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United States 

Environmental Protection 

Agency 

Office of Water 

Washington, DC 

United States 

Environmental Protection Agency 

National Pollutant Discharge Elimination 

System (NPDES) Permit Writers’ Manual 

This guidance was developed by staff within the U.S. Environmental Protection Agency’s (EPA’s) Office of 

Wastewater Management and addresses development of wastewater discharge permits under the National 

Pollutant Discharge Elimination System (NPDES). NPDES permit development is governed by existing 

requirements of the Clean Water Act (CWA) and the EPA NPDES implementing regulations. CWA provisions and 

regulations contain legally binding requirements. This document does not substitute for those provisions or 

regulations. Recommendations in this guidance are not binding; the permitting authority may consider other 

approaches consistent with the CWA and EPA regulations. When EPA makes a permitting decision, it will make 

each decision on a case-by-case basis and will be guided by the applicable requirements of the CWA and 

implementing regulations, taking into account comments and information presented at that time by interested 

persons regarding the appropriateness of applying these recommendations to the situation. This guidance 

incorporates, and does not modify, existing EPA policy and guidance on developing NPDES permits. 

EPA may change this guidance in the future. 

Water Permits Division 

Office of Wastewater Management 

Washington, DC 20460 

(4203) 

www.epa.gov/npdes

EPA-833-K-10-001 

September 2010 
Acknowledgements 

David Hair and Pravin Rana, United States Environmental Protection Agency (EPA), Office of Water, Office of 

Wastewater Management, Water Permits Division, Washington, DC, were the team leaders for the development and 

production of this manual. 

Many individuals assisted in this effort, including the following: 

EPA, Office of Water, Office of Wastewater Management, Water Permits Division, Washington, DC 

 Mohammed Billah 

 Pat Bradley 

 Elaine Brenner 

 Jennifer Chan 

 Kawana Cohen 

 Juhi Saxena 

 Louis Eby 

 Jack Faulk 

 Sara Hilbrich 

 Jamie Hurley 

 Caitlin Kovzelove 

 Tom Laverty 

 Jennifer Molloy 

 Deborah Nagle 

 Jan Pickrel 

 Jane Rice, ORISE Intern 

 Greg Schaner 

 Martha Segall 

 George Utting 

 Kevin Weiss 

 Marcus Zobrist 

EPA, Office of Water, Washington, DC 

 Bob Bastian, Office of Wastewater Management, Municipal Support Division 

 Tom Gardner, Office of Science and Technology, Standards and Health Protection Division 

 Meghan Hessenauer, Office of Science and Technology, Engineering and Analysis Division 

 Carey Johnston, Office of Science and Technology, Engineering and Analysis Division 

 Dick Reding, Office of Science and Technology, Engineering and Analysis Division 

 Marla Smith, Office of Science and Technology, Engineering and Analysis Division 

Additional EPA Contributors 

 Robert Hargrove, Office of Enforcement and Compliance Assurance, Office of Federal Activities, Washington, DC 

 Robert Klepp, Office of Enforcement and Compliance Assurance, Office of Civil Enforcement, 

Washington, DC 

 Doug Corb, Region 1 New England NPDES Municipal Permit Branch, Boston, MA 

Jennifer Duckworth and Gregory Currey, Tetra Tech, Inc., Permits and Regulatory Support, Fairfax, VA managed 

production and technical support for development of the manual. 

Additional contributors from Tetra Tech, Inc. for development, design, and final production of this document include 

 Krista Carlson 

 Jim Collins 

 Chuck Durham 

 Steve Geil 

 Shari Goodwin 

 John Kosco 

 I-Hsin Lee 

 Gregory Mallon 

 Betty Peterson 

 Gregory Savitske 

 Peter Sherman 

 Kristin Schatmeyer 

 Jeff Strong 

Cover and Exhibit 1-2 Photo Credits

1. Natchez-Tennessee Tombigbee Waterway—Peter Cada, Tetra Tech, Inc. 

2. Municipal Publicly Owned Treatment Works—Ohio Environmental Protection Agency 

3. Municipal Separate Storm Sewer System—USDA NRCS 

4. Concentrated Animal Feeding Operation—USDA NRCS 

5. Incidental Vessel Discharges—Smithsonian Environmental Research Center, 

National Ballast Information Clearinghouse 

6. Non-Municipal (Industrial)—EPA 

7. Construction Stormwater—Barry Tonning, Tetra Tech, Inc. 

8. Combined Sewer Overflow—EPA 
September 2010 NPDES Permit Writers’ Manual 

i

Contents 

Introduction to the Manual ............................................................................................................. vii

Purpose of this Manual .............................................................................................................vii 

Publications Referenced .......................................................................................................... viii 

Legislative and Regulatory Citations........................................................................................ viii 

Electronic NPDES Information ...................................................................................................ix 

CHAPTER 1. Development of the Clean Water Act and the NPDES Program ........................ 1-1

1.1 History of Water Pollution Control in the United States.................................................. 1-1 

1.2 Evolution of the NPDES Program .................................................................................. 1-3 

1.3 NPDES Statutory Framework ........................................................................................ 1-5 

1.3.1 Permit ................................................................................................................ 1-5

1.3.2 Pollutant............................................................................................................. 1-6

1.3.3 Waters of the United States...............................................................................1-6 

1.3.4 Point Source...................................................................................................... 1-7 

CHAPTER 2. Regulatory Framework and Program Areas of the NPDES Program ................ 2-1

2.1 Regulatory Framework of the NPDES Program............................................................. 2-1 

2.2 Federal and State Responsibilities ................................................................................2-2 

2.2.1 State NPDES Program Authority....................................................................... 2-2 

2.2.2 Roles and Responsibilities of the Federal and State Authorities ....................... 2-4 

2.3 NPDES Program Areas ................................................................................................. 2-5 

2.3.1 NPDES Program Areas Applicable to Municipal Sources ................................. 2-5 

2.3.2 NPDES Program Areas Applicable to Non-Municipal Sources........................ 2-10 

2.4 Major/Minor Facility Designation.................................................................................. 2-17 

2.5 Growth and Change in the NPDES Program ............................................................... 2-17 

CHAPTER 3. Overview of the NPDES Permitting Process ....................................................... 3-1

3.1 Types of Permits............................................................................................................ 3-1 

3.1.1 Individual Permits .............................................................................................. 3-1 

3.1.2 General Permits................................................................................................. 3-1 

3.2 Major Components of a Permit ...................................................................................... 3-2 

3.3 Overview of the Development and Issuance Process for NPDES Individual Permits .... 3-3 

3.4 Overview of the Development and Issuance Process for NPDES General Permits ...... 3-5 

CHAPTER 4. NPDES Permit Application Process..................................................................... 4-1

4.1 Who Applies for an NPDES Permit?.............................................................................. 4-1 

4.2 Application Deadlines .................................................................................................... 4-3 

4.3 Application Forms and Requirements for Individual Permits.......................................... 4-3 

4.3.1 Form 1: General Information..............................................................................4-5 

4.3.2 Form 2A: New and Existing POTWs.................................................................. 4-5 

4.3.3 Form 2S: New and Existing TWTDS ................................................................. 4-6 

4.3.4 Form 2B: New and Existing Concentrated Animal Feeding Operations 

(CAFOs) and Concentrated Aquatic Animal Production (CAAP) Facilities ........ 4-7 

4.3.5 Form 2C: Existing Manufacturing, Commercial, Mining, and Silvicultural 

Discharges......................................................................................................... 4-8 

4.3.6 Form 2D: New Manufacturing, Commercial, Mining, and Silvicultural 

Discharges of Process Wastewater................................................................... 4-8 

4.3.7 Form 2E: Manufacturing, Commercial, Mining, and Silvicultural Facilities 

that Discharge Only Non-Process Wastewater.................................................. 4-8 
September 2010 NPDES Permit Writers’ Manual 

4.3.8 Form 2F: Stormwater Discharges Associated with Industrial Activities ............. 4-9 

4.3.9 Stormwater Discharges Associated with Construction Activity .......................... 4-9 

4.3.10 Stormwater Discharges from Small MS4s ....................................................... 4-11 

4.3.11 Cooling Water Intake Structures...................................................................... 4-11 

4.4 Requirements for NPDES General Permits ................................................................. 4-12 

4.5 Application Review ...................................................................................................... 4-13 

4.5.1 The Complete Application................................................................................ 4-14 

4.5.2 Common Omissions in Applications ................................................................ 4-14 

4.5.3 The Accurate Application................................................................................. 4-16 

4.6 Facility Information Review.......................................................................................... 4-17 

4.6.1 Permit File Review........................................................................................... 4-17 

4.6.2 Facility Site Visits............................................................................................. 4-19 

4.7 Confidential Information............................................................................................... 4-21

CHAPTER 5. Technology-Based Effluent Limitations .............................................................. 5-1

5.1 Technology-based Effluent Limitations for POTWs ....................................................... 5-2 

5.1.1 Secondary and Equivalent to Secondary Treatment Standards ........................ 5-2 

5.1.2 Adjustments to Equivalent to Secondary Standards.......................................... 5-4 

5.1.3 Applying Secondary Treatment Standards, Equivalent to Secondary 

Treatment Standards, and Adjusted Standards................................................. 5-6 

5.2 Technology-Based Effluent Limitations for Industrial (Non-POTW) Dischargers ......... 5-13 

5.2.1 Effluent Guidelines .......................................................................................... 5-14 

5.2.2 Applying Effluent Guidelines through NPDES Permits .................................... 5-23 

5.2.3 Case-by-Case TBELs for Industrial Dischargers ............................................. 5-44 

CHAPTER 6. Water Quality-Based Effluent Limitations ........................................................... 6-1

6.1 Determine Applicable Water Quality Standards............................................................. 6-2 

6.1.1 Components of Water Quality Standards .......................................................... 6-3 

6.1.2 Water Quality Standards Modifications.............................................................. 6-9 

6.1.3 Water Quality Standards Implementation ........................................................ 6-11 

6.2 Characterize the Effluent and the Receiving Water ..................................................... 6-12 

6.2.1 Step 1: Identify Pollutants of Concern in the Effluent....................................... 6-13 

6.2.2 Step 2: Determine Whether Water Quality Standards Provide for 

Consideration of a Dilution Allowance or Mixing Zone..................................... 6-15 

6.2.3 Step 3: Select an Approach to Model Effluent and Receiving Water 

Interactions......................................................................................................6-16 

6.2.4 Step 4: Identify Effluent and Receiving Water Critical Conditions.................... 6-16 

6.2.5 Step 5: Establish an Appropriate Dilution Allowance or Mixing Zone .............. 6-20 

6.3 Determine the Need for WQBELs................................................................................ 6-22 

6.3.1 Defining Reasonable Potential ........................................................................ 6-23 

6.3.2 Conducting a Reasonable Potential Analysis Using Data ............................... 6-23 

6.3.3 Conducting a Reasonable Potential Analysis without Data ............................. 6-30 

6.4 Calculate Parameter-specific WQBELs ....................................................................... 6-31 

6.4.1 Calculating Parameter-specific WQBELs from Aquatic Life Criteria ................ 6-31 

6.4.2 Calculating Chemical-specific WQBELs based on Human Health Criteria 

for Toxic Pollutants .......................................................................................... 6-35 

6.5 Calculate Reasonable Potential and WQBELs for WET .............................................. 6-36 

6.5.1 Types of WET Tests ........................................................................................ 6-36 

6.5.2 Expressing WET Limitations or Test Results................................................... 6-37 

6.5.3 Determining the Need for WET Limitations...................................................... 6-38 

6.6 Antidegradation Review............................................................................................... 6-40 

6.6.1 Tier 1 Implementation...................................................................................... 6-41 

6.6.2 Tier 2 Implementation...................................................................................... 6-41 

6.6.3 Tier 3 Implementation...................................................................................... 6-42 

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September 2010 NPDES Permit Writers’ Manual 

CHAPTER 7. Final Effluent Limitations and Anti-backsliding.................................................. 7-1

7.1 Determining Final Effluent Limitations............................................................................7-1 

7.2 Applying Anti-backsliding Requirements........................................................................ 7-2 

7.2.1 Anti-backsliding Statutory Provisions................................................................. 7-2 

7.2.2 Anti-backsliding Regulatory Provisions.............................................................. 7-4 

CHAPTER 8. Monitoring and Reporting Conditions ................................................................. 8-1

8.1 Establishing Monitoring Conditions................................................................................ 8-1 

8.1.1 Purposes of Monitoring......................................................................................8-2 

8.1.2 Monitoring Location ........................................................................................... 8-2 

8.1.3 Monitoring Frequency........................................................................................ 8-5 

8.1.4 Sample Collection.............................................................................................. 8-7 

8.2 Additional Monitoring Requirements and WET Testing ................................................. 8-9 

8.2.1 Biosolids (Sewage Sludge)................................................................................ 8-9 

8.2.2 Combined Sewer Overflows (CSOs) and Sanitary Sewer Overflows (SSOs).. 8-11 

8.2.3 Stormwater Monitoring Considerations............................................................ 8-11 

8.2.4 WET Monitoring............................................................................................... 8-12 

8.3 Analytical Methods....................................................................................................... 8-13 

8.4 Reporting Monitoring Results....................................................................................... 8-14 

8.5 Recordkeeping Requirements ..................................................................................... 8-14 

CHAPTER 9. Special Conditions ................................................................................................ 9-1

9.1 Special Conditions Potentially Applicable to Any Type of Discharger............................ 9-1 

9.1.1 Additional Monitoring and Special Studies ........................................................ 9-2 

9.1.2 Best Management Practices (BMPs)................................................................. 9-3 

9.1.3 Compliance Schedules...................................................................................... 9-8 

9.2 Special Conditions for Municipal Facilities..................................................................... 9-9 

9.2.1 The National Pretreatment Program................................................................ 9-10 

9.2.2 Biosolids (Sewage Sludge).............................................................................. 9-13 

9.2.3 Combined Sewer Overflows (CSOs) ............................................................... 9-15 

9.2.4 Sanitary Sewer Overflows (SSOs)................................................................... 9-20 

CHAPTER 10. Standard Conditions of NPDES Permits............................................................ 10-1

10.1 Types of Standard Conditions...................................................................................... 10-1 

10.2 Other Standard Conditions .......................................................................................... 10-3 

CHAPTER 11. NPDES Permit Administration............................................................................ 11-1

11.1 Other Federal Laws Applicable to NPDES Permits ..................................................... 11-1 

11.1.1 Endangered Species Act ................................................................................. 11-1 

11.1.2 National Environmental Policy Act................................................................... 11-2 

11.1.3 National Historic Preservation Act Amendments ............................................. 11-3 

11.1.4 Coastal Zone Management Act ....................................................................... 11-3 

11.1.5 Wild and Scenic Rivers Act.............................................................................. 11-3 

11.1.6 Fish and Wildlife Coordination Act................................................................... 11-4 

11.1.7 Essential Fish Habitat Provisions .................................................................... 11-4 

11.2 Documentation for Development of the Draft Permit ................................................... 11-4 

11.2.1 Administrative Record ..................................................................................... 11-8 

11.2.2 Fact Sheets and Statements of Basis.............................................................. 11-8 

11.3 Items to Address before Issuing a Final Permit ......................................................... 11-10 

11.3.1 Public Notice.................................................................................................. 11-11 

11.3.2 Public Comments .......................................................................................... 11-12 

11.3.3 Public Hearings ............................................................................................. 11-13 

11.3.4 Environmental Justice Considerations........................................................... 11-14 

11.3.5 EPA and State/Tribal Roles in Reviewing Draft Permits................................ 11-14 

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September 2010 NPDES Permit Writers’ Manual 

11.3.6 Schedule for Final Permit Issuance ............................................................... 11-15 

11.4 Administrative Actions after Final Permit Issuance .................................................... 11-16 

11.4.1 Permit Appeals .............................................................................................. 11-16 

11.4.2 Modification or Revocation and Reissuance of Permits................................. 11-18 

11.4.3 Permit Termination ........................................................................................ 11-20 

11.4.4 Permit Transfer..............................................................................................11-21 

11.5 Permit Compliance and Enforcement ........................................................................ 11-21 

11.5.1 Compliance Monitoring.................................................................................. 11-22 

11.5.2 Quarterly Noncompliance Reports................................................................. 11-23 

11.5.3 Enforcement .................................................................................................. 11-25 

Appendix A. Acronyms, Abbreviations and Glossary............................................................. A-1

A.1 Acronyms and Abbreviations .........................................................................................A-1 

A.2 Glossary.........................................................................................................................A-4 

Appendix B. Index to the CWA and NPDES Regulations........................................................ B-1

B.1 Index to Sections of the CWA ........................................................................................B-1 

B.2 Index to NPDES Regulations.........................................................................................B-3 

Appendix C. Priority Pollutants................................................................................................. C-1

Appendix D. New Source Dates by Effluent Guideline Category ........................................... D-1

Exhibits 

Exhibit 1-1 Important milestones of clean water program development ...........................................1-1 

Exhibit 1-2 Common point source discharges of pollutants to waters of the United States..............1-8 

Exhibit 2-1 Regulations related to the NPDES program...................................................................2-2 

Exhibit 2-2 Federal NPDES regulations (40 CFR Part 122) .............................................................2-3 

Exhibit 2-3 Summary of federal and state/territorial/tribal roles in the NPDES permitting 

program .........................................................................................................................2-5 

Exhibit 2-4 NPDES program areas and applicable regulations ........................................................2-6 

Exhibit 3-1 Permit components ........................................................................................................3-3 

Exhibit 3-2 Major steps to develop and issue NPDES individual permits .........................................3-4 

Exhibit 3-3 Major steps to develop and issue NPDES general permits ............................................3-5 

Exhibit 4-1 Effect of court decisions on § 122.3 ...............................................................................4-2 

Exhibit 4-2 When to apply for an NPDES permit..............................................................................4-3 

Exhibit 4-3 EPA application requirements for NPDES individual permits .........................................4-4 

Exhibit 4-4 Permit application review process ................................................................................4-13 

Exhibit 4-5 Considerations for an application to be complete.........................................................4-15 

Exhibit 4-6 Example of required testing during application review .................................................4-16 

Exhibit 4-7 Considerations for an application to be accurate..........................................................4-18 

Exhibit 5-1 Developing effluent limitations........................................................................................5-1 

Exhibit 5-2 Secondary treatment standards .....................................................................................5-2 

Exhibit 5-3 Equivalent to secondary treatment standards ................................................................5-3 

Exhibit 5-4 State-specific adjusted TSS requirements .....................................................................5-5 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 5-5 Steps to establish technology-based discharge limitations for POTWs..........................5-6 

Exhibit 5-6 Effluent limitations calculated from secondary treatment standards...............................5-7 

Exhibit 5-7 POTW mass based limitation calculation equation and example calculations ...............5-8 

Exhibit 5-8 Summary of CWA technology levels of control ............................................................5-15 

Exhibit 5-9 Visual example of TSS LTA, maximum daily limitation and average monthly 

limitation.......................................................................................................................5-21 

Exhibit 5-10 Steps for applying effluent guidelines to direct discharges.........................................5-23 

Exhibit 5-11 Table of existing point source categories (June 2010) ...............................................5-24 

Exhibit 5-12 Examples of identifying applicable effluent guidelines using SIC codes.....................5-25 

Exhibit 5-13 Examples of identifying the subcategory with the applicable effluent guidelines........5-27 

Exhibit 5-14 Example of calculating mass-based effluent limitation from production-normalized 

effluent guidelines........................................................................................................5-31 

Exhibit 5-15 Example narrative requirement from the Concentrated Aquatic Animal Production 

effluent guideline—Subpart A [§ 455.11(a)].................................................................5-33 

Exhibit 5-16 Exclusion of wastewaters in metal finishing effluent guidelines..................................5-34 

Exhibit 5-17 Excerpts from preamble to OCPSF effluent guidelines regarding applicability of 

effluent guidelines........................................................................................................5-34 

Exhibit 5-18 Building block approach for applying effluent guidelines ............................................5-36 

Exhibit 5-19 Example of tiered discharge limitations ......................................................................5-38 

Exhibit 5-20 Variances from effluent guidelines .............................................................................5-40 

Exhibit 5-21 Summary of factors considered when developing case-by-case TBELs ....................5-46 

Exhibit 5-22 Tools for developing case-by-case TBELs using BPJ................................................5-48 

Exhibit 6-1 Developing effluent limitations........................................................................................6-1 

Exhibit 6-2 Standards-to-permits process ........................................................................................6-2 

Exhibit 6-3 Aquatic life criteria example: Cadmium (dissolved)........................................................6-5 

Exhibit 6-4 Human health criteria example: Dichlorobromomethane................................................6-7 

Exhibit 6-5 Steps for characterizing the effluent and receiving water.............................................6-13 

Exhibit 6-6 Parts of a TMDL ...........................................................................................................6-14 

Exhibit 6-7 Example of lognormal distribution of effluent pollutant concentrations and projection 

of critical concentration (Cd).........................................................................................6-18 

Exhibit 6-8 Regulatory mixing zones for aquatic life criteria ...........................................................6-21 

Exhibit 6-9 Examples of maximum mixing zone sizes or dilution allowances under incomplete 

mixing conditions by waterbody type ...........................................................................6-22 

Exhibit 6-10 Steps of a reasonable potential analysis with available data......................................6-23 

Exhibit 6-11 Simple mass-balance equation ..................................................................................6-24 

Exhibit 6-12 Example of receiving water concentrations in an incomplete mixing situation 

determined using an incomplete mixing water quality model .......................................6-26 

Exhibit 6-13 Mass-balance equation for reasonable potential analysis for conservative pollutant 

under conditions of rapid and complete mixing............................................................6-27 

Exhibit 6-14 Example of applying mass-balance equation to conduct reasonable potential 

analysis for conservative pollutant under conditions of rapid and complete mixing .....6-28 

Exhibit 6-15 Reasonable potential determination in an incomplete mixing situation ......................6-29 

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September 2010 NPDES Permit Writers’ Manual 

vi

Exhibit 6-16 Calculating parameter-specific WQBELs from aquatic life criteria..............................6-31 

Exhibit 6-17 Example of applying mass-balance equation to calculate WLAs for conservative 

pollutant under conditions of rapid and complete mixing .............................................6-33 

Exhibit 6-18 Example of lognormal distribution of effluent pollutant concentrations and 

calculation of WLA.......................................................................................................6-34 

Exhibit 6-19 Example of typical dilution series ...............................................................................6-36 

Exhibit 6-20 Example of toxic units ................................................................................................6-37 

Exhibit 6-21 Using the ACR............................................................................................................6-38 

Exhibit 6-22 Example of mass-balance equation for a WET reasonable potential analysis ...........6-39 

Exhibit 7-1 Developing effluent limitations........................................................................................7-1 

Exhibit 7-2 Application of anti-backsliding rules ...............................................................................7-5 

Exhibit 7-3 Backsliding examples.....................................................................................................7-6 

Exhibit 8-1 Examples of specifying monitoring locations in permits .................................................8-3 

Exhibit 8-2 Visual interpretation of time-proportional composite monitoring.....................................8-8 

Exhibit 8-3 Visual interpretation of flow-proportional composite monitoring .....................................8-8 

Exhibit 8-4 Minimum requirements for sewage sludge monitoring, based on method of sludge 

use or disposal.............................................................................................................8-10 

Exhibit 9-1 Example BMP plan requirement.....................................................................................9-6 

Exhibit 9-2 Categories of CSO permitting conditions .....................................................................9-17 

Exhibit 9-3 Nine minimum CSO controls ........................................................................................9-17 

Exhibit 9-4 Elements of the long-term CSO control plan ................................................................9-18 

Exhibit 11-1 Other federal laws applicable to NPDES permits .......................................................11-1 

Exhibit 11-2 Reasons for good documentation...............................................................................11-5 

Exhibit 11-3 Administrative process for EPA-issued NPDES permits ............................................11-6 

Exhibit 11-4 Typical administrative process for state-issued NPDES permits................................11-7 

Exhibit 11-5 Elements of the administrative records for a draft permit ...........................................11-8 

Exhibit 11-6 Required elements of a fact sheet..............................................................................11-9 

Exhibit 11-7 Actions for which public notice is required................................................................11-11 

Exhibit 11-8 Contents of the public notice ....................................................................................11-12 

Exhibit 11-9 Elements of the administrative records for a final permit..........................................11-16 

Exhibit 11-10 Causes for permit modification...............................................................................11-19 

Exhibit A-1 Acronyms and abbreviations......................................................................................... A-1 

Exhibit A-2 Glossary........................................................................................................................ A-5 

Exhibit B-1 Index to sections of the CWA........................................................................................ B-1 

Exhibit B-2 Index to NPDES regulations ......................................................................................... B-3 

Exhibit C-1 Priority pollutants from 40 CFR Part 423, Appendix A.................................................. C-1 

Exhibit D-1 New source dates by effluent category......................................................................... D-2 
September 2010 NPDES Permit Writers’ Manual 

vii

Introduction to the Manual 

This manual reviews the statutory and regulatory framework of the National Pollutant Discharge 

Elimination System (NPDES) program and examines technical considerations for developing NPDES 

permits for wastewater discharges. The manual is designed, primarily, for new permit writers becoming 

acquainted with the NPDES program and the process of permit writing, but can also serve as a reference 

for experienced permit writers or anyone interested in learning about the legal and technical aspects of 

developing NPDES permits. This manual replaces the 1996 U.S. EPA NPDES Permit Writers’ Manual1

<www.epa.gov/npdes/pubs/owm0243.pdf>, which updated the 1993 Training Manual for NPDES Permit 

Writers2 <www.epa.gov/npdes/pubs/owm0339.pdf>. 

To assist the reader, acronyms and abbreviations are defined for the first use in each chapter and in 

Appendix A of the manual. Endnotes are provided at the end of each chapter. 

Purpose of this Manual 

The purpose of this NPDES Permit Writers’ Manual (manual) is to provide a general reference for 

permitting authorities that outlines and explains the core elements of the NPDES permit program. The 

core elements form the foundation of the NPDES program on which guidance for specific areas of the 

program (e.g., stormwater, concentrated animal feeding operations) can be built. While the guidance for 

these core program areas will be applicable in many cases, the U.S. Environmental Protection Agency 

(EPA) recognizes that each EPA Regional Office or authorized state, territory, or tribe (hereafter state) 

will tailor specific aspects of its NPDES permitting procedures to address state and local laws and sitespecific concerns and conditions. 

The specific objectives and functions of this manual are as follows: 

 Provide an overview of the scope and the statutory and regulatory framework of the NPDES 

program. 

 Describe the essential components of a permit and provide an overview of the permitting process. 

 Describe the different types of effluent limitations and the legal and technical considerations 

involved in developing effluent limitations. 

 Describe the legal and technical considerations involved in developing other permit conditions 

including 

− Monitoring and reporting requirements. 

− Special conditions. 

− Standard conditions. 

 Describe other permitting considerations including 

− Variances. 

− Anti-backsliding. 

− Other applicable statutes. 
September 2010 NPDES Permit Writers’ Manual 

 Explain the administrative process for issuing, modifying, revoking and terminating NPDES 

permits. 

This manual is not intended to be a standalone reference document. Rather, it establishes the framework 

for NPDES permit development and should be supplemented, where necessary, by additional EPA and 

state regulations, policy, and detailed guidance applicable to specific types of dischargers and 

circumstances. To that end, this manual identifies and references relevant regulations, policy, and other 

guidance documents throughout the text. 

Publications Referenced 

This manual provides links to publications available online that supplement the information in the 

manual. All documents available electronically were accessed and available as of the date of this 

manual’s publication. Some documents are not available in an electronic format. In those instances, 

readers should check the following sources to determine the availability of and to obtain printed copies of 

the documents: 

 Office of Water Resource Center (OWRC) <www.epa.gov/safewater/resource/>

OWRC is a contractor-operated facility providing document delivery, information/referral, and 

reference services to public users and EPA staff interested in Office of Water Program 

information 

phone: 202-566-1729 or 800-832-7828, fax: 202-566-1736, e-mail: 

<center.water-resource@epa.gov>. 

 EPA Library Services and Repositories <www.epa.gov/natlibra/libraries.htm> 

EPA’s library services and repositories provide access to information about the environment and 

related scientific, technical, management, and policy information. Library services 

<www.epa.gov/natlibra/library_services.html> are delivered through the National Library Network 

<www.epa.gov/natlibra/index.html>. 

 National Service Center for Environmental Publications (NSCEP) <www.epa.gov/ncepihom/> 

NSCEP, formerly NCEPI, maintains and distributes EPA publications in hardcopy, CD ROM and 

other multimedia formats. The publication inventory includes more than 7,000 titles 

phone: 513-489-8190 or 800-490-9198, fax: 513-489-8695, e-mail: ncepimal@one.net. 

 National Technical Information Service (NTIS) <www.ntis.gov/> 

NTIS is the largest central resource for government-funded scientific, technical, engineering, and 

business related information covering more than 350 subject areas from more than 200 federal 

agencies 

phone: 703-605-6050 or 888-584-8332, fax: 703-605-6900, e-mail: customerservice@ntis.gov. 

Legislative and Regulatory Citations 

There are a number of different conventions used to cite legislation and regulations. In this manual, the 

following conventions have been used: 

 When citing the United States Code, the abbreviation U.S.C. is used. The abbreviation is 

preceded by the Title of the U.S.C. and then followed by the section number. 

 Example: 16 U.S.C. 1531 et seq. and 33 U.S.C. §§ 1251-1387. 

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September 2010 NPDES Permit Writers’ Manual 

 When citing the Clean Water Act, the abbreviation CWA is used. The abbreviation is followed by 

the word section and then the section number. 

 Example: CWA section 402 and CWA section 402(o). 

 When citing the Code of Federal Regulations (CFR), the convention depends on the location of 

the reference. For first references, the abbreviation CFR is preceded by the title number of the 

CFR and followed either by the word Part (if it is a part—a whole number) or the number of the 

subsection (if it is a subpart/subsection). For subsequent references, the title and CFR are omitted 

and just the word Part or the section symbol (§) is used. 

 Example: First citation: 40 CFR Part 136 or 40 CFR 122.44 

 Subsequent citations: Part 136 or § 122.44. 

Almost all the regulatory citations in this manual are for Title 40 of the CFR (with the exception of the 

other federal laws referenced in section 11.1 of this manual). Any other Titles are explicitly referenced 

and in the format for the first regulatory citation (e.g., 50 CFR Part 402). 

Electronic NPDES Information 

Websites and electronically stored publications and data are available to help permit writers draft NPDES 

permits. Tools have been created to assist permit writers with specific aspects of permit development and 

are discussed in their respective sections. The electronic tools listed below apply to all aspects of permit 

development and serve as valuable references for the permit writer. 

NPDES Website and Resources 

The Water Permits Division (WPD) within the EPA Office of Water (OW), Office of Wastewater 

Management, has developed a comprehensive NPDES Website <www.epa.gov/npdes> with technical and 

regulatory information about the NPDES permit program, information on related programs and initiatives, 

and documents published by WPD. Where applicable, this manual references the NPDES Website and 

provides links to relevant documents on that site. This manual also references other EPA and non-EPA 

websites that contain information that might be helpful to NPDES permit writers. Note, however, that 

EPA is not responsible for information provided on websites outside the EPA Website <www.epa.gov>. 

WPD also has prepared several websites and other resources to help permit writers draft permits. This 

manual references those websites and resources in the appropriate section of this manual. 

Electronic Permitting Tools 

Many EPA Regions and authorized states have developed tools to help them manage the permit issuance 

process. Electronic permitting tools range from spreadsheets and word processing applications to 

sophisticated Web-based systems that enable permitting authorities to manage their entire environmental 

program. For example, some states have built systems that enable dischargers to electronically sign and 

submit discharge reports; create, track, and store permit documents; and manage enforcement, 

compliance, and inspections related to permits. As technologies continue to evolve, many permitting 

authorities are likely to begin using more information technology applications to manage the process of 

permitting. 

ix
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x

ICIS-NPDES 

Together with OW, the Office of Enforcement and Compliance Assurance (OECA) is responsible for 

oversight of implementation of the NPDES program. OW is responsible for the NPDES implementing 

regulations and oversight of permit issuance by states and EPA Regions. OECA, along with its regional, 

state, tribal and local counterparts, is responsible for tracking and maintaining enforcement and 

compliance activities, monitoring and enforcement and compliance status of the regulated community, 

and reviewing and evaluating program performance. OECA also maintains national data systems to 

support program management and oversight of the NPDES program. 

The Permit Compliance System (PCS), one of two national NPDES electronic databases, supports the 

management and oversight of the NPDES program. Since the last modernization of PCS in 1985, the 

NPDES program has evolved significantly to include additional program requirements, such as the 

NPDES program for stormwater and implementation of the Combined Sewer Overflow Control Policy. 

Because of limitations to PCS, OECA is working to phase out this system and move to a more modern 

data management system described below. 

The Integrated Compliance Information System for NPDES permits (ICIS-NPDES)

<https://icis.epa.gov/icis>, the successor to PCS, provides an updated system that enables national program 

management and oversight activities such as 

 Permit tracking and management. 

 Compliance monitoring. 

 NPDES program management. 

 Enforcement actions. 

ICIS-NPDES is a Web-based system with an electronic database capable of handling the large amount of 

data generated by and about the NPDES program. Section 11.5.1.1 of this manual provides more 

information on ICIS-NPDES as it relates to NPDES permit compliance. 

Hyperlinks in this Document 

Where a website provides supplementary information or is referenced in this manual, the actual site or 

higher level site address appears in the symbols < > so that readers will have a reference to the address 

even in a printed version of this document. In the electronic version of the manual, the text in carats is 

also the hyperlink to the referenced website. Care has been taken to provide the correct Web addresses 

and hyperlinks; however, these references can change or become outdated after this manual’s publication. 

 

1

 U.S. Environmental Protection Agency. 1996. U.S. EPA NPDES Permit Writers’ Manual. EPA-833-B-96-003. U.S. 

Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/owm0243.pdf>. Separate 

sections of this document are also available on the NPDES Website by going to <www.epa.gov/npdes>, clicking on Publications 

and entering NPDES Permit Writers’ Manual in the Search box. 

2

 U.S. Environmental Protection Agency. 1993. Training Manual for NPDES Permit Writers. EPA-833-B-93-003. U.S. 

Environmental Protection Agency, Office of Wastewater Management, Washington, DC. 

<www.epa.gov/npdes/pubs/owm0339.pdf>. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 1: Development of the Clean Water Act and the NPDES Program 1-1

CHAPTER 1. Development of the Clean Water Act and the 

NPDES Program 

This chapter presents an overview of the history of water pollution control in the United States and the 

evolution and accomplishments of the National Pollutant Discharge Elimination System (NPDES) 

Program. 

1.1 History of Water Pollution Control in the United States 

Major water pollution control legislation in the United States dates back to the end of the 19th century. 

Exhibit 1-1 presents a summary of key legislative and executive actions in the history of clean water 

program development in the United States. 

Exhibit 1-1 Important milestones of clean water program development 

1899 Rivers and Harbors Act 

1948 Federal Water Pollution Control Act (FWPCA) 

1965 Water Quality Act 

1970 Executive Order–U.S. Environmental Protection Agency (EPA) established 

1970 Refuse Act Permit Program (RAPP) 

1972 FWPCA Amendments 

1977 Clean Water Act (CWA) 

1987 Water Quality Act (WQA) 

The first major water pollution control statute was the 1899 Rivers and Harbors Act, which established 

permit requirements to prevent unauthorized obstruction or alteration of any navigable water of the 

United States. That act focused on navigation rather than water quality. 

The 1948 Federal Water Pollution Control Act (FWPCA) initiated the federal government’s 

involvement in water pollution control for public health protection. The act allotted funds to state and 

local governments for water pollution control and emphasized the states’ role in controlling and 

protecting water resources with few federal limitations or guidelines. The act, however, did charge the 

U.S. Surgeon General with developing comprehensive programs to eliminate or reduce the pollution of 

interstate waters. 

Over the next two decades, Congress became increasingly interested in the problem of water quality 

degradation. From 1956 through 1966, it enacted four major laws to strengthen the federal role in water 

pollution control, including the FWPCA Amendments of 1956 and the FWPCA Amendments of 1961. 

Those statutes focused primarily on providing funding to municipalities to construct wastewater treatment 

plants. 

Just a few years later, Congress further strengthened federal water pollution control laws by enacting the 

1965 Water Quality Act. This law created the Federal Water Pollution Control Administration and 
September 2010 NPDES Permit Writers’ Manual 

represented a major regulatory advancement in water pollution control by requiring states to develop 

water quality standards for interstate waters by 1967. The Water Quality Act also called for states to 

quantify the amount of pollutants that each discharger could release without exceeding the water quality 

standards (i.e., pollutant loadings). Despite escalating public concern and increased public spending, only 

about half of the states developed water quality standards by 1971. Furthermore, enforcement of the 

federal statute was minimal because the regulatory agencies had to demonstrate a direct link between a 

discharge and a health or water quality problem, and the scientific data to make such demonstrations were 

often lacking. Finally, there were no criminal or civil penalties for violations of statutory requirements. 

Growing concern about the environment prompted President Nixon to form the U.S. Environmental 

Protection Agency (EPA) in 1970 to enforce environmental compliance and consolidate federal 

pollution control activities. That year, the President also created the Refuse Act Permit Program 

(RAPP) through Executive Order 11574 and under the authority of section 13 of the 1899 Rivers and 

Harbors Act (a section also known as the Refuse Act). This new permitting program was focused on 

controlling industrial water pollution. EPA and the U.S. Army Corps of Engineers (Corps) would prepare 

the program requirements and the Corps would administer the program. EPA was tasked with developing 

guidelines on effluent quality for 22 different categories of sources. A discharger would apply for a 

permit, and the Corps would ask EPA if the proposed effluent levels were consonant with state water 

quality standards and with the newly developed guidelines on effluent quality. States would be asked to 

examine permit applications and advise EPA whether existing or proposed treatment processes would 

ensure that established water quality standards would be met. EPA would review the state’s response for 

interstate waters and instruct the Corps whether to issue the permit. However, the U.S. District Court for 

the District of Columbia struck down RAPP (Kalur v. Resor, Civ. Action No. 1331-71 [D.D.C. Dec. 21, 

1971]) because the program would allow the issuance of permits to discharge refuse to non-navigable 

tributaries of navigable waterways, which the Court said exceeded the authority given in the Act, and 

because the regulations implementing the program did not require compliance with certain procedural 

requirements of the National Environmental Policy Act. 

Because of the perceived need for a discharge permit program, and to rectify the problems encountered in 

earlier water pollution control legislation, Congress enacted the FWPCA Amendments of 1972. This 

legislation, which was passed over a Presidential veto in November 1972, provided a comprehensive recodification and revision of past federal water pollution control law. The 1972 amendments marked a 

distinct change in the philosophy of water pollution control in the United States and marked the beginning 

of the present water programs, including the NPDES permit program. Under those amendments, the 

federal government assumed a major role in directing and defining water pollution control programs. In 

establishing the basis for clean water programs, Congress sought a balance between economics 

(considering both the costs and benefits of cleanup) and ecology (setting deadlines and ambitious 

requirements for reducing discharges and restoring water quality). 

The FWPCA Amendments of 1972 established a series of goals in section 101. Perhaps the most notable 

goal was that the discharge of pollutants into navigable waters be eliminated by 1985. Although that goal 

remains unmet, it underlies the CWA approach to establishing the technology standards that are 

implemented through technology-based effluent limitations (TBELs) in NPDES permits. The FWPCA 

Amendments of 1972 also set an interim goal of achieving, “water quality [that] provides for the 

protection and propagation of fish, shellfish, and wildlife and provides for recreation in and on the water” 

by July 1, 1983. That goal is commonly referred to as the fishable, swimmable goal of the act and is one 

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of the factors that states must consider in the development of their water quality standards. The water 

quality standards are implemented in NPDES permits through water quality-based effluent limitations 

(WQBELs). By prohibiting the discharge of a pollutant or pollutants from a point source to waters of the 

United States—except as in compliance with the statute, the FWPCA Amendments of 1972 also 

established the important principle that the discharge of pollutants to navigable waters is not a right. 

Since 1972, the FWPCA has been further amended on several occasions, including the 1977 Clean 

Water Act (CWA), which is now the name for the statute, and the 1987 Water Quality Act (WQA). 

Both of these statutes are discussed further in section 1.2 below with regard to their impact on the 

evolution of the NPDES program. Exhibit B-1, Index to Sections of the CWA, in Appendix B of this 

document matches the key sections of the CWA to their appropriate reference in the United States Code

(U.S.C.). This information is at U.S.C., Title 33 (Navigation and Navigable Waters), Chapter 26 (Water 

Pollution Prevention and Control), 1251-1387 (33 U.S.C. §§ 1251-1387)

<www.epa.gov/lawsregs/laws/cwa.html>. 

1.2 Evolution of the NPDES Program 

Section 402 of Title IV of the FWPCA, Permits and Licenses, created today’s system for permitting 

wastewater discharges, known as the NPDES program. Under the requirements of the program, a point 

source may be authorized to discharge pollutants into waters of the United States by obtaining a permit. 

Section 1.3 below discusses this basic statutory framework in detail. A permit provides two types of 

control: technology-based limitations (based on the technological and economic ability of dischargers in 

the same category to control the discharge of pollutants in wastewater) and water quality-based 

limitations (to protect the quality of the specific waterbody receiving the discharge). 

The FWPCA Amendments of 1972 established several important requirements and deadlines. Municipal 

facilities were required to meet secondary treatment standards by July 1, 1977. Industrial facilities were 

required to meet two levels of technology standards: Best Practicable Control Technology Currently 

Available (BPT) and Best Available Technology Economically Achievable (BAT), which would bring 

them further toward the goal of eliminating the discharge of all pollutants. [CWA section 301 (b)(2)(A)]. 

Compliance deadlines for BPT and BAT were established as of July 1, 1977, and July 1, 1983, 

respectively. 

In addition to BPT and BAT requirements for industrial categories, the 1972 FWPCA Amendments 

established new source performance standards (NSPS) or best available demonstrated control technology 

including where practicable a standard permitting no discharge of pollutants [CWA section 306(a)]. The 

Legislative History indicates that Congress believed that technologies would be more affordable for new 

dischargers who could plan control technologies at the design phase. The standards represent state-of-theart control technologies for new sources because the permittees have the opportunity to install the most 

efficient production processes and the latest in treatment technologies during construction. NSPS are 

effective on the date the facility begins operation, and the facility must demonstrate compliance within 

90 days of start-up. 

EPA tried to set national, uniform effluent limitations guidelines and standards (effluent guidelines) as a 

basis for technology-based limitations; however, most effluent guidelines were not in place when the first 

set of permits was issued between 1973 and 1976. About 75 percent of the first round permits were issued 

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September 2010 NPDES Permit Writers’ Manual 

under a section of the act that allows a permit writer to use his or her best professional judgment to 

establish case-by-case limitations. Using that approach, a single permit writer developed effluent 

limitations for a specific facility using his or her knowledge of the industry and the specific discharge, 

rather than using a set of national standards and limitations developed by EPA for the entire industry. 

This first round of permitting focused on conventional pollutants, which generally are found in sanitary 

waste from households, businesses, and industries. CWA section 304(a)(4) and Title 40 of the Code of 

Federal Regulations (CFR) 401.16 designate the conventional pollutants with oil and grease added to 

§ 401.16 in 1979. The following are formally designated as conventional pollutants: 

 Five-day Biochemical Oxygen Demand (BOD5). 

 Total Suspended Solids (TSS). 

 pH. 

 Fecal Coliform. 

 Oil and Grease. 

The 1972 FWPCA Amendments, however, also required that EPA publish a list of toxic pollutants within 

90 days and propose effluent standards for those pollutants 6 months later. EPA was not able to meet 

those requirements because of the lack of information on treatability. The Natural Resources Defense 

Council (NRDC) sued EPA, resulting in a court supervised consent decree (NRDC et al. v. Train, 

8 E.R.C. 2120, DDC 1976) that identified the following: 

 Toxic (priority) pollutants to be controlled. 

 Primary industries for technology-based control. 

 Methods for regulating toxic discharges through the authorities of the FWPCA Amendments. 

The provisions of the consent decree were incorporated into the framework of the 1977 FWPCA 

Amendments, formally known as the CWA. This statute shifted the emphasis of the NPDES program 

from controlling conventional pollutants to controlling toxic pollutant discharges. CWA section 307(a)(1) 

required EPA to publish a list of toxic pollutants or combination of pollutants. Those pollutants often are 

called the priority pollutants and are listed in § 401.15. The terms toxic pollutant and priority pollutant

are used interchangeably throughout this document. 

CWA section 307(a) originally identified 65 toxic pollutants and classes of pollutants for 21 major 

categories of industries (known as primary industries). That list was later further defined as the current 

list of 126 toxic pollutants. The priority pollutants are listed in Appendix C of this document and in 

Appendix A of Part 423. Note that the list goes up to 129; however, there are only 126 priority pollutants 

because 017, 049, and 050 were deleted. 

The 1977 CWA adjusted technology standards to reflect the shift toward control of toxics, clarified and 

expanded the concept of BAT controls, created a new level of control for conventional pollutants, and 

made changes to strengthen the industrial pretreatment program. The 1977 law created a new pollutant 

category, nonconventional pollutants, that included pollutants (such as chlorine and ammonia) not 

specifically categorized as conventional or toxic. The CWA clarified that BAT covers both toxic and 

nonconventional pollutants, extended the compliance deadline for BAT for toxic pollutants to July 1, 

1984, established a three-year deadline for compliance with BAT for newly listed toxics, and gave 

industries until as late as July 1, 1987 to meet BAT requirements for nonconventional pollutants. In 

addition, conventional pollutants, controlled by BPT and BAT in the first round of permitting, were now 

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September 2010 NPDES Permit Writers’ Manual 

subject to a new level of control termed Best Conventional Pollutant Control Technology (BCT). The 

CWA established a compliance deadline for BCT of July 1, 1984. BCT was not an additional 

performance standard, but replaced BAT for the control of conventional pollutants. Finally, among other 

changes, the 1977 CWA authorized EPA to approve local pretreatment programs and required authorized 

states to modify their programs to provide for local pretreatment program oversight. 

The 1977 CWA recognized that the technology-based limitations were not able to prevent the discharge 

of toxic substances in toxic amounts in all waterways. To complement its work on technology-based 

limitations, EPA initiated a national policy in February 1984 to control toxics using a water quality 

approach. On February 4, 1987, Congress amended the CWA with the 1987 WQA that outlined a strategy 

to accomplish the goal of meeting state water quality standards. The 1987 WQA required all states to 

identify waters that were not expected to meet water quality standards after technology-based controls on 

point source were imposed. Each state then had to prepare individual control strategies to reduce toxics 

from point and nonpoint sources to meet the water quality standards. Among other measures, those plans 

were expected to address control of pollutants beyond technology-based levels. 

The 1987 WQA further extended the compliance deadline for BAT- and BCT-based effluent limitations, 

this time to a new deadline of March 31, 1989. The 1987 WQA also established new schedules for issuing 

NPDES permits to industrial and municipal stormwater dischargers. In addition to meeting water qualitybased standards, industrial stormwater discharges must meet the equivalent of BAT and BCT effluent 

quality standards. Municipal separate storm sewer systems (MS4s) were required to have controls to 

reduce pollutant discharges to the maximum extent practicable (MEP), including management practices, 

control techniques and system design and engineering methods, and such other provisions as the 

Administrator deems appropriate for the control of such pollutants [CWA section 402(p)(3)(B)]. The 

1987 WQA also required EPA to identify toxics in sewage sludge and establish numeric limitations to 

control such toxics. A statutory anti-backsliding requirement in the WQA specified the circumstances 

under which an existing permit can be modified or reissued with less stringent effluent limitations, 

standards, or conditions than those already imposed. 

Since 1987, there have been minor revisions to the CWA (e.g., Combined Sewer Overflow program 

requirements). However, the basic structure of the NPDES program remains unchanged from the 

framework established in the 1972 FWPCA Amendments. 

1.3 NPDES Statutory Framework 

As noted in section 1.2 above, under the NPDES program any point source that discharges or proposes to 

discharge pollutants into waters of the United States is required to obtain an NPDES permit. 

Understanding how each of these terms (i.e., permit, pollutant, waters of the United States, and point 

source) is defined is the key to defining the scope of the NPDES program. 

1.3.1 Permit 

A permit is a license, issued by the government to a person or persons granting permission to do 

something that would otherwise be illegal without the permit. An NPDES permit typically is a license for 

a facility to discharge a specified amount of a pollutant into a receiving water under certain conditions; 

however, NPDES permits can also authorize facilities to process, incinerate, landfill, or beneficially use 

Chapter 1: Development of the Clean Water Act and the NPDES Program 1-5
September 2010 NPDES Permit Writers’ Manual 

biosolids (sewage sludge). A discharger does not have a right to receive a permit, and permits may be 

revoked for cause such as noncompliance with the conditions of the permit. 

1.3.2 Pollutant 

The term pollutant is defined in CWA section 502(6) and § 122.2. The statute defines pollutant very 

broadly and includes any type of industrial, municipal, or agricultural waste (including heat) discharged 

into water. For regulatory purposes, pollutants are grouped into three categories under the NPDES 

program: conventional, toxic, and nonconventional. 

 Conventional pollutants are those defined in CWA section 304(a)(4) and § 401.16 (BOD5, TSS, 

fecal coliform, pH, and oil and grease). 

 Toxic (priority) pollutants are those defined in CWA section 307(a)(1) (and listed in § 401.15 

and Appendix A of Part 423) and include 126 metals and manmade organic compounds (see 

Exhibit C-1 in Appendix C of this document). 

 Nonconventional pollutants are those that do not fall under either of the above categories 

(conventional or toxic pollutants) and include parameters such as chlorine, ammonia, nitrogen, 

phosphorus, chemical oxygen demand (COD), and whole effluent toxicity (WET). 

Sewage from vessels and, under certain conditions, water, gas, or other material injected into wells to 

facilitate production of oil or gas or water derived in association with oil and gas production and disposed 

of in a well are specifically excluded from the definition of pollutant under the NPDES program. 

1.3.3 Waters of the United States 

The CWA regulates discharges to navigable waters. CWA section 502(7) defines navigable waters as 

“waters of the United States, including the territorial seas.” NPDES regulations define waters of the 

United States to mean, 

 Waters that are currently used, were used in the past, or may be susceptible to use in interstate or 

foreign commerce, including waters subject to the ebb and flow of the tide. 

 Interstate waters including interstate wetlands. 

 Other waters that could affect interstate or foreign commerce. 

 Impoundments of waters of the United States. 

 Tributaries of the above categories of waters. 

 Territorial seas. 

 Wetlands adjacent to other waters (except wetlands themselves) in the above categories. 

Wetlands are further defined in § 122.2. In addition, the definition of waters of the United States contains 

exclusions for waste treatment systems (other than certain cooling ponds) designed to meet the 

requirements of the CWA and also for prior converted croplands, which is mostly relevant to the CWA 

section 404 permitting program administered by the Corps. 

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Waters of the United States covers a broad range of surface waters. The CWA does not give EPA the 

authority to regulate ground water quality through NPDES permits. If a discharge of pollutants to ground 

water reaches waters of the United States, however, it could be a discharge to the surface water (albeit 

indirectly via a direct hydrological connection, i.e., the ground water) that needs an NPDES permit. 

The scope of waters of the United States has been the subject of several U.S. Supreme Court cases (the 

most recent as of the time of publication of this manual being a decision from 2006 in the combined 

Rapanos/Carabell wetland cases) and numerous lower court cases. The court cases often have been 

difficult to interpret, resulting in much litigation and an evolving understanding of the exact scope of 

waters subject to CWA jurisdiction. Also, permit writers should keep in mind that discharges through 

non-jurisdictional features that reach waters of the United States may need a permit even if the discharge 

is not directly to a jurisdictional waterbody. EPA Regional wetlands staff have significant expertise in 

jurisdictional issues related to the scope of waters of the United States. Some Regions have interoffice 

teams to address jurisdictional issues that come up in the different CWA programs. In addition, guidance 

on waters of the United States is on EPA’s Office of Wetlands, Oceans, and Watersheds Website

<www.epa.gov/wetlands/guidance/CWAwaters.html>. 

1.3.4 Point Source 

Pollutants can enter water via a variety of pathways including agricultural, domestic and industrial 

sources. For regulatory purposes, these sources generally are categorized as either point sources or 

nonpoint sources. The term point source is defined in CWA section 502(14) and § 122.2 to include any 

discernible, confined, and discrete conveyance from which pollutants are or may be discharged. Point 

source discharges include discharges from publicly owned treatment works (POTWs), industrial process 

wastewater discharges, runoff conveyed through a storm sewer system, and discharges from concentrated 

animal feeding operations (CAFOs), among others (see Exhibit 1-2). Return flows from irrigated 

agriculture and agricultural stormwater runoff specifically are excluded from the definition of a point 

source. 

Pollutant contributions to waters of the United States may come from both direct and indirect discharges. 

Direct discharge (which is synonymous with discharge of a pollutant) is defined by the NPDES 

regulations at § 122.2 to include any addition of any pollutant or combination of pollutants to a water of 

the United States from any point source. An indirect discharger is defined as, “a nondomestic discharger 

introducing pollutants to a POTW.” Under the national program, NPDES permits are issued only to direct 

dischargers. The National Pretreatment Program controls industrial and commercial indirect dischargers 

(for more on pretreatment, see section 2.3.1.2 of this manual). 

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Exhibit 1-2 Common point source discharges of pollutants to waters of the United States 

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Chapter 2: Regulatory Framework and Program Areas of the NPDES Program 2-1

CHAPTER 2. Regulatory Framework and Program Areas 

of the NPDES Program 

This chapter discusses the regulatory framework of the National Pollutant Discharge Elimination System 

(NPDES) program, identifies the types of activities regulated under the NPDES program, describes the 

roles and responsibilities of federal and state governments, and presents the program areas that address 

the various types of regulated activities. 

2.1 Regulatory Framework of the NPDES Program 

Chapter 1 discussed how Congress, in Clean Water Act (CWA) section 402, required the U.S. 

Environmental Protection Agency (EPA) to develop and implement the NPDES permit program. While 

Congress’ intent was established in the CWA, EPA was required to develop specific regulations to carry 

out the congressional mandate. The regulations developed by EPA to implement and administer the 

NPDES program primarily are in Title 40 of the Code of Federal Regulations (CFR) Part 122

<www.epa.gov/lawsregs/search/40cfr.html>. 

The CFR is an annual codification of the general and permanent rules published in the Federal Register

(FR) by the executive departments and agencies of the federal government. The CFR is divided into 50 

titles that represent broad areas subject to federal regulation. Title 40 covers protection of the 

environment. The FR is a legal publication that contains federal agency regulations; proposed rules and 

notices; and executive orders, proclamations and other presidential documents. The National Archives 

and Records Administration, an independent federal agency responsible for managing all federal records, 

publishes the FR and CFR. The text of all final regulations is found in the CFR. The background and 

implementation information related to these regulations, however, are found in the preamble to the 

regulations contained in the FR. This information is important to permit writers because it explains the 

legal, technical, and scientific bases on which regulatory decisions are made. 

Exhibit 2-1 lists regulations in 40 CFR that are related to the NPDES program, and Exhibit 2-2 is an 

outline of the federal NPDES regulations from Part 122. The regulations at § 123.25 should be referenced 

for information applicable to state NPDES programs. Exhibit B-2 in Appendix B of this document is an 

Index to NPDES Regulations that provides regulatory citations by topic area. 
September 2010 NPDES Permit Writers’ Manual 

Exhibit 2-1 Regulations related to the NPDES program 

Regulation (40 CFR) Subject 

Part 121 State certification 

Part 122 The federal NPDES permit program 

Part 123 State program requirements 

Part 124 Procedures for decision making 

Part 125 Technology standards 

Part 129 Toxic pollutant effluent standards 

Part 130 Water quality planning and management 

Part 131 Water quality standards 

Part 133 Secondary treatment regulations 

Part 135 Citizen suits 

Part 136 Analytical procedures 

Part 257 State sludge disposal regulations 

Part 401 General provisions for effluent limitations guidelines and standards (effluent guidelines) 

Part 403 General pretreatment regulations 

Parts 405-471 Effluent guidelines 

Part 501 State sewage sludge management program requirements 

Part 503 Standards for use or disposal of sewage sludge 

2.2 Federal and State Responsibilities 

This section discusses the relationship between federal and state governments in the administration of the 

NPDES program and the process by which a state can become authorized. 

2.2.1 State NPDES Program Authority 

EPA may authorize qualified state, territorial, or tribal government agencies to implement all or parts of 

the NPDES program. States, territories, or tribes (hereafter states) are authorized through a process 

defined by the CWA section 402(b) and NPDES regulations Part 123. A state wanting to be authorized to 

administer the NPDES program submits to EPA a letter from the governor requesting review and 

approval of its program submission, a Memorandum of Agreement (MOA), a Program Description, a 

Statement of Legal Authority (also known as an Attorney General’s Statement or AG Statement), and the 

underlying state laws and regulations. EPA determines whether the package is complete within 30 days of 

receipt. Within 90 days of receipt, EPA renders a decision to approve or disapprove the program. The 

time for review can be extended by agreement. The process of authorization includes a public review and 

comment period, and a public hearing. 

States may apply for the authority to issue one or more of the following five types of NPDES 

authorization: 

 NPDES Base Program for individual municipal and industrial facilities. 

 General Permit Program. 

 Pretreatment Program. 

 Federal Facilities Program. 

 Biosolids (Sewage Sludge) Program. 

