safe level of protection for most individuals. On the other hand, the criteria do not 

account for additive or synergistic effects of multiple contaminants on human health, and they 

contain the assumption that 100% of exposures come from ingesting fish, shellfish, or waters 

from surface water sources, thus no account is taken of exposures resulting from air, other 

foodstuffs, or groundwater-derived or public drinking water supplies.

Human health criteria are derived by equations that reflect both technical information and policy 

decisions. Many issues associated with establishing human health criteria are complex and 

controversial, but the basic equation and concepts used to derive the criteria are simple. EPA 

changed the methodology for calculating human health criteria in 2000. This resulted in changes 

to some human health criteria, however, EPA did not revise the National Toxic Rule based on 

the new methodology. The following text is from the EPA fact sheet on the revised 

methodology.
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VII-2

Revised Methodology for Deriving Health-Based Ambient 

Water Quality Criteria (2000)

Fact Sheet; October 2000

We have published revisions to the 1980 Ambient Water Quality Criteria National Guidelines to 

better protect human health. The 1980 Ambient Water Quality Criteria National Guidelines 

outline the methodology used by states and tribes to develop human health water quality criteria. 

Revisions to the 1980 guidelines incorporate significant scientific advances in key areas such as 

cancer and non-cancer risk assessments, exposure assessments, and bioaccumulation in fish. The 

revised methodology will provide more flexibility for decision-making at the state, tribal and 

EPA regional levels. It is most likely that the methodology will result in more stringent criteria 

for bioaccumulatives and generally similar values of nonbioaccumulatives. 

Human Health Water Quality Criteria

Human health ambient water quality criteria (AWQC) are numeric values limiting the amount of 

chemicals present in our nation's waters. Human health criteria are developed under Section 

304(a) of the Clean Water Act of 1972 and are designed to protect human health. Water quality 

criteria are developed by assessing the relationship between pollutants and their effect on human 

health and the environment. These criteria are used by states and Indian tribes to establish water 

quality standards and ultimately provide a basis for controlling discharges or releases of 

pollutants. 

The Clean Water Act (CWA) requires EPA to develop, publish and revise ambient water quality 

criteria (AWQC). In 1980, EPA published AWQC for 64 pollutants/pollutant classes and 

provided a methodology for deriving the criteria. These national guidelines addressed three 

types of endpoints: noncancer, cancer and organoleptic (taste and odor) effects. 

The states and tribes use these criteria to develop water quality standards for each water body. 

EPA is required to review periodically criteria adopted by states and tribes. The revisions to the 

EPA's 1980 methodology will help states and tribes establish water quality criteria and standards 

that protect human health. They provide detailed means for developing water quality criteria, 

including systematic procedures for evaluating cancer risk, noncancer health effects, human 

exposure, and bioaccumulation potential in fish. 

EPA Methodology for Deriving Criteria

States and tribes must develop water quality standards that include designated uses and water 

quality criteria necessary to support those uses. The Methodology is the guidance for states and 

tribes to help them establish water quality criteria and standards to protect human health. It 

provides detailed means for developing the water quality criteria, including systematic 

procedures for evaluating cancer risk, noncancer health effects, human exposure, and 

bioaccumulation potential in fish. 
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-3

Risk assessment practices have evolved significantly since 1980, particularly in the areas of 

cancer and noncancer risk assessments (with new information, procedures, and numerous 

published Agency guidelines), exposure assessments (with new studies on human intake and 

exposure patterns, and new science policy guidelines) and methodologies on accounting for 

bioaccumulation in fish. 

General Background of the Revision Process

Revisions began with a national workshop in 1992, where participants discussed critical issues. 

Based on individual expertise, attendees were assigned to technical workgroups including cancer 

risk, noncancer risk, exposure, and bioaccumulation in fish. 

EPA submitted recommendations from the workshop for review and comment by the EPA 

Science Advisory Board. EPA created a workgroup in 1994, including program office and 

regional participants, to revise the methodology. Numerous stakeholder participation activities 

were conducted between 1995 and 1998, including presentations to the Federal-State Toxicology 

and Risk Analysis Committee and several multi-regional water quality coordinator's meetings in 

1996 and 1997, which included participants from EPA regions, states, tribes and some industry. 

Following publication of the draft Methodology revisions, written public comments were 

accepted. Further presentations included the 1998 Annual Meeting of the Society For Risk 

Analysis and the 1999 Annual Meeting of the Society of Toxicology. In May 1999, a peer 

review workshop was held. A public stakeholders meeting was also held then. EPA received 

extensive input on the Methodology from each of these groups. EPA considered all comments 

and incorporated a substantial portion of them into the final AWQC Methodology Revisions. 

Major Methodology Revisions

Publication of final revisions satisfies the requirements of the CWA that EPA periodically revise 

criteria for water quality to reflect accurately the latest scientific knowledge on the kind and 

extent of all identifiable effects on health and welfare that may be expected from the presence of 

pollutants in any body of water. These Final AWQC Methodology Revisions to the 1980 

AWQC National Guidelines are necessitated by the many significant scientific advances made 

during the past 20 years in the key areas of cancer and noncancer assessments, exposure 

assessments, and bioaccumulation in fish. 

The major revisions are in four assessment areas: cancer, non-cancer, exposure, and 

bioaccumulation. 

For carcinogen (cancer) risk assessment: 

• Recommend more sophisticated methods to comprehensively determine the likely mechanism of 

human carcinogenicity. 

• Recommend a mode of action (MOA) approach to determine the most appropriate low- dose 

extrapolation for carcinogenic agents. 
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-4

For noncarcinogens: 

• Use EPA guidance on assessing noncarcinogenic effects of chemicals and for the Reference 

Dose (RfD) derivation. 

• Recommend consideration of other issues related to the RfD process including: integrating 

reproductive/ developmental, immunotoxicity, and neurotoxicity data into the calculation. 

• Recommend the use of quantitative dose-response modeling for the derivation of RfDs. 

• Provide guidance for states and tribes on the use of an alternative value from the RfD point 

estimate, within a limited range, to reflect the inherent imprecision of the RfD. 

For exposure assessment: 

• Encourage states and tribes to use local studies on fish consumption that better reflect local 

intake patterns and choices. 

• Recommend default fish consumption values for the general population, recreational fishers and 

subsistence fishers. 

• Account for other sources of exposure, such as food and air, when deriving AWQC for 

noncarcinogens and nonlinear carcinogens. 

For bioaccumulation: 

• Focus on the use of bioaccumulation factors (BAFs), instead of bioconcentration factors (BCFs) 

for estimating potential human exposure to contaminants via the consumption of contaminated 

fish and shellfish. 

• Use high quality field data over laboratory or model-derived estimates for deriving BAFs, since 

field data best reflect factors which can affect the extent of bioaccumlation (e.g., chemical 

metabolism, food web structure). 

EPA does not plan to completely revise all of the criteria developed in 1980 or those updated as 

part of the 1992 National Toxics Rule. Partial updates of all criteria may be necessary. EPA will 

continue to develop and update toxicology and exposure data needed in the derivation of AWQC 

that may be impractical for the states and regions to obtain. 

Methodology Revisions Implementation by EPA/States

EPA's future role in developing AWQC for the protection of human health will include: 

• The development of revised criteria for chemicals of high priority and national importance 

(including, but not limited to, chemicals that bioaccumulate, such as PCBs, dioxin, and mercury). 

• The development or revision of AWQC for some additional priority chemicals. 

• Technical assistance to states and tribes on the toxicology, exposure and bioaccumulation 

methods, and review of state/tribal water quality standards. 

EPA encourages states and tribes to use the revised methodology to develop or revise AWQC to 

reflect local conditions appropriately. EPA believes that AWQC inherently require several risk 

management decisions that are, in many cases, better made at the state and regional level (e.g., 

fish consumption rates, target risk levels). 
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-5

Effect on State and EPA Regional Offices

The revised methodology will provide more flexibility for decision-making at state, tribal and 

EPA regional levels. EPA believes the AWQC require several risk management decisions that 

are often better made at the state, tribal and regional level. The methodology will probably result 

in more stringent criteria for bioaccumulatives (due to the use of BAFs instead of BCFs) and 

generally similar, or less stringent, values of nonbioaccumulatives. 

The formulas for calculating human health criteria are presented below.

The generalized equations for deriving AWQC based on noncancer effects are:

Noncancer Effects2

( )

4

2

i i

i

BW AWQC RfD RSC

DI FI BAF =

 

 

=• •

+ •

  ∑

2. Although appearing in this equation as a factor to be multiplied, the RSC can also be an amount subtracted. Refer 

to the explanation key below.

Cancer Effects: Nonlinear Low-Dose Extrapolation

( )

4

2

i i

i

POD BW AWQC RSC UF DI FI BAF =

 

 

= ••

+ •

  ∑

Cancer Effects: Linear Low-Dose Extrapolation

( )

4

2

i i

i

BW AWQC RfD

DI FI BAF =

 

 

= •

+ •

  ∑

where:

AWQC = Ambient Water Quality Criterion (mg/L)

RfD = Reference dose for noncancer effects (mg/kg-day)

POD = Point of departure for carcinogens based on a nonlinear low-dose
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-6

extrapolation (mg/kg-day), usually a LOAEL, NOAEL, or LED10

UF = Uncertainty Factor for carcinogens based on a nonlinear low-dose

extrapolation (unitless)

RSD = Risk-specific dose for carcinogens based on a linear low-dose

extrapolation (mg/kg-day) (dose associated with a target risk, such

as 10-6) (Note: The RSD for Washington State is 10-6)

RSC = Relative source contribution factor to account for non-water

sources of exposure. (Not used for linear carcinogens.) May be

either a percentage (multiplied) or amount subtracted, depending on

whether multiple criteria are relevant to the chemical.

BW = Human body weight (default = 70 kg for adults)

DI = Drinking water intake (default = 2 L/day for adults)

FIi = Fish intake at trophic level (TL) I (I = 2, 3, and 4) (defaults for total

intake = 0.0175 kg/day for general adult population and sport

anglers, and 0.1424 kg/day for subsistence fishers). Trophic level

breakouts for the general adult population and sport anglers are:

TL2 = 0.0038 kg/day; TL3 = 0.0080 kg/day; and TL4 = 0.0057

kg/day.

BAFi = Bioaccumulation factor at trophic level I (I=2, 3 and 4), lipid

normalized (L/kg)

2. IMPLEMENTATION - OVERVIEW

The process for developing an effluent limit based on human health (Figure VII-1) parallels the 

existing process for developing aquatic life-based limits. However, there are some differences in 

the procedures used to determine whether a discharge will have a reasonable potential 

determination made for the human health-based criteria. These include two steps where the 

discharge is evaluated for (1) likelihood of discharging chemicals of concern, and (2) an 

evaluation by the agency of whether that discharge is a high priority in the permitting scheme or 

not.

The process of performing a reasonable potential determination is similar to that used for 

evaluating aquatic impacts as indicated by chronic aquatic life-based criteria. The differences 

between the two are the model inputs used to represent the critical flow conditions, the criterion 

values, and the probability values. Other input data, such as the default value for the coefficient 

of variation of effluent variability and statistical confidence level remain the same.
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-7

3. SCREENING AND PRIORITIZATION

Screening and prioritizing discharges to determine whether a reasonable potential determination 

should be made is a two step process.

Step 1. After receipt of an NPDES application, the application should be screened to determine 

if it is a "low risk" discharge or a discharge undergoing modification. These discharges will be 

omitted from implementation at the present time. "Low risk" discharges include non-process 

cooling waters without biocides, gravel mining operations without asphalt processes, or other 

facilities where the permit writer has data or process knowledge to indicate that chemicals 

regulated under the human health criteria are absent. This determination must be made based on 

data or process information pointing to absence of chemicals, and cannot be based on a lack of 

data indicating the presence of chemicals. Discharges undergoing technology-based upgrades or 

improvements that are required by an Ecology order or permit (as specified below) will be 

omitted in order to allow the effluent to stabilize under the new treatment regime. These 

discharges will be considered for human health-based limits after their upgrades are completed. 

These discharges include all industrial storm water dischargers covered under the department's 

general industrial storm water permit and all municipal storm water discharges. If a discharger is 

in the planning phase of upgrades in response to an Ecology requirement, the discharger should 

be told that the effluent will be evaluated for impacts to human health after the upgrades are 

completed. This will allow the discharger to make plans for more extensive upgrades or process 

changes earlier on, if desired, and may result in cost savings. After a discharge has been 

evaluated based on the above criteria, the applicant will either be given no further consideration 

for human health-based permitting at the present time, or will go on to a second prioritization 

step.

Step 2. If the screening step results in a "likelihood" finding, the application should be reviewed 

to determine whether the discharge is a high priority in agency permitting. Those discharges 

termed "high priority" will go on to have a full reasonable potential determination made on them. 

The following discharges are classed as high priorities:

1. All major dischargers.

2. Discharges for which existing data or knowledge of processes indicates the known or 

probable presence of chemicals with human health-based criteria.

3. Facilities discharging to a receiving water that is 303(d)-listed for a chemical with human 

health-based criteria, and that chemical is expected to be in the effluent.

If a discharge fits into any of the three groups described above, a reasonable potential 

determination must be conducted for that discharge. If a discharge does not fit into the groups 

described above, the application should not be considered further for human health-based 
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-8

effluent limits, but the permit writer should consider requiring submittal of a priority pollutant 

scan with the next permit application.

4. THE REASONABLE POTENTIAL DETERMINATION 

The following section reviews the design criteria for making a determination of reasonable 

potential of a violation of the water quality criteria for human health. A summary of these is 

presented in Table VII-2.

4.1 Which Criteria?

A reasonable potential determination is conducted for each chemical in a discharge that (1) has 

an associated human health-based criterion, and (2) has been found (or is known to exist) in the 

discharge during the last permit cycle or upon application.

4.2 Effluent and Background Concentration

Use the 50th percentile effluent concentration for reasonable potential analysis. If there is less 

than 10 effluent data points use a multiplier on the highest effluent concentration to estimate the 

50th percentile concentration. If there is more than 10 values use the cumulative percentile 

calculation at a 95% confidence to derive the 50th percentile (Excel).

For background concentration(s), use 0 for measured value(s) below the MDL and use the MDL

for values between the MDL and the QL. For multiple data points use the geometric mean

4.3 Mixing Zones

The NTR allows states to use mixing zones already placed in state standards, or to default to an 

application of the criteria at the "end-of-pipe"(40 CFR 131.36(c)(2)(i).

Washington's Water Quality Standards (Chapter 173-201A WAC) specifies mixing zone sizes 

for acute and chronic criteria. The mixing zone specified for chronic aquatic life-based criteria 

will be used for the human health-based criteria. This mixing zone allows for some dilution 

when calculating effluent limits, but is still protective of human health.
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VII-9

Figure VII-1. Process for Implementing Human Health Criteria

NPDES PERMIT APPLICATION RECEIVED

IS THIS DISCHARGE A LOW RISK OR IN THE PROCESS OF

INSTALLING TECHNOLOGY-BASED TREATMENT? THESE

INCLUDE:

1. FACILITIES UNDER A COMPLIANCE SCHEDULE FOR

UPGRADES OR TREATMENT MODIFICATIONS

2. NON-PROCESS COOLING WATER WITHOUT BIOCIDES

3. GRAVEL MINING WITHOUT ASPHALT OPERATIONS

4. INDUSTRIAL AND MUNICIPAL STORMWATER

DISCHARGES

5. FACILITIES WITH PROCESS OR EFFLUENT DATA WHICH

INDICATES NONE OF THE 91 CHEMICALS WITH HUMAN

HEALTH CRITERIA ARE PRESENT.

NO FURTHER

CONSIDERATION

IS THIS DISCHARGE A HIGH AGENCY PRIORITY:

- A MAJOR DISCHARGER

- THE EFFLUENT OR PROCESS DATA INDICATES PROBABLE

DISCHARGE OF CHEMICALS WITH HUMAN HEALTH

CRITERIA, OR

- A FACILITY WHICH DISCHARGES TO A RECEIVING WATER

LISTED ON THE 303(d) LIST FOR HUMAN HEALTH

CHEMICAL(S) EXPECTED TO BE IN THE EFFLUENT?*

NO FURTHER

CONSIDERATION

FOR CURRENT

PERMIT CYCLE.

CONSIDER PP

SCAN IN THE

PERMIT OR AT

NEXT

APPLCATION

CONDUCT ANALYSIS FOR REASONABLE POTENTIAL TO VIOLATE THE WATER QUALITY

STANDARDS FOR HUMAN HEALTH

REASONABLE POTENTIAL ?

REQUIRE EFFLUENT MONITORING

FOR POLLUTANTS WITH HH

CRITERIA

PLACE EFFLUENT LIMITS AND COMPLIANCE

MONITORING IN THE PERMIT, GRANT

COMPLIANCE SCHEDULE AND REQUIRE SOURCE

CONTROL AS NECESSARY

YES

NO

NO

NO OR

UNCERTAIN

YES

* SEE CH VI, SECT. 3.3.11
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-10

4.4 Plant Design Flows

The following plant design flows should be used when conducting a human health-based 

reasonable potential determination. Note that the flows differ depending on whether the criterion 

is based on cancer or non-cancer effects (see Table VII-1 to determine this).

Carcinogens

Municipal Effluent - Use the annual average design flow as specified in the engineering 

report, permit application, or a projection of the average annual flow over the life of the 

permit.

Industrial Effluents - Use the annual average flow based on the permit application or DMR 

analysis.

Non-carcinogens

Municipal Effluent - Use the dry weather design flow if the facility flows are within 15% of 

design capacity. If the facility is operating well below design during the critical receiving 

water period, and there is no substantial projected increase in flows for the period of the next 

permit, then use the historical flow as defined by the highest monthly average flow for the 

past three years during the time of year when the critical receiving water period is likely to 

occur.

Industrial Effluents - Use the historical flow as defined by the highest monthly average flow 

for the past three years during the period when the critical receiving water flow is most 

likely to occur. If flows are expected to increase during the life of the permit the highest 

average monthly flow must be estimated.

4.5 Critical Flow Conditions

The NTR specifies that critical receiving water flow conditions in a state's standards may be used 

to determine effluent limits for human health criteria. WAC 173-201A-020 allows the state 

flexibility when determining the critical condition for riverine systems ("...may be assumed equal 

to the 7Q10 flow event unless determined otherwise by the department") and contains a narrative 

statement that can be used to determine a marine critical condition.

The flows used to conduct a reasonable potential determination are specified below, and follow 

the guidance in the NTR as closely as possible. Note that different flows are specified for 

criteria based on cancer effects and non-cancer effects.
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-11

Carcinogens

Freshwater Critical Condition - Use the harmonic mean flow for the representative period 

of record. The representative period is the period that best represents flows as they now 

exist. For instance, if a dam was constructed that modified flows, use data from the time 

after the dam was constructed to determine the critical flow.

Marine/Estuarine Critical Condition - Use the median velocity taken over one tidal cycle 

or from as many tidal cycles as are available in the period of record.

Non-carcinogens

Freshwater Critical Condition - Use the 30Q5 if available or use the 7Q10 as an estimate 

of the 30Q5.

Marine/Estuarine Critical Condition - Use the median velocity taken over one tidal cycle 

or from as many tidal cycles as are available in the period of record.

4.6 Coefficient of Variation of Effluent Concentration

Use 0.6, as is used for aquatic life-based permitting, or the best available estimate (see Chapter 

VI).

4.7 Dilution Factor

Use a value derived from a reliable model (as is used for aquatic life-based permitting) or from 

an ambient dilution study or use percent of flow if that is more stringent. If reliable values are 

not available, estimate flows or use percent of flow to determine reasonable potential and then 

insert a requirement in the permit for the discharger to provide a reliable dilution value to the 

department no later than the next permit reapplication (see Chapter XIII, Monitoring).

4.8 Statistical Confidence Level

Use an alpha equal to 0.05 when calculating reasonable potential.

4.9 Background Data on Chemical Concentrations

Use available background data on chemical concentrations in the water column, or use zero as a 

default value if reliable data are not available.
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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VII-12

Table VII-1. Design conditions for water quality-based permitting of human health criteria.

Design Conditions for Mixing Zone/Ratio Analysis - Human Health 

Criteria

Parameter Pollutant Critical Design Condition

Carcinogen The design effluent flow is defined as the annual 

average flow based on the engineering report, 

permit application or DMR analysis.

Facility 

Effluent 

(Flow)

NoncarcinogenThe design effluent flow is defined as the highest 

monthly average plant effluent flow for the past 

three years during the critical flow or when critical 

condition is likely to occur. If plant effluent flows 

are expected to increase during the life of the 

permit, the highest average monthly flow must be 

estimated.

Carcinogen -

Freshwater

The design receiving water current velocity is 

defined as the current velocity at the harmonic 

mean flow for the representative period of record.

The diffuser depth is defined as the depth at the 

harmonic mean flow.

Receiving 

Water 

(Characteris

tics)

Noncarcinogen -

Freshwater

The design receiving water current velocity is 

defined as the current velocity at the 30-day low 

flow period with a recurrence interval of 5 years 

(30Q5) if available or at 7Q10.

The diffuser depth is defined as the depth at the 

30Q5 or 7Q10 low flow period.

Carcinogen -

Saltwater

The design receiving water current velocity is 

defined as the 50th percentile current velocity 

derived from a cumulative frequency distribution 

analysis. The current velocity frequently 

distribution analysis should be conducted, at 

minimum, over one tidal cycle.

The design ambient density profile is defined as the 

density profile that results in average mixing.

The diffuser depth is defined as the depth at 

MLLW. For estuaries, the diffuser depth is defined 

as the smaller of the median water depth at either 
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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Design Conditions for Mixing Zone/Ratio Analysis - Human Health 

Criteria

Parameter Pollutant Critical Design Condition

the ebb tide or the flood tide during the critical 

receiving water period.

Noncarcinogen -

Saltwater

The design receiving water current velocity is 

defined as the 50th percentile current velocity 

derived from a cumulative frequency distribution 

analysis. The current velocity frequency 

distribution analysis should be conducted, at 

minimum, over one tidal cycle.

The design ambient density profile is defined as the 

density profile that results in average mixing.

The diffuser depth is defined as the depth at 

MLLW. For estuaries, the diffuser depth is defined 

as the smaller of the median water depth at either 

the ebb tide or the flood tide during the critical 

receiving water period.
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Miscellaneous Design Conditions for Mixing Zone/Ratio Analysis

Parameter No. of 

Data 

Points

Methodology

Receiving 

Water 

Background 

Concentration 

(Human 

Health)

N/A The geometric mean of receiving water 

concentrations is used to determine reasonable 

potential. If background is between the MDL and 

the QL use the MDL. If the background 

concentration is below the MDL, use 0. If no 

background data is available use 0.

Effluent 

Concentration 

(Human 

Health)

N/A Use the 50th percentile effluent concentration. If 

there is less than 10 effluent data points use the 

following multipliers (see box following) on the 

highest effluent concentration to estimate the 50th 

percentile concentration. If there is more than 10 

values use the cumulative percentile calculation at 

a 95% confidence to derive the 50th percentile 

(Excel).

Dilution Ratio 

Unidirectional 

flow 

(freshwater)

N/A Flux average

Dilution Ratio 

Multidirection

al flow 

(marine)

N/A Flux average 

Reflux N/A Assume reflux reduces the dilution factor by 1/2 or 

use site-specific data.

The point of compliance with the human health criteria is the boundary of the 

chronic mixing zone.

Chronic design conditions are used for both the initial mixing and the far-field 

mixing calculations. 
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NUMBER OF EFFLUENT 

SAMPLES FOR DETERMINING 

REASONABLE POTENTIAL FOR 

HUMAN HEALTH CRITERIA

FACTORS BY WHICH TO 

MULTIPLY THE HIGHEST 

EFFLUENT CONCENTRATION 

VALUE TO ESTIMATE THE 50TH 

PERCENTILE VALUE (CV = 0.6, 

95% CONFIDENCE)

1 2.5

2 1.5

3 1.2

4 1.0

5 0.9

6 0.9

7 0.8

8 0.8

9 0.7

10 0.7

The values in this table were calculated using EPA's method (TSD, Section 3.3.2) 

of estimating quantile values from a limited data set presumed to be log normally 

distributed.

5. RESULTS OF THE REASONABLE POTENTIAL 

DETERMINATION

The reasonable potential determination will result in three possible outcomes. These are "yes", 

"no", or "can't determine". The following paragraphs explain how to set up permit requirements 

for the three possible results.

5.1 Yes, a Reasonable Potential Exists to Exceed Water Quality 

Standards 

If the reasonable potential determination shows that there is a potential for one or more water 

quality criteria to be exceeded, then effluent limits should be placed in the permit for the 

constituent(s) of concern (TSDCALC). The effluent limits are calculated by setting the average 
CHAPTER VII. WATER QUALITY-BASED EFFLUENT LIMITS FOR SURFACE WATER – HUMAN HEALTH (JULY 04)

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monthly limit equal to the WLA and using Table 5-3 of the TSD (99th and 95th percentile) to 

calculate the maximum daily limit. The HUMAN-H spreadsheet in TSDCALC will perform a 

determination of reasonable potential and calculate limits if there is a reasonable potential. The 

permit should also contain a compliance schedule if one is needed. The length of the compliance 

schedule should be evaluated individually for each facility. The permit should also contain 

source control requirements in order to ensure that efforts to comply with the permit limits in a 

timely manner are being made. These source control requirements should be set out in a phased 

approach. For instance, initial requirements should be to evaluate sources of pollutants, and 

examine ways to control those sources. That phase should be followed by requirements to 

implement methods of control. The timing of the requirements will differ from facility to 

facility. In some cases, where sources are already known and may be easily controllable, short 

compliance schedules may be appropriate. In other cases, unknown sources or reduction issues 

may make a longer compliance schedule appropriate. Source reduction requirements should be 

aimed at pollution prevention, and, if possible, not be aimed at treatment methods that would 

involve large capital expenditures by dischargers. Compliance schedules should be shorter if 

fishing, shellfishing, or drinking water uses of the receiving water body are known or suspected 

to be impaired.

5.1.1. Compliance Monitoring

Permits with effluent limits should also contain requirements for priority pollutant scan 

monitoring during wet and dry seasons of years three and four of the permit. Effluent limits 

must be monitored at least once yearly. The recommended frequency is one/month.

5.2 No, a Reasonable Potential Does Not Exist to Exceed Water 

Quality Standards

If the results of the reasonable potential indicate that an exceedance of water quality standards is 

unlikely to occur, the permit should not contain effluent limits. The permit should, however, 

contain requirements for priority pollutant scan monitoring once during the wet and once during 

the dry seasons of year three of the permit. This information should be submitted with the next 

permit application. In addition, other information may be needed to more clearly make a 

reasonable potential determination at the next permit reissuance. These will be factors that are 

acceptable for decision making at this time, but about which valid biological or engineering 

issues still need to be addressed. For instance, using a river model program to estimate dilution 

is frequently acceptable, but in some cases the physical characteristics of the river (e.g., river 

bottom topography, curvature of river) make a field dilution study desirable to validate the 

model. In this case, although a reasonable potential determination can be made with the 

available data, the permit should contain requirements for a field dilution study to calibrate or 

verify modeling work.
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5.3 The Result of the Reasonable Potential Determination is 

Ambiguous, or, "Can't Determine".

The result "can't determine" will likely result from poor or incomplete effluent data, background 

data or unreliable dilution estimates. If this outcome occurs the permit should be issued with 

requirements to conduct two priority pollutant scans during year three of the permit, one during 

the wet season and one during the dry season. These data should be submitted with the 

appropriate DMRs. In addition, the permit should contain requirements to provide data to clarify 

any other factors leading to the "can't determine" finding. For instance, if the reasonable 

potential determination does not yield a reliable "yes" or "no" result because of unreliable 

dilution information, the permit should require that a dilution study be performed during the 

permit cycle, with data available, at latest, with the next permit application.

6. ANALYTICAL METHODS

See Table VI-5 for the analytical methods that should be used for general priority pollutant 

scans. In general, it is not effective to require an individual and different method for each 

chemical in a priority pollutant scan. Instead, the usual default will be to require the most 

sensitive analytical method for a particular chemical analysis that will measure a suite of 

chemicals (e.g., Method 608 for pesticides).
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CHAPTER VIII. WATER QUALITY-BASED LIMITS FOR GROUND WATER (JULY 2011)

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CHAPTER VIII. DERIVING WATER QUALITYBASED EFFLUENT LIMITATIONS FOR THE 

PROTECTION OF GROUND WATER QUALITY

In Washington, any commercial or industrial operation discharging wastewater to ground must 

have a discharge permit. The permit writer, in developing that permit, must consider the effect 

of the discharge on the quality of ground water.

1. GROUND WATER CRITERIA AND STANDARDS

The Water Quality Standards for Ground Waters of the State of Washington (Chapter 173-200 

WAC) are similar to the water quality standards for surface waters. They define the beneficial 

uses to be protected, they specify the concentrations of chemicals to protect the beneficial uses, 

they have an antidegradation section, and they generally define the point of compliance.

The implementation process for the ground water standards is found in Implementation Guidance 

for the Ground Water Quality Standards, Ecology Publication 96-02. Other guidance documents 

for those wanting to apply for discharges to land are given in Section 3 below.

1.1 Numeric Criteria

The numeric criteria within the ground water standards are divided into I. Primary and 

Secondary Contaminants and Radionuclides and II. Carcinogens. 

2. De MINIMIS APPLICATION OF FOOD PROCESS 

WASTEWATER

General:

De minimis application of food process wastewater to land via irrigation for the purpose of 

treatment is an application that occurs infrequently (e.g., once per year), on a limited area (e.g., 

one-time applications to a specific field), and/or at a nutrient loading rate that is well below the 

crop requirement. If managed properly, de minimis applications of food process wastewater 

benefits both the discharger and the environment by prolonging the viability of wastewater 

disposal sites, and providing nutrient benefit for crops. To qualify as a de minimis discharge, the 

permittee must clearly demonstrate in an Engineering Report that the discharge will have 

minimal potential to impact ground water. All de minimis discharges will be authorized by 

conditions set forth in a state waste discharge permit. To make this type of operation viable, a 

process and permit language was developed to allow these types of applications.
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Review Process:

If a food processing facility intends to propose a de minimis discharge at the time it submits a 

discharge permit application, an Engineering Report, as per Chapter 173-240 WAC, or an 

addendum to an existing approved engineering report must accompany the permit application. 

At a minimum the engineering report must include a description of soil and crop types, depth to 

ground water, distance to any surface water, proposed wastewater irrigation schedule, percent of 

nutrient crop need per year provided by the wastewater, and a statement that the proposed de 

minimis application will be protective of the existing and future beneficial uses of the ground 

water. This is similar to the requirements for submission of an “Abbreviated Engineering 

Report” detailed in Chapter 3 of Guidelines for Preparation of Engineering Reports for 

Industrial Wastewater Land Application Systems (Ecology Publication 93-36). An addendum to 

an existing engineering report must give details of the proposed de minimis application and 

evaluate hydrogeologic conditions at the proposed sites. The facility manager, in coordination 

with the project proponent, will determine if additional evaluation is required for a proposal for 

de minimis application. Adequate guidance currently exists (Implementation Guidance for the 

Ground Water Quality Standards (Ecology Publication 96-02), Guidance for Submission of an 

Engineering Report for Industrial Wastewater Land Treatment Systems, and the Irrigation 

Management Practices Manual, etc.) that allows Ecology to evaluate de minimis application 

proposals from food processors. These manuals provide enough flexibility for Ecology to 

evaluate the need for additional hydrogeologic information and to determine what type of 

monitoring is needed. Review of the Engineering Report will help determine if additional 

hydrogeologic evaluation is needed and what type of monitoring (e.g., effluent quality, 

application monitoring, farm plan evaluation, etc.) is needed to insure the protection of the state's 

ground water resource. After Ecology’s approval of the Engineering Report or addendum, 

permit language should be included to condition the application of wastewater in accordance 

with that described in the Engineering Report or addendum and to address monitoring needs (See 

the following permit language section)

Facilities that decide to make de minimis applications while their current permit is in effect must 

request a permit modification and submit the same type of engineering report or addendum 

discussed above. Approval of the engineering report will result in the permit being modified to 

include new de minimis permit language (See the following permit language section)

Permit Language:

The following is sample permit language to address de minimis wastewater applications of food 

process wastewater to ground. Some sections or conditions may need to be modified by the 

permit writer to address the exact discharge proposal.
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Section S1 (Discharge Limitations)

Beginning on the effective date of this permit and lasting through the expiration date of this 

permit, the Permittee is authorized to apply (state type or source of wastewater) 

during the months of (state month or months of application) to varied crop production 

acreages located (give general location) via ________(state method of 

application)_________ subject to the following limitations:

Hydraulic Loading not to exceed (give condition) and shall not cause ponding or runoff 

of wastewater

Nitrogen (e.g., Total, Nitrate, Ammonia, etc.) Loading not to exceed ____(give condition)_____ 

BOD (e.g., 5-day, soluble, etc.) Loading not to exceed ___(give condition)_____

Solids (e.g., total dissolved, total volatile, etc.) Loading not to exceed ___(give 

condition)______

Chloride not to exceed ____(give condition)______

Other design limiting parameter(s) (give condition) 

(Optional text)

Beginning on the effective date of the permit and lasting through the expiration date of this 

permit, the Permittee is authorized to use wastewater for dust control subject to the provisions of 

the BMPs in their Dust Abatement and Road Management Plan*. The water cannot be used on 

publicly owned lands or roads. 

*See Fresh Fruit Packing General Permit, S5.B.3 and S5.B.5 for guidance.

Section S2 (Monitoring Requirements)

Wastewater

(Monitoring requirements will be site specific and dependent on wastewater characterization 

information presented in the engineering report. The following is an example of wastewater 

monitoring requirements and conditions.)
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Parameter Units

Sampling 

Frequency

Sample Type

Flow 1 gallons/acre; inches/acre; 

gallons/day

Site specific measured

TKN (as N) mg/L; lbs/acre; lbs/day Site specific grab

NH3-N mg/L; lbs/acre; lbs/day Site specific grab

Nitrate (as N) mg/L; lbs/acre; lbs/day Site specific grab

BOD (5-day; total; 

soluble)

mg/L; lbs/acre;lbs/day Site specific grab

Solids (total dissolved; 

dissolved; dissolved 

inorganic)

mg/L; lbs/acre; lbs/day Site specific grab

COD mg/L; lbs/acre; lbs/day Site specific grab

Conductivity umhos/cm Site specific grab

Chloride mg/L; lbs/acre; lbs/day Site specific grab

1 The total amount of wastewater applied to the crop production field and for dust control shall 

be reported each month.

Section S_. IRRIGATION AND CROP PLAN

Annual Summary of Farm Operations for Previous year

This summary shall include:

1.-5.: Use existing permit language

6.. (Depending on site specific conditions and wastewater characteristics in the engineering 

report, add any appropriate reporting conditions for the annual summary submittal)
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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CHAPTER IX. DERIVING EFFLUENT LIMITS 

FOR THE PROTECTION OF AQUATIC 

SEDIMENTS

Permit managers must consider the effect of a proposed discharge to surface waters on the 

quality of aquatic sediments and limit the concentrations of pollutants that cause an exceedance 

of the sediment quality standards (SQS). 

This chapter acquaints the permit writer with the basis of the sediment quality standards and 

defines the permit writer's initial tasks of implementing the standards. This chapter is derived 

from a more comprehensive document called the Sediment Source Control Standards User 

Manual (Ecology 1993). Permit managers who become involved in authorizing sediment impact 

zones (SIZ) or deriving effluent limits based on the sediment quality standards should read the 

Sediment Source Control Standards User Manual to understand those procedures.

This chapter outlines the permit writers tasks for implementing the sediment management 

standards, discusses the sediment quality standards, presents the overall approach for 

implementing the sediment source control standards including the authorization of the SIZ and 

then discusses in more detail the narrative and technical screening conducted by permit writers. 

Sediment monitoring guidance is located in Section 7 of Chapter XIII Monitoring Guidelines. 

Permit writers should realize that the processes described here are only for assessment and 

control of sediment contamination near the point of discharge. Protection from farfield 

contamination relies on customary technology-based and surface water quality-based pollutant 

controls.

1. PERMIT WRITER'S TASKS

For permits to Puget Sound 

Complete the narrative evaluation sheet and the technical evaluation sheets, send a copy of the 

completed sheets when submitting the draft permit for QA review, and discuss the results in the 

fact sheet. Require baseline monitoring or monitoring for model runs if indicated by the 

evaluation. Consult with the Sediment Management Unit (SMU) on the specifics of the 

monitoring requirements. Compare monitoring results with the sediment quality standards.
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For permits to other marine waters

Complete the narrative evaluation sheets and the technical evaluation sheets, attach copies of the 

completed sheets to the draft permit for QA review, and discuss the results in the fact sheet. 

Require baseline monitoring or monitoring for model runs if indicated by the evaluation. 

Consult with the Sediment Management Unit on the specifics of the monitoring requirements. 

Compare sediment quality data with the sediment quality standards on a case-by-case basis.

For permits to low saline waters

Complete the narrative and technical evaluation sheets and send a copy of the completed sheets 

with the draft permit for QA review. Require sediment-related monitoring or other sediment 

requirements only after consultation with the SMU. 

For permits to fresh water

Evaluate the possibility of sediment contamination on a pollutant-specific and facility-specific 

basis. Contact the SMU before placing any sediment-related requirements in permits.

2. THE SEDIMENT MANAGEMENT STANDARDS

Several state laws provide Ecology with the authority to address sediment contamination issues 

in Washington State waters. The most important of these laws, for purposes of implementing the 

Sediment Management Standards, is the Water Pollution Control Act, Chapter 90.48 of the 

Revised Code of Washington (RCW). The Water Pollution Control Act provides Ecology with 

the authority to regulate point and nonpoint source discharges in order to limit discharge-related 

impacts to sediment quality. The Sediment Management Standards rule (Chapter 173-204 

WAC) was developed by Ecology to:

• Establish chemical, biological, and other criteria as standards for the quality of sediments to 

protect beneficial uses and human health. These specific criteria values within the Sediment 

Management Standards are called the Sediment Quality Standards (SQS). The SQS are 

equivalent to the numerical criteria in the surface water quality standards.

• Apply the sediment quality standards (SQS) as the basis for the management and reduction 

of pollutant discharges

• Provide a management and decision process for the cleanup of contaminated sediments.

Additional background information on the development of and rationale for the Sediment 
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Management Standards is available in the Final Environmental Impact Statement for the 

Washington State Sediment Management Standards (Ecology 1990).

The Sediment Management Standards address three main issues. 

First, the rule establishes a narrative sediment quality goal defined as no acute or chronic adverse 

effects on biological resources and no significant health risk to humans caused by sediment 

contamination. The SQS establish the long-term management goal for the quality of sediments 

throughout the state. The SQS are defined by:

• Numerical chemical concentration criteria (chemical concentration criteria for Puget Sound 

marine sediment quality are provided in WAC 173-204-320(2))

• Biological effects criteria (biological effects criteria for Puget Sound marine sediment 

quality are provided in WAC 173-204-320(3))

• Human health criteria (currently under development); WAC 173-204-320(4) and (5)).

Sediments that exceed the SQS criteria are predicted to have adverse effects on biological 

resources or to pose significant human health risks. The SQS criteria may be revised as new data 

are developed regarding the toxicity of contaminants in sediments to human health and the 

environment.

A significant difference between the SQS and the surface water quality standards is that the SQS 

can be superseded by a demonstration that no significant biological effects are occurring. A 

discharger who finds that the SQS are exceeded at the point of discharge may elect to let the 

results stand as an exceedance of the criteria or, alternatively, to conduct biological testing to 

show compliance with the standards.
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TABLE IX-1. MARINE SEDIMENT QUALITY STANDARDS AND SEDIMENT 

IMPACT ZONE MAXIMUM ALLOWABLE CONTAMINATION LEVELS FOR 

PUGET SOUNDa

Chemical Parameter SQS SIZmax

Metals (mg/kg dry weight)

 Arsenic 57 93

 Cadmium 5.1 6.7

 Chromium 260 270

 Copper 390 390

 Lead 450 530

 Mercury 0.41 0.59

 Silver 6.1 6.1

 Zinc 410 960

Nonionizable Organic Compounds (mg/kg organic carbonb)

 Aromatic Hydrocarbons

 Total LPAHc 370 780

 Naphthalene 99 170

 Acenaphthylene 66 66

 Acenaphthene 16 57

 Fluorene 23 79

 Phenanthrene 100 480

 Anthracene 220 1,200

 2-Methylnaphthalene 38 64

 Total HPAHd 960 5,300

 Fluoranthene 160 1,200

 Pyrene 1,000 1,400

 Benz[a]anthracene 110 270

 Chrysene 110 460

 Total benzofluoranthenese 230 450

 Benzo[a]pyrene 99 210

 Indeno[1,2,3-c,d]pyrene 34 88

 Dibenzo[a,h]anthracene 12 33

 Benzo[g,h,i]perylene 31 78

 Chlorinated Benzenes

 1,2-Dichlorobenzene 2.3 2.3

 1,4-Dichlorobenzene 3.1 9

 1,2,4-Trichlorobenzene 0.81 1.8
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Chemical Parameter SQS SIZmax

 Hexachlorobenzene 0.38 2.3

 Phthalate Esters

 Dimethyl phthalate 53 53

 Diethyl phthalate 61 110

 Di-n-butyl phthalate 220 1,700

 Butyl benzyl phthalate 4.9 64

 Bis[2-ethylhexyl]phthalate 47 78

 Di-n-octyl phthalate 58 4,500

 Miscellaneous

 Dibenzofuran 15 58

 Hexachlorobutadiene 3.9 6.2

 N-nitrosodiphenylamine 11 11

 PCBs 12 65

Ionizable Organic Compounds (μg/kg dry weight; parts per billion)

 Phenol 420 1,200

 2-Methylphenol 63 63

 4-Methylphenol 670 670

 2,4-Dimethylphenol 29 29

 Pentachlorophenol 360 690

 Benzyl alcohol 57 73

 Benzoic acid 650 650

Note: HPAH - high molecular weight polycyclic aromatic hydrocarbon

LPAH - low molecular weight polycyclic aromatic hydrocarbon

PCB - polychlorinated biphenyl

SIZmax - Sediment Impact Zone maximum allowable contamination level 

(WAC 173-204-420)

SQS - Sediment Quality Standards (WAC 173-204-320)

a Where laboratory analysis indicates a chemical is not detected in a sediment 

sample, the detection limit should be reported. Where chemical criteria in this 

table represent the sums of individual compounds (e.g., total LPAHs and total 

HPAHs) or groups of isomers (e.g., total PCBs), and a chemical analysis 

identifies an undetected value for one or more individual compounds or groups of 

isomers, the detection limit should be used for calculating the sum of the 

respective compounds or groups of isomers.

b The listed values represent concentrations in parts per million "normalized" on 

a total organic carbon basis. To normalize to total organic carbon, the dry-weight 

concentration for each parameter is divided by the decimal fraction representing 

the percent total organic carbon content of the sediment.
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c The total LPAH criteria are to be compared to the sum of the concentrations of 

the following LPAH compounds: naphthalene, acenaphthylene, acenaphthene, 

fluorene, phenanthrene, and anthracene. 2-Methylnaphthalene is not included in 

the LPAH definition. The total LPAH criteria are not the sums of the 

corresponding criteria listed for the individual LPAH compounds.

d The total HPAH criteria are to be compared to the sum of the concentrations of 

the following HPAH compounds: fluoranthene, pyrene, benz[a]anthracene, 

chrysene, total benzofluoranthenes, benzo[a]pyrene, indeno[1,2,3-c,d]pyrene, 

dibenzo[a,h]anthracene, and benzo[g,h,i]perylene. The total HPAH criteria are 

not the sums of the corresponding criteria listed for the individual HPAH 

compounds.

e The total benzofluoranthenes criteria are to be compared to the sums of the 

concentrations of the b, j, and k isomers of benzofluoranthene.

The numerical chemical concentration criteria and biological effects criteria presently contained 

in the rule (WAC 173-204-320(2) and (3)) apply only to marine sediments in Puget Sound. 

Similar criteria for other marine sediments and for freshwater and low-salinity sediments of 

Washington State are currently being developed by Ecology (WAC 173-204-320(1)(c), 173-204-

330, and 173-204-340). Until such criteria are adopted into the Sediment Management 

Standards, rule compliance with the narrative standard for other marine, freshwater, and lowsalinity sediments will be determined on a case-by-case basis. This document presents a process 

for such case-by-case determinations in Part 4.4.

Second, the Sediment Management Standards set forth a process for managing sources of 

sediment contamination (WAC 173-204-400 through 173-204-420). The SSCS specifically 

address the following aspects of this process:

• A requirement that discharges with the potential to impact receiving sediments have 

received all known, available, and reasonable methods of prevention, control, and treatment 

(AKART) prior to discharge, and/or the application of best management practices (BMPs), 

as appropriate

• Monitoring procedures for evaluating the potential for a discharge to impact the receiving 

sediments

• Procedures for determining whether a discharge is eligible for a sediment impact zone (SIZ), 

which would allow contamination in the receiving sediments to exceed the SQS

• If a SIZ is to be authorized, methods for determining appropriate restrictions (e.g., on the 

allowable areal extent or level of contamination and biological effects)

• SIZ renewal, maintenance, and closure requirements.
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Although the SSCS allow eligible discharges to cause receiving sediments to exceed the SQS, 

the SSCS also set forth specific chemical and biological criteria (WAC 173-204-420) that define 

the maximum level of chemical contamination or biological effects above the SQS that will be 

allowed within an authorized SIZ. This ceiling on chemical contamination and biological effects 

is referred to as the SIZ maximum allowable contamination level, or SIZmax.

Third, the Sediment Management Standards set forth a decision process for identifying 

contaminated sediment sites and determining appropriate cleanup responses (WAC 173-204-500 

through 173-204-590). Natural recovery is recognized as a viable response option for sediments 

that are expected to recover unaided to at least the minimum cleanup level within a 10-year time 

frame. Natural recovery to the SQS may take more than 10 years.

There should be consistency in the levels of sediment contamination and biological effects that 

will be allowed to remain in the environment following source control measures and cleanup at 

contaminated sediment sites. For this reason, the same numerical chemical concentration criteria 

and biological effects criteria have been established for the maximum level of chemical 

contamination or biological effects allowable within an authorized SIZ (i.e., SIZmax; WAC 173-

204-420) and the maximum level of chemical contamination or biological effects allowable once 

cleanup is complete (i.e., MCUL; WAC 173-204-520). These standards have been set at 

chemical concentrations or biological effects levels established by the narrative sediment quality 

regulatory goals that correspond to a “minor adverse effects level” (equal to or higher than the 

SQS).

The narrative goal of the Sediment Management Standards has also been formulated to be 

consistent and compatible with the sediment quality goals of the Puget Sound Dredged Disposal 

Analysis (PSDDA) program, which addresses the management and disposal of sediments 

dredged as part of navigational maintenance or construction activities. Consistency is 

established by setting the SIZmax, CSL, and MCUL at chemical concentrations and biological 

effects levels that are as similar as possible to the PSDDA guidelines for unconfined, open-water 

disposal of dredged material (i.e., PSDDA Site Condition II). Exact correspondence is currently 

not possible because slightly different sets of biological tests and test interpretation guidelines 

are used for the two programs. For the purpose of testing sediments under the various sediment 

management programs, the Puget Sound Estuary Program protocols (PSEP 1991c) provide 

consistent procedures for sediment sampling, chemical analyses, and biological testing, but the 

interpretation of the results is program-specific.

3. OVERVIEW OF THE PROCESS

Figure IX-1 provides an overview of the permitting process and authorization of a SIZ. For the 

sake of simplicity, the process depicted in Figure IX-1 is linear. However, the actual decision-
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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making process followed by permit managers and SMU staff has multiple decision points and 

pathways, which are described in greater detail in subsequent sections of this chapter and in the 

Sediment Source Control Standards Users Manual. In addition, some of the steps illustrated in 

Figure IX-1 are actually implemented in a phased or iterative manner, which is not easily 

represented in this linear flowchart (e.g., the evaluation of the potential for sediment impacts 

may include both generalized and site-specific computer model runs, which are conducted before 

and after, respectively, the request for a SIZ application). This section only discusses in detail 

the part of the process up to the application of the SIZ.

In the following subsections, the primary provisions and requirements of the SSCS with respect 

to the sediment source control standards permitting process are described. This process 

generally follows the 10-step process outlined in WAC 173-204-400(1)(a)–(j), but the order of 

discussion in the following subsections has been modified slightly to correspond to the 

permitting process as implemented by the WQP. The subsections of the rule corresponding to 

each step are indicated. When appropriate, reference is made to subsequent chapters of this 

manual for implementation guidance.

3.1 Evaluation of the Potential for a Discharge to Impact Receiving 

Sediments (WAC 173-204-400(1)(a))

A screening-level evaluation of the potential for a discharge to cause sediment impact is 

conducted when a permit application is accepted for a new or existing discharge. The screeninglevel evaluation, which consists of both narrative and technical evaluations, is described in 

Section 4.

If the screening-level evaluation indicates that it is unlikely that the discharge would adversely 

impact the receiving sediments, the permit is issued or renewed without sediment monitoring, a 

SIZ authorization, or sediment quality-based effluent limits. The evaluation sheets are sent to the 

SMU.

If the screening-level evaluation indicates a potential for a discharge to adversely impact 

receiving sediments the sediment-related information is forwarded to the SMU with the 

evaluation sheets. The SMU then runs a generalized SIZ computer model(s) (such as the Cornell 

Mixing Zone Expert System [CORMIX], or Water Quality Analysis Simulation Program 

[WASP]) using readily available information. The purpose of this generalized model run is to 

determine whether the discharge has the potential to cause an exceedance of the SQS numerical 

criteria (Table IX-1) within a 10-year period from the date of Ecology's evaluation of the 

ongoing discharge or the starting date of the proposed discharge, whichever is later (WAC 173-

204-415(2)).

If there is evidence of an SQS violation, if sufficient data are available, and if the discharge is 

from a priority facility (see Figure IX-1), a site-specific model run will also be performed. 
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Additional data required for either the generalized or site-specific model runs may be requested 

from the discharger. The results of these model runs and application of the SMU's best 

professional judgment provide the basis for predicting the potential for a discharge to result in 

sediment impacts. The generalized and site-specific model runs are described in the Sediment 

Source Control User Manual. In some cases, a compliance schedule may be established during 

the period required for collection of additional data to support application of the models.

In addition to the modeling data, monitoring data may be used to evaluate the potential for a 

discharge to cause an exceedance of the SQS. Guidance on the use of monitoring data for this 

purpose is provided in Chapter XIII Section 7.
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Figure IX-1. Overview of process and responsibilities for the protection of aquatic sediments.

TASK RESPONSIBILITY

Wastewater Discharge Permit Application Discharger

Screening-level Evaluation of the

Potential for Sediment Impacts Water Quality Program

Detailed Evaluation of the Potential for

Sediment Impacts Sediment Management Unit (SMU)

Application for sediment impact zone (SIZ) Sediment Management Unit

Assess Eligibility for SIZ Sediment Management Unit

Sediment Management Unit

Develop SIZ Specifications and

Sediment Quality-Based Effluent

Limits

Develop Monitoring Requirements

Notify Public and Affected Landowners

Sediment Management Unit/ Water Quality

Water Quality

Authorize SIZ (if appropriate) Water Quality

Monitoring of

SIZ Sediment Management/Water Quality

Renewal or Modification of

SIZ Sediment Management Unit/Water Quality

Closure of SIZ Sediment Management Unit/Water Quality

TASK RESPONSIBILITY

Wastewater Discharge Permit Application Discharger

Screening-level Evaluation of the

Potential for Sediment Impacts Water Quality Program

Detailed Evaluation of the Potential for

Sediment Impacts Sediment Management Unit (SMU)

Application for sediment impact zone (SIZ) Sediment Management Unit

Assess Eligibility for SIZ Sediment Management Unit

Sediment Management Unit

Develop SIZ Specifications and

Sediment Quality-Based Effluent

Limits

Develop Monitoring Requirements

Notify Public and Affected Landowners

Sediment Management Unit/ Water Quality

Water Quality

Authorize SIZ (if appropriate) Water Quality

Monitoring of

SIZ Sediment Management/Water Quality

Renewal or Modification of

SIZ Sediment Management Unit/Water Quality

Closure of SIZ Sediment Management Unit/Water Quality
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3.2 Application for a SIZ (WAC 173-204-400(1)(b))

If the results of the generalized SIZ computer model run indicate that the discharge has the 

potential to impact sediments, Ecology will require an application for a SIZ. WAC 173-204-

200(22) defines a SIZ as:

...an area where the applicable sediment quality standards of WAC 

173-204-320 through 173-204-340 are exceeded due to ongoing 

permitted or otherwise authorized wastewater, storm water, or 

nonpoint source discharges, and authorized by the department within 

a federal or state wastewater or storm water discharge permit, or other 

formal department authorization.

By the authority of WAC 173-204-415(4)(a), Ecology may require a discharger to submit any 

information needed to run the SIZ models (simulating sediment contamination over a 10-year 

period) to determine whether a SIZ is necessary and to determine the areal extent and location of 

the SIZ associated with the discharge. The SMU is responsible for requesting and evaluating 

applications for SIZs. SIZ application procedures are described in the Sediment Source Control 

Standards Users Manual. When an application is received, the SMU will notify the Washington 

Department of Natural Resources (DNR) Division of Aquatic Lands, U.S. Army Corps of 

Engineers (Corps), and any port districts whose aquatic lands may be included within the 

proposed SIZ (WAC 173-204-415(2)(f)).

3.3 SIZ Eligibility Requirements (WAC 173-204-400(1)(c) and (f))

Once a SIZ application is received, the discharge must be evaluated to determine whether it is 

eligible for a SIZ. The SMU is responsible for the eligibility evaluation.

All discharges are required to be operating with AKART and/or BMPs in place, as appropriate, 

or to be on a compliance schedule to meet these requirements, as a condition of a discharge 

authorization (Chapters 90.48, 90.52, and 90.54 RCW). This issue will, therefore, be addressed 

early in the discharge permitting process, regardless of the potential for the discharge to cause an 

impact to receiving sediments. However, to determine whether a new discharge or one not yet 

operating with AKART/BMPs in place will adversely impact receiving sediments, 

AKART/BMPs must be identified and assessed in the initial screening evaluation. Chapter IV of 

this manual should be consulted for guidance on the process of determining AKART/BMPs for a 

given discharge. This evaluation will be conducted before a permit application is forwarded to 

the SMU for SIZ evaluation.

WAC 173-204-415(3) requires the discharger to submit to Ecology information concerning the 

location of the proposed SIZ. This section also requires that SIZs authorized by Ecology avoid 

whenever possible, and minimize adverse impacts to, areas of special importance. A SIZ must 
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also be authorized in a manner consistent with the antidegradation policy of the state, as set forth 

in WAC 173-204-120.

The areal extent of a SIZ will be determined based on the results of the modeling and the 

application of the SMU's best professional judgment. When the model results indicate that a SIZ 

may impact an area of special importance or property owned by someone other than the 

discharger, it may be necessary to alter the discharge characteristics (e.g., by relocating the 

discharge, reducing effluent loading) to avoid impacting such areas.

3.4 Development of SIZ Specifications 

(WAC 173-204-400(1)(d),(e), and (g))

After determining that the discharge is eligible for a SIZ, detailed model simulations are run 

using site-specific information provided in the SIZ application. The CORMIX and WASP 

models, or other SIZ model(s) can be used. The SMU is responsible for application of 

contaminant fate and transport modeling to the discharge.

The site-specific model run is used to reduce the uncertainty associated with the generalized 

model run, develop SIZ specifications, and evaluate the potential for the discharge to exceed the 

SIZmax numerical criteria over a 10-year period from the date of Ecology's evaluation of an 

ongoing discharge or the start date of a proposed discharge, whichever is later (WAC 173-204-

415(4)). The site-specific model may also be used to establish sediment quality-based effluent 

limits necessary to achieve acceptable levels of sediment quality. WAC 173-204-415(4) 

specifies that the models be run by Ecology or by the discharger, as required by Ecology.

In addition to the modeling data, monitoring data may be used to evaluate the potential for a 

discharge to cause an exceedance of the SIZmax numerical criteria. Guidance on the use of 

monitoring data for this purpose is provided in Chapter XIII Section 7.

As stated in WAC 173-204-415(1)(e), SIZs authorized by Ecology shall include the minimum 

practicable surface area, not to exceed the surface area allowed by WAC 173-204-415(4). WAC 

173-204-415(4) in turn requires that the location of the SIZ, its areal extent, and the degree of 

allowable effects within the SIZ be determined by applying the SIZ models (CORMIX, WASP, 

and/or other SIZ model[s] approved by Ecology) as limited by the standards of that section, and 

by application of best professional judgment.

Any overlap of the SIZs for two or more discharges predicted through the use of the SIZ models 

or based on best professional judgment will be authorized only in the event that the SIZmax

chemical and biological criteria are not exceeded as a result of the overlap. If multiple 

discharges would result in sediment contamination above the SIZmax, a wasteload allocation 

process would be necessary (WAC 173-204-415(4)(b)(ii)). The SMU is responsible for running 

the SIZ models for this purpose and will work with Ecology's Environmental Assessment 
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Program and the WQP in developing wasteload allocations.

WAC 173-204-415(1)(f) also requires that the chemical concentrations and biological effects 

levels within an authorized SIZ be maintained at the lowest levels possible. Ecology is required 

to consider the relationship between environmental effects, technical feasibility, and cost in 

determining the minimum practicable chemical concentration and biological effects levels, 

within the range of contamination that will be allowed in an authorized SIZ. In no case should 

the adverse effects to biological resources within an authorized SIZ exceed the minor adverse 

effects level as a result of the discharge, as determined by the procedures set forth in WAC 173-

204-415(5). This activity is the responsibility of the SMU.

3.5 SIZ Monitoring and Maintenance Requirements

(WAC 173-204-400(1)(i))

All SIZ authorizations should include monitoring and maintenance requirements designed to 

ensure that the specifications included in the authorization are not violated. Such requirements 

should include sediment and effluent monitoring and procedures for maintenance restoration of 

sediments (i.e., if the discharge results in sediment contamination or biological effects that 

exceed the maximum levels allowed in the SIZ authorization, capping or dredging of the 

contaminated sediments may be required). Permit managers and SMU staff jointly develop 

monitoring and maintenance requirements.

3.6 Public Notice and Landowner Notification Procedures

(WAC 173-204-400(1)(h))

In accordance with WAC 173-204-415(1)(j), all proposed SIZ authorizations are subject to 

public notice, comment, and hearing procedures as required by the state laws and regulations 

applicable to the specific discharge. When determining the need for, location, and/or design of 

the SIZ, Ecology is required to consider all comments received during public review of the 

application. The permit manager is responsible for public notice and landowner notifications. 

However, as discussed above, the SMU will also notify DNR, the Corps, and affected port 

districts early in the process of reviewing a SIZ application. The discharger should also be 

encouraged to make an early effort to identify and coordinate with the potentially affected 

landowner(s).

In some cases, an authorized SIZ will be located on property owned or used by someone other 

than the source discharger. Recognizing that the potential sediment impact resulting from the 

discharge may be of concern to the other individual(s), WAC 173-204-415(2)(e) requires that 

Ecology and the discharger make a reasonable effort to identify and notify all landowners, 

adjacent landowners, and lessees potentially affected by the proposed SIZ. Under the authority 

of WAC 173-204-415(2)(e)(viii), affected landowners, adjacent landowners, and lessees may 

comment on a proposed SIZ. Any such comments are to be submitted in writing to Ecology 
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within 30 days from the date of receipt of the notification letter, or by an extended due date 

approved by Ecology. WAC 173-204-415(5)(e) also requires that affected landowners be given 

the opportunity to review all SIZ maintenance action plans before the action is implemented. 

3.7 Renewal, Modification, and Elimination of Authorized SIZs 

Over Time (WAC 173-204-400(1)(j))

The goal of Ecology is to manage source control activities to reduce and ultimately eliminate 

adverse effects on biological resources and significant threats to human health resulting from 

sediment contamination (WAC 173-204-410(1)(a)). In support of that goal, it is Ecology's 

policy to minimize the number, areal extent, and adverse effects of all authorized SIZs, with the 

intent to eliminate the existence of all SIZs whenever practicable (WAC 173-204-410(1)(b)). 

This goal will be achieved through modification of existing SIZ specifications and by limiting 

the renewal of SIZs when possible. However, the rule addresses exceptions to this general 

policy by requiring that Ecology consider environmental effects, technical feasibility, and cost in 

determining when it is practicable to minimize or eliminate a SIZ.

WAC 173-204-415(8) sets forth the conditions under which a SIZ authorization may be renewed. 

These conditions include:

• When the discharge is operating with AKART/BMPs in place

• When the discharger demonstrates that the discharge activities comply with the SSCS and 

with the existing SIZ authorization

• When the discharger demonstrates that a reduction in the areal extent of the SIZ and/or the 

level of contamination within the SIZ is not practicable, and therefore the SIZ cannot be 

reduced or eliminated.

WAC 173-204-415(7) specifically authorizes Ecology to modify a SIZ authorization under the 

following conditions:

* When the nature of the discharge activity has changed

* When new information indicates that a modification of the SIZ authorization is 

appropriate

* When the standards or regulations upon which the permit was based have changed

* When there is advancement in technology that applies to the discharge under 

consideration.
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This section should be interpreted to provide Ecology with the authority to both restrict and relax 

SIZ specifications, as appropriate, based on a consideration of environmental effects, technical 

feasibility, and cost, consistent with the requirements of the SSCS.

Guidance for determining whether it is practicable to modify or eliminate a SIZ, whether SIZ 

maintenance activities should be required, or whether a SIZ should be renewed at the end of the 

permit cycle without modification is provided in the Sediment Source Control Standards Users 

Manual. SMU staff and permit managers share the responsibility for this determination. Permit 

managers will conduct an initial screening of the renewal application. If it appears that a SIZ 

authorization should be modified, the renewal application will be forwarded to the SMU for a 

detailed evaluation.

3.8 Closure and Restoration of SIZs (WAC 173-204-400(1)(I))

WAC 173-204-415(6) requires that all SIZ authorizations include a SIZ closure plan. The 

purpose of this plan is to identify the method or methods of cleanup that the discharger will 

implement upon closure of the SIZ. The responsibility for overseeing SIZ closure and 

restoration activities will be determined by Ecology on a case-by-case basis.

4. SCREENING-LEVEL EVALUATION OF POTENTIAL 

FOR SEDIMENT IMPACTS

The general process for determining whether a SIZ is needed and for developing SIZ 

specifications is illustrated in Figure IX-2. The first step in this process is for the permit 

manager to perform a screening-level evaluation of whether the discharge has the potential to 

impact sediment quality. This chapter describes the screening-level evaluation, which includes 

both narrative and technical evaluations. The WQ Program has determined that all major 

dischargers to Puget Sound will conduct sediment sampling.

Screening-level evaluations are required for all marine surface water discharges to determine 

their potential to cause an exceedance of the SQS numerical criteria.

4.1 Initiation of Activities

In the initial stages of the permitting process, three general categories of activities that relate to 

sediment quality impacts are initiated by the permit manager:

• Assess Status of Source Control—The status of source control activities is routinely 

assessed to determine whether AKART and BMPs are in place. If the facility has not 

yet achieved AKART/BMPs, a compliance schedule should be developed, and 
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estimates should be made of effluent characteristics (including contaminant 

concentrations) to be achieved with AKART/BMPs.

• Perform Screening-Level Evaluation of the Potential for Sediment Impacts—

Existing information on the qualitative and quantitative characteristics of the facility, 

discharge, and receiving environment is reviewed to determine whether there is a 

potential for a discharge to cause sediment quality impacts.

• Evaluate Baseline Monitoring Data—Available baseline monitoring data for 

sediments and receiving water in the vicinity of the discharge should be identified and 

reviewed. If the screening-level evaluation indicates the potential for a discharge to 

cause sediment impacts, and if available baseline data are inadequate, additional 

baseline monitoring may be necessary. Monitoring data and other local sediment data 

(e.g., data in the SMU SEDQUAL database) will also be used at a number of decision 

points in the SIZ development process.

These activities are discussed on the following page.
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Figure IX-2. Screening-level Evaluation of Potential for Sediment Impacts

Permit Application

Conduct Narrative Evaluation

Does Narrative

Evaluation Indicate a

Potential for Violation

of the SQS?

- No baseline monitoring 

- Discuss lack of

potential in the fact sheet

- Send evaluation sheets 

with draft permit to QA

reviewer

No

Are Data

Available to

Conduct Technical

Evaluation?

Yes

- Require baseline sediment monitoring

in the permit or by order and discuss in

the fact sheet

Conduct Technical

Evaluation

No

Yes

Does Technical 

Evaluation Indicate

Potential for Sediment

Contamination?

- No Baseline Monitoring or

other Sediment Requirements.

- Identify the Lack of Potential

in the Fact Sheet

- Send Worksheet with the

draft permit to QA reviewer

No

Are Data Available

for a General Computer

Run?

Yes

SMU runs the

General Model

Require Data

Collection in the

Permit or by

Order.

Consult SMU Regarding Further

Requirements

Yes

No
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4.1.1 Assess Status of Source Control

WAC 173-204-400(2) requires all permits or other authorizations for wastewater, stormwater, 

and nonpoint source discharges to surface waters of the state to be conditioned so that the 

discharger is operating with AKART and/or BMPs prior to discharge, as required by Chapters 

90.48, 90.52, and 90.54 RCW. Thus, all regulatory actions taken under the Sediment 

Management Standards are based on the assumption that the discharger either is operating with 

AKART and/or BMPs in place, or is on a compliance schedule to meet these requirements. 

Chapter IV should be consulted for guidance on the process of identifying AKART/BMPs for the 

various types of discharges.

Ecology recognizes that it may take some time for an existing discharge to come into compliance 

with the requirements of AKART. If a discharge of this type has the potential to impact 

receiving sediments before coming into compliance with AKART, a SIZ may be authorized 

while a compliance schedule is being implemented. If receiving sediments become 

contaminated above the level allowed within the SIZ before AKART is in place, Ecology may 

require the discharger to conduct maintenance restoration of the impacted sediments before or as 

part of the SIZ authorization.

The permit manager should also document recent changes in treatment processes and assess time 

trends in discharge loading characteristics. If a compliance schedule is to be implemented for the 

achievement of AKART/BMPs, it will be necessary to estimate effluent characteristics 

(including contaminant concentrations) to be achieved with AKART/BMPs for SIZ modeling 

and authorization.

In addition to the AKART/BMP requirement, WAC 173-204-415(1)(d) requires that the 

discharger adequately addresses alternative waste reduction, recycling, and disposal options. 

The permit manager is responsible for verifying this requirement, which would normally be 

addressed in the discharger's solid waste plan, spill plan, and/or pollution prevention plan.

4.1.2. Perform Screening-Level Evaluation of the Potential for Sediment 

Impacts

The initial screening-level evaluation of the potential for a discharge to impact receiving 

sediments is based primarily on readily available qualitative and quantitative information. The 

evaluation consists of two parts, a narrative evaluation and a technical evaluation.

In general, facilities handling or producing known contaminants that are commonly associated 

with pollution problems are considered to have a potential for causing sediment contamination 

and will generally undergo a detailed evaluation by the SMU. If relevant contaminant loading 

data are available for the discharge, screening equations can be applied as part of the technical 

evaluation, and a preliminary assessment of the potential for sediment impacts can be made.

Facilities that have been in place and discharging wastewater at a steady rate for several years 

can also be evaluated through direct measurement of chemical concentrations or biological 
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effects in the receiving sediments. If no sediment contamination or biological effects are found, 

it may be assumed that there is little potential for sediment contamination to occur in the future 

unless the loading rate is expected to increase. Alternatively, if a discharger is being granted an 

increase in permitted contaminant loading rates, evaluation of existing sediment conditions may 

not be sufficient, and the detailed evaluation may be necessary.

Once the screening-level evaluation is complete, the worksheets should be filed with the permit 

application and a copy of the worksheets forwarded to the SMU. If the screening-level 

evaluation indicates that there is little or no potential for sediment impacts, the permit manager 

may determine that no specific sediment-related provisions need to be included in the discharge 

permit. If there is considered to be a potential for sediment impacts, the permit manager should 

evaluate available baseline monitoring data, or, if available baseline monitoring data are 

inadequate, the discharger should be required to collect the necessary baseline monitoring data 

(see Part 4.1.3).

The narrative and technical evaluation steps are described in detail in subsections 4.2 and 4.3, 

which include worksheets that can be used in the evaluation.

4.1.3. Evaluate Baseline Monitoring Data

The results of any baseline sediment quality monitoring, if available, should be reviewed by the 

permit manager to establish baseline sediment quality conditions. These monitoring data, as well 

as available regional monitoring data from other programs (e.g., data in the SMU SEDQUAL 

database), should be reviewed early in the permitting process to identify any additional 

monitoring that may be required and to identify data that may be used to evaluate the need for a 

SIZ.

In the sediment source control process, early evaluation of available baseline monitoring data is 

important because it assists in identifying sediment contaminants that may have been contributed 

by other permitted or unpermitted (and possibly historical) discharges. In addition, this 

evaluation may enable Ecology to identify the single or multiple ongoing discharges contributing 

to sediment contamination in a given area, and thus to regulate these discharges as appropriate.

In cases where no baseline monitoring has previously been conducted and the result of the 

screening-level evaluation is a judgment that the discharge has the potential to cause sediment 

impacts, a requirement for baseline monitoring should be included in the permit. The permit 

manager is responsible for developing baseline monitoring requirements, where appropriate, with 

assistance of the SMU. In cases where there are also insufficient data available to run even the 

generalized SIZ model, additional monitoring requirements should be included in the permit for 

the collection of the necessary data. Guidance on the development of monitoring requirements 

to support use of the models is also provided in Chapter XIII.
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In cases where there is a potential for sediment impacts and the needed monitoring data have not 

yet been collected, the permit may be issued or renewed without a SIZ authorization, but with the 

requirement for appropriate monitoring to be conducted early in the permit cycle. Once the 

necessary monitoring has been completed, the data can be used to complete the detailed 

evaluation of the potential to cause sediment impacts. If the result of the detailed evaluation is 

that a SIZ is needed, the permit can then be modified to authorize a SIZ.

4.2 Narrative Evaluation of the Potential for Sediment Impacts

The narrative evaluation may be used to identify facilities that have a low potential for sediment 

impacts, based on the general characteristics of the facility and the nature of the discharge. 

Facilities identified as having a low potential for sediment impacts by the narrative evaluation 

need not be evaluated using the more detailed technical evaluation. The permit manager should 

conduct the narrative evaluation by filling out the narrative evaluation worksheet (Figure IX-3). 

If the facility has any of the characteristics identified in Item 1 of the worksheet, its discharge is 

considered to have the potential for causing adverse sediment impacts. If the discharge is one of 

the types identified in Item 2 of the worksheet, or if the facility has none of the characteristics 

identified in Item 1 of the worksheet, the discharge is not considered to have a potential for 

causing adverse sediment impacts. The permit manager should indicate in response to Item 3 

whether or not the discharge is considered to have the potential to cause adverse sediment 

impacts.

Although a definitive assessment of a discharge's eligibility for a SIZ can only be made after the 

development of SIZ specifications, it is appropriate as part of the narrative evaluation to provide 

a preliminary indication of whether the discharge would be eligible for a SIZ. One of the criteria 

for authorization of a SIZ is that it not adversely affect an area of special importance and that it 

be in the public interest. The permit manager should make this determination during the 

narrative evaluation and indicate to the SMU if the discharge is eligible for a SIZ.

4.3. Technical Evaluation of the Potential for 

Sediment Impacts

If the narrative evaluation identified the facility as having the potential for sediment impacts and 

if the necessary data are available, the screening-level evaluation should also include a technical 

evaluation, as described below. This evaluation uses readily available information on the 

discharge, along with any baseline monitoring data, to determine whether there is a potential for 

the SQS numerical criteria to be exceeded in the receiving sediments. If there are insufficient 

data to conduct the technical evaluation, the discharger will be required to provide the data 

necessary to further evaluate the need for a SIZ (see Chapter XIII, Section 7).

To date, SQS numerical criteria have only been promulgated for marine sediments within Puget 

Sound. Hence, the technical evaluation procedures described in this section currently apply only 
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to discharges to Puget Sound marine environments. Use of these procedures for evaluating 

discharges to non-Puget Sound marine environments may be appropriate based on the case-bycase application of best professional judgment by the permit manager, with guidance from the 

SMU. Until SQS numerical criteria for sediments in freshwater and low-salinity environments 

are developed, other evaluation procedures will have to be used for discharges to those 

environments (see Subsection 3.4).

If there are chemicals of concern in a marine discharge that have SQS numerical criteria (see 

Table IX-1), the permit manager should complete the technical evaluation worksheets and attach 

them to the narrative evaluation. If the discharge is of concern, but not enough data are available 

to complete the technical evaluation or the chemicals of concern do not have SQS numerical 

criteria, the permit application should be forwarded to the SMU for a case-by-case evaluation.

4.3.1 Methods of Evaluation

Sediment contaminant concentrations can be measured directly or can be estimated using a 

variety of sampling methods. These methods include sampling particles or sediments in sumps, 

drains, or the receiving environment, or sampling suspended particulate matter in the water 

column or suspended solids in an effluent entering the receiving water. In addition, the results of 

biological tests may be used to evaluate the potential for impacts to sediments. Alternatively, 

data on the total chemical concentrations in an effluent can be used to estimate the chemical 

concentrations associated with discharged particles. Once sediment or particle chemistry has 

been determined, the concentrations can be compared directly to the SQS numerical criteria to 

evaluate whether a discharge has the potential to cause an exceedance of the standards. Methods 

for sampling sediment and suspended particulate matter are described in greater detail in Chapter 

XIII.

Figures IX-3 through IX-7 provide worksheets for completing the technical evaluation. In 

addition to information provided in the permit application, existing effluent monitoring data and 

baseline monitoring data should be reviewed and used in the evaluation. The following four 

types of data may be used (see Sections 1–4 of the technical evaluation worksheet):

* Chemical Concentrations in Source Sediments and Effluent Suspended Solids —

These data include the concentrations of chemicals in sediments that may accumulate at points 

within the facility downstream of any treatment processes (e.g., ditch, outfall, sump) or the 

concentrations of chemicals associated with suspended solids in the effluent. Because these data 

are most closely related to source characteristics, this section of the worksheet should always be 

completed if such data are available.

* Chemical Concentrations in Receiving Sediments and Settling Particulate Matter 

in the Water Column — Baseline monitoring data or other data on receiving sediments near the 

point of discharge are most useful in evaluating potential impacts from a source that has been 

ongoing at a similar level of discharge for 5 years or more. If such data are available near 
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existing outfalls, this section of the worksheet should be completed, unless there is sufficient 

reason to believe that receiving sediments would only be contaminated due to historical or 

ongoing sources unrelated to the discharge. This section of the worksheet should also be 

completed if there are data available on the chemistry of settling particulate matter obtained from 

sediment traps in the receiving water column, and if there is sufficient reason to believe that the 

material obtained from those sediment traps is associated with the discharge.

* Biological Test Data for Receiving Sediments — These data include baseline 

monitoring data or other biological tests performed on sediments collected near the outfall. This 

section of the worksheet should be completed if the appropriate types of biological tests have 

been conducted, unless there is sufficient reason to believe that receiving sediments would only 

be contaminated due to historical or ongoing sources unrelated to the discharge.

* Effluent Monitoring Data — Effluent monitoring data (i.e., total chemical 

concentrations in the effluent) can also be used to estimate the potential for sediment impacts, 

although the relationship between these data and the potential for sediment impacts is less direct 

than for the types of data described above. This section of the worksheet should be completed if 

representative effluent data are available, and may be especially useful if the discharger proposes 

a new or substantially different type of discharge than has been present in the past.

Each of the sections of the worksheet is independent, and any one of the sections alone may 

indicate the potential for sediment contamination. However, if more than one type of data is 

available, each applicable section of the worksheet should be completed. This additional 

information will assist the SMU in performing the subsequent detailed evaluation.

Figures IX-3 through IX-8 are on the following pages IX-24 through IX-30.

Figure IX-3. Screening-Level Evaluation of the Potential for Sediment Impacts. Part A. 

Narrative Evaluation.

Figure IX-4. Screening-Level Evaluation of the Potential for Sediment Impacts. Part B. 

Technical Evaluation. Summary Sheet.

Figure IX-5. Screening-Level Evaluation of the Potential for Sediment Impacts. Section 1. 

Chemical Concentration in Source Sediments and Effluent Suspended Solids.

Figure IX-6. Screening-Level Evaluation of the Potential for Sediment Impacts. Section 2. 

Chemical Concentrations in Receiving Sediments and Settling Particulate Matter in the 

Water Column.

Figure IX-7. Screening-Level Evaluation of the Potential for Sediment Impacts. Section 3. 

Biological Test Data for Receiving Sediments.
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Figure IX-8. Screening-Level Evaluation of the Potential for Sediment Impacts. Section 4. 

Effluent Monitoring Data. 
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 Screening-Level Evaluation of the Potential for Sediment Impacts 

 Part A. Narrative Evaluation 

Applicant:

Waste Discharge Permit No.:

Location:

1. A discharge is generally considered not to have a risk for causing adverse sediment impacts if 

the facility has all of the following three characteristics:

 a freshwater discharge to marine water, and

 has secondary wastewater treatment or equivalent and  discharges to an area with an average tidal velocity of 1 cm/sec or greater. If any one of these three factors is not applicable proceed to 2.

2. A discharge is generally considered to have a risk for causing adverse sediment impacts if the facility meets any of the following criteria (check any that apply and attach a brief explanation):

 Uses, stores, produces as a product or waste, or transfers any hazardous substance listed in 40 CFR 302.4, with a statutory code of 1 or 2, [referring to Sections 311(b)(4) or 307(a) of the Clean 

Water Act] unless:

The facility is designed and managed so that these substances are kept fully physically 

separated at all times, including spills or any other accidental release, from any part of the wastewater collection, treatment, or discharge system or stormwater system; or

The amount of any hazardous substance at the facility is never more than the statutory reportable 

quantity listed in 40 CFR 302.4.

 Discharges any chemical pollutant listed in Appendix D of 40 CFR Part 122, Table II, in its effluent 

(attach a list of any such pollutants known to be discharged).

 Has a reasonable potential to violate water quality standards for any pollutant in Appendix D of 40 CFR Part 122, Table III (attach a list of any such pollutant known to be discharged).

 Discharges other potentially deleterious substances, such as any of the following (check any that apply):

_____ Solid inorganic materials (e.g., paint chips, slag)

_____ Radionuclides

_____ Other (describe)

 Belongs to any industry category identified in 40 CRF Part 122, Appendix A.

 Is a municipal facility that receives a discharge from any industry category identified in 40 CFR Part 403, Appendix C.

 Any facility with whole effluent toxicity detected during the last five years based on:

• Less than 80 percent survival in 100 percent effluent; or

• The no observed effects concentration for chronic toxicity being less than or equal to the acute critical effluent concentration; and

• Not attributable to a known chemical

 Any facility with suspected sediment toxicity because of apparent damage to aquatic biota in the 

immediate vicinity of the discharge.

 Any other discharge that Ecology determines has the potential to include toxic substances that may 

accumulate in the sediment.

3. The following types of discharges (check if applicable) are generally not believed to have a potential for causing adverse sediment impacts unless one of the above factors, in item 2, applies:

 Once-through noncontact cooling water without biocides
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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 Municipal plants discharging less than one-half million gallons per day of effluent that are regulated only for conventional pollutants

 Drinking water treatment plants

 Sand and gravel mining operations

 Sump pump discharges of ground water or rainwater

 Construction dewatering

 Fish hatcheries and other aquaculture

 Boiler blowdown

 Any other discharger that Ecology determines does not have the potential to discharge toxic pollutants

3. Based on the narrative evaluation above, is there a potential for sediment impacts from this discharge?

 Yes. If yes, answer the following question.

 No

4. Is there a preliminary indication that the discharge would be eligible for a SIZ?

 Yes

 No. If no, describe the reason(s) the discharge may be ineligible.

Permit Manager: ___________________________________________ Date:

(print name)

________________________________________ (Signature)
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Screening-Level Evaluation of the Potential for Sediment Impacts

 Part B. Technical Evaluation 

Applicant:

Waste Discharge Permit No.:

Location:

SUMMARY

Potential for

Sediment Impact?

No Available

Data

Worksheets Attached: YES NO

 Section 1. Source Sediments   

 Section 2. Sediment Chemistry   

 Section 3. Sediment Biological Tests   

 Section 4. Effluent Chemistry   

Permit Manager: ___________________________________________ Date:

(print name)

________________________________________ (Signature)
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Section 1 Chemical Concentrations in Source Sediments and Effluent Suspended Solids 

Types of Data: Number of Samples:

  Ditch Sediments Analyte Groups:

  Sump Sediments

  Outfall Sediments

  Effluent Suspended Solids

Detected Analytes

Maximum

Concentration

(mg/kg)a SQS

(mg/kg)a

Exceeds SQS?

YES NO

Number of

Samples

Exceeding 

SQS

1.  

2.  

3.  

4.  

5.  

6.  

7.  

8.  

9.  

10.  

11.  

12.  

13.  

14.  

15.  

16.  

17.  

18.  

19.  

20.  

a mg/kg dry weight or organic carbon normalized, as appropriate (see Section 3.3.3).
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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Section 2 

 

Chemical Concentrations in Receiving Sediments and 

Settling Particulate Matter in the Water Column 

Types of Data: Number of Samples:

  Receiving Sediments Analyte Groups:

  Settling Particulate Matter in the Water Column

Detected Analytes

Maximum

Concentration

(mg/kg)a SQS

(mg/kg)a

Exceeds SQS?

YES NO

Number of

Samples

Exceeding 

SQS

1.  

2.  

3.  

4.  

5.  

6.  

7.  

8.  

9.  

10.  

11.  

12.  

13.  

14.  

15.  

16.  

17.  

18.  

19.  

20.  

Is there reason to believe that historical or other ongoing sources of contamination unrelated to the discharge 

may have contributed to the exceedances of SQS shown? If so, explain below:

a mg/kg dry weight or organic carbon normalized, as appropriate (see Section 3.3.3).
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Section 3 

 

 

Biological Test Data 

for Receiving Sediments 

 

 

Type of Test

Total 

Number

of Stations

Exceeds

SQS?

YES NO

Number of

Stations

Exceeding SQS

 Amphipod Bioassay  

 Larval Bioassay

Type  

 

 

 

 Benthic Infauna  

 Neanthes Bioassay  

 Microtox® Bioassay  

Is there reason to believe that historical or other ongoing sources of contamination unrelated to the discharge 

may have contributed to the exceedances of SQS shown? If so, explain below:
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Section 4 

 

 

Effluent Monitoring Data 

Number of Samples:

Average TSS (mg/L):

Analyte Groups:

Detected Analytes

Average

Concentration

(μg/L)

Cp

(mg/kg)a SQS

(mg/kg)a

Exceeds SQS?

 YES NO

1.  

2.  

3.  

4.  

5.  

6.  

7.  

8.  

9.  

10.  

11.  

12.  

13.  

14.  

15.  

16.  

17.  

18.  

19.  

20.  

Cp Concentration of a contaminant associated with suspended solids in the effluent

a

 mg/kg dry weight or organic carbon normalized, as appropriate (see Section 3.3.3).
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4.3.2. Instructions for the Technical Evaluation Worksheet

The following sections provide further explanations and instructions for completing each section 

of the technical evaluation worksheet. This worksheet should be completed along with the 

narrative evaluation worksheet and filed with the permit application. A copy of the worksheet 

should be forwarded to the SMU. Any data used in the screening-level evaluation should also be 

forwarded to the SMU with the worksheet; these data will be used in the subsequent detailed 

evaluation. The permit manager should also provide the SMU with electronic and hard copies of 

water quality dilution zone model runs, spreadsheets, and any other data and information used to 

assess compliance with water quality and sediment quality standards.

If neither the narrative nor the technical evaluations indicate that a discharge has the potential to 

cause sediment impacts, the permit should be issued or renewed by the permit manager without a 

SIZ authorization or sediment quality-based effluent limits. No sediment monitoring should be 

required in the permit. The permit manager should identify the lack of potential for sediment 

impacts in the fact sheet accompanying the permit.

Because the screening-level evaluation (including the narrative and technical evaluations) is 

highly conservative, it may indicate the potential for impacts for certain facilities where no actual 

impact would occur. Therefore, if either the narrative or technical evaluation indicates that a 

discharge has a potential for sediment impacts, the discharge will be further evaluated by the 

SMU.

Summary Page

The summary page is shown in Figure IX-4. To complete the summary page, the permit 

manager should perform the following steps:

1. In the space provided, fill in the name of the applicant, the waste discharge permit number, 

and the location of the existing or proposed discharge (e.g., latitude and longitude or state 

plane coordinates; attach a map showing the discharge, if available) or attach those from the 

fact sheet.

Review available data for the permit, including data provided in the permit application, existing 

effluent monitoring data, and baseline monitoring data, to determine what types of data are 

available for the evaluation. Check the appropriate boxes to indicate which types of data 

are used in the evaluation.

Fill out and attach the appropriate worksheets.

Summarize the results of the evaluation on the summary sheet by checking the “yes,” “no,” or 

“no available data” box for each worksheet used.
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Sign and date the worksheet.

Attach all data used in the evaluation and forward the worksheet to the SMU. Include a copy of 

the worksheet in the permit file for the applicant.

Section 1. Chemical Concentrations in Source Sediments and Effluent Suspended Solids

The potential for a discharge to cause an exceedance of the SQS in adjacent sediments can be 

evaluated by directly comparing SQS numerical criteria with concentrations of contaminants in 

sediments that may accumulate at points within the facility downstream of any treatment 

processes (e.g., ditch, sump, outfall). Sediments collected from such locations are likely to be 

more indicative of source characteristics than are receiving sediments in the immediate vicinity 

of the point of discharge, because the latter may be affected by other factors, including historical 

contamination, contributions from other sources, and burial by and mixing with natural 

sediments.

If there are no sediments present in ditches, sumps, or outfalls, or if these sediments have not 

been sampled, it may be possible to collect suspended solids in the effluent and determine their 

chemical concentrations. Methods for the collection of suspended solids in the effluent are 

discussed in Chapter XIII Section 7. Care must be taken to collect a sample that is representative 

of the effluent.

The worksheet for Section 1 is shown in Figure IX-4. To complete the worksheet for Section 1, 

the permit manager should perform the following steps:

1. Indicate the type of data available and the number of samples collected. Also note the 

analyte groups (e.g., metals, semi-volatile organic compounds) that were analyzed. If source 

sediments were analyzed, any available information (qualitative or quantitative) on the grain 

size of the sediments sampled should be appended to the worksheet.

2. In the first column, list the detected analytes for which SQS numerical criteria are available 

(Table IX-1).

List the maximum concentration measured for each analyte. If the SQS numerical criteria for 

the contaminants measured are listed in mg/kg organic carbon, the organic carbon 

normalization procedure described in Part 4.3.3 must be completed before comparing the 

data to the criteria. Otherwise, concentrations should be listed in mg/kg dry weight.

Compare the maximum concentrations detected to the SQS numerical criteria listed in Table 

IX-1. Check the appropriate boxes to indicate whether the criteria are exceeded. For each 

contaminant, also indicate the number of samples for which the contaminant exceeds the 

criteria. If any of the sample concentrations exceed the SQS numerical criteria, there is a 

potential for sediment impacts from the discharge.
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Attach the completed worksheet to the summary page.

Section 2. Chemical Concentrations in Receiving Sediments and Suspended Particulate 

Matter in the Water Column

If there are no sediments associated with the source pathway (e.g., sediments do not accumulate 

at points within the facility downstream of any treatment processes), surface sediments near the 

point of discharge can be collected and analyzed. If surface sediment sampling is used to assess 

contaminant concentrations, only the uppermost sediment horizon (i.e., 0–2 cm), reflecting the 

most recently deposited sediments, should be collected. Because receiving sediments respond 

relatively slowly to changes in source characteristics, receiving sediment data should not be used 

unless the discharge being evaluated is an existing source that has been discharging at a similar 

rate for at least 5 years.

Because bottom sediments respond slowly to changes in source characteristics, sampling of 

suspended particulate matter in the water column may provide a more reliable method for 

verifying the effects of a discharge on receiving sediments. However, suspended particulate 

matter in the water column (receiving environment) may also be mixed with particles from other 

sources or facilities (potentially including resuspended bottom sediments). Sampling of 

suspended particulate matter in the water column can be performed over a period of time using a 

sediment trap. Because sediment traps collect only settling particles in the water column, use of 

sediment traps is the most appropriate sampling method for evaluating the impact on sediment 

quality of particulate matter settling out of the water column. This sampling technique is 

discussed in greater detail in Chapter XIII Section 7.

The worksheet for Section 2 is shown in Figure IX-5. To complete the worksheet for Section 2, 

the permit manager should perform the following steps:

1. Indicate the type of data available and the number of stations at which samples were 

collected. Also note the analyte groups (e.g., metals, semivolatile organic compounds) that 

were analyzed.

3. In the first column, list the detected analytes for which SQS numerical criteria are available 

(Table IX-1).

List the maximum concentration measured for each analyte. If the SQS numerical criteria for 

the contaminants measured are listed in mg/kg organic carbon, the organic carbon 

normalization procedure described in Part 4.3.3 must be completed before comparing the 

data to the criteria. Otherwise, concentrations should be listed in mg/kg dry weight.

Compare the maximum concentrations detected to the SQS numerical criteria listed in Table 
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IX-1. Check the appropriate boxes to indicate whether the criteria are exceeded. For each 

contaminant, also indicate the number of stations at which the contaminant exceeds the 

criteria. If any of the sample concentrations exceed the SQS numerical criteria, there is a 

potential for sediment impacts from the discharge.

Explain in the space provided whether there is any reason to believe that historical 

contamination and/or the presence of other ongoing sources may have contributed to the 

SQS exceedances listed.

Attach the completed worksheet to the summary page.

Section 3. Biological Test Data for Receiving Sediments

Use of biological test data for receiving sediments is the most direct way of evaluating whether 

sediment impacts are occurring, because such tests directly measure adverse effects on 

organisms of interest. However, because receiving sediments respond relatively slowly to 

changes in source characteristics, this section of the worksheet should only be used if the 

discharge being evaluated is an existing source that has been discharging at a similar rate for at 

least 5 years.

SQS biological effects criteria for Puget Sound have been established for the following types of 

tests (WAC 173-204-315):

• Amphipod bioassay (Rhepoxynius abronius)

• Larval bioassays:

– Pacific oyster (Crassostrea gigas)

– Blue mussel (Mytilus edulis)

– Purple sea urchin (Strongylocentrotus purpuratus)

– Sand dollar (Dendraster excentricus)

• Benthic infauna

• Juvenile polychaete bioassay (Neanthes arenaceodentata)

• Microtox bioassay (Photobacterium phosphoreum)

Therefore, only these types of biological data can be used in the screening-level evaluation.
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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The worksheet for Section 3 is shown in Figure IX-6. To complete the worksheet for Section 3, 

the permit manager should perform the following steps:

1. Indicate the type(s) of biological tests for which data are available. List the number of 

stations at which samples were collected for each test.

2. Compare the results of each test to the SQS biological effects criteria for that test listed in 

Table IX-2. To compare observed adverse effects to the SQS biological effects criteria, it 

must first be determined whether the effects observed are statistically significant. The 

permit applicant should perform this test. If this information is not provided, contact the 

SMU for instructions or assistance in interpreting the results of biological tests.

Check the appropriate boxes to indicate whether the SQS biological effects criteria are 

exceeded. For each test, also indicate the number of stations that exceed the SQS biological 

effects criteria. If the sediments exceed the SQS biological effects criteria for one or more 

of the tests, there is a potential for sediment quality impacts.

Explain in the space provided whether there is any reason to believe that historical 

contamination and/or the presence of other ongoing sources may have contributed to the 

SQS exceedances listed.

Attach the completed worksheet to the summary page.

Section 4. Effluent Monitoring Data

If appropriate data are not available to conduct the evaluations in worksheet Sections 1–3, the 

results of effluent chemical analyses can be used as an indicator of whether that discharge has the 

potential to result in exceedance of the SQS numerical criteria near the outfall. Because effluent 

sampling and analysis is a standard part of NPDES permit requirements, such data may be 

available when sediment quality data are not. To use effluent data as an indicator of potential 

contamination in sediments, a relationship must be derived between effluent and sediment 

quality.

This part of the evaluation uses effluent monitoring data to provide an estimate of potential 

sediment quality near a point of discharge. The equation used in the evaluation is based on the 

assumption that for contaminants likely to accumulate in the sediments, and for which there are 

SQS numerical criteria, most of the total contaminant concentration in an effluent (or in the 

receiving water) will be found on the suspended solids fraction. This assumption may not be 

applicable to certain classes of contaminants (i.e., highly soluble contaminants). Furthermore, 

this equation does not directly predict the impact of the effluent on sediments around the point of

discharge, and it does not account for dilution of the effluent by ambient water during initial 

mixing or for dilution of effluent suspended solids by particles from other sediment sources.
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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However, the concentration of a contaminant associated with suspended solids in the effluent 

(Cp) derived using this equation can be directly compared with the SQS numerical criterion for 

that contaminant. For chemicals with SQS numerical criteria that are normalized to organic 

carbon (i.e., nonpolar, nonionizable organic compounds), the additional normalization for 

organic carbon (i.e., dividing the dry-weight contaminant concentration for the suspended solids 

fraction by the organic carbon content of the suspended solids fraction) should be applied (see 

Part 4.3.3.).

Cp can be estimated from effluent monitoring data as follows:

where:

Cp = concentration of contaminant associated with suspended solids in the effluent (mg/kg dry 

weight)

Ct = total concentration of contaminant in the effluent (mg/L)

TSS = total suspended solids in the effluent (mg/L)

106 = conversion factor (mg/kg).

If all contaminant concentrations on the suspended solids in the effluent are less than or equal to 

the SQS numerical criteria, the screening criterion is passed.

This equation incorporates the assumption that all contaminants are associated with suspended 

solids (or particulate organic carbon) in the effluent. This is a conservative assumption intended 

to provide an environmentally protective analysis; therefore, it may be possible using this 

equation to screen out a number of discharges with very little expenditure of time and resources.

There are two scenarios in which this equation may be overly conservative. First, if most of the 

contaminants are expected to be in the dissolved form, this equation could greatly overestimate 

the concentration of a contaminant associated with suspended solids. Second, if the 

concentration of TSS is very low, the concentrations of contaminants associated with the 

suspended solids may appear to be very high, and the screening criterion may be failed. 

However, in the latter scenario there may or may not be significant loading of contaminants to 

x10 TSS

C C = t 6 p
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the sediments in the immediate vicinity of the point of discharge. In either of these two 

scenarios, the permit manager should contact the SMU for guidance on the appropriate course of 

action.

It should be noted that this equation may be of only limited applicability for effluents that have 

very low TSS concentrations (e.g., biological treatment of municipal wastewater may yield a 

TSS concentration of only 10–30 mg/L). Depending on the magnitude of the SQS numerical 

criteria for individual contaminants, the total contaminant concentration in the effluent necessary 

to cause an exceedance of the criteria may be at or below commonly achievable detection limits 

in cases of low TSS concentrations (e.g., at a TSS concentration of 30 mg/L, a total arsenic 

concentration of greater than 1.7 μg/L would cause exceedance of the SQS numerical criterion 

for arsenic). For contaminants with higher SQS numerical criteria, use of the equation may still 

be valuable for effluents with low TSS concentrations.

The worksheet Section 4 is shown in Figure IX-7. To complete the worksheet Section 4, the 

permit manager should perform the following steps:

1. Indicate the number of samples collected and the analyte groups (e.g., metals, semivolatile 

organic compounds) that were analyzed. The WQP typically recommends that 10 samples be 

collected over a period of time to adequately characterize the nature and variability of a 

discharge's effluent quality. For the purposes of this screening-level evaluation, the results of 

the analysis of at least 10 samples should be evaluated. If fewer samples are available, they 

should still be evaluated, although the conclusion should be qualified.

