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Background 

The Office of Wastewater Management of the U.S. Environmental Protection Agency’s (EPA’s) 

Office of Water prepared this guidance document to assist municipalities that own or operate publicly 

owned treatment works (POTWs) in developing and implementing local pretreatment programs. 

Section 402(b) of the Clean Water Act (CWA) provides for EPA to authorize a State to 

administer its own National Pollutant Discharge Elimination System (NPDES) permit program. In order 

to be authorized, a State program must include adequate authority to issue permits that ensure compliance 

with the CWA including section 307(b) pretreatment standards. The program must ensure that permits 

issued to POTWs include a program to assure compliance with pretreatment standards by significant 

sources introducing pollutants subject to such standards to the POTW. [Section 402(b)(8), 33 U.S.C. § 

1342(b)(8)]. This guidance will assist POTWs in their efforts to meet their requirement to develop 

pretreatment programs. 

Disclaimer 

The discussion in this document is intended solely as guidance. This guidance is not a 

regulation nor does not it substitute for any requirements under the CWA or EPA’s regulations. 

Thus, it does not impose legally binding requirements on EPA, States, municipalities or the regulated 

community. The general descriptions provided in this document may not apply to a particular situation 

based upon the circumstances. This guidance does not confer legal rights or impose legal obligations 

upon any member of the public. 

Among other things, the document describes existing requirements with respect to industrial 

dischargers and POTWs under the CWA and its implementing regulations at 40 CFR 122, 123, 124, and 

403 and chapter I, subchapter N. While EPA has made every effort to ensure the accuracy of the 

discussion in this guidance, a discharger’s obligations are determined, in the case of directly discharging 

POTWs, by the terms of their NPDES permit and EPA’s regulations or, in the case of indirect 

dischargers, by permits or equivalent control mechanisms issued to POTW industrial users or by 

regulatory requirements. Nothing in this guidance changes any statutory or regulatory requirement. In 

the event of a conflict between the discussion in this guidance and any permit or regulation, the permit or 

regulation would be controlling. EPA and local decision makers retain the discretion to adopt 

approaches on a case-by-case basis that differ from those described in this guidance where appropriate 

and authorized by EPA regulations, State law, or local ordinances. 

Mention of trade names or commercial products does not constitute endorsement or 

recommendation for their use. 

EPA may decide to revise this guidance without public notice to reflect changes in the Agency’s 

approach to implementing pretreatment standards or to clarify and update text. To determine whether the 

Agency has revised this guidance and/or to obtain copies, contact the Water Permits Division at 

(202) 564-9545. You can also determine whether EPA has revised or supplemented the information in 

this guidance by accessing the document at: http://www.epa.gov/NPDES/pretreatment. 
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 1 2 3 4 5 6

CONTENTS

Acronyms .......................................................................... xi

Glossary .......................................................................... xv

Chapter 1 - Introduction ............................................................. 1 - 1

1.1 Purpose of This Manual ................................................... 1 - 1

1.2 Local Limits Statutory Authority ............................................ 1 - 1

1.3 Local Limits Process ..................................................... 1 - 1

1.4 National Pretreatment Standards ............................................ 1 - 2

1.4.1 Prohibited Discharges ................................................ 1 - 2

1.4.2 Categorical Standards ................................................ 1 - 3

1.4.3 Local Limits ....................................................... 1 - 3

1.5 The Relationship of Local Limits to Categorical Standards ....................... 1 - 3

1.6 Organization of the Guidance Manual ........................................ 1 - 4

Chapter 2 - Overview of Local Limits Development ...................................... 2 - 1

2.1 Local Limits Decision Tree ................................................ 2 - 1

2.2 MAHL Approach to Local Limits Development ................................ 2 - 3

2.2.1 Step 1: Determine Pollutants of Concern ................................ 2 - 4

2.2.2 Step 2: Collect and Analyze Data ....................................... 2 - 4

2.2.3 Step 3: Calculate MAHLs for Each POC ................................. 2 - 4

2.2.4 Step 4: Designate and Implement Local Limits ............................ 2 - 4

2.2.5 Step 5: Addressing Collection System Concerns ........................... 2 - 4

Chapter 3 - Determining Pollutants of Concern .......................................... 3 -

3.1 National POCs .......................................................... 3 - 1

3.2 Other Potential POCs ..................................................... 3 -

3.2.1 NPDES Permit Conditions ............................................ 3 - 2

3.2.2 Water Quality Criteria ............................................... 3 -

3.2.3 Sludge Quality Standards ............................................. 3 - 4

3.2.4 Air Quality Standards ................................................ 3 -

3.2.5 Resource Protection Criteria .......................................... 3 - 5

3.2.6 Prohibitions on Treatment Plant Interference ............................. 3 -

3.2.7 Prohibitions to Protect the Treatment Works, Collection System, and Workers . . . 3 - 5

3.2.8 Scans of POTW Influent, Effluent, and Sludge to Identify Priority Pollutants .... 3 -

3.2.9 Evaluations of Industrial and Commercial Discharges ...................... 3 - 7

3.2.10 Hauled Waste ..................................................... 3 - 8

3.2.11 Remediation Site Waste ............................................. 3 - 9

3.2.12 Hazardous Wastes ................................................. 3 - 11

3.3 Approval Authority Screening Process to Select Pollutants for Local Limits Sampling

Program and Limit Development ........................................... 3 - 11

3.4 Summary ............................................................. 3 - 12

Chapter 4 - Data Needed to Develop Local Limits ........................................ 4 - 1

4.1 Sampling Locations ...................................................... 4 - 2

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4.1.1 At the POTW ...................................................... 4 - 2

4.1.2 In the Collection System ............................................. 4 - 3

4.1.3 At Industrial Users .................................................. 4 - 4

4.2 Pollutants for Which POTWs Should Sample .................................. 4 - 4

4.3 Sampling Frequencies .................................................... 4 - 5

4.3.1 Sampling Frequencies for Initial Program Development ..................... 4 - 5

4.3.2 Sampling Frequencies for Ongoing Evaluation ............................ 4 - 6

4.4 Other Sampling Tips ..................................................... 4 - 7

4.5 Sampling Methods ....................................................... 4 - 8

4.6 Analytical Methods ..................................................... 4 - 10

4.7 Information Collection and Maintenance .................................... 4 - 13

4.8 Review and Evaluation of Analytical Results ................................. 4 - 13

4.9 Flow Data ............................................................. 4 - 14

4.9.1 Total POTW Flow ................................................. 4 - 14

4.9.2 Sludge Flow to the Digester .......................................... 4 - 14

4.9.3 Sludge Flow to Disposal ............................................ 4 - 14

4.9.4 Flows from Controlled Sources ....................................... 4 - 15

4.9.5 Flows from Uncontrolled Sources ..................................... 4 - 16

4.10 Summary ............................................................ 4 - 16

Chapter 5 - Calculation of Maximum Allowable Headworks Loadings ........................ 5 - 1

5.1 Calculation of Removal Efficiencies ......................................... 5 - 1

5.1.1 Removal Efficiency Calculation Methodologies ........................... 5 - 3

5.1.2 Guidance on Using Different Methodologies ............................. 5 - 5

5.1.3 Data Quality ....................................................... 5 - 6

5.1.4 Applying Removal Efficiencies Reported by Others ........................ 5 - 7

5.2 Calculation of Allowable Headworks Loadings ................................ 5 - 8

5.2.1 Determination of Suitable Environmental Criteria ......................... 5 - 8

5.2.2 Effluent-Quality Based AHLs ........................................ 5 - 11

5.2.3 Sludge-Quality Based AHLs ......................................... 5 - 14

5.2.4 Inhibition-Based AHLs ............................................. 5 - 19

5.2.5 Air-Quality Based AHLs ............................................ 5 - 21

5.3 AHLs for Conventional and Non-Conventional Pollutants ....................... 5 - 21

5.3.1 BOD/TSS ........................................................ 5 - 22

5.3.2 Ammonia ........................................................ 5 - 23

5.3.3 Oil and Grease .................................................... 5 - 23

5.4 Determination of the Maximum Allowable Headworks Loading ................. 5 - 25

5.5 Sample MAHL Calculation .............................................. 5 - 25

5.6 Summary ............................................................. 5 - 26

Chapter 6 - Designating and Implementing Local Limits ................................... 6 - 1

6.1 Determination of the Need for New Local Limits ............................... 6 - 1

6.1.1 Actual Loadings vs. MAHL ........................................... 6 - 2

6.1.2 Noncompliance Due to Pass Through or Interference ....................... 6 - 2

6.1.3 Establishing Local Limits for Conventional Pollutants ...................... 6 - 2

6.2 Calculation of Maximum Allowable Industrial Loading ......................... 6 - 4

6.2.1 Uncontrolled Sources ............................................... 6 - 5

6.2.2 Hauled Waste ...................................................... 6 - 6

6.2.3 Safety Factor ...................................................... 6 - 6

6.2.4 Expansion/Growth Allowance ......................................... 6 - 7

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6.3 Comparison of MAIL Allocation and Implementation Methods ................... 6 - 7

6.4 Allocation of MAILs Among Controlled Sources ............................... 6 - 8

6.4.1 Limit Duration ..................................................... 6 - 8

6.4.2 Allocation Approaches .............................................. 6 - 10

6.5 Common Sense Assessment ............................................... 6 - 13

6.6 Best Management Practices ............................................... 6 - 14

6.7 Approval Authority and Adoption Process ................................... 6 - 15

6.8 Public Participation ..................................................... 6 - 17

6.9 Control Mechanisms .................................................... 6 - 18

6.10 Summary ............................................................ 6 - 19

Chapter 7 - Local Limits Reviews and Detailed Re-Evaluations ............................. 7 - 1

7.1 Reviews ............................................................... 7 - 1

7.1.1 Comparison of Current Loadings with MAHLs ............................ 7 - 1

7.1.2 Review of Compliance History ........................................ 7 - 3

7.1.3 Next Steps ......................................................... 7 - 3

7.2 Detailed Local Limits Re-Evaluation ........................................ 7 - 3

7.2.1 Step 1: Assess Current Conditions ...................................... 7 - 4

7.2.2 Step 2: Collect and Analyze Data ....................................... 7 - 5

7.2.3 Step 3: Recalculate Existing, or Determine New, MAHLs ................... 7 - 6

7.2.4 Step 4: Implement the Local Limits ..................................... 7 - 6

7.3 Summary .............................................................. 7 - 7

Chapter 8 - Local Limits to Address Concerns About Collection Systems ...................... 8 - 1

8.1 Fires and Explosions ..................................................... 8 - 1

8.1.1 Flashpoint Limit .................................................... 8 - 1

8.1.2 Lower Explosive Limit Monitoring ..................................... 8 - 2

8.1.3 Sample Headspace Monitoring ........................................ 8 - 2

8.1.4 Flammability and Explosivity Discharge Screening Levels .................. 8 - 3

8.2 Corrosion .............................................................. 8 - 4

8.2.1 pH ............................................................... 8 - 4

8.2.2 Corrosive Pollutants ................................................. 8 - 4

8.3 Flow Obstructions ....................................................... 8 - 5

8.4 Temperature ............................................................ 8 - 6

8.5 Toxic Gases, Vapors, and Fumes ............................................ 8 - 7

8.6 Summary .............................................................. 8 - 8

Chapter 9 - Questions and Answers ................................................... 9 - 1

9.1 General ................................................................ 9 - 1

9.2 Potential Pollutants of Concern ............................................. 9 - 3

9.3 Sampling and Analysis ................................................... 9 - 3

9.4 Determining MAHLs ..................................................... 9 - 5

9.5 Establishing Local Limits ................................................. 9 - 7

9.6 Oversight and Public Participation ......................................... 9 - 12

9.7 Implementation and Enforcement of Local Limits ............................. 9 - 13

9.8 POTW Operations ...................................................... 9 - 14

9.9 Industrial Users ........................................................ 9 - 14

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List of Tables 

Table 1-1: Comparison of Categorical Pretreatment Standards and Local Limits ................ 1 - 4

Table 3-1: Selected Information Sources for Determining Potential POCs ..................... 3 - 8

Table 4-1: Minimum Recommended Sampling Days for Initial Local Limits Development ........ 4 - 6

Table 4-2: Minimum Recommended Sampling Frequencies for Ongoing Local Limits

Analysis and Evaluation ................................................... 4 - 7

Table 4-3: How to Prepare a Flow-Proportioned Grab Composite Sample ..................... 4 - 10

Table 4-4: Example of a Flow-Proportioned Average

Based on Grab Sample Results and Flow Intervals .............................. 4 - 10

Table 4-5: MDLs (μg/L) for EPA Wastewater Analytical Methods .......................... 4 - 12

Table 5-1: Options for Managing Sampling Results Below the ML in Removal 

Efficiency Calculations .................................................... 5 - 6

Table 5-2: Suggested Criteria or Standards to be Considered

For Each POC in the Development of AHLs .................................... 5 - 9

Table 5-3: Land Application Requirements ............................................. 5 - 15

Table 6-1: Data for Implementation of MAHLs .......................................... 6 - 4

Table 6-2: Options for Allocating and Implementing Local Limits ........................... 6 - 9

List of Exhibits 

Exhibit 2-1: Example MAHL Determination Based on AHLs ............................... 2 - 3

Exhibit 2-2: Example MAIL Determination ............................................. 2 - 3

Exhibit 3-1: EPA’s 15 POCs ......................................................... 3 - 2

Exhibit 3-2: Pollutants Regulated Under 40 CFR Part 503 .................................. 3 - 4

Exhibit 5-1: Be Conservative in Selecting Criteria ....................................... 5 - 11

Exhibit 5-2: How to Convert Dissolved Metals Criteria to Total Metals Criteria ................ 5 - 13

Exhibit 5-3: The Challenge in Determining Plant Inhibition Values .......................... 5 - 19

Exhibit 5-4: Inhibition Value Study by Chesterfield County (VA) ........................... 5 - 19

Exhibit 5-5: Less BOD, More Ammonia and Phosphorous ................................. 5 - 22

Exhibit 5-6: City of Richland (WA) POTW Evaluates FOG Removal Efficiency ............... 5 - 24

Exhibit 5-7: City of Portland (OR) Uses Current Influent Loading to Develop 

Non-Polar FOG Local Limit .............................................. 5 - 25

Exhibit 6-1: Safety Factor Example .................................................... 6 - 6

Exhibit 6-2: Background Allocation .................................................. 6 - 10

Exhibit 6-3: Local Limits Documentation .............................................. 6 - 18

Exhibit 7-1: Why Local Limits Should Be Re-evaluated ................................... 7 - 3

Exhibit 7-2: When to Recalculate or Develop Local Limits ................................. 7 - 4

Exhibit 7-3: An Example of Changing the Method for Allocating Local Limits ................. 7 - 7

List of Equations 

Equation 5.1: Removal Efficiency Calculated Using Average Daily Removal Efficiency .......... 5 - 3

Equation 5.2: Removal Efficiency Calculated Using Mean Removal Efficiency ................. 5 - 4

Equation 5.3: Plant Removal Efficiency Calculated Using ADRE and Sludge Data .............. 5 - 5

Equation 5.4: Plant Removal Efficiency Calculated Using MRE and Sludge Data ............... 5 - 5

Equation 5.5: AHL Based on NPDES Permit Limit ...................................... 5 - 11

Equation 5.6: AHL Based on Water Quality Criteria ..................................... 5 - 12

Equation 5.7: Converting Table 2 Cumulative Loading Rates to Dry Sludge Concentrations ...... 5 - 16

Equation 5.8: Converting Table 4 Annual Loading Rates to Dry Sludge Concentrations ......... 5 - 16

Equation 5.9: AHLs Based on Sludge Land Application and Surface Disposal Criteria .......... 5 - 17

Equation 5.10: AHLs Based On Secondary Treatment Inhibition............................ 5 - 20

Equation 5.11: AHLs Based On Tertiary Treatment Inhibition .............................. 5 - 20

viii
Equation 5.12: AHLs Based On Sludge Digestion Inhibition (Conservative Pollutants) .......... 5 - 21

Equation 5.13: AHLs Based On Sludge Digestion Inhibition (Non-conservative Pollutants) ...... 5 - 21

Equation 5.14: AHLs Based On Air Criteria and Volatization Rates ......................... 5 - 21

Equation 5.15: AHLs Based On Air Criteria and Existing Emissions ........................ 5 - 21

Equation 6.1: Actual Loading vs. MAHL Calculation ..................................... 6 - 2

Equation 6.2: MAIL Calculation ...................................................... 6 - 4

Equation 6.3: Uncontrolled Loading Calculation ......................................... 6 - 5

Equation 6.4: IU Contributory Flow Calculation ........................................ 6 - 11

Equation 6.5: Mass Proportion Method for a Mass-Based Local Limit ....................... 6 - 11

Equation 6.6: Mass Proportion Method for a Concentration-Based Limit ..................... 6 - 11

Equation 6.7: Uniform Allocation of Background Loading ................................ 6 - 11

Equation 6.8: Uniform Concentration Limit Calculation .................................. 6 - 12

List of Figures 

Figure 2-1: POTW Local Limits Decision Tree .......................................... 2 - 2

Figure 3-1: Determining Hauled Waste Characteristics ................................... 3 - 10

Figure 5-1: Process Flow Diagram for Calculating MAHL for a Single POC ................... 5 - 2

Figure 5-2: Decile Results for Hypothetical POTW ....................................... 5 - 4

Figure 5-3: POTW Flow Diagram and Environmental Criteria ............................. 5 - 10

Appendices 

Appendix A - List of Supplemental Documents .......................................... A-1

Appendix B - Industrial Categories with Pretreatment Standards ............................. B-1

Appendix C - Pollutants Regulated by Categorical Pretreatment Standards ..................... C-1

Appendix D - Clean Water Act Priority Pollutants and the Federal Water Quality Criteria ......... D-1

Appendix E - Federal Sewage Sludge Standards .......................................... E-1

Appendix F - Toxicity Characteristic Leachate Procedure (TCLP) Limitations ................... F-1

Appendix G - Literature Inhibition Values .............................................. G-1

Appendix H - Closed-cup Flashpoints for Select Organic Compounds ........................ H-1

Appendix I - Discharge Screening Levels and Henry’s Law Constants for Organic Compounds ..... I-1

Appendix J - OSHA, ACGIH and NIOSH Exposure Levels .................................. J-1

Appendix K - Landfill Leachate Loadings .............................................. K-1

Appendix L - Hauled Waste Loadings .................................................. L-1

Appendix M - Hazardous Waste Constituents - RCRA Appendix VIII ........................ M-1

Appendix N - Statistical Approach to Determining Sampling Frequency....................... N-1

Appendix O - Minimizing Contamination ............................................... O-1

Appendix P - Methods for Calculating Removal Efficiency .................................. P-1

Appendix Q - Methods for Handling Data Below Detection Level ........................... Q-1

Appendix R - Priority Pollutant Removal Efficiencies ..................................... R-1

Appendix S - Specific Gravity of Sludge ................................................ S-1

Appendix T - Sludge AHL Equations Using Flow (in metric units) ............................ T-1

Appendix U - POTW Configurations .................................................. U-1

Appendix V - Domestic Pollutant Loadings ............................................. V-1

Appendix W - Best Management Practices Mini-Case Studies ............................... W-1

Appendix X - Region 1, Reassessment of Technically Based Industrial Discharge Limits Checklist . X-1

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x
ACRONYMS

ACGIH American Conference of Governmental Industrial Hygienists

ADRE Average Daily Removal Efficiency

AHL Allowable Headworks Loading

AMSA Association of Metropolitan Sewerage Agencies

BPJ Best Professional Judgment

BMP Best Management Practice

BOD Biochemical Oxygen Demand

CAA Clean Air Act

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CFR Code of Federal Regulations

CIU Categorical Industrial User

CWA Clean Water Act

CWF Combined Wastestream Formula

EPA United States Environmental Protection Agency

FOG Fats, Oils, and Greases

HAP Hazardous Air Pollutant

HEM Hexane Extractable Materials

ICP Inductively Coupled Plasma

IF Interval Flow

IQR Interquartile Range

IU Industrial User

IWS Industrial Waste Survey

I&I Inflow and Infiltration

xi 
LEL Lower Explosive Limit

MAHL Maximum Allowable Headworks Loading

MAIL Maximum Allowable Industrial Loading

MCL Maximum Contaminant Level

MDL Method Detection Limit

MG Million Gallons

MGD Million Gallons per Day

ML Minimum Level of Quantitation

MLE Maximum Likelihood Estimation

MRE Mean Removal Efficiency

MSDS Material Safety Data Sheet

NAAQS National Ambient Air Quality Standards

NESHAP National Emission Standards for Hazardous Air Pollutants

NIOSH National Institute for Occupational Safety and Health

NPDES National Pollutant Discharge Elimination System

OSHA Occupational Safety and Health Administration

PEL Permissible Exposure Limit

POC Pollutant of Concern

POTW Publicly Owned Treatment Works

PS Percent Solids

QA/QC Quality Assurance/Quality Control

RCRA Resource Conservation and Recovery Act

REL Recommended Exposure Limit

ROS Regression Order Statistic

SGT-HEM Silica Gel Treated Hexane Extractable Materials

xii 
SIP State Implementation Plan

SIU Significant Industrial User

SUO Sewer Use Ordinance

STEL Short-Term Exposure Limit

TCLP Toxicity Characteristic Leaching Procedure

TLV Threshold Limit Value

TMDL Total Maximum Daily Load

TPH Total Petroleum Hydrocarbons

TRE Toxicity Reduction Evaluation

TSD Technical Support Document

TSS Total Suspended Solids

TWA-TLV Time Weighted Average Threshold Limit Value

UIC Underground Injection Control

VOC Volatile Organic Compound

WET Whole Effluent Toxicity

WQC Water Quality Criteria

WQS Water Quality Standards

WWTP Wastewater Treatment Plant

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xiv
GLOSSARY

1Q10. The lowest average flow for a one-day period that is expected to occur once every ten years. 

1Q10 flows are generally available in the background documentation for the POTW’s NPDES permit and 

also may be obtained from the local district office of the US Geological Survey 

(http://water.usgs.gov/local_offices.html). 

7Q10. The lowest average flow for a seven-day period that is expected to occur once every ten years. 

7Q10 flows are generally available in the background documentation for the POTW’s NPDES permit and 

also may be obtained from the local district office of the US Geological Survey 

(http://water.usgs.gov/local_offices.html). 

Biochemical Oxygen Demand (BOD). A measurement of the amount of oxygen utilized by the 

decomposition of organic material, over a specified time period (usually 5 days) in a wastewater sample. 

It is used as a measurement of the readily decomposable organic content of wastewater. When five days 

are prescribed the acronym BOD5 is used. 

Allowable Headworks Loading (AHL). The estimated maximum loading of a pollutant that can be 

received at a POTW’s headworks that should not cause a POTW to violate a particular treatment plant or 

environmental criterion. AHLs are developed to prevent interference or pass through. 

American Conference of Governmental Industrial Hygienists (ACGIH). The American Conference 

of Governmental Industrial Hygienists is a member-based organization and community of professionals 

that advances worker health and safety through education and the development and dissemination of 

scientific and technical knowledge. 

Approval Authority. The Director in a NPDES State with an approved State pretreatment program or 

the appropriate EPA Regional Administrator in a non-NPDES State or NPDES State without an approved 

State pretreatment program (40 CFR 403.3). The Approval Authority approves POTW pretreatment 

programs, oversees POTW program implementation, and assumes the responsibility of the Control 

Authority for those POTWs that do not have a pretreatment program. 

Clean Water Act (CWA). The primary Federal law that protects our nation’s waters, including lakes, 

rivers, aquifers and coastal areas. It provides for the establishment of comprehensive programs that 

include standards, technical tools, permitting, enforcement and financial assistance to address the many 

causes of pollution and poor water quality, including municipal and industrial wastewater discharges, 

polluted runoff from urban and rural areas, and habitat destruction. 

Clean Air Act (CAA). The Federal Clean Air Act is the Federal law that forms the basis for the national 

air pollution control effort. Basic elements of the act include National Ambient Air Quality Standards 

for major air pollutants, Hazardous Air Pollutants Standards, State attainment plans, motor vehicle 

emissions standards, stationary source emissions standards and permits, acid rain control measures, 

stratospheric ozone protection, and enforcement provisions. 

Code of Federal Regulations (CFR). A codification of the general and permanent rules published in 

the Federal Register by the executive departments and agencies of the Federal Government. The CFR is 

divided into 50 titles, which represent broad areas subject to Federal regulation. EPA’s regulations are in 

xv 
Title 40. Each title is divided into chapters, which usually bear the name of the issuing agency. Each 

chapter is further subdivided into parts covering specific regulatory areas. Large parts may be subdivided 

into subparts. All parts are organized in sections, and most citations to the CFR are provided at the 

section level. 

Combined Wastestream Formula (CWF). As defined in 40 CFR 403.6 (e), a procedure under EPA’s 

pretreatment regulations for calculating alternative discharge limits at industrial facilities where a 

regulated wastestream from a categorical industrial user is combined with other wastestreams prior to 

treatment. 

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). CERCLA, 

commonly known as Superfund, was enacted by Congress in 1980. This law created a tax on the 

chemical and petroleum industries and provided broad Federal authority to respond directly to releases or 

threatened releases of hazardous substances that may endanger public health or the environment. 

Control Authority. As defined in 40 CFR 403.12, the POTW if the POTW’s submission for its 

pretreatment program (40 CFR 403.3(t)) has been approved in accordance with the requirements of 40 

CFR 403.11. If the submission has not been approved, the Control Authority is the Approval Authority. 

The Control Authority is responsible for implementing the pretreatment program, including 

establishment of control mechanisms for compliance assessment and enforcement of national standards, 

categorical standards, and local limits. 

Conservative Pollutants. Pollutants that are presumed not to be destroyed, biodegraded, chemically 

transformed, or volatilized within the POTW. Conservative pollutants introduced to a POTW ultimately 

exit the POTW solely through the POTW’s effluent and sludge. Most metals are considered conservative 

pollutants. 

Flashpoint. The lowest temperature at which vapor combustion will propagate away from its source of 

ignition. 

Headworks. The point at which wastewater enters a wastewater treatment plant. The headworks may 

consist of bar screens, comminuters, a wet well or pumps. 

Industrial User (IU). Non-domestic source of pollutants into a POTW regulated under Section 307(b), 

(c) or (d) of the Clean Water Act. 

Industrial Waste Survey (IWS). The process of identifying and locating industrial users and 

characterizing their industrial discharges. 

Inflow and Infiltration (I&I). Infiltration is the seepage of groundwater into a sewer system, including 

service connections. Seepage frequently occurs through defective or cracked pipes, pipe joints, 

connections or manhole walls. Inflow is the water discharged into a sewer system and service 

connections from sources other than regular connections. This includes flow from yard drains, 

foundation drains and around manhole covers. Inflow differs from infiltration in that it is a direct 

discharge into the sewer rather than a leak or seepage into the sewer itself. 

Inhibition. Inhibition occurs when pollutant levels in a POTW’s wastewater or sludge cause operational 

problems for biological treatment processes involving secondary or tertiary wastewater treatment and 

alter the POTW’s ability to adequately remove BOD, TSS, and other pollutants. 

xvi 
Interference. EPA uses the term “interference” in its regulations to describe a discharge that, alone or 

with discharges from other sources, inhibits or disrupts a POTW, its treatment processes and operations, 

or its sludge processes, use, or disposal and, therefore, causes a violation of the POTW’s NPDES permit, 

increases the magnitude or duration of such a violation, or prevents the proper use or disposal of sewage 

sludge in compliance with the Clean Water Act, Solid Waste Disposal Act, Toxic Substance Control 

Acts, or the Marine Protection, Research and Sanctuaries Act. 

Lower Explosive Limit (LEL). The minimum concentration in air at which a gas or vapor will explode 

or burn in the presence of an ignition source. 

Maximum Contaminant Level (MCL). The maximum permissible level of a contaminant in water 

delivered to any user of a public water system. An MCL is an enforceable standard. 

Maximum Allowable Industrial Loading (MAIL). The estimated maximum loading of a pollutant that 

can be received at a POTW’s headworks from all permitted industrial users and other controlled sources 

without causing pass through or interference. The MAIL is usually calculated by applying a safety factor 

to the MAHL and discounting for uncontrolled sources, hauled waste and growth allowance. 

Maximum Allowable Headworks Loading (MAHL). The estimated maximum loading of a pollutant 

that can be received at a POTW’s headworks without causing pass through or interference. The most 

protective (lowest) of the AHLs (see definition) estimated for a pollutant. 

Method Detection Limit (MDL). The minimum concentration of an analyte that can be measured and 

reported with 99 percent confidence that the analyte concentration is present as determined by a specific 

laboratory method in 40 CFR Part 136, Appendix B. 

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 ML is calculated by multiplying the MDL 

by 3.18 and rounding the result to the number nearest (1, 2, or 5) x 10n

 where n is an integer. 

National Ambient Air Quality Standards (NAAQS). Standards established by EPA that apply for 

outside air throughout the country. 

National Institutes for Occupational Safety and Health (NIOSH). The National Institute for 

Occupational Safety and Health is the Federal agency responsible for conducting research and making 

recommendations for the prevention of work-related disease and injury. The Institute is part of the 

Centers for Disease Control and Prevention. 

National Pollutant Discharge Elimination System (NPDES). The permitting system established by 

the Clean Water Act, which regulates the discharge of pollutants into the waters of the United States. 

Such a discharge is prohibited unless a NPDES permit is issued by EPA or, where authorized, a State; or 

a Native American tribal government. 

Non-conservative Pollutants. Pollutants that are presumed to be destroyed, biodegraded, chemically 

transformed, or volatilized within the POTW to some degree. 

xvii 
Occupational Safety and Health Administration (OSHA). The Occupational Health and Safety 

Administration is part of the U.S. Department of Labor. It regulates worker conditions and was founded 

in 1971 to save lives, prevent injuries and protect the health of America’s workers. 

Pass Through. A discharge that enters the waters of the United States from a POTW in quantities or 

concentrations that, alone or with discharges from other sources, either causes a violation of any 

requirement of the POTW’s NPDES permit, or increases the magnitude or duration of a violation of the 

POTW’s NPDES permit. 

Pollutant of Concern (POC). Any pollutant that might reasonably be expected to be discharged to the 

POTW in sufficient amounts to pass through or interfere with the works, contaminate its sludge, cause 

problems in its collection system, or jeopardize its workers. 

Pretreatment. As defined in 40 CFR 403.3, “pretreatment” means the reduction of the amount of 

pollutants, the elimination of pollutants, or the alteration of the nature of pollutant properties in 

wastewater prior to or in lieu of discharging or otherwise introducing such pollutants into a POTW. 

Priority Pollutant. Pollutants listed by the EPA Administrator under Clean Water Act Section 307 (a). 

The list of the current 126 Priority Pollutants can be found in 40 CFR Part 423, Appendix A. 

Publicly Owned Treatment Works (POTW). A treatment works, as defined by Section 212 of the 

CWA, that is owned by the State or municipality. This definition includes any devices and systems used 

in the storage, treatment, recycling, and reclamation of municipal sewage or industrial wastes of a liquid 

nature. It also includes sewers, pipes and other conveyances only if they convey wastewater to a POTW 

treatment plant [40 CFR 403.3]. Privately owned treatment works, Federally owned treatment works, 

and other treatment plants not owned by municipalities are not considered POTWs. 

Resource Conservation and Recovery Act (RCRA). Passed by Congress in 1976, RCRA gave EPA 

the authority to control hazardous wastes from the “cradle to grave.” This includes the generation, 

transportation, treatment, storage, and disposal of hazardous waste. RCRA also set forth a framework for 

the management of non-hazardous wastes. The 1986 amendments to RCRA enabled EPA to address 

environmental problems that could result from underground tanks storing petroleum and other hazardous 

substances. RCRA focuses only on active and future facilities and does not address abandoned or 

historical sites (see CERCLA). The Federal Hazardous and Solid Waste Amendments are the 1984 

amendments to RCRA that required phasing out land disposal of hazardous waste. Some of the other 

mandates of this strict law include increased enforcement authority for EPA, more stringent hazardous 

waste management standards, and a comprehensive underground storage tank program. 

Sewer Use Ordinance (SUO). A legal mechanism implemented by a local government entity that sets 

out, among others, requirements for the discharge of pollutants into a POTW. 

Short-Term Exposure Level (STEL). Concentrations to which a worker should not be exposed for 

longer than 15 minutes and which should not be repeated more than four times per day, with at least one 

hour between exposures (commonly accepted exposure limits identified by the ACGIH). 

Significant Industrial User (SIU). As defined in 40 CFR 403.3, all users subject to Categorical 

Pretreatment Standards under 40 CFR 403.6 and 40 CFR chapter I, subchapter N; and any other 

industrial user that discharges an average of 25,000 gallons per day or more of process wastewater to a 

POTW (excluding sanitary, non-contact cooling and boiler blowdown wastewater); contributes a process 

xviii 
wastestream that makes up 5 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 defined in 40 CFR 

403.12(a) 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)]. 

State Implementation Plan (SIP). An EPA-approved State plan required by the Clean Air Act for the 

establishment, regulation, and enforcement of air pollution standards. 

Time Weighted Average Threshold Limit Value (TWA-TLV). The concentration to which a worker 

can be exposed for 8 hours per day, 40 hours per week and not have any acute or chronic adverse health 

effects (commonly accepted exposure limits identified by the ACGIH). 

Total Maximum Daily Load (TMDL). Total Maximum Daily Load is a calculation of the maximum 

amount of a pollutant from point and non-point sources that a waterbody can receive and still meet water 

quality standards, and an allocation of that amount to the pollutant's sources. The Clean Water Act, 

Section 303, establishes the water quality standards and TMDL programs. 

Total Suspended Solids (TSS). A measure of the suspended solids in wastewater, effluent, or water 

bodies, determined by tests for “total suspended non-filterable solids.” 

Toxicity Characteristic Leaching Procedure (TCLP). A laboratory procedure designed to predict 

whether a particular waste is likely to leach chemicals into groundwater at dangerous levels. Details are 

provided in 40 CFR Part 261. 

Volatile Organic Compound (VOC). As defined in 40 CFR 50.100, “volatile organic compounds” 

means any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic 

carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical 

reactions. 

Whole Effluent Toxicity (WET) Tests. Whole effluent toxicity is the aggregate toxic effect of an 

effluent measured directly by an aquatic toxicity test. Aquatic toxicity methods designed specifically for 

measuring WET have been codified in 40 CFR 136. WET test methods employ a suite of standardized 

freshwater, marine, and estuarine plants, invertebrates, and vertebrates to estimate acute and short-term 

chronic toxicity of effluents and receiving waters. 

xix 
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xx
CHAPTER 1 -

INTRODUCTION 

1.1 PURPOSE OF THIS MANUAL 

This manual provides guidance to municipalities on the development and implementation of local 

controls or limits on discharges to publicly owned treatment works (POTWs). This manual replaces the 

Guidance Manual on the Development and Implementation of Local Discharge Limitations Under the 

Pretreatment Program issued by the U.S. Environmental Protection Agency (EPA) in December 1987. 

The audience for this manual is the POTW personnel responsible for local pretreatment program 

implementation. The manual provides practical technical assistance and reasoned guidance on the 

following: 

C Determining pollutants of concern (POCs)

C Collecting and analyzing data

C Calculating maximum allowable headworks loadings (MAHLs) for each POC

C Designating and implementing local limits

C Performing local limits reviews and re-evaluations

C Developing local limits to address concerns about collection systems

Appendix A contains a list of supplemental EPA documents to this manual. If a POTW is located in a 

State with an approved pretreatment program, POTW personnel should also refer to guidance manuals 

and spreadsheets available from State Approval Authorities. 

1.2 LOCAL LIMITS STATUTORY AUTHORITY 

A component of the National Pollutant Discharge Elimination System (NPDES) Program, the National 

Pretreatment Program was developed by EPA to control the discharge of pollutants from POTWs. The 

statutory authority for the National Pretreatment Program lies in the Federal Water Pollution Control Act 

of 1972, which was amended by Congress in 1977 and renamed the Clean Water Act (CWA). Under 

Section 307(b), EPA must develop Pretreatment Standards that prevent the discharge of pollutants that 

pass through, interfere with, or are otherwise incompatible with POTWs. The 1977 amendments to the 

CWA required POTWs to ensure compliance with the pretreatment standards by each significant local 

source introducing pollutants subject to pretreatment standards into a POTW. To meet the requirements 

of the 1977 amendments, EPA developed the General Pretreatment Regulations for Existing and New 

Sources of Pollution [40 Code of Federal Regulations(CFR) Part 403]. 

1.3 LOCAL LIMITS PROCESS 

To protect its operations and to ensure that its discharges comply with State and Federal requirements, a 

POTW will design its local limits based on site-specific conditions. Among the factors a POTW should 

consider in developing local limits are the following: the POTW’s efficiency in treating wastes; its history 

of compliance with its NPDES permit limits; the condition of the water body that receives its treated 

effluent; any water quality standards that are applicable to the water body receiving its effluent; the 

POTW’s retention, use, and disposal of sewage sludge; and worker health and safety concerns. The 

General Pretreatment Regulations require the following: 

1 - 1
C POTWs that are developing pretreatment programs must develop and enforce specific limits 

on prohibited discharges, or demonstrate that the limits are not necessary [40 CFR 

403.8(f)(4)]. 

C POTWs that have approved pretreatment programs must continue to develop and revise local 

limits as necessary [40 CFR 403.5(c)(1)]. 

C POTWs that do not have approved pretreatment programs must develop specific local limits 

if pollutants from non-domestic sources result in interference or pass through and such 

occurrence is likely to recur [40 CFR 403.5(c)(2)]. 

EPA and the States have approved more than 1,400 POTW pretreatment programs. Each program must 

develop, implement, and enforce technically based local limits. Because most of the POTWs that require 

pretreatment programs now have them, only a few new programs are approved each year. Work on local 

limits continues, however, because POTWs with approved programs must periodically review these local 

limits. EPA regulations require that POTWs with approved programs must “provide a written technical 

evaluation of the need to revise local limits under 40 CFR 403.5(c)(1), following permit issuance or 

reissuance” [ 40 CFR 122.44(j)(2)(ii)]. Additionally, EPA recommends that Control Authorities review 

the adequacy of local limits if current wastewater treatment plant performance fails or will fail to attain 

applicable NPDES, State, or local permit requirements or other operational objectives, including water 

quality objectives of receiving waters; and if the performance shortcomings may be reasonably attributed 

to pass through or interference caused by a POC. Finally, Control Authorities may find it beneficial to reevaluate their local limits when a change in POTW operations results in a significant change in 

operational objectives; when the POTW experiences a significantly different influent flow or pollutant 

characteristics; or when a significant alteration of key environmental criteria occurs. 

1.4 NATIONAL PRETREATMENT STANDARDS 

The National Pretreatment Program consists of three types of national pretreatment standards established 

by regulation that apply to industrial users (IUs). These include prohibited discharges, categorical 

standards, and local limits. Prohibited discharges, comprised of general and specific prohibitions, apply 

to all IUs regardless of the size or type of operation. Categorical standards apply to specific process 

wastewater discharges from particular industrial categories. Local limits are site-specific limits developed 

by the POTW to enforce general and specific prohibitions on IUs. 

1.4.1 PROHIBITED DISCHARGES 

Prohibited discharges include both general and specific prohibitions, as described below: 

C General prohibitions [40 CFR 403.5(a)] forbid the discharge to a POTW of any pollutant that 

causes pass through or interference. Pass through means a discharge that causes a violation 

of any requirement of the POTW’s NPDES permit. Interference refers to a discharge that 

inhibits or disrupts the POTW, its treatment process or operations, or its sludge processes and 

that leads to a violation of the NPDES permits or any other applicable Federal, State, or local 

regulation. 

C Specific prohibitions [40 CFR 403.5(b)(1) to (8)] forbid the following eight categories of 

pollutant discharges to POTWs: 1) Pollutants that create fire or explosion hazards; 

2) Pollutants that will cause structural damage due to corrosion; 3) Pollutants that will cause 

obstructions in the flow of discharges to the POTW; 4) Pollutants released at excessive rates 

of flow or concentrations; 5) Excessive heat in amounts that inhibit biological activity; 

1 - 2
6) Certain oils that cause pass through or interference; 7) Pollutants that result in the presence 

of toxic gases, vapors, or fumes; and 8) Trucked or hauled pollutants, except at discharge 

points designated by the POTW. 

1.4.2 CATEGORICAL STANDARDS 

Categorical standards are uniform, technology-based, and applicable nationwide. Developed by EPA, 

these standards apply to specific categories of IUs and limit the discharge of specified toxic and nonconventional pollutants to POTWs. Expressed as numerical limits and management standards, the 

categorical standards are found at 40 CFR 405 through 471. They include specific limitations for 35 

industrial sectors. Appendix B provides a list of the industries for which EPA has promulgated 

categorical standards. Appendix C contains a list of pollutants regulated by categorical pretreatment 

standards. 

1.4.3 LOCAL LIMITS 

Local limits are developed by POTWs to enforce the specific and general prohibitions, as well as any 

State and local regulations. The prohibitions and categorical standards are designed to provide a 

minimum acceptable level of control over IU discharges. They do not, however, take into account sitespecific factors at POTWs that may necessitate additional controls. For example, a POTW that discharges 

into a river designated a “scenic river” under the Wild and Scenic Rivers Act may have extremely 

stringent discharge limits. To comply with its discharge permit, the POTW may need to exert greater 

control over IU discharges. This additional control can be obtained by establishing local limits. 

1.5 THE RELATIONSHIP OF LOCAL LIMITS TO CATEGORICAL STANDARDS 

Categorical standards and local limits are complementary types of pretreatment standards.1 The former 

are developed to achieve uniform technology-based water pollution control nationwide for selected 

pollutants and industries. The latter are intended to prevent site-specific POTW and environmental 

problems due to non-domestic discharges. As shown in Table 1-1, local limits can be broader in scope 

and more diverse in form than categorical standards. The development of local limits requires the 

assessment of local conditions and the judgment of POTW personnel. 

EPA’s promulgation of categorical standards does not relieve a POTW from its obligation to evaluate the 

need for and to develop local limits to meet the general and specific prohibitions in the General 

Pretreatment Regulations. Because specific prohibitions and categorical standards provide only general 

protection against pass through and interference, local limits based on POTW-specific conditions may be 

necessary. Developed in accordance with 40 CFR 403.5(c), local limits are Pretreatment Standards for 

the purposes of CWA Section 307(d) [see 40 CFR 403.5(d)]. Therefore, EPA can take enforcement 

actions against an IU that violates a local limit. Affected third parties also may sue IUs or POTWs with 

approved pretreatment programs for violations of local limits under the CWA’s citizen suit provisions. A 

POTW may impose local limits on an IU that are more stringent, or cover more pollutants, than an 

applicable categorical standard. This may be necessary for the POTW to meet its discharge permit or 

sludge quality limits. If a local limit is less stringent than an applicable categorical standard, however, the 

industry to which the local limit applies still must meet the applicable categorical standard. Guidance on 

permitting, including the comparison of Categorical Standards and local limits, is available in two EPA 

1

A direct comparison of categorical standards and local limits may not be possible because local limits may apply at 

the point(s) where an IU connects to the POTW collection system, while categorical standards may apply at the end of the IU’s 

regulated process(es) or immediately after pretreatment prior to mixing with other unregulated wastewater flows. 

1 - 3 
guidance manuals: Industrial User Permitting Guidance Manual (EPA 833-B-89-001, September 1989) 

and Guidance Manual for the Use of Production-Based Pretreatment Standards and the Combined 

Wastestream Formula (EPA 833-B-85-210, September 1985). 

Characteristic Categorical Standards Local Limits 

Agency responsible for development EPA Control Authority (usually POTW) 

Potential sources regulated Industries specified in Clean Water 

Act, or as determined by EPA 

All non-domestic dischargers 

Objective Uniform national control of nondomestic discharges 

Protection of POTW and local 

environment 

Pollutants regulated Primarily Priority Pollutants listed 

under Clean Water Act Section 307 

(toxic and non-conventional pollutants 

only) 

Any pollutant that may cause pass 

through or interference 

Basis Technology based Technically based on site-specific factors: 

C Allowable headworks loadings 

C Toxicity reduction evaluation 

C Technology in use 

C Management practice 

Point of application At the end of the regulated 

process(es) or in-plant 

Depends on development methodology 

[usually at the point of discharge(s) into 

the collection system] 

Table 1-1: Comparison of Categorical Pretreatment Standards and Local Limits 

1.6 ORGANIZATION OF THE GUIDANCE MANUAL 

This guidance manual provides an organized approach to the development and re-evaluation of local 

limits. Chapter 2 outlines the general approach for determining when to develop and when to re-evaluate 

local limits (providing a roadmap through the remainder of the manual). It also provides an overview of 

the local limits development process using the maximum allowable headworks load approach. Chapters 3 

through 6 cover limit development and implementation. Chapter 7 discusses reviews and re-evaluations 

of local limits, and Chapter 8 describes approaches to local limits development based on collection system 

concerns. The final chapter, Chapter 9, provides additional information in a question-and-answer format 

on numerous issues that have arisen in local limits development efforts. 

1 - 4
CHAPTER 2 -

OVERVIEW OF LOCAL LIMITS DEVELOPMENT

Local limits development is a continual process for Control Authorities (usually POTWs). Technically 

based limits are typically developed when a Control Authority/POTW first creates its local pretreatment 

program. As noted in Chapter 1, a POTW required to develop a pretreatment program also must develop 

and enforce local limits, as necessary, to protect against pass through, interference, and conditions 

detrimental to the collection system infrastructure or dangerous to workers. In addition, a Control 

Authority’s legal authority to impose local limits on industrial and commercial users actually derives 

from State law. Therefore, State law must confer the minimum Federal legal authority on a Control 

Authority. Section 6.7 of Chapter 6 provides a more complete discussion of the need for and application 

of this authority. 

Once local limits have been developed, POTWs may wish to review them periodically and revise them as 

necessary. Chapter 2 provides an overview of the local limits development process. 

2.1 LOCAL LIMITS DECISION TREE 

Figure 2-1 presents a decision tree that POTWs can use to determine the appropriate local limit 

implementation procedures. POTWs can follow the approach to evaluate their need for new local limits, 

and the adequacy of existing limits. Three months before their annual reports are due, POTWs with 

approved pretreatment programs are encouraged to evaluate their local limits through a “review” or a 

“detailed re-evaluation” process if the plant went through significant changes the past year. Then the 

results may be discussed in their annual reports. Although EPA recommends reviewing the entire 

manual, following the steps presented in Figure 2-1 will lead readers to the chapters of this manual that 

are appropriate for their situations. 

Whenever possible, EPA recommends development of local limits to address constituents that could pass 

through or cause interference before such problems occur. While developing a new local limit, or reevaluating an existing one, a POTW will need to consider all relevant plant and environmental 

information—including trends that may indicate likely future conditions. Anticipating changes and 

setting local limits accordingly may reduce the need for future revisions, saving POTW resources and 

enhancing IU compliance. For example, a POTW that anticipates changing its sludge disposal practices 

can develop local limits that will be protective of more restrictive sludge standards that may apply in the 

near future. Similarly, if economic growth within the service area is likely, a POTW can factor in a 

safety margin, or hold some allowable headworks loading capacity in reserve so that an allocation will be 

available in the future. Otherwise, new industrial hook-ups may have to be prohibited, or local limits 

may have to be revised. 

2 - 1
Figure 2-1: POTW Local Limits Decision Tree on Tree 

Start 

Has a technically-based 

local limits evaluation 

been performed? 

Did your evaluation 

determine a need 

for local limits? 

Has your local limits 

evaluation been 

approved by EPA or 

the State? 

Has your POTW 

developed 

technically-based 

local limits? 

Are approved local limits 

incorporated into local law 

and being implemented? 

Have there been any 

significant changes1 since 

your last local limits 

evaluation? 

Has the State or 

EPA required your 

POTW to develop 

and implement a 

pretreatment 

program? 

Await direction from 

EPA or State 

Perform detailed reevaluation 

Go to Chapter 7 

Has your POTW 

experienced pass 

through or interference 

in the past year? 

pro

of 

Has the 

Approval Authority 

requested that 

you develop 

local limits? 

Develop local 

limits after 

consultation with 

Approval Authority 

Go to Chapter 3 

Perform interim 

local limit review 

Go to Chapter 7 

Implement local 

limits 

Go to Chapter 6 

Yes 

Yes 

Yes 

No 

Yes 

No 

No 

Yes 

Yes No 

Yes 

Yes 

No 

Yes 

No Yes

No No 

1 Significant changes may 

modification to the POTW 

a new treatment plant, ch

discharge limitations, new 

water quality standards foincreased discharges to th

discharge or sludge dispo

No 

Start 

Has a technically-based 

local limits evaluation 

been performed? 

Did your evaluation 

determine a need 

for local limits? 

Has your local limits 

evaluation been 

approved by EPA or 

the State? 

Has your POTW 

developed 

technically-based 

local limits? 

Has your POTW 

developed 

technically-based 

local limits? 

Are approved local limits 

incorporated into local law 

and being implemented? 

Have there been any 

significant changes1 since 

your last local limits 

evaluation? 

Have there been any 

significant changes1 since 

your last local limits 

evaluation? 

Has the State or 

EPA required your 

POTW to develop 

and implement a 

pretreatment 

program? 

Has the State or 

EPA required your 

POTW to develop 

and implement a 

pretreatment 

program? 

Await direction from 

EPA or State 

Perform detailed reevaluation 

Go to Chapter 7 

Has your POTW 

experienced pass 

through or interference 

in the past year? 

pro

of 

pro

of 

Has the 

Approval Authority 

requested that 

you develop 

local limits? 

Develop local 

limits after 

consultation with 

Approval Authority 

Go to Chapter 3 

Perform interim 

local limit review 

Go to Chapter 7 

Implement local 

limits 

Go to Chapter 6 

Yes 

Yes 

Yes 

No 

Yes 

No 

No 

Yes 

Yes No 

Yes 

Yes 

No 

Yes 

No Yes

No No 

1 Significant changes may 

modification to the POTW 

a new treatment plant, ch

discharge limitations, new 

water quality standards foincreased discharges to th

discharge or sludge dispo

No 

2 - 2
2.2 MAHL APPROACH TO LOCAL LIMITS DEVELOPMENT 

EPA recommends that POTWs base their local Exhibit 2-1: Example MAHL Determination

limits on the maximum allowable headworks Based on AHLs

loading (MAHL)

1

 calculated for each pollutant of To determine the MAHL for cadmium, a POTW: concern. A pollutant’s MAHL is determined by

first calculating its allowable headworks loading � Determines that it will meet its NPDES permit limit if

(AHL)2

 for each environmental criterion; the 

the AHL at its headworks does not exceed 14 lb/day.

most stringent AHL would be the MAHL (see � Determines that it will meet its land application 

requirements for sludge if the AHL at its headworks 

Exhibit 2-1). does not exceed 30 lb/day. 

� Reviews its records and determines that an AHL at the 

The MAHL approach enables POTWs to headworks of 60 lb/day would protect its operations 

from toxic inhibition. calculate local limits taking into account the Assuming no other criteria apply to this plant, its MAHL for portion of the MAHL that is readily controllable cadmium would be 14 lb/day (the most limiting criterion).

(i.e., from industrial users (IUs)) and the portion 

that is not as easy to control (i.e., from domestic 

sources and background concentrations). The 

maximum allowable industrial loading (MAIL) is the 

portion of the MAHL available to IUs. It is based on 

sampling data (see Exhibit 2-2). As discussed in 

Chapter 6, local limits are based on the allocation of 

MAILs as uniform concentrations that apply to all 

IUs, as mass allocations provided individually to each 

IU, or some combination of the two options. 

Calculating MAHLs is not the appropriate method to 

evaluate all pollutants. Pollutants may create 

collection system conditions that can be harmful to 

workers such as fires, explosions, corrosion, flow 

Exhibit 2-2: Example MAIL Determination 

To determine the MAIL for cadmium, a POTW collects 

sampling data and finds that 6 of the 10 lb of cadmium 

received at its treatment plant every day comes from 

domestic/background/commercial (i.e., uncontrollable) 

sources. 

With a MAHL of 14 lb/day for cadmium—and assuming 

no other uncontrollable sources exist—the MAIL would 

be 8 lb/day (14 lb/day allowable minus 6 lb/day from 

uncontrollable sources). 

obstructions, high temperature, and toxic fumes. To address these issues, EPA recommends that POTWs 

consider the options presented in Chapter 8. Developing and implementing local limits with the MAHL 

approach requires the following five basic steps: 

1. Determine the pollutants of concern (POCs)3 

2. Collect and analyze data 

3. Calculate MAHLs for each POC 

4. Designate and implement the local limits 

5. Address collection system concerns 

1

A MAHL is the estimated maximum loading of a pollutant that can be received at a POTW’s headworks without 

causing pass through or interference. It is the most protective (lowest) of AHLs (see definition) estimated for an individual 

pollutant. 

2

An AHL is the estimated maximum loading of a pollutant that can be received at a POTW’s headworks that should not 

cause a POTW to violate a particular treatment plant or environmental criterion. AHLs are developed to prevent interference or 

pass through. 

3

A POC is any pollutant that might reasonably be expected to be discharged to the POTW in sufficient amounts to pass 

through or interfere with the works, contaminate its sludge, cause problems in its collection system, or jeopardize its workers. 

2 - 3 
2.2.1 STEP 1: DETERMINE POLLUTANTS OF CONCERN 

The first step in the MAHL approach is to identify the pollutants that should be evaluated to determine 

the need for local limits to control them. Among these are pollutants with known environmental criteria 

(such as limits in the POTW’s NPDES permit), other pollutants that are known to be discharged to the 

POTW, and pollutants known to be discharged to POTWs in general. The POTW should collect a 

limited amount of screening data to determine which of these potential pollutants of concern should be 

subject to more extensive data collection through the local limits sampling program. Chapter 3 discusses 

the procedures POTWs can use to determine POCs. 

2.2.2 STEP 2: COLLECT AND ANALYZE DATA 

After identifying the POCs that warrant a closer look, the POTW should undertake the collection of the 

necessary data, including additional sampling and analysis of selected wastewater streams and sludge to 

gauge the potential impacts of these POCs. The recommended procedures for collecting and analyzing 

data used to calculate MAHLs are provided in Chapter 4. 

2.2.3 STEP 3: CALCULATE MAHLS FOR EACH POC 

After collecting and evaluating the necessary data, the POTW should calculate AHLs for each POC 

based on its treatment efficiency and on environmental criteria for pass through and interference. As 

previously noted, the most stringent AHL will determine the MAHL. Chapter 5 discusses the procedures 

used by POTWs to calculate MAHLs. 

2.2.4 STEP 4: DESIGNATE AND IMPLEMENT LOCAL LIMITS 

Having calculated the MAHLs, the POTW needs to compare these allowable loadings with the actual and 

potential loadings received at the treatment plant to determine whether local limits are needed for each 

POC. Once the need has been established, the POTW develops appropriate local limits. This process 

will include determining the amount of each pollutant that can be allocated to IUs, submitting a 

development package to the Approval Authority for its review and approval, incorporating the local 

limits into local law (which includes following public notice requirements), and applying the local limits 

to the IUs. Chapter 6 discusses these implementation procedures. 

2.2.5 ADDRESS COLLECTION SYSTEM CONCERNS 

In addition to the MAHL approach to setting local limits, POTWs may need to develop local limits to 

address collection system concerns – fires and explosions, corrosion, flow obstructions, high 

temperature, and toxic gases, vapors or fumes – to meet the requirements of 40 CFR 403.5(b) regarding 

prohibited discharges. Chapter 8 discusses developing limits to address these concerns. 

2 - 4
CHAPTER 3 -

DETERMINING POLLUTANTS OF CONCERN

POTWs develop local limits to protect their collection systems, treatment plants, the health and safety of 

their workers, and the environment. Chapter 3 provides guidance on identifying which pollutants of 

concern (POCs) need to be controlled to meet these goals and to meet Federal, State, and local 

requirements. 

A POC is any pollutant that might reasonably be expected to be discharged to the POTW in sufficient 

amounts to cause pass through or interference, cause problems in its collection system, or jeopardize its 

workers. Pollutants that are contributing to or known to cause operational problems are also considered 

POCs even if the pollutants are not currently causing National Pollutant Discharge Elimination System 

(NPDES) permit violations. Some Approval Authorities have guidelines that POTWs can use in 

determining POCs, and POTWs should contact their Approval Authority for details. The methods used to 

determine POCs should account for daily fluctuations in POTW pollutant loadings and for the fact that 

decisions often are based on limited data. 

3.1 NATIONAL POCS 

EPA has identified 15 pollutants often found in POTW sludge and effluent that it considers potential 

POCs. They are listed in Exhibit 3-1. Ten of the pollutants were first identified in the Guidance Manual 

on the Development and Implementation of Local Discharge Limitations Under the Pretreatment 

Program (EPA 833-B87-202, December 1987).1 EPA added molybdenum and selenium because they are 

part of the Federal biosolids regulations for the land application of sludge. EPA added the conventional 

pollutants 5-day Biochemical Oxygen Demand (BOD5) and total suspended solids (TSS) because many 

POTWs have ongoing problems with excessive loadings of these pollutants from industrial and 

commercial sources. EPA also added ammonia as a “conditional” POC, for POTWs that accept nondomestic sources of ammonia, because many POTWs experience toxicity in their effluent from ammonia. 

EPA recommends that each POTW, at a minimum, screen for the presence of the 15 pollutants presented 

in Exhibit 3-1 using data on industrial user (IU) discharges and collected from samples of POTW influent, 

effluent, and sludge. 

1 Cadmium, chromium, copper, lead, nickel, and zinc are listed “because of their widespread occurrence in POTW 

influents and effluents in concentrations that warrant concern. Also, since they are usually associated with the suspended solids 

in the wastestream, their presence may prohibit the beneficial reuse of municipal sewage sludge and reduces the POTW options 

for safe sludge disposal.” Memorandum entitled “Local Limits Requirements for POTW Pretreatment Programs,” from Rebecca 

W. Hanmer, Director, Office of Water Enforcement and Permits, to Regional Water Management Division Directors and NPDES 

State Directors, August 5, 1985. [Copy of memo located in Appendix B of Guidance Manual on the Development and 

Implementation of Local Discharge Limitations Under the Pretreatment Program (EPA 833-B87-202), December 1987.] 

Arsenic, cyanide and silver are “not as widespread in POTW influents as the six metals but they have particularly low biological 

process inhibition values and/or aquatic toxicity values. In the case of cyanide, production of toxic sewer gases is also a 

concern.” Guidance Manual on the Development and Implementation of Local Discharge Limitations Under the Pretreatment 

Program (EPA 833-B87-202, December 1987) p. 2-17. 

3 - 1 
3.2 OTHER POTENTIAL POCS 

To identify additional potential POCs, EPA recommends that a 

POTW: 

C Determine the environmental standards and other 

statutory and regulatory requirements that it must meet. 

C Define measures necessary to protect the plant, 

collection system, and workers. 

C Identify the pollutants in the POTW influent, effluent, 

and sludge. 

C Identify pollutants for which a total maximum daily 

load (TMDL) has been or will be developed for the 

POTW’s receiving water. 

C Characterize IU and other non-domestic discharges 

Exhibit 3-1: EPA’s 15 POCs 

10 Original POCs 

Arsenic Lead 

Cadmium Mercury 

Chromium Nickel 

Copper Silver 

Cyanide Zinc 

5 New POCs 

Molybdenum

Selenium

5-day Biochemical Oxygen Demand 

Total Suspended Solids

Ammonia (for plants that accept

non-domestic sources of ammonia)

including hauled wastewater to assess which discharges, and which pollutants in those 

discharges, pose potential problems. 

C Consider pollutants that have contributed to operational or maintenance problems at the 

POTW. 

At a minimum, a POTW’s local limits must ensure that a POTW will meet the statutory and regulatory 

requirements of the Clean Water Act, General Pretreatment Regulations, and any applicable State or local 

requirements. Because NPDES permit conditions, sludge disposal practices, and State and local 

requirements vary from one POTW to another, they need to be addressed through local limits. 

3.2.1 NPDES PERMIT CONDITIONS 

The term “NPDES permit” as used in this guidance means either an EPA- or a State-issued permit. The 

NPDES permit issued to a POTW typically contains the following: 

C Specific effluent limitations. 

C Water quality-based toxic pollutant limitations. 

C Whole effluent toxicity (WET) requirements expressed either as a narrative limitation (e.g., 

“no toxics in toxic amounts”) or a numerical criterion. 

C Criteria and other conditions for sludge use or disposal. 

C Removal efficiency requirements (e.g., “85-percent removal of BOD”). 

C Requirements that the POTW be well operated and maintained. 

3 - 2
These permit conditions, and other applicable requirements, establish the objectives that the POTW must 

meet to prevent pass through and interference. POTWs are required to prohibit discharges from IUs in 

amounts that result in or cause a violation of any requirement of the POTW’s NPDES permit [see 

403.2(a)&(b), 403.3(i) and 403.3(n)]. If pass through or interference is the result of inadequately 

pretreated industrial discharges, the POTW must develop local limits for the pollutants responsible for the 

pass through or interference. 

Examples of POCs stemming from NPDES permit conditions include the following: 

C Pollutants with specific limits. 

C Pollutants that have caused violations or operational problems at the POTW, including 

conventional pollutants. 

C Pollutants reasonably expected to lead to pass through, interference, sludge contamination, 

collection system problems, or increased worker jeopardy. 

C Pollutants designated as “monitor only” in the NPDES permit.2 

C Pollutants responsible for toxicity found through WET testing. 

3.2.2 WATER QUALITY CRITERIA 

Water quality criteria have been developed by EPA for protection of surface water, including receiving 

water for permitted discharges. States may adopt EPA’s criteria, or establish more stringent criteria of 

their own.3 A POTW does not have to develop a local limit for every pollutant for which there is a water 

quality standard or criterion. However, EPA recommends that where a POTW permit includes a narrative 

water quality-based condition (e.g., “no discharge of toxics in toxic amounts”), the POTW may wish to 

evaluate the discharge of a particular toxic pollutant by considering its effect on water quality for that 

pollutant relative to EPA or State criteria for the pollutant. EPA recommends that any pollutant that has a 

“reasonable potential” to be discharged in amounts that could exceed water quality standards or criteria 

should be considered a POC and evaluated accordingly.

4 

2 Only discrete pollutants should be considered when a “monitor only” requirement is present in an NPDES permit. 

Where the POTW is required to conduct scans for priority pollutants, the entire set of pollutants would not need to be 

considered. 

3 Federal water quality criteria are listed in Appendix D, but readers should contact their States to determine whether 

stricter criteria must be met. 

4

 Discharge of a pollutant that results in a violation of a water quality standard is actionable even if the discharger’s 

NPDES permit does not include a specific permit condition limiting the discharge of that particular pollutant. The Ninth Circuit 

has held that a general permit condition prohibiting the discharge of wastewater that violates water quality standards, including a 

State water quality standard expressed as a broad narrative criterion, subjects a POTW to citizen suit under Section 505 of the 

Clean Water Act. See Northwest Environmental Advocates, et al. v. City of Portland, 56 F.3d 979 (9th Cir. 1995). In 

appropriate conditions, therefore, Section 403.5(c) would require a POTW to develop local limits to ensure compliance with the 

POTW’s permit condition requiring it to comply with State water quality standards. Such conditions consist of those where the 

record demonstrates that a discharge from a POTW is causing or would cause violation of State water quality standards, 

including qualitative or broad narrative criteria, and the permit includes a permit condition prohibiting a discharge that violates 

State water quality standards. 

3 - 3 
3.2.3 SLUDGE QUALITY STANDARDS 

POTWs must prohibit IU discharges in amounts 

that cause a violation of applicable sludge 

disposal or use regulations, or that restrict the 

POTW’s use of its chosen sludge disposal or use 

option. The national sludge standards are found 

at 40 CFR Part 503 and are shown in Exhibit 3-2. 

They are based on human health and 

environmental risks and include numerical 

pollutant limits, operational standards, 

management practices, and requirements for 

sampling, record keeping, and reporting. The 

sludge use and disposal options are: 

C Land application 

C Surface disposal 

C Incineration 

Exhibit 3-2: Pollutants Regulated Under 40 

CFR Part 503 

The pollutants that are regulated depend on the type of 

sludge disposal method used: 

C Land application: arsenic, cadmium, copper, lead, 

mercury, molybdenum, nickel, selenium, zinc. 

C Surface disposal: arsenic, chromium, nickel 

C Incineration: beryllium and mercury (National Emission 

Standards for Hazardous Air Pollutants under 40 CFR 

Part 61), lead (National Ambient Air Quality Standard), 

plus arsenic, cadmium, chromium, nickel (risk-specific 

concentrations). 

C Deposition in a municipal solid waste landfill 

To dispose of its sludge by land application, surface disposal, or incineration, a POTW must ensure that 

its sludge meets the pollutant limits that apply to the selected disposal option. Therefore, any pollutant 

limited by an applicable sludge disposal standard should be considered a POC and evaluated. If sewage 

sludge is disposed of in a municipal solid waste landfill, no specific pollutant limitations apply; however, 

narrative requirements in 40 CFR 257, 258, and 261 do apply. 

The sludge standards found at 40 CFR 503 are presented in Appendix E. States are free to establish their 

own sludge use and disposal standards, as long as they are at least as stringent or are as protective as the 

Federal requirements. POTWs should contact their Approval Authorities or other State agencies for a 

copy of the relevant State standards and adhere to the more stringent standards. EPA recommends that 

POTWs consider the attainment of EPA “clean sludge” standards. These are spelled out in Table 3 of 40 

CFR 503.13, and provide the broadest choice of beneficial use options for sludge disposal. Further, 

achievement of these standards is consistent with the objectives of the National Pretreatment Program, 

which are listed at 40 CFR 403.2. 

POTWs that normally dispose of their sludge in landfills also may be adversely affected by IU discharges. 

EPA recommends that these POTWs also develop local limits to ensure their sludge disposal options are 

not restricted. When slated for disposal in a landfill, sludge and residual ash from the incineration of 

sludge should be tested using the Toxicity Characteristic Leaching Procedure (TCLP) discussed in 

Appendix II of 40 CFR Part 261. Sludge is considered a hazardous waste if TCLP test results on sludge 

exceed concentrations listed in the TCLP method. Hazardous wastes must be disposed of in accordance 

with the Resource Conservation and Recovery Act (RCRA), which will likely increase disposal costs. 

The pollutant limits for the TCLP rule are listed in Appendix F. 

3.2.4 AIR QUALITY STANDARDS 

Air quality standards are generally not the basis for POCs. However, there are circumstances where a 

State adopts a State Implementation Plan (SIP), to comply with National Ambient Air Quality Standards 

(NAAQS), that requires a POTW to control emission standards. In addition, POTWs should be aware 

that on October 21, 2002, amendments to the National Emission Standards for Hazardous Air Pollutants 

(NESHAP) for POTWs were finalized. All newly re-constructed or new treatment plants required to 

3 - 4
develop a pretreatment program (40 CFR 403.8) and defined as major sources of hazardous air pollutants 

(HAP) must institute air pollution controls (covers on emission points) or demonstrate low HAP 

emissions. In addition, the regulations define industrial POTWs as those that provide treatment and 

control for a wastestream regulated by an industrial NESHAP. (The industrial discharger complies with 

NESHAP by using the treatment and controls located at the POTW.) In effect, the industrial POTW acts 

as an agent of the industrial facility by treating the facility’s wastewater to meet NESHAP. As of 1999, 

EPA had identified only six POTWs that are major sources of HAP. Several POTWs have been identified 

as industrial POTWs, and these numbers may increase as more industrial NESHAP are promulgated (40 

CFR Part 63, Subpart VVV, 63.1580-1595). 

3.2.5 RESOURCE PROTECTION CRITERIA 

POTWs should be aware that some States integrate resource protection (watershed and aquifer protection) 

criteria into permits separate from NPDES permits (for example, aquifer protection permits in the arid 

Southwest States.) EPA recommends that POTWs consider those pollutant limits in determining POCs. 

3.2.6 PROHIBITIONS ON TREATMENT PLANT INTERFERENCE 

The General Pretreatment Regulations include prohibitions, at 40 CFR 403.5(a), against the discharge by 

any user of a POTW of pollutants that cause interference. Interference, as defined by EPA, means a 

discharge that inhibits or disrupts a POTW and therefore causes a violation of the POTW’s NPDES 

permit or non-compliance with the POTW’s sewage sludge requirements. Consequently, EPA 

recommends that a POTW consider pollutants that may interfere with the treatment work’s operation to 

be potential POCs. And if a POTW has experienced interference in the past, the pollutants that caused the 

interference should be considered POCs. Where a POTW has identified the pollutant that caused an 

interference event and eliminated the problem – for example a one-time event that is not expected to 

reoccur – the pollutant need not be considered a POC. 

Although some pollutant discharges may not cause NPDES permit or sludge disposal violations, they 

might disrupt POTW operations or increase operation and maintenance costs. For example, IU discharges 

that inhibit a POTW’s biological treatment system could reduce treatment efficiency and, as a result, 

increase operating costs. Inhibition may result in the production of sludge that requires special treatment 

before disposal, or that requires disposal in a manner not generally used by the POTW. Therefore, EPA 

recommends that POTWs also consider pollutants that are known to cause operational or maintenance 

problems. 

Some pollutants that can cause inhibition, and the estimated concentrations at which inhibitory effects 

have been reported, are listed in Appendix G. The inhibition data presented in Appendix G should be 

used with caution. Data collected at other POTWs must be examined carefully to assure that the 

treatment process and unit operations are similar to the POTW for which local limits are being developed. 

POTWs are encouraged to develop site-specific inhibition data for their POTW, and rely on Appendix G 

only to verify the values. 

3.2.7 PROHIBITIONS TO PROTECT THE TREATMENT WORKS, COLLECTION SYSTEM, AND WORKERS 

The prohibitions in this category apply to discharges of pollutants that can cause a fire or explosion, 

corrosive structural damage at the treatment plant, obstruction of flow, inhibition of biological activity 

due to heat, and discharges that cause the formation of toxic gases, vapors, or fumes. A local sewer use 

ordinance that applies to a POTW typically contains definitions or local limits that implement the specific 

prohibitions. Definitions may consist of descriptions from 40 CFR 403.5(b), or more specific quantitative 

3 - 5
definitions (e.g., specific readings on an explosimeter to protect against fire or explosion). Specific 

quantitative limits generally are more effective for avoiding ambiguity and for supporting IU compliance 

and POTW enforcement of IU non-compliance. Chapter 8 provides additional detail on procedures for 

identifying POCs based on these concerns and for setting local limits to address these concerns. 