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Exhibit 2-2 Federal NPDES regulations (40 CFR Part 122) 

Subpart A–Definitions and General Program Requirements 

§ 122.1 Purpose and scope 

§ 122.2 Definitions 

§ 122.3 Exclusions 

§ 122.4 Prohibitions 

§ 122.5 Effect of a permit 

§ 122.6 Continuation of expiring permits 

§ 122.7 Confidentiality of information 

Subpart B–Permit Application and Special NPDES Program Requirements 

§ 122.21 Applications 

§ 122.22 Signatories to permit applications and reports 

§ 122.23 Concentrated animal feeding operations 

§ 122.24 Concentrated aquatic animal production 

§ 122.25 Aquaculture projects 

§ 122.26 Stormwater discharges 

§ 122.27 Silviculture activities 

§ 122.28 General permits 

§ 122.29 New sources and new dischargers 

§ 122.30-122.37 MS4s 

Subpart C–Permit Conditions 

§ 122.41 Standard conditions applicable to all permits 

§ 122.42 Standard conditions applicable to specified categories of permits 

§ 122.43 Establishing permit conditions 

§ 122.44 Establishing limitations, standards, and other permit conditions 

(a) Technology basis 

(b) Other basis (not WQ) 

(c) Reopeners 

(d) Water quality basis 

(e) Toxic (priority) pollutants 

(f) Notification levels 

(g) 24 Hour reporting 

(h) Duration of permits 

(i) Monitoring 

(j) Pretreatment program 

(k) Best management practices (BMPs) 

(l) Anti-backsliding 

(m) Privately owned treatment works 

(n) Grants 

(o) Sewage sludge 

(p) Coast Guard 

(q) Navigation 

(r) Great Lakes 

(s) Qualifying programs 

§ 122.45 Calculating limitations 

(a) Outfalls and discharge points 

(b) Production basis 

(c) Metals 

(d) Continuous discharges 

(e) Non-continuous discharges 

(f) Mass limitations 

(g) Pollutants in intake water 

(h) Internal waste streams 

(i) Discharge into wells, into publicly owned 

treatment works or by land application 

§ 122.46 Duration of permits 

§ 122.47 Schedules of compliance 

§ 122.48 Requirements for recording and reporting of monitoring results 

§ 122.49 Consideration under federal law 

§ 122.50 Disposal into wells, into publicly owned treatment works or by land application 

Subpart D–Transfer, Modification, Revocation and Reissuance, and Termination of Permit 

§ 122.61 Transfer of permits 

§ 122.62 Modification or revocation and reissuance of permits 

§ 122.63 Minor modifications of permits 

§ 122.64 Termination of permits 

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A state can receive authorization for one or more of the NPDES program components. For example, a 

state might receive authorization for the NPDES Base Program, General Permit Program, and 

Pretreatment Program, but not the Federal Facilities Program or Biosolids Program. In such a case, EPA 

continues to issue permits to federal facilities (e.g., facilities on military installations, federal lands) for 

discharges originating within the state and continues to implement the Biosolids Program. (Section 2.2.2 

below provides additional discussion of Biosolids Program implementation.) 

If EPA approves a program, the state assumes permitting authority in lieu of EPA. All new permit 

applications would then be submitted to the state agency for NPDES permit issuance. Certain permits 

issued before authorization might continue under EPA administration as set forth in the MOA. Even after 

a state receives NPDES authorization, EPA continues to issue NPDES permits on tribal lands within the 

boundaries of the state (if the tribe is not administering its own approved NPDES program). Following 

authorization, EPA also continues its national program management responsibilities by ensuring that state 

programs meet applicable federal requirements. If EPA disapproves the program, EPA remains the 

permitting authority for that state. 

The State Program Status Website <www.epa.gov/npdes/authorization> provides the current authorization 

status for the states. 

2.2.2 Roles and Responsibilities of the Federal and State Authorities 

Until a state program is authorized, EPA is the permitting authority that issues all permits, conducts all 

compliance and monitoring activities, and enforces all program requirements. 

As noted above, if a state has only partial authority, EPA will implement the other program activities. For 

example, where a state has an approved NPDES program but has not received EPA approval of its state 

sewage sludge management program, the EPA Region is responsible for including conditions to 

implement the Part 503 Standards for the Use or Disposal of Sewage Sludge in permits issued to 

treatment works treating domestic sewage (TWTDS) in that state. EPA could issue a separate permit with 

the applicable sewage sludge standards and requirements, or collaborate with the state on joint issuance of 

NPDES permits containing the Part 503 sewage sludge standards. The same process also applies where a 

state has not received approval of its pretreatment program or federal facilities program. One exception to 

that process is where an NPDES-authorized state is not approved to implement the general permit 

program. In such cases, EPA may not issue a general permit in that state as clarified in the memorandum 

EPA’s Authority to Issue NPDES General Permits in Approved NPDES States1

<www.epa.gov/npdes/pubs/owm0444.pdf>. 

Once a state is authorized to issue permits, EPA generally is precluded from issuing permits in the state; 

however, EPA must be provided with an opportunity to review certain permits and may formally object to 

elements that conflict with federal requirements. If the permitting agency does not satisfactorily address 

the points of objection, EPA will issue the permit directly. Once a permit is issued through a government 

agency, it is enforceable by the approved state and federal agencies (including EPA) with legal authority 

to implement and enforce the permit. Private citizens may also bring a civil action in federal court against 

an alleged violator or against the EPA Administrator for alleged failure to enforce NPDES permit 

requirements. Exhibit 2-3 presents a summary of federal and state roles before and after program 

authorization. 

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Exhibit 2-3 Summary of federal and state/territorial/tribal roles in the 

NPDES permitting program 

Before state/territorial/tribal program approval: 

 EPA issues permits 

 EPA conducts compliance and monitoring activities 

 EPA enforces 

 State/territory/tribe reviews permits and grants CWA section 401 certification 

After state/territorial/tribal program approval: 

 State/territory/tribe issues permits 

 State/territory/tribe conducts compliance and monitoring activities 

 State/territory/tribe enforces 

 EPA provides administrative, technical and legal support 

 EPA ensures state program meets federal requirements 

 EPA offers NPDES program training 

 EPA oversees grants to states (e.g., CWA section 106) 

 EPA reviews permits and, as necessary, comments or objects 

 EPA oversees and, as necessary, assumes enforcement of permits 

2.3 NPDES Program Areas 

NPDES permittees can be broadly classified as municipal (publicly owned treatment works [POTWs] and 

related discharges) and non-municipal facilities. Federal facilities fall into the broader category of nonmunicipal facilities. Within those broad categories, there might also be specific types of activities that are 

subject to unique programmatic requirements in the NPDES regulations. Exhibit 2-4 provides an 

overview of the different activities related to municipal and non-municipal sources; identifies the NPDES 

program areas that address these activities; and identifies the applicable regulations for each NPDES 

program area. 

2.3.1 NPDES Program Areas Applicable to Municipal Sources 

The NPDES regulations establish technology-based effluent requirements applicable to discharges from 

POTWs. In addition to effluent requirements, the NPDES regulations establish other programmatic 

requirements applicable to other POTW activities (e.g., sewage sludge disposal and management, 

stormwater discharges from the treatment plant site) or activities that may be conducted by a municipality 

(e.g., municipal separate storm sewer systems, combined sewer overflows). A description of those 

programs and how they relate to NPDES permits is provided in the following sections. 

2.3.1.1 Publicly Owned Treatment Works (POTWs) 

The federal regulations at § 403.3 define a POTW as a treatment works (as defined in CWA section 212) 

that is owned by a state or municipality [as defined in CWA section 502(4)]. The 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. Finally, the term also means the municipality that has the jurisdiction 

over the indirect discharges to and the discharges from the treatment works. Federally owned treatment 

works, privately owned treatment works, and other treatment plants not owned by a state or municipality 

are not considered POTWs. 

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Exhibit 2-4 NPDES program areas and applicable regulations 

Source Program areas 

Applicable regulations 

(40 CFR) 

Municipal (POTWs) effluent discharges 

Part 122 

Part 125 

Part 133 

Indirect non-municipal discharges (Pretreatment) 

Part 122 

Part 403 

Parts 405-471 

Biosolids (sewage sludge) use and disposal 

Part 122 

Part 257 

Part 501 

Part 503 

Combined sewer overflow (CSO) discharges Part 122 

Part 125 

Sanitary sewer overflow (SSO) discharges Part 122 

Municipal 

Municipal separate storm sewer systems (MS4s) discharges Part 122 

Part 125 

Process wastewater discharges 

Part 122 

Part 125 

Parts 405-471 

Non-process wastewater discharges Part 122 

Part 125 

Stormwater discharges associated with industrial activity Part 122 

Part 125 

Stormwater discharges from construction activities* Part 122 

Part 125 

Cooling water intake structures (CWIS) 

Part 122 

Part 125 

Part 401 

Concentrated animal feeding operations (CAFOs) 

Part 122 

Part 123 

Part 125 

Part 412 

Concentrated aquatic animal production (CAAP) facilities 

Part 122 

Part 125 

Part 451 

Nonmunicipal 

(Industrial) 

Vessel Discharges Part 122 

* Though stormwater discharges from construction activity resulting in disturbance of 5 or more acres of total land area technically 

are considered, “stormwater discharges associated with industrial activity” as defined by §122.26(b)(14)(x), these discharges are 

commonly referred to as stormwater discharges from large construction activities. 

POTWs receive, primarily, domestic sewage from residential and commercial customers. Larger POTWs 

also typically receive and treat wastewater from industrial facilities (indirect dischargers) connected to the 

collection system. The types of pollutants treated by a POTW always include conventional pollutants and 

may include nonconventional and toxic pollutants, depending on the characteristics of the sources 

discharging to the POTW. The treatment provided by a POTW typically produces a treated effluent and a 

biosolids (sewage sludge) residual. 

2.3.1.2 The National Pretreatment Program 

The National Pretreatment Program <www.epa.gov/npdes/pretreatment> regulates the introduction of 

nondomestic (i.e., industrial and commercial) wastewater to POTWs. Because such discharges are treated 

by the POTW before release to a water of the United States, they are termed indirect discharges. The 

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pretreatment program prohibits industrial and commercial indirect dischargers from discharging 

pollutants to a POTW that will pass through the POTW to receiving waters or interfering with POTW 

treatment processes or contaminating sewage sludge. The federal program also requires certain indirect 

dischargers to meet technology-based requirements developed specifically for such POTW users that are 

similar to those for direct dischargers. 

EPA’s pretreatment regulations require certain POTWs to develop a pretreatment program, the 

requirements of which are generally included as conditions of a POTW’s NPDES permit. The federal 

regulations specifying which POTWs must have pretreatment programs, and the authorities and 

procedures that must be developed by the POTW before program approval, are in Part 403. The 

requirement to develop and implement a local pretreatment program typically is included as a special 

condition in the POTW’s NPDES permit. Section 9.2.1 of this manual includes a discussion on 

incorporating pretreatment special conditions into permits. 

2.3.1.3 Biosolids (Sewage Sludge) 

In 1987 Congress amended CWA section 405 to establish a comprehensive sewage sludge program

<www.epa.gov/OW-OWM.html/mtb/biosolids/index.htm>. The program regulates the use and disposal of sewage 

sludge by POTWs and by other TWTDS. TWTDS include facilities that generate sewage sludge, provide 

commercial treatment of sewage sludge, manufacture a product derived from sewage sludge, or provide 

disposal of sewage sludge. CWA section 405 required EPA to develop technical standards that establish 

sewage sludge management practices and acceptable levels of toxic pollutants in sewage sludge. The 

terms biosolids, sewage sludge, and municipal sludge are used interchangeably throughout this document. 

Regulations for state sewage sludge program approval are at Part 123 or Part 501 (depending on whether 

the state wishes to administer the sewage sludge program under its NPDES program or under another 

program, e.g., a solid waste program). The technical standards governing sewage sludge use and disposal 

are in Part 503. TWTDS not otherwise subject to the NPDES permit requirements under CWA section 

402 must apply for and receive a permit addressing standards for use and disposal of sewage sludge in 

Part 503. Details of this rule are described in A Plain English Guide to the EPA Part 503 Biosolids Rule2

<www.epa.gov/owm/mtb/biosolids/503pe/>. Where applicable, sewage sludge management requirements may be 

included as a special condition in permits issued to POTWs. Section 9.2.2 of this manual includes a 

discussion on incorporating special conditions that address sewage sludge requirements. 

2.3.1.4 Combined Sewer Overflows (CSOs) 

An additional concern for some older POTWs may be combined sewer systems (CSS), which are 

wastewater collection systems owned by a state or municipality [as defined by CWA section 502(4)] that 

convey sanitary wastewater (domestic, commercial and industrial wastewaters) and stormwater through a 

single-pipe system to a POTW [as defined by § 403.3(q)]. EPA estimates that CSSs serve about 40 

million people in 772 communities nationwide <www.epa.gov/npdes/cso/csodem>. During dry weather, CSSs 

collect and convey domestic, commercial, and industrial wastewater to a POTW; however, during periods 

of rainfall, snowmelt, and other forms of precipitation, the systems can become overloaded. When that 

overloading occurs, the CSS can overflow at designed relief points and discharge a combination of 

untreated sanitary wastewater and stormwater directly to a surface waterbody. 

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A combined sewer overflow (CSO) <www.epa.gov/npdes/cso> is the discharge from a CSS at a point before 

the POTW. CSOs can be a major source of water pollution in communities served by CSSs. CSOs often 

contain high levels of suspended solids (SS), pathogenic microorganisms, toxic pollutants, floatables, 

nutrients, oxygen-demanding organic compounds, oil and grease, and other pollutants, causing water 

quality standards to be exceeded. 

To address CSOs, EPA issued the National CSO Control Strategy (54 FR 37370, September 8, 1989). 

While implementation of the 1989 strategy has resulted in progress toward controlling CSOs, significant 

public health and water quality risks remain. To expedite compliance with the CWA, and to elaborate on 

the 1989 strategy, EPA, after collaboration with other CSO stakeholders (communities with CSSs, state 

water quality authorities, and environmental groups), published the CSO Control Policy

<www.epa.gov/npdes/cso/controlpolicy> (59 FR 18688, April 19, 1994). The 1994 CSO policy represents a 

comprehensive national strategy to ensure that municipalities, permitting authorities, water quality 

standards authorities, and the public engage in a comprehensive and coordinated planning effort to 

achieve cost-effective CSO controls that ultimately meet appropriate health and environmental objectives. 

The Wet Weather Water Quality Act of 2000 stipulates that NDPES permits, enforcement orders, or 

decrees must conform to the 1994 CSO Policy [CWA section 402(q)]. 

Before issuing a permit with conditions that address CSOs, permit writers should consult the CSO 

Control Policy and associated guidance. Section 9.2.3 of this manual includes a discussion on 

incorporating appropriate CSO permit conditions. 

2.3.1.5 Sanitary Sewer Overflows (SSOs) 

Properly designed, operated, and maintained sanitary sewer systems are meant to collect and transport all 

the sewage that flows into them to a POTW; however, occasional, unintentional spills of raw sewage from 

municipal sanitary sewers occur in almost every system. Such types of releases are called sanitary sewer 

overflows (SSOs) <www.epa.gov/npdes/sso>. 

SSOs have a variety of causes including severe weather, improper system operation and maintenance, and 

vandalism. EPA estimates that over 40.000 SSO events occur per year in the United States (excluding 

basement backups). Overflows of untreated wastewater can present risks of human exposure when 

released to certain areas, such as streets, private property, basements, and receiving waters used for 

drinking water, fishing and shellfishing, or contact recreation. A description of the extent of human health 

and environmental impacts caused by releases of untreated sewage, along with other information, is 

provided in the Report to Congress on the Impacts and Control of CSOs and SSOs3

<www.epa.gov/npdes/csossoreport2004>. That 2004 report shows that NPDES permit requirements establishing 

clear reporting, record keeping, third party notification of overflows from municipal sewage collection 

systems, and clear requirements to properly operate and maintain the collection system, are critical to 

effective program implementation. 

EPA has developed a draft fact sheet <www.epa.gov/npdes/pubs/sso_fact_sheet_model_permit_cond.pdf> and draft 

model permit conditions <www.epa.gov/npdes/pubs/sso_model_permit_conditions.pdf> that explain how NPDES 

permitting authorities can better address SSOs and sanitary sewer collection systems. Section 9.2.4 of this 

manual discusses incorporation of conditions to address SSOs in NPDES permits. 

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2.3.1.6 Municipal Separate Storm Sewer Systems (MS4s) 

Stormwater from major metropolitan areas is a significant source of pollutants discharged to waters of the 

United States. While rainfall and snow are natural events, the nature of stormwater discharges and their 

impact on receiving waters are greatly affected by human activities and land use. Stormwater from lands 

modified by human activities, such as metropolitan areas and urban streets, can affect surface water 

resources by modifying natural flow patterns or by elevating pollution concentrations and loadings. 

To address such concerns, the 1987 amendments to the CWA added section 402(p), a provision that 

directed EPA to establish phased NPDES requirements for stormwater discharges. Phase I of the 

stormwater program addresses permits for discharges from medium and large MS4s serving a population 

of 100,000 or more, as well as certain categories of industrial activity, including construction activity 

disturbing greater than 5 acres. Phase II expanded the stormwater program to include small MS4s and 

construction activity disturbing between 1–5 acres. 

The MS4 stormwater application regulations (Phase I) established requirements for a two-part permit 

application that allowed large and medium local governments to help define priority pollutant sources in 

the municipality and to develop and implement appropriate controls for such discharges to MS4s (55 FR 

47990, November 16, 1990). Part II of the application requires municipal applicants to propose municipal 

stormwater management programs to control pollutants to the maximum extent practicable (MEP) and to 

effectively prohibit non-stormwater discharges to the municipal system. Medium and large MS4 operators 

are required to submit comprehensive permit applications and are issued individual permits. 

Phase II of the stormwater program extended the NPDES permitting program to small MS4s in urbanized 

areas (64 FR 68722, December 8, 1999). The Phase II MS4 regulations require small MS4s to develop a 

program to address six minimum control measures that include BMPs and measurable goals for each 

BMP. Permit writers have the option of permitting regulated small MS4 operators using an individual 

permit, a general permit, or a modification of an existing Phase I MS4’s individual permit (although the 

vast majority of small MS4s have been covered under general permits). 

Municipal stormwater management programs combine source controls and management practices that 

address targeted sources in the boundaries of the municipal system. For example, a municipality that 

expects significant new development may focus more on proposing requirements for new development 

and construction. On the other hand, a municipality that does not expect significant new development 

could focus more on municipal activities that affect stormwater quality such as: maintenance of leaking 

sanitary sewers, road de-icing and maintenance, operation of municipal landfills, flood control efforts, 

and control of industrial contributions of stormwater. 

MEP is not precisely defined so as to allow maximum flexibility in MS4 permitting to optimize 

reductions in stormwater pollutants on a location-by-location basis (64 FR 68754, December 8, 1999). 

Therefore, permit writers must rely on application requirements specified in the regulations and the 

applicant’s proposed management program when developing appropriate permit conditions. The 

stormwater Phase II rule was challenged in the courts, with the U.S. Court of Appeals for the Ninth 

Circuit generally upholding the Phase II rule but remanding three issues back to EPA. EPA issued 

guidance on April 16, 2004 for how new general permits should address the remanded issues of public 

availability of notices of intent (NOIs), opportunity for public hearings, and permitting authority reviews 

of NOIs titled Implementing the Partial Remand of the Stormwater Phase II Regulations Regarding 

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Notices of Intent & NPDES General Permitting for Phase II MS4s4

<www.epa.gov/npdes/pubs/hanlonphase2apr14signed.pdf>. 

In addition to information on the Stormwater Discharges From Municipal Separate Storm Sewer Systems 

(MS4s) Website <www.epa.gov/npdes/stormwater/municipal>, EPA has developed the following guidance 

documents and memoranda to help permit writers and permittees implement the municipal stormwater 

program: 

 Guidance Manual for the Preparation of Part 2 of the NPDES Permit Applications for Discharge 

from Municipal Separate Storm Sewer Systems5

 <www.epa.gov/npdes/pubs/owm0246.pdf>. 

 Interim Permitting Approach for Water Quality-Based Effluent Limitations in Stormwater 

Permits6

 <www.epa.gov/npdes/pubs/swpol.pdf>. 

 Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm 

Water Sources and NPDES Permit Requirements Based on Those WLAs7

<www.epa.gov/npdes/pubs/final-wwtmdl.pdf>. 

 MS4 Program Evaluation Guidance8

 <www.epa.gov/npdes/pubs/ms4guide_withappendixa.pdf>. 

 MS4 Permit Improvement Guide9

 <www.epa.gov/npdes/pubs/ms4permit_improvement_guide.pdf>. 

The application requirements for stormwater discharges from MS4s serving a population greater than 

100,000 and for stormwater discharges from small MS4s are discussed in sections 4.3.10 and 4.3.11 of 

this manual. 

2.3.2 NPDES Program Areas Applicable to Non-Municipal Sources 

Non-municipal sources include industrial and commercial facilities, industrial stormwater (including large 

construction activities), and discharges from small construction activity, concentrated animal feeding 

operations (CAFOs) and concentrated aquatic animal production (CAAP) facilities. Unlike municipal 

sources, the types of raw materials, production processes, treatment technologies used and pollutants 

discharged at industrial facilities vary widely and are dependent on the type of industry and specific 

facility characteristics. The operations, however, generally are carried out within a more clearly defined 

area; thus, the collection systems are less complex than POTW collection systems. In addition, unlike 

biosolids at POTWs, the NPDES program does not regulate residuals (sludge) generated by nonmunicipal facilities. 

Non-municipal facilities can have discharges of stormwater that might be contaminated through contact 

with manufacturing activities or raw material and product storage, or they can have non-process 

wastewater discharges such as non-contact cooling water. In addition, some non-municipal facilities take 

in cooling water. Those discharges and intakes may be regulated under an NPDES permit in addition to 

any process wastewater. 

2.3.2.1 Process Wastewater 

Industrial and commercial facilities often use water in the manufacture and processing of products. The 

regulations at § 122.2 define process wastewater as, “[a]ny water which, during manufacturing or 

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

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

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Process wastewater can contain pollutants at levels that could affect the quality of receiving waters. The 

NPDES permit program establishes specific requirements for discharges of process wastewater from 

industrial and commercial sources. If a facility discharges directly to surface water, it would require an 

individual or general NPDES permit. An industrial or commercial facility also may discharge wastewater 

to a municipal sewer system, which would be covered under the NPDES pretreatment program. Many 

types of industrial facilities, whether they discharge directly to surface water or to a municipal sewer 

system, are covered by effluent guidelines and standards (see section 5.2 of this manual). The stormwater 

that runs off the property of an industrial or commercial facility or from a construction site might require 

an NPDES permit under the industrial stormwater program (see section 2.3.2.3 below). 

2.3.2.2 Non-Process Wastewater 

Industrial and commercial facilities often use water for purposes other than processing products, such as 

using non-contact cooling water for heat exchange, and may discharge wastewater from sources such as 

sanitary or cafeteria wastes. Like process wastewater, non-process wastewater is regulated under the 

NPDES program. Non-process wastewater might also be important to the permit writer when drafting 

monitoring conditions for facilities where the non-process wastewater dilutes the concentration of 

pollutants of concern in process wastewater. The permit writer must ensure that specified monitoring 

locations ensure accurate measurement for compliance with all effluent limitations. 

2.3.2.3 Stormwater Associated with Industrial Activity 

To minimize the impact of stormwater discharges from industrial facilities, the NPDES program includes 

an industrial stormwater permitting component. Operators of industrial facilities included in 1 of the 11 

categories of stormwater discharges associated with industrial activity that discharge or propose to 

discharge stormwater to an MS4 or directly to waters of the United States require authorization under an 

NPDES industrial stormwater permit. EPA published permit regulations and permit application 

requirements for stormwater discharges associated with industrial activity in 55 FR 48063, November 16, 

1990. 

Permit Regulations for Stormwater Associated with Industrial Activity 

The regulations define stormwater discharges associated with industrial activity as discharges from any 

conveyance used for collecting and conveying stormwater and that is directly related to manufacturing, 

processing, or raw materials storage areas at an industrial plant. The regulations at § 122.26(b)(14)(i - xi) 

identify the following 11 industrial categories required to apply for NPDES permits for stormwater 

discharges: 

 Facilities subject to stormwater effluent guidelines, new source performance standards, or toxic 

pollutant effluent standards under Parts 400-471 (Subchapter N). 

 Certain heavy manufacturing facilities (lumber, paper, chemicals, petroleum refining, leather 

tanning, stone, clay, glass, concrete, ship construction). 

 Active and inactive mining operations and oil and gas operations with contaminated stormwater. 

 Hazardous waste treatment, storage, or disposal facilities, including Resource Conservation and 

Recovery Act (RCRA) Subtitle C facilities. 

 Landfills, land application sites, open dumps, and RCRA Subtitle D facilities. 

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 Recycling facilities, including metal scrap yards, battery reclaimers, salvage yards, and 

automotive junkyards. 

 Steam electric power generating facilities, including coal-handling sites. 

 Transportation facilities that have vehicle maintenance shops, equipment cleaning operations, or 

airport deicing operations. 

 Major POTW sludge handling facilities, including on-site application of sewage sludge. 

 Construction activities that disturb five acres or more (see subsection below). 

 Light industrial manufacturing facilities. 

Operators of industrial facilities that are federally, state- or municipally owned or operated that meet the 

above descriptions must also submit applications. 

EPA issued a final rule for Phase II of the stormwater program in 64 FR 68722, December 8, 1999. That 

rule clarified that stormwater discharges from industrial facilities that have no exposure of industrial 

activities or materials to stormwater may be conditionally excluded from the stormwater permitting 

program. To qualify for the no exposure exclusion, the industrial operator must complete a no exposure 

certification form and submit this to EPA once every 5 years. For more information, see the Conditional 

No Exposure Exclusion Website <www.epa.gov/npdes/stormwater/noexposure>. 

Generally, EPA- or state-issued general permits regulate stormwater discharges from industrial, 

construction and Phase II municipal sources, while Phase I municipal sources usually are issued 

individual permits. In some cases, stormwater conditions may be incorporated into a comprehensive 

individual NPDES permit for a facility or a stormwater-specific individual NPDES permit. Incorporating 

permit conditions to address stormwater discharges associated with industrial and construction activities 

into an individual facility permit is discussed in the subsections below. For more information regarding 

the scope of the NPDES stormwater program, see the NPDES Stormwater Program Website

<www.epa.gov/npdes/stormwater>. 

Permit Conditions for Stormwater Discharges Associated with Industrial Activity 

All stormwater discharges associated with industrial activity that discharge stormwater through a separate 

MS4 or discharge directly to waters of the United States are required to obtain an NPDES permit. 

Because of the large number of facilities requiring permits, EPA and most NPDES-authorized states 

choose to issue general permits to regulate stormwater discharges. The Phase I rule in 1990 established 

the concept of a permitting exemption for industrial facilities with little or no likelihood of discharging 

contaminated stormwater; however, this exemption was not well-defined or required to be submitted to 

the NPDES permitting authority. The Phase II rule in December 1999 clarified and expanded the no 

exposure certification requirement to require industrial facilities with no exposure of industrial processes 

to stormwater to submit a written certification notifying EPA or the authorized state that the facility 

wishes to be excluded from the NPDES program. 

Each industrial facility covered under an EPA-issued stormwater general permit must meet the numeric 

and non-numeric effluent limitations established in the general permit. Industrial facilities can meet those 

effluent limitations by implementing control measures, including BMPs, that control the discharge of 

stormwater associated with industrial activity. 

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The EPA- and state-issued stormwater general permits generally require the facility to develop and 

implement a site-specific stormwater pollution prevention plan (SWPPP). The SWPPP describes the 

control measures, whether structural or nonstructural, which are used for controlling stormwater 

discharges from the industrial facility. The special conditions component of EPA’s stormwater general 

permits identifies the requirements that must be documented in the SWPPP, including the following: 

 A description of potential pollutant sources at the facility, including the following: 

− A map of the facility indicating the drainage areas of the site and the industrial activities that 

occur in each drainage area. 

− An inventory of materials that could be exposed to stormwater. 

− A description of the likely sources of pollutants from the site and a prediction of the 

pollutants likely to be present in the stormwater. 

− The history of spills and leaks of toxic and hazardous materials over the past 3 years. 

 The measures and controls that will be implemented to prevent or minimize pollution of 

stormwater, including the following: 

− Good housekeeping or upkeep of industrial areas exposed to stormwater. 

− Preventive maintenance of stormwater controls and other facility equipment. 

− Spill prevention and response procedures. 

− Testing of outfalls to ensure that there are no illicit discharges. 

− Employee training on pollution prevention measure and controls, and record keeping. 

A permit writer’s best sources of information for developing appropriate special conditions for 

stormwater control measures are other stormwater general permits. Using existing general permits as the 

basis for special conditions is encouraged because doing so will reduce duplication of effort. A listing of 

individual and general permits (stormwater and non-stormwater) issued by EPA and authorized states is 

on the View NPDES Individual and General Permits Website <www.epa.gov/npdes/permitsearch>. In addition 

to the Stormwater Discharge From Industrial Facilities Website <www.epa.gov/npdes/stormwater/indust>, EPA 

published Developing Your Stormwater Pollution Prevention Plan: A Guide for Industrial Operators10

<www.epa.gov/npdes/pubs/industrial_swppp_guide.pdf> to help permit writers identify components of SWPPPs 

and BMPs and to help permittees develop their own plans. Section 4.3.8 of this manual discusses Form 

2F and individual permit requirements for stormwater discharges associated with industrial activity. 

Permit Conditions for Stormwater Discharges associated with Construction Activities 

EPA and most NPDES-authorized states have issued NPDES general stormwater permits for discharges 

associated with construction activity that are separate from the industrial stormwater general permits. The 

Phase I stormwater regulations require permit coverage for all construction activity that results in the 

disturbance of five acres or greater of the total land area. This includes disturbance of less than five acres 

of total land area that is part of larger common plan of development or sale if the larger common plan will 

ultimately disturb five acres of more. The Phase II stormwater regulations require permit coverage for all 

construction activity that result in land disturbance of equal to or greater than one acre and less than five 

acres. This includes the disturbance of less than one acre of total land area that is part of a larger common 

plan of development or sale if the larger common plan will ultimately disturb equal to or greater than one 

and less than five acres. Since March 2003, most construction activity disturbing one to five acres has 

been required to comply with the conditions of the relevant NPDES permit (typically under the relevant 

construction general permit for stormwater discharges), though states have the option of not requiring the 

submittal of NOIs for stormwater discharges associated with small construction activity. 

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EPA and NPDES-authorized state permitting authorities may include permit conditions that incorporate 

qualifying state or local erosion and sediment control program requirements by reference. A qualifying 

state or local erosion and sediment control program is one that includes the requirements at § 122.44(s). 

Once EPA or an NPDES authorized state identifies and incorporates a qualifying local program in their 

NPDES construction general permit, operators can follow the erosion and sediment control requirements 

of the qualifying local program. By incorporating the qualifying local program by reference the 

permitting authority can avoid duplicative or conflicting erosion and sediment control requirements 

between the local program requirements and the NPDES general permit control requirements addressing 

stormwater discharges associated with construction activity. Operators that are engaged in construction 

activity within a qualifying program must still submit an NOI under the appropriate construction general 

permit and comply with all other permit conditions. 

The permit requirements in a construction general permit may be similar to those in an industrial general 

permit, including the development of a SWPPP. In addition to the Stormwater Discharges from 

Construction Activities Website <www.epa.gov/npdes/stormwater/construction>, EPA also developed the 

Stormwater Pollution Prevention Plans for Construction Activities Website

<www.epa.gov/npdes/swpppguide>. Section 4.3.9 of this manual discusses individual permit requirements for 

stormwater discharges associated with construction activity. 

2.3.2.4 Cooling Water Intake Structures 

CWA section 316(b) provides that any standard established pursuant to CWA sections 301 or 306 and 

applicable to a point source will require that the location, design, construction, and capacity of cooling 

water intake structures reflect the best technology available for minimizing adverse environmental 

impact. This CWA provision is unique because it addresses the intake of water, in contrast to other 

provisions that regulate the discharge of pollutants into waters of the United States. EPA has established 

national performance standards under CWA section 316(b) designed to reduce the impingement and 

entrainment of fish and other aquatic organisms as they are drawn into a facility’s cooling water intake 

structure(s). Impingement occurs when organisms are trapped against cooling water intake structures by 

the force of water being drawn through the intake structure. Entrainment occurs when organisms are 

drawn through a cooling water intake structure into a cooling system, through the heat exchanger, and 

then pumped back out into the waterbody. For more information, see section 4.3.12 of this manual. 

In April 1976, EPA published regulations at Part 402 to address cooling water intake structures. Fiftyeight electric utility companies challenged the final rule. The U.S. Court of Appeals for the Fourth Circuit 

remanded the rule in 1977, and in 1979, EPA withdrew Part 402. Beginning in 1977, NPDES permit 

authorities made decisions implementing CWA section 316(b) on a case-by-case basis using best 

professional judgment (BPJ) (§§ 125.90(b) and 401.14). 

In the 1990s, EPA began developing CWA section 316(b) regulations establishing national standards. 

EPA divided the rulemaking into three phases: 

 Phase I addressed new facilities and was completed in December 2001 (Part 125, Subpart I). 

 Phase II addressed existing electric generating plants that use at least 50 million gallons per day 

(mgd) of cooling water was completed in July 2004 (Part 125, Subpart J). 

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 Phase III addressed other existing facilities, including small existing electric generating plants 

that use less than 50 mgd of cooling water, manufacturers, and new offshore and coastal oil and 

gas extraction facilities. 

The Phase III regulations, finalized in June 2006, establish national standards only for new offshore and 

coastal oil and gas extraction facilities (Part 125, Subpart N). EPA decided that other Phase III industrial 

facilities withdrawing water for cooling purposes would not be covered by national standards but would 

continue to be subject to CWA section 316(b) requirements set by the NPDES Permitting Director on a 

case-by-case, BPJ basis (§§ 125.90(b) and 401.14). 

All three regulations were subject to judicial challenges. While the Phase I rule was largely upheld, the 

court reviewing the Phase II regulation rejected a number of its provisions. Under remands from the 

reviewing courts, EPA is reevaluating the Phase II regulation and the decision in the Phase III regulation 

not to establish national standards for existing Phase III facilities. In the interim, as noted above, NPDES 

permits must include CWA section 316(b) conditions developed on a case-by-case basis. For the most 

current information on regulatory requirements, see the Cooling Water Intake Structure Program Website

<www.epa.gov/waterscience/316b/>, and for additional Cooling Water Intake Structures regulatory 

requirements, see section 4.3.12 of this manual. 

2.3.2.5 Concentrated Animal Feeding Operations (CAFOs) 

Animal feeding operations (AFOs) are agricultural facilities where animals are kept and raised in confined 

situations. AFOs typically maintain animals, feed, and manure and have production operations in a 

limited land area. Manure and wastewater from AFOs have the potential to contribute pollutants such as 

nitrogen and phosphorus, organic matter, sediments, pathogens, heavy metals, hormones, antibiotics, and 

ammonia to the environment. An AFO is a lot or facility (other than an aquatic animal production facility) 

where the following conditions are met: 

 Animals have been, are, or will be stabled or confined and fed or maintained for a total of 45 days 

or more in any 12-month period. 

 Crops, vegetation, forage growth, or post-harvest residues are not sustained in the normal 

growing season over any portion of the lot or facility. 

AFOs that meet the regulatory definition of a CAFO, or that are designated as CAFOs by the permitting 

authority, and that discharge or propose to discharge are required to be permitted under the NPDES 

permitting program. 

An animal operation must meet the definition of an AFO [§ 122.23(b)(1)] before it can be considered a 

CAFO. To be defined as a CAFO, an AFO must meet the regulatory definition [§§ 122.23(b)(4) or 

122.23(b)(6)] of a large or medium CAFO or must be designated by the permitting authority 

[§ 122.23(c)]. Only CAFOs that discharge or propose to discharge are subject to NPDES permitting 

requirements. 

CAFOs are subject to requirements that limit discharges from the production area and requirements 

applicable to land application areas under the control of the CAFO operator. Large CAFOs are subject to 

a no discharge requirement for production areas, whereas other CAFOs are subject to BPJ requirements 

for their production areas. One of the principal substantive pollution control conditions in any CAFO 

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permit is the requirement to implement the terms of the nutrient management plan (NMP) incorporated 

into the permit when permit authorization is granted. For more information, see the Animal Feeding 

Operations Website <www.epa.gov/npdes/cafo>. In addition, section 4.3.4 of this manual discusses 

application requirements for CAFOs. 

2.3.2.6 Concentrated Aquatic Animal Production (CAAP) Facilities 

CAAP facilities also are regulated under the NPDES program. In 2004 EPA promulgated new effluent 

guidelines that address CAAP facilities. The effluent guidelines apply to CAAP facilities (flow-through, 

recirculating, and net pen) that directly discharge wastewater and have annual production equal to or 

greater than 100,000 pounds of aquatic animals. The rule requires a BMP plan and implementation of 

measures, including recordkeeping and reporting requirements, to minimize discharges of solids, to 

prevent spills of drugs, feed, and chemicals that could result in discharges to waters of the United States, 

and to ensure proper maintenance of the facility. A facility that does not meet the effluent guideline 

threshold might still need an NPDES permit if it meets the CAAP facilities thresholds established in the 

NPDES regulations at § 122.24(b) or if it is designated as a CAAP facility under the designation authority 

in § 122.24(c). For more information, see the Aquatic Animal Production Industry Effluent Guidelines 

Website <www.epa.gov/guide/aquaculture/>. 

2.3.2.7 Vessel Discharges 

On March 30, 2005, the U.S. District Court for the Northern District of California (in Northwest 

Environmental Advocates et al. v. EPA) ruled that the EPA regulation excluding discharges incidental to 

the normal operation of a vessel from NPDES permitting exceeded the Agency’s authority under the 

CWA. On September 18, 2006, the Court issued an order revoking this regulation [40 CFR 122.3(a)] as of 

September 30, 2008. EPA appealed the District Court’s decision, and on July 23, 2008, the Ninth Circuit 

upheld the decision, leaving the September 30, 2008, vacatur date in effect. In response to the Court 

order, EPA developed two proposed permits to regulate discharges from vessels. The district court 

ultimately extended the date of vacatur to February 6, 2009. 

In July 2008, Congress amended the CWA (P.L. No. 110-288) to add a new section 402(r), which 

excludes discharges incidental to the normal operation of a recreational vessel from NPDES permitting. 

Instead, it directs EPA to regulate those discharges under a newly created CWA section 312(o). As a 

result of the law, EPA did not finalize the previously proposed Recreational Vessel General Permit and is 

instead undertaking rulemaking to develop BMPs for these vessels under the authority of CWA section 

312(o). 

In July 2010 P.L. 111-215 (Senate Bill S. 3372) was signed into law. This law amends P.L. 110-299 

(Senate Bill S. 3298), which generally imposes a moratorium during which time neither EPA nor states 

may require NPDES permits for discharges incidental to the normal operation of commercial fishing 

vessels and other non-recreational vessels less than 79 feet. As a result, of P.L. 110-299, the Vessel 

General Permit (VGP) does not cover vessels less than 79 feet, or commercial fishing vessels, unless they 

have ballast water discharges. P.L. 111-215 extended the expiration date of the moratorium from July 31, 

2010, to December 18, 2013. 

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Chapter 2: Regulatory Framework and Program Areas of the NPDES Program 2-17

As a result of the court ruling, EPA issued the VGP on December 18, 2008. The 2008 VGP regulates 

discharges incidental to the normal operation of vessels operating in a capacity as a means of 

transportation. The VGP includes the following: 

 general effluent limits applicable to all discharges. 

 general effluent limits applicable to 26 specific discharge streams. 

 narrative water-quality based effluent limits. 

 inspection, monitoring, recordkeeping, and reporting requirements. 

 additional requirements applicable to certain vessel types. 

EPA estimates that approximately 61,000 domestically flagged commercial vessels and approximately 

8,000 foreign flagged vessels could be affected by this permit. 

Because this area of the NPDES permit program is relatively new and continues to evolve, for the most 

current information, see EPA’s Vessel Discharges Website <www.epa.gov/npdes/vessels>. 

2.4 Major/Minor Facility Designation 

In addition to categorizing facilities as municipal and non-municipal, EPA has also developed criteria to 

determine which of the sources should be considered major facilities. The distinction was made initially 

to assist EPA and states in setting priorities for permit issuance and reissuance. The regulations at § 122.2 

define major facility as, “any NPDES facility or activity classified as such by the Regional Administrator, 

or in the case of approved state programs, the Regional Administrator in conjunction with the [s]tate 

Director.” All facilities that are not designated as majors are considered minor facilities. 

Through policy, including the memoranda Procedures for Revising the Major Permit List11

<www.epa.gov/npdes/pubs/owm0364.pdf> and Delegation of Updates to Major/Minor Lists12

<www.epa.gov/npdes/pubs/owm0142.pdf>, EPA has established working definitions for POTW and nonmunicipal major facilities. For POTWs, major facilities are those that have a design flow of one million 

gallons per day or greater or serve a population of 10,000 or more or cause significant water quality 

impacts. Non-POTW discharges are classified as major facilities on the basis of the number of points 

accumulated using the NPDES Permit Rating Work Sheet <www.epa.gov/npdes/pubs/owm0116.pdf>. The 

worksheet evaluates the significance of a facility using several criteria, including toxic pollutant potential, 

flow volume, and water quality factors such as impairment of the receiving water or proximity of the 

discharge to coastal waters. 

2.5 Growth and Change in the NPDES Program 

The basic structure of the NPDES program has remained the same since the 1972 Federal Water Pollution 

Control Act amendments, but as EPA develops new regulations, policies, and guidance or modifies 

existing program requirements and guidance, the existing program is refined and new aspects of the 

program can emerge. To stay informed about the most recent program developments, permit writers 

should visit EPA’s NPDES Program Website <www.epa.gov/npdes/> frequently. 
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2-18 Chapter 2: Regulatory Framework and Program Areas of the NPDES Program 

1

 Prothro, M. 1983. EPA’s Authority to Issue NPDES General Permits in Approved NPDES States. U.S. Environmental 

Protection Agency, Office of Water. Memorandum, July 11, 1983. <www.epa.gov/npdes/pubs/owm0444.pdf>.

2

 U.S. Environmental Protection Agency. 1994. A Plain English Guide to the EPA Part 503 Biosolids Rule. EPA/832/R-93/003. 

U.S. Environmental Protection Agency, Office of Wastewater Management, Washington, DC. 

<www.epa.gov/owm/mtb/biosolids/503pe/>. 

3

 U.S. Environmental Protection Agency. 2004. Report to Congress on the Impacts and Control of CSOs and SSOs. EPA 833-R04-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/csossoreport2004>. 

4

 Hanlon, J.A. 2004. Implementing the Partial Remand of the Stormwater Phase II Regulations Regarding Notices of Intent & 

NPDES General Permitting for Phase II MS4s. U.S. Environmental Protection Agency, Office of Wastewater Management. 

Memorandum, April 16, 2004. <www.epa.gov/npdes/pubs/hanlonphase2apr14signed.pdf>. 

5

 U.S. Environmental Protection Agency. 1992. Guidance Manual for the Preparation of Part 2 of the NPDES Permit 

Application for Discharges from Municipal Separate Storm Sewer Systems. EPA-833/B-92-002. U.S. Environmental Protection 

Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/owm0246.pdf>. 

6

 Perciasepe, R. 1996. Interim Permitting Approach for Water Quality-Based Effluent Limitations in Stormwater Permits. U.S. 

Environmental Protection Agency, Office of Water. Memorandum, September 1, 1996. <www.epa.gov/npdes/pubs/swpol.pdf>. 

7

 Wayland, R.H., III, and J.A. Hanlon. 2002. Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) 

for Storm Water Sources and NPDES Permit Requirements Based on Those WLAs. U.S. Environmental Protection Agency, 

Office of Wetlands, Oceans and Watersheds and Office of Wastewater Management. Memorandum, November 22, 2002. 

<www.epa.gov/npdes/pubs/final-wwtmdl.pdf>. 

8

 U.S. Environmental Protection Agency. 2007. MS4 Program Evaluation Guidance. EPA-833-R-07-003. U.S. Environmental 

Protection Agency, Office of Wastewater Management. Washington, DC. 

<www.epa.gov/npdes/pubs/ms4guide_withappendixa.pdf>. 

9

 U.S. Environmental Protection Agency. 2010. MS4 Permit Improvement Guide. EPA833-R-10-001. U.S. Environmental 

Protection Agency. Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/ms4permit_improvement_guide.pdf> 

10 U.S. Environmental Protection Agency. 2009. Developing Your Stormwater Pollution Prevention Plan: A Guide for Industrial 

Operators. EPA 833-B-09-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/industrial_swppp_guide.pdf>. 

11 Dougherty, Cynthia. 1988. Procedures for Revising the Major Permit List. U.S. Environmental Protection Agency, Permits 

Division. Memorandum, December 28, 1988. <www.epa.gov/npdes/pubs/owm0364.pdf>. 

12 Pendergast, James F. 1995. Delegation of Updates to Major/Minor Lists. U.S. Environmental Protection Agency, Office of 

Wastewater Management. Memorandum, February 6, 1995. <www.epa.gov/npdes/pubs/owm0142.pdf>. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 3: Overview of the NPDES Permitting Process 3-1

CHAPTER 3. Overview of the NPDES Permitting Process 

This chapter presents an overview of the different types of National Pollutant Discharge Elimination 

System (NPDES) permits, the major permit components, and the permit development and issuance 

process. The permit process is illustrated by flow charts. The tasks identified within the flow charts are 

described in detail in subsequent chapters. 

3.1 Types of Permits 

The two basic types of NPDES permits are individual and general permits. These permit types share the 

same components but are used under different circumstances and involve different permit issuance 

processes. 

3.1.1 Individual Permits 

An individual permit is a permit specifically tailored to an individual facility. Upon receiving the 

appropriate application form(s), the permitting authority develops a permit for that facility on the basis of 

information from the permit application and other sources (e.g., previous permit requirements, discharge 

monitoring reports, technology and water quality standards, total maximum daily loads, ambient water 

quality data, special studies). The permitting authority then issues the permit to the facility for a specific 

period not to exceed 5 years, with a requirement to reapply before the expiration date. 

3.1.2 General Permits 

A permitting authority develops and issues a general permit to cover multiple facilities in a specific 

category of discharges or of sludge use or disposal practices. General permits can be a cost-effective 

option for agencies because of the large number of facilities that can be covered under a single permit. 

According to Title 40 of the Code of Federal Regulations (CFR) 122.28(a)(2), general permits may be 

written to cover stormwater point sources or other categories of point sources having the following 

common elements: 

 Sources that involve the same or substantially similar types of operations. 

 Sources that discharge the same types of wastes or engage in the same types of sludge use or 

disposal. 

 Sources that require the same effluent limitations or operating conditions, or standards for sewage 

sludge use or disposal. 

 Sources that require the same monitoring where tiered conditions may be used for minor 

differences within a class (e.g., size or seasonal activity). 

 Sources that are more appropriately regulated by a general permit. 

The regulations at § 122.28(a)(1) provide for general permits to cover dischargers within an area 

corresponding to specific geographic or political boundaries such as the following: 

 Designated planning area. 

 Sewer district. 

 City, county, or state boundary. 
September 2010 NPDES Permit Writers’ Manual 

 State highway system. 

 Standard metropolitan statistical area. 

 Urbanized area. 

The regulation also allows a general permit to cover any other appropriate division or combination of 

such boundaries. For example, EPA has issued general permits that cover multiple states, territories, and 

tribes where EPA is the permitting authority. 

Where a large number of similar facilities require permits, a general permit allows the permitting 

authority to allocate resources in a more efficient manner and to provide more timely permit coverage 

than issuing an individual permit to each facility. In addition, using a general permit ensures consistent 

permit conditions for comparable facilities. 

3.2 Major Components of a Permit 

All NPDES permits consist, at a minimum, of five sections: 

 Cover Page: Contains the name and location of the permittee, a statement authorizing the 

discharge, and a listing of the specific locations for which a discharge is authorized. 

 Effluent Limitations: The primary mechanism for controlling discharges of pollutants to 

receiving waters. A permit writer spends the majority of his or her time, when drafting a permit, 

deriving appropriate effluent limitations on the basis of applicable technology and water quality 

standards. 

 Monitoring and Reporting Requirements: Used to characterize wastestreams and receiving 

waters, evaluate wastewater treatment efficiency, and determine compliance with permit 

conditions. 

 Special Conditions: Conditions developed to supplement numeric effluent limitations. Examples 

include additional monitoring activities, special studies, best management practices (BMPs), and 

compliance schedules. 

 Standard Conditions: Pre-established conditions that apply to all NPDES permits and delineate 

the legal, administrative, and procedural requirements of the NPDES permit. 

In addition to the components of the permit, a fact sheet or statement of basis explaining the rationale for 

permit conditions makes up part of the documentation that supports a draft permit. Section 11.2 of this 

manual includes additional discussion of permit documentation and the required elements of a fact sheet 

or statement of basis. 

Although the major sections of a permit listed above are part of all permits, the contents of some sections 

vary depending on the nature of the discharge (e.g., municipal effluent, industrial process wastewater, 

stormwater, vessel discharges) and whether the permit is issued to an individual facility or to multiple 

dischargers (i.e., a general permit). Exhibit 3-1 shows the components of a permit and highlights some 

distinctions between the contents of NPDES permits for municipal (i.e., POTW) and industrial facilities. 

Permit writers should note that it is common for different permitting authorities to use different names for 

each section of a permit. 

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Exhibit 3-1 Permit components 

3.3 Overview of the Development and Issuance Process for NPDES 

Individual Permits 

While the limitations and conditions in NPDES individual permits are unique to each permittee, the 

process used to develop the limitations and conditions and issue each permit generally follows a common 

set of steps. Exhibit 3-2 illustrates the major steps to develop and issue NPDES individual permits and 

also serves as an index for the subsequent chapters of this manual by identifying which chapter presents 

more detailed information on each step. 

For individual permits, the permitting process generally begins when a facility operator submits an 

application. After receiving the application and making a decision to proceed with the permit, the permit 

writer reviews the application for completeness and accuracy. When the permit writer determines that the 

application is complete and has any additional information needed to draft the permit, the permit writer 

develops the draft permit and the justification for the permit conditions (i.e., the fact sheet or statement of 

basis). 

The first major step in the permit development process is deriving technology-based effluent limitations 

(TBELs). Following that step, the permit writer derives effluent limitations that are protective of state 

water quality standards (i.e., water quality-based effluent limitations [WQBELs]) as needed. The permit 

writer then compares the TBELs with the WQBELs and, after conducting an anti-backsliding analysis if 

necessary, applies the final limitations in the NPDES permit. The permit writer must document the 

decision-making process for deriving limitations in the permit fact sheet. It is quite possible that a permit 

will have limitations that are technology-based for some parameters and water quality-based for others. 

For example, a permit could contain effluent limitations for total suspended solids (TSS) based on 

national effluent limitations guidelines and standards (effluent guidelines) (technology-based), limitations 

for ammonia based on preventing toxicity to aquatic life (water quality-based), and limitations for 5-day 

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biochemical oxygen demand (BOD5) that have different bases, such as an average monthly limitation 

based on effluent guidelines and a maximum daily limitation based on water quality standards. 

Exhibit 3-2 Major steps to develop and issue NPDES individual permits 

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September 2010 NPDES Permit Writers’ Manual 

After effluent limitation development, the permit writer develops appropriate monitoring and reporting 

requirements and facility-specific special conditions. The permit writer then adds standard conditions, 

which are the same for all permits. 

The next step is to provide an opportunity for public participation in the permit process and EPA review 

of the permit or, in the case of an EPA-issued permit, certification under CWA section 401 by the state 

with jurisdiction over the receiving water that the permit will comply with its water quality standards. The 

permitting authority issues a public notice announcing the draft permit and inviting interested parties to 

submit comments. If there is significant public interest, the permitting authority can hold a public hearing. 

Taking into consideration the public comments, the permitting authority then produces a final permit, 

with careful attention to documenting the process and decisions for the administrative record, and issues 

the final permit to the facility. The permitting authority might decide to make significant changes to the 

draft permit according to public comment and then provide another opportunity for public review and 

comment on the revised permit. Section 11.3 of this manual discusses items to address before final permit 

issuance in more detail. 

3.4 Overview of the Development and Issuance Process for NPDES 

General Permits 

The process for developing and issuing NPDES general permits is similar to the process for individual 

permits; however, there are some differences in the sequence of events. Exhibit 3-3 illustrates the major 

steps to develop and issue NPDES general permits. 

Exhibit 3-3 Major steps to develop and issue NPDES general permits 

Chapter 3: Overview of the NPDES Permitting Process 3-5
September 2010 NPDES Permit Writers’ Manual 

3-6 Chapter 3: Overview of the NPDES Permitting Process 

For general permits, the permitting authority first identifies the need for a general permit and collects data 

that demonstrate that a group or category of dischargers has similarities that warrant a general permit. In 

deciding whether to develop a general permit, permitting authorities consider whether 

 A large number of facilities will be covered. 

 The facilities have similar production processes or activities. 

 The facilities generate similar pollutants. 

 Whether uniform WQBELs (where necessary) will appropriately implement water quality 

standards. 

The remaining steps of the permit process are the same as for individual permits. The permitting authority 

develops a draft permit that includes effluent limitations, monitoring conditions, special conditions, and 

standard conditions. The permitting authority then issues a public notice and addresses public comments, 

completes the EPA review or CWA section 401 certification process, develops the administrative record, 

and issues the final permit. The final permit will also establish the requirements for the specific 

information that must be submitted by a facility that wishes to be covered under the general permit. 

After the final general permit has been issued, facilities that wish to be covered under the general permit 

typically submit a Notice of Intent (NOI) to the permitting authority. After receiving the NOI, the 

permitting authority can request additional information describing the facility, notify the facility that it is 

covered by the general permit, or require the facility to apply for an individual permit. 

The following chapters in this manual describe steps in the permitting process in detail. In general, the 

chapters focus on the steps necessary to develop and issue an individual permit, but much of the technical 

discussion applies equally to general permit development.
September 2010 NPDES Permit Writers’ Manual 

Chapter 4: NPDES Permit Application Process 4-1

CHAPTER 4. NPDES Permit Application Process 

This chapter describes the National Pollutant Discharge Elimination System (NPDES) permit application 

process, including the permit writer’s role in reviewing the application and evaluating background 

information about the applicant. Through this process the permit writer gains an understanding of the 

circumstances of the discharge and the characteristics of the proposed effluent, which is necessary to 

develop appropriate permit limitations and conditions. 

4.1 Who Applies for an NPDES Permit? 

The NPDES regulations at Title 40 of the Code of Federal Regulations (CFR) 122.21(a) require that any 

person, except persons covered by general permits under § 122.28, who discharges pollutants or proposes 

to discharge pollutants to waters of the United States must apply for a permit. Further, § 122.21(e) 

prohibits the permitting authority from issuing an individual permit until and unless a prospective 

discharger provided a complete application. This regulation is broadly inclusive and ties back to the Clean 

Water Act (CWA) section 301(a) provision that, except as in compliance with the act, “...the discharge of 

any pollutant by any person shall be unlawful.” 

In most instances, the permit applicant will be the owner (e.g., corporate officer) of the facility. However, 

the regulations at § 122.21(b) require that when a facility or activity is owned by one person but is 

operated by another person, it is the operator’s duty to obtain a permit. The regulations also require the 

application to be signed and certified by a high-ranking official of the business or activity. The signatory 

and certification requirements are at § 122.22. 

Permits (and applications) are required for most discharges or proposed discharges to waters of the United 

States; however, NPDES permits are not required for some activities as specified under the Exclusions

provision in § 122.3. Exceptions include the following: 

 Discharge of dredged or fill materials into waters of the United States which are regulated under 

CWA section 404. 

 The introduction of sewage, industrial wastes or other pollutants into publicly owned treatment 

works (POTWs) by indirect dischargers. 

 Any discharge in compliance with the instructions of an On-Scene Coordinator pursuant to Part 

300 (The National Oil and Hazardous Substances Pollution Contingency Plan) or 33 CFR 

153.10(e) (Pollution by Oil and Hazardous Substances). 

 Any introduction of pollutants from nonpoint source agricultural and silvicultural activities, 

including stormwater runoff from orchards, cultivated crops, pastures, range lands, and forest 

lands, but not discharges from concentrated animal feeding operations as defined in § 122.23, 

discharges from concentrated aquatic animal production facilities as defined in § 122.24, 

discharges to aquaculture projects as defined in § 122.25, and discharges from silvicultural point 

sources as defined in § 122.27. 

 Return flows from irrigated agriculture. 
September 2010 NPDES Permit Writers’ Manual 

 Discharges into a privately owned treatment works, except as the Director may otherwise require 

under § 122.44(m). 

While those types of discharges have been excluded from permitting requirements under the NPDES 

program, they might be subject to controls under other federal or state regulatory programs. 

As of the date of this manual’s publication, the exclusion for certain discharges incidental to the normal 

operation of a vessel is still in the CFR. Similarly, discharges from the application of pesticides consistent 

with all relevant requirements under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) 

(i.e., those relevant to protecting water quality) are excluded from NPDES permit coverage in the 

following two circumstances: (1) the application of pesticides directly to waters of the United States to 

control pests, and (2) the application of pesticides to control pests that are present over waters of the 

United States, including near such waters, where a portion of the pesticides will unavoidably be deposited 

to waters of the United States to target the pests effectively. However, because of court decisions, the 

exclusions for vessels and pesticides are vacated as of February 6, 2009, and April 9, 2011, respectively. 

The effect of the vacaturs on the exclusions in § 122.3 is presented in Exhibit 4-1. 