2. Determine the average concentration of TSS in the effluent and note it in the space provided.

3. In the first column, list the detected analytes for which SQS numerical criteria are available 

(Table IX-1).

4. Determine the average concentration of each contaminant in the effluent samples and write 

the averages in the space provided.

5. For each contaminant, divide the average concentration by the average TSS to get Cp. For 

contaminants whose SQS numerical criteria are in mg/kg organic carbon, convert Cp from 

mg/kg dry weight to mg/kg organic carbon, as described in Part 3.3.3. Fill in the Cp values in 

the space provided.

6. Compare Cp values to the SQS numerical criteria listed in Table IX-1. Check the appropriate 

box for any contaminants for which Cp exceeds the criteria. If any of the contaminants exceed 

SQS numerical criteria, there is a potential for sediment quality impacts.

7. Attach the completed worksheet to the summary page.
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4.3.3. Organic Carbon Normalization

The SQS numerical criteria for nonpolar, nonionizable, organic contaminants are listed in units 

of mg/kg organic carbon. However, sediment data are often reported in mg/kg dry weight. Cp is 

also derived in units of mg/kg dry weight. To convert chemical concentrations expressed as 

mg/kg dry weight to mg/kg organic carbon for comparison to SQS, the following equation is 

used:

where:

TOC = percent total organic carbon of sediments or suspended solids (expressed as a decimal; 

i.e., 1% TOC = 0.01).

For this screening-level analysis, a total organic carbon (TOC) value of 1 percent may be 

assumed in the absence of discharge-specific TOC data. In Puget Sound reference area 

sediments, TOC values range from 0 to 6.1 percent, with a median of 1.4 percent (Pastorok et al. 

1989).

4.4 Alternative Procedures for the Technical Evaluation of the 

Potential for Sediment Impacts in Freshwater, low Salinity, and NonPuget Sound Marine Environments

As described in Subsection 3.3, the current absence of promulgated SQS numerical criteria for 

sediments in freshwater, low-salinity, and non-Puget Sound marine environments necessitates 

the use of alternative procedures for the technical evaluation of the potential for sediment 

impacts. This section describes technical evaluation procedures for discharges into each of those 

environments. After SQS numerical criteria are promulgated for those environments, other 

evaluation procedures will be developed by Ecology.

4.4.1. Technical Evaluation Procedures for Discharges to Freshwater 

Environments

Currently, the Sediment Management Standards have neither SQS numerical criteria nor 

biological effects criteria for freshwater sediments. However, sediment quality values are 

available from other sources (e.g., Ecology's FSEDCRIT report, Appendix D of the Sediment 

Source Control Standards User Manual), and Ecology has two recommended freshwater 

sediment bioassays for evaluating sediment impacts around existing discharges to freshwater 

environments. Therefore, there are tools available for use, on a case-by-case basis using best 

TOC

mg/kg dry weight mg/kg organic carbon =
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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professional judgment, in evaluating the potential for sediment impacts in the vicinity of 

discharges to freshwater environments. These tools require sediment monitoring data from the 

depositional environment in the vicinity of the discharge.

Ecology's FSEDCRIT report includes numerical sediment quality values for a number of metals 

and organic compounds in freshwater sediments. These values were assembled from several 

sources, including the U.S. Environmental Protection Agency (EPA), other states, and Canadian 

agencies. While not directly applicable to Washington State freshwater sediments, they can be 

used, with supporting documentation, on a case-by-case basis using best professional judgment 

with the assistance of the SMU for identifying sediments likely to exhibit adverse effects.

Ecology currently recommends the following sediment bioassays for identifying biological 

impacts in freshwater sediments (Bennett and Cubbage, 1992):

 Amphipod bioassay (Hyalella azteca)

 Microtox® bioassay (Photobacterium phosphoreum).

The protocols for these bioassays (ASTM 1990; PSEP 1991a) do not include test sediment 

interpretation values. For the amphipod bioassay, the SMU recommends that to be considered 

indicative of a potential sediment impact, the test sediment should exhibit mortality that is 

significantly higher (t-test, P≤0.05) than the reference sediment and the test sediment mortality 

should exceed 25 percent (on an absolute basis). For the Microtox® bioassay, to be considered 

indicative of a potential sediment impact, the mean light output of the highest concentration of 

the test sediment should be less than 80 percent of the mean light output of the reference 

sediment, and the two means should be significantly different (t-test, P≤0.05).

In cases where there are existing sediment data (either sediment concentrations of chemicals for 

which there are sediment quality values in the FSEDCRIT report, or the results of sediment 

bioassays), the permit manager has the option of conducting the technical evaluation on a caseby-case basis using best professional judgment or forwarding the permit application materials to 

the SMU for them to perform the technical evaluation. If the permit manager elects to conduct 

the technical evaluation, the concentrations of sediment contaminants (if available) can be 

compared with the appropriate FSEDCRIT sediment quality values (selected with guidance from 

the SMU) using the worksheet Section 2 (Figure IX-5), modified accordingly. If the results of 

one or both sediment bioassays are available, they can be reported on the worksheet Section 3

(Figure IX-6), modified accordingly. The permit applicant should generally perform the tests of 

statistical significance for these bioassays. If this information is not provided, the permit 

manager should contact the SMU for instructions or assistance in interpreting the results.

In the absence of existing sediment data from the vicinity of a discharge to a freshwater 

environment, there are no technical procedures (equivalent to those used for screening Puget 
CHAPTER IX. AQUATIC SEDIMENTS (JULY 2002)

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Sound marine sediments) for evaluating the potential for sediment impacts based only on 

chemical concentrations in source sediments and particles (i.e., worksheet Section 1; Figure IX4) or on effluent monitoring data (i.e., worksheet Section 4; Figure IX-7). If the narrative 

evaluation indicated the potential for sediment impacts, and if only those data types are available 

(or if no data at all are available), the permit manager should issue or renew the permit with a 

requirement for the collection of baseline monitoring data (including sediment chemistry and 

sediment bioassays) so that an evaluation of sediment impacts can be made at a later date.

After the baseline monitoring data become available, the technical evaluation can be completed 

by the permit manager or by the SMU. This may occur during the next permit review cycle or at 

an earlier date, at the discretion of the permit manager.

4.4.2. Technical Evaluation Procedures for Discharges to Low-Salinity 

Environments

Currently, the Sediment Management Standards have neither SQS numerical criteria nor 

biological effects criteria for low-salinity sediments. Unlike the situation for freshwater 

sediments, however, there are no sediment quality values currently available from other sources. 

Application of the SQS numerical criteria for Puget Sound marine sediments to low-salinity 

sediments may be inappropriate. Similarly, the biological effects tests applicable to Puget Sound 

marine sediments may not be applicable to low-salinity sediments. Therefore, there are currently 

no technical evaluation procedures applicable to low-salinity sediments that can be performed by 

the permit manager. Hence, all permit applications received for discharges to such environments 

should be forwarded to the SMU for further evaluation, until such time as appropriate criteria 

and technical evaluation procedures are developed. On a case-by-case basis using best 

professional judgment, the SMU may choose to apply the Puget Sound marine sediment 

chemical criteria or biological effects tests to low-salinity sediments.

4.4.3. Technical Evaluation Procedures for Discharges to Non-Puget Sound 

Marine Environments

Currently, the Sediment Management Standards have neither SQS numerical criteria nor 

biological effects criteria for non-Puget Sound marine sediments. As in the case of low-salinity 

sediments, there are also no sediment quality values currently available from other sources. 

However, the SMU is of the opinion that, until such time as criteria are developed specifically 

for non-Puget Sound marine sediments, the corresponding criteria developed for Puget Sound 

marine sediments can be used, on a case-by-case basis using best professional judgment, for 

evaluating the potential for sediment impacts in those environments. Hence, the technical 

evaluation for discharges to non-Puget Sound marine environments can in the interim be 

conducted by the permit manager using the same procedures as developed for Puget Sound 

marine sediments (see Subsection 4.3).
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CHAPTER X. PRETREATMENT PROGRAM

1. OVERVIEW

Cities have long recognized the need to control tributary industries to keep them from harming 

their sewer systems. After passage of the Clean Water Act, EPA standardized these controls and 

set “categorical” limits for pollution from specific processes of certain types of major industries. 

Both municipal and industrial permit writers implement the pretreatment program. Municipal 

permit writers must add appropriate pretreatment related conditions in permits for Publicly 

Owned Treatment Works (POTWs) and other Treatment Works Treating Domestic Sewage 

(TWTDS). These conditions compel the participation of sewerage agencies in carrying out this 

program. Ecology may require sewerage agencies to develop a program, properly run their 

approved program, or do things to support and reinforce Ecology’s control of their tributary 

industries. Industrial to POTW permit writers must know how to apply categorical standards and 

other applicable pretreatment standards and requirements. The following sections provide an 

overview of pretreatment specific concerns for permit writer in both cases. 

1.1.Federal Pretreatment Rules

Pretreatment Requirements: Federal Regulations describing appropriate controls for nondomestic wastewater are found at 40 CFR§403. These regulations are intended to prevent nondomestic wastewater from having undesirable effects at a POTW. These rules prohibit 

discharges that cause “Pass Through” or “Interference” at the POTW, explosion, vapor toxicity, 

emergency conditions, and sludge contamination. You can find definitions of pretreatment 

related terms at 40 CFR §403.3, and these prohibitions at 40 CFR §403.5. The rules at §403.8 

require POTWs that have a design flow capacity of over 5.0 MGD to develop programs to 

prevent such undesirable effects if they have any industries. 

The rules at §403.8 describe (in general) the required components of an approvable program. 

EPA guidance (See EPA’s Pretreatment Website) significantly augments and refines the brief 

descriptions found there. EPA’s manual “Introduction to the National Pretreatment Program” 

summarizes some of the most important guidance. Staff seeking to run a pretreatment program 

must be conversant with much of this.

The rules beginning at §403.9 describe the process of delegating a pretreatment program. Rules 

at §403.10(e) allow states to take responsibility for the POTW’s program and issue permits to 

control discharges from Industrial Users. 
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Categorical Pretreatment Standards: Under the Clean Water Act (CWA), EPA established 

uniform national standards for some specific industry categories. These are found in sections 

§405 to §471. Where these standards specify Pretreatment Standards for Existing Sources 

(PSES) or Pretreatment Standards for New Sources (PSNS) for processes conducted by the 

industry, and the industry is connected to a POTW, the industry is considered a “Categorical 

Industrial User” (CIU). Where PSNS or PSES standards merely require compliance with the 

general pretreatment regulations (formerly 40 CFR §128, now 40 CFR §403), the industry is not 

considered to be subject to categorical standards or a CIU.

EPA publishes each categorical pretreatment standard as a separate regulation. The standards 

contain limitations for pollutants commonly discharged within each specific industrial category. 

All industries regulated by a particular category are required to comply with these standards, no 

matter where they are located in the United States. Facilities covered by categorical standards 

must comply with any more stringent local limits, state standards, or prohibitive standards. 

Local Limits: EPA has constructed the Pretreatment Regulation to recognize technically based 

local limits as pretreatment standards under section 307(c) of the Clean Water Act. EPA’s 

pretreatment regulations also reinforce that pretreatment permits must require compliance with 

any more stringent state or local requirement. 

Pretreatment Streamlining: EPA revised several sections of the pretreatment rules in November 

2005 in what they termed “streamlining”. The preamble to the rule change, which can be found 

on EPA’s pretreatment web site, provides the best source of information on the scope and EPA’s 

intentions for those changes. EPA has produced nine “fact sheets” that describe the various 

required changes, options allowed, and particulars of each change or new allowance. Permit 

writers should familiarize themselves with this rule change. They should understand the need to 

carefully document, in fact sheets, decisions with respect to the sample type (grab or composite), 

requirements for a slug discharge control plan, and best management practices (BMPs). Permits 

need to include, as enforceable provisions, requirements to develop and follow a slug discharge 

control plan, keep records that show compliance with BMPs, and provide any periodic 

certifications or characterizations.

1.2.Washington State’s rules for non-domestic wastewater

EPA delegated Ecology the authority to issue NPDES permits in 1973 and to administer the 

federal pretreatment program in 1986. Ecology derives its authority to include pretreatment 

related requirements in NPDES permits issued to POTW's through RCW 90.48 and Chapter 173-

220 WAC. These rules allow (at 173-220-150(g)) Ecology to give full or partial delegation to 

POTWs and requires their programs be as stringent as the Department’s. Rules allowing 

delegation of local pretreatment programs are at Chapter 173-208 WAC.

The authority to directly regulate industries discharging to a POTW comes from 90.48 RCW and 

Chapter 173-216 WAC. Ecology’s rules are for permit writers to include all relevant state and 
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federal requirements in such permits. In addition to reinforcing EPA requirements, Washington 

State rules require industries to:

• Obtain approval for plans for construction of wastewater facilities (as described in 

Chapter 173-240 WAC).

• Provide All Known, Available, and Reasonable means of Treatment (AKART).

[Note: Ecology determined that AKART prohibits approval of removal credits (described 

at 40 CFR §403.7)].

• Use an accredited laboratory for their monitoring.

• Comply with Dangerous Waste rules (found at Chapter 173-303 WAC). These rules 

(173-303-071 WAC) exempt discharges to the sewer from DW rules if they identify the 

waste streams that would otherwise be DW in their permit application, and their 

pretreatment permit includes certain language. 

1.3.Philosophy of Washington State’s Pretreatment Program

Federal regulations require POTWs with design flows of 5.0 MGD and SIU’s to develop a 

pretreatment program unless the state assumes this responsibility. These rules also allow 

Ecology to require a smaller POTW to develop a program when they receive wastes that are 

causing problems such as pass through at the POTW, when their problems are most amenable to 

local solutions. On a functional level, Ecology may also have to require a local program when 

the POTW is not providing Ecology the support needed to manage the program for them. 

Ecology would have to rely on Best Professional Judgment (BPJ) to require other TWTDS to 

develop a program. Washington State is one of only a handful of states that has a permit 

program to allow the state to implement the pretreatment program in lieu of a POTW. 

Ecology’s decision to require a municipality to develop a pretreatment program is a regional one. 

The decision should weight the benefits of each option. One of the main factors is whether it is 

less work to permit significant industrial users (SIUs) or to delegate and oversee a local program. 

Permit writers should describe the rationale for delegation decisions in the permit fact sheet 

when the municipality’s permit (State Waste Discharge for TWTDS, and NPDES for POTWs) is

(re)issued. 

Where Ecology does not delegate full responsibility to implement the pretreatment program, 

Ecology will issue permits to SIUs. The POTW may still be required, in its NPDES permit, to 

do a variety of supporting tasks as described in section 2.D. (Similarly, Ecology permits writers 

may place equivalent requirements in TWTDS permits based on BPJ.)

Ecology oversees the approved POTW pretreatment programs of municipalities that have been 

delegated pretreatment program authority. As of 2010, ten Washington municipalities have 

approved POTW pretreatment programs and have been delegated pretreatment authority. These 
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include: METRO (Seattle metropolitan area including Renton and Bellevue), Everett, 

Lynnwood, Pierce County, Spokane, Vancouver, Richland, LOTT (Lacey, Olympia, Tumwater 

and Thurston County), Tacoma, and Yakima. 

2. NPDES PERMITS FOR POTWS:

Ecology’s approved program manual from 1986 describes how Ecology and municipal sewerage 

agencies are to work in concert to carry out the responsibilities of the pretreatment program. 

POTWs and TWTDS, with staff at the local level, may be better situated to carry out certain 

pretreatment related tasks. In such cases, Ecology should assign them the responsibility for 

doing so as an NPDES permit condition. 

The first step in crafting pretreatment related permit conditions is to evaluate the situation and 

decide what pretreatment related needs are. To do this, the permit writer must know what 

problems are symptomatic of poor pretreatment oversight. These include the observation either 

at the POTW or at some point in the collection system of certain conditions as listed below. 

Symptoms of Uncontrolled Industrial Waste Sources Tributary to a POTW:

1. Corrosion to sewer lines, manholes, pump stations, or the POTW headworks

2. Noxious or chemical odors in the collection or treatment system

3. Oil, grease, fuel, solvents, or explosivity alarms

4. Unusual color

5. Excessive foaming 

6. Unexplained reductions in treatment efficiency 

7. Toxicity in WET tests, or periodic reduction in the oxygen uptake rate in aeration basins 

8. Poor settling sludges 

9. High temperatures in sewer lines or at the headworks 

10. High or low pH or unusual pH swings

11. Poor UV transmissivity or loss of the effectiveness of UV disinfection 

12. High or unusual variation in conventional pollutant loading rates (BOD, TSS, ammonia) 

13. High metals concentrations in the influent, effluent, or sludges 

14. High levels of total dissolved solids (e.g., from uncontrolled sources of brines)

15. Debris, sand, or unusual sludges in sewer lines or excessive solids at the headworks

16. Unusual levels of priority pollutants in the effluent or biosolids

In revisiting a POTW’s NPDES permit, the permit writer should both review the POTW’s 

monitoring reports for these symptoms and ask representatives of the POTW (including staff 

who oversee the collection system) about such occurrences. If the POTW shows evidence of 

adverse effects from non-domestic wastes, then the permit writer must decide two things: What 

actions should be taken in response, and the respective roles of Ecology and the POTW in taking 

those actions. 
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The Permit Writer’s challenge will be to develop permit conditions that support and reinforce 

Ecology’s partnership with the POTW. Conditions must compel the POTW to provide the 

support needed for Ecology to, in turn, properly administer the pretreatment program.

The major divisions of this section describe how permit writers craft permit language that 

requires a POTW to: Develop a pretreatment program; Implement their previously delegated 

program; Implement a modified program, or; Support Ecology’s pretreatment program. Of these 

options, the permit writer has the greatest latitude in requiring tasks in support of Ecology’s 

program. Whatever pretreatment related conditions are decided upon, the permit writer will 

typically need to properly document the basis for the conditions in the fact sheet.

Ecology has developed standard language for requiring a POTW to develop a delegated program, 

or to implement their previously delegated or modified program. This wording is in the NPDES 

Permit shell for POTWs. Regional pretreatment specialists are available to help permit managers 

decide what conditions to impose and evaluate whether the POTW has complied with their 

permit requirements (Section 4 of this chapter describes regional pretreatment engineer expertise 

areas). 

2.1.Requiring a POTW to Develop a Pretreatment Program:

2.1.1 Resources

Requiring a POTW to develop a pretreatment program is an involved process. If you are not 

doing it, you can (mercifully) skip to the next section. If you are, it is best to anticipate the level 

of effort required from the outset (about 0.5 FTE*years). Then you can adjust your work plan 

accordingly. Permit writers should never require a POTW to develop a pretreatment program 

without the concurrence of the regional pretreatment engineer and regional manager. Either a 

POTW or a TWTDS may request authority to administer a permit program for their tributary 

IU’s. Ecology is not obliged to approve such requests, and should ensure that any decision 

enhances the protection of waters of the state.

2.1.2 Drivers

Most states that administer the NPDES permit program also operate as the “Approval Authority” 

to require, approve, and oversee local POTW pretreatment programs. EPA rules at 40 CFR 

403.8(a) require certain POTWs to develop a pretreatment program. This includes any POTW or 

group of POTWs owned by the same municipality with a design capacity of 5.0 MGD and 

receiving wastewater subject to pretreatment standards or requirements. State rules at RCW 

90.48.165 and Chapter 173-208 WAC expand on this, empowering Ecology to also delegate 

ANY municipal body the authority to issue permits for the discharge of wastes into their system 

provided Ecology finds the program will protect the quality of the state’s waters (“Waters of the 

State” includes both surface and ground water). 
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Federal rules at 40 CFR 403.10(e) allow states that have developed a permitting program to 

assume the role of the Control Authority instead of requiring the POTW to develop a 

pretreatment program. Ecology developed such a program and received EPA approval of it in 

1986. Ecology therefore may permit the industries that discharge to a municipal sewerage 

system (either a POTW or TWTDS) rather than require a local pretreatment program. When 

Ecology decides to do this, permit writers must document this decision, and clarify which tasks 

Ecology still expects the municipality to carry out (to facilitate Ecology’s permitting program) in 

the municipality’s NPDES or State Waste Discharge permit and fact sheet.

2.1.3 Selection Process

The final responsibility for the selection and scope of a new full or partial program delegation 

rests with the Regional Section Manager. Ecology regional offices are to notify POTWs when 

they are required to develop local pretreatment programs (40 CFR 403.10(f)(2)(i)). To support 

that decision, the regional pretreatment engineer must assess whether:

1. The POTW is willing to assume pretreatment program responsibilities.

2. The POTW is capable of assuming pretreatment program responsibilities.

3. The POTW can overcome challenges posed by the inter-jurisdictional situation.

4. Delegating (in whole or part) the pretreatment program will better achieve the goals of 

pretreatment (better protect the public, the treatment works, and receiving waters).

5. For full program delegations, whether the review, approval, and oversight of the program 

will be less work to Ecology than the continued oversight of Industrial Users, or other 

feasible collaborative options.

Where Ecology decides to require a pretreatment program, Ecology should transmit this 

requirement by NPDES permit condition (per 403.8(a-e), 122.44(j), and 122.62(a)(9)). Upon 

approval of a local program, Ecology will provide an approval letter or Order delegating 

authority to the POTW. Ecology then must amend the POTW’s NPDES permit (under authority 

of 403.8(a-e) and 122.63(g) to include the requirement to implement their approved pretreatment 

program.

2.1.4 How Long Do We Allow to Develop a Program

Federal Regulations at 40 CFR 403.8(b) require municipalities to develop a local program within 

a year of being notified in writing that they are required to have a program by the Approval 

Authority (which in Washington State is Ecology). While EPA has not objected to a longer 

schedule, permit writers should understand that a third party might successfully challenge it. On 

the other hand, some believe that properly developing a well-considered pretreatment program 

may take up to three years. 

2.1.5 Including A Schedule for Delegation

Where Ecology finds a pretreatment program is necessary, Ecology should include a compliance 

schedule in the POTW’s NPDES permit when it is reissued or modified (403.10(f)(2)(iii)). The 

compliance schedule outlines milestones and dates for program completion. Federal rules at 40 
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CFR 403.8(e)(5) also specifically permit Ecology to invoke the authority of section 402(b)(1)(C) 

of the Act to modify or revoke and reissue a POTW's Permit to include a compliance schedule to 

develop a Pretreatment Program. 

The compliance schedule should require the POTW to develop and document the necessary 

authorities, information, and procedures to implement its local program. The next two sections 

describe the typical program elements specified in the compliance schedule for a fully delegated 

program, and the general process for “partial” delegation. 

2.1.6 Contents for Full Delegations

EPA describes the requisite contents for a POTW’s submission for approval of their proposed 

program in 40 CFR 403.9. If the Permit Writer, in concert with the regional Pretreatment 

Specialist, determines that the POTW should develop a program, Ecology must require this in 

the POTW’s NPDES permit or an Order. All delegated pretreatment programs must have the 

basic elements required by regulations. Each permit or Order to develop a local program must 

require the POTW to:

1. Develop a list of Users that will be subject to the proposed Pretreatment Program.

2. Estimate the resources and staff needed to carry out the program and propose a schedule 

for obtaining resources and qualified staff prior to program approval.

3. Develop technically defensible local limits for all pollutants of concern. 

4. Obtain the legal authority to apply and to enforce the requirements of the program C/O:

a. An Ordinance that provides requisite authorities and codifies the local limits, 

b. Inter-jurisdictional agreements that apply the program to outlying areas, and 

c. An assessment by the POTW’s counsel that the POTW’s authorities and IJA’s allow 

them to legally defend applying the program throughout their service area.

5. Develop procedures to ensure compliance with the requirements of a pretreatment 

program. These procedures must include the means to: 

a. Locate all Users potentially subject to the program through both periodic efforts and 

continuous systems, 

b. Properly permit users subject to their program, 

c. Develop a Slug Discharge Control Program,

d. Develop a system for evaluating compliance with permit conditions, 

e. Provide direct oversight including inspecting and sampling, 

f. Take timely and effective enforcement against violations of the program through the 

application of an Enforcement Response Plan, and 

g. Provide for public participation and transparency, and

h. Modify the program to keep pace with Federal and State rule changes.

2.1.7 Stepwise Process for Delegating Programs:

NOTE: The procedures for partial programs will be similar to the procedures developed for fully 

delegated pretreatment programs with the exception that Ecology will not require and review any 
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functions which Ecology is not delegating. The regional pretreatment engineer will typically be 

the lead in carrying out these steps:

1. Ecology determines which pretreatment functions to delegate to the POTW and formally 

notifies the POTW of this determination.

2. Ecology puts the POTW on a compliance schedule to complete development of the 

procedures or includes the requirements in their NPDES permit.

3. The POTW takes the measures necessary to develop a program as described in items 1-5 

above (or the functions required by the Order) and sends three copies to Ecology who has 

60 days to review the submittal. Ecology sends one copy to EPA for review. 

4. Ecology provides comments back to the POTW on any areas that they have not 

adequately addressed. The POTW must address all deficiencies to Ecology’s satisfaction 

before going on to the next step. 

5. Ecology provides public notice of delegation of a pretreatment program. Public notice 

provisions of the POTW’s NPDES permit are adequate for a partial delegation.

6. Ecology notifies IUs of the transfer of responsibilities that result from full or partial 

delegation. 

7. Ecology revises the POTW’s NPDES permit to reflect the municipality's delegated status 

or additional roles and responsibilities.

8. Ecology cancels or the State Waste Discharge Permits of tributary Users when a 

delegated program issues a permit (upon the effective date of that permit). 

9. Ecology modifies permits for IU’s discharging to POTWs which need to reflect 

additional reporting or oversight by POTWs with partial programs.

2.1.8 EPA Role

EPA oversees program delegations as described in 40 CFR 403.9 through being sent a copy of 

the proposed program and objecting within 30 days if it does not meet their standards. There is 

no formal role for the EPA in the selection and delegation of a partial program under the federal 

pretreatment regulations. There are no regulatory requirements that specify the involvement of 

the EPA in partial program delegation other than their right to review and comment on permit 

conditions in NPDES permits issued by Ecology. The municipality is simply acting as Ecology's 

duly appointed agent as provided for in Chapter 90.48 RCW.

EPA also has the opportunity to comment on any partial delegation when we place the partial 

program conditions in a municipality's NPDES permit.

2.1.9 Tribal and Federal Treatment Works or Tributary Facilities

Tribal and Federal Owned Treatment Works: Washington State’s delegation of the NPDES 

permit program in 1973 did not include delegation of the authority to permit tribal or federal 

facilities. Ecology did not seek such delegated responsibility since Ecology’s interpretation of 
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the CWA was that it did not allow delegation of authority commensurate with it. The Clean

Water Act, unlike RCRA, does not give States authority over federal facilities. Ecology 

concluded it may well have less authority to compel compliance with an NPDES permit it 

issues to a federal facility than to compel compliance with an EPA issued permit as a third 

party. Ecology also has the ability to issue 401 certifications, adding state specific 

requirements. 

Federal Facilities Tributary to POTWs: Ecology expects POTWs, as utility providers, to 

ensure any person using their utility does so in accordance with the rules established to protect 

the POTW. Where federal facilities are discharging to a POTW, the POTW should condition its 

services to require compliance with local pretreatment program requirements as a condition of 

discharge. This must be in an enforceable contract with the tributary facility. Ecology should 

include language in the NPDES permit for delegated POTWs requiring the POTW to establish 

such contractual relationships. Where the POTW is not delegated, Ecology has written permits 

for tributary federal facilities which impose requirements on point sources tributary to a POTW. 

This can be done by requiring the federal facility to sample and meet appropriate criteria at 

intermediate discharge points.

Industries on Tribal Lands Tributary to a POTW: Permits for facilities on tribal lands are 

discussed in Chapter II, section 13 of Permit Writer’s Manual. That section discusses discharges 

on tribal lands, but not the rules for a discharge from Tribal Lands to a POTW that is not on 

tribal lands. No law gives tribal activities the right to connect to a POTW without permission of 

that POTW, or to be exempt from categorical standards for indirect discharges. Since the POTW 

would have to construct a pipeline that extends to the tribal lands, such discharges can only be 

initiated with the concurrence of the POTW. POTWs must be VERY careful about agreeing to 

accept any such discharges without appropriate safeguards. A POTW may have no authority to 

enter and inspect such sources of wastewater (which may change over time) unless this right is 

established as a condition of their service. Ecology has been extremely reluctant to assert its 

authorities to require tribal activities discharging to a POTW to obtain a State Waste Discharge 

Permit. Unless and until this changes, Ecology permit writers should be clear with POTWs that 

this puts the burden squarely on their shoulders. 

Problems from Federal and Tribal Industries: Where the POTW doesn’t establish the 

appropriate controls before agreeing to accept the flows from any such activities such discharges 

may cause damage to the POTW, including its treatment process. When Ecology finds this 

happening, they should require the POTW to take action to fulfill its obligation to protect the 

public’s interest in the POTW. If the POTW does not have a pretreatment program, and Ecology 

believes that a pretreatment permit is necessary, Ecology might need to require the POTW to 

develop one. 

2.1.10 Discharges to Ground

Ecology’s municipal permit writers also oversee POTWs and other treatment works treating 

domestic sewage (TWTDS) which discharge to ground. Such facilities and their tributary 
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industries are not subject to the federal pretreatment program at 40 CFR 403. Ecology may, 

however, require such facilities to essentially do the same things a pretreatment POTWs would 

do. The pretreatment program provides a number of important safeguards to protect the sewers, 

treatment process, biosolids, and effluent. These goals are important for discharges to ground as 

well. The difference is that for a discharge to ground, the standards for discharge of the effluent 

are not designed to meet our water quality criteria, but rather our groundwater criteria.

2.2.NPDES Permit Conditions for Delegated Programs

For delegated programs, pretreatment requirements in the municipal NPDES permit must include 

conditions requiring the POTW to properly implement its program, submit an annual report, and 

do proper oversight, enforcement, and verification. All permit writers should be familiar with 

the requirements of the Pretreatment Program because the requirements will become an integral 

part of some municipal NPDES permits.

The Municipal NPDES permit shell contains standard language for requiring a POTW to carry 

out the requirements of its approved program and pretreatment rules of EPA and Ecology. These 

sections were written to be as self-explanatory as possible. However, since each situation is 

unique, it’s best to consult your regional pretreatment engineer when there is any doubt about 

whether a condition is appropriate or not.

Special conditions that may be applicable to delegated programs include additional tasks 

supporting single industry campaigns such as dental amalgam or photo processors. Tasks 

supporting information gathering efforts also may be included. 

2.3.Requiring and Recognizing changes to Delegated Programs

As Federal and State regulations change, delegated pretreatment programs need to be required to 

change in turn. 40 CFR 403.18 describes when POTWs (control authorities) must submit 

changes to Ecology (the approval authority) and when they are substantial enough to require 

approval by Ecology and public notice and opportunity for comment.

Ecology, through its oversight (PCI’s and Audits) may also find that some aspects of the 

program are insufficient or inadequately described. In such cases, POTWs may need to modify 

their program to correct the deficiencies. POTWs should follow the rules of 40 CFR 403.18 

whenever they change their program.

Ecology may also modify pretreatment permits to require monitoring or controls on any pollutant 

for which criteria have been newly promulgated or revised.
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2.4.NPDES Permit Conditions for Non-Delegated Programs

Ecology applies and enforces pretreatment requirements on IUs when Ecology has not delegated 

the authority to run a local pretreatment program to the municipality. Ecology's program for 

direct inspection and control of IUs includes processes and procedures for developing local 

limits, updating and maintaining user inventories, permitting, reviewing reports and plans, 

compliance tracking and monitoring, inspections, and enforcement.

However, Ecology cannot carry out these tasks without the assistance of the municipalities that 

run the treatment works and control discharges to the collection system. Permit writers must 

require domestic treatment works without pretreatment programs to develop and implement 

policies and procedures to support Ecology’s pretreatment program administration as enforceable 

conditions of their NPDES or State Waste Discharge permit. While Ecology will maintain the 

NPDES municipal permit shell with the most up-to-date source of these conditions, typically 

they include requirements for each municipality which owns a portion of the collection system 

to:

• Conduct Industrial User Surveys at a frequency commensurate with the treatment works’ 

design flows. Such surveys must provide Ecology enough information to know whether 

a potential industrial user requires a permit. 

• Prohibit IU’s from discharging either without a permit (where an Ecology “IU to POTW” 

permit is warranted), or in violation of the prohibitions applicable to all discharges;

• Develop local pollutant discharge limits specific to the treatment works where Ecology 

finds such limits are needed to enable Ecology to, in turn, issue permits with a reasonable 

assurance they will protect the treatment works;

• Codify a pretreatment ordinance (including local limits where developed) that gives 

affected users notice and opportunity for comment, gives authorities to the municipality 

to compel certain actions (such as completing survey forms, obtaining a permit, and 

meeting local limits).

• Develop a spill prevention program that protects against spills and slug discharges to the 

treatment works.

Additional tasks which Ecology may require of local POTWs to ensure proper administration of 

the pretreatment program include to:

• Develop and implement a grease control program for food service establishments.

• Develop and require (through ordinance provisions) Best Management Practices (BMPs) 

for small flow industries whose combined contribution to the POTW is a significant 

source of pollutants. These may include photo-processors, dental offices, stormwater 

sources, car washes, dry cleaners, medical service industries, laboratories, and such.

• Issue control mechanisms for such “Minor Industrial Users” (above) that compel periodic 
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certification they are adhering to the BMP’s required by the program.

• Develop “end of process” limits for small flow pretreatment processes such as silver 

limits from silver recovery units used by photo processors (e.g., 5 mg/l) or mercury from 

dental amalgam separators to support appropriate maintenance practices and BMP’s. 

• Develop capacity management strategies and annually report on the flows and loadings 

allocated to industries as a proportion of the total flow and loading capacity available to 

the POTW (may be included with the annual waste load assessment report requirement).

• Collect and tabulate data from industries, trunk lines, biosolids, and POTW influent and 

effluent to show where loadings are coming from and how much reserve capacity is 

available at the POTW. POTWs may be required to report such data annually, and 

compile the results of monitoring from tributary users permitted by Ecology.

• Maintain signed IU Survey forms from all businesses with the potential to discharge nondomestic wastewater. Hold IU’s accountable for obtaining a permit prior to discharging 

wastewater that they should reasonable know is subject to State Waste Discharge permit 

or local BMP’s.

• Undertake sampling and inspection of IU’s permitted by Ecology.

• Review duplicates of the monitoring reports sent by IU’s permitted by Ecology, alert 

Ecology to non-compliance, help develop a response strategy, and tabulate compliance 

data annually.

• Review and ensure the adequacy of Slug Discharge Control Plans that Ecology requires 

of IUs.

• Respond to reports of spills or slug discharges at IU’s permitted by Ecology.

• Issue permits to Industries with compatible pollutants only, or below the flow and loading 

thresholds which would make them SIUs.

2.5.Pretreatment Related NPDES Permit

Fact Sheet Language for POTWs

The municipal NPDES permit fact sheet shell contains standard language explaining the basis for 

common pretreatment related POTW conditions. These address the basis for requiring the 

POTW to run a pretreatment program, or do some of the more common pretreatment tasks. This 

language should be included in the permit to the extent it is applicable. 

When additional pretreatment related requirements are added to the permit (such as those list in 

the section immediately preceding this one), the permit writer must document the basis in the 

fact sheet. This is important for the POTW, future permit managers, and others seeking to 

understand the basis and intent of the requirement.
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3. STATE WASTE DISCHARGE PERMITS FOR NONDOMESTIC WASTE

3.1.Overview of the Permitting Process

Permit writers use State Waste Discharge Permits to control discharges to sewage treatment 

systems (both POTWs and TWTDS). Where the receiving treatment works is owned by a 

municipal corporation and discharges to waters of the United States, the system is termed a 

Publicly Owned Treatment Works (POTW). Federal rules on permit contents found at 40 CFR 

part 403 apply to permits for industries tributary to POTWs. 

When the receiving treatment works discharges to ground or other waters of the state, or is not 

publicly owned, it may not meet the federal definition of a POTW (found at 40 CFR 403.3(q)). 

In such cases, the treatment works is termed a Treatment Works Treating Domestic Sewage 

(TWTDS). Discharges from industries that would be subject to categorical standards if 

discharging to a POTW, but discharges to a TWTDS are not technically CIUs, or subject to 

categorical standards. The same logic applies to industries that would be SIUs if discharging to a 

POTW. While not considered SIUs or CIUs, Ecology can impose equivalent conditions on 

sources of indirect discharges to a TWTDS to similarly protect receiving treatment works based 

on the particular situation.

However, state laws at chapter 173-216 WAC impose the same requirements for discharge to a 

domestic sewage system regardless of whether it is a POTW or a TWTDS. Permit writers 

permitting a sewer customer or “Industrial User” therefore can use the same “IU to POTW” 

permit shell to issue a permit under the authority of that chapter. A number of the conditions in 

the permit shell stem from federal pretreatment requirements applicable to discharges to a 

POTW. Because of this, where discharge is to a TWTDS, the permit writer may have greater 

latitude in imposing such requirements. 

Sources of non-domestic wastewater enter the permitting process through various means. The 

permit assistance center is one means. Their identification by a POTW or TWTDS is another. 

That is why it is so important to include (per the prior section) conditions in NPDES permits for 

POTWs, and State Waste Discharge Permits for other TWTDS that require municipalities have a 

system for identifying such sources and (in turn) requiring them to apply for permits before 

providing sewer service. 

Ecology begins the permitting process for a tributary industry when we hear of a source that may 

be subject to “categorical” standards or may otherwise be an SIU or require a permit. The first 

step in the permitting process is to gather information. Through review of the permit application 

and inspection of the User, the permit writer’s second step is to decide how to categorize the 

User (as a SIU, CIU, or MIU). 

After categorizing the User, the third step is for the permit writer to notify the User of their 
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status. The notification letter should document their categorization, the basis, the status of their 

permit application (if one has been received) and their reporting requirements per 40 CFR 

403.12. These reporting requirements vary depending on whether the User is subject to 

categorical pretreatment standards or not. Both SIU’s and CIU’s must provide a one-time 

notification of discharges of any wastes that would otherwise be hazardous (see 403.12(p)). 

CIUs must be advised that their permit application must satisfy requirements of a baseline 

monitoring report (403.12(b)) and they will need to provide an initial compliance report (per 

403.12(d)) within 90-days after commencing discharge. CIUs should be advised that they lose 

their right to request a categorical determination from EPA once they commence discharge (per 

403.6.(a)(4)) and that this is a requisite step in requesting alternate limits due to fundamentally 

different factors (per 403.13(g)(3)).

The fourth step is to review the industry’s permit application and collect enough information to 

write the permit. Chapter III of the Permit Writer’s Manual and the flow charts of figure III-1, 

III-2, and III-3 describe this process in good detail. Please refer to those areas of this manual. 

The permit writer will need to include appropriate pretreatment standards (below section 3.B), 

and requirements (section 3.C). 

Section 8 of Chapter III of the Permit Writer’s Manual discusses the “Domestic Sewage 

Exclusion” in good detail, and permit writers need to review this section and figure III-5 before 

writing a permit for discharge to a POTW of a waste which would otherwise be a hazardous 

waste. In such cases, the permit writer should ensure that the permit application adequately 

describes the waste (if a permit is not going to be issued), and should specifically authorize the 

discharge of the hazardous constituents in the permit, including a mass or concentration limit for 

the pollutants when feasible. (reference 173-303-070(b)(iii)(G), 173-303-071(3)(a) and 173-

303-803(5)) 

3.2.Pretreatment Standards

The general pretreatment regulations establish three types of pretreatment standards: Discharge 

prohibitions, categorical pretreatment standards, and local limits. The State adds a fourth type of 

standard known as AKART. 

Each is important to properly controlling pollutant discharges into POTW's. Prohibited 

discharge standards (40 CFR 403.5 and 173-216-060 WAC) apply to all sources of non-domestic 

wastewater (industrial and commercial establishments) connected to POTW's. Categorical 

pretreatment standards (40 CFR parts 405 – 471) requiring zero discharge or compliance with 

concentration or production based limits apply to the users in 37 specific industrial categories.

When tasked to write a permit for an industry conducting an operation covered by categorical 

standards, permit writers must apply the more stringent of the categorical standards, local limits, 
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or AKART. All permit writers writing industrial permits should be able to recognize industry 

sectors subject to national categorical standards, and know how to research what specific 

industrial processes are covered by the standards. 

Pollutants subject to categorical limits are not candidates for a “reasonable potential” 

determination. Federal rules require CIU’s to confirm at least semi-annually through selfmonitoring they are meeting the limits for all pollutants limited by the categorical standards. 

Also, a “reasonable potential” determination may not be used to justify removing pollutant limits 

where treatment reduces pollutant levels to below the “reasonable potential” threshold. In such 

cases, the application of AKART requires permit writers to continue to apply the pollutant limits. 

This is necessary to ensure the Permittee continues to provide appropriate treatment (AKART). 

Chapter IV, section 1.2 of this manual describes the process for applying categorical standards 

when permitting a Categorical Industrial User. Permit writers should apply this methodology for 

indirect dischargers subject to categorical standards as well. Permit writers looking to review 

development documents should consult their regional pretreatment coordinator. The 

pretreatment workgroup has compiled references on the “Pot-O-Gold” CD under the folder 

“Categorical Standards”. This compilation includes all published pretreatment standards, a list 

of early development documents, and subdirectories for each categorical standard. The 

development documents which EPA has scanned are included as well. Permit writers can 

probably locate all of these on EPA’s internet web site but it may take longer. Ecology’s library 

also includes a substantial number of development documents.

Local limits are considered “pretreatment standards” under the clean water act when approved by 

Ecology. Local limits may be codified such that they only apply to SIU’s, apply to all users, 

apply to the combined discharge, or apply to the discharge from specific processes. Section 2 

discusses the reasons for Ecology requiring POTWs receiving non-domestic wastewater to 

codify such limits. After approval, Permit Writers should use them to write permits that protect 

the environment, sludge use, and the proper functioning of the collection system and treatment 

works. 

EPA, in 2004 refined their guidance on local limit development, and asks all POTWs which 

require local limits to develop them for all pollutants of concern, and at least the following 

pollutants: Arsenic, Cadmium, Chromium, Copper, Cyanide, Lead, Mercury, Molybdenum, 

Nickel, Selenium, Silver, Zinc, BOD, TSS, and where the POTW is providing nitrification, 

Ammonia. Technically based local limits must consider the pollutant level that would cause 

adverse effects to the POTW (or TWTDS) including: its biological processes, sludge processes, 

sludge use options, and receiving environment (surface waters, groundwater, or air for POTWs 

which incinerate their sludges). In writing permits for industrial users, permit writers should 

consider requiring information on “pollutants of concern” in order to facilitate developing or 

confirming local limits.
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3.3.Other Pretreatment Requirements

Permits must include notification of one time reporting requirements, determination of the User’s 

classification, requirements to submit baseline monitoring and final compliance reports, plans for 

wastewater facilities, and a complete permit application. Permits must contain requisite 

contents.

Discharge Prohibitions: Federal rules at 40 CFR 403.5(A) prohibit discharge of any pollutants 

that cause pass through or interference, and at 403.5(B) specifically prohibit a number of 

discharges. These prohibitions are reinforced in Chapter 173-216 WAC under section 173-216-

060. Permit writers must be conversant with these prohibitions and therefore should read and 

understand these sections. Ecology’s rules for indirect discharges to POTWs goes beyond the 

requirements of 40 CFR 403 in prohibiting:

• Clean storm water, non-contact cooling water in significant volumes, and other clean 

wastewaters that could significantly affect hydraulic loading.

• Wastes with a pH greater than 11.0.

• Dangerous wastes, as prohibited by chapter 173-303 WAC.

Local Prohibitions: Local POTWs may, at their discretion, prohibit the discharge of pollutants 

which they find are not amenable to their treatment process, have a potential to disrupt the 

POTW or pose a threat, or that have caused or contributed to pass through or interference.

Permit Contents (in general) will cover the following topics:

• Permittee Rights to:

o Discharge the waste streams and pollutants identified in the permit application subject 

to the pretreatment standards and requirements of the permit.

o Discharge specific waste streams (identify) at specific outfall locations (describe or 

show).

• Pretreatment Requirements to: 

o Properly treat all wastewater and apply AKART.

o Meet the specific (listed) effluent limits (flow and pollutant concentration or loading 

limits) applicable to each outfall. 

o Average monitoring results over specific time frames (e.g., daily, weekly, monthly).

• Monitoring Requirements to: 

o Monitor flows and specific pollutants on a specific schedule, 

o Take representative samples (grab(s) or composite) using approved (40 CFR 136) 

methods and an accredited laboratory.

• Reporting Requirements to: 

o Send periodic reports (at least semi-annually) that include all applicable 

documentation and monitoring results to a specific person and address.

• Record Keeping Requirements to record for each sample and keep at the facility for at 
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least three years: 

o Who took the sample, where the sample is from, when it was taken (date and time), 

and how it was preserved, 

o Who else had control of the sample, 

o Who analyzed the sample, when it was analyzed, and what analysis method they 

used, 

o What the sample results were, when they were obtained, and when they were 

reported.

• Notification Requirements to:

o Immediately notify the CA and POTW upon discovering noncompliance (including 

failure of continuous flow or monitoring equipment), 

o Resample on discovering limits were exceeded and promptly report the results of resampling.

o Notify before any scheduled bypass, or planned changes to production, chemicals, 

waste streams, water use, and flows.

o Notify before a new or increased discharge of a substance which would be a 

dangerous waste if otherwise disposed of.

• General Permittee Responsibilities to:

o Immediately halt any discharge that threatens to harm any person or the POTW.

o Take actions needed to maintain compliance with permit limits, and act promptly to 

restore compliance.

o Comply with the other permit terms and applicable Laws and Statutes.

o Properly operate and maintain pretreatment systems, follow your approved O&M 

manual, and keep any checklists or log books it describes on site.

o Obtain Ecology review and concurrence before making changes to processes creating 

wastewater or any pretreatment systems.

o Properly handle and dispose of removed substances, retaining records of any waste 

characterization and disposal.

o Provide information relevant to discharges to the control authority or receiving 

POTW upon request.

o Reimburse all costs incurred by Ecology and the POTW due to noncompliance 

including additional monitoring.

o Support any assertion of an affirmative defense with contemporaneous 

documentation.

• Prohibitions Requiring the Permittee to:

o Comply with any general and specific discharge prohibitions.

o Discharge only waste streams from activities or processes identified in this permit. 

o Obtain Ecology approval prior to discharge of any unforeseen wastes (e.g., rinse 

tanks, resin regeneration, or periodic maintenance).

o Not use dilution as a substitute for treatment, and not bypass any treatment 

component except in accordance with an approved O&M Manual. 

• Administrative Requirements Pertaining to:

o How reports must be certified and who can sign them.
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o Requirements to pay for sewer use, capacity, and extra strength charges, any costs 

arising from non-compliance, and penalties assessed under this permit.

o How to request and how Ecology will process changes to the permit.

o Requirements to re-apply for the permit a certain length of time before expiration.

o Rules for transferring the permit to new owner or operator.

o Rules for appealing a permit term or condition.

o Notice that permit conditions are severable, property rights are not established by the 

permit, and enforcement remedies are not exclusive.

• Control Authority Rights:

oTo modify the permit in certain situations and cancel it in other specific situations.

oTo enter the facility without delay.

oTo sample any waste stream and copy any records pertaining to wastes.

oTo inspect the facility and take notes and pictures of activities subject to the permit.

oTo apply injunctive relief to halt any discharge that poses a threat.

oTo apply civil penalties for violations.

oTo pursue criminal prosecution for knowing or willful violations.

oTo determine and annually publish Users in Significant Non-Compliance.

oTo require the Permittee to provide any information needed to make permit decisions.

oTo increase the scope and frequency of monitoring in response to changed conditions or 

noncompliance.

oAnd to extend an expired permit.

• Liabilities: General civil and criminal liabilities apply to noncompliance with the permit.

• Special Requirements:

oTo develop and follow a Slug Discharge Control Plan as a requirement of this permit, 

and promptly modify the plan as changes occur.

oTo report whether compliance schedule milestones have been met when such are 

established by this permit.

oTo provide any plans developed to comply with other environmental media such as 

spills, solid waste, dangerous waste, air pollution, & stormwater.

3.4.State Waste Discharge Permit Fact Sheet Contents

The following topics are typical of a pretreatment permit fact sheet.

• Summary of information in the permit application relevant to permit terms and conditions

• Compliance status with the prior permit if this is a permit renewal.

• Processes producing wastewater and their flow volumes and characteristics (pollutants).

• Whether composite samples or grab samples are appropriate for each pollutant and why.

• Observations from the last inspection of the facility.

• Pretreatment systems, the waste streams they treat, their capacities, and approval status of 

these systems and any O&M manuals per chapter 173-240 WAC.

• Whether reinforcement of O&M manuals or procedures are needed to ensure compliance.
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• Specific processes (if any) subject to categorical standards.

• For CIU’s that combine categorical and non-categorical waste streams for treatment 

before the monitoring point, whether each non-categorical wastestreams is “unregulated” 

or “dilute” (as defined by EPA for use in the combined wastestream formula)

• Applicable pretreatment standards (categorical, local limits, AKART) and how the most 

stringent limitations are applied.

• Whether the Permittee has identified any wastestreams which would otherwise be 

dangerous waste and therefore need to be allowed to discharge under the Domestic 

Sewage Exclusion.

• Whether a compliance schedule is needed for the Permittee to install additional treatment 

to reasonably meet the limits or other requirements of the permit.

• Prohibitions that the discharger has the potential to violate and safeguards to ensure that 

they do not occur.

• Whether the Permittee needs a new or updated slug discharge control plan or any other 

special condition.

• Other permits which the User reasonably needs to obtain in order to comply with 

NPDES, stormwater, Dangerous Waste, or other Ecology permit programs.

• Public involvement documentation (public notice, comments, responses)

• Process Piping and Site Layout

• Definitions of terms used in the permit

4. REGIONAL PRETREATMENT ENGINEER STAFF 

EXPERTISE AREAS

Overview

Federal Regulations at section 40 CFR 403.10(f)(2) require Ecology to provide technical and 

legal assistance to POTWs in developing Pretreatment programs. As a functional necessity, 

Ecology must also provide training and oversight of the non-delegated POTWs that we rely upon 

to implement parts of the pretreatment program where there is no local program. 

Division of Duties

Each region determines how to divide the responsibilities of implementing and overseeing the 

diverse municipal and industrial components of the pretreatment program between their 

pretreatment engineer and municipal and industrial permit writers and facility managers.

Training

Ecology provides training and oversight through the pretreatment workgroup, its chairperson, 

and regional pretreatment engineers. Pretreatment staff support and speak at pretreatment 

training events such as the Northwest Pretreatment Conference, and more general forums such as 

PNCWA meetings. The Pretreatment Workgroup chairperson, in conjunction with regional 
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pretreatment engineers, also arranges separate training events that focus on one or more nondelegated POTW areas of responsibility. These are typically one day events held every two or 

three years at a couple locations.

Delegated Program Oversight

Regional pretreatment engineers support delegated pretreatment programs on both an informal 

and formal level. Informally, they support POTW requests for engineering assistance in plan 

review (Engineering Reports, Plans and Specifications, and O&M Manuals). They also help by 

reviewing permit applications and draft permits when requested. Formal oversight of delegated 

pretreatment programs is provided by conducting pretreatment compliance inspections (PCIs), 

audits, and reviewing the POTW’s annual pretreatment report. Pretreatment reports are required 

and reviewed annually from each delegated municipality 

EPA Oversight

The Ecology – EPA Performance Partnership Agreement establishes several pretreatment 

requirements. Ecology performs PCI’s and Audits at the frequency described in that document. 

As of 2010, that document committed Ecology to conducting PCIs every two years and Audits 

once every five years. Ecology submits copies of PCI’s and Audits to EPA. Ecology will also 

provide the pretreatment related data in EPA’s Required ICIS Database Elements (RIDE) when 

those protocols are established by rule. Ecology will require delegated POTWs to include this 

information in annual reports then as well.

Non-Delegated Program Oversight

Regional pretreatment engineers provide non-delegated POTWs with oversight, guidance, and 

assistance as needed to fulfill their role as partners with Ecology carrying out the pretreatment 

program in their service area. The duties of non-delegated POTWs can vary, but all are charged 

with locating industry that should be subject to the pretreatment program. They must also all 

prohibit industrial discharges until properly controlled by Ecology, and control the myriad 

diffuse sources such as restaurants that collectively pose a threat. 

Expanded Responsibilities

Ecology’s staffing and resource limitations are severe. Accordingly, some POTWs must do 

more than just locate industries. Ecology may need the POTW to develop pretreatment 

standards (local limits) that protect their POTW from adverse effects from non-domestic wastes, 

codify these limits in an Ordinance, and provide an expanded oversight “presence” to businesses. 

The regional pretreatment engineers evaluate the situation and recommend POTW 

responsibilities commensurate with the situation. This may require changes to NPDES permit 

requirements and activities preparatory to developing a local program.

4.1.Conducting Industrial User Surveys

Local POTWs are ideally situated to identify the sources of non-domestic wastewater potentially 

subject to pretreatment standards and requirements. They have direct access to water records, 
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utility billing records for water use, planning department staff and records, tax and business 

license records, and building code enforcement staff. 

For this reason, Ecology’s permit shell assigns this task to non-delegated POTWs at a frequency 

commensurate with the threat. Important factors in evaluating the threat include whether the 

POTW serves an industrial area, if there have been incidents at the POTW that may have been 

caused by non-domestic discharges, and how much flow the POTW receives. 

Part of the information POTWs collect includes the flow and concentrations of pollutants of 

concern. This allows the POTW to estimate the loadings from all their non-domestic dischargers 

which is an important part of developing “technically based” local limits (next section). 

The POTW’s procedures should describe how they keep their survey list updated (through 

ongoing systems such as applications for new business licenses or approval or plans), and the 

interval for periodically re-surveying sewer customers to locate new or changed discharges with 

should be subject to pretreatment requirements.

To assist in this task, Ecology has developed an Industrial User Survey guidance manual. Permit 

writers and regional pretreatment engineers should provide this to POTWs that need technical 

assistance.

4.2.Developing “Technically Based” Local Limits

POTWs must develop local limits for all pollutants of concern to protect the POTW, its solids, 

workers, and the public from harm. To be legally defensible these limits must describe their 

basis. This is referred to as “technically based”.

Local limits for indirect dischargers are analogous to water quality based limits derived by 

Ecology for direct dischargers. Both types of limits are developed protect the receiving 

environment (surface water, groundwater, or POTW). Both also intend to ensure healthy water 

quality in the receiving environment. POTWs must develop Local limits where they have SIU’s 

that are not limited by categorical standards, or when applicable categorical standards do not 

limit pollutants well enough to protect the POTW. This latter case is increasingly common as 

categorical industries use more chemicals that were unavailable when such standards were set.

Federal regulations at 40 CFR 403.5(d) state that where specific limits on pollutant parameters 

are developed by a POTW according to 403.5(c) (which includes notice to affected Users), such 

limits are deemed Pretreatment Standards for the purposes of section 307(d) of the Clean Water 

Act. Ecology should require, as an NPDES permit condition, that any new or revised local limits 

be reviewed and approved by Ecology. This is important as Ecology will have to defend the 

limits should they ever be challenged by a Permittee.
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Categorical standards and local limits are distinct and complementary types of pretreatment 

standards. Categorical standards provide a nationally uniform degree of water pollution control. 

Local limits provide an additional degree of control based on site specific requirements. EPA 

has published guidance on how to develop local limits in their July 2004 manual “Local Limits 

Development Guidance” Ecology has developed and will provide a spreadsheet for tabulating 

and analysis of the data collected during the local limits development process. Ecology has also 

developed a checklist for verifying the completeness of the local limits development document.

Where Permit Writers have questions on how to develop local limits, they should contact their 

regional pretreatment engineers, who can answer these questions or pass them on to the state 

pretreatment engineer. See the monitoring chapter of this manual for a discussion of what 

monitoring requirements should be included in a POTW's NPDES permit for developing and 

updating local limits.

Some municipalities may elect to develop local pollutant discharge limits without being required 

by Ecology. Industrial permit writers should always ask knowledgeable POTW staff about local 

limits when writing a permit for an industry discharging to a POTW. If those local limits satisfy 

the requirements of 403.5(c) they are applicable to all indirect discharges. Permit writers should 

document their findings in such cases in the fact sheet of the permit they are writing. Permit 

writers must apply the most stringent of local limits, categorical standards, BPJ, and AKART.

4.3.Providing Model Pretreatment Ordinance Language

POTWs that have or are developing delegated programs must first develop a Sewer Use 

Ordinance that allow the POTW to legally apply and enforce the local limits, requirements of the 

General Pretreatment Regulations and any other federal, state, or local pretreatment standards 

and requirements needed to control non-domestic dischargers to all tributary users. 

POTWs which support Ecology’s administration of a pretreatment program also need to have the 

authorities to carry out the functions which we require of them. See Section 2.D for a fairly 

comprehensive list of such possible requirements. Where Ecology has approved the technical 

basis for local limits, the POTW needs to codify these local limits in their ordinance so that 

Ecology can support and reinforce them in permits issued by Ecology to indirect dischargers. 

Ecology has developed a model pretreatment ordinance for delegated POTWs. This has been 

used in updating pretreatment programs after EPA’s streamlining of 2006. This language will be 

periodically revised when federal and state rules change. 

Ecology is working on an adaptation of this Ordinance for non-delegated POTWs. One 

complication is that the range of responsibilities for non-delegated POTWs may vary. Until such 

time as that is published, non-delegated POTWs can codify the model ordinance for delegated 

POTWs, but instead of requiring Users to obtain a permit from the POTW, reinforce the 

requirement for them to obtain a permit from Ecology for indirect discharge. 
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4.4.Inspecting and Auditing Delegated Programs

Ecology is obliged to ensure that delegated POTWs implement the Federal Pretreatment Program 

and State Waste Discharge permit program for tributary users and do so in accordance with their 

approved program and applicable rules. Two types of inspections of delegated pretreatment 

programs are the “Pretreatment Compliance Inspection” (PCI) and “Pretreatment Audit”. 

Definitions of these terms, and the current philosophy for their use and scope is found in Chapter 

9 “Pretreatment” of EPA’s July 2004 NPDES Compliance Inspection Manual. EPA has also 

published instructions and checklists for both types of inspections.

During an Audit, Ecology reviews whether the POTW’s program satisfies all applicable state and 

federal rules. This including reviewing whether they have adopted provisions that incorporate 

any revisions to rules since the program was developed. Where Ecology finds that a program is 

not carrying out its approved program, or it needs to amend its approved program to incorporate 

changes to rules or a changed situation, Ecology will apply escalating enforcement measures to 

correct the situation.

During a PCI, Ecology focuses on assessing whether the POTW is properly implementing its 

approved program. The PCI starts with assessing whether the local program locates all 

industries potentially subject to the program, notifies them of appropriate pretreatment related 

requirements, issues appropriate permits, provides proper oversight (frequency and scope of 

inspections and sampling), properly reviews reports, manages files, and effectively responds to 

non-compliance. As part of the PCI, Ecology must assess whether the POTW has sufficient 

staffing to carry out their approved program. Often inspectors will review the annual 

pretreatment report in preparation for conducting a PCI. This report can reveal problems at the 

POTW or continuing non-compliance that needs to be addressed during the PCI.

As part of either an Audit or PCI, Ecology may inspect one or more tributary users. There are 

several purposes for such oversight. First, it allows Ecology to confirm that the IU is properly 

classified, and that pretreatment controls of its permit are appropriate. It also provides an 

assessment of the POTW’s ability to do inspections. And it allows Ecology to provide some 

training for local inspectors that may have few opportunities for such training.

For POTWs without a delegated program, Ecology staff responsible for managing compliance 

with the municipal permit would typically also assess whether the POTW has met the 

pretreatment related permit requirements. This may be done during POTW compliance 

inspections, or based on the POTW not meeting the submittal dates of its permit. The regional 

pretreatment specialist should be asked to assist in this assessment process when the permit 

manager is unsure of the requirements. 
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4.5.Reviewing Pretreatment Related Submittals from POTWs 

There are two major types of pretreatment related submittals—those we have required under the 

POTWs permit and those we haven’t. Pretreatment related submittals that arrive unsolicited can 

range from Engineering Reports and O&M Manuals for tributary Users, to program changes that 

the POTW would like to make. 

Most regions have recognized the value of having an engineer oversee implementation of local 

POTWs so that they can review plans for wastewater facilities. 

Processing NPDES Permit Modifications

When a local pretreatment program has been developed or modified, it must be reviewed and 

approved by Ecology and EPA. Ecology must then issue a public notice of the proposed 

approval and allow for public involvement (a comment period). Ecology must then modify the 

municipal NPDES permit so it incorporates the approved program as an enforceable part of the 

permit. Ecology must also delegate State Waste Discharge permitting authority to the 

municipality while retaining an oversight function. This is required under RCW 90.48.165. 

These procedures should happen concurrently.

4.6.Reviewing Pretreatment Permits

Ecology regional pretreatment engineers have different assigned duties in different regions. In 

some regions they may write all the indirect discharge permits. In others they may provide 

technical assistance to Ecology permit writers writing indirect discharge permits. Ecology also 

provides review of draft permits for delegated programs. Delegation rules at Chapter 173-208 

WAC specify that delegated programs will send all permits to Ecology upon issuance. While 

Ecology has developed other means of ensuring consistency of permits, some POTWs choose to 

continue to use this opportunity to validate their permits. 

4.7.Providing Organized Pretreatment Related Training Events

While much training is done “one-on-one” with POTW staff, another important way that 

Ecology assists POTWs is to provide training events where Ecology staff review our guidance 

and answer common implementation questions. Ecology, as part of pretreatment training, should 

periodically review Ecology guidance and tools for carrying out IU surveys, developing local 

limits, codifying these limits, and should develop instruction around these topic areas. 

Ecology pretreatment training should be focused on reviewing the basics of how the program 

works, how to use available tools, and what references to go to for additional clarifications.

EPA has produced quite a few EPA guidance manuals relating to pretreatment. Ecology’s 

training should provide an overview of these manuals so POTWs can locate guidance in specific 
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areas. The Pretreatment coordinator will maintain a compilation of these EPA manuals, Ecology 

manuals, and other referenced materials that form the basis for pretreatment permit condition and 

program procedures on DVD format. Part of organized training events will include 

disseminating this compendium, and ensuring that regional coordinators have copies for

distribution within their regions.
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CHAPTER XI. RECLAIMED WATER USE

The Washington State Legislature passed the Reclaimed Water Use Act (chapter 90.46 RCW) in 

1992. This law promotes the beneficial use of a new water supply derived from highly treated 

wastewaters. Categories include reclaimed water, greywater and two types of industrial process 

water reuse. This Chapter provides the permit writer with information needed to write these 

permits.

Permits are issued to the owner of the facility generating the reclaimed water and govern the 

water quality, distribution and use of the water supply. Reclaimed Water Act permits are much 

broader than state or NPDES wastewater discharge permits. State law requires a single 

comprehensive permit integrating Ecology Water Quality Program, Water Resource Program 

and Department of Health (DOH) requirements. Agencies and programs must coordinate as 

early in the process as possible. For most projects, Ecology’s Water Quality Program issues the 

permit and includes all requirements. DOH may issue the permit for projects with only 

commercial and industrial uses. Amendments to Chapter 90.46 RCW in 2009 created a “lead 

agency” designation for either Ecology or DOH, whichever agency issues the facility permit. 

The lead agency is required to refer all permit applications to the “nonlead agency” for review 

and consultation, but the nonlead agency may choose to limit the scope of its review.

A reclaimed water permit grants an exclusive right to the use and distribution of the water and 

has stringent requirements for treatment reliability and disinfection. Although a facility may 

produce and discharge a highly treated wastewater effluent (and may even call itself a water 

reclamation facility), the state does not consider a facility a “reclaimed water facility” until a 

permit is issued under Chapter 90.46 RCW.

1. LEARNING THE LANGUAGE 

The permit writer should become familiar with the specialized terms in the Reclaimed Water Use 

statute and the Water Reclamation and Reuse Standards. Consult these sources directly for the 

complete legal definitions: 

Reclaimed Water Use Act (chapter 90.46 RCW)

Water Reclamation and Reuse Standards, Publication # 97-23

We provide plain English working translations of these definitions below:

1.1 Working Definitions:

Agricultural Industrial Process water is a special subset of industrial reuse water and refers to 

adequately and reliably treated water supplies derived from food processing wastewaters for use 

on agricultural lands. 
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Beneficial use refers to the direct use of reclaimed water for specifically stated and permitted 

uses without an intervening discharge to waters of the State. Beneficial use refers to conveyance 

of reclaimed water through pumps and pipes for irrigation, industry, urban non-potable purposes, 

or for planned environmental benefits such as wetlands, maintaining instream flows, lakes or 

aquifer levels. Beneficial use does not include discharge to public waters for planned recovery 

of the reclaimed water. 

Constructed beneficial use wetlands (also called created wetlands) are wetlands created on nonwetland sites to produce or replace (mitigate for) lost natural wetland functions and values. They 

are considered waters of the state. 

Constructed treatment wetlands (also called constructed wetlands) are wetlands constructed with 

reclaimed water for additional polishing of the water or providing public educational or aesthetic 

water features. They are not considered waters of the state. This category does not include 

wetlands used for primary or secondary wastewater treatment. 

Controlled use refers to the indirect use of reclaimed water for specifically stated and permitted 

uses. Controlled use involves the discharge of reclaimed water to public waters (lakes, rivers 

and aquifers) for storage or conveyance followed by the subsequent recovery and beneficial use 

of the reclaimed water. 

Direct ground water recharge refers to subsurface injection of reclaimed water directly to the 

ground water basin. Reclaimed water may be used for in situ environmental benefits such as 

maintaining geological structure or providing base flows to surface waters. The water many also 

be planned for subsequent recovery and use. Ground water recharge may also be used to 

mitigate impacts from other water withdrawals.

Drainfield , as used in this Chapter, refers to the network of subsurface pipes or tiles through 

which reclaimed water is dispersed into the soil for the purpose of ground water recharge

through infiltration in undisturbed native soil. This use of drainfields must meet all requirements 

for ground water recharge by surface percolation. If the drainfields do not provide adequate 

separation from the ground water basins, direct ground water recharge requirements apply.

Greywater refers to domestic wastewater including the wastewater from sinks, showers and 

laundry fixtures but not from toilets and urinals. Standards, procedures and guidelines for reuse 

of greywater are developed by the Department of Health, Office of Environmental Health and 

Safety. Statute requires that the reuse greywater be permitted by Department of Health or local 

health officers based on rules adopted by Department of Health. Contact or refer requests to the 

Large On-site System Program Lead at DOH. Greywater may only be used below the surface 

(such as for drip irrigation). For surface uses, the greywater must be treated to meet the state 

reclaimed water standards appropriate for the use. After treatment, it is considered reclaimed 

water rather than greywater.
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Ground water recharge criteria are specifically defined in the reclaimed water act as the official 

state drinking water standards. For ground water recharge by surface percolation, the law 

requires reclaimed water to meet these criteria in the ground water beneath the recharge site.

Impairment refers to a condition caused by someone or something other than a natural condition 

where a water right holder cannot accomplish the beneficial use(s) for which the right was 

perfected using reasonable care and diligence. Ecology considers a reclaimed water impairment 

analysis in the same context as the issuance of a new water right pursuant to RCW 90.03.290 and 

RCW 90.44.060.

Industrial Reuse Water was added to the statute in 2002. This refers to water supplies derived 

from industrial processing wastewaters that are adequately and reliably treated to a quality 

suitable for another use. This is a very broad category and water quality limitations must 

frequently be decided on a case-by-case basis. 

Land application refers to the beneficial use of reclaimed water for crop or urban landscape 

irrigation. It includes both surface and sub-surface (drip) irrigation methods. It does not include 

dedicated sprayfields used for land treatment and disposal of wastewater. 

Reclaimed water is the original category in the 1992 statute. It is specifically defined as a new 

water supply derived from the adequate and reliable treatment of wastewater containing a 

sewage (or human waste) component. This is most frequently domestic or municipal wastewater 

but also includes any wastewater that contains any amount of sanitary sewage. 

Recycling means the capture and redirection of used water back to the same uses. This may be 

with or without additional treatment. Recycling most frequently occurs in an industrial setting.

Reuse is a more general term referring to the subsequent use of any used water including 

reclaimed water, greywater, stormwater and wastewater. These used waters do not always 

require treatment to be re-used. This becomes confusing because the term water reuse also 

describes the use of reclaimed water (which requires treatment). Under state law, reclaimed 

water is considered a new water supply - not used water - and the more precise term is reclaimed 

water use. 

Surface percolation refers to the application of reclaimed water to the ground surface for the 

planned replenishment of ground water. Reclaimed water may be planned for in situ 

environmental benefits or for subsequent recovery and use. Ground water recharge may also be 

used to mitigate impacts from other water withdrawals. 

Streamflow augmentation means the planned and permitted release of reclaimed water to lakes, 

rivers, streams. The reclaimed water may be used for in situ environmental benefits or planned 

for subsequent recovery and use. Streamflow augmentation may be used to mitigate impacts 

from other water withdrawals. 

Water of the State or State Waters refers to lakes, rivers, ponds, streams, inland waters, 
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underground waters, salt waters, and all other surface waters and watercourses within the 

jurisdiction of the state of Washington. 

Water of the United States is defined by the U.S. E.P.A. as navigable waters, tributaries to 

navigable waters, interstate waters, the oceans out to 200 miles, and intrastate waters which are 

used by interstate travelers for recreation or other purposes, as a source of fish or shellfish sold in 

interstate commerce, or for industrial purposes by industries engaged in interstate commerce.

1.2 Abbreviations and Acronyms

AKART – All known available and reasonable methods of prevention, control and 

treatment.

ART – Adequate and reliable treatment

DOH – State Department of Health

WQP – Water Quality Program

WRP – Water Resources Program

SEA – Shorelands and Environmental Assistance Program

ODW – Office of Drinking Water (DOH)

2. STATUTORY REQUIREMENTS

The permit writer should understand the basic statutory differences between reclaimed water 

permits, wastewater discharge permits and water rights. 

Wastewater discharge permits include the National Discharge Elimination System (NPDES) and 

state waste discharge permits. They are regulated under Chapter 90.48 RCW, the Water 

Pollution Control Act. These permits include treatment, monitoring and siting conditions 

providing for the least harmful disposal of treated wastewater effluent. Wastewater discharges 

must be treated to protect existing beneficial uses in ground or surface water discharges, but the 

wastewater is not planned for a specific beneficial use. This is true even when there is some 

incidental benefit. 

Water right permits are regulated under Chapter 90.03 Water Code and Chapter 90.44 Ground 

Water Code govern the quantity, location and purpose of water use and relation to other water 

uses.

Reclaimed water permits are regulated under a different law, Ch 90.46 RCW, the Reclaimed 

Water Use Act. Reclaimed water is considered a new water supply planned for beneficial use. 

The law requires issuance of a single comprehensive permit governing the water quality, the rate, 

location, and purpose of use. The owner of the permitted facility receives an exclusive right to 

the use and distribution of the reclaimed water and exemption from the Water Code 

appropriative water right permit requirements. The permit is usually issued by Ecology through 
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the Water Quality Program with close coordination with the Water Resources Program and 

DOH. DOH may issue permits that are not under Ecology jurisdiction. 

Combining various permits into the single reclaimed water permit quickly becomes complex. 

Reclaimed water facilities with no wastewater effluent discharges are still issued permits under 

Chapter 90.46 RCW. However, many facilities that generate reclaimed water also have 

wastewater effluent discharges. Effluent discharge may be an alternative when reclaimed water 

quality standards are not met or when there are uses for only some of the treated water. An 

NPDES permit is required under federal law (The Clean Water Act) whenever the water is 

discharged to a water of the United States. When the reclaimed water permit is combined with 

an NPDES or state waste discharge permit, the reclaimed water requirements are usually 

designated as a separate section (called R conditions for reclaimed).

2.1 Reclaimed Water Standards 

Chapter 90.46 RCW funded and required the development of a single set of standards for 

reclaimed water -Water Reclamation and Reuse Standards, 1997. The standards were developed 

cooperatively between the Departments of Ecology and Health. Although authorized by statute, 

it is very important to remember that the standards are not in regulation and must be incorporated 

into the permit to be enforceable. 

The 1997 standards define adequate and reliable treatment (ART) requirements to be met at all 

times. This “at all times” requirement is included because reclaimed water is no longer 

considered a wastewater. ART requirements are in addition to (and generally more stringent 

than) the AKART requirements for wastewater treatment. Although all projects must meet state 

requirements, reclaimed water released to a water of the United States must also meet all federal 

Clean Water Act requirements for discharge.

2.2 Industrial Process Reuse Water 

In 2001 and 2002, amendments to Chapter 90.46 RCW added provisions for two additional types 

of industrial water reuse: agricultural-industrial process water and industrial reuse water. The 

law did not specifically require or fund development of either new standards or regulations for 

the new categories. The wide variety of potential wastewater sources and uses require most 

industrial reuse water decisions to be made on a case-by-case basis. All existing requirements

for water quality and human health protection under Chapter 90.48 RCW still apply. In addition,

the permit must assure that the new water supply meets the ART requirements for the intended 

uses. 

2.3 Water Resources Permitting

Reclaimed water act permits also differ from wastewater discharge permits regarding the legal 

status of the water following discharge from the treatment facility. RCW 90.46.120 gives the 
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owner of a permitted reclamation treatment facility the exclusive right to the use and distribution 

of the reclaimed water generated by the facility. The law specifically exempts the owner from 

the appropriative water right permitting requirements of the state water code4. The exclusive 

right and exemption intends to streamline the permitting process by providing for only one state 

permit with conditions regulating the water quality as well as the location, the rate and the 

purpose of water use. 

Some projects may propose the indirect or controlled use of reclaimed water following discharge 

to waters of the state. As long as the intent of subsequent withdrawal or diversion is recovery of 

the reclaimed water and a portion of the reclaimed water is actually recovered, the complete 

project may be permitted under a single reclaimed water permit. When the reclaimed water is 

discharged as mitigation for withdrawal or diversion of waters of the State (no portion of the 

reclaimed water is recovered), two permits are required: a reclaimed water permit for 

groundwater recharge or streamflow augmentation and a new appropriative water right under 

Chapter 90.03/90.44 RCW.

When wastewater that has been traditionally discharged to waters of the State is planned to be 

diverted for other uses, the Permittee must also meet provisions in RCW 90.46.130. This section 

of the Reclaimed Water Use Act requires that existing water rights not be impaired by the water 

reuse project. For reclaimed water, RCW 90.46.130(1) provides that any compensation or 

mitigation of impairment must be agreeable to the holder of the affected water right. The Water 

Resources Program (WRP) is available to assist the water reuse project proponent in assessing 

the potential to impair existing water rights. WRP also reviews the impairment analysis and 

provides a recommendation to the permit writer and water quality facility manager for project

approvals and permit conditions necessary to avoid impairment of existing water rights. 

2.4Guidance for Coordinated Permits

In some cases it is not possible to issue a single permit that covers both treatment of the 

reclaimed water and the eventual beneficial use. One example of this is an appropriation of state 

water in exchange for groundwater recharge or stream flow augmentation where the 

appropriation does not capture any of the reclaimed water. Examples of this would be an 

appropriation up stream, or upgradient in the same aquifer. The Department does not possess 

statutory authority to grant a single permit for these types of reclaimed water projects, and a 

separate water right (90.03/90.44 RCW) permit must be issued for the appropriation in addition 

to the reclaimed water permit.

 

4 RCW 90.46.120 specifically exempts use and distribution of reclaimed water by the owner of the facility from the permit 

requirements of RCW 90.03.250 and 90.44.060. However, it will be appropriate for the permit writer to consider permit 

conditions and analyses from other portions of the water code when issuing the single combined reclaimed water permit. These 

would include an evaluation of impairment pursuant to RCW 90.46.130, well construction standards, metering and reporting 

requirements, screening provisions and others.
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These types of reclaimed water projects must still demonstrate that no existing water right is 

impaired by their actions and that water quality standards are met.

Additionally, the statutory tests for issuing a new water right must also be met including that 

water is available for appropriation, that the proposed purpose must be a beneficial use of the 

water, and that the application will not impair existing water rights or be detrimental to the 

public welfare. Ecology must process new water right application in the order they are received 

unless they qualify for expedited processing. Reclaimed water projects proposing mitigated use 

of state water may qualify for expedited processing if they meet the requirements in the WAC 

173-152-050 (2)(b) and Ecologies water Budget Neutral Policy (Policy - 1021)

2.4.1 Timing Issues

Because the water right permit and the reuse permit are issued on different time cycles 

coordination between the two permitting programs will be necessary.

For a new reuse facility, discharging reclaimed water (e.g., beneficial use for groundwater 

recharge or instream flows) and seeking a “credit” for a commensurate (or lesser) amount of 

state resources in a different location, the following schedule will typically apply:

1. A 20-year planning projection is completed in a water system plan update. 

2. The water resources permit issues for the 20-year planning projection. 

3. The water quality permit issues for the first 5-year cycle, and then every 5 years 

thereafter (4 total reuse permits over the life of a single water right permit). 

4. At the end of the 20-year cycle, if the facility has not grown as fast as that projected 

initially, the permit could be extended for another 5-year term under RCW 90.03.320. 

5. If the permitted quantity has been put to beneficial use a new water resources permit 

application is required of additional growth. Because use of water under the water 

resources permit is always contingent on equivalent discharge of reclaimed water a 

certificate is not issued.

2.4.2 Water Resources Permit Content

The water right permit would have the following characteristics inherent to every water right 

issued under Chapter 90.03/90.44 RCW, including:
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1. Qi (Instantaneous withdrawal rate)

2. Qa (Annual withdrawal rate)

3. Point of diversion/point of withdrawal 

4. Place of use 

5. Season of use 

6. Purpose of use 

7. Priority Date 

Additionally, it would include provisions that would “marry” it to the reclaimed water permit.

Provision 1: “No withdrawal is authorized under this permit unless mitigation is provided 

consistent with the terms outlined in the DATE Water System Plan or an update thereto 

approved by the Department of Ecology.” Note that this plan will need to include the description 

of the other water rights in play, and contingencies for what happens when the system doesn’t 

meet a water quality parameter (e.g., is not reclaimed water discharge, but rather disposal). This 

is largely a paper exercise because the discharge would typically have occurred, so there would 

not necessarily be a wet water impact. However, there is no “credit” for disposal.

Provision 2: Source metering.

Provision 3: Monitoring data shall be submitted each year. The annual submittal will include a 

monthly accounting of reclaimed water discharged and source water diverted (e.g., debits and 

credits). 

2.4.3 Reuse (Water Quality/Health) Permit Content

The Reuse Permit Fact Sheet would include a narrative of the project in the including the use of 

reclaimed water as mitigation for a subsequent state water diversion. 

The Reuse Permit would be slightly modified to reflect the two permit format.

1. R1 – Limits. Standard (Class A, B, C, or D as appropriate) limits would apply. For 

surface water, include limits for the discharge (disposal) of off specification water. 

Include language that treated wastewater that does not meet the reclaimed water limits is 

effluent, not reclaimed water. This is important for the water right ‘credit’ accounting. 

2. R2 – Monitoring. Include monitoring of the flow meter for the diversion of state water to 

dovetail with the WATER RIGHT permit. 

3. R3 – Reporting. An additional reporting requirement to submit the accounting of the 

water diverted and the reclaimed water produced. The exact accounting would be project 

specific; i.e., the accounting method described in the approved facility plan, and assumed 

in the impairment analysis. The reuse permit would have the same language as 

‘Provision 3’ from the water rights permit. Water Resources would be on the distribution 

list for this submittal. 
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4. R4 – Use and Distribution. The authorized use would be ground water percolation or 

flow augmentation. The reuse plan, use area agreement and other permit requirements 

would regulate how the water was discharged or percolated. The reclaimed water permit 

would put no conditions on the use of the water appropriated through the water right 

permit. 

2.4.4 Changes to the Water Resources Permit 

Because the development schedule for the permit will be 20 years, it is very possible that 

changes could occur during that time, including:

1. Point of withdrawal. Pursuant to RCW 90.44.100, such a change could be made through 

a Showing of Compliance, or a formal change application submitted to Ecology or a 

Conservancy Board.

2. Point of diversion. Point of diversion changes are limited to those authorized by RCW 

90.03.350-370 and for municipalities, under RCW 90.03.570. Once perfected changes 

may be made pursuant to RCW 90.03.380. 

3. Place of use. For municipalities, the place of use would likely change every 6 years with 

a water system plan update by operation of law. 

4. Purpose of use. Most permits would issue for municipal water supply. Purpose of use 

cannot be changed on inchoate permits. Purpose of use may be changed pursuant to 

RCW 90.03.380 once perfected. 

The above changes to a water right permit would generally not necessitate an immediate change 

to the reuse permit, rather it could be addressed (e.g., in the narrative) at the next 5 year update.

2.4.5 Changes to the Reuse (Water Quality/Health) Permit 

Reuse permit changes could cause a change in the water right permit authority if the nature of the 

discharge changed (e.g., location, timing, duration, or other type that could affect the underlying 

no-impairment determination). 

2.5 Wetlands 

Site specific permit provisions in addition to the requirements in the Water Reclamation and 

Reuse Standards may be required for wetlands projects. All projects that propose wetlands 

creation or enhancement should be coordinated with the regional wetlands specialists in the 

Ecology SEA Program. The field of wetland science and the wetland regulatory framework are 

constantly changing. Wetlands are dynamic and highly variable ecosystems and Ecology has 

developed general wetland regulation guidelines that allow the agency to incorporate current 

wetland science, tailor the level of regulation to the type of wetland being affected, and respond 

to site-specific situations.
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2.6 Stormwater 

Stormwater use is generally not covered under Ch 90.46 RCW. However, there are two basic 

ways in which storm flows may be considered part of reclaimed water. In both cases, the 

stormwater is introduced prior to treatment.

1. Normal infiltration and inflow to sanitary sewer systems.

2. Stormwater considered as industrial process wastewater.

Some projects also propose blending stormwater with reclaimed water after treatment. Due to 

the differences in regulatory requirements, combined applications can quickly become complex. 

The blending of stormwater and reclaimed water is discussed under the various categories for use 

of reclaimed water. 

2.7. Department of Health Provisions

Early coordination or consultation between the Department of Ecology and DOH is needed for 

all significant issues related to public health protection. RCW 90.46.030 gives DOH the lead for 

industrial and commercial uses of reclaimed water such as toilet flushing and cooling tower use. 

The DOH review focuses on reliability, advanced treatment and distribution and use

considerations for disease prevention, particularly from pathogens such as protozoa, bacteria and 

viruses. 

3. THE PERMITTING PROCESS

4. This section discusses the general permitting process for most reclaimed water projects. 

Chapter 90.46 RCW requires Ecology to issue a single permit which is essentially a 

combination of a water quality permit, DOH requirements and water right provisions 

governing the location, the rate and purpose of use of the water. A single combined permit 

is issued by the Water Quality Program to the owner of the reclaimed water facility. Since 

the permit requirements for reclaimed water facilities extend beyond the Water Quality 

Program, it is important for the permit writer to coordinate efforts between Ecology Water 

Quality and Water Resources programs and DOH early in the permit process. Failure to do 

so results in project delays and strained relationships. Regional staff should also notify the 

State Lead in Ecology’s Water Quality Program. This is needed for project tracking and is 

helpful in obtaining assistance with the water reuse elements of the proposal.
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3.1. Ecology Water Quality Program Role

The Ecology Water Quality program has the largest regulatory burden for permit administration. 

Under Chapter 90.46 RCW, Ecology has the primary permitting responsibility for land 

application; ground water recharge, wetlands, and streamflow augmentation of reclaimed water 

and for all treatment and uses of agricultural industrial and industrial reuse water (see 

definitions). To streamline procedures, Ecology also has authority under RCW 90.46.030(5) to 

issue permits including commercial and industrial uses of reclaimed water through a formal 

agreement with DOH. Ecology uses the authority under Chapter 90.46 RCW and Chapter 90.48 

RCW to review, approve, permit and inspect the water reclamation and reuse facilities. 

3.1.1 Reclaimed Water Permits

Reclaimed water is, by definition, derived from wastewater with a domestic wastewater 

component. Chapter 90.46 RCW authorizes Ecology to issue a single permit for the treatment 

and beneficial use of reclaimed water. The statute and the Water Reclamation and Reuse 

Standards (1997) specify the treatment and monitoring required for various uses of the reclaimed 

water. These must always be incorporated into the permit to assure that they will be enforceable. 

The Water Quality program is also the lead for coordinating with both DOH and Water 

Resources Program (WRP) during the development of the permit. Both WRP and DOH may 

also include conditions within the permit. 

3.1.2 Agricultural Industrial Process Water Reuse Permits

Beginning in 2001, RCW 90.46.150 authorized Ecology to issue a single permit for agricultural 

reuse of water derived from food processing wastewater. As long as there is no sewage present 

in the wastewater, the requirement for adequate and reliable treatment should be considered 

equal to or higher than the AKART treatment technology requirements for wastewater discharge 

permits from food processing facilities. If the wastewater has a sewage component, then it must 

meet the requirements for reclaimed water under 4.1.1 above. In either case, the treatment must 

assure that the water is safe and appropriate for use as a water supply. Section 14 (under 

development) of this Chapter will provide additional detail on water quality considerations for 

various uses. The permit writer should coordinate with the WRP regarding the potential for 

water right impairment and any additional permit conditions. The law requires Ecology to refer 

the permit application to DOH for review and consultation if a significant risk to public health 

exists in the proposed use of the water. Public health risks that may warrant referral to DOH are 

included under section 4.2.2. If you are uncertain regarding the potential for public health risk in 

a project, contact DOH early in the permitting process. 

3.1.3 Industrial Process Water Reuse Permits

In 2002, RCW 90.46.160 authorized Ecology to issue a single permit for water reuse projects 

derived from industrial process wastewaters. If the industrial wastewater is co-mingled with any 

amount of human sewage, it is considered reclaimed water and as discussed in 4.1.1 above. The 
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law is very broad regarding the types of industrial wastewaters and potential use. Projects are 

likely to be very case specific and no specific standards or regulations have been written to cover 

this category. ART (adequate and reliable treatment) is required in the law to assure that the 

water is safe and appropriate for the proposed uses on sites which are not dedicated for 

wastewater disposal. Ecology has several sets of standards and regulations for industrial 

wastewaters that can be applied on a case-by-case basis to meet this requirement. These include: 

• AKART and Industrial Pre-treatment Standards

• Surface water standards

• Ground water standards

• Water Reclamation and Reuse Standards 

• Section 14 of this Chapter (under development)

When Ecology determines that a significant risk to public health exists in the use of the water, 

the agency is required to refer the application to DOH for review and consultation. Public health 

risks that may warrant referral to DOH are included in Section 4.2.2 of this Chapter. If you are 

uncertain regarding the potential for public health risk in a project, contact DOH early in the 

permitting process. The permit writer should coordinate with the WRP regarding the potential 

for water right impairment and any additional permit conditions.

3.2. Department of Health Role

DOH under RCW 43.70.80 and Chapters 246-271 and 246-272 WAC has the authority to protect 

public health and approve, inspect, and permit municipal wastewater disposal systems. DOH 

also has the permitting lead for commercial and industrial uses of reclaimed water although 

RCW 90.46.030 allows Ecology to issue the permit through interagency agreement. 

3.2.1 Memorandum of Understanding (MOU)

Ecology Water Quality Program and DOH Office of Drinking Water completed an MOU (May 

25, 1995) to more clearly delineate responsibilities. Under the interagency MOU, DOH has 

responsibility for the following:

o Cross -connection control measures and public health requirements for reclaimed 

water permits.

o Notify Ecology of any reclaimed water permit violations through copies of 

inspections, monitoring records or correspondence with Permittee, distributors or 

users. 

o Report any other alleged permit violation to Ecology that is found as a result of a 

DOH inspection or notification.

The MOU also provides that Ecology will:

o Institute a consistent, statewide procedure for DOH to include appropriate public health 

conditions for reclaimed water projects within the permits. 
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o Notify DOH of initial permit applications, renewals or modifications that contain 

reclaimed water provisions.

o Consult with DOH to assure that public health is adequately addressed in engineering 

approvals, permits and enforcement orders. 

o Report to DOH any permit violations of public health significance that may affect 

reclaimed water permits including copies of inspections, monitoring records or 

correspondence with Permittee, distributors or users.

o Notify DOH of any complaints of public health significance on reclaimed water permits

3.2.2 Public Health Risk Consultation

Public health risks in the use of reclaimed water or industrial reuse water that may be of 

interest to DOH include the following: 

• Irrigation or other direct reclaimed water use within areas served by public water 

systems. 

• Installation of non-potable pipelines in a public right-of-way that also incorporates 

potable water lines when pipe separation requirements are not met.

• Projects creating cross connections between reclaimed water and potable water in all 

public water supply systems.

• Projects where aerosols are introduced into public areas.

• Projects with ground water recharge occurring in areas adjacent to or contiguous with 

existing potable source water protection areas.

• Projects where uses might be compromised by microbial pathogens or other contaminants 

in the reclaimed or industrial reuse water.

• Projects where reclaimed water quality for public contact uses could be contaminated 

from other non-potable pipelines such as sanitary sewers. 

3.3. Ecology Water Resources Program Role

Chapter 90.46 RCW requires Ecology to issue a single reclaimed water permit. This permit 

combines the water quality permit with the water right provisions governing the location, the rate 

and purpose of use of the water. Although reclaimed water use is exempt from the permitting 

requirements of the water code, there are several areas where the two programs overlap and 

coordination must occur. In addition, it is important for the water resources program to have 

knowledge of and access to information where water reuse supplies offset the need for other 

water sources. 
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Consideration must be given to the following:

• Impairment of Existing Water Rights.

• Location, rate and purpose of use.

• Controlled Use.

• Blending with other flows.

• Mitigation for New Water Rights.

3.3.1 Impairment of Existing Water Rights

The guidance below is applicable to reclaimed water facilities under RCW 90.46.130(1) which 

are primarily municipal facilities. It may not always apply to the non-impairment provisions 

under RCW 90.46.130(2) for industrial reuse water. Additional guidance will be included in 

Section 14 at a future update. If you have an industrial reuse project, consult the WRP for 

specific help with impairment determination requirements. 

Impairment is defined in Section 2 of this Chapter. RCW 90.46.130(1) indicates that a 

reclaimed water permit should only be issued if there is no impairment of existing downstream 

water rights or if adequate compensation or mitigation is provided for the impairment. To 

mitigate for impairment, the reclaimed water permit may therefore include specific permit 

conditions such as restrictions on the amount of flow that may be diverted at critical times. 

Figure 4.1 on the following page illustrates the importance of the impairment analysis in the 

reclaimed water permitting process.

Assessing the potential for impairment is an essential step in determining the feasibility and cost 

of a reclaimed water project. The purpose of the impairment analysis is to evaluate whether 

existing water right holders will be impaired when a reclaimed water facility decreases or 

eliminates its existing discharge of wastewater and begins to reclaim the water for beneficial 

uses. All downstream water right holders must be considered in the analysis. (See Impairment 

Analysis is required for All Projects below).

Generally, the analysis will be completed and approved as part of the SEPA process. 

Compliance with SEPA is required for approval of the facility plan or engineering report. It is 

important for the proponent to identify and notify all potentially impaired water right holders. 

Public notice requirements are included in Section 4.6 of this Chapter.

The Water Quality facility manager or permit writer should arrange a meeting with the Permittee 

and the Water Resources Program to discuss the project and the level of technical assistance 

available as the Permittee prepares the impairment analysis. The following topics are intended to 

assist the permit writer when working with the Permittee and with the Water Resources Program. 
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Figure 3.1 Permitting Flow Chart for Reclaimed Water Projects

Complete The Impairment Analysis Early. 

Ecology recommends submitting the impairment analysis as early as possible in the 

planning process. Depending on the status of a community’s sewer planning efforts, an 

iterative process may be most appropriate. The proponent completes a scoping analysis at 

the initial stages of a reclaimed water project, followed by a more detailed assessment when

reclaimed water appears feasible. Typically, an impairment analysis must be completed to 

comply with SEPA and is submitted to the department as a component of an approved 

facility plan or engineering report. 

Impairment Analysis Is Required For All Projects. 

Although an analysis is always required, in some cases the scope of the analysis may be 

simple. When no water rights have historically used the wastewater return flow (such as 

marine discharges and wastewater land treatment and disposal facilities that consume the 

water) a short paragraph may be sufficient documentation. For all projects, documentation 

of the impairment analysis must be included in the fact sheet accompanying the draft permit.

Proponent submits Reclaimed Water 

Permit application

Has WR 

previously 

reviewed 

an 

impairment 

Was an 

impairment 

analysis 

submitted with 

the permit 

WQ can proceed with 

review of the application, 

and if complete develop 

Reclaimed Water Permit

The application is not 

complete. Provide 

proponent a list of 

deficiencies including 

the need for an 

impairment analysis.

WR 75 day review of 

impairment analysis

The 

application is 

not complete

Is the 

impairment 

analysis 

adequate?

YES

YES

YES

NO

NO

NO
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Evaluate All Existing Downstream Water Right Holders (6 Steps).

For reclaimed water projects other than a historic marine discharge or land disposal, several 

steps must be completed in evaluating the potential for impairment associated with a 

proposed water reclamation project. 

The first step in evaluating impairment is to determine an initial study area based on the 

maximum possible geographic and geologic boundaries for the analysis. Geologic 

boundaries should be based on hydraulic barriers to water flow, including faults, folds, 

impermeable layers and other geologic features. Geographic boundaries should be based on 

topography, watershed boundaries, and (in surface water settings) a downstream control 

point that is sufficiently separated by distance as to make impairment extremely unlikely. 

The second step in evaluating impairment is to establish the location of this downstream 

control point. A good way to do this is to compare the maximum instantaneous quantity of 

wastewater to be reclaimed with the minimum annual flow in the receiving water body at the 

historical point of waste discharge. If the amount of water to be reclaimed is small 

compared to this minimum flow, it can be argued that this control point is essentially at the 

point of discharge, and impairment of downstream rights is highly unlikely5

. As the ratio of 

reclaimed wastewater to minimum annual stream flow increases however, it becomes 

increasingly likely that this control point is further downstream, and one or more intervening 

downstream water right holders may be impaired. Natural surface and ground water inputs 

between the historical point of discharge and the downstream rights may bring the control 

point closer to the discharge point. 

The goal of this step is to shrink the size of the initial study area from a whole geological 

basin to a smaller portion therein, if at all possible. Outside of this final study area, it is 

highly likely that no water rights will be impaired. 

The third step in evaluating impairment is to identify all existing rights within the final study 

area. Any downstream water right holder in this area whose exercise of a water right relies, 

in whole or in part, on the water body to which wastewater has historically been discharged 

should be evaluated. Ecology has interpreted downstream to mean down gradient in the 

context of groundwater. Ecology water resources staff can assist the project proponent in 

determining the location and characteristics of study area water rights.

The fourth step in evaluating impairment is to determine whether any of those rights may be 

removed from further consideration because they never relied upon the historic wastewater 

 

5 One exception is the potential for impairment of an instream flow adopted by the Department in rule, for which any reduction 

may be considered to be impairment (see Instream Flow Water Rights section).
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discharge. In many cases, the project proponent may not be able to exclude any water right 

holders at this step. However, in some areas where water rights have been adjudicated, it 

may be appropriate to exclude water rights that were perfected before the wastewater 

discharge began and no impairment is likely. In areas where the original source water for 

the wastewater discharge is in another basin or aquifer, such flow may be considered foreign 

and water right holders downstream of the discharge may not have had a right to rely upon 

such flows. Ecology encourages the project proponent to work closely with water resources 

staff where such situations are present.

The fifth step is to determine the most appropriate water right to use as an “indicator right” 

for the impairment evaluation. Often times this is the closest water right to the historic 

discharge.

The sixth step is to evaluate whether the reduced discharge, including timing and frequency 

of occurrence, will impair the indicator water right under the impairment definition. 

Technical evaluations, analytical formulae or modeling may be necessary to make such a 

determination. If no impairment of the indicator right is found, then it may be appropriate to 

determine no impairment will occur to any right in the study area based on this worst-case 

evaluation. If the indicator water right is impaired, further evaluation may be necessary to 

determine how many rights would be impaired in the event that compensation or mitigation 

is proposed. 