Explosive and Flammable Substances 

Explosive and flammable pollutants discharged to a POTW can threaten the integrity of the collection 

system and the health and safety of POTW workers. Under the right conditions, the accumulation of such 

pollutants in treatment works can produce explosions or fires. Local limits can be used to regulate the 

discharge of these explosive or flammable pollutants. Lower explosive limits (LELs) and closed cup 

flashpoints for various organic compounds are provided in Appendices H and I. 

Fume Toxicity 

The fume toxicity level of a pollutant discharged to a POTW indicates the likelihood that a POTW worker 

will suffer an adverse health effect when the level is approached or exceeded. This level can be measured 

by the time weighted average threshold limit value (TWA-TLV), which is the concentration to which a 

worker can be exposed for eight hours per day, 40 hours per week and not have any acute or chronic 

adverse health effects. Similarly, short-term exposure limits (STELs) are concentrations to which a 

worker should not be exposed for longer than 15 minutes or more than four times per day (with at least 

one hour between each exposure). Guidelines on TWA-TLVs and STELs for gases that pose the threat of 

acute or chronic health effects in people can be found in Appendix J. 

Volatile organic compound (VOC) vapors are a major concern because they can be toxic and 

carcinogenic, and may produce acute and chronic health effects after various periods of exposure. Also of 

concern are the hazards associated with toxic gases produced when certain inorganic discharges mix in 

the collection system. For example, acidic discharges can combine with nonvolatile substances such as 

sulfide and cyanide to produce toxic gases and vapors (e.g., hydrogen sulfide and hydrogen cyanide, 

respectively), which are hazardous to people. To respond to this threat, POTWs can establish local limits 

based on the maximum recommended levels of these POCs in air. A list of pollutants and the NIOSH, 

OSHA, and ACGIH guidelines and exposure levels also can be found in Appendix J. 

3.2.8 SCANS OF POTW INFLUENT, EFFLUENT, AND SLUDGE TO IDENTIFY PRIORITY POLLUTANTS 

Historical results of priority pollutant scans of POTW influent, effluent, hauled wastewater, and sludge, 

especially those conducted during the previous 12 months, can help identify pollutants discharged to the 

POTW; and to determine which are potential POCs. Priority pollutants5

 specified under the CWA are 

listed in Appendix D. EPA recommends that a POTW also analyze the influent, effluent, and sludge for 

other pollutants that might reasonably be expected to be present, based on information about IU 

discharges gathered by the POTW from previous sampling and from its industrial waste survey. The 

analytical methods and sampling procedures are reviewed in Chapter 4. 

EPA recommends that the POTW should conduct additional screening for any pollutant found in the 

priority pollutant scans of its influent, effluent, or sludge to determine whether the pollutant should be 

listed as a POC. Although a pollutant found in this way is a potential POC, the POTW may determine, 

based on the pollutant’s concentration and on other data from IUs and commercial dischargers, that the 

pollutant need not be selected as a POC for the full headworks analysis. 

5 POTWs should be familiar with the chemicals and chemical impurities that are added to treat drinking water and 

wastewater or to maintain the collection system. These chemicals may affect the levels of priority pollutants introduced or 

pollutant characteristics being measured at the plant. 

3 - 6 
3.2.9 EVALUATIONS OF INDUSTRIAL AND COMMERCIAL DISCHARGES 

A POTW cannot make informed decisions about potential problem discharges without a comprehensive 

understanding of the IU discharges to its collection system. Whenever possible, EPA encourages the use 

of site-specific (actual) data on IUs and commercial discharges for the identification of POCs. Sitespecific data are particularly important when an individual IU’s discharges make up a large portion of the 

POTW’s total industrial loading, or when POCs are known to be, or are suspected of being, discharged in 

large quantities or concentrations. Monitoring at IU discharge points and at other points in the collection 

system may detect discharges that could cause problems in the collection system or at the treatment 

works. POTWs may decide that discharges from commercial facilities also should be assessed because 

some of these facilities (such as hospitals, dentists’ offices, and photo processors) can be significant 

sources of pollutant loadings. 

In lieu of sampling data, numerous sources of information about IUs, commercial users, and their 

discharges are available to POTWs. Collecting and reviewing data from such sources is an important 

initial step in identifying POCs. Some of the available sources include the following: 

C Industrial waste surveys (IWSs)

C IU permit applications

C The results of IU self-monitoring and POTW compliance monitoring

C The results of POTW inspections of IUs

C Chambers of Commerce and local trade organizations

C General surveillance of the types of facilities in an area

C EPA Pretreatment Program guidance manuals (see Appendix A)

C Approval Authorities

C State pollutant and chemical databases

C The Internet and the World Wide Web

Table 3-1 on the following page presents details on some of these potential sources of information. 

3 - 7
Table 3-1: Selected Information Sources for Determining Potential POCs 

Source Information Provided 

Industrial Waste Survey (IWS) POTWs can request in the IWS information that may help identify and assess the pollutants 

discharged, or potentially discharged, by each user surveyed. 

the IWS can help the POTW: 

C Identify IUs of which the POTW had been unaware, or that have recently moved into the 

POTW’s service area. 

C Identify pollutants likely to be discharged to the collection system that should be 

considered potential POCs. 

C Identify previously unknown characteristics of an IU and its discharges. 

C Evaluate the potential for slug loadings and periods of increased loadings from variable 

discharges (e.g., from facilities that experience seasonal fluctuation in their discharges 

and from batch dischargers). 

C Plan a sampling program to help ensure efficient use of POTW resources. 

C Estimate raw waste loadings of pollutants for which analytical methods are unavailable. 

C Identify opportunities for pollution prevention. 

Most, if not all, POTWs that have approved pretreatment programs will have conducted initial 

IWSs. find it helpful to review IWS data in conjunction with pollutant 

occurrence data for various industries. 

IU Permit Applications Details of the pollutants likely to be discharged by an IU and received at the POTW. 

permits or local ordinances, POTWs can require IUs to provide toxicity data for pollutants 

detected in the IU’s wastewater. 

their raw feedstock, solvents, surfactants, and other chemicals from material safety data 

sheets (MSDSs). 

IU Self-Monitoring, POTW 

Compliance Monitoring, and 

Inspections 

Indications of the pollutants discharged, or potentially discharged, by IUs. 

of information provided by the industrial waste survey and IU permit applications. 

EPA Pretreatment Program 

Guidance Manuals 

Lists of priority pollutants likely to be found in discharges from various industries, lists of 

guidance and other manuals, and information on how to obtain copies of the manuals. 

pretreatment guidance manuals and information on how to obtain copies is provided in 

Appendix A. 

Approval Authorities Data on pollutants detected in direct dischargers’ effluents, which can be reviewed by POTWs 

to identify pollutants that may be discharged by similar IUs in their service areas. 

State Pollutant and Chemical 

Databases 

Sources of information about industrial effluent* 

*The North Carolina Department of Resources and Community Development has created databases using reports of POTW 

effluent toxicity and the associated discharges of toxics from IUs, as well as information provided by chemical manufacturers 

about the chemical characteristics, such as measured toxicity, of biocidal compounds. 

The information gained from 

POTWs also may

Through 

IUs can sometimes get such data from the manufacturers of 

Also, confirmation 

A list of 

Table 3-1: Selected Information Sources for Determining Potential POCs 

Source Information Provided 

Industrial Waste Survey (IWS) POTWs can request in the IWS information that may help identify and assess the pollutants 

discharged, or potentially discharged, by each user surveyed. The information gained from 

the IWS can help the POTW: 

C Identify IUs of which the POTW had been unaware, or that have recently moved into the 

POTW’s service area. 

C Identify pollutants likely to be discharged to the collection system that should be 

considered potential POCs. 

C Identify previously unknown characteristics of an IU and its discharges. 

C Evaluate the potential for slug loadings and periods of increased loadings from variable 

discharges (e.g., from facilities that experience seasonal fluctuation in their discharges 

and from batch dischargers). 

C Plan a sampling program to help ensure efficient use of POTW resources. 

C Estimate raw waste loadings of pollutants for which analytical methods are unavailable. 

C Identify opportunities for pollution prevention. 

Most, if not all, POTWs that have approved pretreatment programs will have conducted initial 

IWSs. POTWs also may find it helpful to review IWS data in conjunction with pollutant 

occurrence data for various industries. 

IU Permit Applications Details of the pollutants likely to be discharged by an IU and received at the POTW. Through 

permits or local ordinances, POTWs can require IUs to provide toxicity data for pollutants 

detected in the IU’s wastewater. IUs can sometimes get such data from the manufacturers of 

their raw feedstock, solvents, surfactants, and other chemicals from material safety data 

sheets (MSDSs). 

IU Self-Monitoring, POTW 

Compliance Monitoring, and 

Inspections 

Indications of the pollutants discharged, or potentially discharged, by IUs. Also, confirmation 

of information provided by the industrial waste survey and IU permit applications. 

EPA Pretreatment Program 

Guidance Manuals 

Lists of priority pollutants likely to be found in discharges from various industries, lists of 

guidance and other manuals, and information on how to obtain copies of the manuals. A list of 

pretreatment guidance manuals and information on how to obtain copies is provided in 

Appendix A. 

Approval Authorities Data on pollutants detected in direct dischargers’ effluents, which can be reviewed by POTWs 

to identify pollutants that may be discharged by similar IUs in their service areas. 

State Pollutant and Chemical 

Databases 

Sources of information about industrial effluent* 

*The North Carolina Department of Resources and Community Development has created databases using reports of POTW 

effluent toxicity and the associated discharges of toxics from IUs, as well as information provided by chemical manufacturers 

about the chemical characteristics, such as measured toxicity, of biocidal compounds. 

3.2.10 HAULED WASTE 

When determining POCs, EPA recommends that POTWs consider the pollutants in, and resultant 

pollutant loadings from, any hauled waste that they accept for treatment and disposal.6 Hauled waste has 

the potential to cause pass through, interference, or problems in the collection system as well as to 

endanger POTW personnel. Although it typically consists of domestic sewage or septage, hauled waste 

tends to be more concentrated than typical domestic wastewater and can contain the following: 

6

 The General Pretreatment Regulations cover “pollutants from non-domestic sources covered by Pretreatment 

Standards that are indirectly discharged into or transported by truck or rail or otherwise introduced into POTWs” [40 CFR 

403.1(b)]. This means that any hauled waste from industries subject to categorical pretreatment standards should comply with 

the standards before being accepted for treatment at the POTW. A POTW that has implemented a federally required 

pretreatment program should have adequate legal authority to regulate its receipt of all non-domestic waste, including nondomestic hauled waste. 

3 - 8 
C Industrial and commercial waste

C Grease and sand trap waste

C Chemical toilet waste

C Hazardous waste

C Groundwater remediation site waste

C Landfill leachate (see Appendix K for landfill leachate loadings)

An EPA analysis of nine POTWs found that hauled septage may contain relatively high amounts of heavy 

metals and organic solvents.7 Many POTWs receive hauled chemical toilet wastes as well as septage. 

Chemical toilet waste may contain significant concentrations of paradichlorobenzene (up to 14,000 μg/L) 

as a deodorizing chemical. In March 1995, a truckload of contaminated solvent was discharged to the 

Wareham, Massachusetts POTW and resulted in one plant employee suffering from upper respiratory 

problems and major treatment plant disruption as half of the digester microorganisms were killed. 

Many POTWs accept only domestic wastes from waste haulers and will specify this limitation in their 

sewer use ordinances. If accepting hauled industrial wastes, however, the POTW should ensure that any 

potential POCs in these wastes are identified and considered in the local limits evaluation. Additional 

information on the acceptance and characterization of hauled wastes at POTWs is available in the 

Guidance Manual for the Control of Waste Hauled to Publicly Owned Treatment Works (EPA/833-B98-

003). 

The guidance discusses collection of information on waste haulers, characterization of hauled waste 

received, evaluation of potential impacts and the development and implementation of controls. Figure 3-1 

on the following page is a flow chart from this manual on characterizing hauled waste. The guidance also 

includes case studies of successful waste hauler programs. POTWs should periodically monitor hauled 

wastes to confirm that only appropriate wastes are being brought by waste haulers and to identify any 

potential POCs that should be addressed by local limits. 

3.2.11 REMEDIATION SITE WASTE 

Waste from remediation sites, especially groundwater remediation sites, may be discharged to the 

collection system or hauled to POTWs for treatment and disposal. Site operators should provide the 

receiving POTW with information on waste volume, pollutants present, and pollutant concentrations. 

POTWs can use such information to identify potential POCs. Remediation wastes from sites being 

cleaned up under the Comprehensive Environmental Response, Compensation, and Liability Act 

(CERCLA) may include: 

C Landfill leachate

C Contaminated groundwater

C Aqueous waste stored in containers

C Wastes from tanks and surface impoundments

C Treatment sludges

C Runoff from contaminated soils

7

 The monitoring data provided to the nine POTWs by septage haulers are summarized in Appendix L. 

3 - 9 
Figure 3-1: Determining Hauled Waste Characteristics Figure 3-1: Determining Hauled Waste Characteristics 

Does Waste Meet 

Categorical Limits? 

Begin 

acceptance/permitting 

process** 

Yes 

No 

No 

Yes 

No 

No 

Yes 

No 

No 

Source of Waste 

Domestic* Non-domestic* 

Hazardous Categorical 

Reject 

Require Pretreatment 

or Reject 

Does Waste Meet Local 

Limits? 

Will Waste Cause Toxic 

Fumes/Gases, 

Flammable or Explosive 

Conditions? 

Will Waste Cause a 

Health & Safety 

Hazard? 

Will Waste Cause 

Corrosion or Exceed 

pH Limits? 

Will Waste Cause Slug 

Loading/Interference/ 

Pass Through? 

Compare to Pollutants/Concentrations to 

Applicable Laws 

Non-domestic, Noncategorical Landfill Leachate Remedial Site Waste 

Yes Yes 

Yes *If a waste load consists of non-domestic and domestic waste, the load should be 

considered non-domestic and that branch of 

the flow chart should be followed. 

**Discharge permits should be issued to 

waste haulers (see Section 3.2.3) and 

wasteloads should be properly manifested. 

Yes 

Does Waste Meet 

Categorical Limits? 

Begin 

acceptance/permitting 

process** 

Yes 

No 

No 

Yes 

No 

No 

Yes 

No 

No 

Source of Waste 

Domestic* Non-domestic* 

Hazardous Categorical 

Reject 

Require Pretreatment 

or Reject 

Does Waste Meet Local 

Limits? 

Will Waste Cause Toxic 

Fumes/Gases, 

Flammable or Explosive 

Conditions? 

Will Waste Cause a 

Health & Safety 

Hazard? 

Will Waste Cause 

Corrosion or Exceed 

pH Limits? 

Will Waste Cause Slug 

Loading/Interference/ 

Pass Through? 

Compare to Pollutants/Concentrations to 

Applicable Laws 

Non-domestic, Noncategorical Landfill Leachate Remedial Site Waste 

Yes Yes 

Yes *If a waste load consists of non-domestic and domestic waste, the load should be 

considered non-domestic and that branch of 

the flow chart should be followed. 

**Discharge permits should be issued to 

waste haulers (see Section 3.2.3) and 

wasteloads should be properly manifested. 

Yes 

3 - 10
Wastes from CERCLA sites commonly contain trichloroethylene, lead, toluene, benzene, polychlorinated 

biphenyls, chloroform, tetrachloroethylene, phenol, arsenic, and cadmium. Although many CERCLA 

wastes are quite dilute, some sites have reported high concentrations of metals and organics. EPA 

recommends that POTWs considering whether to accept CERCLA clean-up wastes require detailed 

analyses and treatability testing before making any decisions. Data from these activities can be used to 

determine the presence of POCs. Additional guidance on CERCLA wastes is available from the CERCLA 

Site Discharges to POTWs Guidance Manual (EPA 542/6-90-005). POCs identified from the analysis of 

remediation waste may include pollutants that require analytical methods not currently listed in 40 CFR 

Part 136. 

3.2.12 HAZARDOUS WASTES 

Wastes identified as hazardous under the Resource Conservation and Recovery Act (RCRA)8 can be 

legally introduced to a POTW by being discharged into the collection system through an IU’s normal 

sewer connection. RCRA hazardous wastes may be transported to the POTW by truck, rail, or dedicated 

pipeline if the POTW is complying with the RCRA permit-by-rule requirements for treatment, storage, 

and disposal facilities found at 40 CFR 270.60. A POTW that accepts hazardous wastes may need 

considerable resources to comply with CWA and RCRA requirements. The responsibility and liability of 

POTWs accepting hazardous wastes in this manner are explained in EPA’s 1987 document Guidance 

Manual for the Identification of Hazardous Wastes Delivered to POTWs by Truck, Rail, or Dedicated 

Pipeline. POTWs should note that acceptance of hazardous waste by truck, rail, or dedicated pipe (even 

unknowingly) will make them subject to the RCRA permit-by-rule requirements. 

When mixed with domestic sewage in a POTW's collection system before reaching the boundary of the 

treatment works’ property, RCRA hazardous wastes are excluded from regulation under RCRA by the 

Domestic Sewage Exclusion, 40 CFR 261.4(a)(1). (They are, however, subject to the CWA, must be 

reported to the POTW, and should meet all applicable categorical and local discharge limits.) As part of 

their implementation of the industrial pretreatment program, municipal officials should ensure that IUs 

control and properly manage their hazardous waste. EPA recommends that the POTW determine which 

pollutants are being discharged and should evaluate whether the pollutants ought to be considered POCs. 

POCs identified from the analysis of remediation waste may include pollutants that require analytical 

methods not currently listed in 40 CFR Part 136. 

3.3 APPROVAL AUTHORITY SCREENING PROCESS TO SELECT POLLUTANTS FOR LOCAL LIMITS 

SAMPLING PROGRAM AND LIMIT DEVELOPMENT 

Before undertaking collection and analysis of sampling data for the development of local limits discussed 

in the next chapter, EPA recommends that a POTW conduct a screening to determine which potential 

POCs should be included in the full headworks analysis. Some Approval Authorities have guidelines that 

POTWs can use in determining POCs. POTWs should contact their Approval Authority for details. With 

input from the Approval Authority, a POTW may then complete POC screening, plan and implement its 

local limits sampling program (Chapter 4), and conduct a headworks analysis for each remaining POC on 

its list (Chapter 5). Although the screening process can reduce the number of potential POCs subject to 

the POTW’s more extensive local limits sampling program, EPA recommends in general that local limits 

sampling and headworks analysis be conducted for the following: 

8 Hazardous wastes are wastes listed as hazardous at 40 CFR 261.31-33, or wastes that exceed specified levels of 

ignitability, corrosivity, reactivity, or toxicity as defined at 40 CFR 261.21-24. RCRA also lists hazardous constituents, 

chemicals of concerns in listed waste in 40 CFR 261, Appendix VIII. These constituents are reproduced in Appendix M of this 

manual. 

3 - 11 
C EPA’s 15 POCs (see Exhibit 3-1). 

C Any pollutant for which the POTW has a pre-existing local limit, has an applicable NPDES 

limit, State limit, or sludge disposal limit, or has caused inhibition or other problems in the 

past. 

3.4 SUMMARY 

After reviewing Chapter 3, POTWs should be able to determine POCs. As explained above, pollutants 

should be designated POCs if they: 

C Are on EPA’s list of 15 pollutants that a POTW should assume to be of concern. 

C Have a pre-existing local limit. 

C Are limited by a permit or applicable environmental criteria. 

C Have caused operational problems in the past. 

C Have important implications for the protection of the treatment works, collection system, or 

the health and safety of POTW workers. 

EPA recommends that a POTW check with their Approval Authority for methodologies to screen out 

certain POCs, before expending resources on local limits sampling discussed in Chapter 4. 

3 - 12
CHAPTER 4 -

DATA NEEDED TO DEVELOP LOCAL LIMITS

Developing maximum allowable headworks loadings (MAHLs), maximum allowable industrial loadings 

(MAILs), and local limits requires various types of data. Some of the data come from dischargers to the 

POTW, some come from the operation of the POTW itself, and some come from characterizations of the 

conditions in the POTW’s receiving water. Data such as flows can be measured directly, but other data 

are acquired by taking samples from the POTW’s wastestream and analyzing them to determine which 

pollutants are present. Accurate and defensible local limits cannot be developed without the collection of 

site-specific data on pollutant loadings at the POTW and on the POTW’s removal of those pollutants. 

Collecting those data requires a systematic effort. Chapter 4 discusses the types of data that are required 

and the methods to obtain them. It is recommended that POTWs seek input from their Approval 

Authority on their sampling plans. 

POTWs already conduct some sampling because the majority of NPDES permits require that POTW 

effluent be monitored for constituents such as biochemical oxygen demand (BOD), fecal coliform 

bacteria, total suspended solids (TSS), residual chlorine, and pH. In addition, many POTW NPDES 

permits place limits on nitrogen, phosphorus, and trace metals. Because this monitoring is unlikely to 

provide all of the data needed for a meaningful local limits calculation, EPA recommends that POTWs 

that have approved pretreatment programs routinely sample at other sites within the treatment works, both 

for local limits development and to remain up to date on their loadings of each pollutant. 

The sampling and analysis that support the determination of MAHLs and MAILs are used to: 

C Identify or confirm the presence of individual pollutants

C Determine pollutants of concern (POCs)

C Determine current POTW pollutant loadings

C Calculate pollutant-removal efficiencies

C Determine site-specific inhibition thresholds

C Estimate loadings from industrial users (IUs), domestic, and other sources

The sampling and flow data needed to calculate local limits are as follows: 

C Pollutant concentration data from POTW (influent, effluent, primary effluent, sludge), 

collection system, receiving stream, and IUs. 

C Flow data, such as total POTW flow, POTW sludge flow to the digester, POTW sludge flow 

to disposal, IU flows, receiving stream, hauled waste, domestic flows, and commercial flows. 

If the POTW conducts influent, effluent, and sludge sampling as part of its pretreatment program, the data 

may be used in subsequent local limits reviews and headworks analyses. EPA recommends that POTWs 

collect sampling and flow data from the sources noted above to develop a mass balance of pollutant 

loadings to and pollutant releases from the wastewater treatment plant. If based on accurate monitoring 

data, the mass loadings can be used to verify measured background loadings (see Section 6.2.1). 

4 - 1
4.1 SAMPLING LOCATIONS 

In EPA’s view, POTWs will want to establish sampling locations within both the treatment works and the 

collection system. EPA provides guidance on suggested sampling locations, as detailed below. 

4.1.1 AT THE POTW 

Most samples in support of local limits development are taken inside the POTW to determine removal 

rates and the amount of pollutants in sludge. Therefore, at a minimum, EPA recommends that a POTW 

establish one point to sample influent, one point to sample effluent, and one point to sample sludge. 

C POTW Influent. EPA recommends that samples be taken at the POTW’s headworks to 

determine the average and maximum levels at which POCs enter the treatment plant. Influent 

sampling provides data to be used in calculating POTW-specific removal efficiencies and in 

establishing the level at which the plant is loaded relative to the MAHL. The sample should 

be drawn from a location that permits the collection of raw wastewater before it is mixed with 

any wastestreams returned to the headworks from operations within the POTW. 

C POTW Effluent. Sampling the treatment works’ effluent is essential to determining the 

POTW’s overall removal efficiency. Samples taken to demonstrate compliance with the 

POTW’s NPDES permit can be used for this purpose. In addition, the sampling location used 

for NPDES compliance can also be used to draw samples for POCs that do not have NPDES 

permit limits or NPDES monitoring requirements. 

C POTW Sludge. EPA’s sludge disposal regulations require that sludge be sampled at the time 

of its disposal and after addition of conditioners to determine the percentage of solids it 

contains. For those POTWs that use land application for sludge disposal, EPA recommends 

that they also sample periodically for other pollutants. The frequency of sampling depends 

on the amount of sludge generated annually. Sludge samples taken to support compliance 

with the sludge disposal regulations found at 40 CFR 503 can also be used to calculate local 

limits. 

C Other Suggested Sites. EPA encourages POTWs to develop site-specific data for the 

development of local limits. In particular, site-specific data on pollutant concentrations in 

various unit processes is valuable for developing site-specific inhibition values. For example, 

a POTW that digests its sludge, either aerobically or anaerobically, should sample the 

digester contents to determine the levels of pollutants, primarily metals, that are known to 

cause digester upset. As discussed in the next chapter, one requirement of a local limit is to 

guard against plant upset, including digester inhibition. Little information on digester 

inhibition is available in the literature and site-specific inhibition is difficult to measure. 

Consequently, site-specific information on pollutant concentrations that did not cause 

digester inhibition are sometimes used to estimate allowable loadings of pollutants to the 

digester. Similar data on the level of pollutants that did not cause inhibition should be 

collected on influent to secondary and tertiary biological treatment processes. 

4 - 2
4.1.2 IN THE COLLECTION SYSTEM 

Knowing the relative contributions of uncontrolled sources (domestic users, inflow and infiltration (I&I), 

treatment chemicals added to sewers, drinking water, storm water, and some or all of a POTW’s 

commercial dischargers) is important in determining the amount of loading to be allocated to IUs. 

Uncontrolled sources can contribute significant loadings of pollutants and can therefore have a profound 

effect on the amount of pollutants available for IUs. However, wastestreams from uncontrolled sources 

are assumed to contain lower pollutant concentrations than wastestreams from IUs. The pretreatment 

regulations do not regulate domestic sources. POTWs may choose not to monitor or control commercial 

sources, either because of the lower concentrations or because too many sources make regulation 

impractical. 

In order to measure pollutant loadings from uncontrolled sources, EPA recommends that a POTW take 

samples from a point within the collection system that isolates these sources. EPA recommends that 

POTWs designate representative sampling locations within their collection systems based on the 

following considerations: 

C The size of the service area or collection system. 

C The variability of pollutant concentrations and loadings from one sector of the collection 

system to another. (For example, newer areas of a collection system may have higher 

concentrations of copper, while older areas may have higher concentrations of zinc or lead.) 

C Whether a sewer section is separate or combined or subject to excessive I&I. 

C Types of commercial establishments represented. 

C Whether more than one drinking water system operates within the POTW’s service area. 

(Different water systems may have different water sources, or may add different chemicals to 

treat the water or to control corrosion.) 

Under most circumstances, a POTW with a small service area will need to establish at least two sampling 

points within its collection system. More sampling locations may be needed in areas likely to have 

different pollutant concentrations based on the factors cited above. POTWs should remember that lower 

loadings from uncontrolled sources give greater flexibility in determining how much of a given pollutant 

will be available for IUs through the MAIL. Consequently, EPA recommends more extensive sampling 

in areas of the collection system where uncontrolled loadings appear to consume all of the calculated 

MAHLs. Other tips for sampling include the following: 

C POTWs should take care not to sample during or after periods of heavy rainfall when I&I is 

also high. Flows at these times will be diluted, and will not be representative of typical 

residential and commercial flows. I&I sometimes contributes to pollutant loadings—for 

example, in areas where mining once occurred and heavy rains wash pollutants from slag 

piles into collection systems. Such instances should be dealt with on a case-by-case and 

pollutant-by-pollutant basis through the POTW’s Approval Authority. 

4 - 3
C Although characterizing domestic and commercial loadings separately may appear to be 

useful, the loadings can be combined to determine the loadings from the aggregate of 

uncontrolled sources, particularly if cost is a consideration. Only if a POTW intends to 

regulate commercial sources separately would background levels need to be determined for 

both domestic and commercial sources. 

C The results of POTW influent sampling can serve as a check on the sampling points selected 

by the POTW to determine uncontrolled loadings. If the POTW’s headworks levels are 

consistently lower than the levels from the residential and commercial source sampling 

points, then the sampling points do not accurately represent the background levels, or an 

inordinate amount of I&I may be present. 

4.1.3 AT INDUSTRIAL USERS 

Sampling at IUs is helpful if a POTW wants to set local limits based on IU need through one of the 

various allocation methods available to the treatment works (see Section 6.3). In order to use one of these 

methods, the POTW should know the mass of each POC discharged by each IU so it can rank the users by 

size and, therefore, by need. For these cases, flows should be measured at, and samples taken from, each 

IU. These data are probably available from the POTW’s routine compliance monitoring and the IUs’ 

self-sampling programs. Therefore, if the POTW has already collected such data, there probably is no 

need to make a special effort during local limits development unless a new POC has been identified. 

Concentration and mass loading data from each IU also can be used to assess the impact a MAIL will 

have on the POTW’s industrial base. This assessment will help the POTW to determine how the local 

limit should be allocated among IUs. Moreover, knowing each facility’s level of discharge tells the 

POTW which facilities will have difficulty meeting any new limits. 

4.2 POLLUTANTS FOR WHICH POTWS SHOULD SAMPLE 

In general, a POTW should sample for all the pollutants to be included in the calculation of MAHLs and 

the possible development of local limits, including the following: 

C The 15 national POCs 

S Arsenic 

S Cadmium 

S Chromium 

S Copper 

S Cyanide 

S Lead 

S Mercury 

S Molybdenum 

S Nickel 

S Selenium 

S Silver 

S Zinc 

S 5-day Biochemical Oxygen Demand 

S Total Suspended Solids 

S Ammonia 

4 - 4
C Any POTW-specific POCs 

C Clean Water Act (CWA) organic priority pollutants 

C TCLP pollutants (if the POTW disposes, or is likely to dispose, of its sludge in landfills) 

4.3 SAMPLING FREQUENCIES 

Local limits usually are scrutinized during their initial development, reviews, NPDES permit renewals, 

and when detailed re-evaluations are conducted. Conducted over different time periods, these efforts 

often have different data requirements and consequently, results. The initial development of local limits, 

for example, may require rapid data collection and analysis to meet the schedule for developing a 

Pretreatment Program submission, of which local limits evaluation is a part. In contrast, reviews and 

detailed re-evaluations should be based on data collected as part of a routine, long-term sampling effort. 

Detailed below are suggested sampling frequencies for initial program development and ongoing 

evaluation. The reader should note that these minimum sampling frequencies are recommendations. The 

POTW has flexibility to adjust their sampling frequencies based on local concerns and economics. In 

addition, EPA has provided guidance on establishing a sampling frequency through statistical means1

 in 

Appendix N. 

4.3.1 SAMPLING FREQUENCIES FOR INITIAL PROGRAM DEVELOPMENT 

To support the initial development of local limits, samples should be collected to provide the data 

necessary to identify POCs, determine MAHLs, calculate MAILs, and implement local limits. Although 

such sampling frequently occurs during a short period, the sampling program should account for the dayto-day variability at a POTW and for all the pollutants known or suspected to be present in the POTW’s 

influent. Table 4-1 presents the sampling frequencies for influent, effluent, and sludge, as well as 

suggested sampling frequencies for domestic and commercial dischargers. The limited number of 

sampling events may not generate enough data to calculate the POTW’s efficiency at removing every 

pollutant in its influent. In such cases, some Approval Authorities may allow—or even require—the use 

of literature values if they believe a POTW’s sampling provides less accurate information. 

1 The use of statistical analyses can help establish an acceptable minimum number of samples needed to adequately 

represent a population of pollutants in the influent and effluent at an acceptable confidence level. Appendix N provides guidance 

on the number of samples needed to estimate the true sampling mean based on confidence level, relative error, and variation of 

the data. Depending on the desired confidence level and relative error, the number of samples needed can be cost-prohibitive. 

For example, to be 90 percent confident that your sampling mean lies within +/- 10 percent of the true mean, the number of 

samples needed is 68 (when the sample set has a coefficient of variation of 0.5). A program of continual sampling could ensure 

that sufficient data are available and distribute the costs of sampling over time. 

4 - 5 
Table 4-1: Minimum Recommended Sampling Days* for Initial Local Limits Development 

Parameter 

POTW 

Residential/ 

Commercial 

Influent 

(days to 

sample) 

Effluent 

(days to sample 

Sludge 

(days to 

sample) 

Collection 

System 

(days to sample) 

Organic Priority Pollutants (1) 1 - 2 1 - 2 1 1 - 2 

National POCs (2) 7 - 14 7 - 14 2 7 

POTW-specific POCs (2) 7 - 14 7 - 14 2 7 

Percent solids, sludge (3) 2 

TCLP pollutants (4) 1 

*Sampling days are defined as the number of days that samples are collected for a parameter. s should be 

consecutive days for National POCs and POTW-specific POCs. hour composite samples unless sampling 

methods only allow for grab samples (see Section 4.5). 

(1) Conducted once or twice to determine potential POCs. 

(2) The range of values for sampling days (7-14) for influent and effluent sampling of POCs is a minimum recommended range for 

the number of days to sample. TWs that are small [up to 5 million gallons per day (MGD)] should have at least 7 consecutive 

sampling days for POCs while larger POTWs (5-10 MGD) should have at least 14 consecutive sampling days. 

than 10 MGD should consider more sampling according to local concerns and economics. should seek input from the 

Approval Authority for their sampling plan. 

(3) The sludge regulations at 40 CFR Part 503 already require the percentage of solids to be determined every day that sludge is 

applied to land. 

(4) Sample for TCLP pollutants if sludge is disposed, or is likely to be disposed, in a landfill. 

Sampling day

Samples should be 24-

PO

POTWs larger 

POTWs 

4.3.2 SAMPLING FREQUENCIES FOR ONGOING EVALUATION 

The sampling frequencies presented in Table 4-2, based on POTW flow, should be used for ongoing 

evaluations. The importance of sampling POTW influent should not be overlooked. Not only is this 

sampling essential for calculating POTW removal efficiency, it also enables the POTW to calculate the 

headworks loading of each pollutant and compare it to the MAHL, thus indicating the degree to which the 

treatment works is loaded. The data from headworks sampling also are used to determine when a local 

limit must be adopted. If cost becomes a constraint, EPA recommends that sampling to calculate removal 

rates focus on removal throughout the treatment works and that literature values be used for intermediate 

process removal rates. 

4 - 6
Table 4-2: Minimum Recommended Sampling Frequencies for Ongoing 

Local Limits Analysis and Evaluation 

Parameter Location Less than 

5 MGD 

5 – 10 

MGD 

10 – 50 

MGD 

Greater 

than 50 

MGD 

Pollutants for which local limits were 

adopted 

Influent, 

Effluent, 

Sludge 

Once every 3 

months 

Once every 3 

months 

Once every 3 

months 

Once every 2 

months 

Pollutants for which MAHLs were 

calculated, but for which no local limits 

were adopted 

Influent, 

Effluent, 

Sludge 

Once every 

12 months 

Once every 6 

months 

Once every 6 

months 

Once every 3 

months 

Organic Priority Pollutants Influent Once per 

year 

Once per 

year 

Once per 

year 

Once every 6 

months 

TCLP Pollutants (1), sludge Sludge Once per 

year 

Once per 

year 

Once per 

year 

Once per 

year 

Sludge percent solids and specific 

gravity (2) 

Sludge Once every 6 

months 

Once every 4 

months 

Once every 3 

months 

Once every 2 

months 

(1) Conducted if sludge is (or is likely to be) disposed of in a landfill. 

(2) The sludge regulations at 40 CFR Part 503 already require the percentage of solids to be determined every 

day that sludge is applied to land. 

4.4 OTHER SAMPLING TIPS 

Local limits sampling should attempt to depict the POTW under typical operating conditions. Therefore, 

the sampling program should not bias the results by using sampling procedures that ignore the day-to-day 

and seasonal variability that the POTW expects to encounter. To ensure that sampling data are 

representative of the variety of conditions, EPA recommends that the POTW consider the following 

points when setting its sampling schedule: 

C Sampling should be conducted randomly and should be representative of the different days, 

months, and conditions throughout the year. If a POTW establishes a rigid sampling 

schedule (for example, the first Wednesday of each month), it may bias the local limits 

development process. 

C If infrequent, yet routine, activities are conducted within the POTW, its collection system, or 

at its IUs, the sampling schedule established by the POTW should collect data representative 

of these events. Such activities should be represented in the sampling at approximately the 

frequency at which they occur. Sampling documentation should note if any activity of this 

type occurred during the sampling period. Examples of infrequent, yet routine, activities 

include receipt of hauled waste, tank cleaning, or other maintenance activities that might 

affect wastewater characteristics. 

4 - 7
C Ideally, POTW sampling should account for hydraulic retention times between the influent 

and effluent sampling points. If unlagged historical data show wastestream loadings do not 

vary by more than 10 percent and POTW removal efficiencies remain relatively constant, 

delayed sampling based on hydraulic retention time may not be critical. However, because 

the retention time for sludge will likely be greater than the period when local limits 

monitoring occurs and because of the nature of the sludge sampling procedure itself, neither 

more frequent sludge sampling nor lagging samples for sludge retention times is warranted. 

C The sampling schedule should ensure the collection of samples that are representative of the 

weather conditions that affect POTW operations (i.e., wet weather; hot or cold ambient 

temperatures). 

4.5 SAMPLING METHODS 

The purpose of any sampling is to accurately quantify the contents of the wastestream being sampled. 

Samples of wastewater typically are one of three types: flow-proportioned composites, time composites, 

or grab samples. Each type has its use in the local limits development process, but the 24-hour, flowproportioned composite samples are the most accurate for this purpose. This sampling technique should 

be used whenever feasible for all pollutants except those that require grab samples. 

A flow-proportioned sample, sometimes called a flow-weighted sample, is one in which a set aliquot of 

the wastestream is taken after the passage of a set amount of wastewater. Samples are commonly taken 

by an automatic sampler connected to a device that measures flow. For example, a 500 milliliter (mL) 

sample may be taken from the wastestream every time 1,000 gallons has been discharged. The sample 

volumes and flow intervals are usually determined by the capacity of the sampler and the expected total 

flow of the source. 

Time-composite samples consist of equal-volume aliquots taken at regular intervals throughout the 

sampling period. Because the volume of discharge can vary between the times aliquots are drawn, timecomposite samples are not considered to be as accurate as flow-proportioned samples. However, the 

accuracy of the time-composite samples approaches that of the flow-proportioned samples as the 

wastestream’s flow rate becomes increasingly uniform. Time-composite samples can be used to 

accurately profile pollutants for local limits development, but the statistical variability of their data will be 

greater than that of flow-proportioned samples. Consequently, more time-composite samples will be 

required to support a given confidence interval. EPA generally recommends using flow-proportioned 

samples instead of time-composite samples. 

4 - 8
Grab samples are individual aliquots collected at intervals of at least 15 minutes without regard to flow 

rate. They normally are drawn manually, rather than by automatic equipment. During the local limits 

development process, grab samples should be avoided for most pollutants, except for the following: 

C pH

C Cyanide

C VOCs

C Total phenols

C Oil and grease

C Total petroleum hydrocarbons

C Sulfide

C Flashpoint

C Temperature

When grab samples are required, at least four should be collected, although more than 12 grab samples 

are desirable. If enough grab samples are taken over the sampling period, they may be combined to create 

a grab composite sample. The aliquots must be collected in separate containers, preserved appropriately, 

and either composited manually at the laboratory to create a single sample for analysis, or analyzed 

separately and the results averaged into a single value. If the interval wastestream flow between each 

grab sample is known, a flow-proportioned grab composite sample may be prepared (see Table 4-3). As 

an alternative, the grab samples may be analyzed separately and the results averaged according to flow 

weight (see Table 4-4). Samples to be analyzed for pH should not be manually composited, however, and 

the results for pH should not be averaged. 

Sludge samples require that a composite sample be taken of the sludge mass. To do that, a POTW 

should use the sampling technique specified for demonstrating compliance with the sludge regulations 

found at 40 CFR 503. Specifically, several aliquots are taken from randomly selected locations within the 

sludge mass and the aliquots are composited to form a single sample for analysis. As with other types of 

composite sampling, the more aliquots taken, the more accurate the determination of pollutant levels. 

Additional discussion of this sampling method can be found in Environmental Regulations and 

Technology: Control of Pathogens and Vector Attraction in Sewage Sludge, 1999 Edition (EPA/625-R92-013), POTW Sludge Sampling and Analysis Guidance Document (EPA/833-B-89-100), and A Plain 

English Guide to the EPA Part 503 Biosolids Rule (EPA/832-R-93-003). 

4 - 9
Table 4-3: How to Prepare a Flow-Proportioned Grab Composite Sample 

Sample 

Sample Collection/Meter 

Read Date and Time 

Meter Reading 

in million 

gallons(MG) 

Interval Flow 

(IF) Volume 

(MG) 

Flow-Proportioned 

Composite 

(IF/TF * 1000 mL) 

08/16/99 @ 01:12 6,306.5 -

1 08/16/99 @ 06:00 6,307.5 1.0 128 mL 

2 08/16/99 @ 10:48 6,309.2 1.7 218 mL 

3 08/16/99 @ 15:36 6,312.0 2.8 359 mL 

4 08/16/99 @ 20:34 6,313.5 1.5 192 mL 

5 08/17/99 @ 01:12 6,314.3 0.8 103 mL 

Total Flow (TF) 7.8 

Note: This example assumes that a 1-liter (1,000-mL) composite sample is prepared. If a different composite volume is used, 

calculate the flow proportioned composite (the individual grab sample volume to be included in the grab composite) using that 

volume. 

Table 4-4: Example of a Flow-Proportioned Average 

Based on Grab Sample Results and Flow Intervals 

Sample 

Sample Collection 

Date and Time 

Total Cyanide 

(TC) (μg/L) 

Interval Flow 

(IF) Volume 

(MG) 

Flow-Proportioned 

Average 

(IF/TF * TC) 

1 08/16/99 @ 06:00 49 1.0 6 μg/L 

2 08/16/99 @ 10:48 120 1.7 26 μg/L 

3 08/16/99 @ 15:36 110 2.8 39 μg/L 

4 08/16/99 @ 20:34 97 1.5 19 μg/L 

5 08/17/99 @ 01:12 20 0.8 2 μg/L 

Average: 79 Total Flow (TF): 

7.8 

Flow-weighted Average: 92 μg/L 

4.6 ANALYTICAL METHODS 

NPDES and pretreatment regulations require that all wastewater samples be analyzed for the presence of 

pollutants using the approved methods found at 40 CFR Part 136. EPA recommends that these analytical 

methods also be used in the development of local limits. When sampling sludge for metals and total 

solids, however, the requirements in the sludge regulations in 40 CFR Part 503 still apply.

2 

2

The analysis of sludge for the presence of metals should be performed according to EPA test method SW-846 and for 

total solids according to Part 2540 G of the Standard Methods for the Examination of Water and Wastewater, 18th Edition. 

4 - 10 
A principal reason for using the Part 136 methods is to allow the comparison of local limits and 

categorical limits to determine which are more stringent, as required by the General Pretreatment 

Regulations. However, a POTW may encounter a POC that is not regulated by the categorical standards 

or for which no sampling and analytical techniques are listed in Part 136. In such cases, when the POTW 

adopts the local limit, it would also specify the sampling and analytical technique used for measurement. 

Prior approval, however, must be obtained from the Approval Authority through the provisions of the 

General Pretreatment Regulations at 40 CFR 403.12(g)(4). 

To ensure that samples are analyzed properly, EPA recommends that a POTW consider the following 

factors: 

C Anticipated pollutant concentration. 

C Potential interferences. 

C Total vs. a fraction thereof (e.g., total vs. dissolved metals, or total vs. amenable cyanide3). 

C The minimum detection level (MDL) of the analytical method to detect the presence of 

pollutants in trace amounts and the corresponding minimum level (ML) of quantitation 

(generally 3.18 times the MDL) to determine removal efficiencies. 

When selecting methods, POTWs likely will balance these considerations with the cost of the analyses. 

However, costs should not influence the selection of methods to the extent that necessary detectable levels 

are not achieved. A data set that has a significant number of non-detectable results will provide limited 

information for use in local limits development and may compromise the validity of the local limits. If 

that were to occur, the reduced costs would actually be a waste of money. POTWs should use approved 

methods with the lowest detection levels to ensure the local limits calculation is robust and defensible. If 

some of the analytical results are reported as below the MDL, it may be due to the POTW’s sampling 

techniques or the analytical methods that were selected. Given the need to accurately detect trace levels 

of pollutants, POTWs should thoroughly examine potential sources of gross and trace contamination, then 

select analytical methods that can detect very low levels of pollutants. (See Appendix O on Minimizing 

Contamination in Samples.) 

Table 4-5 presents MDLs for different EPA wastewater analytical methods for metals. The table includes 

some methods – inductively coupled plasma (ICP), flame atomic absorption, and graphite furnace atomic 

absorption – listed in 40 CFR Part 136. The table also includes the 1600 series with detection limits in 

the nanogram per liter range for metals. Of the 1600 series, only Method 1631 for mercury is listed in 40 

CFR Part 136. Although these methods were developed for ambient water quality monitoring,4

 they can 

improve the reliability of the data collected. EPA recommends POTWs check with their Approval 

Authority before adopting the 1600 series methods for wastewater analysis per 40 CFR 403.12(g)(4). 

Also listed in 40 CFR Part 136, Method 1664 has been developed for oil and grease and is actually two 

methods. One is the n-hexane extractable materials (HEM) method and the other is the silica gel treated 

HEM(SGT-HEM). HEM measures all oils and greases while SGT-HEM is specific to mineral oils (non3

Amenable cyanide refers to those metallic, cyanide-bearing compounds that are “amenable” to alkaline chlorination or 

electrochemical chlorination treatment processes that will reduce the cyanide complexes to non-toxic chlorides, carbonates and 

hydroxides. 

4 See EPA Methods and Guidance for Analysis of Water, Version 2, EPA 821-C-99-004, June 1999. 

4 - 11 
Table 4-5: MDLs (μg/L) for EPA Wastewater Analytical Methods 

Method Listed in 40 CFR Part 136 Method Not Listed in 40 CFR Part 136 

Metal 

(Total) 

Flame/ 

Other 

Furnace ICP 

(200.7) 

(1631) (1632) (1637) (1638) (1639) (1640) 

Arsenic 2* 

(206.3) 

1 

(206.2) 

8 0.003 

Cadmium 5 

(213.1) 

0.1 

(213.2) 

1 0.0075 0.013 0.023 0.0024 

Chromium 50 

(218.1) 

1 

(218.2) 

4 

Copper 20 

(220.1) 

1 

(220.2) 

3 0.087 0.024 

Cyanide 5** 

(335.3) 

Lead 100 

(239.1) 

1 

(239.2) 

10 0.036 0.015 0.0081 

Mercury 0.2† 

(245.1) 

0.0002 

Molybdenum 100 

(246.1) 

1 

(246.2) 

4 

Nickel 40 

(249.1) 

1 

(249.2) 

5 0.33 0.65 0.029 

Selenium 2* 

(270.3) 

2 

(270.2) 

20 0.45 0.83 

Silver 10 

(272.1) 

0.2 

(272.2) 

2 0.029 

Zinc 5 

(289.1) 

0.05 

(289.2) 

2 0.14 0.14 

* Gaseous Hydride Method 

† Cold vapor technique 

**Manual Distillation 

ICP - Inductively Coupled Plasma 

Flame/Other = Flame Atomic Absorption unless otherwise indicated 

Furnace - Graphite Furnace Atomic Absorption 

(numbers in parentheses) = EPA-approved analytical methods 

Sources: 40 CFR 136.3 Table 1B and Method 1669, "Sampling Ambient Water for Determination of Metals at EPA 

Water Quality Criteria Levels," EPA, July 1996 (which included information about MDLs for 1600 series). 

polar) and is considered a substitute for the total petroleum hydrocarbon (TPH) analysis. It should be 

noted that compounds other than TPH are extracted by n-hexane and this can lead to test results higher 

than actual TPH values. Laundry detergents and surfactants contribute to the interference. This is a 

potential source of interference when samples are collected. For additional information on sample 

collection, preservation, documentation and analysis, see Industrial User Inspection and Sampling 

Manual for POTWs, EPA Office of Water, EPA 831-B-94-001. 

4 - 12
4.7 INFORMATION COLLECTION AND MAINTENANCE 

To document that sampling was conducted properly, EPA recommends POTWs use field measurement 

records and chain-of-custody records. The latter are used to identify the person(s) who collected a sample 

and the persons who may have handled the sample before it was received by the laboratory. They also 

may be used for inter-laboratory transfers of samples. Chain-of-custody records often contain such 

information as the type of sample collected, the date(s) and time(s) of the collection, any chemical 

preservatives added, type of sample container used (i.e., glass, amber glass, or polyethylene), and sample 

temperature. These records also may include the weather conditions and ambient temperature when the 

sample was taken, the color and odor of the sample, or other pertinent sampling information. 

Laboratory reports not only give POTWs data to use in developing local limits, they also provide data to 

verify that the holding times were met and the appropriate analytical methods were used. In addition to 

the analytical results, reports should contain the unique sample ID assigned by the laboratory, the date 

and time of the sample preparation and analysis, the preparation and analytical methods used, the identity 

of the analysts, and quality control data if problems were encountered (including an explanation of the 

problems and how they were addressed). The POTW will want to maintain these records for as long as 

the data they contain are used to support the local limits developed by the treatment works. 

4.8 REVIEW AND EVALUATION OF ANALYTICAL RESULTS 

To develop sound, technically based local limits, the POTW should, out of necessity, review and evaluate 

the data collected to ensure they are accurate, reliable, and representative. Only data that meet the 

POTW’s quality assurance/quality control (QA/QC) requirements should be used to support the 

development of local limits. The EPA guidance document, Procuring Analytical Services: Guidance for 

Industrial Pretreatment Programs, October, 1998 (EPA 833/B-98-004) provides pretreatment authorities 

and IUs with guidance for procuring analytical services necessary to support CWA programs. (The 

document is available at the “publications” link at http://www.epa.gov/npdes.) 

Sampling data evaluations may reveal improperly collected data, elevated detection limits, and new 

POCs. Improperly collected data may mean a sample was taken from the wrong location, was collected 

as a grab sample instead of a composite, or was improperly handled (i.e., the wrong container was used or 

the required chemical preservative was not added). In response to improperly collected data, the POTWs 

will want to educate the responsible person on data collection requirements and ask for additional samples 

to replace the rejected data. 

Measurements below the MDL are fairly common in sampling for local limits development (such as 

during a scan of organic priority pollutants). However, if an elevated number of non-detects is reported, 

EPA recommends that the POTW: 

C Verify that the method detection limit of the analytical method can address compliance with 

applicable criteria. If necessary, sampling and analysis should be performed at a lower MDL. 

C Evaluate possible matrix interferences, other analytical methods, or sampling problems if an 

elevated number of non-detects are reported unexpectedly. 

4 - 13
New POCs may be identified by a POTW’s sampling of influent, sludge, controlled or uncontrolled 

sources. Additionally, a Toxicity Reduction Evaluation (TRE), or a change in applicable standards could 

identify new POCs. A vigilant POTW may be able to identify changes in loadings quickly and add the 

new POCs to its ongoing regimen of evaluation sampling. New POCs identified as a result of a TRE or a 

change in standards may require multiple samples collected over a short period of time, in addition to 

being added to the POTW’s ongoing sampling program. 

4.9 FLOW DATA 

To calculate MAHLs and MAILs, data about the flow of various wastestreams will need to be collected 

so that mass quantities can be computed. The flows for which data are needed are described in the 

following sections. 

4.9.1 TOTAL POTW FLOW 

POTWs routinely measure the total flow into the treatment works. The measurement of total flow 

encompasses all sources, including industrial, domestic, commercial, and I&I. Any hauled wastes treated 

by the POTW also may be measured at the headworks, depending on where the hauled wastes are 

introduced to the treatment system. Total POTW flow is needed for the calculation of effluent-quality 

based allowable headworks loadings (AHLs) (see Section 5.2.2) and inhibition-based AHLs (see Section 

5.2.4). 

In EPA’s view, the POTW will not want to use design flow to calculate local limits because the purpose 

of a local limit is to protect the treatment works and the environment under existing conditions. If the 

design flow were used and the actual influent flow is significantly less, a mass limit would exaggerate the 

domestic and background loadings of pollutants to the POTW and possibly restrict unnecessarily the 

pollutant load given to IUs. 

4.9.2 SLUDGE FLOW TO THE DIGESTER 

Primary and secondary sludge sent to an aerobic or anaerobic digester will contain sorbed pollutants 

whose mass a POTW will want to determine. The flow and concentration values of sludge will be used to 

calculate an AHL to prevent digester inhibition (see Section 5.2.4). Consequently, the average daily flow 

rate of all sludge flows to digestion will need to be known. 

4.9.3 SLUDGE FLOW TO DISPOSAL 

Because one of the most significant environmental impacts an IU discharge can have is on POTW sludge 

quality and its reuse as a resource, the mass of pollutants in sludge applied to the surface of the land or 

disposed of in landfills will need to be known. Most POTWs do not dispose of sludge every day because 

weather conditions, among other factors, interfere with scheduling. To simplify the calculations, EPA 

recommends that the flow of sludge to disposal be reported as an average over the entire year. This value 

is calculated by dividing the total volume of sludge disposed in million of gallons by 365 to yield the 

average volume of sludge disposed in millions of gallons per day. The sludge flow along with the 

pollutant concentration in sludge are used to calculate an AHL to prevent sludge concentrations from 

exceeding the sludge disposal pollutant concentration criteria (see Sections 5.2.3). 

4 - 14
4.9.4 FLOWS FROM CONTROLLED SOURCES 

Converting MAHLs to MAILs requires knowing the flows from all controlled sources (IUs, hauled waste, 

or specific commercial users) that the POTW intends to regulate with numerical local limits. Some 

commercial sites (such as photo finishers) may discharge pollutants in quantities that can be controlled by 

local limits. Discharges from waste haulers may be regulated by POTWs and thus considered controlled 

sources. Flow rates are commonly determined by compiling flow data from water use records, IU 

inspections, and periodic reporting from controlled sources. Controlled source flow rates are used to 

allocate MAILs among controlled sources. 

Hauled wastes that are a significant source of pollutant loadings should be controlled through local limits. 

Therefore, EPA recommends that the average daily volumes of hauled wastes accepted by the POTW be 

included in the measurement of total industrial flows. While hauled wastes commonly contain high 

concentrations of pollutants, the wastes generally are low in mass. Thus, for a POTW to determine the 

additional loading contributed by hauled wastes, the POTW will need extensive sampling of the wastes. 

Mass loadings can then be calculated and factored into the local limits calculations. 

POTWs usually use the sum of all IUs' total plant wastewater flow to develop local limits. Thus, the local 

limits apply "at the curb," where the flow leaves an IU's property. However, this may pose some 

problems for categorical industrial users (CIUs) because categorical standards always apply at the end of 

the regulated process. Each POTW will need to carefully examine flow data from its IUs to assure that all 

wastewater to be regulated by the local limits is being properly quantified. Analysis results and flow data 

used to evaluate compliance with categorical pretreatment standards may not include all wastewater from 

the industry. Ideally, categorical standards are applied at the end of the regulated processes after 

pretreatment. Other wastestreams not subject to categorical standards, but subject to local limits, may be 

discharged downstream of the categorically regulated process wastewater flow. 

Therefore, there may be more than one sampling location established within a CIU to evaluate 

compliance with local limits and categorical pretreatment standards. Non-categorically regulated 

wastestreams often are discharged before treatment at an IU and upstream of the sampling point. The 

combined wastestream formula (CWF) is used to adjust the CIU standards. Flow and pollutant 

concentration data that represent total plant wastewater from an IU should be used to develop local limits. 

This may require that the developer of local limits become more familiar with all sampling points, sewer 

outfalls, and the wastewater characteristics at each IU, especially CIUs. Detailed discussions on how to 

establish effluent limits for categorical industries that do not segregate regulated wastestreams from 

non-regulated or dilute wastestreams are provided in the Guidance Manual for the Use of 

Production-Based Pretreatment Standards and the Combined Wastestream Formula (EPA 833-B-85-201, 

September 1985) and in the Industrial User Permitting Guidance Manual (EPA 833-B-89-001, 

September 1989). 

4 - 15
4.9.5 FLOWS FROM UNCONTROLLED SOURCES 

Converting MAHLs to MAILs also requires knowing the flows of sources that the POTW does not 

control, such as domestic sources, some commercial sites,5

 infiltration and inflow, storm water, waste 

haulers not regulated by local limits, and others. As discussed in Section 4.1.2 and 6.2.1, sampling points 

to determine uncontrolled source flows must be within sections of the collection system that receive 

wastewater only from these sources. 

4.10 SUMMARY 

After reviewing Chapter 4, POTWs should be able to support the determination of MAHLs through the 

collection of various types of data. The applicability and accuracy of the collected data requires an 

understanding of how pollutant types, sampling locations and frequencies, analytical methods, quality 

assurance and quality control (QA/QC) requirements, and information collection and maintenance 

procedures will affect the overall evaluation process. Chapter 5 describes how to use this information to 

develop MAHLs. 

5 These refer to commercial sources with low pollutant discharges or with too many sites to make regulation practical. 

4 - 16 
CHAPTER 5 -

CALCULATION OF MAXIMUM ALLOWABLE

HEADWORKS LOADINGS

Following the approach suggested by EPA, the POTW will have determined pollutants of concern 

(Chapter 3) and analyzed and collected sufficient data to develop local limits (Chapter 4). This chapter 

presents the methodology for calculating maximum allowable headworks loadings (MAHLs)—the third 

step in the four-step recommended MAHL approach to determining local limits. Later, this guidance will 

show the POTW how to evaluate the need for local limits, calculate and allocate the maximum allowable 

industrial loadings (MAILs), and develop final local limits (Chapter 6). 

A MAHL is an estimate of the upper limit of pollutant loading to a POTW intended to prevent pass 

through or interference. MAHLs are the basis for local limits. As shown in Figure 5-1, a MAHL for a 

single pollutant of concern (POC) is calculated in three steps: 

C Calculate POTW removal efficiency for the POC

C Calculate allowable headworks loadings (AHLs) for each environmental criterion

C Designate as the MAHL the most stringent AHL for the POC 

States have an integral role in the development of MAHLs. In addition to State environmental criteria 

being the basis of many AHL calculations, some Approval Authorities require that the MAHL calculation 

be performed on specific spreadsheet models. The spreadsheet models ensure consistency in the 

collection and analysis of data and simplify the AHL calculation by providing the pertinent State 

standards. POTWs should check with their Approval Authorities to determine if a spreadsheet model is 

recommended. For example, EPA Region 5, EPA Region 7, and EPA Region 8 have spreadsheet models. 

5.1 CALCULATION OF REMOVAL EFFICIENCIES 

Removal efficiency is the fraction or percentage of the influent pollutant loading that is removed from the 

wastestream across an entire wastewater treatment works or specific wastewater treatment unit within the 

works. Removal efficiency values for each POC are fundamental inputs to MAHL calculations. Removal 

efficiency methodologies vary by degree of data quality and calculation method. This section will: 

C Explain three different types of removal efficiency calculations methodologies: average daily 

removal efficiency, mean removal efficiency, and the decile method. 

C Suggest when to use certain methodologies. 

C Offer guidance on data quality. 

C Discuss applying removal efficiencies reported by other POTWs or industry surveys. 

5 - 1
Figure 5-1: Process Flow Diagram for Calculating MAHL for a Single POC 

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5 - 2
5.1.1 REMOVAL EFFICIENCY CALCULATION METHODOLOGIES 

This section explains the three removal efficiency calculation methodologies commonly used by POTWs. 

They are the average daily removal efficiency, the mean removal efficiency, and the decile method.

Average Daily Removal Efficiency

The average daily removal efficiency (ADRE) calculation requires that an influent sample be paired

with a lagged effluent sample to reflect removal efficiency accurately. Samples are lagged by the

hydraulic residence time of wastewater within the 

treatment plant. As shown in Equation 5.1, a series 

of daily removal efficiencies based on paired 

headworks influent (In) and POTW effluent data 

(Epotw, n) is calculated first. This series of removal 

efficiencies is then summed (symbolized in the 

equation by the Greek letter 3) and divided by the 

total number of paired observations (N) to yield the 

removal efficiency (Rpotw) across the entire 

wastewater treatment plant (from headworks to plant 

effluent). To calculate the removal efficiency from 

headworks to primary treatment effluent (Rprim), use 

paired headworks influent (In) and primary treatment 

effluent data (Eprim, n). To calculate the removal 

efficiency from headworks to secondary treatment 

effluent (Rsec), use paired headworks influent (In) and 

secondary treatment effluent data (Esec, n). 

Mean Removal Efficiency 

More flexible than the ADRE method, the mean 

removal efficiency (MRE) can be used with paired 

data lagged for retention time suitable for the ADRE 

method and data that have not been lagged or paired. 

As shown in Equation 5.2, instead of averaging 

observed paired removal efficiencies, the MRE 

calculation first averages (symbolized in the 

equation by the overbars) all plant influent values 

(Ir ) and all plant effluent values (Epotw,t

) separately 

and then calculates removal efficiency across the 

entire wastewater treatment plant from headworks to 

Equation 5.1: Removal Efficiency 

Calculated Using Average Daily Removal 

Efficiency 

Where: 

Rpotw = Plant removal efficiency from headworks to 

plant effluent, as decimal 

Rprim = Removal efficiency from headworks to 

primary treatment effluent, as decimal 

Rsec = Removal efficiency from headworks to 

secondary treatment effluent, as decimal 

In = POTW influent pollutant concentration at 

headworks , mg/L 

Epotw, n = POTW effluent pollutant concentration 

Eprim, n = Primary treatment effluent pollutant 

concentration, mg/L 

Esec,n = Secondary treatment effluent pollutant 

concentration, mg/L 

n = Paired observations, numbered 1 to N 

plant effluent (Rpotw). The MRE calculation averages all headworks influent data (Ir) and all primary 

treatment effluent data (Eprim, x) to calculate the removal efficiency from headworks to primary treatment 

effluent (Rprim). The MRE calculation averages all headworks influent data (Ir) and all secondary 

treatment effluent data (Esec,y ) to calculate the removal efficiency from headworks to secondary treatment 

effluent (Rsec). 

5 - 3
Unpaired historical data from the same time period 

(such as alternating months during the same year) 

should not introduce bias. However, unpaired 

historical data from different time periods, if used in 

the MRE calculation, can introduce bias when 

significant changes in the POTW’s industrial base 

(such as the opening or closing of an industry or the 

installation of significantly more efficient 

pretreatment equipment units or source control) 

occurred between data collection times. Current 

levels of POTW influent should be compared to 

historical levels to determine if they are of the same 

general magnitude. In addition, unpaired sampling 

data representing some unusual one-time event should 

not be included in the MRE calculation. 

Decile Method 

Mean removal efficiency does not indicate how often

the derived removal efficiency was achieved. The

decile method requires at least nine daily removal

efficiency values based on paired sets of influent and

effluent data. However, instead of averaging the daily

removal efficiency values, the decile method sorts

daily removal efficiency data from highest to lowest

and calculates the percentage of the daily removal

efficiency above or below a specified removal

efficiency. The methodology is similar to a data set

median. A median divides an ordered data set into

two equal parts: with half the data set above the

median and the other half below. The decile method

is similar except it divides the ordered data set into 10

equal parts. Therefore, 10 percent of the data set is

below the first decile; 20 percent of the data set is below the second decile, etc. The fifth decile is

equivalent to the data set median. 

The results of an applied decile

method approach are shown in

Figure 5-2.

Equation 5.2: Removal Efficiency 

Calculated Using Mean Removal 

Efficiency 

Where: 

Rpotw = Plant removal efficiency from headworks to 

plant effluent, as decimal 

Rprim = Removal efficiency from headworks to 

primary treatment effluent, as decimal 

Rsec = Removal efficiency from headworks to 

secondary treatment effluent, as decimal 

Ir = POTW influent pollutant concentration at 

headworks, mg/L 

Epotw, t = POTW effluent pollutant concentration, mg/L 

Eprim, x = Primary treatment effluent pollutant 

concentration, mg/L 

Esec, y = Secondary treatment effluent pollutant 

concentration, mg/L 

t = Plant effluent samples, numbered 1 to T 

r = Plant influent samples, numbered 1 to R 

x = Primary treatment effluent samples, 

numbered 1 to X 

y = Secondary treatment effluent samples, 

numbered 1 to Y 

Figure 5-2 shows the decile values

(labeled “Deciles - Percent of Data

Set Less than Stated Efficiency”) on

the Y-axis and the corresponding

removal efficiencies on the X-axis. 

From this figure, a POTW can gain

an understanding of the likelihood of

certain removal efficiencies. As

illustrated at the fifth decile or

median, this hypothetical POTW has

an overall plant removal efficiency

(Rpotw) of 64.5 percent less than half

Figure 5-2: Decile Results for Hypothetical 

POTW 

0% 

10% 

20% 

30% 

40% 

50% 

60% 

70% 

80% 

90% 

100% 

0% 20% 40% 60% 80% 100% 

Removal Efficiency 

Deciles - Percent of Data 

Set Less than Stated 

Efficiency 

5 - 4
of the time. As illustrated in the third decile, the POTW achieves a removal efficiency of below 36 

percent less than 30 percent of the time. If concerned about recurring effluent limitation violations due to 

plant operation variation, the POTW may decide, based on historical knowledge, to use the more 

conservative third decile, instead of the median fifth decile, as the removal efficiency. However, POTWs 

should be aware that a lower removal efficiency for those pollutants that accumulate in sludge would lead 

to lower, more protective, effluent-based local limits but higher, less protective, sludge-based local limits. 

Appendix P includes sample calculations of removal efficiencies using ADRE, MRE, and decile methods. 

Conservative Pollutant Removal Efficiency Derived from Sludge Data 

For conservative pollutants, such as metals, the 

portion removed during POTW processes ends up in 

the sludge. Therefore, for conservative pollutants, 

POTWs can also use sludge data to estimate removal 

efficiency across the entire plant (Rpotw). Sludge data 

should be used in place of effluent data when a 

POTW has influent data above detection but does not 

have adequate effluent data above detection and, 

therefore, believes sludge data provide more 

representative removal efficiencies. (In general, 

accurate representative sampling results are more 

difficult to attain in the sludge than in the POTW 

effluent sampling.) As shown in Equations 5.3 and 

5.4, ADRE and MRE can be used to calculate 

removal efficiency across the entire plant (Rpotw) by 

comparing the sludge and headworks pollutant 

loading. Sludge loading is calculated by multiplying 

the sludge concentration (S) by the sludge flow rate 

(Qsldg), specific gravity (Gsldg), and percentage solids 

(PS). Influent pollutant loading is calculated by 

multiplying the influent concentration (I) by the 

average POTW flow rate (Qpotw). The influent 

pollutant concentration (I) should be a monthly 

average in order to be compared with sludge pollutant 

concentration, which accounts for pollutants that have 

accumulated for 20 to 30 days. The MRE method is 

often more suitable technique than the ADRE in this 

situation because: 

Equation 5.3: Plant Removal Efficiency 

Calculated Using ADRE and Sludge Data 

Equation 5.4: Plant Removal Efficiency 

Calculated Using MRE and Sludge Data 

Where: 

Rpotw = Plant removal efficiency from headworks to 

plant effluent, as decimal 

I n, Ir = POTW influent pollutant concentration at 

headworks, mg/L 

PS = Percentage solids of sludge to disposal, 

Qsldg = Total sludge flow rate to disposal, MGD 

Qpotw = POTW average flow rate, MGD 

Gsldg = Specific gravity of sludge, kg/L 

8.34 = Unit conversion factor 

Sn, Su = Sludge pollutant concentration, mg/kg 

n = Paired observations, numbered 1 to N 

u = Sludge samples, numbered 1 to U 

r = Influent samples numbered 1 to R 

1. Most POTWs will not have monthly average influent pollutant concentrations readily 

available. 

2. Sludge settling times are difficult to estimate when developing paired observations. 

5.1.2 GUIDANCE ON USING DIFFERENT METHODOLOGIES 

EPA offers the following guidance on implementing the three different methodologies: 

C EPA recommends the MRE over the ADRE method if less than ten data pairs are available, 

because it is generally less sensitive to variation in daily removal efficiencies. 

5 - 5 
C Although requiring more data, the decile approach allows for a more comprehensive view of 

removal rates than the ADRE and MRE methods because it provides a frequency distribution 

and allows for explicit incorporation of daily removal efficiency. 

C Although an overall depiction of the POTW removal efficiency frequency is gained in the 

decile method, an individual decile estimate, depending on how conservative the POTW 

wants to be in establishing removal efficiencies, can be less precise than the MRE and ADRE 

estimates. 

Appendix P of this manual provides additional guidance in the form of an example and an examination of 

the different methodologies applied to one data set. 

5.1.3 DATA QUALITY 

This section reviews some issues related to data quality, quantity, and analytical method limits that often 

cause problems during local limits calculations. 

Outliers 

The following two simple tests can be conducted to see if outliers exist in a given data set: 

1. If the data are known to closely follow a “bell-shaped” normal distribution, then any data 

point that lies more than two standard deviations from the mean is considered an outlier. 

2. If the data values do not approximate a normal distribution, outliers can be determined based 

on the interquartile range (IQR) of the data set. The IQR equals the values between the 1st 

and 3rd quartile. Any data point that lies more than 1.5 times this IQR below Q1, or 1.5 times 

this IQR above Q3 is considered an outlier. 

Both of these methods are demonstrated in Appendix P with a sample data set. 

Concentrations Below the Minimum Level of Quantitation (ML) 

A POTW’s sampling program will probably yield some sampling results that indicate a pollutant was 

below the ML in the analyzed sample. The manner in which the POTW uses these data in the local limits 

development process can significantly affect the MAHL calculation. Table 5-1 details the different 

options available to POTW users. 

Table 5-1: Options for Managing Sampling Results Below the ML in Removal Efficiency 

Calculations 

If only a few data values are below the ML: If most data values are below the ML: 

Option 1: Use surrogate value of 1⁄2 ML. Option 1: Re-evaluate the need for a local limit for the 

pollutant. ever, if the pollutant is one of the 15 EPA 

POCs an AHL should be developed.) 

Option 2: Discard the few samples below the ML. 

and effluent data should be discarded in pairs.) 

Option 2: Use removal rate data from other plants. 

Section 5.1.4.) 

(How

(Influent (See 

In general, the surrogate value results in a greater bias when calculating the mean or standard deviation 

and accuracy decreases as the proportion of non-detects increases. 

5 - 6
Other statistical methods—Regression order statistics (ROS), probability plotting, and maximum 

likelihood estimations (MLE)—are detailed in Appendix Q. The probability plotting method provides 

slightly more accurate results when non-detects represent 30 percent or more of the data set. The MLE 

method works well when the data distribution is exactly normal or lognormal

1

 and when non-detects are 

less than 30 percent of the data set. Other references for using statistics to analyze data sets containing 

values below limits include: 

• Appendix E in the Technical Support Document for Water Quality-based Toxics Control, 

EPA/505/2-90-001, March 1991. 