Exhibit 4-1 Effect of court decisions on § 122.3 

Exclusion Issue 

Vessel Discharges 

(www.epa.gov/npdes/vessels) 

The Court’s ruling does not affect vessel discharge exemptions from 

permitting that are specifically provided for in the CWA itself. For example, 

§ 502(6)(A) excludes from the act’s definition of pollutant sewage from vessels 

(including graywater in the case of commercial vessels operating on the Great 

Lakes) and discharges incidental to the normal operation of a vessel of the 

Armed Forces within the meaning of CWA section 312. As another example, 

the CWA section 502(12)(B) provides that discharges from vessels (i.e., 

discharges other than those when the vessel is operating in a capacity other 

than as a means of transportation) do not constitute the, “discharge of a 

pollutant” when such discharges occur beyond the limit of the 3-mile territorial 

sea. Because both a pollutant and a discharge of a pollutant are prerequisites 

to the requirement to obtain an NPDES permit, those two statutory provisions 

have the effect of exempting the vessel discharges they address from the 

requirement to obtain an NPDES permit. In addition, in July 2008, Congress 

amended the CWA to add a new section 402(r) to the act, which excludes 

discharges incidental to the normal operation of a recreational vessel from 

NPDES permitting. For more information, see section 2.3.2.7 of this manual. 

Pesticides 

(www.epa.gov/npdes/aquaticpesticides) 

On January 7, 2009, the 6th Circuit Court vacated the final rule in The 

National Cotton Council of America et al. v. United States Environmental 

Protection Agency. The court held that while an NPDES permit is not required 

for chemical pesticide applications that leave no residuals, an NPDES permit 

is required for discharges (1) from chemical pesticide applications to or over, 

including near water, where there is a residual, or excess pesticide, in the 

water following the application, and (2) from all biological pesticide 

applications regardless of whether a residual is left. On June 8, 2009, the 

court granted a request from the U.S. Department of Justice for a 2-year stay 

of its decision, until April 9, 2011, to provide time for EPA and the states to 

develop and issue NPDES general permits for the discharge of pollutants from 

the application of pesticides. Before April 9, 2011, permits are not required for 

discharges from these applications when applied in accordance with the 

product’s FIFRA label. Certain related activities continue to be exempt from 

permitting under the CWA (i.e., irrigation return flow and agricultural 

stormwater runoff). 

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September 2010 NPDES Permit Writers’ Manual 

4.2 Application Deadlines 

The regulations at § 122.21(c) and (d) specify the time to apply for NPDES permits. Exhibit 4-2 

summarizes the application deadline requirements for dischargers to be covered by an NPDES permit. 

Exhibit 4-2 When to apply for an NPDES permit 

Type of permit Type of discharge Schedule* 

New At least 180 days before the date on which the discharge 

is to commence 

Existing At least 180 days before expiration date of existing permit Individual 

Construction Stormwater At least 90 days before the date on which construction is 

to commence 

New Specified in general permit 

General 

Existing X number of days following issuance of permit 

(specified in the general permit) 

* Authorized states may use more stringent deadlines. 

Anyone proposing a new discharge must apply to the permitting authority no later than 180 days before 

the expected commencement of the discharge if applying for an individual permit. Any person with an 

currently effective individual permit must submit an application to the permitting authority at least 

180 days before the expiration of its existing individual permit unless permission for a later date has been 

granted in accordance with § 122.21(d). For general permits, the deadline for new dischargers to apply is 

specified in the general permit. A general permit also may specify a number of days after the general 

permit’s issuance that operators of existing facilities are given to apply for coverage. Authorized states 

may have different schedules for permit applications, but their schedules may be no less stringent than the 

federal deadlines. The State Director or the Regional Administrator may allow an individual application 

to be submitted at dates later than those specified in the regulations, but not later than the expiration date 

of the existing permit. 

Note that, according to § 122.6, the conditions of an expired NPDES permit remain in effect until the new 

permit is issued, as long as the discharger submitted a complete application in accordance with the 

timeframes prescribed in the regulations (or in accordance with state law, in the case of state-administered 

NPDES programs). If state law does not allow expired permits to remain in effect until a permit is 

reissued, or if the permit application is not on time and complete, the facility may be considered to be 

discharging without a permit from the time the permit expired until the effective date of the new permit. 

4.3 Application Forms and Requirements for Individual Permits 

When a facility needs an individual NPDES permit, it must submit a permit application. Application 

forms and requirements are specific to the type of facility and discharge. NPDES permit application 

requirements are in Part 122, Subpart B and identified on forms developed by the U.S. Environmental 

Protection Agency (EPA). Authorized states are not required to use the EPA application forms; however, 

any alternative form used by an authorized state must include the federal requirements at a minimum. 

Exhibit 4-3 provides an overview of the types of dischargers required to submit NPDES application 

forms, identifies the forms that must be submitted, and references the corresponding NPDES regulatory 

citation. In some cases, a facility might need to file more than one application form. For example, an 

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September 2010 NPDES Permit Writers’ Manual 

existing industrial facility (i.e., renewal) discharging stormwater combined with process and non-process 

wastewater might need to submit Form 1, Form 2C, and Form 2F. Section 2.3 of this manual discusses 

the NPDES program areas that have application requirements presented below. 

Exhibit 4-3 EPA application requirements for NPDES individual permits 

Type of facility or program area Status Forms 

Regulatory citations and 

additional application 

requirements 

(40 CFR) 

Municipal facilities 

 POTWs with design flows greater 

than or equal to 0.1 million gallons 

per day (mgd) 

New and existing 

Form 2A, Parts 

A, B and C; Parts 

D, E, F, or G as 

applicable 

 § 122.21(a)(2)(i)(B) 

 § 122.21(j) 

 POTWs with design flows less than 

0.1 mgd New and existing 

Form 2A, Parts A 

and C; 

Parts D, E, F, or 

G as applicable 

 § 122.21(a)(2)(i)(B) 

 § 122.21(j) 

TWTDS (sewage sludge) New and existing Form 2S  § 122.21(a)(2)(i)(H) 

 § 122.21(q) 

Concentrated animal production 

facilities 

 Concentrated animal feeding 

operations 

 Concentrated aquatic animal 

production facilities 

New and existing Form 1 and 

Form 2B 

 § 122.21(a)(2)(i)(A) and (C) 

 § 122.21(f) and (i) 

Existing Form 1 and 

Form 2C 

 § 122.21(a)(2)(i)(A) and (D) 

 § 122.21(f) and (g) 

New 

(process 

wastewater) 

Form 1 and 

Form 2D 

 § 122.21(a)(2)(i)(A) and (E) 

 § 122.21(f) and (k) 

Industrial facilities 

 Manufacturing facilities 

 Commercial facilities 

 Mining activities 

 Silvicultural activities 

New and existing 

(non-process 

wastewater) 

Form 1 and 

Form 2E 

 § 122.21(a)(2)(i)(A) and (F) 

 § 122.21(f) and (h) 

Stormwater discharges associated 

with industrial activities (except 

stormwater discharges associated 

with construction activity) 

New and existing Form 1 and 

Form 2F 

 § 122.21(a)(2)(i)(A) and (G) 

 § 122.21(f) 

 § 122.26(c) 

Stormwater discharges associated 

with construction activity New and existing Form 1 

 § 122.21(a)(2)(i)(A) 

 § 122.21(f) 

 § 122.26(c)(1)(ii) 

Stormwater discharges from MS4s 

serving a population greater than 

100,000 

New and existing None  § 122.26(d) 

Stormwater discharges from small 

MS4s New and existing None  § 122.33 

 § 122.21(f) 

Cooling water intake structures New and existing None  § 122.21(r) 

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4.3.1 Form 1: General Information 

All facilities applying for an individual NPDES permit, with the exception of POTWs, treatment works 

treating domestic sewage (TWTDS), and municipal separate storm sewer systems (MS4s) applying for a 

municipal stormwater permit, must submit Form 1 <www.epa.gov/npdes/pubs/form_1.pdf>. The type of general 

facility information required by Form 1 is specified in §§ 122.21(a)(2)(i)(A) and 122.21(f) and includes 

the following: 

 Name, mailing address, facility contact, and facility location. 

 Standard industrial classification (SIC) code and a brief description of the nature of the business. 

 Topographic map showing the location of the existing or proposed intake and discharge 

structures. 

4.3.2 Form 2A: New and Existing POTWs 

All new and existing POTWs must submit Form 2A <www.epa.gov/npdes/pubs/final2a.pdf>. EPA issued a final 

rule amending permit application requirements and application forms for POTWs and other TWTDS 

(64 FR 42433, August 4, 1999). The rule consolidated POTW application requirements, expanded toxic 

monitoring requirements for POTWs, and revised the forms used to submit permit applications. POTWs 

must also submit the form for permit renewals. Form 2A replaces Standard Form A and Short Form A. 

POTWs with design influent flows equal to or greater than 100,000 gallons per day (gpd) (0.1 mgd) must 

submit Parts A, B, and C of Form 2A. POTWs with design flows of less than 100,000 gpd must submit 

Parts A and C of Form 2A. Parts A, B and C are referred to as Basic Application Information: 

 Part A of Form 2A contains basic application information for all applicants: 

− Facility and applicant information. 

− Collection system type, areas served, and total population served. 

− Discharges and other disposal methods. 

− If the treatment works discharges effluent to waters of the United States, a description of 

outfalls, receiving waters, and treatment and effluent testing information. 

 Part B of Form 2A collects additional information for applicants with a design flow greater than 

or equal to 0.1 mgd, including inflow and infiltration estimates, a topographic map, process flow 

diagram, and effluent testing data for additional parameters. 

 Part C is a certification that all applicants must complete. 

Form 2A also includes Supplemental Application Information (Parts D–G). POTWs complete these 

additional forms, as applicable, depending on the characteristics of the municipal discharge: 

 Part D requests expanded effluent testing data for metals, volatile organic compounds, acidextractable compounds, and base-neutral compounds. A POTW that discharges effluent to waters 

of the United States and meets one or more of the following criteria must complete Part D: 

− Has a design flow rate greater than or equal to 1 mgd. 

− Is required to have a pretreatment program (or has one in place). 

− Is otherwise required by the permitting authority to provide the information. 

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 A POTW that meets one or more of the following criteria must complete Part E (Toxicity Testing 

Data): 

− Has a design flow greater than or equal to 1 mgd. 

− Is required to have a pretreatment program (or has one in place). 

− Is otherwise required by the permitting authority to submit results of toxicity testing. 

 A POTW that accepts process wastewater from any significant industrial users (SIUs) or receives 

Resource Conservation and Recovery Act (RCRA) or Comprehensive Environmental Response, 

Compensation, and Liability Act (CERCLA) or other remedial wastes must complete Part F. 

SIUs are defined as: 

− All industrial users subject to Categorical Pretreatment Standards under § 403.6 and 40 CFR 

Chapter I, Subchapter N. 

− Any other industrial user for which any of the following is true 

o Discharges an average of 25,000 gpd or more of process wastewater to the POTW 

(excluding sanitary, non-contact cooling, and boiler blowdown wastewater). 

o Contributes a process wastestream that makes up 5 percent or more of the average dryweather hydraulic or organic capacity of the treatment plant. 

o Is designated an SIU by the control authority on the basis that it has a reasonable 

potential for adversely affecting the POTWs operation or for violating any pretreatment 

standard or requirement. 

− The control authority can determine that an industrial user subject to categorical pretreatment 

standards is a nonsignificant categorical industrial user, rather than an SIU, on a finding that 

it never discharges more than 100 gpd of total categorical wastewater and if: 

o Before that finding, the industrial user has consistently complied with all applicable 

categorical pretreatment standards and requirements. 

o The industrial user annually submits a certification statement required in § 403.12(q) and 

any information necessary to support the certification statement. 

o The industrial user never discharges any untreated concentrated wastewater. 

− If an industrial user meets one of the other criteria for determining that it is an SIU (i.e., 

discharges an average of 25,000 gpd of process wastewater), but the control authority finds 

that it has no reasonable potential for adversely affecting the POTW’s operation or for 

violating any pretreatment standards or requirement, the control authority can determine that 

the industrial user is not an SIU. 

 A POTW that has a combined sewer system must complete Part G. Information that must be 

provided in the section includes a system map and diagram, and descriptions of outfalls, 

combined sewer overflow (CSO) events, receiving waters, and operations. 

4.3.3 Form 2S: New and Existing TWTDS 

New TWTDS and TWTDS with effective NPDES permits must submit a new or renewal permit 

application, respectively, using new Form 2S <www.epa.gov/npdes/pubs/final2s.pdf>. Part 1 of Form 2S is to be 

completed by sludge-only facilities; that is, facilities that do not have, and are not applying for, an NPDES 

permit for a direct discharge to surface water. Part 1 collects background information on the facility, 

including identification information, quantities of sewage sludge handled, pollutant concentrations, 

treatment methods, and use and disposal information. 

4-6 Chapter 4: NPDES Permit Application Process 
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Part 2 is used by facilities that already have or are applying for an NPDES permit. It includes five 

sections: 

 All applicants using Part 2 must complete the general information collected by section A. 

 Applicants who either generate sewage sludge or derive a material from sewage sludge must 

complete section B. 

 Applicants who either apply sewage sludge to the land or generate sewage sludge that is applied 

to the land by others (unless the sludge from the facility meets certain exemption criteria) must 

complete section C. 

 Applicants who own or operate a surface disposal site must complete section D. 

 Applicants who own or operate a sewage sludge incinerator must complete section E. 

4.3.4 Form 2B: New and Existing Concentrated Animal Feeding

Operations (CAFOs) and Concentrated Aquatic Animal Production 

(CAAP) Facilities 

In addition to Form 1, owners of new and existing CAFOs (defined in § 122.23) and CAAP facilities 

(defined in § 122.24) must submit Form 2B <www.epa.gov/ne/npdes/2010RevisedCafoFedRegstrForm2b.pdf>. 

Form 2B was significantly modified as part of the final CAFO Rules (68 FR 7176, February 12, 2003, and 

73 FR 70418, November 20, 2008). The type of information required by Form 2B consists of the following: 

 For CAFOs 

− The name of the owner or operator. 

− The facility location and mailing addresses. 

− Latitude and longitude of the production area. 

− A topographic map of the geographic area in which the CAFO is located. 

− Specific information about the number and type of animals. 

− The type of containment and total capacity for storage (tons/gallons). 

− The total number of acres under control of the applicant available for land application. 

− Estimated amounts of manure, litter, and process wastewater generated and amounts 

transferred to other persons per year. 

− A nutrient management plan (NMP) that satisfies the requirements of § 122.42(e). 

 For CAAP facilities 

− The maximum daily and average monthly flow from each outfall. 

− The number of ponds, raceways, and similar structures. 

− The name of the receiving water and the source of intake water. 

− For each species of aquatic animals, the total yearly and maximum harvestable weight. 

− The calendar month of maximum feeding and the total mass of food fed during that month. 

Note that recent revisions to the NPDES regulations require that a CAFO seeking coverage under a permit 

submit its NMP with its application for an individual permit or notice of intent (NOI) to be authorized 

under a general permit. Permitting authorities are required to review the plan and provide the public with 

an opportunity for meaningful public review and comment. Permitting authorities also are required to 

incorporate terms of the NMP as NPDES permit conditions. For more information on the revisions to the 

CAFO regulations, see the Animal Feeding Operations Website <www.epa.gov/npdes/cafo>. 

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Sections 2.3.2.5 and 2.3.2.6 of this manual provide additional information on CAFOs and CAAP 

facilities, respectively. 

4.3.5 Form 2C: Existing Manufacturing, Commercial, Mining, and 

Silvicultural Discharges 

In addition to Form 1, operators of existing (i.e., currently permitted) manufacturing, commercial, mining, 

and silvicultural discharges must submit Form 2C <www.epa.gov/npdes/pubs/3510-2C.pdf>. The type of 

information required in Form 2C includes: 

 Outfall locations. 

 A line drawing of the water flow through the facility. 

 Flow characteristics, sources of pollution, treatment technologies. 

 Production information (if applicable). 

 Improvements (if applicable). 

 Intake and effluent characteristics for conventional, nonconventional and toxic (priority) 

pollutants. 

 Potential discharges not covered by analysis. 

 Biological testing data. 

 Contract laboratory information. 

 Certification and signature. 

Quantitative effluent data requirements for existing industrial dischargers vary depending on the industrial 

category of the facility, the facility’s discharge characteristics and the types of pollutants expected to be 

present in the discharge. 

4.3.6 Form 2D: New Manufacturing, Commercial, Mining, and Silvicultural 

Discharges of Process Wastewater 

In addition to Form 1, operators of new manufacturing, commercial, mining, and silvicultural discharges 

of process wastewater must submit Form 2D <www.epa.gov/npdes/pubs/3510-2D.pdf>. New dischargers are 

those that have not previously obtained permits for a discharge and have not commenced operation. The 

type of information required in Form 2D includes the following: 

 Expected outfall locations. 

 Date of expected commencement of discharge. 

 Expected flow characteristics. 

 Sources of pollutants. 

 Treatment technologies. 

 Production information (if applicable). 

 Expected intake and effluent characteristics. 

4.3.7 Form 2E: Manufacturing, Commercial, Mining, and Silvicultural 

Facilities that Discharge Only Non-Process Wastewater 

In addition to Form 1, operators applying for an individual NPDES permit for manufacturing, 

commercial, mining, and silvicultural facilities that are not regulated by effluent limitations guidelines 

and standards (effluent guidelines) or new source performance standard, and that discharge only 

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September 2010 NPDES Permit Writers’ Manual 

non-process wastewaters, must submit Form 2E <www.epa.gov/npdes/pubs/3510-2E.pdf>. Non-process 

wastewater includes sanitary wastes, restaurant or cafeteria wastes, and non-contact cooling water, but it 

does not include stormwater. Stormwater is specifically excluded from the definition of non-process 

wastewater. Form 2E also may not be used for discharges by educational, medical, or commercial 

chemical laboratories or by POTWs. The type of information required in Form 2E includes the following: 

 Outfall locations. 

 Type of waste discharged. 

 Effluent characteristics, including quantitative data for selected parameters. 

 Flow characteristics. 

 Treatment technologies. 

4.3.8 Form 2F: Stormwater Discharges Associated with Industrial 

Activities 

In addition to Form 1, operators applying for an individual NPDES permit for discharges composed 

entirely of stormwater associated with industrial activity must submit Form 2F

<www.epa.gov/npdes/pubs/3510-2F.pdf>. Applicants whose discharge is composed of stormwater and nonstormwater must also submit Form 2C, 2D, or 2E as appropriate. The type of information required in 

Form 2F includes the following: 

 A topographic map and estimates of impervious surface area. 

 Descriptions of material management practices and control measures. 

 A certification that outfalls have been evaluated for non-stormwater discharges. 

 Descriptions of past leaks and spills. 

 Analytical data from each outfall for several specified parameters. 

EPA developed the Guidance Manual For the Preparation of NPDES Permit Applications For 

Stormwater Discharges Associated With Industrial Activity1 <www.epa.gov/npdes/pubs/owm0241.pdf> to assist 

operators of facilities that discharge stormwater associated with industrial activity in complying with the 

requirements for applying for an NPDES permit. 

4.3.9 Stormwater Discharges Associated with Construction Activity 

Most stormwater discharges associated with construction activities that result in the disturbance of one 

acre or more are covered under a general permit issued by EPA or the authorized state. In cases that a 

general permit does not cover the discharge or the discharger decides that an individual permit is 

necessary for stormwater discharges associated with construction activity, the discharger is required to 

submit Form 1, along with a narrative description of the following: 

 The location (including a map) and the nature of the construction activity. 

 The total area of the site and the area of the site that is expected to undergo excavation during the 

life of the permit. 

 Proposed measures, including best management practices (BMPs), to control pollutants in 

stormwater discharges during construction, including a brief description of applicable state and 

local erosion and sediment control requirements. 

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 Proposed measures to control pollutants in stormwater discharges that will occur after 

construction operations have been completed, including a brief description of applicable state or 

local erosion and sediment control requirements. 

 An estimate of the runoff coefficient of the site and the increase in impervious area after the 

construction addressed in the permit application is completed, the nature of fill material and 

existing data describing the soil or the quality of the discharge. 

 The name of the receiving water. 

4.3.10 Stormwater Discharges from MS4s Serving a Population Greater 

than 100,000 

The stormwater application regulations (55 FR 47990, November 16, 1990) require operators of large or 

medium MS4s to submit two-part applications. Part 1 application information was required to be 

submitted by large MS4s (serving a population greater than 250,000) by November 18, 1991, and by 

medium MS4s (serving a population greater than 100,000 but less than or equal to 250,000) by May 18, 

1992. Part 2 application information was required to be submitted by large MS4s by November 16, 1992, 

and by medium MS4s by May 17, 1993. Those applications could be submitted on a system- or 

jurisdiction-wide basis. Key requirements of each part of the application include [and are further 

addressed in § 122.26(d)] the following: 

 Part 1 

− General information (e.g., name, address). 

− Existing legal authorities to control discharges to the storm sewer system and any additional 

authority that might be required. 

− Source identification information (e.g., storm sewer outfalls, land use information). 

− Discharge characterization, including monthly precipitation estimates, average number of 

storm events, and results from dry-weather flow screening. 

− Characterization plan, including identification of 5 to 10 representative outfalls for 

stormwater sampling. 

− Description of existing stormwater management practices. 

− Descriptions of existing budget and resources available to complete Part 2 of the application 

and implement the stormwater program. 

 Part 2 

− Demonstration of adequate legal authority. 

− Identification of any major storm sewer outfalls not included in Part 1 of the application. 

− Discharge characterization data from three representative storm events. 

− Proposed stormwater management program. 

− Assessment of controls, including expected reductions in pollutant loadings. 

− Fiscal analysis, including necessary capital and operation and maintenance expenditures for 

each year of the permit. 

Under the NPDES regulations, permittees are required to reapply for a new NPDES permit before the 

expiration of their existing permit; however, in the case of stormwater permits for MS4s, Part 1 and Part 2 

application requirements described above were intended only for the initial issuance of an MS4 permit 

and specific requirements for reapplication have not been defined in the regulations. On May 17, 1996, 

EPA issued a policy that sets forth a streamlined approach for reapplication requirements for operators of 

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MS4s (61 FR 41698, August 9, 1996) that allows municipalities to use recommended changes submitted 

in their fourth year annual report required under § 122.42(c)(2), as the principal component of their 

reapplication package. It also encourages changes to monitoring programs to make them appropriate and 

useful to stormwater management decisions. With the policy, EPA seeks to improve municipal 

stormwater management efforts by allowing municipalities to target their resources for the greatest 

environmental benefit. 

4.3.11 Stormwater Discharges from Small MS4s 

The application requirements for small MS4s are addressed in § 122.33. Most states have issued general 

permits for small MS4s; however, regulated small MS4s may seek authorization to discharge under an 

individual permit. The application requirements are different depending on whether the MS4 will implement 

a program under § 122.34 (i.e., a program that follows EPA’s six minimum control measures) or a program 

that varies from § 122.34. EPA anticipates that most MS4s will follow the § 122.34 requirements. 

Regulated small MS4s seeking an individual permit and wishing to implement a program under § 122.34 

(the six minimum control measures) must submit an application to their NPDES permitting authority that 

includes the following: 

 The information required under §§ 122.21(f) and 122.34(d). 

 An estimate of square mileage served by the small MS4. 

 Any additional information that the NPDES permitting authority requests. 

A storm sewer map that satisfies the requirement of § 122.34(b)(3)(i) will also satisfy the map 

requirement in § 122.21(f)(7). 

Regulated small MS4s seeking an individual permit and wishing to implement a program that is different 

from the program under § 122.34 must comply with the permit application requirements of § 122.26(d) 

(for additional information, see section 4.3.10 above). Under § 122.33, the regulated small MS4 is 

required to submit both parts of the application requirements in §§ 122.26(d)(1) and (2) by March 10, 

2003. Small MS4s are not required to submit the information required by §§ 122.26(d)(1)(ii) and (d)(2) 

regarding their legal authority, unless they intend for the permit writer to take such information into 

account when developing their other permit conditions. Regulated small MS4s may jointly apply with 

another regulated entity consistent with the same requirements. 

Additionally, another regulated entity may seek a modification of an existing MS4 permit to include a 

regulated small MS4 as a co-permittee. In such a case, the regulated small MS4 must apply consistent 

with § 122.26 rather than § 122.34. Application requirements of §§ 122.26(d)(1)(iii) and (iv) and 

(d)(2)(iii) do not apply and compliance with §§ 122.26(d)(1)(v) and (d)(2)(iv) can be met by referring to 

the other MS4’s stormwater management program. 

4.3.12 Cooling Water Intake Structures 

Phase I of the CWA section 316(b) rule was finalized on December 18, 2001, in 66 FR 65256. The Phase 

I Rule (Part 125, Subpart I) implements CWA section 316(b) for most new facilities. The rule applies to 

new facilities that use cooling water intake structures to withdraw water from waters of the United States 

and that have or require an NPDES permit. This rule includes new facilities that have a design intake flow 

of greater than 2 mgd and that use at least 25 percent of water withdrawn for cooling purposes. For other 

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new facilities that have or require an NPDES permit but do not meet the 2-mgd intake flow threshold or 

use less than 25 percent of their water for cooling water purposes, the permit authority must implement 

CWA section 316(b) on a case-by-case basis, using best professional judgment (BPJ) (§§ 125.90(b) and 

401.14). 

Phase II of the CWA section 316(b) rule was finalized on July 9, 2004, in 69 FR 41576. In 2007 EPA 

suspended the rule following remand of a number of its provisions by the U.S. Court of Appeals for the 

Second Circuit. CWA section 316(b) requirements for such facilities must be developed on a case-by-case 

basis. 

Phase III of the CWA section 316(b) rule was finalized on June 16, 2006, in 71 FR 35006. The Phase III 

rule (Part 125, Subpart N) implements CWA section 316(b) for new offshore oil and gas extraction 

facilities that use cooling water intake structures to withdraw water from waters of the United States and 

that have or require an NPDES permit. The rule includes facilities with a design intake flow of greater 

than 2 mgd and that use at least 25 percent of water withdrawn for cooling purposes. 

EPA has not established national standards for existing Phase III facilities and is reevaluating its decisions 

in both Phase II and Phase III because of court remands. In the interim, for Phase III facilities not 

regulated under national categorical standards, the permitting authority must implement CWA section 

316(b) on a case-by-case basis, using BPJ (§§ 125.90(b) and 401.14). For the most current information on 

regulatory requirements, see the Cooling Water Intake Structure Program Website

<www.epa.gov/waterscience/316b/>. 

4.4 Requirements for NPDES General Permits 

As previously discussed in section 3.1.2 of this manual, general permits (§ 122.28) are permits developed 

for a specific category of dischargers within a specified geographic or political boundary. Using a general 

permit could simplify the permitting process for both EPA and the discharger. Owners/operators may 

seek coverage under a general permit only if one has been issued that is applicable to the type of facility 

for which coverage is sought and the permit covers the facility’s activities. In addition, the permitting 

authority may determine that a general permit is not appropriate for a facility seeking coverage under the 

general permit and can require the facility to apply for an individual permit. Furthermore, a facility that 

otherwise qualifies for a general permit may opt to apply for an individual permit. 

In most cases, a facility or activity seeking coverage under a general permit must seek coverage by 

submitting an NOI. The information that must be provided by the facility or activity in the NOI is 

specified in the general permit and must include, at a minimum, the following: 

 Legal name and address of the owner or operator. 

 Name and address of the facility. 

 Type of facility or discharges. 

 The receiving stream(s). 

EPA has developed the Electronic NOI (eNOI) for construction sites and industrial facilities that need to 

apply for coverage under EPA’s Construction General Permit (CGP) or Multi-Sector General Permit 

(MSGP), respectively. EPA’s Electronic Stormwater Notice of Intent (eNOI) Website

<www.epa.gov/npdes/stormwater/enoi> presents additional information about eNOI. 

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4.5 Application Review 

The contents of individual NPDES permits are based, in part, on the information included in the 

application. Thus, the application must be complete and accurate before a permit writer can properly 

develop a permit. Exhibit 4-4 depicts the general process for reviewing a permit application, based on a 

chart provided in the Washington Department of Ecology’s Permit Writers’ Manual2

. 

Exhibit 4-4 Permit application review process 

After the initial application review, the permit writer may request that an applicant submit other 

information needed to decide whether to issue a permit and for permit development. The requested 

information could include the following: 

 Additional information, quantitative data, or recalculated data. 

 Submission of a new form (if an inappropriate form was used). 

 Resubmission of the application (if incomplete or outdated information was initially submitted). 

In some situations, a considerable amount of correspondence might be required before the permit writer 

obtains all the information that he or she believes is necessary to draft the permit. 

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September 2010 NPDES Permit Writers’ Manual 

4.5.1 The Complete Application 

The regulations at § 122.21(e) state that the Director, “[must] not issue a permit before receiving a 

complete application...” At a minimum, the application form must have all applicable spaces filled in. 

Instructions for the application form state that all items must be completed and that applicants use the 

statement not applicable (N/A) to indicate that the item had been considered. Blanks on a form can occur 

for a number of reasons, such as the following: 

 The response was inadvertently omitted. 

 The applicant had difficulty determining the correct response and rather than provide misleading 

or incorrect information, left the space blank. 

 The applicant was unwilling to provide the response. 

A permit writer must obtain a response to the blank items by contacting the facility in writing or, in some 

cases, by telephone. Only minor changes should be handled by telephone and even minor items should be 

documented in writing in the permit file. Under no circumstances should a permit writer edit or modify 

the application, which is a legal document that has been signed and certified by the applicant. The original 

application, any subsequent clarifications, and any supplemental information provided by the applicant 

should be clearly identified in the file. The information will become part of the administrative record 

(§ 124.9) for the permit (see section 11.2.1 of this manual), which is critical if any legal challenges 

regarding permit decisions arise. If the changes or corrections to any application are extensive, the permit 

writer may require the permit applicant to submit a new application. 

The permit writer may also require supplementary information, such as more detailed production 

information or maintenance and operating data for a treatment system, to process the permit. According to 

§ 122.21(e), an application is considered complete when the permitting authority is satisfied that all 

required information has been submitted. Supplementary information also can be obtained later when the 

permit writer is actually drafting the permit. The applicant may submit additional information voluntarily 

or be required to do so under CWA section 308 or under a similar provision of state law. 

4.5.2 Common Omissions in Applications 

This section identifies some of the most common omissions and errors found in NPDES permit 

applications and provides examples of ways to identify missing information and verify the accuracy of 

certain data. 

One of the most commonly omitted items from NPDES permit applications is a topographic map of the 

area around the discharge, which is required as an attachment to Form 1, Form 2A, and Form 2S. Other 

industry- or municipality-specific information is also often omitted. For example, industrial applicants 

sometimes fail to submit a line drawing of the water flow through the facility required by Part II-A of 

Form 2C. The line drawing is important for ensuring that the location and description of the outfalls and 

the description of processes (Parts I and II-B of Form 2C) provided by the applicant are accurate. 

Sometimes applicants do not properly submit the effluent data necessary to characterize the facility. 

Below are some required data elements that are commonly omitted from permit applications: 

 Valid whole effluent toxicity (WET) testing data, required from POTWs with design flows 

greater than 1 mgd or those with a pretreatment program. This requirement may be satisfied if the 

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September 2010 NPDES Permit Writers’ Manual 

expiring permit contains a requirement for effluent characterization of WET. The permit writer 

should note the use of this option on the fact sheet. 

 Biosolids (sewage sludge) monitoring data; a description of biosolids use and disposal 

procedures; annual biosolids production volumes; and information on the suitability of the site 

and a description of the site management for land application sites from POTWs and other 

TWTDS. A land application plan is required for any sites not identified in the application. 

 Expected toxics and other pollutants. Non-municipal dischargers categorized as primary 

industries have some mandatory testing requirements for toxic pollutants (see § 122.21, 

Appendix D, Table I and Table II and also listed in Application Form 2C). 

 Production rates and flow data from industrial facilities that are subject to production- or flowbased effluent guidelines. Applicants must use units of measure corresponding to applicable 

effluent guidelines to allow calculation of effluent limitations. 

 Appropriate sample types for all required pollutants and parameters being analyzed (Part 136) 

(see sections 8.1.4 and 8.3 of this manual for more information). For example, only grab samples 

or continuous monitoring may be used for pH, total residual chlorine, and temperature, and only 

grab samples may be used for total phenols and volatile organics. 

Exhibit 4-5 presents three examples of the types of questions that the permit writer should consider to 

determine whether an application is complete. 

Exhibit 4-5 Considerations for an application to be complete 

Example 1: 

A plastics processor submits Form 1 and Form 2C but fails to indicate testing required for any gas 

chromatograph/mass spectrometer (GC/MS) fractions in section V.C. of Form 2C and does not provide any data 

for these pollutants. 

Question:

Did the applicant provide all the required data for the toxic organic pollutants in Form 2C? 

Answer:

No. The plastics processor is required to indicate testing required (in the check box) and provide data from at least 

one sample for each pollutant in the volatile GC/MS fraction (Table 2C-2 in the application form instructions and 

§ 122.21(g)(7)(v)(A) of the NPDES regulations). 

Example 2: 

A soap and detergent manufacturing facility in the liquid detergents subcategory submits Form 1 and Form 2C but 

marks thallium and beryllium as believed absent in section V.C. of Form 2C and did not provide any data for these 

pollutants. 

Question: 

Is it appropriate for this applicant to mark believed absent in this section of Form 2C? 

Answer: 

No. Although an applicant that manufactures liquid detergents is not expected to discharge thallium and beryllium, 

page 2C-3 of the application form instructions and § 122.21(g)(7)(v)(B) require testing for all listed metals by all 

applicants in a primary industry category, such as soap and detergent manufacturers. The indication of believed 

absent is incorrect. The applicant should have indicated testing required and provided the results of at least one 

sample per pollutant. Occasionally, unexpected contaminants could be present in a wastestream. 

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Exhibit 4-5 Considerations for an application to be complete (continued) 

Example 3: 

An integrated slaughterhouse and meat processing facility submits Form 1 and Form 2C and indicates that zinc is 

believed absent from its wastewater. 

Question: 

Is believed absent a proper indication for zinc for this wastewater? 

Answer: 

Possibly. After consulting the effluent guidelines development documents for the Meat and Poultry Products Point 

Source Category, the permit writer determines that metals, including zinc, are often used as feed additives and in 

sanitation products and might be present in the effluent, even though there are no effluent limitations specified for 

zinc in the applicable effluent guideline. The permit writer should contact the applicant and clarify whether zinc 

would be expected to be present in the discharge. 

The comprehensive testing requirements that apply to the various categories of industry are designed to 

determine whether any contaminants (some expected, some unexpected) are present in significant 

quantities and to determine levels of pollutants that are known to be present. Exhibit 4-6 presents an 

example of how a permit writer makes the determination of pollutant data required in the application. 

Exhibit 4-6 Example of required testing during application review 

Consider the plastics processor and the liquid detergents manufacturer mentioned above, and answer the 

following questions: 

Question: 

What pollutant data are needed to characterize the industries above? 

 For which toxic organic pollutants are they required to test? 

 For which heavy metals are they required to test? 

 Which metals would you expect to find in their wastewaters regardless of whether testing is required? 

Answer: 

The application form in Table 2C-2 and § 122.21(g)(7)(ii)(A) of the NPDES regulations require testing of the 

volatile GC/MS fraction by the plastics processor and the volatile, acid, and base/neutral fractions by the liquid 

detergent manufacturer. Page 2C-3 of the application instructions and § 122.21(g)(7)(ii)(B) require testing of all the 

metals listed in item V, Part C1 of the application form as well as cyanide and total phenols by both of these 

primary industry facilities. For information on which, if any, metals might be expected in wastewater discharged by 

these applicants, see the effluent guidelines development documents. 

4.5.3 The Accurate Application 

All information submitted on a permit application must be accurate. Although it might be difficult to 

detect certain inaccuracies, a number of common mistakes can be readily detected. When mistakes are 

detected, they must be corrected. Generally, any correction or edit to the application should be obtained 

from the applicant in writing and will become a part of the administrative record for the permit. 

In most cases, errors in the application will be inadvertent because of the length and complexity of the 

form. Note, however, that the application certification statement indicates, “...that there are significant 

penalties for submitting false information, including the possibility of fine and imprisonment for knowing 

violations.” If the permit writer believes that falsification has occurred, he or she should refer the findings 

to the agency’s enforcement staff. 

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Some of the most common mistakes on permit applications include failing to provide the correct longterm average and daily maximum values, reporting quantified values below known detection limits, and 

using misplaced decimal points or incorrect concentration units. Exhibit 4-7 presents three examples of 

the types of questions that the permit writer should consider while reviewing the permit application for 

accuracy. Additional guidance from EPA might be available to assist permit writers in reviewing 

applications for some of these common errors. For example, an August 23, 2007, memorandum 

Analytical Methods for Mercury in National Pollutant Discharge Elimination System (NPDES) Permits3

<www.epa.gov/npdes/pubs/mercurymemo_analyticalmethods.pdf> describes when a method for mercury is sufficiently 

sensitive for purposes of permit applications and monitoring under a permit. In the memorandum, EPA 

strongly recommends that a permitting authority determine that a permit application that lacks effluent data 

analyzed with a sufficiently sensitive EPA-approved method (such as Method 1631E) is incomplete unless 

and until the facility supplements the original application with data analyzed with such a method. 

4.6 Facility Information Review 

In addition to the submitted application form, the permit writer should assemble other information that 

could be used to develop permit limitations and conditions. 

4.6.1 Permit File Review 

Before developing the draft permit and fact sheet, the permit writer should assemble and review any 

additional background information on the facility. If the permit writer is reissuing an existing permit, 

much of the information should be available in the permit file. Such information would typically include 

 The current permit. 

 The fact sheet or statement of basis for the current permit. 

 Discharge monitoring reports (DMRs). 

 Compliance inspection reports. 

 Engineering reports. 

 Correspondence or information on changes in plant conditions, problems, and compliance issues. 

Much of this information, particularly DMR data, is stored in automated data tracking systems such as 

 Permit Compliance System (PCS) or state databases. 

 Integrated Compliance Information System (ICIS)-NPDES <https://icis.epa.gov>. 

 Online Tracking Information System (OTIS) <www.epa.gov/idea/otis/>. 

 Envirofacts Warehouse <www.epa.gov/enviro/>. 

The permit writer can check with other permit writers who have permitted similar types of facilities to see 

if there are any special considerations related to the type of facility to be permitted. A permit writer might 

also wish to discuss compliance issues, changes, or history of complaints with compliance personnel who 

conducted previous inspections of the facility or with permit writers for other media (e.g., air, solid 

waste). Examples of some other sources of information that the permit writer could use for permit 

development include the following: 

 Receiving water quality data from databases such as the EPA STOrage and RETrieval database 

(STORET) <www.epa.gov/STORET/>. 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 4-7 Considerations for an application to be accurate 

Example 1: 

An industrial applicant provides a daily maximum effluent flow value of 50,000 gpd in its permit application Form 

2C. However, a review of historical water usage records and an old permit application indicate estimated 

wastewater flows ranged from 100,000 to 150,000 gpd. The applicant had not instituted any water use reduction 

measures, significantly changed its process operations, or decreased its number of employees. 

Question: 

Are reported values consistent with historical information? 

Answer: 

No. An inspection of the facility revealed two separate water meters (one for sanitary and one for process water); 

the applicant had overlooked the sanitary meter. Further, the process water meter was found to be defective. 

Subsequent flow monitoring of the actual total wastestream recorded a flow of 125,000 gpd. A new water meter 

was installed, and concurrent wastestream flow monitoring and water meter readings resulted in the following 

water balances: 

 Water In (based on both water meter readings): 

148,000 gpd (131,000 gpd process line and 17,000 gpd sanitary line). 

 Water Out (based on effluent flow monitoring): 

125,000 gpd total treated effluent discharged to the receiving water. 

Evaporative and consumption losses were estimated at 23,000 gpd (15% of total water usage). 

The permit writer should require the applicant to submit a signed and certified letter with the revised flow estimates 

and a new water balance diagram or submit a revised application. 

Example 2: 

An applicant reported its maximum daily flow as 1.2 mgd, the maximum daily suspended solids concentration as 

23 milligrams per liter (mg/L), and the maximum daily mass discharge as 690 pounds per day (lbs/day). 

Question: 

Do the concentration, mass, and flow values correspond? 

Discussion: 

No. Even in the unlikely event that the maximum daily flow and the maximum daily concentration occurred on the 

same day, the mass discharged would be well below the reported value of 690 lbs/day. Using the calculation 

below, the mass discharge that corresponds to the solids concentration (23 mg/L) and flow (1.2 mgd) would be 

230 lbs/day: 

 23 mg/L x 1.2 mgd x 8.34 (lbs)(L)/(mg)(millions of gallons) = 230 lbs/day 

 (conversion factor) 

Because the applicant reported a maximum mass discharge of 690 lbs/day, a significant discrepancy is indicated. 

The permit writer should contact the applicant to resolve the discrepancy. The applicant should submit a signed 

and certified letter clarifying the correct maximum daily mass discharge of suspended solids or submit a revised 

application. 

Example 3: 

The results submitted in the application for total cyanide are all reported as < 1,000 micrograms per liter (μg/L). 

When asked, the applicant indicated that total cyanide was analyzed using EPA Method 335.3 (Color, Auto). 

Question: 

Do concentration values correspond with published method detection limits for the method used? 

Answer: 

No. EPA Method 335.3 for total cyanide has a published method detection limit (MDL) of 5 μg/L. The applicant 

should be able to quantify results for total cyanide at values well below 1,000 μg/L using this method. The 

applicant has most likely used Standard Method 4500-CN (titrimetric) for total cyanide, rather than the testing 

procedure indicated. If total cyanide is expected to be present in the discharge and would be of concern at effluent 

concentrations below 1,000 μg/L, the permit writer should require the applicant to retest for total cyanide using the 

more sensitive method and to submit the results in a signed, certified letter. 

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 Supporting documentation collected by EPA for effluent guidelines and categorical pretreatment 

standards for a variety of industrial categories. 

 Reference textbooks and technical documents that provide information about manufacturing 

processes and wastestreams for specific industry categories, which are available from libraries 

such as 

− National Technical Information Service (NTIS) <www.ntis.gov>. 

− EPA libraries <www.epa.gov/natlibra/libraries.htm>. 

− Office of Water Resource Center (OWRC) <www.epa.gov/safewater/resource/>. 

− National Service Center for Environmental Publications (NSCEP) <www.epa.gov/ncepihom/>. 

 Related environmental permits that could provide site-specific background information about the 

types of pollutants and wastestreams at a facility, including, for example 

− RCRA permits, which regulate the management of hazardous waste by owners and operators 

of treatment, storage, and disposal facilities. 

− Clean Air Act permits, which regulate the discharge of atmospheric pollutants. 

 EPA’s Treatability Manual4

, which is a five-volume guidance manual that provides detailed 

descriptions of industrial processes, potential pollutants from each process, appropriate treatment 

technologies, and cost estimating procedures. 

 The Toxic Release Inventory (TRI) <www.epa.gov/tri/>, which is accessible on EPA’s mainframe 

and through a public online service. The TRI contains information on more than 300 listed toxic 

chemicals released by specific facilities, including chemical identification, quantity of chemicals 

released to various environmental media, off-site waste transfer, and waste treatment and 

minimization information. 

If the permit writer must address special conditions in a permit for a municipal discharger to develop or 

implement a pretreatment program or to address discharges other than the wastewater treatment plant 

discharge, he or she should obtain the information needed to develop these special conditions. For 

example, the permit writer might need information on pretreatment program implementation, combined 

sewer overflows (CSOs), sanitary sewer overflows (SSOs), sewage sludge use or disposal, or stormwater 

discharges relevant to the facility. Such information is in 

 Annual pretreatment reports, pretreatment compliance inspections and audits. 

 CSO reports. 

 Bypass notifications or SSO reports. 

 Stormwater discharge applications or NOIs for a general permit. 

4.6.2 Facility Site Visits 

Facility site visits are an invaluable way to update information on manufacturing processes; obtain 

information about the facility’s operations, equipment or management; and verify application 

information. A site visit also acquaints the permit writer with the people who will be operating under the 

permit and participating in the permit development process. 

Site visits can also allow the permit writer to gain a better understanding of more complex facilities. Site 

visits are especially warranted if significant pollution control or treatment improvements will be required, 

if there have been frequent problems in complying with the existing permit, if there are known problems 

Chapter 4: NPDES Permit Application Process 4-19
September 2010 NPDES Permit Writers’ Manual 

with spills or leaks or with contaminated surface runoff, or if there are other unique on-site activities that 

could affect the characteristics of the discharge from the facility. 

The site visit should include a detailed review of production processes to evaluate the types of toxic or 

hazardous substances that might be present in raw materials, products, and by-products. The permit writer 

should review the water uses, the resulting wastewater streams, and any in-process pollution controls. 

This review is needed to assist in selecting toxic and other pollutants to be limited and in evaluating 

possible in-process control improvements. 

In addition, the site visit should include a review of the performance and operation and maintenance 

practices of wastewater treatment facilities. The review is useful in evaluating the adequacy of existing 

treatment performance and assessing the feasibility of improvements in performance. The permit writer 

should examine effluent monitoring points, sampling methods, and analytical techniques to identify any 

needed changes to monitoring requirements and to evaluate the quality of DMR data. 

Raw material and product storage and loading areas, sludge storage and disposal areas, hazardous waste 

management facilities, including on-site disposal areas, and all process areas should be observed to 

determine the need for controls on surface runoff and specific BMPs. Information from other 

environmental programs (e.g., CERCLA or RCRA) might be important in this regard. 

While on-site, the permit writer should note any housekeeping problems or the need for spill prevention 

actions, which are not usually detectable from permit applications. If allowed, photographs of problem 

areas should be taken for future use during permit preparation. If necessary, the permit writer should meet 

with management to ask questions or clarify information provided on the permit application. If any 

inaccuracies in the application were found because of the site visit, that is the time for the permit writer to 

request corrected information. 

The time required to conduct a site visit will vary according to the complexity of the facility. For facilities 

with only a few basic processes, one main waste treatment system, limited in-process controls, few 

surface runoff outfalls, and limited on-site management of sludge or hazardous wastes, an adequate site 

visit can most likely be completed in one day. Visits to complex, larger plants with several treatment 

systems, numerous outfalls, and extensive ancillary activities may require several days. 

Time spent on site visits often results in time savings during permit preparation. However, time and travel 

resources might not be adequate to allow visits to all facilities to be permitted. In such cases, the permit 

writer might be able to obtain much of the desired information from facility compliance inspections and 

should try to coordinate the timing of compliance inspections with the timing of permit development. 

Aerial photographs may provide much of the needed information on the potential for contamination of 

surface runoff and on ancillary activities without a site visit or inspection. In addition, comparing aerial 

photographs with site and process diagrams provided with the application can provide the permit writer 

with a complete visual description of the facility. Aerial photographs are available from a variety of 

sources, including the U.S. Geological Survey Earth Resources Observation and Science Center 

<eros.usgs.gov/#/Find_Data>; TerraServer <www.terraserver.com>; Google Earth <earth.google.com>; and other 

private contractors. 

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Chapter 4: NPDES Permit Application Process 4-21

 

4.7 Confidential Information 

In accordance with Part 2, information submitted to EPA pursuant to the NPDES permitting regulations 

under Part 122 may be claimed as confidential; however, EPA has determined that the following 

information will not be held confidential (§ 122.7): 

 Name and address of the applicant. 

 Permit applications and information submitted with applications. 

 Permits. 

 Effluent data. 

Information that may be claimed as confidential includes material related to manufacturing processes 

unique to the applicant, or information that might adversely affect the competitive position of the 

applicant if released to the public. Under such circumstances, the permit writer will be required to treat 

the information as confidential in accordance with the requirements in Part 2. Any claims of 

confidentiality must be made at the time of submission or the information will not be considered 

confidential. 

1

 U.S. Environmental Protection Agency. 1991. Guidance Manual For the Preparation of NPDES Permit Applications For 

Stormwater Discharges Associated With Industrial Activity. EPA-505/8-91-002. U.S. Environmental Protection Agency, Office 

of Water, Washington DC, <www.epa.gov/npdes/pubs/owm0241.pdf>. 

2

 Bailey, Gary. 2008. Water Quality Program Permit Writer’s Manual. Publication Number 92-109. Washington State 

Department of Ecology, Water Quality Program, Olympia, WA. <www.ecy.wa.gov/pubs/92109.pdf> 

3

 Hanlon, James A. 2007. Analytical Methods for Mercury in National Pollutant Discharge Elimination System (NPDES) 

Permits. U.S. Environmental Protection Agency, Office of Wastewater Management. Memorandum, August 23, 2007. 

<www.epa.gov/npdes/pubs/mercurymemo_analyticalmethods.pdf>. 

4

 U.S. Environmental Protection Agency. 1980. Treatability Manual: Vol. I. Treatability Data (EPA-600/8-80-042a) publications 

available on NEPIS Website <www.epa.gov/nscep/> as document 600880042A; Vol. II. Industrial Descriptions (EPA-600/8-80-

042b) as document 600880024B; Vol. III. Technologies (EPA-600/8-80-042c) as document 600880024C; Vol. IV. Cost 

Estimating (EPA-600/8-80-042d) as document 600880042d; Vol. V. Summary (EPA-600/8-80-042e) as document 600880024E. 

U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 5: Technology-Based Effluent Limitations 5-1

CHAPTER 5. Technology-Based Effluent Limitations 

One of the major strategies of the Clean Water Act (CWA) in making “reasonable further progress toward 

the national goal of eliminating the discharge of all pollutants” is to require effluent limitations based on 

the capabilities of the technologies available to control those discharges. Technology-based effluent 

limitations (TBELs) aim to prevent pollution by requiring a minimum level of effluent quality that is 

attainable using demonstrated technologies for reducing discharges of pollutants or pollution into the 

waters of the United States. TBELs are developed independently of the potential impact of a discharge on 

the receiving water, which is addressed through water quality standards and water quality-based effluent 

limitations (WQBELs). The NPDES regulations at Title 40 of the Code of Federal Regulations (CFR) 

125.3(a) require NPDES permit writers to develop technology-based treatment requirements, consistent 

with CWA section 301(b), that represent the minimum level of control that must be imposed in a permit. 

The regulation also indicates that permit writers must include in permits additional or more stringent 

effluent limitations and conditions, including those necessary to protect water quality. As described in 

Chapter 7 of this manual, the permit writer might also need to apply anti-backsliding requirements to 

determine the final effluent limitations for the NPDES permit. 

This chapter discusses development of TBELs for publicly owned treatment works (POTWs) and 

industrial (non-POTW) dischargers. Chapter 6 discusses development of WQBELs. Exhibit 5-1 illustrates 

the relationship between TBELs and WQBELs in an NPDES permit and the determination of final 

effluent limitations. 

Exhibit 5-1 Developing effluent limitations 
September 2010 NPDES Permit Writers’ Manual 

5.1 Technology-based Effluent Limitations for POTWs 

The largest category of dischargers requiring individual NPDES permits is POTWs. The federal 

regulations at § 403.3(q) define a POTW as a treatment works (as defined in CWA section 212) that is 

owned by a state or municipality [as defined in CWA section 502(4)]. Under § 403.3(q), that definition 

includes “any devices and systems used in the storage, treatment, recycling and reclamation of municipal 

sewage or industrial wastes of a liquid nature.” The definition also includes “sewers, pipes, and other 

conveyances only if they convey wastewater to a POTW Treatment Plant,” as defined in § 403.3(r). 

Under § 403.3(q), the term POTW “also means the municipality as defined in section 502(4) of the Act, 

which has jurisdiction over the Indirect Discharges to and the discharges from such a treatment works.” 

CWA section 304(d) required the U.S. Environmental Protection Agency (EPA) to publish information 

on the degree of effluent reduction attainable through the application of secondary treatment. Under CWA 

section 301(b)(1)(B), in general, POTWs in existence on July 1, 1977, were required to meet discharge 

limitations based on secondary treatment (or any more stringent limitations established under state law, 

including those necessary to meet state water quality standards). On the basis of those statutory 

provisions, EPA developed secondary treatment regulations, which are specified in Part 133. Later 

amendments to CWA section 304(d) called for EPA to develop alternative standards for certain types of 

POTWs. Those standards are referred to as “equivalent to secondary treatment” standards. 

5.1.1 Secondary and Equivalent to Secondary Treatment Standards 

Several regulations implement the statutory requirements for developing standards and discharge 

limitations based on secondary treatment. EPA has promulgated regulations in Part 133 establishing 

secondary treatment standards, equivalent to secondary treatment standards, and a number of special 

considerations applied on a case-by-case basis. In addition, § 122.44(a)(1) requires that NPDES permits 

include applicable technology-based limitations and standards, while regulations at § 125.3(a)(1) state 

that TBELs for POTWs must be based on secondary treatment standards (which includes the “equivalent 

to secondary treatment standards”) specified in Part 133. 

5.1.1.1 Secondary Treatment Standards 

In Part 133, EPA published secondary treatment standards based on an evaluation of performance data for 

POTWs practicing a combination of physical and biological treatment to remove biodegradable organics 

and suspended solids. The regulation applies to all POTWs and identifies the technology-based 

performance standards achievable based on secondary treatment for 5-day biochemical oxygen demand 

(BOD5), total suspended solids (TSS), and pH. Exhibit 5-2 summarizes the standards. 

Exhibit 5-2 Secondary treatment standards 

Parameter 30-day average 7-day average 

BOD5 30 mg/L (or 25 mg/L CBOD5) 45 mg/L (or 40 mg/L CBOD5) 

TSS 30 mg/L 45 mg/L 

BOD5 and TSS removal (concentration) not less than 85% --

pH within the limits of 6.0–9.0* 

* unless the POTW demonstrates that: (1) inorganic chemicals are not added to the waste stream as part of the treatment 

process; and (2) contributions from industrial sources do not cause the pH of the effluent to be less than 6.0 or greater than 9.0 

mg/L = milligrams per liter 

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The regulation also includes an alternate set of standards that apply to certain facilities employing waste 

stabilization ponds or trickling filters as the principal process. Those standards are called equivalent to 

secondary treatment standards. 

5.1.1.2 Equivalent to Secondary Treatment 

Some biological treatment technologies, such as trickling filters or waste stabilization ponds, are capable 

of achieving significant reductions in BOD5 and TSS but might not consistently achieve the secondary 

treatment standards for these parameters. Congress recognized that unless alternate limitations were set 

for facilities with trickling filters or waste stabilization ponds, which often are in small communities, such 

facilities could be required to construct costly new treatment systems to meet the secondary treatment 

standards even though their existing treatment technologies could achieve significant biological treatment. 

To prevent requiring upgrades where facilities were achieving their original design performance levels, 

Congress included provisions in the 1981 amendments to the Clean Water Act Construction Grants 

program (Public Law 97-117, Section 23) that required EPA to make allowances for alternative biological 

treatment technologies, such as a trickling filters or waste stabilization ponds. In response to that 

requirement, in 1984, EPA promulgated regulations at § 133.105 that include alternative standards that 

apply to facilities using “equivalent to secondary treatment.” A facility must meet the criteria in 

§ 133.101(g) to qualify for application of those alternative standards. 

Equivalent to Secondary Standards 

The equivalent to secondary treatment standards, as specified in § 133.105, are shown in Exhibit 5-3. 

Exhibit 5-3 Equivalent to secondary treatment standards 

Parameter 30-day average 7-day average 

BOD5

not to exceed 45 mg/L 

(or not to exceed 40 mg/L CBOD5) 

not to exceed 65 mg/L 

(or not to exceed 60 mg/L CBOD5) 

TSS not to exceed 45 mg/L not to exceed 65 mg/L 

BOD5 and TSS removal (concentration) not less than 65% --

pH within the limits of 6.0–9.0* 

* unless the POTW demonstrates that: (1) inorganic chemicals are not added to the waste stream as part of the treatment 

process; and (2) contributions from industrial sources do not cause the pH of the effluent to be less than 6.0 or greater than 9.0 

Criteria to Qualify for Equivalent to Secondary Standards 

To be eligible for discharge limitations based on equivalent to secondary standards, a POTW must meet 

all three of the following criteria: 

Criterion #1—Consistently Exceeds Secondary Treatment Standards: The first criterion that must be 

satisfied to qualify for the equivalent to secondary standards is demonstrating that the BOD5 and TSS 

effluent concentrations consistently achievable through proper operation and maintenance of the 

treatment works exceed the secondary treatment standards set forth in §§ 133.102(a) and (b). The 

regulations at § 133.101(f) define “effluent concentrations consistently achievable through proper 

operation and maintenance” as 

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 (f)(1): For a given pollutant parameter, the 95th percentile value for the 30-day average effluent 

quality achieved by a treatment works in a period of at least 2 years, excluding values attributable 

to upsets, bypasses, operational errors, or other unusual conditions. 

 (f)(2): A 7-day average value equal to 1.5 times the value derived under paragraph (f)(1). 

Some facilities might meet this criterion only for the BOD5 limitations or only for the TSS 

limitations. EPA believes that it is acceptable for the permit writer to adjust the limitations for only 

one parameter (BOD5 or TSS) if the effluent concentration of only one of the parameters is 

demonstrated to consistently exceed the secondary treatment standards. 

Criterion #2—Principal Treatment Process: The second criterion that a facility must meet to be 

eligible for equivalent to secondary standards is that its principal treatment process must be a trickling 

filter or waste stabilization pond (i.e., the largest percentage of BOD and TSS removal is from a 

trickling filter or waste stabilization pond system). 