Instream Flow Water Rights Are Included. 

The State is the holder of instream flow “rights” adopted by rule and is required to protect 

these minimum instream flows. Reduction of stream flow that prevents the legal purpose(s) 

of the adopted in-stream flow is considered an impairment of a water right. When instream 

flows could be impaired by the continuous diversion of water for a proposed project, the

Ecology issued water right is typically conditioned as an interruptible right to assure that 

instream flow provisions are met. 

It may be possible to provide compensation or mitigation to ameliorate the impairment of 

the State instream flow water “right”. Ecology has prepared a mitigation digest of past 

projects that have included this type of mitigation. In general, in-kind (e.g., drop for drop) 

mitigation - in both space and time to the impact - is preferred. Ecology may also determine 

that a project is in the overriding consideration of the public interest (OCPI) and elect to not 

enforce the State’s right against the proposed project. However, compensation/mitigation or 

OCPI are rare exceptions.

Surface Water/Groundwater Continuity Must Be Considered. 

The rule governing protection of ground water withdrawal facilities, Chapter 173-150 WAC, 

identifies how qualifying withdrawal facilities for groundwater rights may be impacted by a 

project. In general, a well must fully penetrate an aquifer in order to qualify for impairment 

protection. 
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Indicators of More Complex Impairment Analysis. 

A project whose historic discharge exhibits one or more of the following characteristics 

generally indicates that impairment may occur and that compensation or mitigation may be 

necessary. Impairment may occur if the discharge is:

• To a basin closed to further appropriations by Ecology.

• To a basin with instream flows adopted by rule.

• To an aquifer with declining water levels.

• To a designated groundwater management area.

• To a stream that goes dry.

• To a stream that is managed each year according to priority date. 

• To a basin with Federal Energy Regulatory Commission (FERC) projects with flow 

requirements.

3.3.2 Location, Rate and Purpose of Use

The reclaimed water permit must include conditions identifying the location, rate and purpose of 

use of the reclaimed water. These may be generally defined (similar to requirements in a 

municipal water right) or may be very site specific. The Water Resources Program must be 

aware of reclaimed water use as it makes water resource management decisions. The

coordinated permit conditions provide a method to track reclaimed water use. The Water Reuse 

Workgroup also maintains a summary of existing projects which is updated as new facilities 

come on line.

3.3.3 Controlled Use

Controlled uses are indirect uses involving the release of the reclaimed water to waters of the 

State, with subsequent recovery of the reclaimed water. A single Chapter 90.46 RCW permit is 

required to authorize the project.

When reclaimed water is commingled with waters of the State for indirect use, it does not 

necessarily lose its character as reclaimed water. The owner of the permitted reclamation facility 

may retain the exclusive right to some of the reclaimed water for storage or conveyance and 

subsequent recovery. The intent to retain this exclusive right must be clearly documented in the 

facility plan and regulatory language included in both the fact sheet and the permit.

3.3.4 Combining With Other Withdrawals or Diverted Water Supplies.

When reclaimed water is combined with other diversionary water supplies for an approved use, 

the owner still retains the exclusive right to the reclaimed water. However the combined water 

supply must be consistent with the uses and conditions authorized in the diversionary water right. 

The volumes (rates) of water authorized in the appropriative water right are restricted to the 
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authorized purpose and place of use in the water right. The volume (rate), water quality, 

locations and uses of the reclaimed water must be included in the reclaimed water permit. This 

does not necessarily preclude the use of the combined water for uses or locations not included in 

the appropriative water right. However, it does complicate administrative details. For example –

the use of the combined water at another location along the same pipe route could be authorized 

under the reclaimed water permit provided that the combined water still meets the requirements 

for the proposed use. If each supply is separately determined to be of adequate quality for the 

beneficial use, the combined flow is generally also adequate quality for the use. The specific 

water chemistry of the combined flow should be considered in making this determination during 

the facility planning process. 

3.3.5 Mitigation for New Appropriative Water Rights

Ecology encourages the beneficial use of reclaimed water. However, for some projects it may be 

prohibitively expensive to use the reclaimed water either directly through pumps and pipes or 

indirectly through controlled storage and recovery. Under such circumstances, it may be 

possible to return the reclaimed water to waters of the State in exchange for the use of new state 

water. 

Using reclaimed water as mitigation for state water may be appropriate when the proposed use 

site is geographically or geologically removed from the reclaimed water facility so that 

withdrawal of any of the reclaimed water for use is impractical. 

In this case, the permit must describe the beneficial use of reclaimed water that is proposed 

(streamflow augmentation, groundwater recharge) and identify the appropriative right under 

Chapter 90.03 or 90.44 RCW that is mitigated by the Chapter 90.46 RCW reclaimed water 

permit. Permit language must provide for contingency planning either enforcing interruption of 

the dependent water right or providing an approved, alternate source of water when the 

reclaimed water is not available. 

3.4 Fact Sheets and Documentation

Fact sheets are used to document provisions for reclaimed water and industrial water reuse 

permits. Chapter XIV of the permit writer’s manual contains information on federal and state 

water quality requirements for fact sheet documentation. The permit writer should use this 

chapter as a guide and also include the following types of information which are specific to 

reclaimed water or industrial process water reuse permits. Additional information includes:

1. Document the water rights impairment analysis and any mitigation or compensation 

measures taken. 

2. DOH requirements

Fact sheet boilerplates for reclaimed water permits are included on the Ecology website. 
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3.5 Public Involvement 

There are several requirements for notification of the public of a Permittee’s intent to reclaim 

water. These include SEPA notifications as part of sewer utility planning, application for a 

reclaimed water or NPDES permit and issuance of a permit by Ecology. Ecology recommends 

full and repeated disclosure detailing the project plans relative to historic wastewater discharges 

in public notices. This will minimize the risk associated with legal action following construction 

and use of the reclaimed water facility. Whenever possible, the permit writer should plan to 

issue reclaimed water use permits prior to the beginning of facility construction. This will help 

prevent last minute objections that could hold up or prevent the use of the reclaimed water.

4. TREATMENT TECHNOLOGY REQUIREMENTS

This section provides the more specific permit requirements for assuring adequate treatment and 

water quality for use. The WQP issues the permit governing the quality of the water for public

health protection, environmental protection and suitability of the water for the intended 

beneficial uses authorized in the reclaimed water law. Reclaimed water must meet the ART 

treatment method and reliability requirements, technology-based water quality limits and specific 

use-based standards. The Water Reclamation and Reuse Standards, 1997, govern the use. 

4.1 Source Control and Pre-treatment 

Source Control is the first line of defense. An effective industrial pretreatment program is 

necessary to provide a high quality of influent so that the resulting product will be suitable for 

use. The Water Reclamation and Reuse Standards require the Permittee to either have an 

Ecology delegated industrial wastewater pretreatment program or to assure that all industries 

discharging into the collection system have current waste discharge permits issued by Ecology. 

Regular monitoring of industrial users is required.

4.2 Four Basic Classes 

There are four basic classes of reclaimed water – A, B, C and D – with Class A as the highest 

level. These levels are appropriate for the more traditional direct beneficial uses of reclaimed 

water for irrigation and various commercial and industrial uses. Similar to surface water quality 

use-based standards, the degree of treatment required varies according to the specific use. 

Additional treatment is required for ground water recharge, streamflow augmentation or 

wetlands projects 

The water reclamation treatment systems are derived from requirements for both conventional 

wastewater treatment and drinking water treatment systems. The effectiveness and reliability of 

these measures is considered a critical element of the system. It is not feasible or cost-effective 
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to measure the wide variety of pathogens and pollutants that may be present in the wastewater at 

any given time. 

To assure final quality, the wastewater flows through a series of sequential treatment processes. 

This provides multiple opportunities to remove pollutants and provides a high level of reliability 

to final water quality. None of the required treatment steps may be eliminated and still produce 

reclaimed water. The treatment steps must occur in the order given below:

All reclaimed water requires a minimum level of oxidized, secondary treatment and a high level 

of disinfection (Steps 1 and 4 below). For uses with public contact requiring Class A reclaimed 

water or higher, all 4 treatment techniques are required. Some uses (or source waters) also 

require biological nitrogen removal or other processes to remove specific contaminants. The 

treatment steps must occur in the order given below. 

1. Oxidation – Oxidation refers to the biological secondary treatment process designed to 

remove dissolved organic contaminants. The actual process design depends on requirements 

for nutrient removal or for subsequent advanced treatment processes. The goal is to produce 

a wastewater that has been stabilized to the point that the biochemical oxygen demand 

(BOD5) and the total suspended solids (TSS) do not exceed 30 mg/L on a monthly average. 

Dissolved oxygen is also required to be present following this step. The dissolved oxygen is 

considered necessary to assure that biological oxygen demand remaining after treatment will 

not cause the water to go anoxic or anaerobic which may result in operational problems or 

disinfection (usually chlorine) demand that might reduce the final water quality. Although 

the presence of dissolved oxygen is required for all levels of reclaimed water, the biological 

stabilization it represents is particularly important prior to filtration when nitrogen has not 

been removed to low levels. If the water becomes anoxic, nitrification can begin leading to 

denitrification in the filters, gas bubble formation and clogging or preferential flow paths 

leading to short circuiting in the filter beds. 

2. Coagulation - Class A or higher. This process promotes the aggregation of fine waste 

particles and colloids to improve their removal by settling and filtration. Coagulation usually 

is done by the addition of chemicals such as metallic salts (alum or ferric chloride) and 

polymers. The Water Reclamation and Reuse Standards will allow other equally effective 

methods in standard engineering practice.

3. Filtration – Class A or higher. Filtration removes suspended particles. Because pathogenic 

organisms are often associated with particles, filtration reduces the concentration of 

pathogenic organisms in the water. Filtration also removes particles that can interfere with 

disinfection processes. 

Conventional filtration methods such as sand or cloth filters are considered adequate when 
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on-line average operating turbidity does not exceed 2 nephelometric turbidity units (NTU) or 

5 NTU at any time.

4. Disinfection - Disinfection is essential to destroy waterborne pathogenic organisms such as 

bacteria, viruses, and protozoa. Each Class of reclaimed water has a different total coliform 

standard to indicate that disinfection has occurred to the level appropriate for the allowed 

uses. 

4. 3 Distribution Line Chlorine Residual 

Chlorine residual is required in distribution lines that convey reclaimed water from the treatment 

facility to the use area. This can be considered as an additional pathogen protection barrier but is 

also used to avoid regrowth that results in fouling or plugging of the distribution pipeline. A 

minimum 0.5 mg/L residual is required unless waived for a specific application by both EcologyWQ and DOH-ODW. Beneficial uses that may justify a waiver of chlorine residual include 

wetlands enhancements and groundwater recharge, 

4.4 Advanced Treatment Techniques

4.4.1 Microfiltration and ultrafiltration membranes

Membranes remove particles to very low levels. This treatment technology is increasingly 

popular as membrane quality improves and cost goes down. Our water reuse standards do not 

currently provide an equivalent standard to determine adequate membrane filtration for Class A 

reclaimed water. California has established a technology based membrane filtration standard 

requiring the effluent turbidity to be at or below 0.2 NTU more than 95% of the time and never 

to exceed 0.5 NTU. A properly maintained and operated membrane would consistently achieve 

these levels. Turbidity above these levels could indicate a breach or bypass of the membrane 

process. Therefore, until the adoption of a reclaimed water rule, Ecology and DOH have agreed 

to apply an average turbidity of less than or equal to 0.2 NTU “at all times” and a maximum 

turbidity value of 0.5 NTU. Turbidity spikes above the 0.5 NTU level during the first 5 minutes 

following filter start-up may be acceptable if the permittee can demonstrate that these spikes are 

not due to breaching, bypass, or lack of membrane integrity. For membrane filters, meeting 

these turbidity criteria will be considered equivalent to meeting the coagulation and filtration 

steps required for Class A applications of reclaimed water. 

4.4.2 Nitrogen Removal

Nitrogen removal is generally considered a use-based rather than a technology-based 

requirement. However, for ground water recharge, the removal of nitrogen in the biological

oxidation treatment process step of the reclamation process is a required treatment technology. 
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Most nitrogen in reclaimed water readily converts to nitrate, which is very soluble and mobile in 

the ground water. Ecology therefore limits nitrogen in the final reclaimed water to 10 mg/L of 

total nitrogen to assure ground water protection. 

4.4.3 Reverse Osmosis

Reverse osmosis (RO) is required as a treatment technique for direct ground water recharge as 

defined in Section 2 of this Chapter. RO is a membrane system that removes dissolved salts and 

minerals from solution based on reversing osmotic pressure differentials. RO is also effective 

for pathogen removal. 

4.5 Water Quality Technology Limits 

Table 4.5.1 provides a general summary of the requirements for Class A, B, C, and D reclaimed 

water. Note that disinfection requirements are measured in total coliform and use a 7-day 

median rather than a geometric mean calculation for compliance.

4.5.1 Water Quality Technology Limits Class A-D Reclaimed Water

Table 4.5.1 Summary of Treatment Requirements

Class

Level

Oxidized

Secondary

(BOD/TSS

---- mg/L )

 Coagulated Filtered 

(Turbidity

in NTU)

Disinfection 

(Total Coliform/ 100 MPN mL)

7-Day 

Median 

Single 

Sample

A 30 YES 2 NTU

average

< 2.2 23 

5 NTU 

maximum

B 30 NO NO < 2.2 23 

C 30 NO NO < 23 240 

D 30 NO NO < 240 No

standard
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4.5.2 Class B, C or D Reclaimed Water Quality Limits

Table 4.5.2 provides the basic reclaimed water quality limits and sampling points 

for Class B, C or D water. 

 Water Quality Limits For Class B, C or D Reclaimed Water

Parameter Average Monthlya

Flow MGD (Point of Compliance)

Oxidized Wastewater – Secondary Effluent c

Parameter Average Monthlya Average Weekly b

BOD5 30 mg/L 45 mg/L

TSS 30 mg/L 45 mg/L

Dissolved Oxygen Shall be measurably present in secondary effluent at all times

Disinfected - Reclaimed Water

Total Nitrogen as N Average Monthlya 

mg/L (engineering report)

Sample Maximum d 

mg/L (engineering report)

Total Coliform

Class D

7-day Mediane

240 MPN/ 100 ml 

Sample Maximum f

 Not defined 

Class C 23 MPN/ 100 ml 240 MPN/100ml

Class B 2.2 MPN/ 100 ml 23 MPN/ 100 ml

pH Shall be between 6 and 9 standard units at all times 

Distribution System

Chlorine Residual Minimum Daily

0.5 mg/L

Point of compliance g

a

30 mg/L is the highest value allowable under this permit limit. The average monthly value 

for compliance is calculated as the sum of all daily samples measured during a calendar 

month divided by the number of sample measured that month 

b

45 mg/L is the highest allowable value under this permit limit. The average weekly value 

for compliance is calculated as the sum of all daily samples measured during a calendar week 

divided by the number of daily samples measured during that week.

c The compliance point for BOD and TSS will be in the secondary effluent.

d The sample maximum is defined as the value not to be exceeded by any single sample. 
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 Water Quality Limits For Class B, C or D Reclaimed Water

e The median number of total coliform organisms in the reclaimed water after disinfection is 

determined from the bacteriological results of the last 7 days of analyses. 

f This limit denotes the maximum number of total coliform organisms per 100 milliliters 

allowable in any single sample.

g A chlorine residual of at least 0.5 mg/L shall be maintained in the reclaimed water during 

conveyance to the location of use or to the storage pond if reclaimed water is not directly 

piped to the location of use. 

4.5.3 Water Quality Limits for Class A Reclaimed Water 

Table 4.5.3 provides the basic reclaimed water quality limits and sampling points for Class A 

water. Note that the BOD, TSS, and dissolved oxygen limits are met after the secondary 

treatment step rather than in the final reclaimed water. This assures the effectiveness of the 

treatment technique. Turbidity is regulated after filtration and prior to disinfection. 
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Table 4.5.3 Reclaimed Water Limitations for Class A

Parameter Average Monthlya

Flow MGD (Point of Compliance)

Oxidized Wastewater – Secondary Effluent c

Parameter Average Monthlya Average Weekly b

BOD5 30 mg/L 45 mg/L

TSS 30 mg/L 45 mg/L

Dissolved Oxygen Shall be measurably present in secondary effluent at all times

Coagulated/ Filtered Wastewater – Prior to Disinfection 

Turbidity Average Monthlya

2 NTU

Sample Maximum d

5 NTU

Disinfected - Reclaimed Water

Total Nitrogen as N Average Monthlya 

10 mg/L 

Sample Maximum d 

15 mg/L 

Total Coliform 7-day Mediane

2.2 MPN/ 100 ml 

Sample Maximum f

 23 MPN/100 ml

pH Shall be between 6 and 9 standard units at all times 

Distribution System

Chlorine Residual Minimum Daily

0.5 mg/L

Point of compliance g

a

 30 mg/L is the highest value allowable under this permit limit. The average monthly value 

for compliance is calculated as the sum of all daily samples measured during a calendar 

month divided by the number of sample measured that month 

b

45 mg/L is the highest allowable value under this permit limit. The average weekly value 

for compliance is calculated as the sum of all daily samples measured during a calendar week 

divided by the number of daily samples measured during that week.

c The compliance point for BOD and TSS will be in the secondary effluent.

d The sample maximum is defined as the value not to be exceeded by any single sample. 
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Table 4.5.3 Reclaimed Water Limitations for Class A

e The median number of total coliform organisms in the reclaimed water after disinfection is 

determined from the bacteriological results of the last 7 days of analyses. 

f This limit denotes the maximum number of total coliform organisms per 100 milliliters 

allowable in any single sample.

g A chlorine residual of at least 0.5 mg/L shall be maintained in the reclaimed water during 

conveyance to the location of use or to the storage pond if reclaimed water is not directly 

piped to the location of use. 

4.6 Monitoring Requirements 

4.6.1 Class B, C or D Reclaimed water Monitoring

Table 4.6.1 lists the minimum monitoring requirements for reclaimed water. Note that flow, 

turbidity and chlorine residual must be monitored continuously.

Table 4.6.1 Class B, C or D Reclaimed Water Monitoring Requirements

Parameter Units Sample Pointa Sampling 

Frequency

Sample Type

Flow MGD Continuous Recording 

meter

BOD5 mg/l Influent Weeklyb 24-hour 

composite

Final reclaimed 

water

Weeklyb 24-hour 

composite

TSS mg/l Influent Weeklyb 24-hour 

composite

Final reclaimed 

water

Daily 24-hour 

composite

pH Standard 

Units

Influent Daily Measurement

Disinfected 

reclaimed water

Daily Measurement

Dissolved 

Oxygen

mg/L Final reclaimed 

water

Daily Grabc
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Table 4.6.1 Class B, C or D Reclaimed Water Monitoring Requirements

Parameter Units Sample Pointa Sampling 

Frequency

Sample Type

Temperature Celsius Final reclaimed 

water

Daily Grabc

Total 

Nitrogen (as 

N)- Optional

mg/l Disinfected 

reclaimed water

Monthly 24-hour 

composite

Ammonia 

(as N)-

Optional

mg/L Disinfected 

reclaimed water

Monthly 24-hour 

composite

Nitrate (as 

N)-Optional

mg/L Disinfected reclaimed water Monthly 24-hour 

composite

Total 

Coliformd

No. of org. 

per 100 ml

Disinfected reclaimed water Daily Grabc

Priority 

Pollutants

ug/L Disinfected 

reclaimed water

Once per permit 

cycle – minimum 

– see Ch XIII.

24-hour 

composite

Total 

Chlorine 

Residual

mg/L Water Reuse 

Distribution 

Line

Daily (when in 

use)

Grabc

a Samples shall be taken at (describe location).

b

Weekly is the minimum allowable monitoring requirement. More frequent 

monitoring is appropriate when based on the wastewater treatment facility sizes and 

processes. See Chapter XIII for minimum requirements for most secondary facilities. 

c

Grab samples shall be taken at the same time daily when wastewater characteristics 

are the most demanding on the treatment facilities and disinfection processes.

d As an alternate method, total coliform bacteria may be monitored using the 

ONPUG-MUG test (also called Autoanalysis Colilert System) per latest edition of 

standard methods.
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4.6.2 Class A Reclaimed Water Monitoring

Table 4.6.2 lists the minimum requirements for Class A reclaimed water monitoring. Note that 

flow, turbidity and chlorine residual must be monitored continuously.

. 

Table 4.6.2 Class A Reclaimed Water Monitoring Requirements

Parameter Units Sample Pointa Sampling 

Frequency

Sample Type

Flow MGD Continuous Recording 

meter

BOD5 mg/l Influent Weeklyb 24-hour 

composite

Secondary 

effluent

Weeklyb 24-hour 

composite

TSS mg/l Influent Weeklyb 24-hour 

composite

Secondary

effluent

Daily 24-hour 

composite

pH Standard 

Units

Influent Daily Measurement

Secondary 

effluent

Daily Measurement

Disinfected 

reclaimed water

Daily Measurement

Dissolved 

Oxygen

mg/L Secondary 

effluent

Daily Grabc

Disinfected 

reclaimed water

Daily Grabc

Temperature Celsius Secondary 

effluent

Daily Grabc

Disinfected 

reclaimed water

Daily Grabc

Turbidity NTU Secondary 

effluenta

Daily Grabc
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Table 4.6.2 Class A Reclaimed Water Monitoring Requirements

Parameter Units Sample Pointa Sampling 

Frequency

Sample Type

NTU Filter effluent 

prior to 

disinfection

Continuous recording 

meterd

Coagulant Lbs. Coagulant feed Daily Metered usage

Coagulant 

Aid

Lbs. Coagulant feed Daily Metered usage

Total 

Nitrogen (as 

N)

mg/l Disinfected 

reclaimed water

Monthly 24-hour 

composite

Ammonia 

(as N)

mg/L Disinfected 

reclaimed water

Monthly 24-hour 

composite

Nitrate (as 

N)

mg/L Disinfected reclaimed water Monthly 24-hour 

composite

Total 

Coliforme

No. of org. 

per 100 ml

Disinfected reclaimed water Daily Grabc

Priority 

Pollutants

ug/L Disinfected 

reclaimed water

Once per permit 

cycle 

24-hour 

composite

Total 

Chlorine 

Residual

mg/L Water Reuse 

Distribution 

Line

Daily (when in 

use)

Grabc

a Secondary effluent shall be taken at (describe location)

Disinfected reclaimed water samples shall be taken at (describe locations)

b

Weekly is the minimum allowable monitoring requirement. More frequent 

monitoring is appropriate when based on the wastewater treatment facility sizes and 

processes. See Chapter XIII for minimum requirements for most secondary facilities.

c Grab samples shall be taken at the same time daily when wastewater characteristics 

are the most demanding on the treatment facilities and disinfection processes.

d Filter effluent turbidity analysis shall be performed by a continuous recording 

turbidimeter and shall also be read and recorded at least every four hours. 

e As an alternate method, total coliform bacteria may be monitored using the ONPUGMUG test (also called Autoanalysis Colilert System) per latest edition of standard 

methods.
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4.6.3 Process Operational Monitoring 

Since process monitoring is used as a barrier to assure the quality of the water at all times, it is 

more important than in wastewater discharge permits. Appropriate process monitoring protocols 

for disinfection should be included as permit conditions to protect the quality of the reclaimed 

water. (Guidance under development)

5. DISTRIBUTION AND USE 

This section covers permit requirements for the distribution of reclaimed water as well as 

requirements common to various uses. The remaining sections discuss the specific requirements 

for each type of reclaimed water use. This section is currently under construction and the permit 

writer is referred to the Water Reclamation and Reuse Standards and the Reclaimed Water 

Permit Boilerplate for guidance on permit language. 

5.1 Use-Based Water Quality Limits

All reclaimed water supplies must meet requirements protecting public health and environmental 

quality. In addition, permit requirements should also assure the suitability of the water for the 

planned direct beneficial uses. This does not mean that all contaminants believed present must 

be included as limits or monitoring requirements in every permit. Detection of chemicals at low 

levels does not automatically translate into impacts on human or aquatic health or the suitability 

of the water for the proposed use. For example, USGS water quality assessments may be done at 

the parts-per- trillion levels, which is an amount that can be up to 100 times lower than the 

threshold used for setting standards and guidelines. The permit writer should use best 

professional judgment in determining when additional parameters should be added to the permit 

for limits or environmental monitoring. 

5.2 Discharges from Distribution Maintenance

5.2.1 Flushing Reclaimed Water Lines

Incidental or planned discharges of reclaimed water from distribution system maintenance 

procedures must conform to the permit conditions regarding notification to the regulatory 

agencies and the public. The permit should specify the methods of control, discharge or disposal 

of this water as approved in the engineering report.

5.2.2 Pipeline Repair Discharges

Reclaimed water discharge or drainage resulting from pipeline repair activities is considered an 

unanticipated discharge. Management and disposal of this water must be addressed within the 

Permittee’s operations and maintenance plan. 
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6. IRRIGATION

Irrigation is the most common use of reclaimed water. This section describes the parameters the 

permit writer should consider in permitting irrigation use.

6.1. Class of Reclaimed Water Required for Use.

Table 6.1 lists the minimum class of reclaimed water that may be used for the various types of 

irrigation uses. For uses not listed, consult the Water Reuse Workgroup.

Table 6.1 Class of Reclaimed Water Required for Irrigation Use

Class of Reclaimed 

Water Required

Use A B C D

Irrigation of nonfood Crops

Trees and Fodder, Fiber, and Seed Crops YES YES YES YES

Sod, Ornamental Plants for Commercial Use, and Pasture to Which 

Milking Cows or Goats Have Access

YES YES YES NO

Irrigation of Food Crops

Spray Irrigation - All Food Crops YES NO NO NO

Spray Irrigation - Food Crops Which Undergo Physical or Chemical 

Processing Sufficient to Destroy All Pathogenic Agents

YES YES YES YES

 Surface Irrigation - Food Crops Where There is No Reclaimed Water 

Contact With Edible Portion of Crop

YES YES NO NO

Surface Irrigation – Root crops YES NO NO NO

Surface Irrigation- Orchards and vineyards YES YES YES YES

Surface Irrigation - Food Crops Which Undergo Physical or Chemical 

Processing Sufficient to Destroy All Pathogenic Agents YES YES YES YES

Landscape Irrigation

Restricted Access Areas (e.g., Cemeteries and Freeway Landscapes) YES YES YES NO

Open Access Areas (e.g., Golf Courses, Parks, Playgrounds, 

Schoolyards, and Residential Landscapes) YES NO NO NO

Impoundments

Landscape Impoundments YES YES YES NO

Restricted Recreational Impoundments YES YES NO NO

Nonrestricted Recreational Impoundments YES NO NO NO

Fish Hatchery Basins YES YES NO NO

Decorative Fountains YES NO NO NO
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6.2 Other Considerations for Irrigation Water Quality

The feasibility of using reclaimed water for irrigation is based on several factors beyond those 

listed in the Water Reclamation and Reuse Standards. Problems that may arise from irrigation 

can be broadly classified as follows:

1. Those caused by materials which accumulate in, or leach from, the soil with potentially harmful 

effects on the soil, groundwater or surface waters. The problems that fall into this group include

those caused by heavy metals and dissolved salts, particularly sodium. The severity of the 

problem depends on water quality, soil characteristics and management approach. Salinity can be 

a particular concern in that it influences the soil osmotic potential and specific ion toxicity. This 

can result in degradation of the soil conditions. Sodium, boron and chloride are soluble 

constituents that can interfere with plant growth. Chloride and sodium increase in domestic and 

industrial water usage, especially when water softeners are used

2. Those which cause changes to crop or landscape condition or kill vegetation but can be readily 

corrected.

The problems described in the first group are serious when the toxicity to plants, animals or humans is 

involved. When the water will be used for irrigation purposes, the wastes discharged to sewers must be 

treatable to the quality required for irrigation waters and this should be reflected in the pre-treatment 

permits and local ordinances. Source control may be necessary to assure that wastewaters can be suitably 

treated for beneficial use. Wastewater with significant levels of the following types of contaminants may 

not be able to be reclaimed to a level usable for use in any irrigation projects without advanced treatment 

capable of removing the compounds. 

• Radioactive materials with a half life of more than a few days;

• Pharmacologically active compounds;

• Non-biodegradable toxic organic compounds;

• Wastes containing elevated levels of total dissolved salts;

• Wastes containing high concentrations of metals; and,

• Petrochemical and mining industries output.

Soils which are naturally saline may also not be good candidates for longer term use of reclaimed water 

without additional treatment (such as reverse osmosis) to remove excess salts. 

In many parts of Washington, winter rains frequently saturate the soil profile allowing accumulated salts 

to be leached from the root zone. The effectiveness of winter rains to leach salts from the root zone can 

be approximated by determining whether rainfall over the winter period is sufficient to overfill the crop 

root zone on at least one occasion.

Table 6.2.1 and 6.2.2 below provide the EPA recommended guidelines for maximum levels of various 

contaminants in reclaimed water used for irrigation purposes.
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Table 6.2.1 Recommended Limits for Trace Heavy Metals for Reclaimed Water 

Irrigation

Constituents Long-Term 

Use (mg/L)

Short-Term 

Use (mg/L)

Remarks

Aluminum 5.0 20 Can cause nonproductiveness in acid soils, but soils at 

pH 5.5 to 8.0 will precipitate the ion and eliminate 

toxicity

Arsenic 0.10 2.0 Toxicity to plants varies widely, ranging from 5 mg/L 

for Sudan grass to less than 0.05 mg/L for rice

Beryllium 0.10 0.5 Toxicity to plants varies widely, ranging from 5 mg/L 

for Kale to 0.5 mg/L for bush beans

Boron 0.75 2.0 Essential to plant growth, with optimum yields for 

many obtained at a few tenths mg/L nutrient solutions. 

Toxic to many sensitive plants (e.g., citrus) at 1 mg/L. 

Usually sufficient quantities in reclaimed water to 

correct soil deficiencies, Most grasses are relatively 

tolerant at 2.0 mg/L to 10 mg/L

Cadmium 0.01 0.05 Toxic to beans, beets, and turnips at concentrations as 

low as 0.1 mg/L in nutrient solution. Conservative limits 

recommended.

Chromium 0.1 1.0 Not generally recognized as an essential growth element 

Conservative limits recommended due to lack o 

knowledge on toxicity to plants

Cobalt 0.05 5.0 Toxic to tomato plants at 0.1 mg/L in nutrient solution. 

Tends to be inactivated by neutral and alkaline soils

Copper 0.2 5.0 Toxic to a number of plants at 0.1 mg/L to 1.0 mg/l in 

nutrient solution.

Fluoride 1.0 15.0 Inactivated by neutral and alkaline soils

Iron 5.0 20.0 Not toxic to plants in aerated soils. But can contribute to 

soil acidification and loss of essential phosphorus and 

molybdenum

Lead 5.0 10.0 Can inhibit plant cell growth at very high concentrations

Lithium 2.5 2.5 Tolerated by most crops at up to 5 mg/l and is mobile in 

soil. Toxic to citrus at low doses: recommended limit is 

0.075 mg/L

Manganese 0.2 10.0 Toxic to a number of crops at a few tenths to a few mg/L 
9CHAPTER XI. RECLAIMED WATER USE (JULY 2011)

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in acid soils

Molybdenum 0.01 0.05 Non toxic to plants at normal concentrations in soil and 

water. Can be toxic to livestock if forage is grown in soils 

with high levels of available molybdenum

Nickel 0.2 2.0 Toxic to a number of plants at 0.5 mg/L to 1.0 mg/l; 

reduced toxicity at neutral or alkaline pH 

Selenium 0.02 0.02 Toxic to plants at low concentrations and to livestock if 

forage is grown in soils with low levels of added 

selenium 

Tin, Tungsten, 

& Titanium

Effectively executed by plants; specific tolerance levels 

unknown

Vanadium 0.1 1.0 Toxic to many plants at relatively low concentrations

Zinc 2.0 10.0 Toxic to many plants at widely varying concentrations;

reduced toxicity at increased pH (6 or above) and in 

fine-textured or organic soils.

Table 6.2.2 Recommended Limits for Other Constituents for Reclaimed Water 

Irrigation

Constituent Recommended Limit Remarks

pH 6.0 Most effects of pH on plant growth are indirect (e.g., 

pH effects on heavy metals toxicity described above) 

TDS 500-2000 mg/L Below 500 mg/L, no detrimental effects are usually 

noticed. Between 500 and 1,000 mg/l, TDS in irrigation 

water can affect sensitive plants. At 1,000 to 2,000 

mg/L, TDS levels can affect many crops and careful 

management practices should be followed. Above 

2,000 mg/L, water can be used regularly only for 

tolerant plants on permeable soils

Free Chlorine 

Residual

< 1 mg/L

Source: "Handbook of Wastewater Reclamation & Reuse" by Donald R. Rowe and Isam 

Mohamed Abdel Magid, July 1995"
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6.3 Incidental Site Runoff 

Incidental runoff refers to small amounts of runoff from intended reclaimed water use areas, 

over-spray from sprinklers drifting out of the intended use area, and overflow of reclaimed water 

ponds (see Section 8). Runoff generally does not include water that percolates into the ground 

although a minimal amount could be considered incidental runoff.

Class A reclaimed water is permitted for unrestricted public contact uses and buffers are not 

required or always available. Although reclaimed water applied for irrigation is intended to 

remain on the irrigated areas, incidental runoff or over-spray of minor amounts of reclaimed 

water cannot always be completely prevented. Similarly, it is not possible to entirely prevent the 

runoff of rainwater from areas irrigated with Class A reclaimed water particularly during major 

storm events. 

Although Washington state law no longer regards reclaimed water as wastewater, any amount of 

incidental runoff to waters of the United States could be interpreted to require an NPDES permit. 

This is undesirable since incidental runoff would be of small volumes and individual wastewater 

discharge permits for incidental runoff would be difficult to administer. Customers would not be 

willing to use reclaimed water given the cost and the potential liability associated with either 

securing an individual NPDES permit or ensuring that no incidental runoff will ever leave the 

permitted area. Reclaimed water quality has already been regulated by Ecology and DOH under 

the reclaimed water permit. Once reclaimed, Class A water should be subject to the same 

requirements as other nonpotable water supplies. 

6.3.1 Interpreting Water Quality Laws for Incidental Runoff

Water quality laws should be interpreted consistent with the intent of the Legislature to promote 

reclaimed water use. Consequently, incidental runoff from reclaimed water projects should be 

handled as follows: 

1. Where reclamation requirements prohibit the discharge of waste to waters of the US and 

discharges are not expected to occur, occasional runoff should not trigger the need for 

either an individual NPDES permit or enforcement action.

2. If discharges from reclamation project area occur routinely, such discharges would 

usually be regulated under a municipal storm water NPDES permit. What if they are not 

a Phase 1 or 2 city?

3. An individual NPDES permit should be issued only if necessary to achieve water quality 

objectives. 
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6.3.2 Incidental Runoff Associated with Reclaimed Water Irrigation 

Reclaimed water use facilities should be designed and operated to avoid runoff to waters of 

the State. Nonetheless, incidental runoff is likely to occur at many facilities. The following 

permit language is recommended:

The incidental discharge of reclaimed water to waters of the State is not a violation of 

these requirements if the incidental discharge does not unreasonably affect the 

beneficial uses of the water, and does not result in exceeding an applicable water 

quality objective in the receiving water.

6.4 Incidental Percolation and Ground Water Monitoring

Many irrigation projects use reclaimed water at or below agronomic rates and do not require 

additional ground water monitoring. The reclaimed water is considered suitable for the 

beneficial use when it complies with the treatment and water quality requirements before 

distribution. Ecology promotes water use efficiency through both conservation practices and 

water reuse. A small amount of deep percolation from an efficient and well maintained spray 

irrigation system should not penalized by requiring more monitoring than would be required for 

other water supplies.

Deep percolation of excess irrigation water to the groundwater table from some irrigation 

practices (such as rill or flood irrigation) can be significant. When the beneficial use is 

irrigation, the potential impact of excess percolation to ground water quality should be evaluated.

When reclaimed water irrigation projects are proposed that may adversely impact groundwater, 

the permit writer should consult with the Water Reuse Workgroup and agency hydrogeologists 

regarding permit conditions for ground water protection. Best management practices, additional 

treatment and monitoring requirements should be included in the permit when needed for 

groundwater quality protection. Since these requirements may impact the feasibility of the 

project, the requirements to protect ground water should be established early in the project and 

included in the approved facility plan or engineering report. 

When establishing permit conditions, the permit writer should consider existing irrigation 

practices, the crop, site features and hydrogeology as well as the reclaimed water quality (Class 

A, B, C or D), the amount of reclaimed water used, and the percentage of reclaimed water in the 

total irrigation water supply. Groundwater monitoring programs, if required, may be as simple 

as a series of surficial wells or as complex as an arrangement of wells sampling at various 

depths.

Refer to Section 10, Groundwater Recharge by Surface Percolation for additional assistance with 

ground water monitoring requirements.
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7. IMPOUNDMENTS

This section describes the parameters the permit writer should consider in permitting irrigation 

use.

7.1. Class of Reclaimed Water Required for Use.

Table 7.1 lists the minimum class of reclaimed water that may be used for the various types of 

impoundment use. For uses not listed, consult the Water Reuse Workgroup.

Table 7.1 Class of Reclaimed Water Required for Impoundment Use

Class of Reclaimed 

Water Required

Use A B C D

Impoundments

Landscape Impoundments YES YES YES NO

Restricted Recreational Impoundments YES YES NO NO

Nonrestricted Recreational Impoundments YES NO NO NO

Fish Hatchery Basins YES YES NO NO

Decorative Fountains YES NO NO NO

7.2 Relationship to Stormwater Ponds

Incidental precipitation falling directly on impoundments or water features storing reclaimed 

water is considered reclaimed water. Stormwater ponds, (designed specifically for the diversion, 

retention or treatment of storm water) are not included under Ch 90.46 RCW. Stormwater must 

meet the applicable storm water quality requirements and (if put to beneficial use) obtain 

appropriative water rights. 

7.3 Incidental Runoff from Impoundments

It is not possible to entirely prevent the runoff of rainwater from decorative or storage ponds 

filled with Class A reclaimed water, particularly during major storm events. 

Although Washington state law no longer regards reclaimed water as wastewater, any amount of 

incidental runoff to waters of the United States could be interpreted to require an NPDES permit. 

This is undesirable for several reasons. Incidental runoff would be of small volumes and 

individual customer permits would be difficult to administer. Customers would not be willing to 

use reclaimed water given the cost and the potential liability associated with either securing an 
9CHAPTER XI. RECLAIMED WATER USE (JULY 2011)

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individual NPDES permit or ensuring that no incidental runoff will ever leave the permitted area. 

Reclaimed water quality has already been regulated by Ecology and DOH under the reclaimed 

water permit. Once reclaimed, Class A water should be subject to essentially the same 

requirements as other nonpotable water supplies. 

Water quality laws should be interpreted consistent with the intent of the Legislature to promote 

reclaimed water use. Consequently, incidental runoff from reclaimed water projects should be 

handled as follows: 

1. Where reclamation requirements prohibit the discharge of waste to waters of the US and 

discharges are not expected to occur, occasional runoff should not trigger the need for either 

an individual NPDES permit or enforcement action.

2. If discharges from reclamation project area occur routinely, such discharges would usually be 

regulated under a municipal storm water NPDES permit. 

3. An individual NPDES permit should be issued only if necessary to achieve water quality 

objectives. 

7.4 Releases from Reclaimed Water Ponds

A principal water quality concern with reclaimed water ponds is the presence of locally added 

pollutants, such as fertilizers and algaecides. These same issues exist with potable water ponds.

Reclaimed water ponds should be designed and operated not to spill during dry months. Spills 

should be prohibited during these times. Generally, wet weather regulatory strategies that do not 

require individual NPDES permits fall within the following categories. 

1. The reclaimed water pond is designed not to spill during wet months. Under this 

circumstance, spills that occur under extreme weather conditions or emergencies should 

not be considered for enforcement.

2. Reclaimed water ponds can be drained and refilled with potable water or flushed with 

potable water prior to the onset of the wet season. Flushing will not displace all of the 

reclaimed water but the water quality threat is minimal.

Reclaimed water ponds designed to spill reclaimed water during the wet season must be 

regulated under an NPDES permit.
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8. COMMERCIAL AND INDUSTRIAL USES

This section describes the parameters the permit writer should consider in permitting commercial 

and industrial uses of reclaimed water. (Under development)

8.1. Class of Reclaimed Water Required for Use.

Table 8.1 lists the minimum class of reclaimed water that may be used for the most common 

commercial and industrial uses. For uses not listed, consult the DOH and the Water Reuse 

Workgroup.

Table 8.1

Class of Reclaimed Water Required for Commercial and Industrial Uses

Class of Reclaimed 

Water Required

Use A B C D

Commercial

Flushing of Sanitary Sewers YES YES YES YES

Street Sweeping, Brush Dampening YES YES YES NO

Street Washing, Spray YES NO NO NO

Washing of Corporation Yards, Lots, and Sidewalks YES YES NO NO

Dust Control (Dampening Unpaved Roads and Other Surfaces) YES YES YES NO

Dampening of Soil for Compaction (at Construction Sites, Landfills, 

etc.)

YES YES YES NO

Water Jetting for Consolidation of Backfill around Pipelines YES YES YES NO

Fire Fighting and Protection -Dumping from Aircraft YES YES YES NO

Fire Hydrants or Sprinkler Systems in Buildings YES NO NO NO

Toilet and Urinal Flushing

YES NO NO NO

Ship Ballast

YES YES YES NO

Washing Aggregate and Making Concrete YES YES YES NO

Industrial

Boiler Feed

YES YES YES NO

Cooling – No Creation of Aerosols or Other Mist YES YES YES NO

Cooling Aerosols or Other Mist Created (e.g., Use in Cooling Towers, 

Forced Air Evaporation, or Spraying) YES NO NO NO

Process Water - Without Exposure of Workers YES YES YES NO

Process Water - With Exposure of Workers YES NO NO NO
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9. GROUND WATER RECHARGE BY SURFACE 

PERCOLATION

Reclaimed water (a new water supply) is permitted differently from wastewater effluent disposal 

to ground. The intent of ground water recharge is planned replenishment of the ground water 

either for an in situ value (salt water intrusion barrier, base flows for instream flows, maintain 

geologic structure), for recovery for beneficial uses, or as mitigation for other water withdrawals. 

Ch 90.46 RCW states that reclaimed water use is consistent with the anti-degradation 

requirements in Ecology’s ground water quality regulations, Ch 173-200 WAC. Reclaimed 

water use (by definition) is beneficial use in the public interest and some water quality 

degradation may be allowed. However, the Permittee must demonstrate that the use of reclaimed 

water is in the public interest. This documentation must be included in sufficient detail within 

general sewer plans and facility plans. RCW 90.46.120 also requires documentation in water 

supply plans when the uses will augment or replace potable supplies or create potential for 

development of additional potable supplies. 

Reclaimed water used for groundwater recharge by surface percolation must meet all of the 

following requirements:

• Class A reclaimed water requirements including source control, reliability, emergency 

storage, and water quality. (See Section 4 of this chapter).

• Reduction of total nitrogen in the biological oxidation process.

• State drinking water quality standards in the ground water beneath the recharge site. This 

is usually interpreted to mean in the ground water mound directly beneath the recharge 

site.

• Any additional quality limits established for other contaminants required by Ecology. 

These may be limits either in the reclaimed water or in the ground water. 
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9.1 Water Quality Limitations

Table 9.1 Reclaimed Water Limitations for Ground Water Recharge By 

Surface Percolation

Parameter Average Monthlya

Flow MGD (Point of Compliance)

Oxidized Wastewater – Secondary Effluent c

Parameter Average Monthlya Average Weekly b

BOD5 20 mg/L 30 mg/L

TSS 30 mg/L 45 mg/L

Dissolved 

Oxygen

Shall be measurably present in secondary effluent at all times

Coagulated/ Filtered Wastewater – Prior to Disinfection 

Turbidity Average Monthlya

2 NTU

Sample Maximum d

5 NTU

Disinfected - Reclaimed Water

Total Nitrogen 

as N

Average Monthlya 

10 mg/L 

Sample Maximum d 

15 mg/L 

Total Coliform 7-day Mediane

2.2 MPN/ 100 ml 

Sample Maximum f

 23 MPN/100 ml

pH Shall be between 6 and 9 standard units at all times 

Distribution Line

Chlorine 

Residual

Minimum Daily

0.5 mg/L

Point of compliance g

a The average monthly effluent limitation is defined as the highest allowable 

average of daily discharges over a calendar month, calculated as the sum of all 

daily discharges measured during a calendar month divided by the number of daily 

discharges measured during that month.
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Table 9.1 Reclaimed Water Limitations for Ground Water Recharge By 

Surface Percolation

b The average weekly effluent limitation is defined as the highest allowable 

average of daily discharges over a calendar week, calculated as the sum of all daily 

discharges measured during a calendar week divided by the number of daily

discharges measured during that week.

c The sampling point for BOD and TSS will be the secondary effluent.

d The sample maximum is defined as the value not to be exceeded by any single 

sample. 

e The median number of total coliform organisms in the reclaimed water after 

disinfection does not exceed 2.2 per 100 milliliters, as determined from the 

bacteriological results of the last 7 days for which analyses have been completed. 

f The number of total coliform organisms shall not exceed 23 per 100 milliliters in 

any single sample.

g

A chlorine residual of at least 0.5 mg/L shall be maintained in the reclaimed water 

during conveyance to the use area, or to the storage pond if reclaimed water is not 

directly piped to the use area.

9.2 Ground Water Recharge Criteria

Reclaimed water permits are issued under the authority of both Chapter 90.46 RCW and Chapter 

90.48 RCW. RCW 90.46.080 requires reclaimed water to meet state drinking water contaminant 

criteria which are defined as the state drinking water standards. The state drinking water 

standards are established by the state Board of Health and are listed in Table 9.2 below. These 

ground water recharge criteria are generally consistent with Ecology’s ground water standards 

(chapter 173-200 WAC) as drinking water is often, but not always, the most stringent 

requirement. 

Permit writers are also required to apply the broad mandate to protect and preserve the quality of 

state waters under chapter 90.48 RCW when writing a permit. The provisions of chapter 173-

200 WAC, Water Quality Standards for Groundwaters of the State of Washington must be 

considered on a case by case basis when issuing any reclaimed water permit for groundwater 

recharge. The possible risk to people and to aquatic life can only be partially addressed by 

drinking water standards. Drinking water standards lack criteria for many chemicals and their 

degradation or -breakdown- products. In addition, criteria were developed for individual 

chemicals and do not take into account exposure to mixtures or seasonal high pulses in 

concentrations. Some ground waters also support environmental systems requiring more 

stringent protection than that provided by the board of health criteria. If a more stringent 

standard is considered necessary for a contaminant listed under the state board of health criteria, 

the permit writer must be able to specifically justify and defend the basis for that requirement. 
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For contaminants not included in the state drinking water standards, the law (RCW 90.46.180(2)) 

allows Ecology to establish discharge limits, when justified. These may be in the reclaimed 

water or in the ground water mound. Not all contaminants listed in of the ground water 

standards must be listed in every permit. The permit writer should make a reasonable potential 

determination as to whether or not the parameters are likely to be present in the reclaimed water 

before requiring additional monitoring.

RCW 90.46.080(3) also authorizes Ecology and DOH to jointly authorize a lower ground water 

quality standard. Procedures for authorizing less stringent standards should be generally 

consistent with the overriding public interest processes Ecology uses in justifying exceptions to 

the ground water criteria in WAC 173-200-050(3)(a)(ix). The permit writer should consider 

aquifer vulnerability, the reclaimed water source water characteristics, proposed uses of the 

water and previous water quality information in establishing these requirements. Information on 

potential sources and health impacts in found at the EPA Ground and Drinking Water website.

Table 9.2 Ground Water Recharge Criteria (Drinking Water Standards)

MCL = maximum contaminant level (DOH enforceable standard for human health protection).

Secondary contaminant – may impact the quality and suitability of the water for certain uses 

but is not considered a human health concern for drinking water. (Not a DOH enforceable 

standard).

Contaminant Criterion 

(MCL)

Notes Comparison to Ecology 

WAC

(173-200-040)

Inorganic Chemicals:

Nitrate (as N) 10 mg/L same 

Nitrite (as N) 1 mg/L same 

Antimony (Sb) 6 μg/L not listed 

Arsenic (As) 10 μg/L 10μg/L effective January 23, 2006. 0.050 μg/L

Asbestos 7 * * million fibers/L not listed

Barium (Ba) 2 mg/L 1 mg/L

Beryllium (Be) 4 μg/L not listed 

Cadmium (Cd) 5 μg/L 10 μg/L

Chromium (Cr) 100 μg/L 50 μg/L

Copper (Cu) * * *No MCL - known health 

significance. EPA action level is 

1.3 mg/L

1 mg/L

Cyanide (HCN) 200 μg/L not listed

Fluoride (F) 4 mg/L Also listed as secondary contaminant 

at 2.0 mg/L 

4 mg/L

Lead (Pb) * * *No MCL - known health 

significance. EPA action level is 

50 μg/L
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0.015 mg/L.

Mercury (Hg) 2 μg/L same

Nickel (Ni) 100 μg/L not listed

Selenium (Se) 50 μg/L 10 μg/L

Sodium (Na) * * *No MCL - known health 

significance. EPA action level is 

20 mg/L.

not listed

Thallium (Tl) 2 μg/L not listed

Chloride 250 mg/L Secondary contaminant 250 mg/L

Iron (Fe) 2 mg/L Secondary contaminant 300 μg/L

Manganese(Mn) 50 μg/L Secondary contaminant 50 μg/L

Silver (Ag) 100 μg/L Secondary contaminant. 50 μg/L

Sulfate (SO4) 250 mg/L Secondary contaminant 250 mg/L

Zinc 5 mg/L Secondary contaminant same

Physical Characteristics:

Color 15 Color 

units

Secondary contaminant. same

Total Dissolved 

Solids

500 mg/L Secondary contaminant same

Specific 

Conductivity

700 μmhos/

cm

Secondary contaminant Not listed

Disinfection Bi-products:

Total 

Trihalomethanes 

(TTHM) = the 

sum of the mass 

concentrations of 

chloroform(CHCl3), 

BDCM(CHCl2Br) 

DBCM(CHClBr2)

bromoform(CHBr3).

80 μg/L BDCM (bromodichloromethane) 

DBCM (dibromochloromethane) 

Carcinogenic 

THM levels tend to increase with pH, 

temperature, time, and the level of 

organic matter present. 

individually listed (μg/L):

CHCl3 - 7.0 

BDCM – 0.3

DBCM – 0.5

Bromoform – 5 

Haloacetic acids 

(HAA5) are: 

monochloroacetic 

dichloroacetic 

trichloroacetic 

monobromoacetic 

dibromoacetic 

60 μg/L At high enough concentrations, they 

are poisonous to plants, and some are 

suspected carcinogens.

not listed

Bromate 10 μg/L Only systems using ozone not listed

Chlorite 1.0 mg/L Only systems using chlorine dioxide not listed

Disinfectant Residuals:

Free Chlorine 4.0 mg/L not listed

Chloramines 4.0 mg/L not listed

Chlorine dioxide 0.8 mg/L not listed
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Radionuclides:

Radium 226/228 5 pCi/L May increase cancer risk over long 

exposure

226 - 3 pCi/L

226/228 – 5

Gross Alpha 

Particle Activity

15 pCi/L May increase cancer risk over long 

exposure. Does not include radon or 

uranium

same

Beta Particle 

and Photons

4 mrem Calculated on 2 liter water intake/day 

– average annual dose

Tritium(Total body) -- 20,000 pCi/L

Strontium-90(Bone marrow) --8 pCi/L

May increase cancer risk over long 

exposure.

same

Uranium 30 μg/L May produce toxic effects to the 

kidney. May increase cancer risk over 

long exposure.

none

Organic Chemicals

TT = treatment technique required for contaminant removal.

MGLG = maximum contaminant level goal – level below know or expected health risk.(not DOH 

enforceable)

Acrylamide TT MCLG = zero 0.02 μg/L

Alachlor 2 μg/L MCLG = zero not listed

Atrazine 3 μg/L not listed

Benzene 5 μg/L MCLG = zero 1 μg/L

Benzidine 0.0004 μg/L

Benzo(a)pyrene 

(PAHs)

0.2 μg/L MCLG = zero 0.008 μg/L

BCDM See disinfection byproducts

Bromoform See disinfection byproducts

Carbofuran 40 μg/L

Carbon 

tetrachloride

5 μg/L MCLG=zero 0.3 μg/L

Chlordane 2 μg/L MCLG=zero

CDBM = DBCM- See disinfection byproducts

Chloroform See disinfection byproducts

4 Chloro-2-

methyl aniline

0.1 μg/L

4 Chloro-2-

methyl aniline 

hydrochloride

0.2 μg/L

o-Chloronitrobenzene

3 μg/L 

p-Chloronitrobenzene

5 μg/L

Chlorthalonil 30 μg/L

2,4 D 70 μg/L 0.1 μg/L
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Dalapon 200 μg/L

DBCP 0.2 μg/L DCBP = 1,2 dibromo-3-chloropropane

MCLG = zero

odichlorobenzene

600 μg/L

pdichlorobenzene

75 μg/L

1,2-

dichloroethane

5 μg/L Ethelene chloride 0.5 μg/L

1,1-

dichloroethylene

7 μg/L

Cis and trans 1,2 

dichloroethylene

7 μg/L

Dichloromethane 5 μg/L MCLG = zero

1,2 

dicholopropane

5 μg/L MCLG = zero 0.6 μg/L

Di(2-ethylhexyl) 

adipate

400 μg/L

Di(2-ethylhexyl) 

phthalate

6 μg/L MCLG = zero

Dinoseb 7 μg/L

Dioxin (2,3,7,8-

TCDD)

* μg/L * 0.00003 μg/L 0.0000006 μg/L

Diquat 20 μg/L

Endothall 100 μg/L

Endrin 2 μg/L

Epichlorohydrin TT μg/L TT =

MCLG = zero

8 μg/L

Ethylbenzene 700 μg/L

Ethylene 

dibromide

0.05 μg/L MCLG = zero 0.001 μg/L

Glyphosate 700 μg/L

Heptachlor 0.4 μg/L MCLG = zero 0.02 μg/L

Heptachlor 

epoxide

0.2 μg/L MCLG = zero 0.009 μg/L

Hexachloroenzene 1 μg/L MCLG = zero 0.05 μg/L

Hexachlorocyclopentadiene

50 μg/L

Lindane 0.2 μg/L 0.06 μg/L

Methoxychlor 40 μg/L

Oxamyl (Vydate) 200 μg/L

PCBs

(polychlorinated 

biphenyls)

0.5 μg/L MCLG = zero 0.01 μg/L

Pentachlorophenol 1 μg/L

Picloram 500 μg/L
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Simazine 4 μg/L

Styrene 100 μg/L

Tetrachloroethylene

5 μg/L MCGL = zero 0.8 μg/L

Toluene 1 mg/L

Toxaphene 3 μg/L MCLG = zero 0.08 μg/L

2,4,5-TP (Silvex) 50 μg/L

1,2,4-

Trichlorobenezene

70 μg/L

1,1,1-

Trichloroethane

3 μg/L

Trichloroethylene 5 μg/L MCLG = zero 3 μg/L

Vinyl chloride 2 μg/L MCLG = zero 0.02 μg/L

Xylenes(total) 10 mg/L

9.3 Additional Contaminants of Concern

Ecology may add additional parameters of concern (not listed in the ground water recharge 

criteria above) if there is reason to believe that they are present in the reclaimed water at levels 

that would not adequately protect the beneficial uses of the water.

Table 9.3 lists Parameters from Ecology Ground Water Standards (WAC 173-200-140). These 

are not included in the Ground Water Recharge Criteria. 

Table 9.3 Other Parameters of Concern (WAC 173-200-140)

Physical Characteristics

Parameter Criterion Notes

Corrosivity Noncorrosive 

(narrative) 

EPA secondary drinking water contaminant.

Foaming Agents 0.5 mg/L EPA secondary drinking water contaminant.

Odor 3 threshold odor units EPA secondary drinking water contaminant.

pH 6.5- 8.5 standard 

units. EPA secondary contaminant.

Organic Chemicals-Carcinogens

Contaminant Criterion (μg/L) Notes (under development)

Aldine 0.005 

Aniline 14 

Azobenzene 0.7 

Benzidine 0.0004 

Benzotrichloride 0.007 

Benzyl chloride 0.5 

Bis(chloroethyl)-ether 0.07 

Bis(Chloro-methyl)ether 0.0004

Carbazole 5 
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4 Chloro-2-methyl aniline 0.1 

4 Chloro-2-methyl aniline 

hydrochloride

0.2 

o-Chloro-nitrobenzene 3 

p-Chloro-nitrobenzene 5 

Chlorthalonil 30 

Diallate 1 

DDT (includes DDE and DDD) 0.3

1,2 Dibromoethane 0.001

3,3' Dichlorobenzidine 0.2

1,1 Dichloroethane 1.0

1,3 Dichloropropene 0.2

Dichlorvos 0.3

Dieldrin 0.005

3,3' Dimethoxybenzidine 6

3,3 Dimethylbenzidine 0.007

1,2 Dimethylhydrazine 60

2,4 Dinitrotoluene 0.1

2,6 Dinitrotoluene 0.1

1,4 Dioxane 7.0

1,2 Diphenylhydrazine 0.09

Direct Black 38 0.009

Direct Blue 6 0.009

Direct Brown 95 0.009

Epichlorohydrin 8

Ethyl acrylate 2

Ethylene thiourea 2

Folpet 20

Furazolidone 0.02

Furium 0.002

Furmecyclox 3

Hexachlorocyclohexane (alpha) 0.001

Hexachlorocyclohexane

 (technical) 0.05

Hexachlorodibenzo-p-dioxin, 

mix 0.00001

Hydrazine/Hydrazine sulfate 0.03

2 Methoxy-5-nitroaniline 2

2 Methylaniline 0.2

2 Methylaniline hydrochloride 0.5

4,4' Methylene bis(N,N'-

dimethyl) aniline 2

Methylene chloride

 (dichloromethane) 5

Mirex 0.05

Nitrofurazone 0.06
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N-Nitrosodiethanolamine 0.03

N-Nitrosodiethylamine 0.0005

N-Nitrosodimethylamine 0.002

N-Nitrosodiphenylamine 17

N-Nitroso-di-n-propylamine 0.01

N-Nitrosopyrrolidine 0.04

N-Nitroso-di-n-butylamine 0.02

N-Nitroso-N-methylethylamine 0.004

PAH 0.01

PBBs 0.01

o-Phenylenediamine 0.005

Propylene oxide 0.01

Tetrachloroethylene

 (perchloroethylene) 0.8

P,a,a,a -Tetrachlorotoluene 0.004

2,4 Toluenediamine 0.002

o-Toluidine 0.2

Trichloroethylene 3

2,4,6-Trichlorophenol 4

Trimethyl phosphate 2

9.4 Ground Water Monitoring

Frequency of monitoring should take into account the size of the facility and the impact to 

ground water.

Table 9.4 Suggested Ground Water Monitoring for Recharge by Surface Percolation

Parameter Units Minimum Sampling 

Frequency

Sample Type

Static well water 

elevation

Feet above sea 

level

Quarterly(1) Measurement

Temperature °C Quarterly(1) Measurement

Dissolved Oxygen mg/L Quarterly(1) Grab

pH Standard Units Quarterly(1) Measurement

Conductivity umhos/cm Quarterly(1) Grab

Nitrate NO3 (as N) mg/L Quarterly(1) Grab

Nitrite NO2 (as N) mg/L Quarterly(1) Grab

TKN (as N) mg/L Quarterly(1) Grab

Total Dissolved Solids mg/L Quarterly(1) Grab

Total Coliform 

Bacteria

cfu/100 ml Quarterly(1) Grab

Chloride mg/L Quarterly(1) Grab

Cations/Anions: 

Calcium, Magnesium, 

mg/L Yearly(2) Grab
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Table 9.4 Suggested Ground Water Monitoring for Recharge by Surface Percolation

Parameter Units Minimum Sampling 

Frequency

Sample Type

Potassium, Sodium, 

Bicarbonate, 

Carbonate, Fluoride, 

sulfate

Total Metals: 

Arsenic, Cadmium, 

Chromium, Copper, 

Lead, Mercury, 

Nickel, Silver, Zinc(3)

μg/L Yearly(2) Grab

Total Trihalomethanes 

(TTHM)

mg/L Quarterly(1) Grab

(1)Quarterly is defined as every three months.

(2)Yearly is defined as once within twelve consecutive months. 

(3)Analytical method: Arsenic, EPA 206.3 or 206.2; Cadmium, EPA 2007.7 or 213.2; Chromium, 

EPA 200.7 or 218.2; Copper, EPA 200.7 or 220.2; Lead, EPA 239.2; Mercury, EPA 245.1 or 

245.2; Nickel, EPA 249.2; Silver, EPA 272.2; Zinc, EPA 200.7 or 289.1.

Permittees may prefer to monitor contaminants in the reclaimed water in lieu of ground water 

monitoring. For any parameters monitored in the reclaimed water prior to recharge, the permit 

writer should consider deleting duplicative ground water monitoring requirements. This option 

should be based on site specific conditions - considering the potential for the recharge project to 

adversely impact the quality of the ground water. In some cases, recharging aquifers may 

improve water quality. In others, large volumes of recharge water may cause chemical changes 

directly or indirectly degrading the ground water quality. Ground water monitoring should 

continue in cases where there is concern that the recharge may result in ground water quality 

trends toward higher contaminant concentrations impacting the suitability of the water for 

beneficial use. 

9.5 Blended Flows for Groundwater Recharge

It is more straightforward when stormwater and reclaimed water are not deliberately mixed 

either temporally or sequentially into the same infiltration basin. A stormwater infiltration basin 

should be used only for stormwater. A reclaimed water surface percolation basin should be used 

only for reclaimed water. Historically, the laws governing state water, stormwater, wastewater, 

on-site systems, reclaimed water, conservation and potable and non-potable supply have 

developed independently. Existing laws do not provide equivalent levels of health protection, 

environmental resource protection, and water management. 

i. Existing requirements for treatment and infiltration of stormwater are not 

sufficiently protective for planned recharge of a potable aquifer. Stormwater 

runoff contains many contaminants (oil, particulates, pesticides, pathogens). The 
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quality is not reliable or predictable. 

ii. Reclaimed water recharge is voluntary for specified beneficial use of the water. 

Stormwater management practices are meant to reduce contamination and runoff 

from human activities.

iii. The generator of the reclaimed water has an exclusive right to the water. 

Stormwater is state water - when stormwater is put to a beneficial use, a water 

right is required. 

Exceptions:

Despite the complications, there are cases where it may be desirable to blend stormwater with 

reclaimed water for ground water recharge. 

i. The commingled stormwater and wastewater may be jointly treated to meet the 

more stringent reclaimed water recharge requirements prior to infiltration. It is not 

sufficient to treat the stormwater to stormwater BMP requirements and the 

reclaimed water to reclaimed water requirements.

ii. A combined infiltration system could potentially recharge a designated non-potable 

groundwater with the stormwater treated to stormwater requirements and reclaimed 

water to water reclamation requirements. There must be no chance of potable water 

supply contamination. Examples: A salt water intrusion barrier, a fully contained 

non-potable ASR project, recharge flowing directly to surface waters or wetlands 

through hydraulic continuity. Under state law, only the reclaimed water would 

have an exclusive right attached. If the stormwater is recovered for beneficial use, 

it would require an appropriative water right. 

iii. A combined infiltration system could also be considered where adequate 

stormwater source control (essentially uncontaminated stormwater) or treatment 

assures water quality control. This would be coupled with sufficient soils and travel 

time for natural attenuation and degradation of pollutants through soil-aquifer 

treatment (SAT) for potable water quality protection. Again, only the reclaimed 

water could be recovered under the exclusive right provisions of Ch 90.46 RCW. 

iv. The reclaimed water is not meant for beneficial use and is disposed to ground under 

a waste discharge permit regulating both the wastewater effluent and the storm 

water. The combined discharge must meet Ecology ground water standards and 

wastewater permit requirements.
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CHAPTER XII. ALTERNATIVES AND ADDITIONS 

TO NUMERICAL EFFLUENT LIMITS

There are alternative mechanisms to numerical effluent limits which can be used in permits to 

regulate the discharge of pollutants. These alternative mechanisms are authorized by federal and 

state law for use in both NPDES and state permits. These mechanisms include general 

conditions, special conditions and best management practices.

1. GENERAL CONDITIONS

The general conditions, standard conditions, or boilerplate of a permit are those permit 

conditions that are based on federal or state law or regulation. They delineate the legal, 

administrative, and procedural requirements of the permit. In many cases they are direct quotes 

of the regulations. Most of the federal regulations for the General Conditions are found in 40 

CFR 122.41 and 122.42. In the Washington State permit format most of the General Conditions 

are placed in the back of a permit which is customary. Because Ecology uses standardized 

permit wording some of the direct regulatory requirements have been placed in S1 and S2. The 

General Conditions are the same for every type of NPDES permit and are not to be changed by 

permit writers. The General Conditions and changes to those conditions are reviewed and 

approved by the AAG. If a General Condition is not applicable to a particular discharger, they 

are free to disregard that condition. The General Conditions for state discharge permits are based 

on state law and regulation. The importance of the General Conditions should not be 

underestimated just because they are standardized. The general conditions are very stringent 

permit conditions. 

1.1 The General Conditions for NPDES Permits

The following text is the wording found in individual NPDES permits. Some of these conditions 

are required by regulation. They were placed in the main body of the permit for consistency. 

Permit writers should not alter this text in the permit templates.

S1. DISCHARGE LIMITS 

A. Process Wastewater Discharges

All discharges and activities authorized by this permit must be consistent with the terms 

and conditions of this permit.

The discharge of any of the following pollutants more frequently than, or at a level in 

excess of that identified and authorized by this permit violates the terms and conditions 

of this permit.
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Beginning on the effective date of this permit and lasting through the expiration date, 

the Permittee is authorized to discharge specify allowed waste stream at the permitted 

location subject to complying with the following limits:

S2. MONITORING REQUIREMENTS

B. Sampling and Analytical Procedures

Samples and measurements taken to meet the requirements of this permit must represent 

the volume and nature of the monitored parameters, including representative sampling 

of any unusual discharge or discharge condition, including bypasses, upsets, and 

maintenance-related conditions affecting effluent quality.

Sampling and analytical methods used to meet the monitoring requirements specified in 

this permit must conform to the latest revision of the Guidelines Establishing Test 

Procedures for the Analysis of Pollutants contained in 40 CFR Part 136.

S3. REPORTING AND RECORDKEEPING REQUIREMENTS

The Permittee must monitor and report in accordance with the following conditions. The 

falsification of information submitted to Ecology is a violation of the terms and 

conditions of this permit.

A. Reporting

The first monitoring period begins on the effective date of the permit. The Permittee 

must:

1. Submit monitoring results each month. 

2. Summarize, report, and submit monitoring data obtained during each 

monitoring period on a Discharge Monitoring Report (DMR) form provided, 

or otherwise approved, by Ecology. 

3. Submit DMR forms monthly whether or not the facility was discharging. If 

the facility did not discharge during a given monitoring period, submit the 

form as required with the words "NO DISCHARGE" entered in place of the 

monitoring results.

4. Ensure that DMR forms are postmarked or received by Ecology no later than 

the 15th day of the month following the completed monitoring period, unless 

otherwise specified in this permit. 

5. Submit priority pollutant analysis data no later than forty-five (45) days 

following the monitoring.

6. Send report(s) to Ecology at:

Water Quality Permit Coordinator

Department of Ecology

PO Box 47696

Olympia, WA 98504-7696

 
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All laboratory reports providing data for organic and metal parameters must include the 

following information: sampling date, sample location, date of analysis, parameter 

name, CAS number, analytical method/ number, method detection limit (MDL) or 

laboratory quantitation limit (QL or ML), reporting units, and concentration detected. 

Analytical results from samples sent to a contract laboratory must have information on 

the chain of custody, the analytical method, QA/QC results, and documentation of 

accreditation for the parameter.

B. Records Retention

The Permittee must retain records of all monitoring information for a minimum of 

three (3) years. Such information must include all calibration and maintenance 

records and all original recordings for continuous monitoring instrumentation, 

copies of all reports required by this permit, and records of all data used to 

complete the application for this permit. The Permittee must extend this period of 

retention during the course of any unresolved litigation regarding the discharge of 

pollutants by the Permittee or when requested by Ecology. 

C. Recording of Results

For each measurement or sample taken, the Permittee must record the following 

information:

1. The date, exact place, method, and time of sampling or measurement.

2. The individual who performed the sampling or measurement.

3. The dates the analyses were performed.

4. The individual who performed the analyses.

5. The analytical techniques or methods used. 

6. The results of all analyses. 

D. Additional Monitoring by the Permittee

If the Permittee monitors any pollutant more frequently than required by Condition S2 

of this permit, then the Permittee must include the results of such monitoring in the 

calculation and reporting of the data submitted in the Permittee's DMR.

E. Reporting Permit Violations

The Permittee must take the following actions when it violates or is unable to comply with 

any permit condition: 

a. Immediately take action to stop, contain, and cleanup unauthorized discharges or

otherwise stop the noncompliance and correct the problem.

b. If applicable, immediately repeat sampling and analysis. Submit the results of any 

repeat sampling to Ecology within thirty (30) days of sampling.

1. Immediate Reporting

The Permittee must report any failure of the disinfection system immediately to the 

Department of Ecology's Regional Office 24-hr. number listed below:
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For discharges to marine waters:

The Permittee must report any failure of the disinfection system, any collection 

system overflows which may reach surface waters or any plant bypass discharging 

to a shellfish area immediately to the Department of Ecology and the Department of 

Health, Shellfish Program at the numbers listed below:

For discharges to fresh water 

The Permittee must report any failure of the disinfection system, any collection 

system overflows, or any plant bypass discharging to a water body used as a source 

of drinking water immediately to the Department of Ecology and the Department of 

Health, Drinking Water Program at the numbers listed below:

Department of Health, 

Drinking Water Program

360-521-0323 (business hours) 

360-481-4901 (after business hours)

2. Twenty-four-hour Reporting

The Permittee must report the following occurrences of noncompliance by 

telephone, to Ecology at _____ within 24 hours from the time the Permittee 

becomes aware of any of the following circumstances: 

a. Any noncompliance that may endanger health or the environment, unless 

previously reported under subpart 1, above.

b. Any unanticipated bypass that exceeds any effluent limitation in the permit 

(See Part S4.B., “Bypass Procedures”).

c. Any upset that exceeds any effluent limitation in the permit (See G.15, 

“Upset”).

d. Any violation of a maximum daily or instantaneous maximum discharge 

limitation for any of the pollutants in Section S1.A of this permit.

e. Any overflow prior to the treatment works, whether or not such overflow 

endangers health or the environment or exceeds any effluent limitation in the 

permit. 

3. Report within Five Days

The Permittee must also provide a written submission within five days of the time 

that the Permittee becomes aware of any event required to be reported under 

subparts 1 or 2, above. The written submission must contain: 

a. A description of the noncompliance and its cause. 
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b. The period of noncompliance, including exact dates and times.

c. The estimated time noncompliance is expected to continue if it has not been 

corrected.

d. Steps taken or planned to reduce, eliminate, and prevent recurrence of the 

noncompliance.

e. If the noncompliance involves an overflow prior to the treatment works, an 

estimate of the quantity (in gallons) of untreated overflow.

4. Waiver of Written Reports

Ecology may waive the written report required in subpart 3, above, on a case-bycase basis upon request if a timely oral report has been received.

5. All Other Permit Violation Reporting

The Permittee must report all permit violations, which do not require immediate or 

within 24 hours reporting, when it submits monitoring reports for S3.A 

("Reporting"). The reports must contain the information listed in paragraph E.3, 

above. Compliance with these requirements does not relieve the Permittee from 

responsibility to maintain continuous compliance with the terms and conditions of 

this permit or the resulting liability for failure to comply.

6. Report Submittal

The Permittee must submit reports to the address listed in S3.

F. Other Reporting

The Permittee must report a spill of oil or hazardous materials in accordance with the 

requirements of RCW 90.56.280 and chapter 173-303-145. You can obtain further 

instructions at the following website: 

http://www.ecy.wa.gov/programs/spills/other/reportaspill.htm .

Where the Permittee becomes aware that it failed to submit any relevant facts in a 

permit application, or submitted incorrect information in a permit application, or in any 

report to Ecology, it must submit such facts or information promptly.

The Permittee must submit a new application or supplement at least one hundred eighty 

(180) days prior to commencement of discharges, resulting from the activities listed 

below, which may result in permit violations. These activities include: any facility 

expansions, production increases, or other planned changes, such as process 

modifications, in the permitted facility. 
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The Permittee must keep a copy of this permit at the facility and make it available upon 

request to Ecology inspectors.

S4 (INDUSTRIAL, S5 MUNICIPAL). OPERATION AND MAINTENANCE

The Permittee must, at all times, properly operate and maintain all facilities or systems of 

treatment and control (and related appurtenances) which are installed to achieve compliance 

with the terms and conditions of this permit. Proper operation and maintenance includes 

adequate laboratory controls and appropriate quality assurance procedures. This provision 

requires the operation of back-up or auxiliary facilities or similar systems, which are 

installed by a Permittee only when the operation is necessary to achieve compliance with the 

conditions of this permit.

B. Bypass Procedures

This permit prohibits a bypass which is the intentional diversion of waste streams from 

any portion of a treatment facility. Ecology may take enforcement action against a 

Permittee for a bypass unless one of the following circumstances (1, 2, or 3) applies.

1. Bypass for Essential Maintenance without the Potential to Cause Violation of 

Permit Limits or Conditions.

Bypass is authorized if it is for essential maintenance and does not have the 

potential to cause violations of limits or other conditions of this permit, or adversely 

impact public health as determined by Ecology prior to the bypass. The Permittee 

must submit prior notice, if possible, at least ten (10) days before the date of the 

bypass.

2. Bypass which is Unavoidable, Unanticipated, and Results in Noncompliance of this 

Permit.

This bypass is permitted only if:

a. Bypass is unavoidable to prevent loss of life, personal injury, or severe property 

damage. “Severe property damage” means substantial physical damage to 

property, damage to the treatment facilities which would cause them to become 

inoperable, or substantial and permanent loss of natural resources which can 

reasonably be expected to occur in the absence of a bypass.

b. No feasible alternatives to the bypass exist, such as:

• The use of auxiliary treatment facilities. 

• Retention of untreated wastes.

• Stopping production. 

• Maintenance during normal periods of equipment downtime, but not if the 

Permittee should have installed adequate backup equipment in the exercise 

of reasonable engineering judgment to prevent a bypass. 
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• Transport of untreated wastes to another treatment facility or preventative 

maintenance), or transport of untreated wastes to another treatment 

facility.

c. Ecology is properly notified of the bypass as required in condition S3E of this 

permit.

3. If bypass is anticipated and has the potential to result in noncompliance of this 

permit.

a. The Permittee must notify Ecology at least thirty (30) days before the planned 

date of bypass. The notice must contain: 

• A description of the bypass and its cause. 

• An analysis of all known alternatives which would eliminate, reduce, or 

mitigate the need for bypassing. 

• A cost-effectiveness analysis of alternatives including comparative 

resource damage assessment. 

• The minimum and maximum duration of bypass under each alternative.

• A recommendation as to the preferred alternative for conducting the 

bypass. 

• The projected date of bypass initiation. 

• A statement of compliance with SEPA. 

• A request for modification of water quality standards as provided for in 

WAC 173-201A-410, if an exceedance of any water quality standard is 

anticipated. 

• Details of the steps taken or planned to reduce, eliminate, and prevent 

reoccurrence of the bypass.

b. For probable construction bypasses, the Permittee must notify Ecology of the

need to bypass as early in the planning process as possible. The Permittee must 

consider the analysis required above during preparation of the engineering 

report or facilities plan and plans and specifications and must include these to 

the extent practical. In cases where the Permittee determines the probable need 

to bypass early, the Permittee must continue to analyze conditions up to and 

including the construction period in an effort to minimize or eliminate the 

bypass.

c. Ecology will consider the following prior to issuing an administrative order for 

this type of bypass:

• If the bypass is necessary to perform construction or maintenance-related 

activities essential to meet the requirements of this permit.

• If feasible alternatives to bypass exist, such as the use of auxiliary 

treatment facilities, retention of untreated wastes, stopping production, 
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maintenance during normal periods of equipment down time, or transport 

of untreated wastes to another treatment facility.

• If the Permittee planned and scheduled the bypass to minimize adverse 

effects on the public and the environment.

After consideration of the above and the adverse effects of the proposed bypass and 

any other relevant factors, Ecology will approve or deny the request. Ecology will 

give the public an opportunity to comment on bypass incidents of significant 

duration, to the extent feasible. Ecology will approve a request to bypass by issuing 

an administrative order under RCW 90.48.120. 

C. Duty to Mitigate

The Permittee is required to take all reasonable steps to minimize or prevent any 

discharge or sludge use or disposal in violation of this permit that has a reasonable 

likelihood of adversely affecting human health or the environment.

S4.D. Notification of New or Altered Sources (POTW only)

The Permittee shall submit written notice to the Department whenever any new discharge or a 

substantial change in volume or character of an existing discharge into the POTW is proposed 

which: (1) would interfere with the operation of, or exceed the design capacity of, any portion of 

the POTW; (2) is not part of an approved general sewer plan or approved plans and 

specifications; or (3) would be subject to pretreatment standards under 40 CFR Part 403 and 

Section 307(b) of the Clean Water Act. This notice shall include an evaluation of the POTW's 

ability to adequately transport and treat the added flow and/or wasteload, the quality and volume 

of effluent to be discharged to the POTW, and the anticipated impact on the Permittee’s 

effluent.(40 CFR 122.42(b)). 

The following are general conditions for NPDES individual permits. These are taken directly 

from federal or state regulation. The text may have been changed slightly to improve clarity.

G1. SIGNATORY REQUIREMENTS

A. All applications, reports, or information submitted to Ecology must be signed and 

certified.

(a) In the case of corporations, by a responsible corporate officer.

For the purpose of this section, a responsible corporate officer means: (i) A 

president, secretary, treasurer, or vice-president of the corporation in charge of a 

principal business function, or any other person who performs similar policy- or 

decision making functions for the corporation, or (ii) the manager of one or more 

manufacturing, production, or operating facilities, provided, the manager is 

authorized to make management decisions which govern the operation of the 

regulated facility including having the explicit or implicit duty of making major 

capital investment recommendations, and initiating and directing other 

comprehensive measures to assure long term environmental compliance with 

environmental laws and regulations; the manager can ensure that the necessary 
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systems are established or actions taken to gather complete and accurate information 

for permit application requirements; and where authority to sign documents has been 

assigned or delegated to the manager in accordance with corporate procedures. 

(b) In the case of a partnership, by a general partner.

(c) In the case of sole proprietorship, by the proprietor.

(d) In the case of a municipal, state, or other public facility, by either a principal 

executive officer or ranking elected official.

Applications for permits for domestic wastewater facilities that are either owned or operated 

by, or under contract to, a public entity shall be submitted by the public entity

.

B. All reports required by this permit and other information requested by Ecology must be 

signed by a person described above or by a duly authorized representative of that 

person. A person is a duly authorized representative only if:

1. The authorization is made in writing by a person described above and 

submitted to Ecology.

2. The authorization specifies either an individual or a position having 

responsibility for the overall operation of the regulated facility, such as the 

position of plant manager, superintendent, position of equivalent 

responsibility, or an individual or position having overall responsibility for 

environmental matters. (A duly authorized representative may thus be 

either a named individual or any individual occupying a named position.)

C. Changes to authorization. If an authorization under paragraph B.2 above is no longer 

accurate because a different individual or position has responsibility for the overall 

operation of the facility, a new authorization satisfying the requirements of paragraph

B.2 above must be submitted to Ecology prior to or together with any reports, 

information, or applications to be signed by an authorized representative.

D. Certification. Any person signing a document under this section must make the 

following certification:

I certify under penalty of law, that this document and all 

attachments were prepared under my direction or supervision in 

accordance with a system designed to assure that qualified 

personnel properly gathered and evaluated the information 

submitted. Based on my inquiry of the person or persons who 

manage the system, or those persons directly responsible for 

gathering information, the information submitted is, to the best of 

my knowledge and belief, true, accurate, and complete. I am 

aware that there are significant penalties for submitting false 

information, including the possibility of fine and imprisonment for 

knowing violations.
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G2. RIGHT OF INSPECTION AND ENTRY

The Permittee must allow an authorized representative of Ecology, upon the presentation 

of credentials and such other documents as may be required by law:

A. To enter upon the premises where a discharge is located or where any records must be 

kept under the terms and conditions of this permit.

B. To have access to and copy - at reasonable times and at reasonable cost - any records 

required to be kept under the terms and conditions of this permit.

C. To inspect - at reasonable times - any facilities, equipment (including monitoring and

control equipment), practices, methods, or operations regulated or required under this 

permit.

D. To sample or monitor - at reasonable times - any substances or parameters at any 

location for purposes of assuring permit compliance or as otherwise authorized by the 

Clean Water Act.

G3. PERMIT ACTIONS 

Note: This section derived from 40 CFR 124.5, RCW 90.48.190, 195 and 173-220-150.

This permit may be modified, revoked and reissued, or terminated either at the request of 

any interested person (including the permittee) or upon Ecology’s initiative. However, 

the permit may only be modified, revoked and reissued, or terminated for the reasons 

specified in 40 CFR 122.62, 122.64 or WAC 173-220-150 according to the procedures of 

40 CFR 124.5. 

A. The following are causes for terminating this permit during its term, or for denying a 

permit renewal application:

1. Violation of any permit term or condition.

2. Obtaining a permit by misrepresentation or failure to disclose all relevant facts.

3. A material change in quantity or type of waste disposal.

4. A determination that the permitted activity endangers human health or the 

environment or contributes to water quality standards violations and can only be 

regulated to acceptable levels by permit modification or termination [40 CFR part 

122.64(3)].

5. A change in any condition that requires either a temporary or permanent reduction or 

elimination of any discharge or sludge use or disposal practice controlled by the 

permit [40 CFR part 122.64(4)].

6. Nonpayment of fees assessed pursuant to RCW 90.48.465.

7. Failure or refusal of the permittee to allow entry as required in RCW 90.48.090.
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B. The following are causes for modification but not revocation and reissuance except 

when the permittee requests or agrees:

1. A material change in the condition of the waters of the state.

2. New information not available at the time of permit issuance that would have 

justified the application of different permit conditions.

3. Material and substantial alterations or additions to the permitted facility or activities 

which occurred after this permit issuance.

4. Promulgation of new or amended standards or regulations having a direct bearing 

upon permit conditions, or requiring permit revision.

5. The Permittee has requested a modification based on other rationale meeting the 

criteria of 40 CFR Part 122.62.

6. Ecology has determined that good cause exists for modification of a compliance 

schedule, and the modification will not violate statutory deadlines.

7. Incorporation of an approved local pretreatment program into a municipality’s 

permit.

C. The following are causes for modification or alternatively revocation and reissuance:

1. Cause exists for termination for reasons listed in A1 through A7, of this section, and 

Ecology determines that modification or revocation and reissuance is appropriate.

2. Ecology has received notification of a proposed transfer of the permit. A permit 

may also be modified to reflect a transfer after the effective date of an automatic 

transfer (General Condition G8) but will not be revoked and reissued after the 

effective date of the transfer except upon the request of the new permittee.

G4. REPORTING PLANNED CHANGES

The Permittee must, as soon as possible, but no later than sixty (60) days prior to the 

proposed changes, give notice to Ecology of planned physical alterations or additions to 

the permitted facility, production increases, or process modification which will result in: 

1) the permitted facility being determined to be a new source pursuant to 40 CFR 

122.29(b); 2) a significant change in the nature or an increase in quantity of pollutants 

discharged; or 3) a significant change in the Permittee’s sludge use or disposal practices. 

Following such notice, and the submittal of a new application or supplement to the 

existing application, along with required engineering plans and reports, this permit may 

be modified, or revoked and reissued pursuant to 40 CFR 122.62(a) to specify and limit 

any pollutants not previously limited. Until such modification is effective, any new or 

increased discharge in excess of permit limits or not specifically authorized by this permit 

constitutes a violation.
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G5. PLAN REVIEW REQUIRED

Note: The following is derived from RCW 90.48.110 and WAC 173-240-110(1) 

Prior to constructing or modifying any wastewater control facilities, an engineering report 

and detailed plans and specifications must be submitted to Ecology for approval in 

accordance with Chapter 173-240 WAC. Engineering reports, plans, and specifications 

must be submitted at least one hundred eighty (180) days prior to the planned start of 

construction unless a shorter time is approved by Ecology. Facilities must be constructed 

and operated in accordance with the approved plans.

G6. COMPLIANCE WITH OTHER LAWS AND STATUTES

Nothing in this permit must be construed as excusing the Permittee from compliance with 

any applicable federal, state, or local statutes, ordinances, or regulations.

G7. TRANSFER OF THIS PERMIT

In the event of any change in control or ownership of facilities from which the authorized 

discharge emanate, the Permittee must notify the succeeding owner or controller of the 

existence of this permit by letter, a copy of which must be forwarded to Ecology.

A. Transfers by Modification

Except as provided in paragraph B below, this permit may be transferred by the 

Permittee to a new owner or operator only if this permit has been modified or revoked 

and reissued under 40 CFR 122.62(b)(2), or a minor modification made under 40 CFR 

122.63(d), to identify the new Permittee and incorporate such other requirements as 

may be necessary under the Clean Water Act.

B. Automatic Transfers

This permit may be automatically transferred to a new Permittee if:

1. The Permittee notifies Ecology at least 30 days in advance of the proposed transfer 

date.

2. The notice includes a written agreement between the existing and new Permittee’s 

containing a specific date transfer of permit responsibility, coverage, and liability 

between them.

3. Ecology does not notify the existing Permittee and the proposed new Permittee of 

its intent to modify or revoke and reissue this permit. A modification under the 

subparagraph may also be minor modification under 40 CFR 122.63. If this notice 

is not received, the transfer is effective on the date specified in the written 

agreement.

G8. REDUCED PRODUCTION FOR COMPLIANCE

The Permittee, in order to maintain compliance with its permit, must control production 

and/or all discharges upon reduction, loss, failure, or bypass of the treatment facility until 
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the facility is restored or an alternative method of treatment is provided. This 

requirement applies in the situation where, among other things, the primary source of 

power of the treatment facility is reduced, lost, or fails.

G9. REMOVED SUBSTANCES

Collected screenings, grit, solids, sludges, filter backwash, or other pollutants removed in 

the course of treatment or control of wastewaters must not be resuspended or 

reintroduced to the final effluent stream for discharge to state waters. 

G10. DUTY TO PROVIDE INFORMATION

The Permittee must submit to Ecology, within a reasonable time, all information which 

Ecology may request to determine whether cause exists for modifying, revoking and 

reissuing, or terminating this permit or to determine compliance with this permit. The 

Permittee must also submit to Ecology upon request, copies of records required to be kept 

by this permit.

G11. OTHER REQUIREMENTS OF 40 CFR

All other requirements of 40 CFR 122.41 and 122.42 are incorporated in this permit by 

reference.

G12. ADDITIONAL MONITORING

Ecology may establish specific monitoring requirements in addition to those contained in 

this permit by administrative order or permit modification.

G13. PAYMENT OF FEES

The Permittee must submit payment of fees associated with this permit as assessed by 

Ecology.

G14. PENALTIES FOR VIOLATING PERMIT CONDITIONS

Any person who is found guilty of willfully violating the terms and conditions of this 

permit is deemed guilty of a crime, and upon conviction thereof will be punished by a 

fine of up to ten thousand dollars ($10,000) and costs of prosecution, or by imprisonment 

in the discretion of the court. Each day upon which a willful violation occurs is a 

separate and additional violation. 

Any person who violates the terms and conditions of a waste discharge permit must 

incur, in addition to any other penalty as provided by law, a civil penalty in the amount of 

up to ten thousand dollars ($10,000) for every such violation. Each and every such 

violation is a separate and distinct offense, and in case of a continuing violation, every 

day's continuance is deemed to be a separate and distinct violation.

G15. UPSET

Definition – “Upset” means an exceptional incident in which there is unintentional and 

temporary noncompliance with technology-based permit effluent limits because of 
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factors beyond the reasonable control of the Permittee. An upset does not include 

noncompliance to the extent caused by operational error, improperly designed treatment 

facilities, inadequate treatment facilities, lack of preventive maintenance, or careless or 

improper operation.

An upset constitutes an affirmative defense to an action brought for noncompliance with 

such technology-based permit effluent limits if the requirements of the following 

paragraph are met.

A Permittee who wishes to establish the affirmative defense of upset must demonstrate, 

through properly signed, contemporaneous operating logs or other relevant evidence that: 

1) an upset occurred and that the Permittee can identify the cause(s) of the upset; 2) the 

permitted facility was being properly operated at the time of the upset; 3) the Permittee 

submitted notice of the upset as required in condition S3.E; and 4) the Permittee 

complied with any remedial measures required under S4.C of this permit.

In any enforcement proceedings the Permittee seeking to establish the occurrence of an 

upset has the burden of proof.

G16. PROPERTY RIGHTS

This permit does not convey any property rights of any sort, or any exclusive privilege.

G17. DUTY TO COMPLY

The Permittee must comply with all conditions of this permit. Any permit 

noncompliance constitutes a violation of the Clean Water Act and is grounds for 

enforcement action; for permit termination, revocation and reissuance, or modification; or 

denial of a permit renewal application.

G18. TOXIC POLLUTANTS

The Permittee must comply with effluent standards or prohibitions established under 

Section 307(a) of the Clean Water Act for toxic pollutants within the time provided in the 

regulations that establish those standards or prohibitions, even if this permit has not yet 

been modified to incorporate the requirement.

G19. PENALTIES FOR TAMPERING

The Clean Water Act provides that any person who falsifies, tampers with, or knowingly 

renders inaccurate any monitoring device or method required to be maintained under this 

permit will, upon conviction, be punished by a fine of not more than $10,000 per 

violation, or by imprisonment for not more than two years per violation, or by both. If a 

conviction of a person is for a violation committed after a first conviction of such person 

under this Condition, punishment will be a fine of not more than $20,000 per day of 

violation, or by imprisonment of not more than four (4) years, or by both.

G20. REPORTING REQUIREMENTS APPLICABLE TO EXISTING 
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MANUFACTURING, COMMERCIAL, MINING, AND SILVICULTURAL 

DISCHARGERS (Industrial only)

The Permittee belonging to the categories of existing manufacturing, commercial, 

mining, or silviculture must notify Ecology as soon as they know or have reason to 

believe:

A. That any activity has occurred or will occur which would result in the discharge, on a 

routine or frequent basis, of any toxic pollutant which is not limited in this permit, if 

that discharge will exceed the highest of the following “notification levels:”

1. One hundred micrograms per liter (100 μg/L).

2. Two hundred micrograms per liter (200 μg/L) for acrolein and acrylonitrile; five 

hundred micrograms per liter (500 μg/L) for 2,4-dinitrophenol and for 2-methyl4,6-dinitrophenol; and one milligram per liter (1 mg/L) for antimony.

3. Five (5) times the maximum concentration value reported for that pollutant in the 

permit application in accordance with 40 CFR 122.21(g)(7).

4. The level established by the Director in accordance with 40 CFR 122.44(f).

B. That any activity has occurred or will occur which would result in any discharge, on a 

non-routine or infrequent basis, of a toxic pollutant which is not limited in this permit, if 

that discharge will exceed the highest of the following “notification levels:”

1. Five hundred micrograms per liter (500μg/L).

2. One milligram per liter (1 mg/L) for antimony.

3. Ten (10) times the maximum concentration value reported for that pollutant in the 

permit application in accordance with 40 CFR 122.21(g)(7).

4. The level established by the Director in accordance with 40 CFR 122.44(f).

G21. COMPLIANCE SCHEDULES

Reports of compliance or noncompliance with, or any progress reports on, interim and 

final requirements contained in any compliance schedule of this permit must be submitted 

no later than fourteen (14) days following each schedule date.

G21. CONTRACT REVIEW (municipal only)

The Permittee must submit to Ecology any proposed contract for the operation of any 

wastewater treatment facility covered by this permit. The review is to ensure consistency 

with chapters 90.46 and 90.48 RCW. In the event that Ecology does not comment within a 

thirty (30)-day period, the Permittee may assume consistency and proceed with the contract.
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1.2 The General Conditions for State Permits

As with the NPDES permits some required conditions have been moved to other sections of the 

permit.

G1. SIGNATORY REQUIREMENTS

All applications, reports, or information submitted to Ecology must be signed as follows:

A. All permit applications must be signed by either a principal executive officer or 

ranking elected official.

B. All reports required by this permit and other information requested by Ecology 

must be signed by a person described above or by a duly authorized representative 

of that person. A person is a duly authorized representative only if:

1. The authorization is made in writing by the person described above and is 

submitted to Ecology at the time of authorization, and

2. The authorization specifies either a named individual or any individual 

occupying a named position.

C. Changes to authorization. If an authorization under paragraph B.2. above is no

longer accurate because a different individual or position has responsibility for the 

overall operation of the facility, a new authorization must be submitted to 

Ecology prior to or together with any reports, information, or applications to be 

signed by an authorized representative.

D. Certification. Any person signing a document under this section must make the 

following certification:

"I certify under penalty of law, that this document and all attachments were 

prepared under my direction or supervision in accordance with a system designed 

to assure that qualified personnel properly gathered and evaluated the information 

submitted. Based on my inquiry of the person or persons who manage the system 

or those persons directly responsible for gathering information, the information 

submitted is, to the best of my knowledge and belief, true, accurate, and complete. 

I am aware that there are significant penalties for submitting false information, 

including the possibility of fine and imprisonment for knowing violations."

G2. RIGHT OF ENTRY

Note: Right of Entry derived from RCW 90.48.090. Also see

WAC 173-216-110(3), and WAC 173-220-150(1)(e).

Representatives of Ecology must have the right to enter at all reasonable times in or upon 
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any property, public or private for the purpose of inspecting and investigating conditions 

relating to the pollution or the possible pollution of any waters of the state. Reasonable 

times includes normal business hours; hours during which production, treatment, or 

discharge occurs; or times when Ecology suspects a violation requiring immediate 

inspection. Representatives of Ecology must be allowed to have access to, and copy at 

reasonable cost, any records required to be kept under terms and conditions of the permit; 

to inspect any monitoring equipment or method required in the permit; and to sample the 

discharge, waste treatment processes, or internal waste streams.

G3. PERMIT ACTIONS

Note: This section derived from RCW 90.48.190, 195 and 173-216-130.

This permit is subject to modification, suspension, or termination, in whole or in part by 

Ecology for any of the following causes:

A. Violation of any permit term or condition;

B. Obtaining a permit by misrepresentation or failure to disclose all relevant facts;

C. A material change in quantity or type of waste disposal; 

D. A material change in the condition of the waters of the state; or,

E. Nonpayment of fees assessed pursuant to RCW 90.48.465.

Ecology may also modify this permit, including the schedule of compliance or other 

conditions, if it determines good and valid cause exists, including promulgation or 

revisions of regulations or new information.

G4. REPORTING A CAUSE FOR MODIFICATION

Note: The following section derived from WAC 173-216-110(5) and -040(1)

The Permittee must submit a new application at least 60 days before it wants to discharge 

more of any pollutant, a new pollutant, or more flow than allowed under this permit. 

The Permittee should use the State Waste Discharge Permit application, and submit 

required plans at the same time. Required plans include an Engineering Report, Plans 

and Specifications, and an Operations and Maintenance manual, (see Chapter 173-240 

WAC). Ecology may waive these plan requirements for small changes, so contact 

Ecology if they do not appear necessary. The Permittee must obtain the written 

concurrence of the receiving POTW on the application before submitting it to Ecology. 

The Permittee must continue to comply with the existing permit until it is modified or 

reissued. Submitting a notice of dangerous waste discharge (to comply with Pretreatment 

or Dangerous Waste rules) triggers this requirement as well.