• Use of Statistical Methods in Industrial Water Pollution Control Regulations in the United 

States, Journal of Environmental Monitoring and Assessment, Volume 12:129-148, 1989. 

Although these methods can be applied by those without a background in statistics, EPA strongly 

recommends that a statistician perform the necessary calculations. 

Negative Removal Efficiency 

Negative removal efficiencies, which reflect valuable operational data, should not be summarily 

dismissed as outliers. Unless technical justification (such as poor sampling or analytical technique) to 

remove them is discovered, negative removal rates should be retained in the data set. Described below 

are methods to manage negative removal efficiencies. Appendix P provides sample calculations to 

address negative removal efficiencies. 

Use the MRE Method or Decile Approach. Negative removal efficiencies are attributable to the fact that 

POTWs do not operate in a steady state. Deviations from steady state occur because of variability in 

POTW influent, recycle streams and performance, accumulation of pollutants in POTW sludge, and 

incidental generation of pollutants by POTW operations. This variability often leads to the ADRE 

method of calculating removal efficiency, dependant on retention time lagged data, to yield negative 

removal efficiencies. In these cases, the MRE method, less sensitive to data variability, should eliminate 

negative removals efficiencies unless an underlying problem exists in the sampling, data analysis or plant 

operations. The decile approach, which ranks instead of averages daily removal efficiencies, can be 

applied to data sets with a few negative daily removal efficiencies because it determines efficiency based 

on probability of occurrence and not averaging. 

Manage data below the ML. In addition, negative removal rates often result from the influent and 

effluent concentrations below the ML. Readings below the ML that can lead to negative removal 

efficiencies should be examined as detailed above. 

5.1.4 APPLYING REMOVAL EFFICIENCIES REPORTED BY OTHERS 

Removal efficiencies are based largely on site-specific conditions such as climate, POTW design, 

operation and maintenance, plant conditions, and sewage characteristics. Therefore, EPA strongly 

suggests that site-specific data be used to calculate removal efficiencies. However, some POTWs still do 

not have adequate data to calculate removals after conducting site-specific sampling and using analytical 

1 Log-normal distributions are probability distributions that are closely related to normal distributions: if X is a 

normally distributed random variable, then exp(X) has a log-normal distribution. In other words, the natural logarithm of a 

log-normally distributed variable is normally distributed. 

5 - 7 
methods that achieve the lowest detection levels possible. In these instances, POTWs may selectively use 

removal efficiencies reported by other POTWs or by studies that have been published in professional 

journals or by EPA. EPA urges POTWs to use performance data from plants employing the same 

treatment technology and similar contributing sources. Appendix R provides a listing of removal 

efficiency data for priority pollutants gathered from other POTWs. (These data are the same as those 

presented in the 1987 Local Limit Guidance Manual.) 

5.2 CALCULATION OF ALLOWABLE HEADWORKS LOADINGS 

An AHL is the estimated maximum loading of a pollutant that can be received at a POTW's headworks 

that should not cause a POTW to violate a particular treatment plant limit or environmental criterion. An 

AHL is developed to prevent interference or pass through. An AHL is calculated for each applicable 

criterion: pass through, sludge contamination, air quality standards, and the various forms of interference 

(biological treatment inhibition, sludge digestion inhibition). The AHLs for each POC are calculated 

based on the various suitable environmental criteria, plant flow rates, and plant removal efficiency. After 

calculating a series of AHLs for each POC, the lowest AHL is chosen as the MAHL. 

Local limits development uses a mass-balance approach to determine the AHLs for a POTW based on the 

environmental and treatment plant criteria. With the mass-balance approach, the POTW calculates the 

amount of loading received at the POTW headworks that will still meet the environmental or treatment 

plant criteria that apply to each pollutant. Steady-state equations are used for conservative pollutants 

because the amount of pollutant loading is “conserved” throughout the treatment plant. Conservative 

pollutants can be removed from wastewater via chemical or physical separation or biological treatment 

but always accumulate in the sludge or remain in wastewater. On the other hand, non-conservative 

pollutants may be lost through degradation or volatilization in addition to accumulating in the sludge. 

Because losses through degradation and volatilization do not contribute to pollutant loadings in sludge, it 

is not valid to assume that all non-conservative pollutants removed during plant treatment are transferred 

to sludge. Therefore, for non-conservative pollutants, different equations are used to calculate AHLs 

based on sludge criteria. 

Fate and transport software can estimate the effects of biodegradation, sorption onto solids, and 

volatilization on substances entering a treatment plant. The most widely used model is EPA’s Water9 

model for wastewater collection and treatment systems available at: 

http://www.epa.gov/ttn/chief/software/water/index.html. 

5.2.1 DETERMINATION OF SUITABLE ENVIRONMENTAL CRITERIA 

A properly functioning POTW will be in compliance simultaneously with air, effluent, and sludge 

environmental criteria (see Figure 5-3). For each POC identified, the POTW should examine the 

appropriate environmental criteria to guard against interference or pass through. From these 

environmental criteria, along with flow rates and removal efficiencies, AHLs are calculated. These 

environmental criteria should have all been evaluated as part of the POC development in Chapter 3. 

Table 5-2 shows suggested criteria that should be evaluated for each POC. The next section provides 

details regarding how to use these criteria in the AHL calculation. 

5 - 8
Table 5-2: Suggested Criteria or Standards to be Considered 

For Each POC in the Development of AHLs 

Effluent Based Sludge-Based Air Quality Based Resource Protection 

Based 

NPDES permit: 

effluent limitations, 

water quality-based 

toxic pollutant limits, 

Whole Effluent Toxicity 

(WET) 

[Source: POTW’s own 

NPDES permit] 

State Sludge Quality 

Criteria: 

Federal criteria or 

stricter 

[Source: State 

regulations] 

State Water Quality 

Criteria and Standards: 

adoption of Federal 

criteria or stricter 

[Source: State 

regulations] 

Federal Sludge 

Standards: 

application, surface 

disposal, or 

incineration 

[Source: Appendix E 

or Federal 

regulations 40 CFR 

Part 503] 

National Recommended 

Water Quality Criteria 

for Priority Pollutants: 

freshwater/saltwater 

chronic and acute 

criteria, human health 

for consumption criteria 

[Source: Appendix D or 

National Recommended 

Water Quality CriteriaCorrection. 

EPA 822-Z-99-001] 

Hazardous Waste 

Criteria: oxic 

Characteristic 

Leaching Procedure 

(TCLP) 

[Source: Appendix F 

or Federal 

regulations 40 CFR 

Part 261.24] 

adoption of 

land 

April 1999, 

T

Inhibition-Based 

POTW’s own in-house 

guidelines or criteria 

for process inhibition 

[Source: POTW 

reports detailing 

circumstances 

surrounding last 

inhibition] 

Literature Inhibition 

Values for activated 

sludge, trickling filter, 

and nitrification 

processes 

[Source: Appendix G] 

5 - 9

Local regulatory 

requirements to meet 

National Ambient Air 

Quality Standards 

(NAAQS) 

[Source: State 

Implementation Plan 

or local regulatory 

requirements to meet 

NAAQS ] 

State and local 

groundwater, aquifer, 

and watershed 

protection permits 

[Source: State 

regulations and local 

codes] 
5 - 10

Figure 5-3: POTW Flow Diagram and Environmental Criteria
5.2.2 EFFLUENT-QUALITY BASED AHLS 

National Pollutant Discharge Elimination System (NPDES) Permit

One of the most effective means of restricting the 

discharge of toxic substances into waters of the 

United States is through a NPDES permit limit. As 

illustrated in Equation 5.5, the AHL based on NPDES 

permit limit (AHLnpdes) is the pollutant loading at the 

NPDES permit limit (Cnpdes * Qpotw) divided by the 

fraction of the pollutant not removed by the plant (1-

Rpotw). The NPDES permit limit can appear in many 

forms—specific technology-based effluent 

limitations, water quality-based pollutant limits, 

whole effluent toxicity—and is commonly expressed 

as milligrams per liter and usually specified as a daily 

maximum2

 and/or a monthly average3 discharge limit. 

POTWs should use actual average POTW flow rate 

data for Qpotw and not use design flows (see Exhibit 5-

1). 

Water Quality Standards or Criteria 

In general, POTWs will not have NPDES permit limits 

for all of the POCs established during the local limits 

analysis. In such cases, EPA recommends a POTW 

base its effluent-quality-based AHL on State Water 

Quality Standards (WQS) or Federal Water Quality 

Criteria (WQC).4 State environmental agencies have 

developed WQS that set maximum allowable pollutant 

levels for their water bodies, specific to the receiving 

stream reach’s designated uses. Designated uses are 

identified by taking into consideration the use and 

value of the water body for public water supply, for 

protection of fish, shellfish, and wildlife, and for 

recreational, agricultural, industrial, and navigational 

purposes. Even though the POTW’s NPDES permit 

Equation 5.5: AHL Based on NPDES 

Permit Limit 

Where: 

AHLnpdes = AHL based on NPDES permit limit, lb/day 

Cnpdes = NPDES permit limit, mg/L 

Qpotw = POTW average flow rate, MGD 

Rpotw = Plant removal efficiency from headworks to 

plant effluent, as decimal 

8.34 = Conversion factor 

Exhibit 5-1: Be Conservative in 

Selecting Criteria 

A recurring theme in this guidance manual is to be 

conservative in making your choices. For example, 

a POTW's NPDES permit limit for a single pollutant 

can sometimes be expressed in two forms - daily 

maximum and monthly average. EPA recommends 

that only the more conservative monthly average 

should be used in calculating NPDES-based AHLs. 

Specific policies regarding this issue should be 

explored with your Approval Authorities. See Section 

6.4.1 for a more detailed discussion of the duration 

of local limits. 

may not contain a numeric effluent limit for a POC, the permit will probably contain narrative provisions 

requiring compliance with State WQS and prohibiting the discharge of any toxic pollutants in toxic 

amounts. A local limit based on a State WQS helps ensure that the POTW can comply with the narrative 

permit requirement specifying “no discharge of toxics in toxic amounts.” In the absence of State WQS, 

local limits may be based on the EPA ambient WQC found in Appendix D. These criteria are EPA’s 

recommended maximum pollutant levels for protecting aquatic life. They offer a sound basis for 

developing local limits for pollutants with the potential for causing toxicity problems in the receiving 

2

 Daily maximum is the maximum allowable discharge of a pollutant during a 24-hour period. 

3 Monthly average is the arithmetic average value of all samples taken in a calendar month for an individual pollutant 

parameter. 

4

POTWs should, if possible, use their State’s methodology to convert a WQS to NPDES permit limits and then use 

these calculated NPDES limits to develop the MAHL. Also see Section 3.2.2. 

5 - 11 
stream. A local limit based on WQC generally would fulfill the narrative permit requirement specifying 

“no discharge of toxics in toxic amounts.” 

As illustrated in Equation 5.6, the AHL based on 

water quality criteria (AHLwq) is calculated as the 

hypothetical pollutant loading to the water body at the 

water quality limit [Cwq(Qstr+Qpotw)] adjusted for the 

background loading of the water body (Cstr *Qstr) and 

divided by the fraction of the pollutant not removed 

by the plant (1- Rpotw). The receiving stream 

background concentration (Cstr) can be an average 

background stream concentration. The receiving 

stream (upstream) flow rate (Qstrm) should be either 

the 7Q10 or 1Q105

 flow based on the particular 

criteria used. The average POTW flow rate (Qpotw) 

should be based on actual plant data and not on 

design flows.6 Under most water quality based 

analyses, Equation 5.6 is sufficient and, consequently, 

is the only one presented here. Another method is the 

five-step process based on the one described in EPA’s 

Technical Support Document For Water Qualitybased Toxics Control (EPA, 1991a). 

In general, WQS and WQC are classified into three 

groups: freshwater aquatic life protection, saltwater 

aquatic life protection, and human health protection. 

Equation 5.6: AHL Based on Water 

Quality Criteria 

Where: 

AHLwq = AHL based on water quality criteria, lb/day 

Cstr = Receiving stream background concentration, 

mg/L 

Cwq = State WQS or EPA WQC, mg/L 

Qstr = Receiving stream (upstream) flow rate, MGD 

Qpotw = POTW average flow rate, MGD 

Rpotw = Plant removal efficiency from headworks to 

plant effluent (as decimal) 

8.34 = Conversion factor 

Freshwater and saltwater aquatic life criteria include chronic and acute toxicity criteria. Chronic toxicity 

criteria are designed to protect aquatic organisms from long-term effects over the organisms’ lifetime and 

across generations of organisms, while acute toxicity criteria generally are designed to protect organisms 

against short-term lethality. EPA offers the following guidance on the use of WQS and WQC: 

C	 Hardness, pH, and Temperature Dependence. WQS and WQC for some metals depend on 

the hardness of the receiving water. If the State has not factored this in, then the POTW 

should obtain from the State the appropriate hardness value for its receiving stream and use 

this value to determine the applicable WQS or WQC. Formulas for the common pollutants 

that are affected by hardness can be found in footnote E to Appendix D. In addition, WQS or 

WQC for some inorganic pollutants (e.g., ammonia) are pH- and/or temperature-dependent 

and should be treated similarly. If the State has not established site-specific values, the 

POTW should contact the State permitting authority to obtain appropriate temperature and 

pH values for its receiving stream. These values should then be used to calculate WQS or 

WQC for AHL determinations. 

5

 1Q10 refers to the lowest average flow for a one-day period that is expected to occur once every ten years. 7Q10 

refers to the lowest average flow for a seven-day period that is expected to occur once every ten years. Both values are available 

in the background documentation for the POTW's NPDES permit issuance and also can be obtained from the local district office 

of the US Geological Survey (http://water.usgs.gov/local_offices.html). 

6 Some States develop WQS to take into account dilution from the receiving stream and therefore the AHL calculation 

in Equation 5.6 would not need to be adjusted for the background loading of the water body, Cstr*Qstr. POTWs should consult 

with their State water quality control agencies. 

5 - 12 
C Converting Dissolved Metals to Total Metals. 

WQS and WQC for some metals may be 

expressed in the dissolved form. Most metals 

measurements, however, are reported in the total 

or total recoverable form. Total and total 

recoverable metals concentrations are always at 

least as high as dissolved metals concentrations 

because a fraction of the metal has sorbed to 

particulate matter in the water. If dissolved 

metals WQS or WQC are used to develop local 

limits that are expressed as total metals, local 

limits will be more stringent than if total metals 

concentrations are used for the WQS. Therefore, 

POTWs should convert dissolved metals WQS or 

WQC into the total metals form before using 

them to calculate water quality-based AHLs (see 

Exhibit 5-2). 

C Chronic and Acute Criteria Guidance. Chronic 

and acute criteria should be used in the 

calculation of AHLs to protect receiving water 

quality. POTWs should not develop a monthly 

Exhibit 5-2: How to Convert 

Dissolved Metals Criteria to Total 

Metals Criteria 

NPDES permit writers often use metals 

translators to convert dissolved water quality 

standards or criteria to total recoverable 

equivalents. Translators are specific to each 

metal and may be 1) the theoretical 

partitioning coefficients; 2) experimentally 

determined through site-specific translator 

studies; or 3) the EPA conversion factors 

used to convert dissolved metals criteria to 

total metals criteria. For establishing an 

AHL, EPA recommends the theoretical 

partitioning coefficient to calculate metal 

translators detailed in The Metals Translator: 

Guidance For Calculating A Total 

Recoverable Permit Limit From A Dissolved 

Criterion (EPA/823-B-96-007). 

average limit based solely on chronic criteria or a daily maximum limit based exclusively on 

acute criteria. AHLs should be calculated based on chronic and acute criteria and the more 

stringent criterion used for comparison with other AHLs. 

C Stream Flow Guidance. To calculate limits based on chronic WQS, the receiving stream 

flow rate should be consistent with State recommendations for chronic criteria, such as 7Q10 

flows. To calculate limits based on acute criteria, the POTW should also use the Staterecommended receiving stream flow (e.g., 1Q10). POTWs should consult with their State 

water quality agencies to confirm the correct flow values. 

Resource Protection 

Many State water quality protection laws that are the basis for POTW permits protect all waters of the 

State including groundwater. Some POTWs have discharges that have the potential to impact 

groundwater resources such as water reclamation projects to recharge groundwater, saline intrusion 

barriers (to minimize the intrusion of saline groundwater into fresh groundwater) or disposal of treated 

effluent via underground injection control (UIC) wells. Potential groundwater impacts can also be of 

concern in effluent dominated streams in arid regions of the country. Therefore, groundwater protection 

may need to be considered during local limits development. Some examples of groundwater protection 

requirements that might need to be considered in local limits development include the following: 

• Aquifer Protection Permits and Water Reuse Permits. Arizona issues aquifer protection 

permits and water reuse permits to POTWs that discharge to effluent-dominated streams or 

reuse the water for irrigation or other uses. The effluent limits in these permits are designed 

to protect diminishing groundwater resources and to assure adequate effluent quality for the 

reuse activity.

7 

7

 Communication with John E. Watson, City of Phoenix Water Services Division, February 12, 2003. 

5 - 13 
• State NPDES Permits. New York State law specifies groundwater effluent discharge 

limitations to protect groundwater quality. When an effluent may have an impact on 

groundwater, State Pollutant Discharge Elimination System permits include effluent limits to 

protect groundwater.8 

• Underground Injection Control (UIC)Program Permits. The Miami-Dade County POTW 

system disposes effluent into underground injection wells. The POTW is required to comply 

with UIC permits as well as its NPDES permits. The most stringent standards are being used 

in local limits calculations.9 

UIC, groundwater, or aquifer protection criteria can be used in place of NPDES permit limit (Cnpdes) in 

Equation 5.5 to calculate AHLs based on resource protection. 

5.2.3 SLUDGE-QUALITY BASED AHLS 

In February 1993, EPA issued the Part 503 Biosolids regulations governing the use or disposal of sewage 

sludge. Pollutant levels were established for three disposal alternatives: land application to condition the 

soil or fertilize crops grown in the soil, surface disposal for final disposal, and incineration. The pollutant 

levels, however, are different for each alternative. In addition to the Federal standards, States may have 

sludge standards that are more stringent or that regulate more pollutants. Therefore, POTWs should 

check with their State environmental agencies to confirm the applicable standards. Regardless of how a 

POTW disposes of sludge, POTWs may wish to consider using land application “clean sludge” values 

from 40 CFR 503.13 in their calculation of AHLs. Use of these criteria can improve a POTW’s beneficial 

use options for disposal of sludge. The further achievement of these standards is consistent with the 

objectives of the National Pretreatment Program, which are listed at 40 CFR 403.2. Moreover, the land 

application standards have a more extensive list of pollutants than either surface disposal or incineration 

and they help control discharges of toxic pollutants that the other disposal alternatives do not address. 

The Part 503 Biosolids Regulations also indicate that biosolids placed in a municipal solid waste landfill, 

a fairly common practice, must meet only the Federal provisions of Part 258 RCRA Subtitle D landfill 

regulations or delegated States’ regulations. These provisions generally include a hazardous waste 

evaluation, which is detailed in the last part of this section discussing municipal solid waste landfills. 

Land Application 

Federal sludge use or disposal regulations, found at 40 CFR Part 503, establish limitations for nine 

common metals (arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc) that 

are primarily controlled by the Pretreatment Program. As shown in Appendix E, four types of land 

application limitations were established and are known by the table number in which they appear: 

C Table 1: Ceiling Concentrations [milligrams per kilogram (mg/kg)] establish the maximum 

concentration that can be in sludge when it is land applied. 

C Table 2: Cumulative Pollutant Loading Rates [pounds per acre (lb/acre)] establish the limits 

that cannot be exceeded over the lifetime of the disposal site. 

8

 See Title 6 of the Official Compilation of Codes, Rules and Regulations of the State of New York (6 NYCRR) 

Chapter 10, Part 703.6. 

9

 Memo from M. Mallard Greene, US EPA Region IV dated January 14, 2003 with a copy of the UIC Permit and 

NPDES permit. 

5 - 14 
C Table 3: Pollutant Concentrations (mg/kg) set levels considered “clean” sludge and are 

subject to less restrictive reporting requirements. 

C Table 4: Annual Pollutant Loading Rates (lb/acre/year) establishes maximum loadings that 

can be applied in any given year. 

As illustrated in Table 5-3, sludge standards are applied based on biosolid end use. For all land 

application of biosolids, POTWs must comply with Table 1 ceiling concentrations. If its biosolids are 

applied to agricultural land, a forest, a public-contact site, or a reclamation site, a POTW must comply 

with either the cumulative loading rates in Table 2 or the monthly average pollutant concentrations in 

Table 3. If its biosolids are applied to a lawn or home garden, the sludge pollutant concentration may not 

exceed the monthly average pollutant concentrations in Table 3. If its biosolids are sold or given away in 

a bag or other container for land application, the POTW must comply with monthly average pollutant 

concentrations in Table 3 or the annual pollutant loading rates in Table 4. 

Table 5-3: Land Application Requirements 

Biosolids End Use Table 1 

Ceiling 

limits 

(mg/kg) 

Table 2 

Cumulative 

limits 

(lb/acre) 

Table 3 

“Clean 

Sludge” 

Pol. Conc. 

(mg/kg) 

Table 4 

Annual limits 

(lb/acre/ 

year) 

Applied to agricultural land, forest, 

public contact site, reclamation 

site 

x and x or x 

Applied to lawn or garden x and x 

Sold or given away in bag or 

container 

x and x or x 

To calculate AHLs based on sludge land application criteria, a POTW should: 

C Determine which land application criteria apply to its biosolids by using Table 5-3. 

• Determine the applicable Table 1, 2, 3, or 4 criteria in Appendix E for each POC. 

• Convert the applicable Table 2 cumulative loading rates (Ccum) and applicable Table 4 annual 

pollutant loading rates (Cann) to equivalent sludge standards (Cslgstd) using Equation 5.7 and 

Equation 5.8, respectively. The values for site life (SL) and site area (SA) are determined by a 

POTW’s sludge management plan. The POTW determines how long the sites will be used 

and how much land or acreage is needed for disposal of the total annual volume of sludge 

generated. Generally, the amount of land needed is determined by dividing the total annual 

sludge production by the agronomic application rate for nitrogen based on the crop grown. 

C Determine the lowest sludge concentration standard (Cslgstd) derived from Equation 5.7, 

Equation 5.8, Table 1 Ceiling Concentrations, Table 3 Monthly Average Pollutant 

Concentrations, and suitable State sludge standards. 

5 - 15
C Use Equation 5.9 with the lowest sludge 

concentration standard (Cslgstd) to 

determine the sludge land-applicationbased AHL for conservative pollutants. 

As shown in Equation 5.9, the AHL for 

land application (AHLsldg ) is the pollutant 

loading of sludge at the sludge standard 

[(Cslgstd) * (PS/100) * (Qsldg) * (Gsldg)], 

divided by the overall plant removal 

efficiency (Rpotw). 

EPA offers the following guidance in performing the 

calculations in Equations 5.7 through 5.9: 

C Values greater than the Table 1 ceiling 

concentrations can not be used for Cslgstd, 

because the regulations governing use or 

disposal of sewage sludge (40 CFR Part 

503) expressly prohibit any form of land 

application if the sludge exceeds these 

concentration levels for any regulated 

component. In addition, EPA 

recommends that the POTW consider 

using the more conservative pollutant 

concentration levels for “clean sludge” 

specified in Table 3 because these levels 

are more protective of the environment, 

promote greater flexibility in the 

beneficial use of sludge, and are subject 

to less restrictive reporting and 

management requirements. This grade of 

sludge would meet the criteria for 

“exceptional quality”or “low pollutant 

concentration” sludge.10 

Equation 5.7: Converting Table 2 

Cumulative Loading Rates to Dry Sludge 

Concentrations 

Equation 5.8 : Converting Table 4 Annual 

Loading Rates to Dry Sludge 

Concentrations 

Where: 

Cslgstd = Equivalent sludge standard, mg/kg dry 

sludge 

C cum = Federal or State land application cumulative 

pollutant loading rate, lb/acre over the site 

life 

Cann = Federal or State land application annual 

pollutant loading rate, lb/acre/yr 

Gsldg = Specific gravity of sludge, kg/L 

PS = Percent solids of sludge to disposal 

Q bla = Sludge flow rate to bulk land application 

(agricultural, forest, public contact, or 

reclamation site), MGD 

Qla = Sludge flow rate to non-bulk land application, 

MGD 

SA = Site area, acres 

SL = Site life, years 

3046 = Unit conversion factor 

C Generally, POTWs can assume the specific gravity of sludge (Gsldg) equals that of water (1 

kg/L). For a typical wet sludge containing about 5 percent solids (PS) the specific gravity of 

the sludge does not differ significantly from that of water. However, drier sludges such as 

dewatered sludges with 30 percent solids may have a specific gravity of 1.1 kg/L or greater. 

In these circumstances, if the specific gravity is not considered, AHLs will be understated and 

any local limits based on these AHLs may be unnecessarily conservative. Therefore, the 

POTW can measure the specific gravity of its sludge to correct for the error introduced as the 

percent solids rises. If the POTW does not have data on the specific gravity of its sludge, it 

should assume conservatively that the specific gravity is 1 kg/L. Guidelines for determining 

the specific gravity of sludge are provided in Appendix S. 

10See Chapter 2 in A Plain English Guide to the EPA Part 503 Biosolids Rule, EPA/832/R-93/003, September 1994 

5 - 16 
C If the POTW’s data for sludge flow rate to disposal are expressed in dry metric tons per day 

(or can be converted to dry metric tons per day), a specific gravity factor is not needed. An 

equation for calculating an AHL using dry metric tons per day is provided in Appendix T. 

C Table 1 sludge ceiling concentrations are instantaneous maximum concentrations, while the 

“clean sludge” criteria in Table 3 are monthly average concentrations. See Section 6.4.1 for a 

discussion of how the types of criteria – monthly average, instantaneous maximum – affect 

the type of local limit developed. 

Surface Disposal 

Sludge surface disposal occurs at dedicated disposal 

sites, surface impoundments, waste piles, monofills, 

or dedicated beneficial use sites. The difference 

between surface disposal and land application is that 

land application is performed at rates that do not 

exceed the agronomic rates of the fertilizer value of 

the sludge. For a more extensive discussion of 

surface disposal, see the sludge regulations at 40 CFR 

503.20. Surface disposal regulates only three metals 

(arsenic, chromium, and nickel) at levels near the 

“clean sludge” levels for land application. The 

standards apply to sludge disposed at facilities 

without a liner or a leachate collection system. AHLs 

based on sludge surface disposal quality should be 

calculated in the following manner: 

C Table 1 (40 CFR 503.23) sludge surface 

disposal criteria should be used directly 

as the sludge standard (Cslgstd) in Equation 

5.9 for conservative pollutants. 

Equation 5.9: AHLs Based on Sludge 

Land Application and 

Surface Disposal Criteria 

(for conservative pollutants) 

Where: 

AHLsldg = AHL based on sludge, lb/day 

Cslgstd = Sludge standard, mg/kg dry sludge 

PS = Percent solids of sludge to disposal, 

Qsldg = Total sludge flow rate to disposal, MGD 

Rpotw = Plant removal efficiency from headworks to 

plant effluent, as decimal 

Gsldg = Specific gravity of sludge, kg/L 

8.34 = Unit conversion factor 

C If the sewage sludge unit is less than 150 meters from the property line, Table 2 (40 CFR 

503.23) sludge disposal criteria, based upon distance from the property line, should be used 

directly as the sludge standard (Cslgstd) in Equation 5.9 for conservative pollutants. See 

Appendix E for a list of Table 1 and Table 2 surface disposal options. 

In addition, POTWs should be aware that surface disposal regulations allow for site-specific limits. Site 

owners or operators may have requested surface disposal criteria from the permitting authority in place of 

the Table 1 or Table 2 sludge surface disposal criteria. Therefore, the POTW should check with the 

disposal site owner/operator to determine standards that apply. If the State has developed more stringent 

sludge disposal standards for surface disposal, the POTW needs to use those standards in its calculation of 

AHLs when using Equation 5.9. 

Incineration 

Incineration, the third method of sludge disposal, typically regulates arsenic, cadmium, beryllium, 

chromium, lead, mercury, and nickel. Limits are site-specific and based on feed rate, stack height 

(dispersion factor), incinerator type, and control efficiency. EPA offers the following guidance on 

incineration-based AHLs: 

5 - 17
C POTWs that dispose of their sludge through incineration should determine AHLs based on 

the calculated sludge standards that apply to the sludge feed to the incinerator. These 

standards may have been calculated by the owner/operator of the incinerator (and listed in a 

sludge disposal agreement), the State, or EPA from the equations provided in 40 CFR Part 

503, and should be expressed in mg/kg dry sludge. These standards should be used directly 

as the sludge standard (Cslgstd) in Equation 5.9 to determine the AHL. 

C If no sludge standards have been calculated for the sludge feed to the incinerator, POTWs 

should use the 40 CFR Part 503 equations (provided in Appendix T) to determine the 

maximum pollutant concentrations for the incinerator feed. These standards should be used 

directly as the sludge standard (Cslgstd) in Equation 5.9 to determine the AHL. As a general 

rule, an AHL for incineration will be an order of magnitude or greater than an AHL based on 

land application. 

Municipal Solid Waste Landfill’s Hazardous Waste Requirements 

According to 40 CFR 503.4, “any person who prepares sewage sludge that is disposed in a municipal 

solid waste landfill unit shall ensure that the sewage sludge meets the requirements of 40 CFR Part 

258. . . .” Part 258 does not allow municipal solid waste landfill units to accept hazardous waste. 

Whether a POTW’s sewage sludge is hazardous waste may be determined by using EPA’s TCLP test. If 

determined to be hazardous waste, sludge must be disposed of according to RCRA requirements. POTWs 

cannot dispose of sludge determined to be hazardous waste in solid waste landfills designated for nonhazardous waste. In general, POTWs will not generate sludge that exceeds TCLP limits. 

However, because the costs and liabilities associated with the management and disposal of hazardous 

sludge are high, POTWs may find it advantageous to periodically run the TCLP test on their sludge to 

identify any trends of increasing pollutant concentrations that may lead the sludge to be considered 

hazardous waste. The POTW should compare the quality of its sludge with the limits in the TCLP and, as 

necessary, set local limits to help ensure that the pollutant levels in its sludge do not exceed TCLP levels. 

If TCLP test results are close to or exceed the TCLP limit, the POTW needs to develop AHLs based on 

TCLP criteria. To develop TCLP-based AHLs, the POTW should: 

C Determine the dry weight metals and toxic organics concentrations (in mg/kg dry sludge) that 

would be protective against sludge being classified as hazardous based on the TCLP test from 

sampling data. The POTW can collect site-specific data for both total pollutant 

concentrations in the sludge and TCLP concentrations (10-12 data pairs) and use these data to 

correlate TCLP concentrations with total concentrations in the sludge. 

C Use these dry-weight, correlation-based concentrations directly as the sludge standard (Cslgstd) 

in Equation 5.9 to determine the AHL. 

5 - 18
5.2.4 INHIBITION-BASED AHLS 

Secondary and Tertiary Treatment Unit Inhibition 

Pollutant levels in a POTW’s wastewater or sludge may 

cause operational problems for biological treatment 

processes involving secondary and tertiary treatment. 

Disruption of a POTW’s biological processes is referred to as 

inhibition and can interfere with a POTW’s ability to remove 

biochemical oxygen demand (BOD) and other pollutants. A 

POTW should assess any past or present operational 

problems related to inhibition and follow the protocol 

outlined below. 

C No Past Inhibition Problems at POTW. 

POTWs may not need to calculate AHLs to 

protect against inhibition because current 

loadings are acceptable to the treatment work’s 

biological processes. However, a POTW may 

still choose to calculate AHLs based on 

biological process inhibition criteria to prevent 

future loadings that may cause inhibition and 

should follow the steps outlined below for 

POTWs with past inhibition problems. 

C Past Inhibition Problems at POTW. POTWs 

should calculate AHLs based on inhibition 

criteria. If site-specific data are needed (see 

Exhibits 5-3 and 5-4), the POTW may choose to 

substitute pollutant concentrations that either 

have occurred in the applicable biological 

process or are currently in its influent and have 

not caused inhibition, in place of process 

inhibition values that have been reported in 

studies published by EPA or in professional 

journals. Inhibition criteria for select secondary 

treatment units (such as activated sludge and 

trickling filters) and one tertiary treatment unit 

(nitrification) are presented in Appendix G. 

Site-specific inhibition data are preferred to literature data 

because they more accurately measure pollutant 

concentrations that cause inhibition in actual biological 

treatment environments. Inhibition of biological treatment 

processes could be a function of toxic compounds (not a 

Exhibit 5-3: The Challenge in

Determining 

Plant Inhibition Values

Determining site-specific inhibition values is 

difficult because the exact point at which 

pollutant concentration inhibition takes place 

is difficult to identify. For instance, an 

activated sludge system’s mixed liquor may 

run at about 1 mg/L zinc. An industrial 

discharge causes the plant to violate its 

NPDES permit by upsetting the plant and 

raising the mixed liquor concentration to 100 

mg/L zinc. How can one determine at which 

concentration the inhibition took place? The 

concentration lies somewhere between 1 and 

100 mg/L. An inhibition value set at 100 

mg/L would be incorrect because a lower 

value could have caused the inhibition. 

Some POTWs have attempted to estimate 

site-specific inhibition values by simply using 

the highest observed pollutant concentration 

in the biological process that did not cause 

interference. 

Exhibit 5-4: Inhibition Value Study 

by Chesterfield County (VA) 

Chesterfield County's Pretreatment Program 

conducted a site-specific evaluation of 

inhibition values for several heavy metals as 

part of its recent recalculation of local limits. A 

pilot system was fed with primary effluent from 

the full-scale facility and was loaded with 

varying levels of several heavy metals to 

determine the loading rate that caused 

measurable deterioration in process 

performance. The measured inhibition values 

for this plant were typically found to be much 

higher than those given in Appendix G. In this 

case, the controlling factor became the 

inhibition potential of the anaerobic digesters, 

and it was possible to substantially increase 

the local limits as a result of the data 

generated from pilot testing. [Contact Abha 

Sharma of Chesterfield County (VA) 

Pretreatment program.] 

single toxic compound), synergism, antagonism, pH, temperature, hardness, stressed conditions, 

microorganism acclimation, and the number and variety of microorganisms present. Sometimes based on 

laboratory studies using pure cultures, literature values can indicate inhibition at much lower 

concentrations than in actual biological treatment environments for the following four main reasons: 1) 

organic chemicals combine with the metals and reduce metal availability to the microbes; 2) activated 

sludge environments generally have a variety of organisms present that may not be as sensitive to metal 

5 - 19
concentrations; 3) metals can chelate toxic organics, reducing their toxicity to nitrifiers; 4) acclimated 

biological treatment populations can accept higher concentrations of metal and organic toxins than 

laboratory cultures. In addition to the technical drawbacks, literature values, if eventually the limiting 

basis of a local limit, will most likely engender more regulatory scrutiny. 

Equation 5.10 is used to calculate inhibition-based 

AHLs for secondary treatment processes such as 

aerated lagoons, stabilization ponds, activated 

sludge, rotating biological contactors, and trickling 

filters. Equation 5.11 is used to calculate inhibitionbased AHLs for tertiary treatment for various 

processes to remove nitrogen, phosphorus, 

suspended solids, organics, metals, and dissolved 

solids (see Figure 5-3). As shown in Equation 5.10, 

the AHL based on secondary treatment unit 

inhibition (AHLsec) is calculated by dividing the 

pollutant loading to the secondary treatment unit at 

the inhibition criterion (Cinhib2 * Qpotw) by the fraction 

of the pollutant not removed after primary treatment 

(1 - Rprim). As shown in Equation 5.11, the AHL 

based on tertiary treatment unit inhibition (AHLter) is 

calculated by dividing the pollutant loading to the 

tertiary treatment unit at the inhibition criterion 

(Cinhib3 * Qpotw) by the fraction of the pollutant not 

removed after secondary treatment (1 - Rsec). The 

POTW flow rate (Qpotw) should be calculated using 

actual average flow data and not design flow. 

Appendix U shows where to sample in various plants 

to calculate inhibition-based loading. (Note that in 

many POTWs nutrient removal is often more like an 

advanced secondary process that occurs in the same 

basin as an activated sludge process. In these cases, 

the same primary removal efficiency (Rprim), would 

be used in both Equations 5.10 and 5.11.) 

Sludge Digester Inhibition 

Sludge digestion is also a biological process that can 

Equation 5.10: AHLs Based On 

Secondary Treatment Inhibition 

Equation 5.11: AHLs Based On Tertiary 

Treatment Inhibition 

Where: 

AHLsec = AHL based on secondary treatment 

inhibition, lb/day 

AHLter = AHL based on tertiary treatment inhibition, 

lb/day 

Cinhib2 = Inhibition criterion for secondary treatment, 

mg/L 

Cinhib3 = Inhibition criterion for tertiary treatment, mg/L 

Qpotw = POTW average flow rate, MGD 

Rprim = Removal efficiency from headworks to 

primary treatment effluent, as decimal 

Rsec = Removal efficiency from headworks to 

secondary treatment effluent, as decimal 

8.34 = Unit conversion factor 

be upset if pollutants are allowed to accumulate to toxic levels. Plant-specific sludge digestion inhibition 

thresholds, like inhibition of secondary treatment, are difficult to know. Literature data on sludge digester 

inhibition criteria are listed in Appendix G. The preponderance of sludge digestion inhibition data are for 

anaerobic digesters. There is no publicly available data about the effect of metals on aerobic digestion of 

sludge. 

5 - 20
Equation 5.12: AHLs Based On Sludge 

Digestion Inhibition (Conservative 

Pollutants) 

Equation 5.13: AHLs Based On Sludge 

Digestion Inhibition (Non-conservative 

Pollutants) 

Where: 

AHLdgstr = AHL based on sludge digestion inhibition, 

lb/day 

Linfl = POTW influent loading, lb/day 

Cdgstinhib = Sludge digester inhibition criterion, mg/L 

Cdgstr = Existing pollutant level in sludge, mg/L 

Qdgstr = Sludge flow rate to digester, MGD 

Rpotw = Plant removal efficiency from headworks to 

plant effluent, as decimal 

8.34 = Unit conversion factor 

Using the steady-state mass balance approach across 

the influent to the digester, Equation 5.12 calculates 

the AHL based on sludge digestion inhibition 

(AHLdgstr) for conservative pollutants such as metals. 

AHLdgstr is calculated by dividing the pollutant loading 

at the inhibition criterion to the digester (Cdgstinhib * 

Qdgstr) by the removal efficiency across the entire 

POTW (Rpotw). As shown in Equation 5.13, for nonconservative pollutants (AHLdgstr) is found by 

multiplying the POTW influent loading (Linfl) by the 

ratio of the sludge digester inhibition criterion 

(Cdgstinhib) and the level of the POC in the sludge 

(Cdgstr). 

5.2.5 AIR-QUALITY BASED AHLS 

In rare circumstances, POTWs that have been 

regulated as air pollution sources and have air 

emissions standards for specific toxics may need to 

consider calculating AHLs for those toxics (see 

Section 3.2.4). AHLs based on air emissions 

standards can be calculated using either Equation 

5.14, which uses the air standard and removal 

efficiency by volatization, or Equation 5.15, which 

uses air standards and existing air emissions. The 

POTW can conduct air emissions sampling or conduct 

modeling to predict existing air emissions (Cair). The most widely used model, EPA’s Water9 model for 

wastewater collection and treatment systems, is available at: 

http://www.epa.gov/ttn/chief/software/water/index.html. 

POTWs can determine pollutant removal efficiency by 

volatilization (Rvol) by examining sampling data of 

influent, effluent, sludge, and air and determining the 

portions of the total removal efficiency associated with 

adsorption to the sludge, biodegradation, and 

volatilization. In addition, POTWs can model the 

removal process to predict pollutant removal efficiency 

by volatilization. 

5.3 AHLS FOR CONVENTIONAL AND NONCONVENTIONAL POLLUTANTS 

This section provides guidance on the development of 

AHLs for three conventional pollutants [BOD, Total 

Suspended Solids (TSS), oil and grease] and one nonconventional pollutant (ammonia), whose unique 

circumstances allow for special mechanisms for their 

AHL development. 

Equation 5.14: AHLs Based On Air 

Criteria and Volatization Rates 

Equation 5.15: AHLs Based On Air 

Criteria and Existing Emissions 

Where: 

AHLair = AHL based air emission standards, lb/day 

Linfl = POTW influent loading, lb/day 

Cairstnd = Air emissions standard, grams/day 

Cair = Existing air emissions, grams/day 

R vol = Pollutant removal efficiency by 

volatilization, as decimal 

0.0022 = Unit conversion factor 

5 - 21
5.3.1 BOD/TSS 

One of the most commonly documented industry-related causes of POTW effluent violations is the 

discharge of excessive conventional pollutants, particularly BOD and TSS (see Exhibit 5-5). As stated 

earlier in the chapter on POC development, POTWs should develop MAHLs for all NPDES-permitted 

conventional pollutants and understand the degree to which the plant is loaded. In fact, some EPA 

regions require any wastewater treatment plant that operates at 80 percent of any NPDES permitted 

conventional pollutant MAHL for three months of the calendar 

year to calculate a MAIL and establish local limits for those 

pollutants. To establish MAHLs for BOD and TSS, EPA 

recommends the following: 

• The POTW’s rated average design capacity, along 

with any improvements subsequent to construction 

that have increased plant capacity, should be used 

as a “monthly average”- based MAHL. The 

treatment works is designed to have the capacity to 

consistently treat a specified amount of 

conventional pollutants to acceptable levels for 

discharge. A copy of the approved design capacity 

may be available from the State as part of the 

design or operating manual for the POTW. 

• The POTW’s peak loading capacity should be 

Exhibit 5-5: Less BOD, More 

Ammonia and Phosphorous 

In the late 1980s, the City of Trenton 

Wastewater Treatment Plant (WWTP) 

violated NPDES permits due to excessive 

BOD5 loading. Today, BOD5 loading has 

been cut in half after two industries that 

accounted for half of the BOD5 loading 

upgraded their existing treatment facilities by 

including nutrient addition and longer 

retention times. However, the industries’ 

nutrient addition led to problems with high 

amounts of Ammonia-N and Phosphorous 

discharged to the WWTP. The ratio of BOD 

to Ammonia-N to Phosphorous has 

increased from 100:5:1 to 100:11:2. 

used as the “daily maximum”- based MAHL. Based on a peaking factor, peak loading 

capacity reflects the plant’s ability to handle diurnal, wet weather, or seasonal peaks. 

EPA recognizes that sometimes average design capacity and the corresponding peak loading factor may 

be too conservative when considering the industrial allocation of conventional pollutants. Therefore, the 

POTW can provide a technically defensible argument for establishing a MAHL for the plant. These 

arguments could include the following: 

• Performing mass balance calculations on the entire plant for the current condition, and scale 

up the plant loading until loading rates for individual processes exceed design guidelines, 

including solids handling facilities. 

• Verifying capacity of hydraulic structures. 

• Performing detailed modeling of biological process capacity under current loading conditions 

using software (e.g., BioWin by Envirosim). Calibrate the model to current conditions and 

then increase loading rates to estimate failure. 

• Determining maximum biological process loading compared to typical design guidelines -

including aeration equipment capacity, basin sizing, mixing energy, secondary clarifier 

sizing, return activated sludge/waste activated sludge capacity, nutrient removal capacity, 

winter and peak operation. 

• Evaluating current operating conditions. For example, a plant with three activated sludge 

trains is operating reliably at 2/3 of its design loading with only one train in service. 

5 - 22
• Stress testing of individual processes. Increase loading through a single process train until 

failure is recognized. 

• Benchmarking against similar plants and processes. 

• Pilot or bench-scale testing of unit operations that have been determined to possibly be a 

bottleneck for plant capacity. 

Smaller plants should incorporate a safety factor in developing the BOD/TSS MAHL for the plant using 

these methods. 

5.3.2 AMMONIA 

Typical concentrations of ammonia in untreated domestic wastewater range from 10 to 50 mg/L. 

Therefore, significant non-domestic industrial sources of ammonia will be unusual and the result of 

industry-specific activities. If the POTW was designed to remove ammonia through specific processes 

such as nitrification and denitrification, breakpoint chlorination, or ammonia stripping, the engineering 

specifications that establish design loading rates should be used as the MAHL. However, for most 

conventional activated sludge and trickling filter plants, ammonia removal is incidental, and a study of the 

plant will have to be conducted to determine its removal efficiency. The AHL for ammonia can then be 

determined using Equation 5.5. When the AHL is determined using site-specific removal efficiencies and 

Equation 5.5, a safety factor of at least 20 percent should be applied. NPDES ammonia limits are often 

seasonal, with more stringent limits in place during warmer weather. This needs to be taken into 

consideration in the development of local limits. A seasonal limit for ammonia might be developed for 

IUs as well. 

5.3.3 OIL AND GREASE 

The term fats, oil, and grease (FOG) includes materials of vegetable, animal, and mineral origin. Mineral 

oils include petroleum, hydrocarbon, and or non-polar fats, oils, and grease. Petroleum-based oil and 

grease (non-polar concentrations) occur at businesses using oil and grease; and can usually be identified 

and regulated by municipalities through local limits and associated pretreatment permit conditions. 

Animal-based and vegetable-based oil and grease (polar concentrations) are more difficult to regulate 

when the major source is a large number of restaurants and fast-food outlets in the collection system. 

Collection system issues related to animal-based and vegetable-based oil and grease are addressed in 

Section 8.3 dealing with flow obstructions. 

The pretreatment regulations 40 CFR 403.5(b)(6) prohibit the discharge of “petroleum oil, nonbiodegradable cutting oil, or products of mineral oil origin in amounts that will cause interference or pass 

through.” Most POTWs have adopted 100 mg/L as their local limit for petroleum-based oil and grease 

because of its history of being protective of the treatment plant and receiving stream. Additionally, the 

5 - 23
limit of 100 mg/L is achievable with the application 

of best management practices (BMPs) or generally 

available pretreatment. The basis of the 100 mg/L 

limit is an April 1975 EPA document titled 

Treatability of Oil and Grease Discharged to 

Publicly Owned Treatment Works. This study 

found a dilution of at least two occurs in collection 

systems and that influent to biological treatment 

systems should contain less than 75 mg/L and 

preferably less than 50 mg/L oil and grease of 

mineral or petroleum origin to prevent interference. 

The 100 mg/L was recommended as the value that 

prevents interference based on the dilution. 

However, the basis for the 100 mg/L FOG limit is 

not site specific. The limit should be justified with 

additional information in order to be considered a 

technically based limit. See Exhibit 5-6 for a 

description of how the City of Richland, 

Washington addressed this limit. 

Developing a technically based local limit for FOG 

requires an understanding of the unique manner in 

which oil and grease can cause interference or pass 

through. EPA recommends two different methods: 

• With FOG limits often included in 

NPDES permits, POTWs could 

determine FOG removal efficiency 

using Equation 5.5 to develop an AHL 

based on the plant's numeric NPDES 

permit limits. 

Exhibit 5-6: City of Richland, Washington, 

POTW Evaluates FOG Removal Efficiency 

The Richland POTW and the Washington Department of 

Ecology ("WDOE") sought to address a laundry's inability 

to meet its local limits permit limit of 100 mg/L FOG. 

During 1995, the laundry discharged to the POTW at an 

average of 200 mg/L FOG. 

Monitoring of the POTW indicated average influent levels 

for FOG of 25 mg/L and effluent levels averaging less 

than 1 mg/L -- a FOG removal efficiency of 96 percent. 

Respirometer tests on samples of the laundry's 

wastewater indicated that the wastestream was a 

biodegradable food source and easily metabolized by the 

POTW's microorganisms. 

Despite the relatively high concentration of FOG (200 

mg/L) in the laundry's effluent, based on the results of this 

evaluation, the city eliminated the laundry's FOG effluent 

limit but continued a sampling schedule. Furthermore, 

the results support previous EPA findings that petroleum 

based oil and grease compounds "can be degraded to 

various degrees especially if the microorganisms are 

acclimated to use the compounds as a substrate", and 

that "[i]f oil and grease are biodegradable and in a 

physical state [i.e., emulsified] that does not cause 

clogging or undue maintenance problems in the 

wastewater facilities, the discharge of these substances 

can be accepted in a wastewater treatment system." 

(EPA, Treatability of Oil and Grease Discharged to 

Publicly Owned Treatment Works (April 1975), p. 11) 

City of Richland POTW, Richland Laundry & Dry 

Cleaning, Inc. Wastewater Discharge Permit CR-IU003 

• Although animal- and vegetable-based FOG at reasonable concentrations are easily broken 

down, petroleum-based, non-polar FOG can interfere with both aerobic and anaerobic 

treatment. Petroleum-based oils can coat the organisms responsible for biological treatment 

and result in less effective oxygen transfer rates. In anaerobic processes, excessive 

concentrations of solid grease in digesters can reduce the effectiveness of the process, lead to 

structural damage to pipes and supports as a result of the weight of scum and grease, and 

present accumulation problems when supernatant is recycled. When digesters are well mixed 

and heated to minimize scum loads, reasonable FOG concentrations can be anaerobically 

digested. If these types of process inhibition are occurring, POTWs could calculate FOG 

primary and secondary removal efficiencies, determine FOG inhibition criteria, and use 

Equations 5.10 and 5.11 to determine AHLs based on inhibition. See Exhibit 5-7 for a 

description of how the City of Portland established an inhibition-based local limit for nonpolar FOG. 

5 - 24
5.4 DETERMINATION OF THE MAXIMUM Exhibit 5-7: City of Portland, Oregon Uses ALLOWABLE HEADWORKS LOADING Current Influent Loading to Develop NonPolar FOG Local Limit 

After calculating AHLs for each POC for a variety 

of environmental criteria, MAHL determination is The City of Portland wanted to develop a local limit for 

non-polar FOG to avoid any potential for inhibition at its simple. The lowest (i.e., most stringent) of the AHLs POTW. However, as often is the case in developing

for each POC is selected as the MAHL for that inhibition- based local limits, the MAHL was difficult to 

pollutant. Influent loadings below the MAHL will define (see Exhibit 5-3) because the plant had never 

experienced inhibition. The City determined that “the

lead to compliance with the AHLs based on all POTW had not experienced process inhibition from nonenvironmental and treatment plant criteria. The polar-FOG under these conditions. Therefore the 

development of a local limit based upon current loading MAHL will be used for all further steps of local will be protective against process inhibition." The current 

limits development and evaluation. loading of 8.6 mg/L of non-polar FOG was used as the 

inhibition-based MAHL. 

5.5 SAMPLE MAHL CALCULATION Although using current loading to establish an inhibition 

based MAHL is conservative, the methodology provides a 

scientific basis for the development of local oil and A POTW is attempting to determine the MAHL for grease limits. Based on this MAHL, the City established 

copper. From its local limits sampling plan, the a non-polar FOG local limit of 110 mg/L. 

POTW has determined the following plant data: See Industrial Source Control Division, Bureau of 

Environmental Affairs, City of Portland, Final Report -

C Plant removal efficiency from Update of Local Discharge Standards (April 1996). 

headworks to plant effluent, Rpotw = 0.85 

C Removal efficiency from headworks to

primary treatment effluent, Rprim = 0.65 

C Average plant flow rate, Qpotw = 10 MGD 

C Percent solids in the sludge, PS = 5 percent 

C Specific gravity of sludge, Gsludge = 1 kg/L 

Average sludge flow rate, Qsludge C = 0.05 MGD

For copper, the POTW determines that the suitable environmental criteria are the following: 

C The POTW has a specific copper limit in its NPDES permit, Cnpdes = 1 mg/L copper. 

C With biosolids being used ultimately for lawn application, Federal Sludge Land Application 

Table 3 “Clean Sludge” Limits, Cslgstd = 1,500 mg/kg copper, are applicable. 

C Although inhibition has never taken place at the plant’s activated sludge secondary treatment 

unit, the POTW wants to develop an AHL based on activated sludge inhibition. Based upon 

the highest observed copper concentration in the secondary treatment unit that did not cause 

inhibition, the POTW sets the inhibition criterion for secondary treatment, Cinhib2 = 1 mg/L 

copper. 

The following equations for AHLs based on NPDES limits (Equation 5.5), sludge standards (Equation 

5.9), and secondary treatment inhibition (Equation 5.10) are used. 

5 - 25
From these three AHLs, the most stringent (lowest) AHL based on the sludge standard (AHLsldg) was 

chosen as the MAHL for copper at 37 lb/day. 

5.6 SUMMARY 

After reviewing Chapter 5, POTWs should be able to: 

C Calculate POTW removal efficiencies for each POC

C Calculate AHLs for each environmental criteria

C Determine MAHL as the most stringent AHL for each POC 

Chapter 6 describes how to assess the need for local limits, allocate the maximum allowable industrial 

loadings, and develop and implement final local limits and BMPs. 

5 - 26
CHAPTER 6 -

DESIGNATING AND IMPLEMENTING LOCAL LIMITS

Chapter 6 provides guidance on how to: 

� Determine the need for new local limits after establishing Maximum Allowable 

Headworks Loadings (MAHLs). 

� Calculate Maximum Allowable Industrial Loadings (MAILs). 

� Compare MAIL allocation and implementation methods. 

� Allocate MAILs to controlled dischargers. 

� Perform a common sense assessment of local limits. 

� Use best management practices. 

� Provide public participation. 

� Gain Approval Authority approval. 

� Conduct public outreach. 

� Select the appropriate control mechanism to apply local limits. 

6.1 DETERMINATION OF THE NEED FOR NEW LOCAL LIMITS 

Once a POTW has calculated MAHLs for all of its pollutants of concern (POCs), it can determine for 

which pollutants it will require local limits. In making this pollutant-by-pollutant evaluation, the POTW 

will also want to consider historical issues and the degree to which current influent loadings approach 

calculated MAHLs. For example, the concentration of some pollutants in the POTW influent may be far 

below the calculated MAHLs. These pollutants are unlikely to cause problems for the POTW, so the 

treatment works may conclude that local limits for them are unnecessary. EPA recommends that the 

POTW document such decisions and discuss them with its Approval Authority, as needed. 

Some Approval Authorities require that local limits be established for a specific set of pollutants 

regardless of the outcome of the headworks loading analysis. For example, some Approval Authorities 

specify that local limits be developed for arsenic, cadmium, chromium, copper, cyanide, lead, mercury, 

molybdenum, nickel, selenium, silver, and zinc regardless of whether they are in the POTW’s influent. If 

such specific guidance is not available, EPA recommends that the POTW conduct evaluations for each 

POC. 

6 - 1
No single approach applies for all pollutants at all POTWs. The approaches presented below are 

intended to determine which POCs deserve to be covered by new local limits. In EPA’s view, a POTW 

should not use the approaches below in deciding whether to continue to control a particular 

pollutant by a local limit because the enforcement of the local limit may be the reason that the 

pollutant loading has been reduced or is no longer causing problems. If the local limit were 

removed, industrial users (IUs) may discontinue their use of wastewater pretreatment and POTW 

loadings may increase above the threshold in the criteria. Re-evaluation of existing local limits is 

discussed in Chapter 7. 

6.1.1 ACTUAL LOADINGS VS. MAHL 

Equation 6.1 compares actual POTW loadings to the calculated MAHLs for individual POCs. A POTW 

would use this equation to calculate the percentage of MAHL being received at the POTW. The average 

and highest daily influent loading should be calculated. EPA recommends that local limits are needed 

when: 

� Average influent loading of a toxic pollutant 

exceeds 60 percent of the MAHL. 

� Maximum daily influent loading of a toxic 

pollutant exceeds 80 percent of the MAHL any 

time in the 12-month period preceding the 

analysis. 

� Monthly average influent loading reaches 80 

percent of average design capacity for BOD, 

TSS, and ammonia during any one month in the 

12-month period preceding the analysis. 

Equation 6.1: Actual Loading vs. 

MAHL Calculation 

Where: 

L% = Percentage of the MAHL 

LINFL = Current influent loading (average or 

highest daily), lb/day 

MAHL = Calculated MAHL lb/day 

EPA recognizes that these percentages to trigger local

limits development are default assumptions that can vary from plant to plant. The approach used for

toxic pollutants is more conservative because most POTWs are not designed to treat toxic pollutants.

6.1.2 NONCOMPLIANCE DUE TO PASS THROUGH OR INTERFERENCE 

The basic purpose of the pretreatment program is to prevent pass through and interference, and the 

General Pretreatment Regulations require that local limits be established to prevent them. EPA 

recommends that in the absence of strong evidence that the cause of pass through or interference has 

been eliminated, a POTW retain local limits for the pollutants causing historic violations. By reviewing 

past NPDES permit violations, sludge disposal restrictions, or inhibition incidents, the POTW can 

identify the pollutants for which it should set or maintain local limits. 

6.1.3 ESTABLISHING LOCAL LIMITS FOR CONVENTIONAL POLLUTANTS 

Conventional pollutants such as BOD, TSS and ammonia require additional evaluation before decisions 

are made to set a MAIL and put in place a local limit. Controlling conventional pollutants from IUs must 

be evaluated in a broader context, because the POTW was designed to treat conventional pollutants. A 

6 - 2
comprehensive evaluation of the POTW may be needed (see Section 5.3) and many alternatives in lieu of 

or in addition to local limits may be considered. 

A POTW that is approaching its design capacity for BOD/TSS should begin planning to avoid future 

violations. NPDES permits sometimes include a reporting requirement when the POTW begins to 

operate at 80-90 percent of its original design capacity for 90-180 consecutive days. EPA recommends 

using a similar threshold as a basis for investigating alternatives for reducing or responding to future 

conventional loadings. If the rate of increase in influent conventional pollutants loadings suggests that 

the full capacity of the plant will be utilized within five to seven years, then planning may need to begin 

immediately. The planning need not automatically assume that local limits would be set for conventional 

pollutants. Several alternatives should be investigated in addition to local limits. These include: 

� Minimizing growth of the community by controlling sewer connections. 

� Initiating POTW modifications to optimize performance (through chemical additions, 

filtration, membrane filtration, and other methods). 

� Modifying operation or flow configurations. 

� Expanding POTW capacity via facilities planning. 

� Reducing industrial sources of conventional pollutants through incentives and 

disincentives. 

Each POTW has a unique, historical background of successful operation with respect to conventional 

pollutants, and whether each POTW can operate successfully at a given (elevated) loading will vary from 

plant to plant. Some of these concepts are reviewed in Section 5.3. 

POTW expansions can take up to 5 years. Therefore, it is vitally important to monitor loadings to the 

plant against the POTW design capacity. Failure to plan in a timely manner can result in NPDES 

violations. With respect to nitrogen management, it is useful to note that nitrogen removal at the POTW 

typically requires four times the biological treatment volume needs of BOD, hence the need to quantify 

significant industrial sources of nitrogen to optimize control and treatment. 

6 - 3
6.2 CALCULATION OF MAXIMUM ALLOWABLE INDUSTRIAL LOADING 

MAHLs estimate the maximum combined loadings that can be received at the POTW’s headworks from 

all sources. MAILs developed by the POTW represent the amount of pollutant loadings the POTW can 

receive from controlled sources (i.e., 

industrial users, some commercial 

sources1

, and some hauled waste) that Equation 6.2: MAIL Calculation 

the POTW chooses to control through 

local limits. As shown in Equation 6.2, 

the MAIL is calculated by subtracting 

estimates of: Where: 

MAIL = Maximum allowable industrial loading, lb/day 

MAHL = Maximum allowable headworks loading, lb/day � Loadings from SF = Safety factor, if desired 

uncontrolled sources LUNC = Loadings from uncontrolled sources (uncontrolled sources= 

(Lunc) domestic + some commercial + I&I) 

� Hauled waste not 

HW = Loadings from hauled waste, if not regulated through the local 

limits 

regulated through local GA = Growth allowance. 

limits (HW) 

� Growth allowance (GA) 

from a MAHL adjusted with a safety factor (SF). These four elements of the MAIL calculation– 

loadings from uncontrolled sources, hauled waste, growth allowance, and safety factor – are further 

explained in the next four subsections. Table 6-1 provides a summary on the information needed to 

calculate the MAIL. 

Table 6-1: Data for Implementation of MAHLs 

Parameter Comments Source of Data 

IU and significant 

industrial user (SIU) 

flow 

Total flow from all SIUs and IUs, plus any commercial dischargers 

that the POTW intends to control 

POTW local use sampling 

program, periodic reports from 

SIUs 

Uncontrolled Source 

Pollutant 

Concentrations 

Levels of POCs in domestic and commercial discharges that the 

POTW does not intend to control with local limits 

POTW local use sampling 

program 

Uncontrolled Source 

Flow 

Flow from all uncontrolled sources, either in total or divided by 

type of facility (domestic, commercial, I&I, storm water) 

POTW local use sampling 

program 

Hauled Waste Loadings Based on volume and pollutant concentration data POTW sampling of waste 

hauler loads 

Safety Factor Varies depending on quality and amount of data POTW choice based on data 

analysis 

Growth Allowance Varies based on the projected growth for the area POTW choice based on data 

analysis 

1

 For example, a POTW may choose to regulate or limit the discharges from some or all of its commercial dischargers 

(e.g., dental offices, hospitals, and restaurants), in which case they would be considered controllable sources. 

6 - 4 
6.2.1 UNCONTROLLED SOURCES 

As noted above, some sources of pollutant loadings to the POTW are considered uncontrolled. They 

include domestic users, inflow and infiltration (I&I), treatment chemicals added to sewers, storm water, 

and some or all of a POTW’s commercial dischargers. Because the POTW does not control the loadings 

that these users discharge [except through the general and specific prohibitions in the POTW’s sewer use 

ordinance (SUO)], the POTW needs to subtract these loadings from its MAHLs before it can determine 

the MAIL (see Equation 6.2). EPA recommends the following approach for calculating the contribution 

to the MAHL from these uncontrolled loadings: First, the POTW conducts site-specific monitoring of 

the uncontrolled discharges at sewer trunk lines that receive wastewater from only these sources (see 

Section 4.1.2). This activity will enable the POTW to develop data on average pollutant concentration 

levels. The POTW then multiplies the concentration loadings for each pollutant obtained from these 

locations (CUNC) by the POTW’s total uncontrolled flow rate (QUNC) to determine total loadings to the 

POTW for that specific pollutant from all uncontrolled sources (see Equation 6.3). 

EPA strongly encourages POTWs to use site-specific data for uncontrolled loadings whenever possible. 

Appendix V includes data on pollutant concentrations found in typical domestic wastewater discharges, 

which can be used if site-specific data are not available. Because domestic wastewater values may not be 

representative of the uncontrolled discharges in their systems, POTWs should use care with these data. 

A POTW may find that the total uncontrolled loadings of a particular pollutant approach or exceed the 

MAHL. In these cases, little or no pollutant loading is available for IUs. This situation may arise in part 

because some of the facilities considered uncontrolled are commercial facilities such as gas stations, 

radiator repair shops, car washes, or hospitals, which may discharge high levels of pollutants. These 

facilities may be grouped initially with uncontrolled sources because they are small or have low 

discharge flows. The POTW may need to carefully evaluate the sources it considers uncontrolled to see 

if some of them would be better classified as controlled sources with reducible pollutant loadings. Refer 

to the Supplemental Manual on the Development and Implementation of Local Discharge Limitations 

under the Pretreatment Program (EPA-W21-4002, 

May 1991) for typical pollutant loadings for selected 

commercial industries. This is recommended for 

POTWs whose allocations to uncontrolled sources 

consume most or all of its MAHLs for some 

pollutants. In addition, see Section 9.5 for additional 

guidance addressing this issue. 

If a POTW has considerable loadings from I&I and 

storm water (from combined sewer systems), it 

should try to estimate their loadings and include them 

in the uncontrolled loadings estimate. The POTW 

may be able to select sampling locations that include 

these flows, or it may be able to estimate them by 

analyzing the variations in flow between periods of 

Equation 6.3: Uncontrolled Loading 

Calculation 

Where: 

LUNC = Uncontrolled loading, lb/day 

CUNC = Uncontrolled pollutant concentration, mg/L 

QUNC = Uncontrolled flow rate, MGD 

8.34 = Unit conversion factor. 

wet and dry weather. In some cases, the POTW may be able to decrease the flows and loads from I&I 

and storm water through sewer system rehabilitation and pollution prevention programs so that loads 

from these sources do not consume a substantial portion of the POTW’s MAHLs. 

6 - 5
The POTW may be able to estimate loadings from uncontrolled sources by subtracting loadings of 

controlled sources from total influent loadings. This method may be useful when most or all of a 

POTW’s data for uncontrolled sources are below detection levels for a pollutant. When the data are 

mostly below detection levels, the POTW should carefully evaluate how to handle these data because 

these decisions can greatly affect the loadings available for IUs. Additional guidance on setting local 

limits when uncontrolled source loading exceeds the MAHL has been developed by EPA Region 5 and 

can be found at: http://epa.gov/r5water/npdestek/npdprtg3.htm. 

6.2.2 HAULED WASTE 

As previously noted, POTWs that do not regulate 

waste haulers through local limits will want to 

determine the loads they receive from hauled waste 

and subtract these loads from their MAHLs before 

determining their MAILs. EPA recommends that 

POTWs base the allocations for hauled waste on 

actual data – pollutant concentrations and flows from 

waste haulers collected by sampling hauled waste 

brought to the treatment works. EPA further 

recommends that POTWs regularly sample these 

loads to ensure that they are not hazardous waste, do 

not contain toxic pollutants in amounts greater than 

expected or greater than local limits, and will not 

pose risks to the treatment plant or its workers. In 

addition, EPA reminds POTWs that hauled waste 

subject to categorical limitations must meet those 

limits when accepted at the POTW and that 

pretreatment standards apply to wastes hauled from 

IUs. Additional information on the acceptance and 

characterization of hauled wastes at POTWs is 

available in Guidance Manual for the Control of 

Waste Hauled to Publicly Owned Treatment Works 

(EPA/833-B98-003). The guidance discusses 

collection of information on waste haulers, 

Exhibit 6-1: Safety Factor Example 

If a POTW's data for cadmium were all below detection 

and the POTW used literature data for cadmium 

removal efficiencies, the treatment works should 

consider using a safety factor for cadmium. At the 

same time, if the POTW's zinc data were mostly above 

detection and the daily removal efficiencies were all 

between 60 and 80 percent, the POTW may not need 

to use a safety factor for zinc. The decision to use a 

safety factor for zinc removal on pass through would 

depend on the quality of the data used to calculate the 

removal efficiency. In this example, assume that the 

removal efficiency is based on 12 months of paired 

influent and effluent samples that range from 60 and 

80 percent and collected as hydraulically lagged pairs. 

Because this data set is of high quality, the POTW 

might not use a safety factor. If an ADRE is 

calculated, it will lie in the 60 to 80 percent range. If 

the ADRE is 72 percent, the POTW will want to 

consider the degree of safety that would exist should 

the actual removal efficiency be lower. This, along with 

the potential to violate water quality standards or 

NPDES effluent limits, also needs to be considered. 

Note that the ADRE for pass through is the same value 

used for sludge quality protection calculations. The 

POTW should also examine the data set to determine 

the potential for removals to be higher than the ADRE 

leading to violations of sludge disposal quality criteria. 

characterization of hauled waste received, evaluation of potential impacts and development and 

implementation of controls. 

6.2.3 SAFETY FACTOR 

Determining safety factors is an imprecise process, which has the potential to affect significantly the final 

local limits. A safety factor is site specific and depends on local conditions. The main purpose of a 

safety factor is to address data “uncertainties” that can affect the ability of the POTW to calculate 

accurate local limits. Some Approval Authorities may have mandatory safety factors. At a minimum, 

EPA generally recommends a 10 percent safety factor. The determination of whether a safety factor is 

needed and, if it is, how large the safety factor should be depends on the following elements: 

� The variability of the POTW’s data. 

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� The amount of data the POTW used to develop its MAHLs. 

� The quality of the POTW’s data. 

� The amount of literature data the POTW used. 

� The history of compliance with the parameter. 

� The potential for IU slug loadings (e.g., as a result of chemical spills). 

� The number and size of each IU with respect to the POTW's total flow rate. 

The POTW may use different safety factors for different pollutants. The above elements may vary from 

pollutant to pollutant, making it appropriate for a POTW to use different safety factors (see Exhibit 6-1). 

6.2.4 EXPANSION/GROWTH ALLOWANCE 

A POTW that anticipates a significant amount of growth in the future can consider holding in reserve a 

portion of its MAHLs for this growth. This expansion/growth allowance is separate from the safety 

factor. Anticipated growth should be projected for known, planned expansions such as IUs moving into 

the POTW’s service area or existing IUs expanding their operations, the development of a shopping mall 

or the opening of other commercial businesses in a new office park, or the construction of a new housing 

development. The expansion and growth allowance is most commonly justified for BOD, TSS, and other 

pollutants the POTW was designed to remove. By holding in reserve some of the MAHL, the POTW has 

a portion to allocate to the new discharges and may not need to revise its existing IU permits or SUO. 

6.3 COMPARISON OF MAIL ALLOCATION AND IMPLEMENTATION METHODS 

Uniform-concentration local discharge limitations have become synonymous in the Pretreatment Program 

with the term “local limits.” However, local limits can take many forms based on how MAILs are 

allocated to IUs. The designation and implementation of these MAILs, including the allocation of 

loadings to IUs, are left to each POTW, as long as the implementation procedures do not allow the 

calculated MAHL to be exceeded and provide a reasonable method for making allocations to the IUs. 

This section describes some of the implementation decisions facing POTWs. The selection of an 

appropriate implementation approach is an integral aspect of a POTW’s local limits process. 

A POTW may select any allocation and implementation method that results in enforceable local limits to 

prevent pass through and interference and to comply with the prohibitions in the Federal regulations. 

The POTW should choose the allocation approach that best fits its own situation. It may choose one 

approach for some pollutants and another approach for other pollutants, depending on the amount of 

loading available to IUs and the number of IUs discharging a given pollutant. For example, if only three 

of a POTW’s ten IUs discharge silver, the POTW may prefer to allocate its allowable industrial silver 

loading among the three IUs that discharge silver so that these IUs receive more achievable limits. At the 

same time, if all of the users discharge copper, the POTW may choose to allocate the MAIL for copper to 

all of the users on a uniform basis. All regulated IUs should receive at least a background allocation for 

copper and all other POCs. 