Criterion #3—Provides Significant Biological Treatment: The third criterion for applying equivalent 

to secondary standards is that the treatment works provides significant biological treatment of 

municipal wastewater. The regulations at § 133.101(k) define significant biological treatment as 

using an aerobic or anaerobic biological treatment process in a treatment works to consistently 

achieve a 30-day average of at least 65 percent removal of BOD5. 

A permit writer should consider each facility on a case-by-case basis to determine whether it meets those 

three criteria. To apply the criteria, the permit writer should assemble enough influent, effluent, and flow 

data from the facility to adequately characterize the facility’s performance or require the discharger to 

provide an appropriate analysis. If the facility has made substantial changes in its operations or treatment 

processes during the current permit term, the permit writer, using his or her best professional judgment 

(BPJ), may elect to use data for a period that is representative of the discharge at the time the permit is 

being drafted. Facilities that do not meet all three criteria do not qualify as equivalent to secondary 

treatment facilities. For such facilities, the secondary treatment standards apply. EPA noted in its 

December 1985 Draft Guidance for NPDES Permits and Compliance Personnel—Secondary Treatment 

Redefinition1

 that a treatment works operating beyond its design hydraulic or organic loading limit is not 

eligible for application of equivalent to secondary standards. If overloading or structural failure is causing 

poor performance, the solution to the problem is construction, not effluent limitations adjustment. 

5.1.2 Adjustments to Equivalent to Secondary Standards 

In addition to providing secondary treatment standards and equivalent to secondary treatment standards, 

the federal regulations allow states to make adjustments to the standards and to apply those adjusted 

standards on a case-by-case basis. 

5.1.2.1 Adjusted TSS Requirements for Waste Stabilization Ponds 

In accordance with regulations adopted by EPA in 1977 and revised in 1984, states can adjust the 

maximum allowable TSS concentration for waste stabilization ponds upward from those specified in the 

equivalent to secondary treatment standards to conform to TSS concentrations achievable with waste 

stabilization ponds. The regulation, found at § 133.103(c), defines “SS concentrations achievable with 

waste stabilization ponds” as the effluent concentration achieved 90 percent of the time within a state or 

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appropriate contiguous geographical area by waste stabilization ponds that are achieving the levels of 

effluent quality for BOD5 specified in § 133.105(a)(1) (45 milligrams per liter [mg/L] as a 30-day 

average). To qualify for an adjustment up to as high as the maximum concentration allowed, a facility 

must use a waste stabilization pond as its principal process for secondary treatment and its operations and 

maintenance data must indicate that it cannot achieve the equivalent to secondary standards. EPA has 

published approved alternate TSS requirements in 49 Federal Register (FR) 37005, September 20, 1984. 

Exhibit 5-4 is a summary from the FR notice of the adjusted TSS requirements for each state. 

Exhibit 5-4 State-specific adjusted TSS requirements* 

Location 

Alternate TSS 

limitation 

(30-day average)

(mg/L) Location 

Alternate TSS 

limitation 

(30-day average)

(mg/L) 

Alabama 90 Nebraska 80 

Alaska 70 North Carolina 90 

Arizona 90 North Dakota 

Arkansas 90  North and east of Missouri R. 60 

California 95  South and west of Missouri R. 100 

Colorado Nevada 90 

 Aerated ponds 75 New Hampshire 45 

 All others 105 New Jersey None 

Connecticut None New Mexico 90 

Delaware None New York 70 

District of Columbia None Ohio 65 

Florida None Oklahoma 90 

Georgia 90 Oregon 

Guam None  East of Cascade Mountains 85 

Hawaii None  West of Cascade Mountains 50 

Idaho None Pennsylvania None 

Illinois 37 Puerto Rico None 

Indiana 70 Rhode Island 45 

Iowa South Carolina 90 

 Controlled discharge, 

3 cell 

Case-by-case but 

not greater than 80 South Dakota 120 

 All others 80 Tennessee 100 

Kansas 80 Texas 90 

Kentucky None Utah None 

Louisiana 90 Vermont 55 

Maine 45 Virginia 

Maryland 90  East of Blue Ridge Mountains 60 

Massachusetts None  West of Blue Ridge Mountains 78 

Michigan: 

Controlled seasonal 

discharge 

 East slope counties: Loudoun, 

Fauquier, Rappahannock, Madison, 

Green, Albemarle, Nelson, 

Amherst, Bedford, Franklin, Patrick. 

Case-by-case 

application of 60/78 

limits 

 Summer 70 Virgin Islands None 

 Winter 40 Washington 75 

Minnesota 40 West Virginia 80 

Mississippi None Wisconsin 80 

Missouri 80 Wyoming 100 

Montana 100 Trust Territories and N. Marianas None 

* (49 FR 37005, September 20, 1984) 

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5.1.2.2 Alternative State Requirements (ASRs) 

To further address the potential variations in facility performance arising from geographic, climatic, or 

seasonal conditions in different states, the revised secondary treatment regulations (adopted in 1984) also 

included provisions in § 133.105(d) for ASRs. The ASR provisions give states flexibility to modify the 

maximum allowable concentrations of both BOD5 and TSS for trickling filter facilities and for BOD5 for 

waste stabilization pond facilities. ASRs are set at levels consistently achievable through proper operation 

and maintenance [§ 133.101(f)] by the median facility in a representative sample of facilities within a 

state or appropriate continuous geographical area that meet the definition of facilities eligible for 

treatment equivalent to secondary treatment. Qualifying facilities are eligible to receive limitations up to 

the concentrations specified by the ASRs. 

5.1.3 Applying Secondary Treatment Standards, Equivalent to Secondary 

Treatment Standards, and Adjusted Standards 

Determining whether secondary treatment standards or equivalent to secondary standards apply to a 

POTW and determining the specific discharge limitations for the facility based on either set of standards 

and any other special considerations that might apply can be a complex process. Permit writers should 

remember that compliance with limitations must be measurable and percent removal limitations require 

influent monitoring (for more on establishing monitoring conditions, see section 8.1 of this manual). This 

section presents a step-by-step procedure to establishing technology-based effluent limitations for 

POTWs as shown in Exhibit 5-5. 

Exhibit 5-5 Steps to establish technology-based discharge limitations for POTWs 

Step 1. Determine whether secondary treatment standards or equivalent to secondary treatment 

standards or adjusted standards apply 

Step 2. Calculate effluent limitations based on secondary treatment standards or 

Step 3. Calculate effluent limitations based on equivalent to secondary standards or 

Step 4. Calculate effluent limitations based on adjusted standards 

Step 5. Apply special considerations for further adjustments 

Step 6. Document the application of secondary or equivalent to secondary treatment standards or 

adjusted standards and all special considerations in the fact sheet 

5.1.3.1 Step 1: Determine Whether Secondary Treatment Standards or Equivalent to 

Secondary Treatment Standards or Adjusted Standards Apply 

The first step for permit writers to develop TBELs for municipal dischargers is to determine whether 

secondary treatment standards (discussed in section 5.1.1 above), equivalent to secondary standards 

(discussed in section 5.1.1.2 above), or some adjustments to the equivalent to secondary standards 

(discussed in section 5.1.2 above) apply to the POTW. 

An important consideration for permitting authorities is how to treat new POTW discharges that use a 

waste stabilization pond or trickling filter, or a combination of the two. New facilities or new discharges 

from trickling filters or waste stabilization ponds often are capable of achieving secondary treatment 

standards. In the preamble to the secondary treatment regulation (49 FR 37002, September 20, 1984) and 

in § 133.105(f)(2), EPA noted that when developing permits for new trickling filter and waste 

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stabilization pond facilities, permitting authorities should consider the ultimate design capability of the 

treatment process, geographical and climatic conditions, and the performance capabilities of recently 

constructed facilities in similar situations. 

After determining whether secondary treatment standards or equivalent to secondary treatment standards 

apply to a facility or a discharge, the permit writer applies the appropriate standards to develop effluent 

limitations. Section 5.1.3.2 below (Step 2) details development of effluent limitations for facilities or 

discharges where secondary treatment standards apply; section 5.1.3.3 below (Step 3) details development 

of limitations for facilities that qualify for equivalent to secondary standards; and section 5.1.3.4 below 

(Step 4) details development of limitations for facilities where adjusted standards apply. It is possible that 

a facility with multiple biological treatment processes could have limitations based on a combination of 

the standards (see section 5.1.3.5 below [Step 5]); therefore, those sections are presented as separate steps. 

5.1.3.2 Step 2: Calculate Effluent Limitations Based on Secondary Treatment Standards 

If the facility being permitted is subject to the secondary treatment standards, the permit writer should 

complete Step 2. Otherwise, he or she should move to Step 3 in section 5.1.3.3 below. 

Applying the secondary treatment standards in NPDES permits is straightforward. Where secondary 

treatment standards apply, the permit should include effluent limitations in the permit as presented in 

Exhibit 5-6 below, consistent with the secondary treatment standards and the regulatory requirements in 

§ 122.45(d)(2). 

Exhibit 5-6 Effluent limitations calculated from secondary treatment standards 

Parameter Average monthly limitation Average weekly limitation 

BOD5 30 mg/L (or 25 mg/L CBOD5) 45 mg/L (or 40 mg/L CBOD5) 

TSS 30 mg/L 45 mg/L 

BOD5 and TSS removal (concentration) not less than 85% N/A

pH Within the range of 6.0–9.0 standard units at all times (or expressed 

as instantaneous minimum and maximum limitations)* 

* unless the POTW demonstrates that: (1) inorganic chemicals are not added to the waste stream as part of the treatment 

process; and (2) contributions from industrial sources do not cause the pH of the effluent to be less than 6.0 or greater than 9.0 

Certain provisions in the EPA regulations warrant some clarification. 

First, the secondary treatment standards are stated as 30-day and 7-day averages, whereas § 122.45(d)(2) 

requires that effluent limitations for POTWs be expressed, unless impracticable, as average monthly and 

average weekly limitations. The NPDES regulations in § 122.2 define average monthly and average 

weekly limitations on a calendar period basis. Therefore, EPA recommends that permit writers apply the 

30-day and 7-day average secondary treatment standards directly as average monthly (calendar month) 

and average weekly (calendar week) discharge limitations. 

Second, § 122.45(f)(1) requires that all permit limitations, standards, or prohibitions be expressed in 

terms of mass except in any of the following cases: 

 For pH, temperature, radiation or other pollutants that cannot appropriately be expressed by mass 

limitations. 

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 When applicable standards and limitations are expressed in terms of other units of measure. 

 If in establishing permit limitations on a case-by-case basis under § 125.3, limitations expressed 

in terms of mass are infeasible because the mass of the pollutant discharged cannot be related to a 

measure of operation, and permit conditions ensure that dilution will not be used as a substitute 

for treatment. 

The first condition applies to pH requirements established by secondary treatment standards. In addition, 

because the 30-day and 7-day average requirements for BOD5 and TSS, including percent removal, are 

expressed in terms of concentration, the second condition applies to the standards. Thus, mass-based 

discharge limitations are not specifically required to implement secondary treatment standards; however, 

permit writers can choose to include mass-based limitations in a permit. In general, regulations at 

§ 122.45(b)(1) require using the design flow rate of the POTW to calculate limitations. To calculate a 

mass-based limitation for a POTW (in pounds per day [lbs/day]) a permit writer would use the equation 

and follow the example calculations in Exhibit 5-7. 

Exhibit 5-7 POTW mass based limitation calculation equation and example calculations 

POTW design flow Concentration-based limitation Conversion factor 

in million gallons per day in milligrams per liter 8.34 with units of 

(mgd) 

x 

(mg/L) 

x 

(lbs)(L) / (mg)(millions of gallons) 

A POTW with a design flow of 2.0 mgd would have mass-based limitations calculated from secondary treatment 

standards as follows: 

Mass-based limitation* = POTW design flow x Concentration-based limitation x Conversion factor

BOD5

Average monthly = 2.0 mgd x 30 mg/L x 8.34 (lbs)(L) / (mg)(millions of gallons) = 500 lbs/day

Average weekly = 2.0 mgd x 45 mg/L x 8.34 (lbs)(L) / (mg)(millions of gallons) = 750 lbs/day

TSS 

Average monthly = 2.0 mgd x 30mg/L x 8.34 (lbs)(L) / (mg)(millions of gallons) = 500 lbs/day

Average weekly = 2.0 mgd x 45mg/L x 8.34 (lbs)(L) / (mg)(millions of gallons) = 750 lbs/day

* calculated to 2 significant figures 

5.1.3.3 Step 3: Calculate Effluent Limitations Based on Equivalent to Secondary 

Standards 

If a facility being permitted is subject to the equivalent to secondary standards without any further 

adjustments by the state (e.g., ASRs), the permit writer should complete Step 3. Otherwise, he or she 

should move to Step 4 in section 5.1.3.4 below. 

For facilities that qualify for equivalent to secondary standards, effluent limitations must meet the 

requirements specified in § 133.105 and summarized above in Exhibit 5-3 (not accounting for any further 

approved adjustments). It is important to note that the equivalent to secondary standards specify the 

maximum allowable discharge concentration of BOD5 and TSS and a minimum percent removal 

requirement for qualified facilities. The regulations at § 133.105(f) require a permitting authority to 

include more stringent limitations when it determines that the 30-day average and 7-day average BOD5

and TSS concentrations are achievable through proper operation and maintenance of the treatment works 

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(based on an analysis of the past performance for an existing facility or considering the design capability 

of the treatment process and geographical and climatic conditions for a new facility) would enable the 

treatment works to achieve more stringent limitations than the least stringent effluent quality allowed by 

the equivalent to secondary standards. As noted above, the regulations at § 133.101(f) define, “effluent 

concentrations consistently achievable through proper operation and maintenance” as the 95th percentile 

value for the 30-day average effluent quality achieved by a treatment works in a period of at least 2 years, 

excluding values attributable to upsets, bypasses, operational errors, or other unusual conditions. The 

7-day average value is set equal to 1.5 times the 30-day average value. 

If an existing facility does not have sufficient data to establish past performance, the permit writer could 

include the limitations from the previous permit in the new permit and require monitoring to generate the 

necessary data. In addition, the permit writer could choose to include a provision allowing the permitting 

authority to reopen and, if necessary, modify the permit after reviewing the additional data collected by 

the discharger. 

As with limitations based on secondary treatment standards (shown in Exhibit 5-6 above), limitations 

based on equivalent to secondary standards are expressed as average monthly (calendar month) and 

average weekly (calendar week) limitations. Mass-based limitations can be calculated using the 

procedures outlined above. 

5.1.3.4 Step 4: Calculate Effluent Limitations Based on Adjusted Standards 

If a facility being permitted is subject to the adjusted standards as described in section 5.1.2 above, the 

permit writer should complete Step 4. Otherwise, he or she should move to section 5.1.3.5 below (Step 5). 

As discussed in sections 5.1.2.1 and 5.1.2.2 above, the federal regulations at § 133.103(c) allow states to 

adjust the maximum allowable discharge concentration of TSS for waste stabilization ponds upward from 

what would otherwise be required by the equivalent to secondary standards, and the regulations at 

§ 133.105(d) give states flexibility to adopt ASRs that modify equivalent to secondary requirements for 

both BOD5 and TSS for trickling filter facilities and BOD5 requirements for waste stabilization pond 

facilities. Where one or more of the adjusted standards apply, average monthly limitation(s) generally 

should be set at the lower of the following: 

 The 30-day average concentration of the pollutant that could be achievable through proper 

operation and maintenance of the treatment works. 

 The maximum concentration of the pollutant that would be allowed under the adjusted standard. 

Permit writers should note, however, that if the state has developed an adjusted TSS standard for waste 

stabilization ponds consistent with § 133.103(c), the regulations would allow uniform application of that 

standard to POTWs where waste stabilization ponds are the principal process used for secondary 

treatment and operation and maintenance data indicate that the equivalent to secondary treatment 

standards for TSS cannot be achieved. 

The average weekly limitation can be set equal to 1.5 times the average monthly limitation and massbased limitations may be calculated using the procedures outlined above. 

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5.1.3.5 Step 5: Apply Special Considerations for Further Adjustments 

Part 133 allows a permit writer to make further adjustments when calculating effluent limitations derived 

from secondary treatment standards or equivalent to secondary standards based on several special 

considerations. The permit writer should determine whether any of the special considerations outlined in 

this section apply and, as appropriate, make any further adjustments to the concentration limitations or 

percent removal requirements. The calculated limitations, after making such adjustments, are the final 

technology-based effluent limitations for the POTW. 

Substitution of CBOD5 for BOD5

Wastewater contains carbonaceous oxygen demanding substances and nitrogenous oxygen demanding 

substances. A CBOD5 test measures the 5-day carbonaceous biochemical oxygen demand while the BOD5

test measures the both carbonaceous biochemical oxygen demand and nitrogenous biochemical oxygen 

demand. During nitrification, nitrifying bacteria use a large amount of oxygen to consume nitrogenous 

oxygen demanding substances (unoxidized nitrogen and ammonia-nitrogen) and convert these to oxidized 

nitrate. For wastewaters with significant nitrogen content, basing permit limitations on CBOD5 instead of 

BOD5 eliminates the impact of nitrification on discharge limitations and compliance determinations. EPA 

recognizes that the CBOD5 test can provide accurate information on treatment plant performance in many 

cases and, in Part 133, allows permit writers to use CBOD5 limitations in place of BOD5 limitations to 

minimize false indications of poor facility performance as a result of nitrogenous oxygen demand. 

EPA has established CBOD5 standards for cases where secondary treatment standards or equivalent to 

secondary treatment standards are applied: 

 Secondary Treatment: The CBOD5 secondary treatment performance standards specified by the 

regulations are as follows: 

− 25 mg/L as a 30-day average. 

− 40 mg/L as a 7-day average. 

 The EPA-approved test procedures in Part 136 include a CBOD5 (nitrogen inhibited) test 

procedure. Subject to any state-specific requirements, a permit writer can specify these CBOD5

limitations along with CBOD5 monitoring requirements in any POTW permit requiring 

performance based on secondary treatment standards [§ 133.102(a)(4)]. 

 Equivalent to Secondary Treatment: The CBOD5 equivalent to secondary treatment 

performance standards specified by the regulations are as follows: 

− No greater than 40 mg/L as a 30-day average. 

− No greater than 60 mg/L as a 7-day average. 

 Where data are available to establish CBOD5 limitations, and subject to any state-specific 

requirements, a permit writer may substitute CBOD5 for BOD5 and specify CBOD5 limitations 

and monitoring requirements when applying equivalent to secondary standards. 

Substitution of COD or TOC for BOD5

Chemical oxygen demand (COD) and total organic carbon (TOC) laboratory tests can provide an accurate 

measure of the organic content of wastewater in a shorter time frame than a BOD5 test (i.e., several hours 

versus five days). The regulations at § 133.104(b) allow a permit writer to set limitations for COD or 

TOC instead of BOD5 if a long-term BOD5:COD or BOD5:TOC correlation has been demonstrated. 

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Adjustments for Industrial Contributions 

Under § 133.103(b), treatment works receiving wastes from industrial categories with effluent limitations 

guidelines and standards (effluent guidelines) requirements or new source performance standards for 

BOD5 or TSS, which are less stringent than the secondary treatment standards or, if applicable, the 

equivalent to secondary treatment standards in Part 133, can qualify to have their 30-day BOD5 or TSS 

limitations adjusted upward provided that the following are true: 

 The adjusted 30-day limitations are not greater than the limitations in effluent guidelines or new 

source performance standards, as applicable, for the industrial category. 

 The flow or loading of BOD5 or TSS introduced by the industrial category exceeds 10 percent of 

the design flow or loading to the POTW. 

When making this adjustment, the Part 133 values for BOD5 and TSS should be adjusted proportionately. 

Accordingly, a permit writer should make the adjustment using a flow-weighted or loading-weighted 

average of the two concentration limitations (i.e., the limitations developed from effluent guidelines for 

the industrial facility and the secondary or equivalent to secondary limitations). 

Adjustments to Percent Removal Requirements 

The 85 percent removal requirement (for a 30-day average) in secondary treatment standards was 

originally established to achieve two basic objectives: 

 To encourage municipalities to remove high quantities of infiltration and inflow (I/I) from their 

sanitary sewer systems. 

 To prevent intentional dilution of influent wastewater. 

In facilities with dilute influent that is not attributable to high quantities of I/I or intentional dilution, the 

percent removal requirement could result in forcing advanced treatment rather than the intended 

secondary treatment. Advanced treatment generally refers to treatment processes following secondary 

treatment (e.g., filtration, chemical addition, or two-stage biological treatment). Advanced treatment can 

achieve significantly greater pollutant removals than secondary treatment processes but at a higher cost. 

The regulations at §§ 133.103(a), (d) and (e) provide that, under certain circumstances, permit writers 

may set less stringent limitations for BOD5 and TSS percent removal. The specific circumstances and the 

potential adjustments to the percent removal requirement are as follows: 

 Treatment works that receive less concentrated wastes from combined sewer systems are 

eligible to have less stringent monthly percent removal limitations during wet-weather events 

[§ 133.103 (a)] and, under certain conditions, less stringent percent removal requirements or a 

mass loading limitation instead of a percent removal requirement during dry weather [§ 133.103 

(e)]. The permit writer must determine on a case-by-case basis whether any attainable percentage 

removal level can be defined during wet weather and, if so, what the level should be. To qualify 

for a less stringent percent removal requirement or substitution of a mass limitation during dry 

weather, the discharger must satisfactorily demonstrate the following: 

1. The facility is consistently meeting, or will consistently meet, its permit effluent 

concentration limitations, but cannot meet its percent removal limitations because of less 

concentrated influent. A permitting authority should consider establishing criteria for 

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documenting what constitutes consistently meeting concentration limitations and what 

constitutes being unable to meet percent removal limitations because of less concentrated 

influent. 

2. To meet the percent removal requirements, the facility would have to achieve significantly 

more stringent effluent concentrations than would otherwise be required by the concentrationbased standards. Each permitting authority also should consider establishing criteria for 

demonstrating that this condition is met (e.g., because of dilute influent, X percent of the time 

a discharger would be forced to meet concentration requirements that are X percent more 

stringent than the concentration limitations otherwise applicable to satisfy the percent 

removal requirements). 

3. The less concentrated influent wastewater does not result from either excessive infiltration or 

clear water industrial discharges during dry weather periods. The determination of whether 

the less concentrated wastewater results from excessive infiltration is discussed in regulations 

at § 35.2005(b)(28). This regulation defines nonexcessive infiltration as the quantity of flow 

that is less than 120 gallons per capita per day (domestic base flow and infiltration) or the 

quantity of infiltration that cannot be economically and effectively eliminated from a sewer 

system as determined in a cost-effectiveness analysis. The regulations at § 133.103(e) include 

the additional criterion that either 40 gallons per capita per day or 1,500 gallons per inch 

diameter per mile of sewer may be used as the threshold value for that portion of dry-weather 

base flow attributed to infiltration. If the less concentrated influent wastewater is the result of 

clear water industrial discharges, then the treatment works must control such discharges 

pursuant to Part 403. 

 Treatment works that receive less concentrated wastes from separate sewer systems can 

qualify to have less stringent percent removal requirement or receive a mass loading limitation 

instead of the percent removal requirement provided the treatment plant demonstrates all of the 

following [§ 133.103(d)]: 

1. The facility is consistently meeting or will consistently meet its permit effluent concentration 

limitations but cannot meet its percent removal limitations because of less concentrated 

influent wastewater. For additional detail on this criterion, see discussion above for combined 

sewers during dry weather. 

2. To meet the percent removal requirements, the facility would have to achieve significantly 

more stringent limitations than would otherwise be required by the concentration-based 

standards. For additional detail on this criterion, see the discussion above for combined 

sewers during dry weather. 

3. The less concentrated influent wastewater does not result from excessive infiltration and 

inflow (I/I). The regulation indicates that the determination of whether the less concentrated 

wastewater is the result of excessive I/I will use the definition of excessive I/I at 

§ 35.2005(b)(16), plus the additional criterion that flow is nonexcessive if the total flow to the 

POTW (i.e., wastewater plus inflow plus infiltration) is less than 275 gallons per capita per 

day. The regulation at § 35.2005(b)(16) defines excessive I/I as the quantities of I/I that can 

be economically eliminated from a sewer system as determined in a cost-effectiveness 

analysis that compares the costs for correcting the I/I conditions to the total costs for 

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transportation and treatment of the I/I. This regulation also refers to definitions of 

nonexcessive I/I in §§ 35.2005(b)(28) and 35.2005(b)(29). 

Secondary Treatment Variance for Ocean Discharge—CWA Section 301(h) Variance 

CWA section 301(h) provides for variances from secondary treatment standards for POTWs that 

discharge into ocean waters if the modified requirements do not interfere with attainment or maintenance 

of water quality. Permit writers should note that the deadline to apply for a CWA section 301(h) variance 

(December 29, 1982) has passed, thus no new facilities may apply for this variance. 

Eligible POTW applicants meeting the set of environmentally stringent criteria in CWA section 301(h) 

receive a modified NPDES permit waiving the secondary treatment requirements for the conventional 

pollutants of BOD5, TSS, and pH. EPA issued regulations, developed the Amended Section 301(h) 

Technical Support Document2, and prepared a website titled Amendments to Regulations Issued, the 

Clean Water Act Section 301 (h) Program <www.epa.gov/owow/oceans/discharges/301h.html>. EPA has 

promulgated specific regulations pertaining to CWA section 301(h) that are provided in Part 125, 

Subpart G. 

All CWA section 301(h) variance modified permits must contain the following specific permit conditions: 

 Effluent limitations and mass loadings that will assure compliance with Part 125, Subpart G. 

 Requirements for pretreatment program development, a nonindustrial toxics control program, and 

control of combined sewer overflows. 

 Monitoring program requirements that include biomonitoring, water quality, and effluent 

monitoring. 

 Reporting requirements that include the results of the monitoring programs. 

No new or substantially increased discharges from the point source of the affected pollutant can be 

released above that volume of discharge specified in the permit. 

5.1.3.6 Step 6: Document the Application of Secondary or Equivalent to Secondary 

Treatment Standards and all Adjustments and Considerations in the Fact Sheet 

Permit writers need to document their application of secondary or equivalent to secondary treatment 

standards in the NPDES permit fact sheet for municipal facilities. The permit writer should clearly 

identify the data and information used to determine whether secondary treatment standards or equivalent 

to secondary treatment standards or adjusted standards apply and how that information was used to derive 

effluent limitations for the permit. The permit writer should also note all adjustments and special 

considerations in the fact sheet. The information in the fact sheet should provide the NPDES permit 

applicant and the public a transparent, reproducible, and defensible description of how the NPDES permit 

properly incorporates secondary treatment standards. 

5.2 Technology-Based Effluent Limitations for Industrial 

(Non-POTW) Dischargers 

EPA is required to promulgate technology-based limitations and standards that reflect pollutant reductions 

that can be achieved by categories, or subcategories, of industrial point sources using specific 

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technologies (including process changes) that EPA identifies as meeting the statutorily prescribed level of 

control under the authority of CWA sections 301, 304, 306, 307, 308, 402, and 501 (33 United States 

Code [U.S.C.] 1311, 1314, 1316, 1318, 1342, and 1361). Those national industrial wastewater controls 

are called effluent limitations guidelines and standards (effluent guidelines). Unlike other CWA tools, 

such as water quality standards, effluent guidelines are national in scope and establish performance 

standards for all facilities within an industrial category or subcategory. 

For point sources that introduce pollutants directly into the waters of the United States (direct 

dischargers), the effluent guidelines promulgated by EPA are implemented through NPDES permits as 

authorized in CWA sections 301(a), 301(b), and 402. For sources that discharge to POTWs (indirect 

dischargers), EPA promulgates pretreatment standards that apply directly to those sources and are 

enforced by POTWs and state and federal authorities as authorized in CWA sections 307(b) and (c). 

When developing TBELs for industrial (non-POTW) facilities, the permit writer must consider all 

applicable technology standards and requirements for all pollutants discharged. Without applicable 

effluent guidelines for the discharge or pollutant, permit writers must identify any needed TBELs on a 

case-by-case basis, in accordance with the statutory factors specified in CWA sections 301(b)(2) and 

304(b). The site-specific TBELs reflect the BPJ of the permit writer, taking into account the same 

statutory factors EPA would use in promulgating a national effluent guideline regulation, but they are 

applied to the circumstances relating to the applicant. The permit writer also should identify whether state 

laws or regulations govern TBELs and might require more stringent performance standards than those 

required by federal regulations. In some cases, a single permit could have TBELs based on effluent 

guidelines, BPJ, and state law, as well as WQBELs based on water quality standards. 

Sections 5.2.1 and 5.2.2 below provide an overview of effluent guidelines and development of TBELs in 

NPDES permits using the effluent guidelines. Section 5.2.3 below discusses the development of TBELs 

in the absence of effluent guidelines (i.e., case-by-case limitations developed using BPJ). 

5.2.1 Effluent Guidelines 

Congress saw the creation of a single national pollution control requirement for each industrial category, 

based on the best technology the industry could afford, as a way to reduce the potential creation of 

pollution havens and to attain a high-level water quality in the nation’s waters. Consequently, EPA’s goal 

in establishing effluent guidelines is to ensure that industrial facilities with similar characteristics will 

meet similar effluent limitations representing the best pollution control technologies or pollution 

prevention practices regardless of their location or the nature of the receiving water into which the 

discharge is made. In establishing the effluent guidelines, EPA must consider the industry-wide economic 

achievability of implementing the technology and the incremental costs in relation to the pollutantreduction benefits. 

Effluent guidelines can include numeric and narrative limitations, including best management practices 

(BMPs), to control the discharge of pollutants from categories of point sources. The limitations are based 

on data characterizing the performance of technologies available and, in some cases, from modifying 

process equipment or the use of raw materials. Although the regulations do not require the use of any 

particular treatment technology, they do require facilities to achieve effluent limitations that reflect the 

proper operation of the model technologies selected as the basis for the effluent guidelines and from 

which the performance data were obtained to generate the limitations. Therefore, each facility has the 

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discretion to select any technology design and process changes necessary to meet the performance-based 

discharge limitations and standards specified by the effluent guidelines. 

As of the date of this manual’s publication, EPA has issued effluent guidelines for 56 industrial 

categories, which apply to between 35,000 and 45,000 facilities that discharge directly to waters of the 

United States and another 12,000 facilities that discharge into POTWs. The regulations prevent the 

discharge of more than 1.2 billion pounds of toxic (priority) and nonconventional pollutants each year. 

EPA’s Effluent Guidelines Program Website <www.epa.gov/guide/> provides information on existing 

effluent guidelines, current effluent guidelines rulemaking, and the effluent guidelines planning process. 

5.2.1.1 Statutory Foundation for Effluent Guidelines 

The CWA directs EPA to promulgate effluent guidelines reflecting pollutant reductions that can be 

achieved by existing facilities in categories or subcategories of industrial point sources using specific 

control technologies. In addition, EPA is required to develop effluent guidelines for new sources. Those 

levels of control are summarized below and in Exhibit 5-8. 

Exhibit 5-8 Summary of CWA technology levels of control 

Type of sites regulated BPT BCT BAT NSPS PSES PSNS 

Existing Direct Dischargers X X X 

New Direct Dischargers X 

Existing Indirect Dischargers X 

New Indirect Dischargers X 

Pollutants regulated BPT BCT BAT NSPS PSES PSNS 

Conventional Pollutants X X X 

Nonconventional Pollutants X X X X X 

Toxic (Priority) Pollutants X X X X X 

Best Practicable Control Technology Currently Available (BPT) 

BPT is the first level of technology-based effluent controls for direct dischargers and it applies to all types 

of pollutants (conventional, nonconventional, and toxic). The Federal Water Pollution Control Act 

(FWPCA) amendments of 1972 require that when EPA establishes BPT standards, it must consider the 

industry-wide cost of implementing the technology in relation to the pollutant-reduction benefits. EPA 

also must consider the age of the equipment and facilities, the processes employed, process changes, 

engineering aspects of the control technologies, non-water quality environmental impacts (including 

energy requirements), and such other factors as the EPA Administrator deems appropriate [CWA section 

304(b)(1)(B)]. Traditionally, EPA establishes BPT effluent limitations on the basis of the average of the 

best performance of well-operated facilities in each industrial category or subcategory. Where existing 

performance is uniformly inadequate, BPT may reflect higher levels of control than currently in place in 

an industrial category if the Agency determines that the technology can be practically applied. See CWA 

sections 301(b)(1)(A) and 304(b)(1)(B). 

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Best Conventional Pollutant Control Technology (BCT) 

The 1977 CWA requires EPA to identify effluent reduction levels for conventional pollutants associated 

with BCT for direct discharges from existing industrial point sources. As with BPT, when establishing 

BCT the Agency considers the age of the equipment and facilities, the processes employed, process 

changes, engineering aspects of the control technologies, non-water quality environmental impacts 

(including energy requirements), and such other factors as the EPA Administrator deems appropriate 

[CWA section 304(b)(4)(B)]. In addition, EPA also considers a two-part cost reasonableness test, as 

required by CWA section 304(b)(4)(B), which includes (1) consideration of the reasonableness of the 

relationship between the costs of attaining a reduction in effluent and the effluent reduction benefits 

derived and (2) a comparison of the cost and level of reduction of such pollutants from the discharge from 

POTWs to the cost and level of reduction of such pollutants from a class or category of industrial sources. 

EPA explained its methodology for developing BCT limitations in detail in 51 FR 24974, July 9, 1986

<www.epa.gov/npdes/pubs/fr_bct_1986.pdf>. See CWA sections 301(b)(2)(E) and 304(b)(4). 

Best Available Technology Economically Achievable (BAT) 

For the direct discharge of toxic and non-conventional pollutants, EPA promulgates effluent guidelines 

based on BAT. The FWPCA amendments of 1972 require EPA to consider the cost of achieving effluent 

reductions when defining BAT; however, they do not specifically require EPA to balance the cost of 

implementation against the pollution reduction benefit. The technology selected for BAT must be 

economically achievable [CWA section 301(b)(2)(A)]. EPA generally defines BAT on the basis of the 

performance associated with the best control and treatment measures that facilities in an industrial 

category are capable of achieving. Like BPT and BCT, other factors EPA must consider in assessing BAT 

include the age of equipment and facilities involved, the process employed, process changes, non-water 

quality environmental impacts, including energy requirements, and other such factors as the EPA 

Administrator deems appropriate [CWA section 304(b)(2)(B)]. The Agency retains considerable 

discretion in assigning the weight accorded to these factors. BAT limitations may be based on effluent 

reductions attainable through changes in a facility’s processes and operations. Where existing 

performance is uniformly inadequate, BAT may reflect a higher level of performance than is currently 

being achieved within a subcategory on the basis of technology transferred from a different subcategory 

or category. BAT may be based on process changes or internal controls, even when those technologies are 

not common industry practice. See CWA sections 301(b)(2)(A), (C), (D) and (F) and 304(b)(2). 

New Source Performance Standards (NSPS) 

NSPS reflect effluent reductions that are achievable by direct dischargers based on the best available 

demonstrated control technology. New sources have the opportunity to install the best and most efficient 

production processes and wastewater treatment technologies at the time of construction. As a result, 

NSPS should represent the most stringent controls attainable through the application of the best available 

demonstrated control technology for all pollutants (i.e., conventional, nonconventional, and toxic 

pollutants). In establishing NSPS, EPA is directed to take into consideration the cost of achieving the 

effluent reduction and any non-water quality environmental impacts and energy requirements. See CWA 

section 306. 

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Pretreatment Standards for Existing Sources (PSES) 

PSES are designed to prevent the discharge of pollutants that pass through, interfere with, or are 

otherwise incompatible with the operation of POTWs, including incompatibility with the POTW’s chosen 

biosolids (sewage sludge) disposal methods. The categorical pretreatment standards for existing indirect 

dischargers are technology-based and are analogous to BAT. The general pretreatment regulations, which 

set forth the framework for the implementation of national pretreatment standards, are at Part 403. See 

CWA section 307(b). 

Pretreatment Standards for New Sources (PSNS) 

Like PSES, PSNS are designed to prevent the discharges of pollutants that pass through, interfere with, or 

are otherwise incompatible with the operation of POTWs. PSNS are to be issued at the same time as 

NSPS. New indirect dischargers have the opportunity to incorporate into their facilities the best available 

demonstrated technologies at the time of construction. The Agency considers the same factors in 

promulgating PSNS as it considers in promulgating NSPS. See CWA section 307(c). 

EPA typically does not establish pretreatment standards for conventional pollutants (e.g., BOD5, TSS, oil 

and grease) because POTWs are designed to treat such pollutants, but EPA has exercised its authority to 

establish categorical pretreatment standards for conventional pollutants as surrogates for toxic or 

nonconventional pollutants or to prevent interference. For example, EPA established categorical 

pretreatment standards for new and existing sources with a one-day maximum concentration of 100 mg/L 

oil and grease in the Petroleum Refining Point Source Category in Part 419 based on “the necessity to 

minimize [the] possibility of slug loadings of oil and grease being discharged to POTWs.”3

The final statutory deadline for meeting BPT requirements was July 1, 1977, and the final statutory 

deadline for meeting BCT and BAT requirements was March 31, 1989. When applying applicable 

effluent guidelines, permit writers should note that they do not have the authority to extend the statutory 

deadlines in an NPDES permit; thus, all applicable technology-based requirements (i.e., effluent 

guidelines and case-by-case limitations based on BPJ) must be applied in NPDES permits without the 

benefit of a compliance schedule. In addition, though NSPS do not have specific dates as compliance 

deadlines, they are effective on the date the new source begins discharging. The facility must demonstrate 

compliance with NSPS within 90 days of discharge [see § 122.29(d)]. For more information on 

determining whether a discharge is subject to NSPS, see Appendix D of this manual. For additional 

information on the statutory and regulatory history of the NPDES program, see section 1.2 of this manual. 

5.2.1.2 EPA’s Development of Effluent Guidelines 

EPA establishes national effluent guidelines for a specific industrial sector by regulation after considering 

an in-depth engineering and economic analysis of the industrial sector. EPA’s Industrial Regulations 

Website <www.epa.gov/guide/industry.html> provides development documents for some specific industry 

categories (e.g., Iron and Steel Manufacturing and Metal Products and Machinery). Those documents 

contain additional information on how EPA develops effluent guidelines. 

For each industrial sector, EPA assesses the performance and availability of the best pollution control 

technologies and pollution prevention practices that are available for an industrial category or 

subcategory. The effluent guidelines are promulgated for various industrial categories in 40 CFR, Chapter 

I, Subchapter N - Effluent Guidelines and Standards - Parts 400-471 <www.epa.gov/lawsregs/search/40cfr.html>. 

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In promulgating effluent guidelines, EPA may divide an industrial point source category into groupings of 

subcategories to provide a method for addressing variations between products, raw materials, processes, 

and other factors that result in distinctly different characteristics. Regulation of an industrial category 

using subcategories allows each subcategory to have a uniform set of requirements that take into account 

technological achievability and economic impacts unique to that subcategory. Grouping similar facilities 

into subcategories increases the likelihood that the regulations are practicable and diminishes the need to 

address variations between facilities within a category through a variance process. For more on variances, 

see section 5.2.2.7 below. EPA considers a number of different subcategorization factors during an 

effluent guidelines rulemaking, including the following: 

 Manufacturing products and processes. 

 Raw materials. 

 Wastewater characteristics. 

 Facility size. 

 Geographical location. 

 Age of facility and equipment. 

 Wastewater treatability. 

For each possible treatment technology option for an industry, EPA conducts an analysis of industry-wide 

incremental compliance costs, pollutant loadings and removals, and related non-water quality effects. The 

Agency also performs an economic analysis to assess the financial impact on the industry of 

implementing each option. That entire process involves data collection, rigorous data review, engineering 

analysis, and public comment. EPA selects a technology to serve as the model technology for pollutant 

removal for each required level of control (i.e., BPT, BCT, BAT, NSPS, PSES, and PSNS). Limitations 

and other requirements in the effluent guidelines for each level of control are based on application of the 

model technology to the category or subcategory of facilities. 

Effluent guidelines are not always established for every pollutant present in a point source discharge. In 

many instances, EPA promulgates effluent guidelines for an indicator pollutant. Industrial facilities that 

comply with the effluent guidelines for the indicator pollutant will also control other pollutants (e.g., 

pollutants with a similar chemical structure). For example, EPA may choose to regulate only one of 

several metals present in the effluent from an industrial category, and compliance with the effluent 

guidelines will ensure that similar metals present in the discharge are adequately controlled. Additionally, 

for each industry sector EPA typically considers whether a pollutant is present in the process wastewater 

at treatable concentrations and whether the model technology for effluent guidelines effectively treats the 

pollutant. For example, see Figure 6-1 Pollutant of Concern Methodology

<www.epa.gov/guide/cwt/final/develop/ch6.pdf> on page 6-4 of the Centralized Waste Treatment category 

Technical Development Document. 

The CWA requires EPA to annually review existing effluent guidelines for both direct and indirect 

dischargers. CWA section 304(m) also requires EPA to publish an effluent guidelines program plan every 

2 years. As part of the development of the biennial plan, the public is provided an opportunity to comment 

on a preliminary plan before it is finalized. The preliminary plan is published in odd-numbered years, and 

the final plan is published in even-numbered years. EPA encourages permit writers to participate in the 

effluent guidelines planning process and comment on the preliminary effluent guidelines program plans 

presented on the Effluent Guidelines Biennial Plan Website <www.epa.gov/guide/304m/index.html>. 

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5.2.1.3 Types of Limitations in Effluent Guidelines 

Although the requirements in effluent guidelines generally are numeric limitations on the mass or 

concentration of a pollutant that can be discharged directly into waters of the United States, CWA section 

502(11) defines effluent limitation broadly. This section describes several types of possible expressions 

for the limitations found in effluent guidelines. The permit writer should note that the limitations in 

effluent guidelines might need to be translated into an appropriate form to be included as effluent 

limitations in an NPDES permit. That process is discussed further in section 5.2.2 below. 

Mass- or Concentration-based Numeric Limitations 

Limitations in effluent guidelines generally are expressed as numeric values, which are upper bounds of 

the amount of pollutant that may be discharged. For most pollutants, these limitations are mass-based or 

concentration-based values. They are, in effect, measures of how well the production, wastewater 

treatment, and pollution prevention processes must be operated. In the course of developing effluent 

guidelines regulations, EPA uses data on a number of different pollutants from facilities with the selected 

model technologies to determine the appropriate numeric limitations. The limitations generally consist of 

upper bounds (maximum values) established for both the daily discharge and for the average monthly 

discharge. 

In developing numeric limitations in effluent guidelines, EPA first determines an average performance 

level (the long-term average) that a facility with well-designed and operated model technologies 

reflecting the appropriate level of control is capable of achieving. That long-term average is calculated 

from data taken from facilities using the model technologies that were selected as a basis for the 

limitations. EPA expects that all facilities subject to the limitations will design and operate their treatment 

systems to achieve the long-term average performance level consistently because facilities with welldesigned and operated model technologies have demonstrated that it can be done. The technical 

development document for the effluent guidelines usually identifies the long-term average for the model 

technologies; however, they generally are not part of the limitations in the effluent guidelines or TBELs 

in the permit. The limitations generally are expressed as maximum daily and average monthly limitations

(see definitions in Exhibit A-2 in Appendix A of this document) that include an allowance for variability 

around the long-term average. 

EPA acknowledges that process and treatment systems have inherent variability and, therefore, 

incorporates an allowance for this variation into the limitations specified in the effluent guidelines. That 

allowance is based on statistical analysis of the data from facilities using the model technologies. The 

limitations included in effluent guidelines incorporate all components of variability including shipping, 

sampling, storage, and analytical variability. By accounting for those reasonable excursions above the 

long-term average, the limitations in effluent guidelines generally are well above the actual long-term 

averages. If a facility operates its treatment system to meet the long-term average, EPA expects the 

facility will be able to meet the limitations specified in the effluent guidelines based on that long-term 

average. 

EPA has different objectives in establishing maximum daily and average monthly limitations in effluent 

guidelines. In establishing maximum daily limitations, EPA’s objective is to restrict the discharges on a 

daily basis at a level that is achievable for a facility that targets its treatment at the long-term average. In 

establishing average monthly limitations, EPA’s objective is to provide an additional restriction to help 

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ensure that facilities target their average discharges in a manner that will achieve the long-term average. 

The average monthly limitation requires continuous dischargers to provide ongoing control on a monthly 

basis that complements controls imposed by the maximum daily limitation. To meet the average monthly 

limitation, a facility must counterbalance a value near the maximum daily limitation with one or more 

values well below the maximum daily limitation. To achieve compliance, the values must result in an 

average monthly value at or below the average monthly limitation. As explained below, EPA uses a 

smaller percentile basis for the average monthly limitation than the maximum daily limitation to 

encourage facilities to target their systems to a value closer to the long-term average. 

EPA generally uses statistical procedures to determine the values of the limitations specified in the 

effluent guidelines. Those procedures involve fitting effluent data to distributions and using estimated 

upper percentiles of the distributions. EPA defines the maximum daily limitation as an estimate of the 

99th percentile of the distribution of the daily measurements. The average monthly limitation is an 

estimate of the 95th percentile of the distribution of the monthly averages of the daily measurements. 

EPA bases its limitations on percentiles chosen with the intention that they be high enough above the 

long-term average to accommodate reasonably anticipated variability within control of the facility. In 

conjunction with the statistical methods, EPA performs an engineering review to verify that the 

limitations are reasonable on the basis of the design and expected operation of the control technologies 

and the facility process conditions. Such limitations are translated into effluent limitations in a facility’s 

NPDES permit. Facilities must comply with the effluent limitations in their permits at all times. EPA has 

prevailed in several judicial challenges to its selection of percentiles and on other issues related to 

limitations specified in effluent guidelines. [See, for example, Chemical Manufacturers Association v. 

U.S. Environmental Protection Agency, 870 F.2d 177, 230 (5th Cir. 1989) and National Wildlife 

Federation, et al v. Environmental Protection Agency, 286 F.3d 554 (D.C. Cir. 2002)] 

Exhibit 5-9 depicts an example of TSS data for a facility that is operating around a required long-term 

average level for TSS. The dots represent daily measurements, and the reference lines show the values for 

the long-term average (LTA), the maximum daily limitation (L1), and the average monthly limitation 

(L30). The facility has demonstrated compliance with both the maximum daily and average monthly 

limitations. Daily measurements include values both above and below the long-term average; however, all 

the data values are below the maximum daily limitation. Some individual daily values exceed the average 

monthly limitation; however, within each month, the average of the daily values is less than the average 

monthly limitation. 

EPA generally exercises four basic alternatives in setting mass- or concentration-based numeric 

limitations specified in effluent guidelines: 

 Mass-based, production-normalized limitations (e.g., the pollutant discharge is not to exceed 

1 pound per 1,000 pounds of production). 

 Mass-based, flow-normalized limitations (e.g., the pollutant discharge is not to exceed the mass 

determined by multiplying the process wastewater flow subject to the effluent guideline by the 

concentration requirement in the guideline). 

 Concentration-based limitations (e.g., the pollutant discharge is not to exceed 1 mg of pollutant 

per liter of wastewater). 

 Limitations requiring zero discharge of specific pollutants or all pollutants. 

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Exhibit 5-9 Visual example of TSS LTA, maximum daily limitation and average monthly 

limitation 

Except where a limitation requiring zero discharge of pollutants is applicable, EPA generally prefers 

setting production-normalized, mass-based limitations specified in effluent guidelines, where feasible, 

because production normalized limitations can reflect some expectation that the facility will conserve 

water and can reduce any potential for substituting dilution for treatment. EPA generally establishes 

concentration-based effluent guidelines when production and achievable wastewater flow cannot be 

correlated nationally. For example, in the Metal Finishing point source Category (Part 433), the Agency 

considered but decided against expressing the effluent guidelines as production-normalized mass-based 

effluent guidelines, “With the wide range of operations, product quality requirements, existing process 

configurations, and difficulties in measuring production, no consistent production normalizing 

relationship could be found. Concentration-based limits, however, can be consistently attained throughout 

the industry.” [See 47 FR 38465, 31 August 1982.] 

Numeric Limitations Established at Minimum Levels 

Using percentile estimates to set limitations in effluent guidelines is not a requirement under the CWA. In 

some cases, the model technology for treating a pollutant might be capable of removing that pollutant to 

levels that cannot be reliably measured with existing analytical methods. EPA sometimes sets a 

requirement in the effluent guidelines that the concentration of a pollutant in the discharge must be below 

a minimum level or ML. The ML is the lowest level at which the entire analytical system must give a 

recognizable signal and an acceptable calibration point for the pollutant being analyzed. Where a 

limitation in the effluent guidelines is set at less than the ML, the value of the ML is specified in the 

effluent guidelines regulation on the basis of the analytical methods that EPA used to chemically analyze 

wastewaters in developing the regulation. For example, in the Pulp, Paper, and Paperboard point source 

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category (Part 430) the Daily Maximum BAT effluent guideline for the Tetrachlorodibenzofuran (TCDF) 

congener of dioxin is expressed as <ML for papergrade sulfite (Subpart E) mills, which means “less than 

the minimum level specified in part 430.01(i)” (i.e., 10 picograms/liter for TCDF). If, in the future, 

analytical methods become more sensitive with lower MLs, EPA would determine whether the 

technologies for reducing the amount of the pollutant in the discharge are capable of achieving more 

stringent limitations and, thus, whether it would be appropriate to modify the requirements of the effluent 

guideline. 

EPA has not established average monthly limitations in effluent guidelines when the maximum daily 

limitation is an ML limitation. The purpose of an average monthly limitation is to require continuous 

dischargers to provide better control, on a monthly basis, than required by the maximum daily limitation. 

However, for these pollutants, the data were determined by analytical methods that could not measure 

below the ML specified in the regulations. Thus, even if a permitting authority requires monitoring for the 

pollutants more frequently than once a month, average monthly limitations would still be expressed as 

less than the ML or < ML. 

Other Expressions for Numeric Limitations 

EPA also promulgates effluent guidelines for pollutants that cannot be expressed in terms of mass or 

concentration (e.g., pH, temperature, radiation) or are better expressed through other means (e.g., unitless 

ratios). For example, pH is generally expressed as an acceptable range (e.g., 6.0–9.0 standard pH units). 

Nonnumeric Effluent Limitations 

In some cases, EPA includes nonnumeric or narrative effluent limitations rather than, or in addition to, 

numeric limitations in effluent guidelines. Nonnumeric effluent limitations might include specific BMPs 

or requirements to minimize or eliminate discharges. CWA sections 304(e), 308(a), 402(a), and 501(a) 

authorize the Administrator to prescribe BMPs as part of effluent guidelines and as part of an NPDES 

permit. CWA section 304(e) authorizes EPA to include supplemental BMPs in effluent guidelines for 

toxic or hazardous pollutants for the purpose of controlling “plant site runoff, spillage or leaks, sludge or 

waste disposal, and drainage from raw material storage.” Several effluent guidelines include BMPs as 

requirements. Some effluent guidelines, such as the Concentrated Aquatic Animal Production point 

source category (Part 451), include the BMPs requirement exclusively. Section 9.1.2 of this manual 

further discusses BMPs. 

CWA section 402(a)(1) and (2) and the NPDES regulations at § 122.44(k) also authorize BMPs in 

NPDES permits to control or abate the discharge of pollutants when numeric effluent limitations are 

infeasible, or when the practices are reasonably necessary to achieve effluent limitations and standards or 

to carry out the purposes and intent of the CWA. 

Once EPA establishes effluent guidelines, the permit writer is responsible for translating the limitations 

and other requirements of the effluent guidelines into TBELs and other conditions appropriate for 

inclusion in an NPDES permit. Section 5.2.2 below discusses a step-by-step approach for applying 

effluent guidelines through NPDES permits. 

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5.2.2 Applying Effluent Guidelines through NPDES Permits 

Permit writers need to have a detailed knowledge of the industrial facility applying for a new or reissued 

NPDES permit to identify applicable effluent guidelines and know how to use them to derive TBELs. 

This section provides a step-by-step procedure for applying effluent guidelines to direct discharges 

through NPDES permits as shown in Exhibit 5-10. 

Exhibit 5-10 Steps for applying effluent guidelines to direct discharges 

Step 1. Learn about the industrial discharger 

Step 2. Identify the applicable effluent guidelines category(ies) 

Step 3. Identify the applicable effluent guidelines subcategory(ies) 

Step 4. Determine whether existing or new source standards apply 

Step 5. Calculate TBELs from the effluent guidelines 

Step 6. Account for overlapping or multiple effluent guidelines requirements 

Step 7. Apply additional regulatory considerations in calculating TBELs 

Step 8. Apply additional effluent guidelines requirements 

Step 9. Document the application of effluent guidelines in the fact sheet 

5.2.2.1 Step 1: Learn About the Industrial Discharger 

To write a defensible permit, the permit writer should have a solid understanding of the facility’s 

operations. The permit writer should gather sufficient information to identify applicable effluent 

guidelines and derive TBELs. Facility-specific information the permit writer is likely to need includes the 

following: 

 Industrial processes and raw materials. 

 Products and services. 

 Amount of manufacturing production or servicing. 

 Number of production and non-production days. 

 Current pollution prevention practices and wastewater treatment technology(ies). 

 Discharge location of the wastewater pollutants and potential compliance sampling points. 

 The source and characteristics of the wastewaters (including flow) and pollutants that are being 

discharged or have the potential to be discharged from the facility. 

Sources of information include the facility’s permit application, the current permit and fact sheet (if the 

facility is permitted), discharge monitoring reports, site visits, site inspections (such as compliance 

evaluation inspections for an existing permit), and other information submitted by the facility. The permit 

writer also should identify any information that would assist in determining whether the facility or part of 

the facility is considered a new source (e.g., age of facility and equipment). 

5.2.2.2 Step 2: Identify the Applicable Effluent Guidelines Category(ies) 

As noted above, EPA’s effluent guidelines are at 40 CFR, Chapter I, Subchapter N - Effluent Guidelines 

and Standards, Parts 400–471 <www.epa.gov/lawsregs/search/40cfr.html>. A summary of promulgated effluent 

guidelines is presented on EPA’s Industrial Regulations Website <www.epa.gov/guide/industry.html> and in 

Exhibit 5-11 below. 

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Exhibit 5-11 Table of existing point source categories (June 2010) 

Industry category 

(listed alphabetically) 

40 CFR 

Part 

Industry category 

(listed alphabetically) 

40 CFR 

Part 

Aluminum Forming 467 Meat and Poultry Products 432 

Asbestos Manufacturing 427 Metal Finishing 433 

Battery Manufacturing 461 Metal Molding and Casting 464 

Canned and Preserved Fruits and Vegetable 

Processing 

407 Metal Products and Machinery 438 

Canned and Preserved Seafood Processing 408 Mineral Mining and Processing 436 

Carbon Black Manufacturing 458 Nonferrous Metals Forming and Metal 

Powders 

471 

Cement Manufacturing 411 Nonferrous Metals Manufacturing 421 

Centralized Waste Treatment 437 Oil and Gas Extraction 435 

Coal Mining 434 Ore Mining and Dressing 440 

Coil Coating 465 Organic Chemicals, Plastics, and Synthetic 

Fibers 

414 

Concentrated Animal Feeding Operations 

(CAFOs) 

412 Paint Formulating 446 

Concentrated Aquatic Animal Production 451 Paving and Roofing Materials (Tars and 

Asphalt) 

443 

Copper Forming 468 Pesticide Chemicals 455 

Dairy Products Processing 405 Petroleum Refining 419 

Electrical and Electronic Components 469 Pharmaceutical Manufacturing 439 

Electroplating* 413 Phosphate Manufacturing 422 

Explosives Manufacturing 457 Photographic 459 

Ferroalloy Manufacturing 424 Plastic Molding and Forming 463 

Fertilizer Manufacturing 418 Porcelain Enameling 466 

Glass Manufacturing 426 Pulp, Paper, and Paperboard 430 

Grain Mills 406 Rubber Manufacturing 428 

Gum and Wood Chemicals 454 Soaps and Detergents Manufacturing 417 

Hospitals 460 Steam Electric Power Generating 423 

Ink Formulating 447 Sugar Processing 409 

Inorganic Chemicals 415 Textile Mills 410 

Iron and Steel Manufacturing 420 Timber Products Processing 429 

Landfills 445 Transportation Equipment Cleaning 442 

Leather Tanning and Finishing 425 Waste Combustors 444 

* This category contains only categorical pretreatment standards (no effluent guidelines for direct dischargers). 

The following sources of information might be helpful in identifying applicable effluent guidelines for a 

facility: 

 CFR titles and applicability section of the effluent guidelines. This is first place to look for 

information for identifying applicable effluent guidelines. Each effluent guidelines regulation 

includes an applicability section for the category or each subcategory of the industry. The 

applicability section gives a general description of the types of facilities regulated by the effluent 

guidelines. The applicability sections often define certain industrial operations or other criteria 

(e.g., production or process wastewater flow thresholds) that identify whether a facility is 

regulated by the effluent guidelines. 

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 North American Industry Classification System (NAICS) and Standard Industrial 

Classification (SIC). The current NAICS <www.census.gov/epcd/www/naics.html> and former SIC 

codes <www.census.gov/epcd/www/naicstab.htm> could be helpful to determine the appropriate 

industrial category(ies) for a facility. NAICS and SIC codes were developed and are maintained 

by the federal government as a way to classify establishments by type of activity for comparing 

economic and other types of facility-specific data. Although SIC codes provide a helpful starting 

point for categorizing a facility, permit writers should be cautious of relying exclusively on SIC 

codes for determining the appropriate industrial category. SIC codes were not developed using 

EPA’s industrial classification scheme, or vice versa, and, therefore, the codes might not always 

correspond exactly with the categorization process. In addition, more than one SIC code might 

apply to a single facility. Item V-II of NPDES Application Form l requires that the applicant 

provide the SIC code for the activity covered by the permit application. In some instances, the 

SIC code will identify both the industrial category and the subcategory of a facility. Sometimes 

the SIC code might identify the appropriate industrial category but not the subcategory. Exhibit 

5-12 presents two examples of how a permit writer might identify the applicable effluent 

guidelines using the facilities SIC codes. 