G5. PLAN REVIEW REQUIRED

Note: The following is derived from RCW 90.48.110 and WAC 173-240-110(1) and 

WAC 173-216-040(2). 
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Prior to constructing or modifying any wastewater control facilities, an engineering report 

and detailed plans and specifications must be submitted to Ecology for approval in 

accordance with Chapter 173-240 WAC. Engineering reports, plans, and specifications

should be submitted at least 180 days prior to the planned start of construction. Facilities 

must be constructed and operated in accordance with the approved plans.

G6. COMPLIANCE WITH OTHER LAWS AND STATUTES

Nothing in the permit must be construed as excusing the Permittee from compliance with 

any applicable federal, state, or local statutes, ordinances, or regulations.

G7. TRANSFER OF THIS PERMIT

Note: This section derived from WAC 173-216-120.

This permit is automatically transferred to a new owner or operator if:

A. A written agreement between the old and new owner or operator containing a specific 

date for transfer of permit responsibility, coverage, and liability is submitted to 

Ecology; 

B. A copy of the permit is provided to the new owner and;

C. Ecology does not notify the Permittee of the need to modify the permit.

Unless this permit is automatically transferred according to section A. above, this permit 

may be transferred only if it is modified to identify the new Permittee and to incorporate

such other requirements as determined necessary by Ecology.

G8. PAYMENT OF FEES

The Permittee must submit payment of fees associated with this permit as assessed by 

Ecology. Ecology may revoke this permit if the permit fees established under Chapter 

173-224 WAC are not paid.

G9. PENALTIES FOR VIOLATING PERMIT CONDITIONS

Any person who is found guilty of willfully violating the terms and conditions of this 

permit is guilty of a crime, and upon conviction thereof will be punished by a fine of up 

to ten thousand dollars and costs of prosecution, or by imprisonment in the discretion of 

the court. Each day upon which a willful violation occurs may be deemed a separate and 

additional violation. 

Any person who violates the terms and conditions of a waste discharge permit incurs, in 

addition to any other penalty as provided by law, a civil penalty in the amount of up to 

ten thousand dollars for every such violation. Each and every such violation is a separate 

and distinct offense, and in case of a continuing violation, every day’s continuance is a 

separate and distinct violation.

G10. DUTY TO PROVIDE INFORMATION

The Permittee must submit to Ecology, within a reasonable time, all information which 
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Ecology may request to determine whether cause exists for modifying, revoking and 

reissuing, or terminating this permit or to determine compliance with this permit. The 

Permittee must also submit to Ecology upon request, copies of records required to be kept 

by this permit. 

G11. DUTY TO COMPLY

The Permittee must comply with all conditions of this permit. Any permit 

noncompliance constitutes a violation of the Clean Water Act and is grounds for 

enforcement action; for permit termination, revocation and reissuance, or modification; or 

denial of a permit renewal application.

2. SPECIAL CONDITIONS

Special conditions are requirements placed in permits without limits. They may be similar to 

Best Management Practices (discussed in the next part) but are generally smaller in scope and 

may lead to permit limits. Special conditions are enforceable.

Since special conditions are specific to individual permits, it's difficult to define them in general 

terms. Some examples of special conditions follow.

1. An old complex industrial facility was found on one occasion to be leaking process 

wastewater under the building which then flowed to a small stream. The plumbing at the 

facility was old and in need of repair. In one instance at this facility, process wastewater was 

plumbed to a line carrying and discharging non-contact cooling water. This error occurred 

because the maintenance people were unsure of which pipes were carrying wastewater. 

These problems occurred near permit renewal time. The permit writer wrote a special 

condition in the new permit that required the facility to upgrade the piping in some areas, to 

produce a pipe routing diagram, and to conduct a weekly inspection for leaky wastewater 

plumbing to prevent any further discharges.

2. A sawmill discharged yard runoff and non-contact cooling water which went to a ditch and 

then to a small stream. There was no receiving water data on the temperature or flow for the 

stream. The permit writer placed a special condition in the permit which required a 

temperature study in the receiving water during the summer low flow to determine if the 

discharge was violating water quality standards. The special condition included language to 

alert the permittee that the new information could be used as a basis to modify the permit and 

place temperature limits in it if necessary to meet water quality standards. (See also Chapter 

XIII - Receiving Environment Monitoring)
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3. POLLUTION PREVENTION AND BEST 

MANAGEMENT PRACTICES (BMPs)

This section describes Ecology's process of pollution prevention within the Water Quality 

Program and how to incorporate best management practices into permits.

3.1 Pollution Prevention

Pollution prevention is a priority for the agency and the Water Quality Program. It is inherent in 

the goals of the Clean Water Act (zero discharge) and was one of the five goals in the strategic 

plan the Water Quality Program adopted in 1992.

Pollution prevention has been defined by Ecology as source control of pollutants.

The implementation of pollution prevention into the permit program is based on the premise that 

pollution prevention makes both environmental and economic sense. People will choose to make 

their products or provide their services in less polluting ways if they know they have a choice 

and it appears economical. Permits can be used to nudge people to look at viable alternatives, to 

provide incentives for prevention over treatment or to provide a legally binding framework for a 

project of interest to both the department and the permittee. Permits should not be used to 

mandate expensive studies of impractical alternatives or to mandate zero discharge where it is 

not required and it is not cost effective. The permit should be used as a tool to drive practical 

economical preventative approaches.

Implementation measures include:

Zero Discharge - Permit managers should require permittees to consider and investigate options 

for zero discharge in engineering reports where that option appears viable.

Reduced Monitoring - Reward exemplary performance, especially as a result of source control 

efforts, by reducing monitoring requirements (see Chapter XIII, Section 1.3.2).

Cross Media Shift of Pollutants - Coordinate your actions at facilities with other Ecology and 

local government actions to prevent cross media shifts of pollutants when feasible.

When developing technology-based effluent limits on a case-by-case basis or when developing 

water quality-based limits, the permit manager should identify those situations where there is a 

significant shift of pollutants to some other media such as air or land. These situations should be 

discussed and documented with the appropriate Ecology media programs to look for a mutual 

solution.
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Watershed Scoping - Include a pollution prevention section in watershed scoping documents 

and in watershed workshops with Shorelands and Water Resources look for source reduction and 

water conservation opportunities.

3.2 Best Management Practices

NPDES permits have traditionally focused on chemical-specific numerical effluent limits. To 

improve water quality, the Act provides for water pollution controls, such as Best Management 

Practices, to supplement effluent limitations guidelines. Pursuant to RCW 90.48 and sections 

304 and 402 of the Act, BMPs may be incorporated as permit conditions. In the context of the 

NPDES program, BMPs are actions or procedures to prevent or minimize the potential for the 

release of pollutants or hazardous substances in significant amounts to surface waters. BMPs, 

although normally qualitative, are most effective when used in conjunction with numerical 

effluent limits in NPDES permits. 

Section 402(a)(1) of the Act allows the Administrator to prescribe conditions in a permit 

determined necessary to carry out the provisions of the Act, such as BMPs. The discharges to be 

controlled by BMPs are plant site runoff, spillage or leaks, sludge or waste disposal, and 

drainage from raw material storage.

BMPS are intended to complement other regulatory requirements imposed by RCRA, OSHA, the 

Clean Air Act, and SPCC plans for hazardous substances. Pursuant to section 311 of the Act, 

EPA has promulgated (40 CFR Part 151) requirements that SPCC plans prevent discharges of 

hazardous substances from facilities subject to NPDES permitting requirements. The guidelines 

proposed for hazardous substances SPCC plans are very similar to those required for oil SPCC 

plans in the Oil Pollution Prevention Regulations (40 CFR Part 112). The NPDES BMP 

regulation has also been structured to be similar to the highly successful oil SPCC regulation. 

Even though the State of Washington has no statutory authority to enforce federal SPCC plan 

requirements, the NPDES permitting program and state law (RCW 90.48.010 and RCW 

90.48.520) allow state permit writers to address appropriate spill prevention requirements as 

permit conditions.

EPA has promulgated the BMP regulation as 40 CFR Subpart K (44 FR 32954-5). Industries 

regulated by Subpart K must develop a BMP program and submit it with their permit application.

3.3 Scope of BMPs

Any activity which is associated with the industrial manufacturing or treatment process is subject 

to BMPs. The federal BMP program is only concerned with toxic or hazardous chemical 

discharges. The State of Washington's BMP program is broader and covers the discharge or 

potential discharge of any substance which would affect water quality. All activities or sources 

at the plant should be examined to determine if there is a reasonable potential for equipment 
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failure (e.g., spillage or leakage), natural conditions (e.g., plant site runoff or drainage from raw 

material storage), or other circumstances (e.g., sludge or waste disposal) which could result in 

the discharge of a significant amount of pollutants or hazardous substances to receiving waters. 

For the State of Washington, receiving waters include both surface waters and ground water. 

These activities or sources usually include: material storage areas, loading and unloading areas; 

plant site runoff; in-plant transfer, process, and material handling areas; and sludge disposal 

areas.

Material storage areas include storage areas for toxic and hazardous chemicals which may be raw 

materials, intermediates, final products or by-products. Included are liquid storage vessels that 

range in size from large tanks to 55-gallon drums; dry storage in bags, piles, bins, silos, and 

boxes; and gas storage in tanks and vessels.

Loading and unloading operations involve the transfer of materials to and from trucks or railcars 

but not in-plant transfers. These operations include pumping of liquids or gases from truck or 

railcar to a storage facility or vice versa, pneumatic transfer of dry chemicals to or from the 

loading or unloading vehicle, transfer by mechanical conveyor systems, and transfer of bags, 

boxes, drums, or other containers from vehicles by forklift trucks or other materials handling 

equipment.

Plant runoff is generated principally from rainfall on a plant site. Runoff from material storage 

areas, in-plant transfer areas, loading and unloading areas, and sludge disposal sites potentially 

could become contaminated with toxic pollutants and hazardous substances. Heavy metals from 

sludge (disposal sites are of special concern). Fallout, resulting from the plant air emissions 

which settle on the plant site, may also contribute to contaminated runoff. Contaminated runoff 

may reach a receiving body of water through overland flow, drainage ditches, storm or 

noncontact cooling water sewers, or overflows from combined sewer systems. Contaminated 

runoff can enter ground water by infiltrating through the soil or through recharge zones in 

surface waters.

In-plant transfer areas, process areas, and material handling areas encompass all in-plant transfer 

operations from raw material to final product. Various operations could include transfer of 

liquids or gases by pipelines including devices such as pumps, valves and fittings; movement of 

bulk materials by mechanical conveyor belt systems; and forklift truck transport of bags, drums, 

and bins. All transfer operations within the process area with a potential for release of toxic 

pollutants and hazardous substances to other than the process wastewater system are addressed in 

this grouping.

Sludge and other waste handling areas are potential sources of contamination of receiving 

waters. These operations include landfills, pits, ponds, lagoons, and deep-well injection sites. 

Depending on the construction and operation of these sites there may be a potential for leachate 

containing toxic pollutants or hazardous substances to seep into the ground water, or for liquids 
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to overflow to surface waters from these disposal operations. BMP requirements are not 

intended to duplicate the requirements of RCRA. Actions taken for compliance with RCRA may 

be referenced in the BMP plan submitted with the permit application.

Any facility with an RCRA permit will already have plans addressing BMP requirements (e.g., 

contingency plans, personnel training plans, inspections and maintenance, security, reporting and 

records, compatibility testing, and housekeeping procedures). However, the RCRA requirements 

will usually be applied only to areas involved in the treatment, storage or disposal of hazardous 

waste. So these RCRA procedures may need to be expanded to meet BMP requirements.

3.4 Minimum Requirements for the BMP Plan

BMPs may include some of the same practices used by industry for pollution control, SPCC 

plans for oil and hazardous substances, safety programs, fire protection, protection against loss of 

valuable raw materials or products, insurance policy requirements or public relations. The

minimum requirements of a BMP Plan are listed in Table 1 and are divided into 2 categories: 

general requirements and specific requirements.

Table XI-1. MINIMUM REQUIREMENTS OF A BMP PLAN

A. General Requirements

1. Name and location of facility

Statement of BMP policy and objectives

Review by plant manager

B. Specific Requirements

1. BMP Committee

2. Risk Identification and Assessment

Structural Modifications

Reporting of BMP Incidents

Materials Compatibility

Good Housekeeping

Preventive Maintenance

Inspections and Records

Security

Employee Training

3.4.1 General Requirements

The BMP plan should be organized and described in an orderly narrative format. A description 

of the facility, including the plant name, the type of plant, processes used, and the products 
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manufactured should be included in the BMP plan. A map showing the location of the facility 

and the adjacent receiving waters also should be part of the plan. Any available data about site 

soils or ground water conditions should also be included. Specific objectives for the control of 

toxic pollutants and hazardous substances should be included in a statement of corporate policy. 

The plan should be reviewed by the plant manager.

3.4.2 Specific Requirements

Each of the 9 specific requirements listed in Table IV-1 should be addressed in the BMP plan. 

The size and complexity of the BMP plan will vary with the size, complexity, and location of the 

facility. It is anticipated that the length and detail of the BMP plan will be commensurate with 

the quantity of toxic and hazardous chemicals on site and their opportunity for discharge. The 

fundamental goal of the BMP plan is determining the potential for toxic and hazardous chemicals 

to reach receiving waters, and taking appropriate preventive measures.

3.4.3 BMP Committee

The BMP Committee is a group of individuals within the plant organization which is responsible 

for developing the BMP plan and assisting the plant management in its implementation, 

maintenance and updating. The scope of activities and responsibilities of the BMP Committee 

should include all aspects of the facility's BMP plan, such as identifying toxic and hazardous 

materials handled in the plant; identifying potential spill sources; establishing incident reporting 

procedures; developing BMP inspection and records procedures; reviewing environmental 

incidents to determine and implement necessary changes to the BMP plan; coordinating plant 

incident response cleanup and notifying authorities; establishing BMP training for plant 

personnel; and aiding interdepartmental coordination in carrying out the BMP plan. Other 

committee duties could include reviewing both new construction and changes in processes or 

procedures at the facility relative to spill prevention and control.

The plan should contain a clear statement of the management's policies and responsibilities 

related to BMPs. Authority and responsibility for immediate action in the event of a spill should 

be clearly established and documented in the BMP plan, with the Committee indirectly involved 

in that responsibility. The Committee should advise management on the technical aspects of 

environmental incident control, but should not impede the decision-making process for 

preventing or mitigating spills and incidents. Management should, of course, review and support 

the BMP plan.

The size and composition of the BMP Committee should be appropriate to the size and 

complexity of the plant, and to the specific toxic and hazardous chemicals handled at the plant. 

Facility personnel knowledgeable in spill control and waste treatment such as environmental 

specialists, production foreman, safety and health specialists, and any treatment plant supervisor 

should be included. In some small plants, the committee might consist of the one manager or 

engineer assigned responsibility for environmental control. For very small facilities, the 
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Committee function might even have to be fulfilled by competent engineers or managers from 

the corporate staff or the nearest large plant.

A list of personnel on the BMP Committee should be included in the BMP plan. The list should 

have the office and home telephone numbers of the Committee members, and the names and 

phone numbers of backup or alternate people.

3.4.4 Risk Identification and Assessment

The areas of the plant that are subject to BMP requirements should be identified by the BMP 

Committee. Each such area should be examined for the potential risks for discharges of toxic 

pollutants or hazardous substances to receiving waters. Any existing physical means (dikes, 

diversion ditches, etc.) of controlling such discharges also should be identified.

The areas described above should be clearly indicated on a plant plot plan or drawing. A 

simplified materials flowsheet showing major process operations can be used to indicate the 

direction and quantity of materials flowing from one area to another. Areas with the potential for 

ground water contamination via subsurface infiltration or surface water recharge after spills 

should be identified and indicated on site drawings. The direction of flow of potential spills and 

surface runoff should also be estimated based on site topography and indicated on the plant site 

drawings. Dry chemicals that are either toxic pollutants or hazardous substances should be 

evaluated if they have the potential to reach surface or ground waters in significant quantities via 

rainfall runoff, for example.

A hazardous substance and toxic chemical inventory (materials inventory) should be developed 

as part of the "Risk Identification and Assessment." The detail of the materials inventory should 

be proportionate to the quantity of toxic pollutants and hazardous substances on site and their 

potential for reaching the receiving waters (both surface and ground water). For example:

1. The plant has determined that materials stored in bulk quantities at a tank farm have a high 

potential for reaching the receiving waters via surface runoff or subsurface infiltration in the 

event of structural failure or overfills. Therefore, the materials inventory for the tank farm 

should be detailed, and should provide the identity, quantities, and locations of each material.

2. The plant has determined that materials stored in small quantities at the research laboratory 

have a low potential for reaching the receiving waters. Therefore, the materials inventory for the 

laboratory could be minimally detailed, and may not include the identity, quantity, or location of 

each material but might include an estimate of the total quantity of toxic and hazardous materials 

stored and would provide the location of the laboratory. The rationale for the "low risk" nature 

of the laboratory would be provided in this part of the BMP plan.
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3. The plant has determined that materials used in a batch operation in the manufacturing 

process have a high potential for reaching the receiving water. The plant supplies a variety of 

products through the batch operation process to accommodate fluctuations in public demand. 

Consequently, the materials used for the batch process vary from week to week, often times 

unexpectedly. Therefore, the materials inventory for the batch operation should be detailed but 

remain flexible. The inventory might include the identification of each material expected for 

use, the maximum quantity of material expected for use, and the maximum quantity of material 

that the batch process can handle. The materials inventory could be updated to include any 

material substitutions unanticipated at the time of the original inventory.

The examples above illustrate the flexibility of the materials inventory. A materials inventory 

should be part of the "Risk Identification and Assessment" of every BMP plan but the detail of 

the inventory will vary with the size and complexity of the plant, the quantities of toxic and 

hazardous chemicals on-site, and the potential for those materials to reach surface waters.

The materials inventory and other useful technical information should be made available to the 

BMP Committee but may require separate filing from the BMP plan documents to protect 

proprietary information or trade secrets. This data may include physical, chemical, toxicological 

and health information (e.g., technical bulletins or material safety data sheets) on the toxic 

pollutants and hazardous substances handled; the quantities involved in various operations; and 

the prevention, containment, mitigation, and cleanup techniques that would be used in the event 

of a discharge.

Materials planned for future use in the plant should be evaluated for their potential to be 

discharged in significant amounts to receiving waters. Where the potential is high, the same type 

of technical data described above should be obtained.

3.4.5 Structural Modifications

An important element of BMP implementation involves actual physical changes to the facility 

that prevent the potential release of a pollutant. These physical changes include overflow and 

overfill controls, secondary containment systems, ground water protection barriers, and 

emergency cut-offs. The purpose of these structural modifications to the facility is to confine 

potential pollutants to those portions of the facility where they belong by preventing spills, 

stopping spills that have started, or containing spills that have already happened. Because these 

structural modifications are physical changes, they do not need human intervention to work 

effectively. However, this does not mean that these devices are "fool proof" and do not need to 

be a part of other elements of BMP such as facility inspection programs, employee training or 

spill drills.

Overflow and overfill controls prevent spills in pipes, process vessels or storage tanks by 

stopping or rerouting flow when the unit is full or flow is blocked. The principle is the same as 

the pumps in gas stations which sense the level of gasoline in your car and shut-off when the 
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tank is full. These devices sense the fluid level or the line pressure and automatically stop or 

reroute flow before the point of spillage. Liquids can be rerouted back to their source, to another 

vessel such as a process or storage tank or to secondary containment.

Secondary containment is a facility's extra storage capacity that automatically receives a spill 

from a process or storage unit. This extra storage capacity can be provided by earthen dikes, 

concrete pads, walls or curbing, concrete sumps, or a tank connected down gradient of the 

potential spill source. Secondary containment holds a spill safely until facility personnel can 

recover or dispose of the spilled material. A secondary containment device must be capable of 

holding more than the volume of the largest spill possible at the facility (for example, capable of 

holding more than the volume of the largest tank in a tank farm or 40% of the total volume of all 

drums which can be stored in a drum storage area). The permit writer should realize that other 

environmental programs such as SPCC or RCRA will have specific requirements on the volumes 

of many secondary containment systems.

Ground water protection barriers are made of natural or artificial materials designed to stop spills 

from infiltrating through the soil to contaminate ground water. Natural materials used as ground 

water protection barriers are usually clays that are placed in a layer between the source of the 

spill and the soil overlaying the ground water. Artificial materials take the form of impermeable 

synthetic liners which are placed under the spill source. These ground water protection barriers 

can be used as back-up for secondary containment in the event of an overflow or a structural 

failure such as a crack in a concrete drum storage pad, or they can be used in combination with 

secondary containment such as lining the bottom of a diked area around a tank farm. These 

devices are also useful for lining containment basins for stormwater which could be 

contaminated or for areas such as loading docks which are subject to frequent small spillage. Of 

course, ground water protection barriers are routinely installed under surface impoundments, 

waste piles and landfills.

Emergency cutoffs include many of the overflow/overfill control devices, but also include other 

types of control. One such device is the emergency cutoff for an entire industrial process that 

occurs when the wastewater or air pollution control system fails. A related type of emergency 

cutoff shuts down an industrial operation when internal pressures, chemical reactions or ambient 

vapors threaten an explosion at a facility. Other emergency cutoff systems shut storm sewer 

systems when a monitor has detected gasoline vapors or when special organic absorbents swell 

and block a sewer in reaction to solvents. Emergency cutoffs can also be installed to stop the 

discharge from a failed pollution control device such as a wastewater plant or air pollution 

scrubber.

Any of these structural modifications made to physically prevent the release of pollutants from a 

facility must be included in all of the related BMP activities such as inspections, maintenance, 

personnel training, and spill drills. A disconnected or neglected device will not work in the event 

of a spill. If facility personnel do not know about the functioning of the device, they cannot 
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properly maintain or inspect it. Without training and spill drills which include the devices, 

personnel may misinterpret the cause of an emergency cutoff or may release material from 

secondary containment prematurely. Just because these structural devices operate automatically, 

does not mean that they can be left out of all other BMP elements. The BMP plan must describe 

these physical devices and outline their routine inspection and maintenance in addition to 

including them in personnel training and spill drills.

3.4.6 Reporting of BMP Incidents

A BMP incident reporting system is used to keep records of incidents such as spills, leaks, runoff 

and other improper discharges. The system minimizes recurrence, expedites containment or 

cleanup activities, and complies with legal requirements. Reporting procedures defined by the 

BMP Committee should include these 3 elements upon discharge: 

1. Immediately notify appropriate plant personnel so they can initiate prompt action.

2. Write formal reports for management to review. Management should evaluate the BMP 

incident and consider revising the BMP plan accordingly. 

3. (By law) Notify governmental and environmental agencies if a spill or other discharge reaches 

surface water or ground water. 

The reporting system should designate the means for reporting incidents to responsible company 

and government officials. The names, office telephone numbers, and home telephone numbers 

of key employees ranked in order of responsibility should be listed for immediate reporting of 

BMP incidents to plant management personnel involved in implementation of emergency 

response plans.

The communications system should be described which is available for notification of an 

impending or actual BMP incident. Reliable communications with the person directly 

responsible is necessary to expedite immediate action for preventing, containing, or initiating 

cleanup of a discharge. Such a communication system could include telephone, radio, or alarm 

systems that could signal the location of an incident. Provisions to maintain communications in 

the event of a power failure must be addressed.

Written reports on all BMP incidents should be submitted to the plant's BMP Committee and 

plant management for review. Written reports should include the date and time of the discharge, 

weather conditions, nature of the materials involved, duration, volume, cause, environmental 

problems, countermeasures taken, people and agencies notified, and recommended revisions to 

the BMP plan involving changes to the plant operating procedures and/or equipment to prevent 

recurrence.

Procedures and important information should be outlined in the BMP plan for inclusion in 

reports of BMP incidents to federal, state, and local regulatory authorities. In some 
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circumstances, notifying authorities such as municipal sewage treatment works, drinking water 

treatment plants, and fish and wildlife commissions may be desirable. The BMP plan should list 

the individuals who are responsible for notifying these authorities. The telephone numbers of 

these authorities and of people in the plant who need to be notified should also be listed in the 

BMP plan. The phone numbers should be reviewed periodically for accuracy and might actually 

be used in the course of a "spill drill."

3.4.7 Materials Compatibility

Incompatibility of materials can cause equipment failure through corrosion, fire, or explosion. 

Equipment failure can be prevented by ensuring that the materials of construction for containers 

handling hazardous substances or toxic pollutants are compatible with the containers' contents 

and surrounding environment.

Materials compatibility encompasses 3 aspects: compatibility of the chemicals being handled 

with the materials of construction of the container, compatibility of different chemicals upon 

mixing in a container, and compatibility of the container with its environment. The specific 

requirement of "Materials Compatibility" in the BMP plan should provide procedures to address 

these aspects in the design and operation of the equipment on site handling toxic and hazardous 

materials.

The BMP plan documentation on materials compatibility should describe the engineering 

practices already used in the plant, and should summarize these existing practices with regard to 

corrosion and other aspects of material compatibility. Specific consideration should be given to 

procedures and practices for the mixing of chemicals which might result in fire, explosion or 

unusual corrosion. Thorough cleaning of storage vessels and equipment before use with another 

chemical should be standard practice to avoid unexpected reactions or releases of hazardous 

material. Coatings or cathodic protection should be considered for protecting a buried pipeline 

or storage tank from corrosion.

Where applicable, material testing procedures should be described in the BMP plan. Proposed 

substitutions for currently used toxic or hazardous chemicals should be studied to determine 

whether they are compatible with the construction materials of the existing containers. The 

procedures utilized by the plant or an outside contractor to perform the materials compatibility 

study should be documented. Materials compatibility situations which are covered by the RCRA 

hazardous waste regulations should be referred to in the BMP plan.

3.4.8 Good Housekeeping

Good housekeeping is essentially the maintenance of a clean, orderly work environment and 

contributes to the overall facility pollution control effort. Periodic training of employees on 

housekeeping techniques for those plant areas where the potential exists for discharges reduces 

the possibility of incidents caused by mishandling of chemicals or equipment.
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Examples of good housekeeping include neat and orderly storage of bags, drums, and piles of 

chemicals; prompt cleanup of spilled liquids to prevent significant runoff to surface water or 

infiltration to ground water; sweeping, vacuuming, or other cleanup of accumulations of dry 

chemicals as necessary to prevent them from reaching receiving waters; and provisions for 

storage of containers or drums to keep them from protruding into open walkways or pathways.

Maintaining employee interest in good housekeeping is a vital part of the BMP plan. Methods 

for maintaining good housekeeping goals could include regular housekeeping inspections by 

supervisors and higher management; discussions of housekeeping at meetings; and publicity 

through posters, suggestion boxes, bulletin boards, slogans, incentive programs, and employee 

publications.

3.4.9 Preventive Maintenance (PM)

An effective preventive maintenance (PM) program is important to prevent spills or releases. A 

PM program involves inspection and testing of plant equipment and systems to uncover 

conditions which could cause breakdowns or failures which result in significant discharges of 

chemicals to receiving waters. The program should prevent breakdowns and failures by 

adjustment, repair, or replacement of items. A PM program should include a suitable records 

system for scheduling tests and inspections, recording test results, and facilitating corrective 

action. Most plants have existing PM programs which provide a degree of environmental 

protection. It is not the intent of the BMP plan to require development of a redundant PM 

program. Instead, the objective is to have qualified plant personnel and the BMP Committee 

evaluate the existing plant PM program and recommend to management those changes, if any, 

needed to address BMP requirements.

A good PM program should include the following: (1) identification of equipment or systems to 

which the PM program should apply; (2) periodic inspections or tests of identified equipment 

and systems; (3) appropriate adjustment, repair, or replacement of items; and (4) maintenance of 

complete PM records on the applicable equipment and systems.

The BMP plan documentation on PM may include a list of procedures, examples of record 

keeping, a list of the principal systems to which the PM program is applicable, and directions for 

obtaining the records for any particular system included or referred to in the BMP plan. In 

general, it will be adequate to refer to the scope of existing PM procedures and location of PM 

records.

3.4.10 Inspections and Records

The purpose of the inspection and records system is to detect actual or potential BMP incidents. 

The BMP plan should include written inspection procedures and optimum time intervals between 

inspections. Records to show the completion date and results of each inspection should be 

signed by the appropriate supervisor and maintained for a period of 3 years. A tracking (followup) procedure should be instituted to assure that adequate response and corrective action have 
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been taken. The record keeping portion of this system can be combined with the existing spill 

reporting system in the plant.

While plant security and other personnel may frequently and routinely inspect the plant for BMP 

incidents, these people are not necessarily capable of assessing the potential for such incidents. 

Certain inspections should be assigned to designated qualified individuals, such as maintenance 

personnel or environmental engineering staff.

The inspection and records system should include those equipment and plant areas identified in 

the "Risk Identification and Assessment" portion of the BMP plan as having the potential for 

significant discharges. To determine the inspection frequency and inspection procedures, 

competent environmental personnel should evaluate the causes of previous incidents and assess 

the probable risks for incidents. Furthermore, the nature of chemicals handled, materials of 

construction, and site-specific factors including age, inspection techniques, and costeffectiveness should be considered.

Qualified plant personnel should be identified to inspect designated equipment and plant areas. 

Typical inspections should include examination of pipes, pumps, tanks, supports, foundations, 

dikes, and drainage ditches. Records should be kept to determine if changes in preventive 

maintenance or good housekeeping procedures are necessary.

Material storage areas for dry chemicals should be inspected for evidence of, or the potential for, 

wind blowing which might result in significant discharges. 

Liquid storage areas should be inspected for leaks in tanks, for corrosion of tanks, for 

deterioration of foundations or supports, and for closure of drain valves in containment facilities. 

Inspections could include the examination of seams, rivets, nozzle connections, valves, and 

connecting pipelines. Storage tanks should be inspected for evidence of corrosion, pitting, 

cracks, abnormalities, and deformation and such evidence should then be evaluated.

For in-plant transfer and materials handling of liquids, inspections should include visual 

examination for evidence of deterioration of pipelines, pumps, valves, seals and fittings. The 

general condition of items such as flange and expansion joints, pipeline supports, locking valves, 

catch or drip pans, and metal surfaces also should be assessed.

For loading and unloading operations, inspections during transfer of materials would permit 

immediate response if an incident occurred. The conditions of pipelines, pump, valves, and 

fittings for liquid transfer systems and pneumatic conveying systems used for transferring dry 

chemicals should be inspected. Inspections (together with monitoring) should be used to ensure 

that the transfer of material is complete before flexible or fixed transfer lines are disconnected 

prior to vehicular departure. Before any tank car or tank truck is filled, the lower most drain 

valve and all outlets of such vehicles should be closely examined for evidence of leakage and, if 

necessary, tightened, adjusted, or replaced. Before departure, all tank cars or tank trucks should 
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be closely examined to ensure that all transfer lines are disconnected and that there is no 

evidence of leakage from any outlet.

For plant runoff, inspect the integrity of the stormwater collection system and the diversion or 

overflow structures, and ensure that the drain valves and pump for diked areas are properly 

closed. The plant sewer and storm sewer system should be periodically surveyed to ensure that 

toxic and hazardous pollutants are not discharged in significant amounts. Inspections also should 

include diked areas to ensure that hazardous and toxic chemicals are not discharged from inside 

diked areas to waterways. Any liquid, including rainwater runoff, should be examined, and 

where necessary, analyzed, before being released from the diked areas to a receiving water. The 

permit should include site-specific methods for determining whether rainwater has received 

contamination. For examples, a facility handling acids could check to see that the pH of the 

rainwater is close to neutral, or a facility handling oils could check for sheen on the rainwater 

before discharge. If inspection reveals any indication of contamination, then the rainwater must 

be analyzed and properly treated before discharge.

Visual inspections should include examinations for leaks, seepage, and overflows from land 

disposal sites such as spray fields, pits, ponds, lagoons, and landfills. Other procedures and 

inspection techniques should be considered on a site-specific basis. Any inspections made or 

records kept to comply with a solid waste permit may be included in the BMP plan by reference.

Emergency equipment and supplies for spill control or fire fighting must be inspected to ensure 

that equipment is in good condition and supplies are adequate. The communication system must 

also be inspected.

3.4.11 Security

A security system is needed to prevent accidental or intentional entry to a plant which might 

result in vandalism, theft, sabotage or other improper or illegal use of plan facilities that could 

possibly cause a BMP incident. Most plants have security system to prevent unauthorized entry 

leading to theft, vandalism, sabotage or a spill. The BMP plan should describe those portions of 

the existing security system which ensure that chemicals or other pollutants are not discharged 

either accidentally or deliberately to receiving waters in significant quantities.

The BMP Committee, plant security manager, plant engineer or other qualified plant personnel 

should evaluate the coverage of the existing security system over those areas of the plant 

identified by the "Risk Identification and Assessment" as having the potential for significant 

discharges. They should recommend to plant management any changes necessary to improve the 

security system.

Examples of security measures include: routine patrol of the plant by security guards in vehicles 

or on foot; fencing to prevent intruders from entering the plant site, good lighting; vehicular 

traffic control; a guardhouse or main entrance gate, where all visitors are required to sign in and 
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obtain a visitor's pass; secured or locked entrances to the plant; locks on certain valves or pump 

starters; and television surveillance of appropriate plant sites, such as plant entrance, and loading 

and unloading areas.

Whenever possible, security personnel should be instructed to observe leaks from tanks, valves, 

or pipelines while patrolling the plant and also be informed of the procedures to follow when a 

spill or other discharge is detected. Many plants use contractor or plant security personnel who 

may not be qualified or may not have time to carry out such surveillance. In such cases, the 

surveillance can be incorporated in the "Inspection and Records" specific requirement and should 

be conducted by production or environmental staff.

3.4.12 Employee Training

Employee training programs should result in personnel, at all levels of responsibility, having a 

complete understanding of the BMP plan. Employee training meetings should be conducted at 

least annually to ensure adequate understanding of the objectives of the BMP plan and the 

individual responsibilities of each employee. Typically, these meetings could be a part of routine 

employee meetings for safety or fire protection. Such meetings should highlight previous spill 

events or failures, malfunctioning equipment components, and recently developed BMP 

precautionary measures. Training sessions should review the BMP plan and associated 

procedures. Just as fire drills are used to improve an employee's reaction to a fire emergency, 

spill or environmental incident drills may serve to improve the employee's reactions to BMP 

incidents. Large or complex facilities are required to conduct spill drills on a quarterly or semiannual basis. Smaller facilities are strongly encouraged to conduct spill drills too. Spill drills 

also serve to evaluate the employees' knowledge of BMP-related procedures, and are a 

fundamental part of employee training.

Adequate training in a particular job and process operation is essential for understanding 

potential discharge problems. Knowledge of specific manufacturing operations and how 

discharges could occur, or have occurred in the past, is important in reducing human error that 

can lead to BMP incidents.

The training program must include the protocol used to report discharges to the people 

responsible for implementing countermeasures. In addition, personnel involved in spill response 

should be trained to use cleanup materials such as sorbents, gelling agents, foams, and 

neutralizing agents. They should also be educated in safety precautions, in the side effects of the 

chemicals they are working with, and in possible chemical reactions. Operating manuals and 

standard procedures for process operations should include appropriate sections on the BMP plan 

and the spill control program and must be readily available for reference.

The BMP plan must contain records showing the dates, names and positions of the employees 

trained and also include the lesson plans, subject material covered, and instructors' names and 

positions. BMP-related training may be combined with other forms of training, such as safety, 
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fire prevention, or RCRA required training. 

In addition to permanent personnel, contractors or temporary personnel should be trained in 

procedures for preventing BMP incidents since these individuals may be unfamiliar with the 

normal operating procedures or location of equipment (pipelines, tanks etc.) at the facility. 

Adequate supervision of contractor maintenance personnel should be provided to minimize the 

possibility of BMP incidents resulting from damaging equipment such as buried pipelines. This 

supervision or training must be described in the BMP plan.

3.5 Specific BMPs

Ecology has developed specific BMPs for vehicle and equipment washing (WQ-R-95-56) and for 

prevention of pollution from storm water discharge in the Puget Sound Basin (Ecology 91-75)

3.6 Spill Plans Required by Others

Some facilities are required by other laws to have spill plans. The following Table XII-1 lists 

the facilities that are required to have spill plans for oil and petroleum products under RCW 

90.56. These spill plans are reviewed by the Spill Program. 
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Table XII-1. Facilities Covered by the Spill Program's Facility Oil Handling Regulation, 

for oil spill prevention planning/Chapter 173-180 WAC

Plan ID* Facility Name 

NW006 BP West Coast Products Terminal, Seattle 

NW029 Rainier Petroleum, Seattle

NW008 BP Cherry Point Refinery, Blaine 

NW011 ConocoPhillips Refinery, Ferndale

SW004 Tesoro Terminal, Port Angeles 

NW005 ConocoPhillips Terminal, Renton 

SW002 ConocoPhillips Terminal, Tacoma 

NW002 Tesoro Northwest, Anacortes

NW020 Shell, Seattle

SW003 NuStar, Vancouver 

SW013 Sound Refining, Tacoma

ER006 Chevron Pipeline, Pasco 

SW010 ST Services, Tacoma

NW007 Paramount Petroleum Richmond Beach Terminal, Seattle 

SW005 Tesoro Terminal, Vancouver

ER002 Chevron USA, Pasco 

NW003 Shell Refinery, Anacortes

ER003 Tidewater Terminal, Clarkston

ER004 Tidewater Terminal, Pasco

NW009Kinder Morgan Energy Partners Terminal, Seattle 

NW016 Terasen Pipeline, Bellingham

SW009 US Oil & Refining, Tacoma

SW007 Weyerhaeuser, Longview

NW004 Manchester Naval Fuel Depot, Manchester 

SW017 McNeil Island Corrections Center, Steilacoom 

NW014 Naval Air Station, Whidbey Island 

ER007 Yellowstone Pipeline, Spokane

* The plan ID indicates which region is reviewing the plan. Copies of those plans are available at 

that regional office. Copies of all plans are available at HQ by contacting the Spills Program.
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4. CERTIFIED OPERATORS AT INDUSTRIAL SITES 

WITH DOMESTIC WASTEWATER TREATMENT 

FACILITIES

Many industrial facilities have small domestic wastewater treatment facilities at the site or treat 

small quantities of domestic wastewater with the industrial wastewater. The personnel who work at 

these treatment facilities must be certified in accordance Chapter 173-230 WAC (Certification of 

Operators of Wastewater Treatment Plants). This regulation was primarily intended for municipal 

wastewater treatment plants but it applies to any wastewater treatment plant treating domestic 

wastewater. The level of certification ranges from OIT (operator-in-training) to Group IV. The 

level of certification required is in accordance with the size and complexity of the wastewater 

treatment facility. Wastewater discharge permits for industrial facilities treating domestic 

wastewater should include a requirement for a certified operator. Permit managers who are 

uncertain of the classification of a facility should call the operator certification coordinator, for 

assistance. Inspections of these facilities should verify the operator is certified and that the 

certification is of the proper level.
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XIII. MONITORING GUIDELINES

This chapter presents guidance and provides the technical references and the few statutory 

references which a permit writer should consider when establishing the special permit conditions 

for frequency of sampling, sample types, sampling locations and the analytical methods in a 

wastewater discharge permit. The seven sections of this chapter include:

1. The general considerations of self monitoring.

2. POTW monitoring (excluding land application).

3. Industrial and commercial facility monitoring.

4. WET testing monitoring.

5. Storm water monitoring.

6. Receiving environment monitoring. 

7. Sediment monitoring.

8. Summary checklist.

"Monitoring is truly the cornerstone of the NPDES program. It is the primary 

means of ensuring that the permit limitations are met. It is also the basis for 

enforcement actions against permittees who are in violation of their permit 

limits."

Having so stated in the opening of its primary permit-writing training manual, EPA dedicates 

four pages of a 100 page training manual to the topic of monitoring (EPA, 1987d). There is little 

explicit guidance which provides the permit writer with a framework for decisions relating to 

monitoring. This chapter informs the permit writer of what methods to follow to establish 

monitoring conditions in a permit.

EPA directed the states to require recording and reporting of monitoring results:

"All permits shall specify requirements concerning the proper use, 

maintenance, and installation, when appropriate, of monitoring equipment or 

methods (including biological monitoring methods when appropriate). All 

permits shall specify required monitoring including type, intervals, and 

frequency sufficient to yield data which are representative of the monitored 

activity including when appropriate, continuous monitoring" (40 CFR 122.48).
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"In addition to §122.48, the following monitoring requirements:

(1) To assure compliance with permit limitations, requirements to monitor:

(i) The mass (or other measurement specified in the permit) for each pollutant limited in 

the permit;

(ii) The volume of effluent discharged from each outfall;

(iii) Other measurements as appropriate including pollutants in internal waste streams under 

§122.45(i); pollutants in intake water for net limitations under §122.45(f); frequency, 

rate of discharge, etc., for noncontinuous discharges under §122.45(e); pollutants 

subject to notification requirements under 122.42(a); and pollutants in sewage sludge or 

other monitoring as specified in 40 CFR part 503; or as determined to be necessary on a 

case-by-case basis pursuant to section 405(d)(4) of the CWA.

(iv) According to test procedures approved under 40 CFR part 136 for the analyses of 

pollutants having approved methods under that part, and according to a test procedure 

specified in the permit for pollutants with no approved methods.

(2) Requirements to report monitoring results with a frequency dependent on the nature and 

effect of the discharge, but in no case less than once a year..." (40 CFR 122.44[i])

The two citations quoted above give the permit writer extreme flexibility in monitoring, from 

yearly to continuous. The most important requirement is that the data "are representative of the 

monitored activity."

Washington State regulations provide more detailed requirements.

 " (1) Monitoring. 

 (a) Any discharge authorized by a permit may be subject to such monitoring requirements as 

may be reasonably required by the department, including the installation, use, and 

maintenance of monitoring equipment or methods (including, where appropriate, biological 

monitoring methods). These monitoring requirements would normally include: 

(i) Flow (in gallons per day); 

(ii) Pollutants (either directly or indirectly through the use of accepted correlation 

coefficients or equivalent measurements) which are subject to reduction or elimination 

under the terms and conditions of the permit;
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(iii) Pollutants which the department finds could have a significant impact on the quality of 

surface waters; and

(iv) Pollutants specified by the administrator, in regulations issued pursuant to the FWPCA, 

as subject to monitoring. 

(b) Each effluent flow or pollutant required to be monitored pursuant to (a) of this subsection 

shall be monitored at intervals sufficiently frequent to yield data which reasonably 

characterizes the nature of the discharge of the monitored effluent flow or pollutant. 

Variable effluent flows and pollutant levels may be monitored at more frequent intervals 

than relatively constant effluent flows and pollutant levels which may be monitored at less 

frequent intervals. 

(c) Monitoring of intake water, influent to treatment facilities, internal waste streams, and/or 

receiving waters may be required when determined necessary by the department to verify 

compliance with net discharge limitations or removal requirements, to verify that proper 

waste treatment or control practices are being maintained, or to determine the effects of the 

discharge on the surface waters of the state... 

(3) Reporting of monitoring results. 

(a) The permittee shall periodically report (at a frequency of not less than once per year) on the 

proper reporting form, the monitoring results obtained pursuant to monitoring requirements 

in a permit. In addition to the required reporting form, the department at its discretion may 

require submission of such other results as it determines to be necessary." [WAC 173-220-

210] 

"(1) Any permit issued by the department shall specify conditions necessary to prevent and 

control waste discharges into the waters of the state, including the following, whenever 

applicable:

(g) Any appropriate monitoring, reporting and recordkeeping requirements as specified 

by the department, including applicable requirements under sections 307 and 308 of 

FWPCA" [WAC 173-216-110]”.

The nature and effect of the discharge are important factors in determining monitoring frequency and 

so it is important that the discharge be adequately characterized. The permit writer should recognize 

the costs of monitoring while deciding how much is enough for an adequate characterization.

Consulting with individuals, including the permittee, who are knowledgeable about the facility or 

type of operation will save time on appeals, enforcement and future permit renewal or 

modification efforts. A prime source of information about a facility is the inspector who deals 

with the facility or similar facilities.
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1. GENERAL CONSIDERATIONS OF A SELFMONITORING PROGRAM

The general considerations apply to all facilities in the wastewater permit program administered 

by the Washington State Department of Ecology. Exceptions and additional considerations are 

explained in the chapter sections for POTWs, industrial facilities, storm water and for receiving 

environment monitoring. The general considerations are presented in this section in the 

following sequence:

• Objectives of monitoring.

• Parameters to monitor.

• Frequency of monitoring.

• Special monitoring strategies.

• Sampling and testing methods.

• Sampling locations.

• Data validation, management and reporting.

• Quality assurance and quality control.

All permits must require monitoring of effluent in order to determine if the facility is in 

compliance with the permit. The permit must state the sampling location, frequency, methods of 

analyses, and sample type for each parameter with limits. Parameters without limits may be 

monitored as required by the department. Internal process control monitoring may be required of 

dischargers exhibiting noncompliance. Tiered monitoring and indicator parameters should be 

used when appropriate.

The variability of the effluent is one of the most important factors in establishing monitoring 

frequency, particularly for industrial dischargers, and therefore the degree of monitoring 

frequency is dependent on the characterization of the effluent. The characterization should 

ideally occur as a part of the renewal or application process. A high frequency monitoring study 

is presented as a means of effluent characterization. High frequency monitoring, usually within a 

tiered framework or as a special study, is recommended to characterize effluent.

1.1 Establish Monitoring Objectives

The main purpose of self monitoring requirements is to determine compliance with effluent 

limits and other permit conditions. Monitoring may also be required in order to gather 

information necessary to derive an effluent limit, determine if a limit is necessary or to determine 
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impacts on the receiving environment. 

The parameters, frequency of monitoring, and sampling locations for POTWs are listed in Tables 

XIII-1(A-E) and XIII-2(A-M). The limits and monitoring strategies for POTWs are standardized 

and based on Best Conventional Treatment for pollutants generally associated with municipal 

sewage treatment plants (Section 2. POTW Monitoring). Industrial or commercial facilities 

which have the same type of treatment system, in particular a secondary biological process, 

should receive similar monitoring requirements for the pollutants listed. POTW monitoring 

frequency for permit conditions based on water quality standards and toxic discharges must be 

derived separately.

Discussion and guidance on requirements for monitoring compliance with whole effluent 

toxicity are found in Section XIII-4. The permit writer should use the guidance presented in this 

chapter to determine the monitoring frequency, the level of detail required and the relevancy of 

the testing results toward evaluating the potential for environmental harm from the effluent.

The permit writer should be able to justify the monitoring requirements on the basis of the value 

of the data. Know how the data may be used. The most useful, valid and cost-effective data are 

generated when the purpose or monitoring objectives of monitoring are understood. Some 

general objectives include:

• To determine compliance with technology-based and water quality-based effluent limits.

• To determine adequacy of 0 & M procedures.

• To determine specific impacts on water or sediment quality.

• To determine effectiveness of source control measures and BMPs.

• To determine baseline or background conditions in the receiving environment.

• To determine the variability of the wastewater as a prerequisite to establishment of 

monitoring schedules.

• To characterize the wastewater for determining the need for additional limits.

1.2 Parameters to Monitor

All parameters with effluent limits must have monitoring requirements. Additional parameters to 

monitor will depend on the monitoring objectives explained previously.

Monitoring flow rates is important for determining loading and is required in all NPDES permits 

[40 CFR 122.44(i)]. Methods and techniques of flow measurement are explained in the Water 

Quality Inspection Manual, Ecology, 1992.
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1.2.1 Effluent Monitoring

The pollutant parameters to be monitored in effluent are based on application data, history of the 

facility discharge, pollutants discharged from similar facilities and any applicable EPA 

development documents. Minimum parameters for POTWs are outlined in Section XIII-2. 

The permit may require monitoring of pollutants in the effluent for reasons other than to determine 

compliance with effluent limits. The general objectives stated in section 1.1 contain many 

objectives other than the compliance objective. For example, the objective "to determine 

effectiveness of source control measures" only indirectly determines compliance. BMPs may be 

followed as required in the permit but the BMPs may not be adequate to prevent undesirable 

effects. The monitoring becomes a feedback mechanism to fine tune the BMPs. Another important 

objective is to gather information to determine if further effluent limits are necessary. The authority 

to require monitoring is derived from Section 308 of the FWPCA and 90.48.260 RCW.

The discharger may be required to monitor for pollutants which the permit writer knows or

suspects to be present in the discharge, even those not listed in the permit application. Additional 

parameters to monitor include toxic chemicals or substances that could upset the treatment system. 

These substances could be introduced from raw materials, compounds resulting from chemical 

interactions, or impurities in raw materials including solvents.

1.2.2 Process Control and In-Plant Monitoring

"Monitoring of intake water, influent to treatment facilities, internal waste streams, and/or 

receiving waters may be required when determined necessary by the department to verify 

compliance with net discharge limitations or removal requirements, to verify that proper 

waste treatment or control practices are being maintained, or to determine the effects of a 

discharge on the surface waters of the state." (WAC 173-220-210[1][c])

Process control monitoring refers to monitoring of internal waste streams in order to verify that 

proper waste treatment or control practices are being maintained. In-plant monitoring refers to 

monitoring at internal sample points due to the inability or impracticality to apply limits or 

conditions at the typical point of compliance.

Process Control Monitoring--Process control monitoring may be included in an enforcement order 

when a facility has been out of compliance with its permit. Process control monitoring should not 

be a requirement in the permit in most circumstances. The permit manager may select certain 

internal waste streams for monitoring which can generate data to assist the discharger in efficient 

operation of the treatment system. An enforcement order may also specify monitoring to assist in 

identifying pollutant sources. Reasonable cause for internal process control monitoring includes:

• Enforcement action for permit noncompliance when the monitoring is intended to identify 

the source or cause of noncompliance.
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• Evaluating pollutant inputs from various functional areas of the facility as part of a Toxicity 

Identification Evaluation (TIE), a BMP for pollutant identification or quantification or the 

application of a performance standard for a process employed.

• Other circumstances to verify that proper waste treatment or control practices are being 

maintained (e.g., the certification period for a grant related project or as a condition of a 

demonstration or experimental project) 

The wastewater treatment process will determine the types of process control monitoring needed. 

For industries with biological treatment systems and wastewater characteristics and flows that are 

similar to comparable POTWs, the monitoring frequency can follow the schedules of Table XIII2(A-M). For physical and chemical treatment systems, the permit manager should review any 

development document for the industrial category, the treatability manuals and other engineering 

literature for information regarding parameters to use for process control monitoring.

In-Plant Monitoring--Under both federal (40 CFR 122.45[h]) and state regulation (Chapter 173-

220-210 [1][c] WAC), in-plant monitoring may be required as a permit condition. In-plant 

monitoring for industries may be required at the discretion of the permit writer when reasonable 

cause exists and the cause is explained in the fact sheet. In-plant monitoring may be required:

• When the sample at final discharge is not characteristic of undiluted effluent because of 

dilution from other parts of the plant (and to determine whether the waste flow is being 

diluted to meet effluent limits).

• When interferences among pollutants at the point of discharge would make detection or 

quantification impractical.

• When the final discharge point is inaccessible (but make every effort to require 

accessibility).

• When determining chlorination efficiency.

1.2.3 Indicator Parameters

Indicator parameters may be used in certain instances when a close correlation exists between 

concentrations of pollutants in a wastestream. Indicator tests or observations can be useful in 

determining the effectiveness of the treatment process. Indicator parameters can be used only for 

well documented processes where the effluent concentration of an easily measured component 

parallels the concentration of a component more difficult to measure or detect. The correlation

must be consistent over the range of varying raw material input to the system. A treatment 

process that reduces the concentration of the indicator in equal or less proportion to the 

contaminant of concern is essential.
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Limits on indicators may not be used as a substitute for federally promulgated technology-based 

limits or limits developed on a case-by-case basis on parameters in the discharge. Contaminants 

of interest in the effluent for which no limits are specified can be monitored by an indicator when 

a positive correlation is established. There are correlations between some parameters which allow 

tests for one parameter to indicate the relative value of another parameter. A procedure for 

calculating correlations is located in the Handbook for Sampling and Sample Preservation of 

Water and Wastewater, EPA, 1982b, p.146. Computer software packages such as Excel, the 

agency standard spreadsheet software calculates correlation coefficients. In many cases 

significant correlations exist between the following parameters:

• BOD and TOC

• Chlorides and Conductivity

• Total Dissolved Solids and Conductivity

• Acidity, Alkalinity and pH

• Hardness, Calcium, and Magnesium

Besides the cost considerations, indicator tests are also advantageous if they give quicker feedback 

for process control testing. An example would be analyzing TOC instead of 5 day BOD if a 

reasonably consistent mathematical relationship is established through special comparison studies. 

BOD is not always the most useful indicator of oxygen demand because of the long incubation 

time required to obtain a meaningful result. Once a correlation has been established, the TOC 

measurements can be translated to BOD. Monitoring the effluent for an indicator cannot 

substitute for monitoring on a parameter which has an established effluent limitation.

The utility of an indicator must be explained in the fact sheet. The explanation should be based 

on:

• Similarities between causative pollutants and a convenient monitoring parameter (e.g., 

monitoring Total Petroleum Hydrocarbon to indicate control of polynuclear aromatic 

hydrocarbons where the removal technology equally reduces the concentration of both or 

preferentially reduces the PAH component). 

• The effectiveness of a particular treatment process and a control parameter for that process 

(e.g., limits on TOC to ensure proper performance of an activated carbon process).

Indicators might be appropriate for an industry that generates a waste stream containing metals in 

which the relative concentration of metal pollutants does not vary because of consistent raw 

material composition and internal process control. An internal process control parameter could be 

monitored to assure process stability. One metal could serve as an indicator for most other metals. 

TSS has been used by EPA as an indicator of toxics for some effluent guidelines.

Where there is no water quality criterion for a specific pollutant which causes or contributes to an 

excursion above a narrative criterion, the permit writer may establish effluent limits and monitor 
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an indicator parameter. The permit should require all effluent and ambient monitoring necessary 

to show that the limit on the indicator continues to attain and maintain applicable water quality 

standards [40 CFR 122.44(d)(1)(vi)(C)].

1.3 Monitoring Frequency

"Each effluent flow or pollutant...shall be monitored at intervals sufficiently frequent to 

yield data which reasonably characterizes the nature of the discharge of the monitored 

effluent flow or pollutant. Variable effluent flows and variable pollutant concentrations may 

be monitored at more frequent intervals than relatively constant effluent flows and pollutant 

concentrations which may be monitored at less frequent intervals" [WAC 173-220-

210(1)(b)].

The frequency of sampling should result in the production of data that provide a reasonable 

characterization of the effluent. Reasonableness can be demonstrated on the basis of the value of 

data collected. A primary value of the data is the establishment of effluent variability, an 

important factor in calculating discharge limits, determining compliance and establishing the basis 

for monitoring frequency. Routine compliance monitoring frequency may be adjusted to reflect 

the variability. The intent is to establish a frequency of monitoring which will detect most events 

of noncompliance without requiring needless or burdensome monitoring.

For example, at equivalent average flow rates, a large lagoon system which is not susceptible to 

short circuiting requires less frequent monitoring than an overloaded treatment facility which 

experiences fluctuating flow rates due to infiltration or large batch discharges from an industrial 

user on the system. The large lagoon should have a relatively low coefficient of variation (CV = 

population standard deviation divided by the population mean: sd/mean) compared to the facility 

receiving batch discharges.

1.3.1 Establishing Monitoring Frequency 

The frequencies for monitoring pollutants from a POTW with limits based on a performance 

standard are presented in Section 2 of this chapter. The permit writer should consider these as 

minimum frequencies.

The frequencies for monitoring pollutants for informational purposes, for performance-based 

limited pollutants from non-POTWs or for water quality-based effluent parameters from any 

facility should be derived at the discretion of the permit-writer by one of the two following 

methods.

Method 1. Estimate the variability of the concentration of the parameter by reviewing DMRs and 

the record of similar dischargers. In addition to the estimated variability, other factors for 

determining sampling frequency include:

• Size and design capacity of facility

• Type of treatment
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• Compliance history

• Number of pollutant sources from a facility

• Cost of monitoring relative to the discharger's capability and benefits obtained

• Environmental significance of pollutants

• Receiving water quality (including dilution effects)

• Detection limits and analytical precision/accuracy

• Production schedule of the facility (seasonal, daily, etc.)

• Plant wash down or cleanup schedule

• Number of monthly samples used in developing the permit limit

• Batch type process and discharge or continuous operation

These factors and other facility-specific factors used to determine monitoring frequency should 

be presented and discussed in the permit fact sheet.

Method 2. See Appendix 13.2

1.3.2 Tiered Monitoring

The Puget Sound Water Quality Management Plan, Puget Sound Water Quality Authority, 1991 

states:

"Monitoring requirements included in permits shall be tiered so that if initial 

(baseline) sampling discloses no problems, a reduced monitoring scheme may 

then apply. Likewise, if initial (baseline) sampling indicates the possibility of 

problems, a more frequent and/or more comprehensive monitoring schedule 

would apply. Initial monitoring schemes shall be set to ensure that enough 

data is collected to determine if additional discharge limits should be set."

The concept of tiered monitoring should be considered for all permits. It is a permit program goal 

to require sufficient monitoring to meet the objectives mentioned earlier but to avoid excessive 

monitoring. Tiered monitoring requires that implementation of additional monitoring methods or 

reduction of certain monitoring frequencies be based on the results of previous monitoring. This 

step-wise approach could lead to lower monitoring costs for the permittee while still providing an 

adequate degree of protection for the receiving environment and human health. The term "tiering" 

for this chapter means a reduction or increase in frequency of monitoring within a permit cycle. 

The conditions for increase and decrease are explained in the permit.

The recommendation at this time is to consider tiering only for parameters with established limits. 

Monitoring for information should be done in the context of a "Special Study" with a definite 

beginning and ending established in the permit.
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The use of tiering should be restricted to a one-time reduction in monitoring frequency with no 

provision for reversion to the high frequency in the permit. If the permit manager feels that a 

reversion to high frequency is warranted, require the reversion through an administrative order or 

a subsequent permit modification (minor modification). 

The application of tiering will generally be left to the judgment of the permit writer. Justification 

for the level or degree of monitoring required in the permit should be presented in the fact sheet. 

The time frames associated with establishment of the baseline monitoring period should be 

determined by the permit writer. The initial (baseline) monitoring period should reflect the 

environmental consequence and the likelihood of presence of the pollutant(s). If tiering is also 

used to generate variability and LTA data, these needs should be considered in establishing the 

schedule.

Until there is sufficient data available by the methods stated previously, require a minimum of 10 

observations every month for all pollutants of concern for which there are limits specified as 

explained in the TSD (EPA, 1991). The permit writer should require that data be accumulated 

until the level of variability is established. One approach would be to request that semi-weekly to 

daily monitoring results of effluent parameters be submitted in addition to the routine DMRs 

during the early months of the permit cycle. Analysis of this data would indicate whether 

monitoring frequency can be reduced while maintaining adequate characterization of the effluent. 

This strategy should be explained briefly in the fact sheet. Once variability is established, 

monitoring frequency should be based on the confidence that effluent limit excursions will be 

detected.

The total cost of monitoring for toxic pollutants could be reduced by requiring a high initial 

monitoring frequency that is reduced if the permittee consistently meets the limit. The overall 

purpose of such requirements is to first establish a compliance history using a relatively high 

monitoring frequency and then reduce the frequency if they routinely comply with permit 

conditions. The requirements should be specified in the permit. 

An example of a decrease in monitoring is a requirement to test for chemicals such as volatile 

organics monthly or bimonthly in the first year of a permit cycle, then reduction to annually if no 

volatiles of concern as specified in the permit are detected. This strategy may suffice if the permit 

writer has doubts about information presented in an application or if improvements in pollutant 

control are expected which reduce the likelihood of discharge of volatiles.

The triggers for the tiered elements of a permit must be well defined in the permit and explained in 

the fact sheet. For the above example, the simplest approach is to state the trigger in a footnote in 

the special condition for monitoring frequencies. The footnote should explain to what frequency 

the tiered parameter will revert if not detected or not found to be at a level of concern. The 

numeric "level of concern" must be defined in the permit and explained in the fact sheet. The 

reduction or elimination of monitoring should also be contingent upon the permittee requesting 
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approval from Ecology. The regional DMR data input coordinator must be in the paper trail loop 

of "approval of frequency or parameter-change" in order to be able to track these changes.

It is convenient to begin the permit cycle with baseline monitoring which specifies a high 

frequency of monitoring for the wide variety of pollutants suspected to be present. Elimination or 

reduction of monitoring can be accomplished through compliance and discharge at levels of nonconcern and after written approval from the permit manager. 

An increase in monitoring frequency or scope of monitoring is usually more difficult to 

administer. The trigger for increased monitoring would need to be established and explained. 

Except for relatively simple triggers for additional types of monitoring or increased frequency, the 

recommended approach for an additional monitoring schedule is to issue an administrative order 

based on noncompliance with the permit. The few instances where additional monitoring may be 

required do not justify the resource investment involved in satisfying all possibilities or 

contingencies in the permit text.

A common example of an increase in monitoring is a requirement to test an effluent for toxic 

chemicals when the effluent violates a WET limit. This is discussed further in Chapter VI.

1.3.3 Monitoring Reduction for Exemplary Performance

Another concept related to tiered monitoring is the reduction of monitoring frequency for 

demonstrated good performance. This process is generally applied at the time of permit renewal 

and the monitoring frequency is reduced from some baseline frequency. The following guidance 

is adopted from EPA guidance (EPA memorandum from Robert Perciasepe and Steven A. 

Herman to Regional Administrators, April, 1996). The guidance is applicable to NPDES 

permitted discharges, State permitted discharges, and discharges to a POTW.

Criteria for Exclusion

Facilities whose owners or operators have been criminally convicted under any Federal or State 

environmental statute of falsifying monitoring data or of committing violations which presented 

an imminent and substantial endangerment to public health or welfare will not receive any 

reductions. These facilities may be eligible at any time Ecology determines there has been a

wholesale change in ownership and management from those convicted.

Facilities whose owners or operators have been convicted of any other criminal violation under 

any Federal or State environmental statue will not receive any reductions for at least 5 years from 

the time of conviction.

Facilities where an individual employed by the permittee, but not the permittee itself, was 

convicted of a criminal violation under any Federal or State environmental statute, will be 

eligible for reduced monitoring frequency provided the permittee discovered and self-disclosed 

the violation, and took prompt action to correct the root cause in order to prevent future criminal 

violations.
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Facilities involved in civil environmental, judicial actions brought by the State are eligible for 

consideration of reduction 1 year after completion of injunctive relief and payment of penalty.

Facilities involved in administrative actions are eligible for consideration after the permittee has 

complied with Administrative Order (AO) requirements, and payment of any assessed penalty. 

A permittee that is issued an AO, in conjunction with reissuance of its permit, to extend a 

compliance schedule, may be eligible if the permittee is in compliance with the interim 

milestones and schedule in the AO.

For example, in order to comply with a newly promulgated effluent guideline, an industrial 

sector may be required to install a new technology. Some facilities may not be able to attain the 

new technology immediately so an AO is issued at the time the facility’s permit is reissued. The 

AO sets a compliance schedule to allow the permittee additional time to install the technology 

needed to meet the new effluent guideline limitation.

Facilities are not eligible for monitoring reduction for any parameter that exceeds a one percent 

noncompliance during the past two years. Noncompliance includes monthly average, weekly 

average or daily maximum.

Other permit noncompliance such as failure to submit a DMR or other permit submittals should 

be considered before authorizing a reduction.

Facilities are not eligible for monitoring reduction until at least one permit cycle from the time of 

restoration of lab accreditation if the accreditation was lost for not performing to standards.

Facilities are not eligible for monitoring reduction until at least two years from the time of a 

Class II inspection in which it was found the facility was submitting invalid results.

Monitoring reduction for effluent data which has not been continuously reported over the two 

year period, interrupted or discontinuous data, intermittent, short-term, and batch discharges 

must be considered on a case by case basis. These will require performance data for longer than 

two years to determine a long term average.

New dischargers will be eligible for reduced monitoring after meeting the two year compliance 

requirement. Normally, the reduced monitoring provisions would be applied after one permit 

cycle of five years and at permit reissuance.

Permit writers should evaluate the discharge situation when considering monitoring reduction. 

For example, discharges to a shellfish area should generally not be considered for reduction in 

fecal coliform monitoring and discharge to an AA water body generally should not be considered 

for reduction in toxics monitoring. Permit writers should also evaluate the prospect of the 
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permittee maintaining good performance during the life of the permit. A municipal treatment 

plant that is lightly loaded but is expected to be near capacity by the end of the permit term 

would probably not be meeting the performance criteria by the end of the permit term. Similarly, 

an industrial facility which demonstrates good performance for the past two years because of 

greatly reduced production would not be a good prospect for maintaining good performance if 

production increased during the term of the permit.

Procedures

Reduction of monitoring frequency will generally be granted at time of permit renewal by 

examination of performance in the two years preceding renewal. The amount of reduction is 

dependent upon the ratio of performance for the last two years to the monthly average effluent 

limitation (Table XIII-1A1). The baseline monitoring frequency is discussed in Section 1.4 

below.

Monitoring reduction will be granted during the permit term at the request of the permittee and 

as appropriate. Monitoring reduction during a permit term is a major modification and requires 

public notice. Each request for modification must include documentation from the permittee 

demonstrating eligibility. Permit managers will track the number of requests for modification 

and the disposition of those requests.
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Table XIII-1A1. Allowable Monitoring Frequency Based on Ratio of Long Term Effluent 

Average to the Average Monthly Limit (AML)

Baseline Ratio of Long Term Average to the AML

Monitoring 75-66% 65-50% 49-25% <25% 

7/wk 5/wk 4/wk 3/wk 1/wk 

6/wk 4/wk 3/wk 2/wk 1/wk

5/wk 4/wk 3/wk 2/wk 1/wk

4/wk 3/wk 2/wk 1/wk 1/wk

3/wk 3/wk 2/wk 1/wk 1/wk

2/wk 2/wk 1/wk 2/mo 1/mo

1/wk 1/wk 1/wk 2/mo 1/2mos 

2/month 2/mo 2/mo 2/mo 1/quarter

1/month 1/mo 1/mo 1/quarter 1/6mos

Note: See above eligibility requirements.

Facilities which satisfy the entry criteria but are not experiencing discharges of 75% or less of 

their permitted levels of water quality-based parameters may still be eligible for reductions in 

monitoring/reporting frequencies. Monitoring will only be reduced for such parameters if the

applicant can demonstrate a coefficient of variation (ratio of standard deviation to the mean) of 

0.20 or less and no monthly average limit violation for the two year averaging period. Reduction 

will be allowed as shown in Table XIII-1A2 below.

Table XIII-1A2. Allowable Monitoring Reduction with a Ratio of Long Term Effluent Average 

to Monthly Average Limit 100-76% and a CV of 0.2 or Less.

Baseline Reduced 

Monitoring Monitoring

7/wk 6/wk

6/wk 5/wk

5/wk 4/wk

4/wk 4/wk

3/wk 3/wk

2/wk 2/wk

1/wk 1/wk

2/month 2/month

1/month 1/month
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Permittees that receive monitoring frequency reductions in accordance with Table XIII-1A1 or 

Table XIII-1A2 are still expected to take all appropriate measures to control both the average 

level of pollutants of concern in their discharge (mean) as well as the variability of such 

parameters in the discharge (variance), regardless of any reductions in monitoring frequencies 

granted from the baseline levels. To remain eligible for these reductions, the permittee may not 

have any violations for effluent limitations of the parameters for which reductions have been 

granted or failure to submit DMRs, or may not be subject to a new formal enforcement action. 

For facilities that do not maintain performance levels, Ecology may require increased monitoring 

by minor permit modification or Administrative Order.

Background material on the statistical derivation of the reduction allowance is presented in the 

original EPA memo. This material is reproduced in Appendix XIII. Permit writers may wish to 

alert permittees that this background material points out that the probability of reporting a 

violation increases as the monitoring frequency decreases in some cases.

1.4. Baseline Monitoring Frequencies

The permit writer must establish a baseline monitoring frequency in order to determine any 

allowable reduction for good performance. The baseline monitoring frequency may be 

established by using:

1. The POTW monitoring frequencies given in Section 2 of this chapter.

2. The original monitoring frequency in the permit before any reduction for performance was 

granted.

3. The statistical formulas given in Appendix 13 Part 2.

A baseline must be established each time a reduction in monitoring frequency is granted (usually 

at time of renewal). For example, the first time POTW is granted a reduction in monitoring, the 

baseline is the monitoring frequency in the expiring permit (assuming that the monitoring 

frequency is consistent with Section 2 of this Chapter). At the time of next renewal the baseline 

frequency would be based on the appropriate tables in Section 2 and not on the reduced 

monitoring frequency in the permit. Similarly, if an industrial discharger is granted a reduction 

in monitoring, then at the time of the next renewal the reduction is based on the original 

frequency before the reduction was granted or on a frequency calculated by the statistical 

formulas in Appendix 13. 

Monitoring reductions should be stated in the fact sheet for future reference.
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1.5 Special Monitoring Strategies

Routine effluent and facility monitoring can meet some of the objectives stated at the beginning of 

this chapter but some objectives are best met through the use of special timing strategies and 

studies. Special studies are typically for a single purpose and are conducted during a limited time 

frame within the permit cycle. Section XIII-6 on receiving environment monitoring also discusses 

considerations relevant to special studies of the receiving environment.

1.5.1 Stratified Sampling

Uniform sampling intervals may not always be the best approach, considering the cyclic variations 

in water quality and effluent variability. Stratifying a sampling program into different time 

periods may result data more suited to characterizing the impact of the discharge.

An example is to require increased monitoring frequency during critical receiving water periods to 

measure potential impacts to water quality. Seasonal monitoring schedules could be applied. This 

type of sampling scheme has been used by Ecology for determining compliance with some water 

quality based effluent limits. More frequent sampling may be required during the receiving 

water's critical flow, with less intensive monitoring during the rest of the year. Such an approach 

could be taken for scheduling toxicity testing. Variable sampling frequency could also be used to 

allocate sampling to periods of peak production or times of largest effluent variation.

1.5.2 Unusual Sampling Frequencies

A unique approach is to require that certain parameters traditionally monitored at a frequency of 

quarterly or twice annually be monitored under a non-traditional schedule such as "once every 

fifth month," which results in one monitoring event for each calendar month of a five year permit 

cycle. This method of scheduling frequencies supplies a degree of randomness. True random 

sampling is usually difficult to administer.

1.5.3 Studies to Determine Effluent Variability, A High Frequency Study

The variability can be established by a special monitoring study conducted prior to permit renewal 

or during an early portion of the permit cycle. The survey should cover a span of discharge which 

represents the range of effluent quality and quantity. The sampling frequency on which the data 

are based should be frequent enough to cover a time span of discharge which considers the swings 

in effluent quality and quantity. A high frequency study required by the permit should specify the 

time frame within which the study is to be conducted.

An alternative to a specific permit requirement is to require that the same type of data be generated 

through a permit-required engineering report. The report should involve an intense analysis that 

demonstrates the variation or CV, the co-dependence of variables and the mean or LTA of the 

pollutant concentrations in the discharge. 

The generic factors available for estimating variability listed in section 1.3.1.A should be 
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considered in establishing the schedule for the high frequency study.

This strategy should be explained briefly in the fact sheet. Once variability is established, 

monitoring frequency should be based on the confidence that effluent limit excursions will be 

detected.

1.6 Sampling and Testing Methods

Monitoring requirements in the permit should specify the sampling frequency, the sample type 

(grab, composite or continuous) and the analytical methods for each parameter. A permit 

condition should require the use of sampling and analytical methods conforming to 40 CFR Part 

136.

Detailed information for developing the sampling program is found in the publication, Monitoring 

Industrial Wastewater, EPA, 1973. The information is also applicable to POTWs. Test 

procedures which are approved for NPDES monitoring are listed in Tables IA-IF of 40 CFR 136 

(7/1/2003 update). The tables include methods published in:

Methods for the Chemical Analysis of Water and Wastewater, EPA 600/4-79-020.

Standard Methods for the Examination of Water and Wastewater, 20th Edition, APHA.

Annual Book of ASTM Standards, Volumes 11.01 and 11.02.

Methods for Analysis of Inorganic Substances in Water and Fluvial Sediments, USGS, 1989.

Methods for the analysis of organic chemicals are published in 40 CFR 136, Appendix A. 

Specific requirements and guidance for toxicity testing (bioassays) are included in Chapter 173-

205 WAC, Whole Effluent Toxicity Testing and Limits and are explained in section XIII-4. 

Some parameters and samples may require special considerations. Parameters which have no 

approved testing method in Part 136 can be tested and reported. The permit should specify the test 

method and include a reference. Contact the EA program for assistance in selecting test methods. 

The method itself should be included as an appendix to the fact sheet if the method is not readily 

available to the permittee. An example is saltwater samples, which may require modifications to 

the approved methods to avoid matrix interferences from the high salt content.

Approved analytical methods for parameters usually include sampling and handling requirements. 

Refer to Ecology's Laboratory User's Manual for information regarding sample preservation and 

handling.

The sample type will depend on:
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• The parameter to be monitored. To determine appropriate sample types consult 40 CFR Part 

136, Standard Methods or other approved methods;

• The temporal and pollutant concentration variability of the discharge; and

• The type of limit. Limits based on instantaneous or one hour values may be sampled using 

grab sampling techniques. Limits based on average values or daily maximums may be 

sampled using time or flow proportional composite samples. This is acceptable for certain 

conventional pollutants, nutrients, and bioaccumulative pollutants, for which percent 

removal and total loading to the receiving water are of concern. 

1.6.1 Discrete Grab or Sequential Grab Samples

A grab sample is an individual sample collected in less than 15 minutes time. It represents more 

or less "instantaneous" conditions.

Use grab samples when:

• The wastewater characteristics are relatively constant.

• The parameters to be analyzed are likely to change with storage such as temperature, 

residual chlorine, soluble sulfide, cyanides, phenols, microbiological parameters and pH.

• The parameters to be analyzed are likely to be affected by the compositing process such as 

oil & grease and volatiles.

• Information on variability over a short time period is desired.

• Composite sampling is impractical or the compositing process is liable to introduce artifacts 

of sampling.

• The spatial parameter variability is to be determined. For example, variability through the 

cross section and/or depth of a stream or a large body of water.

• Effluent flows are intermittent from well-mixed batch process tanks. Sample each batch 

dumping event.

Grab samples can measure maximum effect only when the sample is collected during flows 

containing the maximum concentration of pollutants toxic to the test organism.

Another type of grab sample is sequential sampling. A special type of automatic sampling device 

collects relatively small amounts of a sampled waste stream, with the interval between sampling 

either time or flow proportioned. Unlike the automatic composite sampler, the sequential 
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sampling device automatically retrieves a sample and holds it in a bottle separate from other 

automatically retrieved samples. Many individual samples can be stored separately in the unit, 

unlike the composite sampler which combines aliquots in a common bottle. This type of sampling 

is effective for determining variations in effluent characteristics over short periods of time.

1.6.2 Composite Samples

A composite sample consists of a series of individual samples collected over time into a single 

container, and analyzed as one sample. There are two general types of composites and the permit 

writer should clearly express which type is required in the permit:

• Time composite samples collect a fixed volume at equal time intervals and are acceptable 

when flow variability is not excessive. Automatically timed composited samples are usually 

preferred over manually collected composites. Composite samples collected by hand are 

appropriate for infrequent analyses and screening.

• Composite samples can be collected manually if subsamples have a fixed volume at equal 

time intervals when flow variability is not excessive. 

• Flow proportional compositing is usually preferred when effluent flow volume varies 

appreciably over time. The equipment and instrumentation for flow-proportional 

compositing have more downtime due to maintenance problems.

• When manually compositing effluent samples according to flow where no flow measuring 

device exists, use the influent flow measurement without any correction for time lag. The 

error in the influent and effluent flow measurement is insignificant except in those cases 

where extremely large volumes of water are impounded, as in reservoirs.

Use composite samples when:

1. Determining average concentrations, or

2. Calculating mass loading/unit of time.

There are numerous cases where composites are inappropriate. Samples for some parameters such 

as pH, residual chlorine, temperature, cyanides, volatile organics, microbiological tests, oil and 

grease, and total phenols should not be composited. They are also not recommended for sampling 

batch or intermittent processes. Grab samples are needed in these cases to determine fluctuations 

in effluent quality.

For bioassays, composite samples are used unless it is known that the effluent is most toxic at a 

particular time. Some toxic chemicals are short-lived, degrading rapidly, and will not be present 

in the most toxic form after lengthy compositing even with refrigeration or other forms of 

preservation. Require grab samples for bioassays to be taken under those circumstances.
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In the absence of an expressed sampling protocol in regulation, the duration of the compositing 

time period and frequency of aliquot collection is established by the permit writer. Whether 

collected by hand or by an automatic device, the time frame within which the sample is collected 

should be specified in the permit. The number of individual aliquots which compose the 

composite should also be specified. NPDES application requirements specify a minimum of four 

aliquots for non-stormwater discharges lasting four or more hours. The sampling procedures for 

general pretreatment specify a minimum of twelve aliquots for 24-hour composites.

1.6.3 Continuous Monitoring

Continuous monitoring is another option for a limited number of parameters such as TOC, 

temperature, pH, conductivity, fluoride and dissolved oxygen.

Reliability, accuracy and cost vary with the parameter. Continuous monitoring can be expensive, 

so continuous monitoring will usually only be an appropriate requirement for the most significant 

dischargers with variable effluent. The environmental significance of the variation of any of these 

parameters in the effluent should be compared to the cost of continuous monitoring equipment 

available.

The regulations concerning pH limits allow for a period of excursion when the effluent is being 

continuously monitored (40 CFR 401.17). Continuous monitoring or labor-intensive periodic 

monitoring by grab sampling is necessary where pH excursions are allowed.

1.7 Determining the Sampling Location

The permit writer must determine permanent sampling locations, and identify them in the 

monitoring requirements. The permit applicant should provide a description of the effluent outfall 

location and in most cases, a line drawing and description of the flows and processes involved in 

wastewater treatment.

The point at which a sample is collected can make a large difference in the monitoring results. 

Important factors to consider in selecting the sampling station are:

• The flow at the sampling station should be measurable.

• The sampling station should be easily and safely accessible.

• The sample must be truly representative of the effluent during the time period which is 

monitored. The wastewater should be well mixed, such as near a Parshall flume or at a 

location in a sewer with hydraulic turbulence. Weirs tend to enhance the settling of solids 

immediately upstream and the accumulation of floating oil or grease immediately 

downstream. Such locations should be avoided for sampling.

It is often convenient to combine a flow measurement station with a sampling station. When 

flumes are used for flow measurement, the sample is usually well mixed.
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Effluent samples should be collected at the most representative site downstream from all entering 

waste streams. Sampling of POTWs for conventional pollutants and nutrients (except for BOD) 

should be collected downstream of any chlorination or disinfection units.

Separate samples should be taken if two outfalls are used and the effluent which enters the outfalls 

comes from different parts of the plant.

If there is no practical way to sample the effluent, the permit must require that the permittee 

establish an appropriate effluent monitoring station for determining flow rates and compliance 

with effluent limits.

The location of sample sites for receiving environment and benthos testing vary with each 

discharger and the dimensions of any mixing or sediment impact zone. More detail can be found 

in Section 6.

1.8 Quality Assurance/Quality Control

The data gathered in self monitoring programs provides information to decision makers on the 

quantity and quality of the effluent, the adequacy of operation and maintenance procedures, and 

the potential for discharges to affect receiving waters. Given the importance of monitoring data in 

assessing compliance and in assessing whether receiving waters may be affected, it is important 

that the processes involved in generating monitoring data be standardized, comparable among 

dischargers, and free from practices that would generate inaccurate or faulty data. A quality 

assurance or quality control program can help to ensure that data meet the above requirements.

"Quality assurance (QA) has been described as a system of activities that assures the 

producer or user of a product or a service that defined standards of quality with a stated 

level of confidence are met. Quality control (QC) differs in that it is an overall system 

of activities that controls the quality of a product or service so that it meets the needs of 

users. In other words, QC consists of the internal (technical), day to day activities, such 

as use of QC check samples, spikes, etc., to control and assess the quality of the 

measurements, while QA is the management system that ensures an effective QC 

system is in place and working as intended." (Keith, 1991) 

The objective of quality assurance for a self-monitoring program is to ensure the production and 

reporting of valid results. Valid and useful results are those that answer a question or provide a 

basis on which a decision can be made (Keith, 1991). Within Ecology's regulation of selfmonitoring data, the QA of a discharger's self-monitoring program is examined by different 

groups within Ecology. The EA Program's laboratory accreditation group oversees the QA/QC 

program for laboratories. Permitted dischargers are required to have their samples analyzed by 

labs accredited by the state. As part of the laboratory accreditation process, labs must develop an 

approved QA/QC plan that addresses laboratory operations. In addition, with few exceptions, 
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dischargers will use specified and standardized methods (40 CFR 136) to measure compliance 

with permit limitations. These methods are specified in discharge permits by reference to use of 

Part 136 methods.

In most cases, dischargers are not required to submit formal QA plans addressing sampling 

technique because sampling technique is generally uncomplicated, and can be easily checked by 

inspectors during Ecology inspections. Poor sampling technique is likely to result in sample 

contamination, which is generally to the disadvantage of dischargers. However, because some 

dischargers with low dilution now have water quality based effluent limits that are in the low parts 

per billion range, it is important to ensure that sample collection techniques do not introduce 

contamination, and that data can be verified (e.g., by use of appropriate blank samples). 

Contamination can be introduced by improper cleaning of sampling vessels, during sampling, or 

during handling and analysis of the sample in the lab. The laboratory that is preparing sampling 

bottles and analyzing samples will generally depend on the person who does samples to minimize 

contamination in the field. If you suspect that sample contamination is occurring at any point in 

the process of sampling and analysis, you should first discuss your concerns with the discharger. 

In most cases, since sample contamination is not to the benefit of the discharger, they will try to 

determine on their own if a problem exists (e.g., a small corroded area on a composite sampler at 

one municipal discharge was adding from 10-20 ppb of excess nickel to effluent samples, but was 

found after several weeks of examining all possible sources of contamination). If this is not 

effective, you may need to require a formal Ecology inspection with split samples analyzed by the 

state, or even a formal requirement for a full QA/QC sampling plan. When assessing potential 

sample contamination, it is also a good idea to discuss the contaminants with the staff at the 

Manchester Environmental Laboratory to attempt to rule out common laboratory contaminants as 

being present in the discharge. 

Flow data is not compromised by sample contamination, but data verification is important to 

consider when collecting flow measurements during inspections. In some cases flow measurements 

cannot be safely verified because of the position of the flow measurement device. In other cases the 

flow measurement device may not be properly constructed, so there is doubt about the 

measurements produced by the device (e.g., a weir may not be level, thus the original engineering 

calculations used to gauge flow on the weir may not be appropriate for use with the structure as 

built). Data verification for flow devices should be approached carefully, because in many cases 

the cost of verification can be great. In some cases documentation showing proper calibration can 

be presented as a flow verification (inexpensive option), but in other cases complex models may be 

the only way to provide verification. If there is reason to believe that flow data is suspect, the 

permit manager should evaluate whether flow data is a highly critical parameter to verify for the 

discharger at the time. If the discharge is nearing capacity, approaching a water quality based 

concentration limit, or mass loading limits (total mass per day or year) have been imposed on the 

discharge, measurement of flow may be critical. In those cases, flow verification, even if costly, 

should be strongly considered, and may be required. The permit writer should use his/her best 

professional judgment when making the determination of whether a flow verification is needed. 
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If there is a need for the discharger to submit a QA/QC plan for all or a portion of a selfmonitoring program (e.g., if contamination is suspected), the following elements should be 

included in the plan:

1. Project Description - Outlines the scope of the monitoring project.

2. Responsibilities - Identifies the responsibilities of personnel in implementing the QA plan.

3. Quality Assurance Objectives - Identifies the monitoring objectives including quantitative 

objectives for generating and measuring data in terms of accuracy, precision, completeness, 

representativeness, and compatibility.

4. Sampling Procedures - Describes the following for each measurable variable:

• Guideline used to select sample site.

• Specific sampling procedures (including chain of custody requirements).

• Information for special containers, conditions for preparation of sampling equipment 

and containers.

• Sampling preservation methods and holding times.

5. Calibration Procedures, References, and Frequencies - Identifies the procedures for properly 

maintaining the accuracy and precision of field and laboratory equipment, and for properly 

obtaining, using, and storing analytical standards.

6. Analytical Procedures - Identifies standard procedures for sample analysis by reference, and 

describes specialized procedures in detail.

7. Data Reduction, Validation, and Reporting - Provides the data reduction scheme for 

measurement data, including equations used for calculations, criteria used to validate data 

integrity, and methods used to identify and treat abnormal data or statistical outliers.

8. Internal Quality Control Checks and Frequency - Identifies all procedures used to assess 

quality during sample collection and analysis, including the uses and frequency of replicates, 

spikes, blanks, surrogate samples or reference materials, control charts, and calibration 

materials.

9. Quality Assurance Audits - Describes procedures used to determine the effectiveness of the 

QA program and its implementation.
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10. Preventative Maintenance Procedures and Schedules - Details procedures for maintaining 

equipment in a ready state, including lists of critical spare parts.

11. Procedures and Deliverables for Data Validation - Provides a compilation of routine data 

analysis techniques used to assess data precision and accuracy, representativeness, 

comparability, and completeness of the measured parameters.

12. Corrective Action - Identifies predetermined limits for data acceptability beyond which 

corrective action is necessary, the specific corrective action to be taken for out-of-control data 

(including action in response to system and performance audits), and the individual 

responsible for each corrective action.

Additionally, the QA Section of the EA Program has prepared an Ecology publication "Guidelines 

and Specifications for Preparing Quality Assurance project Plans", which specifically addresses 

issues faced by Ecology when sampling in Washington State. Permit writers should consult these 

guidelines as well as consider the items listed above.

Federal regulations require laboratories used by major NPDES dischargers to analyze proficiency 

testing (PT) samples (i.e., they must participate in the DMR-QA program) using the analytical 

methods in 40 CFR Part 136. The EA Program’s Lab Accreditation Section can provide a list of 

accredited laboratories and the analyses they are accredited for to the permit writer. Alternatively, 

Scopes of Accreditation for accredited labs can be accessed at 

http://www.ecy.wa.gov/apps/eap/acclabs/labquery.asp. Additional sampling information is given 

in Handbook for Sampling and Sample Preservation of Water and Wastewater, EPA 

600/4-82-029). Flow measurement is discussed in Monitoring Industrial Wastewater (EPA, 

1973). By specifying, in a permit, a particular method to use for self-monitoring, any QA/QC 

procedures included in that method become permit requirements. Whenever QA/QC standards are 

not met, the analyses should be repeated until the specified level of performance is met. The 

reasons for inadequate QA/QC should be explained by the permittee when retesting is not 

possible. The EA Program or Headquarters staff should be contacted to help review this 

information.

1.9 Data Management

The format of data submitted to Ecology can directly influence how that data is interpreted, 

therefore it is critical that data be given to Ecology in a format most suitable for the data's intended 

use. The information obtained by the permittee's self-monitoring program is submitted to the 

permitting agency using a Discharge Monitoring Report (DMR) with a standardized format. The 

DMR is submitted to Ecology on a regular schedule stated in the permit. Special reports may be 

required in a permit, in which case the permit writer must designate the frequency and format of 

the report. In all cases, the data must be presented in an organized and clear manner, and if 
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necessary, supporting data may be required (e.g., duplicate measures, spike recoveries, etc.). 

These reporting requirements should be specified in the special conditions section of the permit, 

enforcement order, or application requirements notification.

Reporting requirements for WET are given in the canary book (Ecology Publication No. WQ-R95-80, Laboratory Guidance and Whole Effluent Toxicity Test Review Criteria). This manual 

which provides instructions to labs and includes our detailed test review criteria, and is now 

referenced in the acute and chronic WET language in the permit shells. Dischargers should 

instruct labs to follow the instructions for both testing and reporting in the canary book and in the 

EPA toxicity test manuals referenced in the permit language. WET test reports are rejected for 

serious omissions or deviations from these instructions. The test review system has been in place 

for several years now and the labs are familiar with it and its consequences.

The other routine monitoring data required in the permit will be entered into a computerized 

database located at each Region's office. This database is called the Water Permit Life Cycle 

System (WPLCS). The WPLCS will generate compliance reports determining whether or not 

dischargers are in compliance. Even though the WPLCS will generate compliance reports, the 

permit manager may still find it useful to inspect the DMRs because of the information they 

contain, including data on effluent variability and trends in changing effluent quality. All special 

reports should be reviewed by the permit writer or appropriate staff at Headquarters or at the EA 

Program.

Other considerations concerning data interpretation (e.g., quantitation levels) are discussed in 

Chapter VI-4 Effluent Limits Below Quantitation.

2. POTW MONITORING

Regulatory agencies are more involved in the day-to-day operation of POTWs than with industrial 

plants. Some examples of this are the regulatory requirements for operation and maintenance 

(O&M) plans and O&M inspections, operator certification requirements, and historical process 

control monitoring requirements. This involvement is largely due to the history of public funding 

for construction of POTWs and the protection of that investment.

POTWs are a single, large category of discharger for which monitoring guidance has evolved over 

time. The tests, sample points, frequencies, and sample types listed in the accompanying tables 

represent the level of monitoring which seeks to balance the minimum cost to the discharger while 

assuring the permit manager that the POTW is being operated correctly and is meeting the 

conditions of its permit.

This section builds on the previous General Considerations section to provide the permit writer 

more specific guidance for writing a permit for a POTW. Land application monitoring 

information is covered in Implementation Guidance for the Ground Water Quality Standards
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(Ecology 96-02). The following information is included in this section:

• Influent and Effluent Monitoring for:

- Compliance with limits, treatment efficiency,

- Sludge,

- Pretreatment requirements, and

- Whole Effluent Toxicity Testing

• Process Control 

- Use in response to significant noncompliance with limits

- If required, implement in a permit, with an Order or as a requirement for O&M Manual 

update

• Sludge Monitoring

- Satisfy new Part 503 Regulation requirements

- Satisfy pretreatment requirements

• Combined Sewer Overflows

- Provides guidance on CSOs monitoring

- Defines CSO event

• Monitoring Bypasses

- Provides guidance on sampling bypassed flows

2.1 Influent and Effluent Monitoring of POTWs

2.1.1 General

Tables XIII-2(A-E) contain the recommended minimum influent, effluent, and sludge monitoring 

frequencies for various types of POTWs. These tables are organized according to treatment 

method and design flow. For clarity, each table is divided into several types of monitoring such as 

compliance, sludge, WET testing, and pretreatment. 

For conventional pollutants, the minimum recommended frequency for compliance monitoring in 

Tables XIII-2 (A-E) is 1/week. This minimum frequency is suggested for two reasons:

1. It is a reasonable minimum frequency for monitoring compliance with effluent limits. 

2. It fulfills the implicit weekly reporting requirement associated with the seven-day average 

discharge standards described in Chapter 173-221 WAC and 40 CFR 133.102. ""Seven-day 

average" means the arithmetic mean of pollutant parameter values for samples collected in a 

period of seven consecutive days."
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Since the tables represent the minimum recommended frequencies rather than the median

recommended frequencies, it is more likely that more monitoring will be required than less. If 

significantly more or less than the recommended monitoring is required for a particular facility, 

this should be discussed in the fact sheet. Reasons for more monitoring may include:

• Frequent upset.

• Poor O&M performance.

• Discharge to a sensitive environment.

• A coefficient of variation is greater than 0.6 (EPA, 1991).

• Periods of significant non-compliance.

Reasons for less monitoring may include:

• POTW operating significantly below effluent limits

• Non-continuous discharge (seasonal)

• Long detention time (e.g., lagoons)

• Good O&M performance

• Good history of compliance with limits (inspection reports, DMRs)

POTWs are required to sample both the influent and effluent streams for BOD5 and Total 

Suspended Solids in order to determine the removal efficiencies. Secondary treatment is 

generally defined as 85% removal of TSS and BOD5 with a maximum limit of 30 μg/l each 

although exceptions do exist for waste stabilization ponds and trickling filters as discussed in 

Chapter V, Municipal Effluent Limitations and Other Requirements.

Flow may be measured as either inflow or outflow. The sampling point chosen should be 

specified in the permit. However, for some lagoon systems, due to rainfall or evaporation, both 

influent and effluent flow measurement may be required. Also for lagoons, effluent flow 

measurements are preferred for determining compliance with effluent limits.

The permit writer should attempt to identify the period of peak discharge into the POTW from 

the commercial and industrial users expected to be discharging any pollutants of concern and 

then specify monitoring frequencies and sample types that will include the period of peak 

industrial discharge. Monitoring during times of peak commercial and industrial discharge will 

increase the likelihood of detecting the presence of any toxic pollutants which are or maybe of 

concern.

The choice of sampling techniques for chemical-specific analyses is dependent on the type of 

compounds to be measured (e.g., grab sampling for volatile organic compounds, pH, cyanide, oil 

and grease, dissolved oxygen and phenols). More guidance is provided in the Laboratory Users 

Manual, Ecology, 1991b, the Handbook for Sampling and Sample Preservation of Water and 
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Wastewater, EPA-600/4-82-029, EPA, 1982b, the Water Quality Program Inspection Manual, 

Ecology, 1992, Standard Methods for Examination of Water and Wastewaters, 17th Edition, pp. 

1-37 and 1-38, and Chapter XIII-1.5 & 1.6 of this manual.

2.1.2 Influent Monitoring

The influent must be sampled (BOD5,TSS) and measured (flow) ahead of the point of entry of 

recycle flows such as digester supernatant, filter backwash, sludge thickener subnatant or 

supernatant, and any other in-plant recycle flows. Also, influent samples should generally be 

collected just downstream of the coarse screens or grit chamber but may include sampling points 

such as:

• The upflow siphon following a comminutor (in absence of grit chamber).

• The upflow distribution box following pumping from main plant wet well.

• Aerated grit chamber.

• Flume throat (assuming no impact on flow measurement).

• Pump wet well.

BOD5 and TSS monitoring frequency in the influent should usually correspond with effluent 

monitoring frequency to determine compliance with percent removal requirements. However, 

influent monitoring may sometimes be at a higher frequency than effluent monitoring such as 

when influent flows into a lagoon cannot match the evaporative loss.

For parameters other than BOD5 and TSS, any influent monitoring frequency should consider the 

variabilities in wastewater flow and characteristics, the quantity and quality of industrial input to 

the facility, and if the influent monitoring is being required for local pretreatment limits 

development or updating.

If multiple waste streams enter the plant and a representative sample cannot be collected, a flowproportional composite sample of the various inflows may be used for influent analysis.

2.1.3 Effluent Monitoring

Effluent samples for POTWs should be collected downstream of any chlorination/dechlorination 

units or other disinfection units, with the exception of BOD and perhaps WET testing.

Post-chlorination BOD5 samples should be dechlorinated and reseeded as described in Standard 

Methods for the Examination of Water and Wastewater, 18th, 19th, or 20th Edition. The sample for 

the BOD5 test, usually a refrigerated composite, may be drawn prior to chlorination to avoid the 

inhibiting effect of chlorine on biological oxidation. This would require two effluent composite 

samplers (pre- and post-chlorination) which may represent a significant expense for some smaller 

POTWs.
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WET testing samples should be taken following the protocols in Section 4 of this Chapter.

Separate samples should be taken if multiple effluent outfalls representing different treatment 

modes are present. For example, a parallel system with several treatment processes with different 

treatment efficiency requirements such as a trickling filter or lagoons and aeration basin, RBC, etc. 

Multiple discharges from equivalent treatment processes need not be analyzed separately provided 

there is a common effluent outfall that represents the combined total effluent discharge.

A lagoon with a long retention time may require lagged collection of effluent samples relative to 

influent samples for the purpose of determining compliance with the percent removal requirement, 

particularly if a review of historical data indicates a wide seasonal or periodic variation in influent 

concentrations (e.g., seasonal industrial input). A dye study should be used to decide whether it 

makes sense to require a lag time or not.