6 - 7
Table 6-2 on the next page lists issues that POTWs will want to consider when determining how to 

allocate and implement its local limits. Ultimately, the POTW will want to allocate pollutant loadings in 

a fair and sensible way that does not favor any one industry or group of industries, considers the 

economic impacts, maintains compliance with the NPDES permit, and otherwise achieves the 

environmental goals of the program. The allocation method selected may be subject to State and local 

public participation requirements in order for the resulting local limits to become legally enforceable. 

6.4 ALLOCATION OF MAILS AMONG CONTROLLED SOURCES 

A POTW can apply to its controllable sources concentration-based limits (typically in mg/L), or massbased limits (typically in lb/day), or both. The type of limit depends in part on the method chosen by the 

POTW to allocate its MAILs among the controlled dischargers. For example, a POTW that uses the 

uniform concentration method based on total IU flow typically implements a pollutant limit as a single 

concentration (generally in its SUO) applicable to all controlled users. If the POTW allocates its MAILs 

on a case-by-case basis depending on an IU’s need for a certain loading allocation, the POTW may find it 

easier to apply mass-based limits (in individual permits) that allow for the needed loading at the IU. The 

POTW needs to consider the ability to determine and enforce compliance. EPA recommends that the 

POTW consider the IU’s sampling capabilities when determining the type of limits to apply to an IU. An 

IU may not have flow meters or sampling points necessary to determine mass-based limits. In these 

cases, the POTW may instead put concentration-based limits in the IU permits or, potentially, both types 

of limits in the permit. Thus, the POTW may first allocate its MAILs based on loadings, but then apply 

the allocations to IUs as concentration-based limits based on flow. EPA recommends that POTWs use 

mass-based limits only for users that have the capability (or are required to develop the capability) to 

accurately measure their flows at the designated sampling points. Mass-based limits have the added 

benefit of allowing IUs to reduce their water consumption through conservation or recycling without 

affecting their ability to meet local limits. 

6.4.1 LIMIT DURATION 

When applying its local limits, a POTW needs to determine the appropriate limit duration. The POTW 

may establish limits that are daily maximums, monthly averages, or instantaneous maximums. In 

general, a POTW should base the limit duration on the type of criteria – long-term or short-term – used to 

develop the local limit. However, most local limits will be implemented as daily maximums based upon 

two main factors: 1) the short-term nature of the event that the local limit is protecting against; and 

2) the infrequency of IU sampling. Scenarios illustrating this are presented below. 

6 - 8
Table 6-2: Options for Allocating and Implementing Local Limits 

Method Pros Cons 

Allocate MAILs uniformly 

among all IUs and place 

uniform concentration limits in 

the local SUO 

-Limits are clear to IUs 

-Requires little time to calculate limits 

-Easy to determine compliance 

-Need to update SUO when limits change 

-Inflexible 

-Limits may be overly stringent because some 

IUs may get an allocation but do not discharge a 

pollutant 

Place general language about 

complying with local limits in 

the local SUO and announce 

the actual uniform limits outside 

the SUO 

-Do not have to revise the SUO every 

time local limits change 

-Easy to monitor for compliance 

-Relatively easy to calculate limits 

-IUs may not be clear on the limits with which 

they must comply 

-Action may be overlooked by the general public 

and interested parties 

Place general language about 

complying with local limits in 

the local SUO and place 

individual limits in IU permits 

-Do not have to revise the SUO every 

time local limits change 

-Provides flexibility 

-Requires issuing a permit to all IUs to which the 

POTW wants limits to apply 

-Action may be overlooked by the general public 

and interested parties 

Put MAILs in SUO, allocate 

loadings on an IU contributory 

flow or mass proportion basis, 

and place limits in IU permits 

-Only IUs that discharge a pollutant are 

given a full allocation so limits are more 

efficiently allocated 

-Helps avoid setting excessively 

stringent or unattainable limits 

-Requires knowing more about IU discharges 

(need to know their pollutant content) 

-Requires updating the SUO when MAILs change 

-Requires issuing permits to all IUs with specific 

limits 

-May penalize IUs that are currently pretreating if 

others are not 

Put MAILs in SUO, allocate 

loadings on a case-by-case 

basis to those IUs that need an 

allocation for a specific 

pollutant, and place limits in IU 

permits 

-Only IUs that discharge a pollutant are 

given a full allocation so limits are more 

efficiently allocated 

-Helps avoid setting excessively 

stringent or unattainable limits 

-Provides flexibility 

-Requires knowing more about IU discharges 

(need to know their pollutant content) and 

applicable pretreatment systems 

-More time-consuming to determine allocation 

-Can lead to an inequitable allocation among IUs 

-Requires updating SUO when MAILs change 

-Requires issuing permits to all IUs with individual 

limits 

EPA recommends use of a daily maximum in the following circumstances: 

� A local limit based upon short-term criteria should be a daily maximum. For 

example, local limits based upon NPDES permit limits expressed as daily maximums 

should be considered daily maximums. 

� A local limit based upon long-term criteria, BUT protecting against a short-term 

event, should be a daily maximum. For example, a local limit based on chronic water 

quality criteria would appear to warrant assigning a long-term limit duration such as 

monthly average. However, the local limit should be considered a daily maximum 

because the MAHL calculation using water quality criteria is based on either the 

receiving stream's 1Q10 or 7Q10 flows, both of which are short-term phenomena (see 

Equation 5.6). Another short-term condition that leads to a daily maximum limit is 

biological inhibition for both secondary and tertiary treatment, both of which have short 

residence times. 

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� A local limit based upon long-term criteria and protecting against a long-term 

event, BUT the sampling cannot generate a true monthly average, should be a daily 

maximum. For example, monthly average "clean sludge" criteria, can be the basis of a 

local limit. Residence times in sludge digesters and storage facilities are commonly 20 

to 30 days or more. Consequently, to change the concentration to any appreciable 

degree, any excessive loading would have to be maintained for three to four weeks – a 

long-term event. These two factors favor a monthly average type local limit. However, 

an IU will rarely sample for the metals that end up in the POTW sludge more than once a 

month. Therefore, local limits for sludge disposal, although based upon a long-term 

criteria and protecting against a long-term event, should be considered a daily maximum 

limit. 

This means of assigning local limit duration is protective in that it leads to enforcing local limits based on 

monthly average criteria as daily maximums. 

In terms of other duration types, EPA recommends that local limits should be monthly averages when 

the environmental criteria that they are based upon is long term, the protected event is long term, and 

frequent IU sampling can generate a true monthly average. EPA recommends that instantaneous limits 

be developed for pollutants that cannot be composited. A limit derived from a MAHL based on one-hour 

acute toxicity water quality criteria may not be protective if it is implemented as a daily maximum 

instead of as an instantaneous limit. However, if the instantaneous limit is converted to a daily maximum 

limit using a statistical procedure that 

accounts for the variation in 

concentrations over a 24-hour period, the 

daily maximum limit should be adequately 

protective. The EPA Technical Support 

Document (TSD) approach, described in 

the Technical Support Document for Water 

Quality Based Toxics Control (EPA, 

1991a), accounts for these variations. 

Instantaneous limits may also be 

appropriate where Approval Authorities 

require IUs to accumulate all wastewater 

flows in batch tanks. Grab samples can 

then be collected to evaluate an 

instantaneous limit. 

6.4.2 ALLOCATION APPROACHES 

A POTW can use several basic approaches 

to assign limits to its controlled 

dischargers. As noted above, the POTW 

can select different allocation methods for 

different pollutants. Several common 

approaches for allocating MAILs for 

conservative pollutants are described in 

this section. A POTW may choose to use 

Exhibit 6-2: Background Allocation 

When using the IU Contributory Flow Method or Mass Proportion 

method, any user that discharges at or below the background level is 

given a background allocation (unless a different allocation can be 

justified based on actual sample data). Please note that: 

� Background loading can be calculated for each pollutant using the 

uncontrolled concentration for that pollutant and the flow of that 

pollutant from the "non-contributing" industries. (Background flow 

from non-contributing industries may be different for each 

pollutant.) 

� These background "limits" are then applied to non-contributing 

industries. 

� Similar to how estimated uncontrolled source loading can actually 

exceed the MAHL (see Section 6.2.1), estimated loadings from 

non-contributing IUs discharging the pollutant at background 

levels can result in an over-allocation of the MAIL. In other words, 

the estimated loading from IUs discharging at pollutant 

background levels plus the loading from IUs discharging the 

pollutant at local limit levels is greater than the MAIL. Generally, 

this occurs because background levels are set too high. POTWs 

should make sure that their determination of background levels is 

sound and check their allocation method. For instance, a uniform 

concentration specified in a Sewer Use Ordinance for a 

background concentration can lead to an over-allocation error 

(see Equation 6.7 on the next page). 

6 - 10
another method, such as a statistical method, as long as it results in local limits that are enforceable and 

adequately protective. 

Limits Based on IU Contributions of a 

Pollutant 

Two allocation methods divide the MAILs 

among only the controlled dischargers that 

discharge a particular pollutant. These 

methods develop IU-specific discharge 

limits. Any user that discharges at or below 

the background level is given a background 

allocation unless a different allocation can 

be justified based on actual sample data (see 

Exhibit 6-2 on the previous page). 

The IU Contributory Flow method is similar 

to the uniform method described below, 

except that the portion of MAILs above 

background (MAIL - LBACK) is divided by the 

flow rate from controlled sources (QCONTD) 

discharging the pollutant above background. 

The concentration-based limits (CLIM) apply 

only to those users (see Equation 6.4). 

The Mass Proportion method allocates 

MAILs to each controlled discharger in 

proportion to the discharger’s loading of 

that pollutant. To calculate the allowable 

loading for a user (LALLx) the portion of the 

MAIL above background (MAIL - LBACK) is 

multiplied by the ratio of the current loading 

from user x (LCURRx) to the current total 

loading of a pollutant from controlled 

sources (LCURRt). The mass-based loading 

calculated using the mass proportion 

method can be converted to a concentrationbased limit (see Equations 6.5 and 6.6). 

Uniform Limits For All Controlled 

Dischargers 

As illustrated in Equation 6.8 (on the 

following page), the uniform limits method 

of allocating MAILs for conservative 

pollutants yields one limit per pollutant 

(CLIM) that applies to every controlled 

discharger. It requires that the MAIL for 

each pollutant be divided by the total flow 

rate from all controlled dischargers (QCONT), 

Equation 6.4: IU Contributory Flow Calculation 

Equation 6.5: Mass Proportion Method for a 

Mass-Based Local Limit 

Equation 6.6: Mass Proportion Method for a 

Concentration-Based Limit 

Equation 6.7: Uniform Allocation of 

Background Loading 

Where: 

CLIM = Concentration-based limit for all users discharging a 

pollutant, mg/L 

CBACK = Concentration-based limit for all users discharging 

pollutant at or below background, mg/L 

MAIL = Maximum allowable industrial loading, lb/day 

LBACK = Total background loading allocation for all users for 

which no contributory flow limit is being established for 

that pollutant, lb/day 

QCONTD = Flow rate from all industrial and other controlled 

sources discharging the pollutant, MGD 

QBACK = Flow rate from all industrial and other controlled 

sources not discharging the pollutant at or below 

background, MGD 

LALLx = Allowable loading allocated to user x, lb/day 

LCURRx = Current loading from user x, lb/day 

LCURRt = Total current loading to POTW from controlled sources, 

lb/day 

CLIMx = Discharge limit for user x, mg/L 

6 - 11
even those that do not discharge the pollutant. This method can be overly stringent because some IUs

that do not discharge the pollutant will be given an allocation of the MAIL that they may not need. Other

IUs that do discharge that same pollutant may have to pretreat to comply with the local limit.

Basis of IU Needs for Discharge Loading/Case-by-Case Basis

A POTW may set IU-specific limits case by case. This type of allocation relies on the POTW’s judgment

to determine the amount of the MAIL to allocate to each controlled discharger. The limits can be based

on the discharger’s current loading, its need for a continued loading allocation, its ability to apply

pretreatment to achieve certain discharge pollutant levels (i.e., treatability), or any other factor that the

POTW determines is relevant. The POTW needs to ensure that the sum of the allocated loadings does

not exceed the MAIL and that it provides for at least a background allocation for each pollutant for each

user, unless a lower allocation can be justified by sampling data. To ensure that it does not allocate more

than the MAIL, the POTW should develop a mechanism to track the loading allocated to each IU and

compare the allocated total to the MAIL.

Creative Allocation Methods 

In general, once the MAIL is calculated, the 

POTW has substantial flexibility in 

allocating the pollutant load among its IUs 

as long as a margin of safety is maintained, 

the POTW has carefully accounted for all 

allocations, and public notice of the 

allocation is properly issued and allocation 

is adopted. For example, the Hampton 

Roads Sanitation District (HRSD) has 

developed flow-based local limits. 

Industries are placed in one of the following 

flow categories: 

Equation 6.8: Uniform Concentration Limit 

Calculation 

Where: 

CLIM = Uniform concentration limit, mg/L 

MAIL = Maximum allowable industrial loading, lb/day 

QCONT = Total flow rate from industrial and other controlled 

sources, MGD 

8.34 = Unit conversion factor 

� 0 to 9,999 gallons per day (gpd) 

� 10,000 to 19,999 gpd 

� 20,000 to 29,999 gpd 

� 30,000 to 39,999 gpd 

� 40,000 to 199,999 gpd 

� 200,000 to 399,999 gpd 

� Greater than 400,000 gpd 

Uniform limits are applied to each industry within the same flow category. The local limits become 

progressively more stringent as the industry's discharge flow increases. IUs that discharge above 400,000 

gpd are assigned specifically calculated local limits based on domestic loadings and the industrial 

processes from the specific facility. As an illustration, IUs with a flow rate of 0 to 10,000 gpd would 

have a nickel limit of 10.0 mg/L, while those with a rate of 200,000 to 400,000 gpd would have daily 

maximum nickel limit of 1.0 mg/L. HRSD uses this scheme for its local limits for the following 

parameters: arsenic, cadmium, chromium, copper, cyanide, lead, mercury, nickel , phenolic compounds, 

silver, zinc, and non-saponifiable oil and grease. 

Another creative form of MAIL allocation that POTWs may consider is pretreatment trading or effluent 

trading. These programs allow one source to meet its regulatory obligations by using pollutant 

6 - 12
reductions created by another source that has lower pollution control costs. Trading capitalizes on 

economies of scale and the control cost differentials among and between sources. Trading policy is 

applicable to local limits, only. The policy does not apply to categorical standards. EPA supports a 

municipality or regional sewerage authority developing and implementing trading programs among 

industrial users that are consistent with the pretreatment regulatory requirements at 40 CFR Part 403 and 

the municipality's or authority's NPDES permit. See Final Water Quality Trading Policy, EPA, Office of 

Water, Water Quality Trading Policy, January 13, 2003. Available at: 

http://www.epa.gov/owow/watershed/trading/finalpolicy2003.html. 

6.5 COMMON SENSE ASSESSMENT 

After developing and allocating local limits, POTWs should determine whether their local limits pass a 

“common sense test.” An effective public participation process can help with this assessment. Some of 

the questions a POTW should ask to determine if its limits pass the “common sense” test are: 

� Are the limits technologically achievable? Are IUs and other controlled dischargers 

likely to meet these limits with currently available forms of pretreatment and pollution 

prevention (e.g., process modifications)? Local limits are meant to protect the POTW 

and the environment and therefore are not specifically based on technological 

achievability. 

� Can the POTW and dischargers determine compliance with the local limits? Are 

the limits above sampling method detection levels? If the limits are below the detection 

level of the most sensitive analytical method, neither the POTW nor the IUs will be able 

to definitively determine compliance. 

� Are the limits sensible in light of actual conditions at the treatment plant and past 

compliance experience? For example, if the POTW is currently violating its NPDES 

limit for copper but the local limits analysis indicates that the POTW can accept its 

current influent loading and maintain compliance with that limit, the calculations and the 

past experience are in conflict. In this situation, the POTW should determine the 

reason(s) for the inconsistency. 

If a POTW’s calculated limits do not pass the “common sense test,” the POTW may need to reassess its 

limits development process or investigate other options for reducing pollutant loads (e.g., source 

reduction measures). Besides the environmental criteria used in the calculations, the two pieces of data 

that can have the greatest impact on the local limits calculations are the removal rates and the 

uncontrolled pollutant concentrations. A reassessment of the limits development process may show that 

several of the limits are affected by a lack of data and the use of literature values. By conducting 

additional sampling (possibly using lower detection limits), a POTW may obtain better data and, thus, be 

able to calculate more appropriate limits. 

Despite the POTW’s efforts to obtain the best data available for the calculations, the local limit 

calculated for a specific pollutant may at times be unreasonable and warrant other actions to establish 

valid limits. Other options for reducing pollutant loads to the POTW include the following: 

� Adding other commercial facilities to the set of controlled sources and requiring those 

facilities to reduce the pollutant load in their discharges. For example, a POTW’s 

6 - 13
MAHL for silver could be less than the uncontrolled loading resulting in a negative local 

limit. By adding other silver dischargers (e.g., photoprocessors) to the group of 

controlled IUs, the uncontrolled loading may be reduced significantly enough to 

calculate a reasonable limit. 

� Instituting a public education program to reduce problem discharges from domestic and 

other non-industrial (e.g., dental offices) sources. Some POTWs have worked with area 

dental associations to help educate dentists about proper disposal practices for mercury 

amalgam. Other POTWs have held hazardous waste disposal days to reduce the amount 

of household hazardous wastes discharged into sewers. See more on working with 

industry on Best Management Practices (BMPs) in Section 6.6. 

� Limiting acceptance of hauled waste to fewer loads, smaller loads, or lower pollutant 

levels. If hauled wastes contribute significantly to uncontrolled loadings, the POTW 

may need to stop accepting some hauled waste. 

� Conducting an I&I reduction program. Although I&I will generally contain lower 

concentrations of most pollutants than typical domestic sewage, it may contribute 

loadings that can increase problems with limits calculations. 

� Encouraging the replacement of piping that contributes significant loads of copper and 

lead. 

� Examining impurities, such as mercury, in chemicals used by industry, POTWs and 

water suppliers. Additionally, POTWs should be aware that the chemicals used in 

potable water treatment, such as fluoride (hydrofluorosilicic acid additive to prevent 

tooth decay) and zinc (zinc orthophosphate for corrosion control), can contribute to 

POTW pollutant loads. 

A POTW that cannot develop reasonable local limits may need to consider changing sludge disposal 

methods (if sludge is the limiting factor) or, in the long term, expanding the capacity of its treatment 

plant (especially for pollutants such as BOD, TSS, or ammonia). In any event, a POTW that is 

experiencing difficulty developing reasonable limits should contact its Approval Authority to discuss 

possible solutions. 

6.6 BEST MANAGEMENT PRACTICES 

The General Pretreatment Regulations do not specifically address the use of BMPs. The regulations at 

40 CFR 403.5(c) require the POTW only to develop “specific limits” for prohibited discharges. The 

current regulatory language is ambiguous as to whether BMPs may serve in lieu of numeric limits. 

However, the proposed Pretreatment Streamlining Rule (40 CFR Part 403, Streamlining the General 

Pretreatment Regulations for Existing and New Sources of Pollution, July 22, 1999) states that BMPs 

may be enforceable as local limits as an alternative to numerical limits or may supplement local limits. 

BMPs would need to be included in the technical evaluation of local limits. BMPs are defined in the 

NPDES regulations (40 CFR 122.2) as scheduled activities, prohibitions of practices, maintenance 

procedures and other management practices to prevent or reduce pollution. Some recently developed 

Effluent Limitation Guidelines, such as those for Pulp, Paper and Paperboard (40 CFR 430), 

Transportation Equipment Cleaning (40 CFR 442) and Pesticide Formulating, Packaging and 

6 - 14
Repackaging (40 CFR 455), allow for use of BMPs in meeting prescribed limits. BMPs also include 

treatment requirements, operating procedures, sludge or waste disposal, or drainage from raw material 

storage, and practices to control plant site runoff, spillage or leaks. 

Some commercial establishments may discharge pollutants in quantities that can be controlled either by 

local limits or by BMPs. A photofinisher that discharges to a POTW that is critically loaded with silver 

is one example. The POTW might elect to require silver BMPs in lieu of a permit and account for this 

allocation and anticipated reduction in silver in coordination with more traditional permits issued to IUs 

with mass-based or concentration-based local limits. However, to the extent that BMPs are used as an 

alternative or supplement to technically based local limits, the technical evaluation will need to assign an 

allocation to the pollutants and users covered by the BMP. A series of BMP mini-case studies is 

presented in Appendix W. 

EPA suggests the following resources in POTW development of BMPs: 

� Pollution Prevention Information Clearinghouse Resource List: This comprehensive Web 

site has sector-specific guidelines on pollution prevention. 

http://www.epa.gov/opptintr/library/ppicdist.htm 

� Guides to Pollution Prevention: Municipal Pretreatment Program, (EPA 625/R-93/006 

October 1993) 

� Guidance Manual for Developing Best Management Practices, (EPA 833/B-93/004 

October 1993) 

� Pollution Prevention (P2) Guidance Manual for the Pesticide Formulating, Packaging, 

and Repackaging Industry: Implementing the P2 Alternative, (EPA 821-B-98-017 June 

1998) 

� The Massachusetts Water Resources Authority (MWRA) currently prohibits the 

discharge of mercury by industrial facilities to its sewer system. Additionally, MWRA 

imposes an effective discharge limitation for mercury of 1.0 part per billion (ppb) from 

its regulated sources, including hospitals and institutions. To address this complex issue, 

the MWRA established a Mercury Products Work Group to examine the problem and 

develop strategies to reduce the amount of mercury being discharged. Read about this 

effort at: http://www.masco.org/mercury/index.htm. 

6.7 APPROVAL AUTHORITY AND ADOPTION PROCESS 

A Control Authority’s legal authority to impose local limits on industrial and commercial users derives 

from State law. Therefore, State law must confer the minimum Federal legal authority on a Control 

Authority. Where deficient, State law must be modified to grant the minimum requirements. In order to 

apply regulatory authority provided by State law, the Control Authority generally must establish local 

regulations to legally implement and enforce pretreatment requirements. If the Control Authority is a 

6 - 15
municipality, legal authority is detailed in a Sewer Use Ordinance (SUO),

2

 which is usually part of a city 

or county code. Regional Control Authorities frequently adopt similar provisions in the form of “rules 

and regulations.” Likewise, State agencies implementing a State-wide program under 40 CFR 403.10(e) 

set out pretreatment requirements as State regulations, rather than as a SUO. However, local regulations 

cannot give the Control Authority greater authority than that provided by State law. 

Establishing or revising local limits is considered to be a modification of the POTW’s pretreatment 

program. Therefore, the new or changed local limits must be submitted to the Approval Authority for its 

review and approval. The POTW must submit a notice to the Approval Authority that states the basis for 

the modification and must provide a modified program description and other documentation requested by 

the Approval Authority. After a modification is approved by the Approval Authority, it will be 

incorporated into the POTW’s NPDES permit [40 CFR 403.18(e) and 40 CFR122.62]. 

In most instances, the initial adoption of a MAIL or BMP will be a substantial modification where it 

replaces a different form of local limits. Unless the mass-based limit or BMP is specifically tied to an 

existing concentration limit, the switch to mass-based limits or to BMPs will likely result in less stringent 

local limits for at least some group of industrial users. As specified at 40 CFR 403.18(b)(2), making a 

local limit less stringent is considered a substantial modification of a POTW’s pretreatment program. 

Not only is the relaxation of a uniform concentration limit considered a substantial modification, but if a 

POTW calculates a less stringent concentration limit, the MAHL or MAIL also becomes less stringent. 

If this is the case, the Approval Authority may be required to process any new local limits as a substantial 

modification as well. For substantial modifications, the Approval Authority must issue a public notice of 

the request for approval and must provide an opportunity for interested parties to comment or request a 

public hearing. After deciding whether to approve the modification, the Approval Authority must issue a 

public notice of approval or disapproval, unless certain conditions are met [40 CFR 403.18(c)(3)]. 

Non-substantial modifications may be implemented after 45 days, unless the Approval Authority notifies 

the POTW that a modification is disapproved or determines that the modification is substantial (e.g., 

would result in an increase in pollutant loadings at the POTW) [40 CFR 403.18(d)]. To be approved by 

the Approval Authority, local limits must first be made legally enforceable by the POTW. This is 

generally done by incorporating them in the local SUO by following local public noticing procedures. 

The SUO need not contain local limits already allocated to industries. However, at a minimum, the SUO 

should authorize the POTW to establish individual limits through the permits based on the MAIL. 

The activities described above are regulatory requirements that must be met by all Approval Authorities 

and POTWs. Approval Authorities may have different procedures for implementing these requirements, 

and POTWs should check with their Approval Authority for details. In general, however, the approval 

and adoption process includes the following steps: 

2

 Consult Model Pretreatment Ordinance, (EPA 833-B-92-003, June 1992) for recommended formats for a Sewer Use 

Ordinance. 

6 - 16 
(1) The POTW develops or recalculates draft local limits. 

(2) The POTW submits the draft new or revised local limits and supporting documentation 

to the Approval Authority for review,3

 makes the proposed new or revised limits 

available to the public for comment, and provides individual notice to the affected 

parties. 

(3) The Approval Authority notifies the POTW of the adequacy of its submission. The 

submission may be: 

� Not accepted. The Approval Authority provides comments to the POTW, the POTW 

addresses the issues raised in the comments and repeats Step 2. 

� Accepted. The Approval Authority notifies the POTW that its proposed limits have 

been accepted. 

(4) Once accepted by the Approval Authority, the POTW adopts the new or revised limits, 

which also are adopted by all the contributing jurisdictions (i.e., all municipalities in the 

service area). Note that the public must be given the opportunity to review and comment 

according State and local law (see Section 6.8 for a discussion on public participation). 

(5) Once approved and adopted by the control authority (and thereby enforceable), the 

proposed changes to local limits become a formal pretreatment program modification and 

need to be publicly noticed and approved (as noted in the above discussion of regulatory 

requirements) by the Approval Authority. (The specific procedures for review and final 

approval may vary among Approval Authorities. POTWs should check with their 

Approval Authority.) 

6.8 PUBLIC PARTICIPATION 

Section 101(e) of the CWA establishes public participation as one of the goals in the development, 

revision, and enforcement of any regulation, standard, effluent limitation, plan, or program established by 

EPA or any State. The General Pretreatment Regulations encourage public participation by requiring 

public notices or hearings for program approval, removal credits, program modifications, local limits 

development and modifications, and IUs in significant non-compliance. 

POTW pretreatment program approval requests require the Approval Authority (a State or EPA) to 

publish a notice (including a notice for a public hearing) in a newspaper of general circulation within the 

jurisdiction served by the POTW. All comments regarding the request as well as any request for a public 

hearing must be filed with the Approval Authority within the specified comment period, which generally 

lasts 30 days. The Approval Authority is required to account for all comments received when deciding to 

3 Although not required, POTWs are encouraged to submit draft local limits to their Approval Authority for review 

prior to formal submission. This step can be helpful in identifying revisions necessary to make limits approvable and can save 

the POTW (and any contributing jurisdictions) from having to re-adopt revised limits after addressing Approval Authority 

comments. 

6 - 17
approve or deny the submission. The decision is then provided to the POTW and other interested parties, 

and published in the newspaper. All comments received are made available to the public for inspection 

and copying. 

Once a local pretreatment program is approved, the Control Authority (usually the POTW) must 

implement that program as approved. Before there is a significant change in the operation of a POTW 

pretreatment program, a program modification must be initiated. For a substantial program modification, 

such as the development of new or less stringent local limits, the Control Authority is required to notify 

the Approval Authority of the desire to modify its program and the basis for the change. Approval 

Authorities (or POTWs) also are required to issue public notice of the request for a modification, but are 

not required to issue public notice of the decision if no comments are received and the request is 

approved without changes. These changes become effective upon approval by the Approval Authority. 

Federal regulations also require POTWs to notify 

affected persons and groups and give them an 

opportunity to respond before final promulgation 

of a local limit [40 CFR 403.5(c)(3)]. While the 

regulations do not specify the exact public notice 

process that a POTW should follow, EPA 

recommends that the POTW conduct public 

participation in the local limits process as openly 

as possible. This process would include 

notifying affected users and other parties that the 

POTW knows are interested that the POTW is 

beginning a detailed reevaluation of its local 

limits. When new limits are drafted, EPA 

recommends notifying the IUs and other 

interested parties, individually, of the proposed 

limits and announce a public comment period in 

the local newspaper. This public comment 

period can be open while the proposed limits are 

submitted to the Approval Authority for initial 

review, or the POTW can wait until it receives 

Exhibit 6-3: Local Limits Documentation 

Among the items a POTW should keep to document its 

local limits development process are: 

� All data used for determining pollutants of concern and 

performing calculations. 

� Rationale for choosing pollutants of concern. 

� Record of calculations (formulas used) and related 

assumptions. 

� Printouts from any spreadsheets or computer 

programs used. 

� Rationale for choosing local limits (comparison of 

maximum allowable headworks loadings for all 

applicable criteria, allocation methods and 

calculations). 

� Reasons for not setting limits for particular pollutants or 

deleting any existing limits. 

comments from the Approval Authority. In EPA’s view, POTWs should allow sufficient time in their 

limits development process to provide for public participation. A POTW that plans to establish 

individual limits through the permits issued to users also should provide for public comments in the 

permit issuance process. During the comment period, the public may present technical challenges to the 

rationale for a particular local limit. To be adequately prepared to address such challenges, the POTW 

needs to thoroughly document its local limits development process. Similar issues need to be addressed 

during the re-evaluation process as well (see Exhibit 6-3). 

6.9 CONTROL MECHANISMS 

POTWs have discretion in selecting the control mechanism through which they will apply local limits to 

IUs and thereby making them enforceable. Examples of control mechanisms may include a SUO, 

individual permits, and orders. A POTW’s choice of control mechanism may depend on the type of user 

(SIU or non-SIU) and on the method the POTW uses to allocate its MAHLs among its IUs. A POTW 

should consider the following: 

6 - 18 
� An SUO alone may not be adequate with any allocation method other than the uniform 

concentration method. 

� The POTW does not need to allocate its local limits in an SUO. It may instead include 

MAILs in the SUO, then allocate the loadings in individual control mechanisms. Again, 

care must be taken to ensure that the sum of each pollutant allocation does not exceed the 

MAIL. 

� Limits based on the contributory flow method may result in over-allocation of the MAIL 

when uniform concentration values are specified in the SUO for "background 

concentrations" for SIUs that do not discharge the pollutant. POTWs should ensure that 

the implementation of the allocation scheme into a control mechanism does not result in 

an over-allocation of the MAIL. 

� An individual control mechanism (such as a permit) is necessary for most POTW-IU 

relationships. Even if one uniform set of local limits were applicable for all IUs, an 

individual control mechanism may be desirable to specify monitoring locations and 

frequency, special conditions such as solvent management or spill prevention plans, 

applicable categorical standards, and reporting requirements, and to provide clear 

notification to IUs (as required by 40 CFR 403.8). Note that 40 CFR 403.8(f)(1)(iii) 

requires a POTW to control the contribution of SIUs through individual control 

mechanisms (e.g., permits). The development of IU permits is discussed in detail in 

EPA’s Industrial User Permitting Guidance Manual (EPA, 1989a). 

6.10 SUMMARY 

After reviewing Chapter 6, POTWs should understand how to: 

� Determine the need for new local limits after establishing MAHLs. 

� Calculate MAILs. 

� Compare MAIL allocation and implementation methods. 

� Allocate MAILs to controlled dischargers. 

� Perform a common sense assessment of local limits. 

� Use best management practices. 

� Provide public participation. 

� Gain Approval Authority approval. 

� Select the appropriate control mechanism to apply local limits. 

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CHAPTER 7-

LOCAL LIMITS REVIEWS AND DETAILED REEVALUATIONS

According to 40 CFR 122.44(j)(2)(ii), POTWs must “provide a written technical evaluation of the need 

to revise local limits under 40 CFR 403.5(c)(1), following permit issuance or reissuance.” EPA 

recommends that a periodic evaluation of local limits be tied to the permit cycle and that more detailed 

evaluations be conducted on an “as needed” basis. Chapter 7 provides guidance on two means to meet 

this requirement – local limits reviews and detailed re-evaluations –depending on the conditions at the 

POTW. Reviews compare current headworks loadings with the maximum allowable headworks loading 

(MAHL) and examine any recent violations. When plant conditions have changed, EPA suggests a 

detailed re-evaluation be conducted that includes an in-depth look at all the data, criteria, and 

assumptions on which local limits are based to determine whether any changes affecting the local limits 

have occurred. 

7.1 REVIEWS 

For POTWs with past performance problems (pass through, interferences, or collection system issues), 

EPA suggests performing reviews annually as part of its preparation of the Annual Pretreatment Report. 

Reviews are intended as a quick check for any obvious signs that local limits may not be adequately 

protective of its treatment works, its workers, and the environment. This review will help ensure that any 

changes made during the previous year have not weakened the local limits’ effectiveness in protecting the 

POTW from pass through and interference. Presented below is a suggested methodology for performing 

reviews. 

7.1.1 COMPARISON OF CURRENT LOADINGS WITH MAHLS 

During a local limits review, EPA recommends that a POTW identify its maximum daily and maximum 

monthly average headworks loadings during the previous year for each pollutant of concern (POC) for 

which it calculated a MAHL—regardless of whether a local limit for each POC was adopted. Similar to 

the calculations made to determine the need for local limits in Section 6.1, comparisons of the MAHL to 

the headworks loadings will determine if local limits need to be recalculated, or established for additional 

POCs. The comparisons also may indicate if there is a need for an investigation into the cause of 

increased loadings, possibly due to noncompliant industrial users (IUs). 

As previously explained, dividing the headworks loading of all POCs by their respective MAHL will 

yield a “percentage of MAHL” represented by the POC headworks loading (see Equation 6.1). If a POC 

headworks loading is a high percentage of the MAHL, the POTW may choose to revise the local limit for 

that pollutant or develop a local limit for it if none exists. For example, a POTW may decide to develop 

a local limit for any pollutant whose headworks loading is above a “threshold value” of 50 percent of the 

MAHL. EPA recommends maximum threshold values of 60 percent for metals and toxic organics and 80 

percent for non-toxic organics, and conventional pollutants. However, in most circumstances, a POTW 

will use threshold values that are consistent with the criteria it used to determine if a local limit was 

7 - 1
needed for a POC. EPA offers the following guidance on this comparison between MAHLs and POCs 

for which local limits were not established: 

1. If the current POC headworks loading exceeds the MAHL, EPA recommends that 

the POTW establish a local limit for the pollutant, investigate the cause of elevated 

loading, increase its IU monitoring, identify any noncomplying industries, and consider 

undertaking pollution prevention efforts. 

2. If the current POC headworks loading exceeds the established threshold value for 

the first time (i.e., the loading was below the threshold value during the year 

before), EPA recommends the POTW increase monitoring for the POC, or establish a 

local limit for it. 

3. If the current POC headworks loading exceeds the established threshold value for 

the second time, EPA recommends establishing a local limit and increasing POC 

monitoring. 

4. If the current loading is below the established threshold, EPA recommends that the 

POTW review the pollutant’s loading as part of its preparation of next year’s annual 

report. 

Similarly, EPA recommends that the POTW prepare to address situations involving POCs for which local 

limits have already been established in the follow circumstances: 

� If the current POC loading exceeds the MAHL, EPA recommends revising the local 

limit (unless an investigation reveals that the elevated loading is due to an unusual, onetime event), investigating the cause of the high loading, identifying any noncomplying 

industries, increasing monitoring of IUs, and considering adopting pollution prevention 

efforts. 

� If the current POC loading has increased significantly from the previous year (e.g., 

from 55 percent to 75 percent of the MAHL), EPA recommends that the POTW 

investigate the cause of the increased loading, increase its monitoring for the POC, or 

revise the local limit. 

� If the current POC loading is below the established threshold, EPA recommends that 

the POTW review the POC’s loading when it prepares next year’s report. 

As part of its investigation into the cause of an elevated loading, the POTW will investigate whether the 

loading is an aberration. If the high loading resulted from an unusual, or one-time, occurrence, the 

POTW may not need to establish or recalculate the local limit for the POC. For example, if the POC 

load increased as a result of an IU oil spill, the POTW may better address the situation by ensuring that 

the IU properly implements a spill control plan, rather than by setting or revising a local limit. In 

addition, the POTW should also look at whether any sampling or analytical problems caused the 

aberration. 

7 - 2
When the current loading of one or more POCs approaches the MAHL, the POTW can respond in several 

ways. It can compare current IU loadings with the MAILs. If the comparison shows that the increased 

loadings come from domestic or commercial sources, the POTW can educate these sources about 

pollution prevention, or it can impose local limits on the commercial sources rather than change the IU 

local limits. If the IU loadings exceed the MAILs, one or more IU may be violating local limits. Such 

violations should be found during the POTW’s regular review of IU monitoring data. Another response 

is to review the data used to set the local limits in the first place. If changing conditions have affected the 

removal efficiencies, flow rate, or other criteria on which the MAHLs were based, the POTW should 

recalculate the MAHLs. 

7.1.2 REVIEW OF COMPLIANCE HISTORY 

If a review is performed, the POTW will also want to consider its compliance record over the previous 

year to determine whether the local limits it has set provide sufficient protection from pass through and 

interference. If the POTW has violated its NPDES permit or sludge disposal standards, has caused or 

contributed to violations of water quality standards in its receiving waters, or has experienced 

interference of its treatment processes, the POTW’s local limits may not be adequately protective. 

Unless it has identified as the cause of the violation a specific, unusual incident that is unlikely to recur, 

the POTW is required to investigate the violation’s cause and take appropriate enforcement action 

against any noncomplying IUs. Alternatively, the POTW may revise the local limit, or establish a local 

limit if none exists for the pollutants that caused the violations. 

7.1.3 NEXT STEPS 

POTWs that find further action is necessary after conducting reviews outlined above can turn to the 

earlier chapters of this document for guidance on ensuring that local limits remain protective. Chapter 4 

has information about sampling issues; Chapter 5 covers the calculation or recalculation of MAHLs; and 

Chapter 6 discusses the reallocation of existing MAHLs and other implementation issues, such as control 

mechanisms and revisions to the POTW’s sewer use ordinance. 

7.2 DETAILED LOCAL LIMITS RE-EVALUATION 

Periodically, POTWs need to re-evaluate their 

local limits to ensure that they remain protective, 

or to determine whether they should be revised, 

reallocated, or developed for additional 

pollutants (see Exhibit 7-1). As discussed above, 

POTWs may wish to review their local limits 

when preparing their annual Pretreatment 

Program Reports. However, the annual review 

may not have addressed conditions that can 

change over time and undermine the 

effectiveness of local limits. When a POTW 

Exhibit 7-1: Why Local Limits Should Be 

Re-evaluated 

Conditions change over time, and these changes may 

make it necessary to revise some or all of a POTW’s local 

limits. Periodic re-evaluation of local limits will help the 

POTW ensure that the limits are effective in protecting the 

treatment works, its workers, the local collection system, 

and the environment from the effects of interference and 

pass through. 

needs to address changes in its operating conditions or environmental criteria, the data or assumptions 

used to establish local limits in the first place may no longer be appropriate (see Exhibit 7-2). 

As these and other changes occur, the POTW will need periodically to undertake a more detailed reevaluation of its local limits. In addition, if a POTW violates its NPDES permit or sludge requirements, 

7 - 3
but all of its regulated sources have been maintaining compliance, the POTW will need to evaluate the 

adequacy of its local limits to protect the treatment works, its workers, and the environment. 

POTWs can avoid having to re-evaluate local limits for some of the events described in Exhibit 7-2 if 

adequate growth allowances (covered in Section 6.2.4) were used during local limits development. In 

addition, if IU’s have stopped discharging a pollutant, or reduced their discharge of a pollutant, POTWs 

should place the load formerly contributed by those IUs into a reserve account to accommodate future 

growth. If local limits are developed with flexibility, POTWs can respond to changes in IU loadings 

without a complete recalculation and approval of their local limits. 

The detailed re-evaluation of local limits 

is a four-step process: 

1. Assess current conditions 

to determine whether 

existing MAHLs should 

be recalculated or 

reallocated, or additional 

local limits should be 

developed. Also 

determine which 

pollutants need to be 

further evaluated and for 

which criteria. (If only 

re-allocation of existing 

MAHLs is needed, skip to 

step 4.) 

2. Based on the pollutants 

and criteria identified in 

step 1, determine whether 

existing data are 

sufficient. If not, develop 

and implement a local 

limits sampling plan, then 

analyze the data 

collected. 

3. Recalculate the MAHLs 

Exhibit 7-2: When to Recalculate or Develop 

Local Limits 

A POTW that answers ”yes” to any of these questions should reevaluate its local limits: 

� Has the treatment plant been modified, or has a new 

treatment plant been brought on line? 

� Have the treatment plant processes or operation changed 

in a way that affected the removal efficiencies? 

� Has the flow to the treatment plant changed significantly? 

� Is the POTW subject to new or revised NPDES limits? 

� Have the State water quality standards changed for the 

receiving water? 

� Has the POTW changed, or intend to change, its sludge 

disposal method? If yes, will this change affect the sludge 

quality standards that the POTW must meet? 

� Have loadings been affected by new IUs discharging to the 

POTW? 

� Have loadings been affected by IUs that have stopped 

discharging to the POTW? 

� Have loadings been affected by changes in discharges 

from current IUs? 

� Are new data available about the POTW or the IUs that 

invalidate assumptions made during the last local limits 

development effort? 

of pollutants for which local limits have been developed, and determine MAHLs for new 

pollutants. 

4. Implement the local limits. This step may include the reallocation of existing MAILs, if 

required. 

The following sections describe these four steps in more detail. 

7.2.1 STEP 1: ASSESS CURRENT CONDITIONS 

7 - 4
To determine whether MAHLs should be recalculated, MAILs reallocated, or additional local limits 

developed, the POTW first will need to compare its current conditions and requirements with those that 

existed when the local limits were last developed. In this process, EPA suggests that the POTW also 

evaluate whether a new MAHL is required for a POC, or if the previously determined MAHL remains 

valid, but needs to be reallocated. To determine which response is appropriate, the POTW will want to 

consider the change that led it to re-evaluate its local limits in detail. 

Usually, a POTW will undertake a detailed re-evaluation of its local limits in response to one or more 

significant changes at the treatment works or in the discharges it receives. Recalculating existing 

MAHLs or determining MAHLs for new POCs is generally an appropriate response to changes in: 

� Removal efficiencies

� Total POTW or IU loading

� Limiting criteria (NPDES permits, water quality standards, sludge criteria)

� Sludge characteristics or method of disposal (e.g., percent solids, disposal site life)

� Background concentrations of pollutants in receiving water

Simply reallocating existing MAHLs may be appropriate when: 

� Some IUs need a larger loading allocation and other IUs are not using all of their 

allocations. 

� Total POTW flow is unchanged, but the amount of uncontrollable loading relative to the 

IU loading has changed. 

� Total POTW flow has not changed but new IUs have come on line while existing IUs 

have stopped discharging. 

In these cases the current MAHLs are usually still appropriate, and the POTW can skip to step 4. 

Some Approval Authorities have worksheets that POTWs can use to determine whether existing local 

limits need to be recalculated. The worksheets help POTWs compare existing local limits and the data 

on which they are based with current conditions and applicable environmental and treatment plant 

criteria. They consider such parameters as POTW and SIU flows; sludge disposal method and associated 

disposal criteria; occurrence of violations, upsets, and interference; current influent and effluent 

loadings; water quality criteria; and NPDES permits. A copy of one of these worksheets and instructions 

for its use can be found in Appendix X. 

On occasion, a relaxation of local limits may be appropriate. However, in EPA’s view, the POTW first 

should demonstrate that the revised local limits will satisfy all of the minimum Federal and State 

requirements and will adequately protect in-stream water quality and sludge quality. If its analysis shows 

that local limits can be relaxed, the POTW would next determine whether their relaxation will result in 

new or increased IU discharges that will affect the volume or character of POTW influent or effluent. 

Relaxation of local limits would likely result in a major modification that must be approved by the 

Approval Authority in accordance with 40 CFR 403.18(b)(2). 

7.2.2 STEP 2: COLLECT AND ANALYZE DATA 

7 - 5
Properly re-evaluating local limits requires representative sampling data. If sufficient data are not 

available, the POTW obviously will want to develop and implement a sampling plan to provide 

additional data on relevant POCs. The availability of accurate site-specific data is critical to the 

development of sound, technically based local limits. Local limits developed using data from the 

literature are often conservative. 

The data necessary to calculate a MAHL for a new POC may not be available if that pollutant was not 

part of the POTW’s local limits monitoring. Similarly, data collected to support development of a 

current MAHL may not be valid for recalculating the MAHL if the data were collected before any 

changes occurred. For example, upgrading a treatment unit may increase removal efficiencies beyond the 

levels when the POTW conducted most of the sampling for local limits. Consequently, the POTW may 

need to collect new samples to obtain sufficient data that represent current conditions in order to support 

the MAHL’s recalculation. Chapter 4 covers the data needed to develop local limits. 

7.2.3 STEP 3: RECALCULATE EXISTING, OR DETERMINE NEW, MAHLS 

If the results of the analyses conducted in Steps 1 and 2 warrant, the POTW will next recalculate existing 

MAHLs or determine MAHLs for new POCs. Chapter 5 of this guidance covers MAHL calculations. 

The POTW will want to ensure that current data are used for all the variables in the equations for 

calculating MAHLs. 

7.2.4 STEP 4: IMPLEMENT THE LOCAL LIMITS 

The evaluation conducted in Step 1 may indicate that the MAHL for a POC need not be recalculated, but 

rather should be reallocated among the sources of pollutant loadings (IUs, domestic and commercial 

sources, hauled waste, and any reserve for future growth). In such cases, the POTW will go directly from 

step 1 to this step. 

Implementing local limits may involve: 

� Allocating or reallocating MAHLs (between the group of IUs and uncontrollable 

sources, as well as to individual non-domestic sources). 

� Public participation. 

� Approval of revised local limits considered either a “non-substantial” or “substantial” 

modification as defined in 40 CFR 403.18(b). 

� Adoption of local limits and revision of the SUO. 

� Revisions of control mechanisms or IU permits. 

7 - 6
Implementing new and revised local limits is 

covered in Chapter 6 of this guidance. 

Although most of the information presented in 

Chapter 6 applies to both new and revised local 

limits, the POTW may have to take additional 

considerations into account when implementing 

revised local limits. For example, the POTW 

may want to use the same allocation method it 

used previously but may have a different 

number of IUs to consider. Or the POTW may 

want to use a new allocation method (see 

Exhibit 7-3). In addition, the POTW does not 

have to use the same allocation method for 

every POC, but it should document which 

method is used for which pollutant and why. If 

a POTW wants to change its allocation method, 

it should consider how the change may affect its 

Exhibit 7-3: An Example of Changing the 

Method for Allocating Local Limits 

Using the uniform allocation method, a POTW gave all of its 

IUs the same local limit for cadmium through its sewer use 

ordinance. Since then, an IU changed its operating process 

and now generates a significant amount of cadmium. If the 

POTW reallocates cadmium using the same method, the IU 

may be subject to a local limit that will be difficult for it to 

meet. 

The POTW can change its local limits implementation method 

by including the MAILs for cadmium in its SUO and allocating 

cadmium loadings to IUs through individual permits. The new 

allocations would be based on how much loading each IU 

discharger needs. In this way, the POTW can provide the IU 

that changed its operating process with a cadmium allocation 

sufficient for its needs. This would be considered a 

"substantial" modification as defined in 40 CFR 403.18(b). 

existing users. If some IUs become subject to more stringent limits, they may need to install pretreatment 

equipment to remain in compliance with local limits. 

7.3 SUMMARY 

Chapter 7 provides the tools for POTWs to evaluate the circumstances that would lead it to conduct a 

review or re-evaluation of the local limits program. 

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7 - 8
CHAPTER 8-

LOCAL LIMITS TO ADDRESS CONCERNS ABOUT

COLLECTION SYSTEMS

POTWs may need to develop local limits to address concerns about their collection systems and meet the 

requirements found at 40 CFR 403.5(b), which include protecting the health and safety of workers at the 

POTW. Chapter 8 describes methods to address the following collection system concerns: 

� Fires and explosions [40 CFR 403.5(b)(1)] 

� Corrosion [40 CFR 403.5(b)(2)] 

� Flow obstructions [40 CFR 403.5(b)(3)] 

� Temperature [40 CFR 403.5(b)(5)] 

� Toxic gases, vapors, or fumes [40 CFR 403.5(b)(7)] 

POTWs should address each of these potential problems through their local limits development and reevaluation processes. 

8.1 FIRES AND EXPLOSIONS 

The General Pretreatment Regulations prohibit the discharge of pollutants that will create a fire or 

explosion hazard in the POTW. This prohibition includes wastestreams shown to have a closed cup 

flashpoint of less than 140 degrees Fahrenheit (60 degrees Celsius) using the test methods specified at 40 

CFR 261.21. This provision is intended to protect POTW workers and the POTW collection system. To 

comply, a POTW can establish a local limit equal to the flashpoint provision, or opt to develop other 

protection methods. The flashpoint provision and three common alternatives are described below. 

8.1.1 FLASHPOINT LIMIT 

The flashpoint is the lowest temperature at which vapor combustion will propagate away from its source 

of ignition. At temperatures below the flashpoint, vapor combustion immediately above the liquid either 

will not occur, or will occur only at the exact point of ignition. Temperatures above the flashpoint are 

required for combustion to spread. If a POTW prohibits discharges, typically volatile organic 

compounds, that have a closed cup flashpoint of less than 140°F, it will protect against fires and 

explosions. (A flashpoint limit applies to the entire wastestream, not to a specific pollutant.) 

A flashpoint limit ensures that discharges to a POTW will not combust. It is important to note that a 

flashpoint prohibition does not necessarily account for the flammability of mixtures from more than one 

discharger. Dilution effects in sewer systems, however, generally prevent the creation of explosive 

conditions. 

The closed cup is used because this test simulates the confinement of vapors in a sewer. EPA requires a 

flashpoint of less than 140°F [see 40 CFR 403.5(b)]for several reasons: 

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� Ambient temperatures in a sewer are not expected to exceed 140°F. 

� Typical industrial discharges of wastewater are cooler than 140°F. 

� The specified flashpoint is consistent with hazardous waste regulations, which will help 

ensure that POTWs do not face increased hazardous waste liabilities. 

Regulations require that the flashpoint be determined by a Pensky-Martens Closed-Cup Tester, using the 

test method specified in ASTM Standard D-93-79 or D-93-80, or by a Setaflash Closed-Cup Tester, using 

the test method specified in ASTM Standard D-3278-78, or as determined by an equivalent test method 

approved by the EPA Administrator under specified procedures. Appendix H lists closed cup flashpoints 

for select organic compounds. 

8.1.2 LOWER EXPLOSIVE LIMIT MONITORING 

Another way to protect POTW workers is to monitor the collection system for combustible gases. A 

combustible gas detector measures the concentration of these gases and vapors in the air as a percentage 

of the lower explosive limit (LEL). The LEL is the minimum concentration in air at which a gas or vapor 

will explode or burn in the presence of an ignition source. 

LEL monitoring measures pollutant concentrations in the headspace above the wastewater, rather than in 

the wastewater itself. This method makes setting local limits difficult. Consequently, POTWs often use 

LEL monitoring to identify potentially problematic discharges, rather than as a numerical limitation to 

implement and enforce against IUs. LEL monitoring is also an important way to protect POTW workers 

who enter the collection system. 

One approach to monitoring explosion potential is to measure LEL levels at key locations in the 

collection system. Continuous monitoring at pump stations or key manholes can provide a constant 

source of data on the potential for an explosion. Many POTWs establish a percentage of the LEL, 

often 10 to 30 percent, as the level of concern. This ensures that discharges are safely below an 

explosive level. The entire LEL should not be used to establish the level of concern. 

8.1.3 SAMPLE HEADSPACE MONITORING 

Sample headspace monitoring is a discharge screening technique to detect the presence of explosive 

compounds and toxic gases and vapors. Initial screening using this method can identify discharges that 

warrant detailed chemical-specific screening. 

Sample headspace monitoring involves collecting a wastewater sample using proper volatile organic 

sampling techniques (i.e., zero headspace), withdrawing a set percentage of the sample, injecting nitrogen 

gas into the sample container (to maintain a total pressure of one atmosphere), and performing a gas 

chromatography analysis of the sample headspace gas. 

Volatile organic concentrations of the sample headspace gas are converted to an equivalent 

concentration of hexane and compared to a set hexane limit (usually 300 parts per million of 

hexane). Concentrations below the limit are usually deemed sufficient to protect the collection system 

from fires and explosions and to provide minimal protection from toxic gases and vapors. Details of this 

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method are available in Guidance to Protect POTW Workers from Toxic and Reactive Gases and Vapors 

(EPA/812-B-92-001). 

8.1.4 FLAMMABILITY AND EXPLOSIVITY DISCHARGE SCREENING LEVELS 

Discharge screening levels can be used to set local limits on the discharge of pollutants that can create 

flammable or explosive conditions in sewers. This approach requires converting the LELs of individual 

compounds into corresponding IU discharge screening levels. These levels are then compared with 

actual IU discharge concentrations. Appendix I contains a table of discharge screening levels based on 

explosivity. A variety of screening levels have been developed for limiting flammable and explosive 

discharges, including the four-step approach summarized here: 

1. Identify the LEL for each POC. 

2. Use the following equation to convert the compound’s LEL concentration to a vapor 

phase concentration (CVAP) expressed as moles per cubic meter (mol/m3

). (Ten percent 

of the LEL often is used in this equation, instead of the full LEL.) 

CVAP = LEL x P/RT x 1000 = LEL x 40.87 (at 1 atm and 25°C) 

Where:

P = total pressure, 1 atmosphere (assumed)

R = ideal gas constant, 0.08206 atm L/mol °K

T = absolute temperature, 298.15°K (equal to 25°C) (assumed)

3. Determine the Henry’s Law Constant (H) for the POC. This constant converts LEL air 

phase values to corresponding water phase discharge levels. Note that H is presented in 

a variety of units [e.g., (atm m3

)/(mol), (mol/m3)/(mg/L), and (mg/m3)/(mg/L)] and may 

require converting H into the appropriate units of (mol/m3

)/(mg/L). Appendix I contains 

a listing of Henry’s Law constants in various units and provides the appropriate 

conversions. 

4. Calculate the IU discharge screening level (CLVL) using the Henry’s Law expression: 

CLVL = CVAP/H 

Where CLVL is the discharge screening level in mg/L. 

Screening levels derived by this method should be compared directly with the actual IU discharge 

concentrations. Some of the assumptions made using this method are: 

� Although temperature dependent, H typically is reported at 25°C (77°F), which is a 

reasonable estimated temperature of discharges to POTWs. Warmer wastewaters will 

exhibit higher concentrations in the vapor phase, while cooler wastewaters will exhibit 

more of the pollutant in the liquid phase. 

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� The pollutant instantly volatizes to the sewer atmosphere. Although this is a 

conservative assumption, the more turbulence in the sewer, the closer the assumption is 

to actual conditions. In addition, air flow through the sewers prevents the reaching of 

equilibrium, thereby acting to reduce concentrations below threshold levels in the vapor 

phase. 

� The equation does not take into account the solubility effects that result from organic 

contaminants in the wastewater, thereby limiting volatilization into the atmosphere. 

For details of this method, see Guidance to Protect POTW Workers from Toxic and Reactive Gases and 

Vapors (EPA 812-B-92-001). 

8.2 CORROSION 

The General Pretreatment Regulations prohibit discharges of pollutants that will cause corrosive 

structural damage to a POTW. The regulations also prohibit discharges with a pH lower than 5.0 unless 

the POTW is specifically designed to accommodate such discharges. 

8.2.1 PH 

Besides the low-end pH limit specified in the General Pretreatment Regulations, EPA recommends 

POTWs evaluate the need to set upper pH limits or more stringent low-end pH limits. A POTW should 

set an upper pH limit if corrosion damage attributable to high-pH discharges is identified. An upper limit 

pH of up to 12.5 may be an appropriate upper limit in lieu of any identified high pH corrosion concerns. 

However, because wastewater of pH 12.5 or higher is considered a hazardous waste (exhibiting the 

characteristic of corrosivity) under 40 CFR 261.22(a)(1), additional reporting and liability results when 

hazardous waste is discharged to a sanitary sewer. The POTW needs to set an upper pH limit that is 

protective of the POTW, but also allows for some margin of safety to avoid characterization as hazardous 

waste. 

EPA acknowledges that there are advantages to accepting high pH industrial wastewater. These include: 

� Reducing odor emissions from the collection system and plant processes due to a 

reduction in the amount of aqueous hydrogen sulfide. 

� Aiding the nitrification process (which often requires an external source of alkalinity). 

� Improving precipitation and removal of toxic heavy metals by primary clarification. 

� Limiting IU use of acids to neutralize high pH effluent and thus minimizing chloride and 

sulfate ions detrimental to POTW operation. 

8.2.2 CORROSIVE POLLUTANTS 

In addition to discharges whose pH is high or low, the following pollutants can contribute to the 

corrosive properties of wastewater: 

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� Sulfide and sulfate. Much of the sulfide in collection systems is present as hydrogen 

sulfide due to the anaerobic degradation of sulfate. This degradation occurs where 

oxygen is absent and organic matter is present. Collection systems are particularly 

conducive to this reaction if wastewater is allowed to stagnate. The formation of 

hydrogen sulfide is primarily a function of the collection system’s design, however, and 

not a function of the characteristics of industrial discharges. Hydrogen sulfide corrodes 

metals such as iron, copper, lead, and zinc. It is also a precursor to sulfuric acid, which 

corrodes concrete and metals. Sulfate causes corrosion by reacting with the calcium in 

concrete to form calcium sulfate, which can cause concrete to crack. For more 

information, see Detection, Control, and Correction of Hydrogen Sulfide Corrosion in 

Existing Wastewater System, (EPA-832-R92-001, September 1992). 

� Chloride. This pollutant can adversely affect inorganic films and precipitates that form 

on sewer wall and provide a physical barrier that protects from chemical corrosion. Not 

only can chloride decay and penetrate these coatings, it can also prevent them from 

developing by forming more soluble metal chloride instead. 

� Chlorine. By reacting to form hydrochloric (HCl) and hypochlorous (HOCl) acids that 

decrease the pH of wastewater, chlorine can increase the rate at which iron and steel 

corrode. 

� Nitrate and nitrite. They can contribute to iron and steel corrosion. 

� Dissolved salts. The electrolytic action of dissolved salts on the base material can 

corrode concrete, asbestos-cement, and cement mortar. 

� Suspended solids. The abrasive and erosive contact of suspended solids with sewer 

pipes and pumps can cause corrosion, particularly at joints, elbows, bends, and other 

non-uniform areas. 

� Organic compounds. If present in excessive concentrations, organic compounds such 

as solvents will promote the dissolution of gaskets and rubber and plastic linings. 

8.3 FLOW OBSTRUCTIONS 

The discharge of solid or viscous pollutants in amounts that will obstruct flows to POTWs and result in 

interference is prohibited by the General Pretreatment Regulations. The greatest threat of obstruction in 

POTWs comes from polar fats, oils, and greases (FOG) of animal and vegetable origin. Typical sources 

include restaurants, residences, food processors, and food-based industries. Certain polar FOGs, such as 

non-ionic surfactants, do not contribute to flow obstruction. Additional discussions on the potential for 

interference and pass through due to FOG are provided in Section 5.3.3. 

Although more compatible with wastewater treatment operations than non-polar mineral oil or 

petroleum-based oil and grease, polar FOG can accumulate and congeal in collection systems, pumping 

stations, and treatment plants. By obstructing influent flows, polar FOG reduces the capacity of pipes 

and pumps, interferes with POTW instruments (such as flow meters and probes), reduces treatment 

efficiency, and increases POTW operation and maintenance costs. Polar FOG can interfere with the 

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POTW's collection system through blockages when the wastewater cools sufficiently to allow the 

suspended fat, oil, or grease to congeal. This condition is a function primarily of interceptor size, length, 

and slope; ambient temperature; wastewater temperature; and concentration of FOG. These factors vary 

throughout the collection system. To develop a technically based FOG limit for protecting the collection 

system, empirical data (observations and measurements) are needed to document problems and 

contributing factors. The empirical data along with generally available pretreatment and control 

measures for FOG become the technical basis for the proposed local limit. 

To collect data, the POTW first identifies collection system sections that have a critical low slope (i.e., 

relatively flat) profile and may be subject to low temperatures. Data are collected that identify FOG 

levels corresponding to deposition rates of solidified oil and grease. The level of oil and grease at which 

deposition is negligible would be the basis for the collection system MAHL. 

Local limits on FOG may require POTWs to investigate and monitor the activities of non-SIUs that are 

the sources of FOG. The use of controls other than numerical limitations may be a more appropriate way 

to address the problem of FOG from non-SIUs. These controls can include: 

� Requirements to install and maintain grease traps 

� Pretreatment requirements

� Best management practices 

� Prohibitions of specific materials, such as free-floating FOG

� Prohibitions of FOG that are in a solid or semisolid form

� Surcharge programs

� Cost recovery efforts to defray the expenses associated with cleaning sewers 

� Pollution prevention measures

Many POTWs have oil and grease control programs. The Oregon Association of Clean Water Agencies 

has authored Fats, Oil, and Grease Best Management Practices Manual: Information, Pollution 

Prevention, and Compliance Information for Publicly Owned Treatment Plants. The manual provides 

municipal pretreatment staff, along with restaurant and fast food business managers and owners, with 

information about animal and vegetable-based oil and grease pollution prevention techniques focused on 

their businesses. The techniques are effective in both reducing maintenance costs for business owners, 

and preventing oil and grease discharges to the sewer system. Go to: 

http://www.oracwa.org/Pages/intro.htm to review the manual. 

8.4 TEMPERATURE 

The General Pretreatment Regulations prohibit heat discharges that will inhibit biological activity in a 

POTW and result in interference. And in no case can discharges increase the temperature at the 

POTW headworks above 40°C (104°F) unless the Approval Authority, upon request of the POTW, 

approves alternative temperature limits. 

The dilution of heated industrial wastewaters in the collection system typically ensures compliance with 

this prohibition. Temperature is generally more of a hazard to workers who must enter the sewer system 

than it is to POTW treatment operations. A POTW that encounters IU discharges hot enough to prevent 

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or restrict sewer entry should require the IU to reduce the temperature of its discharge. The installation 

of heat exchangers on high-temperature discharges may help the IU save on heating costs for its facility 

or its process streams. 

8.5 TOXIC GASES, VAPORS, AND FUMES 

The General Pretreatment Regulations prohibit the discharge of pollutants that lead to the accumulation 

of toxic gases, vapors, or fumes in the POTW in sufficient quantity to cause acute worker health and 

safety problems. 

Discharge screening levels can be developed to identify IU discharges that have the potential to generate 

toxic gases or vapors in the sewer. A common approach is to convert gas and vapor toxicity criteria for 

individual compounds into corresponding IU discharge screening levels using Henry’s Law Constants. 

These constants relate the concentration of a constituent in the air to the corresponding equilibrium 

concentration in the water. The screening levels should be compared to the actual pollutant 

concentrations in the IU discharge. Calculating these wastewater screening levels is a three-step process: 

� Identify the toxicity criteria, also known as the threshold concentration (CVAP, in mg/m3), 

for the POC. Typical threshold values are available from the National Institute for 

Occupational Safety and Health’s (NIOSH’s) Recommended Exposure Limits (RELs), 

the Occupational Safety and Health Administration’s (OSHA’s) Permissible Exposure 

Limits (PELs), and the American Conference of Governmental Industrial Hygienists’ 

(ACGIH) Threshold Limit Values (TLVs). Each organization can provide chronic and 

acute exposure thresholds that can be used to develop screening levels. See Appendix J 

for a listing of some of these threshold concentrations. Consistent with the specific 

prohibitions for toxic gases, vapors, and fumes, screening levels may be based most 

appropriately on acute worker health and safety levels (i.e., short-term exposure levels or 

ceiling concentrations). 

� Identify the Henry’s Law Constant (H) for the POC and convert the constant to the 

appropriate units of (mg/m3

)/(mg/L). Appendix I contains a listing of Henry’s Law 

constants in various units and the appropriate conversions. 

� Calculate the IU discharge screening level (CLVL) from the Henry’s Law expression: 

CLVL = CVAP/H 

Where: 

CLVL = IU discharge screening level (in mg/L) 

CVAP = Threshold concentration (in mg/m3

) 

As with the flammability and explosivity screening level, this screening method assumes instantaneous 

volatilization of the pollutants to the atmosphere and does not consider the dilution of IU wastewater in 

the collection system. Therefore, these screening levels will in many cases be more conservative than 

necessary to protect POTW workers. 

These screening levels address only the toxicities of individual compounds, but mixtures of toxic 

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compounds can be evaluated against an adjusted threshold value of the mixture of all the toxic 

compounds. Appendix I contains a table of discharge screening levels based on fume toxicity. Details 

on the specifics of using the discharge screening level method, including evaluating mixtures of toxic 

gases, vapors, or fumes, is available in EPA’s Guidance to Protect POTW Workers from Toxic and 

Reactive Gases and Vapors (EPA 812-B-92-001). 

8.6 SUMMARY 

After reviewing Chapter 8, POTWs should be able to address collection system concerns: fire and 

explosions, corrosion, flow obstructions, temperature, and toxic gas, vapors and fumes. 

8 - 8
CHAPTER 9 -

QUESTIONS AND ANSWERS 

This chapter presents EPA’s responses to many commonly asked questions about local limits 

development and implementation. The questions and answers are grouped by topic for ease of finding 

subjects of interest. 

9.1 GENERAL 

Q: Once I establish a local limit, will I ever be able to drop it? 

A: As emphasized throughout this guidance, development of local limits is a continuing, dynamic 

process. EPA recommends a re-evaluation of specific local limits whenever there are significant 

changes in the overall program as a step that every prudent Control Authority should do on a 

regular basis. If changes in IU discharge conditions or installed treatment technologies at the 

POTW dictate that some pollutants of concern (POCs) are no longer present or are present only 

in concentrations that will not cause pass through, interference, or degradation of sludge 

quality, then the local limits for those pollutants may be dropped after appropriate procedures 

are taken. However, POTWs should be cautioned that dropping a particular local limit 

completely may motivate IUs to discontinue a treatment process designed to remove or recycle 

that particular pollutant. POTWs should have a complete understanding of the makeup of 

untreated IU wastestreams before dropping a local limit completely. The regulations at 40 CFR 

403.18(c) specify that eliminating or changing a local limit to make it less stringent requires 

notification of the Approval Authority and appropriate public notice because such actions are 

considered substantial program modifications. 

Q: How do multi-jurisdictional systems affect local limit requirements? 

A: For multi-jurisdictional systems in which one Control Authority accepts industrial wastes from 

one or more other, independent municipalities, EPA strongly recommends that all contributing 

jurisdictions adopt a set of local limits that are at least as stringent as those of the Control 

Authority that maintains the collection system and operates the receiving POTW. If this policy is 

impractical, then the contributing jurisdictions should agree to a maximum total mass loading of 

pollutants that would be discharged to the primary collection system and POTW. As an 

alternative, the contributing jurisdiction may adopt two sets of local limits and apply to each IU 

the limit appropriate to the treatment works to which the user discharges. Consult EPA’s 

Multijurisdictional Pretreatment Programs Guidance Manual (EPA 833-B-94-005, June 1994) for 

additional information. 

Q: Do a minimum number of parameters need to be evaluated? 

A: There is no minimum number of parameters required by regulation. EPA recommends that the 

need for local limits be evaluated for a list of specific pollutants. EPA recommends that 

technical evaluations for POCs by every POTW should include a determination of the need for 

9 - 1
limits for arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, zinc, and cyanide. 

This Guidance adds total suspended solids, 5-day biochemical oxygen demand, ammonia, 

molybdenum and selenium to the list of recommended minimum pollutants to be considered as 

POCs. 

Q: Do local limits have to be developed individually for multiple treatment works? Is it necessary 

that identical numeric local limits be established? 

A: There is no regulatory requirement that a Control Authority develop local limits that are specific 

to a single treatment works. However, EPA recommends that the Control Authority perform a 

separate evaluation for each works to determine if each plant is being protected and not subject 

to pass through or interference problems. After completing these independent evaluations, the 

Control Authority can determine whether individual local limits should be provided to the IUs 

that discharge into the parts of the system served by a particular treatment works. The only 

regulatory requirement is that there be local limits developed that prevent pass through and 

interference and are enforceable on a technical basis. The preferred method is to establish 

MAILs individually for the treatment plants, but if that is politically infeasible, then set a single, 

conservative local limit (i.e., the lowest limit developed in the assessment for the individual 

treatment works) for a POC. The limit should then apply to all IUs that discharge to the POTW, 

without regard as to which works actually treats the wastewater discharged by a particular IU. 

Q: Can best management practices (BMPs) and best professional judgment (BPJ) limits be applied 

in lieu of the traditionally derived numeric local limits? 

A: The General Pretreatment Regulations do not specifically address the use of BMPs and BPJ as 

local limits. The regulations at 40 CFR 403.5 (c) require the POTW only to develop “specific 

limits” for prohibited discharges. The current regulatory language is ambiguous as to whether 

BMPs could serve in lieu of numeric limits. BMPs may reduce the amount of the POC at the 

headworks thus leaving more pollutant loading to be distributed as numerical limits to facilities 

that cannot control their discharge through BMPs. If adopted, the proposed Pretreatment 

Streamlining Rule would specify that BMPs could be considered as local limits and also fulfill 

the statutory requirements of Section 307 (d) of the Clean Water Act. As with BMPs, using BPJ 

to develop local limits is not specifically prohibited. If adopted following the process in 40 CFR 

403.5, BPJs are enforceable. 

Q: Can local limits evaluation and development be contracted out? 

A: In EPA’s view, the optimum process is for the Control Authority to evaluate and develop the 

appropriate local limits because it provides the Control Authority with a better understanding of 

limit development and the importance of compliance. However, recognizing the fact that some 

Control Authorities may be severely constrained by an overextended workforce, or require 

access to technical expertise that is not internally available, the Control Authority may secure 

the necessary manpower and expertise through an outside consultant or engineering firm. 

However, the Control Authority should be aware that any mistakes or improper determinations 

would be its legal responsibility if the Approval Authority, an IU, or any outside party challenges 

the POTW on the assignment of the limits. 