Exhibit 5-12 Examples of identifying applicable effluent guidelines using SIC codes 

Example 1 

A facility that performs the primary smelting and refining of copper reports SIC code 3331 in its NPDES 

permit application. By scanning the list of industrial point source categories, the permit writer can 

determine that the facility is regulated by effluent guidelines in the Nonferrous Metals Manufacturing point 

source category (Part 421). In this case, the SIC code also indicates that the facility is likely regulated by 

effluent guidelines in the Primary Copper Smelting Subcategory. 

Example 2 

A facility that manufactures ethyl acrylate and 2-ethylhexyl acrylate (acrylic acid esters) reports the SIC 

code 2869 (Industrial Organic Chemicals, Not Elsewhere Classified) in its NPDES permit application. By 

scanning the list of industrial point source categories, the permit writer can determine that facility is likely 

regulated by effluent guidelines in the Organic Chemicals, Plastics, and Synthetic Fibers (OCPSF) 

category (Part 414). 

 EPA’s Development Documents and Compliance Guides. EPA produces a number of 

documents that will aid permit writers in identifying applicable effluent guidelines and 

incorporating them into NPDES permits. In particular, development documents summarize the 

data and information EPA used to develop the effluent guidelines. Such documents are extremely 

useful in identifying the applicability of the effluent guidelines and how to incorporate the 

effluent guidelines into NPDES permits. EPA may also publish a compliance guide for permit 

writers and industry. EPA’s Effluent Guidelines Website <www.epa.gov/guide/> provides available 

documents for specific industrial categories. 

 FR Notices. The preamble text to the FR notices containing the proposed and final effluent 

guidelines rulemakings also provide additional insight into applicability of the effluent guidelines. 

EPA’s Effluent Guidelines Website <www.epa.gov/guide/> provides FR notices for specific 

industrial categories. For example, the preambles to recently promulgated effluent guidelines 

typically list the SIC and NAICS codes for the potentially regulated facilities. Each Part in the 

CFR identifies the relevant FR notices. For example, § 419.11 (i.e., specialized definitions for 

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September 2010 NPDES Permit Writers’ Manual 

Subpart [subcategory] A for the Petroleum Refining point source category) identifies 47 FR 

46446, October 18, 1982, as amended at 50 FR 28522, July 12, 1985, as its source. 

 EPA Industry Experts. EPA has a number of subject matter experts

<www.epa.gov/guide/contacts.html> at its headquarters office in Washington, D.C. that are available to 

answer questions on specific effluent guidelines. EPA’s NPDES Contacts in Regional Offices

<www.epa.gov/npdes/regionalcontacts> also offer assistance in sorting through the different effluent 

guidelines and NPDES regulations. 

 EPA’s Effluent Guidelines Planning Support Documents. EPA’s Effluent Guidelines Biennial 

Plan Website <http://water.epa.gov/lawsregs/lawsguidance/cwa/304m/> provides technical support 

documents and other information supporting EPA’s biennial effluent guidelines program plans. 

 EPA’s Sector Notebooks. EPA’s Sector Notebooks

<www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/index.html> describe specific 

U.S. industries and governments and provide a holistic approach by integrating processes, 

applicable regulations, and other relevant environment information. 

 Other Sources. Other sources of information include resources identified below in Exhibit 5-23, 

BPJ Permitting Tools. Permit and fact sheet and information from similar facilities might aid in 

identifying applicable effluent guidelines. However, the permit writer should not assume that a 

similar facility was correctly categorized in its permit and should examine the rationale for how 

the other permit writer identified any applicable effluent guidelines before relying on another 

permit to identify the applicable category. 

Permit writers should be aware that effluent guidelines from two or more industrial point source 

categories might apply to a single facility. Step 6 below, provides additional information on overlapping 

or multiple effluent guidelines requirements. 

5.2.2.3 Step 3: Identify the Applicable Effluent Guidelines Subcategory(ies) 

In promulgating effluent guidelines, EPA may divide an industrial point source category into groupings 

called subcategories to provide a method for addressing variations between products, raw materials, 

processes, and other factors that result in distinctly different effluent characteristics or treatment options. 

Some effluent guidelines categories cover a variety of industrial sectors (e.g., the Nonferrous Metals 

Manufacturing point source category has 31 subcategories). It is important for the permit writer to 

correctly identify the applicable subcategory to derive TBELs. 

The process of identifying the applicable effluent guidelines requires close review and comparison of 

information obtained from Step 1 and Step 2 above. Just as effluent guidelines from two or more 

industrial categories can apply to a single facility, it also is true that requirements from two or more 

subcategories could apply to a single facility. 

Exhibit 5-13 presents two examples of how a permit writer can identify the subcategory containing the 

applicable effluent guidelines using information from the NPDES permit application. 

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Exhibit 5-13 Examples of identifying the subcategory with the applicable effluent guidelines 

Example 1 

A permit writer has identified the facility from Example 2 in Exhibit 5-12 above as potentially regulated by the 

effluent guidelines in the OCPSF point source category (Part 414) <www.epa.gov/guide/ocpsf/>. The permit writer 

can determine from a further review of the industrial categorization discussion in the OCPSF Development 

Document and the guidance document that the facility is likely subject to effluent guidelines in Subpart G (Bulk 

Organic Chemicals). Specifically, the applicability criteria section in Subpart G (§ 414.70) states, “The provisions of 

this subpart are applicable to the process wastewater discharges resulting from the manufacture of the following: 

SIC 2865 and 2869 bulk organic chemicals and bulk organic chemical groups.” Further, acrylic acid esters are 

listed in § 414.70 as an OCPSF product group. 

Example 2 

A large poultry slaughterhouse annually produces 200 million pounds of whole, halved, quarter or smaller meat 

cuts and reports SIC Code 2015 in its NPDES permit application. The permit writer reviewed the list of effluent 

guidelines and identified that the facility is likely regulated by effluent guidelines in the Meat and Poultry Products 

point source category (Part 432) <www.epa.gov/guide/mpp/>. The permit writer reviewed the preamble to the final 

effluent guidelines rule and the rule’s development document. In that effluent guidelines regulation, EPA used 

NAICS codes to assist in applicability decisions. See 69 FR 54475, September 8, 2004. The permit writer used the 

U.S. Census Bureau’s SIC to NAICS crosswalk website <www.census.gov/epcd/www/naicstab.htm> to identify the 

NAICS code (311615). Using the NAICS code, the permit writer can narrow the list of potentially applicable 

subcategories to the Poultry First Processing (Subpart K) or the Poultry Further Processing (Subpart L) 

subcategories. After reviewing the applicability criteria of both subcategories, the permit writer determined that only 

the effluent guidelines in Subpart K are likely applicable because the facility performs slaughtering operations, 

which are not regulated by Subpart L. Finally, the permit writer also needed to compare the average annual 

production of the facility (200 million pounds) with the production threshold in the effluent guidelines (100 million 

pounds per year). Because the facility produces more than the production threshold, the effluent guidelines in 

Subpart K are applicable to this facility. See §§ 432.112 and 432.113. In this example the permit writer would use 

the effluent guidelines for ammonia (as N), BOD5, fecal coliform, oil and grease (as HEM), TSS, and total nitrogen 

to derive effluent limitations as detailed in section 5.2.2.5 below. 

5.2.2.4 Step 4: Determine whether Existing or New Source Standards Apply 

Section 5.2.1.1 above defines the different control technologies that apply to direct dischargers: BPT, 

BCT, BAT, and NSPS. The first three apply to existing direct dischargers, and the fourth to new sources. 

To determine whether existing source standards (i.e., BPT, BCT, and BAT) or NSPS apply to the facility, 

the permit writer must determine whether the facility or any part of the facility is a new source. A new 

source is defined in § 122.2 as a building, structure, facility, or installation that discharges pollutants or 

could discharge pollutants and for which construction began after promulgation of the applicable effluent 

guidelines or after proposal of the applicable effluent guidelines, but only if the effluent guidelines are 

promulgated within 120 days. Thus, the discharger’s entire facility could be subject to new source 

standards (e.g., a brand new facility). Permit writers should note that the new source date for indirect 

dischargers is the date on which the pretreatment standard for new sources is proposed. See §403.3(m)(1). 

Additional criteria for determining whether a discharge is a new source are defined in § 122.29(b) to 

cover situations where a facility is adding a new building or process line that results in a discharge to the 

waters of the United States. Such an addition would result in a new source if any of the following is true 

for the source: 

 Is constructed at a site at which no other source is located. 

 Totally replaces the process causing the discharge from an existing source. 

 Has processes that are substantially independent of an existing source at the same site. 

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Furthermore, some effluent guidelines, such as the effluent guidelines for the Pulp, Paper, and Paperboard 

Point Source Category in Part 430, include additional criteria for making new source determinations. See 

§ 430.01(j). 

Appendix D of this manual provides the applicable new source dates used in making new source 

determinations by effluent guideline category as provided in Appendix B of the EPA memorandum New 

Source Dates for Direct and Indirect Dischargers4 <www.epa.gov/npdes/pubs/newsource_dates.pdf> sent by the 

directors of the Water Permits Division and the Engineering and Analysis Division to the Regional Water 

Division Directors. Permit writers can use Appendix D of this manual to find the date for determining 

whether a facility or part of a facility is subject to NSPS. 

Where a new source is the result of a new installation of process equipment at an existing facility, part of 

the facility might be subject to existing source standards and other parts of the facility subject to new 

source standards. Permit writers should identify whether the facility has installed any process equipment 

after the last issuance of the NPDES permit and apply the criteria from § 122.29(b) on a case-by-case 

basis to new construction or new processes, while applying existing source requirements to the existing 

portions of the facility. Sometimes it can be difficult to distinguish between a new source and a 

modification or alteration of an existing source, especially when modifications have occurred slowly over 

time. The permit writer should consult the effluent guidelines regulation to determine if it defines more 

specifically what constitutes a new source. 

It is important to remember that after the effective date of a new source standard, the CWA stipulates that 

it is unlawful for any owner or operator to operate such a source in violation of those standards. See 

33 U.S.C. 1316(e) and 1317(d). EPA’s regulations specify that a new source “[must] install and have in 

operating condition, and [must] start up all pollution control equipment” required to meet applicable 

standards before beginning to discharge. The regulations also indicate that the owner or operator of a new 

source must meet all applicable standards within “the shortest feasible time (not to exceed 90 days).” See 

§ 122.29(d)(4). 

In addition to the requirement to meet NSPS upon beginning to discharge, an EPA-issued NPDES permit 

for a new source is a federal action subject to the requirements of the National Environmental Policy Act 

(NEPA), 33 U.S.C. 1371(c)(1). For more information on NEPA and the NPDES program, see section 

11.1.2 of this manual. 

For existing facilities and existing sources (where NSPS do not apply), existing source standards (i.e., 

BPT, BCT, BAT) apply. The permit writer would use the more stringent technology level of control for 

each pollutant. For example, the BPT level of control in the Veneer Subcategory of the Timber Products 

Processing category (Part 429, Subpart B) allows a discharge of process wastewater and identifies 

effluent guidelines for BOD5 and pH, while the BAT level of control bans the direct discharge of process 

wastewater. Consequently, the NPDES permit for a facility regulated by the Veneer Subcategory must use 

the more stringent BAT requirements and prohibit the direct discharge of process wastewater. The 

effluent guidelines for the Renderers subcategory of the Meat and Poultry Products point source category 

(Subpart J, Part 432) provide another example. In those effluent guidelines, the BCT requirements for 

BOD5, oil and grease, and TSS are more stringent than the corresponding BPT requirements. 

Accordingly, the permit writer would use the more stringent BCT requirements, rather than the BPT 

requirements, to derive numeric permit limitations for an existing renderer. 

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5.2.2.5 Step 5: Calculate TBELs from the Effluent Guidelines 

Once a permit writer has identified the effluent guidelines that apply to a facility, he or she then uses 

those effluent guidelines to calculate applicable TBELs. 

EPA’s regulations at § 122.45(f)(1) stipulate that all pollutants limited in permits must have limitations, 

standards or prohibitions expressed in terms of mass except under any of the following conditions: 

 For pH, temperature, radiation, or other pollutants that cannot appropriately be expressed by mass 

limitations. 

 When applicable standards or limitations are expressed in terms of other units of measure. 

 If in establishing technology-based permit limitations on a case-by-case basis, limitations based 

on mass are infeasible because the mass or pollutant cannot be related to a measure of production 

(e.g., discharges of TSS from certain mining operations). The permit conditions must ensure that 

dilution will not be used as a substitute for treatment. 

Thus, the type of limitation (i.e., mass, concentration, or other units) calculated for a specific pollutant at 

a facility will depend on the type of pollutant and the way limitations are expressed in the applicable 

effluent guideline. Generally, effluent guidelines include both maximum daily and monthly average 

limitations for most pollutants. Though the effluent guidelines use different terms for monthly effluent 

limitations (e.g., monthly average, maximum for monthly average, average of daily values for 30 

consecutive days), the requirements are expressed in NPDES permits as average monthly limitations as 

defined in § 122.2. 

As stated in Steps 1 and 2 above, the permit writer would use many sources of information to calculate 

TBELs. From those sources, the permit writer should identify the source and characteristics of the 

wastewaters (including flow) and pollutants being discharged, or that have the potential to be discharged, 

and whether and how those pollutants are regulated by effluent guidelines. In particular, the permit writer 

should identify the following: 

 The appropriate permit compliance point(s) (which might be specified in the effluent guidelines). 

 Wastewaters subject to the applicable effluent guidelines and whether they are commingled with 

other wastewaters not regulated by effluent guidelines (e.g., sanitary wastewaters before the 

permit compliance point). 

 Reasonable measure of the facility’s actual long-term daily production and average number of 

production days per year regulated by effluent guidelines (necessary for derived effluent 

limitations from production-normalized effluent guidelines). 

 Average daily facility flows at the compliance point(s) regulated by effluent guidelines. 

 Average daily facility flows at the compliance point(s) not regulated by effluent guidelines. 

That information is used in conjunction with the effluent guidelines for TBEL calculations as discussed 

below. 

Chapter 5: Technology-Based Effluent Limitations 5-29
September 2010 NPDES Permit Writers’ Manual 

Calculating Mass-based TBELs from Production-Normalized Effluent Guidelines 

Most effluent guidelines requirements are mass-based and expressed in terms of allowable pollutant 

discharge per unit of production or some other measure of production (i.e., production normalized). 

Permit writers incorporate such production-normalized effluent guidelines into NPDES permits as massbased TBELs by using a reasonable measure of the permittee’s actual long-term daily production. The 

objective in determining the production for a facility is to develop a single estimate of the long-term 

average daily production that can reasonably be expected to prevail during the next term of the permit 

(i.e., not the design production rate). Permit writers may establish such a production rate using the past 3 

to 5 years of facility data. For example, the permit writer might wish to use the average daily production 

rate calculated using the highest annual production from the previous 3 to 5 years. Whatever value is 

selected, the permit writer should ensure that the production rate used in deriving mass-based effluent 

limitations is representative of the actual production likely to prevail during the next term of the permit. 

The examples in Exhibit 5-14 illustrate the application of production-based effluent guidelines using the 

approach where annual production data are available. In Example 1 in Exhibit 5-14, the highest annual 

production rate during the past 5 years was used as the estimate of production. If historical trends, market 

forces, company plans to decrease production, or plant designs and capital expenditures for an increase in 

production indicated that a different level of production would prevail during the permit term, the permit 

writer could consider a different basis for estimating production or establish tiered discharge limitations, 

as discussed in section 5.2.2.7 below. 

Calculating Mass-based TBELs from Flow-Normalized Effluent Guidelines 

In some cases, permit writers are directed to calculate mass-based TBELs from flow-normalized effluent 

guidelines that are expressed as concentrations. For example, the Organic Chemicals, Plastics, and 

Synthetic Fibers (OCPSF) effluent guidelines <www.epa.gov/waterscience/guide/ocpsf/> in Part 414 state that 

facilities “must achieve discharges not exceeding the quantity (mass) determined by multiplying the 

process wastewater flow subject to [the effluent guideline] times the concentration listed in the [effluent 

guideline]...” The Development Document for Effluent Limitations Guidelines and Standards for the 

Organic Chemicals, Plastics and Synthetic Fibers Point Source Category5

<www.epa.gov/waterscience/guide/ocpsf/#guidance> directs the permit writer to “use a reasonable estimate of 

process wastewater discharges and the concentration limitations [in the effluent guideline] to develop 

mass limitations for the NPDES permit.” Thus, the process for calculating the TBELs is similar to the 

process used with production-normalized effluent guidelines, but rather than using a reasonable measure 

of the actual daily production, the permit writer would use a reasonable measure of the actual daily flow 

rate as the basis for calculating the TBELs. 

As with estimating production to calculate TBELs, the objective in determining a flow estimate for a 

facility is to develop a single estimate of the actual daily flow rate (in terms of volume of process 

wastewater per day), which can reasonably be expected to prevail during the next term of the permit (i.e., 

not the design flow rate). Permit writers can establish that flow rate using the past 3 to 5 years of facility 

data in a manner similar to the method used to determine production. For example, the permit writer 

might wish to use the highest average daily flow rate from the average daily flows calculated for each of 

the past 3 to 5 years. The value selected should be representative of the actual flow likely to prevail 

during the next term of the permit. 

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Exhibit 5-14 Example of calculating mass-based effluent limitation from productionnormalized effluent guidelines6

Example 1 

Facility A has produced 331,000 tons, 301,500 tons, 321,500 tons, 330,000 tons, and 331,500 tons of product per 

year for the previous 5 years operating 255 days per year. 

Question: 

What would be a reasonable measure of production for permitting purposes? 

Answer: 

Using the highest year of production (331,500 tons per year) might be an appropriate and reasonable measure of 

production, if this figure is representative of the actual production expected to occur over the next term of the 

permit. Permit writers also should check to see if the maximum yearly value is within a certain percentage 

(e.g., 20 percent–see section 5.2.2.7 below) of the average value. In evaluating gross production figures, the 

number of production days should be considered. If the number of production days per year is not comparable, the 

permit writer would need to convert the numbers to production per day before comparing them. In this example, all 

the yearly production figures were based on 255 days per year of production, so they may be compared directly. 

The 331,500 tons per year figure is the maximum for the past 5 years, which is only 2.6 percent above the average 

annual production of 323,100 tons. Therefore, 331,500 tons is a reasonable measure of the annual production for 

the facility. 

Example 2 

For the same facility in Example 1 above with an annual production of 331,500 tons, the production-normalized 

effluent guidelines for zinc are 0.1 lbs/1,000 lbs as monthly average and 0.15 lbs/1,000 lbs as daily maximum. 

Question: 

What are the resulting zinc technology-based effluent limitations for the NPDES permit? 

Answer: 

The annual production would be converted to an average daily production rate to apply the effluent guidelines. To 

convert from the annual production rate to an average daily rate, divide the annual production rate by the number 

of production days per year. To determine the number of production days, subtract the total number of normally 

scheduled non-production days from the total days in a year. Because Company A normally has 255 production 

days per year, the annual production rate of 331,500 tons per year would yield an average production daily rate of 

1,300 tons per day. 

Monthly average discharge limitation for zinc*: 

1,300 tons/day x 2,000 lbs/ton x 0.10 lbs/1,000 lbs = 260 lbs/day

Daily maximum discharge limitation for zinc*: 

1,300 tons/day x 2,000 lbs/ton x 0.15 lbs/1,000 lbs = 390 lbs/day 

* calculated to 2 significant figures 

Calculating TBELs from Concentration-based Effluent Guidelines 

Permit writers might want to develop mass-based limitations for facilities with concentration-based 

effluent guidelines (e.g., for a facility does not have adequate water conservation practices). Mass-based 

permit effluent limitations encourage water conservation (e.g., minimize the potential for diluting process 

wastewaters by non-process wastewater, more efficient use of water) and pollution prevention (e.g., 

reduce waste loads to wastewater treatment facilities by physically collecting solid materials before using 

water to clean equipment and facilities). Additionally, for facilities with on-site wastewater treatment 

systems, the combination of water-reduction technologies and practices and well-operated wastewater 

treatment will reduce the volume and mass of discharged wastewater pollution (i.e., after treatment). 

Another benefit of mass-based permit effluent limitations is that they provide the permittee with more 

flexibility. Permittees may elect to control their wastewater discharges through more efficient wastewater 

control technologies and pollution-prevention practices that result in lower pollutant concentrations in the 

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September 2010 NPDES Permit Writers’ Manual 

discharged wastewater, or more efficient water conservation practices that result in less wastewater 

volume discharged from industrial operations), or both. 

“EPA strongly supports water conservation and encourages all sectors, including municipal, industrial, 

and agricultural, to achieve efficient water use. EPA does not intend for its regulations to present a barrier 

to efficient water use in any industrial sector.” See final 2006 Effluent Guidelines Program Plan in 71 FR 

76655, December 21, 2006. 

When calculating mass-based effluent limitations, the permit writer should use a conversion factor and 

document in the fact sheet the conversion factors used to calculate the permit limitations (e.g., 

concentration [mg/L] × flow [mgd] × 8.34 [conversion factor] = permit limitation [lbs/day]). 

Additionally, guidance for implementing concentration-based limitations in effluent guidelines may direct 

permit writers to develop mass-based TBELs. For example, the Permit Guidance Document 

Transportation Equipment Cleaning Point Source Category (40 CFR 442)7

 industry states: 

The effluent limitations guidelines and standards for the TEC industry are concentration-based and 

adhere to the building block concept. Each regulated wastestream in an outfall is typically assigned a 

mass-based discharge allowance based on a calculation of its applicable concentration-based 

limitation and annual average flow. The sum of the allowances is the total mass discharge allowance 

for the outfall. In other words, the applicable permit limitations for facilities in more than one 

subcategory is the sum of the mass loadings based upon production in each subcategory and the 

respective subcategory effluent limitations guidelines. Mass-based limitations for unregulated or 

dilution wastewater streams at direct discharging facilities are established using [BPJ]. 

Where a permit writer cannot determine a reasonable measure of actual flow for a regulated discharge, 

concentration-based TBELs may be determined by directly applying the concentration-based limitations 

in effluent guidelines to the regulated flow and accounting for non-regulated flows at the point of 

compliance for the TBELs. 

Supplementing Mass-based TBELs with Concentration Limitations 

Even where effluent guidelines require permit writers to calculate mass-based TBELs, a permit writer 

may determine that it is beneficial to include concentration-based limitations to supplement the massbased limitations. Where effluent limitations are expressed in terms of mass, a provision at § 122.45(f)(2) 

allows the permit writer, at his or her discretion, to express limitations in additional units (e.g., 

concentration units). Where limitations are expressed in more than one unit, the permittee must comply 

with both. The permit writer may determine that expressing limitations in terms of both concentration and 

mass encourages the proper operation of a treatment facility at all times. 

Supplementing mass-based limitations with concentration-based limitations may be especially appropriate 

where the requirements in the effluent guidelines are flow-normalized (i.e., the effluent guidelines 

includes a concentration requirement but directs the permit writer to calculate a mass-based TBEL using 

the concentration requirement and the wastewater flow). The permit writer may determine that if the 

permit includes only mass-based limitations derived from the concentration-based limitations in the 

effluent guidelines, a permittee could increase its effluent pollutant concentrations above the applicable 

concentration requirements during low flow periods (i.e., reduce the efficiency of the wastewater 

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treatment) and still meet its mass-based permit limitations. Supplementing the mass-based TBELs with 

concentration limitations would discourage the reduction in treatment efficiency during low-flow periods 

and require proper operation of treatment units at all times. 

Incorporating Narrative Requirements from Effluent Guidelines 

The permit writer should also ensure that any applicable narrative effluent guidelines controls or 

requirements are included in the permit. For example, the effluent guidelines for Concentrated Aquatic 

Animal Production facilities (Part 451) consist of narrative requirements implemented through BMPs. 

Another example, related to monitoring and compliance rather than effluent limitations, is found in the 

Metal Finishing effluent guidelines. The effluent guidelines allow a facility to make a statement regarding 

total toxic organics (TTO) in lieu of monitoring for toxic organics. Exhibit 5-15 provides an example 

narrative requirement representing BPT performance standards for Concentrated Aquatic Animal 

Production facilities, Subpart A (flow through and recirculating systems) § 455.11(a). 

Exhibit 5-15 Example narrative requirement from the Concentrated Aquatic Animal 

Production effluent guideline—Subpart A [§ 455.11(a)] 

Except as provided in [§§] 125.30 through 125.32, any existing point source subject to this subpart must meet the 

following requirements, expressed as practices (or any modification to these requirements as determined by the 

permitting authority based on its exercise of its best professional judgment) representing the application of BPT: 

(a) Solids control. The permittee must: 

(1) Employ efficient feed management and feeding strategies that limit feed input to the minimum amount 

reasonably necessary to achieve production goals and sustain targeted rates of aquatic animal growth in order to 

minimize potential discharges of uneaten feed and waste products to waters of the [United States] 

(2) In order to minimize the discharge of accumulated solids from settling ponds and basins and production 

systems, identify and implement procedures for routine cleaning of rearing units and off-line settling basins, and 

procedures to minimize any discharge of accumulated solids during the inventorying, grading and harvesting 

aquatic animals in the production system. 

(3) Remove and dispose of aquatic animal mortalities properly on a regular basis to prevent discharge to waters of 

the [United States], except in cases where the permitting authority authorizes such discharge in order to benefit 

the aquatic environment. 

5.2.2.6 Step 6: Account for Overlapping or Multiple Effluent Guidelines Requirements 

There are instances when one facility includes both new and existing sources, produces multiple products 

or services, or includes production or services belonging to more than one category or subcategory. In 

such cases, the permit writer must examine the applicable effluent guidelines closely to ensure that 

(1) one guideline does not supersede another; and (2) the effluent guidelines are properly applied. 

Superseding Effluent Guidelines 

EPA tries to minimize the overlap of different effluent guidelines by providing exclusions in the 

applicability sections. The effluent guidelines in the Metal Finishing point source category (Part 433) are 

an example of where EPA has tried to minimize the overlap of multiple effluent guidelines for certain 

wastewater discharges. Exhibit 5-16 presents the applicability section in Part 433 [§ 433.10(b)], which 

specifically excludes certain wastewaters from the Metal Finishing effluent guidelines. Another example 

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is the preamble to the OCPSF effluent guidelines. The preamble identifies numerous circumstances where 

the OCPSF regulations are superseded by effluent guidelines for other industrial categories. Exhibit 5-17 

presents excerpts from the preamble (52 FR 42523, November 5, 1987) to illustrate the point. 

Exhibit 5-16 Exclusion of wastewaters in metal finishing effluent guidelines 

In some cases, effluent limitations and standards for the following industrial categories might be effective and 

applicable to wastewater discharges from the metal finishing operations listed above [in paragraph (a)]. In such 

cases these Part 433 limitations shall not apply and the following regulations shall apply: [emphasis added] 

 Nonferrous metal smelting and refining (40 CFR part 421) 

 Coil coating (40 CFR Part 465) 

 Porcelain enameling (40 CFR Part 466) 

 Battery manufacturing (40 CFR Part 461) 

 Iron and steel (40 CFR Part 420) 

 Metal casting foundries (40 CFR Part 464) 

 Aluminum forming (40 CFR Part 467) 

 Copper forming (40 CFR Part 468) 

 Plastic molding and forming (40 CFR Part 463) 

 Nonferrous forming (40 CFR Part 471) 

 Electrical and electronic components (40 CFR Part 469) 

Exhibit 5-17 Excerpts from preamble to OCPSF effluent guidelines regarding applicability of 

effluent guidelines 

 For the purposes of this regulation, OCPSF process wastewater discharges are defined as discharges from all 

establishments or portions of establishments that manufacture products or product groups listed in the 

applicability sections of this regulation, and are included within the following U.S. Department of Commerce 

Bureau of the Census Standard Industrial Classification (SIC) major groups: 

- SIC 2865: Cyclic Crudes and Intermediates, Dyes, and Organic Pigments. 

- SIC 2869: Industrial Organic Chemicals, not Elsewhere Classified. 

- SIC 2821: Plastic Materials, Synthetic Resins, and Nonvulcanizable Elastomers. 

- SIC 2823: Cellulosic Man-Made Fibers. 

- SIC 2824: Synthetic Organic Fibers, Except Cellulosic. 

The OCPSF regulation does not apply to process wastewater discharges from the manufacture of organic 

chemical compounds solely by extraction from plant and animal raw materials or by fermentation processes. 

 The OCPSF regulation does not apply to discharges from OCPSF product/process operations [that] are 

covered by the provisions of other categorical industry effluent limitations guidelines and standards if the 

wastewater is treated in combination with the non-OCPSF industrial category regulated wastewater. (Different 

processes manufacture some products or product groups and some processes with slight operation condition 

variations give different products. EPA uses the term product/process to mean different variations of the same 

basic process to manufacture different products as well as to manufacture the same product using different 

processes.) 

 The process wastewater discharges by petroleum refineries and pharmaceutical manufacturers from production 

of organic chemical products specifically covered by 40 CFR Part 419 Subparts C and E and Part 439 Subpart 

C, respectively, that are treated in combination with other petroleum refinery or pharmaceutical manufacturing 

wastewater, respectively, are not subject to the OCPSF regulation no matter what SIC code they use to report 

their products. 

 Today’s OCPSF category regulation applies to plastics molding and forming processes when plastic resin 

manufacturers mold or form crude intermediate plastic material for shipment off-site. The regulation also applies 

to the extrusion of fibers. Plastics molding and forming processes, other than those described above are 

regulated by the Plastics Molding and Forming effluent guidelines and standards (40 CFR Part 463). 

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Exhibit 5-17 Excerpts from preamble to OCPSF effluent guidelines regarding applicability of 

effluent guidelines (continued) 

 Public comments requested guidance relating to the coverage of OCPSF research and development facilities, 

standalone OCPSF research and development, pilot plant, technical service, and laboratory bench scaleoperations are not covered by the OCSPF regulation. However, wastewater from such operations conducted in 

conjunction with and related to existing OCPSF manufacturing operations at OCPSF facilities is covered by the 

OCPSF regulation because these operations would most likely generate wastewater with characteristics similar 

to the commercial manufacturing facility. Research and development, pilot plant technical service, and 

laboratory operations [that] are unrelated to existing OCPSF plant operations, even though conducted on-site, 

are not covered by the OCPSF regulation because they may generate wastewater with characteristic dissimilar 

to that from the commercial OCPSF manufacturing facility. 

 Finally, as described in the following paragraphs, this regulation does not cover certain production that has 

historically been reported to the Bureau of Census under a non-OCPSF SIC subgroup heading, even if such 

production could be reported under one of the five SIC code groups covered by today’s regulation. 

Multiple Effluent Guidelines Requirements 

NPDES permit writers often find that a facility employs multiple processes each with its own effluent 

guidelines requirement. In addition, sometimes effluent guidelines from multiple categories and 

subcategories apply to wastewaters for a single facility. When a facility is subject to effluent guidelines 

for two or more processes in a subcategory or to effluent guidelines from two or more categories or 

subcategories, the permit writer must apply each of the applicable effluent guidelines to derive TBELs. In 

applying multiple effluent guidelines, the permit writer should use measures of actual production or flow 

that are reasonable with respect to operation of multiple processes at the same time. For example, if 

maximum production for one process can occur only when there is reduced production for a second 

process, it might not be reasonable to assume maximum production levels for both processes at the same 

time when applying the effluent guidelines. If all wastewaters regulated by effluent guidelines are treated 

separately but are combined before the discharge, the permit writer may establish internal outfalls and 

separately apply the effluent guidelines at the respective internal outfall as discussed in § 122.45(h) and in 

Step 7 below. 

More commonly, wastewater streams regulated by effluent guidelines are combined during or before 

treatment. In such a case, the permit writer combines the allowable pollutant loadings from each set of 

requirements or from each set of effluent guidelines to arrive at a single TBEL for the facility using a 

building block approach. The building block approach as applied to a facility with multiple processes in 

the Primary Tungsten subcategory of the Primary Nonferrous Metals Manufacturing point source 

category (Part 421, Subpart J) is presented in Exhibit 5-18. The same principles illustrated in the exhibit 

would apply to a facility with processes subject to requirements from multiple subcategories or categories 

that are combined before or during treatment. 

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Exhibit 5-18 Building block approach for applying effluent guidelines 

A facility is subject to Part 421, Subpart J (Primary Tungsten). The facility uses a tungstic acid rinse, an acid leach 

wet air pollution control system, and an alkali leach wash in its manufacturing process. 

The Maximum daily production rate for the facility is: 

 4.7 million pounds per day of Tungstic Acid (as W) 

 3.5 million pounds per day of Sodium Tungstate (as W) 

Question: 

What is the technology-based effluent limit for lead at the facility? 

Answer: 

BPT calculation for lead (§ 421.102): 

 a) Tungstic acid rinse:

 (4.7 million lbs/day) × (17.230 lbs/million lbs) = 80.981 lbs/day 

 b) Acid leach wet air pollution control:

 (4.7 million lbs/day) × (15.040 lbs/million lbs) = 70.688 lbs/day 

 c) Alkali leach wash:

 (3.5 million lbs/day) × (0.000 lbs/million lbs) = 0.000 lbs/day 

 d) Total allowable discharge = 80.981 + 70.688 + 0.000 = 151.669 = 152 lbs/day

BAT calculation for lead (§ 421.103): 

 a) Tungstic acid rinse:

 (4.7 million lbs/day) × (11.490 lbs/million lbs) = 54.003 lbs/day 

 b) Acid leach wet air pollution control:

 (4.7 million lbs/day) × (1.003 lbs/million lbs) = 4.7141 lbs/day 

 c) Alkali leach wash:

 (3.5 million lbs/day) × (0.000 lbs/million lbs) = 0.000 lbs/day 

 d) Total allowable discharge = 54.003 + 4.7141 + 0.000 = 58.7171 = 59 lbs/day*

The technology-based maximum daily limitation for lead at the facility is the BAT limitation of 59 lbs/day. That 

value is compared with the water quality-based effluent limitation for lead, to ensure that all applicable standards 

are implemented through the final effluent limitations. 

* calculated to 2 significant figures

The building block approach is applied in other circumstances as well, such as 

 Mixture of mass-based and concentration-based requirements: The limitations in effluent 

guidelines for some pollutants are mass-based, production-normalized limitations in some 

subparts and concentration-based limitations in other subparts. When all the wastewater streams 

go to the same treatment system, the permit writer would need to convert the concentration-based 

limitations to mass-based limitations so they could be combined with the mass-based, productionnormalized limitations and applied to the combined wastewater streams. 

 Mixture of different concentration-based requirements: Some facilities could have multiple 

operations that are each subject to different concentration-based requirements for the same 

pollutant but with wastewater streams that combine before treatment. In such a case, the permit 

writer can establish a flow-weighted concentration-based limitation as the TBEL for the 

combined wastewater streams or convert the concentration-based requirements to equivalent 

mass-based requirements using flow data and then combine the mass-based requirements into a 

single limitation for the combined wastewater streams. 

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 Mixture of regulated and unregulated wastewater streams: In some cases, wastewater streams 

containing a pollutant regulated by the applicable effluent guidelines requirements can combine 

with other wastewater streams that do not have effluent guidelines requirements that regulate the 

pollutant. In such a case, the permit writer could use BPJ to establish a TBEL for the unregulated 

wastewater stream(s) (see section 5.2.3 below) and, as appropriate, calculate a final TBEL for the 

combined wastewater streams. For example, if one of the wastewater streams contributing to an 

industrial facility’s discharge is sanitary wastewater, the permit writer might use BPJ to apply the 

treatment standards for domestic wastewater and calculate BOD5 limitations for that wastewater 

stream. The secondary treatment standards, discussed in section 5.1 above, could be used to 

calculate mass-based limits for the sanitary wastewater using the concentration-based 

requirements and an estimate of flow rate that is expected to represent the flow rate during the 

proposed permit term. A final TBEL for BOD5 could be calculated for the combined sanitary and 

process wastewater streams by combining the two mass limitations using the building block 

approach. 

 Mixture of wastewater streams containing a pollutant with wastewater streams not 

containing the pollutant: If a wastewater stream that does not contain a pollutant is combined 

with another wastewater stream that contains the pollutant (and has applicable requirements in the 

effluent guidelines or requirements determined by the permit writer using BPJ), the permit writer 

must ensure that the non-regulated waste stream does not dilute the regulated waste stream to the 

point where the pollutant is not analytically detectable. If that occurs, the permit writer will most 

likely need to establish internal outfalls, as allowed under § 122.45(h) and in Step 7 below. 

For examples of addressing combined wastewater streams, see section 15.3.3 on page 15-10 of EPA’s 

Technical Development Document for the Final Effluent Limitations Guidelines and Standards for the

Meat and Poultry Products Point Source Category (40 CFR 432)8

<www.epa.gov/waterscience/guide/mpp/final/tdd15.pdf>. 

Facilities with Both New and Existing Sources 

Finally, as noted above, if effluent guidelines are applicable to an existing facility, and that facility adds a 

new production line, which becomes a new source, the permit writer should calculate TBELs for the 

subsequent permit using BPT, BCT, and BAT standards for the existing production line and NSPS for the 

new production line, as discussed in section 5.2.2.4 above. 

5.2.2.7 Step 7: Apply Additional Regulatory Considerations in Calculating TBELs 

The permit writer must consider several additional requirements when deriving TBELs from effluent 

guidelines. Those additional requirements consist of evaluating or accounting for the following: 

 Expected significant increases or decreases in production during the permit term for tiered 

discharger limitations. 

 Internal outfalls. 

 Requests for a variance from effluent guidelines. 

The following sections provide an overview of those topics. 

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Tiered Discharge Limitations 

If production rates are expected to change significantly during the life of the permit, the permit writer can 

include tiered (alternate) TBELs as allowed by § 122.45(b)(2)(ii)(A)(i). Tiered TBELs would apply to 

mass-based effluent limitations and would become effective when production or flow (or some other 

measure of production) exceeded a threshold value, such as during seasonal production variations. 

Generally, up to a 20 percent fluctuation in production is considered to be within the range of normal 

variability, while changes in production higher than 20 percent could warrant consideration of tiered 

limitations. Exhibit 5-19 illustrates application of tiered limitations. 

Exhibit 5-19 Example of tiered discharge limitations 

Plant B produced approximately 40 tons per day of product during spring and summer months (i.e., March through 

August) and 280 tons per day during fall and winter months during the previous 5 years. Production during the fall 

and winter months is significantly higher than during the off-season, and the discharger has made a plausible 

argument that production is expected to continue at that level. The effluent guidelines requirements for Pollutant Z 

are 0.08 lbs/1,000 lbs for the average monthly limitation and 0.14 lbs/1,000 lbs for the maximum daily limitation. 

Question: 

What are appropriate tiered effluent limitations for Plant B? 

Answer: 

The first tier or lower limitations would be based on a production rate of 40 tons per day. The limitations would 

apply between March and August. 

Monthly average limitation: 

40 tons/day × 2,000 lbs/ton x 0.08 lbs/1,000 lbs = 6.4 lbs/day*

Daily maximum limitation: 

40 tons/day × 2,000 lbs/ton x 0.14 lbs/1,000 lbs = 11.2 lbs/day = 11 lbs/day*

The second tier or higher limitations would be based on a production rate of 280 tons per day. Those limitations 

would apply between September and February. 

Monthly average limitation: 

280 tons/day × 2,000 lbs/ton x 0.08 lbs/1,000 lbs = 44.8 lbs/day = 45 lbs/day*

Daily maximum limitation

280 tons/day × 2,000 lbs/ton x 0.14 lbs/1,000 lbs = 78.4 lbs/day = 78 lbs/day*

* calculated to 2 significant figures 

Permit writers should include tiered limitations in a permit only after careful consideration of production 

data and only when a substantial increase or decrease in production is likely to occur. In the example 

above, the lower limitations would be in effect when production was at low levels (March through 

August). During periods of significantly higher production (September through February), the higher 

limitations would be in effect. In addition, a tiered or alternate set of limitations might be appropriate in 

the case of special processes or product lines that operate during certain times only. 

Permit writers could base thresholds for tiered limitations on an expected increase in production during 

the term of the permit that will continue through the duration of the permit term. For example, if a facility 

plans to add a process line and significantly expand production in year 3 of the permit term, the permit 

could specify a higher tier of limitations that go into effect when the facility reports reaching a production 

level specified in the permit. 

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Permit writers must detail in the permit the thresholds and time frames when each tier applies, measures 

of production, and special reporting requirements. Special reporting requirements include provisions such 

as the following: 

 The facility notifying the permitting authority a specified number of business days before the 

month it expects to be operating at a higher level of production and the duration this level of 

production is expected to continue. 

 The facility reporting, in the discharge monitoring report, the level of production and the 

limitation and standards applicable to that level. 

A detailed discussion of the rationale and requirements for any tiered limitations should be provided in 

the fact sheet for the permit. 

Internal Outfalls 

The NPDES regulations at § 122.45(h) give NPDES permit writers the authority to identify internal 

outfalls when effluent limitations at the final outfall are impractical or infeasible. These internal 

compliance points might be necessary to ensure proper treatment of persistent, bioaccumulative, and toxic 

pollutants that are discharged in concentrations below analytic detection levels at the final effluent outfall 

or other pollutants that may be diluted by flows (e.g., cooling water) not containing the pollutant. Some 

effluent guidelines may require the use of internal outfalls unless the effluent limitations are adjusted 

based on the dilution ratio of the process wastewater to the wastewater flow at the compliance point. 

Examples of effluent guidelines with required internal compliance points include the Metal Finishing 

effluent guidelines (Part 433) and the Pulp, Paper, and Paperboard effluent guidelines (Part 430). 

Accordingly, the permit writer should identify any internal outfall monitoring that might be required by 

the applicable effluent guidelines and include monitoring requirements in the final permit. 

Effluent Guidelines Variances 

The CWA and federal regulations provide limited mechanisms for variances from requirements in 

effluent guidelines. An NPDES permit applicant must meet very specific data and variance application 

deadline requirements before a variance may be granted. A variance provides a unique exception to a 

particular requirement, and the permit writer should not expect to routinely receive variance requests. 

Nevertheless, the permit writer should be aware of the major types of variances and the basic 

requirements for each, because the permit writer will most likely be the person to conduct the initial 

reviews of such requests before submitting them for review to the State Director (if applicable) or to EPA. 

Variance applications are submitted by the NPDES permit applicant and must be submitted before the 

close of the public comment period of the permit, except for Fundamentally Different Factors (FDF) 

variance requests, which must be requested by the NPDES permit applicant within 180 days of the 

effluent guidelines publication. The permit writer should consult § 124.62 for the specific procedures for 

decisions regarding various types of variances. Exhibit 5-20 lists the available variances from effluent 

guidelines. 

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Exhibit 5-20 Variances from effluent guidelines 

Legislation 

(CWA section) Type 

Regulation 

(40 CFR) Approval authority 

Application 

deadline 

301(g) Nonconventional 

Pollutant 

Part 125, Subpart F 

(Reserved)

EPA Region 

HQ delegated 

authority 

During permit 

comment period 

301(n) 

Fundamentally 

Different Factors 

(FDF) 

Part 125, Subpart D

EPA Region 

HQ delegated 

authority 

180 days from the 

date the limitation or 

standard is published 

in the FR 

— Net Intake or 

Net/Gross § 122.45(g)

NPDES state 

or EPA Region in 

absence of approved 

state NPDES program 

During permit 

comment period 

The following paragraphs further discuss the variances listed in Exhibit 5-20 and the factors that are 

considered in a technical review of a variance request. 

Nonconventional Pollutant—CWA Section 301(g) Variance 

CWA section 301(g) and the regulations at § 122.21(m)(2) provide for a variance from new or revised 

BAT effluent guidelines for certain nonconventional pollutants because of local environmental factors, so 

long as the discharger demonstrates that it is meeting BPT and that the discharge does not prevent 

attainment of water quality standards and would not result in additional requirements on other point or 

nonpoint sources. The pollutants for which a facility may request a CWA section 301(g) variance are 

ammonia, chlorine, color, iron, and phenols (as measured by the colorimetric 4-aminoantipyrine [4AAP] 

method). The CWA also provides a process to petition to include additional pollutants on this list. 

Industries with facilities that have applied for CWA section 301(g) variances include Iron and Steel 

Manufacturing (Part 420), Steam Electric Power Generating (Part 423), Inorganic Chemicals 

Manufacturing (Part 415), Nonferrous Metals Manufacturing (Part 421), Aluminum Forming (Part 467), 

and Pesticides Chemicals (Part 455) facilities. 

In addition to meeting the application deadline, the discharger must file a variance application that meets 

the following requirements: 

 The proposed modified requirements must result in compliance with BPT and water quality 

standards of the receiving stream. 

 No additional treatment will be required of other point or nonpoint source dischargers as a result 

of the variance approval. 

 The modified requirements will not interfere with attainment or maintenance of water quality to 

protect public water supplies, or with protection and propagation of a balanced population of 

shellfish, fish, and wildfowl, and will allow recreational activities in and on the water. 

 The modified requirements will not result in quantities of pollutants that can reasonably be 

anticipated to pose an unacceptable risk to human health or the environment, cause acute or 

chronic toxicity, or promote synergistic properties. 

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The permit writer should review the request to ensure that it complies with each of the requirements for 

this type of variance. This variance request can involve a great deal of water quality assessment, including 

aquatic toxicity, mixing zone and dilution model analysis, and possible site-specific criterion 

development. In addition, it might be necessary to assess many complex human health effects, including 

carcinogenicity, teratogenicity, mutagenicity, bioaccumulation, and synergistic propensities. Permit 

writers may use EPA’s Draft Technical Guidance Manual for the Regulations Promulgated Pursuant to 

Section 301(g) of the Clean Water Act of 1977 40 CFR Part 125 (Subpart F)

<www.epa.gov/npdes/pubs/owm0008.pdf> to assess a completed variance request. 

Fundamentally Different Factors—FDF Variance 

Alternative effluent limitations or standards different from the otherwise applicable requirements in 

effluent guidelines may be authorized by EPA if an individual facility is fundamentally different with 

respect to factors considered in establishing the limitations or standards otherwise applicable to that 

facility’s industrial category. Such a modification is known as a fundamentally different factors (FDF) 

variance. 

Facilities must submit all FDF variance applications to the appropriate Director, as defined at § 122.2, no 

later than 180 days from the date the limitations or standards are published in the FR [see CWA section 

301(n)(2) and § 122.21(m)(1)(i)(B)(2)]. An FDF variance is not available to a new source subject to 

NSPS. 

EPA regulations at Part 125, Subpart D, authorizing the EPA Regional Administrators to establish 

alternative limitations and standards, further detail the substantive criteria used to evaluate FDF variance 

requests for direct dischargers. The regulations at § 125.31(d) identify six factors that may be considered 

in determining if a facility is fundamentally different: 

 Nature or quality of pollutants contained in the raw process wastewater. 

 Volume of the process wastewater and effluent discharged. 

 Non-water quality environmental impact of control and treatment of the raw wasteload. 

 Energy requirements of the application of control and treatment technology. 

 Age, size, land availability, and configurations of discharger’s equipment or facilities as well as 

processes employed, process changes, and engineering aspects of the application of control 

technology. 

 Cost of compliance with required control technology. 

The Agency must determine whether, on the basis of one or more of those six factors, the facility in 

question is fundamentally different from the facilities and factors considered by EPA in developing the 

nationally applicable effluent guidelines. The regulation also lists four other factors that may not provide 

a basis for an FDF variance: 

 Infeasibility of installation within the time allowed by the CWA. 

 Assertion that the national limitations cannot be achieved with the appropriate waste treatment 

facilities installed (if the assertion is not based on one or more of the six FDF factors above). 

 A discharger’s ability to pay for the required water treatment. 

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 The impact of a discharge on local receiving water quality. 

In addition, under § 125.31(b)(3), a request for limitations less stringent than the national limitation may 

be approved only if compliance with the national limitations would result in either of the following: 

 Removal cost wholly out of proportion to the removal cost considered during development of the 

national limitations. 

 Non-water quality environmental impact (including energy requirements) fundamentally more 

adverse than the impact considered during development of the national limitations. 

The conditions for approval of a request to modify applicable pretreatment standards and factors 

considered are the same as those for direct dischargers. 

The legislative history of CWA section 301(n) underscores the necessity for the FDF variance applicant 

to establish eligibility for the variance. EPA’s regulations at § 125.32(b)(1) are explicit in imposing that 

burden on the applicant. The applicant must show that the factors relating to the discharge controlled by 

the applicant’s permit, which are claimed to be fundamentally different are, in fact, fundamentally 

different from those factors considered by the EPA in establishing the applicable effluent guidelines. The 

pretreatment regulations incorporate a similar requirement at § 403.13(h)(9). 

Intake Allowance or Net/Gross Variance 

Some facilities might be unable to comply with effluent guidelines because of pollutants in their intake 

water. Under certain circumstances, the NPDES regulations allow credit for pollutants in intake water. 

Specifically, permit writers are authorized to grant net credits for the quantity of pollutants in the intake 

water where (1) the applicable effluent guidelines specify that the guidelines are to be applied on a net 

basis; or (2) the pollution control technology would, if properly installed and operated, meet applicable 

effluent guidelines without the pollutants in the intake waters. The following requirements are included in 

§ 122.45(g) for establishing net limitations: 

 Credit for conventional pollutants, such as BOD5 or TSS, are only authorized where the 

constituents resulting in the effluent BOD5 and the TSS are similar between the intake water and 

the discharge. 

 Credit is authorized only up to the extent necessary to meet the applicable limitation or standard, 

with a maximum value equal to the influent concentration. 

 Intake water must be taken from the same body of water into which the discharge is made. 

 Net credits do not apply to the discharge of raw water clarifier sludge generated during the 

treatment of intake water. 

Permit writers must include influent monitoring in the permit when this type of variance is granted. 

Thermal Discharge—CWA Section 316(a) Variance 

CWA section 316(a) and the regulations at § 122.21(m)(6) provide for variances from thermal effluent 

limitations in NPDES permits. EPA has only promulgated thermal limitations in effluent guidelines for 

two industrial sectors: Beet Sugar Processing Subcategory of the Sugar Processing Point Source Category 

(Part 409 Subpart A) and the Cement Manufacturing Point Source Category (Part 411, Subparts A and B). 

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Most thermal limitations are based on water quality standards, so most thermal variances actually are not 

true technology-based variances. Dischargers must apply for a thermal discharge variance with its permit 

application if the thermal effluent limitation is based on an effluent guideline or during the permit 

comment period if the thermal effluent limitation is based on a WQBEL. 

Regulations for submitting and reviewing thermal discharge variance requests are promulgated at Part 

125, Subpart H. The approval authority for a thermal discharge variance request is the state permitting 

authority or the EPA Region if there is no approved state NPDES program. Less stringent alternative 

thermal effluent limitations may be included in permits if the discharger properly demonstrates that such 

effluent limitations are more stringent than necessary to assure the protection and propagation of a 

balanced, indigenous community of shellfish, fish and wildlife in and on the body of water into which the 

discharge is made, taking into account the cumulative impact of its thermal discharge together with all 

other significant impacts on the species affected. Once a variance is granted, the discharger must still 

reapply for the variance each permit term. The majority of thermal variance requests are from power 

plants seeking relief from water-quality based effluent limitations. 

Climate Change Considerations 

Evaluation of requests for variances under CWA section 316(a) requires consideration of the change 

to the ambient water temperature because of an effluent discharge. The studies provided by 

applicants to support their requests frequently include historical thermal data for the receiving water. 

Permitting authorities should be aware that the effects of global climate change could alter the thermal 

profile of some receiving waters making the historical record of thermal conditions less representative 

of future conditions. Where appropriate, water quality models should take these potential changes into 

account. 

5.2.2.8 Step 8: Apply Additional Requirements in Effluent Guidelines 

The effluent guidelines could provide additional requirements for permit writers to consider when 

applying them in NPDES permits. 

Industrial Stormwater 

Industrial stormwater is sometimes regulated by effluent guidelines. In particular, effluent guidelines 

often regulate stormwater for industrial activities that are unsheltered (e.g., mining, outdoor processing, 

outside storage of product materials). Examples of contaminated stormwater regulated by effluent 

guidelines include the Concentrated Animal Feeding Operations (Part 412), Fertilizer Manufacturing (Part 

418), Petroleum Refining (Part 419), Iron and Steel Manufacturing (Part 420), Pulp, Paper, and 

Paperboard (Part 430), Metal Products and Machinery (Part 438), and Ore Mining and Dressing (Part 

440) point source categories. The permit writer should identify any specific stormwater controls that may 

be required by the applicable effluent guidelines accordingly. 

Stormwater not regulated by effluent guidelines that is commingled with process wastewater will require 

the adjustment of the effluent limitations as discussed in Step 6 above. Section 2.3.2.3 of this manual 

provides additional information about stormwater discharges associated with industrial activities. 

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Identify the Analytical Methods for Measuring Compliance with TBELs 

The permit writer should ensure that the permit specifies the use of the correct analytical methods for 

demonstrating compliance with TBELs derived from effluent guidelines. The effluent guidelines often 

require specific analytical methods. For example, the General Definitions section of the Meat and Poultry 

Products effluent guidelines [§ 432.2(l)] states, “The approved methods of analysis for the following six 

parameters [Ammonia (as N), BOD5, Oil and Grease (O&G), O&G as hexane extractable material 

(HEM), Total Nitrogen, TSS] are found in Table 1B in [§] 136.3. The nitrate/nitrite part of total 

nitrogen may also be measured by EPA Method 300.0 (incorporated by reference, see § 432.5).” 

Section 8.3 of this manual provides additional information on analytical methods in the NPDES 

permitting process. 

Documentation and Recordkeeping Requirements 

Specific documentation and recordkeeping requirements (e.g., solvent management plans, BMP plans, 

alternative monitoring requirements) may be included in the applicable effluent guidelines. The permit 

writer should ensure that the documentation and recordkeeping requirements are included in the NPDES 

permit. For example, to use the alternative monitoring compliance method for controlling toxic organics 

in the Metal Finishing effluent guidelines, the NPDES permit applicant must not only make a certification 

statement (see Exhibit 5-15), but must also “submit a solvent management plan that specifies to the 

satisfaction of the permitting authority (or, in the case of indirect dischargers, the control authority) the 

toxic organic compounds used; the method of disposal used instead of dumping, such as reclamation, 

contract hauling, or incineration; and procedures for ensuring that toxic organics do not routinely spill or 

leak into the wastewater” as required by § 433.12(b). Other examples of such documentation and 

recordkeeping requirements include the BMP Plans used in the Oil and Gas Extraction (Part 435) and the 

Concentrated Aquatic Animal Production effluent guidelines (Part 451), the pollution prevention 

alternative in the Pesticide Chemicals effluent guidelines (Part 455), and alternative monitoring 

requirements (e.g., certification in lieu of monitoring for chloroform, in the Pulp, Paper, and Paperboard 

effluent guidelines (Part 430). 

5.2.2.9 Step 9: Document the Application of Effluent Guidelines in the Fact Sheet 

Permit writers need to document their application of effluent guidelines in the NPDES permit fact sheet. 

The permit writer should clearly identify the data and information used to determine the applicable 

effluent guidelines and how that information was used to derive effluent limitations for the permit. The 

information in the fact sheet should provide the NPDES permit applicant and the public a transparent, 

reproducible, and defensible description of how the NPDES permit properly incorporates effluent 

guidelines. 

Similarly, permit writer should also document the rationale for concluding that there are no applicable 

effluent guidelines for a discharge or pollutant. In such cases, TBELs may be determined by the permit 

writer on a case-by-case basis as discussed in section 5.2.3 below. 

5.2.3 Case-by-Case TBELs for Industrial Dischargers 

As previously stated, § 125.3(a) indicates that technology-based treatment requirements under CWA 

section 301(b) represent the minimum level of control that must be imposed in an NPDES permit. 

5-44 Chapter 5: Technology-Based Effluent Limitations 
September 2010 NPDES Permit Writers’ Manual 

Where EPA-promulgated effluent guidelines are not applicable to a non-POTW discharge, such 

requirements are established on a case-by-case basis using BPJ. 

5.2.3.1 Legal Authority to Establish Case-by-Case TBELs 

Case-by-case TBELs are developed pursuant to CWA section 402(a)(1), which authorizes the EPA 

Administrator to issue a permit that will meet either all applicable requirements developed under the 

authority of other sections of the CWA (e.g., technology-based treatment standards, water quality 

standards, ocean discharge criteria) or, before taking the necessary implementing actions related to those 

requirements, “such conditions as the Administrator determines are necessary to carry out the provisions 

of this Act.” The regulation at § 125.3(c)(2) specifically cites this section of the CWA, stating that 

technology-based treatment requirements may be imposed in a permit “on a case-by-case basis under 

section 402(a)(1) of the Act, to the extent that EPA-promulgated effluent limitations are inapplicable.” 

Further, § 125.3(c)(3) indicates that “where promulgated effluent limitations guidelines only apply to 

certain aspects of the discharger’s operation, or to certain pollutants, other aspects or activities are subject 

to regulation on a case-by-case basis to carry out the provisions of the Act.” When establishing case-bycase effluent limitations using BPJ, the permit writer should cite in the fact sheet or statement of basis 

both the approach used to develop the limitations, which is discussed further below, and how the 

limitations carry out the intent and requirements of the CWA and the NPDES regulations. 