Samples should be collected during "typical" discharge periods. An evaluation of the condition of 

the facility's treatment system can be made by comparing the effluent sample concentrations of 

BOD, TSS, and other pollutants to long-term historical averages and/or permitted values for these 

parameters.
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Table XIII-2A. RECOMMENDED MINIMUM MONITORING FOR POTWs 

DISCHARGING TO SURFACE WATERS

For: 1. All Treatment Plants < 0.1 MGD Average Design Flow

Monitoring Type

(Plant category)

Test Sample Pt. Frequency Sample Type

Compliance

(1)

Flow, mgd Infl. or Fin. Eff. Continuous Measurement

" pH Final effluent 5/week Grab

" BOD5 Infl.; Fin. Eff.a 1/week; 

1/week

24-hr. 

Composite

" TSS Infl.; Fin. Eff. 1/week; 

1/week

24-hr. 

Composite

" Tot. Res. Cl2 Chlorinated Eff.f

, 

Fin. Eff.g

5/week Grab

" Fecal 

Coliform

Fin. Eff. 1/week c Grab

Sludge

See Chapter 

XIII-2.3,

See Chapter XIII2.3, Table XIII-3See Chapter 

XIII-2.3,

WET Test. See Chap. 

XIII-4

Final Eff.

(See also reapplication requirements for NH3, TKN, NO2+NO3, O+G, Total P, and TDS in 

Chapter III, Section 3)
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Table XIII-2B. RECOMMENDED MINIMUM MONITORING FOR 

POTWs DISCHARGING TO SURFACE WATERS--

For: 1. Trickling Filter Plants < 0.5 MGD Average Design Flow

 2. RBC Plants < 0.5 MGD Average Design Flow

 3. Sewage Lagoons < 0.5 MGD Average Design Flow

Monitoring Type

(Plant category)

Test Sample Pt. Frequency Sample Type

Compliance

(1,2,3)

Flow, mgd Infl. or Fin. Eff. Continuous Measurement

" pH Final effluent Daily Grab

" BOD5 Infl.; Fin. Eff.a 1/week; 

1/week

24-hr. Composite

" TSS Infl.; Fin. Eff. 1/week; 

1/week

24-hr. Composite

" Tot. Res. Cl2 Chlorinated Eff.f

, 

Fin. Eff.g

Daily Grab

" Fecal 

Coliform

Fin. Eff. 1/week c Grab

Sludge

(1,2,3)

See Chapter 

XIII-2.3,

See Chapter XIII2.3, Table XIII-3See Chapter 

XIII-2.3,

Sludge

(3)

Sludge Depth Each Cell, 

numerous 

locations

2/year Measurement

WET Test. See Chap. 

XIII-4

Final Eff.

(See also reapplication requirements for NH3, TKN, NO2+NO3, O+G, Total P, and TDS in 

Chapter III, Section 3)
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Table XIII-2C. RECOMMENDED MINIMUM MONITORING FOR 

POTWs DISCHARGING TO SURFACE WATERS--

For: 1. Trickling Filter Plants 0.5-2.0 MGD Average Design Flow

2. RBC Plants 0.5-2.0 MGD Average Design Flow

3. Sewage Lagoons > 0.5 MGD Average Design Flow

4. Activated Sludge Plant < 2.0 MGD Average Design Flow

5. Oxidation Ditches

Monitoring 

Type

(Plant category)

Test Sample Pt. Frequency Sample Type

Compliance

(1,2,3,4,5)

Flow, mgd Infl. or Fin. Eff. b Continuous Measurement

" pH Final effluent Daily Grab

" BOD5 Infl.; Fin. Eff.a 2/week; 2/week 24-hr. Composite

" TSS Infl.; Fin. Eff. 2/week; 2/week 24-hr. Composite

" Tot. Res. Cl2 Chlorinated Eff.f

, Fin. Eff.g Daily Grab

" Fecal Coliform Fin. Eff. 2/week c Grab

Sludge

(1,2,3,4,5)

See Chapter XIII2.3See Chapter XIII-2.3, See Chapter XIII-2.3,

Sludge (3)

Sludge Depth Each Cell, numerous locations 2/year Measurement

WET Test.

(1,2,3,4,5)

See Chapter XIII-4 Final Eff.

(See also reapplication requirements for NH3, TKN, NO2+NO3, O+G, Total P, and TDS in Ch III, Section 6)

Pretreatment

(1,2,3,4,5)

(see 2.1.4)

Oil and grease, pH, 

priority pollutant 

metals, and cyanide

Priority pollutant 

Influent

Final effluent

Sludge

Quarterlyd

Quarterlyd

1 taken within 30 days 

after influent sample

24 hour compositee

except grab for O&G

24 hour compositee

Grab

24 hour compositee
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Monitoring 

Type

(Plant category)

Test Sample Pt. Frequency Sample Type

organics and other 

toxic pollutants 

likely to be present

Influent

Final effluent

Sludge

Annuallyd

Annuallyd

1 taken within 30 days 

after influent sample

24 hour compositee

Grab
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Table XIII-2D. RECOMMENDED MINIMUM MONITORING FOR 

POTWs DISCHARGING TO SURFACE WATERS--

For: 1. Trickling Filter Plants > 2.0 MGD Average Design Flow

2. RBC Plants > 2.0 MGD Average Design Flow

3. Activated Sludge Plant 2.0 - 5.0 MGD Average Design Flow

Monitoring Type

(Plant category)

Test Sample Pt. Frequency Sample Type

Compliance

(1,2,3)

Flow, mgd Infl. or Fin. Eff. Continuous Measurement

" pH Final effluent Daily/

Continuous

Grab/

Measurement

" BOD5 Infl.; Fin. Eff.a 3/week; 

3/week

24-hr. Composite

" TSS Infl.; Fin. Eff. 3/week; 

3/week

24-hr. Composite

" Tot. Res. Cl2 Chlorinated 

Eff.f, Fin. Eff.g

Daily Grab

" Fecal Coliform Fin. Eff. 3/week c Grab

Sludge

(1,2,3)

See Chapter 

XIII-2.3,

See Chapter 

XIII-2.3,

See Chapter 

XIII-2.3,

WET Test.

(1,2,3)

See Chapter 

XIII-4

Final Eff.

(See also reapplication requirements for NH3, TKN, NO2+NO3, O+G, Total P, and TDS in 

Ch III, Section 3)

Pretreatment

(1,2,3)

(see 2.1.4)

Oil and grease, 

pH, priority 

pollutant metals, 

and cyanide

Influent

Final effluent

Quarterlyd

Quarterlyd

24 hour 

compositee

, 

except grab for 

O&G
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Monitoring Type

(Plant category)

Test Sample Pt. Frequency Sample Type

Pretreatment

(1,2,3)

(see 2.1.4)

Priority pollutant 

organics and 

other toxic 

pollutants likely 

to be present

Sludge

Influent

Final effluent

Sludge

1 taken 

within 30 

days after 

influent 

sample

Annuallyd

Annuallyd

1 taken 

within 30 

days after 

influent 

sample

24 hour 

compositee

Grab

24 hour 

compositee

24 hour 

compositee

Grab
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Table XIII-2E. RECOMMENDED MINIMUM MONITORING FOR 

POTWs DISCHARGING TO SURFACE WATERS

FOR: 1. ACTIVATED SLUDGE PLANTS > 5.0 MGD AVERAGE DESIGN FLOW

Monitoring Type

(Plant category) Test Sample Pt. Frequency Sample Type

Compliance

(1)

Flow, mgd Infl. or Fin. Eff. Continuous Measurement

" pH Final effluent Continuous Measurement

" BOD5 Infl.; Fin. Eff.a 5/week; 5/week 24-hr. 

Composite

" TSS Infl.; Fin. Eff. 5/week; 5/week 24-hr. 

Composite

" Tot. Res. Cl2 Chlorinated Eff.f

, 

Fin. Eff.g

Daily Grab

" Fecal Coliform Fin. Eff. Daily c Grab

Sludge

(1)

See Chapter XIII2.3,See Chapter XIII2.3,See Chapter 

XIII-2.3,

WET Test.

(1)

See Chapter XIII4Final Eff.

(See also reapplication requirements for NH3, TKN, NO2+NO3, O+G, Total P, and TDS in Ch

III, Section 3)

Pretreatment

(1)

(see 2.1.4)

Oil and grease, 

pH, priority 

pollutant metals, 

and cyanide

Priority pollutant 

Influent

Final effluent

Sludge

Quarterlyd

Quarterlyd

1 taken within 

24 hour 

compositee

, 

except grab 

for O&G.

24 hour 

compositee

Grab
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Monitoring Type

(Plant category) Test Sample Pt. Frequency Sample Type

Pretreatment

(1)

(see 2.1.4)

organics and 

other toxic 

pollutants likely 

to be present

Influent

Final effluent

Sludge

30 days after 

influent sample

Annuallyd

Annuallyd

1 taken within 

30 days after 

influent sample

24 hour 

compositee

24 hour 

compositee

Grab

NOTES:

a

. Samples for BOD5 analysis may be taken before or after the disinfection process. If taken after, the 

sample must be dechlorinated and reseeded.

b

. Influent flow must be provided if the permittee requests relief from 85% removal requirement as 

allowed in WAC 173-221-050. Influent flow monitoring is recommended for all lagoons to track 

influent loading.

c

. Sampled concurrently with Total Residual Chlorine (before dechlorination, if applicable).

d

. The days selected for sampling shall be rotated annually or quarterly (e.g., first quarter sample 

Monday, second quarter sample Tuesday, etc.). If the facility has undergone screening and 

prioritization for human health criteria the testing must be done during a wet season and a dry season.

e

. Cyanide, Volatile Organics and Phenols must be taken as a minimum of 4 grab samples and 

separately analyzed in place of each 24 hour composite.

f

. Sampled before dechlorination, if applicable.

g

. Sampled after dechlorination, if applicable.

DEFINITIONS:

"Continuous" means readings are being taken and recorded at all times.

"Daily" in these tables is equivalent to 7 days/week.
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"Final Effluent" means wastewater which is exiting, or has exited, the last treatment process or operation. 

Typically, this is after or at the exit from the chlorine contact chamber or other disinfection process.

"Grab" means an individual sample collected in less than fifteen minutes.

"Influent" means the raw sewage flow excluding any sidestreams returned to the headworks of the plant. 

"24-hour composite" means a series of individual samples collected over a 24 hour period into a single 

container, and analyzed as one sample. 

2.1.4 Pretreatment

2.1.4.1 Monitoring for local limit development

The federal pretreatment regulation 403.8(f)(4) requires pretreatment POTWs to develop local 

pollutant discharge limitations for any pollutants which cause Pass Through or Interference, or 

demonstrate they are not necessary. This requirement to develop local limits becomes Ecology's 

in the non-delegated pretreatment POTWs.

All pretreatment POTWs, both delegated and non-delegated, are required to have influent, 

effluent, and sludge sampled for toxic pollutants in order to characterize the industrial input and to 

determine if pollutants are or have the potential to interfere with the treatment process or pass 

through the plant to sludge or the receiving water. The monitoring data are used by Ecology or the 

municipality to develop technically defensible local limits which commercial and industrial users 

must meet.

A delegated POTW must conduct monitoring to support the development of local limits as a 

condition of its POTW Pretreatment Program. For non-delegated pretreatment POTWs, the 

permit writer may choose to have the POTW conduct the monitoring for Ecology so that local 

limits can be developed by Ecology for the non-delegated POTWs. Measurement of pH, Oil and 

Grease, priority pollutants (metals and organics), and any other pollutants likely to be present from 

commercial or industrial users are used as indicators to determine the need for local limits.

The list of priority pollutants to be monitored for is contained in 40 CFR part 122, Appendix D, 

Table II (organics) and Table III (metals and cyanide). Other toxic pollutants that should be 

monitored for if likely to be present are listed in 40 CFR part 122, Appendix D, Table V.

In addition to quantifying pH, oil and grease, and all priority pollutants, a reasonable attempt 

should be made to identify all other substances and quantify all organic pollutants shown to be 

present by gas chromatograph/mass spectrometer (GC/MS) analysis per 40 CFR 136, Appendix. 

A, Methods 624 and 625. Determinations of pollutants should be attempted for each fraction 

which produces identifiable spectra on total ion plots (reconstructed gas chromatograms). 

Determinations should be attempted from all peaks with responses 5% or greater than the nearest 
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internal standard. The 5% value is based on internal standard concentrations of 30 μg/l, and must 

be adjusted downward if higher internal standard concentrations are used or adjusted upward if 

lower internal standard concentrations are used. Non-substituted aliphatic compounds may be 

expressed as total hydrocarbon content. Identification shall be attempted by a laboratory whose 

computer data processing programs are capable of comparing sample mass spectra to a 

computerized library of mass spectra containing at least sixty-thousand (60,000) compounds, with 

visual confirmation by an experienced analyst. (Note: The current National Institute of Standards 

and Technology GC/MS computerized library of mass spectra, covers 62,000 compounds. The 

phone number of the NIST Office of Standards Data is 301-975-2208). For all detected 

substances which are determined to be pollutants, additional sampling and appropriate testing shall 

be conducted to determine concentration and variability, and to evaluate trends (refer to 

"Determining Reasonable Potential", Chapter VI).

Local limits development requires one year of data collection. To develop local limits, the permit 

writer should require that each pretreatment POTW establish a data base from sampling and 

analysis over one year. Sampling will include both wet and dry weather flows. The sample 

locations, types, and frequencies are specified in the matrix below and apply to all pollutants as 

discussed in this section on monitoring for local limit development.

Matrix of monitoring requirements for local limits development

Location Sample Type Frequencyb

Raw Influent 24 hour compositea Once quarterly

Primary Clarifier 

Effluent

24 hour compositea Once quarterly concurrently 

with influent

Final Effluent 24 hour compositea Once quarterly concurrently 

with influent

Sludge Grab Taken within 30 days 

following influent sampling

*a. Cyanide, Volatile Organics, and Phenols must be taken as a minimum of 4 grab samples and separately analyzed in place of 

each 24 hour composite.

*b. The days selected for sampling shall be on days when industrial flow to the POTW is expected to be at a maximum and 

rotated quarterly (e.g., first quarter sample Monday, second quarter sample Tuesday, etc.).

At a minimum, Ecology should require all pretreatment POTWs to establish local limits for pH, 

oil and grease, the priority pollutant metals, cyanide, and phenols.

A pretreatment POTW is required to analyze for priority pollutants and any other toxic pollutants 

likely to be present. After local limits have been established, it is recommended that the 

monitoring frequency for toxic pollutants not be less than annually for toxic organics and not less 
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than quarterly for toxic metals, unless reduced monitoring can be justified. 

For additional information of identifying pollutants of concern, the permit writer is encouraged to 

consult the EPA Guidance Manual of the Development and Implementation of Local Discharge 

Limitations Under the Pretreatment Program, (EPA, 1987a).

2.1.4.2 Monitoring for updating of local limits

The federal pretreatment regulation 403.5(c) requires pretreatment POTWs to continue to update 

local pollutant discharge limitations for any pollutants which cause Pass Through or Interference. 

This requirement to update local limits becomes Ecology's in the non-delegated pretreatment POTWs.

The POTW should continue to survey its commercial and industrial users to find out what toxic 

metals and organics are reasonably expected to be present in its influent at detectable levels and 

then analyze its plant influent, effluent, and sludge for those pollutants. A reasonable attempt 

should be made to identify all other substances and quantify all pollutants shown to be present by 

GC/MS analysis per 40 CFR 136, Appendix. A, Methods 624 and 625. Determinations of 

pollutants should be attempted for each fraction which produces identifiable spectra on total ion 

plots (reconstructed gas chromatograms). Determinations should be attempted from all peaks with 

responses 5% or greater than the nearest internal standard. The 5% value is based on internal 

standard concentrations of 30 μg/l, and must be adjusted downward if higher internal standard 

concentrations are used or adjusted upward if lower internal standard concentrations are used. 

Non-substituted aliphatic compounds may be expressed as total hydrocarbon content. 

Identification shall be attempted by a laboratory whose computer data processing programs are 

capable of comparing sample mass spectra to a computerized library of mass spectra containing at 

least sixty-thousand (60,000) compounds with visual confirmation by an experienced analyst. 

(Note: The current National Institute of Standards and Technology GC/MS computerized library 

of mass spectra, covers 62,000 compounds. The phone number of the NIST Office of Standards 

Data is 301-975-2208). For all detected substances which are determined to be pollutants, 

additional sampling and appropriate testing shall be conducted to determine concentration and 

variability, and to evaluate trends (refer to "Determining Reasonable Potential", Chapter VI).

All pretreatment POTWs, both delegated and non-delegated, are required to continue monitoring 

influent, effluent, and sludge for toxic pollutants in order to characterize the industrial input and to 

determine if pollutants are or have the potential to interfere with the treatment process or pass 

through the plant to sludge or the receiving water. The monitoring data is used by Ecology or the 

municipality to update the local limits for commercial and industrial users. The remainder of this 

section on pretreatment monitoring will focus on the monitoring requirements for pretreatment 

POTWs with established local limits.

A delegated POTW must conduct monitoring to support the update of its local limits as a 

condition of its POTW Pretreatment Program. For non-delegated pretreatment POTWs, the 

permit writer may choose to have the POTW conduct the monitoring for Ecology so the local 
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limits can be updated. This section, including Tables XIII-1C, D, and E, establishes the 

monitoring that should be conducted for updating of local limits. Measurement of pH, Oil and 

Grease, priority pollutants (metals and organics), or any other pollutants of concern that are likely 

to be present from commercial or industrial users are used as indicators to determine compliance 

with local limits or the need for additional local limits.

The list of priority pollutants to be monitored for is contained in 40 CFR part 122, Appendix D, 

Table II (organics) and Table III (metals and cyanide). Other toxic pollutants which should be 

monitored for if likely to be present are listed in 40 CFR part 122, Appendix D, Table V.

A pretreatment POTW is required to analyze for priority pollutants and any other toxic pollutants 

likely to be present. After local limits have been established, it is recommended that the 

monitoring frequency for toxic pollutants not be less than annually for toxic organics and not less 

than quarterly for toxic metals, unless reduced monitoring can be justified. 

For additional information of identifying pollutants of concern, the permit writer is encouraged to 

consult the EPA Guidance Manual of the Development and Implementation of Local Discharge 

Limitations Under the Pretreatment Program, (EPA, 1987a).

2.2 Process Control Monitoring

2.2.1 General

Process control monitoring provides a check on the efficiency of the treatment process and it 

allows the operator to make adjustments to optimize the process efficiency. It was commonly 

required as a permit condition in the past, especially for those facilities having difficulty 

complying with their permit limitations. Recently however, several factors have combined to 

limit the use of process control monitoring in permits:

1. Workload considerations emphasizing effluent limit compliance. 

2. A general reluctance to initiate enforcement for noncompliance with permit process control 

parameters.

3. An internal policy memorandum suggesting process control monitoring be left out of 

permits (Stan Springer, July, 1990).

4. Language in Puget Sound Water Quality Plan Element P-8 suggesting that permit managers 

"leave most of the in-plant process control monitoring to the discretion of the discharger 

except in cases of significant non-compliance, as necessary to meet permit effluent limits."

Process control monitoring should not be required in permits. This type of monitoring is best 

implemented as part of an enforcement action for non-compliance and may be placed in an order. 

Routine process control monitoring may also be implemented through the submission of an updated 

O&M Manual. 
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-43

2.2.2 Tables XIII-3(A-M)

These tables present suggested process control monitoring for POTWs applicable to O&M 

manual revision and administrative orders. Because process control monitoring is applicable to 

relatively few facilities and tends to be facility specific, it should be a matter of the professional 

judgment of the permit manager in consultation with the permittee. Frequencies should be 

established that allow for the minimum amount of resource investment for the discharger while 

assuring the best available treatment. 

It may be advantageous to require a short-term intensive survey in order to determine appropriate 

sampling times and frequencies, and to establish possible correlations between parameters such 

as TOC and BOD5, or BOD5 and CBOD5. Daily sampling for one to two months during both the 

wet season and dry season is recommended for short-term studies. In the long run, conducting a 

short-term study may save the POTW from sampling more frequently than necessary or 

sampling during non-representative times. If a correlation is determined between TOC and 

BOD5, the permit writer may allow the permittee to substitute TOC tests for BOD5 for process 

control. This allows the operator to respond quickly with process adjustments. The COD can 

also be related empirically to BOD5 or TOC but the Manchester Laboratory has recommended 

the use of alternative equivalent methods (BOD5 and TOC) to eliminate the generation of highly 

toxic hazardous waste. A method for determining a correlation between parameters may be 

found in chapter four of the Handbook for Sampling and Sample Preservation of Water and 

Wastewater, EPA, 1982b. The topic of indicators is presented in Chapter XIII-1.

POTWs with industrial pretreatment programs or significant industrial input require more 

extensive in plant testing if current or expected concentrations of pollutants in the influent are 

detrimental to the secondary process. (e.g., priority pollutant analysis of primary effluent, in 

addition to the influent, is warranted to determine whether interference will result).

When sampling waste streams within the POTW, sampling points that are most representative of 

the process area (e.g., the common channel for secondary clarifiers) should be chosen and 

unwanted waste streams should be avoided. For branching flows, samples should be taken ahead 

of the branching point or from each stream after the branching point.

Samples on the aeration basin influent in the activated sludge process must be taken ahead of the 

point of entry of the recycle sludge. Sampling points should be located where the flow stream is 

well mixed.

In addition to sampling at the established process control locations, other unit processes may be 

sampled periodically when the variability of a parameter adversely affects the efficiency of a unit 

process. The basis for additional monitoring should be explained in the fact sheet.

Samples should be collected from channels at mid-channel and mid-depth where the flow is 

turbulent, well-mixed, and the settling of solids is minimal. Sampling should avoid skimming the 
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-44

water surface, or dragging the channel bottom. The sampling of wastewater for immiscible liquids, 

such as oil and grease, requires special attention and no specific rule can be given for selection of 

the most representative site because of wide range of conditions encountered in the field.

Sampling locations may be specified in an order or O&M Manual using a schematic flow 

diagram of the treatment process that shows the direction of flow between the processes, and 

shows all recycle flows. All sampling points should be identified on the schematic diagram. 

Include final sludge and/or other solids disposal where applicable. List all tests, sampling 

methods, frequencies, and sample types with the monitoring requirements.

The timing and frequency of sampling should be based on the relative complexity of the influent 

and the processes, as opposed to the design capacity of the facility. 

If additional information is needed for process control monitoring for individual processes, Table 

5.2 in the Handbook for Sampling and Sample Preservation of Water and Wastewater, EPA, 

1982b, includes minimum sampling recommendations for each treatment process.
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Table XIII-3A. SUGGESTED PROCESS CONTROL MONITORING 

FOR POTWs APPLICABLE TO O&M MANUAL REVISION AND 

ADMINISTRATIVE ORDERS –

FOR: ACTIVATED SLUDGE PLANTS < 2 MGD AVERAGE DESIGN FLOW

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

RAS 2/week Measurement

pH Primary Effluent

Aeration Basin

Digester(s) (An/A)a

Digester Feed Sludge (An/A)

5/week

5/week

5/week

Daily

Grab

BOD5 Primary Effluent 2/week Grab

TSS Primary Effluent

Aeration Basin(MLSS)

RAS

WAS

2/week

2/week

2/week

1/event

Grab

Dissolved O2 Influent

Final Effluent

Aeration Basin(s)

Primary Effluent

Digester (A)

Daily

Daily

Daily

5/week

Daily

Grab

Temperature Influent

Digester(s) (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

30 Minute

Settleometer 

Activated Sludge 2/week Grab

SVI, Loading Index Aeration Basin 2/week Grab

Mean Cell Res. Time Calculation 2/week

Volatile Acids Digester (An) 1/week Grab

Alkalinity Digester (An) 1/week Grab

Gas Analysis & Vol.:CO2 Digester(s) (An) Daily Grab

% Total Solids Digester Feed Sludge

Digester (An/A)

Stabilized Sludge

1/week a

1/week a

1/week a

Grab
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XIII-46

Test Sample Pt. Frequency Sample Type

Volume & lbs. to Waste WAS

Primary Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement

Additional Process Control Monitoring To Consider

Ammonia Influent

Aerators (Mixed Liquor)

Final Effluent

1/week

1/week

2/week

Grab

Nitrate Aerators (Mixed Liquor) 1/week Grab

Settleable Solids Influent

Final Effluent

2/week

2/week

Grab

Vol. Suspended Solids Aeration Basin 2/week Grab

Food/Mass Calculation 2/week

Centrifuge Spin Aeration Tank Conc.

Return Sludge Conc.

Waste Sludge Conc.

3/week

3/week

3/week

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-47

Table XIII-3B.SUGGESTED PROCESS CONTROL MONITORING FOR 

POTWs APPLICABLE TO O&M MANUAL REVISION 

AND ADMINISTRATIVE ORDERS

FOR: ACTIVATED SLUDG PLANTS BETWEEN 2 AND 5 MGD AVERAGE DESIGN 

FLOW

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

RAS Daily Measurement

pH Primary Effluent

Aeration Basin

Digester(s) (An/A)

Digester Feed Sludge 

(An/A)

Daily

Daily

Daily

Daily

Grab

BOD5 Primary Effluent 3/week Grab

TSS Primary Effluent

Aeration 

Basin(MLSS)

RAS

WAS

3/week

3/week

3/week

1/event

Grab

Dissolved O2 Influent

Final Effluent

Aeration Basin(s)

Primary Effluent

Daily

Daily

Daily

Daily

Grab

Temperature Influent

Digester(s) (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

30 Minute

Settleometer 

Activated Sludge 5/week Grab

SVI, Loading Index Aeration Basin 3/week Grab

Mean Cell Res. Time Calculation 5/week

Vol. Acids Digester (An) 2/week Grab

Alkalinity Digester (An) 2/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) Daily Grab

% Total Solids Digester Feed Sludge 3/week b Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Test Sample Pt. Frequency Sample Type

Digester(s) (An/A)

Stabilized Sludge

3/week b

3/week b

Volume & lbs. to 

Waste

WAS

Primary Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement

Additional Process Control Monitoring To Consider

Ammonia Influent

Aerators (Mixed 

Liquor)

Final Effluent

2/week

2/week

Daily

Grab

Nitrate Aerators (Mixed 

Liquor)

Clarifier Effluent

2/week

2/week

Grab

Settleable Solids Influent

Final Effluent

5/week

5/week

Grab

Vol. Suspended Solids Aeration Basin 2/week Grab

Food/Mass Calculation 3/week

Centrifuge Spin Aeration Tank Conc.

Return Sludge Conc.

Waste Sludge Conc.

5/week

5/week

5/week

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-49

Table XIII-3C.SUGGESTED PROCESS CONTROL MONITORING FOR 

POTWs APPLICABLE TO O&M MANUAL REVISION 

AND ADMINISTRATIVE ORDERS—

FOR: ACTIVATED SLUDGE PLANTS > 5 MGD AVERAGE DESIGN FLOW

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

RAS Daily Measurement

pH Primary Effluent

Aeration Basin

Digester(s) (An/A)

Digester Feed Sludge 

(An/A)

Daily

Daily

Daily

Daily

Grab

BOD5 Primary Effluent 5/week Grab

TSS Primary Effluent

Aeration 

Basin(MLSS)

RAS

WAS

5/week

5/week

5/week

1/event

Composite

Grab

Grab

Grab

Dissolved O2 Influent

Final Effluent

Aeration Basin(s)

Primary Effluent

Daily

Daily

Daily

Daily

Grab

Temperature Influent

Digester(s) (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

30 Minute

Settleometer 

Activated Sludge Daily Grab

SVI, Loading Index Aeration Basin 5/week Grab

Mean Cell Res. Time Calculation 5/week

Volatile Acids Digester(s) (An) 3/week Grab

Alkalinity Digester (An) 3/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) Daily Grab

% Total Solids Digester Feed Sludge

Digester(s) (An/A)

5/week b

5/week b

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-50

Test Sample Pt. Frequency Sample Type

Stabilized Sludge 5/week b

Volume & lbs. to 

Waste

WAS

Primary Sludge

Per Event or 

Daily

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement

Additional Process Control Monitoring To Consider

Ammonia Influent

Aerators (Mixed 

Liquor)

Final Effluent

2/week

2/week

Daily

Grab

Nitrate Aerators (Mixed 

Liquor)

Clarifier Effluent

2/week

2/week

Grab

Settleable Solids Influent

Final Effluent

Daily

Daily

Grab

Vol. Suspended Solids Aeration Basin 2/week Grab

Food/Mass Calculation 5/week

Centrifuge Spin Aeration Tank Conc.

Return Sludge Conc.

Waste Sludge Conc.

Daily

Daily

Daily

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-51

Table XIII-3D. SUGGESTED PROCESS CONTROL MONITORING 

FOR POTWs APPLICABLE TO O&M MANUAL 

REVISION AND ADMINISTRATIVE ORDERS--

For: Package Aeration Plants < 0.1 MGD Average Design Flow

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

RAS 2/week Measurement

TSS Mixed Liquor

RAS

WAS

2/week

2/week

1/event

Grab

Dissolved O2 Influent

Final Effluent

Aeration Basin(s)

Digester (A)

5/week

5/week

5/week

5/week

Grab

Temperature Aeration Basin(s) 5/week Measurement

Chlorine Usage (Effluent Disinfection) 5/week Measurement

30 Minute

Settleometer 

Mixed Liquor 2/week Grab

SVI, Loading Index Aeration Basin 2/week Grab

Mean Cell Res. Time Calculation 2/week

% Total Solids Unstabilized Sludge

Digester(s) (An/A)

Stabilized Sludge

1/month b

1/month b

1/month b

Grab

Volume & lbs. to 

Waste

WAS

Primary Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Additional Process Control Monitoring To Consider

Ammonia Influent

Aerators (Mixed 

Liquor)

Final Effluent

1/week

1/week

2/week

Grab

Settleable Solids Final Effluent 2/week Grab

Food/Mass Calculation 2/week

Centrifuge Spin Aeration Tank Conc.

Return Sludge Conc.

Waste Sludge Conc.

2/week

2/week

2/week

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-53

Table XIII-3E.SUGGESTED PROCESS CONTROL MONITORING FOR 

POTWs APPLICABLE TO O&M MANUAL REVISION 

AND ADMINISTRATIVE ORDERS

For: Oxidation Ditches

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

RAS

WAS

2/week

per event

Measurement

pH Ditch

Digester(s) (An/A)

Daily

3/week

Grab

TSS Aeration Basin 

(MLSS)

RAS

WAS

2/week

2/week

per event

Grab

Dissolved O2 Influent

Final Effluent

Aeration Basin(s)

Digester (A)

Daily

Daily

Daily

2/week

Grab

Temperature Influent Daily Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

30 Minute

Settleometer 

Activated Sludge 2/week Grab

SVI, Loading Index Aeration Basin 2/week Grab

Mean Cell Res. Time Calculation 2/week

% Total Solids Unstabilized Sludge

Digester(s) (An/A)

Stabilized Sludge

1/week b

1/week b

1/week b

Grab

Volume & lbs. to 

Waste

WAS

Primary Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-54

Additional Process Control Monitoring To Consider

Ammonia Influent

Aerators (Mixed 

Liquor)

Final Effluent

1/week

1/week

2/week

Grab

Nitrate Mixed Liquor

Clarifier Effluent

1/week

1/week

Grab

Settleable Solids Final Effluent 2/week Grab

Food/Mass Calculation 2/week

Centrifuge Spin Aeration Tank Conc.

Return Sludge Conc.

Waste Sludge Conc.

3/week

3/week

3/week

Grab

Alkalinity Influent

Clarifier Effluent

1/week

1/week

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-55

Table XIII-3F.SUGGESTED PROCESS CONTROL MONITORING FOR 

POTWs APPLICABLE TO O&M MANUAL REVISION 

AND ADMINISTRATIVE ORDERS—

FOR: TRICKLING FILTER PLANTS ≤0.5 MGD AVERAGE DESIGN FLOW

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

Trickling Filter 

Recycle

Daily Measurement

pH Primary Effluent

Filter Effluent

Digester(s) (An/A)

Digester Feed Sludge 

(An/A)

5/week

5/week

5/week

1/week

Grab

TSS Aeration Basin (MLSS)

RAS

WAS

2/week

2/week

per event

Grab

Dissolved O2 Influent

Final Effluent

Primary Effluent

Filter Effluent

Aerobic Digester (A)

Daily

Daily

2/week

2/week

Daily

Grab

Temperature Influent

Digesters (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent 

Disinfection)

Daily Measurement

30 Minute

Settleometer 

Activated Sludge 2/week Grab

SVI, Loading Index Aeration Basin 2/week Grab

Mean Cell Res. Time Calculation 2/week

Volatile Acids Digester (An) 1/week Grab

Alkalinity Digester (An) 1/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) 5/week Grab

% Total Solids Digester Feed Sludge

Digester(s) (An/A)

Stabilized Sludge

1/week b

1/week b

1/week b

Grab

Volume & lbs. to 

Waste

Waste Primary 

Sludge

Filter Sludge

Per Event

Per Event

Measurement
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Test Sample Pt. Frequency Sample Type

Sludge Blanket Depth Secondary Clarifiers Daily Measurement

Recirculation Ratio Filter Effluent/

Filter Influent

1/week Measurement

Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

1/week

2/week

Grab

Settleable Solids Trickling Filter Eff.

Final Effluent

2/week

2/week

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-57

Table XIII-3G. SUGGESTED PROCESS CONTROL MONITORING 

FOR POTWs APPLICABLE TO O&M MANUAL

REVISION AND ADMINISTRATIVE ORDERS—

FOR: TRICKLING FILTER PLANTS 0.5 TO 2.0 MGD AVERAGE DESIGN FLOW 

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

Trickling Filter 

Recycle

Daily Measurement

pH Primary Effluent

Filter Effluent

Digester(s) (An/A)

Digester Feed Sludge 

(An/A)

5/week

Daily

5/week

Daily

Grab

TSS Aeration Basin (MLSS)

RAS

WAS

2/week

2/week

per event

Grab

Dissolved O2 Influent

Final Effluent

Primary Effluent

Filter Effluent

Digester (A)

Daily

Daily

2/week

2/week

Daily

Grab

Temperature Influent

Digesters (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

30 Minute

Settleometer 

Activated Sludge 2/week Grab

SVI, Loading Index Aeration Basin 2/week Grab

Mean Cell Res. Time Calculation 2/week

Volatile Acids Digester (An) 1/week Grab

Alkalinity Digester (An) 1/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) Daily Grab

% Total Solids Digester Feed Sludge

Digester(s) (An/A)

Stabilized Sludge

1/week b

1/week b

1/week b

Grab

Volume & lbs. to 

Waste

Waste Primary 

Sludge

Filter Sludge

Per Event

Per Event

Measurement
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Test Sample Pt. Frequency Sample Type

Sludge Blanket Depth Secondary Clarifiers Daily Measurement

Recirculation Ratio Filter Effluent/

Filter Influent

Daily Measurement

Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

1/week

2/week

Grab

Nitrate Influent

Final Effluent

1/week

1/week

Grab

Settleable Solids Trickling Filter Eff.

Final Effluent

2/week

2/week

Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-59

Table XIII-3H. SUGGESTED PROCESS CONTROL MONITORING 

FOR POTWs APPLICABLE TO O&M MANUAL 

REVISION AND ADMINISTRATIVE ORDERS

For: Trickling Filter Plants > 2.0 MGD Average Design Flow

Test Sample Pt. Frequency Sample Type

Flow, mgd

Instantaneous

Trickling Filter 

Recycle

Daily Measurement

pH Primary Effluent

Filter Effluent

Digester(s) (An/A)

Digester Feed Sludge

Daily

Daily

Daily

Daily

Grab

BOD5 Primary Effluent 3/week Grab

TSS Primary Effluent 3/week Grab

Dissolved O2 Influent

Final Effluent

Primary Effluent

Filter Effluent

Daily

Daily

Daily

Daily

Grab

Temperature Influent

Digesters (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

Volatile Acids Digester (An) 2/week Grab

Alkalinity Digester (An) 2/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) Daily Grab

% Total Solids Digester Feed Sludge

Digester(s) (An/A)

Stabilized Sludge

3/week b

3/week b

3/week b

Grab

Volume & lbs. to Waste Waste Primary Sludge

Filter Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

2/week

Daily

Grab

Nitrate Influent

Final Effluent

2/week

2/week

Grab

Settleable Solids Trickling Filter Eff.

Final Effluent

3/week

Daily

Grab

Total Solids Supernatant 3/week Grab
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-61

Table XIII-3I. SUGGESTED PROCESS CONTROL MONITORING FOR 

POTWs APPLICABLE TO O&M MANUAL REVISION 

AND ADMINISTRATIVE ORDERS

For: Sewage Lagoons < 0.5 MGD Average Design Flow

Test Sample Pt. Frequency Sample Type

pH Each Cell 1/week Grab

Dissolved O2 Influent

Final Effluent

Each Cell

2/week

2/week

1/week

Grab

Temperature Influent

Each Cell

2/week

1/week

Measurement

Chlorine Usage (Effluent 

Disinfection)

Daily Measurement

Lagoon Depth Each Cell 1/week Measurement

Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

1/week

2/week

Grab

Settleable Solids Final Effluent 1/week Grab

Dissolved O2 Lagoon Profile 1/month

Precipitation/Evaporation On-site Daily
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-62

Table XIII-3J. SUGGESTED PROCESS CONTROL MONITORING FOR 

POTWs APPLICABLE TO O&M MANUAL REVISION 

AND ADMINISTRATIVE ORDERS--

For: Sewage Lagoons > 0.5 MGD Average Design Flow

Test Sample Pt. Frequency Sample Type

pH Each Cell Daily Grab

Dissolved O2 Influent

Final Effluent

Each Cell

Lagoon Profile

2/week

2/week

1/week

1/month

Grab

Temperature Influent

Each Cell

2/week

1/week

Measurement

Chlorine Usage (Effluent 

Disinfection)

Daily Measurement

Lagoon Depth Each Cell 1/week Measurement

Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

1/week

2/week

Grab

Nitrate Influent

Final Effluent

1/week

1/week

Grab

Settleable Solids Final Effluent 2/week Grab

Precipitation/Evaporation On-site Daily
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-63

Table XIII-3K. SUGGESTED PROCESS CONTROL MONITORING 

FOR POTWs APPLICABLE TO O&M MANUAL 

REVISION AND ADMINISTRATIVE ORDERS--

For: RBC Plants < 0.5 MGD Average Design Flow

Test Sample Pt. Frequency Sample Type

pH Primary Effluent

RBC Tank

Digester(s) (An/A)

Digester Feed Sludge

5/week

5/week

5/week

1/week

Grab

Dissolved O2 Influent

Final Effluent

Primary Effluent

RBC Tank Effluent

Daily

Daily

2/week

2/week

Grab

Temperature Influent

Digester(s) (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

Volatile Acids Digester (An) 1/week Grab

Alkalinity Digester (An) 1/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) 5/week Grab

% Total Solids Digester Feed Sludge

Digester(s) (An/A)

Stabilized Sludge

1/week b

1/week b

1/week b

Grab

Volume & lbs. to Waste Waste Primary Sludge

Waste RBC Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

1/week

2/week

Grab

Settleable Solids Final Effluent 2/week Grab

Soluble BOD5 Primary Effluent

RBC Tank Effluent

1/week

1/week

Grab

Load Cell 1/week Report

Dissolved O2 Profile RBC Tank 1/week Grab

Bio-Growth 

Observations

RBC 1/week
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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XIII-65

Table XIII-3L. SUGGESTED PROCESS CONTROL MONITORING 

FOR POTWs APPLICABLE TO O&M MANUAL REVISION AND 

ADMINISTRATIVE ORDERS--

For: RBC Plants 0.5-2.0 MGD Average Design Flow

Test Sample Pt. Frequency Sample Type

pH Primary Effluent

RBC Tank

Digester(s) (An/A)

Digester Feed Sludge 

(An/A)

Daily

Daily

Daily

1/week

Grab

Dissolved O2 Influent

Final Effluent

Primary Effluent

RBC Tank Effluent

Daily

Daily

2/week

2/week

Grab

Temperature Influent

Digester(s) (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

Volatile Acids Digester (An) 2/week Grab

Alkalinity Digester (An) 2/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) Daily Grab

% Total Solids Digester Feed Sludge

Digester(s) (An/A)

Stabilized Sludge

3/week b

3/week b

3/week b

Grab

Volume & lbs. to Waste Waste Primary Sludge

Waste RBC Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

1/week

2/week

Grab

Settleable Solids Final Effluent 2/week Grab

Soluble BOD5 Primary Effluent

RBC Tank Effluent

1/week

1/week

Grab

Load Cell 1/week Report

Dissolved O2 Profile RBC Tank 1/week Grab

Bio-Growth 

Observations

RBC 1/week
CHAPTER XIII. MONITORING GUIDELINES (JULY 2008)

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Table XIII-3M. SUGGESTED PROCESS CONTROL MONITORING 

FOR POTWs APPLICABLE TO O&M MANUAL REVISION AND 

ADMINISTRATIVE ORDERS--

For: RBC Plants > 2.0 MGD Average Design Flow

Test Sample Pt. Frequency Sample Type

pH Primary Effluent

RBC Tank

Digester(s) (An/A)

Digester Feed Sludge

Daily

Daily

Daily

1/week

Grab

BOD5 Primary Effluent 3/week Grab

TSS Primary Effluent 3/week Grab

Dissolved O2 Influent

Final Effluent

Primary Effluent

RBC Tank Effluent

Daily

Daily

Daily

Daily

Grab

Temperature Influent

Digester(s) (An/A)

Daily

Daily

Measurement

Chlorine Usage (Effluent Disinfection) Daily Measurement

Volatile Acids Digester (An) 2/week Grab

Alkalinity Digester (An) 2/week Grab

Gas Analysis & Vol.: CO2 Digester(s) (An) Daily Grab

% Total Solids Digester Feed Sludge

Digester(s) (An/A)

Stabilized Sludge

3/week b

3/week b

3/week b

Grab

Volume & lbs. to Waste Waste Primary Sludge

Waste RBC Sludge

Per Event

Per Event

Measurement

Sludge Blanket Depth Secondary Clarifiers Daily Measurement
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Additional Process Control Monitoring To Consider

Ammonia Influent

Final Effluent

1/week

2/week

Grab

Settleable Solids Final Effluent 2/week Grab

Soluble BOD5 Primary Effluent

RBC Tank Effluent

1/week

1/week

Grab

Load Cell 1/week Report

Dissolved O2 Profile RBC Tank 1/week Grab

Bio-Growth 

Observations

RBC 1/week

NOTE:

a

. An = anaerobic, A = aerobic

b

. "Digester feed" or "unstabilized" sludge samples may be taken when wasting from primary 

and secondary clarifiers to an aerobic digester, anaerobic digester, or sludge drying beds. 

"Stabilized sludge" samples can be taken when wasting from the sludge treatment 

recommended in the schedule.
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2.3 POTW Sludge Monitoring and Special Conditions

Sludge (biosolids) disposal and the associated monitoring is a program separate from the NPDES 

permit process and codified in 40 CFR 503. See Chapter V, Section 5. Biosolids for the current 

status of sludge and biosolids. Ecology may require sludge monitoring in permits in order to 

develop local limits under authority of 40 CFR 403 (see Chapter X, Section 6).

2.3.1 Sampling of Sewage Sludge

For flowing sludge, collect samples at the measuring weirs, or at another point where the sludge 

is well mixed.

Recommended sludge sampling locations are:

• Primary Sludge--Draw sludge from the settling tank hoppers into a well or pit before 

pumping, mix well and then collect a representative sample directly from this well. 

Alternatively, collect samples from openings in pipe near the sludge pumps or from the 

pump itself.

• Activated Sludge--Collect samples at the pump suction well, the pump or adjacent piping or 

the point of discharge of the return sludge to the primary effluent. The sample point should 

be located in a region of good agitation to maintain the suspension of solids.

• Digested Sludge--Collect samples at the point of the discharge of the digester drawoff pipe 

to the drying beds or the drying equipment. For batch sludges in digesters, collect samples 

from a mixed sink which is fed through lines attached at different levels in the digester. Be 

certain to remove sludge accumulated in the lines prior to sampling. For batch sludges in 

tanks, mix thoroughly if possible and collect samples. Collect samples at various depths and 

locations in the tank. Mix samples together prior to analysis.

• Bed Dried Sludge--Collect equal sized samples at several points within the bed without 

including sand. Mix thoroughly.

• Filtered Sludge--Collect equal size portions at the filter discharge.

The variability of sludge creates a need for frequent initial sampling in order to determine 

sampling frequencies. Samples should be composited, and should consist of at least 3 

individually obtained samples. Batch operations should be sampled at the beginning, middle and 

end of a discharge, or more frequently if high variability is suspected. Tapped lines should also 

be sampled in three separate intervals because of variations in the sludge at the drawoff source 

(i.e., clarifier, digester, etc.). Sludges treated in aerobic or anaerobic digesters have long 

detention times within the digesters. Therefore, sampling should be no more frequent than the 

detention time of the digester.
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Collect grab samples when analyzing for a parameter which is unstable, for example ammonia, 

or when analysis is required as soon as possible (e.g., sludge volume index test for activated 

sludge samples).

Analysis of composite samples is recommended in all other situations to reduce effects of sludge 

variability. Use at least three individual samples to form the composite. Wherever possible, 

collect frequent grab samples and composite according to flow rate.

Use manual sampling techniques in most situations unless special adaptations can be made for 

reliable automatic samplers. Automatic samplers have problems because of high fouling 

potential due to the solids content of the wastewater.

2.4 Combined Sewer Overflows 

WAC 173-245-090(1) requires municipalities with combined sewer overflows (CSO's) to make 

an annual report to Ecology. The annual report must discuss three topics:

1. The past year's frequency and volume of combined sewage discharged from each CSO site, 

or group of CSO sites in close proximity.

2. The past year's CSO reduction accomplishments.

3. The projects planned for the next year.

To report on #1 above, the WAC requires field monitoring. The extent of field monitoring 

necessary should be agreed upon in advance by Ecology and the municipality. The agreement 

should be formalized by incorporating the monitoring schedule within the appropriate NPDES 

permit when it is renewed.

The purposes of the monitoring are to determine whether any CSO is increasing in volume or 

frequency over the "baseline annual" condition (see WAC 173-245-020), and to determine the 

success of CSO reduction efforts. Any increase triggers a requirement to accomplish additional 

CSO reduction (WAC 173-245-090(1)(a). 

Actual flow recording equipment in each discharge location is preferable. If the discharge is not 

accessible to flow recording equipment, establish a relationship between flow in the sewer 

trunkline and flow in the discharge pipe to which the trunk overflows. If the discharger can 

establish a relationship between frequencies and quantities of overflows among a group of 

CSO's, then monitoring at one of the locations can suffice. Note that all parties should agree to 

these indirect measurements as satisfactory to determine compliance with the requirements of 

WAC 173-245-090(1). 
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As described in Chapter V, Section 3.4.2, if the municipality has chosen at-site treatment 

facilities (e.g., primary treatment and disinfection) for CSO control, the permit writer can choose 

to permit the facility under the same permit as that for the secondary treatment plant, or write a 

separate permit. In either case, the permit should include numerical limits for the discharge, flow 

capacity limits for the facility, and reporting requirements. The influent and effluent during each 

storm event must be sampled for total suspended solids. The effluent during each storm event 

must be sampled for settleable solids. The sample types can be flow- or time-weighted 

composites for the time of the discharge. Flow-weighted is preferable since it will more 

accurately estimate actual discharge quality and quantity over the discharge.

2.5 Monitoring Bypasses

When emergency bypasses are made to a different outfall or discharge point, due to high inflows 

or treatment plant problems, separate samples of the bypassed flows should be taken (Design of 

301(h) Monitoring Programs for Municipal Wastewater Discharges to Marine Waters, EPA 

430/9-82-010, EPA, 1982a).

Reporting of bypasses (and by implication monitoring) is required in 40 CFR 122.41 (l) and (m). 

Noncompliance that endangers health or the environment must be reported including "any 

unanticipated bypass which exceeds any effluent limitation in the permit." In certain emergency 

situations, when all available manpower is required to correct the problem, monitoring the 

bypass may be difficult or even impossible. However, data on the total amount of wastewater 

bypassed and limited conventional pollutants such as BOD5 and TSS may be helpful in 

understanding the effects of a bypass. Fecal coliforms in particular should be sampled because 

this test can provide both an indication of the concern to public health and, in certain situations, 

the amount of dilution afforded to the raw sewage by I/I. If the bypass occurs at a location where 

sampling is difficult, grab samples may substitute for composite samples.

3. INDUSTRIAL AND COMMERCIAL FACILITY 

MONITORING

The general considerations from part 1 of this chapter apply to all facilities discharging under the 

terms of wastewater permits issued by the department. Knowledge of the general considerations 

is necessary in order to write a permit in accordance with department guidelines. The topics 

which are expanded and exceptional for industrial and commercial facilities are presented in this 

section. This section is not intended to absolutely apply to indirect dischargers (industrial users) 

although some of the principles will apply. The topics discussed are:
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1. Influent monitoring

2. Effluent monitoring frequency

The monitoring strategy of industrial and commercial wastewaters, because of the many different 

types of facilities, is less amenable to categorization than POTW monitoring. The operational 

processes that generate wastewater and the resultant effluents are much more diverse in 

industrial and commercial facilities. Individual wastewaters vary significantly with industry type 

and facility. Also, the influent pollutants may not be treated by biological treatment. Toxic and 

nonconventional pollutants are often the factors limiting the efficiency of wastewater treatment 

for industries.

For facilities with conventional pollutants that have biological treatment similar to POTWs, use 

the monitoring frequencies of Tables XIII-1(A-E) for facilities of comparable flows. Dairy 

products and other food processors may fit this approach.

The permit must contain monitoring requirements for all pollutants in the effluent with limits. 

Regulation states that the frequency of monitoring must result in a reasonable characterization of 

the nature of the discharge. A reasonable characterization should produce the variability and 

quantity of pollutant concentrations or loadings in the effluent as described earlier in Chapter 

XIII-1.3.

3.1 Influent Monitoring

Depending on the treatment process used, it may be beneficial to require an industry to monitor 

influent to the treatment process and the facility. Influent monitoring may be necessary when 

there is a change in process or treatment technology, when the source of effluent toxicity or 

violations of permit conditions are unknown, or when the influent process water is known or 

suspected to contain unusually high concentrations of a contaminant. Evaluating the removal 

efficiencies for certain pollutants may help to trace the sources of problems, and may be used to 

determine whether a facility is meeting AKART by comparing with treatment efficiencies of 

similar facilities or treatment systems.

Effluent limits based on treatment technology can be influenced by the quality of influent. Upon 

request of the discharger, credits for input water under certain conditions may be applied to the 

calculation of pollutants generated by the industrial process. This is only the case for 

technology-based limits and does not apply to water quality based limits. The permit must 

specify the frequency and sample point for data on input water. This should be concurrent with 

sampling frequencies for effluent sampling parameters where this is a factor. (40 CFR 

122.45[g])
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3.2 Effluent Monitoring

The most prevalent monitoring required by wastewater discharge permits is the monitoring at 

point of compliance, the effluent outfall. Until recently this was usually the only monitoring 

required for industries. There are virtually no regulations and little guidance for establishing 

frequency of monitoring.

An exception is found in the pretreatment regulations, 40 CFR Part 403.12. Significant 

Industrial Users (SIUs) must report results of wastewater analyses at least semi-annually to the 

Control Authority. The Control Authority is Ecology for all state waste discharge permits issued 

to Industrial Users.

Generally the permit writer is faced with a decision to either increase frequency over past 

permits and face the wrath of the permittee or imitate the monitoring requirements from other 

accepted permits. 

Other than the SIUs, there is no fixed guidance from EPA on establishment of monitoring 

frequencies for industrial or commercial facilities.

"The decision on the monitoring frequency is case-specific and needs to 

consider a number of factors, including those listed below:

• Type of treatment process, including retention time

• Environmental significance and nature of the pollutant or pollutant parameter

• Cost of monitoring relative to the discharger's capabilities and benefit obtained

• Compliance history

• Number of monthly samples used in developing the permit limit

• Effluent variability

Based upon an array of data analyzed for both individual chemicals and whole effluent toxicity, 

and independent of other considerations, EPA has observed that ideally 10 or more samples per 

month provides the greatest statistical likelihood that the average of the various monthly values 

will approach the true monthly LTA value. In practice, however, selection of monitoring 

frequencies will need to consider the previously mentioned factors and arrive at a reasonable 

compromise of the appropriate considerations" (TSD, page 113, EPA, 1991)
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A facility not given to extreme fluctuations can be adequately regulated by selecting a frequency 

based on the single high-frequency monitoring study explained in Section XIII-1.4.3. Armed 

with enough data, the permit writer can calculate limits, establish the projected LTA, and 

determine a protective monitoring frequency capable of detecting a violation of the limits within 

a certain degree of confidence. 

When needed to establish frequency of monitoring, the single high frequency monitoring study 

should occur during the application phase of the permit but this is not always possible. Some 

dischargers are too slow or lack the initiative to supply the data outside the structure of the 

permit. In these cases the permit writer should include a requirement in the permit which 

requires the discharger to conduct the high-frequency study during a critical phase of production. 

The high frequency monitoring study should be conducted at each permit cycle for some 

dischargers, unless other factors are present. The use of DMR and other data in lieu of the high 

frequency monitoring study is explained in Section 1.3.1. High frequency monitoring during the 

fourth year of a typical five year permit cycle will supply variability information for the renewal 

of the permit.

4. WET TESTING MONITORING

4.1 Recommended Test Frequency for Characterization

Whole effluent toxicity tests are relatively expensive. Therefore, the test frequency should be 

related to the probability of any discharger having whole effluent toxicity. The following table 

ranks some factors associated with the discharger or the receiving water. A permit manager may 

use other factors to increase or decrease the rank of any discharge. A permit manager may also 

change the relative weight of the factors listed. All factors considered should be explained in the 

fact sheet.

The EPA application form 2A for municipal dischargers requires WET testing data with the 

application. The specific requirements are based on the size of the discharge. The requirements 

are given at the end of Table XIII-4.
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Table XIII-4 DISCHARGE RANKING SYSTEM

Applicant: NPDES Permit # 

 

 

 

 

A. Toxicity Likelihood (Circle the scores for all that apply.)

1. 5 points Uses, stores, produces as a product or waste, or transfers hazardous substances 

listed in 40 CFR 302.4 with a statutory code of 1 or 2 with adequate Best 

Management Practices (adequate secondary containment, good housekeeping, 

good employee training, thorough self-inspection, sufficient emergency 

planning and spill control equipment, etc.) 

2. 20 points Uses, stores, produces as a product or waste, or transfers hazardous substances 

listed in 40 CFR 302.4 with a statutory code of 1 or 2 with inadequate Best 

Management Practices (no or undersized secondary containment, poor housekeeping, little employee training, poor self-inspection, little emergency 

planning, insufficient spill control equipment, history of spills which have 

reached receiving water, etc.) 

3. 15 points Discharges in the effluent any toxic pollutant listed in Appendix D of 40 CFR 

Part 122

4. 15 points Discharger belongs in an industry category identified in 40 CFR Part 122, 

Appendix A

5. 15 points Discharger is a municipal facility which receives a discharge from any 

industry category identified in 40 CFR, Parts 405-471, unless the municipality 

has an adequate pretreatment program which establishes and enforces local 

limits

6. 10 points Any facility with toxicity detected during past acute toxicity testing based on 

less than 80% survival in 100% effluent

7. 15 points Any facility with known or suspected receiving water impacts

Sum of scores in part A: 
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Table XIII-4 . Continued

B. Potential For Impact

1. Average Annual Discharge Flow Volume (Circle one score.)*

a. 5 points Flow < 0.5 mgd

b. 10 points Flow 0.5 mgd to 12.5 mgd

c. 15 points Flow 12.5 mgd to 25 mgd

d. 20 points Flow 25 mgd to 37.5 mgd

e. 25 points Flow 37.5 mgd to 50 mgd

f. 30 points Flow > 50 mgd

2. Chronic Critical Effluent Concentration at Edge of Mixing Zone (Circle one score. If not 

known, estimate or double the score in category B)* 

a. 1 point CCEC < 0.1% effluent

b. 5 points CCEC = 0.1% effluent to 2% effluent

c. 10 points CCEC = 2% effluent to 4% effluent 

d. 15 points CCEC = 4% effluent to 6% effluent

e. 20 points CCEC = 6% effluent to 8% effluent

f. 25 points CCEC = 8% effluent to 10% effluent

g. 30 points CCEC > 10% effluent

Sum of scores in part B: 

C. Multiply the sum of scores from part A by the sum of scores in part B to rank the discharge: 
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Table XIII-4 Continued

D. Discharge Ranks*

Rank 1- greater than 2500 points

Rank 2- 1500 points to 2500 points

Rank 3- 750 points to 1500 points

Rank 4- 100 points to 750 points

Rank 5- less than 100 points

*Borderline values go to any adjacent group at the discretion of the permit manager.

EPA Form 2a Requirements for Part E -WET data at the time of application.

Part E is required for all municipal dischargers with a design flow of 1 MGD or more, treatment 

works with an approved pretreatment program (and those that should have one), and any other 

municipal discharger directed by Ecology to submit WET data.

Part E requirements

• If chronic dilution factor ≥ 1000 – acute testing only with 2 species quarterly for a minimum 

of one year.

• If chronic dilution factor is between 100 and 1000 – acute or chronic testing with 2 species 

quarterly for a minimum of one year.

• If chronic dilution factor < 100 – chronic testing with 2 species quarterly for a minimum of 

one year.
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Table XIII-4 . Continued 

TESTING FREQUENCY

DISCHARGE 

RANK

EFFLUENT CHARACTERIZATION

Acute Toxicity Chronic Toxicity

RANK 1

6/year,

1 fish

1 invert.

6/year,

1 fish

1 invert.

1 algal*

RANK 2

6/year,

1 fish

1 invert.

4/year,

1 fish

1 invert.

1 algal*

RANK 3

4/year,

1 fish

1 invert.

4/year,

1 fish

1 invert.

RANK 4

4/year,

1 fish

1 invert.

2/year,

1 fish

1 invert.

RANK 5

2/year,

1 fish

1 invert.

2/year,

1 fish

1 invert.

* optional at permit manager's discretion
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4.2 Sampling

Samples for whole effluent toxicity testing may be composite or grab samples. Twenty four 

hour composite samples are recommended except:

a. when the permit manager has reason to believe that the effluent is significantly more toxic at 

a certain time of day,

b. when the permit manager suspects that toxicity may be lost by the compositing process (for 

example, chlorine or volatile organics vaporizing out of solution, or surfactants adsorbing to 

the composite sampler),

c. or when the toxicity testing will require a sample volume in excess of composite sampler 

volume which is usually about five gallons. Grab samples can be composited in these cases.

Samples taken for toxicity testing should be cooled to 4 degrees Celsius and sent to the lab 

immediately. The lab should begin the toxicity testing as soon as possible but no later than 36 

hours after the time that sampling was begun.

Sampling should be evenly spaced during the year and timed to catch the maximum seasonal 

variation. For example, if sampling frequency is 2/year, then these should be taken in the 

summer and winter.

5. STORM WATER MONITORING

The Clean Water Act did not exempt storm water from regulation. Storm water is considered 

wastewater and if it flows in a conveyance it is a point source discharge. Storm water discharges 

have not been regulated in a consistent manner under the Clean Water Act because of funding 

limitations and because control mechanisms and monitoring requirements are different from 

other point sources.

As other point source pollution sources came under control, it was apparent that storm water was 

often the cause of non-attainment of the water quality standards. The 1987 amendments to the 

Act explicitly required storm water permits. These storm water requirements have been clarified 

in EPA rule making. The regulatory history of storm water pollution control is reviewed in 56 

FR 40948 (August 16, 1991). Storm water is unique in that EPA has established that the 

implementation of best management practices constitutes BCT/BAT for storm water discharges 

associated with industrial activity. The fact sheet to the EPA industrial storm water permit says 

that BMP's identified in pollution prevention plans substitute for numeric limitations for the 

general class of industrial storm water.
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Ecology has several types of storm water permits and the monitoring requirements are different 

for each type.

5.1 Types of Storm Water Permits

5.1.1 Industries with Effluent Guidelines That Include Storm Water

EPA has promulgated effluent guidelines for some industries which include storm water 

requirements. The following industrial categories have storm water requirements:

• Cement Manufacturing

• Feedlots

• Fertilizer Manufacturing

• Petroleum Manufacturing

• Steam Electric

• Coal Mining

• Ore Mining and Dressing

• Mineral Mining and Processing

• Asphalt Emulsion

These categories of dischargers have effluent limitations in regulation and they address either 

"non-process wastewater" or wastewater from material storage piles. Even though some of these 

limitations specify the design storm (i.e., 10 year 24 hour storm) they do not specify monitoring 

frequency. Therefore the only regulatory monitoring requirement is the minimum of once per 

year as specified in 40 CFR 122.44(i)(2). These categories of dischargers receive individual 

permits which cover storm water discharges. The permit writer for one of these categories of 

discharge must review the development document to determine which waste streams are covered 

in the effluent limitations. If a permit writer finds that a waste stream in one of these categories 

of discharge is not covered by the effluent guidelines, the effluent limitations for that waste 

stream are developed on a case-by-case basis. 

5.1.2 Industries With Effluent Guidelines

Some industries with effluent guidelines for the process wastewater have storm water that mixes 

with the process wastewater before the point of discharge. The permit typically includes both 

types of wastewater. An example of this type is the timber products processing category. These 

categories of dischargers would generally receive individual permits that include effluent 

limitations developed on a case-by-case basis for the storm water component.
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5.1.3 Industries Without Effluent Guidelines but With Existing Individual 

Permits

These are usually industries that have permits because of some demonstrated water quality 

problem from storm water runoff or because they are a remedial cleanup site. This category of 

discharger has an individual permit that contains storm water effluent limitations developed a 

case-by-case basis.

5.1.4 Industrial Stormwater General Permit

Ecology reissued a general permit for industrial storm water on October 21, 2009. This general 

permit requires the permittees to develop and implement a pollutant reduction plan (SWPPP) and 

conduct quarterly effluent monitoring. 

5.1.5 Municipal General Permit

Ecology has issued a general storm water permits to municipalities with a population greater than 

250,000 (Phase 1) and to municipalities with populations between 100,000 and 250,000.

5.1.6 Dual Permits

A permit writer who is permitting an industrial facility may find the previous permit or the 

effluent guidelines do not cover storm water discharge at the facility. This facility must have 

submitted a Notification of Intent (NOI) to be covered under the Industrial Baseline Storm Water 

General permit if it is included in the regulations. Most industries are included in the SIC codes 

that require storm water permits.

A facility should not be removed from coverage under the Baseline General Permit unless the 

permit manager considers the pollution control approach or the timing of the general permit to be 

inappropriate for that facility. Ecology will not charge a facility a fee for coverage under the 

storm water general permit if they have an individual permit. The Baseline Storm Water permit 

may be inappropriate for facilities which the permit manager has reason to believe may be 

having significant water quality impacts, or where the discharge is a "significant contributor of 

pollutants" (40 CFR 122.28(b)(2)(i)(G)). 

Some industries may not be required to be covered under the general permit but the permit 

manager has reason to believe the storm water discharge from the facility is causing pollution 

and therefore requires control. These facilities would be issued an individual permit.

If the permit manager decides to remove a facility from dual coverage and address the storm 

water discharge within an individual permit, the wastewater characterization process must meet 

the requirements in federal regulations. 

Federal regulations require submission of form 2F (40 CFR 122.26(c)) for characterizing the 
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amount and nature of the storm water. This form requires submission of sampling data and an 

assessment of the site. This form is appropriate for facilities which the permit writer wants to 

obtain storm water quality data now rather than waiting until about 1997 under the Baseline 

Storm Water General Permit.

If the permit manager wants to include stormwater in an individual process waste water permit, 

but doesn't want to wait until the form 2F is submitted before issuing the permit, the monitoring 

requirements of form 2F should be included in the monitoring requirements of the permit. The

other option is a permit requirement to submit a form 2F and to comply with the sampling 

requirements of the storm water regulations. 

5.2 Wastewater Characterization for Industrial Storm Water

The storm water regulations contain some specific requirements for characterizing storm water 

pollutant concentrations and loading. Permit managers should require these sampling processes 

in individual permits so as to be consistent with the regulations. The requirements for storm 

water sampling are contained in NPDES Storm Water Sampling Guidance Document (EPA 833-

B-92-001). This document should be referenced in permits requiring storm water 

characterization.

The regulations require a grab sample for the first flush of the precipitation event during the first 

30 minutes of a discharge and a flow-weighted composite for the rest of the storm event. The 

first flush grab sample is not required if the storm water is from a detention basin with a 

detention time of 24 hours or more. The flow weighted composite samples must be collected 

during the first three hours of the discharge or the entire period of discharge if less than three 

hours in length. 

The regulations also specify the pollutants to be analyzed in each sample. 

The first flush sample must be analyzed for: 

• Oil/grease, 

• pH, 

• BOD, 

• COD, 

• TSS, 

• Total P, 

• Nitrate and nitrite nitrogen, 

• Total Kjeldahl nitrogen, 
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• Any pollutant in the facilities effluent guideline, 

• Any additional pollutants that are in the facility's permit including those for the purpose of 

characterization of the process waste stream, and 

• Any pollutant that the applicant denotes as believed to be present on the form 2F.

The composite sample must be analyzed for all the parameters in the first flush sample except 

oil/grease and pH unless they happen to be parameters given in the permittees individual permit. 

For certain industries EPA's General Industrial Storm Water Permit specifies pollutant 

parameters to be monitored (refer to Table XIII-5).

The storm water regulations are explicit on the storm event to be sampled to characterize the 

storm water discharge. The storm event must produce 0.1 inch of precipitation and occur at least 

72 hours from the last 0.1 inch of precipitation. The duration and total precipitation for the storm 

event should be from 0.5 to 1.5 times the average or median storm event for the area.

The regulations also require that the permittee measure flow rate, estimate volume for the storm 

event sampled and provide the method of flow estimation. The permittee must also provide: 

• The date and duration (in hours) of the storm event(s) sampled.

• The rainfall measurements or estimates of the storm event (in inches) which generated the 

sampled runoff. 

• The duration between the storm event sampled and the end of the previous measurable storm 

event. 

The sample volume is not specified in regulation but is contingent upon the number of pollutants 

to be analyzed. The samples generally should be a minimum of four liters for the first grab and 

three liters for the composite sample.

The regulations do not require an automatic sampler for storm water but they do place a 

restriction on manual sampling. Samples collected manually for composite samples must be 

taken once in each hour for three hours and at least 15 minutes apart. The EPA guidance 

document contains a good discussion of the advantages and disadvantages of automatic versus 

manual sampling. The document also presents several strategies for sampling to meet the intent 

of the regulations.
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5.3 Compliance Monitoring

The frequency of compliance monitoring is based upon the permit manager’s best professional 

judgment. The permit manager should review the general considerations for determining the 

frequency of compliance monitoring given in the earlier sections of this chapter. For industries 

listed in Table XIII-5, the permit writer should use the monitoring frequencies required by EPA 

as the minimum monitoring frequencies.

For some storm water discharges the first flush flow may contain many times the concentration 

of pollutants than sometime later in the storm event. The first flush concentration may also be 

dependent upon the season. An industry that has a large amount of deposition from air pollutants 

would have the highest concentration of pollutants in the first heavy rain of the fall. This time of 

the year is also a low flow period for streams that are dependent upon ground water recharge. 

The short term biological impact (acute toxicity) would be greatest at this time and a grab sample 

of the first heavy fall rain would be the best predictor of impact. Grab samples are not as 

important in facilities with storm water storage basins with long detention times. 

For effluent limits based on treatment, composite samples are important for determining average 

performance. Composite samples are better at predicting loading of pollutants to a water body.

The permit manager should consider using tiered monitoring as discussed in an earlier section of 

this chapter. The reduction of monitoring frequency could be based upon compliance with 

effluent limits or upon a demonstrated reduction of pollutants attributable to implementation of 

Best Management Plans.
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Table XIII-5. EPA STORM WATER GENERAL PERMIT POLLUTANT 

PARAMETERS

Type of Facility Type of Storm Water 

Discharge Parameters

Monitoring 

Frequency

Reporting 

Frequency

EPCRA,

Section 313 

Facilities subject to 

Reporting 

Requirements for 

Water Priority 

Chemicals

Storm water discharges 

that come into contact 

with any equipment, tank, 

container, or other vessel 

or area used for storage of 

a Section 313 water 

priority chemical, or 

located at a truck or rail 

car loading or unloading 

area where a section 313 

water priority chemical is 

handled

Oil and Grease, BOD5, 

COD, TSS, Total Kjeldahl 

Nitrogen1

, (NH3-N1 

NO3+NO2-N)3 Total 

Phosphorus, pH, acute 

whole effluent toxicity2

, 

any Section 313 water 

priority chemical for 

which the facility reports.

Semi-annual Annual

Primary Metal 

Industries (SIC 33)

All storm water 

discharges associated with 

industrial activity

Oil and Grease, COD, 

TSS, pH, acute whole 

effluent toxicity2

, Total 

Recoverable Lead, Total 

Recoverable Cadmium, 

Total Recoverable Copper, 

Total Recoverable 

Arsenic, Total 

Recoverable Chromium, 

and any pollutant limited 

in an effluent guideline to 

which the facility is 

subject.

Semi-annual Annual

Land Disposal 

Units/Incinerators/

BIFs

Storm water discharges 

from active or inactive 

land disposal units 

without a stabilized cover 

that have received any 

waste from industrial 

facilities other than 

construction sites; and 

storm water discharges 

from incinerators and 

BIFs that burn hazardous 

waste

Total Recoverable 

Magnesium, Magnesium 

(dissolved), Total Kjeldahl 

Nitrogen, COD, TDS, 

TOC, Oil and Grease, pH, 

Total Recoverable 

Arsenic, Total 

Recoverable Barium, Total 

Recoverable Cadmium, 

Total Recoverable 

Chromium, Total Cyanide, 

Total Recoverable Lead, 

Total Mercury, Total 

Recoverable Selenium, 

Total Recoverable Silver, 

acute WET 2

Semi-annual Annual
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Table XIII-5. EPA STORM WATER GENERAL PERMIT POLLUTANT 

PARAMETERS

Type of Facility Type of Storm Water Discharge Parameters Monitoring 

Frequency

Reporting 

Frequency

Animal Handling/ 

Meat Packing 

Facilities

Storm water discharges from 

animal handling areas, manure 

management areas, production 

waste management areas 

exposed to precipitation at meat 

packing plants, poultry packing 

plants, facilities that 

manufacture animal and marine 

fats or oils.

BOD5, Oil and Grease, 

COD, TSS, Total Kjeldahl 

Nitrogen (TKN), (NH3, 

NO3,NO2)

3

, Total 

Phosphorus, pH, Fecal 

Coliform

Annual Retain on 

site.

Chemical and 

allied Product 

Manufacturers/Ru

bber 

Manufacturers 

(SIC 28 & 30)

Storm water discharges that 

come into contact with solid 

chemical storage piles

Oil and Grease, COD, 

TSS, pH, any pollutant 

limited in an effluent 

guideline to which the 

facility is subject.

Annual Retain on 

site.

Automobile 

Junkyards

Storm water discharges 

exposed to:

a) over 250 auto/truck bodies 

with drivelines, 250 drivelines, 

or any combination thereof

b) over 500 auto/truck units

c) over 100 units dismantled 

per year where automotive 

fluids are drained or stored.

Oil and Grease, COD, 

TSS, pH, any pollutant 

limited in an effluent 

guideline to which the 

facility is subject.

Annual Retain on 

site.

Lime 

Manufacturing 

Facilities

Storm water discharges that 

have come into contact with 

lime storage piles

Oil and Grease, COD, 

TSS, pH, any pollutant 

limited in an effluent 

guideline to which the 

facility is subject.

Annual Retain on 

site.

Oil-Fired Steam 

Electric Power 

Generating 

Facilities

Storm water discharges from 

oil handling sites

Oil and Grease, COD, 

TSS, pH, any pollutant 

limited in an effluent 

guideline to which the 

facility is subject.

Annual Retain on 

site.
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Table XIII-5. EPA STORM WATER GENERAL PERMIT POLLUTANT 

PARAMETERS

Type of 

Facility

Type of Storm Water 

Discharge

Parameters Monitoring 

Frequency

Reporting 

Frequency

Cement 

Manufacturing 

Facilities and 

Cement Kilns

All storm water 

discharges associated 

with industrial activity 

(except those from 

material storage piles 

that are not eligible 

for coverage under 

this permit)

Oil and Grease, 

COD, TSS, pH, any 

pollutant limited in 

an effluent guideline 

to which the facility 

is subject.

Annual Retain on site.

Wood 

Treatment 

Facilities 

Industrial 

Facilities with 

Coal Piles

Storm water 

discharges from coal 

pile runoff

Oil and Grease, pH, 

TSS (TOC)3

, Total 

Recoverable Copper, 

Total Recoverable 

Nickel, Total 

Recoverable Zinc

Semi-annual Annual

Battery 

Reclaimers

Storm water 

discharges from areas 

for storage of lead 

acid batteries, 

reclamation products, 

or waste products, and 

areas used for lead 

acid battery 

reclamation

Oil and Grease, 

COD, TSS, pH, Total 

Recoverable Copper, 

Total Recoverable 

Lead, (Cd)3

Semi-annual Annual

Airports (with 

over 50,000 

flight 

operations per 

year)

Storm water 

discharges from 

aircraft or airport 

deicing areas

Oil and Grease, 

BOD5, COD, TSS, 

pH, and the primary 

ingredient used in the 

deicing materials

Annual Retain on site
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Table XIII-5. EPA STORM WATER GENERAL PERMIT POLLUTANT 

PARAMETERS

Type of Facility Type of Storm Water 

Discharges

Parameters Monitoring 

Frequency

Reporting 

Frequency

Coal-fired Steam 

Electric Facility

Storm water discharges 

from coal handling sites 

(other than runoff from 

coal piles which is not 

eligible for coverage 

under this permit)

Oil and Grease, pH, 

TSS, Total 

Recoverable Copper, 

Total Recoverable 

Nickel, Total 

Recoverable Zinc

Annual Retain on site.

Ready-mix 

Concrete 

Facilities

All storm water 

discharges associated 

with industrial activity

Oil and Grease, COD, 

TSS, pH, any pollutant 

limited in an effluent 

guideline to which the 

facility is subject

Annual Retain on site.

Ship Building 

and Repairing 

Facilities

All storm water 

discharges associated 

with industrial activity

Oil and Grease, COD, 

TSS, pH, any pollutant 

limited in an effluent 

guideline to which the 

facility is subject, 

(Total Recoverable 

Copper, Organo-tins)3

Annual Retain on site.

Notes:

1 A discharger is not subject to the monitoring requirements provided the discharger 

makes a certification for a given outfall, on an annual basis, under penalty of law, that 

material handling equipment or activities, raw materials, intermediate products, final 

products, waste materials, by-products, industrial machinery or operations, significant 

materials from past industrial activities, or, in the case of airports, deicing activities, 

that are located in areas of the facility that are within the drainage area of the outfall 

are not presently exposed to storm water and will not be exposed to storm water for the 

certification period.

2 A discharger may, in lieu of monitoring for acute whole effluent toxicity, monitor for 

pollutants identified in Tables II and II of Appendix D of 40 CFR Part 122 that the 

discharger knows or has reason to believe are present at the facility site. Such 

determinations are to be based on reasonable best efforts to identify significant quantities of 

materials or chemicals present at the facility.

3 Recommendations by the Washington Department of Ecology.
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6. RECEIVING ENVIRONMENT MONITORING

Requirements to monitor receiving environments are a necessary component of some NPDES 

permits. Most receiving environment monitoring programs will be aimed at determining (1) the 

background concentrations of parameters in the receiving environment, and (2) the dilution 

available in the ambient environment for a proposed or existing discharge. A much less common 

need will be the requirement for assessment of impacts in receiving environments (please refer to 

the specific section on the media you are concerned with to determine when this need may exist). 

Effluent limits that are calculated using appropriate data from dilution studies and ambient 

background level studies should not cause impacts to the aquatic life, drinking water, or sediment 

uses upon which the state's Water Quality Criteria are based. However, in some cases concerns 

will arise that prompt the permit writer to consider whether a monitoring survey to assess 

impacts is necessary. These cases are most likely to occur when beneficial uses that are not yet 

assigned protective criteria are concerned (e.g., wildlife uses). 

The arrangement of this chapter is as follows:

1. The regulatory authority Ecology can use to require monitoring (6.1 General Considerations 

for Monitoring Receiving Environments);

2. Guidance to use when determining when and how to require effluent dilution and ambient 

background monitoring (6.1 General Considerations for Monitoring Receiving 

Environments); and,

3. Considerations to be aware of when a study to assess impacts to receiving environments may 

be necessary (in almost all circumstances the permit writer will work with the E.A. Program 

and the appropriate headquarters section to develop these requirements).

a. What circumstances may prompt you to consider monitoring (6.1.1).

b. How to determine if monitoring is needed (6.1.1 and 6.1.2).

c. The steps needed to logically develop or review a receiving environment survey to 

get the greatest amount of useful data in the most cost effective way (6.1.3 through 

6.1.5). This section also advises on when the EAP Program and Headquarters should 

be consulted within the course of determining environmental monitoring 

requirements, and what type of assistance you can expect from those groups.

Note: Throughout this section the permit manager is directed to contact both EAP and 

headquarters when determining the specifics of simple or complex receiving environment 

surveys. This has been emphasized because of the need to assure thorough understanding of the 

goals of surveys by all parties participating in their design. During the design of complex 
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surveys, headquarters will assist the permit manager to clearly transmit the goals of a receiving 

environment monitoring project to EAP, and will work to ensure that EAP understands the 

regulatory need for studies, and the way in which data will be used. This process is 

recommended as one way of "translating" survey needs between the more regulatory 

requirement-based permit managers and the environmental assessment-based group at EAP. 

This should expedite a more thorough review of survey proposals and result in more effective 

monitoring programs. 

6.1 General Considerations for Monitoring Receiving Environments

Environmental monitoring commonly includes surveys of surface and ground water, sediments 

and soils, and biota. In the State of Washington, major NPDES dischargers are likely to be 

required to perform some type of receiving environment monitoring. Minor dischargers may 

also be required to monitor receiving waters. By far the most frequent need for monitoring will 

be prompted by a lack of information of discharge specific dilution and ambient background 

concentrations of pollutants or other water quality parameters (e.g., hardness or pH). Other 

factors that could prompt the need for additional monitoring would likely be founded on a 

concern that the existing water quality criteria (based on toxicity to aquatic life and benthic 

invertebrates, and, drinking water concerns) are not providing adequate protection for other 

designated beneficial uses in waters of the state.

The decision to require or not require receiving environment monitoring must be explained in the 

fact sheet. Ecology has the regulatory authority to require surface water, sediment, soil, and 

groundwater monitoring. Regulatory authority for receiving environment monitoring is 

described below.

STATE AUTHORITY

Our state authority derives from RCW 90.48 and is expressed in Chapters 173-220 and 173-216 

WAC.

Chapter 173-220 is explicit in the authorization to require receiving water monitoring.

WAC 173-220-210(1)(c). 

"(c) Monitoring of intake water, influent to treatment facilities, internal waste streams, 

and/or receiving waters may be required when determined necessary by the 

Department to verify compliance with net discharge limitations or removal 

requirements, to verify that proper waste treatment or control practices are being 

maintained, or to determine the effects of the discharge on the surface waters of the 

state."
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The state regulatory authority for receiving environment monitoring for ground discharges is 

clear but not explicit.

WAC 173-216-110 (1)(g).

"(1) Any permit issued by the Department shall specify conditions necessary to prevent 

and control waste discharges into the waters of the state, including the following, 

whenever applicable:

(g) Any appropriate monitoring, reporting and record keeping requirements as 

specified by the Department, including applicable requirements under sections 

307 and 308 of FWPCA;"

The WAC includes language that specifically allows Ecology to require environmental 

monitoring information as part of a permit application:

WAC 173-216-070 (4)(c).

"(4) The requirement for a permit application will be satisfied, if the discharger files:

(c) Any other information determined as necessary by the Department."

WAC 173-216-080 (1)(c) and (d).

"(1) Any information submitted pursuant to this chapter may be claimed as 

confidential.... Claims of confidentiality for the following information will be 

denied:

(c) description of proposed receiving waters;

(d) description of quality and quantity of receiving water; and..."

FEDERAL AUTHORITY

Ecology is authorized to implement the Clean Water Act by RCW 90.48.260 which states:

"The Department of Ecology is hereby designated as the State Water Pollution 

Control Agency for all purposes of the Federal Clean Water Act as it exists on 

February 4, 1987, and is hereby authorized to participate fully in the programs 

of the act as well as take all action necessary to secure to the state the benefits 

and to meet the requirements of the act."
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Ecology's authority under RCW 90.48.260 allows it to exercise whatever powers it needs "to 

meet the requirements" of the Clean Water Act. Whenever the Clean Water Act requires certain 

authority of an NPDES state, Ecology has that authority. The Clean Water Act, in 33 U.S.C. § 

1342, requires that states be able to issue permits which apply federal effluent limitations and 

"[t]o inspect, monitor, enter, and require reports to at least the same extent as required in Section 

1318..." 33 U.S.C. § 1342(b).

Section 308 of The Clean Water Act as Amended by the Water Quality Act of 1987, Public Law 

100-4 [33 U.S.C. § 1318] states, in part: 

"Whenever required to carry out the objective of this Act, including but not limited 

to (1) developing or assisting in the development of any effluent limitation, or other 

limitation, prohibition, or effluent standard, pretreatment standard, or standard of 

performance under this Act; (2) determining whether any person is in violation of 

any effluent limitation, or other limitation...

(a) the Administrator shall require the owner or operator of any point source to 

(i) establish and maintain such records, (ii) make such reports, (iii) install, use, 

and maintain such monitoring equipment or methods (including, where 

appropriate, biological monitoring methods), (iv) sample such effluent (in 

accordance with such methods, at such locations, at such intervals, and in such 

manner as the Administrator shall prescribe), and (v) provide such other 

information as he may reasonably require;"

The federal regulation which comes from this section of law is 40 CFR 122.41(h) which states: 

"(h) Duty to provide information. The permittee shall furnish to the Director, 

within a reasonable time, any information which the Director may request to 

determine whether cause exists for modifying, revoking and reissuing, or 

terminating this permit or to determine compliance with this permit." 

The legal test of monitoring and testing under the federal Clean Water Act demands only that the 

monitoring or testing be reasonably required for some purpose under the Act - including that of 

developing any new effluent limitation.
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COURT OPINIONS ON SECTION 308

Referring to Section 308, the circuit court in Natural Resources Defense Council v. U.S. 

Environmental Protection Agency, 822 F.2d at 119, (D.C. Cir. 1987) commented upon the broad 

discretion granted by the statute:

The breadth of this statutory grant of authority is obvious. In our view, the 

statute's sweep is sufficient to justify broad information disclosure

requirements relating to the Administrator's duties, as long as the disclosure 

demands which he imposes are "reasonable."

In United States Steel v. Train, 556 F.2d 822, 850 (7th Cir. 1977), the company argued that an 

NPDES permit provision requiring a study of the impact of cooling water intake structures on 

aquatic life was unreasonable. The court rejected the argument saying:

U.S. Steel's argument that, even if applicable, the permit provision is 

unreasonable must also be rejected. Not even a "rough cost-benefit analysis" is 

necessary as a basis for the requirement that the company conduct a study of 

the impact of the present cooling-water intake structures on aquatic life in Lake 

Michigan. Such a study, intended to assist EPA in developing 316(b) effluent 

limitations, is well within the agency's 308 [33 U.S.C. § 1318] authority.

The court's reasoning that "not even a 'rough cost-benefit analysis' is necessary" is important, 

because it confirms that there is no requirement in the statute that the cost of the monitoring must 

somehow be proportional to the value of the data expected to be obtained. These determinations 

are left to the discretion of the permitting agency.

Permitting agencies not only have broad discretion on whether to require monitoring, but the 

choice of what particular test to require is perhaps even more a matter of agency discretion. 

Courts only require that the agency's choices in the scientific arena be "rational" - that is, that 

these choices have some scientific support. If the agency's choice has scientific support, a court 

will not attempt to substitute its judgment for that of the agency by weighing the merits and 

demerits of competing scientific approaches. These limitations on review of Clean Water Act 

scientific judgments are discussed in Reynolds Metals Company v. U.S. Environmental 

Protection Agency, 760 F.2d 549, 558-59 (4th Cir. 1985):

The scope of our review is further colored by the policy of the Clean Water 

Act and the sophisticated data evaluations mandated by that lengthy and 

complicated statute. The Act expresses a congressional insistence to eliminate 

water pollution within a short time-span... Further, technological and scientific 

issues, such as those presented in this case, are by their very nature difficult to 
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resolve by traditional principles of judicial decision making. For this reason 

"[w]e must look at the decision not as the chemist, biologist or statistician that 

we are qualified neither by training nor experience to be, but as a reviewing 

court exercising our narrowly defined duty of holding agencies to certain 

minimal standards of rationality." More specifically, we note that an agency's 

data selection and choice of statistical methods are entitled to great deference, 

and its conclusions with respect to data and analysis need only fall within a 

"zone of reasonableness."

The court went on to note, "[a]s frequently has been written, we do not sit as a scientific body 

minutely comparing competing research methods and results." 760 F.2d at 560.

This echoes the sentiments expressed in the earlier opinion in Weyerhaeuser Company v. Costle, 

590 F.2d 1011, 1026 (D.C. Cir. 1978):

Where existing methodology or research in a new area of regulation is 

deficient, the agency necessarily enjoys [a] broad discretion to attempt to 

formulate a solution to the best of its ability on the basis of available 

information.". . . Indeed, the mere fact that the counsel on both sides in this 

suit could draw upon the opinions of diverse experts sitting virtually at their 

elbows during preparation of their briefs, while we are faced to decide between 

their resulting arguments on the basis of our "generalists" judicial 

backgrounds, argues for restraint on our part. In sum, unless we are quite 

certain of our basis for doing so, we must be slow to overturn the Agency's 

judgment, whichever way it may incline, when Congress has required it to act 

quickly and decisively despite the lack of exact data.[Citations omitted; 

footnotes omitted.]

The cases provide some "real world" examples of how these standards of review are applied. In 

Natural Resources Defense Council v. U.S. Environmental Protection Agency, supra, the court was 

reviewing an EPA requirement that each NPDES permit applicant provide EPA with a list of "any 

toxic pollutant which the applicant currently uses or manufactures as an intermediate or final 

product or byproduct." Industry argued that this requirement was invalid because EPA was 

authorized only to regulate toxic discharges and not toxics which may be involved only in some 

intermediate manufacturing step. The court stated, "[t]he indications are abundant that EPA was 

intended to possess broad latitude in identifying and regulating suspected toxics." EPA had 

identified three reasons for requiring the information: (1) to make sure that the effluent limitations 

in the permit covered the right toxicants; (2) to provide guidance on what to test for in the effluent; 

and (3) to aid setting "best management practices" that might be imposed to prevent spills. The 

court found these reasons sufficient to require the information under 33 U.S.C. § 1318.

A final example of a federal case construing 33 U.S.C. § 1318 is American Petroleum Institute 
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vs. Environmental Protection Agency, 787 F.2d 965, 978 (5th Cir. 1986). In this case, the court 

rejected a challenge to use of a bioassay test in making NPDES permit determinations:

The nub of the industry's contention is that the bioassay test, based on a fourday long exposure of critical marine fauna to drilling mud, creates a 

completely unrealistic situation which would never occur in nature because of 

the rapid dispersion of drilling mud from an offshore platform as a result of 

simple dilution, currents, and storms...

API's suggestion that the dynamic ocean environment would never result in the 

extended exposure to drilling mud contemplated by the 96-hour LC-50 test 

commends itself to common sense. On the other hand, API concedes that test 

to be perhaps the most widely accepted benchmark for toxicity evaluations by 

EPA. Therefore, EPA has not selected a patently irrational methodology to 

measure the relative toxicity of generic Mud No.1. Under such circumstances, 

we are required to resist API's attempts to substitute our judgment for that of 

the agency...and must sustain its choice.[Citations omitted.]

The court in American Petroleum Institute, supra, used the approach which Ecology believes 

defines the criteria for determining if receiving environment is appropriate. These criteria are: 

(1) Are the test(s) required in the permit or as part of the permit application being imposed for an 

allowable purpose under state law or under 33 U.S.C. § 1318 (that is, to carry out some objective 

of the Clean Water Act)? Typically these purposes are to require the permittee to monitor for 

information for permit development or to demonstrate the discharge is not causing harm. (2) Are 

the specific test methods "reasonable," in that they have scientific support?

The permit writer should be clear these questions are answered in the fact sheet when requiring 

receiving environment monitoring.

Common Monitoring Requirements:

The two most common reasons to consider and require receiving environment monitoring are:

• To attain data on ambient conditions in receiving waters for use in calculating effluent 

limits, and;

• To determine flows and dilution in the vicinity of the discharge (i.e., field verification of 

mixing zone models).

By far the most common reason to require receiving environment monitoring is to provide 

background data to use when permit limits are calculated. These data can be required upon 

application, or can be specified in the preceding permit as a special study. Both options have 
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advantages and disadvantages. Requesting ambient data upon application, especially if the 

request is not specific as to detection limits, QA/QC, and sampling locations and depths, can 

result in submittal of data that are not appropriate to use in limit calculation. Requiring 

background data within a permit can result in an additional work-load for the permit manager if 

study plans need review and approval. The recommended approach is to require a special study 

as a permit requirement. Ideally, as many of the data reporting requirements as possible should 

be incorporated into the requirement. Studies should address the most necessary types of data 

needed for effluent limit calculation, including temperature, hardness, and/or toxins measures. 

Copies of all data and reports should be submitted to the Basin Planning and Standards Section 

for incorporation into statewide reports.

There are two general ways to place receiving water studies in permits, permit applications, and 

enforcement orders. The first method is to describe the sampling program in detail in the permit. 

In many cases this is the best method for simple studies that will be conducted by the permittee 

(e.g., measuring copper concentration at one ambient background site to determine the 

concentration of copper in ambient water during critical flow conditions, or, estimating dilution 

near the discharge point). When using this method, the permit manager should specify any 

applicable sampling and analytical protocols to be used, as well as sample location and timing. 

The specific protocols for these simple studies, for different environmental media, can be found 

in the media-specific sections at the end of this chapter.

The second method is to specify the study objectives and to allow the permittee to submit draft and 

final study plans, acceptable to Ecology, within a specified time period (e.g., within 90 days of 

permit issuance). It is important to note that discussing the need to conduct receiving monitoring 

studies with the discharger and other interested parties during the permitting process can help to 

formulate survey objectives early-on, and will help the discharger by giving them early warning 

that they must start to budget for a sampling program. This is the best approach for studies that are 

conducted by a consultant for the permittee. If the permit manager requires the permittee to submit 

a sample plan, the qualifications of the people doing the work should be submitted for approval. 

The study plan should address the variables and information needs associated with fulfilling the 

objective. All study plans must be approved by Ecology. When the second method of requiring a 

study is used, the permit manager should discuss the specific problem, the study objectives, and 

any constraints of the study with the Program Development Services Section (or other appropriate 

headquarters group) and EAP. Experts on commercial laboratory and permittee analytical 

capabilities are in the Quality Assurance Section in the EA Program.

Infrequent Monitoring Requirements:

The third and least common reason to consider requiring receiving environment monitoring is to 

determine whether the permitted discharge is causing a detrimental impact to the environment in 

the vicinity of the discharge (i.e., environmental assessment). 

Effluent data are often the first indicator that a receiving environment may be undergoing 
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damage due to discharges, thus effluent quality should be characterized before a receiving 

environment study is required. Environmental monitoring should focus on effects that could be 

caused by chemicals and other properties that are present in the effluent. In some cases 

biological or chemical effects may already be identified in a receiving water (e.g., abnormal 

blooms or die-off of algae, deleterious concentrations of toxins in wildlife, or, exceedances of 

state standards and associated ambient toxicity). If any of these occur, the main focus of a 

receiving water survey will be to gather data to assist Ecology to identify the cause(s) of the 

impact. Studies that can determine cause and effect in natural systems are generally difficult to 

design, and expensive to finance. Studies to determine complex cause and effect issues should 

always be discussed with the PSMS and the EILS Program in order to clarify objectives and 

determine the most effective sampling design. In addition, the permit writer may wish to consult 

the following documents when planning and considering a monitoring program: Guidelines and 

Specifications for Preparing Quality Assurance Plans, (Ecology, 1991a) and, Technical 

Guidance for Assessing the Quality of Aquatic Environments in Washington State, (Ecology, 

1990a)

A general process for deciding whether to require a receiving environment study to determine 

impacts consists of the following steps (Baker and Wolff, 1987):

1. Define and clarify the problem (what is the major concern you are interested in?) 

(Section 6.1.1)

Specify objectives and constraints (Section 6.1.2)

Develop alternative strategies (solutions) that address objectives and constraints (alternative 

sample designs including parameters to be monitored, sampling locations, 

methodologies for sample collection and analysis, and timing and frequency of 

sampling) (Section 6.1.3)

Evaluate the alternative sampling designs (Section 6.1.4)

Choose the best sampling design (Section 6.1.5)

This process is discussed in more detail below (Sections 6.1.1 through 6.1.5).

6.1.1 Define and Clarify the Problem 

For our purposes, an environmental study is a way of addressing a problem with one or more 

effluents. Defining the specific problem you are concerned with is critical to the success of the 

project. Some examples of problems you may find include:

• High levels of fecal coliform in publicly used shellfish beds near a municipal discharge 

point.
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• Detectable mercury concentrations in an effluent that discharges to a quiescent and organicrich environment, leading you to suspect sediment or organismal accumulation.

• You do not have background data to use when calculating effluent limits for copper and 

nickel.

• Repeated acute toxicity violations lead you to suspect that ambient effects are occurring 

outside the mixing zone for acute toxicity.

• You discover that effluent conveyed through a storm drain is directly entering a rocky 

intertidal area at low tide, and you wish to determine the areal extent of the effluent in the 

intertidal zone.

• Fish kills or other events occur downstream of a discharge.

• Dredge spoils from a ditch contain elevated concentrations of certain pollutants.

• Contamination that is characteristic of dairy farms is found in a drinking water well located 

downgradient from a large dairy.

Sampling should focus directly on the suspected or observed problems. Sampling of surface 

waters and sediments is discussed below. More details on sampling these and other media can 

be found in sections 6.3 through 6.6.

The decision to require the permittee to monitor the receiving environment should be based on a 

knowledge or indication that the discharge may be adversely affecting the receiving 

environment. This knowledge or indication will generally come from effluent monitoring data or 

from observable impairment of the environment. The following are cases for which receiving 

environment monitoring could be considered:

1. Problem: The facility discharges to a 304(1) water body.

Comment: Point source discharges that contribute to Water Quality Standards violations 

will be identified in technical reports being prepared for each of the water bodies on the 

304(l) short list. The "short list" is comprised of water bodies that do not meet the Water 

Quality Standards due to point source discharges of toxins. Facilities that discharge to 

these water bodies, and especially those facilities identified as contributing to these 

standards violations, could be required to perform receiving environment monitoring that 

is focused on effects caused by the toxin of concern. This could include ambient toxicity 

testing, water chemistry, bioaccumulation studies, and others. When deciding if impact 
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assessment is necessary, the permit writer should consider whether monies spent on 

addressing the listing are better spent in clarifying the problem (monitoring) or on 

reducing discharges of problem pollutants.

Problem: The facility discharges chemicals that meet technology- and water quality-based 

limits but is suspected of causing problems because of the high sensitivity of an 

indigenous species in the receiving environment.

Comment: A facility may be meeting technology- and water quality-based limits but be 

discharging to a receiving water which traditionally serves as a spawning habitat for a 

species which is particularly sensitive to a component of the effluent. If environmental 

surveys are proposed, monitoring may be concentrated on seasons in which resident 

organisms are particularly sensitive to effluent. With this particular problem, however, it 

may be possible to satisfy concerns with the receiving water by doing toxicity tests with 

species that are closely related (e.g., same genus and habit) to the indigenous species of 

concern, instead of trying to identify impacts in the receiving environment. Although 

toxicity tests are costly, environmental monitoring programs that adequately address both 

physical and biological variability in a natural system (i.e., the data is good enough to 

answer the original question instead of yielding an ambiguous result because of high 

variability) can be much more expensive.