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9.2 POTENTIAL POLLUTANTS OF CONCERN 

Q: If a pollutant is below the detection level in influent, effluent, and sludge, may a POTW exclude 

it as a POC (and not develop a MAHL), even if it is one of EPA’s 15 pollutants? 

A: Yes, it may. If a POC is not detected in the influent, effluent, or sludge during the POTW ‘s 

assessment of the need for local limits, an accurate calculation of the MAHL for that particular 

pollutant is not possible. The goal of setting stringent local limits is to protect the POTW and 

avoid violations of NPDES permit. However, if no MAHL is established for a “potential” POC, 

there is always the possibility that a new industrial user (or users) of the system will discharge 

wastes that are in excess of the POTW’s ability or capacity to treat such wastes. Therefore, EPA 

recommends that MAHLs be developed for all 15 EPA-designated POCs even if local limits are 

not adopted. Of course, POTWs should assess a new user’s impact on local limits before 

granting authorization to discharge. 

Q: Should local limits be developed as dissolved metals, total metals, or both? How does 

hexavalent chromium relate to total chromium, and which should be used for local limits 

development? 

A: While it may be desirable to develop local limits for both dissolved and total metals, in reality it 

may be impractical because of cost. POTW data are developed almost exclusively in terms of 

“total” because of NPDES requirements and the fact that Categorical Pretreatment Standards 

are always expressed as total. Because the POTW should be able to apply the more stringent of 

either the local limit or the Categorical Standard, it makes sense to develop the local limits as 

“total” values. Although the dissolved form of metals is usually more toxic, POTWs need to 

control the total metal entering the treatment works because particulate metal or metal 

compounds may exert some toxicity or may later be resolubilized. A large percentage of the 

toxic metals present in aeration basins at some treatment works has come from recycled solids 

handling sidestreams. These contributions can continue to exert a toxic effect long after the 

source has been controlled. Although most heavy metals “passing through” a treatment works 

are discharged into receiving waters in the dissolved form, significant concentrations of heavy 

metals may accumulate as fine particulates in the sludge produced at the POTW. By 

implementing local limits to control total metal concentrations, a POTW will reduce the chances 

for pass through and ensure that the quality of the sludge is not degraded. Local limits should 

be developed for total chromium. Hexavalent chromium is the more toxic of the two forms of the 

metal, but it can be converted to a total chromium value by using proper mathematical 

equations. If a POTW has contributions of hexavalent chromium, EPA recommends it develop 

local limits for both hexavalent chromium and total chromium. The basis of the limits will likely 

be different because the allowable holding time for hexavalent chromium samples is less than 24 

hours. 

9.3 SAMPLING AND ANALYSIS 

Q: What analytical requirements and quality assurance/quality control procedures apply to local 

limits evaluation sampling? 

A: There are no different or “special” quality assurance/quality control procedures that apply 

strictly to local limits sampling. EPA recommends that all wastewater sampling for POCs follow 

9 - 3
prescribed protocols found in 40 CFR Part 136 (Guidelines for Establishing Test Procedures for 

the Analysis of Pollutants) and information provided in EPA-issued technical guidance. When 

sampling sludge for metals and total solids, however, the requirements in the sludge regulations 

at 40 CFR Part 503 apply. Therefore, EPA recommends that the analysis of sludge for the 

presence of metals be performed according to EPA test method SW-846 and for total solids 

according to Part 2540 G of the Standard Methods for the Examination of Water and 

Wastewater, 18th Edition. 

Q: Are there minimum analytical detection levels that should be achieved when analyzing samples 

for local limits? 

A: As discussed in Chapter 3, a POTW’s NPDES permit conditions, sludge disposal practices, and 

State and local requirements need to be addressed through local limits. Therefore, the analytical 

techniques for detecting POCs need to be able to identify and quantify concentration levels that 

are at least as stringent as the prescribed maximum concentrations for conventional and nonconventional pollutant effluent limitations, water quality-based toxic pollutant limitations, whole 

effluent toxicity (WET) requirements, and any numeric criteria for sludge use and disposal 

practices. In addition, POTWs will want to specify the lowest reasonable detection limit for a 

local limit monitoring to minimize the possibility of a POC being reported as“non-detectable.” 

Q: Is it necessary to account for hydraulic detention time through the treatment works when 

conducting sampling? 

A: Treatment works sampling should account for hydraulic detention times within the plant 

whenever possible. Developing relevant removal efficiencies depends in part on accounting for 

hydraulic detention times. For some systems, such as lagoon systems, hydraulic detention times 

may be lengthy (e.g., 21 days). If it is not feasible to account for detention times, local limits can 

still be developed, but the options for determining removal rates will be reduced. Various 

methods for determining removal efficiencies are reviewed in Chapter 5. 

Q: Do I have to outline a sampling plan for the local limits evaluation? 

A: Outlining a sampling plan for local limits evaluation is not required by 403 regulations, 

although some Approval Authorities may require submission of such a plan. However, EPA 

highly recommends that a POTW develop a sampling program to ensure that it has adequate 

data for developing local limits that have sound technical bases. A sampling program can also 

enable a POTW to use fewer resources for evaluating local limits by providing the data 

necessary to determine and justify that local limits are not necessary for some pollutants and by 

enabling the POTW to manage its data and ensure that unnecessary sampling is not performed. 

Information regarding local limits data collection is reviewed in Chapter 4. 

Q: Is sampling and analysis of the receiving stream necessary? 

A: Receiving stream data (flow and ambient background concentrations of pollutants) provide key 

input parameters for allowable headworks loading (AHL) calculations when NPDES permit 

limits do not exist and the POTW needs to evaluate for pass through based on water quality 

standards. These data may already be available from sources such as the U.S. Geological 

Survey, State environmental agencies, and the POTW’s NPDES permit. Therefore, a POTW may 

9 - 4
not need to conduct sampling and analysis of the receiving stream to gather these values. 

However, if these data are not available, the POTW will want to consider sampling the receiving 

water so that AHLs can be calculated based on applicable values. The Approval Authority may 

require this information on a case-by-case basis for individual IUs. Other dischargers to the 

same portion of the receiving stream may already have performed sampling and may be willing 

to share the data or the costs of new monitoring. 

9.4 DETERMINING MAHLS 

Q: Water quality standards have been established for our treatment works’ receiving waters, but no 

water quality-based effluent limitations are included in our permit. Is it necessary to include the 

analysis for an allowable headworks loading (AHL) based on water quality standards in this 

case? 

A: Yes, it is. If a POC loading measured at the headworks exceeds a MAHL that was set by the 

AHL for a water quality standard, there may be pass through of the pollutant, thereby causing a 

violation of the water quality standard and (consequently) of the Clean Water Act. In general, 

POTWs will not have NPDES permit limits for all of the POCs established during the local limits 

analysis. In such cases, a POTW may base its effluent-quality-based AHL on State Water 

Quality Standards (WQS) or Federal Water Quality Criteria (WQC). State environmental 

agencies have developed WQS that set maximum allowable pollutant levels for their water 

bodies, specific to the receiving stream reach’s designated uses. Even though the POTW’s 

NPDES permit may not contain a numeric effluent limit for a POC, the permit probably will 

contain narrative provisions requiring compliance with State WQS and prohibiting the discharge 

of any toxic pollutants in toxic amounts. A local limit based on a State WQS fulfills the narrative 

permit requirement specifying “no discharge of toxics in toxic amounts.” See Section 3.2.2 and 

the associated footnotes for additional information. 

Q: How much literature data are acceptable in deriving MAHLs? How much site-specific data are 

sufficient? How recent must data be for deriving MAHLs? 

A: The answers to these questions will vary significantly from facility to facility. Depending on the 

POC and on the type and accuracy of the data available, a considerable range of techniques are 

acceptable for deriving the MAHL. EPA recommends that the Control Authority make a caseby-case determination about type and age of data that are sufficient to calculate accurate, 

technically defensible MAHLs. For example, data collected prior to major construction should 

not be used. However, the most accurate and technically defensible limits are the result of using 

site-specific data, rather than “generic” removal efficiency data derived from average, nationallevel treatment works “literature” data. 

Q: We do not have NPDES or sludge limits for all of the POCs required to be evaluated; further, 

there are no State WQS for these pollutants. What criteria are we supposed to use in our 

evaluation? 

A: Sludge, NPDES, or water quality criteria may not exist for all POCs. In these instances, the 

POTW may want to develop MAHLs based on system design criteria, air quality standards, 

inhibition criteria, or worker health and safety standards. In addition, the POTW will want to 

9 - 5
determine the original purpose for adding a POC (e.g., WET test failure) and establish criteria 

through researching other applicable standards and guidelines. 

Q: How does a POTW develop local limits based on a NPDES WET limit? 

A: Nothing in the pretreatment regulations prohibits using Whole Effluent Toxicity (WET) test data 

as the basis for developing a local limit. WET tests are primarily designed to protect the 

receiving waters from the aggregate toxic effect of a mixture of pollutants in the effluent. The 

WET approach is most useful for complex effluents where it may be infeasible to identify and 

regulate all toxic pollutants in the discharge, or where chemical-specific pollutants are set, but 

synergistic effects are a problem. However, unless you can identify each compound in the 

effluent that produces measurable acute or chronic toxicity concentrations, WET testing cannot 

be used to set local limits for a particular POC. If the toxic pollutant or pollutant parameter 

cannot be identified, then a POTW will want to evaluate all of the possible POCs present in the 

mixture. In this situation, WET test data may not be a cost-effective methodology for identifying 

POCs for evaluation in the local limits development process. The guidance Toxicity Reduction 

Evaluation Guidance for Municipal Wastewater Treatment Plants (EPA/833-B-99-002, August 

1999) provides further information on conducting a Toxicity Identification Evaluation. 

Q: Influent and effluent pollutant concentrations are below quantifiable levels yet the pollutant is 

detected in the sludge. What removal rate should I use? 

A: EPA recommends that a POTW first evaluate those levels below the minimum level of 

quantitation (ML) as outlined in Section 5.1.3. If the methodologies outlined in Section 5.1.3 do 

not allow the calculation of a removal rate, a POTW then may selectively use removal 

efficiencies reported by other POTWs or by studies that have been published in professional 

journals or by EPA. Appendix R provides a list of removal efficiency data for priority pollutants 

gathered from other POTWs. 

Q: Why should POTWs use the Table 3 Land Application Part 503 sludge standards when the 

POTW’s sludge is disposed in a landfill? 

A: POTWs are encouraged to use the Table 3 standards because the Pretreatment Regulations list 

recycling of sludge as one of the goals of the program. Land application standards help meet 

this goal and also allow for more sludge disposal options, because the Table 3 standards are the 

most stringent. EPA recommends that POTWs consider the attainment of EPA “clean sludge” 

standards, that are delineated in Table 3 of 40 CFR 503.13, and provide the broadest choice of 

beneficial use options for sludge disposal. Further achievement of these standards is consistent 

with the objectives of the National Pretreatment Program, which are listed at 40 CFR 403.2. 

Additionally, until a sludge landfill is properly closed and abandoned there is always a potential 

for the leachate to affect groundwater. See Appendix K for landfill leachate loadings. In some 

cases, collected leachate can be trucked (as hauled waste) to a POTW and treated to non-toxic 

concentration levels. For this option to be viable, the metals content of the sludge should be 

limited to concentrations that will not cause potential pass through or interference problems for 

the POTW. Table 3 sludge standards for land application cover all nine toxic metals, while the 

surface disposal sludge standards specify limits only for arsenic, chromium and nickel. 

Imposing land application standards on sludge increases the probability that the leachate can be 

successfully treated in the future at a POTW. Nevertheless, if a POTW has a choice of disposal 

9 - 6
options, EPA recommends that it use land application disposal techniques because they are 

generally more controllable and have less potential for serious environmental degradation of 

surface water and groundwater. 

9.5 ESTABLISHING LOCAL LIMITS 

Q: All of my influent, effluent, and sludge concentration data for a specific pollutant are below the 

method detection limit. Can the pollutant still be considered a POC and local limits established? 

A: Yes. The Control Authority (generally, the POTW) has the authority to consider any chemical 

compound or pollutant as a potential POC and establish a local limit for that pollutant. If your 

POTW serves a high-growth municipality or incorporated area where the number and type of 

non-domestic users change frequently, it may be prudent to establish a MAHL limit in your 

ordinances for any pollutant that could potentially cause interference, pass through, or degrade 

your sludge quality—even if the concentration of that pollutant is currently below detection 

levels. Several statistical approaches to evaluating “below detection level” or below 

quantitation level data are discussed in Section 5.1.3 and Appendix Q. 

Q: If a POTW’s local limits evaluation indicates that its sludge disposal method (e.g., land 

application) is the most limiting factor, may the POTW pursue a less stringent sludge disposal 

method (e.g., landfill)? 

A: The determination of the manner in which the sewage sludge is used or disposed of is a local 

determination. As long as a POTW adheres to all of the regulatory requirements specified in 40 

CFR Part 503, it may select the optimum method of sludge disposal. EPA recommends that 

POTWs consider the attainment of EPA “clean sludge” standards, that are delineated in Table 3 

of 40 CFR 503.13, and provide the broadest choice of beneficial use options for sludge disposal. 

Further, achievement of these standards is consistent with the objectives of the National 

Pretreatment Program, which are listed at 40 CFR 403.2. 

Q: What do I do when my total domestic/background loading of a pollutant is equal to or greater 

than my MAHL, so I have no allowable loading for IUs? 

A: The POTW may wish to consider a program that involves short-term, intermediate, and longterm measures. Short-term measures include evaluating the data and calculations used to 

develop the local limits to assess the validity of results. Intermediate measures include 

establishing interim local limits, looking into other possible sources of pollutants (including 

expansion of your list of IUs), and determining how to manage these sources. Long-term 

measures involve evaluating controls for users not already covered by your pretreatment 

program. If the short-term measures do not take care of the problem and provide loadings to 

allocate to IUs, the POTW would proceed to intermediate measures, and then, if necessary, to 

long-term measures. Examples of activities for each of the steps are listed below: 

Short-term 

� Ensure that all significant industrial and commercial dischargers of the pollutants have 

been identified. 

9 - 7
� Evaluate all sampling sites that have been used to estimate background concentration to 

ensure that commercial facilities were not missed and are not contributing pollutants of 

concern to the sampling location. 

� Use actual sewer trunk line monitoring data in place of any literature data used in 

determining total domestic pollutant loadings to the POTW. 

� Use removal efficiencies based on in-plant monitoring in place of any literature removal 

efficiencies used in determining MAHLs. 

� Verify the applicability of criteria (e.g., sludge disposal standards, and water quality 

criteria) used as the basis for AHL calculations. 

� Verify that appropriate sampling locations have been used, and that samples are 

representative (i.e., do not reflect peak loading periods only). 

� Check the accuracy of all calculations made and the reliability of data used. 

� Evaluate the method for handling non-detect monitoring results (e.g., equal to the 

detection level was used) and consider using other conventions (e.g., half the detection 

level). 

� If the MAHL is based on inhibition criteria, current headworks loadings are greater than 

the inhibition criteria and the POTW has not experienced inhibition, the current 

loadings may be a more appropriate basis for inhibition values. 

Intermediate 

� Verify the sampling frequency through statistical methods. 

. � Collect additional sampling data to refine values used (e.g., for removal efficiencies) or 

replace literature values. 

� If hauled waste is being accepted, consider discontinuing this practice or instituting a 

program to determine individual wastewater components versus those contained in the 

septage. 

� If chemicals are added in the plant or sewer system (e.g., to control root growth), 

consider alternatives that do not introduce POCs. 

� Calculate a mass balance for the collection system (i.e., check if the sum of industrial 

plus domestic/commercial plus any hauled waste loadings are between 80 percent and 

120 percent of the total influent loading). If not, one or more sources may not be 

accounted for or data may be invalid. 

� Establish interim local limits such as a local limit equal to the POTW’s NPDES permit 

limit, to the NPDES limit adjusted for the POTW removal efficiency for a particular 

9 - 8
pollutant, or to the lowest achievable method detection level (so that IU compliance with 

the limit can be determined). If the POTW is not experiencing pass through or 

interference for a given pollutant (e.g., no NPDES limit or sludge disposal criterion 

violations, no collection system problems), consider substituting the current influent 

loading for the MAHL and recalculate the allowable industrial loading. The interim 

limits should be replaced as long-term measures take effect. 

Long-term 

� Require industries to perform pollutant minimization/prevention evaluations. 

� Consider implementing measures to address or regulate elevated loadings from nonindustrial sources. These non-industrial sources include nonpoint sources (e.g., runoff) 

discharging to combined sewers, elevated pollutant levels in water supplies, household 

disposal of chemicals into sanitary sewers, and toxic pollutant discharges from 

commercial sources (e.g., photo labs or dry cleaners). 

Pollution prevention/minimization programs can address each of these sources. Nonpoint 

sources of pollutants may be addressed through combined sewer overflow control programs and 

urban and agricultural chemical management programs. The POTW may be able to reduce 

elevated pollutant levels in water supplies by working with the local water department. For 

example, elevated levels of metals in water supplies often arise from corrosion in water 

distribution pipes. The local water department may be able to reduce corrosion by adjusting the 

pH of the water supply. The POTW may be able to assist the water company in developing a 

program to optimize the use of chemical additives in lieu of making simple adjustments to the pH 

by using acidic or caustic chemical agents. The POTW can make efforts to educate the public on 

proper disposal of household chemicals and to provide chemical and used-oil recovery facilities. 

Each of these efforts is not directly part of the local limits process. 

Reducing toxic pollutant discharges from commercial facilities is generally most effectively 

addressed through local limits. Commercial sources of pollutants, such as radiator shops, car 

washes, hospitals, laundries and photo processors, are often not considered significant sources 

of toxics because they typically have relatively low flows or are assumed to have insignificant 

pollutant levels in their discharges. However, these commercial sources may discharge at 

surprisingly high pollutant loading levels and are potential IUs that should be considered for 

control during local limits development. In some cases, the POTW may best address these 

sources through pollution prevention/minimization efforts, such as providing guidance to small 

commercial dischargers (e.g., informing dentists about how they can reduce mercury discharges 

to sewers). 

Q: How useful are priority pollutant data in determining the need for and in setting local limits? 

A: The “best case scenario” is that a POTW knows everything about each of its IUs, including the 

manufacturing processes involved and the types and amounts of pollutants discharged into the 

collection system by a particular facility. However, despite the requirements to notify the POTW 

of any changed discharges, some facilities might install new process technology, change to the 

9 - 9
production of new chemical compounds, or use new or substitute chemicals in their processes. 

In these cases, new POCs might be introduced into the POTW. Use of priority pollutant scan 

data would provide added insurance that none of the 126 priority pollutants are being 

introduced (inadvertently or otherwise) into a POTW before problems with pass through, 

interference or sludge quality are detected by other analytical means. 

Q: Do local limits apply to all IUs? Do they have to be included in all permits issued by the 

POTW? 

A: The assignment of local limits depends on how the MAIL calculations were performed and how 

the sewer use ordinance requires the local limits to be implemented. There is no regulatory 

requirement that “all limits” be included in every permit. However, the regulations at 40 CFR 

403.8(f)(1) require that the contribution to the POTW by each Industrial User be ‘controlled’ 

through permit, order, or similar means, to ensure compliance with applicable Pretreatment 

Standards and Requirements. The regulations also specify that permits issued to Significant 

Industrial Users (SIUs) must contain certain minimum conditions, which include: “Effluent 

limits based on applicable general pretreatment standards in part 403 of this chapter, 

categorical pretreatment standards, local limits, and State and local law.” [40 CFR 

403.8(f)(1)(iii)(C)] 

The applicability issue is determined by the local limit allocation method (i.e., uniform 

concentration, mass proportion, industrial contributory) that the POTW chooses when 

developing the local limits and how the POTW expressly states the applicability of the local 

limits within its sewer use ordinance (SUO). The Control Authority may elect to codify local 

limits in the local SUO or place general enabling authority language about local limits in the 

SUO and announce the actual limits by another mechanism (e.g., as a technical directive, etc.). 

Including the limits in the SIU permit provides individual notice to a permittee of the pollutant 

limits that are applicable to that particular SIU. 

Q: My local limits re-evaluation indicates that a less stringent local limit than the one currently in 

the ordinance can be applied. Is this allowed in light of EPA’s anti-backsliding policy? 

A: First, you need to consider the full meaning of the “anti-backsliding” policy. The “antibacksliding” concept associated with NPDES permit limits does not apply to local limits. Local 

limits apply to a particular IU and can be raised or lowered based on the periodic re-evaluation 

of the need for those limits. Second, a POTW may need to modify its SUO before it may impose a 

less stringent limit. Otherwise, the permit may conflict with the POTW’s authority. Third, in the 

case of a Categorical Industrial User discharge regulated by a categorical effluent standard, the 

more stringent limit (either the local limit or the categorical standard) must be 

applied—regardless of the local limit established for that pollutant. Though rare, some 

categorical standards may be made less stringent as a result of removal credits (40 CFR 403.7). 

Also, because any less stringent change in prescribed local limits would be a significant 

program modification, you must notify and seek the approval of the Approval Authority prior to 

making such a change. 

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Q: Is effluent trading of local limits allowed? 

A: Yes. A POTW may decide to negotiate with its IUs in allocating its calculated allowable 

industrial loadings. However, the POTW needs to ensure that no more than the total MAHL is 

allocated among domestic/background sources, IUs, commercial sources not considered IUs by 

the POTW, and other sources of loadings such as hauled waste. Effluent trading, which must be 

authorized in the POTW’s sewer use ordinance, may result in a program modification, as defined 

in 40 CFR 403.18 and results of the trades should be incorporated into any control mechanisms 

(see Section 6.4.2). 

Q: If a calculated local limit is excessive (i.e., a large number), should the POTW implement this 

limit? 

A: The POTW should consider the potential IU discharge for the particular pollutant and the 

possibility that a high limit might encourage increased discharges to the system. Of course, the 

POTW must receive Approval Authority concurrence on the local limit. 

Q: How do I develop local limits for other pollutants (e.g., BTEX compounds) that may be specific 

to certain users? 

A: For BTEX, some options to consider for determining if pass through or interference will occur 

include: 

� Fume toxicity criteria. 

� Aquatic life protection criteria. 

� Worker safety and health criteria. Consult the Guidance to Protect POTW Workers 

from Toxic and Reactive Gases and Vapors (EPA, 1992). 

Once the most stringent criteria are determined, POTWs may want to compare the proposed 

local limit with BTEX treatment technology. The Model NPDES Permit for Discharges Resulting 

from the Cleanup of Gasoline Released from Underground Storage Tanks (EPA, 1989) contains 

two sets of effluent limits: 1) BTEX of 100 μg/L and benzene of 5 μg/L (assumes approximately 

15 mg/L of dissolved product is treated to a removal efficiency of 99.5 percent, which can be 

achieved with a commercially available stripper unit), and 2) BTEX of 750 μg/L and benzene of 

50 μg/L (assumes approximately 15 mg/L of dissolved product is treated to a removal efficiency 

of 95 percent, using equipment that a small business is more likely to purchase). 

Q: How should IU-specific limits be developed for “atypical”dischargers (i.e., groundwater 

cleanups, hauled waste, landfill leachate, and underground storage tank cleanups) containing 

pollutants for which no local limits or MAHLs are established and which cannot be measured at 

the headworks? 

A: First, EPA recommends you ensure that your local ordinance gives you the authority to impose 

limits for pollutants that are not specifically listed in your ordinance limits or other document 

9 - 11
pertaining to local limits adoption policy. Second, EPA suggests that you review the 

Supplemental Manual on the Development and Implementation of Local Discharge Limitations 

under the Pretreatment Program (EPA-W21-4002, May 1991) and relevant RCRA site 

remediation guidelines (for underground storage tanks and groundwater contamination) to 

determine what types and concentrations of pollutants are typically discharged by these 

wastewater sources. The POTW next may determine (on a site-specific basis) which of these 

sources are likely to be a problem and establish a sampling program for the sewer trunk lines 

into which the wastewater is discharged. If this sampling program identifies the potential for an 

adverse impact on the POTW, then specific local limits can be developed and incorporated into 

the discharge permit of the IU(s) that are problematic. The Guidance to Protect POTW Workers 

from Toxic and Reactive Gases and Vapors (EPA, 1992) provides additional data relating to 

health and safety concerns. 

9.6 OVERSIGHT AND PUBLIC PARTICIPATION 

Q: What kind of public participation should I expect during the local limits development process? 

A: Although the public does not usually become actively involved in the development process, the 

CWA established public participation as an integral part of developing any regulatory program, 

including standards and effluent limitations associated with the pretreatment program. 

Obviously, “public” participation includes all affected entities. The IUs are critically important 

participants in the whole local limits development process. The General Pretreatment 

Regulations encourage public participation by requiring public notices or hearings on local 

limits development. Federal regulations require POTWs to notify affected persons and groups 

and give them an opportunity to respond before final promulgation of a local limit [40 CFR 

403.5(c)(3)]. Any subsequent modifications that are deemed significant modifications (as 

defined in 40 CFR 403.18 (b) ) must be publicly noticed. Minor modifications, such as the 

adoption of a more stringent local limit for a POC, do not require public notice. However, the 

POTW must ensure that it has the authority to impose more stringent limits. Modifications to 

local limits for pH and reallocation of the MAIL are considered to be minor program 

modifications and do not require public notice (see Sections 6.7 - 6.9). 

Q: Do I need Approval Authority approval to implement and enforce local limits? 

A: No, you do not unless you are making changes to your legal authority or amending your local 

limits to make them less stringent than those currently incorporated in your approved 

pretreatment program. In accordance with 40 CFR 403.18, changes to legal authority or 

making local limits less stringent is considered a significant modification to the approved 

pretreatment program and must therefore be approved by the Approval Authority. However, 

modifications to local limits for pH and reallocation of the MAIL are considered to be minor 

program modifications and do not require Approval Authority approval or public noticing. As 

prescribed in 40 CFR Part 403, the authority to develop and enforce local limits needs to be 

incorporated into a POTW’s pretreatment program at the time of program approval (see 

Sections 6.7 - 6.9). 

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9.7 IMPLEMENTATION AND ENFORCEMENT OF LOCAL LIMITS 

Q: Are local limits enforceable if not contained in a sewer use ordinance (SUO)? 

A: Local limits are enforceable if included in a valid user permit or similar enforceable control 

mechanism. From a notification standpoint, local limits may be more difficult to enforce if the 

SUO does not specifically reference them so that IUs know what is expected of them. Even if the 

limits are not in the SUO, the Control Authority must ensure that it has the legal authority to 

enforce limits or procedures in documents other than the SUO and that all required public 

participation procedures are conducted. The Control Authority will need to evaluate the 

availability of resources and the respective burden of enforcing local limits before deciding 

whether to use general language about complying with local limits versus putting specific MAIL 

values in its SUO (see Sections 6.7 - 6.9). 

Q: Can my State or EPA take enforcement action against IUs in my jurisdiction for violations of 

local limits? 

A: All local limits developed in accordance with the provisions stated in 40 CFR 403.5(c) are 

deemed to be Pretreatment Standards for the purposes of Section 307(d) of the Clean Water Act. 

Consequently, EPA or the State Approval Authority may take enforcement action against any 

industrial user for a violation of a local limit. The CWA also provides that affected third parties 

may bring “citizen suits” against users for violations of these local limits. 

Q: How can a POTW justify imposing stringent local limits on IUs when the POTW is not subject 

to an NPDES permit limit or sludge standards for the same pollutant? 

A: If a POTW believes that one or more POCs may cause or have the potential to cause damage to 

the system infrastructure (i.e., corrosion, erosion, disruption of plant treatment efficiencies), 

affect worker safety and health, or negatively impact water quality, it must impose a local limit 

for these POCs. The use of site-specific data (rather than less precise“literature” data) for local 

limits calculations will always produce better, more technically defensible limits. In addition, 

POTWs have the ability to establish land application of its sludge as the goal of its pretreatment 

program and to use sludge land application criteria (as opposed to sludge surface disposal 

criteria) in the development of the limits. 

Q: Can a POTW allocate local limits to non-categorical SIUs only and require CIUs to comply with 

the categorical standards only? 

A: This is an allocation method issue. As long as the appropriate categorical standards are 

imposed on the CIUs and the sum of the loadings allocated to all IUs does not exceed the total 

MAIL, the POTW may assign MAILs as it sees fit (i.e., each IU need not be given the identical 

limit for a particular POC). Note that if the POTW establishes a MAIL for a pollutant, then EPA 

recommends that CIUs receive an allocation for that pollutant even if the categorical standard 

does not regulate that pollutant. Also, note that local limits based on the general prohibitions 

(e.g., corrosion, flammability, etc.) would still need to be applied to categorical industries. 

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9.8 POTW OPERATIONS 

Q: Our POTW consists of multiple treatment plants. Wastewater flow and sludges can be diverted 

between them. How does this affect local limits evaluation and development? 

A: To ensure that all treatment plants are protected from pass through, interference, and sludge 

degradation, each treatment plant should calculate allowable headworks loadings. The MAHL 

can then be selected from the most stringent AHL. This practice will effectively impose a safety 

factor on all of the treatment plants in the POTW and avoid any disruption of the plant treatment 

process or violation of the POTW’s NPDES discharge permit. 

Q: Is expansion of my POTW’s service area cause for me to re-evaluate local limits? 

A: EPA recommends that a POTW evaluate the characteristics of its “new” service area to 

determine how the POTW’s current local limits requirements would be affected. Although not an 

absolute requirement (due to presumed safety factors built into a POTW’s local limits 

determination), it is always prudent to re-evaluate the local limits calculations if the expansion 

will add a number of SIUs to the POTW’s collection system. The decision about what triggers 

the need for a re-evaluation is left to the POTW. However, as has been previously noted, EPA 

recommends that local limits be re-evaluated periodically whenever there are significant 

changes in the mix of IUs or in the total daily flow through the system (see Exhibit 7-2). 

Q: How do contract operations or privatization affect local limits evaluations and development? 

A: A POTW’s type of management should have no impact on the evaluation and development of 

local limits. Local limits are designed to protect the POTW from pass through, interference, or 

degradation of sewage sludge. As long as the public has some fiduciary interest in the POTW 

the need for local limits should be assessed on a routine basis. If the POTW is sold to a private 

entity, then the 403 regulations regarding local limits would no longer apply upon reissuance of 

the permit. The new owner of the treatment plant is not required to develop or implement local 

limits unless it is made a management practice requirement in its new NPDES permit. 

Q: Is it possible to develop local limits for a wastewater treatment lagoon where sludge is dredged 

only every 20 years? 

A: The POTW can always develop local limits based on water quality. A lagoon system would not 

be significantly different than any other type of system in that respect. For sludge, the POTW 

should ensure that the sludge, when dredged, will meet the standards for its chosen sludge 

disposal option by establishing local limits protective of that option. 

9.9 INDUSTRIAL USERS 

Q: If a new significant industrial user/categorical industrial user (SIU/CIU) commences its process 

discharge, or if an existing SIU/CIU ceases its process discharge, is a local limits re-evaluation 

necessary? 

A: It depends. If the SIU/CIU contributes a “significant percentage” (as determined by the POTW 

based on total design flow or number of IUs contributing a particular POC) of the total loading 

9 - 14
for a particular pollutant or pollutants, then EPA recommends that the POTW recalculate the 

local limits. However, if the SIU/CIU in question does not have the capability of adversely 

affecting the entire POTW, then (depending upon the allocation method, SUO language, or 

applicable categorical standards) the local limits can be specified in the IU’s discharge permit. 

Q: If I have CIUs with specific, numeric categorical pretreatment standards, is it necessary for me to 

apply local limits to these CIUs for these pollutants? 

A: No, it is not necessary unless the numeric categorical standards for a specific POC covered by 

local limits are less stringent than the values specified in the local limits. In this case, the more 

stringent local limits must prevail (see Section 1.5). 

Q: Does promulgation of new categorical pretreatment standards affect local limits evaluation? 

A: The promulgation of a new categorical standard should have no effect on local limits 

requirements. All industrial users subject to the categorical standard(s) will have to meet that 

discharge standard. However, if the categorical standard for a particular POC is less stringent 

than the local limit set for that pollutant, the more stringent local limit must be met by the IUs 

subject to the categorical pretreatment standard. In addition, if the new categorical standard is 

more stringent than the local limit, the“freed up” loading could be reallocated to the other IUs. 

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APPENDICES

Appendix A - List of Supplemental Documents ........................................... A-1

Appendix B - Industrial Categories with Pretreatment Standards ............................. B-1

Appendix C - Pollutants Regulated by Categorical Pretreatment Standards ..................... C-1

Appendix D - Clean Water Act Priority Pollutants and the Federal Water Quality Criteria ......... D-1

Appendix E - Federal Sewage Sludge Standards .......................................... E-1

Appendix F - Toxicity Characteristic Leachate Procedure Limitations ......................... F-1

Appendix G - Literature Inhibition Values ............................................... G-1

Appendix H - Closed-cup Flashpoints for Select Organic Compounds ......................... H-1

Appendix I - Discharge Screening Levels and Henry’s Law Constants for Organic Compounds ..... I-1

Appendix J - OSHA, ACGIH and NIOSH Exposure Levels ................................. J-1

Appendix K - Landfill Leachate Loadings ............................................... K-1

Appendix L - Hauled Waste Loadings .................................................. L-1

Appendix M - Hazardous Waste Constituents - RCRA Appendix VIII ........................ M-1

Appendix N - Statistical Approach to Determining Sampling Frequency ....................... N-1

Appendix O - Minimizing Contamination in Samples ...................................... O-1

Appendix P - Methods for Calculating Removal Efficiency ................................. P-1

Appendix Q - Methods for Handling Data Below Detection Level ............................ Q-1

Appendix R - Priority Pollutant Removal Efficiencies ...................................... R-1

Appendix S - Specific Gravity of Sludge ................................................ S-1

Appendix T - Sludge AHL Equations Using Flow (in metric units) ........................... T-1

Appendix U - POTW Configurations ................................................... U-1

Appendix V - Domestic Pollutant Loadings .............................................. V-1

Appendix W - Best Management Practices Mini-Case Studies .............................. W-1

Appendix X - Region 1, Reassessment of Technically Based Industrial Discharge Limits Checklist . . X-1

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APPENDIX A -

LIST OF SUPPLEMENTAL DOCUMENTS

GENERAL GUIDANCE ON PRETREATMENT 

TITLE DATE EPA Number NTIS Number ERIC 

Number 

CERCLA Site Discharges to POTWs 

Guidance Manual 

August 1990 540-G-90-005 PB90-274531 W150 

Control Authority Pretreatment Audit 

Checklist and Instructions 

May 1992 

Control of Slug Loadings To POTWs: 

Guidance Manual 

February 1991 21W-4001 

Environmental Regulations and Technology: 

The National Pretreatment Program 

July 1986 625-10-86-005 PB90-246521 W350 

Guidance for Conducting a Pretreatment 

Compliance Inspection 

September 

1991 

300-R-92-009 PB94-120631 W273 

Guidance For Developing Control Authority 

Enforcement Response Plans 

September 

1989 

PB90-

185083/AS 

Guidance for Reporting and Evaluating 

POTW Noncompliance with Pretreatment 

Implementation Requirements 

September 

1987 

PB95-157764 W304 

Guidance Manual for POTW Pretreatment 

Program Development 

Guidance Manual for POTWs to Calculate 

the Economic Benefit of Noncompliance 

Guidance Manual for Preparation and 

Review of Removal Credit Applications 

Guidance Manual for Preventing 

Interference at POTWs 

Guidance Manual for the Control of Wastes 

Hauled to Publicly Owned Treatment Works 

Guidance Manual for the Identification of 

Hazardous Wastes Delivered to Publicly 

Owned Treatment Works by Truck, Rail, or 

Dedicated Pipe 

Guidance Manual for the Use of ProductionBased Pretreatment Standards and the 

Combined Wastestream Formula 

Guidance Manual on the Development and 

Implementation of Local Discharge 

Limitations Under the Pretreatment Program 

Guidance on Evaluation, Resolution, and 

Documentation of Analytical Problems 

Associated with Compliance Monitoring 

Guidance on the Privatization of Federally 

Funded Wastewater Treatment Works 

Guidance to Protect POTW Workers From 

Toxic And Reactive Gases And Vapors 

October 1983 PB93-186112 W639 

September 

1990 

833-B-93-007 

July 1985 833-B-85-200 

September 

1987 

833-B-87-201 PB92-117969 W106 

September 

1999 

833-B-98-003 

June 1987 PB92-149251 W202 

September 

1985 

833-B-85-201 PB92-232024 U095 

December 

1987 

833-B-87-202 PB92-129188 W107 

June 1993 821-B-93-001 

August 2000 832-B-00-002 

June 1992 812-B-92-001 PB92-173236 W115 

A-1
-- --

-- --

-- --

-- --

-- --

-- -- --

-- --

-- -- --

-- --

GENERAL GUIDANCE ON PRETREATMENT 

TITLE DATE EPA Number NTIS Number ERIC 

Number 

Guides to Pollution Prevention: Municipal 

Pretreatment Programs 

Industrial User Inspection and Sampling 

Manual For POTWs 

Industrial User Permitting Guidance Manual 

Metals Translator: Guidance for Calculating 

a Total Recoverable Permit Limit from a 

Dissolved Criterion 

Model Pretreatment Ordinance 

Multijurisdictional Pretreatment Programs: 

Guidance Manual 

National Pretreatment Program: Report to 

Congress 

NPDES Compliance Inspection Manual 

Pollution Prevention (P2) Guidance Manual 

for the Pesticide Formulating, Packaging, 

and Repackaging Industry: Implementing 

the P2 Alternative 

POTW Sludge Sampling and Analysis 

Guidance Document 

Prelim User’s Guide, Documentation for the 

EPA Computer Program/Model for 

Developing Local Limits for Industrial 

Pretreatment Programs at Publicly Owned 

Treatment Works, Version 5.0 

Pretreatment Compliance Inspection and 

Audit Manual For Approval Authorities 

Pretreatment Compliance Monitoring and 

Enforcement Guidance and Software 

(Version 3.0) 

Procedures Manual for Reviewing a POTW 

Pretreatment Program Submission 

Procuring Analytical Services: Guidance for 

Industrial Pretreatment Programs 

Region III Guidance for Setting Local Limits 

for a Pollutant Where the Domestic Loading 

Exceeds the Maximum Allowable 

Headworks Loading 

Protecting the Nation's Waters Through 

Effective NPDES Permits: A Strategic Plan 

FY 2001 and Beyond 

RCRA Information on Hazardous Wastes for 

Publicly Owned Treatment Works 

Report to Congress on the Discharge of 

Hazardous Wastes to Publicly Owned 

Treatment Works 

October 1993 625-R-93-006 

April 1994 831-B-94-001 PB94-170271 W305 

September 

1989 

833-B-89-001 PB92-123017 W109 

June 1996 823-B-96-007 

June 1992 833-B-92-003 PB93-122414 W108 

June 1994 833-B-94-005 PB94-203544 W607 

July 1991 21-W-4004 PB91-228726 W694 

September 

1994 

300-B-94-014 

June 1998 821-B-98-017 

August 1989 833-B-89-100 

January 1997 

July 1986 833-B-86-100 PB90-183625 W277 

(Manual) 

September 

1986 

(Software) 

September 

1992 

(Software) 

831-F-92-001 

(Software) 

PB94-118577 

(Software) 

W269 

October 1983 833-B-83-200 PB93-209880 W137 

October 1998 833-B-98-004 

June 1994 

June 2001 833-R-01-001 

September 

1985 

833-B-85-202 PB92-114396 W351 

February 1986 530-SW-86-004 PB86-184017 & 

PB95-157228 

W922 & 

W692 

A-2
--

--

-- --

-- --

GENERAL GUIDANCE ON PRETREATMENT 

TITLE DATE EPA Number NTIS Number ERIC 

Number 

Supplemental Manual On the Development 

And Implementation of Local Discharge 

Limitations Under The Pretreatment 

Program 

May 1991 21W-4002 PB93-209872 W113 

Source: Updated, originally part of U.S. EPA’s Introduction to the National Pretreatment Program, EPA-833-B-98-002,

February 1999, pp. 51-52

GUIDANCE ON INDUSTRY PRETREATMENT STANDARDS 

TITLE DATE EPA Number NTIS Number ERIC 

Number 

Aluminum, Copper, And Nonferrous Metals 

Forming And Metal Powders Pretreatment 

Standards: A Guidance Manual 

December 

1989 

800-B-89-001 PB91-145441 W119 

Guidance Manual For Battery Manufacturing 

Pretreatment Standards 

August 1987 440-1-87-014 PB92-117951 W195 

Guidance Manual for Electroplating and 

Metal Finishing Pretreatment Standard 

February 1984 440-1-84-091-G PB87-192597 W118 

Guidance Manual For Implementing Total 

Toxic Organics (TTO) Pretreatment 

Standards 

September 

1985 

440-1-85-009-T PB93-167005 W339 

Guidance Manual For Iron And Steel 

Manufacturing Pretreatment Standards 

September 

1985 

821-B-85-001 PB92-114388 W103 

Guidance Manual for Leather Tanning and 

Finishing Pretreatment Standards 

September 

1986 

800-R-86-001 PB92-232024 W117 

Guidance Manual for Pulp, Paper, and 

Paperboard and Builders’ Paper and Board 

Mills Pretreatment Standards 

July 1984 PB92-231638 W196 

Guidance Manual for the Use of ProductionBased Pretreatment Standards and the 

Combined Wastestream Formula 

September 

1985 

833-B-85-201 PB92-232024 U095 

Permit Guidance Document: Pulp, Paper, 

and Paperboard Manufacturing Point 

Source Category (40 CFR Section 430) 

May 2000 821-B-00-003 PB2002-

106590 

Permit Guidance Document: Transportation 

Equipment Cleaning Point Source Category 

(40 CFR 422) 

March 2001 821-R-01-021 

Small Entity Compliance Guide: Centralized 

Waste Treatment Guidelines and 

Pretreatment Standards (40 CFR 437) 

June 2001 821-B-01-003 

Source: Updated, originally part of U.S. EPA’s Introduction to the National Pretreatment Program, EPA-833-B-98-002,

February 1999, pp. 51-52

A-3
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A-4
APPENDIX B -

INDUSTRIAL CATEGORIES WITH PRETREATMENT STANDARDS

Source: U.S. EPA’s Introduction to the National Pretreatment Program, EPA-833-B-98-002, February 

1999, Figure 13, p. 14. (Updated) 

Category 

(SIC Codes)* 

[NAICS Codes]** 

40 CFR 

Part (Subparts) 

Type of

Standard*** Overview of Pretreatment Standards 

Aluminum Forming 

(3353, 3354, 3355, 3357, 

3363) 

[331315, 331316, 331319, 

331521] 

467(A-F) PSES 

PSNS 

Limits are production-based, daily maximums and 

monthly averages. 

from certain operations. 

Battery Manufacturing 

(3691, 3692) 

[335911, 335912] 

461(A-G) PSES 

PSNS 

Limits are production-based, daily maximums and 

monthly averages. ed from 

any process not specifically identified in the 

regulations. 

Carbon Black Manufacturing 

(2895) 

[325182] 

458 (A-D) PSNS Limits are for Oil & Grease only (no limit duration 

specified). 

Centralized Waste Treatment 

(4953) 

[562211, 562219 ] 

437 (A-D) PSES 

PSNS 

Limits are concentration-based, daily maximums and 

monthly averages. 

Coil Coating 

(3411, 3479, 3492) 

[332431, 332812] 

465 (A-D) PSES 

PSNS 

Limits are production-based, daily maximums and 

monthly averages. 

Commercial Hazardous Waste 

Combustors 

(4953, 2819, 2869, 3241, 

1422, 1429, 1459) 

[562213, 212312, 325188, 

325199, 327310] 

444 (A) PSES 

PSNS 

Limits are concentration-based daily maximums or 

maximum monthly averages. 

Concentrated Animal Feeding 

Operations 

(0211, 0213, 0214, 0241, 

0251, 0252, 0253, 0254, 0259, 

0272) 

[112112, 11221, 11241, 

11242, 112111, 11212, 11232, 

11231, 11233, 11234, 11239, 

11292] 

412 (B) PSNS Discharge of process wastewater is prohibited, 

except when there is an overflow resulting from a 

chronic or catastrophic rainfall event. 

Copper Forming 

(3351, 3357, 3463) 

[331421, 331422, 332112] 

468 (A) PSES 

PSNS 

Limits are production-based, daily maximums and 

monthly averages. 

Electrical and Electronic 

Components 

(3671, 3674, 3679) 

[334411, 334413, 334419] 

469 (A-D) PSES 

PSNS 

Limits are concentration-based, daily maximums and 

30-day averages or monthly averages (varies per 

subpart and pollutant parameter). 

allowed in lieu of monitoring for certain pollutants 

when a management plan is approved and 

implemented. 

Subpart C prohibits discharges 

No discharge is allow

Certification is 

B-1
Category 

(SIC Codes)* 

[NAICS Codes]** 

40 CFR 

Part (Subparts) 

Type of 

Standard*** Overview of Pretreatment Standards 

Electroplating 

(3471, 3672) 

[332813, 334412] 

413 (A-B, DH) 

PSES Limits are concentration-based (or alternative massbased equivalents), daily maximums and four 

consecutive monitoring days averages. wo sets of 

limits exist, depending on if facility discharges more 

or less than 10,000 gallons per day of process 

wastewater. on is allowed in lieu of 

monitoring for certain pollutants when a management 

plan is approved and implemented. 

Fertilizer Manufacturing 

(2873, 2874, 2875) 

[325311, 325312, 325314] 

418 (A-G) PSNS Limits may specify zero discharge of wastewater 

pollutants (Subpart A), production-based daily 

maximums and 30-day averages (Subparts B-E) or 

concentration-based (Subparts F-G) with no limit 

duration specified. 

Glass Manufacturing 

(3211, 3221, 3296) 

[327211, 327212, 327993] 

426 (H, KM) 

PSNS Limits are either concentration- or production-based, 

daily maximums and monthly averages. 

Grain Mills 

(2041, 2043, 2044, 2045, 

2046, 2047) 

[311111, 311211, 311212, 

311213, 311221, 311230] 

406 (A) PSNS Discharge of process wastewater is prohibited at a 

flow rate or mass loading rate which is excessive 

over any time period during the peak load at a 

POTW. 

Ink Formulating 

(2893) 

[325910] 

447 (A) PSNS Regulations specify no discharge of process 

wastewater pollutants to the POTW. 

Inorganic Chemicals 

Manufacturing 

(2812, 2813, 2816, 2819) 

[325120, 325131, 325181, 

325188] 

415 (A-BO) PSES 

PSNS 

Limits vary for each subpart with a majority of the 

limits concentration-based, daily maximums and 30-

day averages, or may specify no discharge of 

wastewater pollutants. Numerous subparts have no 

pretreatment standards. 

Iron and Steel Manufacturing 

(3312, 3315, 3316, 3317, 

3479) 

[331111, 331210, 331221, 

331222, 332812] 

420 (A-F, HJ, L, M) 

PSES 

PSNS 

Limits are production-based, daily maximums and 30 

day averages, or may specify no discharge of 

wastewater pollutants. 

Leather Tanning and Finishing 

(3111) 

[316110] 

425 (A-I) PSES 

PSNS 

Limits are concentration-based, daily maximums and 

monthly averages. 

volume dictates applicable pretreatment standards. 

Metal Finishing 

(Industry groups: 34, 35, 36, 

37, 38) 

[Industry Subsectors: 332, 

333, 334, 336] 

433 (A) PSES 

PSNS 

Limits are concentration-based, daily maximums and 

monthly averages. ion is allowed for certain 

pollutants where a management plan is approved 

and implemented. 

Metal Molding and Casting 

(3321, 3322, 3324, 3325, 

3365, 3366, 3369) 

[331511, 331512, 331513, 

331524, 331525, 331528] 

464 (A-D) PSES 

PSNS 

Limits are primarily production-based, daily 

maximums and monthly averages. 

certain processes are prohibited (Subparts A-C). 

Nonferrous Metals Forming 

and Metal Powders 

(3356, 3357, 3363, 3497, 

3499) 

[331491, 331422, 331521, 

332117, 332999] 

471 (A-J) PSES 

PSNS 

Limits are production-based, daily maximums and 

monthly averages. 

regulations prohibit the discharge of wastewater 

pollutants. 

T

Certificati

In certain instances, production 

Certificat

Discharges from 

In some instances, the 

B-2
Category 

(SIC Codes)* 

[NAICS Codes]** 

40 CFR 

Part (Subparts) 

Type of 

Standard*** Overview of Pretreatment Standards 

Nonferrous Metals 

Manufacturing 

(2819, 3331, 3334, 3339, 

3341) 

[331311, 331312, 331314, 

331411, 331419, 331423, 

331492] 

421 (B-AE) PSES 

PSNS 

Limits are production-based, daily maximums and 

monthly averages. he majority of the Subparts 

have both existing and new source limits, with others 

having solely new source requirements. 

instances, the regulations prohibit the discharge of 

wastewater pollutants. 

Oil and Gas Extraction 

(1311) 

[211111] 

435 (D) PSES 

PSNS 

Regulations specify no discharge of process 

wastewater (drilling fluieds, deck drainage, etc.) 

pollutants to the POTW. 

Organic Chemicals, Plastics, 

and Synthetic Fibers 

(2821, 2823, 2824, 2865, 

2869) 

[325211, 325221, 325222, 

32511, 325132, 325192, 

325188]] 

414 (B-H, K) PSES 

PSNS 

Limits are mass-based (concentration-based 

standards multiplied by process flow), daily 

maximums and monthly averages. 

metals and cyanide apply only to metal- or cyanidebearing wastestreams. 

Paint Formulating 

(2851) 

[325510] 

446 (A) PSNS Regulations specify no discharge of process 

wastewater pollutants to the POTW. 

Paving and Roofing Materials 

(Tars and Asphalt) 

(2951, 2952, 3996) 

[324121, 324122, 326192] 

443 (A-D) PSNS Limits are for Oil & Grease only (no limit duration 

specified). 

Pesticide Chemicals 

(2879) 

[325320] 

455 (A, C, 

E) 

PSES 

PSNS 

Limits are mass-based (concentration-based 

standards multiplied by process flow), daily 

maximums and monthly averages. 

specifies no discharge of process wastewater 

pollutants but provides for pollution prevention 

alternatives. 

process wastewater pollutants. 

Petroleum Refining 

(2911) 

[324110] 

419 (A-E) PSES 

PSNS 

Limits are concentration-based (or mass-based 

equivalent), daily maximums. 

Pharmaceutical Manufacturing 

(2833, 2834) 

[325411, 325412] 

439 (A-D) PSES 

PSNS 

Limits are concentration-based, daily maximums and 

monthly averages. 

certify they do not use or generate cyanide in lieu of 

performing monitoring to demonstrate compliance. 

Porcelain Enameling 

(3431, 3469, 3479, 3631, 

3632, 3633, 3639) 

[332116, 332812, 332998, 

335221, 335222, 335224, 

335228] 

466 (A-D) PSES 

PSNS 

Limits are concentration-based (or alternative 

production-based), daily maximums and monthly 

averages. 

operations. 

T

In some 

Standards for 

Subpart C 

Subpart E specifies no discharge of 

Subpart A and C facilities may 

Subpart B prohibits discharges certain 

Pulp, Paper, and Paperboard 

(2611, 2621, 2631) 

[322110, 322121, 322122, 

322130] 

430 (A-G, IL) 

PSES 

PSNS 

Limits are production-based or concentration-based 

(or alternative production-based) daily maximums 

and monthly averages. hese facilities may certify 

they do not use certain compounds in lieu of 

performing monitoring to demonstrate compliance. 

Facilities subject to Subparts B and E must also 

implement Best Management Practices as identified. 

Rubber Manufacturing 

(2822) 

[325212] 

428 (E-K) PSNS Limits are concentration- or production-based, daily 

maximums and monthly averages. 

T

B-3
Category 

(SIC Codes)* 

[NAICS Codes]** 

40 CFR 

Part (Subparts) 

Type of 

Standard*** Overview of Pretreatment Standards 

Soap and Detergent 

Manufacturing 

(2841) 

[325611] 

417 (O-R) PSNS Regulations specify no discharge of process 

wastewater pollutants to the POTW. 

Steam Electric Power 

Generating 

(4911) 

[221112] 

423 PSES 

PSNS 

Limits are either concentration-based, daily 

maximums, or “maximums for any time,” or 

compliance can be demonstrated through 

engineering calculations. 

regulations prohibit the discharge of wastewater 

pollutants. 

Timber Products Processing 

(2421, 2435, 2436, 2491, 

2493, 2499) 

[321114, 321219, 321211, 

321212] 

429 (F-H) PSES 

PSNS 

All PSNS (and PSES for Subpart F) prohibit the 

discharge of wastewater pollutants. 

Subparts G and H are concentration-based, daily 

maximums (with production-based alternatives). 

Transportation Equipment 

Cleaning 

(4491, 4499, 4741, 7699) 

[484230, 488320, 488390, 

488210] 

442 (A-C) PSES 

PSNS 

Limits are concentration-based daily maximums. 

Subpart A and B allow for a pollutant as an 

alternative to achieving PSES or PSNS. 

In some instances, the 

PSES for 

* SIC = Standard Industrial Classification, 1987 SIC Manual 

** NAICS = North American Industry Classification System, 1997 NAICS Manual. 

*** PSNS = Pretreatment Standard New Source; PSES = Pretreatment Standard Existing Source 

B-4
C-1

APPENDIX C -

POLLUTANTS REGULATED BY CATEGORICAL PRETREATMENT

STANDARDS Aluminum Forming Battery Manufacturing Carbon Black Manufacturing Centralized Waste Treatment

Coil Coating

Copper Forming

Electrical and Electronic Components

Electroplating

Feedlots

Fertilizer Manufacturing

Glass Manufacturing

Grain Mills

Ink Formulating

Inorganic Chemicals Manufacturing

Iron and Steel Manufacturing

Leather Tanning and Finishing

Metal Finishing

Metal Molding and Casting

Nonferrous Metals Form./Metal Powders

Nonferrous Metals Manufacturing

Oil and Gas

Organic Chems., Plastics, and Syn. 

Paint Formulating

Paving and Roofing Materials

Pesticide Chemicals

Petroleum Refining

Pharmaceutical Manufacturing

Porcelain Enameling

Pulp, Paper, and Paperboard

Rubber Manufacturing

Soap and Detergent Manufacturing

Steam Electric Power Generating

Timber Products Processing

Transportation Equip. Cleaning

Waste Combustors

Flow Restrictions

Only

X X X X

Ammonia (as N) X X X X X X

BOD X

COD X X

Fluoride X X X X X X

Nitrate (as N) X

Oil and Grease X X X X X X X X X

Oil (mineral) X

Organic Nitrogen

(as N) X

pH X X X

Phenols X X X

Phosphorus X X

Sulfide X

TSS X X

1,1-

Dichloroethane X X X X

1,1-

Dichloroethylene X X X X X X

1,1,1-

Trichloroethane XXXX X X X X X

1,1,2-

Trichloroethane X X X X X

1,1,2,2-Tetrachloroethane X X X

1,2-

Dichlorobenzene X X X X X X X

1,2-

Dichloroethane X X X X X X X

1,2-

Dichloropropane X X X X

1,2-Diphenylhydrazine X X X X

1,2-transDichloroethylene X X X X Fibers

X

X

X

X

X

X

X
Aluminum Forming

Battery Manufacturing

Carbon Black Manufacturing

Centralized Waste Treatment

Coil Coating

Copper Forming

Electrical and Electronic Components

Electroplating

Feedlots

Fertilizer Manufacturing

Glass Manufacturing

Grain Mills

Ink Formulating

Inorganic Chemicals Manufacturing

Iron and Steel Manufacturing

Leather Tanning and Finishing

Metal Finishing

Metal Molding and Casting

Nonferrous Metals Form./Metal Powders

Nonferrous Metals Manufacturing

Oil and Gas

Organic Chems., Plastics, and Syn. 

Paint Formulating

Paving and Roofing Materials

Pesticide Chemicals

Petroleum Refining

Pharmaceutical Manufacturing

Porcelain Enameling

Pulp, Paper, and Paperboard

Rubber Manufacturing

Soap and Detergent Manufacturing

Steam Electric Power Generating

Timber Products Processing

Transportation Equip. Cleaning

Waste Combustors

C-2

1,2,4-Trichlorobenzene X X

XXX

1,3-Dichlorobenzene X X

XXX

1,3-Dichloropropene 

XXXX

1,4-Dichlorobenzene X X

XXXX

2-Chloroethyl

vinyl ether

(mixed) 

XX

2-Chloronaphthalene 

XX

2-Chlorophenol XXXXX

2-Nitrophenol XXXX

2,3-Dichloroaniline

X

2,3,4,6-Tetrachlorophenol

X

2,4-

Dichlorophenol X X X X

X

2,4-Dimethyl-

phenol 

XXX

2,4-Dinitrophenol XX

2,4-Dinitrotoluene 

XXX

2,4,5-Trichlorophenol

X

2,4,6-Trichlorophenol 

XXXXXX

2,6-Dinitrotoluene 

XXX

3,3-Dichlorobenzidine 

XX

3,4,5-Trichlorocatechol

X

3,4,5-Trichloroguaiacol

X

3,4,6-Trichlorocatechol

X

3,4,6-Trichloroguaiacol

X

4-Bromophenyl

phenyl ether 

XX

Fibers

XXX

X

X

X

XX

X

X

XX
Aluminum Forming

Battery Manufacturing

Carbon Black Manufacturing

Centralized Waste Treatment

Coil Coating

Copper Forming

Electrical and Electronic Components

Electroplating

Feedlots

Fertilizer Manufacturing

Glass Manufacturing

Grain Mills

Ink Formulating

Inorganic Chemicals Manufacturing

Iron and Steel Manufacturing

Leather Tanning and Finishing

Metal Finishing

Metal Molding and Casting

Nonferrous Metals Form./Metal Powders

Nonferrous Metals Manufacturing

Oil and Gas

Organic Chems., Plastics, and Syn. 

Paint Formulating

Paving and Roofing Materials

Pesticide Chemicals

Petroleum Refining

Pharmaceutical Manufacturing

Porcelain Enameling

Pulp, Paper, and Paperboard

Rubber Manufacturing

Soap and Detergent Manufacturing

Steam Electric Power Generating

Timber Products Processing

Transportation Equip. Cleaning

Waste Combustors

C-3

4-Chlorophenyl

phenyl ether X X

4-Nitrophenol X X X X X

4,4-DDD X X X

4,4-DDE X X X

4,4-DDT X X

4,5,6-Trichloroquaiacol X

4,6-Dinitro-ocresol X X X

Acenaphthene X X X X X

Acenaphthylene X X X X

Acetone X

Acrolein X X

Acrylonitrile X X

Aldrin X X

Alpha-BHC X X

Alphaendosulfan X X

Anthracene X X X X X X X

Benzene X X X X X X X

Benzidine X X X

Benzo (b)

fluoranthene X X X X

Benzo (a)

anthracene X X X

Benzo (ghi)

perylene X X X

Benzo (a) pyrene X X X X X X

Benzo (k)

fluoranthene X X X

Beta-BHC X X X

Beta-endosulfan X X

Bis (2-chloroethoxy) methane X X

Bis (2-chloroisopropyl) ether X X

Bis (2-chloroethyl) ether X X X

Bis (2-ethylhexyl) phthalate X X X X X X X X

Bromoform X X X X Fibers

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
Aluminum Forming

Battery Manufacturing

Carbon Black Manufacturing

Centralized Waste Treatment

Coil Coating

Copper Forming

Electrical and Electronic Components

Electroplating

Feedlots

Fertilizer Manufacturing

Glass Manufacturing

Grain Mills

Ink Formulating

Inorganic Chemicals Manufacturing

Iron and Steel Manufacturing

Leather Tanning and Finishing

Metal Finishing

Metal Molding and Casting

Nonferrous Metals Form./Metal Powders

Nonferrous Metals Manufacturing

Oil and Gas

Organic Chems., Plastics, and Syn. 

Paint Formulating

Paving and Roofing Materials

Pesticide Chemicals

Petroleum Refining

Pharmaceutical Manufacturing

Porcelain Enameling

Pulp, Paper, and Paperboard

Rubber Manufacturing

Soap and Detergent Manufacturing

Steam Electric Power Generating

Timber Products Processing

Transportation Equip. Cleaning

Waste Combustors

C-4

Butyl benzyl

phthalate X X X X X

Carbon

tetrachloride X X X X X X

Carbazole X

Chlordane (tech.

mix. &

metabolites) 

X X

Chlorobenzene X X X X X X X

Chlorodibromomethane X X X

Chloroethane X X X

Chloroform XXXX X X X X X X X

Chrysene X X X X

Cresol X

Delta-BHC X X X

Di-n-butyl

phthalate X X X X X X X

Di-n-octyl

phthalate X X

Dibenzo (a,h)

anthracene X X X

Dichlorobromomethane X X X X X

Dieldrin X X

Diethyl phthalate X X X X X X

Diethylamine X

Dimethyl

phthalate X X X X

Endosulfan

sulfate X X X

Endrin X X X

Endrin aldehyde X X X X

Ethyl acetate X

Ethylbenzene X X X X X X X

Fluoranthene X X X X X X X

Fluorene X X X X X

Gamma-BHC X X X

Heptachlor

epoxide X X

Heptachlor X X Fibers

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
Aluminum Forming

Battery Manufacturing

Carbon Black Manufacturing

Centralized Waste Treatment

Coil Coating

Copper Forming

Electrical and Electronic Components

Electroplating

Feedlots

Fertilizer Manufacturing

Glass Manufacturing

Grain Mills

Ink Formulating

Inorganic Chemicals Manufacturing

Iron and Steel Manufacturing

Leather Tanning and Finishing

Metal Finishing

Metal Molding and Casting

Nonferrous Metals Form./Metal Powders

Nonferrous Metals Manufacturing

Oil and Gas

Organic Chems., Plastics, and Syn. 

Paint Formulating

Paving and Roofing Materials

Pesticide Chemicals

Petroleum Refining

Pharmaceutical Manufacturing

Porcelain Enameling

Pulp, Paper, and Paperboard

Rubber Manufacturing

Soap and Detergent Manufacturing

Steam Electric Power Generating

Timber Products Processing

Transportation Equip. Cleaning

Waste Combustors

C-5

Hexachlorobenzene X X X X

Hexachlorobutadiene X X

Hexachlorocyclo

pentadiene X X X

Hexachloroethane X X X

Indeno (1,2,3-

cd)pyrene X X X

Isobutylaldehyde X

Isophorone X X X X

Isopropyl acetate X

Isopropyl ether X

Methyl formate X

Methyl bromide X X X X

Methyl cellosolve X

Methyl Isobutyl

Ketone X

Methyl chloride X X X X X

Methylene

chloride XXXX X X X X X X

n-Amyl acetate X

n-Butyl acetate X

n-Decane X

n-Heptane X

n-Hexane X

N-nitrosodi-npropylamine X X X X

N-nitrosodimethylamine X X X

N-nitrosodiphenylamine X X X X X

n-Octadecane X

Naphthalene X X X X X X X X X

Nitrobenzene X X X

Non-polar

material (SGTHEM)X

Parachlorometacresol X X X X

PCB–1016 X X X X Fibers

X

X

X

X

X

X

X

X

X

X

X

X
Aluminum Forming

Battery Manufacturing

Carbon Black Manufacturing

Centralized Waste Treatment

Coil Coating

Copper Forming

Electrical and Electronic Components

Electroplating

Feedlots

Fertilizer Manufacturing

Glass Manufacturing

Grain Mills

Ink Formulating

Inorganic Chemicals Manufacturing

Iron and Steel Manufacturing

Leather Tanning and Finishing

Metal Finishing

Metal Molding and Casting

Nonferrous Metals Form./Metal Powders

Nonferrous Metals Manufacturing

Oil and Gas

Organic Chems., Plastics, and Syn. 

Paint Formulating

Paving and Roofing Materials

Pesticide Chemicals

Petroleum Refining

Pharmaceutical Manufacturing

Porcelain Enameling

Pulp, Paper, and Paperboard

Rubber Manufacturing

Soap and Detergent Manufacturing

Steam Electric Power Generating

Timber Products Processing

Transportation Equip. Cleaning

Waste Combustors

C-6

PCB–1221 X X X

PCB–1232 X X X

PCB–1242 X X X X

PCB–1248 X X X X

PCB–1254 X X X

PCB–1260 X X X

Pentachlorophenol X X X X X

Phenanthrene X X X X X X X X

Phenol X X X X X

Pyrene X X X X X

TCDF X

Tetrachlorocatechol X

Tetrachloroethylene X X X X X X X X X

Tetrachloroguaiacol X

Tetrahydrofuran X

Toluene XXXX X X X X X X

Toxaphene X X

Trichloroethylene X XXX X X X X

Trichlorosyringol X

Triethylamine X

Vinyl chloride X X X X

Xylenes X

2,3,7,8-

tetrachlorodibenzo-p-dioxinX X X

Organic

Pesticide Active

Ingredients

X

Antimony X X X X X X

Arsenic X X X X X X

Asbestos X

Barium X

Beryllium X

Cadmium X X X X X X X X X X

Chromium, Total X X XXXXX XXXX X X X X X X X X X Fibers

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
Aluminum Forming

Battery Manufacturing

Carbon Black Manufacturing

Centralized Waste Treatment

Coil Coating

Copper Forming

Electrical and Electronic Components

Electroplating

Feedlots

Fertilizer Manufacturing

Glass Manufacturing

Grain Mills

Ink Formulating

Inorganic Chemicals Manufacturing

Iron and Steel Manufacturing

Leather Tanning and Finishing

Metal Finishing

Metal Molding and Casting

Nonferrous Metals Form./Metal Powders

Nonferrous Metals Manufacturing

Oil and Gas

Organic Chems., Plastics, and Syn. 

Paint Formulating

Paving and Roofing Materials

Pesticide Chemicals

Petroleum Refining

Pharmaceutical Manufacturing

Porcelain Enameling

Pulp, Paper, and Paperboard

Rubber Manufacturing

Soap and Detergent Manufacturing

Steam Electric Power Generating

Timber Products Processing

Transportation Equip. Cleaning

Waste Combustors

C-7

Chromium,

Hexavalent X X

Cobalt X X X X

Copper X X X X X X X X X X X X X

Cyanide, Total X X X X X X X X X X X X X X

Cyanide,

Amenable X

Gold X

Indium X

Iron X X

Lead X X X X X X X X X X X X X X X X X X

Manganese X X

Mercury X X X X X X X

Molybdenum X X X

Nickel X X X X X X X

Palladium X

Platinum X

Selenium X X X

Silver X X X X X X X

Tantalum X

Thallium X

Tin X X

Titanium X X X

Tungsten X

Vanadium X

Zinc XX XXXXX X X XXX X X X X X X X X

Source: Updated from the 1991 National Pretreatment Program Report to Congress, pp. 5-6. Fibers

X

X

X X X X X

X

X X
This page intentionally left blank. 

C-8
APPENDIX D -

CLEAN WATER ACT PRIORITY POLLUTANTS AND THE FEDERAL

WATER QUALITY CRITERIA

The appendix below lists, in three tables, the National Recommended Water Quality Criteria for: 

• Specific chemical compounds that are identified by unique Chemical Abstract Service (CAS) 

registry numbers; 

• Priority pollutants in the form of the Criteria Maximum Concentration (CMC) and Criterion 

Continuous Concentration (CCC); 

• Non-priority pollutants in the form of the Criteria Maximum Concentration (CMC) and Criterion 

Continuous Concentration (CCC) for non-priority pollutants; 

• Organoleptic effects in the form of Organoleptic Effect Criteria. 

Please see page D-16 for further discussion and definitions of these criteria. 