5.2.3.2 Identifying the Need for Case-by-Case TBELs 

As noted above, case-by-case TBELs are established in situations where EPA promulgated effluent 

guidelines are inapplicable. That includes situations such as the following: 

 When EPA has not yet promulgated effluent guidelines for the point source category to which a 

facility belongs (e.g., a facility that produced distilled and blended liquors [SIC code 2085] and is 

part of the miscellaneous foods and beverages category, which does not now have any applicable 

effluent guidelines). 

 When effluent guidelines are available for the industry category, but no effluent guidelines are 

available for the facility subcategory (e.g., discharges from coalbed methane wells are not now 

regulated by effluent guidelines; however, EPA considers the coalbed methane industrial sector 

as a potential new subcategory of the existing Oil and Gas Extraction point source category [Part 

435] because of the similar industrial operations performed [i.e., drilling for natural gas 

extraction]). 

 When effluent guidelines are available for the industry category but are not applicable to the 

NPDES permit applicant (e.g., facilities that do not perform the industrial operation triggering 

applicability of the effluent guidelines or do not meet the production or wastewater flow cutoff 

applicability thresholds of the effluent guidelines). For example, assume that the poultry 

slaughterhouse in Example 2 of Exhibit 5-13 above produces 50 million pounds of whole, halved, 

quarter or smaller meat cuts annually. In that case, any TBELs for the facility would be case-bycase limitations developed using BPJ because the facility is below the annual production 

threshold of 100 million pounds listed in the effluent guideline (Part 432, Subpart K). 

 When effluent guidelines are available for the industry category, but no effluent guidelines 

requirements are available for the pollutant of concern (e.g., a facility is regulated by the effluent 

guidelines for Pesticide Chemicals [Part 455] but discharges a pesticide that is not regulated by 

Chapter 5: Technology-Based Effluent Limitations 5-45
September 2010 NPDES Permit Writers’ Manual 

these effluent guidelines). The permit writer should make sure that the pollutant of concern is not 

already controlled by the effluent guidelines and was not considered by EPA when the Agency 

developed the effluent guidelines. 

Generally, case-by-case limitations are appropriate when at least one of the conditions listed above 

applies and the pollutant is present, or expected to be present, in the discharge in amounts that can be 

treated or otherwise removed (e.g., implementation of pollution prevention measures). The resources 

listed in sections 5.2.2.2 above and 5.2.3.4 below will help the permit writer in making such 

determinations. For example, EPA’s effluent guidelines planning support documents on EPA’s Effluent 

Guidelines Biennial Plan Website <http://water.epa.gov/lawsregs/lawsguidance/cwa/304m/> identify facilities and 

industrial sectors that currently are not regulated by effluent guidelines. 

5.2.3.3 Factors Considered When Developing Case-by-Case TBELs 

The NPDES regulations at § 125.3(c)(2) require that permit writers developing case-by-case effluent 

limitations consider the following: 

 The appropriate technology for the category class of point sources of which the applicant is a 

member, based on all available information. 

 Any unique factors relating to the applicant. 

The regulations also require that, in setting case-by-case limitations, the permit writer consider several 

specific factors established in § 125.3(d) to select a model treatment technology and derive effluent 

limitations on the basis of that treatment technology. That process and the factors considered by the 

permit writer are the same factors required to be considered by EPA in developing effluent guidelines 

and, therefore, are often referred to as the CWA section 304(b) factors. The factors are summarized below 

in Exhibit 5-21. The permit writer evaluates case-by-case limitations based on BPT, BCT, and BAT and 

uses the more stringent technology level of control for each pollutant of concern. 

Exhibit 5-21 Summary of factors considered when developing case-by-case TBELs 

For BPT requirements (all pollutants) 

 The age of equipment and facilities involved* 

 The process(es) employed* 

 The engineering aspects of the application of various types of control techniques* 

 Process changes* 

 Non-water quality environmental impact including energy requirements* 

 The total cost of application of technology in relation to the effluent reduction benefits to be achieved from such 

application 

For BCT requirements (conventional pollutants) 

 All items in the BPT requirements indicated by an asterisk (*) above 

 The reasonableness of the relationship between the costs of attaining a reduction in effluent and the derived 

effluent reduction benefits 

 The comparison of the cost and level of reduction of such pollutants from the discharge of POTWs to the cost 

and level of reduction of such pollutants from a class or category of industrial sources 

For BAT requirements (toxic and non-conventional pollutants) 

 All items in the BPT requirements indicated by an asterisk (*) above 

 The cost of achieving such effluent reduction 

5-46 Chapter 5: Technology-Based Effluent Limitations 
September 2010 NPDES Permit Writers’ Manual 

The CWA also gives the permit writer the authority to consider process changes to evaluate case-by-case 

limitations. As previously stated, technology-based controls in NPDES permits are performance-based 

measures. EPA incorporates technology-based controls in NPDES permits that correspond to the 

application of an identified technology (including process changes) but does not require dischargers to 

install the identified technology. Therefore, EPA leaves to each facility the discretion to select the 

technology design or process changes necessary to meet the TBELs specified in the NPDES permit. 

The permit writer might need to establish a monitoring-only requirement in the current NPDES permit to 

identify pollutants of concern and potential case-by-case limitations for the subsequent NPDES permit 

renewal. 

5.2.3.4 Resources for Developing Case-by-Case TBELs 

There are numerous resources for identifying candidates for model technologies or process changes and 

developing case-by-case TBELs using BPJ. Exhibit 5-22 lists some example references that permit 

writers can use to derive such limitations. 

5.2.3.5 Statistical Considerations When Establishing Case-by-Case TBELs 

The quality of the effluent from a treatment facility will normally vary over time. If, for example, BOD5

data for a typical treatment plant were plotted against time, one would observe day-to-day variations of 

effluent concentrations. Some of that behavior can be described by constructing a frequencyconcentration plot. From the plot, one could observe that for most of the time, BOD5 concentrations are 

near some average value. Any treatment system can be described using the mean concentration of the 

parameter of interest (i.e., the long-term average) and the variance (or coefficient of variation) and by 

assuming a particular statistical distribution (usually lognormal). 

When developing a case-by-case limitation, permit writers can use an approach consistent with the 

statistical approach EPA has used to develop effluent guidelines. Specifically, the maximum daily 

limitation could be calculated by multiplying the long-term average achievable by implementation of the 

model technology or process change by a daily variability factor determined from the statistical properties 

of a lognormal distribution. The average monthly limitation can be calculated similarly except that the 

variability factor corresponds to the distribution of monthly averages instead of daily concentration 

measurements. The daily variability factor is a statistical factor defined as the ratio of the estimated 99th 

percentile of a distribution of daily values divided by the mean of the distribution. Similarly, the monthly 

variability factor is typically defined as the estimated 95th percentile of the distribution of monthly 

averages divided by the mean of the distribution of monthly averages. 

A modified delta-lognormal distribution could be fit to concentration data and variability factors 

computed for the facility distribution. The modified delta-lognormal distribution models the data as a 

mixture of measured values and observations recorded as values less than the detectable level. This 

distribution often is selected because the data for many analytes consist of such a mixture of measured 

values and results below the detectable level. The modified delta-lognormal distribution assumes that all 

non-detected results have a value equal to the detection limitations and that the detected values follow a 

lognormal distribution. 

Chapter 5: Technology-Based Effluent Limitations 5-47
September 2010 NPDES Permit Writers’ Manual 

Exhibit 5-22 Tools for developing case-by-case TBELs using BPJ 

Permit file information 

 Current and previous NPDES application forms. 

 Previous NPDES permit and fact sheet. 

 Discharge monitoring reports. 

 Compliance inspection reports. 

Information from existing facilities and permits 

 NPDES Individual and General Permits for other NPDES permits issued to facilities in the same region or state, 

or that include case-by-case limitations for the same pollutants. 

 Toxicity reduction evaluations for selected industries. 

 Other media permit files (e.g., Resource Conservation and Recovery Act [RCRA] permit applications and Spill 

Prevention Countermeasure and Control [SPCC] plans. 

 ICIS-NPDES <https://icis.epa.gov/icis> data. 

 Literature (e.g., technical journals and books). 

Effluent guidelines development and planning information 

 Industry experts within EPA headquarters, EPA Regions, and states <www.epa.gov/guide/contacts.html>. 

 Development Documents, CWA section 308 questionnaires, screening and verification data, proposed and final 

regulations, contractor’s reports, and project officer contacts <www.epa.gov/guide>. 

 EPA’s Technical Support Documents <http://water.epa.gov/lawsregs/lawsguidance/cwa/304m/> and records 

supporting EPA’s biennial effluent guidelines program plans also provide additional useful information. In 

particular, such resources provide a sample of the current limitation and latest developments in industrial 

pollutant prevention, water conservation, and wastewater treatment. The Technical Support Documents also 

identify industrial sectors not currently regulated by effluent guidelines. 

Statistical guidance 

 Effluent Guidelines Technical Development Support Documents, such as the Development Document for Final 

Effluent Limitations Guidelines and Standards for the Iron and Steel Manufacturing Point Source Category 

<www.epa.gov/guide/>. 

Economics guidance 

 Protocol and Workbook for Determining Economic Achievability for NPDES Permits9

<www.epa.gov/npdes/pubs/protocol_npdespermits.pdf> and <www.epa.gov/npdes/pubs/workbook_econ_permits.pdf>. 

 BCT Cost Test Guidance <www.epa.gov/npdes/pubs/owm0009.pdf>. 

Guidance for BMP-based limitations 

 Guidance Manual for Developing Best Management Practices (BMPs)10

<www.epa.gov/npdes/pubs/owm0274.pdf>. 

 Storm Water Management for Industrial Activities: Developing Pollution Prevention Plans and 

BMPs11<www.epa.gov/npdes/pubs/contents_indguide.pdf>. 

 National Menu of Stormwater Best Management Practices <www.epa.gov/npdes/stormwater/menuofbmps>. 

For more details on EPA’s use of statistical methods for developing effluent guidelines, refer to 

Development Document for Final Effluent Limitations Guidelines and Standards for the Iron and Steel 

Manufacturing Point Source Category <www.epa.gov/guide/ironsteel/reg/tdd.htm>. 

5.2.3.6 Documenting Case-by-Case TBELs in the Permit Fact Sheet 

Permit writers will need to document the development of case-by-case limitations in the NPDES permit 

fact sheet. The permit writer should clearly identify the data and information used in developing these 

effluent limitations and how that information was used. The permit writer also should document the 

rationale for concluding that there are no applicable effluent guidelines for the industrial wastewater or 

pollutant discharge. The information in the fact sheet should provide the NPDES permit applicant and the 

public a transparent, reproducible, and defensible description of how the BPJ limitations comply with the 

CWA and EPA regulations. 

5-48 Chapter 5: Technology-Based Effluent Limitations 
September 2010 NPDES Permit Writers’ Manual 

Chapter 5: Technology-Based Effluent Limitations 5-49

 1

 U.S. Environmental Protection Agency. 1985. Draft Guidance for NPDES Permits and Compliance Personnel—Secondary 

Treatment Redefinition. U.S. Environmental Protection Agency. Office of Water Enforcement and Permits. Washington, DC. 

2

 U.S. Environmental Protection Agency. 1994. Amended Section 301(h) Technical Support Document. EPA-842-B-94-007. 

U.S. Environmental Protection Agency. Office of Wetlands Oceans and Watersheds, Washington, DC. 

3

 U.S. Environmental Protection Agency. 1977. Interim Final Supplement for Pretreatment to the Development Document for the 

Petroleum Refining Industry Existing Point Source Category, EPA-440-1-76-083A. Page 92. U.S. Environmental Protection 

Agency, Office of Water and Hazardous Materials, Washington, DC. Publication available on NEPIS Website 

<www.epa.gov/nscep/> as document 440176083A. 

4

 Boornazian, Linda and Mary Smith. 2006. New Source Dates for Direct and Indirect Dischargers. U.S. Environmental 

Protection Agency, Office of Water Memorandum. September 28, 2006. <www.epa.gov/npdes/pubs/newsource_dates.pdf>. 

5

 U.S. Environmental Protection Agency. 1987. Development Document for Effluent Limitations Guidelines and Standards for 

the Organic Chemicals, Plastics and Synthetic Fibers Point Source Category. EPA 440-1-87-009. Page IX-9. 

<www.epa.gov/waterscience/guide/ocpsf/#guidance>. 

6

 Jordan, J.W. 1984. Calculations of Production-Based Effluent Limits. U.S. Environmental Protection Agency, Office of Water, 

Washington, DC. Memorandum, December 18, 1984. <www.epa.gov/npdes/pubs/owm0427.pdf>. 

7

 U.S. Environmental Protection Agency. 2001. Permit Guidance Document: Transportation Equipment Cleaning Point Source 

Category (40 CFR 442), p. 30. EPA-821-R-01-021. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/waterscience/guide/teci/tecguid.pdf>. 

8

 U.S. Environmental Protection Agency. 2004. Technical Development Document for the Final Effluent Limitations Guidelines 

and Standards for the Meat and Poultry Products Point Source Category (40 CFR 432), EPA-821-R-04-011. U.S. Environmental 

Protection Agency, Office of Water, Washington, DC. <www.epa.gov/waterscience/guide/mpp/final/tdd15.pdf>. 

9

 Putnam, Hayes and Bartlett, Inc. 1982. Protocol and Workbook for Determining Economic Achievability for National Pollutant 

Discharge Elimination System Permits. U.S. Environmental Protection Agency, Permits Division, Washington, DC. 

<www.epa.gov/npdes/pubs/protocol_npdespermits.pdf.> and <www.epa.gov/npdes/pubs/workbook_econ_permits.pdf> 

10 U.S. Environmental Protection Agency. 1993. Guidance Manual for Developing Best Management Practices (BMP). EPA 

833-B-93-004. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/owm0274.pdf>. 

11 U.S. Environmental Protection Agency. 1992. Storm Water Management for Industrial Activities: Developing Pollution 

Prevention Plans and BMPs. EPA 832-R-92-006. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/contents_indguide.pdf>. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 6: Water Quality-Based Effluent Limitations 6-1

CHAPTER 6. Water Quality-Based Effluent Limitations 

When drafting a National Pollutant Discharge Elimination System (NPDES) permit, a permit writer must 

consider the impact of the proposed discharge on the quality of the receiving water. Water quality goals 

for a waterbody are defined by state water quality standards. By analyzing the effect of a discharge on the 

receiving water, a permit writer could find that technology-based effluent limitations (TBELs) alone will 

not achieve the applicable water quality standards. In such cases, the Clean Water Act (CWA) and its 

implementing regulations require development of water quality-based effluent limitations (WQBELs). 

WQBELs help meet the CWA objective of restoring and maintaining the chemical, physical, and 

biological integrity of the nation’s waters and the goal of water quality that provides for the protection 

and propagation of fish, shellfish, and wildlife and recreation in and on the water (fishable/swimmable). 

WQBELs are designed to protect water quality by ensuring that water quality standards are met in the 

receiving water. On the basis of the requirements of Title 40 of the Code of Federal Regulations (CFR) 

125.3(a), additional or more stringent effluent limitations and conditions, such as WQBELs, are imposed 

when TBELs are not sufficient to protect water quality. Exhibit 6-1 illustrates the relationship between 

TBELs and WQBELs in an NPDES permit, as well as the determination of final effluent limitations. 

Exhibit 6-1 Developing effluent limitations 

CWA section 301(b)(1)(C) requires that permits include any effluent limitations necessary to meet water 

quality standards. As illustrated above, to satisfy that requirement, permit writers implement a process to 

determine when existing effluent limitations (e.g., TBELs) and existing effluent quality are not sufficient 

to comply with water quality standards and to, where necessary, develop WQBELs. Exhibit 6-2 illustrates 

the four basic parts of the standards-to-permits process used to assess the need for and develop WQBELs. 
September 2010 NPDES Permit Writers’ Manual 

After completing that process, the permit writer determines the final effluent limitations, includes any 

compliance schedules and interim effluent limitations, as appropriate, and documents all his or her 

decisions and calculations. 

Exhibit 6-2 Standards-to-permits process 

This chapter provides basic information on the standards-to-permits process. For more detailed 

information on water quality standards and water quality-based permitting, and some of the specific 

topics discussed in this chapter, refer to the NPDES Website <www.epa.gov/npdes> and Water Quality 

Standards Website <www.epa.gov/waterscience/standards>. 

6.1 Determine Applicable Water Quality Standards 

CWA section 303(c) and Part 131 establish the framework for water quality standards. The CWA and 

implementing regulations require states to develop and, from time to time, revise water quality standards 

applicable to waters of the United States, or segments of such waterbodies, that are in the jurisdiction of 

the state. States must review their water quality standards at least once every 3 years and revise them as 

appropriate. Wherever attainable, water quality standards should protect water quality that provides for 

the protection and propagation of fish, shellfish and wildlife, and recreation in and on the water (i.e., the 

CWA section 101(a)(2) fishable/swimmable goal). In establishing standards, states must consider the use 

and value of their waters for public water supplies, propagation of fish and wildlife, recreation, agriculture 

and industrial purposes, and navigation. The U.S. Environmental Protection Agency (EPA) has provided 

information regarding procedures for developing water quality standards in the Water Quality Standards 

Regulation at Part 131 and EPA’s Water Quality Standards Handbook: Second Edition1

<www.epa.gov/waterscience/library/wqstandards/handbook.pdf.> (hereafter WQS Handbook). Under CWA section 

510, states may develop water quality standards that are more stringent than those required by the CWA. 

6-2 Chapter 6: Water Quality-Based Effluent Limitations 
September 2010 NPDES Permit Writers’ Manual 

EPA Regions review and approve or disapprove new and revised water quality standards adopted by 

states. The purpose of EPA’s review is to ensure that the new and revised water quality standards meet 

the requirements of the CWA and the Water Quality Standards Regulation. Water quality standards 

adopted and submitted to EPA after May 30, 2000, must be approved by EPA before they may be used to 

implement the CWA (e.g., used in NPDES permitting). If an EPA Region disapproves a submitted new or 

revised state water quality standard, and the state does not adopt the necessary changes within 90 days of 

notification of the disapproval, EPA must promptly propose and promulgate a replacement standard [see 

§ 131.22(a)]. 

When writing an NPDES permit, the permit writer must identify and use the state water quality standards 

in effect for CWA purposes. EPA maintains a compilation of current state water quality standards on the 

Water Quality Standards: State, Tribal, & Territorial Standards Website 

<www.epa.gov/waterscience/standards/wqslibrary/>. In addition, EPA’s Water Quality Standards: Laws and 

Regulations Website <www.epa.gov/waterscience/standards/rules/> provides federally promulgated standards 

applicable to specific states. The remainder of this section provides permit writers with a general 

overview of water quality standards and how they are implemented in NPDES permits. 

6.1.1 Components of Water Quality Standards 

Water quality standards comprise three parts: 

 Designated uses. 

 Numeric and/or narrative water quality criteria. 

 Antidegradation policy. 

Each of those three components, along with general policies that also may be included in state water 

quality standards, is described below. 

6.1.1.1 Designated Uses (§ 131.10) 

The first part of a state’s water quality standards is a classification system for waterbodies based on the 

expected uses of those waterbodies. The uses in this system are called designated uses. The regulations at 

§ 131.10(a) describe various uses of waters that are considered desirable and that must be considered 

when establishing water quality standards. Those uses include public water supplies, propagation of fish, 

shellfish, and wildlife, recreation in and on the water, agricultural, industrial, and other purposes 

including navigation. The regulations allow states to designate more specific uses (e.g., cold water aquatic 

life) [see § 131.10(c)] or uses not specifically mentioned in the CWA, with the exception of waste 

transport and assimilation, which are not acceptable designated uses [see § 131.10(a)]. States must also 

consider and ensure the attainment and maintenance of the water quality standards of downstream waters 

when establishing designated uses [see § 131.10(b)]. 

The regulations in § 131.10(j) effectively establish a rebuttable presumption that the uses in CWA section 

101(a)(2) (fishable/swimmable) are attainable. If a state fails to designate a given waterbody for such 

uses, or wishes to remove such uses, it must provide appropriate documentation demonstrating why such 

uses are not attainable. This analysis is commonly called a Use Attainability Analysis (UAA) (see 

§ 131.3(g) and section 6.1.2.1 below). 

Chapter 6: Water Quality-Based Effluent Limitations 6-3
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6.1.1.2 Water Quality Criteria (§ 131.11) 

The second part of a state’s water quality standards is the set of water quality criteria sufficient to support 

the designated uses of each waterbody. EPA’s Water Quality Standards Regulation at § 131.11(a) requires 

states to adopt water quality criteria using sound scientific rationale and to include sufficient parameters 

or constituents to protect the designated use. If a waterbody has multiple use designations, the criteria 

must support the most sensitive use. The regulation at § 131.11(b) allows states to adopt both numeric and 

narrative water quality criteria. Numeric water quality criteria are developed for specific parameters to 

protect aquatic life and human health and, in some cases, wildlife from the deleterious effects of 

pollutants. States establish narrative criteria where numeric criteria cannot be established, or to 

supplement numeric criteria. Criteria newly adopted or revised on or after May 30, 2000, do not become 

effective for purposes of the CWA until approved by EPA [see § 131.21(c)]. 

CWA section 304(a) directs EPA to develop, publish, and, from time to time, revise criteria for water 

quality accurately reflecting the latest scientific knowledge on the following: 

 The kind and extent of all identifiable effects on health and welfare, including effects on aquatic 

life and recreational uses, that may be expected from the presence of pollutants in any body of 

water. 

 The concentration and dispersal of pollutants or their byproducts through biological, physical, and 

chemical processes. 

 The effects of pollutants on biological community diversity, productivity, and stability. 

EPA’s recommended criteria developed under CWA section 304(a) assist states in developing their water 

quality standards. EPA’s numeric criteria are ambient levels of individual pollutants or parameters or they 

describe conditions of a waterbody that, if met, generally will protect the CWA section 101(a)(2) fishable 

and swimmable uses. EPA’s recommended criteria developed under CWA section 304(a) do not reflect 

consideration of economic impacts or the technological feasibility of meeting the chemical concentrations 

in ambient water. EPA provides a table of the nationally recommended CWA section 304(a) criteria on 

the National Recommended Water Quality Criteria Website <www.epa.gov/waterscience/criteria/wqctable/>. The 

regulation at § 131.11(b)(1) indicates that, in establishing numeric criteria, states may (1) adopt EPA’s 

recommended criteria published under CWA section 304(a), (2) adopt those criteria modified to reflect 

site-specific conditions, or (3) adopt criteria based on other scientifically defensible methods. 

CWA section 303(c)(2)(B) specifically requires states to adopt numeric criteria for CWA section 307(a) 

toxic (priority) pollutants for which EPA has published recommended criteria if the discharge or presence 

of the pollutant can reasonably be expected to interfere with designated uses. Furthermore, § 131.11(a)(2) 

requires states to review water quality data and information on discharges to identify specific water 

bodies where toxic pollutants might be adversely affecting water quality or attainment of designated uses 

or where levels of toxic pollutants would warrant concern and to adopt criteria for such toxic pollutants 

applicable to the waterbody that are sufficient to protect the designated use. As discussed in section 1.2 

and presented in Exhibit C-1 in Appendix C of this manual, the CWA section 307(a) list contains 

65 compounds and families of compounds, which EPA has interpreted to include 126 toxic (priority) 

pollutants. 

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September 2010 NPDES Permit Writers’ Manual 

Numeric Criteria—Aquatic Life 

Numeric criteria for the protection of aquatic life are designed to protect aquatic organisms, including 

both plants and animals. EPA’s aquatic life criteria address both short-term (acute) and long-term 

(chronic) effects on both freshwater and saltwater species. Each of those criteria generally consists of 

three components: 

 Magnitude: The level of pollutant (or pollutant parameter), usually expressed as a concentration, 

that is allowable. 

 Duration: The period (averaging period) over which the in-stream concentration is averaged for 

comparison with criteria concentrations. 

 Frequency: How often criteria may be exceeded. 

Are criteria and effluent limitations expressed in the same terms? 

Generally, criteria and effluent limitations are not expressed in the same terms. As discussed above, 

criteria are generally expressed as a magnitude, duration and frequency. Effluent limitations in NPDES 

permits are generally expressed as a magnitude (e.g., milligrams per liter, micrograms per liter) and an 

averaging period (e.g., maximum daily, average weekly, average monthly). A permit writer should be 

aware of the procedures used by his or her permitting authority to appropriately reflect the magnitude, 

duration, and frequency components of aquatic life criteria when determining the need for and 

calculating effluent limitations for NPDES permits. Typically, the components of the criteria are 

addressed in water quality models through the use of statistically derived receiving water and effluent 

flow values that ensure that criteria are met under critical conditions (see section 6.2 below). 

Exhibit 6-3 is an example of freshwater aquatic life criteria for cadmium from the National 

Recommended Water Quality Criteria Website <www.epa.gov/waterscience/criteria/wqctable/> and at 66 FR 

18935, April 12, 2001, Notice of Availability of 2001 Update: Aquatic Life Criteria Document for 

Cadmium <www.epa.gov/EPA-WATER/2001/April/Day-12/w9056.htm>. 

Exhibit 6-3 Aquatic life criteria example: Cadmium (dissolved) 

Except possibly where a locally important species is unusually sensitive, freshwater aquatic organisms and their 

uses should not be affected unacceptably if 

Chronic criterion: 

The 4-day average concentration (in micrograms per liter [μg/L]) does not exceed the numerical value given by 

e(0.7409[ln(hardness)]-4.719) (1.101672 – [(ln hardness)(0.041838)]) more than once every 3 years on average. 

Acute criterion: 

The 24-hour average concentration (in μg/L) does not exceed the numerical value given by 

e(1.0166[ln(hardness)]-3.924) (1.136672 – [(ln hardness)(0.041838)]) more than once every 3 years on average. 

It is apparent that the acute and chronic aquatic life criteria for cadmium are not simply single numbers. 

Rather, they are expressed as a magnitude, a duration (4-day average or 24-hour average), and a 

frequency (not more than once every 3 years). Furthermore, the magnitude is expressed by a formula that 

is hardness-dependent, as is the case for most criteria for metals. 

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The magnitude of other aquatic life criteria can vary according to other conditions in the water or even 

based on the presence or absence of certain aquatic life. For example, EPA’s 1999 recommended 

ammonia criteria vary according to pH, temperature, the presence or absence of salmonid species, and the 

presence or absence of early life stages of fish. A permit writer must be aware of the applicable criteria 

and any state regulations, policies, and procedures for interpreting numeric criteria and for implementing 

the criteria in NPDES permits. The durations of aquatic life criteria vary as well. For example, EPA’s 

criteria recommendations for ammonia include a 30-day average chronic criterion. Also, many acute 

criteria for toxic pollutants are expressed as a 1-hour average. The frequency component of most aquatic 

life criteria specifies that they should be exceeded no more than once every three years. 

Some states have adopted numeric criteria for nutrients as part of their water quality standards. EPA has 

developed nutrient criteria recommendations that are numeric values for both causative (phosphorus and 

nitrogen) and response (chlorophyll a and turbidity) variables associated with the prevention and 

assessment of eutrophic conditions. EPA’s recommended nutrient criteria are different from most of its 

other recommended criteria, such as the criteria for cadmium and ammonia. First, EPA’s recommended 

nutrient criteria are ecoregional rather than nationally applicable criteria, and they can be refined and 

localized using nutrient criteria technical guidance manuals. Second, the recommended nutrient criteria 

represent conditions of surface waters that have minimal impacts caused by human activities rather than 

values derived from laboratory toxicity testing. Third, the recommended nutrient criteria are do not 

include specific duration or frequency components; however, the ecoregional nutrient criteria documents 

indicate that states may adopt seasonal or annual averaging periods for nutrient criteria instead of the 

1-hour, 24-hour, or 4-day average durations typical of aquatic life criteria for toxic pollutants. The 

ecoregional nutrient criteria documents, technical guidance manuals, and other information on EPA’s 

nutrient criteria recommendations, are available on the Water Quality Criteria for Nitrogen and 

Phosphorus Pollution Website <www.epa.gov/waterscience/criteria/nutrient/>.

Water quality standards also typically include aquatic life criteria for parameters such as temperature and 

pH that are not chemical constituents. Criteria for pH generally are expressed as an acceptable pH range 

in the waterbody. Temperature criteria might be expressed as both absolute temperature values (e.g., 

temperature may not exceed 18 degrees Celsius [°C]) and restrictions on causing changes in temperature

in the waterbody (e.g., discharges may not warm receiving waters by more than 0.5 °C). 

In addition to criteria for individual pollutants or pollutant parameters, many states include in their water 

quality standards criteria for dissolved oxygen. Often, criteria for dissolved oxygen are addressed by 

modeling and limiting discharges of oxygen-demanding pollutants such as biochemical oxygen demand 

(BOD), chemical oxygen demand (COD), and nutrients (phosphorus and nitrogen). 

Finally, states could also include in their water quality standards numeric criteria to address the effect of 

mixtures of pollutants. For example, whole effluent toxicity (WET) criteria protect the waterbody from 

the aggregate and synergistic toxic effects of a mixture of pollutants. WET is discussed in detail later in 

this chapter. 

Numeric Criteria—Human Health 

Human health criteria for toxic pollutants are designed to protect people from exposure resulting from 

consumption of fish or other aquatic organisms (e.g., mussels, crayfish) or from consumption of both 

water and aquatic organisms. These criteria express the highest concentrations of a pollutant that are not 

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expected to pose significant long-term risk to human health. Exhibit 6-4 is an example of human health 

criteria for dichlorobromomethane. 

Exhibit 6-4 Human health criteria example: Dichlorobromomethane 

For the protection of human health from the potential carcinogenic effects of dichlorobromomethane through 

ingestion of water and contaminated aquatic organisms, the ambient water criterion is determined to be 0.55 μg/L. 

For the protection of human health from the potential carcinogenic effects of dichlorobromomethane through 

ingestion contaminated aquatic organisms alone, the ambient water criterion is determined to be 17 μg/L. 

These values were calculated based on a national default freshwater/estuarine fish consumption rate of 

17.5 grams per day. 

Other criteria for protection of human health (e.g., bacteria criteria) consider a shorter-term exposure 

through uses of the waterbody such as contact recreation. EPA’s current bacteria criteria 

recommendations use enterococci and Escherichia coli bacteria as indicators and include two 

components: a geometric mean value and a single sample maximum value. EPA has developed 

information on implementing those criteria in water quality standards on the Microbial (Pathogen) Water 

Quality Criteria Website <www.epa.gov/waterscience/criteria/humanhealth/microbial/>. 

Other Numeric Criteria 

In addition to aquatic life and human health criteria, some state water quality standards include other 

forms of numeric criteria, such as wildlife, sediment, and biocriteria. 

Wildlife criteria are derived to establish ambient concentrations of chemicals that, if not exceeded, will 

protect mammals and birds from adverse impacts resulting from exposure to those chemicals through 

consumption of aquatic organisms and water. EPA established four numeric criteria to protect wildlife in 

the Great Lakes system in its Final Water Quality Guidance for the Great Lakes System

<www.epa.gov/EPA-WATER/1995/March/Day-23/pr-82.html> (60 FR 15387, March 23, 1995). 

In a healthy aquatic community, sediments provide a habitat for many living organisms. Controlling the 

concentration of pollutants in the sediment helps to protect bottom-dwelling species and prevents harmful 

toxins from moving up the food chain and accumulating in the tissue of animals at progressively higher 

levels. For more information on this topic, see EPA’s Suspended and Bedded Sediments Website

<www.epa.gov/waterscience/criteria/sediment/>. 

The presence, condition and numbers of types of fish, insects, algae, plants, and other organisms are data 

that, together, provide direct, accurate information about the health of specific bodies of water. Biological 

criteria (biocriteria) are narrative or numeric expressions that describe the reference biological integrity 

(structure and function) of aquatic communities inhabiting waters of a given designated aquatic life use. 

Biocriteria are based on the numbers and kinds of organisms present and are regulatory-based biological 

measurements. They are used as a way of describing the qualities that must be present to support a desired 

condition in a waterbody, and they serve as the standard against which biological assessment results are 

compared. EPA’s Biocriteria: Uses of Data in NPDES Permits Website

<www.epa.gov/waterscience/biocriteria/watershed/npdes.html> provides more information on the use of 

bioassessment information. 

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Narrative Criteria 

All states have adopted narrative water quality criteria to supplement numeric criteria. Narrative criteria 

are statements that describe the desired water quality goal for a waterbody. Narrative criteria, for 

example, might require that discharges be “free from toxics in toxic amounts” or be “free of objectionable 

color, odor, taste, and turbidity.” Narrative criteria can be the basis for limiting specific pollutants for 

which the state does not have numeric criteria [§ 122.44(d)(1)(vi)] or they can be used as the basis for 

limiting toxicity using WET requirements where the toxicity has not yet been traced to a specific pollutant 

or pollutants [§ 122.44(d)(1)(v)]. For toxic pollutants, EPA’s Water Quality Standards Regulation at 

§ 131.11(a)(2) requires states to develop implementation procedures for toxics narrative criteria that 

address how the state intends to regulate point source discharges of toxic pollutants to water quality 

limited segments. 

6.1.1.3 Antidegradation Policy (§ 131.12) 

The third part of a state’s water quality standards is its antidegradation policy. Each state is required to 

adopt an antidegradation policy consistent with EPA’s antidegradation regulations at § 131.12. A state’s 

antidegradation policy specifies the framework to be used in making decisions about proposed activities 

that will result in changes in water quality. Antidegradation policies can play a critical role in helping 

states protect the public resource of water whose quality is better than established criteria levels and 

ensure that decisions to allow reductions in water quality are made in a public manner and serve the 

public good. Along with developing an antidegradation policy, each state must identify the method it will 

use to implement the policy. It is important for permit writers to be familiar with their state’s 

antidegradation policy and how that policy is to be implemented in NPDES permits. 

A state’s antidegradation policy provides three levels of protection from degradation of existing water 

quality: 

 Tier 1: This tier requires that existing uses, and the level of water quality necessary to protect the 

existing uses, be maintained and protected. 

 Tier 2: Where the quality of waters exceeds levels necessary to support propagation of fish, 

shellfish, and wildlife and recreation in and on the water (sometimes referred to as high-quality 

waters), Tier 2 requires that this level of water quality be maintained and protected unless the 

state finds, after full satisfaction of the intergovernmental coordination and public participation 

provisions of the state’s continuing planning process, that allowing lower water quality is 

necessary to accommodate important economic or social development in the area where the 

waters are located. In allowing any such degradation or lower water quality, the state must assure 

water quality adequate to protect existing uses fully and must assure that there will be achieved 

the highest statutory and regulatory requirements for all new and existing point sources and all 

cost-effective and reasonable best management practices for nonpoint source control.

 Tier 3: This tier requires that the water quality of outstanding national resources waters

(ONRWs) be maintained and protected.

States take a variety of approaches to implementing antidegradation policies. Some states designate their 

waters as Tier 1, Tier 2 (high-quality water) or Tier 3 waters in their antidegradation implementation 

methods, while others designate a waterbody as a Tier 2 or high-quality water only when activities that 

would degrade water quality are proposed. In some cases, states may have classified the waterbody as 

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receiving a tier of protection for all pollutant-related parameters, whereas in other cases, tiers of 

protection have been determined on a parameter-by-parameter basis. 

6.1.1.4 General Policies (§ 131.13) 

In addition to the three required components of water quality standards, states may, at their discretion, 

include in their standards policies that generally affect how the standards are applied or implemented. 

Examples of such policies include mixing zone policies, critical low flows at which criteria must be 

achieved, and the availability of variances. Some general policies are discussed in more detail later in this 

chapter. As with the other components of water quality standards, general policies are subject to EPA 

review and approval if they are deemed to be new or revised water quality standards (i.e., if they 

constitute a change to designated use(s), water quality criteria, antidegradation requirements, or any 

combination). 

Additional and more detailed information on water quality standards is available in the WQS Handbook. 

6.1.2 Water Quality Standards Modifications 

Permit writers should be aware of several types of modifications to water quality standards that could 

permanently or temporarily change the standards and, thus, change the fundamental basis of WQBELs. 

Those modifications, described below, are as follows: 

 Designated use reclassification. 

 Site-specific water quality criteria modification. 

 Water quality standard variance. 

6.1.2.1 Designated Use Reclassification 

Once a use has been designated for a particular waterbody or segment, that use may not be removed from 

the water quality standards except under specific conditions. To remove a designated use, the state 

demonstrates that attaining that use is not feasible because of any one of the six factors listed in 

§ 131.10(g). The regulations at § 131.10(j) specifically require a state to conduct a UAA if the designated 

uses for a waterbody do not include the uses in CWA section 101(a)(2) (i.e., fishable/swimmable uses); if 

the state wishes to remove designated uses included in CWA section 101(a)(2) from its water quality 

standards; or if the state wishes to adopt subcategories of CWA section 101(a)(2) uses with less stringent 

criteria. The WQS Handbook discusses UAAs and removing designated uses in detail. Reclassifying a 

waterbody’s designated uses, as supported by a UAA, is a permanent change to both the designated use(s) 

and the water quality criteria associated with that (those) use(s). 

States may conduct a UAA and remove a designated use but not if it is an existing use. Existing uses are 

defined in § 131.3 as those uses actually attained in the waterbody on or after November 28, 1975 (the 

date of EPA’s initial water quality standards regulation at 40 Federal Register 55334, November 28, 

1975). At a minimum, uses are deemed attainable if they can be achieved by the implementing effluent 

limits required under CWA sections 301(b) and 306 and by implementing cost effective and reasonable 

best management practices (BMPs) for nonpoint source control. EPA’s Water Quality Standards: UAA 

Website <www.epa.gov/waterscience/standards/uses/uaa/index.htm> provides additional information and some 

example UAAs. 

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6.1.2.2 Site-Specific Water Quality Criteria Modification 

As noted above, CWA sections 303(a)–(c) require states to adopt water quality criteria sufficient to 

protect applicable designated uses. In some cases, a state might find that the criteria it has adopted to 

protect a waterbody or segment of a waterbody do not adequately account for site-specific conditions. In 

such cases, states have the option of modifying water quality criteria on a site-specific basis. Setting sitespecific criteria might be appropriate where, for example, a state has adopted EPA’s CWA section 304(a) 

criteria recommendations and finds that physical or chemical properties of the water at a site affect the 

bioavailability or toxicity of a chemical, or the types of local aquatic organisms differ significantly from 

those actually tested in developing the EPA-recommended criteria. Site-specific criteria modifications 

change water quality criteria permanently while continuing to support the current designated uses. 

Development of site-specific criteria for aquatic life is discussed in section 3.7 of the WQS Handbook for 

cases when (1) there might be relevant differences in the toxicity of the chemical in the water at the site 

and laboratory dilution water (Water-Effect Ratio Procedure) and (2). the species at the site are more or 

less sensitive than those used in developing the natural criteria (Species Recalculation Procedure). EPA’s 

Office of Science and Technology (OST) has developed the Interim Guidance on Determination and Use 

of Water-Effect Ratios for Metals <www.epa.gov/waterscience/standards/handbook/handbookappxL.pdf> in 

Appendix L of the WQS Handbook and the Streamlined Water-Effect Ratio Procedure for Discharges of 

Copper2 <www.epa.gov/waterscience/criteria/copper/copper.pdf>. In addition, pages 90-97 of Appendix L provide 

guidance for using the Species Recalculation Procedure. States may also consider establishing aquatic life 

criteria based on natural background conditions. Further information can be found in the memo 

Establishing Site Specific Aquatic Life Criteria Equal to Natural Background3

<www.epa.gov/waterscience/library/wqcriteria/naturalback.pdf>. 

6.1.2.3 Water Quality Standard Variance 

Water quality standard variances are changes to water quality standards and have similar substantive and 

procedural requirements as what are required to remove a designated use. Unlike use removal, variances 

are time-limited and do not permanently remove the current designated use of a waterbody. Variances are 

usually discharger- and pollutant-specific, though some states have adopted general variances. Where a 

state has adopted a general variance, the analyses necessary for the variance have been completed on a 

watershed-wide or statewide basis and, therefore, the process of obtaining a variance is simplified for 

individual dischargers in that watershed or state. 

A variance might be appropriate where the state believes that the existing standards are ultimately 

attainable and that, by retaining the existing standards rather than changing them, the state would ensure 

that further progress is made in improving the water quality toward attaining the designated uses while the 

variance is in effect. State-adopted variances have been approved by EPA where, among other things, the 

state’s standards allow variances and the state demonstrates that meeting the applicable criteria is not 

feasible on the basis of one or more of the factors outlined in § 131.10(g). A variance typically is granted 

for a specified period and must be reevaluated at least once every 3 years as reasonable progress is made 

toward meeting the standards [see section 5.3 of the WQS Handbook and § 131.20(a)]. 

Modifications of water quality standards could affect effluent limitations in permits in several ways. 

Specifically, the modifications can change the fundamental basis for WQBELs, potentially affecting an 

assessment of the need for WQBELs and possibly resulting in either more or less stringent WQBELs than 

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would otherwise be required. It is the permit writer’s responsibility to ensure that any EPA-approved 

modification of water quality standards is properly reflected in an affected NPDES permit. 

6.1.3 Water Quality Standards Implementation 

As previously noted, CWA section 301(b)(1)(C) requires NPDES permits to establish effluent limitations 

as necessary to meet water quality standards. Effluent limitations and other conditions in NPDES permits 

may be based on a parameter-specific approach or a WET testing approach to implementing water quality 

standards. A third approach to implementing water quality standards, using biocriteria or bioassessment, 

is not directly accomplished through NPDES permit effluent limitations but can lead to effluent 

limitations for specific parameters or for WET. Each of those approaches to implementing water quality 

standards is discussed briefly below. 

What procedures should permit writers use to implement water quality standards? 

The terminology used and procedures described in this manual when discussing both assessing the 

need for and calculating WQBELs are based on the procedures in EPA’s Technical Support Document 

for Water Quality-Based Toxics Control4 <www.epa.gov/npdes/pubs/owm0264.pdf> (hereafter TSD). Those 

procedures were developed specifically to address toxic pollutants but have been appropriately used 

to address a number of conventional and nonconventional pollutants as well. Permit writers should be 

aware that most permitting authorities have developed their own terminology and procedures for water 

quality-based permitting, often derived from, but with variations on, EPA’s guidance. For example, 

EPA itself promulgated Final Water Quality Guidance for the Great Lakes System (60 FR 15387, 

March 23, 1995) with minimum water quality criteria, antidegradation policies, and implementation 

procedures, including permitting procedures based on the TSD. Under the CWA, Illinois, Indiana, 

Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin were required to adopt 

procedures for the Great Lakes system that are consistent with that guidance. Permit writers should 

always consult the applicable permitting regulations, policy, and guidance for the approved water 

quality-based permitting procedures in their state. 

6.1.3.1 Parameter-Specific Approach 

The parameter-specific approach uses parameter-specific criteria for protection of aquatic life, human 

health, wildlife, and sediments, as well as any other parameter-specific criteria adopted into a state’s 

water quality standards. The criteria are the basis for analyzing an effluent, deciding which parameters 

need controls, and deriving effluent limitations that will control those parameters to the extent necessary 

to achieve water quality standards in the receiving water. Parameter-specific WQBELs in NPDES permits 

involve a site-specific evaluation of the discharge (or proposed discharge) and its potential effect on the 

receiving water or an evaluation of the effects of multiple sources of a pollutant on the receiving water 

(e.g., through a total maximum daily load [TMDL] analysis). The parameter-specific approach allows for 

controlling individual parameters, (e.g., copper, BOD, total phosphorus) before a water quality impact has 

occurred or for helping return water quality to a level that will meet designated uses. 

6.1.3.2 Whole Effluent Toxicity (WET) Approach 

WET requirements in NPDES permits protect aquatic life from the aggregate toxic effect of a mixture of 

pollutants in the effluent. WET tests measure the degree of response of exposed aquatic test organisms to 

an effluent. The WET approach is useful for complex effluents where it might be infeasible to identify 

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and regulate all toxic pollutants in the effluent or where parameter-specific effluent limitations are set, but 

the combined effects of multiple pollutants are suspected to be problematic. The WET approach allows a 

permit writer to implement numeric criteria for toxicity included in a state’s water quality standards or to 

be protective of a narrative “no toxics in toxic amounts” criterion. Like the parameter-specific approach, 

the WET approach allows permitting authorities to control toxicity in effluents before toxic impacts occur 

or may be used to help return water quality to a level that will meet designated uses. 

6.1.3.3 Bioassessment Approach 

The biocriteria approach is used to assess the overall biological integrity of an aquatic community. As 

discussed in section 6.1.1.2 above, biocriteria are numeric values or narrative statements that describe the 

biological integrity of aquatic communities inhabiting waters of a given designated aquatic life use. When 

incorporated into state water quality standards, biocriteria and aquatic life use designations serve as direct 

endpoints for determining aquatic life use attainment. Once biocriteria are developed, the biological 

condition of a waterbody can be measured through a biological assessment, or bioassessment. 

A bioassessment is an evaluation of the biological condition of a waterbody using biological surveys and 

other direct measurements of resident biota in surface waters. A biological survey, or biosurvey, consists 

of collecting, processing, and analyzing representative portions of a resident aquatic community to 

determine the community structure and function. The results of biosurveys can be compared to the 

reference waterbody to determine if the biocriteria for the designated use of the waterbody are being met. 

EPA issued guidance on this approach in Biological Criteria: National Program Guidance for Surface 

Waters5 <www.epa.gov/bioindicators/html/biolcont.html>. As previously discussed, biocriteria generally are not 

directly implemented through NPDES permits but could be used in assessing whether a waterbody is 

attaining water quality standards. Nonattainment of biocriteria could lead to parameter-specific effluent 

limitations where the permitting authority is able to identify specific pollutant(s) and source(s) 

contributing to that nonattainment (see EPA’s Biocriteria: Uses of Data – Identify Stressors to a 

Waterbody Website <www.epa.gov/waterscience/biocriteria/uses/stressors.html>) or could lead to WET limitations 

where the permitting authority identifies sources of toxicity to aquatic life. EPA’s Biocriteria: Uses of 

Data - NPDES <www.epa.gov/waterscience/biocriteria/watershed/npdes.html> provides examples on the use of 

bioassessment information in the NPDES permitting process. 

Sections 6.2–6.4 below discuss, in detail, implementing water quality standards using the parameterspecific approach to assess the need for and develop effluent limitations in NPDES permits. Section 6.5 

below provides additional detail on WET requirements in NPDES permits. 

6.2 Characterize the Effluent and the Receiving Water 

After identifying the most current, approved, water quality standards that apply to a waterbody, a permit 

writer should characterize both the effluent discharged by the facility being permitted and the receiving 

water for that discharge. The permit writer uses the information from those characterizations to determine 

whether WQBELs are required (section 6.3 below) and, if so, to calculate WQBELs (section 6.4 below). 

Characterizing the effluent and receiving water can be divided into five steps as shown in Exhibit 6-5 and 

discussed in detail below. 

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Exhibit 6-5 Steps for characterizing the effluent and receiving water 

Step 1. Identify pollutants of concern in the effluent 

Step 2. Determine whether water quality standards provide for consideration of a dilution 

allowance or mixing zone 

Step 3. Select an approach to model effluent and receiving water interactions 

Step 4. Identify effluent and receiving water critical conditions 

Step 5. Establish an appropriate dilution allowance or mixing zone 

6.2.1 Step 1: Identify Pollutants of Concern in the Effluent 

There are several sources of information for and methods of identifying pollutants of concern for 

WQBEL development. For some pollutants of concern, the permit writer might not need to conduct any 

further analysis and could, after characterizing the effluent and receiving water, proceed directly to 

developing WQBELs (section 6.4 below). For other pollutants of concern, the permit writer uses the 

information from the effluent and receiving water characterization to assess the need for WQBELs 

(section 6.3 below). The following subsections identify five categories of pollutants of concern for 

WQBEL development. 

6.2.1.1 Pollutants with Applicable TBELs 

One category of pollutants of concern includes those pollutants for which the permit writer has developed 

TBELs based on national or state technology standards or on a case-by-case basis using best professional 

judgment. By developing TBELs for a pollutant, the permit writer has already determined that there will 

be some type of final limitations for that pollutant in the permit and must then determine whether more 

stringent limitations than the applicable TBELs are needed to prevent an excursion above water quality 

standards in the receiving water (see Exhibit 6-1 above). A permit writer can determine whether the 

TBELs are sufficiently protective by either proceeding to calculate WQBELs as described in section 6.4 

below and comparing them to the TBELs or by assuming that the maximum daily TBEL calculated is the 

maximum discharge concentration in the water quality assessments described in section 6.3 below. 

6.2.1.2 Pollutants with a Wasteload Allocation from a TMDL 

Pollutants of concern include those pollutants for which a wasteload allocation (WLA) has been assigned 

to the discharge through a TMDL. Under CWA section 303(d), states are required to develop lists of 

impaired waters. Impaired waters are those that do not meet the water quality standards set for them, even 

after point sources of pollution have installed the minimum required levels of pollution control 

technology. The law requires that those jurisdictions establish priority rankings for waters on their CWA 

section 303(d) list and develop TMDLs for those waters. 

What is a WLA? 

The term WLA refers to the portion of a receiving water’s loading capacity that is allocated to one of its 

existing or future point sources of pollution [see § 130.2(h)]. The WLA could be allocated through an 

EPA-approved TMDL, an EPA or state watershed loading analysis, or a facility-specific water quality 

modeling analysis. 

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A TMDL is a calculation of the maximum amount of a single pollutant that a waterbody can receive and 

still meet water quality standards and an allocation of that amount to the pollutant’s sources. The portions 

of the TMDL assigned to point sources are WLAs, and the portions assigned to nonpoint sources and 

background concentrations of the pollutant are called load allocations (LAs). The calculation must 

include a margin of safety to ensure that the waterbody can be used for the purposes designated in the 

water quality standards, to provide for the uncertainty in predicting how well pollutant reduction will 

result in meeting water quality standards, and to account for seasonal variations. A TMDL might also 

include a reserve capacity to accommodate expanded or new discharges in the future. Exhibit 6-6 depicts 

the parts of a TMDL. 

Exhibit 6-6 Parts of a TMDL 

TMDL = ΣWLA + ΣLA + Margin of Safety + Reserve Capacity

The NPDES regulations at § 122.44(d)(1)(vii)(B) require that NPDES permits include effluent limitations 

developed consistent with the assumptions and requirements of any WLA that has been assigned to the 

discharge as part of an approved TMDL. Thus, any pollutant for which a WLA has been assigned to the 

permitted facility through a TMDL is a pollutant of concern. 

Permit writers might also choose to consider any pollutant associated with an impairment of the receiving 

water a pollutant of concern, regardless of whether an approved TMDL has been developed for that 

pollutant, a WLA has been assigned to the permitted facility, or the permitted facility has demonstrated 

that the pollutant is present in its effluent. Permitting authorities might consider monitoring requirements 

to collect additional data related to the presence or absence of the impairing pollutant in a specific 

discharge to provide information for further analyses. 

6.2.1.3 Pollutants Identified as Needing WQBELs in the Previous Permit 

Another category of pollutants of concern includes those pollutants that were identified as needing 

WQBELs in the discharger’s previous permit. Permit writers must determine whether the conditions 

leading to a decision to include WQBELs for the pollutant in the previous permit continue to apply. 

Where those conditions no longer apply, the permit writer would need to complete an anti-backsliding 

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analysis to determine whether to remove the WQBELs from the reissued permit. Chapter 7 of this manual 

provides additional information on anti-backsliding requirements of the CWA and NPDES regulations. In 

addition, the permit writer might need to conduct an antidegradation analysis if the revised limitation 

would allow degradation of the quality of the receiving water. 

6.2.1.4 Pollutants Identified as Present in the Effluent through Monitoring 

Pollutants of concern also include any pollutants identified as present in the effluent through effluent 

monitoring. Effluent monitoring data are reported in the discharger’s NPDES permit application, 

discharge monitoring reports and special studies. In addition, the permitting authority might collect data 

itself through compliance inspection monitoring or other special study. Permit writers can match 

information on which pollutants are present in the effluent to the applicable water quality standards to 

identify parameters that are candidates for WQBELs. 

6.2.1.5 Pollutants Otherwise Expected to be Present in the Discharge 

A final category of pollutants of concern includes those pollutants that are not in one of the other 

categories but are otherwise expected to be present in the discharge. There might be pollutants for which 

neither the discharger nor the permitting authority have monitoring data but, because of the raw materials 

stored or used, products or by-products of the facility operation, or available data and information on 

similar facilities, the permit writer has a strong basis for expecting that the pollutant could be present in 

the discharge. Because there are no analytical data to verify the concentrations of these pollutants in the 

effluent, the permit writer must either postpone a quantitative analysis of the need for WQBELs and 

generate, or require the discharger to generate, effluent monitoring data, or base a determination of the 

need for WQBELs on other information, such as the effluent characteristics of a similar discharge. A 

discussion on determining the need for WQBELs without effluent monitoring data is provided in section 

6.3.3 below. 

6.2.2 Step 2: Determine Whether Water Quality Standards Provide for 

Consideration of a Dilution Allowance or Mixing Zone 

Many state water quality standards have general provisions allowing some consideration of mixing of 

effluent and receiving water when determining the need for and calculating WQBELs. Depending on the 

state’s water quality standards and implementation policy, such a mixing consideration could be 

expressed in the form of a dilution allowance or regulatory mixing zone. A dilution allowance typically is 

expressed as the flow of a river or stream, or a portion thereof. A regulatory mixing zone generally is 

expressed as a limited area or volume of water in any type of waterbody where initial dilution of a 

discharge takes place and within which the water quality standards allow certain water quality criteria to 

be exceeded. Section 6.2.5 below discusses dilution allowances and mixing zones in greater detail. 

State water quality standards or implementation policies might indicate specific locations or conditions 

(e.g., breeding grounds for aquatic species or bathing beaches) or water quality criteria (e.g., pathogens, 

pH, bioaccumulative pollutants, or narrative criteria) for which consideration of a dilution allowance or 

mixing zone is not allowed or is otherwise considered inappropriate. 

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6.2.3 Step 3: Select an Approach to Model Effluent and Receiving Water 

Interactions 

Where consideration of a dilution allowance or mixing zone is not permitted by the water quality 

standards or is not appropriate, the relevant water quality criterion must be attained at the point of 

discharge. In such cases, there is no need for a water quality model to characterize the interaction between 

the effluent and receiving water. In this situation effluent limitations are based on attaining water quality 

criteria at the “end of the pipe.” 

Where a dilution allowance or mixing zone is permitted, however, characterizing the interaction between 

the effluent and receiving water generally requires using a water quality model. In the majority of 

situations, and in all of the examples provided in this manual, permit writers will use a steady-state water 

quality model to assess the impact of a discharge on its receiving water. Steady-state means that the 

model projects the impact of the effluent on the receiving water under a single or steady set of design 

conditions. Because the model is run under a single set of conditions, those conditions generally are set at 

critical conditions for protection of receiving water quality as discussed in section 6.2.4 below. The 

permit writer would determine the amount of the dilution allowance or the size of the mixing zone that is 

available under these critical conditions as provided in section 6.2.5 below. 

6.2.4 Step 4: Identify Effluent and Receiving Water Critical Conditions 

Where steady-state models are used for water quality-based permitting, an important part of 

characterizing the effluent and receiving water is identifying the critical conditions needed as inputs to the 

water quality model. Permit writers should discuss selection of critical conditions with water quality 

modelers or other water quality specialists. Identifying the right critical conditions is important for 

appropriately applying a water quality model to assess the need for WQBELs and to calculate WQBELs. 

Some key effluent and receiving water critical conditions are summarized below. 

What if I am not a water quality modeler? 

Permit writers are not always water quality modelers, nor do they necessarily need to be experts in 

this field. Many permitting authorities have a team of water quality specialists who model point source 

discharges to provide data required for permit writers to assess the need for and develop WQBELs. In 

some cases, this team might even calculate WQBELs directly for the permit writers, who then only 

need to compare them to TBELs and determine the final effluent limitations for the NPDES permit. 

Permit writers should, at a minimum, familiarize themselves with water quality modeling concepts 

presented in this manual, particularly the identification of critical conditions input to a steady-state 

water quality model, and should consult water quality modelers or other water quality specialists as 

needed in the process of NPDES permit development. 

6.2.4.1 Effluent Critical Conditions 

In most any steady-state water quality model there will be at least two basic critical conditions related to 

the effluent: flow and pollutant concentration. 

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Effluent Flow 

Effluent flow (designated Qd in the water quality modeling equations used in this manual) is a critical 

design condition used when modeling the impact of an effluent discharge on its receiving water. A permit 

writer should be able to obtain effluent flow data from discharge monitoring reports or a permit 

application. Permitting authority policy or procedures might specify which flow measurement to use as 

the critical effluent flow value(s) in various water quality-based permitting calculations (e.g., the 

maximum daily flow reported on the permit application, the maximum of the monthly average flows from 

discharge monitoring reports for the past three years, the facility design flow). Permit writers should 

follow existing policy or procedures for determining critical effluent flow or, if the permitting authority 

does not specify how to determine this value, look at past permitting practices and strive for consistency. 

Effluent Pollutant Concentration 

Permit writers can determine the critical effluent concentration of the pollutant of concern (designated Cd) 

by gathering effluent data representative of the discharge. To establish the critical effluent pollutant 

concentration from the available data, EPA has recommended considering a concentration that represents 

something close to the maximum concentration of the pollutant that would be expected over time. In most 

cases, permit writers have a limited effluent data set and, therefore, would not have a high degree of 

certainty that the limited data would actually include the maximum potential effluent concentration of the 

pollutant of concern. In addition, the NPDES regulations at § 122.44(d)(1)(ii) require that permit writers 

consider the variability of the pollutant in the effluent when determining the need for WQBELs. To 

address those concerns, EPA developed guidance for permit writers on how to characterize effluent 

concentrations of certain types of pollutants using a limited data set and accounting for variability. This 

guidance is detailed in EPA’s TSD. 