Problem: The facility is associated with periodic spills or the discharge of high 

concentrations of toxins.

Comment: The purpose of sediment and water column monitoring in this case would 

be to determine whether degradation of the receiving environment has occurred due to 

occasional discharge of highly concentrated contaminants. Permits issued for 

combined sewer overflows and storm drains would fall into this category. The timing 

of receiving water sampling is critical for detecting effects from storm events. Of 

particular interest are violations of acute criteria associated with storm water in well 

flushed areas, and violations of chronic criteria that last days, weeks, or longer in 

poorly flushed areas (e.g., estuarine areas removed from major flushing currents or 

lacking significant riverine inflow). 

Problem: Facility expansions, production increases, or process modifications are proposed 

that may result in new or substantially increased discharges of pollutants or a change in 

the nature of the discharge.

Comment: Permittees in this category are required to submit a new application or 

supplement to the previous application. The information submitted with the application 

or supplement should indicate expected changes in effluent quality or quantity. Permit 

managers will use that information to determine if the change in the facility could result 
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in discharge of effluent that could potentially impact the environment. The proper 

receiving environment data collected before and after the proposed change occurs could 

help to identify environmental impacts caused by the change. If an environmental 

survey is required, the sampling program should focus on effects that are expected to 

occur due to the changes in effluent. In many cases the use of dilution information and 

ambient background data to calculate effluent limits will provide enough reassurance to 

reduce the need for impact assessment. 

Problem: A facility is suspected of discharging effluent that may be causing or contributing 

to observed environmental impacts such as recurring algae blooms or fish kills. A 

facility is discharging to a water body on the 305(b) list or suspected of contributing to 

violations of water quality standards in the receiving environment.

Comment: When trying to draw cause and effect relationships (e.g., fish kill caused by 

a specific effluent discharge) it is critical to gather as much operational data on the 

discharge as possible. Review of operational data may indicate periodic presence of 

toxins in effluent that are not caught by self monitoring (e.g., filter backflush and 

disinfection that has not been dechlorinated prior to discharge), and review of 

monitoring data may indicate levels of chemicals that could drive receiving water to 

develop toxic conditions during critical periods or in certain downstream areas (e.g., 

depletion of oxygen caused by excessive BOD). This information can sometimes lower 

the cost of environmental surveys by focusing the objectives toward the effects most 

likely to occur. 

Problem: A facility's discharge is a source of ongoing public concern regarding the actual 

or potential effects on the biota of the receiving environment. 

Comment: When the concern is due to the location of the discharge in or near a 

sensitive receiving environment, benthic biota, sediment, bioaccumulation, or water 

column studies may be appropriate. If the public is concerned, the permit manager 

should try to clarify the specific concerns of the public (e.g., mercury uptake and 

toxicity to wildlife; uptake of toxins by fish and shellfish that may cause a hazard to 

human health; public believes the environment in the area of discharge does not get 

any flushing, and consequently toxins may be accumulating to levels dangerous to 

either humans or other biota). In some cases, these fears may be allayed by reviews of 

existing information. Sometimes a review of existing information will prompt the 

permit manager to suspect that the public concerns are based on realities, or will bring 

up other concerns with the area. In that case environmental surveys should be required. 

Because of the environmental and political complexities associated with surveys 

prompted by widespread public involvement, the permit manager should confer with 

the Program Development Services Section, EAP, and any applicable resource agencies 
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before formulating specific sampling objectives.

Complex receiving environment monitoring should not be required of facilities that discharge 

effluents that have little potential to impact the environment and do not fall under a category 

listed above. For example, facilities that discharge into areas with strong currents would have no 

accumulated bottom sediments. However, even these facilities may be required to sample 

background water chemistry to establish data on which to base permit limits, or to measure 

bioaccumulation of toxins, or to perform other specific studies.

6.1.2 Specify Monitoring Objectives and Constraints

Specific monitoring objectives state the variables that are to be observed, and the time frame or 

time period during which the observations should occur. Several objectives may develop from 

thoughtful consideration of the initial problem. Clearly expressed and specific objectives are 

critical to proper sampling design and use of data. In addition, when you define monitoring 

objectives and constraints, it is important to determine what the regulatory outcome of the 

monitoring will be. If the data you gather is intended to result in modification of a discharge 

permit, then you should clearly define the result that will trigger a permit modification. 

Examples of objectives include:

• To determine the concentrations of priority pollutant metals in the receiving water before a 

new facility commences discharging.

• To determine if concentrations of lead and zinc in the receiving water are exceeding water 

quality criteria during low flow months.

The following is an example of a specific monitoring objective to determine compliance with 

sediment quality standards:

• To determine if the concentrations of cadmium, lead, zinc and mercury in sediments near the 

outfall are exceeding the sediment quality standards during year four of the issued permit.

Other constraining factors can limit the way in which specific objectives are addressed and may 

be both scientific and operational (Baker and Wolff, 1987). An example of an objective and 

some discharge-specific constraints are illustrated in the following example:

Objective: Determine a background copper concentration in ambient waters to use when 

calculating an effluent limit.

Constraints: Sampling must occur during critical conditions (low flow).

Data must be collected and analyzed using ultra-clean techniques.
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Preconcentration of samples must be done if copper concentrations are below 

the levels of detection using graphite furnace AA.

Because of time constraints, the permit manager is willing to calculate the 

limit based on samples collected over one summer that occurs during a 

drought period.

In some cases you will address problems that deal with more than one environmental media, 

such as assessing sediments and water in the same area, or determining sediment toxicity and 

sediment chemistry. If more than one media is being tested, be sure to formulate your objectives 

and constraints in such a way as to best address all media. In many cases you will use data from 

one media to interpret the data from another media (sediment chemistry data can help interpret 

causes of sediment toxicity). In such cases try to coordinate the sample sites, sampling times, 

and choice of parameters for measurement to make them as useful and comparable as possible.

6.1.3 Develop Alternative Sampling Strategies that Address Objectives and 

Constraints.

When the problem has been defined, and the objectives and their constraints have been clearly 

and precisely set out, alternative sampling strategies to address the objectives and constraints 

should be developed. In effect, this means that several different ways of answering the same 

question may exist, and these should be developed and designed in detail. If you require the 

discharger to submit a sampling plan, they will submit one or more of the potential sampling 

designs. In most cases you will first consider the chemical and physical parameters you want to 

sample, the analytical methods to measure them, and then the general location of the sample 

sites. Are you interested in sediment toxicity caused by cadmium accumulation in sediments? Is 

the area subject to dredging, currents, navigation, or high winds? Can the area be safely 

sampled? Are there rip tides, can divers be used, or can benthic grabs be safely used in the area? 

What are the windows of safety for sampling (not at maximum tidal exchange, not during 

afternoon high winds, etc...)? What is the direction and speed of groundwater flow? In other 

words, how will you design your sampling program to fit the environment and environmental 

compartment you are interested in (i.e., determine its statistical design to fit your specific 

sampling objectives)? Some of these concerns are discussed below:

Chemical and Physical Parameters--The choice of the appropriate physical and chemical 

parameters to sample for in a particular study are directly dependent on the problem, objectives, 

and constraints that have been previously defined. It is important that sampling be focused in 

order to (1) produce data adequate to answer the question you are asking, and (2) to minimize the 

amount of useless or ambiguous data collected in the study. It is also important to enhance the 

comparability of the data that is collected with data collected in other sampling programs. In 

order to enhance data comparability, there are specific chemical and physical measurements that 

should be taken with each sample that you collect. Lists of required analyses for each sampling 
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media (receiving waters on surface, receiving waters in subsurface, sediments, etc....) are 

described in sections 6.2 through 6.6. In some cases the parameter you are monitoring will be 

included in the list of required analyses. At other times the usefulness of the data you are 

interested in will be enhanced by collecting data on all parameters in the required list of analyses.

Sampling and Analytical Methods--After you decide on the parameters you wish to measure in 

the samples, decide the specific methods to be used for sample collection and chemical analysis. 

These include preparation of sampling containers, detailed field protocols, and specifying 

analytical methods. Specific protocols have been developed for most media (e.g., Recommended 

Protocols for Measuring Metals in Puget Sound Water, Sediment and Tissue Samples, Tetra 

Tech, Inc., 1986a). The protocols that should be used for specific types of receiving 

environment monitoring are described in sections 6.2 through 6.6. In some cases you may want 

to use different methods than those in the specified sampling protocol (e.g., ultra-clean sampling 

for metals in surface waters, preconcentration of metals in order to yield lower detection limits). 

In those cases the analytical methods you wish to use should be referenced. The practical aspects 

of finding labs that can perform alternative analytical methods should be discussed with the PDS 

section and the EA Program. In other cases you may wish to specify changes in sample 

replication or collection methods to fit the particular media, site, and statistical analysis of a 

particular survey. Any changes in sample collection methods should be clearly described.

Sampling Locations--In most cases, such as sampling for background data, it will not be difficult 

to choose sampling sites. The sites will be in "clean" areas of water bodies (or other media), or 

they will be at the edge or just outside of a designated mixing zone. The size of the mixing zone 

will be determined during effluent limit calculation. In many cases the study you require may be 

a field verification of a mixing zone model that has been used to calculate limits. These types of 

studies have straight-forward survey designs. However, some surveys will address more 

complex objectives, in which case the design should always be discussed with the PDS Section 

(or other appropriate sections at headquarters) and with the EA Program. In many cases those 

groups will help formulate or review alternative test designs for the permit manager.

Consider the Statistical Analyses--In some cases no statistical analyses will be necessary, as in 

cases where one sample is being collected for direct comparison of chemical concentrations in 

the environment with state standards. 

If you are considering a complex monitoring survey, the sample locations you choose, and the 

spatial configuration of those sites, will in large part depend on the statistical analysis you choose 

to use. For example, if you are comparing a far-field station to a near-field station, you might 

choose to use the Student's t-test to distinguish between stations. If you are interested in looking 

at a larger area with numerous stations, you might choose to use one of the many analysis of 

variance tests, followed by multiple comparison testing, and your station locations would be set 

up with proper replication and siting. A consideration of which statistical analyses to use will 

force you to define a testable hypothesis (e.g., mercury concentrations in sediment are elevated at 
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the discharge point as compared to surrounding "clean" areas at the p=0.05 level), and choose the 

proper statistical procedure to interpret the data you collect (e.g., T-test, parametric two-way 

ANOVA for use with random box design). Specific design considerations for each media 

(surface waters, ground waters, sediments, etc....) are discussed in sections 6.2 through 6.6. 

(Note: You may wish to refer to a statistical text when determining a sample design. Sokal and 

Rohlff, 1981, Biometry, Second Edition, has good coverage of most statistics you will be 

interested in.) Remember that complex designs should always be discussed with the EA 

Program, and the headquarters section that addresses the media you are sampling. In 

many cases these groups will assist you to formulate and review test designs.

Your consideration of statistical analyses will include review of other similar studies whose data 

may indicate the likely distributions or variability of data in certain areas. For instance, you may 

discover from looking at USGS sediment monitoring data from an area you are interested in that 

(1) mercury data are log normally distributed, (2) that mercury concentrations should be 

normalized for organic carbon, and (3) that three replicates of superficial sediments per station 

will adequately assess variability so that station to station differences can be determined. 

Existing data can prove invaluable when designing sampling programs. In most cases, however, 

existing data will not be available for you to use, in which case you will have to decide how to 

handle the unknown variability of the parameter you are measuring.

Variability: Variability can be caused by several factors, including variability introduced during 

sampling and sample analysis, and by temporal and spatial components.

Sources of temporal variability include cyclic flow patterns of municipal treatment plants, tidal 

cycles, seasonal cycles, El Nino southern oscillation cycles, and dredging schedules. Spatial

variability occurs over small (e.g., within one scoop of sediment) to large (e.g., within Puget 

Sound) distances, with both vertical and horizontal components. 

When dealing with sources of variability it is best to minimize the variability by controlling 

(equalizing) as many factors as possible. Variability introduced during sampling and analysis 

can be controlled to a large degree by standardizing the sampling and analytical techniques used 

within and among sampling surveys. Use of the Puget Sound Protocols will help to reduce 

variability and enhance comparability of data. Reducing variability can also take the form of 

including temporal controls (e.g., collect all samples at high slack tide on the same day or on 

consecutive days) or spatial controls (e.g., sample unpolluted reference sites to determine 

"background " conditions, take enough replicates to characterize each station, and only collect 

oxidized sediment layer). These types of controls will all result in more useful data by limiting 

variability and enhancing comparability. Ideally, your sampling design will control for as many 

variables as possible. In the long run, a thorough consideration of sources of variability and 

ways to try to minimize variability is likely to save money, either by pointing out effective ways 

to sample, or by pointing out that some problems may be too complex to affordably answer. 

Sample replication is frequently a point of controversy when designing surveys. 
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Sample replication is often necessary to adequately characterize the variability at a site and is 

often expensive, thus it is a source of controversy. Remember that reducing the number of 

replicates can lead to collection of data that yields ambiguous interpretations, and is frequently 

useless for regulatory decisions. If it turns out that a monitoring program that can adequately 

answer a question is too costly to consider, then the permit manager should rethink the original 

problem and objectives. At this point communication with other parties is particularly important. 

The permit manager should consider discussion with the EA Program, the appropriate 

headquarters section, other state and federal regulatory agencies, state and federal resource 

agencies, academia, and any other interested party. Brainstorming with other persons can lead to 

new perspectives on how to address a question, or can lead to solutions that could be found more 

easily in other environmental compartments, or at less cost. In many cases other monitoring 

options may exist that can adequately respond to the concern.

6.1.4 Examine the Alternative Sampling Designs

After generating detailed sampling designs, the permit manager should evaluate the effectiveness 

and cost of the different designs, whether submitted by a discharger or developed by Ecology. It 

is critical at this point to first weed out any designs that appear to have a likelihood of yielding 

ambiguous data (i.e., that may not give you enough data to answer the question you are asking). 

Secondly, consider cost. Will two studies yield equally useful data on which to base a decision, 

but one is much less costly than the other? If so, recommend the one of lesser cost. In most 

cases (e.g., gathering background ambient data to use in the calculation of permit limits) cost will 

not be prohibitive. However, if the cost of the survey that will yield useful data is out of 

proportion to the magnitude of the problem being addressed, try to find another way to "ask the 

question" (e.g., can less frequent tissue accumulation studies be substituted for frequent water 

column monitoring for mercury?), and generate sampling designs for use with the new question. 

Can a less expensive study be done in a lab that will also address the real problem being 

considered? And will the public, resource agencies, and Ecology feel comfortable with the data 

generated? Ecology has a regulatory mandate, as part of their NPDES delegation, to fulfill the 

pertinent requirements of the Clean Water Act and to assure compliance with permit limits, and 

Ecology must ensure that it has appropriate data to make regulatory decisions that will be 

protective of water quality and beneficial uses. 

6.1.5 Choose the Best Sampling Design

At this point in the five-step process of planning/reviewing an environmental survey, the permit 

manager should have already examined the problem thoroughly, developed precise and well 

thought out objectives and criteria, evaluated effluent quality and operations, and be familiar 

with the advantages and disadvantages of alternative sampling designs. The permit manager, 

after conferring with the EA Program and the appropriate Ecology headquarters section, should 

choose the best study design, and require that study as part of a permit application, as a permit 

requirement, or in an enforcement order. 
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6.2 Surface Water Monitoring

6.2.1 Parameters

When requiring receiving water monitoring, all samples should be measured for the following 

characteristics:

Temperature,

Dissolved oxygen,

Conductivity if freshwater or, salinity if estuarine/marine

Turbidity or light transmittance at depths,

pH

Salinity or Hardness

These data will add to the comparability of data collected in monitoring programs conducted 

throughout the state. Other parameters that you choose for measurement should be directly 

related to the objective and the specific conditions of the study. These may include the 

following:

Nutrients

Fecal coliform

Chlorophyll-a

BOD5, COD or TOC

Water column profiles

Ambient toxicity tests

Toxic pollutants (metals, volatile organics, priority pollutants, other) 

Water column dilution, currents, etc.

Others

In many cases receiving water studies will be required to determine if the Water Quality 

Standards are being met in the water column. Each water body classification has water quality 

standards for the following parameters:

Temperature

Dissolved oxygen

pH

Turbidity

Fecal coliform

Total dissolved gas

In addition, water quality standards based on aquatic toxicity have been developed for the 

following toxic substances:

Aldrin/Dieldrin Heptachlor
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Ammonia Lindane

Cadmium Lead

Chlordane Mercury

Chlorine Nickel

Chloropygifos Parathion

Chromium 3+ PCBs

Chromium Pentachlorophenol

Copper Selenium

Cyanide Silver

DDT & metabolites Toxaphene

Endosulfan Zinc

Endrin

All water body classifications are required to meet standards based on aquatic toxicity. Human 

health-based criteria for 91 toxic compounds have been issued to the state by the EPA. If those 

chemicals are detected in effluent at concentrations that merit concern, either tissue 

bioaccumulation or water column studies may be required. Guidance on setting limits based on 

human health is given in Chapter VII.

Ambient toxicity should be measured with organisms that tolerate the natural salinity of the 

water body. This will allow a truer measure of toxicity in the water column than if samples 

undergo salinity modification. For example, ambient brackish waters should be measured with 

organisms tolerant of brackish salinities, instead of requiring addition of artificial salts to enable 

use of a marine organism not tolerant of brackish salinities. Always choose the test organism 

that will require the smallest amount of sample modification. 

6.2.2 Sampling Locations

Water quality criteria apply at the end-of-pipe unless a mixing zone is established. If a mixing 

zone is established, its spatial boundaries will be specified in the permit. The mixing zone 

boundary can be set between the discharge point and the distance limits specified in WAC 173-

201A. If the objective of the receiving water survey is to determine background concentrations 

of toxins (or other characteristics) to use in the calculation of effluent limits, locate the sampling 

station as near to the discharge as possible, but in an area not affected by the discharge of any 

effluents. In most circumstances this will be an easy and straightforward task. However, the 

task may become complex in poorly flushed areas of estuarine circulation (tidal cycles that dilute 

effluent with previously discharged effluent from the same source), or where multiple effluents 

are discharged into the same water body. In complex areas, waste-load allocations may be 

necessary to allocate discharge capacity to numerous discharges. If this type of situation exists, 

contact the Program Development Services Section at headquarters.

In order to accurately set sampling station locations that address the survey objectives, it may be 

necessary to field-verify computer models of mixing and dilution in receiving waters. Typical 
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situations where this could occur are in shallow areas affected by both tidal currents and 

regularly occurring strong winds (e.g., wind may move effluent plume into areas that are not 

predicted by models), in rivers with "side bank" discharges, or in areas where accumulation of 

toxins in sediments does not match the pattern of effluent flow predicted by models. A dilution 

study can include use of floats, dyes, salts, and other devices, can include samples from all 

depths, and can last from hours to weeks (or longer). A natural component of the effluent may 

be used if the differential between the concentration in the effluent and receiving water is large. 

In most cases, however, a dye is added to the effluent in proportion to the effluent flow. The 

specific type of study you choose to require will depend directly on the types of questions you 

plan to ask in any future receiving water surveys, and on the physical characteristics of the 

discharge area. The EA Program should be contacted before specific dilution study methods are 

determined. The information from dilution studies will prove useful when used to locate 

sampling stations.

Depending on the specific objectives of the receiving water survey, the following sampling 

location considerations may apply:

Rivers --

Reference or control stations may be located upstream from the discharge point, but downstream 

from other sources of pollutants or dilution (e.g., other discharges or tributaries). Data from 

reference or control stations can be compared to data collected from stations at or below the 

point of discharge, or for calculating effluent limits.

Stations chosen to assess the effectiveness of effluent limits (i.e., whether or not Water Quality 

Standards are being exceeded) are generally located downstream of the discharge point, in 

an area where complete mix of the effluent occurs. The boundaries of the mixing zone used 

in setting effluent limits will be specified in the permit and fact sheet. Sampling this area is 

important when determining whether narrative criteria, as measured by ambient toxicity, are 

being met.
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Stations located downstream from the discharge point and mixing zone can provide data to 

assess the instream effects caused by discharges. Your list of considerations when selecting 

downstream sampling stations and depths might include the following:

• The different densities of the wastewater constituents, such as floating oils, or 

settling suspended solids.

• The distribution of the wastewater constituents in the receiving water, resulting 

from either poor mixing or stratification (for example, vertical distribution patterns 

which may need to be determined).

• Public beaches, shellfish beds, eelgrass beds or other biologically productive areas 

that may be affected by the discharge of pollutants.

• Chemical or biological reactions, such as growth of algae in upper layers of the 

water which may cause changes in pH, or exertion of a BOD sag miles downstream 

of the discharge.

• The convenience and accessibility for sampling the area.

These types of information will help focus your choice of sampling site to a particular place and 

time that best address the objectives and constraints of the survey. In general, only complex 

receiving water surveys will require the use of sample stations located downstream of mixing 

zones.

Marine or Estuarine Systems --

Sampling tidally influenced environments is almost always more complex than sampling 

unidirectional-flow river systems. In most cases the selection of sampling stations for marine or 

estuarine receiving waters will follow the same general riverine principles of control stations and 

full mix station, with practices adapted to the tidal marine environment. Additional factors to 

consider include tidal cycles, current patterns, bottom currents and counter-currents, 

stratification, climatic conditions, seasonal fluctuations, dispersion of discharges, wind induced 

surface currents, and multi-depth sampling. If a problem develops that may be caused by a 

marine/estuarine discharger, and that problem can only be addressed by a complex receiving 

water survey, it is appropriate to perform a dilution study prior to choosing sample sites.

Water current and chemical data for some areas of Puget Sound exist. It would be worthwhile to 

consult any studies conducted by the Coast Guard, the Corps of Engineers, NOAA, USGS, 

universities, or private research done in areas you are focusing on. That data can help you 

determine whether initial surveys (preliminary surveys that will give you enough information to 

set up the real receiving water survey) are necessary. The EA Program may be able to provide 
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some references. Marine and estuarine sampling will require some kind of station positioning 

method. 

Considerable stratification can occur in estuaries because of the differing densities of saltwater 

and freshwater. Freshwater flows enter estuaries as point source discharges, as sheets of storm 

water runoff, and in rivers and other smaller tributaries. Freshwater is more buoyant than salt 

water, and will rise to the surface unless it is entrained in a current underneath a salt water layer. 

It is essential to determine the extent of stratification when starting a survey of an unknown 

estuarine area. This can be done by determining salinity at different locations and depths over 

tidal cycles and over seasons. Because stratification is important to know about when 

calculating effluent limits and when designing a field survey, it should always be considered 

during survey design. Stratification is not difficult to measure, but the field time and gear needed 

to measure stratification can be expensive. If data indicating the extent of stratification is not 

available, the permit writer should require the discharge to provide the information only for 

times of maximum concern. 

It is possible for stratification to occur in one part of an estuary and not in another. A wedge of 

fresh river water overriding more dense saltwater is a specific mechanism of stratification 

commonly seen at and in the vicinity of river mouths. In that situation, when the discharge of 

pollution is in the saltwater layer, the contamination will be concentrated near the bottom of the 

freshwater wedge at the flood tide. Where stratification is suspected, samples at different depths 

will be needed to measure vertical distribution. Dilution studies will generally be needed to 

determine plume movement and dispersion during times of stratification. These studies should 

generally be conducted under the perceived "worst case" dilution conditions (e.g., time of least 

flushing flows, accounting for low slack tides and ebb tides). 

6.2.3 Specify Methods for Sample Collection and Analysis

The general sampling methods for receiving water surveys conducted within Puget Sound are 

detailed in the Puget Sound Protocols. The analytical methods chosen for a specific survey 

should, as far as possible, be consistent with both the Puget Sound Protocols and the Ambient 

Monitoring Program. In some cases other methods may be more appropriate to address the 

survey's objective. 

The choice of specific field methods and equipment used to collect samples will in large part be 

determined by the type of representative sample required to address the survey objectives, and 

the chosen analytical methods. In almost all cases grab samples will be collected because of the 

limited availability, expense, and vandalism problems associated with in-situ composite 

samplers. Determine the depth of sampling based on the position of the plume and the particular 

chemicals or physical properties you are interested in. Equipment preparation and type should 

follow the guidance in the Puget Sound Protocols. If you are planning to measure many different 

constituents of the sample, make sure that the sample collection gear fulfills the specifications of 

all the different analyses. This might mean collecting more than one sample per station. In all 
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cases, parameters that are subject to change during storage (dissolved gases, residual chlorine, 

soluble sulfide, temperature and pH) should be determined in the field.

Unless a special data need arises, samples collected from Puget Sound for metals determinations 

should follow the sample collection, analytical methods and the QA/QC procedures outlined in 

the Recommended Protocols for Measuring Metals in Puget Sound Water, Sediment and Tissue 

Samples (1986a). The sample collection methods for water column samples provides guidance 

for using water bottle samplers that also applies to sampling the water column of fresh waters. 

In general, water column samples collected for analysis of toxins have not been collected with 

replication. This has in large part been due to cost considerations. In situations where water 

column concentrations are compared to the Water Quality Standards, lack of replication may not 

be particularly important. However, in more complex surveys the statistical design of the survey 

will drive any data interpretation. An estimate of the sample variance is frequently needed for a 

statistical test powerful enough to yield useful data, and more than one sample is needed to 

estimate the sample variance. The needed replication cannot accurately be known without a 

characterization of the variability of the constituent of concern in the water body, which can be a 

prohibitively expensive task. Additionally, other sources of variability that affect the system are 

often uncharacterized (e.g., local currents). The Permit Manager should be aware that smallscale spatial variability of toxins in waters are not well characterized, and studies conducted 

without replication lack an estimate of the sample variance of the parameter, which can hinder 

interpretation of sampling results. Always discuss the design of complex receiving water 

studies with the EA Program and the appropriate headquarters unit.

Dilution studies should be conducted using methods in the following references:

USGS. 1985. Kilpatrick, F.A., and Cobb, E.D., Measurement of Discharge Using Tracers. 

Chapter A16. Techniques of Water-Resources Investigations of the USGS, Book 3, Application of Hydraulics. U.S. Department of the Interior. Reston, VA.

USGS. 1986. Wilson, J.F., Cobb, E.D., Kilpatrick, F.A. Fluorometric Procedures for Dye 

Tracing. Chapter A12. Techniques of Water-Resources Investigations of the USGS, Book 3, 

Application of Hydraulics. U.S. Department of the Interior. Reston, VA.

Doneker, R.L. and Jirka, G.H. 1990. Cormix1: An expert system for Hydrodynamic mixing zone 

analysis of Conventional and Toxic Submerged Single Port Discharges. USEPA, 

Environmental Research Laboratory, Athens, GA. EPA/600-3-90/012.

Akar, P.J. and Jirka, G.H. 1990. Cormix2: An Expert System for Hydrodynamic Mixing Zone 

Analysis of Conventional and Toxic Multiport Diffuser Discharges. USEPA Environmental 

Research Laboratory, Athens, GA. Draft, July 1990.
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Yearsley, J. 1991. Diffusion in near-shore and riverine environments. USEPA Region 10. EPA 

910/9-87-168.

Also review the material in Appendix 6.

6.2.4 Specify the Timing and Frequency for Sampling

Predictable variations in the quantity and quality of effluent, as well as seasonal variations in the 

receiving water, will help to establish the timing and frequency for a receiving water sampling 

program. In most cases a "worst case" scenario will be of interest, which for the majority of 

river dischargers will be at low summertime flows. For estuarine dischargers worst case could 

correspond to times of minimum flushing and maximum stratification.

Some data interpretation difficulties may occur when determining compliance with water quality 

standards that were developed with toxicity test exposure periods ranging from instantaneous 

maximum (silver) to 4-day averages (e.g., zinc). If you collect one grab sample on one day, is 

that sufficient to determine compliance with a standard that was developed with a 4-day average 

exposure? In general, because one-time grab samples are the type of data which is most practical 

and least expensive to collect, those data will be directly compared to Water Quality Standards to 

assess compliance. If the discharger is not willing to use one sample to measure water body 

compliance, the discharger should be allowed and encouraged to sample multiple times over an 

appropriate time period to collect data that is even more representative for comparison to the 

Water Quality Standards.

6.3 Sediment Monitoring

The protocols for sediment monitoring, as well as when sediment monitoring is necessary, are 

discussed in Section 7.

6.4 Crop/Soil/Vadose Monitoring

The Criteria for Sewage Works Design states that for land application, background soil samples 

sufficient to characterize the field area shall be tested prior to land application. Additional soil 

samples shall be collected and retained permanently to allow the original soil to be physically 

compared with the soil after application begins. The depth to the permanent ground water table 

shall be determined.

Chemical data on the soil will be analyzed on an annual basis for a possible build-up of heavy 

metals, salts, a pH change, or any other parametric change that may indicate a reduction in soil 

renovation capacity or fertility.
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6.5 Groundwater Monitoring

See Chapter VIII

6.6 Biological Surveys

Some of the various types of surveys commonly used to assess effects of pollution on biota 

include ambient water and sediment toxicity testing, analyses of benthic infaunal populations and 

communities, measures of bioaccumulation in resident or transplanted organisms, analyses of 

fish populations, and a variety of sub-lethal physiological, histopathological, and biochemical 

biomarkers (e.g., production of metallothionen and metal binding proteins, or, lesions in skin, 

ovary, liver, or other organs). The types of monitoring commonly encountered in NPDES 

monitoring programs include toxicity testing, benthic infaunal surveys, and measures of 

bioaccumulation. 

Guidance for monitoring sediment toxicity and benthic infaunal populations and communities is 

given in the Sediment Source Control Users Manual, Ecology, 1993. Guidance addressing 

bioaccumulation testing will be addressed during an upcoming rule-making on human healthbased water quality criteria. Bioaccumulation testing guidance for purposes other than to address 

human health are currently being developed, and will be inserted in this section when they are 

complete. Before that time, if characteristics of an effluent lead to the conclusion that problems 

exist that can most efficiently be addressed using bioaccumulation testing, the permit writer 

should contact the Program Development Services Section to discuss appropriate sample designs 

and organisms.

6.7 Data Compatibility

As required in the 1991 Puget Sound Water Quality Plan, monitoring data shall be gathered 

using the "Puget Sound Protocols (Tetra Tech, 1986b) when available". In addition, dischargers 

shall use data formats compatible with Storet.

7. SEDIMENT MONITORING

This section discusses the monitoring associated with the protection of aquatic sediments from 

waste water discharges. Specifically this section discusses:

• The general types of monitoring that may be conducted in support of the sediment source 

control process

• The different types of monitoring data that are applicable to the sediment source control 

process and their differing objectives

• Methods for the collection of monitoring data
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• Factors to be considered in the development of appropriate monitoring requirements

• Interpretation of the monitoring results in light of the monitoring objectives.

Permit managers who have permittees which require sediment impact zones (SIZ) should review 

the Sediment Source Control Standards User Manual for more detail on monitoring associated 

with sediment impact zones.

7.1. General Types of Monitoring in the

Sediment Source Control Process

There are four general types of monitoring that may be conducted in support of the sediment 

source control process:

• Baseline monitoring — Conducted prior to authorization of a SIZ to collect information 

that will be used in determining whether such an authorization is likely to be necessary.

• SIZ application monitoring — Conducted to collect information to support application of 

the SIZ models.

• Maintenance monitoring — Conducted during the term of a permit that includes an 

authorized SIZ, with the intent to determine whether the SIZ should be renewed, reduced, or 

eliminated; to determine whether areas of special importance have been adversely impacted 

by the discharge; and to determine the conditions for SIZ reauthorization.

• Closure monitoring — Conducted following closure of a SIZ to demonstrate successful 

restoration of sediment quality.

Baseline monitoring, SIZ application monitoring, maintenance monitoring, and closure 

monitoring are the responsibility of the discharger. The need for and extent of each of these 

types of monitoring will vary depending on discharge- and site-specific characteristics. In 

certain cases, it may be possible for the discharger to use data previously collected in other 

monitoring programs in lieu of conducting baseline monitoring.

In addition to these four general types of monitoring conducted in support of the sediment source 

control process, there are other situations in which additional monitoring may be appropriate. 

For example, Ecology or an interested third party may conduct additional monitoring to assess 

discharge or receiving environment conditions independent of the assessment provided by the 

discharger. In the event Ecology determines that modification of the conditions of the SIZ 

authorization is necessary, the discharger may also conduct additional monitoring to rebut the 

conclusions of Ecology's determination.
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7.2 Monitoring Objectives

Monitoring objectives vary with the type of monitoring being conducted. The objectives for the 

four general types of monitoring are described below.

7.2.1. Baseline Monitoring

The primary objective of baseline monitoring is to collect information to confirm a best 

professional judgment decision of the potential to violate the SQS. The data will be used in 

determining whether a SIZ authorization is likely to be necessary. Such data may be used for:

• Application of simple screening tools (e.g., information on the nature of the wastewater to 

be discharged, based either on knowledge of the type of facility or on actual chemical 

analyses of the wastewater)

• Definition of baseline environmental conditions in the vicinity of the discharge (e.g., 

chemical or biological characteristics of the sediments).

Baseline monitoring data can also be used to identify other potential contaminant sources in the

area or to relieve the discharger from liability for sediment contamination contributed by other 

permitted or unpermitted (and possibly historical) discharges.

7.2.2. SIZ Application Monitoring

The objective of SIZ application monitoring is to collect the necessary data to support the use of 

generalized or site-specific models to predict future sediment conditions under specific discharge 

scenarios (e.g., more detailed information on characteristics of the wastewater as well as on 

physical and chemical conditions in the receiving environment). In cases where an existing, 

permitted point source has been discharging at a similar flow and wastewater quality for a 

sufficiently long period (e.g., 10 years), there is reason to believe steady-state contaminant 

concentrations may have been reached. In such cases, existing sediment conditions alone may 

indicate whether there is a need for a SIZ in the absence of detailed modeling.

7.2.3 Maintenance Monitoring

The objectives of maintenance monitoring are to collect data necessary to:

• Determine whether the SIZ should be renewed, reduced, or eliminated

• Determine whether areas of special importance have been adversely impacted by the 

discharge

• Determine the conditions for SIZ reauthorization.
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Such monitoring may include chemical and/or biological assessments of conditions within the 

SIZ to demonstrate that the maximum allowable contaminant concentrations and/or biological 

effects levels have not been exceeded within the SIZ. Assessments of chemical and/or biological 

conditions in areas beyond the SIZ may also be used to demonstrate that the spatial limits of the 

authorized SIZ have not been exceeded.

7.2.4. Closure Monitoring

For instances of SIZ closure that involve active cleanup, the objective of closure monitoring is to 

demonstrate that the cleanup was successful at restoring sediment quality to acceptable levels 

(i.e., to contaminant concentrations and/or biological effects levels below SQS) within the SIZ. 

For instances of SIZ closure that involve natural recovery of the sediments, the objective of 

closure monitoring is to verify predictions regarding the efficacy of natural processes in restoring 

sediment quality to acceptable levels within the SIZ.

7.3. Types of Monitoring Data

There are several types of monitoring data that are applicable to the sediment source control 

process:

• Physical data on the receiving environment

• Chemical data on the receiving environment

• Biological data on the receiving environment

• Physical data on the wastewater discharge

• Chemical data on the wastewater discharge

• Whole-effluent toxicity test data.

Some types of monitoring data may be useful for only one phase of the sediment source control 

process. For example, physical monitoring of the receiving environment may be required to 

provide input for the SIZ models used to determine whether a SIZ should be authorized for a 

given discharge, but may not be necessary after a SIZ is authorized. Other types of monitoring 

data may be useful for all phases of the sediment source control process. For example, chemical 

or biological monitoring of the receiving environment may be required to determine whether a 

SIZ should be authorized, to demonstrate compliance with conditions of an authorized SIZ, or to 

document successful remediation of sediment contamination following SIZ closure. The various 

types of monitoring data and the potential uses of the data are described in greater detail below.
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7.3.1. Physical Data on the Receiving Environment

Data on physical conditions in the receiving environment may be useful in determining whether 

sediment impacts are likely to occur. For example, physical evidence of a high-energy, 

nondepositional receiving environment in the vicinity of the discharge would suggest that 

sediment impacts are unlikely to occur.

Data on physical conditions in the receiving environment are also collected to support 

application of the SIZ models. The types of physical data that may need to be collected include 

vertical profiles of the density of the receiving water (generally calculated from the temperature 

and salinity of the receiving water), water depth, bottom topography, ambient current velocities, 

particulate concentrations in the water column, ambient sedimentation rates, and physical 

characteristics of the sediments (e.g., sediment grain size). The SIZ models can be run with 

varying degrees of site-specific data. In some cases, default values for many of the model input 

parameters can be used, while in other cases, detailed site-specific data are required to run the 

models. Guidance on the appropriate data requirements for various types of SIZ model runs is 

provided in the WASP Application Guidance Manual (Ecology, in preparation).

7.3.2. Chemical Data on the Receiving Environment

The collection of sediment chemistry data may be important for several reasons. Data on 

contaminant concentrations in the sediments around an existing discharge that are collected 

during baseline monitoring can be compared with the SQS numerical criteria to determine 

whether there is a need for a SIZ. If none of the contaminants exceed the SQS numerical criteria, 

and there has been neither a substantial change in the wastewater composition or flow over the 

past several years nor an expected change in the next 10 years, then it is unlikely that a SIZ will 

be needed. Exceedances of the SQS numerical criteria, however, suggest the need for further 

analyses to determine whether a SIZ will be required. Exceedances of the SQS numerical 

criteria would not necessarily require authorization of a SIZ because:

• The exceedances of SQS numerical criteria may be historical or otherwise unrelated to the 

discharge in question

• Modeling may indicate that sediment contaminant concentrations are expected to be below 

SQS numerical criteria within 10 years

• The discharge may not be eligible for a SIZ.

In the event that site-specific data are needed for running the SIZ model(s), it will likely be 

necessary to measure existing sediment contaminant concentrations.
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In certain circumstances, it may be appropriate to collect data on subsurface as well as surface 

sediment quality conditions. Contaminant concentrations in subsurface sediments may be used 

to investigate changes associated with increases or decreases in contaminant loading over time, 

and may be important in establishing sedimentation rates that may be used in evaluating the 

efficacy of natural recovery.

Sediment chemistry data will also be useful for both maintenance and closure monitoring. The 

contaminant concentrations in sediments within an authorized SIZ will be monitored to 

determine whether there are any exceedances of applicable limits (i.e., SIZmax or other limits 

established specifically for that SIZ). Contaminant concentrations in sediments beyond the 

authorized SIZ will also be monitored to determine whether there are any exceedances of SQS 

numerical criteria. Finally, contaminant concentrations in the sediments following SIZ closure 

will be monitored to evaluate whether the predicted reductions in contaminant concentrations 

following natural recovery, or the target contaminant concentrations following active restoration, 

are achieved.

7.3.3. Biological Data on the Receiving Environment

Biological monitoring data, which consist of information on the abundances of naturally 

occurring benthic infaunal organisms and the results of sediment bioassays, are used for two 

basic purposes in the sediment source control process. First, WAC 173-204-315 allows for the 

use of acute and chronic effects biological tests to confirm designation of Puget Sound marine 

sediments using the procedures described in WAC 173-204-310(2). Sediments that have either 

passed or failed the initial designation procedures based on compliance with the SQS numerical 

criteria may be subject to confirmatory designation using these biological tests. The results of 

these biological tests may override the initial designation based on sediment chemistry alone. 

Hence, confirmatory testing using these biological tests may be important in determining the 

potential need for a SIZ. If the sediments around a wastewater discharge have one or more 

chemicals that exceed the criteria of WAC 173-204-320(2), these sediments would be designated 

as failing the SQS and the discharge would be considered for authorization of a SIZ, unless the 

results of the biological tests indicate the absence of adverse effects. Conversely, even if the 

sediments pass the chemical criteria of WAC 173-204-320(2), there may be reason(s) to conduct 

biological tests on the sediments (e.g., if there are potentially toxic chemicals known to be 

present in the sediments for which there are no SQS numerical criteria). Failure of one or more 

of the biological tests would result in the designation of the sediments as failing the SQS, and the 

discharge would be considered for authorization of a SIZ.

Second, biological tests are used in the sediment source control process to identify the maximum 

biological effects level that may be authorized within a SIZ. The SIZmax biological effects levels 

can be established using one of two methods (see Table IX-2). While designation of sediments 

as failing the SQS requires only one of the biological tests of WAC 173-204-315 to be failed by 

the criteria of WAC 173-204-320(3), the SIZmax biological effects level is exceeded when any 

two of the biological tests exceed the criteria of WAC 173-204-320(3). Alternatively, the SIZmax
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biological effects level is also considered to be exceeded when any one of the biological tests 

exceeds the criteria of WAC 173-204-420(3), each of which requires a greater biological effect 

than the corresponding criteria of WAC 173-204-320(3).

7.3.4. Physical Data on the Wastewater Discharge

The collection of physical data on the wastewater discharge will likely be necessary to provide 

input for the SIZ models. The types of physical data likely to be needed include:

• the flow of the discharge (to estimate total loading to the receiving water), 

• the density of the wastewater (generally calculated from the measured or estimated 

temperature of the wastewater if the salinity of the wastewater approximates that of fresh 

water, or from both the temperature and salinity if it does not), and 

• the concentration of suspended solids in the wastewater. Physical processes such as 

flocculation and coagulation may affect the concentration of suspended solids following 

discharge to the receiving environment, but these processes are not presently addressed in 

the SIZ models.

As previously indicated, the SIZ models can be run with varying degrees of site-specific data. In 

some cases, default values for many of the model input variables can be used, while in other 

cases, detailed site-specific data are required to run the models. Guidance on the appropriate 

data requirements for various types of SIZ model runs is provided in the WASP Application 

Guidance Manual (Ecology, in preparation).

7.3.5. Chemical Data on the Wastewater Discharge

Data on the chemical characteristics of the wastewater may be used for several purposes. Data 

on the concentrations of chemical contaminants in the wastewater that are routinely collected as 

part of NPDES monitoring may be used in simple screening tools to determine whether the 

discharge has the potential to cause exceedances of the SQS numerical criteria. The data 

required for this purpose include the concentrations of any of the contaminants in the wastewater 

for which there are SQS numerical criteria, as well as the concentration of suspended solids in 

the wastewater. These data may also be used in the SIZ models to evaluate the need for a SIZ. 

Data on the concentrations of chemical contaminants in the wastewater may also be used to 

verify that the discharge is achieving AKART or some other level of required treatment defined 

on the basis of achievable wastewater concentrations. Finally, data on the concentrations of 

chemical contaminants in the wastewater may be used to identify contaminants that may be 

targeted for investigation in monitoring of the receiving water or sediments.
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7.3.6. Whole-Effluent Toxicity Test Data

Data on whole-effluent toxicity may be useful for assessing the likelihood of adverse biological 

effects in the sediments. This is especially true when the same organisms (e.g., bivalve larvae) 

were used in the whole-effluent toxicity tests as would be used in assessing sediment impacts. If 

a toxic effect was demonstrated in a whole-effluent toxicity test, this may suggest the need for 

biological testing of the sediments in the vicinity of the discharge, especially if the cause of the 

toxicity is not apparent.

7.4. Methods for Collecting Monitoring Data

This section briefly describes the methods appropriate for collecting various types of monitoring 

data. In cases where the methods have been described in other documents, appropriate 

references to those documents are provided. For methods that are not well documented, 

additional details are provided, although the level of detail is necessarily brief.

7.4.1. Physical Monitoring of the Receiving Environment

Data on physical conditions in the receiving environment collected to support application of the 

SIZ models may include vertical density profiles, ambient current velocities, ambient suspended 

particulate matter concentrations, sedimentation rates, sediment grain size, water depth, and 

bottom topography. Methods for collecting these data are described briefly in the following 

sections.

Vertical Density Profiles

Vertical density profiles, which may be necessary for detailed discharge modeling, are typically 

generated from temperature and salinity data. Temperature and salinity (or conductivity) are 

generally measured electronically using submersible probes (e.g., conductivity-temperaturedepth devices, or CTD) lowered from a boat. In some cases, temperature may be measured using 

reversing thermometers, and salinity may be determined by returning the samples to the 

laboratory for measurement with a salinometer. Recommended procedures for measuring 

temperature and salinity are described in PSEP (1991b). Measurements should be made over the 

entire water column at the site of the discharge and at sufficient intervals to provide 

representative data for periods of maximum and minimum stratification.

Ambient Current Velocities

Ambient current velocities are typically measured using current meters. Multiple current meters

are usually arrayed along a taut-line mooring, which is deployed in the immediate vicinity of an 

outfall. Records of currents are typically made over periods of several weeks; the period of 

monitoring should take into account the possible effects of variations in both tidal influences and 

nontidal influences (e.g., wind-induced currents), and should be scheduled to include periods of 

both spring and neap tides.
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Ambient Suspended Particulate Matter Concentrations

Determination of ambient suspended particulate matter concentrations normally entails 

collection of water samples from the water column and analysis for TSS. Sample collection and 

analytical procedures are described in PSEP (1991b). If ambient TSS data are required, the 

sampling strategy should address the temporal and spatial variability of this variable, which is 

likely to be high.

Sedimentation Rates

The most common method of estimating sedimentation rates is through the use of sediment traps, 

which are cylinders, closed at the bottom, that are placed vertically in the water column to collect 

settling particulate matter (see U.S. GOFS [1989] and Norton [1990] for descriptions of sediment 

trap design and use). Sedimentation rates (i.e., the rate at which particulate matter settles out of 

the water column) should not be confused with sediment accumulation rates (i.e., the rate at 

which sediments accumulate on the bottom after accounting for loss functions such as 

resuspension and biodegradation). Because sediment traps are routinely left in place for up to 3 

months and occasionally for up to 6 months, they are useful for characterizing average loadings 

of suspended solids from an intermittent or variable source, such as a storm drain, as well as for 

characterizing local area sedimentation rates. The advantage of sediment traps is that they 

collect particulate matter settling out of the water column before it is commingled with sediments 

on the bottom. The primary disadvantage is that the particulate matter collected is from all 

sources, both natural and anthropogenic, and not just from the discharge of interest.

Sediment traps should be used in areas that do not receive heavy boat traffic. The traps should 

be placed close to the source, far enough above the bottom that sediment resuspension will not 

substantially dilute the particulate matter from the source that is found in the trap. Traps are 

typically poisoned with sodium azide, mercuric chloride, or salt to minimize biotransformation 

of organic chemicals. However, a poison should be selected that does not interfere with the 

analytes of interest. To minimize preservation concerns, valves that prevent entry of 

zooplankton into the traps have been incorporated into recent sediment trap designs.

Sediment Grain Size

Determination of sediment grain size may be important in assessing the potential for sediment 

deposition and in modeling sediment resuspension. Sample collection and analysis procedures 

are described in PSEP (1986). The sampling strategy should take into account spatial differences 

in sediment grain size, as well as temporal differences that may occur, especially in areas with 

seasonal differences in flow regime.

Water Depth and Bottom Topography

In cases where relatively detailed bathymetric charts exist for the vicinity of a discharge, 

sufficient information on water depth and bottom topography may already be available. In other 

cases, it may be necessary to conduct a bathymetric survey, generally using echosounding 

equipment, to provide such information.
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7.4.2. Chemical Monitoring of the Receiving Environment

Chemical monitoring of the receiving environment may be used to evaluate existing sediment 

quality, to provide input for the SIZ models, to evaluate historical changes in contaminant 

loading, and to use for both maintenance and closure monitoring. Chemical monitoring includes 

conventional sediment variables, sediment contaminant concentrations, and concentrations of 

contaminants associated with suspended particulate matter. Methods for the collection of these 

data are described briefly in the following sections.

Conventional Sediment Variables

Measurement of conventional sediment variables is valuable to help interpret the concentrations 

of sediment contaminants. TOC, for instance, should be measured whenever the concentrations 

of nonionizable organic compounds are to be measured, because the SQS numerical criteria for 

those compounds are TOC-normalized. Acid-volatile sulfides (AVS) should be measured 

whenever the concentrations of metals are to be measured, because AVS data are useful for 

interpreting the toxicity of metals in sediments. Analysis of ammonia is also potentially useful 

for interpreting bioassay results. Guidelines for the collection of sediment samples and for the 

analyses of conventional sediment variables are provided in PSEP (1986).

Sediment Contaminant Concentrations

To determine whether sediment samples contain any contaminants at concentrations above the 

SQS or to use contaminant concentrations for input to the SIZ models, the sediments should be 

analyzed for all contaminants for which there are SQS numerical criteria and for all contaminants 

that are either known or suspected to be present in the wastewater of a subject discharge. There 

may be other potentially toxic contaminants known or suspected to be in the subject wastewater 

for which there are presently no criteria (i.e., “other toxic, radioactive, biological, or deleterious 

substances,” see WAC 173-204-320(5)). These contaminants should also be analyzed for, using 

methods to be determined on a case-by-case basis, because their presence in the sediments may 

necessitate the assessment of the concentration below which they would have no adverse effects.

Guidelines for the collection of sediment samples are provided in PSEP (1986). Metals should 

be analyzed according to the guidelines provided in PSEP (1989a), and organic compounds 

should be analyzed according to the guidelines provided in PSEP (1989b). Recommended 

sample preparation methods, cleanup methods, analytical methods, and detection limits for 

sediments are presented in Table XIII-6. It is important that subsamples of sediment samples 

analyzed for nonionizable organic compounds be analyzed for TOC as well in order to normalize 

the resulting concentrations by their TOC contents. It is also important that the analytical 

laboratory be instructed to employ all necessary methods to attempt to achieve the recommended 

detection limits.
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Concentrations of Contaminants Associated with Suspended Particulate Matter

It is expected that it will rarely be necessary to directly measure the concentrations of 

contaminants associated with suspended particulate matter in the receiving environment. This 

information might be necessary in cases where it is not practical to directly measure the 

concentrations of contaminants in wastewater suspended solids and the information is needed for 

the application of screening procedures or modeling techniques. If such information is 

necessary, the use of filtration or continuous centrifugation may be considered to collect the 

suspended solids, although neither method may be practical because of the large volumes of 

water that must be filtered or centrifuged. Alternatively, concentrations of contaminants 

associated with suspended particulate matter in the receiving water may be measured using 

sediment traps to collect the particulate matter; these methods have been successfully employed 

in Commencement Bay waterways by Norton (1990).
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Table XIII-6 . Recommended Sample Preparation Methods, Cleanup Methods, Analytical 

Methods and Detection Levels for Sediments.

Chemical Recommended 

Sample 

Preparation 

Methodsa

Recommended 

Sample 

Cleanup 

Methodsb

Recommended

Analytical 

Methodsc

Recomme

nded

Detection 

Limitsd

( g

Metals

Arsenic PSEP -- 7060/7061 100

Cadmium PSEP -- 7130/7131 100

Chromium PSEP -- 7190/7191 5,000

Copper PSEP -- 7210 100

Lead PSEP -- 7420/7421 100

Mercury --e -- 7471 10

Silver PSEP -- 7760 100

Zinc PSEP -- 7950 200

Nonionizable Organic Compounds

LPAH Compounds

Naphthalene 3540/3550 3640/3660 8270/1625C 10

Acenaphthylene 3540/3550 3640/3660 8270/1625C 10

Acenaphthene 3540/3550 3640/3660 8270/1625C 10

Fluorene 3540/3550 3640/3660 8270/1625C 10

Phenanthrene 3540/3550 3640/3660 8270/1625C 10

Anthracene 3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

HPAH Compounds

Fluoranthene 3540/3550 3640/3660 8270/1625C 10

Pyrene 3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

Chrysene 3540/3550 3640/3660 8270/1625C 10

Total 3540/3550 3640/3660 8270/1625C 10

Benzo[a]pyrene 3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

Chlorinated 

1,2-Dichlorobenzene 3540/3550 3640/3660 8270/1625C/8240 10
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Chemical Recommended 

Sample 

Preparation 

Methodsa

Recommended 

Sample 

Cleanup 

Methodsb

Recommended

Analytical 

Methodsc

Recomme

nded

Detection 

Limitsd

( g

3540/3550 3640/3660 8270/1625C/8240 10

3540/3550 3640/3660 8270/1625C/8240 10

3540/3550 3640/3660 8270/1625C 10

Phthalate Esters

Dimethyl 3540/3550 3640/3660 8270/1625C 10

Diethyl phthalate 3540/3550 3640/3660 8270/1625C 10

Di-n-butyl phthalate 3540/3550 3640/3660 8270/1625C 10

Butyl benzyl 3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

Di-n-octyl phthalate 3540/3550 3640/3660 8270/1625C 10

Miscellaneous Extractable Compounds

Dibenzofuran 3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

PCBs

PCB Aroclors 3540/3550 3620/364- 8080 1

Ionizable Organic 

Phenol 3540/3550 3640/3660 8270/1625C 10

2-Methylphenol 3540/3550 3640/3660 8270/1625C 10

4-Methylphenol 3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 10

3540/3550 3640/3660 8270/1625C 50

Benzyl alcohol 3540/3550 3640/3660 8270/1625C 50

Benzoic acid 3540/3550 3640/3660 8270/1625C 50

Other Analyses

Ammonia --

g -- Plumb (1981) 100

Grain size --

g -- Plumb (1981) 1%

Organic carbon, --

g -- 9060 0.1%

Sulfides, acid --

g -- U.S. EPA (1991) 0.1 

Sulfides, total --

g -- Plumb 100

Oil and grease --

g -- PSEP 10,000
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Chemical Recommended 

Sample 

Preparation 

Methodsa

Recommended 

Sample 

Cleanup 

Methodsb

Recommended

Analytical 

Methodsc

Recomme

nded

Detection 

Limitsd

( g

Total solids --

g -- PSEP 0.1% (wet 

wt)

Total volatile 

solids

--

g -- PSEP 0.1%

a Recommended sample preparation methods are: PSEP - Puget Sound Estuary 

Program (PSEP 1989a)

Method 3500 series - sample preparation 

methods from SW-846 (U.S. EPA 1986) and 

updates.

b Recommended sample cleanup methods are: Method 3600 series - sample 

cleanup methods from SW-846 (U.S. EPA 

1986) and updates. c Recommended analytical methods are: Method 7000, 8000, and 9000 series -

analytical methods from SW-846 (U.S. EPA 1986) and updates

Method 1625C - isotope dilution method (U.S. EPA 

1989)

Plumb (1981) - U.S. EPA/U.S. Army Corps of 

Engineers Technical Report EPA/CE-81-1

PSEP - Puget Sound Estuary Program (PSEP 

1986)

Acid volatile sulfide method for sediment (U.S. EPA 

1991).

d In order to achieve the recommended detection limits for organic compounds, it may 

be necessary to use a larger sample size (approximately 100 g), a smaller extract 

volume for gas chromatography/mass spectrometry analyses (0.5 mL), and one of the 

recommended sample cleanup methods, as necessary, to reduce interference. 

Detection limits are on a dry weight basis unless otherwise indicated.

e The sample digestion method for mercury is described in the analytical method 

(Method 7471, SW-846 [U.S. EPA 1986] and updates).

f

Total benzofluoranthenes represent the sum of the b, j, and k isomers.

g Sample preparation methods for sediment conventional analyses are described in the 

analytical methods.
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7.4.3. Biological Monitoring of the Receiving Environment

Biological testing to assess existing sediment quality, to establish the maximum biological 

effects level within an authorized SIZ, or to assess compliance with the SIZ authorization may 

include the conduct of sediment bioassays or the assessment of the naturally occurring 

community of benthic infauna in sediment samples. Methods for conducting these biological 

tests are described briefly in the following sections.

Sediment Bioassays

Four of the biological tests that can be applied to assessments of marine sediment quality in the 

sediment source control process are sediment bioassays, including:

Acute Effects Tests

• Amphipod—A 10-day acute sediment bioassay that assesses mortality of the amphipod 

Rhepoxynius abronius

• Larval—Any one of several acute sediment bioassays that assess mortality and/or 

abnormality of larvae of the following organisms:

- Pacific oyster, Crassostrea gigas

- Blue mussel, Mytilus edulis

- Purple sea urchin, Strongylocentrotus purpuratus

- Sand dollar, Dendraster excentricus

Chronic Effects Tests

• Juvenile polychaete—A 20-day sublethal sediment bioassay that assesses decreases in 

growth of the juvenile polychaete Neanthes arenaceodentata

• Microtox® saline extract—A 15-minute bioassay that assesses decreased bioluminescence 

of the bacteria Photobacterium phosphoreum exposed to a saline extract of the sediment 

sample. Although conducted for a relatively short period of time and therefore generally 

considered to be an acute test, the Sediment Management Standards consider the Microtox® 

bioassay to be a surrogate chronic test because of its high sensitivity.
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Guidelines for the collection of sediment samples and for the conduct of these bioassays are 

provided in PSEP (1991a).

In addition to the chronic sediment bioassays listed above, the assessment of benthic infaunal 

abundance (see below) is also considered to be a chronic biological test.

For confirmatory designation of marine sediments, WAC 173-204-310(2)(a) requires that the 

sediments be tested using two of the acute effects biological tests and one of the chronic effects 

biological tests. For establishing the SIZmax biological effects level, WAC 173-204-420(3)(a) 

also requires that the sediments be tested using two of the acute effects biological tests and one 

of the chronic biological effects tests. In establishing the SIZmax biological effects level, 

however, the only applicable chronic effects tests to choose from are the benthic infaunal 

abundance and juvenile polychaete tests.

Assessment of Benthic Infauna

As indicated above, the fifth biological test that can be applied to assessments of sediment 

quality in the sediment source control process is assessment of the naturally occurring 

community of benthic infauna in samples of the sediment of interest. This chronic effects test 

assesses statistically significant alterations in the abundances of the following major taxa: 

Crustacea, Mollusca, and Polychaeta. Guidelines for the collection and analysis of benthic 

infaunal samples are provided in PSEP (1987b).

7.4.4. Physical Monitoring of the Wastewater

Physical data on the wastewater to be collected to support application of the SIZ models may 

include the concentration of suspended solids in the wastewater, discharge flow, and wastewater 

density. Methods for collecting and analyzing these data are described briefly in the following 

sections.

Concentration of Suspended Solids in the Wastewater

The concentration of suspended solids in the wastewater may be needed for the use of simple 

screening tools and as input to the SIZ models. It is typically reported as the TSS content. The 

collection of samples for analysis of TSS should reflect knowledge of discharge conditions that 

are likely to result in temporal variability of the TSS content of the wastewater. Multiple 

samples are recommended to gain some idea of the variability of TSS content, which for some 

types of discharges may be extremely high. The analysis of TSS is conducted by filtering a 

sample of the wastewater, drying the filter, and weighing the filter by standard methods (APHA 

1989; Method 209C).

Discharge Flow

Information on the flow of the discharge is needed to estimate contaminant loading to the 

receiving environment and for use in the SIZ models. Flow is typically monitored and reported 

for most permitted wastewater discharges, regardless of whether they are under consideration for 
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authorization of a SIZ. Flow can be measured in situ using a variety of methods. There are two 

major categories of methods for measuring flow: direct-discharge and velocity-discharge 

(Metcalf & Eddy 1979). The direct-discharge methods are used most frequently, and relate the 

rate of discharge to one or two easily measured variables, employing devices such as weirs, 

Parshall flumes, Venturi meters, and magnetic flow meters. Flow should preferably be measured 

downstream of all treatment processes, although flow measurements upstream of the treatment 

processes are common for municipal wastewater treatment plants and may be used in the absence 

of downstream measurements. The most useful flow measurements are those made continuously 

and recorded automatically because they provide a temporal record of flow variations.

Wastewater Density

Wastewater density is needed as input for the modeling of initial dilution (e.g., in PLUMES or 

CORMIX). Although wastewater density could be measured directly, it is more typically 

calculated based on the temperature of the wastewater, assuming the salinity of the wastewater 

approximates that of fresh water. Unless the characteristics of an individual discharge suggest 

otherwise (e.g., for a brine discharge), wastewater density may be calculated based on 

temperature alone. Temperature may be measured using either a thermometer or a thermistor. 

Methods are discussed in APHA (1989; Method 212). Measurements of temperature should take 

into account any temporal variability that is likely to occur (e.g., based on seasonal changes or 

changes in treatment processes).

7.4.5. Chemical Monitoring of the Wastewater

Data on the chemical characteristics of the wastewater may include both contaminant 

concentrations in whole wastewater samples as well as contaminant concentrations in wastewater 

suspended solids. Such data may be used in simple screening procedures, as input to the SIZ 

models, as verification of achievement of specific wastewater treatment levels, or as evidence of 

contaminants that should be investigated in the receiving environment. Methods for the 

collection of these data are described briefly in the following sections.

Contaminant Concentrations in Whole Wastewater Samples

Contaminant concentrations in whole wastewater samples may be used in simple screening tools 

(see Chapter 4) or to estimate contaminant loading to the receiving environment. Routine 

analyses of EPA priority pollutant metals and organic compounds are included as monitoring 

requirements for many permitted discharges, regardless of whether they are under consideration 

for authorization of a SIZ. Wastewater samples may be collected as grabs, or as time-averaged 

or flow-weighted composites; the latter are generally preferred because they integrate variations 

in contaminant concentrations over short time scales (e.g., 24 hours). If there is likely to be 

substantial variability in wastewater quality over a longer time period (e.g., because of seasonal 

variations in stormwater runoff), it may be desirable to sample at various time intervals to gain 

an understanding of the range of wastewater quality. Methods for the analysis of EPA priority 

pollutant metals are presented in U.S. EPA (1987); methods for the analysis of EPA priority 

pollutant organic compounds are presented in U.S. EPA (1988a).
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Contaminant Concentrations in Wastewater Suspended Solids

If data are needed on the contaminant concentrations associated with wastewater suspended 

solids, sufficient solid sample must be collected to analyze for the contaminants of interest, and 

this may represent a technical challenge if the concentration of suspended solids is relatively 

low. One method under development for obtaining a sample of suspended solids from a 

wastewater sample is to pass the water through a high-speed, continuous centrifuge. This 

method is capable of retaining all the suspended solids present in the water. The use of a 

centrifuge will normally require continuous collection at the discharge facility for greater than a 

24-hr period. Because this procedure would involve collection of suspended solids over a 

relatively short time period, its best use would be to characterize sources that are continuous and 

relatively stable. Alternatively, a periodic monitoring program could be employed. Use of a 

continuous centrifuge for the collection of wastewater suspended solids is still under 

development by Ecology, and there is currently no approved protocol for this procedure.

A less costly method of obtaining suspended solids from wastewater is filtration. However, 

compared to the centrifuge method, filtration is time consuming, technically difficult, and may 

not be appropriate for use when a large water sample is needed to collect the required amount of 

solids for analysis. A discussion of the relative merits of the centrifuge and filtration methods 

can be found in Horowitz (1986). Methods for analysis of suspended solids samples are 

discussed in Tetra Tech (1986). Ecology (1991a) provides details on collection and analysis of 

suspended solids using a centrifuge.

7.5. Development of Appropriate Monitoring Requirements

This subsection describes the factors to be considered in the development of baseline, SIZ 

application, maintenance, and closure monitoring requirements.

Pursuant to WAC 173-204-400(5), Ecology is authorized to specify in discharge permits the 

locations and methods for collection and analysis of representative samples of wastewater, 

receiving water, and sediments that will be required of the discharger. In determining the 

appropriate monitoring requirements, WAC 173-204-400(6) requires Ecology to consider the 

following factors as they relate to the potential for the discharge to violate the SQS:

• Discharge suspended solids characteristics

• Discharge contaminant concentrations, flow, and loading rates

• Sediment chemical concentrations and biological effects levels

• Receiving water characteristics (e.g., vertical density profiles, ambient current velocities)
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• The geomorphology of sediments

• Cost mitigating factors such as the available resources of the discharger

• Other factors determined necessary by Ecology.

General issues to be considered in the development of monitoring requirements for all permitted 

discharges are discussed in other sections of this chapter.

The process for establishing monitoring requirements described in the other sections applies to 

all permitted discharges, whether or not they have the potential for impacting sediments or they 

are being considered for authorization of a SIZ. Certain aspects of the monitoring requirements 

pertinent to the sediment source control process overlap with aspects of the monitoring 

requirements for permitted discharges in general, and, in fact, certain information needs in the 

sediment source control process may already have been filled through the collection of 

monitoring data under an existing permit. In other cases, the information needs of the sediment 

source control process may be distinct and therefore require the collection of new and/or 

different types of monitoring data.

7.5.1. Development of Baseline Monitoring Requirements

The development of baseline monitoring requirements is the responsibility of the permit 

manager, with guidance and assistance from the SMU, as necessary. The baseline monitoring 

requirements should be described in detail in the discharge permit, or, in some cases, in a 

companion order.

If the result of the narrative and technical evaluations (Chapter IX) is a judgment that the 

discharge does not have the potential for causing sediment impacts, collection of baseline 

monitoring data may not be necessary. For discharges identified by the narrative and technical 

evaluations as having the potential for sediment impacts, there is expected to be a range of 

required baseline monitoring. In some cases, although there may be a potential for sediment 

impacts, the combination of discharge and receiving environment characteristics (e.g., a 

relatively small discharge with low levels of most priority pollutants, discharging to an 

environment not known to have sediment impacts, in the absence of other nearby discharges) is 

such that any sediment impacts would not likely be severe or widespread. In such cases, the only 

required baseline monitoring may be chemical analyses of sediments in the immediate vicinity of 

a marine discharge, or chemical analyses of sediments and sediment bioassays in the immediate 

vicinity of a freshwater discharge. In cases where sediment impacts might be expected to be 

more severe or widespread (e.g., a relatively large discharge with high levels of a number of 

priority pollutants, discharging to an environment known to have water and/or sediment quality 

problems, in the presence of other nearby discharges), more extensive baseline monitoring may 

be required.
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Under certain circumstances, the need for baseline monitoring data may already have been 

satisfied by previous studies. In such cases, the evaluation of the need for a SIZ can proceed 

without further data collection. In other cases, the collection of additional baseline monitoring 

data will be necessary to confirm whether there are exceedances of SQS in the vicinity of the 

discharge. If the data needs are relatively minor (e.g., collection and chemical analysis of a few 

surface sediment samples), the discharger may be required to collect the data prior to evaluation 

of the need for a SIZ. If, however, the data needs are extensive, the baseline monitoring 

requirements should be specified in the renewed permit (in the case of previously permitted 

discharges) or in the initial permit (for previously unpermitted discharges). By including the 

baseline monitoring requirements in the permit, issuance of the permit will not be unnecessarily 

delayed while an evaluation of the need for a SIZ is conducted. Authorization of a SIZ, if 

deemed appropriate, can then occur at a later time after the baseline monitoring data become 

available and are evaluated.

In developing baseline monitoring requirements for an individual discharge, it is important to 

understand that the intent is only to determine whether currently there are exceedances of SQS in 

the vicinity of the discharge, and whether they appear to be caused by the discharge. Baseline 

monitoring is not intended to accurately delimit the area over which there are exceedances of 

SQS, or to definitively tie those exceedances to the discharge. Baseline monitoring should 

therefore be able to detect exceedances of SQS near the discharge and then to determine whether 

such exceedances are of greater magnitude near the discharge or of a more general, area wide

nature, which might suggest contaminant inputs from other local sources.

For small discharges with only a low likelihood of sediment impacts, an array of only six stations 

may suffice if they are located along a transect extending from the point of discharge to a point 

downstream (in the direction of predominant current flow) sufficiently far away from the 

discharge to be beyond likely effects of the discharge. If flow is unidirectional (e.g., in a river), 

it may suffice to have one station of the transect upstream of the discharge to define ambient 

conditions. If flow is bidirectional (e.g., as in many Puget Sound marine environments where 

tidal currents predominate), the six stations might be arranged along a transect spanning the 

discharge along the axis of predominant current flow. Given the diversity of possible discharge 

scenarios, it is not appropriate to give generic guidance on the appropriate spacing of the stations 

along a transect. However, the spacing should take into account both the volume of the 

discharge and the velocity of currents in the vicinity of the discharge.

For larger discharges with a high likelihood of sediment impacts, or for discharges to more 

complex receiving environments, it may be necessary to have two to three transects, each with 

six stations extending out from the point of discharge. Once again, it is not appropriate to give 

generic guidance on the appropriate spacing of the stations along a transect, but the spacing 

should take into account both the volume of the discharge and the velocity of currents in the 

vicinity of the discharge.
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Selection of appropriate baseline monitoring parameters is dependent on the nature of the 

discharge. For most marine discharges, it will be appropriate to collect surface sediment samples 

and analyze them for the contaminants for which there are SQS numerical criteria. Depending 

on how thoroughly the effluent has been characterized, it may be appropriate to analyze the 

surface sediments for additional contaminants, especially any known to be present in the effluent 

and considered potentially toxic to aquatic life. The sediment samples from the various stations 

should be analyzed individually and not composited with those from other stations, so that it will 

be possible to investigate contaminant gradients as evidence of the source of the contaminants.

If chemical analysis of the sediments in the vicinity of a marine discharge reveals exceedance(s) 

of the SQS numerical criteria, consideration should be given to requiring biological testing, 

because the results of biological tests may override a decision based on sediment chemistry 

alone. Biological testing may also be appropriate for marine discharges if there are potentially 

toxic chemicals in the effluent for which there are no SQS numerical criteria. In Puget Sound 

marine environments, the biological testing should include two acute tests and one chronic test 

(see Part 7.4.3) for the available tests to choose from). In non-Puget Sound marine environments, it may be appropriate to use the same tests as for Puget Sound marine environments, but 

this decision should only be made on a case-by-case basis, with guidance from the SMU. In 

freshwater environments, baseline monitoring should always include biological testing with the 

Hyalella azteca and Microtox® sediment bioassays. Appropriate biological tests for low-salinity 

environments have not yet been identified, but may be selected by the SMU on a case-by-case 

basis.

7.5.2. Development of SIZ Application Monitoring Requirements

The development of SIZ application monitoring requirements is the responsibility of the SMU. 

A detailed description of the SIZ application monitoring requirements will be provided to the 

permit manager by the SMU, to be forwarded to the discharger.

7.5.3. Development of Maintenance Monitoring Requirements

The development of maintenance monitoring requirements is the responsibility of the SMU. A 

detailed description of the maintenance monitoring requirements will be provided to the permit 

manager by the SMU for inclusion in the permit.

7.6. Interpretation of Monitoring Results

This section describes procedures for interpreting monitoring results for various purposes in the 

sediment source control process.

7.6.1. Evaluation Criteria for Designation of Sediments as Passing or Failing 

the Sediment Quality Standards

Initial designation of sediments as passing or failing the SQS is made on the basis of chemical 

contaminant concentrations (WAC 173-204-310(1)). Sediments with chemical contaminant 
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concentrations equal to or less than all the applicable chemical and human health criteria are 

designated as not having adverse effects on biological resources or posing a significant threat to 

human health. Sediments having one or more chemical contaminants at concentrations greater 

than the applicable chemical or human health criteria are designated as having adverse effects on 

biological resources or posing a significant threat to human health.

Whether the sediments pass or fail the initial designation based on chemical criteria alone, they 

are potentially subject to confirmatory designation (see WAC 173-204-310(2)) using the 

applicable biological testing procedures of WAC 173-204-315. To confirm the designation of 

these sediments, they should be tested using two of the acute effects biological tests and one of 

the chronic effects biological tests (for brief descriptions of these tests, see Part 7.4.3 above). 

The biological test results for control and reference sediments must meet the performance 

standards of WAC 173-204-315(2). A sediment sample is determined to have an adverse effect 

on biological resources, and therefore is designated as failing the SQS, when any one of the 

biological tests demonstrates the results listed in the SQS column of Table IX-2, notwithstanding 

the initial designation based on sediment contaminant concentrations alone. If the sediment 

sample does not demonstrate any of the results listed in the SQS column of Table IX-2, it is 

designated as passing the SQS, notwithstanding the initial designation based on sediment 

contaminant concentrations alone.

For marine sediments containing other toxic, radioactive, biological, or deleterious substances, 

Ecology will identify appropriate test interpretation standards for initial and confirmatory 

designation. Because these procedures have not yet been developed by Ecology, they are not 

currently discussed in this manual.

7.6.2. Evaluation Criteria for SIZmax Biological Effects Level

The maximum sediment contaminant concentrations allowed within an authorized SIZ as a result 

of a permitted or otherwise authorized discharge are presented in Table IX-1, and are referred to 

as SIZmax. Biological effects within an authorized SIZ are also not to exceed a “minor adverse 

effects level,” which is defined on the basis of the results of biological tests. To determine 

compliance with the SIZmax biological effects criteria, the sediment should be tested using two of 

the acute effects biological tests and one of the chronic effects biological tests (see Part 7.4.3). 

The biological tests employed for demonstrating compliance with the SIZmax biological effects 

criteria of WAC 173-204-420(3) are the same as those used in biological testing for confirmatory 

designation, except that the Microtox® test is omitted as one of the options for a chronic test. 

The biological test results for control and reference sediments must meet the performance 

standards of WAC 173-204-315(2). The sediments are determined to exceed the SIZmax

biological effects criteria when any two of the biological tests exceed the criteria of WAC 173-

204-320(3) or when any one of the tests demonstrates the results shown in the SIZmax biological 

effects criteria column of Table IX-2.
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If, in a given area, the nonanthropogenically affected (i.e., natural background) sediment quality is 

of a lower quality (i.e., having higher contaminant concentrations, causing an adverse biological 

response, or posing a greater threat to human health) than allowed within an authorized SIZ, the 

existing sediment chemical and biological quality criteria will be identified on an area wide basis, 

as determined by Ecology, and used in place of the SIZmax criteria of WAC 173-204-420.

8. SUMMARY CHECKLIST

Monitoring Program Checklist

1. Have all the possible sampling matrices been considered?

- Influent

- Internal waste streams

- Treated process wastewater (effluent)

- Particulates

- Nonprocess wastewater

- Sludge

- Storm water

- Receiving environment

- Water

- Sediment

- Biota

- Groundwater

- CSOs

- Bypasses

2. Are there any water-quality based limits or considerations?

- Numerical criteria

- Narrative criteria (toxicity)

- Beneficial uses (fishable, swimmable)

3. Where do the process wastes end up?

- Surface waters

- Land (application)

- Ground water

- Underground injection

- Landfills
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4. Is there sufficient data to characterize the effluent? Are any special studies needed?

- For statistical comparisons (temporal and spatial)?

- To establish sampling frequencies?

- Are all constituents characterized?

- How variable is the effluent?

5. Is there sufficient data to characterize the potential impact on the receiving environment?

- Is there existing ambient data?

- Is data needed for modeling?

6. Specify parameters to be monitored

- To meet limits

- To create baseline data

- For surveys

- Indicators

- Evaluate acute/chronic toxicity

7. Specify in permit:

- Sampling locations

- Timing and frequency for sampling

- Sample collection and analytical methodologies

- QA/QC

- Data reporting requirements.

8. Will any of the monitoring data be used to trigger an action?

- Effluent biomonitoring

- Survey results

- Receiving environment monitoring

- Local limits policy

- Tiered sampling

- Increase/decrease -monitoring frequency

- Add/eliminate parameters from sampling program

9. What is the size, treatment technology and compliance history of the facility?

10. Does the facility discharge into Puget Sound?

- Plan elements for majors
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CHAPTER XIV. FACT SHEETS AND 

DOCUMENTATION 

This chapter discusses the regulatory requirements for fact sheets. 

As in any process of complex decisions and calculations, documentation is valuable. In the 

permit process the documentation occurs in a fact sheet. A fact sheet sets forth the principal 

facts and the significant legal, procedural and policy decisions considered in preparing the 

permit. Some of the content of fact sheets is directed by federal and state regulation and some 

content is dictated by good project management.

1. FEDERALLY REQUIRED FOR SELECTED PERMITS

The federal NPDES regulations (40 CFR 124.8, 124.56) require a fact sheet for

• every major NPDES facility or activity, 

• every draft permit that incorporates a variance or requires an explanation under 124.56(b), 

• every draft permit which is the subject of widespread public interest or raises major issues,

• every Class I sludge management facility,

• every permit that includes a sewage sludge land application plan, and for

• every permit that includes a variance.

2. STATE REQUIREMENTS FOR ALL PERMITS

The State regulations for surface discharge (WAC 173-220-060) are much simpler - every permit 

must have a fact sheet.

The state regulation requires that fact sheets at a minimum will summarize the following:

• The type of facility or activity which is the subject of the application;

• The location of the discharge in the form of a sketch or detailed description;

• The type and quantity of the discharge, including at least the following:

♦ The rate or frequency of the proposed discharge,

♦ For thermal discharges, the average summer and winter temperatures, and

♦ The average discharge in pounds per day, or other appropriate units, of any pollutants 

which are present in significant quantities or which are subject to limitations or 
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prohibition by state or federal regulation;

• The conditions in the proposed permit;

• The legal and technical grounds for the draft permit determination, including an explanation 

of how conditions meet both the technology-based and water quality-based requirements of 

state and federal law;

• The effluent standards and limitations applied to the proposed discharge;

• The applicable water quality standards, including identification of the uses for which 

receiving waters have been classified;

• How the draft permit addresses use or disposal of residual solids generated by wastewater 

treatment;

• The procedures for the formulation of final determinations (in more detailed form than that 

given in the public notice) including:

♦ The 30-day comment period required by WAC 173-220-050(2);

♦ Procedures for requesting a public hearing and the nature thereof; and

♦ Any other procedures by which the public may participate in the formulation of the final 

determinations.

• RCW 90.48.520 requires the control of toxicants (specific chemicals and overall toxicity) in 

permits. This should be discussed in the fact sheet. 

3. PUGET SOUND PLAN REQUIREMENTS

The Puget Sound Water Quality Management Plan (11/90) requires that in the fact sheet 

accompanying each draft major permit: 

"Ecology shall clearly explain how the draft permit fulfills the goal of reducing 

and eventually eliminating harm from toxic contaminants in Puget Sound, 

including a summary of the information used to determine which limits on 

specific toxicants and/or overall effluent toxicity should be included in the 

permit." 

The plan also requires a discussion in the fact sheet of 4 types of monitoring;

• sediments in the vicinity of every significant outfall, 

• particulate fraction of the effluent,

• acute and chronic toxicity of the effluent and sediments near the outfall,

• biota surveys in the vicinity of each significant outfall,

• water quality at the boundary of the dilution zone. 
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The plan requires a discussion of why these 5 monitoring requirements were not included if 

applicable.

4. FEDERALLY REQUIRED DETAILS

The Federal Regulations also require:

• The name and telephone number of a person to contact for more information

• Any calculations or other necessary explanation of the derivation of specific effluent 

limitations and conditions, including a citation to the applicable effluent limitation guideline 

and the reasons why they are applicable or an explanation of how the alternate effluent 

limitations were developed.

• An explanation of the reasons for including any of the following conditions in a permit:

∗ Limitations to control toxic pollutants

∗ Limitations on internal waste streams

∗ Limitations on indicator pollutants

∗ Limitations set on a case-by-case basis

• For every permit to be issued to a treatment works owned by a person other than a State or 

municipality, an explanation of the decision on regulation of the users (whether to issue a 

separate permit)

• For every permit that includes a sewage sludge land application plan, a brief description of 

how each of the required elements of the land application plan are addressed in the permit.

5. FACT SHEET CONSIDERATIONS

The fact sheet serves a legal requirement and informs a new permit writer of the history of the 

permit. Since the fact sheet is a summary, the permit writer may also wish to submit an internal 

memorandum to the file on some issues too lengthy or not appropriate for the fact sheet but 

which may be useful in the next permitting period. Ecology often spends a considerable amount 

of time debating a permit issue which then becomes an assumption upon which the permit 

conditions are based. Documenting the decision process may prevent a repeat of the debate in 5 

years when the permit is up for reissuance.

EPA is required to maintain an administrative record on their permits to document the decision 

process. This type of procedure is useful for all permit writers. The permit writer should 

document every permit as if it were going to an appeal hearing and as if someone new would be 

reissuing the permit in 5 years.
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The time of writing the fact sheet is an individual preference. Some experienced permit writers 

write a fact sheet before actually drafting the permit conditions, others do it after drafting the 

permit.

The permit writer should use language in the fact sheet that is understandable to a non-technical 

person. Public and permittee support for Ecology's permitting actions is increased if the issues 

are clearly presented in the fact sheet.

Significant comments made on a draft permit in writing or by comment at a public hearing must 

receive a response. The response is presented in a document called a Response to Comments. 

The Response to Comments becomes an addendum to the fact sheet. The original fact sheet may 

or may not be modified to reflect permit changes as a result of comment.

6. FACT SHEET FORMATS

The Permit Workgroup maintains model fact sheets for NPDES and State permits. These are 

available on Outlook.
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CHAPTER XV. PUBLIC INVOLVEMENT

The permit writer must allow the public to observe and influence the decision-making process 

involved in developing a permit. The timing of public involvement was discussed in Chapters II 

and III. Some of the mechanisms for public involvement are the State Environmental Policy Act 

(SEPA), public notice of permits, and public hearings. The public involvement processes may 

be difficult and time-consuming but the permit writer is a public representative and the process is 

an opportunity to demonstrate that we are doing a good job of representing the public interest. 

Some public involvement tasks are required by law.

1. SEPA

A permit writer may become involved in the SEPA process and may occasionally become the 

lead for new dischargers. SEPA requirements are given in Chapter 43.21C RCW and Chapter 

197-11 WAC. 

Regulation exempts reissuance or modification of any wastewater discharge permit from the 

SEPA process as long as the permit contains conditions no less stringent than federal effluent 

limitations and/or state rules and regulations. The exemption applies only to existing discharges, 

not to new source discharges. To conform with the intent of SEPA, an existing, unpermitted 

discharge must undergo SEPA review during the permitting process.

The environmental review process under SEPA generally begins when someone submits a permit 

application to an agency or when an agency proposes some activity, policy, plan, ordinance, or 

regulation. A typical situation for a new discharger is to submit a request for a building permit to 

a municipality or county. That municipality or county then becomes the lead agency on SEPA. 

However, if they feel the environmental issues are too complex, they may request some other 

agency such as Ecology to take the SEPA lead. Most small projects are covered by a checklist 

and a Determination of Nonsignificance. These projects go into a review list circulated by the 

SEPA office. Large projects may require an Environmental Impact Statement.

If a discharger moves into an existing facility and doesn't need a building permit, the permit 

writer may become the lead on SEPA. If the only environmental issue is a proposed wastewater 

discharge which is controlled by treatment, there should not be a need for an environmental 

impact statement. The permit applicant will complete an environmental checklist and 

determination of nonsignificance. The signatory authority on the determination of 

nonsignificance is the person responsible for signing the permit. For multi-program situations in 

the regional offices, the regional director may be the lead and signatory. The permit writer 

should consult Ecology's Responsible Offical's Notebook for SEPA - February 1989 for more 

information on SEPA.
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2. PUBLIC NOTICE OF PERMIT ACTIONS

Ecology uses a common public involvement process for NPDES permits, new state wastewater 

discharge permits, and renewal of state wastewater discharge permits for facilities with an 

increase in volume or change in nature of the wastewater. 

Public notices of permit actions will be widely circulated to increase public awareness and 

encourage public participation early in the permit process.

Ecology assumes that costs associated with public notifications of permit actions and other costs 

of administering the public involvement procedures constitute a portion of the total costs 

incurred to administer the water quality permit program and are, therefore, fee eligible expenses. 

Ecology will administer all public notices and advertisements to ensure that they are published in 

a timely and consistent manner.

Public notices of application and of draft permit may be done on a batch basis for applications 

and permits associated with basin permitting.

3. PUBLIC NOTICE OF APPLICATION (PNOA)

RCW 90.48.170 requires that certain applications be made known through a 

public notice in a news publication.

...Upon receipt of a proper application relating to a new operation, or an 

operation previously under permit for which an increase in volume of wastes or 

change in character of effluent is requested over that previously authorized, the 

department shall instruct the applicant to publish notices thereof by such means 

and within such time as the department shall prescribe. The department shall 

require that the notice so prescribed shall be published twice in a newspaper of 

general circulation within the county in which the disposal of waste material is 

proposed to be made and in such other appropriate information media as the 

department may direct. ...

Based on the above law, the following process has been adopted for PNOAs:

PNOA is required

• for new NPDES and State Waste Discharge Permits and

• for renewal of NPDES permit and State Waste Discharge permit if an increase in the 

volume of waste or change in character is requested.
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To assess whether there has been an increase in volume, the permit writer must confirm 

that the current flows are consistent (within 10%) with those used in the reasonable 

potential calculation performed for the previous permit.

PNOA is not required 

• for renewal of NPDES and State Waste Discharge permit when no increase in volume 

of waste or change in character is requested.

When PNOA is required, PNOAs will be published by Ecology as a 

• legal classified advertisement, to be published at least once each week for 2 

consecutive weeks, and as 

• mailings of PNOAs sent to persons on the general mailing list who have indicated an 

interest in receiving such information. 

• A PNOA may also be a display advertisement, to be published one time, concurrent 

with the first legal classified advertisement, for permits likely to have a high degree of 

public interest. 

PNOAs will use consistent wording and format to identify the types of information that 

Ecology would like to receive from the public and is able to consider in permit decisionmaking. 

In addition to public notice, Ecology is required to notify the director of the Department 

of Fisheries and Wildlife and the secretary of Department of Social and Health Services 

of the application for a permit.

4. PERMITTEE REVIEW

Ecology must send the preliminary draft permit and fact sheet to the permittee for comment. 

Ideally, Ecology will allow the Permittee 30 days to review the documents before the public 

notice of draft (PNOD) period begins. Ecology must specify a date by which comments are due 

and notify the Permittee that the permit issuance process will not be delayed if the date is not 

met. Ecology must notify the Permittee that the draft permit conditions could change as a result 

of the public review process. If the draft permit is substantially different than the existing permit, 

Ecology should offer the Permittee an opportunity to meet. The purpose of the meeting would be 

to explain the new or changed requirements, accept comments from the Permittee on factual 

content, and to discuss the practicality of the monitoring requirements and compliance schedules. 

If the permittee requests substantial changes beyond factual comment and the permit writer 

agrees with those requests, the permit writer should document the discussion and his/her decision 

in the fact sheet. 
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5. PUBLIC NOTICE OF DRAFT PERMIT (PNOD)

A public notice of draft is required for:

• all NPDES permits (including reauthorizations) 

• renewed state permits which have an increase in volume of discharge or a change in the 

characteristics of the discharge and for 

• all new state permits.

Ecology will publish PNODs as legal classified advertisements at least once in the same major 

paper in which the PNOA was published.

PNOD's will also be distributed by mail to "parties of record." Parties of record are those 

persons who responded to the PNOA or who have otherwise requested that they be informed 

about the development of a specific permit.

Ecology may also issue news releases and other informational materials to announce the 

availability of the draft permit for public review.

The comment period following a PNOD will normally be 30 days from the date of the latest 

notice. The comment period can be extended any time the permit section supervisor determines 

that an extension of the comment period will result in greater or more meaningful public input, 

or in any other circumstances the permit section supervisor deems appropriate.

6. DISTRIBUTION OF DRAFT AND FINAL PERMIT 

MATERIALS

Ecology will mail 1 copy of the draft permit, final permit, and fact sheet to parties of record or to 

any other party requesting such information. One copy of the application will be mailed upon 

request.

Draft and final permits, fact sheets, and other permit-related information will be made available 

for public review and copying at the Ecology office from which the draft or final permit was 

issued.
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• Draft permits will normally be retained in the permit file and made available for review and 

comment only until the Final Permit has been issued.

Ecology will bear the cost of copying and mailing draft or final permits and accompanying fact 

sheets to parties of record or others requesting copies of the same as part of its public 

outreach/education program on a 1-copy-per-requestor basis only. Additional copies will be 

supplied as specified in Ecology Policy 10-30, Requests for Ecology Records. Free copies are 

available only for permits which are being developed or considered for renewal.

• Copies of permit-related information other than draft or final permits and accompanying fact 

sheets will be made available for viewing and copying at the Ecology regional office which 

developed the permit. Copies of permit-related materials will be provided by mail as long as 

requests clearly specify the materials desired. 

Draft and final permits and fact sheets and other permit-related materials will also be made 

available, at the discretion of the permit section supervisor, at repositories in appropriate public 

buildings (e.g., libraries, town hall) for the duration of the comment period. 

7. PUBLIC INFORMATIONAL MEETINGS AND 

WORKSHOPS

Informational meetings or workshops will be held any time the permit section supervisor deems 

them appropriate to inform the public about a permit or permit-related issues, to facilitate public 

discussion of permit issues, and to generate more informed, more pertinent public comment on 

permit issues.

Holding discretionary informational meetings neither precludes the need for formal hearings, nor 

creates a demand that formal hearings be held.

• Informational meetings are not required permit procedures. Therefore, informational 

meetings require no extension of the public comment period. However, the comment period 

can be extended at the discretion of the permit section supervisor.

7.1. Informational Meetings Preceding Hearings

Informational meetings are required prior to holding public hearings.
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• Meetings should be held at least 1 week prior to a hearing to allow the public time to study 

the information provided in meetings and to allow the public time to prepare wellconsidered formal comments or responses.

• A brief meeting should also be held immediately prior to a hearing to answer questions and 

address unresolved issues prior to accepting formal testimony, including those hearings for 

which informational meetings are held at an earlier date.

7.2. Public Notice of Informational Meetings

Public Notices of Informational Meetings will normally be included within Notices of Public 

Hearing. However, when a Public Hearing is not planned or when inclusive notices are not 

practical, a Public Notice of Informational Meeting will be

• published at least 1 time in a major newspaper with circulation in the geographic area of the 

discharge, and

• distributed to parties of record by mail. 

The content and format of Public Notices of Informational Meetings will be essentially the same 

as that used to advertise Notice of Public Hearing.

8. HEARINGS

Ecology will hold formal public hearings whenever the permit section supervisor deems that 

there is sufficient interest and a likelihood of meaningful public comment on a permit to warrant 

hearings. (Note that regulations may require public hearings under some circumstances.) 

8.1. Public Notice of Hearing

A Public Notice of Hearing will be published at least once in a major newspaper with circulation 

in the geographical area of the discharge. The public notice will be published at least 30 days 

prior to the hearing. 

The Notice of Hearing will also be mailed to parties of record at least 30 days prior to the 

hearing. 

Notices of Hearing will use a standard format and language which will, at a minimum

• outline permit issues to be discussed, 

• establish time and place of hearings, 
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• include the name of a contact person at Ecology who can supply information or assistance,

• clearly state that testimony can be considered only if it pertains to the conditions of the 

named permit,

• outline the extent of Ecology's authority and interest in the permit, and 

• instruct interested parties on getting their issues placed on the hearing agenda.

Whenever practical, a second Notice of Hearing should be issued l0-l4 days prior to the meeting 

to encourage greater participation.

8.2. Hearing Officer 

A hearing officer will be appointed by the permit section supervisor for each hearing. It will be 

the hearing officer's responsibility, in cooperation with the permit manager, to prepare the 

agenda, and conduct the meeting according to the agenda and the established procedures for 

holding a hearing (distributed by the Ecology Office of Education and Information).

9. PUBLIC NOTICE OF PERMIT ISSUANCE 

Notices of issuance will be mailed by Ecology to parties of record.

10. PUBLIC NOTICES OF OTHER ACTIONS

Notices of appeals of permits will be mailed to parties of record, as will decisions on appeals.

Major modification, suspension (state permits), and revocation (for cause other than cessation of 

discharge), of a wastewater discharge permit each require public review and comment. 

Therefore:

• Ecology will publish a notice of intent to modify, suspend, or terminate a permit as a legal 

classified advertisement in a major newspaper with general circulation in the geographical 

area of discharge.

• Ecology will notify parties of record, by mail, of the department's intent to make a major 

modification to, or to suspend or revoke a permit.

• All subsequent public notification will be implemented using the same procedures as 

outlined for new discharges and permit renewals in the previous sections. This includes 

notice of draft major modifications and may include informational meetings or public 

hearings and notice of resolution of the permit action taken.
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11. WHEN TO GO BACK TO PUBLIC NOTICE WITH A 

REVISED DRAFT PERMIT

There are no regulations requiring Ecology to repeat public notice on a draft permit after it has 

been revised, however, to meet the intent of public notice requirements a revised draft permit 

should go back to public notice under either of the following conditions:

1. When a significant revision to the draft originally public noticed has taken more than 9 

months to complete and there were comments from the first public notice. The draft should 

also go back to EPA for approval if the permit is a major.

or

2. If new information causes the effluent limits or loading to increase.

If an issue is discussed in the first draft and new information submitted by the public causes 

changes in the permit conditions, then another public notice is not necessary. However, if the 

change is lower limitations, the permit writer should inform the permittee before issuing the permit.
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CHAPTER XVI. APPEALS AND VARIANCES

A wastewater discharge permit is an administrative action of the Department of Ecology and is 

subject to both state administrative hearings and court appeals.

Variances are exceptions within the law.

1. APPEAL OF THE FINAL PERMIT TO THE 

POLLUTION CONTROL HEARINGS BOARD (PCHB)

1.1 The PCHB

The PCHB is an independent agency of the state of Washington, composed of 3 members 

appointed by the governor for terms of 6 years. The members are qualified by experience or 

training in environmental matters. At least 1 member is a lawyer, and not more than 2 members 

are of the same political party.

The function of the board is to hear appeals of permit actions (issuance, modification, denial), 

orders, rules, or regulations of Ecology or the air pollution control board. The regulatory 

requirements of the PCHB are given in Chapter 371-08 WAC. 

1.2 Appeal Process

A permit writer may be involved in PCHB appeals of permits, orders, and penalties.

The general process of appeal is:

1. The permit, order, or penalty is issued by the Department

2. The recipient has 30 days to appeal to the PCHB with a copy served to Ecology

3. Upon receipt of a correct appeal the board will set a hearing date. The hearing date is 

usually 4 to 6 months from the time of appeal. The filing of an appeal does not stop the 

requirements of the permit or order. However, the appealing party may also request a stay 

of the requirements of the permit or order until the time the appeal is decided. The PCHB 

will ask Ecology to respond to the request for stay and may schedule a separate hearing on 

the request. The PCHB has the option of moving the appeal hearing date up and hearing 

both issues.

4. The hearing is held and a decision is issued.
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1.2.1 AG Cooperation

The Attorney General's office will assign an assistant AG to work on the appeal. The assistant 

AG is the state's representative in the appeal and the permit writer serves as the technical 

consultant. The permit writer should be aware that the assistant AGs have a very heavy case 

load and they work with a large body of federal and state laws in several programs. The permit 

writer may first have to convince the assistant AG of the technical and legal merits of the 

appealed permit. If the permit fact sheet and other decision documentation are done correctly 

(see Chapter XIV) this should be an easy task. The attorney is the legal expert but you are the 

permit and water quality expert. The permit writer may have to teach the assistant AG about 

water quality in the process of justifying the permit. Preparation of a good permit fact sheet will 

save time here. The permit writer will also be responsible for preparing the submittals of 

evidence (documents and photos). A complete permit file will expedite this task.

1.2.2 Conferences Before the Hearing

Two types of conferences may be held before the hearing. One type is an optional informal 

conference in which a PCHB member is a facilitator. The purpose of the meeting is to see if an 

agreement can be reached before going to hearing. The outcome of the meeting may be a 

settlement, no settlement, or an agreement to continue settlement proceedings. The PCHB has 

the authority to order these meetings, but they usually do so only if requested by one of the 

parties.

If the case proceeds to hearing, a prehearing conference will be held to lay the legal ground rules 

for the hearing. This conference may be held at the end of an informal conference or by 

telephone.

1.2.3 Deposition and Testimony

A permit writer may be required to give a deposition, in which the appellant attorney conducts 

the questioning that would otherwise occur in the hearing. The deposition is transcribed and 

presented as evidence. The appellant attorney may ask some of the same questions at the 

hearing.

After your deposition is transcribed, you'll have an opportunity to read it and make any 

corrections you believe are appropriate. It's extra work but worth the effort. There are no perfect 

transcripts and some are absolute disasters, especially if they concern technical matters. Never 

waive the right to read and sign your transcript.
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During the hearing in front of the PCHB, the permit writer will be examined and cross-examined 

by the appellant attorney and the assistant AG.