D-1
D-2

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR PRIORITY POLLUTANTS

PriorityPollutant

CAS

Number

Freshwater Saltwater

Human Health For

Consumption of:

FR

Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

1 Antimony 7440360 14 B,Z 4300 B 57FR60848

2 Arsenic 7440382 340 A,D,K 150 A,D,K 69 A,D,bb 36 A,D,bb

0.018 C,M,S 0.14 C,M,S

62FR4216057FR60848

3 Beryllium 7440417 J,Z J 62FR42160

4 Cadmium 7440439 4.3 D,E,K 2.2 D,E,K 42 D,bb 9.3 D,bb J,Z J 62FR42160

5a Chromium III 16065831 570 D,E,K 74 D,E,K

J,Z Total J

EPA820/B-96

-001

62FR42160

5b Chromium VI 18540299 16 D,K 11 D,K 1,100 D,bb 50 D,bb J,Z Total J 62FR42160

6 Copper 7440508 13 D,E,K,cc 9.0 D,E,K,cc 4.8 D,cc,ff 3.1 D,cc,ff 1,300 U 62FR42160

7 Lead 7439921 65 D,E,bb,gg 2.5 D,E,bb,gg 210 D,bb 8.1 D,bb J J 62FR42160

8 Mercury 7439976 1.4 D,K,hh 0.77 D,K,hh 1.8 D,ee,hh 0.94 D,ee,hh 0.050 B 0.051 B 62FR421609 Nickel 7440020 470 D,E,K 52 D,E,K 74 D,bb 8.2 D,bb 610 B 4,600 B 62FR42160

10 Selenium 7782492 L,R,T 5.0 T 290 D,bb,dd 71 D,bb,dd

170Z 11,000

62FR42160

IRIS 09/01/91

11 Silver 7440224 3.4 D,E,G 1.9 D,G 62FR42160

12 Thallium 7440280 1.7 B 6.3 B 57FR60848

13 Zinc 7440666 120 D,E,K 120 D,E,K 90 D,bb 81 D,bb 9,100 U 69,000 U 62FR42160

IRIS 10/01/92
D-3

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR PRIORITY POLLUTANTS

Priority Pollutant

CAS

Number

Freshwater Saltwater

Human Health For

Consumption of:

FR Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

14 Cyanide 57125 22 K,Q 5.2 K,Q

1 Q,bb 1 Q,bb 700 B,Z 220,000 B,H

EPA820/B-96-001

57FR60848

15 Asbestos 1332214 7 million

fibers/L 

57FR60848

16 2,3,7,8-TCDD (Dioxin) 1746016 1.3E-8 C 1.4E-8 C 62FR42160

17 Acrolein 107028 320 780 57FR6084818 Acrylonitrile 107131 0.059 B,C 0.66 B,C 57FR60848

19 Benzene 71432 1.2 B,C 71 B,C 62FR42160

20 Bromoform 75252 4.3 B,C 360 B,C 62FR42160

21 Carbon Tetrachloride 56235 0.25 B,C 4.4 B,C 57FR60848

22 Chlorobenzene 108907 680 B,Z 21,000 B,H 57FR6084823 Chlorodibromomethane 124481 0.41 B,C 34 B,C 62FR42160

24 Chloroethane 7500325 2-Chloroethylvinyl Ether 11075826 Chloroform 67663 5.7 B,C 470 B,C 62FR42160

27 Dichlorobromomethane 75274 0.56 B,C 46 B,C 62FR42160

28 1,1-Dichloroethane 7534329 1,2-Dichloroethane 107062 0.38 B,C 99 B,C 57FR60848

30 1,1-Dichloroethylene 75354 0.057 B,C 3.2 B,C 57FR60848

I
D-4

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR PRIORITY POLLUTANTS

Priority Pollutant

CAS

Number

Freshwater Saltwater

Human Health For

Consumption of:

FR

Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

31 1,2-Dichloropropane 78875 0.52 B,C 39 B,C 62FR42160

32 1,3-Dichloropropene 542756 10 B 1,700 B 57FR60848

33 Ethylbenzene 100414 3,100 B,Z 29,000 B 62FR42160

34 Methyl Bromide 74839 48 B 4000 B 62FR42160

35 Methyl Chloride 74873 J J 62FR42160

36 Methylene Chloride 75092 4.7 B,C 1600 B,C 62FR42160

37 1,1,2,2-Tetrachloroethane 79345 0.17 B,C 11 B,C 57FR60848

38 Tetrachloroethylene 127184 0.8 C 8.85 C 57FR60848

39 Toluene 108883 6,800 B,Z 200,000 B 62FR42160

40 1,2-Trans-Dichloroethylene 156605 700 B,Z 140,000 B 62FR42160

41 1,1,1-Trichloroethane 71556 J,Z J 62FR42160

42 1,1,2-Trichloroethane 79005 0.60 B,C 42 B,C 57FR60848

43 Trichloroethylene 79016 2.7 C 81 C 57FR6084844 Vinyl Chloride 75014 2.0 C 525 C 57FR60848

45 2-Chlorophenol 95578 120 B,U 400 B,U 62FR42160

46 2,4-Dichlorophenol 120832 93 B,U 790 B,U 57FR60848

47 2,4-Dimethylphenol 105679 540 B,U 2,300 B,U 62FR42160

48 2-Methyl-4,6-Dinitrophenol 534521 13.4 765 57FR6084849 2,4-Dinitrophenol 51285 70 B 14,000 B 57FR60848

50 2-Nitrophenol 88755

51 4-Nitrophenol 10002752 3-Methyl-4-Chlorophenol 59507 U U
D-5

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR PRIORITY POLLUTANTS

Priority Pollutant

CAS

Number

Freshwater Saltwater

Human Health For

Consumption of:

FR

Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

53 Pentachlorophenol 87865 19F,K 15F,K 13bb 7.9bb 0.28 B,C 8.2 B,C,H 62FR42160

54 Phenol 108952 21,000 B,U 4,600,000

B,H,U

62FR4216057FR60848

55 2,4,6-Trichlorophenol 88062 2.1 B,C,U 6.5 B,C 62FR42160

56 Acenaphthene 83329 1,200 B,U 2,700 B,U 62FR42160

57 Acenaphthylene 20896858 Anthracene 120127 9,600 B 110,000 B 62FR42160

59 Benzidine 92875 0.00012 B,C 0.00054 B,C 57FR60848

60 Benzo (a) Anthracene 56553 0.0044 B,C 0.049 B,C 62FR42160

61 Benzo (a) Pyrene 50328 0.0044 B,C 0.049 B,C 62FR42160

62 Benzo (b) Fluoranthene 205992 0.0044 B,C 0.049 B,C 62FR42160

63 Benzo (ghi) Perylene 19124264 Benzo (k) Fluoranthene 207089 0.0044 B,C 0.049 B,C 62FR42160

65 Bis 2-Chloroethoxy Methane 11191166 Bis 2-Chloroethyl Ether 111444 0.031 B,C 1.4 B,C 57FR60848

67 Bis 2-Chloroisopropyl Ether 39638329 1,400 B 170,000 B 62FR42160

57FR60848

68 Bis 2-Ethylhexyl Phthalate X 117817 1.8 B,C 5.9 B,C 57FR60848

69 4-Bromophenyl Phenyl Ether 10155370 Butylbenzyl Phthalate W 85687 3,000 B 5,200 B 62FR42160

71 2-Chloronaphthalene 91587 1,700 B 4,300 B 62FR42160
D-6

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR PRIORITY POLLUTANTS

Priority Pollutant

CAS

Number

Freshwater Saltwater

Human Health For

Consumption of:

FR

Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

72 4-Chlorophenyl Phenyl Ether 700572373 Chrysene 218019 0.0044 B,C 0.049 B,C 62FR42160

74 Dibenzo (a,h) Anthracene 53703 0.0044 B,C 0.049 B,C 62FR42160

75 1,2-Dichlorobenzene 95501 2,700 B,Z 17,000 B 62FR42160

76 1,3-Dichlorobenzene 541731 400 2,600 62FR42160

77 1,4-Dichlorobenzene 106467 400 Z 2600 62FR42160

78 3,3'-Dichlorobenzidine 91941 0.04 B,C 0.077 B,C 57FR60848

79 Diethyl Phthalate W 84662 23,000 B 120,000 B 57FR60848

80 Dimethyl Phthalate W 131113 313,000 2,900,000 57FR60848

81 Di-n-Butyl Phthalate W 84742 2,700 B 12,000 B 57FR60848

82 2,4-Dinitrotoluene 121142 0.11 C 9.1 C 57FR60848

83 2,6-Dinitrotoluene 60620284 Di-n-Octyl Phthalate 11784085 1,2-Diphenylhydrazine 122667 0.040 B,C 0.54 B,C 57FR60848

86 Fluoranthene 206440 300 B 370 B 62FR4216087 Fluorene 86737 1,300 B 14,000 B 62FR42160

88 Hexachlorobenzene 118741 0.00075 B,C 0.00077 B,C 62FR42160

89 Hexachlorobutadiene 87683 0.44 B,C 50 B,C 57FR6084890 Hexachlorocyclopentadiene 77474 240 B,U,Z 17,000 B,H,U 57FR60848

91 Hexachloroethane 67721 1.9 B,C 8.9 B,C 57FR60848
D-7

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR PRIORITY POLLUTANTS

Priority Pollutant

CAS

Number

Freshwater Saltwater

Human Health For

Consumption of:

FR

Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

92 Indeno (1,2,3-cd) Pyrene 193395 0.0044 B,C 0.049 B,C 62FR42160

93 Isophorone 78591 36 B,C 2,600 B,C IRIS

11/01/97

94 Naphthalene 9120395 Nitrobenzene 98953 17 B 1,900 B,H,U 57FR60848

96 N-Nitrosodimethylamine 62759 0.00069 B,C 8.1 B,C 57FR60848

97 N-Nitrosodi-n-Propylamine 621647 0.005 B,C 1.4 B,C 62FR42160

98 N-Nitrosodiphenylamine 86306 5.0 B,C 16 B,C 57FR60848

99 Phenanthrene 85018100 Pyrene 129000 960 B 11,000 B 62FR42160

101 1,2,4-Trichlorobenzene 120821 260 Z 940 IRIS 11/01/96102 Aldrin 309002 3.0 G 1.3 G 0.00013 B,C 0.00014 B,C 62FR42160

103 alpha-BHC 319846 0.0039 B,C 0.013 B,C 62FR42160

104 beta-BHC 319857 0.014 B,C 0.046 B,C 62FR42160

105 gamma-BHC (Lindane) 58899 0.95 K 0.16 G 0.019 C 0.063 C 62FR42160

106 delta-BHC 319868

107 Chlordane 57749 2.4G 0.0043G,aa 0.09G 0.004G,aa

0.0021 B,C 0.0022 B,C

62FR42160

IRIS 02/07/98

108 4,4-DDT 50293 1.1G 0.001G,aa 0.13G 0.001G,aa 0.00059 B,C 0.00059 B,C 62FR42160

109 4,4-DDE 72559 0.00059 B,C 0.00059 B,C 62FR42160

110 4,4-DDD 72548 0.00083 B,C 0.00084 B,C 62FR42160
D-8

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR PRIORITY POLLUTANTS

Priority Pollutant

CAS

Number

Freshwater Saltwater

Human Health For

Consumption of:

FR

Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

111 Dieldrin 60571 0.24K 0.056K,O 0.71G 0.0019G,aa 0.00014 B,C 0.00014 B,C 62FR42160

112 alpha-Endosulfan 959988 0.22G,Y 0.056G,Y 0.034G,Y 0.0087G,Y 110 B 240 B 62FR42160

113 beta-Endosulfan 33213659 0.22G,Y 0.056G,Y 0.034G,Y 0.0087G,Y 110 B 240 B 62FR42160

114 Endosulfan Sulfate 1031078 110 B 240 B 62FR42160

115 Endrin 72208 0.086K 0.036K,O 0.037G 0.0023G,aa 0.76 B 0.81 B,H 62FR42160

116 Endrin Aldehyde 7421934 0.76 B 0.81 B,H 62FR42160

117 Heptachlor 76448 0.52G 0.0038G,aa 0.053G 0.0036G,aa 0.00021 B,C 0.00021 B,C 62FR42160

118 Heptachlor Epoxide 1024573 0.52G,V 0.0038G,V,

aa

0.053G,V 0.0036G,V,

aa

0.00010 B,C 0.00011 B,C 62FR42160

119 Polychlorinated Biphenyls

PCBs:

0.014 N,aa 0.03 N,aa

0.00017 B,C,P 0.00017 B,C,P

62FR4216063FR16182

120 Toxaphene 8001352 0.73 0.0002aa 0.21 0.0002aa 0.00073B,C 0.00075B,C 62FR42160

Footnotes:A This recommended water quality criterion was derived from data for arsenic (III), but is applied here to total arsenic, which might imply that arsenic (III)

and arsenic (V) are equally toxic to aquatic life and that their toxicities are additive. A 440/5-84-033, January 1985),Species Mean Acute Values are given for both arsenic (III) and arsenic (V) for five species and the ratios of the SMAVs for each species range from 0.6 to

1.7. hronic values are available for both arsenic (III) and arsenic (V) for one species; for the fathead minnow, the chronic value for arsenic (V) is 0.29

times the chronic value for arsenic (III). be available concerning whether the toxicities of the forms of arsenic to aquatic organisms

are additive.

B This criterion has been revised to reflect The Environmental Protection Agency’s q1* or RfD, as contained in the Integrated Risk Information System

(IRIS) as of April 8, 1998. factor (BCF) from the 1980 Ambient Water Quality Criteria document was retained in each

case.

C This criterion is based on carcinogenicity of 10-6 risk. k levels may be obtained by moving the decimal point (e.g., for a risk level of 10-5 ,

move the decimal point in the recommended criterion one place to the right).

D Freshwater and saltwater criteria for metals are expressed in terms of the dissolved metal in the water column. ed water quality criteria

value was calculated by using the previous 304(a) aquatic life criteria expressed in terms of total recoverable metal, and multiplying it by a conversion

factor (CF). onversion Factor" (CF) represents the recommended conversion factor for converting a metal criterion expressed as the totalrecoverable fraction in the water column to a criterion expressed as the dissolved fraction in the water column. onversion Factors for saltwater CCCs

are not currently available. ater CMCs have been used for both saltwater CMCs and CCCs). See "Office of Water

Policy 

In the arsenic criteria document (EP

C

No data are known to 

The fish tissue bioconcentration 

Alternate ris

The recommend

The term "C

(C

Conversion factors derived for saltw
hardness of 100 mg/L. Criteria values for other hardness may be calculated from the following: CMC (dissolved) = exp{mA [ln( hardness)]+ bA} (CF), 

or CCC (dissolved) = exp{mC [ln (hardness)]+ bC} (CF) and the parameters specified in Appendix B to the Preamble- Parameters for Calculating 

Freshwater Dissolved Metals Criteria That Are Hardness-Dependent. 

This recommended water quality criterion is expressed in terms of total recoverable metal in the water column. It is scientifically acceptable to use the 

This value was announced (61FR58444-58449, November 14, 1996) as a proposed GLI 303(c) aquatic life criterion. EPA is currently working on this 

440/5-80-019), Chlordane (EPA 440/5-80-027), DDT (EPA 440/5-80-038), Endosulfan (EPA 440/5-80-046), Endrin (EPA 440/5-80-047), Heptachlor (440/5-80-052), Hexachlorocyclohexane (EPA 440/5-80-054), Silver (EPA 440/5-80-071). The Minimum Data Requirements and derivation procedures were different in the 1980 Guidelines than in the 1985 Guidelines. For example, a “CMC” derived using the 1980 Guidelines was derived to be used as an instantaneous maximum. If assessment is to be done using an averaging period, the values given should be divided by 2 to obtain a value that is more comparable to a CMC derived using the 1985 Guidelines. 

No criterion for protection of human health from consumption of aquatic organisms excluding water was presented in the 1980 criteria document or in 

PCBs are a class of chemicals which include aroclors, 1242, 1254, 1221, 1232, 1248, 1260, and 1016, CAS numbers 53469219, 11097691, 11104282, 

This recommended criterion is based on a 304(a) aquatic life criterion that was issued in the 1995 Updates: Water Quality Criteria Documents for the 

The CMC = 1/[(f1/CMC1) + (f2/CMC2)] where f1 and f2 are the fractions of total selenium that are treated as selenite and selenate, respectively, and 

Protection of Aquatic Life in Ambient Water, (EPA-820-B-96-001, September 1996). This value was derived using the GLI Guidelines 

(60FR15393-15399, March 23, 1995; 40CFR132 Appendix A); the difference between the 1985 Guidelines and the GLI Guidelines are explained on page iv of the 1995 Updates. None of the decisions concerning the derivation of this criterion were affected by any considerations that are specific to 

F

the Great Lakes. 

reshwater aquatic life values for pentachlorophenol are expressed as a function of pH, and are calculated as follows: CMC = exp(1.005(pH)-4.869); 

The derivation of the CCC for this pollutant did not consider exposure through the diet, which is probably important for aquatic life occupying upper 

Nevertheless, sufficient information was presented in the 1980 document to allow the calculation of a criterion, 

and Technical Guidance on Interpretation and Implementation of Aquatic Life Metals Criteria,” October 1, 1993, by Martha G. Prothro, Acting 

Assistant Administrator for Water, available from the Water Resource Center, USEPA, 401 M St., SW, mail code RC4100, Washington, DC 20460; 

and 40CFR§131.36(b)(1). Conversion Factors applied in the table can be found in Appendix A to the Preamble- Conversion Factors for Dissolved 

Metals. 

EPA has not calculated human health criterion for this contaminant. However, permit authorities should address this contaminant in NPDES permit 

EPA is currently reassessing the criteria for arsenic. Upon completion of the reassessment the Agency will publish revised criteria as appropriate. 

The freshwater criterion for this metal is expressed as a function of hardness (mg/L) in the water column. The value given here corresponds to a 

This Criterion is based on 304(a) aquatic life criterion issued in 1980, and was issued in one of the following documents: Aldrin/Dieldrin (EPA 

This criterion for asbestos is the Maximum Contaminant Level (MCL) developed under the Safe Drinking Water Act (SDWA). 

conversion factor of 0.922 that was used in the GLI to convert this to a value that is expressed in terms of dissolved metal. 

11141165, 12672296, 11096825 and 12674112 respectively. The aquatic life criteria apply to this set of PCBs. 

This criterion applies to total pcbs, i.e., the sum of all congener or all isomer analyses. This recommended water quality criterion is expressed as :g free cyanide (as CN)/L. 

CCC = exp(1.005(pH)-5.134). Values displayed in table correspond to a pH of 7.8. 

even though the results of such a calculation were not shown in the document. 

This recommended water quality criterion refers to the inorganic form only. 

CMC1 and CMC2 are 185.9 

criterion and so this value might change substantially in the near future. 

:g/L and 12.83 :g/L, respectively. 

the 

actions using the State's existing narrative criteria for toxics. 

1986 Quality Criteria for Water. 

trophic levels. 

E 

F G 

H 

I J 

K 

L 

M N O P Q R S T 

D-9
0.025 :g/L given on page 23 of the criteria document is based on the Final Residue Value procedure in the 1985 Guidelines. Since the publication of the Great 

This recommended water quality criterion was derived on page 43 of the mercury criteria document (EPA 440/5-84-026, January 1985). The saltwater CCC of 

Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses, PB85-227049, January 1985) and was issued in one of the following criteria 

documents: Arsenic (EPA 440/5-84-033), Cadmium (EPA 440/5-84-032), Chromium (EPA 440/5-84-029), Copper (EPA 440/5-84-031), Cyanide (EPA 440/5-

84-028), Lead (EPA 440/5-84-027), Nickel (EPA 440/5-86-004), Pentachlorophenol (EPA 440/5-86-009), Toxaphene, (EPA 440/5-86-006), Zinc (EPA 

1995 (60FR15393-15399, March 23, 1995), the Agency no longer uses the 

440/5-87- 003). 

Final Residue Value procedure for deriving CCCs for new or revised 304(a) aquatic 

criteria. 

life criteria. 

It is anticipated that industry intends to publish in the peer reviewed literature draft aquatic life criteria generated in accordance with EPA Guidelines. 

EPA will review such criteria for possible issuance as national WQC. 

Although EPA has not published a final criteria document for this compound it is EPA’s understanding that sufficient data exist to allow calculation of aquatic 

This recommended water quality criterion was derived from data for inorganic mercury (II), but is applied here to total mercury. If a substantial portion of the 

This water quality criterion is based on a 304(a) aquatic life criterion that was derived using the 1985 Guidelines (Guidelines for Deriving Numerical National 

This CCC is based on the Final Residue Value procedure in the 1985 Guidelines. Since the publication of the Great Lakes Aquatic Life Criteria Guidelines in 

mercury in the water column is methylmercury, this criterion will probably be under protective. In addition, even though inorganic mercury is converted to methylmercury and methylmercury bioaccumulates to a great extent, this criterion does not account for uptake via the food chain because sufficient data were 

The selenium criteria document (EPA 440/5-87-

not available when the criterion was derived. 

006, September 1987) provides that if selenium is as toxic to saltwater fishes in the field as it is to freshwater 

fishes in the field, the status of the fish community should be monitored whenever the concentration of selenium exceeds 5.0 :g/L in salt water because the 

A more stringent MCL has been issued by EPA. Refer to drinking water regulations (40 CFR 141) or Safe Drinking Water Hotline (1-800-426-4791) for 

Lakes Aquatic Life Criteria Guidelines in 1995 (60FR15393-15399, March 23, 1995), the Agency no longer uses the Final Residue Value procedure for 

T

deriving CCCs for new or revised 304(a) aquatic life criteria. 

his value was derived from data for heptachlor and the criteria document provides insufficient data to estimate the relative toxicities of heptachlor and 

This recommended water quality criterion was derived in Ambient Water Quality Criteria Saltwater Copper Addendum (Draft, April 14, 1995) and was 

When the concentration of dissolved organic carbon is elevated, copper is substantially less toxic and use of Water-Effect Ratios might be appropriate. 

This value was derived from data for endosulfan and is most appropriately applied to the sum of alpha-endosulfan and beta-endosulfan. 

EPA is actively working on this criterion and so this recommended water quality criterion may change substantially in the near future. 

There is a full set of aquatic life toxicity data that show that DEHP is not toxic to aquatic organisms at or below its solubility limit. 

promulgated in the Interim final National Toxics Rule (60FR22228-222237, May 4, 1995). 

heptachlor epoxide. 

values. 

saltwater CCC does not take into account uptake via the food chain. 

V W X Y 

Z 

aa bb 

cc 

dd 

ee 

ff 

gg hh 

D-10
D-11

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR NON-PRIORITY POLLUTANTS

Priority Pollutant CAS Number

Freshwater Saltwater

Human Health For

Consumption of:

FR Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

1 Alkalinity -- * 20000 F * Gold Book

2 Aluminum pH 6.5 - 9.0 7429905 750 G,I 87 G,I,L * 53FR33178

3 Ammonia 7664417 FRESHWATER CRITERIA ARE pH DEPENDENT -- SEE DOCUMENT 

SALTWATER CRITERIA ARE pH AND TEMPERATURE DEPENDENT

EPA822-R-98-008

EPA440/5-88-004

4 Aesthetic Qualities -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book5 Bacteria -- FOR PRIMARY RECREATION AND SHELLFISH USES -- SEE DOCUMENT Gold Book

6 Barium 7440393 1,000 A Gold Book

7 Boron -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book

8 Chloride 16887006 860000 G 230000 G 53FR19028

9 Chlorine 7782505 19 11 13 7.5 C Gold Book

10 Chlorophenoxy Herbicide

2,4,5,-TP

93721 10 A Gold Book

11 Chlorophenoxy Herbicide

2,4-D

94757 100 A,C Gold Book

12 Chlorpyrifos 2921882 0.083 G 0.041 G 0.011 G 0.0056 G Gold Book

13 Color -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book

14 Demeton 8065483 0.1 F 0.1 F Gold Book

15 Ether, Bis Chloromethyl 542881 0.00013 E 0.00078 E IRIS 01/01/91

16 Gases, Total Dissolved -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book17 Guthion 86500 0.01 F 0.01 F Gold Book18 Hardness -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book

* * ** * *

D

F

F
D-12

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR NON-PRIORITY POLLUTANTS

Priority Pollutant CAS Number

Freshwater Saltwater

Human Health For

Consumption of:

FR Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

19 Hexachlorocyclo-hexaneTechnical 319868 0.0123 0.0414 Gold Book

20 Iron 7439896 1000 F 300 A Gold Book

21 Malathion 121755 0.1 F 0.1 F Gold Book

22 Manganese 7439965 50 A 100 A Gold Book23 Methoxychlor 72435 0.03 F 0.03 F 100 A,C Gold Book24 Mirex 2385855 0.001 F 0.001 F Gold Book

25 Nitrates 14797558 10,000 A Gold Book

26 Nitrosamines -- 0.0008 1.2427 Dinitrophenols 25550587 70 14,000 Gold Book

28 Nitrosodibutylamine,N 924163 0.0064 A 0.587 A Gold Book

29 Nitrosodiethylamine,N 55185 0.0008 A 1.24 A Gold Book

30 Nitrosopyrrolidine,N 930552 0.016 91.9 Gold Book

31 Oil and Grease -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book32 Oxygen, Dissolved 7782447 WARMWATER AND COLDWATER MATRIX -- SEE DOCUMENT Gold Book33 Parathion 56382 0.065 J 0.013 J Gold Book34 Pentachlorobenzene 608935 3.5 E 4.1 E IRIS 03/01/88

35 pH -- 6.5 - 9 F 6.5 - 8.5 F,K 5 - 9 Gold Book

36 Phosphorus Elemental 7723140 0.1 F,K Gold Book37 Phosphate Phosphorus -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book

F

O
D-13

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR NON-PRIORITY POLLUTANTS

Priority Pollutant CAS Number

Freshwater Saltwater

Human Health For

Consumption of:

FR Cite/Source

CMC

(:g/L)

CCC

(:g/L)

CMC

(:g/L)

CCC

(:g/L)

Water +

Organism

(:g/L)

Organism

Only

(:g/L)

38 Solids Dissolved and

Salinity

-- 250,000 A Gold Book

39 Solids Suspended and

Turbidity

-- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book

40 Sulfide-Hydrogen Sulfide 7783064 2.0 F 2.0 F Gold Book

41 Tainting Substances -- NARRATIVE STATEMENT -- SEE DOCUMENT Gold Book42 Temperature -- SPECIES DEPENDENT CRITERIA -- SEE DOCUMENT Gold Book

43 Tetrachlorobenzene,1,2,4,5- 95943 2.3 E 2.9 E IRIS03/01/91

44 Tributyltin TBT -- 0.46 N 0.063 N 0.37 N 0.010 N 62FR42554

45 Trichlorophenol,2,4,5- 95954 2,600 B,E 9800 B,E IRIS 03/01/88

Footnotes:A This human health criterion is the same as originally published in the Red Book which predates the 1980 methodology and did not utilize the fish ingestion

BCF approach. lue is now published in the Gold Book.

B The organoleptic effect criterion is more stringent than the value presented in the non priority pollutants table.C A more stringent Maximum Contaminant Level (MCL) has been issued by EPA under the Safe Drinking Water Act. water regulations

40CFR141 or Safe Drinking Water Hotline (1-800-426-4791) for values.

D According to the procedures described in the Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and

Their Uses, except possibly where a very sensitive species is important at a site, freshwater aquatic life should be protected if both conditions specified in

Appendix C to the Preamble--Calculation of Freshwater Ammonia Criterion are satisfied.

E This criterion has been revised to reflect The Environmental Protection Agency’s q1* or RfD, as contained in the Integrated Risk Information System (IRIS) as

of April 8, 1998. used to derive the original criterion was retained in each case.

F The derivation of this value is presented in the Red Book (EPA 440/9-76-023, July, 1976).

G This value is based on a 304(a) aquatic life criterion that was derived using the 1985 Guidelines (Guidelines for Deriving Numerical National Water Quality

Criteria for the Protection of Aquatic Organisms and Their Uses, PB85-227049, January 1985) and was issued in one of the following criteria documents:Aluminum (EPA 440/5-86-008); Chloride (EPA 440/5-88-001); Chlorpyrifos (EPA 440/5-86-005).

I This value is expressed in terms of total recoverable metal in the water column.J This value is based on a 304(a) aquatic life criterion that was issued in the 1995 Updates: Water Quality Criteria Documents for the Protection of Aquatic Life

in Ambient Water (EPA-820-B-96-001). Guidelines (60FR15393-15399, March 23, 1995; 40CFR132 Appendix A); the

differences between the 1985 Guidelines and the GLI Guidelines are explained on page iv of the 1995 Updates. rning this criterion was

affected by any considerations that are specific to the Great Lakes.

F

M

This same criterion va

Refer to drinking 

The fish tissue bioconcentration factor (BCF) 

This value was derived using the GLI 

No decision conce
For open ocean waters where the depth is substantially greater than the euphotic zone, the pH should not be changed more than 0.2 units from the naturally 

occurring variation or any case outside the range of 6.5 to 8.5. For shallow, highly productive coastal and estuarine areas where naturally occurring pH 

variations approach the lethal limits of some species, changes in pH should be avoided but in any case should not exceed the limits established for fresh 

water, i.e., 6.5-9.0. 

This value was announced (62FR42554, August 7, 1997) as a proposed 304(a) aquatic life criterion. Although EPA has not responded to public comment, EPA 

bass in water with pH= 6.5-6.6 and hardness <10 mg/L. Data in “Aluminum Water-Effect Ratio for the 3M Plant Effluent Discharge, Middleway, West 

Virginia” (May 1994) indicate that aluminum is substantially less toxic at higher pH and hardness, but the effects of pH and hardness are not well quantified at 

this time. (2) In tests with the brook trout at low pH and hardness, effects increased with increasing concentrations of total aluminum even though the 

concentration of dissolved aluminum was constant, indicating that total recoverable is a more appropriate measurement than dissolved, at least when particulate 

aluminum is primarily aluminum hydroxide particles. In surface waters, however, the total recoverable procedure might measure aluminum associated with 

clay particles, which might be less toxic than aluminum associated with aluminum hydroxide. (3) EPA is aware of field data indicating that many high quality 

waters in the U.S. contain more than 87 :g aluminum/L, when either total recoverable or dissolved is measured. 

There are three major reasons why the use of Water-Effect Ratios might be appropriate. (1) The value of 87 :g/L is based on a toxicity test with the striped 

U.S. EPA. 1973. Water Quality Criteria 1972. EPA-R3-73-033. National Technical Information Service, Springfield, VA.; U.S. EPA. 1977. Temperature 

U.S. EPA. 1986. Ambient Water Quality Criteria for Dissolved Oxygen. EPA 440/5-86-003. National Technical Information Service, Springfield, VA. 

is publishing this as a 304(a) criterion in today’s notice as guidance for States and Tribes to consider when adopting water quality criteria. 

Criteria for Freshwater Fish: Protocol and Procedures. EPA-600/3-77-061. National Technical Information Service, Springfield, VA. 

According to page 181 of the Red Book: K 

L 

M 

N 

O 

D-14
D-15

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR ORGANOLEPTIC EFFECTS

Pollutant CAS Number

Organoleptic Effect Criteria

(:g/L) FR Cite/Source

1 Acenaphthene 83329 20 Gold Book

2 Monochlorobenzene 108907 20 Gold Book

3 3-Chlorophenol -- 0.1 Gold Book4 4-Chlorophenol 106489 0.1 Gold Book

5 2,3-Dichlorophenol -- 0.04 Gold Book

6 2,5-Dichlorophenol -- 0.5 Gold Book

7 2,6-Dichlorophenol -- 0.2 Gold Book

8 3,4-Dichlorophenol -- 0.3 Gold Book

9 2,4,5-Trichlorophenol 95954 1 Gold Book

10 2,4,6-Trichloropehnol 88062 2 Gold Book

11 2,3,4,6-Tetrachlorophenol -- 1 Gold Book12 2-Methyl-4-Chlorophenol -- 1800 Gold Book

13 3-Methyl-4-Chlorophenol 59507 3000 Gold Book

14 3-Methyl-6-Chlorophenol -- 20 Gold Book

15 2-Chlorophenol 95578 0.1 Gold Book

16 Copper 7440508 1000 Gold Book

17 2,4-Dichlorophenol 120832 0.3 Gold Book

18 2,4-Dimethylphenol 105679 400 Gold Book

19 Hexachlorocyclopentadiene 77474 1 Gold Book

20 Nitrobenzene 98953 30 Gold Book
be exposed briefly without resulting in an unacceptable effect. The Criterion Continuous Concentration (CCC) is an estimate of the highest concentration of a 

The CMC and CCC are just two of material in surface water to which an aquatic community can be exposed indefinitely without resulting in an unacceptable effect. 

the six parts of a aquatic life criterion; the other four parts are the acute averaging period, chronic averaging period, acute frequency of allowed exceedence, and 

chronic frequency of allowed exceedence. Because 304(a) aquatic life criteria are national guidance, they are intended to be protective of the vast majority of the aquatic communities in the United States. 

This compilation lists all priority toxic pollutants and some non priority toxic pollutants, and both human health effect and organoleptic effect criteria 

issued pursuant to CWA §304(a). Blank spaces indicate that EPA has no CWA §304(a) criteria recommendations. For a number of non-priority toxic pollutants not 

listed, CWA §304(a) “water + organism” human health criteria are not available, but, EPA has published MCLs under the SDWA that may be used in establishing 

water quality standards to protect water supply designated uses. Because of variations in chemical nomenclature systems, this listing of toxic pollutants does not duplicate the listing in Appendix A of 40 CFR Part 423. Also listed are the Chemical Abstracts Service CAS registry numbers, which provide a unique identification for each chemical. 

The Criteria Maximum Concentration (CMC) is an estimate of the highest concentration of a material in surface water to which an aquatic community can 

The human health criteria for the priority and non priority pollutants are based on carcinogenicity of 10 -6 risk. Alternate risk levels may be obtained by 

moving the decimal point (e.g., for a risk level of 10 -5 , move the decimal point in the recommended criterion one place to the right). 

Because of variations in chemical nomenclature systems, this listing of pollutants does 

not duplicate the listing in Appendix A of 40 CFR Part 423. Also listed are the Chemical Abstracts Service (CAS) registry numbers, which provide a 

unique identification for each chemical. 

NATIONAL RECOMMENDED WATER QUALITY CRITERIA 

FR Cite/Source 

NATIONAL RECOMMENDED WATER QUALITY CRITERIA FOR ORGANOLEPTIC EFFECTS 

Gold Book 

Gold Book 

45FR79341 

Organoleptic Effect Criteria 

CAS Number 

Criteria Recommendations for Priority Pollutants, Non Priority Pollutants and Organoleptic Effects 

(:g/L) 

30 

300 

5000 

Criteria Maximum Concentration and Criterion Continuous Concentration 

These criteria are based on organoleptic (taste and odor) effects. 

87865 

108952 

7440666 

Human Health Risk 

Pollutant 

Pentachlorophenol 

General Notes: 

Additional Notes: 

Phenol 

Zinc 

21 22 23 

1. 

1. 

2. 

3. 

D-16
The compilation contains 304(a) criteria for pollutants with toxicity-based criteria as well as non-toxicity based criteria. The basis for the non-toxicity based 

criteria are organoleptic effects (e.g., taste and odor) which would make water and edible aquatic life unpalatable but not toxic to humans. The table includes criteria 

for organoleptic effects for 23 pollutants. Pollutants with organoleptic effect criteria more stringent than the criteria based on toxicity (e.g., included in both the priority and non-priority pollutant tables) are footnoted as such. 

The Chemical Abstract Services number (CAS) for Bis(2-Chloroisopropyl) Ether, has been corrected in the table. The correct CAS number for this chemical is 

39638-32-9. Previous publications listed 108-60-1 as the CAS number for this chemical. 

In the 1980 Selenium document, a criterion for the protection of human health from consumption of water and organisms was calculated based on a BCF of 6.0 

L/kg and a maximum water-related contribution of 35 mg Se/day. Subsequently, the EPA Office of Health and Environmental Assessment issued an errata notice (February 23, 1982), revising the BCF for selenium to 4.8 L/kg. In 1988, EPA issued an addendum (ECAO-CIN-668) revising the human health criteria for selenium. Later in the final National Toxic Rule (NTR, 57 FR 60848), EPA withdrew previously published selenium human health criteria, pending Agency review 

of new epidemiological data. 

The 304(a) criteria for metals, shown as dissolved metals, are calculated in one of two ways. For freshwater metals criteria that are hardness-dependent, the 

dissolved metal criteria were calculated using a hardness of 100 mg/L as CaCO3 for illustrative purposes only. Saltwater and freshwater metals’ criteria that are not 

hardness-dependent are calculated by multiplying the total recoverable criteria before rounding by the appropriate conversion factors. The final dissolved metals’ 

criteria in the table are rounded to two significant figures. Information regarding the calculation of hardness dependent conversion factors are included in the 

footnotes. 

The compilation includes footnotes for pollutants with Maximum Contaminant Levels (MCLs) more stringent than the recommended water quality criteria in 

the compilation. MCLs for these pollutants are not included in the compilation, but can be found in the appropriate drinking water regulations (40 CFR 141.11-16 

Many of the values in the compilation were published in the proposed California Toxics Rule (CTR, 62FR42160). Although such values were published 

pursuant to Section 303(c) of the CWA, they represent the Agency’s most recent calculation of water quality criteria and thus are published today as the Agency’s 

304(a) criteria. Water quality criteria published in the proposed CTR may be revised when EPA takes final action on the CTR. 

In the 1980 criteria documents, certain recommended water quality criteria were published for categories of pollutants rather than for individual pollutants 

within that category. Subsequently, in a series of separate actions, the Agency derived criteria for specific pollutants within a category. Therefore, in this 

compilation EPA is replacing criteria representing categories with individual pollutant criteria (e.g., 1,3-dichlorobenzene, 1,4-dichlorobenzene and 

and 141.60-63), or can be accessed through the Safe Drinking Wat

1,2-dichlorobenzene). 

er Hotline (800-426-4791) or the Internet (http://www.epa.gov/ost/tools/dwstds-s.html). 

Water Quality Criteria published pursuant to Section 304(a) or Section 303(c) of the CWA 

Correction of Chemical Abstract Services Number 

Calculation of Dissolved Metals Criteria 

Maximum Contaminant Levels 

Specific Chemical Calculations 

Human Health 

Organoleptic Effects 

Category Criteria 

Selenium 

(1) 

A. 

4. 

5. 

6. 7. 

8. 9. 

10. 

D-17
This compilation includes human health criteria for selenium, calculated using a BCF of 4.8 L/kg along with the current IRIS RfD of 0.005 mg/kg/day. EPA 

included these recommended water quality criteria in the compilation because the data necessary for calculating a criteria in accordance with EPA’s 1980 human 

health methodology are available. 

Aquatic Life (2) 

This compilation contains aquatic life criteria for selenium that are the same as those published in the proposed CTR. In the CTR, EPA proposed an acute 

criterion for selenium based on the criterion proposed for selenium in the Water Quality Guidance for the Great Lakes System (61 FR 58444). The GLI and CTR 

proposals take into account data showing that selenium’s two most prevalent oxidation states, selenite and selenate, present differing potentials for aquatic toxicity, as well as new data indicating that various forms of selenium are additive. The new approach produces a different selenium acute criterion concentration, or CMC, 

depending upon the relative proportions of selenite, selenate, and other forms of selenium that are present. 

EPA notes it is currently undertaking a reassessment of selenium, and expects the 304(a) criteria for selenium will be revised based on the final reassessment 

(63FR26186). However, until such time as revised water quality criteria for selenium are published by the Agency, the recommended water quality criteria in this compilation are EPA’s current 304(a) criteria. 

1,2,4-Trichlorobenzene and Zinc B. 

Human health criteria for 1,2,4-trichlorobenzene and zinc have not been previously published. Sufficient information is now available for calculating water 

quality criteria for the protection of human health from the consumption of aquatic organisms and the consumption of aquatic organisms and water for both these 

compounds. Therefore, EPA is publishing criteria for these pollutants in this compilation. 

Chromium (III) C. 

The recommended aquatic life water quality criteria for chromium (III) included in the compilation are based on the values presented in the document titled: 

1995 Updates: Water Quality Criteria Documents for the Protection of Aquatic Life in Ambient Water, however, this document contains criteria based on the total recoverable fraction. The chromium (III) criteria in this compilation were calculated by applying the conversion factors used in the Final Water Quality Guidance 

for the Great Lakes System (60 FR 15366) to the 1995 Update document values. 

Ether, Bis (Chloromethyl), Pentachlorobenzene, Tetrachlorobenzene 1,2,4,5-, Trichlorphenol D. 

Human health criteria for these pollutants were last published in EPA’s Quality Criteria for Water 1986 or “Gold Book”. Some of these criteria were calculated 

using Acceptable Daily Intake (ADIs) rather than RfDs. Updated q1*s and RfDs are now available in IRIS for ether, bis (chloromethyl), pentachlorobenzene, tetrachlorobenzene 1,2,4,5-, and trichlorophenol, and were used to revise the water quality criteria for these compounds. The recommended water quality criteria for ether, bis (chloromethyl) were revised using an updated q1*, while criteria for pentachlorobenzene, and tetrachlorobenzene 1,2,4,5-, and trichlorophenol were 

derived using an updated RfD value. 

PCBs E. 

These criteria replace the In this compilation EPA is publishing aquatic life and human health criteria based on total PCBs rather than individual arochlors. 

previous criteria for the seven individual arochlors. Thus, there are criteria for a total of 102 of the 126 priority pollutants. 

D-18
-- --

-- --

-- --

Conversion Factors for Dissolved Metals 

Metal 

Conversion Factor 

freshwater CMC 

Conversion Factor 

freshwater CCC 

Conversion Factor 

saltwater CMC 

Conversion Factor 

saltwater CCC1 

Arsenic 1.000 1.000 1.000 1.000 

Cadmium 1.136672-[(ln 

hardness)(0.041838)] 

1.101672-[(ln 

hardness)(0.041838)] 

0.994 0.994 

Chromium III 0.316 0.860 

Chromium VI 0.982 0.962 0.993 0.993 

Copper 0.960 0.960 0.83 0.83 Lead 1.46203-[(ln 

hardness)(0.145712)] 

1.46203-[(ln 

hardness)(0.145712)] 

0.951 0.951 

Mercury 0.85 0.85 0.85 0.85 Nickel 0.998 0.997 0.990 0.990 

Selenium 0.998 0.998 Silver 0.85 0.85 Zinc 0.978 0.986 0.946 0.946 

D-19
-- -- --

 Parameters* for Calculating Freshwater Dissolved Metals Criteria That Are Hardness-Dependent 

Chemical mA bA mC bC 

Freshwater Conversion Factors (CF) 

Acute Chronic 

Cadmium 1.128 -3.6867 0.7852 -2.715 1.136672-[ln 

(hardness)(0.041838)] 

1.101672-[ln 

(hardness)(0.041838)] 

Chromium III 0.8190 3.7256 0.8190 0.6848 0.316 0.860 

Copper 0.9422 -1.700 0.8545 -1.702 0.960 0.960 

Lead 1.273 -1.460 1.273 -4.705 1.46203-[ln 

(hardness)(0.145712)] 

1.46203-[ln 

(hardness)(0.145712)] 

Nickel 0.8460 2.255 0.8460 0.0584 0.998 0.997 

Silver 1.72 -6.52 0.85 

Zinc 0.8473 0.884 0.8473 0.884 0.978 0.986 

* Where mA and bA are conversion factors to calculate CMC and mC and bC are 

conversion factors necessary to calculate CCC 

D-20
Appendix C - Calculation of Freshwater Ammonia Criterion 

1. The one-hour average concentration of total ammonia nitrogen (in mg N/L) does not exceed, more than once 

every three years on the average, the CMC calculated using the following equation: 

0.275 39.0

CMC = 

1 107.204− pH + 1 10pH − 7.204 + + 

In situations where salmonids do not occur, the CMC may be calculated using the following equation: 

0.411 58.4

CMC = 

1 107.204− pH + 1 10pH − 7.204 + + 

2. The thirty-day average concentration of total ammonia nitrogen (in mg N/L) does not exceed, more than once 

every three years on the average, the CCC calculated using the following equation: 

0.0858 3.70

CCC = 

1 107.688− pH + 1 10pH − 7.688 + + 

and the highest four-day average within the 30-day period does not exceed twice the CCC. 

Source: U.S. EPA’s National Recommended Water Quality Criteria-Correction, EPA-822-Z-99-001, 

April 1999, pp. 7-25; http://www.epa.gov/OST/standards/wqcriteria.html 

D-21
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D-22
APPENDIX E -

FEDERAL SEWAGE SLUDGE STANDARDS Pollutant Ceiling Concentration* Monthly Average Pollutant Concentration* Cumulative Pollutant Loading Rates* Annual Pollutant Loading Rate* (Table 1, 40 CFR 503.13) (Table 3, 40 CFR 503.13) (Table 2, 40 CFR 503.13) (Table 4, 40 CFR 503.13) mg/kg lbs/1000 lbs 

mg/kg lbs/1000 lbs kg/hectare lbs/acre** kg/hectare/ 365-day period lbs/acre/ 365-day period** 

Arsenic 75 75 41 41 41 37 2 1.8 

Cadmium 85 85 39 39 39 35 1.9 1.7 

Copper 4,300 4,300 1,500 1,500 1,500 1,338 75 67 

Lead 840 840 300 300 300 268 15 13 

Mercury 57 57 17 17 17 15 0.85 0.76 

Molybdenum 75 75 - - - - - -

Nickel 420 420 420 420 420 375 21 19 

Selenium 100 100 100 100 100 89 5 4.5 

Zinc 7,500 7,500 2,800 2,800 2,800 2,498 140 125 

Biosolids Land Application Limitations 

* ** Calculated using metric standards specified in 40 CFR 503.13 multiplied by the conversion factor of 0.8922. 

Dry weight. 

Source: 40 CFR §503.13, Tables 1-4, October 25, 1995 

E-1
Surface Disposal 

Distance from the Boundary of Active 

Biosolids Unit to Surface Disposal Site 

Property Line (meters) 

Pollutant Concentration* 

Arsenic 

(mg/kg) 

Chromium 

(mg/kg) 

Nickel 

(mg/kg) 

0 to less than 25 30 200 210 

25 to less than 50 34 220 240 

50 to less than 75 39 260 270 

75 to less than 100 46 300 320 

100 to less than 125 53 360 390 

125 to less than 150 62 450 420 

Equal to or greater than 150 73 600 420 

* Dry-weight.

Source: 40 CFR Part 503.23 Table 1 and 2.

Conversion Factors 

pounds per acre (lbs/ac) x 1.121 = kilograms per hectare (kg/ha)

kilograms per hectare (kg/ha) x 0.8922 = pounds per acre (lbs/ac)

pound (lb) = 0.4536 kilogram (kg)

kilogram (kg) = 2.205 pounds (lbs)

English ton = 0.9072 metric tonne

metric tonne = 1.102 English ton

E-2
APPENDIX F -

TOXICITY CHARACTERISTIC LEACHATE PROCEDURE

LIMITATIONS

EPA Hazardous 

Waste No. Contaminant CAS No. 

1 Regulatory Level (mg/L) 

D004 Arsenic 7440–38–2 5.0 

D005 Barium 7440–39–3 100.0 

D018 Benzene 71–43–2 0.5 

D006 Cadmium 7440–43–9 1.0 

D019 Carbon tetrachloride 56–23–5 0.5 

D020 Chlordane 57–74–9 0.03 

D021 Chlorobenzene 108–90–7 100.0 

D022 Chloroform 67–66–3 6.0 

D007 Chromium 7440–47–3 5.0 

D024 o-Cresol 95-48-7 200.0 2 

D024 m-Cresol 108–39–4 200.0 2 

D025 p-Cresol 106–44–5 200.0 2 

D026 Cresols 200.0 2 

D016 2,4-D 94–75–7 10.0 

D027 1,4-Dichlorobenzene 106–46–7 7.5 

D028 1,2-Dichloroethane 107–06–2 0.5 

D029 1,1-Dichloroethylene 75–35–4 0.7 

D030 2,4-Dinitrotoluene 121–14–2 0.13 3 

D012 Endrin 72–20–8 0.02 

D031 Heptachlor (and its 

epoxide) 

76–44–8 0.008 

D032 Hexachlorobenzene 118–74–1 0.13 3 

D033 Hexachlorobutadiene 87–68–3 0.5 

D034 Hexachloroethane 67–72–1 3.0 

D008 Lead 7439–92–1 5.0 

D013 Lindane 58–89–9 0.4 

D009 Mercury 7439–97–6 0.2 

D014 Methoxychlor 72–43–5 10.0 

D035 Methyl ethyl ketone 78–93–3 200.0 

D036 Nitrobenzene 98–95–3 2.0 

D037 Pentachlorophenol 87–86–5 100.0 

D038 ridine 110–86–1 5.0 3 

D010 Selenium 7782–49–2 1.0 

D011 Silver 7440–22–4 5.0 

D039 Tetrachloroethylene 127–18–4 0.7 

D015 Toxaphene 8001–35–2 0.5 

D040 Trichloroethylene 79–01–6 0.5 

Py

F-1
EPA Hazardous 

Waste No. Contaminant CAS No. 

1 Regulatory Level (mg/L) 

D041 2,4,5-Trichlorophenol 95–95–4 400.0 

D042 2,4,6-Trichlorophenol 88–06–2 2.0 

D017 2,4,5-TP (Silvex) 93–72–1 

D043 Vinyl chloride 75–01–4 

1.0 

0.2 

1 Chemical Abstracts Service number. 

2 If o-, m-, and p-Cresol concentrations cannot be differentiated, the total cresol (D026) 

concentration is used. The regulatory level of total cresol is 200 mg/L. 

3 Quantitation limit is greater than the calculated regulatory level. The quantitation limit 

therefore becomes the regulatory level. 

Source: 40 CFR 261.24 

F-2
APPENDIX G -

LITERATURE INHIBITION VALUES

Pollutant 

Reported Range of Activated Sludge 

Inhibition Threshold 

Levels, mg/L 

References* 

METALS/NONMETAL INORGANICS 

Ammonia 480 (4) 

Arsenic 0.1 (1), (2), (3) 

Cadmium 1 - 10 (2), (3) 

Chromium (VI) 1 (2), (3) 

Chromium (III) 10 - 50 (2), (3) 

Chromium (Total) 1 - 100 (1) 

Copper 1 (2), (1), (3) 

Cyanide 0.1 - 5 

5 

(1), (2), (3) 

(1) 

Iodine 10 (4) 

Lead 1.0 - 5.0 

10 - 100 

(3) 

(1) 

Mercury 0.1 - 1 

2.5 as 

(2), (3) 

(1) 

Nickel 1.0 - 2.5 

5 

(2), (3) 

(1) 

Sulfide 25 -30 (4) 

Zinc 0.3 - 5 

5 - 10 

(3) 

(1) 

Hg (II) 

ORGANICS 

Anthracene 500 (1) 

Benzene 100 - 500 

125 - 500 

(3) 

(1) 

2-Chlorophenol 5 

20 - 200 

(2) 

(3) 

1,2 Dichlorobenzene 5 (2) 

1,3 Dichlorobenzene 5 (2) 

1,4 Dichlorobenzene 5 (2) 

2,4-Dichlorophenol 64 (3) 

2,4 Dimethylphenol 40 - (3) 

2,4 Dinitrotoluene 5 (2) 

1,2-Diphenylhydrazine 5 (2) 

Ethylbenzene 200 (3) 

Hexachlorobenzene 5 (2) 

Naphthalene 500 

500 

500 

(1) 

(2) 

(3) 

Nitrobenzene 30 - 500 

500 

500 

(3) 

(1) 

(2) 

200 

G-1
Reported Range of Activated Sludge 

Pollutant Inhibition Threshold References* 

Levels, mg/L 

Pentachlorophenol 0.95 (2) 

50 (3) 

75 - 150 (1) 

500 (1) 

500 (2) 

50 - 200 (3) 

200 (2) 

200 (1) 

200 (3) 

50 - 100 (1) 

Surfactants 100 - 500 (4) 

Phenanthrene 

Phenol 

Toluene 

2,4,6 Trichlorophenol 

Pollutant Reported Range of Trickling Filter References* Inhibition Threshold Levels, mg/L 

Chromium (III) 3.5 - 67.6 (1) 

Cyanide 30 (1) 

Pollutant Reported Range of Nitrification 

Inhibition Threshold Levels, mg/L References* 

METALS/NONMETAL INORGANICS 

Arsenic 1.5 (2) 

Cadmium 5.2 (1), (2) 

Chloride 180 (4) 

Chromium (VI) 1 - 10 [as (CrO4 )

2-] (1) 

Chromium (T) 0.25 - 1.9 

1 - 100 

(trickling filter) 

(1), (2), (3) 

(1) 

Copper 0.05 - 0.48 (2), (3) 

Cyanide 0.34 - 0.5 (2), (3) 

Lead 0.5 (2), (3) 

Nickel 0.25 - 0.5 

5 

(2), (3) 

(1) 

Zinc 0.08 - 0.5 (2), (3) 

ORGANICS 

Chloroform 10 (2) 

2,4-Dichlorophenol 64 (3) 

2,4-Dinitrophenol 150 (2) 

Phenol 4 

4 - 10 

(2) 

(3) 

G-2
Pollutant 

Reported Range of Anaerobic 

Digestion Inhibition Threshold 

Levels, mg/L 

References* 

METALS/NONMETAL INORGANICS 

Ammonia 1500 - 8000 (4) 

Arsenic 1.6 (1) 

Cadmium 20 (3) 

Chromium (III) 130 (3) 

Chromium (VI) 110 (3) 

Copper 40 (3) 

Cyanide 4 - 100 

1 - 4 

(1) 

(2), (3) 

Lead 340 (3) 

Nickel 10 

136 

(2), (3) 

(1) 

Silver 13 - 65** (3) 

Sulfate 500 - 1000 (4) 

Sulfide 50 - 100 (4) 

Zinc 400 (3) 

ORGANICS 

Acrylonitrile 5 

5 

(3) 

(2) 

Carbon Tetrachloride 2.9 - 159.4 

10 - 20 

2.0 

(1) 

(3) 

(2) 

Chlorobenzene 0.96 - 3 

0.96 

(1) 

(2) 

Chloroform 1 

5 - 16 

10 - 16 

(2) 

(1) 

(3) 

1,2-Dichlorobenzene 0.23 - 3.8 

0.23 

(1) 

(2) 

1,4-Dichlorobenzene 1.4 - 5.3 

1.4 

(1) 

(2) 

Methyl chloride 3.3 - 536.4 

100 

(1) 

(2) 

Pentachlorophenol 0.2 

0.2 -

(2) 

(1) 

Tetrachloroethylene 20 (2) 

Trichloroethylene 1 - 20 

20 

20 

(1) 

(2) 

(3) 

Trichlorofluoromethane - (2) 

1.8 

* Total pollutant inhibition levels, unless otherwise indicated.

** Dissolved metal inhibition levels.

(1) Jenkins, D.I., and Associates. 1984. Impact of Toxics on Treatment Literature Review.

G-3
(2) Russell, L. L., C. B. Cain, and D.I. Jenkins. 1984. Impacts of Priority Pollutants on Publicly 

Owned Treated Works Processes: A Literature Review. 1984 Purdue Industrial Waste 

Conference. 

(3) Anthony, R. M., and L. H. Briemburst. 1981. Determining Maximum Influent Concentrations 

of Priority Pollutants for Treatment Plants. Journal Water Pollution Control Federation 

53(10):1457-1468. 

(4) U.S. EPA. 1986, Working Document; Interferences at Publicly Owned Treatment Works. 

September 1986. 

Source: EPA’s Guidance Manual on the Development and Implementation of Local Discharge 

Limitations Under the Pretreatment Program, December 1987, pp. 3-44 to 3-49. 

G-4
APPENDIX H -

CLOSED-CUP FLASHPOINTS FOR SELECT ORGANIC COMPOUNDS

Pollutant Closed Cup 

Flashpoint (/F) 

Acrolein -15 

Acrylonitrile 30 

Benzene 12 

Chlorobenzene 82 

Chloroethane (Ethyl chloride) -58 

1,1-Dichloroethane 2 

1,2-Dichloroethane (Ethylene dichloride) 56 

1,1-Dichloroethylene (Vinylidene chloride) -2 

Trans-1,2-Dichloroethylene, (1,2-Dichloroethylene) 36-39 

1,2-Dichloropropane (Propylene dichloride) 60 

Ethylbenzene 55 

Toluene 40 

Source: Online NIOSH Pocket Guide to Chemical Hazards at 

http://www.cdc.gov/niosh/npg/npg.html. 

H-1
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H-2
APPENDIX I -

DISCHARGE SCREENING LEVELS AND HENRY’S LAW CONSTANTS

FOR ORGANIC COMPOUNDS

Discharge Screening Levels Based on Explosivity 

Pollutant LELs(1) 

% volume / 

volume 

LELs 

(mol/m3

) 

Acrolein 2.8 1.15 

Acrylonitrile 

Benzene 

Chlorobenzene 1.3 

Chloroethane 3.8 

1,1-Dichloroethane 5.4 

1,2-Dichloroethane 6.2 

1,1-Dichloroethylene 6.5 

Trans-1,2-Dichloroethylene 5.6 

1,2-Dichloropropane 3.4 

Ethyl benzene 0.8 

Hydrogen Cyanide 5.6 

Hydrogen Sulfide 4.0 

Methyl bromide 10.0 

Methyl chloride 8.1 

Methylene Chloride 13.0 

Toluene 1.1 

1,1,2-Trichloroethane 6.0 

1,1,1-Trichloroethane 7.5 

3.0 

1.2 

Trichloroethylene 8.0 (F) 

Vinyl Chloride 3.6 

1.23 

0.49 

0.53 

1.55 

2.21 

2.54 

2.66 

2.29 

1.39 

0.33 

2.30 

1.64 

4.09 

3.31 

5.32 

0.45 

2.45 

3.07 

3.20 

1.47 

Henry's Law 

Constant 

(mol/m3

)/(mg/L) 

8.7E-05 

8.4E-05 

2.9E-03 

1.3E-03 

7.0E-03 

2.4E-03 

4.9E-04 

1.2E-02 

4.0E-03 

1.0E-03 

3.1E-03 

1.7E-4 

1.7E-2 

2.7E-03 

7.4E-03 

1.2E-03 

3.0E-03 

2.6E-04 

5.2E-03 

3.1E-03 

1.7E-02 

MW 

(g/mol) 

Discharge 

Screening 

Level (mg/L) 

56.1 13163 

53.1 14586 

78.1 169 

112.6 395 

65.5 222 

99 909 

99 5221 

97 215 

97 571 

113 1326 

106.2 106 

27 13529 

34 96 

95 1521 

50.5 450 

84.9 4307 

92.1 152 

133.4 9611 

133.4 591 

131.4 1029 

62.5 88 

Lower Explosive Limits (LELs) assumed for 25°C unless noted otherwise. 

MW = molecular weight 

Source: Updated in 2002 via the online NIOSH Pocket Guide to Chemical Hazards at 

http://www.cdc.gov/niosh/npg/npg.html 

I-1
Discharge Screening Levels Based upon Fume Toxicity 

Pollutant 

Exposure 

Limit* 

(mg/m3

) 

Henry's 

Law 

Constant 

(mg/m3

/ 

mg/L) 

Discharge 

Screening 

Level 

(mg/L) 

Acrolein 0.23 4.9 0.047 

Acrylonitrile 21.70 4.5 4.822 

Benzene 228.0 0.014 

Bromoform 5.17 22.8 0.227 

Carbon Tetrachloride 12.58 1185.0 0.011 

Chlorobenzene 345.75 151.0 2.290 

Chloroethane 2,640.00 449.0 5.880 

Chloroform 9.76 163.5 0.060 

Dichloroethane, 1,1- 405.00 240.4 1.685 

Dichloroethane,1,2- 8.10 48.1 0.168 

Dichloroethylene, 1,1- 19.80 1202.1 0.016 

Trans-Dichloroethylene,1,2- 794.00 389.3 2.040 

Dichloropropane,1,2 20 118.5 4.289 

Ethyl benzene 542.50 327.0 1.659 

Hydrogen Cyanide 5.17 4.5 1.149 

Hydrogen Sulfide 14.00 414.4 0.034 

Methyl bromide 77.80 255.5 0.305 

Methyl chloride 207.00 371.6 0.557 

Methylene Chloride 433.75 104.8 4.139 

Tetrachlorethane, 1,1,2,2- 34.35 18.6 1.847 

Tetrachloroethylene 678.00 717.1 0.945 

Toluene 565.50 272.5 2.075 

Trichloroethane, 1,1,2- 54.60 34.1 1.601 

Trichloroethane, 1,1,1 1,911.00 692.7 2.759 

Trichloroethylene 10.74 408.7 0.026 

Vinyl Chloride 12.80 1048.0 0.012 

3.19 

508.

Source 

TLV-STEL 

PEL-Ceiling, REL- Ceiling 

REL-STEL 

PEL-TWA, TLV-TWA, REL-TWA 

REL-STEL 

PEL-TWA 

PEL-TWA 

REL-STEL 

PEL-TWA, TLV-TWA, REL-TWA 

REL-STEL 

TLV-TWA 

PEL-TWA, TLV-TWA, REL-TWA 

TLV-STEL 

TLV-STEL, REL-STEL 

TLV-Ceiling, REL-STEL 

REL-Ceiling 

PEL-Ceiling 

TLV-STEL 

PEL-STEL 

PEL-TWA 

TLV-STEL 

REL-STEL 

PEL-TWA, TLV-TWA, REL-TWA 

REL-Ceiling 

REL-Ceiling 

PEL Ceiling 

*Exposure limits are lowest of acute toxicity data (NIOSH REL-STEL, ACGIH TLV-STEL, OSHA PELSTEL, NIOSH REL-Ceiling, ACGIH TLV-Ceiling, OSHA PEL-Ceiling) converted from ppm to mg/m3 

through conversion factor. If acute toxicity data were not available, the highest chronic exposure limit 

(NIOSH REL-TWA, ACGIH TLV-TWA, OSHA PEL-TWA) was used. See Appendix J of this manual 

for full list of acute and chronic exposure data. 

Discharge Screening Level = Exposure Limit / Henry’s Law Constant. 

I-2
Henry's Law Constants Expressed in Alternate Units 

Pollutant 

Henry's Law 

Constant(2) 

M/atm @ 298 K 

(25°C) 

Henry's Law 

Constant 

(atm m3

 / mol) 

Henry's Law 

Constant 

(mol/m3

 / mg/L) 

Henry's Law 

Constant 

(mg/m3

 / mg/L) 

Acrolein 8.2 0.00012 0.000087 4.9 

Acrylonitrile 0.00011 0.000084 4.5 

Benzene 0.0056 0.0029 228 

Bromoform 0.00056 0.000091 23 

Carbon Tetrachloride 0.029 0.0077 1185 

Chlorobenzene 0.27 0.0037 0.0013 151 

Chloroethane 0.089 0.011 0.007 449 

Chloroform 0.25 0.004 0.00137 164 

1,1-Dichloroethane 0.17 0.0059 0.0024 240 

1,2-Dichloroethane 0.85 0.0012 0.00049 48 

1,1-Dichloroethylene 0.034 0.029 0.012 1202 

Trans-1,2-Dichloroethylene 0.105 0.0095 0.004 389 

1,2-Dichloropropane 0.345 0.0029 0.001 119 

Ethyl benzene 0.125 0.008 0.0031 327 

Hydrogen Cyanide 9.3 0.00011 0.00017 4.5 

Hydrogen Sulfide 0.1 0.01 0.017 414.4 

Methyl bromide 0.16 0.0063 0.0027 256 

Methyl chloride 0.11 0.0091 0.0074 372 

Methylene Chloride 0.39 0.0026 0.0012 105 

1,1,2,2,-Tetrachlorethane 2.2 0.00045 0.00011 19 

Tetrachloroethylene 0.057 0.018 0.00432 717 

Toluene 0.15 0.0067 0.003 273 

1,1,2-Trichloroethane 1.2 0.00083 0.00026 34 

1,1,1-Trichloroethane 0.059 0.017 0.0052 693 

Trichloroethylene 0.1 0.01 0.0031 409 

Vinyl Chloride 0.039 0.026 0.017 1048 

9.15 

0.18 

1.8 

0.034 

Source: Compilation of Henry’s Law Constants for Inorganic and Organic Species of Potential 

Importance in Environmental Chemistry, R. Sanders 1999 (version 3). 

H (atm m3

/mol) = [986.9 * H (M/atm)]-1 

H (mg/m3

 / mg/L) = 40,893 * H(atm m3 / mol) 

H (mol/m3

 mg/L) = H (mg/m3 / mg/L) / (1000 * MW) 

MW = molecular weight in grams per mole 

I-3
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I-4
APPENDIX J -

OSHA, ACGIH AND NIOSH EXPOSURE LEVELS

EXPOSURE LIMITS FROM VARIOUS AGENCIES FOR VOLATILE ORGANIC PRIORITY 

POLLUTANTS 

OSHA Permissible 

Exposure Limits 

ACGIH Threshold 

Limit Values 

NIOSH 

Recommended 

Exposure Limits 

Volatile Organic 

Compounds 

mg/m3 

per ppm 

TWA 

ppm 

STEL 

ppm 

TVA 

ppm 

STEL 

ppm 

TWA 

ppm 

STEL 

ppm 

Acrolein 2.29 0.1 0.1 0.1 0.3 

Acrylonitrile 2.17 2 C 10 2 1 C 10 

Benzene 3.19 1 5 .5 2.5 0.1 1 

Bromoform 10.34 0.5 0.5 

Carbon Tetrachloride 6.29 10 C 25 5 10 2 

Chlorobenzene 4.61 75 

Chloroethane 

(Ethyl chloride) 2.64 1000 

Chloroform 4.88 C 50 10 2 

Dichloroethane, 1,1- 4.05 100 100 

Dichloroethane,1,2-

(Ethylene dichloride) 4.05 50 C 100 10 1 2 

Dichloroethylene, 1,1-

(Vinylidene chloride) 3.96 5 

transDichloroethylene,1,2-

(1,2-Dichloroethylene) 

3.97 200 200 200 

Dichloropropane,1,2-

(Propylene dichloride) 4.62 75 75 110 

Ethyl benzene 4.34 100 100 100 125 

Hydrogen Cyanide 1.10 10 C 4.7 4.7 

Hydrogen Sulfide 1.40 C 20 10 15 C 10 

Methyl bromide 3.89 C 20 1 

Methyl chloride 2.07 100 C 200 50 100 

Methylene Chloride 

(Dichloromethane) 3.47 25 125 50 

Tetrachlorethane, 

1,1,2,2- 6.87 5 

Tetrachloroethylene 

(Perchloroethylene) 6.78 100 C 200 25 100 

Toluene 3.77 200 C 300 50 100 150 

Trichloroethane, 1,1,2- 5.46 10 10 

Trichloroethane, 1,1,1 

(Methyl Chloroform) 5.46 350 350 450 350 

Trichloroethylene 5.37 100 C 200 50 100 25 C 2 

Vinyl Chloride 2.56 1 5 

C 

0.5 

10 

100 

100 

125 

1 

10 

C 

C 5 

J-1
Occupational Safety and Health Administration Permissible Exposure Limits (PELs) (29 CFR 1910.1000) 

PEL time-weighted average (TWA) concentrations must not be exceeded during any 8-hour workshift of 

a 40-hour workweek. PEL short-term exposure limit (STEL) must not be exceeded over a 15-minute 

period unless noted otherwise. PEL ceiling concentrations (designated by “C” preceding the value in the 

STEL column) must not be exceeded during any part of the workday; if instantaneous monitoring is not 

feasible, the ceiling must be assessed as a 15-minute TWA exposure. OSHA values were updated in 2002 

via the online NIOSH Pocket Guide to Chemical Hazards. http://www.cdc.gov/niosh/npg/npg.html. 

American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) 

TLV Time-weighted average (TVA) concentrations are for a conventional 8-hour workday and a 40-hour 

workweek for which it is believed that nearly all workers may be repeatedly exposed, day after day, 

without adverse effect. TLV short-term exposure limit (STEL) concentrations are the 15-minute TWA 

exposure which should not be exceeded at any time during a workday even if the 8-hour TWA is within 

the TLV-TWA. TLV ceiling concentrations (designated by a “C” preceding the value in the STEL 

column) should not be exceeded during any part of the working exposure. ACGIH values found in the 

ACGIH 2002 TLVs and BEIs. 

National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limits (RELs) 

REL time-weighted average (TWA) concentrations must not be exceeded over a 10-hour workday during 

a 40-hour workweek. REL short-term exposure limits (STELs) are a 15-minute TWA exposure that 

should not be exceeded at any time during a workday. A ceiling REL, designated by “C” preceding the 

value in the STEL column, should not be exceeded at any time. NIIOSH values updated in 2003 via the 

online NIOSH Pocket Guide to Chemical Hazards at http://www.cdc.gov/niosh/npg/npg.html. 

J-2
APPENDIX K -

LANDFILL LEACHATE LOADINGS

Landfill Leachate Monitoring Data* 

Maximum Pollutant Minimum Concentration 

(mg/L) 

Antimony

Arsenic

Barium

Cadmium

Chromium (T)

Copper

Cyanide

Iron

Lead

Manganese

Mercury

Nickel

Selenium

Silver

Zinc

Acetone

Benzene

Benzoic Acid

Chlorobenzene

Chloroethane

p-chloro-m-Cresol

1,4-Dichlorobenzene

1,1-Dichloroethane

1,2-Dichloroethane

Ethylbenzene

Methyl Butyl Ketone

Methyl Ethyl Ketone

4-Methylphenol

Naphthalene

N-Nitrosodiphenylamine

Pentachlorophenol

Phenol

Concentration (mg/L) 

INORGANICS 

0.008 

0.002 

<0.1 

< 0.001 

0.007 

0.007 

0.04 

1.5 

0.005 

0.63 

< 0002 

0.003 

< 002 

< 0.01 

< 01 

0.3 

0.13 

0.55 

1.25 

12.1 

10.87 

0.05 

4500 

9.8 

73.2 

0.002 

12.09 

0.02 

0.05 

58 

ORGANICS 

2.8 

< 0.002 

0.02 

0.011 

< 0.001 

0.018 

< 0.005 

< 0.001 

< 0.005 

0.017 

0.028 

5.3 

0.065 

< 0.01 

0.011 

0.016 

0.008 

2.8 

0.031 

< 0.4 

0.011 

< 0.1 

0.018 

< 0.4 

0.052 

6.8 

0.54 

0.16 

29 

0.065 

<0.4 

0.011 

0.016 

2.9 

Average Concentration 

(mg/L) 

0.142 

0.042 

0.201 

0.03 

0.633 

0.395 

0.029 

33.8 

0.156 

13.224 

0.002 

0.55 

0.01 

0.019 

12.006 

2.8 

0.025 

0.19 

0.011 

0.021 

0.018 

0.101 

0.002 

1.136 

0.171 

0.094 

13.633 

0.065 

0.113 

0.011 

0.016 

1.06 

K-1
Pollutant Minimum Concentration 

(mg/L) 

Toluene 

Trichloroethene 

1,1,1-Trichloroethane 

2,4-Dimethyl Phenol 

Diethyl Phthalate 

Dimethyl Phthalate 

Di-N-Butyl Phthalate 

Vinyl Acetate 

Vinyl Chloride 

0.0082 

< 0.001 

0.011 

0.005 

0.11 

0.0049 

0.0044 

0.25 

< 0.002 

Maximum 

Concentration (mg/L) 

1.6 

< 0.1 

0.022 

< 0.4 

0.11 

0.0049 

0.0044 

0.25 

0.21 

Average Concentration 

(mg/L) 

0.735 

0.025 

0.019 

0.107 

0.11 

0.0049 

0.0044 

0.25 

0.067 

* Number of detections/number of observations could not be determined from data provided. 

Source: U.S. EPA’s Supplemental Manual on the Development and Implementation of Local Discharge 

Limitations Under the Pretreatment Programs, May 1991, pp. 1-30 and 1-31. “Pollutant levels 

reported below specified detection limit were considered in the data analysis and, for the purpose 

of statistical analysis, were considered to be equal to the detection limit.” 

Most Common Landfill Leachates* 

Pollutant Concentration Range 

(parts per million) 

INORGANICS** 

Arsenic 0.0002 - 0.982 

Barium 0.11 - 5 

Cadmium 0.007 - 0.15 

Chloride 31 - 5,475 

Chromium (Total) 0.0005 - 1.9 

Copper 0.03 - 2.8 

Iron 0.22 - 2,280 

Lead 0.005 - 1.6 

Manganese 0.03 - 79 

Nickel 0.02 - 2.2 

Nitrate 0.01 - 51 

Sodium 12 - 2,574 

Sulfate 8 - 1,400 

ORGANICS*** 

1,1-Dichloroethane 0.004 - 44 

Trans-1,2-Dichloroethylene 0.002 - 4.8 

Ethylbenzene 0.006 - 4.9 

Methylene Chloride 0.002 - 220 

Phenol 0.007 - 28.8 

Toluene 0.006 - 18 

K-2
* Leachate data is compiled from a database of 70 MSWLFs [U.S. EPA 1988. Summary of Data on 

Municipal Solid Waste Landfill Leachate Characteristics-Criteria for Municipal Solid Waste 

Landfills (40 CFR Part 258) - Subtitle D of Resource Conservation and Recovery Act 

(Background Document)]. Washington, DC: Office of Solid Waste. 