By studying effluent data for numerous facilities, EPA determined that daily pollutant measurements of 

many pollutants follow a lognormal distribution. The TSD procedures allow permit writers to project a 

critical effluent concentration (e.g., the 99th or 95th percentile of a lognormal distribution of effluent 

concentrations) from a limited data set using statistical procedures based on the characteristics of the 

lognormal distribution. These procedures use the number of available effluent data points for the 

measured concentration of the pollutant and the coefficient of variation (or CV) of the data set, which is a 

measure of the variability of data around the average, to predict the critical pollutant concentration in the 

effluent. Exhibit 6-7 provides an example of a lognormal distribution of effluent pollutant concentrations 

and projection of a critical effluent pollutant concentration (Cd). For additional details regarding EPA’s 

guidance, see Chapter 3 of the TSD. Many permitting authorities have developed procedures for 

estimating a critical effluent pollutant concentration that are based on or derived from those procedures. 

For pollutants with effluent concentrations that do not follow a lognormal distribution, permit writers 

would rely on alternative procedures developed by their permitting authority for determining the critical 

effluent pollutant concentration. 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 6-7 Example of lognormal distribution of effluent pollutant concentrations and 

projection of critical concentration (Cd) 

CV 

Relative frequency

Cd

(projected critical pollutant concentration 

in the effluent) 

Concentration 

6.2.4.2 Receiving Water Critical Conditions 

As with the effluent, flow (for rivers and streams) and pollutant concentration are receiving water critical 

conditions used in steady-state water quality models. In addition, depending on the waterbody and 

pollutant of concern, there could be additional receiving water characteristics that permit writers need to 

consider in a water quality model. 

Receiving Water Upstream Flow 

For rivers and streams, an important critical condition is the stream flow upstream of the discharge 

(designated Qs). That critical condition generally is specified in the applicable water quality standards and 

reflects the duration and frequency components of the water quality criterion that is being addressed. For 

most pollutants and criteria, the critical flow in rivers and streams is some measure of the low flow of that 

river or stream; however, the critical condition could be different (for example, a high flow, where wet 

weather sources are a major problem). If a discharge is controlled so that it does not cause water quality 

criteria to be exceeded in the receiving water at the critical flow condition, the discharge controls should 

be protective and ensure that water quality criteria, and thus designated uses, are attained under all 

receiving water flow conditions. 

Examples of typical critical hydrologically based low flows found in water quality standards include the 

7Q10 (7-day average, once in 10 years) low flow for chronic aquatic life criteria, the 1Q10 low flow for 

acute aquatic life criteria, and the harmonic mean flow for human health criteria for toxic organic 

pollutants. The permit writer might examine stream flow data from the state or the U.S. Geological 

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Survey to determine the critical flow at a point upstream of the discharge. The permit writer might also 

account for any additional sources of flow or diversions between the point where a critical low flow has 

been calculated and the point of discharge. EPA also has developed a biologically based flow method that 

directly uses the durations and frequencies specified in the water quality criteria. 

Climate Change Considerations 

As noted in this section, the receiving water upstream flow is an important factor in modeling the 

interaction between the effluent discharge and a river or stream. In most instances, state water quality 

standards or implementation policies establish the critical low flows that should be used in modeling 

this interaction. The most common source of upstream flow data for water quality modelers is historical 

flow gage data available through the U.S. Geological Survey. Modelers should be aware that the 

effects of climate change could alter historical flow patterns in rivers and streams, making these 

historical flow records less accurate in predicting current and future critical flows. Where appropriate, 

water quality modelers should consider alternate approaches to establishing critical low flow conditions 

that account for these climatic changes. 

Receiving Water Background Pollutant Concentration 

In addition to determining the critical effluent concentration of the pollutant of concern, the permit writer 

also should determine the critical background concentration of the pollutant of concern in the receiving 

water before the discharge (designated Cs) to ensure that any pollutant limitations derived are protective 

of the designated uses. Permitting authority policies or procedures often address how to determine that 

critical background concentration value for the pollutant. For example, using ambient data or working 

with the discharger to obtain reliable ambient data, the permit writer might use the maximum measured 

background pollutant concentration or, perhaps, an average of measured concentrations as the critical 

condition. Ambient data will provide the most reliable characterization of receiving water background 

pollutant concentration. EPA encourages permitting authorities to collect and use actual ambient data, 

where possible. Where data are not available, however, the state might have other procedures, such as 

establishing that without valid and representative ambient data, no dilution or mixing will be allowed 

(i.e., criteria end-of-pipe), or using a percentage of an applicable water quality criterion or a detection, 

quantitation, or other reporting level. The permit writer should consult the permitting authority’s policies 

and procedures or, if there are no policies or procedures available, look at past permitting practices and 

maintain consistency with those practices when determining the critical receiving water background 

concentrations. 

Other Receiving Water Characteristics 

For waterbodies other than free-flowing rivers and streams, there might be critical environmental 

conditions that apply rather than flow (e.g., tidal flux, temperature). In addition, depending on the 

pollutant of concern, the effects of biological activity and reaction chemistry might be important in 

assessing the impact of a discharge on the receiving water. In such situations, additional critical receiving 

water conditions that might be used in a steady-state water quality model include conditions such as pH, 

temperature, hardness, or reaction rates, and the presence or absence of certain fish species or life stages 

of aquatic organisms, to name a few. 

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Sections 6.3 and 6.4 below provide further discussion of how critical conditions are applied in a water 

quality model to determine the need for and calculate WQBELs. 

6.2.5 Step 5: Establish an Appropriate Dilution Allowance or Mixing Zone 

Following verification of whether the applicable water quality standards allow any consideration of 

effluent and receiving water mixing and, for a steady-state modeling approach, the critical conditions that 

apply to the effluent and receiving water, permit writers can determine how the effluent and the receiving 

water mix under critical conditions. Based on this determination, permit writers can then establish the 

maximum dilution allowance or mixing zone allowed by the water quality standards for each pollutant of 

concern. 

6.2.5.1 Type of Mixing Under Critical Conditions 

On the basis of requirements in the water quality standards, the dilution allowance or mixing zone used in 

water quality models and calculations are likely to vary depending on whether there is rapid and complete 

mixing or incomplete mixing of the effluent and receiving water under critical conditions. Thus, the 

permit writer needs to understand something about how the effluent and receiving water mix under 

critical conditions. 

Rapid and complete mixing is mixing that occurs when the lateral variation in the concentration of a 

pollutant in the direct vicinity of the outfall is small. The applicable water quality standards might specify 

certain conditions under which a permit writer could assume that rapid and complete mixing is occurring, 

such as the presence of a diffuser. Some standards may also allow a demonstration of rapid and complete 

mixing in cases where the conditions for simply assuming rapid and complete mixing are not met. For 

example, the applicable water quality standards might specify a distance downstream of a discharge point 

by which the pollutant concentration across the stream width must vary by less than a certain percentage 

to assume that there is rapid and complete mixing. 

If the permit writer cannot assume rapid and complete mixing and there has been no demonstration of 

rapid and complete mixing, the permit writer should assume that there is incomplete mixing. Under 

incomplete mix conditions, mixing occurs more slowly and higher concentrations of pollutants are present 

in-stream near the discharge as compared to rapid and complete mixing. Thus, an assumption of 

incomplete mixing is more conservative than an assumption of rapid and complete mixing. For 

waterbodies other than rivers and streams (e.g., lakes, bays, and the open ocean) the permit writer usually 

would assume incomplete mixing. 

6.2.5.2 Maximum Dilution Allowance or Mixing Zone Size 

Once a permit writer determines whether the applicable water quality standards allow consideration of 

some ambient dilution or mixing and determines the type of mixing taking place (rapid and complete 

mixing versus incomplete mixing), he or she would again consult the water quality standards to determine 

the maximum size of the dilution allowance or mixing zone that may be considered in water quality 

modeling calculations. 

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Dilution Allowances in Rapid and Complete Mix Situations 

The maximum permissible dilution allowance for rivers and streams under conditions of rapid and 

complete mixing should be indicated in the water quality standards or standards implementation policy. 

For example, some water quality standards allow a permit writer to use up to 100 percent of the critical 

low flow of a river or stream as a dilution allowance in water quality models and calculations when there 

is rapid and complete mixing. In some cases, water quality standards implement a factor of safety by 

permitting only a percentage of the critical low flow to be used as a dilution allowance, even when there 

is rapid and complete mixing under critical conditions. Water quality standards might incorporate such a 

factor of safety to account for any uncertainty related to other conditions in the waterbody or to ensure 

that some assimilative capacity is retained downstream of the discharge being permitted. Recall as well 

that for some pollutants (e.g., pathogens in waters designated for primary contact recreation, 

bioaccumulative pollutants), the water quality standards or implementing procedures might not authorize 

any dilution allowance, even where the effluent and receiving water mix rapidly and completely. 

Dilution Allowances and Regulatory Mixing Zones in Incomplete Mix Situations 

In an incomplete mixing situation, the water quality standards or implementation policies might allow 

some consideration of ambient dilution. Rather than permitting as much as 100 percent of the critical low 

flow as a dilution allowance, however, they will likely specify either a limited dilution allowance (such as 

a percentage of the critical low flow) or the maximum size of a regulatory mixing zone. A regulatory 

mixing zone is a limited area or volume of water where initial dilution of a discharge takes place and 

within which the water quality standards allow certain water quality criteria to be exceeded. While the 

criteria may be exceeded within the mixing zone, the use and size of the mixing zone must be limited 

such that the waterbody as a whole will not be impaired and such that all designated uses are maintained 

as discussed in section 6.2.5.3 below. Exhibit 6-8 is a diagram illustrating the concept of a regulatory 

mixing zone. The mixing zone often is a simple geometric shape inside of which a water quality criterion 

may be exceeded. The geometric shape does not characterize how mixing actually occurs. Actual mixing 

is described using field studies and a water quality model. 

Exhibit 6-8 Regulatory mixing zones for aquatic life criteria 

Chapter 6: Water Quality-Based Effluent Limitations 6-21
September 2010 NPDES Permit Writers’ Manual 

Note that Exhibit 6-8 above illustrates two different mixing zones, one for an acute aquatic life criterion 

and one for a chronic aquatic life criterion. The water quality standards could specify different maximum 

mixing zones sizes for different pollutants, different types of criteria, and different waterbody types. 

Exhibit 6-9 provides examples of different maximum mixing zone sizes and dilution allowances. 

Exhibit 6-9 Examples of maximum mixing zone sizes or dilution allowances under incomplete 

mixing conditions by waterbody type* 

For rivers and streams: 

 Mixing zones cannot be larger than 1/4 of the stream width and 1/4 mile downstream 

 Mixing must be less than 1/2 stream width with a longitudinal limit of 5 times the stream width 

 Dilution cannot be greater than 1/3 of the critical low flow 

For lakes and the ocean: 

 Mixing zones for lakes cannot be larger than 5% of the lake surface 

 A maximum of 4:1 dilution is available for lake discharges 

 A maximum of 10:1 dilution is available for ocean discharges 

 The maximum size mixing zone for the ocean is a 100-foot radius from the point of discharge 

* Examples were adapted from state standards and procedures and do not reflect EPA guidance or recommendations. 

Permit writers should always check the applicable water quality standards to see if mixing zones are 

permitted and determine the maximum mixing zone size for the waterbody type, pollutant of concern, and 

specific criterion being considered. 

6.2.5.3 Restrictions on Dilution Allowance or Mixing Zone Size 

In addition to specifying the maximum dilution allowance or mixing zone size allowed under both rapid 

and complete mixing conditions and incomplete mixing conditions, the water quality standards or 

implementation policies generally include constraints that could further limit the available dilution 

allowance or mixing zone size to something less than the absolute maximum allowed. For example, one 

restriction on the size of the acute mixing zone could be that it must be small enough to ensure that the 

potential time of exposure of aquatic organisms to a pollutant concentration above the acute criterion is 

very short, and organisms passing through that acute mixing zone will not die from exposure to the 

pollutant. Such a restriction might lead the permitting authority to give a discharger an acute mixing zone 

for a specific pollutant that is smaller than the maximum size allowed by the water quality standards or to 

not allow any acute mixing zone at all. Other possible restrictions on dilution and mixing zone size 

include preventing impairment of the integrity of the waterbody as a whole and preventing significant 

risks to human health. For example, a permitting authority might restrict the size of a mixing zone for a 

human health criterion to prevent the mixing zone from overlapping a drinking water intake. 

6.3 Determine the Need for WQBELs 

After determining the applicable water quality standards and characterizing the effluent and receiving 

water, a permit writer determines whether WQBELs are needed. This section provides an overview of 

that process. 

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6.3.1 Defining Reasonable Potential 

EPA regulations at § 122.44(d)(1)(i) state, “Limitations must control all pollutants or pollutant parameters 

(either conventional, nonconventional, or toxic pollutants) which the Director determines are or may be 

discharged at a level that will cause, have the reasonable potential to cause, or contribute to an excursion 

above any [s]tate water quality standard, including [s]tate narrative criteria for water quality.” [emphasis 

added] Because of that regulation, EPA and many authorized NPDES states refer to the process that a 

permit writer uses to determine whether a WQBEL is required in an NPDES permit as a reasonable 

potential analysis. Wording the requirements of the regulation another way, a reasonable potential 

analysis is used to determine whether a discharge, alone or in combination with other sources of 

pollutants to a waterbody and under a set of conditions arrived at by making a series of reasonable 

assumptions, could lead to an excursion above an applicable water quality standard. The regulation also 

specifies that the reasonable potential determination must apply not only to numeric criteria, but also to 

narrative criteria (e.g., no toxics in toxic amounts, presence of pollutants or pollutant parameters in 

amounts that would result in nuisance algal blooms). A permit writer can conduct a reasonable potential 

analysis using effluent and receiving water data and modeling techniques, as described above, or using a 

non-quantitative approach. Both approaches are discussed below. 

6.3.2 Conducting a Reasonable Potential Analysis Using Data 

When determining the need for a WQBEL, a permit writer should use any available effluent and receiving 

water data as well as other information pertaining to the discharge and receiving water (e.g., type of 

industry, existing TBELs, compliance history, stream surveys), as the basis for a decision. The permit 

writer might already have data available from previous monitoring or he or she could decide to work with 

the permittee to generate data before permit issuance or as a condition of the new permit. EPA 

recommends that monitoring data be generated before effluent limitation development whenever possible. 

Monitoring should begin far enough in advance of permit development to allow sufficient time to conduct 

chemical analyses. Where data are generated as a condition of the permit (for example for a new 

permittee), it might be appropriate for the permit writer to include a reopener condition in the permit to 

allow the incorporation of a WQBEL if the monitoring data indicate that a WQBEL is required. 

A reasonable potential analysis conducted with available data can be divided into four steps as shown in 

Exhibit 6-10 and discussed in detail below. 

Exhibit 6-10 Steps of a reasonable potential analysis with available data 

Step 1. Determine the appropriate water quality model 

Step 2. Determine the expected receiving water concentration under critical conditions 

Step 3. Answer the question, “Is there reasonable potential?” 

Step 4. Document the reasonable potential determination in the fact sheet 

6.3.2.1 Step 1: Determine the Appropriate Water Quality Model 

Steady-state or dynamic water quality modeling techniques can be used in NPDES permitting. As 

discussed in section 6.2.3 above, the examples in this manual consider only steady-state modeling 

techniques, which consider the impact of a discharge on the receiving water modeled under a single set of 

critical conditions. 

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September 2010 NPDES Permit Writers’ Manual 

The specific steady-state model used will depend on the pollutant or parameter of concern and whether 

there is rapid and complete mixing or incomplete mixing of the effluent and the receiving water under 

critical conditions. For example, to model dissolved oxygen in a river, the permit writer might choose the 

Streeter-Phelps equation. For modeling heavy metals in an incomplete mix situation, the permit writer 

might choose the CORMIX model. For pollutants such as BOD, nutrients, or non-conservative 

parameters, the effects of biological activity and reaction chemistry should be modeled, in addition to the 

effects of dilution, to assess possible impacts on the receiving water. This manual focuses only on dilution 

of a pollutant discharged to the receiving water and does not address modeling biological activity or 

reaction chemistry in receiving waters. For additional information, permit writers should discuss 

modeling that accounts for biological activity or reaction chemistry with water quality modelers or other 

water quality specialists as needed and consult EPA’s Water Quality Models and Tools Website

<www.epa.gov/waterscience/models/>. 

For many pollutants such as most toxic (priority) pollutants, conservative pollutants, and pollutants that 

can be treated as conservative pollutants when near-field effects are of concern, if there is rapid and 

complete mixing in a river or stream, the permit writer could use a simple mass-balance equation to 

model the effluent and receiving water. The simple mass-balance equation as applied to a hypothetical 

facility, ABC, Inc., discharging Pollutant Z to a free-flowing stream called Pristine Creek is presented in 

Exhibit 6-11 below. 

Exhibit 6-11 Simple mass-balance equation 

Mass = Flow (Q) 

in million gallons per day (mgd) or 

cubic feet per second (cfs)

X Pollutant concentration (C) 

in milligrams per liter (mg/L)

QsCs + QdCd = QrCr

where 

Qs = stream flow in mgd or cfs above point of discharge 

Cs = background in-stream pollutant concentration in mg/L 

Qd = effluent flow in mgd or cfs 

Cd = effluent pollutant concentration in mg/L 

Qr = resultant in-stream flow, after discharge in mgd or cfs 

Cr = resultant in-stream pollutant concentration in mg/L (after complete mixing occurs) 

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6.3.2.2 Step 2: Determine the Expected Receiving Water Concentration under Critical 

Conditions 

When using a steady-state model, the permit writer, or water quality modeler, determines the impact of 

the effluent discharge on the receiving water under critical conditions. This step examines how this 

steady-state analysis is conducted in situations where there is incomplete mixing and then provides a 

detailed discussion of this analysis for situations where there is rapid and complete mixing. 

How are critical conditions defined? 

When using a steady-state water quality model, permit writers generally input values that reflect critical 

conditions. State permitting procedures should guide permit writers in this task. When characterizing 

the effluent and receiving water for water quality-based permitting, the permit writer should follow the 

permitting authority’s policies and procedures for selecting the critical conditions to use in a steadystate model. The discussion in section 6.2.4 above provides a discussion of how those values might 

be selected. 

Permit writers generally would input into a steady-state model for a reasonable potential analysis the 

critical conditions identified in the effluent and receiving water characterization discussed in section 6.2.4 

above. Recall that critical conditions include the following: 

 Effluent critical conditions 

− Flow. 

− Pollutant concentration. 

 Receiving water critical conditions 

− Flow (for rivers and streams). 

− Pollutant concentration. 

− Other receiving water characteristics such as tidal flux, temperature, pH, or hardness 

(depending on the waterbody and pollutant of concern) 

As discussed in section 6.2.4.1 above, EPA and other permitting authorities have developed guidance for 

determining those critical conditions. Permit writers should rely on their permit authority’s policies and 

procedures or past practices to determine values for all other critical conditions. 

Expected Receiving Water Concentration in an Incomplete Mixing Situation 

Exhibit 6-12 illustrates a situation where there is incomplete mixing of a discharge from a hypothetical 

facility, Acme Co., with the receiving water, the Placid River. The concentration of the pollutant of 

concern discharged by Acme Co. (Pollutant Y) is highest nearest the point of discharge and gradually 

decreases until the pollutant is completely mixed with the receiving water. To determine expected 

receiving water concentrations resulting from the Acme Co.’s discharge of Pollutant Y to the Placid 

River, the permit writer, or water quality modeler, would use the appropriate incomplete mixing model, 

calibrated to actual observations from field studies or dye studies, to simulate mixing under critical 

conditions. In Step 3 below, the concentrations of the pollutant of concern in the receiving water, as 

predicted by the water quality model, will be overlaid by a regulatory mixing zone established by the 

applicable water quality standard to determine whether WQBELs are needed. 

Chapter 6: Water Quality-Based Effluent Limitations 6-25
September 2010 NPDES Permit Writers’ Manual 

Exhibit 6-12 Example of receiving water concentrations in an incomplete 

mixing situation determined using an incomplete mixing water quality model 

Expected Receiving Water Concentration in Rapid and Complete Mixing Situation 

For many pollutants, if there is rapid and complete mixing in a river or stream, the permit writer could use 

the simple mass-balance equation presented in Exhibit 6-11 above to determine the expected receiving 

water concentration of the pollutant of concern under critical conditions. As noted previously, the simple 

mass-balance equation is a very basic steady-state model that can be used for most toxic pollutants, 

conservative pollutants, and other pollutants for which near-field effects are the primary concern. In 

Exhibit 6-13, that equation is applied to ABC Inc.’s, discharge of Pollutant Z (a conservative pollutant) to 

Pristine Creek under conditions of rapid and complete mixing. The mass-balance equation is rearranged 

to show how it would be used in a reasonable potential analysis. 

To use the simple mass-balance equation to predict receiving water impacts for a reasonable potential 

analysis, the permit writer needs to input one value for each variable and solve the equation for Cr, the 

downstream concentration of the pollutant. Because this model, like other steady-state models, uses a 

single value for each variable, the permit writer should be sure that the values selected reflect critical 

conditions for the discharge and the receiving water. In Exhibit 6-14, those critical conditions have been 

identified and the equation has been solved for Cr. 

It is important for permit writers to remember that, in some situations, the selected steady-state model 

could be more complex than the simple mass-balance equation shown. For example, there could be other 

pollutant sources along the stream segment; the pollutant might not be conservative (e.g., BOD); or the 

parameter to be modeled might be affected by multiple pollutants (e.g., dissolved oxygen affected by 

BOD and nutrients). For illustrative purposes, this example focuses on a situation where using a simple 

mass-balance equation is sufficient (i.e., rapid and complete mixing of a conservative pollutant in a river 

or stream under steady-state conditions). 

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Exhibit 6-13 Mass-balance equation for reasonable potential analysis for conservative 

pollutant under conditions of rapid and complete mixing 

The mass-balance equation can be used to determine whether the discharge from ABC Inc., would cause, 

have the reasonable potential to cause, or contribute to an excursion above the water quality standards 

applicable to Pristine Creek. The equation is used to predict the concentration of Pollutant Z, a conservative 

pollutant, in Pristine Creek under critical conditions. The predicted concentration can be compared to the 

applicable water quality criteria for Pollutant Z. Assume the discharge mixes rapidly and completely with 

Pristine Creek.

Mass = Flow (Q) 

in million gallons per day (mgd) 

or cubic feet per second (cfs)

X Pollutant concentration (C) 

in milligrams per liter (mg/L)

QsCs + QdCd = QrCr

where 

Qs = critical stream flow in mgd or cfs above point of discharge 

Cs = critical background in-stream pollutant concentration in mg/L 

Qd = critical effluent flow in mgd or cfs 

Cd = critical effluent pollutant concentration in mg/L 

Qr = resultant in-stream flow, after discharge in mgd or cfs (Qr = Qs + Qd) 

Cr = resultant in-stream pollutant concentration in mg/L (after complete mixing occurs) 

Rearrange the equation to determine the concentration of Pollutant Z in the waterbody downstream of a 

discharge under critical conditions: 

r

dd ss

r Q

))(CQ())(C(Q C  

Chapter 6: Water Quality-Based Effluent Limitations 6-27
September 2010 NPDES Permit Writers’ Manual 

Exhibit 6-14 Example of applying mass-balance equation to conduct reasonable potential 

analysis for conservative pollutant under conditions of rapid and complete mixing 

Mass-Balance Equation: QsCs + QdCd = QrCr 

Dividing both sides of the mass-balance equation by Qr gives the following: 

r

dd ss

r Q

))(CQ())(C(Q C  

where Cr is the receiving water concentration downstream of the discharge 

The following values are known for ABC Inc. and Pristine Creek: 

Qs = critical upstream flow (water quality standards allow a dilution allowance 

 of up to 100% of 1Q10 low flow for rapid and complete mixing) = 1.20 cfs 

Cs = critical upstream concentration of Pollutant Z in Pristine Creek = 0.75 mg/L 

Qd = critical discharge flow = 0.55 cfs 

Cd = statistically projected critical discharge concentration of Pollutant Z = 2.20 mg/L 

Qr = downstream flow = Qd + Qs = 0.55 + 1.20 = 1.75 cfs 

Acute aquatic life water quality criterion for Pollutant Z in Pristine Creek = 1.0 mg/L 

Find the projected downstream concentration (Cr) by inserting the given values into the equation as follows: 

cfs) (1.75

mg/L) cfs)(0.75 (1.20)mg/L cfs)(2.20 (0.55 Cr

 

Cr = 1.2 mg/L of Pollutant Z*

* calculated to 2 significant figures 

6.3.2.3 Step 3: Answer the Question, Is There Reasonable Potential? 

The next step in the reasonable potential analysis is to consider the results of water quality modeling to 

answer the question, Is there reasonable potential?

 For most pollutants, if the receiving water pollutant concentration projected by a steady-state 

model (e.g., a simple mass-balance equation or a more complex model) exceeds the applicable 

water quality criterion, there is reasonable potential, and the permit writer must calculate 

WQBELs. (Note that for dissolved oxygen, reasonable potential would occur if the water quality 

model indicates that the projected effluent concentration of the oxygen-demanding pollutants 

would result in depletion of dissolved oxygen below acceptable values in the receiving water). 

 If the projected concentration is equal to or less than the applicable criterion, there is no 

reasonable potential and, thus far, there is no demonstrated need to calculate WQBELs. 

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September 2010 NPDES Permit Writers’ Manual 

Reasonable Potential Determination in an Incomplete Mixing Situation 

To determine whether there is reasonable potential in an incomplete mixing situation, the permit writer 

would compare the projected concentration of the pollutant of concern at the edge of the regulatory 

mixing zone or after accounting for the available dilution allowance, with the applicable water quality 

criterion. Exhibit 6-15 illustrates the reasonable potential determination for Acme Co. in a situation where 

the regulatory mixing zone is described by a geometric shape. In the example, the water quality criterion 

for Pollutant Y being considered is 2.0 micrograms per liter (μg/L). The illustration shows that at many 

points along the edge of the regulatory mixing zone specified by the water quality standards, which is 

represented by the rectangle, the concentration of Pollutant Y exceeds 2.0 μg/L. Therefore, there is 

reasonable potential, and the permit writer must calculate WQBELs for Pollutant Y for Acme Co. 

Exhibit 6-15 Reasonable potential determination in an incomplete mixing situation 

Reasonable Potential Determination in a Rapid and Complete Mixing Situation 

In the rapid and complete mixing example for ABC, Inc., shown in Exhibit 6-14 above, a projected 

downstream concentration (Cr) of 1.2 mg/L of Pollutant Z was calculated. The permit writer would 

compare the calculated concentration to the acute aquatic life water quality criterion of 1.0 mg/L for 

Pollutant Z in Pristine Creek presented in Exhibit 6-14. Because 1.2 mg/L > 1.0 mg/L, the projected 

downstream concentration exceeds the water quality criterion; therefore, there is a reasonable potential for 

the water quality criterion to be exceeded, and the permit writer must calculate WQBELs for Pollutant Z. 

A permit writer should repeat the reasonable potential analysis for all applicable criteria for the pollutant 

of concern and must remember that the critical conditions could differ depending on the criterion being 

evaluated. For example, the critical stream flow used when considering the acute aquatic life criterion 

might be the 1Q10 low flow, whereas the critical stream flow used when considering the chronic aquatic 

life criterion might be the 7Q10 low flow. If calculations demonstrate that the discharge of a pollutant of 

concern would cause, have the reasonable potential to cause, or contribute to an excursion of any one of 

the applicable criteria for that pollutant, the permit writer must develop WQBELs for that pollutant. 

Chapter 6: Water Quality-Based Effluent Limitations 6-29
September 2010 NPDES Permit Writers’ Manual 

In addition, it is important for permit writers to remember that they must repeat the reasonable potential 

analysis for each pollutant of concern and calculate WQBELs where there is reasonable potential. For 

each pollutant for which there is no reasonable potential, the permit writer should consider whether there 

are any existing WQBELs in the previous permit and whether they should be retained. The permit writer 

would complete an anti-backsliding analysis (see Chapter 7 of this manual) to determine whether it is 

possible to remove any existing WQBELs from the reissued permit. 

6.3.2.4 Step 4: Document the Reasonable Potential Determination in the Fact Sheet 

As a final step, permit writers need to document the details of the reasonable potential analysis in the 

NPDES permit fact sheet. The permit writer should clearly identify the information and procedures used 

to determine the need for WQBELs. The goal of that documentation is to provide the NPDES permit 

applicant and the public a transparent, reproducible, and defensible description of how each pollutant was 

evaluated, including the basis (i.e., reasonable potential analysis) for including or not including a WQBEL 

for any pollutant of concern. 

6.3.3 Conducting a Reasonable Potential Analysis without Data 

State implementation procedures might allow, or even require, a permit writer to determine reasonable 

potential through a qualitative assessment process without using available facility-specific effluent 

monitoring data or when such data are not available. For example, as noted in section 6.2.1.2 above, 

where there is a pollutant with a WLA from a TMDL, a permit writer must develop WQBELs or other 

permit requirements consistent with the assumptions of the TMDL. Even without a TMDL, a permitting 

authority could, at its own discretion, determine that WQBELs are needed for any pollutant associated 

with impairment of a waterbody. A permitting authority might also determine that WQBELs are required 

for specific pollutants for all facilities that exhibit certain operational or discharge characteristics (e.g., 

WQBELs for pathogens in all permits for POTWs discharging to contact recreational waters). 

Types of information that the permit writer might find useful in a qualitative approach to determining 

reasonable potential include the following: 

 Effluent variability information such as history of compliance problems and toxic impacts. 

 Point and nonpoint source controls such as existing treatment technology, the type of industry, 

POTW treatment system, or BMPs in place. 

 Species sensitivity data including in-stream data, adopted water quality criteria, or designated 

uses. 

 Dilution information such as critical receiving water flows or mixing zones. 

The permit writer should always provide justification for the decision to require WQBELs in the permit 

fact sheet or statement of basis and must do so where required by federal and state regulations. A 

thorough rationale is particularly important when the decision to include WQBELs is not based on an 

analysis of effluent data for the pollutant of concern. 

After evaluating all available information characterizing the nature of the discharge without effluent 

monitoring data for the pollutant of concern, if the permit writer is not able to decide whether the 

discharge causes, has the reasonable potential to cause, or contributes to an excursion above a water 

6-30 Chapter 6: Water Quality-Based Effluent Limitations 
September 2010 NPDES Permit Writers’ Manual 

quality criterion, he or she may determine that effluent monitoring should be required to gather additional 

data. The permit writer might work with the permittee to obtain data before permit issuance, if sufficient 

time exists, or could require the monitoring as a condition of the newly issued or reissued permit. The 

permit writer might also include a clause in the permit that would allow the permitting authority to reopen 

the permit and impose an effluent limitation if the required monitoring establishes that there is reasonable 

potential that the discharge will cause or contribute to an excursion above a water quality criterion. 

6.4 Calculate Parameter-specific WQBELs 

If a permit writer has determined that a pollutant or pollutant parameter is discharged at a level that will 

cause, have reasonable potential to cause, or contribute to an excursion above any state water quality 

standard, the permit writer must develop WQBELs for that pollutant parameter. This manual presents the 

approach recommended by EPA’s TSD for calculating WQBELs for toxic (priority) pollutants. Many 

permitting authorities apply those or similar procedures to calculate WQBELs for toxic pollutants and for 

a number of conventional or nonconventional pollutants with effluent concentrations that tend to follow a 

lognormal distribution. Permit writers should consult permitting authority policies and procedures to 

determine the methodology specific to their authorized NPDES permitting program, including the 

approach for pollutants with effluent concentrations that do not follow a lognormal distribution. 

6.4.1 Calculating Parameter-specific WQBELs from Aquatic Life Criteria 

The TSD process for calculating WQBELs from aquatic life criteria follows five steps as shown in 

Exhibit 6-16 and discussed in detail below. 

Exhibit 6-16 Calculating parameter-specific WQBELs from aquatic life criteria 

Step 1. Determine acute and chronic WLAs 

Step 2. Calculate long-term average (LTA) concentrations for each WLA 

Step 3. Select the lowest LTA as the performance basis for the permitted discharger 

Step 4. Calculate an average monthly limitation (AML) and a maximum daily limitation (MDL) 

Step 5. Document the calculation of WQBELs in the fact sheet. 

6.4.1.1 Step 1: Determine Acute and Chronic WLAs 

Before calculating a WQBEL, the permit writer will first need to determine the appropriate WLAs for the 

point source discharge based on both the acute and chronic criteria. A WLA may be determined from a 

TMDL or calculated for an individual point source directly. Where an EPA-approved TMDL has been 

developed for a particular pollutant, the WLA for a specific point source discharger is the portion of that 

TMDL that is allocated to that point source, as discussed in section 6.2.1.2 above. Where no TMDL is 

available, a water quality model generally is used to calculate a WLA for the specific point source 

discharger. The WLA is the loading or concentration of pollutant that the specific point source may 

discharge while still allowing the water quality criterion to be attained downstream of that discharge. Of 

course, the WLA calculation should take into account any reserve capacity, safety factor, and 

contributions from other point and nonpoint sources as might be required by the applicable water quality 

standards regulations or implementation policies. 

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When a WLA is not given as part of a TMDL or where a separate WLA is needed to address the nearfield effects of a discharge on water quality criteria, permit writers will, in many situations, use a steadystate water quality model to determine the appropriate WLA for a discharge. As discussed in section 6.3 

above, steady-state models generally are run under a single set of critical conditions for protection of 

receiving water quality. If a permit writer uses a steady-state model with a specific set of critical 

conditions to assess reasonable potential, he or she generally may use the same model and critical 

conditions to calculate a WLA for the same discharge and pollutant of concern. 

As with the reasonable potential assessment, the type of steady-state model used to determine a WLA 

depends on the type of mixing that occurs in the receiving water and the type of pollutant or parameter 

being modeled. As discussed in section 6.3.2 above, permit writers can use the mass-balance equation as a 

simple steady-state model for many pollutants, such as most toxic (priority) pollutants or any pollutant 

that can be treated as a conservative pollutant when considering near-field effects, if there is rapid and 

complete mixing in the receiving water. For pollutants or discharge situations that do not have those 

characteristics (e.g., non-conservative pollutants, concern about effects on a downstream waterbody), a 

water quality model other than the mass-balance equation would likely be more appropriate. 

The mass-balance equation is presented again in Exhibit 6-17. In the exhibit, the equation is rearranged to 

show how it would be used to calculate a WLA for a conservative pollutant discharged to a river or 

stream under conditions of rapid and complete mixing. 

6.4.1.2 Step 2: Calculate LTA Concentrations for Each WLA 

The requirements of a WLA generally must be interpreted in some way to be expressed as an effluent 

limitation. The goal of the permit writer is to derive effluent limitations that are enforceable, adequately 

account for effluent variability, consider available receiving water dilution, protect against acute and 

chronic impacts, account for compliance monitoring sampling frequency, and assure attainment of the 

WLA and water quality standards. In developing WQBELs, the permit writer develops limitations that 

require a facility to perform in such a way that the concentration of the pollutant of concern in the effluent 

discharged is nearly always below the WLA. 

To accomplish that goal, EPA has developed a statistical permit limitation derivation procedure to 

translate WLAs into effluent limitations for pollutants with effluent concentration measurements that tend 

to follow a lognormal distribution. EPA believes that this procedure, discussed in Chapter 5 of the TSD, 

results in defensible, enforceable, and protective WQBELs for such pollutants. In addition, a number of 

states have adopted procedures based on, but not identical to, EPA’s guidance that also provide 

defensible, enforceable, and protective WQBELs. Permit writers should always use the procedures 

adopted by their permitting authority. In addition, permit writers should recognize that alternative 

procedures would be used to calculate effluent limitations for pollutants with effluent concentrations that 

cannot generally be described using a lognormal distribution. 

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Exhibit 6-17 Example of applying mass-balance equation to calculate WLAs for conservative 

pollutant under conditions of rapid and complete mixing 

Mass Balance Equation: QsCs + QdCd = QrCr

where 

Qs = background stream flow in mgd or cfs above point of discharge 

Cs = background in-stream pollutant concentration in mg/L 

Qd = effluent flow in mgd or cfs 

Cd = effluent pollutant concentration in mg/L = WLA

Qr = resultant in-stream flow, after discharge in mgd or cfs 

Cr = resultant in-stream pollutant concentration in mg/L (after complete mixing occurs) 

Rearrange the equation to determine the WLA (Cd) for ABC Inc., necessary to achieve the acute water quality 

criterion for Pollutant Z in Pristine Creek (Cr) downstream of the discharge: 

d

ssrr

d Q

CQCQ C  

The following values are known for ABC Inc., and Pristine Creek: 

Qs = critical upstream flow (water quality standards allow a dilution allowance 

 of up to 100% of 1Q10 low flow for rapid and complete mixing) = 1.20 cfs 

Cs = upstream concentration of Pollutant Z in Pristine Creek = 0.75 mg/L 

Qd =discharge flow = 0.55 cfs 

Qr = downstream flow = Qd + Qs = 0.55 + 1.20 = 1.75 cfs 

Cr = acute water quality criterion for Pollutant Z in Pristine Creek = 1.0 mg/L 

Determine the WLA for ABC Inc., by inserting the given values into the equation as follows: 

cfs) 55.0(

 mg/L)75.0 cfs)(20.1( mg/L)0.1 cfs)(75.1( C Inc. ABCforWLA d

 

Cd = 1.5 mg/L of Pollutant Z* 

* calculated to 2 significant figures 

For those pollutants with effluent concentrations that do follow a lognormal distribution, the distribution 

can be described by determining a long-term average (or LTA) that ensures that the effluent pollutant 

concentration remains nearly always below the WLA and by the CV, a measure of the variability of data 

around the LTA. Exhibit 6-18 illustrates a lognormal distribution with the LTA, CV, and WLA highlighted. 

When applying aquatic life criteria, a permit writer generally establishes a WLA based on the acute aquatic 

life criterion and a WLA based on the chronic aquatic life criterion. Thus, the permit writer determines two 

LTAs—one that would ensure that an effluent concentration is nearly always below the acute WLA and one 

that would ensure that an effluent concentration nearly always below the chronic WLA. Each LTA, acute 

and chronic, would represent a different performance expectation for the discharger. 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 6-18 Example of lognormal distribution of effluent pollutant concentrations and 

calculation of LTA 

6.4.1.3 Step 3: Select the Lowest LTA as the Performance Basis for the Permitted 

Discharger 

EPA recommends that WQBELs be based on a single performance expectation for a facility; therefore, 

once a permit writer has calculated LTA values for each WLA, he or she would select only one of those 

LTAs to define the required performance of the facility and serve as the basis for WQBELs. Because 

WQBELs must assure attainment of all applicable water quality criteria, the permit writer would select 

the lowest LTA as the basis for calculating effluent limitations. Selecting the lowest LTA would ensure 

that the facility’s effluent pollutant concentration remains below all the calculated WLAs nearly all the 

time. Further, because WLAs are calculated using critical receiving water conditions, the limiting LTA 

would also ensure that water quality criteria are fully protected under nearly all conditions. 

6.4.1.4 Step 4: Calculate an Average Monthly Limitation (AML) and a Maximum Daily 

Limitation (MDL) 

The NPDES regulations at § 122.45(d) require that all effluent limitations be expressed, unless 

impracticable, as both AMLs and MDLs for all discharges other than POTWs and as both AMLs and 

average weekly limitations (AWLs) for POTWs. The AML is the highest allowable value for the average 

of daily discharges over a calendar month. The MDL is the highest allowable daily discharge measured 

during a calendar day or 24-hour period representing a calendar day. The AWL is the highest allowable 

value for the average of daily discharges over a calendar week. For pollutants with limitations expressed 

in units of mass, the daily discharge is the total mass discharged over the day. For limitations expressed in 

other units, the daily discharge is the average measurement of the pollutant over the period of a day. Relative frequency

CV 

LTA WLA 

Concentration 

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September 2010 NPDES Permit Writers’ Manual 

In the TSD, EPA recommends establishing an MDL, rather than an AWL, for discharges of toxic 

pollutants from POTWs. That approach is appropriate for at least two reasons. First, the basis for the 

AWL for POTWs is the secondary treatment requirements discussed in section 5.1.1.1 of this manual and 

is not related to the need for assuring attainment of water quality standards. Second, an AWL, which 

could be the average of up to seven daily discharges, could average out peak toxic concentrations and, 

therefore, the discharge’s potential for causing acute toxic effects might be missed. An MDL would be 

more likely to identify potential acutely toxic impacts. 

Chapter 5 of the TSD includes statistical tools for calculating MDLs and AMLs from the LTA value 

selected in Step 3 above. Again, note that those procedures apply to pollutants with effluent concentration 

measurements that tend to follow a lognormal distribution. EPA has not developed guidance on 

procedures for calculating effluent limitations for pollutants with effluent concentrations that generally 

cannot be described using a lognormal distribution. For such pollutants, permit writers should use other 

procedures as recommended by their permitting authority in its policies, procedures, or guidance. 

Whether using the TSD procedures or other procedures for calculating WQBELs, the objective is to 

establish limitations calculated to require treatment plant performance levels that, after considering 

acceptable effluent variability, would have a very low statistical probability of exceeding the WLA and, 

therefore, would comply with the applicable water quality standards under most foreseeable conditions. 

6.4.1.5 Step 5: Document Calculation of WQBELs in the Fact Sheet 

Permit writers should document in the NPDES permit fact sheet the process used to develop WQBELs. 

The permit writer should clearly identify the data and information used to determine the applicable water 

quality standards and how that information, or any applicable TMDL, was used to derive WQBELs and 

explain how the state’s antidegradation policy was applied as part of the process. The information in the 

fact sheet should provide the NPDES permit applicant and the public a transparent, reproducible, and 

defensible description of how the permit writer properly derived WQBELs for the NPDES permit. 

6.4.2 Calculating Chemical-specific WQBELs based on Human Health 

Criteria for Toxic Pollutants 

Developing WQBELs for toxic pollutants affecting human health is somewhat different from calculating 

WQBELs for other pollutants because (1) the exposure period of concern is generally longer (e.g., often a 

lifetime exposure) and (2) usually the average exposure, rather than the maximum exposure, is of 

concern. EPA’s recommended approach for setting WQBELs for toxic pollutants for human health 

protection is to set the AML equal to the WLA calculated from the human health toxic pollutant criterion 

and calculate the MDL from the AML. Section 5.4.4 of the TSD describes statistical procedures used for 

such calculations for pollutants with effluent concentrations that follow a lognormal distribution. Once 

again, for pollutants with effluent concentrations that do not follow a lognormal distribution, permit 

writers should use other procedures as specified by their permitting authority. 

If the permit writer calculates chemical-specific WQBELs from human health criteria, he or she should 

compare the limitations to any other calculated WQBELs (e.g., WQBELs based on aquatic life criteria) 

and TBELs and apply antidegradation and anti-backsliding requirements to determine the final limitations 

that meet all technology and water quality standards. As discussed above, that process should be 

documented in the fact sheet for the NPDES permit. 

Chapter 6: Water Quality-Based Effluent Limitations 6-35
September 2010 NPDES Permit Writers’ Manual 

6.5 Calculate Reasonable Potential and WQBELs for WET 

WET tests measure the degree of response of exposed aquatic test organisms to an effluent mixed in some 

proportion with control water (e.g., laboratory water or a non-toxic receiving water sample). WET testing 

is used as a second approach, in addition to the chemical-specific approach, to implementing water 

quality standards in NPDES permits. This section provides a brief introduction to WET testing and WET 

limitations. 

Test of Significant Toxicity (TST) 

At the time of the writing of this guidance manual, EPA had recently published a new statistical 

approach that assesses the whole effluent toxicity (WET) measurement of wastewater effects on 

specific test organisms’ ability to survive, grow, and reproduce. This new approach is called the Test of 

Significant Toxicity (TST) and is a statistical method that uses hypothesis testing techniques based on 

research and peer-reviewed publications. The hypothesis test under the TST approach examines 

whether an effluent, at the critical concentration (e.g., in-stream waste concentration [IWC]), and the 

control within a WET test differ by an unacceptable amount (the amount that would have a measured 

detrimental effect on the ability of aquatic organisms to thrive and survive). The TST implementation 

document and the TST technical document are available at the NPDES WET Website

<www.epa.gov/npdes/wet>. 

6.5.1 Types of WET Tests 

In many WET tests, the effluent and control water are mixed in varying proportions to create a dilution 

series. Exhibit 6-19 is an example of a typical dilution series used in WET testing. 

Exhibit 6-19 Example of typical dilution series 

Percent Dilution Water

100 50 25 12.5 6.25 Percent Effluent 

100

0

0 50 75 87.5 93.75 

There are two types of WET tests: acute and chronic. An acute toxicity test usually is conducted over a 

short time, generally 96 hours or less, and the endpoint measured is mortality. The endpoint for an acute 

test is often expressed as an LC50 (i.e., the percent of effluent that is lethal to 50 percent of the exposed 

test organisms). A chronic toxicity test is usually conducted during a critical life phase of the organism 

and the endpoints measured are mortality and sub-lethal effects, such as changes in reproduction and 

growth. A chronic test can occur over a matter of hours or days, depending on the species tested and test 

endpoint. The endpoint of a chronic toxicity test often is expressed in one of the following ways: 

 No observed effect concentration (NOEC), the highest concentration of effluent (i.e., highest 

percent effluent) at which no adverse effects are observed on the aquatic test organisms. 

 Lowest observed effect concentration (LOEC), the lowest concentration of effluent that causes 

observable adverse effects in exposed test organisms. 

6-36 Chapter 6: Water Quality-Based Effluent Limitations 
September 2010 NPDES Permit Writers’ Manual 

 Inhibition concentration (IC), a point estimate of the effluent concentration that would cause a 

given percent reduction in a biological measurement of the test organisms. 

 Effect concentration (EC), a point estimate of the effluent concentration that would cause an 

observable adverse effect in a given percentage of test organisms. 

For additional information on WET monitoring and WET test methods, see section 8.2.4 of this manual. 

6.5.2 Expressing WET Limitations or Test Results 

There are two options for expressing WET limitations or test results. First, WET limitations or test results 

can be expressed directly in terms of the WET test endpoints discussed above (e.g., LC50, NOEC, and 

IC25). Alternatively, the limitations or test results can be expressed in terms of toxic units (TUs). A TU is 

the inverse of the sample fraction, calculated as 100 divided by the percent effluent. Exhibit 6-20 presents 

example TUs for expressing acute and chronic test results. 

Exhibit 6-20 Example of toxic units 

If an acute test result is a LC50 of 60 percent, that result can be expressed as 

 TU 7.1unitstoxic acute 7.1

60

100   a

If a chronic test result is an IC25 of 40 percent effluent, that result can be expressed as 

chronic 5.2 TU 5.2unitstoxic 

40

100   c

It is important to distinguish acute TUs (TUa) from chronic TUs (TUc). The difference between TUa and 

TUc can be likened to the difference between miles and kilometers. Both miles and kilometers are used to 

measure distance, but a distance of 1.0 mile is not the same as a distance of 1.0 kilometer. Likewise, both 

TUa and TUc are expressions of the toxicity of an effluent, but 1.0 TUa is not the same as 1.0 TUc. It is 

possible, however, to determine the relationship between the acute toxicity of an effluent and the chronic 

toxicity of that same effluent, just as it is possible to determine the relationship between miles and 

kilometers (i.e., through a conversion factor). Unlike the conversion between miles and kilometers that 

remains constant, the conversion factor between acute and chronic toxic units varies from effluent to 

effluent. 

For an effluent, the permit writer could develop a conversion factor that would allow conversion of TUa

into equivalent TUc or vice versa. This conversion factor is known as an acute-to-chronic ratio (ACR) for 

that effluent. The ACR for an effluent may be calculated where there are at least 10 sets of paired acute 

and chronic WET test data available. The ACR is determined by calculating the mean of the individual 

ACRs for each pair of acute and chronic WET tests. Where there are not sufficient data to calculate an 

ACR for an effluent (i.e., less than 10 paired sets of acute and chronic WET test data), EPA recommends 

a default value of ACR = 10. Exhibit 6-21 presents examples showing how the ACR converts TUa into 

TUc, how to calculate an ACR from existing data, and how, once an ACR is calculated, a permit writer 

could estimate the chronic toxicity of an effluent sample from its measured acute toxicity or vice versa. 

Chapter 6: Water Quality-Based Effluent Limitations 6-37
September 2010 NPDES Permit Writers’ Manual 

Exhibit 6-21 Using the ACR 

The ACR is expressed 

25

50

IC

LC 

Chronic Endpoint

Endpoint Acute ACR  

A TU is the inverse of the sample fraction. 

Therefore, by definition 

25

c

50

a

IC

100 TU 

LC

100 TU  

Consequently, toxicity as percent sample, 

may be expressed 

c 25 a

50

TU

100 IC 

TU

100 LC  

Substituting into the original equation gives 

a

c

c

a

25

50

TU

TU

TU

100

TU

100

IC

LC ACR 

Example 1

Given: LC50 = 28%, IC25 = 10% 

8.2

10% 

28% 

IC

LC ACR

25

50 

Example 2

Given: TUa = 3.6, TUc = 10.0 

8.2

3.6

10.0

TU

TU ACR a

c



LC50

(% effluent) 

IC25

(% effluent) ACR 

62 10 6.2 

18 10 1.8 

68 25 2.7 

61 10 6.1 

63 25 2.5 

70 25 2.8 

17 5 3.4 

35 10 3.5 

35 10 3.5 

35 25 1.4 

47 10 4.7 

Example 3 

Given: Toxicity data for a facility’s effluent 

for C. dubia. as presented in the 

table to the right. 

The ACR in the third column is calculated 

using the following equation: 

25

50

IC

LC ACR 

Mean 3.5 

Example 4 

Given: TUa = 1.8, ACR = 3.5 

c a

a

c

TU x ACRTU 

TU

TU ACR  

a c

a

c

a c TU 6.3TU 1.8x 

TU

TU TU Estimated   3.5TU x ACR 

6.5.3 Determining the Need for WET Limitations 

If a state has numeric criteria for WET, a permit writer could use the results of WET tests to project acute 

or chronic toxicity in the receiving water after accounting for the applicable dilution allowance or mixing 

zone made available in the water quality standards. The permit writer would compare the projected 

toxicity of the receiving water to the applicable water quality criterion for WET. If the projected toxicity 

exceeds the applicable numeric water quality criterion for WET, the discharge would cause, have the 

reasonable potential to cause, or contribute to an excursion above the applicable water quality standards, 

and the permit writer must develop a WQBEL for WET [see § 122.44(d)(1)(iv)]. In that way, numeric 

criteria for WET can be treated similarly to chemical-specific criteria. Exhibit 6-22 provides an example 

of how the mass-balance equation is used to conduct a reasonable potential analysis for WET. 

6-38 Chapter 6: Water Quality-Based Effluent Limitations 
September 2010 NPDES Permit Writers’ Manual 

Exhibit 6-22 Example of mass-balance equation for a WET reasonable potential analysis 

The mass-balance equation can be used to determine whether the discharge from ABC Inc. would cause, have 

the reasonable potential to cause, or contribute to toxicity in Pristine Creek that exceeds the numeric water quality 

criteria for acute or chronic toxicity. Assume the discharge mixes rapidly and completely with Pristine Creek. 

Mass-Balance Equation: QsCs + QdCd = QrCr 

Dividing both sides of the mass-balance equation by Qr gives the following: 

r

ssdd r Q

))(CQ())(C(Q C  

The following values are known for ABC Inc. and Pristine Creek: 

Qs = Critical upstream flow (1Q10 for acute protection) = 23.6 cfs 

 (7Q10 for chronic protection) = 70.9 cfs 

Cs = Upstream toxicity in Pristine Creek (acute) = 0 TUa

 (chronic) = 0 TUc

Qd = Discharge flow = 7.06 cfs 

Cd = Discharge toxicity (acute) = 2.50 TUa

 (chronic) = 8.00 TUc

Qr = Downstream flow = Qd + Qs

Acute Water Quality Criterion in Pristine Creek = 0.3 TUa

Chronic Water Quality Criterion in Pristine Creek = 1.0 TUc

Find the downstream concentration (Cr) by inserting the given values into the equation as follows: 

For acute toxicity: 

a

a a

r TU 58.0

cfs23.6cfs7.06

)TU 0)(cfs 6.23()TU cfs)(2.5 (7.06 C  

 

The downstream concentration (Cr) exceeds the water quality criterion for acute toxicity of 0.3 TUa. 

For chronic toxicity: 

c

c c

r TU 72.0

cfs70.9cfs7.06

)TU 0)(cfs 9.70()TU cfs)(8.00 (7.06 C  

 

The downstream concentration (Cr) does not exceed the water quality criterion for chronic toxicity of 1.0 TUc. 

In Exhibit 6-22 above, the downstream concentration under critical conditions for the acute water quality 

criterion (Cr = 0.58 TUa) exceeds the water quality criterion for acute toxicity (0.3 TUa); therefore there is 

reasonable potential and WET limitations are required. WET limitations would be calculated in much the 

same way as limitations on specific chemicals. The limitations would be calculated to ensure that WET 

criteria are not exceeded after any available dilution or at the edge of the applicable mixing zone. 

Chapter 6: Water Quality-Based Effluent Limitations 6-39
September 2010 NPDES Permit Writers’ Manual 

Where state water quality standards do not include numeric criteria for WET, a permit writer could 

evaluate the need for WQBELs for WET on the basis of narrative criteria; specifically, a narrative 

criterion stating that waterbodies must be free from toxics in toxic amounts. To make it easier for a permit 

writer to readily establish WET limitations in this situation, the permitting authority should have a policy 

for implementing the narrative criterion. Following the permitting authority’s policy, if the permit writer 

determines that a discharge causes, has the reasonable potential to cause, or contributes to an in-stream 

excursion above a narrative criterion, the regulations at § 122.44(d)(1)(v) require that the permit include 

WQBELs for WET unless the permit writer demonstrates that parameter-specific limitations for the 

effluent are sufficient to attain and maintain applicable numeric and narrative water quality criteria. In 

other words, the permit must include WET limitations unless the permit writer is able to determine the 

specific pollutants that are the source of toxicity and include parameter-specific limitations for those 

pollutants that assure, and will continue to assure, attainment of water quality standards. If there are no 

criteria in the state water quality standards for the specific parameters causing the toxicity, the permit 

writer can establish WQBELs using one of three approaches outlined in § 122.44(d)(1)(vi): 

 Use EPA’s national recommended criteria. 

 Calculate a numeric criterion that will attain and maintain the applicable narrative criterion. 

 Control the pollutant using an indicator parameter for the pollutant of concern. 

A permit also could include a requirement to conduct a toxicity identification evaluation and toxicity 

reduction evaluation (TIE/TRE) as a special condition in an NPDES permit. (Chapter 9 of this manual 

presents more information on special conditions.) A TIE/TRE is a site-specific study designed to 

systematically investigate and identify the causes of effluent toxicity problems, isolate the sources of that 

toxicity, identify and implement appropriate toxicity control options, and confirm the effectiveness of 

those control options and the reduction in toxicity. The permit writer might require a TIE/TRE when 

WET limitations are exceeded or, if there are no WET limitations in the permit, where WET testing 

demonstrates an unacceptable level of effluent toxicity. Because WET testing indicates the degree of 

toxicity of an effluent, but does not specifically identify the cause of that toxicity or ways to reduce 

toxicity, a TIE/TRE is necessary to achieve compliance with effluent limitations or other effluent toxicity 

requirements in NPDES permits. If a TIE/TRE is not required through the special conditions section of 

the permit, it could be required via a CWA section 308 letter, a CWA section 309 administrative order, or 

a consent decree. 

6.6 Antidegradation Review 

Early in the permit development process, a permit writer should check the state’s antidegradation policy 

and implementation methods to determine what tier(s) of protection, if any, the state has assigned to the 

proposed receiving water for the parameter(s) of concern. The regulations concerning antidegradation and 

each of the tiers are described above in section 6.1.1.3. The tier of antidegradation protection is important 

for determining the required process for developing the water quality-based permit limits and conditions. 

In some cases, where a waterbody is classified as Tier 3 for antidegradation purposes, the permit writer 

might find that it is not possible to issue a permit for the proposed activity. 

If the state has not specified the tier, the permit writer will need to evaluate, in accordance with the state’s 

implementation procedures, whether the receiving waterbody is of high water quality for the parameters 

of concern, and thus will require Tier 2 protection. After identifying the tier(s) of protection for the 

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September 2010 NPDES Permit Writers’ Manual 

proposed receiving waterbody and parameter(s) of concern, the permit writer should consult the state’s 

antidegradation implementation procedures relevant to the tier(s). 

The following sections provide methods permit writers should consider for implementing, through the 

WQBEL development process, the three levels of protection typically found in a state’s antidegradation 

policy. Implementation of the state’s antidegradation policy could have a significant effect on the 

calculation of WQBELs. 

6.6.1 Tier 1 Implementation 

All waterbodies receive at least Tier 1 protection. Tier 1 protection means that the permit writer must 

include limits in the permit sufficient to maintain and protect water quality necessary to protect existing 

uses. In practice, for a Tier 1 receiving waterbody, the permit writer typically calculates the WQBELs on 

the basis of the applicable criteria because the state’s designated uses and criteria to protect those uses 

must be sufficient to protect the existing uses. If a Tier 1 waterbody is impaired for a parameter that 

would be present in the proposed discharge, the permit writer should identify and consult any relevant 

TMDLs to determine what quantity of pollutant (if any) is appropriate. 