1.2.4 PCHB Determination

Sometime after the conclusion of the hearing the PCHB will 

issue a final determination and order. This may take up to a 

year. Either party in the hearing may then request a 

reconsideration of the final determination. After review of the 

case the PCHB will issue a decision and order. This decision 

and order may be appealed to a state superior court and thence 

appealed to the Federal Supreme Court, if necessary.

The PCHB has specific regulatory authority for wastewater 

discharge permits. If the PCHB determines, upon appeal, that a 

permit is invalid in any respect it will direct Ecology to reissue the permit in accordance with the 

directive and any applicable federal or state law. 

1.2.5. Assistance

Staff in the Program Development Services Section have time allotted to assist in permit appeals.

2. VARIANCES

2.1 The Federal Variances

The Clean Water Act provides a mechanism for modifying requirements of the Act in 

exceptional cases. These modifications are called variances. There are very specific provisions 

which must be met by an applicant before a variance may be granted. As the term implies, a 

variance is an exceptional situation. A permit writer might never work on a variance but should 

know what they are and the general procedure for handling them.

Variances are requested during the rulemaking period or during the first permit period after 

completion of the rulemaking.

2.1.1 Economic 301(c) (No guidance developed by EPA)

Section 301 (c) provides for a variance for non-conventional pollutants from BAT effluent 

guidelines due to economic factors. The variance may also apply to non-guideline limits (40 

CFR 122.21(m)(2)(ii). The request for the variance from effluent limitations developed from 

BAT guidelines is normally filed by the discharger during the public notice period for the draft 

permit. Other filing time periods may apply as specified in 40 CFR 122.21(m)(2). The 

The AG's office and the Program 

Development Services Section have 

material to assist you in depositions 

and hearings.
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application for the variance must show that the modified requirements will 

• represent the maximum use of technology within the economic capability of the 

owner/operator, and 

• result in further progress toward the "no discharge goal". 

The cost tests for evaluating this variance request are the same as given in the BPJ permitting for 

BAT. The applicant must pass these cost tests and, in addition, show compliance with BPT 

limitations and water quality standards.

2.1.2 Water Quality 301(g) (No guidance developed by EPA)

The CWA provides for a variance from BAT effluent guidelines for ammonia, chlorine, color, 

iron, and total phenols. The discharger must file a variance application which meets the 

following requirements:

• The modified requirements must result in compliance with BPT limits, pretreatment 

guidelines, or water quality standards of the receiving stream, whichever is applicable.

• No additional treatment will be required of other point or non-point source dischargers as a 

result of the variance approval. 

• And the modified requirements will not interfere with attainment or maintenance of water 

quality to protect public water supplies, protection and propagation of a balanced population 

of shellfish, fish, and wildfowl, and allow recreational activities in and on the water. Also, 

the modified requirements will not result in quantities of pollutants which may reasonably 

be anticipated to pose an unacceptable risk to human health or the environment, acute or 

chronic toxicity, or synergistic properties.

This variance request requires the discharger to perform water quality monitoring for toxicity, 

human health effects and dilution. It may also require the development of site-specific water 

quality criteria. 

If a discharger wants both a 301(g) variance and a 301 c variance, the requests must be submitted 

and considered together.

2.1.3 POTW Discharge to Marine Waters 301(h) (40 CFR Part 125, Subpart 

G)

This section allows POTW'S that discharge to marine waters a conditional exemption from 

secondary treatment. The variance is conditional upon meeting water quality standards, 

conducting receiving water monitoring, limiting the discharge of toxics through pretreatment of 
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industrial wastes, and providing primary treatment. 

2.1.4 Innovative Technology 301(k) (40 CFR Part 125, Subpart C)

This section provides an extension of the deadline for compliance with effluent guidelines for up 

to 2 years if the discharger meets the following criteria:

• Uses an innovative production process that will result in an effluent reduction greater than 

required.

• Installs an innovative control technique that is likely to reduce the effluent below required 

levels.

• Achieves the required BAT effluent limits with an innovative system which is expected to 

cost significantly less.

• This system must also have the potential for industry-wide application.

A process should have been used less than 5 years to qualify as innovative. Industry-wide 

application is defined as being applicable to 2 or more facilities in 1 or more industrial category.

2.1.5 Fundamentally Different Factors 301(n) (40 CFR Part 125, Subpart D)

This section provides for variances based upon fundamentally different factors (FDF). FDF 

variances for direct dischargers are available from effluent guidelines for BPT, BCT, and BAT if 

the individual facility is found to be fundamentally different from the factors considered in 

establishing the effluent guidelines. Approval of a FDF variance can result in an effluent

limitation which is less stringent for a particular pollutant than would result from application of 

the national effluent guidelines. The FDF variance must be requested by the discharger within 

180 days from the time an effluent limit is promulgated or revised. No FDF variance can be 

approved if it results in violations of water quality standards.

2.2 The State Requirements

The Clean Water Act allows state requirements to be more stringent than federal requirements. 

The State of Washington has language in its water pollution law which is technology-based (see 

discussion of all known, available, and reasonable treatment (AKART) in Chapter IV). This 

language may negate the use of the CWA variances in this state. A good example is the 301(h) 

variance for municipal discharges to marine waters. Several Puget Sound municipalities were 

preparing to apply for marine waivers (authorized by the 1977 amendments to the CWA) and 

were discharging to marine waters with primary treatment. In 1984, the Department of Ecology 

determined that primary treatment did not conform to state law, specifically, the discharges did 

not provide AKART. That decision was appealed by the cities to the PCHB. The PCHB ruled 

that AKART for municipal discharges was secondary treatment.
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REFERENCES

Chapter references include references from corresponding appendices.

CHAPTER I.

Puget Sound Water Quality Authority. 1987. Puget Sound Water Quality Management Plan. 

Amended in 1989 and 1991. 318 p.

Water Pollution Control Federation. 1987. The Clean Water Act of 1987. 318 p.

Miller, L.A., R.S. Taylor, L.A. Monk. 1990. NPDES Permit Handbook. Government Institutes, 

Inc., Washington, D.C. 271 p.

CHAPTER II.

U. S. Environmental Protection Agency. 1995. Revised Policy Statement on Scope of Discharge 

Authorization and Shield Associated with NPDES permits. Memo from Perciasepe, Herman and 

Nelson to Regional Administrators.

CHAPTER IV

Miller, L.A., R.S. Taylor, L.A. Monk. 1990. NPDES Permit Handbook. Government Institutes, 

Inc., Washington, D.C. 271 p.

CHAPTER V

Ecology 1998. Criteria for Sewage Works Design. Ecology publication #98-37 WQ.

Restrepo-Postada, P.J. and Peter S. Eagleson, 1982. Identification of Independent Rainstorms, 

Journal of Hydrology, 55, 303-319

Lukas, Andy and M. Steve Merrill, 1996, CSO Event Definition (Task 16.01 Technical 

Memorandum), Brown and Caldwell.

Mau, Russell, 1999, Design Storm Statistical Analysis (Draft Memo to ERO), CTE Consultants.

Nicholson, G. and Adderley, V. 1994, TM 7.1: Rainfall Analysis for CSO Facilities Planning, 
REFERENCES (JULY 2002)

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CH2M Hill Technical Memorandum 7.1.

Woodward-Clyde Consultants. 1989. Analysis of Storm Event Characteristics for Selected 

Rainfall Gages Throughout the United States (Draft) prepared for the U.S. Environmental 

Protection Agency.

OTAK, Inc. 1989. Columbia Slough Planning Study, Task 7.2, Representative Year Rainfall 

Analysis. Prepared for OTAK, Inc. for Brown and Caldwell and submitted to the City of 

Portland, Bureau of Environmental Services.

CHAPTER VI.

Dilks, David and James Pendergast. 2000. Comparison of Dynamic and Steady-State Models for 

Determining Water Quality Based National Pollutant Discharge Elimination System for Toxics, 

Water Environment Research, March/April, 225-229.

Ecology. 1984. Shellfish Protection Strategy. Washington State Department of Ecology, April 

1984. WDOE 84-4.

Fisher H.B., E.J. List, C.Y. Koh, J. Imberger, and N.H. Brooks. 1979. Mixing in Inland and 

Coastal Waters. Academic Press. New York.

Gilbert, R.O. 1987. Statistical Methods for Environmental Pollution Monitoring. Van Nostrand 

Reinhold Company. New York.

Pelletier, G. 1996. Applying Metals Criteria to Water Quality-Based Discharge Limits, EPA 

Project Completion Report (Grant No. CP990497-01-0), Watershed Assessments Section, 

Environmental Assessment Program, Washington State Department of Ecology.

U. S. Environmental Protection Agency. 1982. Revised Section 301(h) Technical Support 

Document. 430/9-82-001.

U. S. Environmental Protection Agency, Office of Water. 1985a. Technical Support Document 

for Water Quality-based Toxics Control. 

U. S. Environmental Protection Agency. 1985b. Water Quality Assessment: A Screening 

Procedure for Toxic and Conventional Pollutants (Revised 1985). Part II. EPA/600/6-85/002b. 

U. S. Environmental Protection Agency. 1986. Quality Criteria for Water. EPA 440/5-86-001.

U. S. Environmental Protection Agency. 1988. Technical Guidance on Supplementary Stream 

Design Conditions for Steady State Modeling. EPA Office of Water. Washington, D.C.
REFERENCES (JULY 2002)

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U. S. Environmental Protection Agency, Office of Water. 1991. Technical Support Document for 

Water Quality-based Toxics Control. EPA/505/2-90-001.

U. S. Environmental Protection Agency, 1993. Memorandum from Martha Prothro, Acting 

Assistant Administrator for Water. Office of Water Policy and Technical Guidance on 

Interpretation and Implementation of Aquatic Life Metals Criteria. Office of Water, 

Washington, D.C.

U. S. Environmental Protection Agency, 1995. Method 1669: Sampling Ambient Water for Trace 

Metals at EPA Water Quality Criteria Levels. EPA 821-R-95034.

U. S. Environmental Protection Agency, 1996a. Memorandum from Jeanette L. Kranacs and 

Henry D. Kahn, USEPA to Gary Bailey, Ecology, Autocorrelation of Cyanide in Anacortes 

Refinery Effluent, March 20, 1996.

U. S. Environmental Protection Agency, 1996b. Memorandum from Jeanette L. Kranacs and 

Henry D. Kahn, USEPA, to Gary Bailey, Ecology, Data Requirements for Analysis of 

Autocorrelation in Effluent Discharge, June 25, 1996

CHAPTER VIII

Canter, LW, and Knox, RC, 1985, Septic Tank System Effects on Ground Water Quality, Lewis 

Publishers, Chelsea, MI, 336p.

Hantzsche, N., Finnemore, E. J., 1992, Predicting Ground-Water Nitrate-Nitrogen Impacts, 

Ground Water, Volume 30, No. 4, July-August, pp 490-499.

Hem, J.D., 1985, Study and Interpretation of the Chemical Characteristics of Natural Water, US 

Geological Survey Water-Supply Paper 2254, Washington DC, 263 p.

Kaplan, O.B., 1987, Septic Systems Handbook, Lewis Publishers, Chelsea, MI, 290 p.

Kramer, R., 1987, Report on Septic Tank Systems in Arizona, Report to the Legislature, Arizona 

Department of Health Services, 26 p.

Miller, DW, 1980, Waste Disposal Effects on Ground Water, Premier Press, Berkeley, CA, 512p.

Nelson, M.E. et al, 1988, Predicting Nitrogen Concentrations in Ground Water: An Analytical 

Model, Matopma; Water Well Association, Focus Conference on Eastern Ground Water Issues, 

pp. 16-39.
REFERENCES (JULY 2002)

Permit Writer’s Manual

R-4

Perkins, R.J., 1984, Septic Tanks, Lot Size and Pollution of Water Table Aquifers, Journal of 

Environmental Health, (May/June) Volume 46, No. 6, pp 298-304.

Office of Financial Management, 1991, 1991 Population, Trends for Washington State, Olympia, 

WA, 128 p.

US Environmental Protection Agency, 1980, Design Manual Onsite Wastewater Treatment and 

Disposal Systems, Technology Transfer Publication 1012, Cincinnati, OH, 392p.

CHAPTER IX.

Akar, P.J. 1989. CORMIX2: an expert system for hydrodynamic mixing zone analysis of 

conventional and toxic submerged multiport discharges. Thesis. Cornell University, School of 

Civil and Environmental Engineering, Ithaca, NY.

APHA. 1989. Standard methods for the examination of water and wastewater. Seventeenth 

Edition. American Public Health Association, Washington, DC. 1,268 pp.

ASTM. 1990. Standard guide for conducting sediment toxicity tests with freshwater 

invertebrates. ASTM Standard E1383-90. American Society for Testing and Materials, 

Philadelphia, PA.

Baumgartner, D.J., W.E. Frick, P.J.W. Roberts, and C.A. Bodeen. 1992. Dilution models for 

effluent discharges. U.S. Environmental Protection Agency, Pacific Ecosystems Branch, 

ERL-N, Newport, OR. 168 pp.

Bennett, J., and J. Cubbage. 1992. Evaluation of Bioassay Organisms for Freshwater Sediment 

Toxicity Testing. Washington Department of Ecology, Environmental Investigations and 

Laboratory Services, Olympia, WA.

Doneker, R.L., and G.H. Jirka. 1989. CORMIX1: an expert system for hydrodynamic mixing 

zone analysis of conventional and toxic submerged single port discharges. Technical Report. 

U.S. Environmental Protection Agency, Environmental Research Laboratory, Athens, GA.

Ecology. In preparation. WASP application guidance manual. Washington Department of 

Ecology, Sediment Management Unit, Olympia, WA.

Ecology 1990. Final environmental impact statement for the Washington State Sediment 

Management Standards. Chapter 173-204 WAC. Washington Department of Ecology, Olympia, 

WA.
REFERENCES (JULY 2002)

Permit Writer’s Manual

R-5

Ecology. 1991a. Evaluation of high-speed centrifugation for the characterization of municipal 

and industrial wastewater particulates. Report in progress. Washington Department of 

Ecology, Compliance Monitoring Section, Olympia, WA.

Ecology. 1991b. Guidance for determination and allocation of total maximum daily loads 

(TMDL) in Washington State. Washington Department of Ecology, Watershed Assessments 

Section, Environmental Investigations and Laboratory Services Program, Olympia, WA.

Ecology. 1991c. Sediment cleanup standards user manual. Washington Department of 

Ecology, Sediment Management Unit, Olympia, WA.

Ecology. 1991d. Sediment site ranking, SEDRANK guidance document. Prepared for 

Washington Department of Ecology by PTI Environmental Services, Bellevue, WA. 

Washington Department of Ecology, Sediment Management Unit, Olympia, WA.

Ecology. 1992b. Procedures for public involvement, NPDES and state wastewater discharge 

permits. October 1, 1992 policy statement. Washington Department of Ecology, Olympia, WA.

Ecology 1993. Sediment Source Control Standards User Manual. 

Horowitz, A.J. 1986. Comparison of methods for the concentration of suspended sediment in 

river water for subsequent chemical analysis. Environmental Science and Technology 

20(2):155-160.

Metcalf & Eddy. 1979. Wastewater engineering: treatment/disposal/reuse. Second Edition. 

McGraw Hill Book Company, New York, NY. 920 pp.

Norton, D. 1990. Use of sediment traps to monitor contaminant flux to City Waterway 

sediments: interim report. Washington Department of Ecology, Environmental Investigations 

and Laboratory Services Program, Olympia, WA. 32 pp.

Pastorok, R.A., R. Sonnerup, J.J. Greene, M.A. Jacobson, L.B. Read, and R.C. Barrick. 1989. 

Interim performance standards for Puget Sound reference areas. Prepared for Washington 

Department of Ecology, Olympia, WA. PTI Environmental Services, Bellevue, WA.

Plumb, R.H., Jr. 1981. Procedure for handling and chemical analysis of sediment and water 

samples. Technical Report EPA/CE-81-1. U.S. Environmental Protection Agency and U.S. 

Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS.

PSEP. 1986. Recommended protocols for measuring conventional sediment variables in Puget 

Sound. Prepared for Puget Sound Estuary Program by Tetra Tech, Inc. In: Recommended 
REFERENCES (JULY 2002)

Permit Writer’s Manual

R-6

Protocols for Measuring Selected Environmental Variables in Puget Sound. U.S. Environmental 

Protection Agency Region 10, Seattle, WA.

PSEP. 1987a. Puget Sound environmental atlas. Prepared for U.S. Environmental Protection 

Agency, Puget Sound Estuary Program; Puget Sound Water Quality Authority; and U.S. Army 

Corps of Engineers. Evans-Hamilton, Inc. and D.R. Systems, Inc., Seattle, WA.

PSEP. 1987b. Recommended protocols for sampling and analyzing subtidal benthic 

macroinvertebrate assemblages in Puget Sound. Prepared for Puget Sound Estuary Program by 

Tetra Tech, Inc. In: Recommended Protocols for Measuring Selected Environmental Variables 

in Puget Sound. U.S. Environmental Protection Agency Region 10, Seattle, WA.

PSEP. 1989a. Recommended guidelines for measuring metals in Puget Sound water, sediment, 

and tissue samples. Prepared for Puget Sound Estuary Program by PTI Environmental Services. 

In: Recommended Protocols for Measuring Selected Environmental Variables in Puget Sound. 

U.S. Environmental Protection Agency Region 10, Seattle, WA.

PSEP. 1989b. Recommended guidelines for measuring organic compounds in Puget Sound 

sediment and tissue samples. Prepared for Puget Sound Estuary Program by PTI Environmental 

Services. In: Recommended Protocols for Measuring Selected Environmental Variables in 

Puget Sound. U.S. Environmental Protection Agency Region 10, Seattle, WA.

PSEP. 1991a. Recommended guidelines for conducting laboratory bioassays on Puget Sound 

sediments. In: Recommended Protocols for Measuring Selected Environmental Variables in 

Puget Sound. U.S. Environmental Protection Agency Region 10, Puget Sound Estuary Program, 

Seattle, WA.

PSEP. 1991b. Recommended guidelines for measuring conventional marine water-column 

variables in Puget Sound. Prepared for Puget Sound Estuary Program by PTI Environmental 

Services. In: Recommended Protocols for Measuring Selected Environmental Variables in 

Puget Sound. U.S. Environmental Protection Agency Region 10, Seattle, WA.

PSEP. 1991c. Recommended protocols for measuring selected environmental variables in 

Puget Sound. U.S. Environmental Protection Agency Region 10, Office of Puget Sound, Puget 

Sound Estuary Program, Seattle, WA.

PTI. 1991. Recommended sediment impact and recovery zone models and case study analysis. 

Prepared for Washington Department of Ecology, Olympia, WA. PTI Environmental Services, 

Bellevue, WA.

Tetra Tech. 1986. Analytical methods for U.S. EPA priority pollutants in particulate matter 

from discharges and receiving waters. Prepared for Washington Department of Ecology and 
REFERENCES (JULY 2002)

Permit Writer’s Manual

R-7

U.S. Environmental Protection Agency. Tetra Tech, Inc., Bellevue, WA. 75 pp. + appendices.

U.S. EPA. 1986. Test methods for evaluating solid waste (SW-846): physical/chemical 

methods. U.S. Environmental Protection Agency, Office of Solid Waste, Washington, DC.

U.S. EPA. 1987. U.S. EPA Contract Laboratory Program statement of work for inorganic 

analysis, multi-media, multi- concentration. U.S. Environmental Protection Agency, 

Washington, DC.

U.S. EPA. 1988a. U.S. EPA Contract Laboratory Program statement of work for organic 

analysis, multi-media, multi-concentration. U.S. Environmental Protection Agency, 

Washington, DC.

U.S. EPA. 1988b. WASP4: a hydrodynamic and water quality model. Model theory - users 

manual and programmers guide. EPA/600/3-87/039. U.S. Environmental Protection Agency, 

Washington, DC.

U.S. EPA. 1989. Method 1625C: semivolatile organic compounds by isotope dilution GC/MS. 

U.S. Environmental Protection Agency, Office of Water Regulations and Standards, Industrial 

Technology Division, Washington, DC.

U.S. EPA. 1991. Analytical method for determination of acid volatile sulfide in sediment. U.S. 

Environmental Protection Agency, Office of Science and Technology, Health and Ecological 

Criteria Division, Washington, DC.

U.S. GOFS. 1989. Sediment trap technology and sampling. U.S. Global Ocean Flux Study 

Planning Report Number 10. G. Knauer and V. Asper (eds). University of Southern Mississippi, 

Center for Marine Science.

CHAPTER XIII.

Akar, P.J. and Jirka, G.H. 1990. Cormix2: An Expert System for Hydrodynamic Mixing Zone 

Analysis of Conventional and Toxic Multiport Diffuser Discharges. USEPA Environmental 

Research Laboratory, Athens, GA. Draft.

American Public Health Assoc., American Water Works Assoc., and Water Pollution Control 

Federation. 1985. Standard Methods for the Examination of Water and Wastewater, Sixteenth 

Edition.

American Society for Testing and Materials. 1992. Annual Book of ASTM Standards, Volumes 

11.04.
REFERENCES (JULY 2002)

Permit Writer’s Manual

R-8

Baker, J.M. and W.J. Wolff. 1987. Biological Surveys of Estuaries and Coasts.

Doneker, R.L. and Jirka, G.H. 1990. Cormix1: An expert system for Hydrodynamic mixing zone 

analysis of Conventional and Toxic Submerged Single Port Discharges. USEPA, Environmental

Research Laboratory, Athens, GA. EPA/600-3-90/012.

Ecology 1993. Sediment Source Control Standards User Manual.

Keith, L.H. 1991. Environmental Sampling and Analysis: A Practical Guide. Lewis Pub. Inc., 

ISBN 0-87371-381-8, 129 pp. 

Puget Sound Water Quality Authority. 1991. Puget Sound Water Quality Management Plan.

Tetra Tech. 1986a. Recommended Protocols for Measuring Metals in Puget Sound Water, 

Sediment and Tissue Samples.

Tetra Tech. 1986b. Recommended Protocols for Measuring Selected Environmental Variables 

in Puget Sound.

U.S. Environmental Protection Agency. 1973. Handbook for Monitoring Industrial Wastewater. 

U.S. Environmental Protection Agency. 1979. Methods for the Chemical Analysis of Water and 

Wastewater, EPA 600/4-79-020.

U.S. Environmental Protection Agency. 1982a. Design of 301(h) Monitoring Programs for 

Municipal Wastewater Discharges to Marine Waters. EPA 430/9-82-010.

U.S. Environmental Protection Agency. 1982b. Handbook for Sampling and Sample 

Preservation of Water and Wastewater. EPA-600/4-82-029. 

U.S. Environmental Protection Agency. 1984. NPDES Compliance Inspection Manual.

U.S. Environmental Protection Agency. 1987a. Guidance Manual for the Development and 

Implementation of Local Discharge Limitations Under the Pretreatment Program.

U.S. Environmental Protection Agency. 1987b. Short-Term Methods for Estimating the Chronic 

Toxicity of Effluents and Receiving Waters to Marine and Estuarine Organisms, EPA/600/4-

87/028.

U.S. Environmental Protection Agency. 1987c. Permit Writer's Guide to Water Quality-Based 

Permitting for Toxic Pollutants. EPA 440/4-87-005.
REFERENCES (JULY 2002)

Permit Writer’s Manual

R-9

U.S. Environmental Protection Agency. 1987d. Training Manual for NPDES Permit Writers. 

U.S. Environmental Protection Agency. 1989. Short-Term Methods for Estimating the Chronic 

Toxicity of Effluents and Receiving Waters to Freshwater Organisms, EPA/600/4-89/001.

U.S. Environmental Protection Agency. 1990. Methods for Measuring the Acute Toxicity of 

Effluents to Freshwater and Marine Organisms, EPA/600/4-90/027.

U.S. Environmental Protection Agency. 1991. Technical Support Document for Water Quality 

Based Toxics Control.

U.S. Environmental Protection Agency. 1992. NPDES Storm Water Sampling Guidance 

Document, EPA 833-B-92-001.

U.S. Geological Survey. 1989. Methods for Analysis of Inorganic Substances in Water and 

Fluvial Sediments.

U.S. Geological Survey. Kilpatrick, F.A., and Cobb, E.D. 1985. Measurement of Discharge 

Using Tracers. Chapter A16. Techniques of Water-Resources Investigations of the USGS, Book 

3, Application of Hydraulics. U.S. Department of the Interior. Reston, VA. 

U.S. Geological Survey. Wilson, J.F., Cobb, E.D., Kilpatrick, F.A. 1986. Fluorometric 

Procedures for Dye Tracing. Chapter A12. Techniques of Water-Resources Investigations of the 

USGS, Book 3, Application of Hydraulics. U.S. Department of the Interior. Reston, VA.

Washington State Department of Ecology. 1998. Criteria for Sewage Works Design. Ecology 

Publication No. 98-37WQ.

Washington State Department of Ecology. 1991a. Guidelines and Specifications for Preparing 

Quality Assurance Plans. 

Washington State Department of Ecology. 1991b. Laboratory Users Manual. 

Washington State Department of Ecology. 1990a. Technical Guidance for Assessing the 

Quality of Aquatic Environments in Washington State.

Washington State Department of Ecology. 1992. Water Quality Program Inspection Manual.

Washington State Department of Ecology. 1990b. Water Quality Technical Guidance Manual.

Yearsley, J. 1991. Diffusion in near-shore and riverine environments. USEPA Region 10. EPA 

910/9-87-168.
REFERENCES (JULY 2002)

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APPENDIX 1. (JULY 2004)

Permit Writer’s Manual

APP1-1

APPENDIX 1

1. INDEX TO NPDES REGULATIONS

SUBJECT CFR NUMBER

301(b) - see Fundamentally Different Factors

301(c)................................................................................ ............................... 122.21(1)(2)

301(g)............................................................................................................... 122.21(1)(2)

301(h) - Secondary treatment waiver............................................................... 122.21(m)(1)

122.56

301(k)............................................................................................................... 122.21(m)(2)

122.21(l)(3)

122.90

301(k)............................................................................................................... 122.21(l)(4)

125.20

316(a)................................................................................ ............................... 122.21(l)(6)

125.70

124.51(7)(a)

124.66

401(a) State Certification......................................................... ...................... 124.54

124.65

Administrative Procedures Act

Permit Continuation............................................................................ 122.6

Administrative Record..................................................................................... 124.9

Alternate Test Procedures................................................................................ 136.4

Anti-Backsliding (Reissued Permits)............................................................... 122.44(l)

Application....................................................................................................... 122.21

Completeness.............................................................. ............................... 122.21(e)

124.3(c)-(g)

Existing Facilities....................................................................................... 122.21(g)

Municipal................................................................... ................................ 122.21(j)

Submittal Deadline (Time to Apply)................................... ...................... 122.21(c)

Aquaculture...................................................................................................... 122.25

125.10

Aquatic Animal Production Facilities

Application................................................................. ........................ 122.21(h)(2)

Definition............................................................................................ 122.24

Appendix A
APPENDIX 1. (JULY 2004)

Permit Writer’s Manual

APP1-2

Average Monthly Discharge Limitation .......................................................... 122.2

Average Weekly Discharge Limitation (POTW)........................... ................. 122.2

Backsliding.......................................................................... ............................ 122.62(a)(15)

122.62(a)(17)

Best Management Practices

Definition............................................................................................ 122.2

122.44(k)

125.100

Best Professional Judgment (Case-by-Case)................................. .................. 125.3

Boilerplate (General) Permit Conditions........................................ ................. 122.41 - 122.44

Bypass.............................................................................................................. 122.41(m)

Calculating NPDES Permit Conditions........................................ ................... 122.45

Case-by-Case Limitations................................................................................ 122.44(a), 125.3

Case-by-Case Permits............................................................. ......................... 124.52

Coast Guard......................................................................... ............................ 122.44

Coastal Zone Management Act........................................................................ 122.49(d)

Combined Sewers (stormwater/wastewater..................................................... 133.103(a)

Combined Wastes (municipal/industrial)....................................... ................. 133.103(b)

Comments During Public Notice Period.......................................................... 124.13

Compliance Schedules..................................................................................... 122.41(l)(5)

122.47

122.62(a)(13)

Computation of Time....................................................................................... 124.20

Concentrated Animal Feeding Operations

Application................................................................................................. 122.23

Definition................................................................... ................................ 122 Appendix B

Concentrated Aquatic Animal Production....................................................... See Aquatic Animal Production

Conditions applicable to all Permits................................................................ 122.41

Confidentiality of Information......................................................................... 122.7

Consolidation of Permit Processing................................................................. 124.4

Continuation of Expiring Permits................................................ .................... 122.6

Conventional Pollutants................................................................................... 401.16

DMR - See Discharge Monitoring Report

Daily Average - See Average Monthly

Daily Maximum - See Maximum Daily

Definitions........................................................................................................ 122.2

124.2

401.11

Denial of Permit............................................................................................... 124.6(b)

Public Notice.............................................................................................. 124.10(a)(i)
APPENDIX 1. (JULY 2004)

Permit Writer’s Manual

APP1-3

Design Flow (POTW)...................................................................................... 122.45(b)

Dilution/Ocean................................................................................................. 125.123(d)(1)(i)

Dilution/Pollution.................................................................. .......................... 122.45(f)(1)(iii)

Discharge Monitoring Report (DMR)........................................... .................. 122.41(l)(4)(i)

Discharge of Pollutants - Definition............................................. ................... 122.2

Disposal into well, POTW, or land application.............................. ................. 122.50

122.45(i)

Draft Permit........................................................................ ............................. 124.6

Duration of Permits.......................................................................................... 122.46

Duty to Comply................................................................................................ 122.41(a)

Duty to Mitigate............................................................................................... 122.41(d)

Duty to Provide Information............................................................................ 122.41(h)

Duty to Reapply.................................................................... ........................... 122.41(b)

Effective Date...................................................................... ............................ 124.15

Effluent Limits for Continuous Discharges....................................... 122.45(d)

EIS - Public Notice for New Source................................................................ 124.10(b)(1)

EIS - Final........................................................................................................ 124.61

Endangered Species Act........................................................... ....................... 122.49(c)

EPA Review and Objection to State Issued NPDES Permits...........................123.44

Environmental Impact Statement

New Source................................................................................................ 122.29(c)

NEPA....................................................................... .................................. 40 CFR Part 6

Evidentiary Hearing Procedures................................................. ..................... 124.71 - 124.91

Ex Parte Communication......................................................... ........................ 124.78

Exclusions (from NPDES permits).................................................................. 122.3

Existing Source - Definition...................................................... ...................... 122.29(a)(3)

Expiration Dates (Duration of Permits)......................................... .................. 122.46, 124.20

Extension of Public Comment Period.............................................................. 124.12(c)

Extension of Permits........................................................................................ 122.46(b)

122.6

Fact Sheets.......................................................................... ............................. 124.8

124.56

Feedlots (see concentrated animal feeding operations)

Filter Backwash.................................................................... ........................... 125.3(g)

Fish and Wildlife Coordination Act................................................................. 122.49(e)

Fish Farms (see aquatic animal production facilities)

Flow Monitoring Required.................................................................... .......... 122.44(i)(1)(ii)

403.12(b)(4)

Fundamentally Different Factors................................................ ..................... 122.21(l)(1)

125.30

122.44(d)(8)

General Permits................................................................................................ 122.28
APPENDIX 1. (JULY 2004)

Permit Writer’s Manual

APP1-4

Public Notice.............................................................................................. 124.10(c)(2)(i)

Special Procedures..................................................................................... 124.58

Innovative Technology - see 301(k)

Inspection and Entry............................................................... ......................... 122.41(i)

Intake Credits (technology-based)................................................................... 122.45(g)

Instream Aeration............................................................................................. 125.3(f)

Internal Waste Streams............................................................ ........................ 122.45(h)

Introduction of New Pollutants - POTW....................................... .................. 122.42(b)

Issuance and Effective Dates..................................................... ...................... 124.15

124.60

Mass Limitations.............................................................................................. 122.45(f)

Maximum Daily Discharge Limitations........................................ .................. 122.2

Metals............................................................................................................... 122.45(c)

Minor Modifications............................................................... ......................... 122.62

Modifications....................................................................... ............................ 122.62

122.5

Monitoring and Recording............................................................................... 122.48(b)

Monitoring and Records.......................................................... ........................ 122.41(j)

Monitoring Reports.................................................................................... 122.41(l)(4)

Requirements............................................................... .............................. 122.44(i)

Record keeping............................................................ .............................. 122.21(o)

Monitoring Waiver (for guideline-listed pollutants)........................................ 122.44(a)(2)

NPDES - Definition.............................................................. ........................... 122.2

National Environmental Policy Act................................................................. 122.49(g)

National Historic Preservation Act.............................................. .................... 122.49(b)

Navigation........................................................................................................ 122.44(q)

124.58

Need to Halt or Reduce Activity Not a Defense.............................................. 122.41(c)

Net/Gross............................................................................ ............................. 122.45(g)

New Discharger - Definition............................................................................ 122.2

New Source - Application POTW............................................... .................... 122.21(j)

Application industrial................................................................................. 122.21(k)

Criteria...................................................................... ................................. 122.29(b)

Definition................................................................... ................................ 122.2

Mitigation Measures...................................................... ............................ 122.44(d)(9)

Prohibited Discharges.................................................... ............................ 122.4(i)

Public Notice.............................................................................................. 124.10(a)(1)(vi)

No Discharge Zones (Vessels)......................................................................... 140.4

Non-Advisory Panel Procedures...................................................................... 124.111 - 124.128

Non-Continuous Discharges...................................................... ...................... 122.45(e)

Noncompliance - Anticipated..................................................... ..................... 122.41(l)(2)

Other........................................................................ .................................. 122.41(l)(7)
APPENDIX 1. (JULY 2004)

Permit Writer’s Manual

APP1-5

Notification Levels........................................................................................... 122.42(a)

122.44(f)

Ocean Discharge Criteria................................................................................. 125.120

Offshore Oil and Gas Facilities........................................................................ 122.28(c)

On-Site Construction (New Source)............................................. ................... 122.29(c)(4)

Operation and Maintenance....................................................... ...................... 122.41(e)

Permit Application Forms................................................................................ 122.1(d)(1)

Permit Shield.................................................................................................... 122.5(a)(1)

pH - Continuous Monitoring............................................................................ 401.17

Planned Changes.............................................................................................. 122.41(l)(1)

Pollutant - Definition.............................................................. ......................... 122.2

Pollutants in Intake Water (Net/Gross)............................................................ 122.45(g)

POTW - Applications.............................................................. ........................ 122.21(j)

Pretreatment........................................................................ ............................. 122.44(j)

40 CFR 403

Primary Industry................................................................... ........................... 122 Appendix A

Privately Owned Treatment Works.............................................. ................... 122.44(m)

Production-Based Limits.......................................................... ....................... 122.45(b)

Prohibitions (No permit may be issued)...........................................................122.4

Proper Operation and Maintenance.............................................. ................... 122.41(e)

Property Rights..................................................................... ........................... 122.41(g)

Public Hearings (Public Notice)................................................. ..................... 124.10(b)(2)

124.10(d)(2)

124.12

Public Notice.................................................................................................... 124.10(d)

Contents.................................................................... ................................. 124.10(d)

Reapplication....................................................................... ............................ 122.21(d)

Reasonable Potential (violation of WQ standards).......................................... 122.44(d)(1)(i)-(vi)

Record Keeping.................................................................... ..................... 122.21(o)

122.41(j)(2)

Reopener Clause.................................................................... .......................... 122.44(c)

Reopening of Public Comment Period.......................................... .................. 124.14

Response to Comments.................................................................................... 124.17

Retention of Records........................................................................................ 122.41(j)(2)

Revocation and Reissuance.............................................................................. 122.62

124.5

Secondary Treatment Requirements................................................................ 133

Secondary Treatment Variance (see 301(h))

Sewage Sludge................................................................................................. 122.44(o)

Signatory Requirements................................................................................... 122.22

Silviculture....................................................................................................... 122.27

Small Business Exemption........................................................ ...................... 122.21(g)(8)
APPENDIX 1. (JULY 2004)

Permit Writer’s Manual

APP1-6

Standard Conditions......................................................................................... 122.41

State Certification ................................................................. .......................... 124.53

State Certification (301(h)).............................................................................. 124.54

124.55

States more Restrictive............................................................ ........................ 122.1(f)

Statement of Basis............................................................................................ 124.7

Statutory Deadlines for POTW........................................................................ 125.3(a)(1)

Statutory Deadlines for non-POTW................................................................. 125.3(a)(2)

Statutory Variances and Extensions................................................................. 125.3(b)

Stays of Contested Permit Conditions........................................... .................. 124.16

124.60

Storm Water..................................................................................................... 122.26

Application and Deadline ................................................................... 122.26(e)

Technology Based Effluent Limits............................................... ................... 122.44(a)

Ten Year Protection Period for New Sources and Dischargers....................... 122.29(d)

Termination of Permit...................................................................................... 122.64

Thermal Dischargers (see 316(a))

TMDL...................................................... ...................................... 130.7

Toxic Pollutants (definition)............................................................................ 122.2

Toxic Pollutants-List........................................................................................ 401.15

Transfer of Permit............................................................................................ 122.41(l)(3)

122.61

Total Toxic Organics (TTO)............................................................................ varies by categorysee 413.02(i) for

an example

Twenty-four hour Reporting............................................................................ 122.41(l)(6)

122.44(g)

Upset................................................................................. ............................... 122.41(n)

Water Quality Standards.................................................................................. 122.44(d)

Federally Promulgated............................................................................... 131

Waters of the U.S. (and Wetlands)- definition............................... ................. 122.2

Whole Effluent Toxicity - definition............................................ ................... 122.2

Wild and Scenic Rivers Act............................................................................. 122.49(a)
APPENDIX 4. TECHNOLOGY-BASED LIMITS (JULY 2002)

Permit Writer’s Manual

APP4-1

APPENDIX 4

I. AUTOCORRELATION 

The background material for this example is presented in Chapter IV, Part 4.

Adjustment of Monthly Average Effluent Limitations for Autocorrelation.

The Department of Ecology required an industrial discharger to monitor its cyanide discharge for 

several years prior to permit renewal. The data is presented below in Table AP4-1. The data 

indicated a reasonable potential for violation of the water quality standards and the necessity of a 

water quality-based effluent limit in the new permit. The facility requested an adjustment of the 

average monthly effluent limit due to autocorrelation. The request and data were passed on to 

USEPA for assistance in evaluating the autocorrelation. Calculation of autocorrelation involves 

two steps: 1. calculation of autocovariance and then 2. using the autocovariance to calculate the 

significant autocorrelation coefficients. These coefficients are used in calculating the monthly 

average effluent limitation.

An example is presented to show the process but the example shows a one week cycle and would 

probably not be granted an adjustment to the effluent limit. The facility used in this example 

applied for an autocorrelation adjustment but also provided the data for a higher site-specific 

water quality criteria for cyanide. With the higher criteria, they no longer showed a reasonable 

potential or required an effluent limit.

Table AP4-1. Effluent cyanide data.

DATE Cyanide ug/l DATE Cyanide ug/l DATE Cyanide ug/l

3/2/90 38 7/3/90 15 12/16/93 79

3/3/90 70 7/5/90 10 12/22/93 38

3/4/90 50 7/10/90 11 12/29/93 47

3/5/90 66 7/12/90 10 01/05/94 27

3/6/90 52 7/17/90 3 01/12/94 33

3/7/90 35 7/19/90 5 01/19/94 28

3/14/90 40 7/24/90 3 01/26/94 42

3/15/90 47 7/26/90 4 02/02/94 29

3/22/90 3 8/1/90 5 02/09/94 37

3/23/90 23 8/2/90 5 02/16/94 87

3/27/90 2 8/7/90 5 02/23/94 44
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3/30/90 18 8/16/90 3 03/01/94* 70

4/3/90 35 8/20/90 4 03/02/94 45

4/4/90 30 8/23/90 4 03/09/94 43

4/5/90 32 8/28/90 3 04/06/94 20

4/6/90 34 8/30/90 5 04/13/94 12

4/9/90 39 4/1/91 60 04/19/94 15

4/12/90 44 4/8/91 10 04/27/94 26

4/17/90 48 03/26/93 60 05/04/94 22

4/19/90 51 03/30/93 56 05/11/94 23

4/25/90 64 04/02/93 58 05/18/94 16

4/26/90 33 04/06/93 40 05/25/94 21 

4/29/90 70 04/08/93 74 06/01/94 19 

4/30/90 34 04/12/93 66 06/08/94 17 

5/8/90 15 04/19/93 52 06/15/94 15 

5/10/90 13 04/22/93 37 06/30/94 23

5/15/90 20 04/25/93 39 07/06/94 20

5/17/90 20 05/10/93 21 07/13/94 15

5/22/90 23 05/12/93 13 7/20/94 11

5/24/90 18 05/14/93 12 7/27/94 10

5/29/90 8 6/1/93* 20 8/3/94 14

5/31/90 12 06/16/93 13 8/10/94 10

6/5/90 10 06/18/93 11 8/17/94 4

6/7/90 2 06/21/93 9 8/24/94 13

6/12/90 2 06/24/93 13 8/31/94 8

6/14/90 2 07/10/93 19 9/7/94 35

6/19/90 23 07/12/93 18 9/14/94 26

6/21/90 17 07/14/93 12 9/21/94 38

6/26/90 13 07/16/93 15 9/28/94 46

6/28/90 14 07/29/93 20 10/5/94 5

08/04/93 13 10/11/94 6

DATE Cyanide ug/l

10/18/94 4

10/26/94 4

11/2/94 35

11/9/97 44

11/17/94 34

11/22/94 35

11/30/94 26
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12/7/94 43

12/14/94 53

12/21/94 30

12/28/94 34

1/5/95 34

1/11/95 53

1/26/95 46

2/1/95 41

2/8/95 49

2/15/95 24

2/22/95 19

3/1/95 32

3/8/95 33

3/15/95 22

3/29/95 23

Calculation of Autocovariance Estimates

The cyanide data consists of 144 individual daily composite samples representing concentration 

measurements taken during the period March 2, 1990 to March 29, 1995. Days with no samples 

are considered missing observations. For purposes of calculating the autocovariances, let z1, z2, 

..., zN denote the N concentration measurements. The following formula (Box & Jenkins, 1976, 

p.32) was used to calculate the estimate of the autocovariance:

C

N k Zt Z Z Z t

N k

= − t k − =

−

∑ +

1

1

( )( )

where,

N = number of observations = 144

k = lag between observations in days = 0,1,...,30

t = the day, where

t = 1 = March 2,1990

t = 2 = March 3,1990

t = 3 = March 4,1990

 •

 •

 •

t = 1854 = March 29,1995

Days on which concentration amounts were not reported are considered to be missing 

observations. Therefore only those values of t where data has been reported will be used to 
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calculate autocovariances.

The following lists t=1 through t=13 and gives some calculation examples:

value of t date concentration amount

1 3/2/90 38

2 3/3/90 70

3 3/4/90 50

4 3/5/90 66

5 3/6/90 52

6 3/7/90 35

 7 – 12 3/8/90 - 3/13/90 missing

13 3/14/90 40

The mean of the concentration amounts for the entire data set is:

Z

N

Zt

t

N k

= = =

−

∑1 26 9653

1

.

Note: Only use those values of t where concentration amounts exist.
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Calculations for a lag of one day using all measurements one day apart (i.e., k=1). For 

example:

value of t calculation

1 (38-26.9653)(70-26.9653) = 474.875

2 (70-26.9653)(50-26.9653) = 991.291

3 (50-26.9653)(66-26.9653) = 899.153

4 (66-26.9653)(52-26.9653) = 977.222

 6 - 13 *

• •

• •

• •

 1853 *

N = 144 Sum of contributions = 5759.7696

Autocovariance of lag two = 8784.0864/144 = 61.0006

* concentration amount two days from this value of t is missing and therefore cannot contribute 

toward an autocovariance for a lag of two. Concentration values two days apart must exist to be 

included in the calculation of the autocovariance for lag two.

It is recommended (Box & Jenkins, 1976, p.33) that k not be larger than N/4. In our case, we 

recommend that k not be larger than 30 since the limits are calculated on a monthly basis. The 

estimate of the kth lag autocorrelation is

rk= C

C

k

o

The number of observations used to estimate rk and ck need not be equal. Therefore missing data 

are not a problem, however missing data does prevent standard time series modeling. Estimates 

of autocovariance and autocorrelation for lags 1-30 are given in Table AP4-2.

A lag of 7 indicates the autocorrelation for observations 7 days apart. (For example, successive 

Mondays would have a lag of 7, successive Tuesdays would have a lag of 7, etc.)
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Table AP4-2. Estimates of Autocovariance and Autocorrelation: Lags 0-30

Lag Autocovariance Autocorrelation

0 367.117

1 39.9984 0.10895

2 61.0006 0.16616

3 33.7574 0.09195

4 44.5250 0.12128

5 37.6707 0.10261

6 49.7120 0.13541

7 101.503 0.27649

8 27.0599 0.07371

9 39.8864 0.10865

10 28.6923 0.07816

11 16.0746 0.04379

12 32.0776 0.08738

13 61.6921 0.16804

14 75.6883 0.20617

15 8.7124 0.02373

16 18.3915 0.05010

17 16.0578 0.04374

18 -4.7897 -0.01305

19 17.2813 0.04707

20 9.6339 0.02624

21 68.9943 0.18794

22 0.4231 0.00115

23 19.9909 0.05445

24 -0.0996 -0.00027

25 -1.4486 -0.00395

26 18.0623 0.04920

27 9.7315 0.02651

28 57.6594 0.15706

29 -0.4159 -0.00113

30 14.6503 0.03991
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Significance of Autocovariances

Using

var[rk] = 1

N

to approximate the variance of the autocorrelations (Box & Jenkins, 1976, p.35), where N = 144, 

the approximate variance is 0.006944. The corresponding approximate standard error is 

0.083307. The approximate standard error is compared to the autocorrelations (Box & Jenkins, 

1976, p.36). In cases where the autocorrelation is greater than two standard deviations 

(0.166614) the autocovariance was considered significant. Autocovariances for lags 2, 7, 13, 14, 

and 21 were significant. Adjustment for the lag 2 autocorrelation was not made in our limitation 

calculations because daily monitoring would be required to implement such limits properly and 

the permit writer had indicated a requirement of weekly monitoring.

Calculation of Limits

Calculation for limits using the covariance of lags 7, 14, and 21 days follows:

Var[Mean(X)] = (1/16)[4 * Var(X) + 6 * 0.27649 Var(X) +

 4 * 0.20617 Var(X) + 2 * 0.18794 Var(X)]

 = .25 Var (X) + 0.10368 VAR (X) + 0.05154 Var (X)

+ 0.02349 Var (X)

 = 0.42871

1. Performance-based Limit

a. Calculate μ and σ as above as the mean and standard deviation of the ln(CN) values.

μy = 2.96442

σy = 0.91308

σy

2 = 0.83372

b. Calculate the estimated mean and standard deviation of the CN values as:

E(X) = exp (μy + σy

2

/2)
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= exp (2.96442 + 0.83372/2)

= exp (3.38128)

= 29.40839

Var(X) = exp (2 * μy + σy

2

) * [exp (σy

2

) - 1]

 = exp (2 * 2.96442 + 0.83372)

* [exp (0.83372) - 1]

 = exp (6.76256) * [exp (0.83372) -1]

 = (864.85339) * (1.30187)

 = 1125.9266

c. Calculate the estimated mean and variance of the average of 4 weekly CN values used 

in a monthly average. Include the autocovariance effect.

n = 4

σ4

2 = ln {0.42871 * Var(X) / E[(X)]2 + 1}

 = ln {(0.42871 * 1126 / [29.4]2

) + 1}

 = ln 1.55848

 = 0.44371

μ4 = ln (E(X)) - 0.5σ4

2

 = ln (29.4) - 0.5 * (0.44371)

 = 3.38099 - 0.22186

 = 3.15913

d. Calculate the 95th percentile monthly average limit

X.95 = exp {μ4 + 1.645σ4}

= exp {3.15913 + 1.645 (0.66611)}

= exp {4.25488}

= 70.44836

e. Calculate the 99th percentile daily average limit

X.99 = exp {μy + 2.326σy}

= exp {2.96442 + 2.326(0.91308)}

= exp {5.08824}

= 162.10496

2. Calculating the limit based on the proposed site specific acute water quality standard for CN 

of 9.85μg/l.

a. WLA = (9.85 μg/l)(13) = 128 μg/1
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b. Calculate the LTA using the CV calculated from the lognormal distribution

CV = [exp(σy

2

) - 1]0.5

 = [exp(0.83372) - 1]0.5

 = 1.30187]0.5

 = 1.14100

σ2 = ln(CV2 + 1)

 = ln(1.141002 + 1)

 = ln(2.30188)

 = 0.83373

LTA = WLA {exp[0.5σ

2 - zσ]}

 = 128 {exp[0.5(0.83373) - 2.326(0.91309)]}

 = 128 {exp[-1.70698]}

 = 128 {0.18141}

 = 23.22048

c. Calculate the MDL and the AML

MDL = LTA {exp[zσ - 0.5σ

2

]}

 = 23.22048 {exp [2.326(0.91309) - 0.5(.83373)]

 = 23.22048 {exp [1.70698]}

 = 23.22048 {5.51229}

 = 127.99801

AML = LTA {exp[zσ4 - 0.5σ4

2

]}

σ4

2 = ln [(0.42871)CV2 + 1]

 = ln [(0.42871)(1.14100)2 + 1]

 = ln [1.55813]

 = 0.44349

AML = 23.22048 {exp[(1.645)(0.66595) -

(0.5)(0.44349)]

 = 23.22048 {exp[0.87375]}

 = 23.22048 {2.39588}

 = 55.63348

Table AP4-3 illustrates the different results obtained when considering no autocorrelation, 

autocorrelation at lag 7, autocorrelation at lags 7 and 14, and autocorrelation at lags 7, 14, and 
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APP4-10

21. The limits increase with the amount of autocorrelation included in the calculation. Positive 

autocorrelation increases the variance which increases the limit.

Table AP4-3. Comparison of Limit

Lags

Considered

Significant

PerformanceBased AMLWater Quality- Based

AML

σ4

2

None

(Independent)

47.3 48.5 .282

Lag 7 66.9 52.8 .378

Lags 7 and 14 69.4 54.8 .424

Lags 7,14,21 70.5 55.6 .444

Note: MDL’s are the same no matter how many lags are considered significant. For the 

Performance based limit it would be 159.3 and the water quality-based limit is 128

II. NEW SOURCE 
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APP6-1

APPENDIX 6

1. GUIDANCE FOR CONDUCTING MIXING ZONE 

ANALYSES

The key products from a mixing zone analysis are the dilution factors. They are used in 

conjunction with the water quality criteria for calculating reasonable potentials and effluent 

limits. There are aquatic life-based water quality criteria and human health-based water quality 

criteria. The former are applied at the acute and chronic mixing zone boundaries; the latter are 

(presently) applied at the chronic boundary. The methodology for conducting aquatic life-based 

analyses and human health-based analyses are similar. The permit manager should be consulted 

about the need for a human health-based analysis.

It is essential to have a working knowledge of how water quality-based effluent limits are 

developed in Washington state. This knowledge can be gained through reading and 

understanding the Water Quality Standards for Surface Waters of the State of Washington (in 

particular the subparts on Toxic Substances and Mixing Zones), EPA’s Technical Support 

Document (EPA, 1991), and the Department of Ecology’s Permit Writer’s Manual (in particular 

Chapters VI and VII) - and through experience. This Guidance provides the specific, detailed 

information that is needed to select the correct values for the effluent and receiving water 

parameters, select the appropriate model, and determine when a dye study should be used. As 

with the Permit Writer’s Manual, it’s expected that ample justification will be provided

whenever the guidance is not followed.

1.1 SELECTING VALUES FOR MODEL INPUT PARAMETERS

Steady-state models are the most frequently used tools for conducting mixing zone analyses. 

The value(s) chosen for each effluent and receiving water variable (parameter) is derived from a 

data subset, which corresponds to a specified period of time. The specified period of time should 

encompass and be limited to the most likely occurrence of the critical condition, as defined in the 

Water Quality Standards (e.g., a season when a 7Q10 is most likely to occur or the time when a 

particular stage of tide occurs). The term ‘reasonable worst-case’ is applied to the value(s).

The durations established for the aquatic life-based water quality criteria are one-hour (acute) 

and four-day (chronic). There are two types of human health-based water quality criteria: Those 

based on non-cancer effects and those based on cancer effects. The same concept of reasonable 

worst-case applies in non-cancer analyses as applies in aquatic life-based analyses. The concept 

of average values applies to carcinogenic human health-based analyses because the duration 

established for these criteria is the expected life span.
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APP6-2

Critical condition scenario refers to a scenario containing reasonable worst-case parameters, 

which has been set up to run in a mixing zone model (e.g., critical condition scenario to 

determine mixing at the chronic boundary). Steady-state mixing zone models are applied using a 

combination of these parameters (e.g., effluent flow, current speed, depth, density, etc.) packaged 

to simulate either a critical condition or (in the case of carcinogenic human health-based) an 

average condition. It’s understood that each critical condition scenario (by itself) has a low 

probability of occurrence. [Discharges to tidally-influenced rivers where a saltwater wedge is 

present are an exception. In these situations there is usually a high probability of occurrence 

because some of the parameters in the critical condition are known to occur simultaneously 

(e.g., during low tides, the predominance of freshwater may always create a minimum depth and 

well-mixed profile; while during high tides a stratified profile may always exist)].

A mixing zone analysis conducted with a steady-state model should include a sensitivity 

analysis. A sensitivity analysis is a series of scenarios organized such that only one reasonable 

worst-case value in each scenario is changed while all others are held constant in a logical 

progression. Figure 1 is an example of a sensitivity analysis.

The state-of-the-art mixing zone models accept time-series data. They are referred to as dynamic 

models, but it’s still necessary to calculate reasonable worst-case values for most of the 

parameters. These models are assuming more importance as expanded data sets become 

available.

In some circumstances the primary tool in a mixing zone analysis may be a dye study - with a 

model filling a secondary role. One such circumstance would be when it’s apparent that an 

effluent plume doesn’t develop normally (for any number of reasons). The dilution factors must 

then be measured directly in the field. However, these are the dilution factors for one set of 

effluent and receiving water conditions only, and a model may still be necessary for analyzing 

other sets of conditions that are quite different from those present during the dye study.

Those reasonable worst-case and average parameters that are required input to the critical 

condition scenarios are discussed in subsections 1.1.1-1.1.8. Subsections 1.1.9 and 1.1.10 

discuss other parameters which aren’t essential to using the models, but are essential ingredients 

in a complete mixing zone analysis. Subsection 1.1.11 addresses two other factors which must 

be considered before arriving at the correct dilution factors for the acute and chronic boundaries: 

The Standards require that mixing zones not occupy more than a certain percentage of the 

channel width and that, in rivers and streams, the effluent flowrate not utilize more than a certain 

percentage of the available receiving water flowrate in the process of dilution. So actually, the 

dilution factor to use when determining whether the effluent contributes to acute or chronic 

toxicity must be the lowest one of three that can be generated for both the acute and chronic 

boundaries.
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APP6-3

1.1.1 Municipal Effluent Flowrate

For critical condition scenarios at the acute boundary, the flow-rate to use depends on how close 

to design capacity the plant is presently operating. If the plant is operating at less than 85% of 

the dry weather design flow during the critical condition, then the flow-rate to use is the highest 

daily maximum plant effluent flow for the past three years during the season in which the critical 

condition is likely to occur. If the facility is operating between 85 and 100% of dry weather 

design flow during the critical condition, then use a peaking factor applied to dry weather design 

to determine acute design flow. The peaking factor is a ratio of daily maximum to monthly 

average flows derived from actual plant data during the critical season. A peaking factor may 

also be available in the engineering report for the facility.

For critical condition scenarios at the chronic boundary, the flow-rate to use depends on how 

close to design capacity the plant is presently operating. If the plant is operating at less than 85% 

of dry weather design flow during the critical condition, then the flowrate to use is the highest 

monthly average plant effluent flow for the past three years during the season in which the 

critical condition is likely to occur. If the facility is operating between 85 and 100% of dry 

weather design flow during the critical condition, then use the dry weather design flow. For 

average condition (human health-based) scenarios, the flow-rate to use is the annual average 

design flow as specified in the engineering report, permit application, or projection of annual 

average flow over the life of the permit by analyzing Discharge Monitoring Report (DMR) data.

1.1.2 Industrial Effluent Flowrate

For critical condition scenarios at the acute boundary, the flowrate to use is the highest daily 

maximum flow for the past three years during the season in which the critical condition is likely 

to occur. If plant effluent flows are expected to increase during the life of the permit, the highest 

daily maximum flow must be estimated.

For critical condition scenarios at the chronic boundary, the flowrate to use is the highest 

monthly average flow for the past three years during the season in which the critical condition is 

likely to occur. If plant effluent flows are expected to increase during the life of the permit, the 

highest average monthly flow must be estimated. For average condition (human health-based) 

scenarios, the flow-rate to use is the annual average design flow based on permit application or 

DMR analysis.

1.1.3 CSO Flowrate

For critical condition scenarios at the acute boundary, the flowrate to use is the highest 

equivalent twenty-four hour average for the past three years during the season in which the 

critical condition is likely to occur. If plant influent flows are expected to increase during the life 

of the permit, the highest daily maximum flow must be estimated.

For critical condition scenarios at the chronic boundary, the flowrate to use is the highest 

equivalent monthly average flow (total volume of all discharge events in a month divided by the 
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APP6-4

total hours of discharge in that month) for the past three years during the season in which the 

critical condition is likely to occur. If plant influent flows are expected to increase during the life 

of the permit, the highest average monthly flow must be estimated. For average condition 

(human health-based) scenarios, the flowrate to use is the annual equivalent average flow based 

on data provided in the permit application or DMR analysis.

1.1.4 Intermittent Effluent Flowrate

For analyses at both the acute and chronic boundaries, it is necessary to use an instantaneous 

flow when the effluent flowrate is intermittent. (Steady-state (averaged) effluent flowrates are a 

commonly accepted approximation of inherent variability - but only for continuous discharges). 

The reasonable worst-case flowrate to use is the maximum that can occur - whether through 

pumps or gravity flow. The resultant model generated dilution factor for the acute boundary 

must then be adjusted upward by a ratio of maximum flowrate to one-hour, time-averaged 

flowrate (if the maximum flowrate occurs for less than one hour); and the resultant dilution 

factor for the chronic boundary must then be adjusted upward by a ratio of maximum flowrate to 

four-day, time-averaged flowrate.

1.1.5 Stormwater Flowrate

For analyses at the acute boundary, the flowrate to use in western Washington is the average of 

the peak one-hour flowrate generated by the two-year, six-hour storm event. For analyses at the 

chronic boundary, the flowrate to use in western Washington is an estimate of the average runoff generated by the two-year, 72-hour storm event (Ecology, 1993) (Ecology, 1995). Guidance 

for other areas of the state is evolving.

1.1.6 Current

For aquatic life-based analyses at both the acute and chronic boundaries in unidirectional waters, 

both low flow and high flow condition currents should be used. The low flow velocity to use is 

that which occurs with the 7-day low flow period with a recurrence interval of 10 years (7Q10 by 

the appropriate statistical method). The high flow velocity to use is that which occurs with the 

7Q10 high flow. For non-carcinogenic human health-based analyses, the current velocity 

associated with a 30Q5 flow should be used if available - or a 7Q10. For carcinogenic human 

health-based analyses, the velocity associated with the harmonic mean flow for the 

representative period of record should be used. These can usually be calculated if a crosssectional profile of the channel bottom has been measured.

Determining the reasonable worst-case current in tidally-influenced water is deceptively 

difficult. It is true that dilution factors at the hydrodynamic mixing zone boundary (also referred 

to as the end of initial dilution or near-field) are increased by increased current velocities 

(assuming other variables are held constant). Conversely, the lower the current velocity, the 

lower the dilution factor at the end of initial dilution. Early EPA guidance (e.g., that guidance 

written for the 301(h) waiver application process) suggested that currents approaching zero 

contributed to critical condition scenarios. However, what is true at the hydrodynamic mixing 
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APP6-5

zone boundary is not necessarily true at a regulatory mixing zone boundary - because the two are 

not synonymous. (Refer to Figure 5 in the 3PLUMES User's Manual (EPA, 1994) for 

confirmation of this statement).

Roberts’ Froude number (F) is a dimensionless number which characterizes the importance of 

current velocity relative to the buoyancy flux. It evolved from research into plume behavior and 

mixing in marine waters. As a dependent variable, it is calculated automatically whenever a case 

is set up in the DOS PLUMES model and appears in the [Roberts’ F] cell on the 3PLUMES 

interface. Small values of the Roberts' Froude number signify little effect of current on mixing. 

According to Roberts (1991) the current exerts no effect on dilution if Roberts’ F < 0.1. (Refer 

to section 1.3.2 Range of the Experiments for additional information).

For analyses at the acute boundary in tidally-influenced water, the velocity to use in a model 

operating in the steady-state is the 10th percentile velocity. This is defined as both the 10th and 

the 90th percentile velocities derived from a cumulative frequency distribution analysis. The 

distribution analysis should be produced from a data set consisting of periodic readings taken by 

an instrument deployed over a neap and spring tide cycle. A field data set this comprehensive 

could also be used as a time-series file in the newer version models. In the absence of a 

comprehensive field data set, a sensitivity analysis should be run using a wide range of possible 

velocities which could reasonably occur for any 1-hour duration. The velocity which produces 

the lowest dilution should be considered the reasonable worst-case velocity.

For analyses at the chronic boundary in tidally-influenced water, the reasonable worst-case 

velocity is defined as the 50th percentile current velocity derived from a cumulative frequency 

distribution analysis. In the absence of a comprehensive field data set, a sensitivity analysis 

should be run using a wide range of velocities, any of which could reasonably occur as the 

average velocity for any 4-day duration. The velocity which produces the lowest dilution should 

be considered the reasonable worst-case velocity.

1.1.7 Depth

For aquatic life-based analyses at both the acute and chronic boundaries in unidirectional water, 

use the depth of the port(s) during a 7Q10 low flow period. For non-carcinogenic human healthbased analyses, use the depth at 30Q5 or 7Q10. For carcinogenic human health-based analyses, 

use the depth at the harmonic mean flow. These can usually be calculated if a cross-sectional 

profile of the channel bottom has been measured.

For analyses at both the acute and chronic boundaries in marine water (sea level), use the depth 

of the port(s) at Mean Lower Low Water (MLLW) - the depth given on most nautical charts. 

For analyses at both the acute and chronic boundaries in upstream tidally-influenced riverine 

waters, use the depth of the port(s) at MLLW during a 7Q10 low flow period. (Salt water 

wedges and a situation wherein the elevation of the river bottom at the outfall location is lower 
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APP6-6

than the surface elevation of the MLLW will require special considerations).

[Note: EPA mixing zone models should be used advisedly when the depth is less than 5 times 

the plume diameter. Refer to section 1.3.5 Boundary Conditions.]

1.1.8 Stratification

The density profile to use in aquatic life-based analyses is the one that results in the least mixing. 

Generally, this is either the minimum or maximum stratification, defined as follows: 

"Minimums" are characterized by profiles that extend to the same depth as the outfall with (1) 

the smallest differential between sigma-t values at the bottom and top of the profile; and (2) 

collectively, the highest sigma-t values. "Maximums" are characterized by profiles that extend to 

the same depth as the outfall with (1) the largest differential between sigma-t values at the 

bottom and the plume trapping depth; and (2) collectively, the lowest sigma-t values. Some 

profiles which are profoundly nonlinear warrant special consideration (e.g., saltwater wedges and 

nascent densities (Refer to section 1.3.8 Nascent Density and Buoyancy)).

[Note: Sigma-t is defined as (mass density (kg/m3

) – 1000)]

The density profile to use in human health-based analyses is the one that results in average 

mixing. This is determined as follows: (1) Generate the dilution factors for the two profiles 

(minimum and maximum), (2) calculate the reciprocal of the dilution factors to convert them to 

effluent concentrations, (3) calculate the average of the reciprocal dilution factors (average 

effluent concentration), and (4) calculate the reciprocal of the average effluent concentration and 

use that as the harmonic mean dilution factor.

In Puget Sound, changes in density correlate most closely to changes in season. Minimum 

stratifications frequently occur in October, while maximum stratifications frequently occur from 

May 1-July 15 (NOAA, 1981). There is little or no correlation between changes in stages of tide 

and changes in profiles. For this reason, one day of field measurements conducted during a neap 

or spring tide is of limited value – even though it may be in close proximity to the outfall. There 

is probably more value in the long-term, monthly salinity-temperature-depth (STD) data from 

Ecology’s Ambient Monitoring Program – even though it may not be in close proximity. 

Ecology’s data are available on the Internet at the Ecology website 

(www.ecy.wa.gov/programs/eap/env-info.html) 

[Note: The manufacturer of SEABIRD field monitoring equipment has proprietary software for 

downloading, analyzing, and presenting STD data. SEAPLOT is a module of this software 

which may prove useful for quickly reviewing the graphs of stratification profiles from a large 

STD data set – such as a station from Ecology’s Ambient Monitoring Program.]
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1.1.9 Pollutants of Concern

All toxic effects testing has some degree of uncertainty associated with it. The more limited the 

amount of test data available, the larger the uncertainty. A statistical approach has been 

developed to better characterize the effects of receiving water and effluent variability and reduce 

uncertainty in the process of deciding whether to require an effluent limit.

The statistical approach to use when determining the background concentration in the receiving 

water for aquatic life-based analyses depends on the number of data points. For 20 or fewer 

samples, the geometric mean of the receiving water values should be multiplied by a factor of 

1.74 to estimate the 90th percentile. This estimated background value should then be used in 

conjunction with the plant effluent data to evaluate reasonable potential to cause an exceedance 

of the criteria for aquatic life protection and to derive effluent limits.

For 21 or more samples, the reasonable worst-case value is the 90th percentile value derived 

from a cumulative frequency distribution analysis of a complete data set. A complete data set 

should include at least three years of ambient data from the critical season. This derived 

background value should be used in conjunction with the plant effluent data to evaluate 

reasonable potential to cause a violation of the criteria for aquatic life protection and to derive 

effluent limits.

The statistical approach to use when determining the background concentration for human 

health-based analyses when there are multiple data points is the geometric mean. Use 0 for 

value(s) below the MDL and use the MDL for values between the MDL and the QL (Refer to 

section 4. Effluent Limits Below Quantitation in Chapter VI of the Permit Writer’s Manual) .

The statistical approach to use when determining the concentration in the plant effluent for 

aquatic life-based analyses also depends on the number of data points. For 20 or fewer samples, 

assume a coefficient of variation (CV) of 0.6 and use the reasonable potential multiplying factors 

to calculate the estimated 95th percentile value. These factors can be found in Table 3-2 of the 

TSD (EPA, 1991) or calculated using the algorithm in Ecology’s Excel spreadsheet called 

TSDCALC.XLW – which is available at the Ecology website 

(http://www.ecy.wa.gov/programs/eap/pwspread/pwspread.html). This estimated value should 

then be used in conjunction with the background receiving water data to evaluate a reasonable 

potential to cause a violation of the criteria for aquatic life/human health protection and to derive 

effluent limits.

For 21 or more samples, calculate the CV and the 95th percentile effluent value. . This effluent 

value should then be used in conjunction with the background receiving water data to evaluate a 

reasonable potential to cause a violation of the criteria for aquatic life/human health protection 

and to derive effluent limits.

The statistical approach to use when determining the concentration in the plant effluent for 
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human health-based analyses is to use the 50th percentile concentration. If there are less than 10 

data points use a multiplier on the highest concentration to estimate the 50th percentile 

concentration. (The multipliers can be found in Table VII-2 of the Permit Writer’s Manual). If 

there are more than 10 values use the cumulative percentile calculation at a 95% confidence to 

derive the 50th percentile. (a statistical routine in a spreadsheet software such as Excel can do 

these calculations)..

The present temperature standards are as ‘not to exceed’ values (no averaging period). The 95th

percentile effluent and highest observed or expected receiving water values for the critical season 

should be used. The criterion must be met at the edge of the chronic boundary. Addressing the 

second part of the standard pertaining to ‘incremental temperature rise’ is beyond the scope of 

this guidance.

It may be necessary to do an analysis of immediate dissolved oxygen demand (IDOD) when 

effluent becomes a relatively high percentage of the receiving water flowrate. The 10th 

percentile value for effluent D.O. concentration and 10th percentile receiving water value for the 

critical season and time of day should be input to a mass-balance equation. Such an equation is 

available from Ecology in the Excel workbook called PWSPREAD (the particular spreadsheet is 

IDOD2). The D.O. criterion must be met at the edge of the chronic boundary.

1.1.10 Other Parameters

Temperature, pH, and hardness are the most noteworthy examples of other parameters, which 

may not be considered pollutants of concern, but are required to determine the toxic effects of 

other pollutants (e.g., ammonia). When selecting a reasonable worst-case value for temperature 

and pH, use the 90th percentile value derived from a cumulative frequency distribution analysis 

of a complete data set. For hardness, use the 10th percentile value. A complete data set should 

include at least three years of DMR or ambient data corresponding to the critical season. If 

annual data (from all months) are used to select the value, then the 95th or 5th percentile value 

from the frequency distribution should be used. For limited data sets (n<20) the upper or lower 

percentile values can be estimated by methods in Gilbert (1987).

1.1.11 Other Factors

The subpart pertaining to mixing zones in the Water Quality Standards restricts the width of a 

water body that can be “occupied” by both the acute and chronic mixing zones to twenty-five 

percent. Implementation of this restriction involves generating a dilution factor (DF) at a lateral 

boundary, which is located such that the width of the specified mixing zone does not occupy 

more than 25% of the channel width. The Channel width must be determined during a 7Q10 (in 

freshwater), MLLW (in sea level marine water), or combination thereof (in upstream tidallyinfluenced riverine waters). The dilution factor can be generated in one of two ways: (1) Use a 

model and note the DF associated with the plume diameter at the point where the plume has 

spread to one of the lateral boundaries; or (2) use dye and measure the DF at the lateral 

boundary(ies).
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This same subpart of the Standards restricts the flowrate in rivers and streams that can be 

“utilized” by an effluent flowrate to 25% at the chronic mixing zone boundary and to 2.5%at the 

acute mixing zone boundary. Formulation of this dilution factor for a receiving water involves 

solving the volume fraction equation:

( ) DF Q Q

Q

amb e

e

= +

(1)

where

Qamb is the receiving (ambient) water flowrate; and

Qe is the effluent flowrate.

The ambient portion must first be reduced by the appropriate percentage to give the amount 

available for dilution before the equation is solved for DF.

The dilution factor then for freshwater and narrow estuaries is the lesser of the factors calculated as 

% of flow or dilution at the spatial boundary as determined by modeling.

1.2 UNDERSTANDING INITIAL DILUTION THEORY

The general theory behind wastefield formation is easily understood. Visualize wastewater 

discharged horizontally as a jet from a single round port or a series of jets from ports spaced at 

equal distances along a diffuser. If the wastewater has a lower density than the surrounding 

water, then the resulting buoyancy force deflects the jet(s) upward forming plumes which are 

swept downstream by the current. The plume(s) entrain ambient water as they rise, causing them 

to be diluted and decreasing the density difference between them and the ambient. If the ambient 

is stratified, then its density at the depth of the ports is greater than near the surface. The greater 

density ambient water is entrained initially, and the rising, expanding plumes can reach a level 

where their density is the same as the surrounding water (i.e., neutral buoyancy). This is the 

trapping depth.

If the receiving water is unstratified, then its density is the same throughout the water column. In 

marine water the plume will always surface - if it remains intact. In freshwater the plume will 

nearly always surface. (Ambient temperatures equal to or less than 4 degrees Centigrade may 

generate exceptions. Refer to section 1.3.8 Nascent Density and Buoyancy).

The more specific theory behind initial dilution is less easily understood. It applies downstream 

from the port(s) until the turbulent kinetic energy generated by the buoyancy and momentum of 

the discharge dissipates. This is commonly referred to as the hydrodynamic mixing zone, initial 

dilution, or the near-field. (The term initial dilution will be used because near-field is defined 

and used differently in section 1.6 Conducting a Dye Study). Generally, initial dilution ceases 

because a layer boundary (water surface or trapping depth) is encountered. At the end of initial 

dilution, the wastefield is said to be established. The established wastefield then passes into "farfield". Designers of the outfall can usually affect what occurs in the hydrodynamic mixing zone, 
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but have little or no control over what occurs in the far-field.

All initial dilution models are based on the conservation principles of mass, momenta, and 

energy. The most important principle is that of conservation of mass - the equation of continuity. 

In mixing zone modeling it’s better understood as the entrainment equation. Different models 

use different conceptual "building blocks" for constructing their plumes along the trajectory. But 

regardless, the initial mass of the plume building block plus that added, or entrained, over some 

discrete period of time has to be conserved (i.e., there has to be a mass balance).

Another important aspect of a mass balance involves knowing the effect of water movement, 

which is determined with the conservation of momentum principle. Like the mass balance 

approach, accounting is undertaken for fluid momentum in a defined building block. Horizontal 

momentum is conserved. It is the product of building block mass and horizontal velocity and is 

increased by the horizontal momentum of the fluid that is entrained in the same period of time. 

Vertical momentum is not conserved but is altered by buoyancy, which arises from the density 

difference between the building block and the ambient water. Kinetic and thermal energy are 

conserved.

1.2.1 The Conceptual Dilution Factor

The volume fraction equation (Refer to section 1.1.11 Other Factors, equation (1)) is the simplest 

formulation of the dilution factor. Qamb was defined somewhat differently in equation (1) than it 

will be defined here; it is replaced by Qa in the following equation:

( ) DF Q Q

Q

a e

e

= +

(1a)

where,

Qa is the volume flux of receiving (ambient) water entrained in the plume from an outfall at 

some sampling point in the plume; and

Qe is the volume flux of effluent in the plume.

The Qa value is easier to visualize than to obtain directly; i.e., it is extremely difficult to measure at 

any sampling point that might be chosen in the plume. What can be measured directly in the plume 

is the concentration of a pollutant of concern (or a dye tracer) at any sampling point whose location 

is a known measured distance from the outfall. Call this concentration (Cp). The background 

concentration in the ambient water (Ca) and the concentration being discharged in effluent (Ce) can 

also be measured.
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To understand initial dilution theory it is necessary to formulate the dilution factor using the basic 

mass balance equation:

(Qa Ca ) (Qe Ce ) (Qa Qe )Cp

∗ + ∗ = + (2)

The volume fluxes (including the Qa that’s so difficult to measure) can be factored out of the 

equation by algebraic manipulation:

If the % effluent is represented by the term X; then the % ambient water 

which has been entrained in the plume of effluent that emerged from the outfall must 

be (1-X), because the sum of the two is 100% of the water in the plume. 

Substituting (1-X) for Qa and X for Qe (and understanding from equation (1) that 1 / 

X = DF) gives

( )

( ) DF

C C

C C

e a

p a

= −

− (3)

A DF calculated using equation (3) is an empirical result for the particular sampling point where the 

Cp value is measured.

An initial dilution model generates dilution factors using outfall, effluent, and receiving water 

characteristics supplied to it. Each DF that prints out is for a particular calculated distance as the 

model iterates along the plume trajectory away from the outfall. Depending on the model used, the 

DF (and Cp) may be calculated simply using the volume fraction equation, or the Cp may be 

calculated as an actual, effective diluted concentration (depending on whether the model accepts Ce

and Ca as inputs).

Rearranging equation (3) gives

C C

DF

C

DF p = e a





 



 + − 



 



 



 



 1 1 1 (4)

Again depending on the model used, the printout may occur repeatedly reflecting the model’s 

iterative process along the plume trajectory or it may occur only upon completion of initial dilution. 

Whatever the capability of the model, it is imperative that its generated Cps can be validated; i.e.,

compared to measured Cps at the same distance from the outfall to establish how well the model is 

simulating the plume. A dye tracer is generally better for this task because dye can be measured in 

situ with a fluorometer.
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1.2.2 Theoretical Models

The two theoretical models mentioned in this Guidance are UM (or UM3) and UDKHDEN (or 

DKHW). They both solve the equations of fluid motion and mass transport using an integration 

scheme in which they march forward in discrete increments along the trajectory of the buoyant 

jet (prompting the phrase “jet-integral models”, which often appears in the literature). UM is a 

Lagrangian model and uses a time increment; UDKHDEN is an Eulerian model and uses a 

distance increment.

The basic model building block in UM is the wafer-shaped plume element; in UDKHDEN it’s 

the control volume. In theoretical modeling terms the building block mass is incremented by the 

amount of fluid that flows over the outside boundary of the building block during each time or 

distance increment. The theoretical models, using these analytical tools, are capable of yielding 

fair approximations for the turbulent-flow problems encountered in mixing zone analyses. But, 

this particular field (i. e., the field of fluid mechanics) is more heavily involved with empirical 

work than are other fields because these analytical tools are not capable of yielding exact 

solutions to many of the problems.

1.2.3 Empirical Models

A considerable amount of experimental evaluation has been done using dynamic similitude 

(models and towing tanks in the laboratory) and dimensional analysis. This led to the 

development of empirically-derived curve fit equations to make dilution predictions and verify 

accuracy of the theoretical models. Eventually, the graphs and equations in the original papers 

were codified and became useful models in their own right.

The empirical models, like RSB (or NRFIELD) and CORMIX, predict initial dilution by 

stringing together a series of building blocks called length scales. Each length scale evolves 

from an empirically-derived curve-fit equation and is, literally, a distance along the trajectory 

where one parameter predominates (i.e., controls the flow). Once strung together by this 

analysis, the length scales should describe the relative importance of all parameters - discharge 

volume flux, momentum flux, buoyancy flux, ambient crossflow, and density stratification -

throughout the trajectory. For example, the solution for a pure jet can be applied as an 

approximate solution to that portion of a buoyant jet in a crossflow where jet momentum 

dominates the flow. Likewise, the results for a pure plume can be applied to the buoyancydominated regions for the buoyant jet. The length scales are linked by "appropriate transition 

conditions" to create a path for the trajectory through completion of initial dilution. These 

transition conditions are relative unknowns and a cause for concern.

1.2.4 Average Versus Centerline

When conducting mixing zone analyses it is necessary to have an elementary understanding of 

the difference between average and centerline plume concentrations (and dilutions) and the role 

of each in modeling. In theoretical models average concentrations are integral to the integration 
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APP6-13

scheme, center-of-mass of the building block, and total mass flux. Centerline concentrations 

become important when determining the potential for acute toxicity to organisms.

Plume velocities in a cross section of each building block (perpendicular to the path of the 

trajectory) resemble a bell-shaped curve. Concentrations, on the other hand, do not resemble a 

bell-shaped curve (i.e., peak concentrations do not occur at the same location as the center-ofmass). Therefore, an average concentration involves weighting the concentration distribution by 

the velocity distribution. This average may be referred to as either a “top hat” or “flux-average”, 

depending upon how it is formulated in a particular model. It is the value to be multiplied by the 

total plume volume flux to get total mass flux, which is passed on to the farfield algorithm.

In theoretical models, the ratio between centerline and average concentration varies between 2

(1.44) (for a fully-merged line plume) and 1.94 (for round plumes). It depends on a number of 

factors: The type of bell-shaped curve employed by a particular model (two examples are 3/2 

power profile and Gaussian), the plume geometry, where the building block is on the trajectory 

relative to the point of discharge, and whether the individual plumes have merged. Models 

employing the 3/2 power profile may deliver more accurate ratios because that curve better 

“feathers” the cross-section into complete ambient.

It is difficult to quantify the relationship between average and centerline values based on 

empirical measurements. Average dilution is difficult to measure in the laboratory, and virtually 

impossible to measure in the field since it is necessary to define the plume boundary and know 

the velocity distribution over the plume cross-section. Some direct measurements of average 

dilutions by Roberts (1991) indicate that the average may differ by only 10 to 20% from the 

centerline in stagnant currents and is 0% when Roberts’ F < 0.1. Suffice it to say, these peak-tomean ratios are still the subject of research in the plume modeling community (Frick, et al, 

2000). When initial dilution ends due to contact with a layer boundary the distinction between 

average and centerline ends soon afterward. There is no longer an elliptical plume - it becomes 

more rectangular.

For aquatic life-based analyses at both the acute and chronic boundaries in unidirectional water, 

centerline values should be used. For all other analyses flux-average values should be used. All 

comparisons of outputs between models must use centerline values.

1.3 CHOOSING AN INITIAL DILUTION MODEL

1.3.1 Descriptions

Steady-state models have been the most frequently used tools for conducting mixing zone 

analyses. Three of the more commonly used models are theoretical: UM, UDKHDEN, and 

VSW. Two are empirical: RSB and CORMIX. Three were included in the DOS-based interface 

(platform) called 3PLUMES which was released by EPA in about 1993: UM, VSW, and RSB.
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Dynamic models with the capability of using time-series data are rapidly coming of age as more 

effluent and receiving water data become available. In 2000 EPA released a new Windowsbased platform called Visual Plumes which houses the DOS PLUMES interface but also 

provides a dynamic model capability for three of these models: UM (renamed UM3, 

UDKHDEN (renamed DKHW), and RSB (renamed NRFIELD). In 2000 a Windows-based 

version of CORMIX with dynamic model capability was also released.

UM3 is the current version of the earlier models UOUTPLM (vintage 1979), UMERGE (vintage 

1985), and UM (vintage 1993). It is a three-dimensional model (e.g., it simulates plumes that 

bend in a three-dimensional trajectory). It uses the 3/2 power profile to calculate the ratio and 

determine the centerline concentration as a function of the top hat concentration that it predicts. 

The ratio changes continuously with each integration step along the trajectory (EPA, 1994). 

Merging is simulated with the reflection technique (Turner, 1970). It is not able to recognize 

and address lateral boundary constraints (Refer to section 1.3.5 Boundary Condition(s)) It 

transitions smoothly to a farfield algorithm (Refer to section 1.5.1 FARFIELD).

DKHW is a three-dimensional model. It considers either single or multiport discharges at an 

arbitrary horizontal angle into a stratified, flowing current. The current speed and density can 

vary with depth. The dilution factor generated is the flux-averaged which is, at all points on the 

trajectory, 1.15 times the centerline dilution factor. It terminates when the surface is reached, the 

plume reaches its maximum rise height, or when errors are encountered. It does not transition to 

a farfield algorithm, but this is not a problem (Refer to section 1.5 CHOOSING A FARFIELD 

MODEL).

VSW stands for Very Shallow Water. It is the only initial dilution model that will provide 

reliable results when the depth approaches three pipe diameters - or less. VSW employs the 

reflection technique (Turner, 1970), which is the same algorithm employed by UM to simulate 

merging of multiple plumes. A user's manual for VSW can be found at Appendix 6.2 of the 

Permit Writer’s Manual.

NRFIELD is an updated version of RSB and ULINE which is based on experimental studies of 

multiport diffusers in marine water as described in Roberts (1991). It requires at least four ports. 

Its strengths are: (1) It is set up and run through both the DOS PLUMES and Visual Plumes 

interfaces, so that many cases can be run quickly and compared to UM3 results; (2) it simulates 

opposing-port diffusers; and (3) the user is advised whenever the model is operating outside the 

range of the experiments. (Refer to section 1.3.2 Range of the Experiments). One present 

shortcoming of RSB is that it does not provide dilution factors for distances prior to the end of 

initial dilution, although it does transition smoothly to the same farfield algorithm employed by 

UM3. It uses a constant centerline-to-flux-average ratio of 1.15.

CORMIX stands for CORnell MIXing zone models. The package consists of CORMIX1, 

CORMIX2, and CORMIX3 for the analysis of submerged single port discharges, submerged 
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diffusers, and surface discharges, respectively. EPA's decision to proceed with the development 

of CORMIX was an attempt to utilize accumulated laboratory and field experience to compile a 

set of methods and empirical models to bridge the gaps that were evident in theoretical modeling 

at that time. The original system was designed for the non-specialist model user, so that plume 

predictions could be made without having prior knowledge about dilution modeling.

A concern is its infrequent, but unpredictable, creation of plume trajectories with discontinuities. 

These may be due to the transition conditions. (Refer to section 1.2.3 Empirical Models). 

“CORMIX1 & CORMIX2 near-field simulations now use the jet integral model CORJET for 

simulations. A few simulation modules still do use ‘empirical’ approach, but these cases are 

now in the minority” (Doneker, 1997). The strengths of this model are its ability to acknowledge 

the effects of boundary constraints and gravitational collapse. CORMIX2 uses the “equivalent 

slot diffuser” concept and thus neglects the details of the individual jets issuing from each 

diffuser port and their merging process. It assumes that the flow emerges from a long slot 

discharge with equivalent dynamic characteristics (Jirka et al, 1996b). Thus, mixing is based on 

the plume characteristics after the individual ports have merged. The initial dilution modules in 

CORMIX generate only centerline values.

UM3 should perform well for a majority of the critical condition scenarios encountered -

particularly in tidally-influenced waters. It can also be used frequently for the purpose of 

comparing dilutions with the other models. The following sections (1.3.2 – 1.3.8) discuss 

specific circumstances and outfall configurations which might influence which model is selected 

or how a particular mixing zone analysis is conducted.

1.3.2 Range of the Experiments

“Empirical models are most effective when prototype and model variables and conditions match 

closely. When they do not, the predictions can degrade substantially. In other words, it is often 

difficult to extrapolate to conditions which were not included in the experimental design [range 

of experiments] on which the models are based. Since it is often not clear to the user when 

extrapolation occurs, this can be a real problem” (EPA, 1994). Inaccurate extrapolations are 

manifested in the form of discontinuities in the plume trajectory.

The authors of RSB (NRFIELD) went through a careful consideration of the possible critical 

condition scenarios which their model might be expected to analyze before choosing the range of 

experiments (Roberts et al, 1989). The studies were conducted with the following experimental 

configuration: (1) A straight diffuser consisting of horizontally discharging round ports which 

were uniformly spaced; (2) ports discharging from both sides of the diffuser through T-shaped 

risers; (3) marine water - both density-stratified and well-mixed; (4) current at an arbitrary angle 

relative to the diffuser axis; and (5) individual plumes merging rapidly. As a result, there is a 

straightforward approach to determining whether the model will be operating within this range:
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The two length scale ratios l

l

m

b

and s

lb

are diffuser parameters which characterize the 

significance of source momentum flux and port spacing, respectively. (Refer to

section 1.2 UNDERSTANDING INITIAL DILUTION THEORY for an explanation 

of length scales and fluxes). Note that these length scale ratios encompass all of the 

"diffuser" parameters: jet exit velocity, port diameter, port spacing, effluent density, and 

ambient stratification. The model is operating within its range of "diffuser" parameters 

when:

0.31 < s

lb

< 1.92 , and

0.078 < l

l

m

b

< 0.5

Roberts' Froude number (F) is a more important parameter. The tests were run at 

differing current speeds to obtain F in the range 0 (zero current speed) to 100. As was 

stated in section 1.1.6 Current, values of F < 0.1 signify no effect of current on dilution.

The effect of current also depends on its direction relative to the diffuser axis (Θ is the 

horizontal angle). Tests were run with Θ = 90o

, 45o and 0 o (parallel to the current).

The length scale ratios, F, and Θ for each scenario are included in the output for each RSB model 

run. It then becomes a simple matter to determine whether the model is operating within its 

capability. Consideration should be given to using Figure 13 in Roberts (1991) (included as 

Figure 2) if the length scale ratios l

l

m

b

and s

lb

are less than 0.2 and 0.3, respectively. The 

normalized equation on the x-axis of the graph must be solved for Sm - the minimum initial 

dilution.

[Note: The volume flux per unit length of diffuser (q) is easily calculated. The Roberts Froude 

number (F)[Roberts F], buoyancy flux per unit length of diffuser (b)[buoy flux], and BruntVaisalla frequency (N)[N (freq)] needed to solve for Sm are included on the DOS PLUMES 

interface among the "red" cells. The “red” cells can also be used to calculate other fluxes, length 

scales, and length scale ratios].
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1.3.3 Densimetric Froude Number Less Than 1 or Negative

The densimetric Froude number is the ratio of the momentum to the buoyancy of the plume. It is 

an important number when analyzing plume performance in marine water. It is of less 

importance in freshwater because the buoyancy of the plume is often near zero.

If the Froude number is less than 1, then the plume separates from the bottom of the port orifices 

allowing ambient water to flow into the diffuser. This may also occur in marine waters if the 

total area of the port orifices exceeds 70% of the diffuser cross-section area. Either of these two

conditions will result in unbalanced flows, and the diffuser section must be evaluated 

hydraulically as a manifold prior to completing the mixing zone analysis (Ecology, 1998). Tideflex valves are being used with more frequency under these conditions. Red Valve Company is a 

good source of information on how to simulate these valves in UM3 and DKHW.

UM and UM3 signal this condition in several ways: (1) The input cell [Froude #] contains the 

number; and (2) the output from the run may contain the message "absolute value Froude # < 1, 

potential diffuser intrusion", or the message "begin overlap". UM3 should generate accurate 

results as the Froude Number approaches zero - provided the correct conditions are described to 

it. RIVPLUM5 or FARFIELD may be a better choice in most freshwater ambients whenever 

the plume has very little momentum. (Refer to section 1.5 CHOOSING A FARFIELD 

MODEL).

[Note: UDKHDEN has a built-in safeguard which causes it to terminate and display an “IHLF11” error message when the Froude number is less than 2.5 and it cannot provide an accurate 

answer.]

If the Froude Number is negative, then the effluent is more dense than the ambient water. The 

plume may hit bottom (Refer to section 1.3.5 Boundary Condition(s)); or perform even more 

atypical (Refer to section 1.3.8 Nascent Density and Buoyancy).

1.3.4 Overlap Condition

This condition is associated with low momentum/high buoyancy plumes (i.e., when the upward 

curvature of the plume is great). As UM3 iterates through the curvature the bottom portions of 

consecutive plume building blocks (elements) actually overlap, resulting in physically unreal 

negative volume and negative mass. The radius of each element, and entrainment, are overestimated. Plumes that perform in this manner and surface will usually protrude upstream from 

the outfall. Output from a UM3 run which is performing through this condition will contain the 

error message "begin overlap". The results from UM should not be used unless the following 

information appears in the output after the message: (1) An "end overlap" message indicating 

the cessation of the condition causing the error, and (2) relatively little change in the dilution 

between the "begin overlap" and "end overlap" messages.

[Note: It may be necessary to invoke the ^R command in DOS PLUMES in order to force the 
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model to simulate through the "end overlap" message to maximum rise. This will allow the 

comparison to be made between dilutions at the beginning and end of overlap.]

Refer to section 1.3.2 Range of the Experiments to determine whether NRFIELD can be used 

under those conditions when UM3 should not be used.

1.3.5 Boundary Condition(s)

Boundary conditions are side, surface, and/or bottom constraints which interfere with 

entrainment of receiving water into the plume. Banks, levees, docks, shallow water, port(s) 

discharging directly on the bottom, and confined embayments are all examples. The concern is 

whether the model will reflect these interferences accurately by limiting the entrainment. An 

additional consideration is whether the constraints are more likely to affect initial dilution or 

farfield entrainment.

If side boundaries are in close proximity such that initial dilution entrainment is likely to be 

affected, then CORMIX should be used exclusively - provided there do not appear to be 

discontinuities. CORMIX simply gives a cautionary message acknowledging attachment to the 

side boundary, but does not proceed to calculate adjusted dilutions. Side boundaries may 

become interferences in the farfield phase of the plume, such as when the plume attaches to the 

bank downstream in a unidirectional river or stream. Then it may be appropriate to use 

RIVPLUM5, if the attachment (or close proximity) affects horizontally transverse spreading of

the mixed effluent. Otherwise, the Constant Eddy algorithm may be appropriate. (Refer to 

section 1.5 CHOOSING A FARFIELD MODEL).

It is suggested that all of the models except VSW be used with caution in shallow waters (i.e.,, 

less than five pipe diameters deep) and not be used at all if it is very shallow water (i.e., less than 

three plume diameters deep). VSW (in DOS PLUMES) is the best choice. If UM (in DOS 

PLUMES) is used, consideration should be given to using the “Pause” command to force the 

model to terminate initial dilution when the plume width is the same as the depth of water (The 

plume is no longer entraining properly). RIVPLUM5 is a very good alternative in unidirectional 

waters. (Refer to section 1.5 CHOOSING A FARFIELD MODEL). If the discharge is 

actually to the surface of the receiving water (e.g., during mean lower low water (MLLW)), then 

either VSW or CORMIX3 should be used. Justifying the model chosen is advised.

Plumes that surface inside one or both of the two regulatory boundaries are a common 

occurrence in estuarine receiving waters because of the additional buoyancy. The surface is the 

one boundary condition that all five models signal decisively. However, simulations from that 

point to either or both of the regulatory boundaries may be suspect. (Refer to section 1.4 

UNDERSTANDING FARFIELD THEORY).

UM3 will issue a "-> bottom hit" message when the extremities of the plume element intersect 

the bottom. The bottom is assumed to be either (1) at a distance below the port equal to the port 
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elevation [port elev], or (2) at the deepest ambient depth (in the column headed [depth] on the 

interface) - whichever is greater. Often times this constraint can be ignored or eliminated. 

Frequently it is the downstream portion of the plume which hits the bottom. Since this is not the 

primary entraining surface of the plume, the condition can be ignored, as long as it isn't violated 

excessively. The condition can be eliminated by increasing the deepest ambient depth (in the 

[depth] column), as long as it is reasonable to do so (e.g., anytime there is a positive gradient to 

the bottom in the direction of the plume trajectory).

1.3.6 Extreme Horizontal Angle

The horizontal angle is defined in UM as the angle between the axis of the diffuser and the 

current (i.e., an angle of 90 degrees simulates a situation where the effluent plume(s) and current 

are co-flowing). The dialogue box on the DOS PLUMES interface indicates that UM is valid 

over angles ranging from 45 to 135 degrees; it can also be used advisedly for angles between 20 

and 45 degrees, and 135 and 160 degrees. It's most accurate at 90 degrees because UM is a twodimensional model. The effect of changing the direction of the current simply reduces the 

spacing between ports, invoking a pseudo-three-dimensional version. UDKHDEN may be a 

better choice the further away from 90 degrees the horizontal angle is because it's a true threedimensional model.

In the Windows-based version (Visual Plumes), UM3 is a three-dimensional model. The 

horizontal angle is determined using the scientific convention, in which zero degrees is to the 

east. The angle increases in the counter-clockwise direction; thus north is 90 degrees. Extreme 

horizontal angles are less of a concern than with UM.

It is recommended that RSB (NRFIELD) be used for multi-port diffusers in marine water -

particularly if the diffuser is an opposing-port configuration. (Refer to section 1.3.7 Opposingport Diffuser Configuration). It evolved from an EPA model (ULINE), which was designed to 

simulate multi-port configurations where upstream plumes are bent over by the current to 

interact with downstream plumes. (These zero and 180 degree horizontal angle situations are 

termed line plumes). It may also be the model of choice for many other horizontal angles, 

including negative (i.e., a counter-flowing situation). . However, it must perform within its range 

of experiments. (Refer to section 1.3.2 Range of the Experiments).

UM3 can be adapted to simulate line plumes in freshwater - and in marine water when 

NRFIELD is not appropriate. The procedure to follow is relatively straightforward: Run UM to 

simulate one plume (using the actual flowrate from only one of the ports in the diffuser). 

Assume that it is the most upstream plume. The output from this case will provide enough 

information about the plume trajectory so that an estimate can be made of the horizontal distance 

this plume will travel before merging with the plume from the next downstream port. The output 

will also provide the average concentration within the plume at this point of merging. This 

concentration is then input as the ambient pollutant concentration [amb conc] to the UM case for 

the next downstream port. The procedure is completed for this particular critical condition 

scenario when the last downstream port in the sequence is simulated.
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In order for this procedure to accurately simulate line plumes, the interaction among upstream 

and downstream plumes must be quite thorough. This can be determined by examining the 

output from the first UM run to see whether the plume is sufficiently strongly bent over to 

envelop most of the downstream plume’s trajectory. This procedure is explained in a citation by 

Frick (1996). It may sometimes be advisable to compare dilutions from several models and 

provide justification for the one chosen.

1.3.7 Opposing-port Diffuser Configuration

Opposing-port diffuser configurations have ports discharging in opposite directions. The 

configuration may consist of paired ports which are directly opposite each other or staggered 

ports, which are all equal distance apart but alternate from one side to the other.