** Leachate data from 62 landfills. 

*** Leachate data from 53 landfills. 

Source: U.S. EPA’s National Pretreatment Program Report to Congress, July 1991, p. 3-81. 

Contaminant Concentration Ranges in Municipal Leachate 

Pollutant 

Parameter 

George 

(1972) 

Chain

/DeWalle 

(1977) 

BOD 

pH 

TSS 

9 - 54,610 

3.7 - 8.5 

6 - 2,685 

Alkalinity 0 - 20,850 

Bicarbonate 

Chlorides 

COD 

Fluorides 

Hardness 0 - 22,800 

NH3-Nitrogen 0 - 1,106 

NO 

-Nitrogen 

34 - 2,800 

0 - 89,520 

Organic 

Nitrogen 

OrthoPhosphorus 

Sulfates 

Sulfide 

TOC 

TDS 

Total-KNitrogen 

Total 

Phosphorus 

Total Solids 

0 - 1,300 

1 - 1,826 

0 - 42,276 

0 - 1,416 

1 - 154 

Aluminum 

Arsenic 

Barium 

Beryllium 

81 - 33,360 2,200 -

720,000 

3.7 - 8.5 3.7 - 8.5 

10 - 700 13 - 26,500 

Metry/ 

Cross 

(1977) 

CONVENTIONAL 

Cameron 

(1978) 

Wisconsin 

Report 

(20 Sites) 

Sobotka 

Report 

(44 Sites) 

9 - 55,000 ND - 195,000 7 - 21,600 

3.7 - 8.5 5 - 8.9 5.4 - 8.0 

2 - 140,900 28 - 2,835 

NON-CONVENTIONAL 

0 - 20,850 310 - 9,500 0 - 20,900 ND - 15,050 0 - 7,375 

3,260 - 5,730 

4.7 - 2,467 47 - 2,350 34 - 2,800 2 - 11,375 120 - 5,475 

40 - 89,520 800 -

750,000 

0 - 9,000 6.6 - 97,900 440 - 50,450 

0 - 2.13 0 - 0.74 0.12 - 0.790 

0 - 22,800 35 - 8,700 0 - 22,800 52 - 225,000 0.8 - 9,380 

0 - 1,106 0.2 - 845 0 - 1,106 11.3 - 1,200 

0.2 - 1,0.29 4.5 - 18 0 - 5,0.95 

2.4 - 550 4.5 - 78.2 

6.5 - 85 0.3 - 136 0 - 154 

1 - 1,558 20 - 1,370 0 - 1,826 ND - 1,850 8 - 500 

0 - 0.13 

256 - 28,000 ND - 30,500 5 - 6,884 

584 - 44,900 100 - 51,000 0 - 42,300 584 - 50,430 1,400 -

16,120 

2 - 3,320 47.3 - 938 

0 - 130 ND - 234 

0 - 59,200 1,900 -

25,873 

METALS 

0 - 122 ND - 85 0.010 - 5.07 

0 - 11.6 ND - 70.2 0 - 0.08 

0 - 5.4 ND - 12.5 0.01 - 10 

0 - 0.3 ND - 0.36 0.001 - 0.01 

K-3
Pollutant 

Parameter 

George 

(1972) 

Chain 

/DeWalle 

(1977) 

Metry/ 

Cross 

(1977) 

Cameron 

(1978) 

Wisconsin 

Report 

(20 Sites) 

Sobotka 

Report 

(44 Sites) 

Boron 0.3 - 73 0.867 - 13 

Cadmium 0.03 - 17 0 - 0.19 ND - 0.04 0 - 0.1 

Calcium 5 - 4,080 60 - 7,200 240 - 2,570 5 - 4,000 200 - 2,500 95.5 - 2,100 

Total 

Chromium 

0 - 33.4 ND - 5.6 0.001 - 1.0 

Copper 0 - 9.9 0 - 9.9 0 - 10 ND - 4.06 0.003 - 0.32 

Cyanide 0 - 0.11 ND - 6 0 - 4.0 

Iron 0.2 - 5,500 0 - 2,820 0.12 - 1,700 0.2 - 5,500 ND - 1,500 0.22 - 1,400 

Lead 0 - 0.5 <0.10 - 2.0 0 - 5.0 0 - 14.2 0.001 - 1.11 

Magnesium 16.5 - 15,600 17 - 15,600 64 - 547 16.5 - 15,600 ND - 780 76 - 927 

Manganese 0.06 - 1,400 0.09 - 125 13 0.06 - 1,400 ND - 31.1 0.03 - 43 

Mercury 0 - 0.064 ND - 0.01 0 - 0.02 

Molybdenum 0 - 0.52 0.01 - 1.43 

Nickel 0.01 - 0.8 ND - 7.5 0.01 - 1.25 

Potassium 2.8 - 3,770 28 - 3,770 28 - 3,800 2.8 - 3,770 ND - 2,800 30 - 1,375 

Sodium 0 - 7,700 0 - 7,700 85 - 3,800 0 - 7,700 12 - 6,010 

Titanium 0 - 5.0 <0.01 

Vanadium 0 - 1.4 0.01 

Zinc 0 - 1,000 0 - 370 0.03 - 135 0 - 1,000 ND - 731 0.01 - 67 

All concentrations in mg/L, except pH (standard units). 

ND = Non-detect 

Source: U.S. EPA’s Technical Development Document for Proposed Effluent Limitations Guidelines and 

Standards for the Landfills Point Source Category, EPA 821-R-97-022, January 1998, Table 6-3. 

* Literature sources were: 

George, J. A., Sanitary Landfill-Gas and Leachate Control, the National Perspective, Office of Solid 

Waste Management Programs, U.S. EPA, 1972. 

Chian, E. S., and F. B. DeWalle, Evaluation of Leachate Treatment, Volume I, Characterization of 

Leachate, EPA-600/2-77-186a. 

Metry, A. A., and F. L. Cross, Leachate Control and Treatment, Volume 7, Environmental Monograph 

Series, Technomic Publishing Co., Westport, CT, 1977. 

Cameron, R. D., The Effect of Solid Waste Landfill Leachates on Receiving Waters, Journal AWWA, 

March 1978. 

McGinley, Paul M., and Peter Met. Formation, Characteristics, Treatment and Disposal of Leachate from 

Municipal Solid Waste Landfills, Wisconsin Department of Natural Resources Special Report, August 1, 

1984. 

Sobotka & Co., Inc., Case History Data Compiled and Reported to the U.S. Environmental Protection 

Agency Economic Analysis Branch, Office of Solid Waste, 1986. 

K-4
APPENDIX L -

HAULED WASTE LOADINGS

Septage Hauler Monitoring Data 

Pollutant Number of 

Detections 

Number of 

Samples 

Minimum 

Concentration 

(mg/L) 

Maximum 

Concentration 

(mg/L) 

Average

Concentration

(mg/L) 

INORGANICS 

144 145 0 3.5 0.141 

128 128 0.002 202 5.758 

825 1097 0.005 8.1 0.097 

931 1019 0.01 34 0.49 

16 32 < 0.003 3.45 0.406 

963 971 0.01 260.9 4.835 

575 577 0.001 1.53 0.469 

464 464 0.2 2740 39.287 

962 1067 < 0.025 118 1.21 

5 5 0.55 17.05 6.088 

582 703 0.0001 0.742 0.005 

813 1030 0.01 37 0.526 

237 272 < 0.003 5 0.099 

11 25 < 015 1 0.076 

959 967 < 0.001 444 9.971 

Arsenic

Barium

Cadmium

Chromium (T)

Cobalt

Copper

Cyanide

Iron

Lead

Manganese

Mercury

Nickel

Silver

Tin

Zinc

COD

Acetone

Benzene

Ethylbenzene

Isopropyl Alcohol

Methyl Alcohol

Methyl Ethyl Ketone

Methylene Chloride

Toluene 

Xylene 

NONCONVENTIONALS 

ORGANICS 

183 510 

118 

112 

115 

117 

117 

115 

115 

113 

87 

118 0 

112 0.005 

115 0.005 

117 1 

117 1 

115 1 

115 0.005 

113 0.005 

87 0.005 

183 117500 21247.951 

210 

3.1 

1.7 

391 

396 

240 

2.2 

1.95 

0.72 

10.588 

0.062 

0.067 

14.055 

15.84 

3.65 

0.101 

0.17 

0.051 

Source: U.S. EPA’s Supplemental Manual on the Development and Implementation of Local Discharge 

Limitations Under the Pretreatment Programs, 21W-4002, May 1991, pp. 1-27 and 1-28. 

“Pollutant levels reported below specified detection limit were considered in the data analysis 

and, for the purpose of statistical analysis, were considered equal to the detection limit.” 

L-1
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L-2
APPENDIX M -

HAZARDOUS WASTE CONSTITUENTS - RCRA APPENDIX VIII

Constituent CAS No. Hazardous 

Waste No. 

A2213 30558-43-1 U394 

Acetonitrile 75-05-8 U003 

Acetophenone 98-86-2 U004 

2-Acetylaminefluarone 53-96-3 U005 

Acetyl chloride 75-36-5 U006 

1-Acetyl-2-thiourea 591-08-2 P002 

Acrolein 107-02-8 P003 

Acrylamide 79-06-1 U007 

Acrylonitrile 107-13-1 U009 

Aflatoxins 1402-68-2 -

Aldicarb 116-06-3 P070 

Aldicarb sulfone 1646-88-4 P203 

Aldrin 309-00-2 P004 

Allyl alcohol 107-18-6 P005 

Allyl chloride 107-18-6 -

Aluminum phosphide 20859-73-8 P006 

4-Aminobiphenyl 92-67-1 -

5-(Aminomethyl)-3-isoxazolol 2763-96-4 P007 

4-Aminopyridine 504-24-5 P008 

Amitrole 61-82-5 U011 

Ammonium vanadate 7803-55-6 P119 

Aniline 62-53-3 U012 

Antimony 7440-36-0 -

Antimony compounds, N.O.S. - -

Aramite 140-57-8 -

Arsenic 7440-38-2 -

Arsenic compounds, N.O.S. - -

Arsenic acid 7778-39-4 P010 

Arsenic pentoxide 1303-28-2 P011 

Arsenic trioxide 1327-53-3 P012 

Auramine 492-80-8 U014 

Azaserine 115-02-6 U015 

Barban 101-27-9 U280 

Barium 7440-39-3 -

Barium compounds, N.O.S. - -

Barium cyanide 542-62-1 P013 

Bendiocarb 22781-23-3 U278 

Bendiocarb phenol 22961-82-6 U364 

Benomyl 17804-35-2 U271 

Benz[c]acridine 225-51-4 U016 

Benz[a]anthracene 56-55-3 U018 

Benzal chloride 98-87-3 U017 

Benzene 71-43-2 U019 

Benzenearsonic acid 98-05-5 -

Benzidine 92-87-5 U021 

Benzo[b]fluoranthene 205-99-2 -

Benzo[j]fluoranthene 205-82-3 -

Benzo(k)fluoranthene 207-08-9 -

Benzo[a]pyrene 50-32-8 U022 

p-Benzoquinone 106-51-4 U197 

Benzotrichloride 98-07-7 U023 

Benzyl chloride 100-44-7 P028 

Beryllium powder 7440-41-7 P015 

Beryllium compounds, not otherwise specified (NOS) - -

M-1
Constituent CAS No. Hazardous 

Waste No. 

Bis(pentamethylene)-thiuram tetrasulfide 120-54-7 -

Bromoacetone 598-31-2 P017 

Bromoform 75-25-2 U225 

4-Bromophenyl phenyl ether 101-55-3 U030 

Brucine 357-57-3 P018 

Butyl benzyl phthalate

Butylate

Cacodylic acid

Cadmium

85-68-7 -

2008-41-5 -

75-60-5 U136 

7440-43-9 -

Cadmium compounds, NOS 

Calcium chromate 

-

13765-19-0 

-

U032 

Carbofuran 

Carbofuran phenol 

Carbon disulfide 

Carbon oxyfluoride 

Carbon tetrachloride 

Carbosulfan 

Chloral 

Calcium cyanide 

Carbaryl 

Carbendazim 

592-01-8 P021 

63-25-2 U279 

10605-21-7 U372 

1563-66-2 P127 

1563-38-8 U367 

75-15-0 P022 

353-50-4 U033 

56-23-5 U211 

55285-14-8 P189 

75-87-6 U034 

305-03-3 U035 

57-74-9 U036 

Chlorambucil 

Chlordane 

Chlordane (alpha and gamma isomers) 

Chlorinated benzenes, NOS 

- U036 

- -

Chlorinated ethane, NOS 

Chlorinated fluorocarbons, NOS 

-

-

-

-

Chlorobenzene 

Chlorobenzilate 

p-Chloro-m-cresol

2-Chloroethyl vinyl ether

Chloroform

Chloromethyl methyl ether

beta-Chloronaphthalene

o-Chlorophenol

1-(o-Chlorophenyl)thiourea

Chloroprene

3-Chloropropionitrile

Chromium

Chromium compounds, NOS

Chrysene

Citrus red No. 2

Coal tar creosote

Copper cyanide

Copper dimethyldithiocarbamate

Creosote

Cresol (Cresylic acid)

Crotonaldehyde

m-Cumenyl methylcarbamate 

Cyanides (soluble salts and complexes), NOS - P030 

Cyanogen 460-19-5 P031 

Cyanogen bromide 506-68-3 U246 

Cyanogen chloride 506-77-4 P033 

Chlorinated naphthalene, NOS 

Chlorinated phenol, NOS 

Chlornaphazin 

Chloroacetaldehyde 

Chloroalkyl ethers, NOS 

p-Chloroaniline 

- -

- -

494-03-1 U026 

107-20-0 P023 

- -

106-47-8 P024 

108-90-7 U037 

510-15-6 U038 

59-50-7 U039 

110-75-8 U042 

67-66-3 U044 

107-30-2 U046 

91-58-7 U047 

95-57-8 U048 

5344-82-1 P026 

126-99-8 -

542-76-7 P027 

7440-47-3 -

- -

218-01-9 U050 

6358-53-8 -

8007-45-2 -

544-92-3 P029 

137-29-1 -

- U051 

1319-77-3 U052 

4170-30-3 U053 

64-00-6 P202 

M-2
Constituent CAS No. Hazardous 

Waste No. 

Cycasin 14901-08-7 -

1134-23-2 -

131-89-5 P034 

50-18-0 U058 

94-75-7 U240 

Cycloate

2-Cyclohexyl-4,6-dinitrophenol

Cyclophosphamide

2,4-D

2,4-D, salts, esters 

Daunomycin 

Dazomet 

- U240 

20830-81-3 U059 

533-74-4 -

72-54-8 U060 

72-55-9 -

50-29-3 U061 

2303-16-4 U062 

226-36-8 -

DDD 

DDE 

DDT 

Diallate 

Dibenz[a,h]acridine 

Dibenz[a,j]acridine 

Dibenz[a,h]anthracene 

7H-Dibenzo[c,g]carbazole 

Dibenzo[a,e]pyrene 

Dibenzo[a,h]pyrene 

Dibenzo[a,i]pyrene 

1,2-Dibromo-3-chloropropane 

Dibutyl phthalate 

224-42-0 -

53-70-3 U063 

194-59-2 -

192-65-4 -

189-64-0 -

189-55-9 U064 

96-12-8 U066 

84-74-2 U069 

95-50-1 U070 

541-73-1 U071 

o-Dichlorobenzene 

m-Dichlorobenzene 

p-Dichlorobenzene 

Dichlorobenzene, NOS 

106-46-7 U072 

25321-22-6 -

3,3’-Dichlorobenzidine 

1,4-Dichloro-2-butene 

91-94-1 U073 

764-41-0 U074 

Dichlorodifluoromethane 

Dichloroethylene, NOS 

1,1-Dichloroethylene 

1,2-Dichloroethylene 

Dichloroethyl ether 

Dichloroisopropyl ether 

Dichloromethoxy ethane 

Dichloromethyl ether 

2,4-Dichlorophenol 

2,6-Dichlorophenol 

Dichlorophenylarsine 

Dichloropropane, NOS 

Dichloropropanol, NOS 

Dichloropropene, NOS 

1,3-Dichloropropene 

Dieldrin 

75-71-8 U075 

25323-30-2 -

75-35-4 U078 

156-60-5 U079 

111-44-4 U025 

108-60-1 U027 

111-91-1 U024 

542-88-1 P016 

120-83-2 U081 

87-65-0 U082 

696-28-6 P036 

26638-19-7 -

26545-73-3 -

26952-23-8 -

542-75-6 U084 

60-57-1 P037 

1,2:3,4-Diepoxybutane

Diethylarsine

Diethylene glycol, dicarbamate

1,4-Diethyleneoxide

Diethylhexyl phthalate

N,N'-Diethylhydrazine

O,O-Diethyl S-methyl dithiophosphate

Diethyl-p-nitrophenyl phosphate

Diethyl phthalate

O,O-Diethyl O-pyrazinyl phosphoro- thioate

Diethylstilbesterol

Dihydrosafrole

Diisopropylfluorophosphate (DFP)

Dimethoate

1464-53-5 U085 

692-42-2 P038 

5952-26-1 U395 

123-91-1 U108 

117-81-7 U028 

1615-80-1 U086 

3288-58-2 U087 

311-45-5 P041 

84-66-2 U088 

297-97-2 P040 

56-53-1 U089 

94-58-6 U090 

55-91-4 P043 

60-51-5 P044 

3,3'-Dimethoxybenzidine 119-90-4 U091 

p-Dimethylaminoazobenzene 60-11-7 U093 

M-3
Constituent CAS No. Hazardous 

Waste No. 

7,12-Dimethylbenz[a]anthracene 57-97-6 U094 

119-93-7 U095 

79-44-7 U097 

57-14-7 U098 

540-73-8 U099 

122-09-8 P046 

105-67-9 U101 

3,3'-Dimethylbenzidine

Dimethylcarbamoyl chloride

1,1-Dimethylhydrazine

1,2-Dimethylhydrazine

alpha,alpha-Dimethylphenethylamine

2,4-Dimethylphenol

Dimethyl phthalate

Dimethyl sulfate

131-11-3 U102 

77-78-1 U103 

644-64-4 P191 

25154-54-5 -

Dimetilan 

Dinitrobenzene, NOS 

4,6-Dinitro-o-cresol 

4,6-Dinitro-o-cresol salts 

534-52-1 P047 

- P047 

2,4-Dinitrophenol 

2,4-Dinitrotoluene 

51-28-5 P048 

121-14-2 U105 

2,6-Dinitrotoluene 

Dinoseb 

606-20-2 

88-85-7 

U106 

P020 

Di-n-octyl phthalate 

Diphenylamine 

1,2-Diphenylhydrazine 

Di-n-propylnitrosamine 

Disulfiram 

117-84-0 U017 

122-39-4 -

122-66-7 U109 

621-64-7 U111 

97-77-8 -

298-04-4 P039 

541-53-7 P049 

115-29-7 P050 

145-73-3 P088 

72-20-8 P051 

- P051 

106-89-8 U041 

Disulfoton 

Dithiobiuret 

Endosulfan 

Endothall 

Endrin 

Endrin metabolites 

Epichlorohydrin 

Epinephrine 

EPTC 

51-43-4 P042 

759-94-4 -

Fluoroacetic acid, sodium salt

Formaldehyde

Formetanate hydrochloride

Formic acid

Formparanate

Glycidylaldehyde

U238 

P101 

-

U114 

U114 

U067 

U077 

U359 

P054 

U115 

U116 

U076 

U118 

U119 

P097 

-

206-44-0 U120 

7782-41-4 P056 

640-19-7 P057 

62-74-8 P058 

50-00-0 U122 

23422-53-9 P198 

64-18-6 U123 

17702-57-7 P197 

765-34-4 U126 

Ethyl carbamate (urethane)

Ethyl cyanide

Ethyl Ziram

Ethylenebisdithiocarbamic acid

Ethylenebisdithiocarbamic acid, salts and esters

Ethylene dibromide

Ethylene dichloride

Ethylene glycol monoethyl ether

Ethyleneimine

Ethylene oxide

Ethylenethiourea

Ethylidene dichloride

Ethyl methacrylate

Ethyl methanesulfonate

Famphur

Ferbam

51-79-6 

107-12-0 

14324-55-1 

111-54-6 

-

106-93-4 

107-06-2 

110-80-5 

151-56-4 

75-21-8 

96-45-7 

75-34-3 

97-63-2 

62-50-0 

52-85-7 

14484-64-1 

Fluoranthene 

Fluorine 

Fluoroacetamide 

M-4
Constituent CAS No. Hazardous 

Waste No. 

Halomethanes, NOS - -

Heptachlor

Heptachlor epoxide

Heptachlor epoxide (alpha, beta, and gamma isomers)

Heptachlorodibenzofurans

Heptachlorodibenzo-p-dioxins

Hexachlorobenzene

76-44-8 P059 

1024-57-3 -

- -

- -

- -

118-74-1 U127 

Hexachlorobutadiene 

Hexachlorocyclopentadiene 

Hexachlorodibenzo-p-dioxins 

Hexachlorodibenzofurans 

87-68-3 U128 

77-47-4 U130 

- -

- -

Hexachloroethane 

Hexachlorophene

Hexachloropropene

Hexaethyl tetraphosphate

Hydrazine

Hydrogen cyanide

Hydrogen fluoride

Hydrogen sulfide

Indeno[1,2,3-cd]pyrene

3-Iodo-2-propynyl n-butylcarbamate

Isobutyl alcohol

Isodrin

67-72-1 U131 

70-30-4 U132 

1888-71-7 U243 

757-58-4 P062 

302-01-2 U133 

74-90-8 P063 

7664-39-3 U134 

7783-06-4 U135 

193-39-5 U137 

55406-53-6 -

78-83-1 U140 

465-73-6 P060 

119-38-0 P192 

120-58-1 U141 

Isolan 

Isosafrole 

Kepone 

Lasiocarpine 

Lead 

143-50-0 U142 

303-34-1 U143 

7439-92-1 -

- -

301-04-2 U144 

7446-27-7 U145 

1335-32-6 U146 

58-89-9 U129 

Lead compounds, NOS 

Lead acetate 

Lead phosphate 

Lead subacetate 

Lindane 

Maleic anhydride 

Maleic hydrazide 

Malononitrile 

108-31-6 U147 

123-33-1 U148 

109-77-3 U149 

Manganese dimethyldithiocarbamate 15339-36-3 P196

Melphalan

Mercury

Mercury compounds, NOS

Mercury fulminate

Metam Sodium

148-82-3 U150 

7439-97-6 U151 

- -

628-86-4 P065 

137-42-8 -

Methacrylonitrile 126-98-7 U152

Methapyrilene 

Methiocarb 

91-80-5 U155 

2032-65-7 P199 

Methomyl 

Methoxychlor 

Methyl bromide 74-83-9 U029 

Methyl chloride 74-87-3 U045 

Methyl chlorocarbonate 79-22-1 U156 

Methyl chloroform 71-55-6 U226 

3-Methylcholanthrene 56-49-5 U157 

4,4’-Methylenebis(2-chloroaniline) 101-14-4 U158 

Methylene bromide 74-95-3 U068 

Methylene chloride 75-09-2 U080 

Methyl ethyl ketone (MEK) 78-93-3 U159 

Methyl ethyl ketone peroxide 1338-23-4 U160 

Methyl hydrazine 60-34-4 P068 

Methyl iodide 74-88-4 U138 

16752-77-5 P066 

72-43-5 U247 

M-5
Constituent CAS No. Hazardous 

Waste No. 

Methyl isocyanate 624-83-9 P064 

75-86-5 P069 

80-62-6 U162 

66-27-3 -

298-00-0 P071 

56-04-2 U164 

1129-41-5 P190 

2-Methyllactonitrile 

Methyl methacrylate 

Methyl methanesulfonate 

Methyl parathion 

Methylthiouracil 

Metolcarb 

Mitomycin C 

MNNG 

315-18-4 P128 

50-07-7 U010 

70-25-7 U163 

2212-67-1 -

Mexacarbate 

Molinate 

Mustard gas 

Naphthalene 

1,4-Naphthoquinone 

alpha-Naphthylamine 

beta-Naphthylamine 

alpha-Naphthylthiourea 

Nickel 

505-60-2 -

91-20-3 U165 

130-15-4 U166 

134-32-7 U167 

91-59-8 U168 

86-88-4 P072 

7440-02-0 -

Nickel compounds, NOS - -

Nickel carbonyl

Nickel cyanide

Nicotine

13463-39-3 P073 

557-19-7 P074 

54-11-5 P075 

- P075 

10102-43-9 P076 

100-01-6 P077 

98-95-3 U169 

10102-44-0 P078 

Nicotine salts 

Nitric oxide 

p-Nitroaniline 

Nitrobenzene 

Nitrogen dioxide

Nitrogen mustard

Nitrogen mustard, hydrochloride salt

Nitrogen mustard N-oxide

Nitrogen mustard, N-oxide, hydro- chloride salt

Nitroglycerin

p-Nitrophenol

2-Nitropropane

Nitrosamines, NOS

51-75-2 -

- -

126-85-2 -

- -

55-63-0 P081 

100-02-7 U170 

79-46-9 U171 

35576-91-1D -

N-Nitrosodi-n-butylamine 

N-Nitrosodiethanolamine 

924-16-3 

1116-54-7 

U172 

U173 

N-Nitrosodiethylamine 

N-Nitrosodimethylamine 

N-Nitroso-N-ethylurea 

N-Nitrosomethylethylamine 

N-Nitroso-N-methylurea 

N-Nitroso-N-methylurethane 

N-Nitrosomethylvinylamine 

N-Nitrosomorpholine 

N-Nitrosonornicotine 

55-18-5 U174 

62-75-9 P082 

759-73-9 U176 

10595-95-6 -

684-93-5 U177 

615-53-2 U178 

4549-40-0 P084 

59-89-2 -

16543-55-8 -

N-Nitrosopiperidine 100-75-4 U179

N-Nitrosopyrrolidine 

N-Nitrososarcosine 

930-55-2 U180 

13256-22-9 -

Octamethylpyrophosphoramide 

Osmium tetroxide 

99-55-8 U181 

152-16-9 P085 

20816-12-0 P087 

23135-22-0 P194 

5-Nitro-o-toluidine 

Oxamyl 

Paraldehyde 

Parathion 

123-63-7 U182 

56-38-2 P089 

Pebulate 

Pentachlorobenzene 

1114-71-2 -

608-93-5 U183 

- -

- -

Pentachlorodibenzo-p-dioxins 

Pentachlorodibenzofurans 

M-6
Constituent CAS No. Hazardous 

Waste No. 

Pentachloroethane 76-01-7 U184 

Pentachloronitrobenzene (PCNB)

Pentachlorophenol

Phenacetin

82-68-8 U185 

87-86-5 F027 

62-44-2 U187 

Phenol 108-95-2 U188

Phenylenediamine

Phenylmercury acetate

Phenylthiourea

Phosgene

Phosphine

Phorate

25265-76-3 -

62-38-4 P092 

103-85-5 P093 

75-44-5 P095 

7803-51-2 P096 

298-02-2 P094 

Phthalic acid esters, NOS 

Phthalic anhydride 

Physostigmine 

Physostigmine salicylate 

2-Picoline 

- -

85-44-9 U190 

57-47-6 P204 

57-64-7 P188 

109-06-8 U191 

Polychlorinated biphenyls, NOS -

Potassium cyanide

Potassium dimethyldithiocarbamate

Potassium n-hydroxymethyl-n-methyl-dithiocarbamate

Potassium n-methyldithiocarbamate

151-50-8 P098 

128-03-0 -

51026-28-9 -

137-41-7 -

7778736 -

506-61-6 P099 

2631-37-0 P201 

23950-58-5 U192 

Potassium pentachlorophenate 

Potassium silver cyanide 

Promecarb 

Pronamide 

1,3-Propane sultone

n-Propylamine

Propargyl alcohol

Propham

Propoxur

Propylene dichloride

1,2-Propylenimine

Propylthiouracil

Prosulfocarb

1120-71-4 U193 

107-10-8 U194 

107-19-7 P102 

122-42-9 U373 

114-26-1 U411 

78-87-5 U083 

75-55-8 P067 

51-52-5 -

52888-80-9 U387 

Pyridine 110-86-1 U196

Reserpine 

Resorcinol 

50-55-5 U200 

108-46-3 U201 

Selenium compounds, NOS 

Selenium dioxide 

81-07-2 U202 

- U202 

94-59-7 U203 

7782-49-2 -

- -

7783-00-8 U204 

7488-56-4 U205 

144-34-3 -

630-10-4 P103 

7440-22-4 -

- -

506-64-9 P104 

Saccharin 

Saccharin salts 

Safrole 

Selenium 

Selenium sulfide 

Selenium, tetrakis(dimethyl-dithiocarbamate) 

Selenourea 

Silver 

Silver compounds, NOS

Silver cyanide

Silvex (2,4,5-TP)

Sodium cyanide

Sodium dibutyldithiocarbamate

Sodium diethyldithiocarbamate

Sodium dimethyldithiocarbamate

Sodium pentachlorophenate

Streptozotocin

Strychnine

93-72-1 F027 

143-33-9 P106 

136-30-1 -

148-18-5 -

128-04-1 -

131522 None 

18883-66-4 U206 

57-24-9 P108 

- P108 

95-06-7 -

Strychnine salts 

Sulfallate 

M-7
Constituent CAS No. Hazardous 

Waste No. 

TCDD 1746-01-6 -

Tetrabutylthiuram disulfide 

1,2,4,5-Tetrachlorobenzene 

1634-02-2 -

95-94-3 U207 

Tetrachlorodibenzo-p-dioxins 

Tetrachlorodibenzofurans 

-

-

-

-

Tetrachloroethane, NOS 

1,1,1,2-Tetrachloroethane 

25322-20-7 -

630-20-6 U208 

2,3,4,6-Tetrachlorophenol

2,3,4,6-tetrachlorophenol, potassium salt

2,3,4,6-tetrachlorophenol, sodium salt

Tetraethyldithiopyrophosphate

Tetraethyl lead

Tetraethyl pyrophosphate

Tetramethylthiuram monosulfide

Tetranitromethane

79-34-5 U209 

127-18-4 U210 

58-90-2 F027 

53535276 -

25567559 -

3689-24-5 P109 

78-00-2 P110 

107-49-3 P111 

97-74-5 -

509-14-8 P112 

7440-28-0 -

- -

1314-32-5 P113 

563-68-8 U214 

1,1,2,2-Tetrachloroethane 

Tetrachloroethylene 

Thallium 

Thallium compounds, NOS 

Thallic oxide 

Thallium(I) acetate 

Thallium(I) carbonate 

Thallium(I) chloride 

Thallium(I) nitrate 

Thallium selenite 

6533-73-9 U215 

7791-12-0 U216 

10102-45-1 U217 

12039-52-0 P114 

Thallium(I) sulfate 

Thioacetamide 

7446-18-6 

62-55-5 

P115 

U218 

59669-26-0 U410 

39196-18-4 P045 

74-93-1 U153 

23564-05-8 U409 

Thiodicarb 

Thiofanox 

Thiomethanol 

Thiophanate-methyl 

Thiophenol 

Thiosemicarbazide 

108-98-5 P014 

79-19-6 P116 

Thiourea 62-56-6 U219 

Thiram 137-26-8 U244 

Tirpate 26419-73-8 P185 

Toluene 108-88-3 U220 

Toluenediamine 25376-45-8 U221 

Toluene-2,4-diamine 95-80-7 -

Toluene-2,6-diamine 823-40-5 -

Toluene-3,4-diamine 496-72-0 -

Toluene diisocyanate 26471-62-5 U223 

o-Toluidine 95-53-4 U328 

o-Toluidine hydrochloride 636-21-5 U222 

p-Toluidine 106-49-0 U353 

Toxaphene 8001-35-2 P123 

Triallate 2303-17-5 U389 

2,4,6-Tribromophenol 118-79-6 U408 

1,2,4-Trichlorobenzene 120-82-1 -

1,1,2-Trichloroethane 79-00-5 U227 

Trichloroethylene 79-01-6 U228 

Trichloromethanethiol 75-70-7 P118 

Trichloromonofluoromethane 75-69-4 U121 

2,4,5-Trichlorophenol 95-95-4 F027 

2,4,6-Trichlorophenol 88-06-2 F027 

2,4,5-T 93-76-5 F027 

M-8
Constituent CAS No. Hazardous 

Waste No. 

Trichloropropane, NOS 25735-29-9 -

1,2,3-Trichloropropane 96-18-4 -

Triethylamine 121-44-8 U404 

O,O,O-Triethyl phosphorothioate 126-68-1 -

1,3,5-Trinitrobenzene 99-35-4 U234 

Tris(1-aziridinyl)phosphine sulfide 52-24-4 -

Tris(2,3-dibromopropyl) phosphate 126-72-7 U235 

Trypan blue 72-57-1 U236 

Uracil mustard 66-75-1 U237 

Vanadium pentoxide 1314-62-1 P120 

Vernolate 1929-77-7 -

Vinyl chloride 75-01-4 U043 

Warfarin, concentrations less than 0.3% 81-81-2 U248 

Warfarin, concentrations greater than 0.3% 81-81-2 P001 

Warfarin salts, when present at concentrations 

less than 0.3%. - U248 

Warfarin salts, when present at concentrations greater 

than 0.3%. - P001 

Zinc cyanide 557-21-1 P121 

Zinc phosphide, when present at concentrations greater 

than 10%. 1314-84-7 P122 

Zinc phosphide, when present at concentrations of 10% 

or less. 1314-84-7 U249 

Ziram 137-30-4 P205 

Source: 40 CFR Part 261, Subpart D and Appendix VIII - Hazardous Constituents. 

M-9
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M-10
APPENDIX N -

STATISTICAL APPROACH TO DETERMINING SAMPLING

FREQUENCY

The use of statistical analyses can help establish an acceptable minimum number of samples needed to 

adequately represent a population of pollutants influent and effluent at an acceptable confidence level. 

The procedure for establishing an acceptable minimum number of samples is calculated using the 

technique described in: Statistical Methods for Environmental Pollution Monitoring (Gilbert, 1987). This 

text is frequently cited in environmentally related statistical work. The method utilizes Equation 1 to 

calculate the sample size required to estimate the true mean of a population, based on the coefficient of 

variation, a confidence level, and a relative error. The method assumes a normal distribution of samples. 

n = (Z1-"/20/dr)

2 

Where:

n = Sample size required for estimating the true mean, :

Z1-"/2 = Normal deviate of desired confidence level

0 = Coefficient of variation

dr = Relative error

The coefficient of variation is determined by Equation 2. 

0 = s /0

Where: 

s = Standard deviation

0 = Mean

The sample standard deviation is determined by Equation 3. 

Eq. 1 

Eq. 2 

Eq. 3 

The mean and standard deviation used above should be taken from an acceptable past available sample. Both 

an acceptable confidence level and an acceptable relative error must be selected, each of which will vary 

depending on the type of pollutant being measured. Selection of both levels should be determined by the 

POTW based on the situation. The confidence level expresses the certainty of the estimated mean while the 

relative error indicates the accuracy of the estimated mean compared to the true mean. 

Table 1-1 is an example matrix which applies Equation 1 to calculate sample size. 

N-1
Table 1-1. 

Confidence 

Level 

(1-") 

0.80 

(Z0.90 = 1.28) 

Relative 

Error 

Sample Sizes Required for Estimating the True Mean 

Coefficient of Variation (0) 

0.10 0.30 0.50 1.00 1.50 2.00 

2 15 41 164 369 656 

0.90 

(Z0.975 = 1.645) 

1083 

7 

11 

(dr) 

0.10 

0.25 - 3 7 27 59 105 

0.50 - 1 2 7 15 27 

1 - - - 2 4 

0.10 3 25 68 271 609 

0.25 - 4 11 44 98 174 

0.50 - 1 3 11 25 44 

1 - - 1 3 7 

As shown in Table 1-1, establishing the number of samples needed to estimate the true mean is critically 

dependent on a data set’s coefficient of variation (CV). 

For example, a past, reliable sample produced a data set with standard deviation of 2 mg/L and a mean of 2 

mg/L, resulting in CV equal to one. If a confidence level of 0.80 (with a corresponding Z1-"/2 = 1.28) and a 

relative error of 0.25 are determined to be adequate, then Equation 1 is used as follows: 

n = (1.28 * 1 / .25)2

 = 26.21 

The sample size must then be rounded to the next whole number, in this case, 27. The 27 samples may be 

taken throughout the year if desired, or as determined by the POTW. In the case of taking the samples 

throughout the year, the POTW might take two samples per month and an additional three samples at random 

times during the year. One sample may be evaluated for multiple contaminants; however, each location 

would need to be sampled independently. 

Under these conditions, there would be 80% confidence that the estimated mean from 27 samples (as 

illustrated in Table 1-1) would be within + 25% of the true mean. Therefore, if the estimated mean is 4 mg/L, 

there would be 80% confidence that the true mean is within the interval of 3 to 5 (i.e., 4 + 1). If a confidence 

level of 0.90 and relative error of 0.10 were desired, the number of samples would increase substantially. 

Under these conditions, there would be 90% confidence that the estimated mean from 271 samples (as 

illustrated in Table 1-1) would be within + 10% of the true mean. Therefore, if the estimated mean was 2 

mg/L, there would be 90% confidence that the true mean was within the interval of 1.8 to 2.2 (i.e., 2 + 0.2). 

Source: SAIC. 1998. POTW Metals Analysis Project, Task 3 Deliverable to U.S. EPA Region VIII, EPA, 

Contract No. 68-C4-0068; Work Assignment Number PS-3-1, SAIC Project Number 01-0833-08-

2696-800, August 25, 1998. 

N-2
APPENDIX O -

MINIMIZING CONTAMINATION IN SAMPLES

Some of the data reported as below the detection level (BDL) may be the result of the POTW sampling 

techniques and chosen analytical methods. With the need to accurately detect trace levels of pollutants, 

POTWs should thoroughly examine potential sources of gross and trace contamination and select analytical 

methods that can detect very low levels of pollutants. EPA has established new performance based1

 sampling 

and analysis methods (1600 series) for measuring 13 toxic metals in the low ppt to ppb range. While these 

methods were developed for ambient water quality monitoring, POTWs may apply some of the concepts in 

Method 1669, Sampling Ambient Water for Determination of Metals at EPA Water Quality Criteria Levels, 

to improve the reliability of data collected, potentially even utilizing analytical methods 1631, 1632, 1636-40. 

Excerpts from Section 4.2.2 of Method 1669 are provided below. 

Minimizing Contamination: Sampling Location, Sampling Equipment and Materials, and Chemicals: 

C Where possible, limit exposure of the sample and equipment in areas of higher contamination, e.g., 

downwind from the sludge beds. 

C Minimize contact with airborne dust, dirt, particulate matter, or vapors from automobile exhaust; 

cigarette smoke; nearby corroded or rusted bridges, pipes, poles, or wires; nearby roads; and even 

human breath. Areas where nearby soil is bare and subject to wind erosion should be avoided. 

C Clean the sampling equipment and minimize the time between cleaning of equipment and use. 

C Use metal-free equipment, i.e., equipment should be nonmetallic and free of material that may 

contain metals of interest. When it is not possible to obtain equipment that is completely free of the 

metal(s) of interest, the sample should not come into direct contact with the equipment. 

C Do not use sampling equipment where there are indications that it may not be clean, e.g., sampler 

tubing or collection bottle is stained, has not been changed out in some time, was used to collected 

a sample of a slug load that hit the WWTP, etc. 

C Avoid contamination by carryover. Contamination may occur when a sample containing low 

concentrations of metals is processed immediately after a sample containing relatively high 

concentrations of these metals. 

C Where possible, do not collect, process, or ship samples containing high concentrations of metals 

(e.g., untreated effluents, in-process waters, landfill leachates) at the same time as samples being 

collected for trace metals determinations. 

C Wear clean, non-talc dusted gloves during all operations involving handling of equipment, samples, 

and blanks. Change gloves once they have become contaminated. 

1

An alternate procedure or technique may be used so long as neither samples nor blanks are contaminated when 

following alternate procedures. 

O-1
C Fluoropolymer (FEP, PTFE), 

conventional or linear 

polyethylene, polycarbonate, 

polysulfone, polypropylene, or 

ultrapure quartz are the 

preferred materials for coming 

in contact with samples. 

Fluoropolymer or glass 

containers are preferred for 

samples that will be analyzed 

for mercury because mercury 

vapors can diffuse in or out of 

other materials, resulting either 

in contamination or low-biased 

results. 

Lot Analyses of Metals in Different Grades of Nitric Acid 

(SOURCE-FISHER-INTERNET) 

Highest Grade Higher Grade High Grade 

Antimony <0.01 ppb <0.1 ppb 

Arsenic <0.1 ppb <0.3 ppb #4 ppb 

Cadmium <0.005 ppb <0.1 ppb 

Chromium <0.03 ppb #9 ppb #100 ppb 

Copper #0.05 ppb <1 ppb #50 ppb 

Lead #0.01 ppb <0.3 ppb #100 ppb 

Mercury <0.1 ppb <0.5 ppb 

Nickel #0.1 ppb <1 ppb #50 ppb 

Selenium <0.5 ppb 

Silver <0.005 ppb <0.1 ppb 

C The following materials have been found to contain trace metals: Pyrex, Kimax, methacrylate, 

polyvinyl chloride, nylon, Vycor, highly colored plastics, paper cap liners, pigments used to mark 

increments on plastics, and rubber. It is recommended that these materials not be used to hold 

liquids that come in contact with the sample or must not contact the sample. 

C Use an appropriate grade of chemicals when prepping equipment/materials and chemically 

preserving samples. 

Quality Control: 

C Serial numbers should be indelibly marked or etched on each piece of Apparatus so that 

contamination can be traced, and logbooks should be maintained to track the sample from the 

container through the sampling process to shipment to the laboratory. Chain-of-custody procedures 

should be used so that contamination can be traced to particular handling procedures or lab 

personnel. 

C Equipment blanks should be periodically generated and analyzed to identify contamination that may 

result from improper preparation or handling of sampling equipment and bottles in the laboratory. 

Equipment blanks include processing reagent water (i.e., water known not to contain pollutants at 

detectable levels) through sampling equipment and sample bottle(s) prior to taking the equipment 

or bottle(s) to the field. 

C A trip blank should be periodically generated and analyzed to identify incidental contamination that 

may occur to sampling equipment/bottles while in transit to and from the sampling location. 

Essential, reagent water is place in a sample bottle prior to going to the field. 

C Field blanks should be periodically generated and analyzed to identify contamination that may occur 

to sampling equipment/bottles while in the field. Like equipment blanks, it involves process reagent 

water through the sampling equipment/bottle. 

O-2
APPENDIX P -

METHODS FOR CALCULATING REMOVAL EFFICIENCY

There are three methods of calculating removal efficiencies: average daily removal efficiency (ADRE) 

method, mean removal efficiency (MRE) method, and the decile approach. 

ADRE across a plant is defined as: 

Where: 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

I n = POTW g/L 

Epotw, n = POTW 

n = Paired observations, numbered 1 to N 

As defined in Equation 5.2, the MRE across a plant is defined as: 

Where: 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

Ir = POTW g/L 

Epotw, t = POTW g/L 

t = Plant effluent samples, numbered 1 to T 

r = Plant influent samples, numbered 1 to R 

It is important to realize that the portion of the pollutant removed through a treatment process is transferred 

to another wastestream, typically the sludge. For conservative pollutants, such as metals, all the pollutant 

from the influent ends up in either the effluent or the sludge. ple, a 93% overall plant removal 

means that 93% of the cadmium in the influent is transferred to the sludge, while 7% remains in the effluent 

wastewater. 

1. REVIEW OF THE DATA SET AND EXCLUSION OF CERTAIN DATA 

A good first step in determining removal efficiencies is to review the data set. identify any 

data values that are extremely high or low. e isolated extreme values, there are formal statistical 

procedures that can be applied to evaluate whether a value can be classified as an “outlier” relative to the rest 

of the data set. ethods most widely used to make this determination are described in the following two 

paragraphs. 

If the data is known to closely follow a normal distribution, then any data point that lies more than two 

standard deviations from the mean is considered an outlier. Consider, for example, the DRE data values 

As defined in Equation 5.1, the 

influent pollutant concentration at headworks , m

effluent pollutant concentration 

influent pollutant concentration at headworks, m

effluent pollutant concentration, m

For exam

This review can 

If there ar

Two m

P-1
located in Table 1 of this appendix, and assume that this data is from a normal distribution. The 15 

observations have a mean of 52.69 and a standard deviation of 34.65. Using this method, any data point that 

lies outside of the range -16.61 to 121.99, or 52.69 ± 2*34.65, can be considered an outlier. In this case, one 

value, -20.25, falls outside of the range and can be determined to be an outlier. 

However, the DRE data values do not approximate a “bell-shaped” normal distribution. In this case, outliers 

can be determined based on the interquartile range (IQR) of the data set. First, order the data from smallest 

to largest and locate the data points that fall at the 25th percentile (also referred to as the first quartile or Q1), 

and the 75th percentile (also referred to as the third quartile or Q3). The IQR is equal to the value of the 

observation at Q3 minus the value of the observation at Q1. Any data point that lies more than 1.5 times this 

IQR below Q1, or above Q3, is considered an outlier. Again, consider the data in Table 1, but now make no 

assumptions about the distribution of the population from which the sample was taken. The Q1 and Q3 of 

this data set are located at 38.04 and 78.5 respectively. Based on these values, the IQR is equal to 40.46 (78.5 

- 38.04). Any value that falls below -22.65 (38.04 - 1.5*40.46), or above 139.19 (78.5 + 1.5*40.46), can be 

considered an outlier. In this case, there are no values that fall outside of the range and, consequently, no 

values should be determined to be outliers. 

Both of these methods are meant to determine any values that may be candidates for exclusion from the data 

set. Data exclusion should be performed only if technical justification exists to support such action (e.g., poor 

removals due to temporary maintenance or operational problems or known sampling problems). For 

example, if an examination of the data set shows that an unusually high influent value is from the same 

sampling day/event as an unusually high effluent value, this occurrence of corresponding extreme values 

should be investigated to determine if the data values can be explained by technical or operational problems 

not related to treatment system performance (e.g., maintenance, repair, or sampling problems). If this is the 

case, dropping the data pair from the data set may be appropriate. 

Review of the data may also show patterns such as increasing effluent values over time. If a similar pattern 

is not observed for the influent values, this will generate a pattern of decreasing DREs over time. A graph 

or plot of DRE against sampling day/event (in order from first to most recent sample) can help identify such 

trends. This may alert the POTW to operational problems that should be investigated. A plot can also 

highlight unusually low DREs that call for further review, such as checking laboratory quality control samples 

to determine if blank or duplicate samples indicate anything out of the ordinary. If abnormalities are found 

in laboratory QA/QC (quality assurance/quality control) data, the POTW may consider excluding the affected 

values from the data set. 

Table 1 contains an example data set of 15 influent and effluent sample pairs for zinc. The influent and 

effluent concentrations have been converted to loadings using the POTW flows for the sample days. The 

influent and effluent concentrations may be used instead of converting to loadings. Whether loadings or 

concentrations are used will likely have little impact on the results of the ADRE and decile approaches. 

Influent and effluent flows are probably similar (if not the same) for a data pair and therefore will have little 

effect on the relative size of the influent and effluent values, so DREs will change little. However, converting 

to loadings may have a noticeable impact on the MRE method if a POTW has high variability in its flows. 

Because influent and effluent loadings for high flow days will increase more relative to influent and effluent 

loadings for low flow days, the net effect is to give greater weight to the removal rates on those days with 

high flows. If the POTW has high variability in its flows, it should evaluate whether its removal rates tend 

to go up and down in relation to flow. If so, the POTW should consider calculating an MRE using both 

concentrations and loadings and evaluating which is more appropriate. 

P-2
1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Table 1. Removal Efficiency Example 

Sample 

Day Date 

Influent Load 

(lbs/day) 

Effluent Load 

(lbs/day) 

DRE 

(%) 

3/4/99 518.22 111.41 78.50 

3/5/99 163.98 173.99 -6.10 

3/6/99 110.15 97.64 11.36 

3/7/99 1739.93 474.41 72.73 

3/8/99 266.48 320.45 -20.25 

4/15/99 170.48 105.15 38.32 

5/11/99 473.16 132.67 71.96 

5/12/99 314.19 148.96 52.59 

5/13/99 306.68 132.69 56.73 

5/14/99 232.57 92.63 60.17 

5/15/99 226.52 72.60 67.95 

6/15/99 533.25 98.87 81.46 

7/1/99 141.43 87.63 38.04 

7/15/99 1166.77 103.90 91.10 

8/1/99 2301.00 97.88 95.75 

Average 577.65 150.06 52.69 

Review of the data shows that: 

C The data set does not require removal of outliers. 

C The three particularly high influent values (sample days 4, 14, and 15) all have 

DREs of more than 70%, so the high influent values do not appear to make the data 

candidates for elimination. 

C There are two effluent values (sample days 4 and 5) that are significantly higher than 

the others. For one, the corresponding influent value is also high and the DRE is 

73%. For the other day, the DRE is negative (-20%) because the influent value is 

relatively low. These results are from samples taken on two consecutive days 

(March 7 and March 8), which may indicate that the POTW treatment system was 

experiencing some operational difficulties or interference at the time. The POTW 

should investigate the matter to determine if there are valid reasons for dropping 

these data from the removal calculations data set. 

C There are two negative DREs (one for March 8) calculated from the influent and 

effluent data pairs. They occurred three days apart and may indicate temporary 

operational problems, so the POTW should investigate the matter (as noted above). 

A plot of the data may help the POTW identify any data concerns that should be investigated. Based on the 

review of data for this example, it was determined that no justification exists for excluding any of the data 

from the data set. 

2. CALCULATION OF REMOVAL EFFICIENCIES 

Once the data set has been reviewed, the POTW can proceed to calculating removal efficiencies. The 

following sections describe each of the methods for calculating removal efficiencies and perform the 

calculations using the example data set in Table 1. 

P-3
2.1 Average Daily Removal Efficiency (ADRE) 

The ADRE is calculated by first calculating a DRE for each pair of influent and effluent values (i.e., an 

influent value and an effluent value from the same sampling day/event are used to calculate a DRE). This 

set of DREs is then averaged to determine the ADRE for a pollutant. Use of the ADRE method requires that 

a POTW only use data for the sampling days/events for which it has both an influent and an effluent value, 

and the influent value is greater than zero. 

Example 

For the example data set in Table 1, the ADRE is calculated as: 

ADRE = [78.5+(-6.1)+11.36+72.73+(-20.25)+38.32+71.96+52.59+56.73+60.17+67.95+81.46+38.04 

+91.10+95.75)]/15 = 52.69% 

2.2 Mean Removal Efficiency (MRE) 

The MRE is calculated by using the same formula as for the DRE (shown at the beginning of the Appendix), 

but instead of using individual influent and effluent values from sampling days/events, the set of influent 

values is first averaged to determine the average influent value and the same is done for the set of effluent 

values (either concentrations or loadings). These average values are then used in the DRE equation to result 

in the MRE for a pollutant. Unlike the ADRE method, the MRE method does not require paired influent and 

effluent values from the same sampling days/events. The MRE can be based on influent and effluent sample 

values that are not always paired (e.g., one effluent sample is lost or destroyed, so the influent average is 

based on one more value than the effluent average). However, the POTW should use caution in building the 

data sets for calculating influent and effluent averages because if too many unpaired values are used the 

removal efficiencies may be meaningless because the influent data and effluent data may represent different 

time periods, and treatment plant conditions do vary over time. 

Example 

For the example data set in Table 1, the MRE is calculated as: 

Average of the influent values = 577.65 lbs/day 

Average of the effluent values = 150.06 lbs/day 

MRE = 100*(577.65-150.06)/577.65 = 74.02% 

2.3 Comparison of Results from ADRE and MRE Methods 

Note that the MRE (74.02%) is higher than the ADRE (52.69%). The three days with the highest influent 

loadings have relatively high DREs and the two negative DREs (Day 2 and Day 5) occur on days with values 

that are not significantly greater than the other days. In the ADRE calculation, each day/DRE is given the 

same weight as the others, while the MRE method gives greater weight to the days with greater loadings. 

This means that the high removals on the days with high influent loadings affect the MRE more than the other 

days do, leading to a higher MRE, while the negative values do not have as great an impact because they 

occur on days with less elevated influent and effluent values If each DRE were to be weighted by its 

proportion of the total loading, the result would be the same as with the MRE method. 

P-4
Usually, the MRE and ADRE are slightly different from each other, and can be quite different (as in the 

example presented here). The POTW can calculate both and decide if one of the estimates is the most 

appropriate for use in AHL calculations. The POTW can also use the decile approach to determine 

representative removal efficiencies. 

2.4 Decile Approach 

The decile approach, unlike the above methods, considers how often the actual DRE will be above or below 

a specified removal rate, thereby taking into account the variability of POTW removal efficiencies over time. 

The decile approach involves putting the set of DREs (calculated using the formula presented at the beginning 

of this appendix) in order from least to greatest and then determining nine decile values. Each decile is the 

value below which a certain percentage of the DREs fall. For example, the first decile is the value below 

which 10% of the DREs fall. Similarly, the second decile is the value below which 20% of the DREs fall, 

on up to the ninth decile, which is the value below which 90% of the DREs fall. The fifth decile is the median 

and half of the DREs fall below this number. To apply the decile approach, a minimum of nine DREs are 

required. If exactly nine DREs are available, the nine estimated deciles are simply the nine DREs. If more 

then nine DREs are used, the POTW needs to calculate the nine decile estimates. 

Tables 2 and 3 below illustrate use of the decile approach for the example zinc data set. The steps are: 

C Step 1: Take the set of DREs and put the values in order from smallest to largest (see Table 2). 

C Step 2: The entries for Column 1 are obtained by performing the two calculations. First, define the 

location for the first decile and then calculate the next eight multiples of that location value to 

determine the location for the second through ninth deciles. The first location is determined by the 

equation: (N+1)/10, where N = the number of data pairs/DREs used. For the example data set, N=15, 

so the location for the first decile is (15+1)/10 = 1.6. The location for the second decile is 2 x 1.6 = 

3.2, the location for the third decile is 3 x 1.6 = 4.8, and so on up to the ninth decile of 9 x 1.6 = 14.4. 

(Column 1 in Table 3) 

C Step 3: For each decile, take the whole number part of the value in Column 1 and place it in Column 

2 (e.g., the first decile is 1.6, so the whole number part is 1; the fourth decile is 6.4, so the whole 

number part is 6). 

C Step 4: The entries in Column 3 of Table 3 are taken from the ordered list of DREs in Table 2. The 

whole number values in Column 2 correspond to the entry in the ordered list in Table 2 [e.g., the 

whole number part for the first decile is 1, so entry 1 (-20.25%) from Table 2 is the correct value and 

is placed in Column 3 of Table 3; similarly, the fourth decile whole number part is 6, so value 6 

(52.59%) is placed in Column 3 of Table 3 for the fourth decile]. 

C Step 5: Following a similar procedure as in Step 4, values for Column 4 are taken from Table 2 and 

place in Table 3, except that this time the values taken from Table 2 are the ones that immediately 

follow the Column 3 entries [e.g., for the first decile, the value placed in Column 4 is -6.10, which 

is value 2 (the value immediately after value 1) from Table 2; for the fourth decile, the value placed 

in Column 4 is 56.73, which is value 7 from Table 2]. 

C Step 6: Fill in Column 5 by subtracting Column 3 from Column 4 and entering the result. 

C Step 7: Similar to the process for filling Column 2 (explained in Step 3) of Table 3, place the decimal 

part of the Column 1 entries in Column 6 of Table 3 (e.g., for the first decile, use 0.6; for the fourth 

decile, use 0.4). 

P-5
C Step 8: Fill in Column 7 by multiplying the values in Column 5 by the values in Column 6 and 

entering the result. 

C Step 9: Add Column 3 and Column 7 and enter the result in Column 8 of Table 3. These values are 

the estimated deciles. 

Table 2. Set of DREs Sorted in Ascending Order 

1 3 10 11 12 13 14 15 

-20.25 -6.1 11.36 38.04 38.32 52.59 56.73 60.17 67.95 71.96 72.73 78.50 81.46 91.10 95.75 

2 4 5 6 7 8 9 

Table 3. Decile Approach for Zinc Example 

Deciles Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Column 8 

1st 1.6 1 -20.25 -6.10 14.15 0.6 8.490 -11.76 

2nd 3.2 3 11.36 38.04 26.68 0.2 5.336 16.70 

3rd 4.8 4 38.04 38.32 0.28 0.8 0.224 38.26 

4th 6.4 6 52.59 56.73 4.14 0.4 1.656 54.25 

5th 8.0 8 60.17 67.95 7.78 0 0.000 60.17 

6th 9.6 9 67.95 71.96 4.01 0.6 2.406 70.36 

7th 11.2 11 72.73 78.50 5.77 0.2 1.154 73.88 

8th 12.8 12 78.50 81.46 2.96 0.8 2.368 80.87 

9th 14.4 14 91.10 95.75 4.65 0.4 1.860 92.96 

The main value of the decile approach is that it provides an estimate of how often a POTW is expected to 

exceed certain removal values, such as the ADRE and MRE. For the example, the ADRE is 53% and the 

MRE is calculated as 74%. If the POTW uses either one of these values, what amount of the time will its 

removal efficiency exceed those values? This can be estimated using the decile approach. The ADRE of 

53% falls between the third and fourth deciles (38.26% and 54.25%, respectively), meaning that the actual 

removal efficiency is estimated to exceed the ADRE 60% to 70% of the time [(e.g., the third decile means 

that 30% of the time values will fall below that value (38.26% in this case)]. The MRE of 74% lies between 

the seventh and eight deciles (73.88% and 80.87%, respectively), so the POTW is estimated to exceed the 

MRE 20% to 30% of the time. 

In developing local limits, appropriate removal efficiencies must be selected for calculation of AHLs for each 

pollutant. POTWs have often selected a pollutant’s ADRE for local limits calculations. EPA recommends 

that POTWs consider using the decile approach or the MRE method because they better account for 

variabilities in removal efficiencies over time. For example, because a higher removal efficiency means more 

pollutant is removed to the sludge, if the POTW used the ADRE from the above example (which is likely 

exceeded 60% to 70% of the time) to calculate an AHL to protect sludge quality, the resulting AHL may not 

be adequately protective. More pollutant will likely be removed to the sludge 60% to 70% of the time, so 

loadings in the sludge will higher than was estimated in the AHL calculations and may lead to exceedances 

of sludge disposal standards. 

A different approach that may address this concern is to use one decile for AHL calculations to protect sludge 

quality (for sludge disposal and for sludge digester inhibition for conservative pollutants) and a different 

decile for AHL calculations for protection against Pass Through concerns (e.g., NPDES permit limits). For 

example, a POTW can base its sludge quality-based AHLs on the seventh decile removal which means that 

greater removals to sludge and hence greater sludge loadings would be estimated to occur 30% of the time. 

P-6
Similarly, the POTW can use the third decile for calculating its water quality-based AHLs because lower 

removals (and hence higher effluent loadings) would be estimated to occur about 30% of the time. 

use of these deciles estimates that AHLs would be exceeded 30% of the time, in reality this is not highly 

likely. If the entire AHL is allocated to IUs, all IUs would have to discharge at their maximum allowed level 

to reach the AHL. the removal achieved is greater than the seventh decile, more loading would go 

to the sludge than is provided for with the AHL. me IUs discharge at below their allocated loadings, 

which is very likely at any given time, the likelihood of exceeding the allowed loading to the sludge is much 

lower. 

3. NON-CONSERVATIVE POLLUTANTS 

The above discussion of removal efficiency calculations applies to conservative pollutants (e.g., metals). 

However removal efficiencies for non-conservative pollutants can be used to calculate AHLs based on Pass 

Through criteria (e.g., biological process inhibition data, NPDES permit limits) and the guidance above can 

be used for non-conservative pollutants only in these cases. Conservative pollutant removal efficiencies are 

determined by pollutant concentrations in the POTW influent and effluent streams. ption applied 

to conservative pollutants (that removed pollutants are exclusively transferred to the POTW’s sludge streams) 

cannot be extended to non-conservative pollutants because losses through degradation and volatilization do 

not contribute to pollutant loadings in sludge. efore, non-conservative pollutant removal efficiencies 

cannot be used in deriving AHLs from criteria/standards applicable to the POTW’s sludge streams (e.g., 

digester inhibition, sludge disposal). 

Equation 5.13, -conservative pollutants, based on criteria for sludge digester 

inhibition, is: 

Where: 

AHLdgstr = AHL based on sludge digestion inhibition, lb/day 

Linfl = POTW influent loading, lb/day 

Cdgstinhib = Sludge digester inhibition criterion, mg/L 

Cdgstr = Existing pollutant level in sludge, mg/L 

The equation can be rewritten as: 

Where the factor Cdgstr/Linfl is a partitioning factor that relates the pollutant level in the POTW sludge, Cdgstr, 

to the headworks loading of the pollutant, Linfl. ation of an allowable 

loading based upon sludge digestion inhibition, AHLdgstr, from a sludge digester inhibition criteria, Cdgstinhib, 

for a non-conservative pollutant. ine the partitioning factor for a particular pollutant, the POTW’s 

influent and sludge must be routinely sampled for that pollutant. 

Although 

Then if 

If so

The presum

Ther

for calculating AHLs for non

The partitioning factor enables calcul

To determ

P-7
The factor Cdgstr/Linfl expresses non-conservative pollutant removals to sludge. Non-conservative pollutant 

removals to sludge are highly variable, and are dependent on such factors as wastewater temperature, ambient 

air temperature, biodegradation rates (which are temperature dependent), aeration rates, and POTW influent 

flow. Because non-conservative pollutant removals to sludge are highly variable, the variability in nonconservative pollutant sludge partitioning factors should be addressed in the local limits development process. 

The procedures and recommendations presented in this manual for addressing removal efficiency variability 

for conservative pollutants (e.g., the calculation of mean removals and the decile approach) can be extended 

to addressing variability in non-conservative pollutant sludge partitioning factors. In calculating sludge 

AHLs, the sludge partitioning factor should be used in place of the removal efficiency for non-conservative 

pollutants. 

P-8
APPENDIX Q -

METHODS FOR HANDLING DATA BELOW DETECTION LEVEL

The occurrence of values below the detection limit (DL) in environmental data sets is a major statistical 

complication. Uncertainty about the actual wastewater treatment plant influent and effluent values below the 

DL can bias subsequent statistical analyses to determine the removal efficiencies. 

The various approaches to handling below detection level (BDL) data can be broken into three main 

categories: 

C Regression order statistic (ROS) and probability plotting (MR) methods 

C Maximum likelihood estimation (MLE) methods 

C Simple replacement of a single value (e.g., detection limit or one half detection limit). 

Although this discussion focuses on handling data below the detection limit, the same techniques can be 

applied to those data below the minimum level of quantitation (ML) as well. These methods can be applied 

by those without a background in statistics. However, EPA strongly recommends a statistician perform these 

data manipulations. 

REGRESSION ORDER STATISTIC (ROS) AND PROBABILITY PLOTTING (MR) METHODS 

Both the original ROS and the MR methods are based on ordered statistics of observed data and the 

assumption that data come from a normal or log-normal distribution. If Y is from a normal distribution with 

mean : and standard deviation F (Y ~ N(:,F)) and Z is from a normal distribution with mean 0 and standard 

deviation 1 (Z ~ N(0, 1)), statistical theories show that Y = :+ F Z when Y and Z are at the same percentiles 

in their respective distributions. For a given observation (sampling result) Y that is above the detection limit, 

we can calculate the “order statistic”, i.e., the proportion of observations that are less than Y. This order 

statistic of Y is an estimate of the percentile. The corresponding Z value is available by either using existing 

computer program or checking the normal distribution table. In other words, we have a list of observations 

that are above the detection limit (Y1, Y2, ..., Ym) and a list of Z values (Z1, Z2, ..., Zm) that are of the same 

percentiles as the respective Y values. By performing a regression analysis of Y against Z, the resulting 

intercept and slope are estimates of the mean and standard deviation of the distribution of Y. 

When the data are from a log-normal

2 distribution, a log transformation is needed before the regression. The 

estimated mean and standard deviation is for the log-transformed variable. To convert the estimates to the 

original metric, the standard log-normal distribution results should be used. For example, if Y is from a lognormal distribution, and estimated mean and variance for log(Y) are : and F, the mean of Y is and the 

+  variance of Y is e2μ σ2 



 e

σ2 

− 1

 .  

Alternatively, one may use the regression equation to “fill in” the missing (BDL) values. This is possible 

because we can calculate the order statistics for all BDL values. For example, suppose we have 20 out of 100 

observations are BDL. The order statistics for the 20 BDL values are 0.01, 0.02, ..., 0.20. Using these order 

statistics, we can get the corresponding Z values Z1, Z2, ..., Z20. Substitute these Z values into the regression 

model, we have the 20 fill-in Y values. 

2

 Log-normal distributions are probability distributions which are closely related to normal distributions: if X is a 

normally distributed random variable, then exp(X) has a log-normal distribution. In other words: the natural logarithm of a 

log-normally distributed variable is normally distributed. 

Q-1 
To recap, we first define the variables used in this method: 

n = Total number of observations 

k = Number of BDL observations 

Yi

= Value of the ith ranked observation 

To utilize the ROS method, data are first ranked from smallest to largest so that Yn is the largest data value 

and Y1 through Yk are the unknown BDL values. If an approximately normal distribution is expected, each 

Yi

 is plotted on the y-axis against the expected normal order statistic Zi for each rank i. The following linear 

regression is used to obtain : and F, using only the points above the DL (i.e., i = k+1,...,n). 

Yi = :+ F Zi 

One may use the estimated intercept and slope as the mean and standard deviation. Alternatively, one may 

use the above equation to obtain appropriate “fill-in” values for each of the k BDLs using the Z-statistic. The 

mean and standard deviation are then calculated using traditional formulas applied to both the observed and 

filled-in data. Thus, the estimated data are based on the assumption of normality, while the observed data 

are used directly with no assumption about their distribution. This method is relatively robust to departures 

from normality or lognormality (Gilliom and Helsel 1986). 

If a distribution is expected to be skewed, then log(Yi

) is plotted against Zi and the fitted data and the observed 

data are transformed back to original units from which the mean and standard deviation are calculated 

(Gilliom and Helsel 1986). Transformation of the data, rather than the summary statistics, avoids inherent 

transformation bias (Helsel 1990). 

MR METHOD 

The MR method, an extension of the ROS method, accounts for multiple detection limits. When there is only 

one detection limit, the k-BDL values are assigned order statistics of 1 through k. When there are multiple 

detection limits, it is not obvious how to assign the order statistic for some of the data, both below or above 

some detection limits. For example, suppose we have the following five observations: <100, 110, <200, 250, 

and 300. It is obvious that the two largest observations, 250 and 300 should receive order statistics of 4 and 

5. But the rest is not clear, because the value labeled as <200 can be 199 or 9. Helsel and Cohn (1988) 

developed a plotting position method for assigning order statistics when there are multiple detection limits. 

The idea is that although we don’t know exactly where the value, say <200, should fall, we can lay out all 

possible positions for this particular value and take the average rank of all possible ranks. For example, the 

value labeled as <200 can be the smallest (rank 1), the second smallest (rank 2), or the third smallest (rank 

3), the average rank is (1+2+3)/3 = 2. The value 110 can be the second smallest or the third smallest, 

therefore a rank of (2+3)/2 = 2.5. Finally, the observation <100 receives a rank of (1+2)/2=1.5. Once the 

order statistics are assigned, one may use the same regression analysis method in the ROS method. When 

there is only one detection limit, the MR method is the same as the ROS method. 

Helsel and Cohn (1988) found that if a single estimating method for several descriptive statistics is desired 

and the sampling distribution of a data set is unknown, the MR method should be utilized. The actual plotting 

procedure for the MR method is detailed in Appendix B of Estimation of Descriptive Statistics for Multiple 

Censored Water Quality Data (Helsel and Cohn, 1988). 

Q-2
MAXIMUM LIKELIHOOD ESTIMATION (MLE) METHOD 

The MLE method is based on a specific probabilistic assumption about the observations. For example, 

suppose the data we observed (Y1, Y2, ..., Yn) are from a normal distribution with unknown mean and standard 

deviation. The likelihood of observing a specific value, say Yi

, is calculated by the normal distribution density 

function: 

(Yi −μ )

2 

( ) = 

2πσ 

1 

e 

− 2σ2

L Yi 

The likelihood for a BDL value is: 

  2 

e 

− 1 

2

2 2 

πσ 

σ

 X − μ 



DL

L Y( ) = ∫ dX k −∞ 

The likelihood of observing all the data (Y1, Y2, ..., Yn), both below and above the detection limit is the product 

of all individual likelihoods. The likelihood of observing all data is a very complicated function of : and F. 

A different set of : and F values will lead to a different likelihood value. The maximum likelihood estimator 

is the pair of : and F values that maximize the likelihood function. Because the likelihood function is often 

very complicated, computation of the MLE method is difficult. 

Gilliom and Helsel (1986) found that the ROS and the MR methods appear to be more robust to departures 

from distributional assumptions. 

MLE methods have been shown to have the smallest mean-squared error (i.e., higher accuracy) of available 

techniques when the data distribution is exactly normal or lognormal (Harter and Moore 1966). However, 

simulation results indicate that ROS and MR methods are superior when distribution shape population is 

unknown (Gilliom and Helsel 1986). 

In a simulation study by Newman et al. (1989) comparing mean and standard deviation estimates between 

MLE and ROS, the results were similar. However, the MLE method provided slightly more accurate results 

when BDL values comprised less than 30 percent of the data set, while ROS methods provided slightly more 

accurate results when BDL values represented 30 percent or more. 

SIMPLE SUBSTITUTION METHODS 

Simple substitution methods simply replace the below detection value with another value, such as zero, the 

detection limit, or one-half the detection limit. Both ROS and MLE methods offer substantial advantages 

over most simple replacement methods (Gilbert 1987, Gleit 1985, Helsel and Gilliom 1986, Newman et 

al.1989). 

In general, replacement methods result in a greater bias when calculating the mean or standard deviation. 

Additionally, their relative performance worsens as the proportion of BDLs increases (Gilliom and Helsel 

1986). Helsel (1989) reasons that because large differences may occur in the resulting estimates for any given 

population, and because the choice of the replacement value is essentially arbitrary without some knowledge 

of instrument readings below the reporting limit, estimates resulting from simple substitution are not 

defensible. 

Q-3
CONCLUSION 

The MR method is most applicable for use in local limits development because of the data set’s multiple 

detection limits and unknown parent distribution. Additionally, the MR method is recommended when the 

data set contains a relatively high percentage of BDL values. 

Further information on statistical methods can be found in the literature listed below. 

LITERATURE REVIEW LIST/REFERENCES 

Gilliom and Helsel 1986. Estimation of distribution parameters for censored trace level water quality data: 

1 Estimation techniques. Water Resources Research 22:135-146. 

Gleit 1985. Estimation for small normal data sets with detection limits. Environmental Science Technology 

19:1201-1206. 

Harter and Moore 1966. Local-Maximum-Likelihood estimation of the parameters of three-parameter 

lognormal populations from complete and censored samples. Journal of American Statistical Association 

61:842-851. 

Helsel, D. R. 1990. Less Than Obvious: Statistical treatment of data below the detection limit. 

Environmental Science and Technology 24:1766-1774. 

Helsel and Cohn 1988. Estimation of Descriptive Statistics for Multiple Censored Water Quality Data. 

Water Resources Research 24:1997-2004. 

Newman, Dixon, Looney, and Pinder 1989. Estimating the mean and variance for environmental samples 

with below detection limit observations. Water Resources Bulletin 25:905-916. 

Porter, Ward, and Bell 1988. The Detection Limit: Water quality monitoring data are plagued with levels 

of chemicals that are too low to be measured precisely. Environmental Science Technology Vol. 22, No. 8. 

Travis and Land. 1990. Estimating the Mean of Data Sets with Nondetectable Values. Environmental 

Science Technology Vol. 24, No. 7. 

Q-4
ATTACHMENT - DESCRIPTION OF THE MR METHOD 

Method: 

(1) If an analytical result is reported as ND (to be referred to as a nondetect), set the result ci

 = 1. 

Annotate the result with a “<” and consider this observation to be “< a detection limit.” 

(2) Divide the observations into two groups: Nondetects, those observations annotated with a “<” sign, 

and detects. 

(3) Let m = number of distinct detection limits. 

(4) Let Aj

 = number of detected observations at or above the jth detection limit (j = 1,...,m) and below 

the next highest detection limit. 

(5) Let Bj

 = number of detected and nondetected observations below the jth detection limit (j = 1,...,m). 

(6) Let pe,j = pe,j+1 + (Aj

/[Aj + Bj])(1 - pe,j+1), and solve iteratively for j = m,m-1,...,2,1. By convention, 

pe,m+1 = 0. 

(7) Determine plotting positions, p(i), for detected observations as: 

p(i) = (1 - pe,j) + (pe,j - pe,j+1)@r/(Aj

 + 1), where r is the rank of the ith observation above the jth 

detection limit. If detected observations are “tied,” arbitrarily order the “tied” observations before 

assigning ranks. Whether the “tied” observations are arbitrarily ordered or assigned the same midrank (average of the corresponding ranks) is expected to be of negligible importance. If detected 

observations are present below the lowest detection limit, assume the “0th detection limit” is 0, and 

consequently pe,0 = 1. 

(8) Assign plotting positions, pc(i), for nondetected observations as: 

pc(i) = (1- pe,j)@r/(Cj

 + 1), r = 1,...,Cj. Cj is the number of nondetected values known only to be less 

than the jth detection limit (j = 1,...m). The formula for Cj

 is: Cj = Bj - (Aj-1 + Bj-1), where A0 = B0 

= 0. Plotting positions are therefore assigned separately within the j groups of nondetects (j=1,...,m). 

(9) Perform a simple linear regression using only the detected observations. The natural logarithm of 

the detected observations (zi

 = ln(yi)) is the dependent variable, and the normal quantile associated 

with the corresponding plotting position (M-1(p(i))) is the independent variable, where M-1(@) is the 

normal quantile. 

^ ^ ^ (10) Use the estimated regression line (zi

 = b0 + b1@M-1(pc(i))) to “fill in” (using the terminology of Helsel 

and Cohn) estimated natural logarithm values for nondetected observations, based on the normal 

quantile associated with the calculated plotting position (pc(i)). 

(11) Calculate a natural log mean (:^) and log standard deviation (F^) of the detected and “filled in” 

observations using the formulas below. Assume zi

 = ln(yi), where zi represents the natural logarithm 

of detected observations where available, and "filled in" estimated natural logarithm values where 

nondetects were observed. 

Q-5
(1)

(2) 

(12) Use the values of :

^ and F^ to estimate a 90th percentile using a lognormal distribution: 90 = exp (:^ 

+ 1.282@F

^ ). 

An example of the MR method is given below. 

Comments: 

Although the algorithm for determining plotting positions when multiple detection limits are present 

appears rather cumbersome, as described in the 12-step process above, the process of fitting a regression line 

to order statistics is well-established as a method for determining parameters of a distribution. 

method utilizes plotting positions to “spread” nondetected observations along a continuum, rather than simply 

substituting an arbitrary value for each nondetected measurement. 

values to be “spread out” rather than all fixed at a single point, as would be the case with simple substitution 

methods. 

The MR method described above directly mimics the methods of Helsel and Cohn. 

article by Helsel and Cohn contains an inaccurate formula for Cj

, which has been revised above. 

the article did not address ties in detected observations and detected observations below the lowest detection 

limit. 

At least two detected observations are necessary to estimate a regression line. , this 

procedure is not useful when 0 or only 1 detected observation is present. 

Software which utilizes the MR method to compute summary statistics is available. The feasibility 

of utilizing the software available at this site for implementation among numerous POTWs must be explored 

further. For example, the software is restrictive in some ways, such as the format of data which can be 

processed. 

Reference: 

Helsel, D.R., and T.A. Cohn. Estimation of Descriptive Statistics for Multiple Censored Water Quality 

Data. Water Resources Research 24:1997-2004. 

P

The ROS 

In practice, one would expect nondetected 

However, the 

In addition, 

These questions have been addressed in Steps 7 and 9 above. 

Consequently

1988. 

Q-6
EXAMPLE OF THE MR METHOD 

Suppose we have a set of data from multiple sources with varying detection limits. When combined, the data 

set is ordered as follow: 

Data Summary 

<50 <200 <400 100 300 500 

<50 <200 <400 100 300 500 

<50 <200 <400 700 

1000 

1200 

In order to provide estimates of the mean and standard deviation, it is necessary to fill-in the non-detected 

values. Once the non-detected values are filled-in, sample mean and standard deviation can be estimated. The 

following are the MR steps for filling in the nondetected values. 

1. Summary statistics: 

n = 18

m = 3 (1st detection limit = 50, 2nd detection limit = 200, 3rd detection limit = 400)

A1 = 2 (2 detects $50 but <200)

A2 = 2 (2 detects $200 but <400)

A3 = 5 (5 detects $400)

B1 = 3 (3 nondetects <50)

B2 = 8 (3 nondetects <50, 3 nondetects <200, and 2 detects <200)

B3 = 13 (3 nondetects <50, 3 nondetects <200, 3 nondetects <400, 2 detects <200, and 2 detects <400)

C1 = 3 (3 nondetects <50)

C2 = 3 (3 nondetects <200)

C3 = 3 (3 nondetects <400)

pe,3 = pe,4 + (A3/[A3 + B3])(1 - pe,4) = 0 + (5/[5+13])@1 = 0.278

pe,2 = pe,3 + (A2/[A2 + B2])(1 - pe,3) = 0.278 + (2/[2+8])@(1-0.278) = 0.422

pe,1 = pe,2 + (A1/[A1 + B1])(1 - pe,2) = 0.422 + (2/[2+3])@(1 - 0.422) = 0.653

Q-7
-----------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------

 2. Determination of plotting positions: 

Nondetected observations: 

Plotting Position 

xi j r pe,j Cj pc(i) = (1- pe,j)@r/(Cj + 1) 

<50 1 1 0.653 3 0.087 

<50 1 2 0.653 3 0.173 

<50 1 3 0.653 3 0.260 

<200 2 1 0.422 3 0.144 

<200 2 2 0.422 3 0.289 

<200 2 3 0.422 3 0.433 

<400 3 1 0.278 3 0.181 

<400 3 2 0.278 3 0.361 

<400 3 3 0.278 3 0.542 

Detected observations: 

Plotting Position 

xi j r pe,j pe,j+1 Aj p(i) = (1 - pe,j) + (pe,j - pe,j+1)@r/(Aj

 + 1) 

100 1 1 0.653 0.422 2 0.424 

100 1 2 0.653 0.422 2 0.500 

300 2 1 0.422 0.278 2 0.626 

300 2 2 0.422 0.278 2 0.674 

500 3 1 0.278 0 5 0.769 

500 3 2 0.278 0 5 0.815 

700 3 3 0.278 0 5 0.861 

1000 3 4 0.278 0 5 0.907 

1200 3 5 0.278 0 5 0.954 

3. Linear regression 

A simple linear regression is then performed using the following detected observations and their 

associated plotting points. The regression is based on zi as the dependent variable and p(i) as the independent 

variable. 

xi zi

 = ln(xi) p(i) M-1(p(i)) 

100 4.605 

100 4.605 

300 5.704 

300 5.704 

500 6.215 

500 6.215 

700 6.551 

1000 6.908 

1200 7.090 

0.424 -0.192 

0.500 0.000 

0.626 0.321 

0.674 0.451 

0.769 0.736 

0.815 0.896 

0.861 1.085 

0.907 1.323 

0.954 1.685 

Q-8
------------------------------------------------------------------------

The regression equation based on these nine detected observations is: 

^ zi

 = 4.9614 + 1.4186@M-1(p(i)) 

4. Fill-in 

This equation is used to “fill in” estimated nondetect values for the nine nondetects above. The results of the 

calculation are shown below: 

^ pc(i) M-1(pc(i)) zi 

<50 0.087 

<50 0.173 

<50 0.260 

<200 0.144 

<200 0.289 

<200 0.433 

<400 0.181 

<400 0.361 

<400 0.542 

-1.360 3.032 

-0.942 3.625 

-0.643 4.049 

-1.063 3.453 

-0.556 4.173 

-0.169 4.722 

-0.912 3.668 

-0.356 4.456 

0.106 5.112 

^ The z ^ 2 are shown below: 

4.605 5.704 6.551 3.032 3.453 3.668 

4.605 6.215 6.908 3.625 4.173 4.456 

5.704 6.215 7.090 4.049 4.722 5.112 

i

 and the zi from the two tables above are then combined to estimate a natural log mean and a log ^ standard deviation. The data and calculated values for : and F

^ : = 4.9937 ^ F

^ 2 = 1.5632 (F = 1.2503) 

^ ^ The calculated values for : and F can then be used for estimating the arithmetic mean of the sample: m = exp( 

^

: + 0.5 F

^ 2) = 322.241 and sample standard deviation s = m eσ$2 

− 1 = 626.168. In some instances, one may ^ be interested in the 90th percentile of the data, which can be estimated as P90 = exp (: + 1.282@F

^ ) = 732.585. 

It is worthwhile to note that these calculations are based on the assumption that the data follow a log-normal 

distribution. For most water quality related variables, such as BOD concentration, the log-normal distribution 

is appropriate. However, when percent removal is the variable of concern, log-normal is no longer an 

appropriate probability distribution. Instead, one may apply the MR method to the concentration variables 

first and calculate the percent removal after the non-detected concentration values have been filled-in. 

Q-9

xi 
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Q-10
APPENDIX R -

PRIORITY POLLUTANT REMOVAL EFFICIENCIES

Priority Pollutant Removal Efficiencies (%) Through Primary Treatment* 

Priority Pollutant Median Number of POTWs with 

Removal Data** 

METAL/NONMETAL INORGANICS 

Cadmium 15 6 of 40 

Chromium 27 12 of 40 

Copper 22 12 of 40 

Cyanide 27 12 of 40 

Lead 57 1 of 40 

Mercury 10 8 of 40 

Nickel 14 9 of 40 

Silver 20 4 of 40 

Zinc 27 12 of 40 

ORGANICS 

Benzene 25 8 of 40 

Chloroform 14 11 of 40 

1,2-trans-Dichloroethylene 36 9 of 40 

Ethylbenzene 13 12 of 40 

Naphthalene 44 4 of 40 

Phenol 8 11 of 40 

Butyl benzyl phthalate 62 4 of 40 

Di-n-butyl phthalate 36 3 of 40 

Diethyl phthalate 56 1 of 40 

Tetrachloroethylene 4 12 of 40 

1,1,1-Trichloroethane 40 10 of 40 

Trichloroethylene 20 12 of 40 

* Pollutant removals between POTW influent and primary effluent. From Fate of Priority Pollutants 

in Publicly Owned Treatment Works, Volume I (EPA 440/1-82/303), U.S. Environmental Protection 

Agency, Washington, D.C., September 1982, p. 61. 

** Median removal efficiencies from a data base of removal efficiencies for 40 POTWs. Only POTWs 

with average influent concentrations exceeding three times each pollutant’s detection limit were 

considered. 

Source: U.S. EPA’s Guidance Manual on the Development and Implementation of Local Discharger 

Limitations Under the Pretreatment Program, December 1987, p. 3-55. 

R-1
Priority Pollutant Percent Removal Efficiencies (%) Through Activated Sludge Treatment* 

Priority Pollutant Range 

METALS/NONMETAL INORGANICS** 

Arsenic 11-78 

Cadmium 25-99 

Chromium 25-97 

Copper 2-99 

Cyanide 3-99 

Lead 1-92 

Mercury 1-95 

Nickel 2-99 

Selenium 25-89 

Silver 17-95 

Zinc 23-99 

31 

33 

68 

67 

41 

39 

50 

25 

33 

50 

64 

ORGANICS** 

44 

50 

50 

50 

67 

36 

40 

37 

75 

47 

50 

39 

39 

76 

50 

80 

75 

75 

67 91 

80 96 

67 83 

67 91 

86 97 

62 77 

78 90 

68 86 

90 98 

72 87 

67 92 

64 87 

62 90 

86 95 

80 93 

93 98 

85 94 

89 98 

Anthracene 29-99 

Benzene 25-99 

Chloroform 17-99 

1,2-trans-Dichloroethylene 17-99 

Ethylbenzene 25-99 

Methylene chloride 2-99 

Naphthalene 25-98 

Phenanthrene 29-99 

Phenol 3-99 

Bis (2-ethylhexyl) phthalate 17-99 

Butyl benzyl phthalate 25-99 

Di-n-butyl phthalate 11-97 

Diethyl phthalate 17-98 

Pyrene 73-95 

Tetrachloroethylene 15-99 

Toluene 25-99 

1,1,1-Trichloroethane 18-99 

Trichloroethylene 20-99 

Second 

Decile Median Eight 

Decile 

Number of POTWs 

with Removal Data 

45 53 5 of 26 

67 91 19 of 26 

82 91 25 of 26 

86 95 26 of 26 

69 84 25 of 26 

61 76 23 of 26 

60 79 20 of 26 

42 62 23 of 26 

50 67 4 of 26 

75 88 24 of 26 

79 88 26 of 26 

5 of 26

18 of 26

24 of 26

17 of 26

25 of 26

26 of 26

16 of 26

6 of 26

19 of 26

25 of 26

16 of 26

19 of 26

15 of 26

2 of 26

26 of 26

26 of 26

23 of 26 

25 of 26 

* Pollutant removals between POTW influent and secondary effluent (including secondary clarification).

Based on a computer analysis of POTW removal efficiency data (derived from actual POTW influent and 

effluent sampling data) provided in U.S. EPA’s Fate of Priority Pollutants in Publicly Owned Treatment

Works, Volume II (EPA 440/1-82/303), September 1982. 

** For the purpose of deriving removal efficiencies, effluent levels reported as below detection were set equal

to the reported detection limits. All secondary activated sludge treatment plants sampled as part of the 

study were considered. 

Source: U.S. EPA’s Guidance Manual on the Development and Implementation of Local Discharger Limitations 

Under the Pretreatment Program, December 1987, p. 3-56. 

R-2
Priority Pollutant Removal Efficiencies (%) Through Trickling Filter Treatment* 

Priority Pollutant 

Cadmium

Chromium

Copper

Cyanide

Lead

Mercury

Nickel

Silver

Zinc

Benzene

Chloroform

1,2-trans-Dichloroethylene

Ethylbenzene

Methylene chloride

Naphthalene

Phenol

Bis (2-ethylhexyl) phthalate

Butyl benzyl phthalate

Di-n-butyl phthalate

Diethyl phthalate

Tetrachloroethylene

Toluene

1,1,1-Trichloroethane 

Trichloroethylene 

Range Second 

Decile Median Eighth 

Decile 

Number of POTWs 

with Removal Data 

METALS/NONMETAL INORGANICS** 

93 6 of 11 

71 9 of 11 

89 9 of 11 

79 8 of 11 

70 6 of 11 

62 9 of 11 

7 9 f 1 o 1

86 8 of 11 

81 9 of 11 

5

33-96 

5-92 

12-97 

7-88 

4-84 

14-80 

7-72 

11-93 

14-90 

33 68 

34 55 

32 61 

33 59 

25 55 

33 50 

1 9 

38 66 

34 67 

1 2

ORGANICS** 

5-98 

21-94 

14-99 

45-97 

5-98 

33-93 

50-99 

4-98 

25-90 

29-97 

17-75 

26-99 

17-99 

23-99 

50-99 

50 75 

50 73 

50 50 

50 80 

28 70 

40 71 

75 84 

21 58 

37 60 

41 60 

40 57 

53 80 

80 93 

75 89 

67 94 

93 7 of 11 

84 9 of 11 

96 7 of 11 

91 10 of 11 

85 10 of 11 

87 6 of 11 

96 8 of 11 

81 10 of 11 

77 9 of 11 

82 10 of 11 

67 8 of 11 

93 10 of 11 

97 10 of 11 

97 10 of 11 

98 10 of 11 

* Pollutant removals between POTW influent and secondary effluent (including secondary clarification). 

Based on a computer analysis of POTW removal efficiency data (derived from actual POTW influent and 

effluent sampling data) provided in U.S EPA’s Fate of Priority Pollutants in Publicly Owned Treatment 

Works, Volume II, (EPA 440/182/303), September 1982. 

** For the purpose of deriving removal efficiencies, effluent levels reported as below detection were set 

equal to the reported detection limits. All secondary trickling filter plants sampled as part of the study 

were considered. 

Source: U.S. EPA’s Guidance Manual on the Development and Implementation of Local Discharger 

Limitations Under the Pretreatment Program, December 1987, p. 3-57. 

R-3
Priority Pollutant Removal Efficiencies (%) Through Tertiary Treatment* 

Priority Pollutant Range 

METALS/NONMETAL INORGANICS** 

Cadmium 33-81 

Chromium 22-93 

Copper 8-99 

Cyanide 20-93 

Lead 4-86 

Mercury 33-79 

Nickel 4-78 

Silver 27-87 

Zinc 1-90 

Second 

Decile Median Eighth 

Decile 

50 50 

62 72 

58 85 

32 66 

9 52 

43 67 

7 7 

55 62 

50 78 

1 1

ORGANICS** 

40 50 

32 53 

50 83 

80 89 

31 57 

33 73 

80 88 

59 76 

50 63 

27 50 

29 38 

80 91 

83 94 

79 94 

62 93 

54 2 of 4 

64 3 of 4 

93 2 of 4 

94 3 of 4 

78 4 of 4 

86 3 of 4 

96 4 of 4 

94 4 of 4 

85 4 of 4 

70 4 of 4 

50 3 of 4 

97 4 of 4 

97 4 of 4 

97 4 of 4 

98 4 of 4 

Benzene 5-67 

Chloroform 16-75 

1,2-trans-Dichloroethylene 50-96 

Ethylbenzene 65-95 

Methylene Chloride 11-96 

Naphthalene 25-94 

Phenol 33-98 

Bis (2-ethylhexyl) phthalate 45-98 

Butyl benzyl phthalate 25-94 

Di-n-butyl phthalate 14-84 

Diethyl phthalate 20-57 

Tetrachloroethylene 67-98 

Toluene 50-99 

1,1,1-Trichloroethane 50-98 

Trichloroethylene 50-99 

Number of POTWs 

with Removal Data 

73 3 of 4 

89 4 of 4 

98 4 of 4 

83 4 of 4 

77 3 of 4 

75 4 of 4 

7 3 f o 4 

82 3 of 4 

88 4 of 4 

5

* Pollutant removals between POTW influent and tertiary effluent (including final clarification). Based 

on a computer analysis of POTW removal efficiency data (derived from actual POTW influent and 

effluent sampling data) provided in U.S. EPA’s Fate of Priority Pollutants in Publicly Owned Treatment 

Works, Volume II (EPA 440/1-82/303), September 1982. Tertiary treatment was taken to include POTWs 

with effluent microscreening, mixed media filtration, post aeration, and/or nitrification/denitrification. 

** For the purpose of deriving removal efficiencies, effluent levels reported as below detection were set 

equal to the reported detection limits. All tertiary treatment plants sampled as part of the study were 

considered. 

Source: U.S. EPA’s Guidance Manual on the Development and Implementation of Local Discharger 

Limitations Under the Pretreatment Program, December 1987, p. 3-58. 

R-4
APPENDIX S -

SPECIFIC GRAVITY OF SLUDGE

Equation to determine specific gravity of wet sludge 

The allowable headworks loading (AHL) equations presented in Chapter 5 for sewage sludge disposal contain 

a factor for the specific gravity of sludge (sludge density). This factor accounts for differences in the density 

of sludge based on the percent solids of sludge to disposal. e unit conversion factor (8.34) in the same 

equations converts the overall units into pounds per day (lbs/day), using a specific gravity or density of sludge 

equal to 1 kg/L, which assumes that sludge has the same density as water. sludge density 

is different from the density of water, the unit conversion factor is not fully accurate. 

of a sludge increases, the density of the sludge increases and therefore the error introduced by the inaccurate 

unit conversion factor increases. inaccuracy, the numerator of the AHL equation should be 

multiplied by the specific gravity of the dewatered sludge (as noted in Chapter 6). 

dewatered before disposal, the inaccuracy produced by using the unit conversion factor (8.34) without a 

specific gravity factor would probably not be significant. 

The POTW can determine the specific gravity (density) of its sludge prior to disposal through a simple 

laboratory measurement. The POTW should take this measurement as part of its local limits monitoring 

program and average the resulting data set (e.g., 7-10 data points) to determine a representative sludge 

specific gravity (density) factor for use in local limits calculations. ate the specific 

gravity of its sludge using the equations below and information on the percent solids. 

For a typical wet sludge at 10% solids, the approximate density is 1.03 kg/L. For a typical dewatered sludge 

at 30% solids, the approximate density is 1.11 kg/L. ay reach a density of 1.2 to 

1.3 kg/L, which would result in a 20% to 30% conservative error in the calculation of an AHL if a specific 

gravity factor is not used. ount of volatile solids in the sludge in 

comparison with the amount of fixed mineral solids, which vary with percent solids, and the densities of each 

of these types of solids. 

Where: 

MWS = Mass of wet sludge (kg) 

SWS = Specific gravity of wet sludge (kg/L) 

MS = Mass of dry sludge solids (kg) 

SS = Specific gravity of sludge solids (kg/L) 

MW = Mass of water (kg) 

SW = Specific gravity of water (kg/L) 

Th

If the dewatered 

As the percent solids 

To correct this 

If a sludge is not 

The POTW can also estim

A sludge at 50% solids m

All of these values depend on the am

Equation to determine specific gravity of dry sludge solids 

S-1
Where: 

MF = Mass of fixed solids (kg) 

SF = Specific gravity of fixed solids (kg/L) 

MV = Mass of volatile solids (kg) 

SV = Specific gravity of volatile solids (kg/L) 

The result from the second equation is used in the first equation. 

Example 

Sludge is 10% solids: 

Assume solids consist of 33% fixed mineral solids with a specific gravity of 2.5 kg/L and 67% volatile solids 

with a specific gravity of 1.2 kg/L. 

To determine the specific gravity of the dry sludge solids, use the second equation: 

which results in Ss = 1.45 kg/L. 

yields SWS = 1.03 kg/L. 

Using this value in the first equation: 

S-2
APPENDIX T -

SLUDGE AHL EQUATIONS USING FLOW (IN METRIC UNITS) 

Some POTWs may have sludge flow data available in dry metric tons per day, rather than MGD. The AHL 

equations for sludge disposal in Chapter 6 can be converted to use sludge flow data in these units. e of 

the equations in Chapter 6 are presented below using flows in dry metric tons per day. Use of these “dry 

flows” eliminates the need for the specific gravity factor in the equations. 

GENERAL SLUDGE EQUATION FOR CONSERVATIVE POLLUTANTS 

Where: 

LINFL = Allowable influent loading, lbs/day 

CCRIT = Sludge criteria, mg/kg dry sludge 

QSLDG = Total sludge flow to disposal, dry metric tons per day 

RPOTW = Removal efficiency across POTW (as decimal) 

0.0022 = Unit conversion factor 

LAND APPLICATION 

As explained in Chapter 6, determining the land application sludge criteria for use in the general sludge 

equation requires that the POTW first convert 40 CFR §503 Table 2 and Table 4 sludge criteria into values 

in mg/kg of dry sludge units. Table 4 criteria are in metric units (kg/ha), they must be 

converted into English units (lbs/acre) so that they can be used with the equations in Chapter 6 which use 

other English units (e.g., flow in MGD, area in acres). provided in both 

metric and English units in Appendix E. 

Another option is for POTWs to use the land application criteria equations in metric units (e.g., area in 

hectares, flow in dry metric tons per day), thus eliminating the need to convert Table 2 and Table 4 values 

to English units. These equations are provided below. These equations avoid the need for a specific gravity 

factor because they use also use a “dry flow” for sludge. 

Where: 

CCRIT = Sludge criteria, mg/kg dry sludge 

CCUM = Federal (Table 2 of 40 CFR 503.13) or State land application cumulative pollutant loading 

rate, kg/ha 

SA = Site area, hectares 

SL = Site life, years 

QLA = Sludge flow to bulk land application at an agricultural, forest, public contact, or reclamation 

site, dry metric tons per day 

0.365 = Unit conversion factor 

Som

Because Table 2 and 

Table 2 and Table 4 criteria are 

T-1
Arsenic, Cadmium, 

Chromium, Nickel 

Lead 

Beryllium, Mercury, 

pollutants with State limits 

Where: 

CCRIT = Sludge criteria, mg/kg dry sludge 

CANN = Federal (Table 4 of 40 CFR 503.13) or State land application annual pollutant loading rate, 

kg/ha 

AWSAR = Annual whole sludge application rate, metric tons per hectare per year dry weight basis 

0.001 = Unit conversion factor 

INCINERATION 

Sludge standards for maximum pollutant concentrations in sludge feed to the incinerator need to be in mg/kg 

dry sludge to be used in the equations at the beginning of Section 6.2.3 to calculate AHLs. 

disposing of sludge through incineration may already have sludge standards in mg/kg dry sludge, such as 

through a waste disposal agreement with the operator of a sludge incincerator. in Chapter 6, if no 

sludge standards have been calculated for the sludge feed to the incinerator, POTWs should use the Part 503 

equations (provided below) to determine the maximum pollutant concentrations for the incinerator feed. 

These maximum concentrations are then used in the equations at the beginning of Section 6.2.3 to calculate 

AHLs. 

Where: 

CCRIT = Sludge criteria, mg/kg dry sludge 

NESHAP = National emission standard for beryllium or mercury from 40 CFR Part 61, g/day 

NAAQS = National Ambient Air Quality Standard for lead, ug/m3 

RSC = Federal risk specific concentration limit for arsenic, cadmium, chromium, or nickel 

from 40 CFR 503.43, ug/m3 

CE = Control efficiency (removal efficiency) for sewage sludge incinerator for the given 

pollutant (as a decimal) 

QINC = Sludge flow to incinerator (i.e., sewage sludge feed rate), dry metric tons per day 

DF = Dispersion factor, ug/m3

/g/sec 

0.1 and 86,400 = Unit conversion factors 

For pollutants with State incinerator emissions standards, limits should be entered in g/day in place of the 

NESHAPs limits in the first equation above. 

A POTW 

As noted 

T-2
APPENDIX U -

POTW CONFIGURATIONS

The diagrams and discussions below demonstrate sampling locations to develop allowable headworks 

loadings (AHLs). For illustrative purposes, in this appendix all three plants must determine the AHLs based 

upon effluent limitations, secondary treatment inhibition, sludge digester inhibition, and sludge land 

application. Three different plants, with very different secondary treatment trains, are diagramed below along 

with sampling points for the AHL calculations. 

Diagram A 

Raw Wastewater 

Bar 

Screen 

and Grit 

Chamber 

Effluent 

Land 

Application 

Primary 

Clarifier 

Secondary 

Clarifier 

High Rate 

Sludge 

Digester 

Gravity 

Thickener 

Belt Filter 

Press 

Secondary 

Clarifier 

Trickling 

Filter 

Sludge 

Degritter 

Aeration 

Basin 

Chlorine 

Contact 

Chambers 

X

X 

X 

X 

A

B

C D

E

X 

AHL FOR SECONDARY TREATMENT INHIBITION 

At this POTW a trickling filter and an activated sludge system (aeration basin) operated in parallel provide 

secondary treatment of the raw wastewater. The concentration of a pollutant that could cause inhibition at 

the trickling filter may be different than the pollutant concentration that causes inhibition (known as the 

inhibition threshold level) at the aeration basin. The plant must determine a headworks loading protective 

of these two secondary treatment units. Using Equation 5.10, an AHL based on secondary treatment 

inhibition can be calculated. 

U-1
Trickling Filter 

Aeration Basin 

Where: 

AHLinhab = AHL based on aeration basin inhibition, lbs/day 

AHLinhtf = AHL based on trickling filter inhibition, lbs/day 

Cinhab = Inhibition criteria for aeration basin, mg/L 

Cinhtf = Inhibition criteria for trickling filter, mg/L 

Qpotw = Total POTW flow, MGD 

Rprim = Removal efficiency from headworks to primary treatment effluent as a decimal (See 

Section 5.1.1 for calculating removal efficiencies) 

8.34 = Unit conversion factor 

The equations to calculate the AHL based on trickling filter and aeration basin inhibition includes an 

inhibition criteria for the trickling filter, Cinhtf, and aeration basin, Cinhab, respectively. Both equations use the 

same removal rate, Rprim, from the headworks to the primary treatment effluent. Rprim can be determined by 

sampling loading at point “A,” the headworks, and point “B,” primary clarifier effluent (See Section 5.1 for 

these calculations). Qpotw can be determined through flow sampling at point “A” as well. AHLab and the AHLtf 

would be calculated, pared and the more stringent selected. 

AHL FOR SLUDGE DIGESTER INHIBITION 

This plant must determine a headworks loading protecting the high-rate sludge digester from inhibition. 

Using Equation 5.12, an AHL based on sludge digester inhibition can be calculated. 

Where: 

AHLinhhrsd = AHL based on high-rate sludge digester inhibition, lbs/day 

Cinbhrsd = High-rate sludge digester inhibition criteria, mg/L 

Qhrsd = Sludge flow to high-rate sludge digester, MGD 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

8.34 = Unit conversion factor 

The equation to calculate the AHL based on high-rate sludge digester inhibition includes an inhibition criteria 

for the digester, Cinbhrsd, sludge flow to the digester, Qhrsd , and an overall plant removal rate from headworks 

to plant effluent, Rpotw. Qhrsd can be determined sampling flow at point “C,” the sludge wastestream from 

gravity thickener to digester. Rpotw can be determined by sampling at point “A,” headworks before the 

bar screen and grit chamber, and at point “E,” the effluent after the chlorine contact chambers. 

com

by

the 

U-2
AHL FOR EFFLUENT LIMITS 

The plant must determine headworks loading that would lead to effluent from its chlorine contact chambers 

(CCC) comply with NPDES Permit limits. Using Equation 5.5, the AHL based on NPDES Permit limit can 

be calculated. 

Where: 

AHLeffccc = AHL based on CCC effluent compliance with NPDES, lbs/day 

Cnpdes = NPDES permit limit, mg/L 

Qpotw = POTW 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

8.34 = Conversion factor 

The equation to calculate the AHL based on CCC effluent compliance with NPDES includes the NPDES 

permit limit, Cnpdes, total POTW flow, Qpotw, and an overall plant removal rate from headworks to plant 

effluent, Rpotw. Rpotw can be determined by sampling loading at point “A,” 

screen and grit chamber, and at point “E,” the effluent after the chlorine contact chambers. Qpotw can be 

determined through sampling flow at point “A” as well. 

AHL FOR SLUDGE APPLICATION 

The plant must determine a headworks that would lead to sludge from the belt filter press suitable for land 

application. on sludge land application can be calculated. 

Where: 

AHLsabfp = AHL based on compliance with sludge application standards, lbs/day 

Cslgstd = Sludge standard, mg/kg dry sludge 

PS = Percent solids of sludge leading to belt filter press 

Qbfp = Total sludge flow to belt filter press, MGD 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

Gsldg = Specific gravity of sludge leading to filter press, kg/L 

8.34 = Unit conversion factor 

The equation to calculate the AHL based on belt filter press sludge compliance with sludge standards includes 

the sludge limit, Cslgstd ; the flow, percent solids and specific gravity of sludge leading press, 

Qbfp, PS, and Gsldg, respectively; and the overall plant removal rate from headworks to plant effluent, Rpotw. 

Rpotw can be determined by sampling loading at point “A,” the headworks before the bar screen and grit 

chamber, and at point “E,” the effluent after the chlorine contact chambers. Qbfp, PS, and Gsldg, can be 

determined through sampling point “D” the sludge waste stream to the belt filter press. 

flow, average, MGD 

the headworks before the bar 

Using equation 5.9 an AHL based

to the belt filter 

U-3
AHL FOR SECONDARY TREATMENT INHIBITION 

At this POTW a standard rate trickling filter, a high rate trickling filter, and rotating biological contactors 

(RBCs) operated in parallel provide secondary treatment of the raw wastewater. Each of these biological 

units is preceded by a different primary clarifier. An AHL (to prevent inhibition) should be determined for 

each of these biological unit processes because: 

Diagram B 

Raw Wastewater Effluent 

A

Chlorine 

Contact 

Chamber 

Gravity 

Thickener 

X 

X 

H

Land 

Application 

RBCs 

Bar 

Screen 

Grit 

Chamber 

Primary 

Clarifier #1 

Std. Rate 

Trickling 

Filter 

Secondary 

Clarifier #1 

High Rate 

Trickling 

Filter 

Primary 

Digester 

Secondary 

Digester 

Primary 

Clarifier #2 

Primary 

Clarifier #3 

Secondary 

Clarifier #2 

Secondary 

Clarifier #3 

Wet

Well

Vacuum 

Filter 

X 

X 

X 

X 

X 

X 

B

C

D

E

F

G

C The concentration of a pollutant that could cause inhibition at the standard rate trickling filter, high rate 

trickling filter, and RBCs are different. 

C The design and operational loadings to each of the secondary treatment units are different and therefore 

loading is different. 

C The primary clarifiers may have different removal efficiencies and therefore the pollutant concentrations 

to each of the secondary treatment unit may be different. 

The three equations listed below can be used to calculate secondary treatment inhibition. 

U-4
Standard Trickling Filter 

High-Rate Trickling Filter 

RBCs 

Where: 

AHLinhstf = AHL based on standard trickling filter inhibition, lbs/day 

AHLinhhrtf = AHL based on high-rate trickling filter inhibition, lbs/day 

AHLinhrbc = AHL based on RBC inhibition, lbs/day 

Cinhstf = Inhibition criteria for standard trickling filter, mg/L 

Cinhhrtf = Inhibition criteria for high-rate trickling filter, mg/L 

Cinhrbc = Inhibition criteria for RBC, mg/L 

Qpotw = Total POTW flow, MGD 

Rprim1 = Removal efficiency from headworks to primary clarifier #1 effluent as a decimal (See 

Section 5.1.1 for calculating removal efficiencies) 

Rprim2 = Removal efficiency from headworks to primary clarifier #2 effluent as a decimal 

Rprim3 = Removal efficiency from headworks to primary clarifier #3 effluent as a decimal 

8.34 = Unit conversion factor 

Each of the AHL equations has an inhibition criteria for each secondary treatment unit, Cinhstf , Cinhhrtf,, and 

Cinhrbc and removal rates from the headworks to corresponding primary clarifier unit effluent, Rprim1, Rprim2, 

and Rprim3. sampling locations “A” and “B” is used to calculate the removal efficiency from 

headworks to the primary clarifier #1 effluent, Rprim1. sampling locations “C” is used to 

calculate the removal efficiency from headworks to primary clarifier #2 effluent, Rprim2. sampling 

locations “A” and “D” is used to calculate the removal efficiency from headworks to primary clarifier #3 

effluent, Rprim3. Qpotw can be determined at sampling point “A.” The AHLinhstf, AHLinhhrtf, and AHLinhrbc should 

be calculated, compared, and the most stringent (smallest) selected. 

AHL FOR SLUDGE DIGESTER INHIBITION 

This plant must determine a headworks loading protecting both the primary and secondary sludge digesters 

from inhibition. on sludge digester inhibition can be calculated. 

Primary Digester 

Data from

Data from “A”and 

Data from

Using Equation 5.12, an AHL based 

U-5
Secondary Digester 

Where: 

AHLinbpd = AHL based on primary digester inhibition, lbs/day 

AHLinbsd = AHL based on secondary digester inhibition, lbs/day 

Cinbpd = Primary digester inhibition criteria, mg/L 

Cinbsd = Primary digester inhibition criteria, mg/L 

Qpd = Sludge flow to primary digester, MGD 

Qsd = Sludge flow to secondary digester, MGD 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

8.34 = Unit conversion factor 

The equations to calculate the AHL based on sludge digester inhibition include primary and secondary 

inhibition criteria, Cinbpd and Cinbsd, sludge flow to the primary and secondary digesters, Qpd and Qsd, and an 

overall plant removal rate from headworks to plant effluent, Rpotw. Qpd can be determined sampling flow 

at point “E,” the sludge wastestream to the primary digester. Qsd can be determined sampling flow at 

point “F,” the sludge wastestream from the primary digester to the secondary digester. Rpotw can be 

determined by sampling loading at point “A,” the headworks before the bar screen and grit chamber, and at 

point “H,” the effluent after the chlorine contact chambers. AHLinbpd and AHLinbsd should be calculated, 

compared and the more stringent selected. 

AHL FOR EFFLUENT LIMITS 

The plant must determine headworks loading that would lead to effluent from its chlorine contact chambers 

(CCC) comply with NPDES Permit limits. it limit can 

be calculated. 

Where: 

AHLeffccc = AHL based on CCC effluent compliance with NPDES, lbs/day 

Cnpdes = NPDES permit limit, mg/L 

Qpotw = POTW 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

8.34 = Conversion factor 

The equation to calculate the AHL based on CCC effluent compliance with NPDES includes the NPDES 

permit limit, Cnpdes, total POTW flow, Qpotw, and an overall plant removal rate from headworks to plant 

effluent, Rpotw. Rpotw can be determined by sampling at point “A,” the headworks before the bar screen and 

grit chamber, and at point “H,” the effluent after the chlorine contact chambers. Qpotw can be determined 

through sampling flow at point “A” as well. 

by

by

Using Equation 5.5, the AHL based on NPDES Perm

flow, average, MGD 

U-6
AHL FOR SLUDGE APPLICATION 

The plant must determine a headworks that would lead to sludge from the vacuum filter suitable for land 

application. Using equation 5.9 an AHL based on sludge land application can be calculated. 

Where:

AHLsavf = AHL based on compliance with sludge application standards, lbs/day

Cslgstd = Sludge standard, mg/kg dry sludge

PS = Percent solids of sludge leading to vacuum filter

Qvf = Total sludge flow to vacuum filter, MGD

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal)

Gsldg = Specific gravity of sludge leading to vacuum filter, kg/L

8.34 = Unit conversion factor

The equation to calculate the AHL based on vacuum filter sludge compliance with sludge standards includes

the sludge limit, Cslgstd ; the flow, percent solids and specific gravity of sludge leading to the belt filter press,

Qvf, PS, and Gsldg, respectively; and the overall plant removal rate from headworks to plant effluent, Rpotw.

Rpotw can be determined by sampling at point “A,” the headworks before the bar screen and grit chamber, and

at point “H,” the effluent after the chlorine contact chambers. Qvf, PS, and Gsldg, can be determined through

sampling at point “G” the sludge waste stream to the vacuum filter.

Diagram C 

Raw Wastewater Effluent 

Landfill 

X 

A

E F G

2nd Stage 

Aeration 

Basin 

3rd Stage 

Aeration 

Basin 

1st Stage 

Clarifier 

2nd Stage 

Clarifier 

Final 

Clarifier 

Ozone 

Treatment 

Air 

Flotation 

Thickener 

Primary 

Clarifier 

1st Stage 

Aeration 

Basin 

Gravity 

Thickener 

Plate and 

Frame 

Press 

Sludge 

Digester X X

X 

X X

X 

X 

B C D

H

U-7
1st Stage Aeration Basin 

2nd Stage Aeration Basin 

3rd Stage Aeration Basin 

AHL FOR SECONDARY TREATMENT INHIBITION 

At this POTW three activated sludge units (aeration basins) operated in series provide secondary treatment 

of the raw wastewater. a pollutant entering the First Stage Aeration Basin would be 

different from the concentration of that pollutant entering the Second Stage Aeration Basin and the Third 

Stage Aeration Basin because of the removal occurring in each unit. 

be determined for each of these secondary treatment units. 

Where: 

AHLinhab1 = AHL based on 1st Stage Aeration Basin inhibition, lbs/day 

AHLinhab2 = AHL based on 2nd Stage Aeration Basin inhibition, lbs/day 

AHLinhab3 = AHL based on 3rd Stage Aeration Basin inhibition, lbs/day 

Cinhab1 = Inhibition criteria for 1st Stage Aeration Basin, mg/L 

Cinhab2 = Inhibition criteria for 2nd Stage Aeration Basin, mg/L 

Cinhab3 = Inhibition criteria for 3rd Stage Aeration Basin, mg/L 

Qpotw = Total POTW flow, MGD 

Rprim = Removal efficiency from headworks to primary treatment effluent as a decimal (See Section 

5.1.1 for calculating removal efficiencies) 

Rab1 = Removal efficiency from headworks to 1st Stage Aeration Basin effluent as a decimal 

Rab2 = Removal efficiency from headworks to 2nd Stage Aeration Basin effluent as a decimal 

8.34 = Unit conversion factor 

Each of the equations to calculate AHLs for secondary treatment has it own inhibition criteria for each basin, 

Cinhab1, Cinhab2, and Cinhab3 and corresponding removal rate, Rprim, Rab1, and Rab2, respectively, for the 1st, 2nd , 

and 3rd stage aeration basins. sampling locations “A” and “B” is used to determine the removal 

efficiency from headworks to primary clarifier effluent, Rprim. Data from sampling locations “A” and “C” is 

used to determine the removal efficiency from headworks to 1st stage clarifier effluent, Rab1. Data from 

sampling locations “A” and to determine the removal efficiency from headworks to 2nd stage 

clarifier effluent, Rab2. Qpotw can be determined by sampling at location “A.” The AHLinhab1, AHLinhab2 , and 

AHLinhab3 should be calculated, compared, and the most stringent (smallest) selected. 

The concentration of 

An AHL (to prevent inhibition) should 

Data from

“D” is used 

U-8
AHL FOR SLUDGE DIGESTER INHIBITION 

This plant must determine a headworks loading protecting the sludge digester from inhibition. Using 

Equation 5.12, an AHL based on sludge digester inhibition can be calculated. 

Where: 

AHLinhsd = AHL based on sludge digester inhibition, lbs/day 

Cinhsd = Sludge digester inhibition criteria, mg/L 

Qsd = Sludge flow to sludge digester, MGD 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

8.34 = Unit conversion factor 

The equation to calculate the AHL based on high-rate sludge digester inhibition includes an inhibition criteria 

for the digester, Cinhsd, sludge flow to the digester, Qsd , and an overall plant removal rate from headworks to 

plant effluent, Rpotw. Qsd can be determined sampling flow at point “E,” the sludge wastestream from air 

flotation thickener to the digester. Rpotw can be determined by sampling loading at point “A,” the headworks 

before the bar screen and grit chamber, and at point “H,” the effluent after the ozone treatment unit. 

AHL FOR EFFLUENT LIMITS 

The plant must determine headworks loading that would lead to effluent from its ozone treatment unit (OTU) 

comply with NPDES Permit limits. it limit can be 

calculated. 

Where: 

AHLeffotu = AHL based on OTU effluent compliance with NPDES, lbs/day 

Cnpdes = NPDES permit limit, mg/L 

Qpotw = POTW 

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal) 

8.34 = Conversion factor 

The equation to calculate the AHL based on OTU effluent compliance with NPDES includes the NPDES 

permit limit, Cnpdes, total POTW flow, Qpotw, and an overall plant removal rate from headworks to plant 

effluent, Rpotw. Rpotw can be determined by sampling loading at point “A,” 

screen and grit chamber, and at point “H,” the effluent after the OTU. Qpotw can be determined through 

sampling flow at point “A” as well. 

by

Using Equation 5.5, the AHL based on NPDES Perm

flow, average, MGD 

the headworks before the bar 

U-9
AHL FOR SLUDGE APPLICATION 

The plant must determine a headworks that would lead to sludge from the plate and frame press (PFP) suitable 

for land application. Using equation 5.9 an AHL based on sludge land application can be calculated. 

Where:

AHLsapfp = AHL based on compliance with sludge application standards, lbs/day

Cslgstd = Sludge standard, mg/kg dry sludge

PS = Percent solids of sludge leading to PFP

Qpfp = Total sludge flow to PFP, MGD

Rpotw = Plant removal efficiency from headworks to plant effluent (as decimal)

Gsldg = Specific gravity of sludge leading to PFP, kg/L

8.34 = Unit conversion factor

The equation to calculate the AHL based on PFP sludge compliance with sludge standards includes the sludge

limit, Cslgstd ; the flow, percent solids and specific gravity of sludge leading to the PFP, Qpfp, PS, and Gsldg,

respectively; and the overall plant removal rate from headworks to plant effluent, Rpotw. Rpotw can be

determined by sampling loading at point “A,” the headworks before the bar screen and grit chamber, and at

point “H,” the effluent after the OTU. Qpfp, PS, and Gsldg, can be determined through sampling flow at point

“E” the sludge waste stream to the PFP. 

U-10
APPENDIX V -

DOMESTIC POLLUTANT LOADINGS

Residential/Commercial Trunkline Monitoring Data 

Pollutant Number of 

Detections 

Minimum Number of Concentration Samples 

Maximum 

Concentration 

(mg/L) 

Average 

Concentration 

(mg/L) 

0.088 0.007 

0.216 

0.42 

0.11 0.008 

0.007 0.006 

1.2 0.034 

0.74 0.14 

0.37 0.082 

0.27 

3.4 

2.04 0.058 

0.031 0.031 

0.161 0.087 

0.054 0.002 

1.6 0.047 

30.2 

0.7 0.7 

1.052 0.019 

1.28 0.231 

0.115 

0.3 

0.255 

0.989 

28.8 

Arsenic

Barium

Boron

Cadmium

Chromium (III)

Chromium (T)

Copper

Cyanide

Fluoride

Iron

Lead

Lithium

Manganese

Mercury

Nickel

Phosphate

Total Phosphorous

Silver

Zinc

Chloroform

1,1-Dichloroethene

1,1-Dichloroethane

Trans-1,2-Dichloroethene

Fluoranthene

Methylene Chloride

Phenols

Bis (2-ethylhexyl) Phthalate

Pyrene

Tetrachloroethene

1,2,4-Trichlorobenzene

Total BHC

4,4-DDD 

Total Endosulfan 

(mg/L) 

INORGANICS 

140 

3 

4 

361 

1 

311 

603 

7 

2 

18 

433 

2 

3 

218 

313 

2 

1 

181 

636 

205 0.0004 

3 0.04 

4 0.1 

538 0.00076 

2 < 0.005 

522 < 0.001 

607 0.005 

7 0.01 

2 0.24 

18 0.0002 

540 0.001 

2 0.03 

3 0.04 

235 < 0.0001 

540 < 0.001 

2 27.4 

1 0.7 

224 0.0007 

638 0.01 

ORGANICS 

21 

2 

1 

1 

2 

7 

2 

5 

2 

5 

1 

30 <0.002 

29 0.005 

28 0.026 

28 0.013 

5 0.00001 

30 0.00008 

2 0.00002 

5 0.00002 

3 0.00001 

29 0.00001 

3 <0.002 

PESTICIDES 

3 

3 

3 

3 0.001 

3 0.00026 

3 0.002 

0.069 

0.008 

0.026 

0.013 

<0.001 

0.055 

0.00003 

0.022 

<0.005 

0.037 

0.035 

0.009 

0.007 

0.026 

0.013 

0.001 

0.027 

0.000025 

0.006 

0.0002 

0.014 

0.013 

0.001 0.001 

0.0004 0.0003 

0.002 0.002 

V-1
Source: U.S. EPA’s Supplemental Manual on the Development and Implementation of Local Discharge 

Limitations Under the Pretreatment Programs, May 1991. “Pollutant levels reported below specified 

detection limit were considered in the data analysis and, for the purpose of statistical analysis, were 

considered equal to the detection limit.” 

V-2
APPENDIX W -

BEST MANAGEMENT PRACTICES MINI-CASE STUDIES

POTWs can implement best management practice (BMP) programs to gain control over wastewater 

discharges from commercial sources. By developing a less formal source control program with emphasis 

on source control, education, BMPs, as-needed inspections, and individual or “general” permits, POTWs can 

gain additional control over uncontrolled wastewater discharges from commercial sources. Source control 

programs should place emphasis on certain specific pollutants of concern. For example, silver and mercury 

are often of great concern to POTWs because of NPDES permit requirements. 

The commercial sources of wastewater that are addressed by BMP-based source control tend to have lower 

pollutant concentrations and loadings than other more traditional industrial facilities regulated by the 

traditional pretreatment program. Taken as a group, however, numerous uncontrolled commercial 

establishments may represent a significant source control opportunity that can lead to measurable 

improvement in environmental quality. Several pretreatment programs have documented pollutant 

reductions after the implementation of BMP and source reduction programs. 

Several BMP/source control programs implemented at several POTWs are summarized in the following 

paragraphs to illustrate a variety of approaches that have been taken to utilize BMPs for the control of 

commercial sources of wastewater. Programs reviewed include: East Bay Municipal Utility District 

(EBMUD) in Oakland, California; Metropolitan Wastewater in San Diego, California; Seattle 

Metropolitan/King County in Washington State; Western Lake Superior Sanitary District, Duluth, Minnesota; 

and the Connecticut Department of Environmental Protection (CT DEP), Hartford, Connecticut. 

EAST BAY MUNICIPAL DISTRICT (EBMUD), OAKLAND, CA 

EBMUD has been issuing pollution prevention permits (PPPs) since 1988. EBMUD began their PPP 

program in response to tighter air emission standards and more stringent NPDES permit requirements. As 

a result, EBMUD had to augment headworks sampling and analysis programs for the development and local 

limits. Based on attentive tracking of regulatory requirements over the past 10 years, EBMUD has 

sequentially identified POCs, identified commercial users contributing those pollutants, and developed PPPs 

with best management practice requirements. 

When EBMUD recognizes a pollutant of concern, they follow step-wise procedures. First, information on 

businesses and commercial activities that may be contributing the targeted POC is collected and refined. 

Next, EBMUD engages in an outreach program and works with the businesses to define BMPs. Finally, 

EBMUD issues the PPP and evaluates compliance. Generally, there is one sector of business activity that 

is responsible for the specific pollutant. For example, silver is linked to the photo finishers. EBMUD works 

with representatives of the commercial sector to research and develop BMPs that will effectively minimize 

the pollutant in effluent wastewater. 

EBMUD believes that the most important aspect of a successful PPP program is education, outreach, and user 

awareness combined with an enforceable permit. When conducting outreach, EBMUD gets in touch with 

each user to confirm the nature of their business and the processes they use at the business that can contribute 

wastewater and pollutants of concern. The establishment is asked to participate in educational workshops 

to review EBMUD's concerns, review and refine preliminary methods to prevent pollutant releases and lay 

the groundwork for successful communications and understanding of the problem and the solution. Users 

are introduced to the permitting and enforcement process in a non-threatening forum. EBMUD’s inventory 

of users is based on water supply account information. Whenever a user opens a water account, it is 

W-1
automatically characterized for wastewater and source control purposes. A revenue collection system ($3.25 

per commercial account per month) assures adequate funding for the PPP program. 

EBMUD staff researches ideas for generalized BMPs through discussions with the business sector and State 

trade group associations. Each of the EBMUD staff tracks one or more business sectors and are responsible 

for knowing current pollution control measures and trends. During the research phase of BMP development, 

each user that is a potential contributor of a POC is sent a letter to notify them that EBMUD is working on 

a PPP and reviewing the anticipated time frame for permit issuance. 

The PPP includes similar BMPs for each permittee. Some examples include silver recovery canisters 

connected in series to optimize removal of silver with a required logging procedure that assures canisters are 

changed at the appropriate frequency to eliminate break through. EBMUD PPPs vary in length from two to 

8 pages and are issued in industry group batches for a duration of 5 years. In the administration of their PPP 

program, EBMUD conducts visits/inspections of the permittees, provides follow up education, distributes fact 

sheets, procedures and posters illustrating acceptable waste and wastewater disposal procedures. During the 

life of a 5-year permit, EBMUD tries to inspect the permittee at least once or twice. Based on the findings 

of the initial visit, and the degree to which the permittee is implementing the prescribed BMPs, the follow 

up frequency is set. When EBMUD fails to get cooperation from businesses, they initiate enforcement 

actions. As an example, EBMUD sought and obtained a $27,000 penalty from a dry cleaner. 

A partial list of the businesses for which EBMUD has developed BMPs and PPP permits includes: 

• Photofinishers 

• Boat ards Y

• Dry Cleaners 

• Auto Repairs 

• Print Shop 

• Radiator Repair Shops 

• Furniture Stripping 

METROPOLITAN WASTEWATER, SAN DIEGO, CA 

Metropolitan Wastewater issues sector-specific BMP discharge authorizations to commercial customers. 

These authorizations require: 

• Specific pollution prevention measures. 

• An initial certification of compliance. 

• On-going semi-annual “reminder” certifications for businesses to demonstrate familiarity 

with their pollution prevention measures. 

Metropolitan Wastewater covers a variety of sectors with this program. General permits are issued to film 

processing and dry cleaners. The photo processing BMPs are based on the Code of Management Practice for 

Silver Dischargers (AMSA 1996) developed by the Silver Council in concert with the Association of 

Metropolitan Sewerage Agencies and EPA. Metropolitan Wastewater conducted workshops to review silver 

control BMPs with their users. Boat repair yards or dry docks are required to submit their own customized 

BMPs which are incorporated into a permit. Food establishment discharge permits are also issued and require 

grease removal equipment, operation and maintenance, and compliance with general and specific discharge 

prohibitions. Auto repair shops that have steam-cleaning operations are required to have a sump for all O&G 

W-2
wastewater from steam cleaning operations. San Diego has initiated a more aggressive program to enforce 

grease trap cleaning particularly at food establishments. They have discovered that excessive amounts of 

grease buildup contribute to dry weather flows into San Diego and Mission Bay. Analytical/Research Labs 

are required to implement a solvent certification program that is very similar to the total toxic organic (TTO) 

certification program for metal finishers and electroplaters. 

San Diego has a 301(h) waiver for their wastewater treatment facility, allowing conditional discharge of 

wastewater without full secondary treatment. One condition of the waiver requires the City to reexamine their 

local limits every year and reassess loadings from all sources (domestic, SIU, and non-SIU contributions). 

The IU is considered a "contributor" of a pollutant of concern (presently one of six heavy metals) if the user 

has one of the six metals in its effluent at a concentration that is two standard deviations above the average 

domestic concentration. Once the IU is deemed to be a “contributor” of a pollutant of concern, wastewater 

flow is evaluated to determine whether the load is significant enough to be assigned to the “allocated” versus 

“non-allocated” load for their local limits accounting procedures. When the load is significant, the user is 

included in the allocated portion of headworks load calculations and the user is required to comply with local 

limits. Users with minor concentrations or loadings of pollutants of concern are not required to comply with 

local limits. However, they may still be required to comply with BMPs and general permit requirements. 

SEATTLE METROPOLITAN/KING COUNTY, WASHINGTON 

Seattle Metropolitan /King County (Seattle Metro) has a very large and active pollution prevention program 

that has acquired a great deal of information on dental mercury source control. Dental facilities in the Seattle 

Metro collection system are subject to the mercury local limits. After strong lobbying by the Dental 

Association against mandatory BMPs, dental facilities currently have latitude in controlling mercury through 

BMPs. Seattle Metro has developed a variety of tools to control mercury, including: 

• A certified list of the vendors and technologies that are able to achieve a 90% reduction in metals. 

• Videotape on mercury and silver source control from dental offices entitled “Amalgam Waste 

Conference.” 

• A dental facility waste management poster and a booklet entitled, “Waste Management Guidelines 

for Dental Facilities.” 

• Records on the amount of amalgam that is being reclaimed by recyclers as a means of tracking the 

success of their education efforts. 

• Voucher program that gives $500 to dental offices to obtain one of the approved metal removal units 

identified in the list above. 

• Educational materials (posters, videos, booklets). 

WESTERN LAKE SUPERIOR SANITARY DISTRICT (WLSSD), DULUTH, MINNESOTA 

With support from the Great Lakes Protection Fund, the WLSSD conducted a two-year Mercury Zero 

Discharge Project to examine the sources of mercury to its wastewater treatment plant and to determine how 

to reduce or eliminate those sources. This project included cooperative initiatives with industries known to 

be discharging mercury, programs aimed at specific uses of mercury, a monitoring program to identify 

additional sources and a public awareness campaign. In addition to these external programs, WLSSD also 

examined its own facilities and practices. 

W-3
WLSSD has authored the Blueprint for Mercury Elimination, Mercury Reduction Project Guidance for 

Wastewater Treatment Plants, March, 1997. Selected for an AMSA National Environmental Achievement 

Award for excellence in Public Information & Education, the document examines sources of mercury in the 

environment, reviews contributions to the wastewater collection system, and gives examples of success stories 

on mercury source reduction. Appendices to the document provide useful "how to" references for 

implementing a source reduction program, such as a sample news release for a mercury reduction project, 

sample letters to mercury contributors, telephone survey forms to interview possible contributors, survey 

forms for hospitals and dental offices. 

CONNECTICUT DEPARTMENT OF ENVIRONMENTAL PROTECTION (CT DEP), HARTFORD, CONNECTICUT 

In 1992, CT DEP began a Statewide general permit program. The program established requirements for 

industries that were not SIUs, regulated by CT DEP’s State-run pretreatment permitting program, but were 

a potential source of concern for POTWs. The general permitting program is “self implementing” and 

expects commercial establishments to be made aware of general permit program requirements by the local 

Town officials, the State, or through consultants. Thus, the general permitting program avoids the resource 

intensive individual permitting of traditional programs. 

The program works in the following manner. An IU assesses their eligibility for a general permit (versus a 

traditional pretreatment permit). CT DEP encourages industries to determine eligibility for a general permit, 

as the permitting process is quicker and less costly for the IU and CT DEP. Each general permit identifies 

BMPs that must be followed by each permit holder. CT DEP conducts selective auditing and enforcement 

of general permit holders, and facilities that may have failed to register for a general permit. By publicizing 

the enforcement actions and penalties, industries are made aware of their duties to have a permit and comply 

with the BMPs, record keeping, monitoring, and where applicable, effluent limits. General permits 

developed by CT DEP include the following sectors: 

1. Constructions and Operation of Certain Recycling Facilities 

2. Car Wash Wastewater 

3. Domestic Sewage of 50,000 gallons per day or 5% of the POTW Design Flow 

4. Groundwater Contamination Recovery Systems 

5. Hydrostatic Pressure Testing 

6. Minor Boiler Blowdown 

7. Minor Non-Contact Cooling Water 

8. Minor Photographic Processing 

9. Minor Tumbling and Cleaning of Parts Wastewater 

10. Storm Water Associated with Industrial Activities 

11. Storm Water and Dewatering Wastewaters - Construction Activities 

12. Vehicle Service Floor Drain and Car Wash Wastewater 

13. Storm Water Associated with Commercial Activities 

14. Minor Printing and Publishing Wastewater 

15. Water Treatment Wastewater - Commercial 

16. Food Processing Wastewater 

17. Public Swimming Pool Backwash 

18. Water Softening/Treatment Unit Wastewater-Individual Homes (under development) 

W-4
APPENDIX X -

REGION 1, REASSESSMENT OF TECHNICALLY BASED INDUSTRIAL

DISCHARGE LIMITS CHECKLIST

Attachment A. 

EPA - New England 

Reassessment of Technically Based Industrial Discharge Limits 

Under 40 CFR 122.21(j)(4), all Publicly Owned Treatment Works (POTWs) with approved Industrial 

Pretreatment Programs (IPPs) shall provide the following information to the Director: a written evaluation 

of the need to revise local industrial discharge limits under 40 CFR 403.5(c)(1). 

Below is a form designed by the U.S. Environmental Protection Agency (EPA - New England) to assist 

POTWs with approved IPPs in evaluating whether their existing Technically Based Local Limits 

(TBLLs) need to be recalculated. The form allows the permittee and EPA to evaluate and compare 

pertinent information used in previous TBLLs calculations against present conditions at the POTW. 

Please read direction below before filling out form. 

ITEM I. 

* In Column (1), list what your POTW’s influent flow rate was when your existing TBLLs were 

calculated. In Column (2), list your POTW’s present influent flow rate. Your current flow rate 

should be calculated using the POTW's average daily flow rate from the previous 12 months. 

* In Column (1) list what your POTW’s SIU flow rate was when your existing TBLLs were 

calculated. In Column (2), list your POTW’s present SIU flow rate. 

* In Column (1), list what dilution ratio and/or 7Q10 value was used in your old/expired NPDES 

permit. In Column (2), list what dilution ratio and/or 7Q10 value is presently being used in your 

new/reissued NPDES permit. 

The 7Q10 value is the lowest seven day average flow rate, in the river, over a ten-year period. 

The 7Q10 value and/or dilution ratio used by EPA in your new NPDES permit can be found in 

your NPDES permit “Fact Sheet.” 

* In Column (1), list the safety factor, if any, that was used when your existing TBLLs were 

calculated. 

* In Column (1), note how your biosolids were managed when your existing TBLLs were 

calculated. In Column (2), note how your POTW is presently disposing of its biosolids and how 

your POTW will be disposing of its biosolids in the future. 

ITEM II. 

* List what your existing TBLLs are - as they appear in your current Sewer Use Ordinance (SUO). 

X-1
ITEM III. 

* Identify how your existing TBLLs are allocated out to your industrial community. Some 

pollutants may be allocated differently than others, if so please explain. 

ITEM IV. 

* Since your existing TBLLs were calculated, identify the following in detail: 

(1) if your POTW has experienced any upsets, inhibition, interference or pass-through as a 

result of an industrial discharge. 

(2) if your POTW is presently violating any of its current NPDES permit limitations -

include toxicity. 

ITEM V. 

* Using current sampling data, list in Column (1) the average and maximum amount of pollutants 

(in pounds per day) received in the POTW's influent. Current sampling data is defined as data 

obtained over the last 24 month period. 

All influent data collected and analyzed must be in accordance with 40 CFR 136. Sampling data 

collected should be analyzed using the lowest possible detection method(s), e.g., graphite furnace. 

* Based on your existing TBLLs, as presented in Item II., list in Column (2), for each pollutant the 

Maximum Allowable Industrial Headwork Loading (MAIHL) values derived from an applicable 

environmental criteria or standard, e.g., water quality, sludge, NPDES, inhibition, etc. For each 

pollutant, the MAIHL equals the calculated Maximum Allowable Headwork Loading (MAHL) 

minus the POTW's domestic loading source(s). For more information, please see p. 3-28 in 

EPA’s Guidance Manual on the Development and Implementation of Local Limits Under the 

Pretreatment Program, 12/87. 

ITEM VI. 

* Using current sampling data, list in Column (1) the average and maximum amount of pollutants 

(in micrograms per liter) present in your POTW’s effluent. Current sampling data is defined as 

data obtained during the last 24-month period. 

All effluent data collected and analyzed must be in accordance with 40 CFR 136. Sampling data 

collected should be analyzed using the lowest possible detection method(s), e.g., graphite furnace. 

* List in Column (2A) what the Water Quality Standards (WQS) were (in micrograms per liter) 

when your TBLLs were calculated, please note what hardness value was used at that time. 

Hardness should be expressed in milligram per liter of calcium carbonate. 

List in Column (2B) the current WQSs or “Chronic Gold Book” values for each pollutant 

multiplied by the dilution ratio used in your new/reissued NPDES permit. For example, with a 

dilution ratio of 25:1 at a hardness of 25 mg/L - calcium carbonate (copper’s chronic WQS equals 

6.54 ug/L) the chronic NPDES permit limit for copper would equal 156.25 ug/L. 

X-2
ITEM VII.

* In Column (1), list all pollutants (in micrograms per liter) limited in your new/reissued NPDES 

permit. In Column (2), list all pollutants limited in your old/expired NPDES permit. 

ITEM VIII. 

* Using current sampling data, list in Column (1) the average and maximum amount of pollutants 

in your POTW's biosolids. Current data is defined as data obtained during the last 24 month 

period. Results are to be expressed as total dry weight. 

All biosolids data collected and analyzed must be in accordance with 40 CFR 136. 

In Column (2A), list current State and/or Federal sludge standards that your facility’s biosolids 

must comply with. Also note how your POTW currently manages the disposal of its biosolids. If 

your POTW is planing on managing its biosolids differently, list in Column (2B) what your new 

biosolids criteria will be and method of disposal. 

In general, please be sure the units reported are correct and all pertinent information is included in your 

evaluation. If you have any questions, please contact your pretreatment representative at EPA - New 

England. 

X-3
--------- ----------- --------- -----------

--------- ----------- --------- -----------

--------- ----------- --------- -----------

--------- ----------- --------- -----------

--------- ----------- --------- -----------

--------- ----------- --------- -----------

--------- ----------- --------- -----------

REASSESSMENT OF TECHNICALLY BASED LOCAL LIMITS


(TBLLs)


POTW Name & Address :


_____________________________________________


NPDES PERMIT # :


_________________________________________________


Date EPA approved current TBLLs :


________________________________


Date EPA approved current Sewer Use Ordinance :


__________________


ITEM I.


In Column (1), list the conditions that existed when your current


TBLLs were calculated. In Column (2), list current conditions or


expected conditions at your POTW.


Column (1) Column (2)


EXISTING TBLLs


POTW Flow (MGD)


SIU Flow (MGD)


Dilution Ratio or


7Q10 (from NPDES Permit)


Safety Factor 


Biosolids Disposal


Method(s)


POLLUTANT


PRESENT CONDITIONS


N/A


NUMERICAL


LIMIT


(mg/L) or (lb/day)


ITEM II.


EXISTING TBLLs 


NUMERICAL LIMIT 


(mg/L) or (lb/day)


POLLUTANT


X-4
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ITEM III.


Note how your existing TBLLs, listed in Item II., are allocated


to your Significant Industrial Users (SIUs), i.e., uniform


concentration, contributory flow, mass proportioning, other. 


Please specify by circling. 


ITEM IV.


Has your POTW experienced any upsets, inhibition, interference or


pass-through from industrial sources since your existing TBLLs


were calculated?


If yes, explain.


_________________________________________________________________


____________________________________________________


Has your POTW violated any of its NPDES permit limits and/or


toxicity test requirements?


If yes, explain.


_________________________________________________________________


____________________________________________________


ITEM V.


Using current POTW influent sampling data fill in Column (1). In


Column (2), list your Maximum Allowable Headwork Loading (MAHL)


values used to derive your TBLLs listed in Item II. In addition,


please note the Environmental Criteria for which each MAHL value


was established, i.e., water quality, sludge, NPDES, etc.


Column (1) Column (2)


Pollutant Influent Data Analyses MAHL Values Criteria


Maximum Average


(lb/day) (lb/day) (lb/day)


Arsenic ------------------


Cadmium ------------------


Chromium ------------------


Copper ------------------


Cyanide ------------------


Lead ------------------


Mercury ------------------


Nickel ------------------


Silver ------------------


Zinc ------------------


Other (List)


------------------


------------------


------------------


X-5
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ITEM VI.


Using current POTW effluent sampling data, fill in Column (1). 


In Column (2A) list what the Water Quality Standards (Gold Book


Criteria) were at the time your existing TBLLs were developed. 


List in Column (2B) current Gold Book values multiplied by the


dilution ratio used in your new/reissued NPDES permit.


Columns


Column (1) (2A) (2B)


Pollutant Effluent Data Analyses Water Quality Criteria


Maximum Average (Gold Book)


From TBLLsToday


(ug/L) (ug/L) (ug/L) (ug/L)


Arsenic


*Cadmium


*Chromium -------------------


*Copper


Cyanide


*Lead


Mercury


*Nickel


Silver


*Zinc


Other (List)


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*Hardness Dependent (mg/L - CaCO3)


ITEM VII.


In Column (1), identify all pollutants limited in your


new/reissued NPDES permit. In Column (2), identify all


pollutants that were limited in your old/expired NPDES permit.


Column (1)


NEW PERMIT


PollutantsLimitations


(ug/L)


Column (2)


OLD PERMIT


PollutantsLimitations


(ug/L)


X-6
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ITEM VIII.


Using current POTW biosolids data, fill in Column (1). In Column


(2A), list the biosolids criteria that was used at the time your


existing TBLLs were calculated. If your POTW is planing on


managing its biosolids differently, list in Column (2B) what your


new biosolids criteria would be and method of disposal.


Columns


Column (1) (2A) (2B)


Pollutant Biosolids Data Analyses Biosolids Criteria


Arsenic


Cadmium


Chromium


Copper


Cyanide


Lead


Mercury


Nickel


Silver


Zinc


Molybdenum


Selenium


Other (List)


Average


(mg/kg)


From TBLLs New


(mg/kg)


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(mg/kg)


X-7