In a current, the upstream plumes create a counter-flowing situation wherein they frequently 

bend over and merge with downstream plumes. UM3 assumes that the diffuser is configured 

with all ports on one side, the downstream side, creating a co-flowing situation. The counterflowing situation resulting in cross-diffuser merging is not simulated explicitly.

The preferred approach to modeling these configurations in freshwater is to simply divide the 

diffuser length by the total number of segments (i.e., total number of ports minus one). The 

quotient is the appropriate spacing; this number should be entered in the cell [spacing] on the 

DOS or Visual PLUMES interface. The number of ports is entered in the cell [# ports]. The 

simulation offered by UM will be quite good if the Roberts' Froude number (F) is > 0.1 because 

at this current speed the plumes from opposite sides of the diffuser merge rapidly.

The preferred approach in marine water is to use RSB - if it will be operating within its range of 

experiments. (Refer to section 1.3.2 Range of the Experiments). It is based on experiments 

conducted in the lab using opposing-port diffusers. However, RSB does require a minimum of 3 

ports in the diffuser; and it presently does not provide dilution factors for intermediate points 

prior to the end of initial dilution. The latter will not be a problem when initial dilution ends 

inside the acute boundary.

An alternative approach, that represents a major simplification and that appears to be fairly 

accurate based on the results of informal modeling trials, is to treat the diffuser as if all ports are 

on one side with half the spacing. This approach works well when the regulatory boundaries are 

beyond the point of merging.

Another acceptable approach for either fresh or marine water involves simulating only 

downstream ports. However, it is best used with paired port configurations. This necessitates 

doubling the flow per port (assuming there is an even number of ports in the diffuser) and 

increasing the diameter of the ports to maintain approximately the same densimetric Froude 

number. With this approach only the downstream ports would be used when determining 
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spacing and number of ports. This method may give better simulations than the preferred 

freshwater approach if the Roberts' Froude number (F) is < 0.1. However, a cautionary message 

will sometimes appear stating that far-field results are unreliable because the plumes did not 

merge prior to the end of initial dilution.

All models assume that the ports point perpendicular to the axis of the diffuser. Staged diffusers 

have ports pointing at an acute angle to the diffuser. Therefore, staged diffusers can only be 

modeled by making additional assumptions, which must be explained in the analysis.

1.3.8 Nascent Density and Buoyancy

It is well understood that the density of water is not a linear function of temperature or salinity, 

e.g., water expands below about four degrees Celsius. However, it is not well understood that 

the non-linear response of water density to changes in temperature and salinity can cause 

surprising and unanticipated changes in plume behavior. A thermally buoyant freshwater plume 

discharged to unstratified freezing freshwater will initially rise, as expected, before unexpectedly 

sinking to the bottom. The plume will rise only briefly before becoming denser than the ambient 

and beginning to sink because, as the plume entrains ambient water and cools, it eventually 

acquires a temperature at which fresh water is at or near maximum density. In another situation, 

a highly buoyant plume may rise less than a less buoyant plume. These phenomena are known 

as the nascent density effect.

Nascent buoyancy effects also occur under many combinations of ambient and effluent salinities 

and temperatures. A high salinity plume, e.g., a blended effluent such as desalination brine and 

sewage, may sink briefly before becoming less dense than the ambient and beginning to rise -

reversing buoyancy. The citation mentioned below contains several additional examples 

involving freshwater discharges to the Columbia River.

The linear density assumption is a popular theoretical and empirical simplification in most 

models. The latest version of UM (8/7/95) is a non-linear model which will simulate nascent 

conditions. A draft citation by Frick et al (1995) is an excellent reference on this subject.

1.4 UNDERSTANDING FARFIELD THEORY

It is reasonable to always assume that the plume’s motion in the ambient receiving water is 

turbulent. Spreading takes place much faster in turbulent flow than in laminar flow. Farfield 

begins with gravitational collapse (also referred to as buoyant spreading or density current). This 

is characterized by lateral spreading of the plume along the layer boundary while it is being 

advected by the ambient current. Plume thickness probably decreases during this phase; the 

mixing rate is relatively small.

Following gravitational collapse, the remainder of farfield mixing is best explained by either the 

theory of turbulent diffusion or shear flow dispersion. Turbulent diffusion employs the turbulent 
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mixing equation of Brooks (1960), wherein the coefficient describing the rate of spread of the 

plume increases with the size of the plume. The best known facet of this theory is the celebrated 

“4/3 Power Law” - which says that the diffusion coefficient is proportional to the 4/3 power of 

the size of the plume. In reality, the Law only applies in homogeneous turbulence far from any 

boundaries.

Shear flow dispersion employs the longitudinal dispersion equation of Taylor (1954) by the 

method of Fischer et al (1979). The theory common to all shear flow is that spreading in the 

direction of flow is caused primarily by the velocity profile in the cross-section. The mechanism 

Taylor analyzed is often referred to as the “shear effect”. It gives a reasonably accurate estimate 

of the rate of longitudinal dispersion in rivers, and a partial estimate of longitudinal in estuaries.

1.5 CHOOSING A FARFIELD MODEL

There are two farfield models which are presently recommended for use. They are code named 

FARFIELD and RIVPLUM5. Each can serve as a stand-alone mixing zone model when 

warranted by the situation and has been set up in spreadsheet format to accommodate this ( 

http://www.ecy.wa.gov/programs/eap/pwspread.html ).

FARFIELD also serves as the farfield algorithm in the 3PLUMES interface, so that it operates in 

conjunction with UM and RSB by taking the plume diameter delivered to it at the cessation of 

initial dilution. This may change in the future, since RSB presently accounts for gravitational 

collapse and the UM/FARFIELD interface does not.

The appropriate farfield model to use in a particular mixing zone analysis depends on the 

combination of conditions involved:

1. The receiving water is sufficiently deep such that a plume will form and pass through 

the initial dilution phase without "Froude number less than 1", "overlap", or "boundary 

constraint" problems. Use FARFIELD as the algorithm (i.e., the version in 3PLUMES 

interface). (Refer to 1.5.1 FARFIELD.)

2. The receiving water is shallow and unidirectional; the effluent is thoroughly mixed 

surface to depth (i.e., no defined plume); and the discharge is a single port or short 

diffuser. Use RIVPLUM5. (Refer to 1.5.2 RIVPLUM5.)

3. There is/are bank constraint(s). Use RIVPLUM5, provided the conditions in 2. above 

are also met. (Refer to 1.5.2 RIVPLUM5.)

4. Other shallow receiving waters (with no bank constraints) which occur with all other 

combinations of effluent plumes and discharger configurations. Use

FARFIELD as a stand-alone model. (Refer to 1.5.1 FARFIELD). A three-dimensional 

advective dispersion equation may also be appropriate.
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Gravitational collapse is not accounted for in the three theoretical, initial dilution models or the 

two farfield models discussed in this section. It may be included in a later version of UM3 in the 

Windows interface (Visual Plumes). The two empirical, initial dilution models (CORMIX and 

NRFIELD) do account for gravitational collapse. This phenomenon was observed during the 

tow-tank experiments, and plume performance during this phase was measured and factored into 

the empirical equations. The interface allows the modeler to choose the diffusivity coefficient 

(the [far dif] cell.

1.5.1 FARFIELD

FARFIELD calculates dilution using the method of N.H. Brooks (1960). Four variations have 

been set up as spreadsheets in an EXCEL workbook - FARFIELD.XLS. The spreadsheets are:

- 3PLUMES algorithms;

- Brook’s exponential diffusivity (4/3 power law);

- Brook’s linear diffusivity; and

- Brook’s constant (eddy) diffusivity.

The "3PLUMES algorithms" spreadsheet calculates dilutions by assuming either an exponential 

increase, a linear increase, or a constant diffusivity - just as the other three spreadsheets do. 

Linear diffusivity was added to the two algorithms already incorporated in the 3PLUMES 

interface in order to make it the same package that is offered by the other three spreadsheets. Its 

utility is in allowing direct comparisons to be made between dilutions at the regulatory 

boundaries as generated by one or the other of the models in 3PLUMES and dilutions generated 

by other initial dilution models which have no far-field algorithm, e.g., UDKHDEN.

The default value for the dispersion coefficient in the 3PLUMES interface, the [far dif] cell, is 

0.0003 m2/3/sec. For areas of high energy dissipation and where there are no constraints, e.g., a 

large, relatively deep embayment, then the value 0.000453 m2/3/sec can be used. In less turbulent 

situations, it may be as low as 0.0001 m2/3/sec.

The exponential increase is referred to as the 4/3 Power Law in the output from 3PLUMES. It is 

Richardson's Law, which is basically only applicable in situations where there is unobstructed 

spread of the plume. It is reasonable to assume that the spread is unobstructed if the plume 

diameter at all locations on its trajectory is less than 1/10 the distance to the nearest side 

boundary. It is unreasonable to assume that diffusivity will increase exponentially when the 

plume can only spread along a nearby side boundary. Provided this boundary does not act as a 

constraint (as discussed in section 1.3.5 Boundary Condition(s)), it is reasonable to assume that 

it will increase as the first power of the plume width (i.e., linearly). Dilutions generated by the 

Constant Eddy Diffusion algorithm should be used in all other situations.
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To understand why "3PLUMES algorithms" differs from the other spreadsheets, it is necessary 

to understand the motivation of the authors of the interface. They felt it was important that users 

of the interface should have to input only one dispersion coefficient in the [far dif] cell; but still 

be able to receive the output from two far-field algorithms - the 4/3 Power Law and the Constant 

Eddy. This resulted in some coding changes in the initial steps of the algorithms (including 

linear diffusivity), where the dispersion coefficient in the [far dif] cell is converted for the first 

and only time to the diffusivity coefficient used in the Brook's equation. The dispersion 

coefficient is multiplied by (the width of the plume field at the end of initial dilution)4/3. The 4/3 

Power Law is described by R.A. Grace (1978).

Following these initial steps, the diffusivity coefficient is either (1) continuously increased 

according to the 4/3 power of the width of the plume field at the end of the previous iteration, (2) 

continuously increased according to the first power of the width of the plume field at the end of 

the previous iteration, or (3) held constant according to the zero power of the width of the plume 

field at the end of the previous iteration. Each algorithm then inserts its coefficient into a 

modified Brooks' Equation, as described in the text associated with equations 66-73 of the User's 

Manual (EPA, 1994).

Each of the other three spreadsheets contains one of the algorithms; they are also based on 

Brook's Equation. Their utility is that they're purer forms, unencumbered by the slight 

inaccuracies associated with the need to input a single dispersion coefficient to an interface. All 

of these far-field algorithms are much simpler and rudimentary than the initial dilution models. 

The quality of the estimates should not, in general, be expected to be as high as the initial 

dilution models. Consequently, if better methods for estimating the far-field dilutions are 

available they should be used.

User instructions for the input section of FARFIELD.XLS are available in another appendix to 

this chapter and on the Internet (http:/www.ecy.wa.gov/programs/eap/pwspread). The user does 

not need to enter or change any values or formulas in the Output section. The spreadsheets 

calculate dilution along the trajectory of the plume and at the specified mixing zone boundary. 

Optional calculation of pollutant concentrations assuming first-order decay rates is also provided.

1.5.2 RIVPLUM5

The spreadsheet RIVPLUM5.XLS calculates dilution using the theory of Taylor (1954) by the 

method described in Fischer et al, (1979) and referred to in EPA's Technical Support Document 

(1991). The analysis considers two-dimensional plume spread (i.e., longitudinal and transverse 

directions), but not vertical mixing (assumed instantaneous). It calculates dilution at a specified 

point of interest downstream in a river. The calculation for dilution factors incorporates the 

boundary effect of shore lines using the method of superposition. This model is based on the 

assumption that: (1) the discharge is a single point source, which is most appropriate for single 

port or short diffusers, or side-bank discharges; (2) the discharge is completely and rapidly 

mixed vertically, which usually only occurs in shallow rivers; (3) the velocity at all points in the 
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channel is equal to mean cross-sectional velocity (i.e., there is no transverse variation in 

velocity); and the transverse dispersion coefficient constant is equal to 0.6 (i.e., a slowly 

meandering river channel). Table 5.3 in Fischer et al, (1979) contains a number of these 

coefficients based on experimental measurements. 

If the diffuser length occupies a substantial portion of the stream width, or the discharge is not 

vertically mixed over the entire water column within the acute mixing zone, an alternative model 

should be used. The spreadsheet also includes optional calculation of the effective origin of a 

wastewater source. User instructions for the input section are available in another appendix to 

this chapter and on the Internet.

1.6 CONDUCTING A DYE STUDY

There are four primary objectives that justify conducting a dye study:

1. Confirm the presence of an eddy.

2. Quantify dilution.

3. Quantify far-field accumulation (reflux).

4. Develop a far-field diffusivity coefficient.

It is advisable to conduct a reconnaissance survey before the main field work. If the receiving 

water is tidally-influenced, then the survey should be conducted at the same time in the neap or 

spring tide cycle and covering the same stages of tide as will be covered during the dye injection. 

Consideration should be given to deploying a meter to record time, current speed and direction, 

and depth of water during the survey in order to develop a thorough understanding of anomalies 

that may be occurring between published tide data and actual field data. Consider taking a crosssection of the channel bottom, if appropriate. These data will allow accurate times to be 

established for dye injection and measurement. It will also afford an opportunity to set up and 

run some preliminary cases; which, in turn, will provide some early estimates of plume 

performance, e.g., trapping depth and horizontal distance to the end of initial dilution.

Concentration of dye in effluent, total loading, and duration of injection deserve careful 

consideration. Each varies in importance depending upon the objectives of the study, and is 

discussed below for each objective. A draft plan of study explaining the methods and QA/QC to 

be employed should be submitted to the Department for review and approval following the 

reconnaissance survey and prior to initiation of the study.
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1.6.1 Confirm the Presence of an Eddy

If the objective of the study is to simply confirm the presence of an eddy, then concentration, 

loading, and duration of injection are all relatively unimportant. It’s only necessary that the path 

of the plume can be traced. If, on the other hand, it is necessary to know the mixing ratio in the 

eddy in order to determine its contribution, then concentration, loading and duration may all be 

important.

1.6.2 Quantify Dilution

Sometimes dilution factors must be measured directly in the field. However, these are dilution 

factors for one set of effluent and receiving water conditions only, and a model may still be 

necessary for analyzing other sets of conditions that are quite different from those present during 

the dye study. (e.g., future growth). Calibration , while admittedly an unpredictable exercise, 

may serve to increase confidence in model performance.

A constant dye concentration in effluent is important. Total loading is not important per se; 

however, it is important that effluent flowrate be at or near its reasonable worst-case. Duration is 

relatively unimportant. In tidally-influenced waters, injection and measurements should begin 

after the start of an ebb tide stage. By using this timing it may be possible to capture one critical 

condition scenario.

The most appropriate location to take the measurements for comparing dilutions from the dye 

study and a model is at the end of the hydrodynamic mixing zone, particularly if the end follows 

rapid surfacing of the plume in shallow water. (Refer to section 1.3.5 Boundary Condition(s)). 

The best way of determining the location is via a reconnaissance survey in conjunction with 

preliminary model runs, using the set of conditions that will be encountered during the field 

work.

A dye study may be the only reliable way to quantify dilutions if boundary constraints are such 

that all model results will be suspect. A critical condition scenario may include a rapidly 

surfacing plume with upstream protrusion and/or side boundaries that are affecting entrainment 

and dilution. (Refer to 1.3.5 Boundary Condition(s)). Measurements would be taken at both 

the acute and chronic boundaries.

A dye study may also be the most reliable way to quantify dilutions at a lateral boundary when 

the width of a mixing zone is restricted to 25% of the channel width. (Refer to section 1.1.11 

Other Factors). The field work should be conducted when conditions are as close as possible to 

a critical condition, as defined in the Water Quality Standards.

In this situation, a constant concentration in effluent and duration of injection are important. 

Total loading is relatively unimportant, per se; however, it is important that effluent flowrate be 

at or near its reasonable worst-case. In tidally-influenced waters, injection and measurements 
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should begin soon after the start of a Lower Low Water slack at sea level during a neap tide or 

soon after a small flood if it’s riverine. This affords the best opportunity to capture a critical 

condition scenario.

[Note: It can be assumed that upstream protrusion does not occur whenever the Roberts’ F is > 

0.1.]

1.6.3 Quantify Far-field Accumulation (Reflux)

This objective warrants considerable discussion because it's difficult to accomplish. Tidal 

currents may cause effluent to accumulate in the receiving water surrounding an outfall in a tidal 

river or estuary. The receiving water may also contain background concentrations of pollutants 

from sources other than effluent. Various methods are available to account for the accumulation 

of effluent and ambient background sources when determining potential to exceed water quality 

criteria or estimating waste load allocations.

There are three methods which are acceptable to Ecology. Two of the methods involve a dye 

study. Total loading and duration are important factors in both methods; concentration in the 

effluent can vary during application. The third method involves simply accepting a default value 

for reflux in lieu of conducting a dye study. Detailed guidance for conducting the methods and 

mass-balance equations follow.

Far-field accumulation of effluent may be estimated based on either of two methods:

• Method 1: the USGS superposition method (Hubbard and Stamper, 1972) may be used by 

injecting the tracer during one tidal day and measuring continuously at a fixed monitoring 

station to determine maximum concentrations during succeeding days until the tracer is 

undetectable; or

• Method 2: the Jirka method (EPA, 1992) may be used by injecting the tracer over several 

tidal cycles (usually five or more) until a quasi-maximum steady state is reached. 

Concentrations of the tracer are usually monitored continuously at a fixed monitoring 

station.

In addition to two methods of tracer injection, two alternative schemes for locating monitoring 

stations are acceptable:

• Alternative 1: tracer concentrations are measured in the near-field at the mixing zone 

boundary in the approximate centerline of the effluent plume; or

• Alternative 2: tracer concentrations are measured in the far-field at some considerable 

distance from the effluent plume at a position that is representative of the source of 

dilution water for the plume.
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Either the superposition or Jirka methods may be used to conduct the tracer studies for both 

Alternatives 1 and 2. A third method is also proposed if a tracer study is not conducted: 

• Method 3: A default correction which can be used as an approximation of far-field 

accumulation will be based on recommendations by EPA (1992).

A number of terms which will be used during this discussion need to be defined.

near-field: at the chronic mixing zone boundary in the approximate center-line of the 

effluent plume.

far-field: at some considerable distance from the effluent plume at a position that is 

representative of the source of dilution water for the plume. 

V: initial maximum effluent concentration (volume fraction of effluent; e.g., 5 

percent effluent corresponds to V of 0.05) during first tidal cycle prior to 

influence of far-field accumulation from previous tidal cycles.

V : quasi-steady-state maximum effluent concentration (volume fraction of 

effluent; e.g., 5 percent effluent corresponds to V of 0.05) after several tidal 

cycles result in equilibrium with far-field accumulation.

rd: return rate of dye or effluent mass discharged in the previous tidal cycle as 

defined in EPA (1992).

DF: initial effluent dilution factor (reciprocal of volume fraction of effluent; e.g., 

5 percent effluent corresponds to DF of 20) during first tidal cycle prior to 

influence of far-field accumulation from previous tidal cycles. DF may be 

estimated using a model (e.g., PLUMES) or by near-field tracer 

measurement. DF is usually determined at a critical condition.

DF: quasi-steady-state effluent dilution factor (reciprocal of volume fraction of 

effluent; e.g., 5 percent effluent corresponds to DF of 20) after several tidal 

cycles (usually 5 or more cycles) result in equilibrium with far-field 

accumulation. DF is usually determined at a critical condition.

Cp: pollutant concentration measured as a flux-average value in the plume at the 

mixing zone boundary. (Refer to section 1.2.4 Average versus Centerline).

Ce pollutant concentration in effluent discharged from the outfall pipe. 
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Ca: pollutant concentration in upstream ambient receiving water (i.e., away from 

the influence of far-field accumulation).

WLA: effluent concentration to use for Waste Load Allocation (acute or chronic) 

for derivation of water quality-based permit limits.

WQC: pollutant concentration for water quality criteria (acute or chronic).

Mass Balance Equations for Alternative 1

If the tracer monitoring station is located in the near-field, then the following mass-balance 

equations are appropriate:

• calculate Jirka's rd from near-field V and V (based on equation 22 in (EPA, 1992)):

( ) r

V V

V d = − (5)

• calculate the near-field DF(acute or chronic boundary), including the effect of far-field 

accumulation of effluent, from model or tracer estimates of DF and estimated rd in the 

previous step (based on equation 22 in (EPA, 1992)):

DF = DF(1− rd ) (6)

• The following equation is appropriate to calculate pollutant concentrations (Cp) at the 

mixing zone boundaries for comparisons with water quality criteria. Near-field dilution 

is corrected for far-field accumulation of effluent in the previous step. The following 

equation incorporates the effect of ambient background (Ca) from sources of pollutants 

other than effluent. Estimates of Ce may also include a reasonable potential multiplier 

using methods in chapter VI of this Manual. Pollutant concentrations (Cp) are estimated 

as follows (based on equation 9 in (EPA, 1994):

C C

DF

C

DF p = e a





 



 + − 



 



 



 



 1 1 1

(4a)
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• calculate acute and chronic WLAs:

WLA = WQC∗ DF − Ca (DF − 1) (7)

Example:

Given: near-field V = .02 (2 percent effluent); near-field V = .07 (7 percent effluent).

Calculation of near-field DF including far-field accumulation of effluent:

( ) rd = − = . .

. . 07 0207

7143; DF = = 1

02

50 . ; therefore, near-field DF = 50(1−.7143) = 14.3

Mass Balance Equations for Alternative 2

If the tracer monitoring station is located in the far-field, then the following mass-balance 

equations are applicable:

• calculate near-field DF, excluding the far-field accumulation of effluent, from a mixing zone 

model or from an additional near-field tracer monitoring station (e.g., near-field DF = 

reciprocal of near-field V)

• calculate the near-field DF (acute or chronic boundary), including the effect of far-field 

accumulation of effluent, by mass balance with near-field DF from the previous step and 

far-field V (based on equation 8 in (EPA, 1994)):

( ( )) DF DF

V DF = 1+ − 1

(8)

• The following equation is appropriate to calculate pollutant concentrations (Cp) at the 

mixing zone boundaries for comparisons with water quality criteria. Near-field dilution 

is corrected for far-field accumulation of effluent in the previous step. The following 

equation incorporates the effect of ambient background (Ca) from sources of pollutants 

other than effluent. Estimates of Ce may also include a reasonable potential multiplier 

using methods in chapter VI of this Manual. Pollutant concentrations (Cp) are estimated 

as follows (based on equation 9 in (EPA, 1994)):

C C

DF

C

DF p = e a





 



 + − 



 



 



 



 1 1 1

(4a)
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• calculate acute and chronic WLAs:

WLA = WQC∗ DF − Ca (DF − 1) (7)

Example:

Given: near-field DF=50 from PLUMES model excluding far-field accumulation of 

effluent; far-field V =.051 (5.1 percent effluent) from tracer study using super-position 

method.

Calculation of near-field DF including far-field accumulation of effluent:

Near-field ( ( )) DF = + − = 50

1 051 50 1

14 3 . .

Mass Balance Equations for Method 3

If it is decided to use a default correction for far-field accumulation, then the following mass 

balance equations are applicable:

• estimate default for Jirka's rd = 0.5 from EPA (1992).

• calculate the near-field DF (acute or chronic boundary), including the effect of far-field 

accumulation of effluent, from model or tracer estimates of DF and estimated rd in the 

previous step (based on equation 22 in (EPA, 1992)):

DF = DF(1− rd ) (6)

• The following equation is appropriate to calculate pollutant concentrations (Cp) at the 

mixing zone boundaries for comparisons with water quality criteria. Near-field dilution 

is corrected for far-field accumulation of effluent in the previous step. The following 

equation incorporates the effect of ambient background (Ca) from sources of pollutants 

other than effluent. Estimates of Ce may also include a reasonable potential multiplier 

using methods in chapter VI of this Manual. Pollutant concentrations (Cp) are estimated 

as follows (based on equation 9 in (EPA, 1994):

C C

DF

C

DF p = e a





 



 + − 



 



 



 



 1 1 1

(4a)
APPENDIX 6. (JULY 2002)

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APP6-32

• calculate acute and chronic WLAs:

WLA = WQC∗ DF − Ca (DF − 1) (7)

Example: 

Given: rd=0.5; DF=50

Calculation of DF: DF = 50(1− 0.5) = 25.

1.6.4 Develop a Farfield Diffusion Coefficient

[RESERVED].

1.7 REFERENCES

Brooks, N. H., 1960. Diffusion of Sewage Effluent in an Ocean Current, Proceedings of the First 

Conference on Waste Disposal in the Marine Environment, pages 246-267, edited by 

E.A. Pearson, Pergamon Press, New York, NY.

Davis, L. R., 1996. Personal communication, Oregon State University, Department of 

Mechanical Engineering, Corvalis OR 97331-6001, July.

Doneker, R. L., 1997. Personal communication, Oregon Graduate Institute, Department of 

Environmental Science and Engineering, Portland OR 97291-1000, July.

Ecology, 1993. Dam Safety Guidelines, Technical Note 3: Design Storm Construction,

Washington state Department of Ecology, Olympia WA, Publication # 92-55G, April.

Ecology, 1995. An Analysis of Regulatory Issues Raised by Application of the NPDES Permit 

Program to Municipal and Industrial Stormwater Discharges (draft issue paper), 

Washington State Department of Ecology, Water Quality Program, Olympia WA, 

December.

Ecology, 1996. An Analysis of the Effect of Discharged Wastewater on the Stillaguamish River 

at Stanwood, Washington state Department of Ecology, Environmental Investigations 

and Laboratory Services Program, Olympia WA 98504-7710, July.

Ecology, 1998. Criteria for Sewage Works Design (the “Orange Book”), as revised, Washington 

state Department of Ecology, Water Quality Program, Olympia WA, Publication # 98-37 

WQ, chapter E2.
APPENDIX 6. (JULY 2002)

Permit Writer’s Manual

APP6-33

EPA, 1991. Technical Support Document for Water Quality-based Toxics Control, U.S. 

Environmental Protection Agency, EPA/505/2-90-001, pages 77-78.

EPA, 1992. Technical Guidance Manual for Performing Waste Load Allocations Book III: 

Estuaries Part 3: Use of Mixing Zone Models in Estuarine Waste Load Allocations, U.S. 

Environmental Protection Agency, EPA/823/R-92/004, section 2.6.

EPA, 1994. Dilution Models for Effluent Discharges, U.S. Environmental Protection Agency, 

EPA/600/R-94/086, Washington, D.C.

Fischer, H.B., E.F. List, R.C.Y. Koh, J. Imberger, and N.H. Brooks, 1979. Mixing in Inland and 

Coastal Waters, Academic Press, Inc., Harcourt Brace Jovanovich Publishers, New York 

NY, pp. 126-127.

Frick, W.E., et al, 1995. Nascent Buoyancy Effects on Blended and Exotic Effluents, Draft, U.S. 

Environmental Protection Agency, Center for Environmental Assessment Modeling, 

Athens GA, April 16.

Frick, W. E., 1996. Estimating Parallel Diffuser Dilutions Using PLUMES UM, U.S. 

Environmental Protection Agency, Center for Environmental Assessment Modeling, 

Athens GA, July 11.

Gilbert, R.O., 1987. Statistical Methods for Environmental Pollution Monitoring, Van Nostrand 

Reinhold, New York.

Glenn, N. L. and D. Giglio, 1997. Kitsap County Mixing Zone Study, Washington state 

Department of Ecology, Environmental Investigations and Laboratory Services Program, 

Olympia WA 98504-7710, July.

Grace, R.A., 1978. Marine Outfall Systems: Planning, Design, and Construction, Prentice-Hall, 

Englewood Cliffs NJ, Chapter 7.

Hubbard, E.F. and W.G. Stamper, 1972. Movement and Dispersion of Soluble Pollutants in the 

Northeast Cape Fear Estuary, North Carolina, Water-supply paper 1873-E, U.S. 

Geological Survey, United States Department of the Interior.

Jirka, G.H., P.K. Akar and J.D. Nash, 1996a. Enhancements to the CORMIX Mixing Zone 

Expert System: Technical Background, Technical report, DeFrees Hydraulics 

Laboratory, School of Civil and Environmental Engineering, Cornell University, Ithaca 

NY 14853-3501.
APPENDIX 6. (JULY 2002)

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APP6-34

Jirka, G.H., R.L. Doneker and S.W. Hinton, 1996b. User’s Manual for CORMIX: A Mixing 

Zone Expert System for Pollutant Discharges into Surface Waters, draft, DeFrees 

Hydraulics Laboratory, School of Civil and Environmental Engineering, Cornell 

University, Ithaca NY 14853-3501, page 16.

NOAA, 1981. A Summary of Knowledge of Puget Sound Related to Chemical Contaminants, 

National Oceanic and Atmospheric Administration, Office of Marine Pollution 

Assessment, Technical Memorandum OMPA-13, Boulder, CO.

Roberts, P.J.W., 1991. Ocean Outfalls, Critical Reviews in Environmental Control, Volume 20, 

Issues 5 & 6, pages 311-339.

Roberts, P.J.W., W.H. Snyder, and D.J. Baumgartner, 1989. Ocean Outfalls. I: Submerged 

Wastefield Formation, Journal of Hydraulic Engineering, Volume 115, No. 1, January.

Taylor, G.I., 1954. The dispersion of matter in turbulent flow through a pipe, Proceedings of R. 

Soc. London Ser., A223, 446-468, Sci. Pap. 2, 466-488.

Turner, D.B., 1970. Workbook of atmospheric dispersion estimates. Office of Air Programs, 

Publication No. AP-26, USEPA, Research Triangle Park, North Carolina.
APPENDIX 6. (JULY 2002)

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APPENDIX 6. (JULY 2002)

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APP6-37

2.0 SPREADSHEETS FOR WATER QUALITY-BASED 

NPDES PERMIT CALCULATIONS

Updated July 2000 by Greg Pelletier 

Several spreadsheets were developed by the Washington State Department of Ecology to aid 

NPDES permit writers. These spreadsheets are referred to in Ecology's Permit Writer's Manual 

(Department of Ecology Publication Number 92-109). Several of the spreadsheets are in separate 

Lotus 1-2-3 WK1 files and also have been combined and reformatted into an Excel 5 workbook.

• DOSAG2.WK1: This spreadsheet calculates critical sag of dissolved oxygen downstream 

from a point source using the Streeter-Phelps equation.

• IDOD2.WK1: This spreadsheet calculates concentrations of dissolved oxygen at a mixing 

zone boundary accounting for dilution of dissolved oxygen and initial dissolved oxygen 

demand.

• NH3FRES2.WK1: This spreadsheet calculates freshwater un-ionized and total ammonia 

criteria from temperature and pH from the formulas modified by EPA which were 

adopted in the 1995 revision to the state water quality standards.

• NH3SALT.WK1: This spreadsheet calculates saltwater total ammonia criteria from 

temperature, pH, and salinity to meet the un-ionized ammonia criteria.

• PHMIX2.WK1: This spreadsheet calculates the pH of a mixture of two sources for 

temperature, pH, and alkalinity.

• RIVPLUM5.WK1: This is a simple dilution model for rivers based on the method in 

chapter 5 of the book "Mixing in Inland and Coastal Waters" by H.B. Fischer et al. (1979, 

Academic Press Inc.)

• PWSPREAD.XLS: This Excel 5 file contains the following spreadsheets as described 

above: 

• dosag2 

• idod2 

• nh3fres2 

• nh3fresh 

• nh3salt 

• phmix2 

• rivplum5 
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• FARFIELD.XLS (requires the Analysis ToolPak Add-In under the "Tools/Add-Ins" 

menu): This Excel 5 workbook calculates far-field mixing of a plume using the method of 

N.H. Brooks (1959, "Diffusion of Sewage Effluent in an Ocean Current," in "Waste 

Disposal in the Marine Environment", edited by E.A. Pearson, pp, 246-267, Pergamon 

Press, New York, NY.) This workbook is useful for estimating dilution beyond the range 

of near-field models such as UDKHDEN or PLUMES/UM using Brook's 4/3-power law, 

linear diffusivity, and constant diffusivity algorithms.

• TSDCALC.XLW is a workbook composed of several spreadsheets. It is used for 

reference and for developing water quality-based permit limits. The individual 

spreadsheets contained in TSDCALC are: 

• criteria.xls 

• ammoniafw.xls 

• reaspot.xls 

• limit.xls 

• performlim.xls 

• human-h.xls

The spreadsheets CRITERIA.XLS and AMMONIA.XLS contain or calculate water 

quality criteria. REASPOT.XLS and LIMIT.XLS determine reasonable potential (to 

violate the water quality standards) and calculate effluent limits. PERFORMLIM.XLS 

calculates performance-based effluent limitations and accounts for autocorrelation if 

known. HUMAN-H.XLS determines reasonable potential and calculates effluent limits 

for human health pollutants.

2.1. DETAILED DESCRIPTIONS AND USER INSTRUCTIONS

Spreadsheet DOSAG2.WK1

Revised October 19, 1993

This spreadsheet calculates the critical dissolved oxygen sag and concentration downstream from 

a point source load of BOD in a river using the Streeter-Phelps equations. The method used is 

documented in EPA/600/6-85/002a (Water Quality Assessment: A Screening Procedure for 

Toxic and Conventional Pollutants in Surface and Ground Water). This spreadsheet is 

recommended for use as a screening tool to determine the potential for dissolved oxygen 

standards to be violated. DOSAG2.WK1 may be overly simplistic for deriving limits for effluent 

BOD. If DOSAG2.WK1 suggests the dissolved oxygen sag is close to or below the water quality 

standard, then a more sophisticated model such as QUAL2E or WASP5 should be used to derive 

appropriate effluent limits. Those water quality models are designed to more accurately simulate 

water movements, mass transport, and water column processes.
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User Instructions for the Input Section

Step 1: Enter the permittees effluent characteristics, including permitted discharge and 

maximum (e.g., weekly) 5-day BOD (referred to as CBOD5 for "carbonaceous" 5-day BOD). 

Carbonaceous 5-day BOD is less than the total 5-day BOD if nitrification occurs during the test. 

The minimum national standards for carbonaceous 5-day BOD in effluent after secondary 

treatment are a monthly average of 25 mg/L and weekly average of 40 mg/L (40 CFR Part 133). 

Guidance for determining if carbonaceous 5-day BOD should be substituted for total 5-day BOD 

is contained in Ecology's Permit Writer's Manual (section V-3.6).

Nitrogenous BOD (NBOD) should also be estimated if it is significant (e.g., if nitrification is not 

significant during secondary treatment). NBOD can be estimated as:

NBOD = 4.57 * (Ammonia N + Organic N)

where concentrations of NBOD, ammonia N and organic N are expressed in mg/L. Effluent 

temperature and dissolved oxygen for the analysis are also entered at this step. The spreadsheet 

may be used to estimate the maximum permissible effluent CBOD5 and NBOD that will meet 

the water quality standards for dissolved oxygen. A trial and error solution is necessary for this 

purpose. Trial values of effluent CBOD5 and NBOD may be entered until the dissolved oxygen 

at the critical sag meets the water quality standard.

Step 2: Enter receiving water characteristics. These will generally be conditions at the 7Q10 

discharge. Upstream CBOD5, NBOD, dissolved oxygen and temperature at the design river flow 

(e.g., 7Q10) should be entered. The local channel elevation and channel slope (e.g., from USGS 

topographic maps) downstream from the discharge should also be entered. Downstream average 

channel depth and velocity at the design flow should be entered also.

If no receiving water data are available, it would be desirable to collect data. Channel crosssections of depth and velocity can be measured during the critical season. If measurements are 

not taken near critical conditions, then Manning's equation may be used to estimate velocity and 

depths from the measurements. Several cross-sections proceeding downstream from the 

discharge may be needed to characterize the river to the point of critical sag if velocities and 

depths are not uniform. Dye studies to measure travel time may be useful if velocities are 

variable. If significant tributaries, groundwater inflows, or other pollutant loads occur before the 

predicted critical sag point, then a more sophisticated model should be used (e.g., QUAL2E).

Measurements of water quality (e.g., dissolved oxygen, ammonia, BOD) in the receiving water 

from upstream and at intervals downstream to the critical sag point are also desirable for model 

calibration. If the model is applied without sufficient data to demonstrate calibration, then the 

model should mainly be used to screen for potential violation of standards. If effluent BOD is 

required to be more restrictive than current technology-based limits, then calibration data are 

probably needed. Separate calibration and verification data sets taken on different dates may be 
APPENDIX 6. (JULY 2002)

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APP6-40

needed in many cases where the accuracy of the model is in question. 

Step 3: Enter the reaeration rate (base e) at 20 degrees C in cell D27. Suggested values using 

empirical equations referenced in EPA/600/6-85/002a are given below cell D27 for guidance in 

selecting an appropriate value. If the calculated values are used, select the most appropriate 

equation based on applicable depth and velocity (e.g., if depth is <1 to 2 feet, then use the value 

shown from the Tsivoglou-Wallace equation).

Step 4: Enter the BOD decay rate (base e) at 20 degrees C in cell D36. A calculated value based 

on the Wright and McDonnell equation referenced in EPA/600/6-85/002a is provided and may 

be entered in cell D36 at Step 4 if desired.

User Instructions for the Output Section

The user does not need to change or enter any values or formulas in the Output Section. The 

travel time and distance to critical sag, deficit at critical sag, and dissolved oxygen concentration 

at critical sag are displayed in the Output Section.

Spreadsheet IDOD2.WK1

Revised October 19, 1993

This spreadsheet calculates the dissolved oxygen concentration at a mixing zone boundary from 

dilution of dissolved oxygen in the effluent and ambient background and immediate dissolved 

oxygen demand of the effluent. The method used is presented in EPA/600/6-85-002b (Water 

Quality Assessment: A Screening Procedure for Toxic and Conventional Pollutants in Surface 

and Ground Water - Part II Revised 1985) and EPA/430/9-82-011 (Revised Section 301(h) 

Technical Support Document).

User Instructions for the Input Section

Step 1: Specify the dilution factor for effluent at the chronic mixing zone boundary. This value 

should represent dilution at critical conditions if the spreadsheet is being used for developing 

NPDES permit limits. The dilution factor used should represent the reciprocal of the volume 

fraction of effluent present at the mixing zone boundary (see Permit Writer's Manual section VI2.1).

Step 2: Enter the background dissolved oxygen concentration in the receiving water. The 10th 

percentile during the critical season is recommended as a reasonable worst case. If no data are 

available it would be desirable to collect data describing background dissolved oxygen 

concentrations during the critical season (e.g., upstream from the discharge to a river).

Step 3: Enter the effluent dissolved oxygen concentration. The 10th percentile during the critical 

season is recommended as a reasonable worst case. 

Step 4: Enter the immediate dissolved oxygen demand (IDOD) of the effluent if known. The 
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IDOD represents the oxygen demand of reduced substances which are rapidly oxidized (e.g., 

sulfides to sulfates). If the effluent contains measurable dissolved oxygen, then the IDOD may be 

negligible. If IDOD is to be determined experimentally, the procedures in Standard Methods 

1979 edition could be followed. However, the method was omitted from Standard Methods in the 

1985 edition because of concerns about the accuracy of the test. 

User Instructions for the Output Section

The user should not enter or change the value or formula in the output section. The dissolved 

oxygen at the mixing zone boundary is presented in the output section.

Spreadsheet NH3FRES2.WK1

Revised December 12, 1994 (NH3FRES2.WK1)

NH3FRES2.WK1 contains the formulas modified by EPA that were adopted in the 1995 revision 

of the state water quality standards. The spreadsheet also calculates the amount of un-ionized 

ammonia present in a sample if total ammonia, temperature, and pH are known.

User Instructions for the Input Section

Step 1: Specify the temperature (design condition at the mixing zone boundary) for which unionized ammonia criteria or concentrations are to be estimated. If the spreadsheet is being used to 

calculate criteria for a NPDES permit limit, the 90th percentile temperature during the critical 

season is recommended for a reasonable worst-case condition. If no data are available it may be 

desirable to collect data during the critical season to describe temperature at the mixing zone 

boundary. 

Step 2: Specify the pH (design condition at the mixing zone boundary) for which un-ionized 

ammonia criteria or concentrations are to be estimated. If the spreadsheet is being used to 

calculate criteria for a NPDES permit limit, the 90th percentile pH during the critical season is 

recommended for a reasonable worst-case condition. If no data are available it may be desirable 

to collect data during the critical season to describe pH at the mixing zone boundary. 

Step 3: Specify the sample total ammonia concentration if known. Entering a value here only 

affects Output Step 2 (calculation of un-ionized ammonia present in a sample). No input is 

required at this step if the spreadsheet is being used only to calculate criteria from temperature 

and pH (i.e., values entered at this step do not affect criteria calculations).

Step 4: Specify "Acute TCAP" according to the Gold Book (enter 20 if salmonids are present; 

25 if salmonids are absent).

Step 5: Specify "Chronic TCAP" according to the Gold Book (enter 15 if salmonids are present; 

20 if salmonids are absent).
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APP6-42

User Instructions for the Output Section

The user should not enter or change any values or formulas in the Output Section. The 

spreadsheet calculates the amount of un-ionized ammonia present in a sample at Output Step 2 if 

the sample total ammonia was specified at Input Step 3. Output Step 3 provides the acute and 

chronic criteria for un-ionized ammonia expressed in ug/L as NH3-N. Output Step 4 provides the 

acute and chronic criteria for total ammonia expressed in ug/L as NH3-N.

Spreadsheet NH3SALT.WK1

Revised October 19, 1993

This spreadsheet calculates water quality criteria for ammonia in saltwater using the method 

specified in EPA 440/5-88-004 (Ambient Water Quality Criteria for Ammonia (Saltwater)-

1989).

User Instructions for the Input Section

Step 1: Specify the temperature (design condition at the mixing zone boundary) for which unionized ammonia criteria are to be estimated. If the spreadsheet is being used to calculate criteria 

for a NPDES permit limit, the 90th percentile temperature during the critical season is 

recommended for a reasonable worst-case condition. If no data are available it may be desirable 

to collect data during the critical season to describe temperature at the mixing zone boundary.

Step 2: Specify the pH (design condition at the mixing zone boundary) for which un-ionized 

ammonia criteria to be estimated. If the spreadsheet is being used to calculate criteria for a 

NPDES permit limit, the 90th percentile pH during the critical season is recommended for a 

reasonable worst-case condition. If no data are available it may be desirable to collect data 

during the critical season to describe pH at the mixing zone boundary.

Step 3: Specify the salinity (design condition at the mixing zone boundary) for which un-ionized 

ammonia criteria are to be estimated. If the spreadsheet is being used to calculate criteria for a 

NPDES permit limit, the 10th percentile salinity during the critical season is recommended for a 

reasonable worst-case condition. If no data are available it may be desirable to collect data 

during the critical season to describe salinity at the mixing zone boundary.

User Instructions for the Output Section

The user should not enter or change any values or formulas in the output section. The acute and 

chronic criteria are expressed three ways: 1) as unionized ammonia in mg/L as NH3 at Output 

Step 5; 2) as total ammonia in mg/L as NH3 at Output Step 6; and 3) as total ammonia in mg/L 

as NH3-N at Output Step 7. For derivation of total ammonia waste load allocations and 

comparisons with effluent total ammonia data, it is recommended that the criteria be expressed 

as total ammonia in mg/L as NH3-N for simplicity. [Note: the criteria in EPA 440/5-88-004 

Tables 2 and 3 are for total ammonia as mg/L as NH3, which should be multiplied by 0.822 to 

convert to mg/L as NH3-N.]
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Spreadsheet PHMIX2.WK1

Revised October 19, 1993

This spreadsheet calculates the pH of a mixture of two flows using the procedure in EPA's 

DESCON program (EPA, 1988. Technical Guidance on Supplementary Stream Design 

Conditions for Steady State Modeling. EPA Office of Water, Washington DC). The major form 

of alkalinity is assumed to be carbonate alkalinity. Also, alkalinity and total inorganic carbon are 

assumed to be conservative.

User Instructions for the Input Section

Step 1: Specify the dilution factor for effluent at the mixing zone boundary. This value should 

represent dilution at critical conditions if the spreadsheet is being used for developing NPDES 

permit limits. The dilution factor used should represent the reciprocal of the volume fraction of 

effluent present at the mixing zone boundary (see Permit Writer's Manual section VI-2.1).

Step 2: Specify the upstream characteristics, including temperature, pH, and alkalinity. For 

development of NPDES permit limits for ammonia, the 90th percentiles during the critical 

season are recommended. If no data are available, it is desirable to collect data describing 

upstream temperature, pH, and alkalinity during the critical season.

Step 3: Specify the effluent characteristics, including temperature, pH, and alkalinity. For 

NPDES permit limits, a reasonable worst case estimate of each may be estimated from DMR 

data (e.g., for ammonia limits use 90th percentile values from the DMR data during the critical 

season). If effluent data are not available then data should be collected during the critical season. 

In many cases, pH in ambient receiving water (at Step 2 above) may be assumed to represent the 

pH in the mixing zone.

User Instructions for the Output Section

The user does not need to enter or change any values or formulas in the Output Section. The 

spreadsheet calculates and displays the pH at the mixing zone boundary at Output Step 4. Some 

important factors that can influence pH are not included in this calculation. For example, 

photosynthesis in the receiving water may increase pH downstream from the mixing zone. In 

many cases where dilution is relatively large (e.g., greater than a dilution factor of 20) the pH in 

the mixing zone will be dominated by ambient conditions. This spreadsheet should be used 

mainly where effluent dilution is relatively low and effluent pH and alkalinity are much different 

than in the receiving water.

Spreadsheet RIVPLUM5.WK1

Revised February 22, 1996

This spreadsheet calculates dilution at a specified point of interest downstream from a point 

discharge to a river. The procedure used is described in Fischer et al., 1979 (Mixing in Inland 

and Coastal Waters, Academic Press) and referred to in EPA/505/2-90-001 (TSD for WQ-based 
APPENDIX 6. (JULY 2002)

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APP6-44

Toxics Control.) The calculation for dilution factors incorporates the boundary effect of 

shorelines using the method of superposition (Fischer et al., equation 5.9.)

This spreadsheet is based on the assumption that the discharge: 1) is a single point source, which 

is most appropriate for single port or short diffusers, or side-bank discharges; and 2) is 

completely and rapidly mixed vertically, which usually only occurs in shallow rivers. If the 

diffuser length occupies a substantial portion of the stream width, or the discharge is not 

vertically mixed over the entire water column within the acute mixing zone, an alternative model 

should be used such PLUMES or CORMIX. RIVPLUM5.WK1 is useful for estimating dilution 

in shallow rivers for side-bank discharges or single-port outfalls. This spreadsheet replaces a 

previous version called RIVPLUM4.WK1 RIVPLUM5.WK1 was modified to include optional 

calculation of the effective origin of a wastewater source.

User Instructions for the Input Section

Step 1: Enter the effluent design flow (see Permit Writer's Manual section VI-3.3.2).

Step 2: Specify the receiving water characteristics, including average channel depth, velocity 

and width downstream from the discharge at the design flow (e.g., at 7Q10. NOTE: The product 

of depth*width*velocity should equal the receiving water discharge rate downstream from the 

discharge).

Also enter either the channel slope downstream from the discharge (e.g., as measured from a 

USGS topographic map) or Manning's "n" coefficient for roughness. Finally, enter either 0 (if 

slope is entered above) or 1 (if Manning's "n" is entered above).

The slope or Manning's "n" are used to estimate shear velocity and transverse mixing 

coefficients. Either method may be used, depending on which data are more readily available. It 

is not necessary to specify both slope and Manning's "n". If comparisons are made between the 

two methods then care should be taken to be sure that slope and Manning's "n" values are 

consistent with velocity, depth, and width data since all are related by Manning's equation.

In general, it is not desirable to overestimate Manning's "n" because a lower value will generally 

be more protective since it will predict a lower transverse mixing coefficient. If the Manning 

option is used, the following values may be appropriate estimates for Manning's "n" (EPA/600/3-

87-007 after Henderson, F.M., Open Channel Flow, Macmillan Co., New York, NY, 1966):

• Artificial channel, earth, smooth, no weeds: 0.020 

• Artificial channel, earth, some stones and weeds: 0.025 

• Natural channel, clean and straight: 0.025 - 0.030 

• Natural channel, winding with pools an shoals: 0.033 - 0.040 

• Natural channel, very weedy, winding and overgrown: 0.075 - 0.150 

If no receiving water data are available, then data collection would be desirable. Measurements 
APPENDIX 6. (JULY 2002)

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APP6-45

of channel cross-sections of width, depth, and velocity should be collected within the mixing 

zone at conditions near critical low flow (e.g., near 7Q10). If conditions are significantly 

different than 7Q10 during measurements, then data may need to be adjusted (e.g., using 

Manning's equation).

Step 3: Enter the distance between the diffuser midpoint and the nearest shoreline of the river 

(e.g., for a side-bank discharge enter 0).

Step 4: Enter the location of the downstream point at which dilution factors will be estimated, 

including the distance downstream from the diffuser and the distance from the nearest shoreline. 

The "point of interest" is the location at which dilution factors will be estimated in the Output 

Section. The highest concentration of effluent downstream from the outfall will be the same 

distance from shore as the point of discharge. Therefore, the distance from shore for the point of 

interest should be the same as for the diffuser midpoint in Step 3 for a worst case. However, the 

dilution at any point downstream may be estimated using any combination of distances 

downstream and from shore for the "point of interest."

Step 5: Enter the transverse mixing coefficient constant. A value of 0.6 is recommended for 

most natural channels. Fischer reports that the transverse mixing coefficient can range from 0.1 

to 0.2 for straight artificial channels. Curves and sidewall irregularities increase the coefficient 

such that in natural streams it is rarely less than 0.4. If the stream is slowly meandering and the 

sidewall irregularities are moderate, then the coefficient is usually in the range of 0.4 to 0.8. 

Therefore, a value of 0.6 is usually recommended in natural channels. Uncertainty in this 

constant is usually at least +/- 50 percent.

Step 6: Enter 0 to use the original equations documented in Fischer et al. (1979), or enter 1 to 

account for the effective origin of the wastewater source in the Fischer et al. equations. Entering 

0 will give results identical to the previous version of the spreadsheet (RIVPLUM4).

The optional correction for effective origin is based on discussion in section 5.1.3 of the Fischer 

et al. text. The dilution factors for some discharges may be underestimated without correction for 

effective origin. 

The dilution model is based on considering a rectangular channel of depth (d) into which is 

discharged M units of mass of effluent per unit time in the form of a vertical line source. A line 

source of M units into a flow of depth (d) is equivalent to a point source of strength M/d in a 

two-dimensional flow, for which the concentration (C) is as follows from equation 5.8 and 5.9 of 

Fischer et al. (the nomenclature is as in Fischer et al.; Qe=effluent flow (L^3/T); u=velocity 

(L/T); d=depth (L); Et=transverse mixing coefficient (L^2/T); x=distance downstream (L); 

y=distance across channel (L); W=channel width (L)):

C = k * C0 / (4*pi*x')^0.5 (eqn 1)

where

 2
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APP6-46

k = SUM {exp[-(y'-2n-y0')^2/4x']+exp[-(y'-2n+y0')^2/4x']} 

 n=-2

C0 = M / (u*d*W)

x' = x*Et/(u*W^2)

y' = y/W

y0' = y' at the source location y=y0

If C represents the effluent volume fraction, then the dilution factor is equal to 1/C. In order to 

apply this equation very close to the effluent outfall, the effective origin may be estimated as 

follows.

• If M is estimated as the product of effluent flow and concentration, then the effluent 

source concentration (Ce) is:

 Ce=M/Qe (eqn 2)

• The offset or correction (x0) for the effective origin of effluent may be estimated as 

follows. First, substitute eqn 2 into eqn 1 for instream C=Ce:

 M/Qe = k * C0 / (4*pi*x')^0.5 (eqn 3)

• Next, solve eqn 3 for x=x0, which is the distance downstream from the effective origin to 

the outfall, such that in-stream concentration equals the effluent concentration at the 

actual outfall location:

 x0 = (k*Qe/d)^2 / (u*4*pi*Et) (eqn 4)

• The effective distance downstream (x) in eqn 1 is then replaced by (x+x0) to account for 

the effective origin of the source.

User Instructions for the Output Section

The user does not need to enter or change any values or formulas in the Output Section. The 

plume characteristics incorporating the shoreline effect are displayed at Step 5 of the Output 

Section, including the approximate distance downstream to complete mix, theoretical maximum 

available dilution at complete mix of effluent with the receiving water, flux-average dilution at 

the specified downstream distance, and the calculated dilution factor at the specified point of 

interest downstream from the discharge.

The distance downstream to complete mixing is often overestimated because most natural 

channels contain sharp bends or changes that increase mixing beyond the processes included in 

the model. The model is most useful for predicting mixing where the channel is represented over 

a relatively short distance (e.g., to the mixing zone boundary).
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APP6-47

Workbook PWSPREAD.XLS

Revised February 22, 1996

This Excel 5 workbook contains the following spreadsheets:

• dosag2 

• idod2 

• nh3fres2 

• nh3salt 

• phmix2 

• rivplum5 

The spreadsheets in PWSPREAD.XLS perform the same calculations as the Lotus 1-2-3 .WK1 

files of the same names. The instructions for each of the sheets in PWSPREAD.XLS are the 

same as for the .WK1 files.

Workbook FARFIELD.XLS

Revised February 22, 1996

[NOTE: This workbook requires the Analysis ToolPak Add-In, which must be configured using 

the "Tools/Add-Ins" menu in Excel 5.]

This Excel 5 workbook calculates far-field mixing of a plume using the method of N.H. Brooks 

(1959, "Diffusion of Sewage Effluent in an Ocean Current," in "Waste Disposal in the Marine 

Environment", edited by E.A. Pearson, pp, 246-267, Pergamon Press, New York, NY.) This 

workbook is useful for estimating dilution beyond the range of near-field models such as 

UDKHDEN or PLUMES/UM using Brook's 4/3-power law, linear diffusivity, and constant 

diffusivity algorithms.

Brooks' model is applied in this workbook using the algorithm of EPA's PLUMES model (1993, 

"Dilution Models for Effluent Discharges," U.S. Environmental Protection Agency, EPA/600/R93/139, Washington, DC.) with the addition of a linear diffusivity algorithm as described by 

R.A. Grace (1978, "Marine Outfall Systems: Planning, Design, and Construction," Prentice-Hall 

Inc., Englewood Cliffs, NJ.)

FARFIELD.XLS contains the following four spreadsheets:

• PLUMES algorithm 

• Brooks' four-thirds power law 

• Brooks' linear diffusivity 

• Brooks' constant diffusivity 

The "PLUMES algorithm" spreadsheet uses the same method as EPA's PLUMES model 

("Dilution Models for Effluent Discharges," U.S. Environmental Protection Agency, 
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APP6-48

EPA/600/R-94/086) to implement Brooks' far-field models. The PLUMES algorithm is 

documented in equations 66-73 of EPA/600/R-94/086. The major difference between the 

"PLUMES algorithm" and the other spreadsheets is in the treatment of the parameter "alpha" in 

the following equation:

epsilon(0) = alpha * b ^n

where epsilon(0) is the lateral diffusion coefficient (L^2/T), b is the width of the plume (L), and 

n is an exponent used to estimate the initial value of epsilon. The PLUMES algorithm assumes 

that the initial value of epsilon(0) at the start of far-field modeling is based on n=4/3 for both the 

4/3 power law and constant diffusivity models. Therefore, the PLUMES algorithm assumes that 

"alpha" has units of L^(2/3)/T and n=4/3 regardless of which Brooks' model is used.

The "PLUMES algorithm" spreadsheet also includes Brooks' linear diffusivity model and uses 

n=4/3 for the initial calculation of epsilon(0). The linear diffusivity model used in the 

spreadsheet is as presented by equation 7-65 of Grace (1978).

The "Brooks' four-thirds power law", "Brooks' linear diffusivity", and "Brooks constant 

diffusivity" spreadsheets differ from the "PLUMES algorithm" spreadsheet by assuming 

different units for "alpha" and different values of n depending on the model being used. "Alpha" 

has units of L^(2/3)/T for the 4/3 power law (n=4/3), L/T for the linear diffusivity model (n=1), 

and L^2/T for the constant diffusivity model (n=0). Brooks' equations as documented in 

equations 7-64, 7-65, and 7-66 of Grace (1978) were used to estimate dilution along the plume 

trajectory.

User Instructions for the Input Section

Step 1: Specify the plume and diffuser characteristics at the start of far-field mixing. The 

computations at the end of a near-field mixing model such as UDKHDEN or PLUMES/UM is 

usually used to define the conditions at the start of far-field mixing. The necessary parameters 

are the flux-average dilution factor at the end of near-field model computations, the estimated 

initial width at the start of far-field mixing (e.g., equation 70 as described in the PLUMES 

manual (EPA/600/R-94/086), and the horizontal distance that the plume travels during the nearfield mixing phase.

Step 2: Specify the horizontal distance from the outfall to the mixing zone boundary along the 

trajectory of the plume (e.g., as defined in WAC 173-201A-100).

Step 3: Specify the parameter "alpha" as described above. The units for "alpha" depend on 

which spreadsheet is used, as discussed above.

Step 4: Specify the horizontal current speed along the far-field plume trajectory.

Step 5 (optional): Specify the initial pollutant concentration and the first-order decay rate. The 
APPENDIX 6. (JULY 2002)

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APP6-49

initial concentration for far-field mixing should be the final concentration at the end of near-field 

mixing.

User Instructions for the Output Section

The user does not need to enter or change any values or formulas in the Output Section. The 

spreadsheets calculate dilution along the trajectory of the plume and at the specified mixing zone 

boundary. Optional calculation of pollutant concentrations assuming first-order decay rates is 

also provided.

2.2 GUIDELINES FOR USING TSDCALC.XLW 

TSDCALC.XLW is a workbook composed of several spreadsheets. Several are duplicates of 

those given above. It is used for reference and for developing permit limits. The individual 

spreadsheets contained in TSDCALC are CRITERIA.XLS, AMMONIA.XLS, REASPOT.XLS, 

LIMIT.XLS, PERFORMLIM.XLS, HUMAN-H.XLS, Fresh-temp.XLS and Marine-temp.XLS. 

The spreadsheets CRITERIA.XLS and AMMONIA.XLS contain or calculate water quality 

criteria. The spreadsheets REASPOT.XLS, and LIMIT.XLS determine reasonable potential (to 

violate the aquatic life water quality standards) and calculate effluent limits. The spreadsheet 

PERFORMLIM.XLS calculates performance-based effluent limitations and accounts for 

autocorrelation if known. The spreadsheet HUMAN-H.XLS determines reasonable potential and 

calculates effluent limits for human health pollutants. The spreadsheets Fresh-temp and Marinetemp determine reasonable potential and limits for temperature. The process and formulas for 

determining reasonable potential and effluent limits in these spreadsheets are taken directly from 

the Technical Support Document for Water Quality-based Toxics Control, (EPA 505/2-90-001). 

The adjustment for autocorrelation is from EPA (1996a), and EPA (1996b) 

CRITERIA.XLS

This spreadsheet is split for convenience of the permit writer. The pollutants of concern can be 

copied from the lower view and pasted in the upper view. The upper view can then be printed 

with only the pollutants of concern. Documentation text is found in rows 186-193.

Input - Cell B199 is a fill-in cell for receiving water TSS concentration, if known. TSS is used 

for calculating the partitioning translator for copper and zinc. If no TSS values are 

placed in this cell, the statewide 95th percentile ratio or the conversion factor is used as 

the default translator. 

Input - Cell B200 is a fill-in cell, which characterizes the TSS data. Place an A in this cell if the 

TSS data is derived from several seasons. Place an S in this cell if the TSS data is only 

from the critical period.

Input - Cell B201 is a fill-in cell for hardness of the receiving water. Hardness is used to 

calculate several of the metal criteria. The hardness value should be the lowest value 

from the critical period if the data set is less than 20, or the 10th percentile value if the 
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APP6-50

data set is 20 or greater. Column A contains the pollutant name, the CAS number, and 

where it is found on the table of effluent characteristics in the NPDES permit 

application. 

Column B is labeled “Priority Pollutant?” A Y in this column means the chemical is a priority 

pollutant (toxic pollutant).

Column C is labeled Carcinogen? A Y in this column means the chemical is a carcinogen.

Columns D through G are the aquatic life water quality criteria for fresh and marine waters.

Columns H and I are the human health criteria for fresh and salt water. These columns are more 

correctly stated as Criteria for consumption of water and organisms (typically fresh water) and 

Criteria for the consumption of organisms only (typically salt water).

Column J gives the source of the criteria and any additional comments. A notation of NTR-HH 

means the human health criteria are from the National Toxics Rule and therefore part of our 

regulatory requirements. A notation of Gold Book means the criterion is a federal EPA criterion. 

These values should be treated as guidance. The “Gold Book” has been modified extensively by 

federal regulations such as the National Toxics Rule and others.

Columns K through N are translators for the metal criteria, which are used for determining 

reasonable potential. The translators for cadmium, copper, lead, and zinc are based on data 

presented by Pelletier (1996).

AMMONIA.XLS

This spreadsheet calculates the freshwater ammonia criteria. The inputs for this spreadsheet are 

temperature, pH of the receiving water at the time of critical condition and whether the receiving 

water is salmonid habitat. 

REASPOT.XLS

This spreadsheet determines if there is a reasonable potential for violation of the aquatic life 

water quality standards based on the input values. There is an example for reasonable potential 

determination for metals in the PWM in Chapter VI.
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APP6-51

Input - Column A - enter the pollutant parameter.

Input - Column B and C – These are the metal criteria translator values taken 

from Criteria.XLS. If there is no value placed here the default value is the 

metal conversion factor.

Input - Column D is the ambient background concentration. For metals use the dissolved 

concentration. If you only have ambient total recoverable data, use the translator to convert 

the total recoverable data to dissolved.

Input - Columns E and F - enter the appropriate acute and chronic water 

quality criteria for the parameter.

Columns G and H are the calculated expected concentrations at the edge of the acute and chronic 

mixing zones. They are calculated from expected effluent concentration, ambient concentration, 

dilution factors and, for metals, the translator. 

Column I compares the expected acute and chronic criteria with the concentration at the edge of 

the appropriate dilution zone. It returns a yes if the expected concentration is higher than the 

criteria or a no if not. Yes indicates a reasonable potential to violate the water quality criteria.

Column J is the upper percentile estimate of the effluent concentration. The recommended value 

to enter is 0.95.

Column K is a calculated value

Input -Column L - Enter in the highest measured effluent concentration

Input -Column M - Enter the coefficient of variation of the effluent parameter (standard 

deviation/mean). The default value is 0.6. If you have more than 10 effluent values this 

value should be calculated instead of using the default.

Input - Column N - Enter the number of data values in the set from which the value entered in 

Column L was taken.

Column P is the calculated value used as a multiplier. Column L is multiplied by this value 

(Column P) to estimate the 95th percentile value of a small data set lognormally distributed. 

This value is equivalent to the multiplier in Table 3.2 95/95 in the TSD. If the permit writer has 

20 or more data points for a parameter in the effluent, the 95th percentile effluent value can be 

calculated more accurately by transforming the data by log or lognormal, finding the 95th 

percentile value and then converting the value back by taking antilog or natural antilog. This 

value is placed in Column L and the number of samples is varied by trial and error until the 
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APP6-52

multiplier in Column P equals 1.0. For example, with a CV of 0.6 column P would have to be 58 

for the multiplier to equal 1.

LIMITS.XLS

This spreadsheet calculates effluent limits for aquatic life pollutants by use of formulas given in 

the Technical Support Document Box 5-2. Limits are required for any parameters that show a 

reasonable potential in the preceding spreadsheet. If the parameter has an extensive database, the 

values should be lognormal transformed (see comment in G2 of PERFORMLIM) and then the 

spreadsheet PERFORMLIM.XLS used to calculate effluent limits.

Input - Column A - enter the parameter

Input - Columns B and C - enter the acute and chronic dilution factors

Input - Columns F, G, and H can be copied from REASPOT.XLS

Column I is the calculated Average Monthly effluent limit

Column J is the calculated Daily Maximum effluent limit

Columns L and M are the calculated wasteload allocations for acute and chronic criteria

Columns N and O are the acute and chronic long term averages necessary to meet the wasteload 

allocations. The smaller of these two (the limiting LTA) is automatically placed in column R.

Column P is the expected coefficient of variation for the LTA. Use the effluent CV if available 

or use the default CV of 0.6.

Column Q is the probability the LTA will meet the WLA (expectation that the water quality 

standards will be met). A value of 0.99 (recommended by EPA) means an expected probability 

of exceedance of 0.01 or 1%.

Column S is the effluent CV. Use the calculated value if available or a default of 0.6 if an actual 

value can’t be calculated.

Columns T and U are the expected probability of error for the effluent limits. The recommended 

values are 0.95 for the AML and 0.99 for the MDL (See the PWM page VI-28 for a discussion).

Input - Column V - The number of samples which will be required per month for compliance 

sampling. If sampling will be less than 1 per month use a value of 1 in this column.
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APP6-53

PERFORMLIM.XLS

This spreadsheet calculates performance-based effluent limits. It will account for autocorrelation 

if the autocorrelation factor is known. The permit manager should assume effluent data is nonnormally distributed and use EXCEL to transform the data using a lognormal transformation. 

A note in cell G2 explains the procedure for lognormal data transformation. Rows 5 through 8 

are input cells. The lognormal transformed mean and variance are placed in cell H5 and H6. 

The number of samples per month that will be required for compliance monitoring is placed in 

cell H7. The autocorrelation factor is placed in cell H8 if it is known. Cells H9 through H13 are 

calculated intermediate values. Cells H15 and H16 are the calculated effluent limits.

HUMAN-H.XLS

This spreadsheet calculates reasonable potential and the effluent limits for human health 

pollutants. Reasonable potential for human health criteria is based on the 50th percentile effluent 

value. This spreadsheet deals with the effluent values in two ways. In a situation where the 

permit writer has 10 or more data points for the effluent concentration, the 50th percentile should 

be calculated by using the statistical calculation in EXCEL or some other software. Place this 

calculated 50th percentile value in column N. Any number in this column is always used for 

calculations if present so it must be 0 unless a calculated percentile value is placed here. In a 

situation with less than 10 data points, the 50th percentile effluent concentration is estimated 

within the spreadsheet by placing the highest observed effluent concentration in column I. The 

estimated coefficient of variation is placed in column J and the expected number of compliance 

monitoring samples is placed in column L. The 50th percentile value is calculated and then is 

used to calculate the expected concentration at the edge of the mixing zone. The dilution factor 

is placed in the last column (o). Carcinogens and non-carcinogens have different design criteria 

for effluent and receiving water flow so the dilution factors may be different for different human 

health pollutants. The spreadsheet calculates the expected concentration at the edge of the 

mixing zone, notes whether an effluent limit is required and, if so, calculates the limits using five 

and one percent error probabilities for average monthly and daily maximum, respectively.

Input -Column A – Enter the pollutant parameter name

Input – Column B – Enter the ambient concentration as the geometric mean of the receiving 

water values.

Input – Column C – Enter the human health criteria value.

Column D – This column calculates the expected concentration at the edge of the chronic mixing 

zone.

Column E – This column returns a yes or no as a determination of reasonable potential. 

Input - Column F – The number of samples expected to be required in the permit for compliance 

monitoring.
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APP6-54

Columns G and H – the calculated monthly average and daily maximum limits. Note that the 

monthly average limit equals the WLA adjusted for the background concentration.

Column I – The expected effluent percentile at 95% confidence. The recommended value is 0.5 

in this column.

Column J – Internal calculation used to calculate multiplier (Col. O).

Input - Column K – The maximum effluent concentration measured.

Input - Column L – The coefficient of variation. The default value is 0.6 but this should be 

calculated from the effluent data if there are 10 or more data points. The coefficient of variation 

is the standard deviation ÷ the mean.

Column M – An internal calculation used to calculate the multiplier (Col. O).

Column N – The number of data points in the data set from which value in Column K was taken.

Column O – The calculated value which is used to multiply the value in Column K to estimate 

the 50th percentile at the 95th percent confidence level. The formula for this multiplier is taken 

from the EPA TSD.

Input - Column P – The calculated 50th percentile effluent concentration. With 10 or more 

effluent data points the 50th percentile value should be calculated and placed in this column. A 

number in this column will take precedence over an estimated value. If the 50th percentile value 

isn’t calculated this column should be 0.

Input - Column Q – The chronic mixing zone dilution factor.

Fresh-temp.XLS and Marine-temp.XLS

These sheets contain two columns for calculating RP during maximum summer temperature and 

the fall or spring spawning season. Blocks A, B, C and D are interim registers for lines 17 and 

18.

3. AN ALTERNATE METHOD FOR ESTIMATING 

UPPER QUANTILES

This method estimates a selected upper percentile value from a distribution assumed to be 

lognormally distributed. The most statistically valid estimate of an upper percentile value is a 

maximum likelihood estimator which is proportional to the population geometric mean. If one 

assumes the population of effluent concentrations to fit a lognormal distribution, this relationship is 

given by:
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APP6-55

Cp = Cmean * exp (Zp*σ - 0.5 *σ2)

Where: Zp = normal distribution factor at pth percentile

 σ2 = ln(CV2 + 1)

To calculate the maximum likelihood estimator of the 95th percentile, the specific relationship 

becomes:

C95 = Cmean * exp (1.645* σ - 0.5* σ2)

if CV is assumed = 0.6,

σ2 = .307

The ratio of the estimated 95th percentile value to the mean (C95/Cmean) = 2.13

A single effluent value or the geometric mean of a group of values is multiplied by the ratio to yield 

the estimate of the 95th percentile value.

The following table shows the ratio of the upper percentile to the mean for the 90th, 95th, and 99th 

percentiles

Ratio of Upper Percentiles to Geometric Mean

Percentile Z Cp/Cmean

90 1.283 1.74 

95 1.645 2.13

99 2.386 3.11

In use with limited data sets assumed to be lognormally distributed, the geometric mean is multiplied 

by the value in the right column above to estimate the percentile given in left column. This 

estimation technique results in lower estimates of upper percentile values than the technique 

discussed in the TSD in Section 3.2.2. for n less than 6. At some number of values it becomes more 

accurate simply to calculate the desired percentile value. Most spreadsheets have this capability. 

The number of values at which this occurs can't be predicted because it depends on the 

characteristics of the population being sampled. Using the TSD upper quantile estimation technique 

on page 56 and calculating where the largest value is greater than the 90th percentile (at 95% 

Confidence), the value of n is 30. In other estimation techniques for lognormal distributions, Gilbert 

(1987) predicts a large sample as n = 20.
APPENDIX 6. (JULY 2002)

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APP6-56

4. GUIDANCE ON THE APPROPRIATE SIZE MIXING 

ZONE FOR A UNIQUE OUTFALL CONFIGURATION

In this situation a 170-foot diffuser runs parallel to the bank of a large river, rather than 

projecting across the river (see Figure 1). The 26 equally spaced eight-inch ports discharge away 

from the bank toward the deeper water. Thus, the plumes are carried downstream by the current 

“one over the other” (serially), rather than adjacent to each other (in parallel). The depth of 

water is 18 feet.

The regulations pertaining to sizing of mixing zones are in the Water Quality Standards for 

Surface Waters ..., WAC 173-201A-100. The freshwater rules apply (while this river is 

influenced by the tide, the flow simply slows but does not reverse). The regulation states that the 

chronic mixing zone shall:

“(i) Not extend in a downstream direction for a distance from the discharge port(s) 

greater than three hundred feet plus the depth of water over the discharge port(s), 

or extend upstream for a distance of over one hundred feet;

(ii) Not utilize greater than twenty-five percent of the flow;

(iii) Not occupy greater than twenty-five percent of the width of the water body.”

This language does not address a serial discharge situation; (i.e., it is not clear from which 

discharge port(s) the 300-foot measurement begins).

The reasonable solution is: If an outfall is configured such that the centerline of the diffuser lies 

parallel to the direction of current flow, then the distance to the downstream chronic mixing 

zone boundary is to be determined by beginning the measurement from the most upstream 

port in the diffuser. The distance from the downstream port to the chronic mixing zone 

boundary will be:

300 ft. + depth of water – length of diffuser. (1)

An acute boundary is 10 percent of the distance allowed for the chronic mixing zone. In this 

situation it will be 10 percent of the distance determined in equation (1). The width of 

these mixing zones will be addressed by subpart (iii) of the regulations mentioned above. 

This solution ensures that length of diffuser is not a factor in size of mixing zone and 

discourages the use of diffusers much longer than 170 feet in this type of configuration.
APPENDIX 6. (JULY 2002)

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APP6-57

The mixing zone will be 148 feet from the downstream port. The acute boundary will be 14.8 

feet from the downstream port. Width of the mixing zone will be very large since this 

outfall is to a large river. 

5. DERIVING THE 7Q10 HIGH FLOW (HF) AND THE 

DESIGN SPILL

5.1. Guidelines for Deriving the 7QHF

Use the record of observed flow data. For the Columbia River use the record from water year 

1974 to the present. 1974 is the year when the last major storage reservoir was built in the 

Columbia River Basin. If data is not available for the location of interest, make reasonable 

calculations based on an approved 7Q10hf for up-river or down-river locations or dams. Flow 

data must include total river flow.

The period of record may be extended by including modeled or transformed data prior to 1974 

that represents the current condition of the basin with all dams in place. If this is done, compare 

Figure 1. Unique Outfall 

Orientation

CURRENT 

DIRECTION

170 FEET

BANK
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APP6-58

results of using data from the observed period of record with the results of using the data from 

the extended period of record. This serves as a check to see if the proposed method for 

extending the period of record gives comparable results.

To the extent possible, take into account any trends or anticipated changes of flows in the future.

Use daily average flows to calculate the 7Q10hf and then determine the highest 7-consecutiveday average peak flow for each year.

Calculate frequency/return interval using standard hydrology methods (see USGS bulletin 17B, 

Guidelines for Determining Flood Flow Frequency, or any hydrology textbook)

Information submitted to Ecology must include documentation of the methods of calculating 

7Q10hf, including assumptions about data, current trends, anticipated changes, quality assurance, 

methods of measurement, methods of transforming historic data and comparisons of 7Q10hf 

values for other dams.

5.2. Determining Design Spill for Gas Abatement

To determine the design spill for gas abatement, use the hourly spill data for high flow months of 

a high flow year (1997 for example) and extrapolate to the 7Q10hf. The high flow months for 

the Columbia River are May and June.
APPENDIX 13 (December 2001)

Permit Writer’s Manual

APP13-1

APPENDIX 13

1. SUPPORTING STATISTICAL STUDY FOR 

PERFORMANCE-BASED REDUCTION OF 

MONITORING (from EPA, April 96)

Effect of Sample Size on Probability of Violation

EPA has done a statistical analysis on the effect of sampling frequency on compliance 

assessment. The basic premise underlying a performance-based reduction approach is that 

maintaining a low average discharge relative to the permit limit results in a low probability of the 

occurrence of a violation for a wide range of sampling frequencies.

The probability of the occurrence of a violation of a monthly average permit limit was 

calculated. Tables 13-1,13-2 and 13-3 display the percentage of time that a monthly average 

permit violation will be reported given sample size and a long-term average to permit ratio. This 

probability is dependent on the true long-term average of the discharge, the permit limit, and the 

monthly sampling frequency. The variables of long-term average and permit limit are both 

reflected in the tables by expressing these as a ratio. Tables 13-1, 13-2, and 13-3 assume a 

normal distribution of monthly averages and show the effect of altering the assumed coefficient 

of variation, using 20%, 60%, and 80%, respectively. 

Obviously, the best estimate of the true monthly average discharge is obtained by daily sampling. 

One can assess the true violation rate of a discharge by looking at the probability calculated 

assuming sampling was done daily (30 times per month). In order to maintain compliance with a 

permit limit, the long term average level of the discharge must be controlled at a level less than 

the permit limit. Reducing the sample size, while increasing the probability that a violation will 

be reported, does not change the underlying probability of reporting a violation associated with a 

baseline estimate of the monthly average calculated with 30 samples. With a constant 

performance, the probabilities of reporting a permit violation increase as the sample size is 

reduced from daily sampling because the variance of the average is inversely proportional to the 

sample size. 

Looking at the true violation rate of a facility sampling daily and operating at 75% of their 

permit limit, these tables show that the probability of a violation in a given month is 1% or less. 

If the long-term average discharge is 65% of the permit limit, the true percentage of violation is 

less than 1%. As sample size decreases for a given discharge/limit ratio, the expected percentage 

of time that the average of the samples collected during the month will exceed the permit limit 

increases. For example, Table 13-3 demonstrates that at a ratio of 65%, the expected violation 

rate is effectively zero. If a subsample of 8 samples per month is taken instead of 30, the facility 
APPENDIX 13 (December 2001)

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APP13-2

has a 3% chance of reporting a violation. If only one sample per month is taken, the chances of 

reporting a violation increase to 25%. The facility performance (true monthly average discharge) 

has not changed, thus "missed" monthly average violations are not an issue. The probabilities 

calculated for very low sampling frequencies reflects the risk assumed by the discharge operator 

that monthly average violations will be reported when in fact the process average is under permit 

limit. If facility performance degrades during the permit term and sampling has been reduced, it 

can be seen that the facility will have probability of reporting violations at a higher rate, even if 

the long-term average is still below the permit limit. An example will illustrate this point. Table 

13-3 shows that if a facility was judged to be at 75% of their permit limit and reduced sampling 

from 16 to 12 times per month, the probability of violation would change from approximately 

5% to 7%. If the long-term average performance degraded to 90% of the permit limit, the 12 

monthly samples would yield expected monthly average permit violations 32% of the time 

instead of 29% of the time if 16 samples were collected. 

Table 13-3 shows probabilities calculated using a more conservative assumption of 80% 

coefficient of variation. The results show that facilities with a long term average of less than or 

equal to 75% have essentially no chance of violating a monthly average limit, hence facilities 

with this performance would be good candidates for performance-based monitoring reductions. 

The reductions in Table XIII-1A1 were designed to maintain approximately the same level of 

reported violations as that experienced with their current (baseline) sampling. 
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APP13-3

Table 13-1. Probability of Reporting Monthly Average Permit Violations at 20% Effluent 

Variability (CV = 0.20; Normal Distribution).

Monthly Sample Size

1

LTA/Permit 30 28 24 20 16 12 8 4 2 1

100% 50% 50% 50% 50% 50% 50% 50% 50% 50% 50%

95% 7% 8% 10% 12% 15% 18% 23% 30% 35% 40%

90% 0% 0% 0% 1% 1% 3% 6% 13% 22% 29%

85% 0% 0% 0% 0% 0% 0% 1% 4% 11% 19%

80% 0% 0% 0% 0% 0% 0% 0% 1% 4% 11%

75% 0% 0% 0% 0% 0% 0% 0% 0% 1% 5%

70% 0% 0% 0% 0% 0% 0% 0% 0% 0% 2%

65% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

60% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

55% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

50% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

40% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

30% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

20% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

1 Ratio of calculated average of at least 2 years of effluent data to monthly average permit limit.
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APP13-4

Table 13-2. Probability of Reporting Monthly Average Permit Violations at 60% Effluent 

Variability (CV = 0.60; Normal Distribution)

Monthly Sample Size

1

LTA/Permit 30 28 24 20 16 12 8 4 2 1

100% 50% 50% 50% 50% 50% 50% 50% 50% 50% 50%

95% 32% 32% 33% 35% 36% 38% 40% 43% 45% 47%

90% 16% 16% 18% 20% 23% 26% 30% 36% 40% 43%

85% 5% 6% 7% 9% 12% 15% 20% 28% 34% 38%

80% 1% 1% 2% 3% 5% 7% 12% 20% 28% 34%

75% 0% 0% 0% 1% 1% 3% 6% 13% 22% 29%

70% 0% 0% 0% 0% 0% 1% 2% 8% 16% 24%

65% 0% 0% 0% 0% 0% 0% 1% 4% 10% 18%

60% 0% 0% 0% 0% 0% 0% 0% 1% 6% 13%

55% 0% 0% 0% 0% 0% 0% 0% 0% 3% 9%

50% 0% 0% 0% 0% 0% 0% 0% 0% 1% 5%

40% 0% 0% 0% 0% 0% 0% 0% 0% 0% 1%

30% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

20% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

1 Ratio of calculated average of at least 2 years of effluent data to monthly average permit limit.
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APP13-5

Table 13-3. Probability of Reporting Monthly Average Permit Violations at 80% Effluent 

Variability (CV = 0.80; Normal Distribution)

Monthly Sample Size

1

LTA/Permit 30 28 24 20 16 12 8 4 2 1

100% 50% 50% 50% 50% 50% 50% 50% 50% 50% 50%

95% 36% 36% 37% 38% 40% 41% 43% 45% 46% 47%

90% 22% 23% 25% 27% 29% 32% 35% 39% 42% 44%

85% 11% 12% 14% 16% 19% 22% 27% 33% 38% 41%

80% 4% 5% 6% 8% 11% 14% 19% 27% 33% 38%

75% 1% 1% 2% 3% 5% 7% 12% 20% 28% 34%

70% 0% 0% 0% 1% 2% 3% 6% 14% 22% 30%

65% 0% 0% 0% 0% 0% 1% 3% 9% 17% 25%

60% 0% 0% 0% 0% 0% 0% 1% 5% 12% 20%

55% 0% 0% 0% 0% 0% 0% 0% 2% 7% 15%

50% 0% 0% 0% 0% 0% 0% 0% 1% 4% 11%

40% 0% 0% 0% 0% 0% 0% 0% 0% 0% 3%

30% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

20% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

1 Ratio of calculated average of at least 2 years of effluent data to monthly average permit limit.

Detailed Protocol for Calculating Probability of Reporting Permit 

Violations

Calculation of probabilities for Tables 13-1 to 13-3

Probability distributions may be used to model effluent data and assess the probability of permit 

violations. The models provide a logical and consistent methodological framework for using 

observed performance data to assess permit limitations in an objective manner. The goal of the 

limitations is to establish performance levels that enforce good treatment and ensure that water 

quality objectives are met. In deriving limitations, sufficient allowance for variation in 

treatment performance is provided such that a well-operated treatment system should be capable 

of compliance with the limitations at all times. In using probability models as the basis for 

limits, it is necessary to select a percentile value such that, within the context of the model, any 
APPENDIX 13 (December 2001)

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APP13-6

meaningful limit will have a non-zero probability of being exceeded. 

The results shown in the tables here are derived from probability distribution functions that may 

be used to model effluent data. That is, the processes are assumed to operate over time in a 

manner that is consistent with past performance. No intervention to change the process or exert 

more or less control over the discharge is assumed.

 

Calculation of the probability that a reported permit violation will occur depends upon: the 

number of individual samples taken during the month, the long-term discharge level, the 

variance of the discharge concentrations, the probability distribution of the individual samples 

during the month, and the permit limit. There are two probability distributions commonly used 

to model effluent data: the lognormal distribution and the normal distribution. The lognormal 

distribution usually provides a good fit to data sets comprised of individual effluent 

measurements because such data typically have two critical lognormal characteristics: they are 

positive valued and positively skewed. Positive skewness means that the data are characterized 

by a tendency for a preponderance of measurements in the lower range of possible values with 

relatively fewer measurements stretched out over a wider range of possible upper values. The 

lognormal also has the property that the logarithms (natural or base 10) of the data are normally 

distributed. The normal distribution has the well-known "bell shape" and is mathematically 

straightforward so that working with the logarithms of effluent data is relatively uncomplicated.

The asymptotic distribution of sample averages is normally distributed. That is, the average of a 

sample of individual measurements will have a distribution that is approximately normally 

distributed regardless of the distribution of the individual measurements. The quality of the 

approximation depends on several factors including the number of individual measurements 

being averaged and the form of the underlying distribution. Although individual effluent 

measurements are rarely normally distributed, it is reasonable in many situations to approximate 

the distribution of the averages of effluent measurements with a normal distribution and thus the 

normal approximation is used in many cases as a model for monthly average effluent limitations. 

The results in Tables 13-1 through 13-3 are based on the assumption of a normal distribution for 

the averages of effluent measurements. Extensive discussion on the statistical modeling of 

effluent data and methodology for setting effluent limitations are contained in EPA's 1991 

Technical Support Document for Water Quality-based Toxics Control (TSD).

The results of calculating probability of a reported violation of a monthly average permit limit 

are shown in Tables 13-1 through 13-3 under different conditions. The purpose of these tables is 

to provide some insight into the effects of changing monitoring requirements. The probability of 

exceeding the monthly limit when the long-term average of the discharge is at the desired value 

can be thought of as the Type I error rate (alpha-level) of the monitoring program. When the 

long-term average exceeds the desired limit, the probability of exceeding the monthly limit is 

now the monitoring program's ability to detect violation increases if the long-term average 

increases over the desired level. It should be understood that if permit limits are held constant 
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APP13-7

and performance measures such as long term average discharge and variability of treatment do 

not change, then reducing the number of monitoring measurements used to calculate the monthly 

average causes the probability of a violation to increase for all values of the long term average 

less than the monthly average permit limit. This has a two-fold effect: 1) the chances of 

reporting a violation even when the long term average is less than the desired level (the Type I 

error rate) go up 2) the sensitivity (ability to detect violations) of the program increases. The 

Tables also show that if the average discharge level is held well below the monthly average limit, 

the chances of a violation are small. The thee tables reflect three different levels of variation in 

the underlying daily data as measured by the coefficient of variation. The coefficient of variation 

(CV) is the ratio of the standard deviation of the distribution to the mean and is often expressed 

as a percentage. The CV is a convenient measure for summarizing the relative variability in a 

data set. The results in Tables 13-1, 13-2, and 13-3 use CVs of 20%, 60% and 80% respectively. 

A coefficient of variation of 60% was used in the TSD to describe a typical level of variation for 

lognormally distributed effluent data. CVs of 80% and 20% were used to show the effects of 

higher and lower levels of variability. 

The probability distribution of the average of N daily measurements taken during a month, MN, 

is given by the following normal probability density function:

where μ is the mean or long term average, and σ is the 

standard deviation of the daily discharges. If μ1 is the 

maximum monthly average allowed by the permit, then the probability that the monthly average 

exceeds the permit maximum is given by P(MN>μ1). Using simple algebra this probability can 

be rewritten as:

where Φ(.) is the standard normal 

cumulative probability function 

(the Microsoft®Excel built-in 

function NORMDIST).

g( M )= 1

2

N

N e

-

N( M - )

2

N 2

2

π

σ

μ

σ

P( M > )= P( M -

N

> -

N

 ) = 1- ( -

N

N ), 1

N 1 1 μ μ

σ

μ μ

σ φ μ μσ
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APP13-8

Since

where C is the coefficient of variation, then the probability of a monthly average exceeding the 

maximum allowable can be calculated using C, N, and the ratio of the long-term average to the 

maximum allowable monthly average using NORMDIST. This is how the values in Tables 13-1, 

13-2, and 13-3 were calculated.

Alternate approaches to probability calculations: 

The probabilities in Tables 13-1 to 13-3 were calculated with the assumption that the distribution 

of the sample means is normal. Individual sample values are generally best fit to a lognormal 

distribution. As discussed in the TSD, the mean of small samples from a lognormal distribution 

is in most cases approximately lognormal. Probabilities can be calculated assuming a lognormal 

distribution by two different methods, a Monte Carlo technique and the Microsoft Excel built-in 

function LOGNORMDIST. The resulting probabilities will be very close to those in the normal 

distribution table for the sample sizes and discharge levels under consideration for monitoring 

reductions, although the probabilities calculated from these two distributions may not be 

comparable for all sample sizes and all discharge levels. 

The statistical evaluations used in this analysis are intended for use only to illustrate the effect 

and benefits of this strategy, alternative statistical techniques and approaches may be utilized in 

other situations.

1

1

-

N

= N

C ( 1

( )

-1), μ μ

σ μ

μ
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APP13-9

2. DETERMINING THE NUMBER OF SAMPLES 

REQUIRED FOR COMPLIANCE MONITORING

This section provides some statistical tools for selection of a monitoring frequency when effluent 

data is available.

It is recommended that the permit writer use formula 3 with a confidence level of 90% and a 

relative error (dr) around the mean of no larger than 20% (0.20) to derive a baseline monitoring 

frequency. Table 1 is compiled from formula 3 for several combinations of confidence level, 

relative error and coefficients of variation. The rest of this section provides background material.

An effluent limit is a control parameter to assure that the long term average (LTA) of a 

wastewater control device or practice is being maintained. The LTA may be derived from the 

performance of a wastewater treatment device or from a wasteload allocation necessary to meet 

water quality standards. We assume the number of samples required to demonstrate compliance 

is the same as that necessary to determine a mean of a sample from a population.

For a sampled population which is normally distributed, in which the samples are not correlated 

over time or space, and in which the number of elements in the sampled population (N) is large 

relative to the standard deviation (σ), the number of samples (n) required to estimate a 

population mean is:

n = (Z1-α/2σ/d)

2

where

Z1-α/2 is the standard normal deviate that cuts off (100α/2)% of the tails of a standard normal 

distribution and 

σ= standard deviation of the sampled population and 

d = error around the mean.

This formula is for a two tailed test where the sample mean may be higher or lower than the true 

mean. In our situation we are only concerned with the situation in which the sample mean is 

higher than the true mean. Therefore, a one-tailed test is appropriate.

n = (Z1-α σ/d)

2 (1

(from Gilbert 1987)
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APP13-10

To estimate a population mean with a error (d) of 20 (plus or minus 10) with a 10% probability 

of type I error (α)when the standard deviation (σ) of the population is 50 requires

n = (Z0.10 50/20)2 = (1.2816*50/20)2 = 10.2 ≈10 samples.

This assumes the data are independently, normally distributed and not correlated over time or 

space.

Effluent data is typically lognormally distributed (Schaeffer, et al. 1980 ) but parametric statistics 

( Χ and s

2 ) are the best estimators of the population parameters if the coefficient of variation 

(η ) is less than 1.2 (Gilbert 1987). A typical coefficient of variation (η ) for conventional 

pollutants from domestic wastewater treatment plants is 0.6. Other pollutants and industrial 

treatment processes typically have a higher CV of 1 to 1.5.

An adjustment for autocorrelation can be made to the formulas for sample numbers if necessary. 

This adjustment increases the number of samples required.

If the standard deviation is uncertain (because of limited previous sampling) then the t

distribution should be used in the place of the standard normal distribution 

n = (t1− n−1 d)

2

α , σ / (2

and the process of determining n becomes iterative.

Start with equation 1 above and use a Z value to approximate n,

n ( )

n

1

2

1

12816 50 20

10

= ∗

≅

. /

then go to a t table to find t0.90, 9 which is 1.383. Placing this value into equation 2 gives 12.

n = (1383∗50 ÷ 20) = 1195 ≅ 12 2 . .

Placing the t value for t.90, 11 which is 1.363 into equation 2 gives 11.6 which is approximately 

12 which then is the answer.

The margin of error can be expressed as relative error (dr) of the mean instead of a absolute value 

and the coefficient of variation (η = σ/μ) can be used as the measure of variability. The formula 

then becomes

n = (Z1− dr )

2

αη / (3

(from Gilbert 1987)

and a table can be produced of some common values (Table 1).
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APP13-11

Table 1. Sample sizes required for Estimating the True Mean μ

Coefficient of Variation (η)

Confidence level

(1-α)

Relative Error

dr 0.60 1.00

.80 .10 26 72

(Z0.80 = .846) .20 6 18

.30 3 8

.50 1 3

.85 .10 41 113

(Z0.85 =1.062) .20 10 28

.30 5 13

.50 2 5

.90 .10 59 164

(Z0.90 = 1.282) .20 15 41

.30 7 18

.50 2 7

.95 .10 97 271

(Z0.95 = 1.645) .20 24 68

.30 11 30

.50 4 11

.99 .10 195 541

(Z0.99 =2.326) .20 49 135

.30 22 60

.50 8 22

The permit writer may adjust sample sizes from Table 1 according to factors discussed in section 

1.3.1 of Chapter XIII.

Formula 3 can be adjusted for uncertainty of the standard deviation by use of the t distribution 

and an iterative process as in formula 2. The number of samples required for a given confidence 

level, relative error and cv will be slightly higher using the t distribution, however, not 

significant for the extra effort.

Zar (1996) presents an alternative method for determining n, the number of samples to determine 

the mean with specified type I (α) and type II (β) error probabilities, as;

n

s = t + t

2

2 1 1

2

δ α υ β υ ( ) ( ), ( ), (4

where

s

2 is the sample variance estimated with v degrees of freedom
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APP13-12

β is the probability of type II error

δ is the size of the error around the mean (d from above)

α, and t are defined as above.

In this equation the number of data required to calculate a confidence interval of a specified 

width depends upon: 1) the width desired - narrow widths require more samples 2) the variability 

in the population - larger variability requires larger sample size 3) the confidence level (type I 

error) and 4) the assurance that the confidence interval will be no larger than that specified (type 

II error).

This formula is also iterative.

To determine the number of samples required to estimate the mean of a sample with a 90% 

probability that the 95% confidence interval will be no wider than 3 mg/l (the effluent limit is 30 

mg/l), then δ = 3 mg/l, β= 0.10, 1-α = 0.95, and α = 0.05. Assume an estimate of the population 

variance from previous sampling : s2 = 18.0388 with v = 24. If we start with a guess of 8 

samples per month then 

t0.05(1),7 = 1.895 and t0.10,(1),7 = 1.415

Using equation 4,

n

s = t + t

2

2 1 1

2

δ α υ β υ ( ) ( ), ( ),

n = (18.0388/9)(1.895+1.415)2

n = 22

for n = 22, t0.05(1),21 = 1.721 and t0.10,(1),21 = 1.323

n = (18.0388/9)(1.721+1.323)2

n = 19

for n = 19, t0.05(1),18 = 1.734 and t0.10(1), 18 = 1.330

n = (18.0388/9)(1.734+1.330)2

n = 19

This formula gives a higher n because of the additional constraint of the type II error.

AN INDUSTRIAL EXAMPLE
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APP13-13

A permit manager proposes to use the following data to derive performance-based effluent limits 

for a discharge from a metal facility. The data are metal concentrations in mg/l from a settling 

basin. The permit writer wants to know the number of samples to determine the monthly 

average such that the type I error (false judgment of noncompliance) will be 5% with a 10% 

interval around the mean.

Mean 0.627260274

Standard Error 0.010826197

Median 0.59

Mode 0.5

Standard 

Deviation

0.206834198

Sample Variance 0.042780385

Kurtosis 5.752860027

Skewness 1.644693358

CV 0.33

Range 1.7

Minimum 0.29

Maximum 1.99

Sum 228.95

Count 365

Confidence 

Level(95.0%)

0.02128972

99th percentile = 0.2135155

A. Using formula 1 to determine the number of samples per month to determine a monthly 

average , with d = 0.06 (10% of the mean), and α =0.05. The data standard deviation s is 

used as an estimator of σ.

n = (Z1-α/2σ/d)

2

n = (1.645 * 0.2068 / 0.06)2 = 32 samples/month
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APP13-14

B. Using formula 2, d = 0.06 or 10% of the mean, α =0.05 and, the data standard deviation, s, as 

an estimator of σ.

n = (t1− 2 n−1 d)

2

α/ , σ /

The Z value is used as an initial estimator for t.

n = (Z.95* 0.2068 / 0.06)2 = (1.645 * 0.2068 / 0.06)2 = 32

n = (t.95,31 * 0.2068 / 0.06) 2 = (1.696 * 0.2068 / 0.06)2 = 34

n = (t.95,33 * 0.2068 / 0.06) 2 = (1.693 * 0.2068 / 0.06)2 = 34 samples/month.

C. Using formula 3 with the coefficient of variation (η) = 0.33, relative error (dr) = 0.10 and α = 

0.05.

n = (Z1− dr )

2

αη /

n = (1.645 * 0.33 / 0.10)2 = 29 samples/month

Using t values in this formula will increase n slightly to 31.

D. Using formula 4 to determine n with β = 0.1 (probability noncompliance is occurring but not 

detected).

n

s = t + t

2

2 1 1

2

δ α υ β υ ( ) ( ), ( ),

( )

n

n

= +

=

0 0428

0 0627

1645 1282

93

2

2 .

. ( . . )