6.6.2 Tier 2 Implementation 

For new or increased discharges that could potentially lower water quality in high-quality waters, Tier 2 

protection provides the state with a framework for making decisions regarding the degree to which it will 

protect and maintain the high water quality. A new or expanded discharge permit application typically 

triggers a Tier 2 antidegradation review. Depending on the outcome of the review, the permit could be 

written to maintain the existing high water quality or could be written to allow some degradation. 

Each state’s antidegradation policy or implementation procedures should describe the Tier 2 

antidegradation review process. Though the process varies among states, EPA’s antidegradation 

regulation at § 131.12 outlines the common elements of the process. To permit a new or increased 

discharge that would lower water quality, the state is required to make a finding on the basis of the 

following: 

 The state must find that allowing lower water quality is necessary for important social or 

economic development in the area in which the waters are located. 

− The state would perform an alternatives analysis to evaluate whether the proposed discharge 

is actually necessary (i.e., whether there are less degrading feasible alternatives) and that 

might include consideration of a wide range of alternatives (e.g. non-discharging options, 

relocation of discharge, alternative processes, and innovative treatments). 

− The state should provide a justification of important social or economic development (or 

both) that would occur as a result of permitting the proposed discharge. 

 The state’s finding must be made after full satisfaction of its own intergovernmental coordination 

and public participation provisions. 

 The state must assure that the highest statutory and regulatory requirements for all new and 

existing point sources will be achieved. 

 The state must assure that all cost-effective and reasonable BMPs for nonpoint source control will 

be achieved. 

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6-42 Chapter 6: Water Quality-Based Effluent Limitations 

 

 The state must assure that water quality will still protect existing uses. 

If, after fulfilling the above conditions of the Tier 2 antidegradation review process, the state makes a 

determination to allow a new or increased discharge that would lower water quality, the permit writer 

may include such limitations in the NPDES permit for that discharge provided the limitations meet all 

other applicable technology and water quality standards. 

6.6.3 Tier 3 Implementation 

States identify their own ONRWs for Tier 3 protection, which requires that the water quality be 

maintained and protected. This is the most stringent level of protection. ONRWs often include waters in 

national or state parks, wildlife refuges, and waters of exceptional recreational or ecological significance. 

Waterbodies can be given Tier 3 protection regardless of their existing level of water quality. Some states 

implement Tier 3 by prohibiting any new or increased discharges to ONRWs or their tributaries that 

would result in lower water quality, with the exception of some limited activities such as those that would 

result in temporary changes in water quality ultimately resulting in restoration. Some states allow 

increased discharges as long as they are offset by equivalent or greater reductions elsewhere in the 

waterbody. 

In addition to Tiers 1, 2, and 3, some states have a class of waters considered outstanding to the state and 

for which the state might have specific antidegradation requirements. Such waterbodies are sometimes 

referred to as Tier 2 1⁄2 waters because implementation of the antidegradation policy for them affords a 

greater degree of protection than Tier 2 but more flexibility than Tier 3. 

Chapter 4 of EPA’s WQS Handbook and the Water Quality Standards Regulation Advance Notice of 

Proposed Rulemaking (64 FR 36742, July 7, 1998) include additional information on implementing 

antidegradation policies. The permit writer should clearly explain the antidegradation analysis and how it 

affects calculation of WQBELs in the fact sheet or statement of basis for the permit. 

1

 U.S. Environmental Protection Agency. 1994. Water Quality Standards Handbook: Second Edition (WQS Handbook). 

EPA 823-B-94-005a. U.S. Environmental Protection Agency, Office of Water, Washington DC. 

<www.epa.gov/waterscience/standards/handbook/>. 

2

 U.S. Environmental Protection Agency. 2001. Streamlined Water-Effect Ratio Procedure for Discharges of Copper. 

EPA-822-R-01-005. U.S. Environmental Protection Agency, Office of Science and Technology, Washington, DC. 

<www.epa.gov/waterscience/criteria/copper/copper.pdf>. 

3

 Davies, Tudor T. 1997. Establishing Site Specific Aquatic Life Criteria Equal to Natural Background. U.S. Environmental 

Protection Agency, Office of Science and Technology, Washington, DC. 

<www.epa.gov/waterscience/library/wqcriteria/naturalback.pdf>.

4

 U.S. Environmental Protection Agency. 1991. Technical Support Document for Water Quality-Based Toxics Control (TSD). 

EPA-505/2-90-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/owm0264.pdf>. 

5

 U.S. Environmental Protection Agency. 1990. Biological Criteria: National Program Guidance for Surface Waters. 

EPA-440/5-91-004. U.S. Environmental Protection Agency, Office of Science and Technology, Washington, DC. 

<www.epa.gov/bioindicators/html/biolcont.html>. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 7: Final Effluent Limitations and Anti-backsliding 7-1

CHAPTER 7. Final Effluent Limitations and 

Anti-backsliding 

As illustrated in Exhibit 7.1, after calculating applicable technology-based effluent limitations (TBELs) 

and water quality-based effluent limitations (WQBELs), the permit writer must determine the final 

effluent limitations that will be included in the National Pollutant Discharge Elimination System 

(NPDES) permit for each pollutant or pollutant parameter. For reissued permits, that determination must 

also include an assessment of whether the revised effluent limitations are consistent with the Clean Water 

Act (CWA) requirements and NPDES regulations related to anti-backsliding. 

Exhibit 7-1 Developing effluent limitations 

7.1 Determining Final Effluent Limitations 

When determining the final effluent limitations, the permit writer must ensure that all applicable statutory 

and regulatory requirements, including technology and water quality standards, are fully implemented. 

 The permit writer determines the calculated limitations (TBELs, WQBELs, or some combination 

of the calculated limitations) that will ensure that all applicable CWA standards are met. 

 As noted above, for reissued permits, if any of the limitations are less stringent than limitations on 

the same pollutant in the previous NPDES permit, the permit writer then conducts an antibacksliding analysis and, if necessary, revises the limitations accordingly. A detailed discussion 

of the anti-backsliding provisions of the CWA and the NPDES regulations is included below in 

Section 7.2. 
September 2010 NPDES Permit Writers’ Manual 

In addition, the permit writer should clearly explain in the fact sheet for the permit how the final 

limitations in the permit were determined and how those limitations meet both technology and water 

quality standards (including antidegradation) and, where appropriate, how an anti-backsliding analysis 

was applied to the final effluent limitations. 

7.2 Applying Anti-backsliding Requirements 

As noted in Section 7.1, after selecting the calculated effluent limitations for a pollutant that ensure that 

all CWA standards are met, the permit writer applies anti-backsliding requirements, as necessary, to 

determine the final effluent limitations. In general, the term anti-backsliding refers to statutory and 

regulatory provisions that prohibit the renewal, reissuance, or modification of an existing NPDES permit 

that contains effluent limitations, permit conditions, or standards less stringent than those established in 

the previous permit. There are, however, exceptions to the prohibition, and determining the applicability 

and circumstances of the exceptions requires familiarity with both the statutory and regulatory provisions 

that address anti-backsliding. 

7.2.1 Anti-backsliding Statutory Provisions 

Clean Water Act (CWA) section 402(o) expressly prohibits backsliding from certain existing effluent 

limitations. CWA section 402(o) consists of three main parts: (1) a prohibition on specific forms of 

backsliding, (2) exceptions to the prohibition, and (3) a safety clause that provides an absolute limitation 

on backsliding. 

7.2.1.1 Statutory Prohibition Against Backsliding 

First, CWA section 402(o)(1) prohibits the relaxation of effluent limitations for two situations: 

 To revise an existing TBEL that was developed on a case-by-case basis using best professional 

judgment (BPJ) to reflect subsequently promulgated effluent limitations guidelines and standards 

(effluent guidelines) that would result in a less stringent effluent limitation. 

 Relaxation of an effluent limitation that is based on state standards, such as water quality 

standards or treatment standards, unless the change is consistent with CWA section 303(d)(4). 

Section 303(d)(4) may be applied independently of section 402(o). 

The prohibition against relaxation of effluent limitations is subject to the exceptions in CWA section 

402(o)(2) and, for limitations based on state standards, the provisions of CWA section 303(d)(4). Those 

exceptions are outlined further in the following sections. 

7.2.1.2 Exceptions for Case-by-Case TBELs 

CWA section 402(o)(2) outlines specific exceptions to the general prohibition against revising an existing 

TBEL that was developed on a case-by-case basis using BPJ to reflect subsequently promulgated, less 

stringent effluent guidelines in a renewed, reissued, or modified permit. CWA section 402(o)(2) provides 

that relaxed limitations may be allowed where 

 There have been material and substantial alternations or additions to the permitted facility that 

justify the relaxation. 

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 New information (other than revised regulations, guidance, or test methods) is available that was 

not available at the time of permit issuance and that would have justified a less stringent effluent 

limitation. If the effluent limitation was based on water quality standards, any changes must result 

in a decrease in pollutants discharged. 

 Technical mistakes or mistaken interpretations of the law were made in issuing the permit under 

CWA section 402(a)(1)(b). 

 Good cause exists because of events beyond the permittee’s control (e.g., natural disasters) and 

for which there is no reasonably available remedy. 

 The permit has been modified under CWA sections 301(c), 301(g), 301(h), 310(i), 301(k), 

301(n), or 316(a). 

 The permittee has installed and properly operated and maintained required treatment facilities but 

still has been unable to meet the effluent limitations (relaxation may be allowed only to the 

treatment levels actually achieved). 

7.2.1.3 Exceptions for Limitations Based on State Standards 

EPA has consistently interpreted CWA section 402(o)(1) to allow relaxation of WQBELs and effluent 

limitations based on state standards if the relaxation is consistent with the provisions of CWA section 

303(d)(4) or if one of the exceptions in CWA section 402(o)(2) is met. The two provisions constitute 

independent exceptions to the prohibition against relaxation of effluent limitations. If either is met, 

relaxation is permissible. 

CWA section 303(d)(4) has two parts: paragraph (A), which applies to nonattainment waters, and 

paragraph (B), which applies to attainment waters. 

 Nonattainment water: CWA section 303(d)(4)(A) allows the establishment of a less stringent 

effluent limitation when the receiving water has been identified as not meeting applicable water 

quality standards (i.e., a nonattainment water) if the permittee meets two conditions. First, the 

existing effluent limitation must have been based on a total maximum daily load (TMDL) or 

other wasteload allocation (WLA) established under CWA section 303. Second, relaxation of the 

effluent limitation is only allowed if attainment of water quality standards will be ensured or the 

designated use not being attained is removed in accordance with the water quality standards 

regulations. This subsection does not provide an exception for establishing less stringent 

limitations where the original limitation was based on state permitting standards (e.g., state 

treatment standards) and was not based on a TMDL or WLA. 

 Attainment water: CWA section 303(d)(4)(B) applies to waters where the water quality equals 

or exceeds levels necessary to protect the designated use, or to otherwise meet applicable water 

quality standards (i.e., an attainment water). Under CWA section 303(d)(4)(B), a limitation based 

on a TMDL, WLA, other water quality standard, or any other permitting standard may only be 

relaxed where the action is consistent with state’s antidegradation policy. 

Although the statute also identifies six exceptions in section 402(o)(2) where effluent limitations 

otherwise subject to the prohibition in section 402(o)(1) may be relaxed, the exceptions for technical 

mistakes or mistaken interpretations and permit modification, which are described above, would not apply 

to WQBELs. 

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7.2.1.4 Exception Safety Clause 

CWA section 402(o)(3) is a safety clause that provides an absolute limitation on backsliding. This section 

of the CWA prohibits the relaxation of effluent limitations in all cases if the revised effluent limitation 

would result in a violation of applicable effluent guidelines or water quality standards, including 

antidegradation requirements. Thus, even if one or more of the backsliding exceptions outlined in the 

statute is applicable and met, CWA section 402(o)(3) acts as a floor and restricts the extent to which 

effluent limitations may be relaxed. The requirement affirms existing provisions of the CWA that require 

effluent limitations, standards, and conditions to ensure compliance with applicable technology and water 

quality standards. 

7.2.2 Anti-backsliding Regulatory Provisions 

Anti-backsliding regulations are found at Title 40 of the Code of Federal Regulations (CFR) 122.44(l). 

The regulations do not specifically address backsliding where a permittee seeks relaxation of an effluent 

limitation that is based on a state treatment standard or water quality standard [i.e., based on CWA section 

301(b)(1)(C), 303(d) or 303(e)]. They do, however, address all other forms of backsliding. 

First, the regulations at § 122.44(l)(1) restrict the relaxation of final effluent limitations and the relaxation 

of standards or conditions contained in existing permits. Thus, this regulation, in effect, addresses all 

types of backsliding not addressed in the CWA provisions (e.g., backsliding from limitations derived 

from effluent guidelines, from new source performance standards, from existing case-by-case limitations 

to new case-by-case limitations, and from conditions such as monitoring requirements that are not 

effluent limitations). Under the regulation, a permittee must meet one of the causes for modification under 

§ 122.62 for the reissued permit to allow relaxation of such limitations, standards, or conditions. 

Second, the regulations at § 122.44(l)(2)(i) directly reflect the specific prohibition imposed by CWA 

section 402(o) on backsliding where a permittee seeks to revise an existing case-by-case TBEL developed 

using BPJ to reflect a subsequently promulgated effluent guideline that is less stringent than the case-bycase requirement. The regulations include the same exceptions to this prohibition that are in CWA section 

402(o)(2) and the same safety clause in CWA section 402(o)(3). 

Thus, if the permit condition being considered for relaxation is either a case-by-case effluent limitation 

developed using BPJ or is any other limitation, standard, or condition other than an effluent limitation 

based on a state standard, the permit writer can apply the requirements in § 122.44(l). For effluent 

limitations based on state standards, the permit writer should apply the provisions of CWA sections 

402(o) and 303(d)(4) directly. Exhibit 7-2 illustrates the process of applying the statutory and regulatory 

provisions addressing anti-backsliding. 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 7-2 Application of anti-backsliding requirements 

Exhibit 7-3 presents some examples of situations when backsliding might be a factor in effluent limitation 

development. 

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Exhibit 7-3 Backsliding examples 

Example 1 

 A publicly owned treatment works (POTW) seeks to relax its WQBEL for Pollutant X 

 The current effluent limitation for Pollutant X is based on a TMDL and WLA for the POTW developed in 

accordance with § 130.7. 

 The POTW is in compliance with its existing effluent limitation, and the applicable water quality standards for 

Pollutant X are attained. 

 The POTW has developed new models with new river flow information. The models indicate that the water 

quality standards for Pollutant X would be maintained with a relaxed permit limitation. 

Question: 

May the effluent limitation for Pollutant X be relaxed? 

Answer: 

Possibly. Under the interpretation discussed above, WQBELs may be relaxed where one of the exceptions in 

CWA sections 402(o)(1) or (2) are met. In this case, although the new information from the models might meet the 

exception requirements criteria under CWA section 402(o)(2)(B)(i), CWA section 402(o)(2) will not justify the 

request unless the state reduces the pollutant loadings from other point sources or nonpoint sources of pollution. 

That is because, as discussed in Section 7.1 above, CWA section 402(o)(2) restricts the use of new information to 

cases where there is a decrease in the amount of pollutants being discharged. 

The CWA section 402(o)(1) exceptions, on the other hand, might justify the request. In this case, the reference to 

CWA section 303(d)(4)(B) in CWA section 402(o)(1) is the relevant exception. CWA section 303(d)(4)(B) provides 

that, for receiving waters that meet water quality standards, permit limitations based on a TMDL or other WLA or 

other permit standard may be relaxed if the state's antidegradation policy requirements are met. 

Example 2 

 The state has established a technology-based treatment standard for fecal coliform pursuant to CWA section 

301(b)(1)(C). 

 The state later relaxes the standard in a revised regulation. 

 A POTW, which has been in violation of its effluent limitation for fecal coliform based on the old standard, 

requests a revision of the limitation to reflect the new standard. 

 Water quality standards for fecal coliform are not being attained. 

 There was no TMDL or WLA developed. The basis of the effluent limitation was a state technology-based 

treatment standard. 

Question: 

May the fecal coliform effluent limitation be relaxed? 

Answer: 

No. Under CWA section 402(o)(1), the applicable provision is CWA section 303(d)(4)(A). This subsection does not 

authorize backsliding in this case (i.e., nonattainment waters) because it applies only to permit limitations based on 

a TMDL or other WLA. Here, the limitation in question is based on a state technology-based treatment standard. 

Furthermore, if the permit sought to apply the exceptions in CWA section 402(o)(2), the new information provision 

would not allow the revision. For purposes of this section of the CWA, new information does not include revised 

regulations.

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Chapter 7: Final Effluent Limitations and Anti-backsliding 7-7

Exhibit 7-3 Backsliding examples (continued) 

Example 3 

 The state has a narrative water quality criterion of no toxics in toxic amounts. 

 On the basis of WET testing data or other information, the state found that the discharge would cause, have 

the reasonable potential to cause, or contribute to an excursion of the water quality standards in the receiving 

water—specifically the narrative water quality criterion. 

 The permitting authority imposed a WET limitation under § 122.44(d)(1)(v). 

 The permittee determines that Pollutant Z is the cause of WET measured in its discharge. 

 The permittee can demonstrate through sufficient data (including WET testing data) that an effluent limitation 

for Pollutant Z will assure compliance with the narrative water quality criterion as well as the state's numeric 

criteria for Pollutant Z, as required by § 122.44(d)(1)(v). 

Question: 

May the state modify the permit to delete the WET limitation and to add the effluent limitation for Pollutant Z? 

Answer: 

Possibly. CWA section 303(d)(4) might justify the action. The applicable provision is CWA section 303(d)(4)(B) 

because the narrative water quality criterion is currently attained. The permittee is complying with the existing WET 

limitation to attain and maintain the criterion. Under CWA section 303(d)(4)(B), the existing effluent limitation may 

be relaxed as long as antidegradation requirements are met and the relaxed limitation will not cause a violation of 

any effluent guidelines or water quality standards applicable to the discharge. In this case, it appears likely that a 

relaxation would be permissible because the permittee can demonstrate that the new limitation for Pollutant Z will 

assure compliance with both the narrative and numeric water quality criteria; however, the permit writer might 

consider continuing WET monitoring to identify other potential sources of toxicity in the future.

Example 4 

 An industrial permittee seeks to revise its WQBEL of 60 mg/L for total suspended solids (TSS) to 100 mg/L, 

which is its actual discharge level. 

 The current effluent limitation is based on a WLA from a TMDL developed in accordance with § 130.7. 

 The water quality standards are not being attained. The ambient concentration of TSS exceeds the applicable 

water quality criteria. 

 An effluent limitation of 100 mg/L is consistent with applicable effluent guidelines. 

 New modeling information shows that the water quality standards will be attained with an effluent limitation of 

75 mg/L TSS. 

Question: 

May the effluent limitation for TSS be revised from 60 mg/L to 100 mg/L? 

Answer: 

No; however, the effluent limitation could be relaxed to 75 mg/L under either CWA sections 402(o)(1) or (2) 

exceptions. 

The water quality standards are not being attained because of TSS. Therefore, under CWA section 402(o)(1), the 

applicable exception is CWA section 303(d)(4)(A). In this case, the permitting authority may allow backsliding to 

75 mg/L because the existing effluent limitation is based on a WLA from a TMDL, and the data show that 

attainment of the water quality standards is assured with an effluent limitation of 75 mg/L (but not with a limitation 

of 100 mg/L).
September 2010 NPDES Permit Writers’ Manual 

Chapter 8: Monitoring and Reporting Conditions 8-1

CHAPTER 8. Monitoring and Reporting Conditions 

This chapter describes the monitoring and reporting conditions that a permit writer establishes in a 

National Pollutant Discharge Elimination System (NPDES) permit. The monitoring and reporting 

conditions require the permittee to conduct routine or episodic self-monitoring of permitted discharges 

and internal operations (where applicable) and report the analytical results to the permitting authority with 

the information necessary to evaluate discharge characteristics and compliance status. Periodic 

monitoring and reporting establish an ongoing record of the permittee’s compliance status and, where 

violations are detected, create a basis for any necessary enforcement actions. 

The monitoring and reporting conditions section of an NPDES permit generally includes specific 

requirements for the following items: 

 Monitoring locations. 

 Monitoring frequencies. 

 Sample collection methods. 

 Analytical methods. 

 Reporting and recordkeeping requirements. 

The following sections provide an overview of the considerations involved in determining appropriate 

monitoring, reporting, and recordkeeping requirements, and how to properly incorporate the appropriate 

requirements in an NPDES permit. 

8.1 Establishing Monitoring Conditions 

The NPDES regulations require facilities discharging pollutants to waters of the United States to 

periodically evaluate compliance with the effluent limitations established in their permits and provide the 

results to the permitting authority. A permit writer should consider several factors when determining the 

specific requirements to be included in the NPDES permit. Inappropriate or incomplete monitoring 

requirements can lead to inaccurate compliance determinations. Factors that could affect sampling 

location, sampling method, and sampling frequency include the following: 

 Applicability of effluent limitations guidelines and standards (effluent guidelines). 

 Wastestream and process variability. 

 Access to sample locations. 

 Pollutants discharged. 

 Effluent limitations. 

 Discharge frequencies (e.g., continuous versus intermittent). 

 Effect of flow or pollutant load or both on the receiving water. 

 Characteristics of the pollutants discharged. 

 Permittee’s compliance history. 
September 2010 NPDES Permit Writers’ Manual 

8.1.1 Purposes of Monitoring 

Monitoring is performed to determine compliance with effluent limitations established in NPDES 

permits, establish a basis for enforcement actions, assess treatment efficiency, characterize effluents and 

characterize receiving water. 

Regulations requiring the establishment of monitoring and reporting conditions in NPDES permits are at 

Title 40 of the Code of Federal Regulations (CFR) 122.44(i) and 122.48. Regulations at § 122.44(i) 

require permittees to monitor pollutant mass (or other applicable unit of measure) and effluent volume 

and to provide other measurements (as appropriate) using the test methods established at Part 136. That 

subpart also establishes that NPDES permits (with certain specific exceptions as discussed in section 

8.1.3 below) must require permittees to monitor for all limited pollutants and report data at least once per 

year. 

Regulations at § 122.48 stipulate that all permits must specify requirements concerning the proper use, 

maintenance, and installation of monitoring equipment or methods (including biological monitoring 

methods when appropriate). NPDES permits must also specify the monitoring type, intervals, and 

frequency sufficient to yield data that are representative of the activity. The following sections focus on 

developing permit monitoring conditions that properly address these regulatory requirements. 

8.1.2 Monitoring Location 

The permit writer should specify the appropriate monitoring location in an NPDES permit to ensure 

compliance with the permit limitations and provide the necessary data to determine the effects of an 

effluent on the receiving water. The NPDES regulations do not prescribe exact monitoring locations; 

rather, the permit writer is responsible for determining the most appropriate monitoring location(s) and 

indicating the location(s) in the permit. Ultimately, the permittee is responsible for providing a safe and 

accessible sampling point that is representative of the discharge [§ 122.41(j)(1)]. 

The permit writer should consider the following questions when selecting a monitoring location: 

 Is the monitoring location on the facility’s property? 

 Is the monitoring location accessible to the permittee and the permitting authority? 

 Will the results be representative of the targeted wastestream? 

 Is monitoring at internal points needed? 

Permit writers should establish monitoring locations where the wastewater is well mixed, such as near a 

Parshall flume or at a location in a sewer with hydraulic turbulence. Weirs tend to enhance the settling of 

solids immediately upstream and the accumulation of floating oil or grease immediately downstream. 

Such locations should be avoided for sampling. 

The permit writer can specify monitoring locations with either a narrative description or a diagram of the 

permittee’s facility. Exhibit 8-1 provides examples of how to specify monitoring locations in a permit 

either by narrative or by diagram. 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 8-1 Examples of specifying monitoring locations in permits 

Narrative 

A. Monitoring Locations 

1. Discharge from the Chemistry-Fine Arts Building must be sampled at the Parshall flume before the 

discharge point for Outfall 001. 

2. Discharge from the Physics Building must be sampled at the Parshall flume before the discharge point for 

Outfall 002. 

3. Discharge from the Research Lab No. 1 must be sampled at the Parshall flume before the discharge point 

for Outfall 003. 

Diagram 

A. Monitoring Locations 

Outfall Description

001 Discharge Pipe: Discharge of wastewater generated by all regulated metal finishing processes 

at the facility. Samples must be collected at the point indicated on the diagram below. 

Final pH 

Adjustment

Tank * Sample Point

*

Parshall Flume

Receiving 

Stream

Outfall

001

The monitoring location will vary depending on the type of monitoring required. The following sections 

discuss monitoring location considerations for each monitoring type. 

8.1.2.1 Influent and source water monitoring locations 

Influent monitoring is monitoring of a wastestream before that wastestream receives treatment. The 

permit writer should require influent monitoring when a characterization of the influent is needed to 

determine compliance with a permit condition, such as the 5-day biochemical oxygen demand (BOD5) 

and total suspended solids (TSS) percent removal limitations required by the secondary treatment 

standards for publicly owned treatment works (POTWs). 

Source water monitoring is the monitoring of source water before use as process water (e.g., river water 

used as contact cooling water). The permit writer should require source water monitoring if intake credits 

are established as specified in § 122.45(g). 

Influent and source water monitoring locations should ensure a representative sample of raw intake water 

before any processes or treatment that could alter the properties of the intake water. 

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September 2010 NPDES Permit Writers’ Manual 

8.1.2.2 Internal monitoring locations 

Internal monitoring is the monitoring of wastestreams at a location within the facility before discharge to 

waters of the United States. The NPDES regulations at § 122.45(h) allow internal monitoring points to be 

established when needed to determine compliance with a standard and in cases where setting an external 

monitoring location is not feasible. The permit writer may require internal monitoring to determine 

compliance with technology-based effluent limitations (TBELs) for a wastestream before commingling 

with other process or non-process wastestreams. Internal monitoring is generally not appropriate for 

determining compliance with water quality-based effluent limitations (WQBELs) unless final effluent 

monitoring is impractical (e.g., the final discharge point is submerged or inaccessible). 

Examples of reasons for requiring designation of internal monitoring locations include the following: 

 Ensuring compliance with effluent guidelines (at non-POTW facilities): When non-process 

wastewaters dilute process wastewaters subject to effluent guidelines, monitoring the combined 

discharge might not accurately allow determination of whether the facility is complying with the 

effluent guidelines. Under such circumstances, the permit writer might consider requiring 

monitoring for compliance with TBELs before the process wastewater is combined with nonprocess wastewater. 

 Ensuring compliance with secondary treatment standards (for POTWs only): Some POTWs 

include treatment processes that do not address pollutants regulated by secondary treatment 

standards and that could interfere with the ability to accurately monitor for compliance with 

secondary treatment standards. Under such circumstances, the permit writer could consider 

requiring monitoring for compliance with limitations derived from secondary treatment standards 

before such processes. For example, the permit could require effluent monitoring for compliance 

with limitations derived from secondary treatment standards after secondary clarification but 

before disinfection. 

 Allowing detection of a pollutant: Instances could arise where the combination of process and 

non-process wastewaters result in dilution of a pollutant of concern such that it would not be 

detectable using approved analytical methods. Internal monitoring would enable characterization 

of the pollutant before dilution with other wastewaters. 

Where the permit writer determines that internal monitoring is necessary, § 122.45(h)(2) states that 

limitations on internal wastestreams may be imposed only where the permit fact sheet sets forth the 

exceptional circumstances requiring application of limitations at those locations. 

8.1.2.3 Effluent monitoring locations 

Effluent monitoring is monitoring of the final effluent after all treatment processes. The permit writer 

should require effluent monitoring to determine compliance with final effluent limitations established in 

the permit. Effluent monitoring also can be used to provide data to assess the possible impact of the 

discharge on the receiving water. 

Effluent monitoring locations should provide a representative sample of the effluent being discharged into 

the receiving water. Effluent monitoring locations should be established after all industrial uses and 

treatment processes. Most importantly, the point where a final effluent limitation applies and the point 

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where monitoring is required must be the same. A logical effluent monitoring point is just before 

discharge to the receiving water. This is particularly true for ensuring compliance with WQBELs. 

8.1.3 Monitoring Frequency 

The permit writer should establish monitoring frequencies sufficient to characterize the effluent quality 

and to detect events of noncompliance, considering the need for data and, as appropriate, the potential 

cost to the permittee. Monitoring frequency should be determined on a case-by-case basis, and decisions 

for setting monitoring frequency should be described in the fact sheet. Some states have their own 

monitoring guidelines that can help a permit writer determine an appropriate monitoring frequency. 

To establish a monitoring frequency, the permit writer should consider the variability of the concentration 

of various parameters by reviewing effluent data for the facility (e.g., from discharge monitoring reports 

[DMRs]) or, without actual data, information from similar dischargers. A highly variable discharge 

should require more frequent monitoring than a discharge that is relatively consistent over time 

(particularly in terms of flow and pollutant concentration). Other factors that should be considered when 

establishing appropriate monitoring frequencies include the following: 

 Design capacity of the treatment facility. The monitoring frequency might need to be increased 

at facilities where the treatment facility is nearing design capacity. For example, at equivalent 

average flow rates, a large lagoon system that is not susceptible to bypasses would require less 

frequent monitoring than an overloaded treatment facility that experiences fluctuating flow rates 

from infiltration or large batch discharges from an industrial user system. The lagoon should have 

a relatively low variability compared to the facility receiving batch discharges. 

 Treatment method used. The monitoring frequency will be similar for similar treatment 

processes. The type of wastewater treatment used by the facility might affect the frequency of 

effluent monitoring. An industrial facility employing biological treatment would have a similar 

monitoring frequency as a secondary treatment plant with the same units used for wastewater 

treatment. If the treatment method is appropriate and achieving high pollutant removals on a 

consistent basis, monitoring could be less frequent than for a plant with little or insufficient 

treatment. 

 Compliance history. The monitoring frequency might need to be adjusted to reflect the 

compliance history of the facility. A facility with problems achieving compliance generally 

should be required to perform more frequent monitoring to characterize the source or cause of the 

problems or to detect noncompliance. 

 Cost of monitoring relative to permittee’s capabilities. The monitoring frequency should not 

be excessive and should be what is necessary to provide sufficient information about the 

discharge. 

 Location of the discharge. The monitoring frequency could be increased if the discharge is to 

sensitive waters or is near a public water supply. 

 Nature of the pollutants. To accurately characterize the discharge, the monitoring frequency 

might be increased for wastewaters with highly toxic pollutants or where the nature of the 

pollutants varies. 

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September 2010 NPDES Permit Writers’ Manual 

 Frequency of the discharge. The monitoring frequency for a wastewater discharged in batches 

infrequently should differ from that for a continuous discharge of highly concentrated wastewater 

or a wastewater containing a pollutant that is found infrequently and at very low concentrations. 

The production schedule of the facility (e.g., seasonal, daily), the plant washdown schedule, and 

other similar factors should be considered. 

 Number of monthly samples used in developing effluent limitations. When establishing 

monitoring frequency, the permit writer should consider the number of monthly samples used in 

developing average monthly WQBELs. If the discharger monitors less frequently than the 

monthly monitoring frequency assumed when developing applicable effluent guidelines or in 

calculating a WQBEL, it could be more difficult for the discharger to comply with its average 

monthly effluent limitations. For example, if an average monthly limitation is established 

assuming a monitoring frequency of four times per month (i.e., the limit is the expected average 

of four samples taken during a month), a discharger taking only one sample per month would 

statistically have a greater chance of exceeding its average monthly limit than if it sampled at 

least four times per month. 

 Tiered limitations. The monitoring frequency requirements should correspond to the applicable 

tiers in cases where the permit writer has included tiered limitations. If a facility has seasonal 

discharge limitations, it might be appropriate to increase the monitoring frequency during the 

higher production season, and reduce the frequency during the off-season. 

 Other Considerations. To ensure representative monitoring, permit conditions could be included 

to require monitoring on the same day, week, or month for parameters that might be correlated in 

some way. For example, coordinating the monitoring requirements for parameters such as 

pathogens and chlorine or metals and pH can provide information for both compliance 

assessment and determination of treatment efficacy. 

A permit writer could also establish a tiered monitoring schedule that reduces or increases the monitoring 

frequency during a permit cycle. Tiered monitoring might be appropriate for discharges where the initial 

sampling shows compliance with effluent limitations, justifying a reduction in monitoring frequency over 

time. Conversely, if problems are found during the initial sampling, more frequent sampling and more 

comprehensive monitoring can be applied. This step-wise approach could lead to lower monitoring costs 

for permittees while still providing the data needed to demonstrate compliance with effluent limitations. 

In 1996 EPA issued Interim Guidance for Performance-Based Reductions of NPDES Permit Monitoring 

Frequencies <www.epa.gov/npdes/pubs/perf-red.pdf>. Under the guidance, NPDES reporting and monitoring 

requirements may be reduced on the basis of a demonstration of excellent historical performance. 

Facilities can demonstrate that historical performance by meeting a set of compliance and enforcement 

criteria and by demonstrating their ability to consistently discharge pollutants below the levels necessary 

to meet their existing NPDES permit limitations. Reductions are determined parameter-by-parameter, on 

the basis of the existing monitoring frequency and the percentage below the limitation at which the 

parameter is being discharged. The reductions are incorporated when the permit is reissued. To remain 

eligible for the reductions, permittees are expected to maintain the parameter performance levels and 

good compliance on which the reductions were based. 

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8.1.4 Sample Collection 

The permit writer must specify the sample collection method for all parameters required to be monitored 

in the permit. The permit writer should determine the sample collection method on the basis of the 

characteristics of each specific discharge. Certain sample collection and storage requirements are 

identified as part of the analytical methods specified in Part 136. (Section 8.3 below presents more on 

analytical methods.) The two most frequently used sampling methods are grab and composite. For more 

detailed information on sample collection methods, permit writers should refer to Chapter 5 (Sampling) of 

the NPDES Compliance Inspection Manual1

<www.epa.gov/compliance/resources/publications/monitoring/cwa/inspections/npdesinspect/npdesmanual.html>. 

8.1.4.1 Grab Samples 

Grab samples are individual samples collected over a period not exceeding 15 minutes and that are 

representative of conditions at the time the sample is collected. Grab samples are appropriate when the 

flow and characteristics of the wastestream being sampled are relatively constant. The sample volume 

depends on the type and number of analyses to be performed. A grab sample is appropriate when a 

sample is needed to 

 Monitor an effluent that does not discharge on a continuous basis. 

 Provide information about instantaneous concentrations of pollutants at a specific time. 

 Allow collection of a variable sample volume. 

 Corroborate composite samples. 

 Monitor parameters not amenable to compositing (e.g., temperature). 

Grab samples can also be used to determine the spatial variability of a parameter or information on 

variability over a short period. They also are useful for monitoring intermittent wastewater flows from 

well-mixed batch process tanks. 

8.1.4.2 Composite Samples 

Composite samples are collected over time, either by continuous sampling or by mixing discrete samples, 

and represent the average characteristics of the wastestream during the sample period. Composite samples 

might provide a more representative measure of the discharge of pollutants over a given period than grab 

samples, and are used when any of the following is true: 

 A measure of the average pollutant concentration during the compositing period is needed. 

 A measure of mass loadings per unit of time is needed. 

 Wastewater characteristics are highly variable. 

Composite samples can be discrete samples (see discussion of sequential sampling in section 8.1.4.3 

below) or a single combined sample and are collected either manually or with automatic samplers. There 

are two general types of composite sampling: time-proportional and flow-proportional. The permit writer 

should clearly express which type is required in the permit. 

Time-proportional composite sample: This method collects a fixed volume (V) of discrete sample aliquots 

in one container at constant time intervals (t) as shown in Exhibit 8-2. 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 8-2 Visual interpretation of time-proportional composite monitoring 

Time-proportional composite monitoring is appropriate when the flow of the sampled stream is constant 

(flow rate does not vary more than ±10 percent of the average flow rate) or when flow-monitoring 

equipment is not available. Automatically timed composited samples are usually preferred over manually 

collected composites. Composite samples collected by hand are appropriate for infrequent analyses and 

screening or if the subsamples have a fixed volume at equal time intervals. 

Flow-proportional composite sample: There are two methods used for this type of sample: constantvolume when the interval time varies between samples, or constant-time when the interval volume 

collected varies between samples as shown in Exhibit 8-3. 

Exhibit 8-3 Visual interpretation of flow-proportional composite monitoring 

The constant-volume, flow-proportional, composite monitoring method collects a constant sample 

volume at varying time intervals proportional to stream flow (e.g., 200 milliliters sample collected for 

every 5,000 gallons of flow). The constant-time, flow-proportional, composite monitoring method 

collects the sample by adjusting the volume of each aliquot as the flow varies, while maintaining a 

constant time interval between the aliquots. 

Flow-proportional composite sampling is usually preferred over time-proportional composite sampling 

when the effluent flow volume varies appreciably over time. If there is no flow-measuring device, 

effluent samples can be manually composited using the influent flow measurement without any correction 

for time lag. The error in the influent and effluent flow measurement is insignificant except in those cases 

where large volumes of water are impounded, as in equalization basins. 

If a sampling protocol is not specified in the regulations, the permit writer should establish the duration of 

the compositing period and frequency of aliquot collection. The permit writer should also establish the 

time frame within which the sample is to be collected and the number of individual aliquots in the 

composite. 

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There are instances where composite samples are inappropriate. For example, the permit application 

regulations at § 122.21(g)(7) indicate that grab samples must be used for sampling several parameters that 

may change during the time it takes to composite the sample. Composite samples can be used for whole 

effluent toxicity (WET) testing; however, if there is concern that there are toxicity spikes or that the 

toxicant is a parameter for which composite sampling is not appropriate, grab samples for WET testing 

could be specified in the permit. 

8.1.4.3 Sequential and Continuous Monitoring 

Sequential monitoring refers to collecting discrete samples in individual containers in regular succession, 

such as timed intervals or discharge increments. Sequential grab samples provide a characteristic of the 

wastestream over a given time. Automatic sequential monitoring may be done with a special type of 

automatic sampling device that collects relatively small amounts of a sampled wastestream with the 

interval between sampling proportioned based on either time or effluent flow. Unlike a combined 

composite sampler, the sequential sampling device automatically retrieves a sample and holds it in a 

bottle separate from other automatically retrieved samples. Many individual samples can be stored 

separately in the unit rather than combining aliquots in a common bottle. 

Continuous monitoring is another option for a limited number of parameters such as flow, total organic 

carbon (TOC), temperature, pH, conductivity, residual chlorine, fluoride, and dissolved oxygen. When 

establishing continuous monitoring requirements, the permit writer should be aware that the NPDES 

regulations concerning pH limitations allow for a period of excursion when the effluent is being 

continuously monitored (§ 401.17). The reliability, accuracy, and cost of continuous monitoring vary with 

the parameter monitored. The permit writer should consider the environmental significance of the 

variation of any of these parameters in the effluent and the cost of continuous monitoring before 

establishing continuous monitoring requirements in the permit. 

8.2 Additional Monitoring Requirements and WET Testing 

A variety of discharges other than traditional POTW or industrial wastewater discharges, including 

biosolids (sewage sludge), combined sewer and sanitary sewer overflows, and stormwater, are regulated 

under the NPDES permit program. In addition, many permits include requirements for WET testing. As 

discussed in this section, a permit writer should account for such unique discharges and testing 

requirements in establishing monitoring requirements. 

8.2.1 Biosolids (Sewage Sludge) 

The purpose of monitoring sewage sludge is to ensure safe use or disposal of the sludge. Sewage sludge 

regulations specified in Part 503 require monitoring of sewage sludge that is applied to land, placed on a 

surface disposal site, or incinerated. The frequency of monitoring is based on the annual amount of 

sewage sludge that is used or disposed of by those methods. POTWs that provide the sewage sludge to 

another party for further treatment (such as composting) must provide that party with the information 

necessary to comply with regulations at Part 503. Sewage sludge disposed of in a municipal solid waste 

landfill unit must meet the criteria for municipal solid waste landfills in the regulations at Part 258. 

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September 2010 NPDES Permit Writers’ Manual 

Exhibit 8-4 shows the minimum monitoring requirements established in Part 503 for sewage sludge 

before use and disposal. More frequent monitoring for any of the required or recommended parameters is 

appropriate when the POTW has any of the following: 

 A highly variable influent load of toxics or organic solids. 

 A significant industrial load. 

 A history of process upsets due to toxics, or of adverse environmental impacts due to sludge use 

or disposal activities. 

Exhibit 8-4 Minimum requirements for sewage sludge monitoring, based on method of sludge 

use or disposal 

Method Monitoring requirements Frequency 

Citation 

(40 CFR) 

Land application 

 Sludge weight and percent total 

solids 

 Metals: As, Cd, Cu, Pb, Hg, Mo, 

Ni, Se, and Zn 

 Pathogen Density 

 Vector Attraction Reduction 

Based on dry weight of sludge in metric 

tons per year: 

 > zero but < 290: annually 

 = or > 290 but < 1,500: quarterly 

 = or > 1,500 but < 15,000: bimonthly 

 = or > 15,000: monthly 

§ 503.16 

Co-disposal in 

municipal solid 

waste landfill 

 Sludge weight and percent total 

solids 

 Passes Paint-Filter Liquid Test 

 Suitability of sludge used as cover 

 Characterize in accordance with 

hazardous waste rules 

Monitoring requirements or frequency not 

specified by Part 503. Determined by 

local health authority or landfill 

owner/operator. 

Part 258 

 Sludge weight and percent total 

solids 

 Metals: As, Cr, Ni (Unlined sites 

only) 

 Pathogen Density 

 Vector Attraction Reduction 

Based on dry weight of sludge in metric 

tons per year: 

 > zero but < 290: annually 

 = or > 290 but < 1,500: quarterly 

 = or > 1,500 but < 15,000: bimonthly 

 = or > 15,000: monthly 

Surface 

disposal: 

lined sites with 

leachate 

collection and 

unlined sites 

 Methane gas  Continuously 

§ 503.26 

 Sludge weight and percent total 

solids 

 Metals: As, Cd, Cr, Pb, and Ni 

Based on dry weight of sludge in metric 

tons per year: 

 > zero but < 290: annually 

 = or > 290 but < 1,500: quarterly 

 = or > 1,500 but < 15,000: bimonthly 

 = or > 15,000: monthly 

 Be and Hg (National Emissions 

Standards) 

 As required by permitting authority 

(local air authority) 

 THC or O2, moisture, combustion 

temperatures  Continuously 

Incineration 

 Air pollution control device 

operating parameters  As required by permitting authority 

§ 503.46 

Notes: 

Monitoring frequencies required by Part 503 may be reduced after 2 years of monitoring, but in no case may be less than once 

per year. 

A successful land application program could necessitate sampling for other constituents of concern (such as nitrogen) in 

determining appropriate agronomic rates. The permit writer will determine additional monitoring requirements. 

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September 2010 NPDES Permit Writers’ Manual 

The sampling and analysis methods specified in § 503.8 and Part 136 should be followed for monitoring 

the required parameters. Without any specific methods in Part 503, guidance on appropriate methods is in 

the following documents: 

 Part 503 Implementation Guidance2

 <www.epa.gov/npdes/pubs/owm0237.pdf>. 

 POTW Sludge Sampling and Analysis Guidance Document3

 <www.epa.gov/npdes/pubs/owm012.pdf>. 

 Control of Pathogens and Vector Attraction in Sewage Sludge4

<www.epa.gov/ORD/NRMRL/pubs/625r92013/625r92013.htm>. 

8.2.2 Combined Sewer Overflows (CSOs) and Sanitary Sewer Overflows 

(SSOs) 

EPA’s Combined Sewer Overflow (CSO) Control Policy (59 FR 18688, April 19, 1994) requires 

monitoring to characterize the combined sewer system, assist in developing a Long-Term Control Plan 

(LTCP), and show compliance with permit requirements. The permit writer should ensure the following: 

 Monitoring is done to develop an initial system characterization as part of the nine minimum 

controls to reduce CSOs and their effect on receiving water quality. Such monitoring includes 

analyzing existing data on precipitation events, on the combined sewer system and CSOs, on 

water quality, and conducting field inspections. 

 As part of the LTCP, a permittee is required to develop a more complete characterization of the 

sewer system through monitoring and modeling. 

 To show compliance with the permit requirements and ultimately the attainment of water quality 

standards, the permittee is required to conduct a post-construction compliance monitoring 

program. Specific monitoring requirements of the post-construction compliance monitoring 

program will be unique to each permittee’s LTCP and should be established as specific 

monitoring conditions in the individual NPDES permit. 

These monitoring conditions should require monitoring of certain key parameters during a representative 

number of CSOs from a representative number of wet-weather events along with ambient water quality 

monitoring to ascertain attainment of water quality standards. EPA has prepared a guidance manual on 

monitoring entitled Combined Sewer Overflows: Guidance for Monitoring and Modeling5

<www.epa.gov/npdes/pubs/sewer.pdf>. 

A facility’s permit might also contain monitoring requirements for sanitary sewer overflows (SSOs). SSO 

monitoring requirements would be developed on a case-by-case basis. 

8.2.3 Stormwater Monitoring Considerations 

Stormwater monitoring requirements vary according to the type of permit regulating the stormwater 

discharge and the activity. Municipal separate storm sewer systems (MS4s) serving more than 100,000 

people (and some serving less than 100,000) are typically issued individual NPDES permits with 

monitoring requirements that are specific to the MS4. Smaller MS4s regulated under the stormwater Phase 

II rule are typically not required to conduct water quality monitoring as a condition in their NPDES general 

permit, though evaluation of measurable goals may include monitoring. EPA’s multi-sector general permit 

(MSGP) for stormwater discharges from industrial facilities includes analytical monitoring requirements 

based on the type of industrial activity. Finally, operators of construction activity regulated under the 

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September 2010 NPDES Permit Writers’ Manual 

construction general permit are typically not required to conduct water quality monitoring; however, some 

states and EPA Regions do require monitoring if the construction activity will discharge to a water 

impaired by sediment. 

Specific monitoring conditions for the federal general stormwater permits are detailed in the most recent 

Construction General Permit or MSGP issued by EPA (available on the EPA Stormwater Program 

Website <www.epa.gov/npdes/stormwater>). Additional documents on stormwater monitoring are: 

 Urban Stormwater BMP Performance: A Guidance Manual for Meeting the National Stormwater 

BMP Database Requirements6

 <www.epa.gov/npdes/pubs/montcomplete.pdf>. 

 Guidance Manual for the Monitoring and Reporting Requirements of the NPDES Stormwater 

Multi-Sector General Permit (MSGP)7

 <www.epa.gov/npdes/pubs/dmr-fin.pdf>. 

8.2.4 WET Monitoring 

The use of WET testing to evaluate the toxicity in a receiving stream is discussed in section 6.4 of this 

manual and on the NPDES WET Website <www.epa.gov/npdes/wet>. The WET (or biomonitoring) test 

procedures were promulgated in § 136.3 (60 FR 53529, October 16, 1995). EPA revised the WET 

methods in 67 FR 69951, November 19, 2002. WET monitoring conditions included in permits should 

specify the particular biomonitoring test to be used, the test species, required test endpoints, and quality 

assurance/quality control procedures. 

To support permitting agencies in implementing WET methods, EPA has revised and published manuals 

for toxicity test protocols: 

 Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and 

Marine Organisms. 5th ed.8

 <www.epa.gov/waterscience/WET/disk2/atx.pdf>. 

 Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to 

Freshwater Organisms. 4th ed.9

 <www.epa.gov/waterscience/WET/disk3/ctf.pdf>. 

 Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to 

Marine and Estuarine Organisms. 3rd ed.10 <www.epa.gov/waterscience/WET/disk1/ctm.pdf>. 

 NPDES Compliance Monitoring Inspector Training: Biomonitoring11 (No Link). 

WET testing samples could be composite or grab samples. Twenty-four hour composite samples are 

suggested except when any of the following are true: 

 The effluent is expected to be more toxic at a certain time of day. 

 Toxicity may be diluted during compositing. 

 The size of the sample needed exceeds the composite sampler volume. 

WET tests are relatively expensive compared to single parameter tests. Therefore, a permit writer should 

carefully consider the appropriate frequency for WET testing. A discharge with highly variable flow or 

observed toxicity should have more frequent monitoring than a discharge that is relatively consistent over 

time. As with other parameters, factors that a permit writer should consider when establishing appropriate 

WET monitoring frequencies include the following: 

 Type of treatment process. 

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September 2010 NPDES Permit Writers’ Manual 

 Environmental significance and nature of the toxicity. 

 Past compliance record or history. 

 Cost of monitoring relative to financial capabilities. 

 Number of monthly samples used in developing the permit limitation. 

 The frequency of intermittent discharges. 

Samples should be evenly spaced throughout the year so that seasonal variability can be ascertained. 

8.3 Analytical Methods 

The permit writer must specify the analytical methods to be used for monitoring. EPA’s Office of Science 

and Technology’s Clean Water Act Analytical Methods Website <www.epa.gov/waterscience/methods/> 

contains information about analytical methods. 

The standard conditions of the permit [§§ 122.41(j)(4) and 122.44(i)] require that, when available, 

permittees use test procedures specified in Part 136 <www.epa.gov/waterscience/methods/basic.htm>. The 

analytical methods contained in Part 136 are established for conventional, toxic (priority), and some 

nonconventional pollutants. Without analytical methods for a parameter, the permit writer should specify 

the analytical method to be used. There are also procedures to apply for approval of alternative test 

methods in accordance with § 136.4. 

While Part 136 identifies the analytical methods approved for use in the NPDES program, additional 

methods information is available through the National Environmental Methods Index (NEMI) 

<www.nemi.gov/>. NEMI is a Web-based, searchable clearinghouse of methods supported by the U.S. 

Geological Survey and EPA’s Office of Water. NEMI contains summaries of more than 1,100 methods 

and describes them by their performance characteristics and their regulatory status, relative cost, detection 

level, detection level type, accuracy, precision, spiking level, instrumentation, lab equipment, and the 

greenness of analytic methods. Permit writers might find that information useful in comparing the 

features of Part 136 methods that will be used for assessing compliance with the calculated effluent 

limitations. 

When establishing effluent limitations for a specific parameter (based on technology or water quality 

regulatory requirements), it is possible for the value of the calculated limit to fall below the method 

detection limit (MDL) and the minimum level (ML) established by the approved analytical method(s). 

Regardless of whether current analytical methods are available to detect and quantify the parameter at the 

concentration of the calculated limitation, the limitation must be included in the permit as calculated. 

In some instances, there might be two or more approved Part 136 analytical methods available for the 

analysis of a parameter. In such cases, the permit should determine whether there is a need to select one 

of the approved methods and to include a requirement in the permit mandating the use of only the selected 

method. That approach might be necessary where an effluent limit is established at a level that is 

quantifiable by one approved method but is below the ML of another approved method. 

Such a situation often occurs where a permit contains a WQBEL for mercury. To clarify the EPA’s 

position with respect to effluent monitoring for mercury, EPA developed a memo Analytical Methods for 

Mercury in National Pollutant Discharge Elimination System (NPDES) Permits12

<www.epa.gov/npdes/pubs/mercurymemo_analyticalmethods.pdf>. 

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Sufficiently Sensitive Methods

At the time of the writing of this manual, EPA had proposed regulations at §§ 122.21(e), 122.44(i), and 

Part 136, to require the use of sufficiently sensitive methods for analyses conducted for NPDES permit 

applications and for compliance monitoring (75 FR 35712, June 23, 2010). To ensure that appropriate 

analytical methods are required and performed, see the most current version of these federal 

regulations and applicable state analytical method regulations and policy. 

8.4 Reporting Monitoring Results 

The NPDES regulations require the permittee to maintain records and periodically report on monitoring 

activities. The regulations at § 122.41(l)(4)(i) require that monitoring results must be reported on a DMR

<www.epa.gov/npdes/pubs/dmr.pdf>. Data reported include both data required by the permit and any additional 

data the permittee has collected consistent with permit requirements. All facilities must submit reports (on 

discharges and sludge use or disposal) at least annually, as required by § 122.44(i)(2). POTWs with 

pretreatment programs must submit a pretreatment report at least annually as required by § 403.12(i). 

However, the NPDES regulation states that monitoring frequency and reporting should be dependent on 

the nature and effect of the discharge or sludge use or disposal. Thus, the permit writer can require 

reporting more frequent than annually. 

8.5 Recordkeeping Requirements 

Generally, the permit writer is required by § 122.41(j) to include in the permit the requirement to retain 

records for at least three years, subject to extension by the State Director. Recordkeeping requirements for 

sewage sludge [§ 122.41(j)] and the CAFO program [§ 122.42(e)(2)] require records be kept five years or 

longer if required by the State Director. The permit writer should designate in the permit where records 

should be kept. 

Monitoring records must include the following: 

 Date, place, time of sampling. 

 Name of sampler. 

 Date of analysis. 

 Name of analyst. 

 Analytical methods used. 

 Analytical results. 

According to § 122.41(j), monitoring records must be representative of the discharge. Monitoring records, 

which must be retained, include continuous strip chart recordings, calibration data, copies of all reports 

for the permit, and copies of all data used to compile reports and applications. 

Sewage sludge regulations under §§ 503.17, 503.27, and 503.47 establish recordkeeping requirements 

that vary depending on the use and disposal method for the sewage sludge. The same recordkeeping 

requirements should be applied to other sludge monitoring parameters not regulated by the Part 503 rule. 

8-14 Chapter 8: Monitoring and Reporting Conditions 
September 2010 NPDES Permit Writers’ Manual 

Chapter 8: Monitoring and Reporting Conditions 8-15

 

1

 U.S. Environmental Protection Agency. 2004. NPDES Compliance Inspection Manual. EPA-305-X-03-001. U.S. 

Environmental Protection Agency, Office of Enforcement and Compliance Assurance, Washington, DC. 

<www.epa.gov/compliance/resources/publications/monitoring/cwa/inspections/npdesinspect/npdesinspect.pdf>.

2

 U.S. Environmental Protection Agency. 1995. Part 503 Implementation Guidance. EPA 833-R-95-001. U.S. Environmental 

Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/owm0237.pdf>. 

3

 U.S. Environmental Protection Agency. 1989. POTW Sludge Sampling and Analysis Guidance Document. EPA-833-B-89-100. 

U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/owm012.pdf>. 

4

 U.S. Environmental Protection Agency. 1992. Control of Pathogens and Vector Attraction in Sewage Sludge. EPA-625/R-92-

013. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC. 

<www.epa.gov/ORD/NRMRL/pubs/625r92013/625r92013.htm>. 

5

 U.S. Environmental Protection Agency. 1999. Combined Sewer Overflows–Guidance for Monitoring and Modeling. EPA-832-

B-99-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/sewer.pdf>. 

6

 U.S. Environmental Protection Agency. 2002. Urban Stormwater BMP Performance: A Guidance Manual for Meeting the 

National Stormwater BMP Database Requirements. EPA-821-B-02-001. U.S. Environmental Protection Agency, Office of 

Water, Washington, DC. <www.epa.gov/npdes/pubs/montcomplete.pdf>. 

7

 U.S. Environmental Protection Agency. 1999. Guidance Manual for the Monitoring and Reporting Requirements of the NPDES 

Stormwater Multi-Sector General Permit (MSGP). U.S. Environmental Protection Agency, Office of Water, NPDES Program 

Branch, Washington, DC. <www.epa.gov/npdes/pubs/dmr-fin.pdf>. 

8

 U.S. Environmental Protection Agency. 2002. Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to 

Freshwater and Marine Organisms, Fifth Edition. EPA-821-R-02-012. U.S. Environmental Protection Agency, Office of Water, 

Washington, DC <www.epa.gov/waterscience/WET/disk2/atx.pdf>. 

9

 U.S. Environmental Protection Agency. 2002. Short-Term Methods for Estimating the Chronic Toxicity of Effluents and 

Receiving Waters to Freshwater Organisms, Fourth Edition. EPA-821-R-02-013. U.S. Environmental Protection Agency, Office 

of Water, Washington, DC. <www.epa.gov/waterscience/WET/disk3/ctf.pdf>.

10 U.S. Environmental Protection Agency. 1994. Short-Term Methods for Estimating the Chronic Toxicity of Effluents and 

Receiving Waters to Marine and Estuarine Organisms, Third Edition. EPA821-R-02-014. U.S. Environmental Protection 

Agency, Office of Water, Washington, DC. <www.epa.gov/waterscience/WET/disk1/ctm.pdf>. 

11 U.S. Environmental Protection Agency. 1990. NPDES Compliance Monitoring Inspector Training: Biomonitoring. 

U.S. Environmental Protection Agency, Office of Water Enforcement and Permits, Washington, DC. NTIS # PB91-145854. 

(No Link) 

12 Hanlon, James A. 2007. Analytical Methods for Mercury in National Pollutant Discharge Elimination System (NPDES) 

Permits. U.S. Environmental Protection Agency, Office of Wastewater Management. Memorandum, August 23, 2007. 

<www.epa.gov/npdes/pubs/mercurymemo_analyticalmethods.pdf>. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 9: Special Conditions 9-1

CHAPTER 9. Special Conditions 

Special conditions in National Pollutant Discharge Elimination System (NPDES) permits supplement 

numeric effluent limitations and require the permittee to undertake activities designed to reduce the 

overall quantity of pollutants being discharged to waters of the United States, to reduce the potential for 

discharges of pollutants, or to collect information that could be used in determining future permit 

requirements. 

There are many different reasons to incorporate special conditions into a permit including: 

 To address unique situations, such as facilities discharging pollutants for which data are absent or 

limited, making development of technology- or water quality-based effluent limitations (TBELs 

or WQBELs) more difficult or impossible. 

 To incorporate preventive requirements, such as requirements to install process control alarms, 

containment structures, good housekeeping practices, and the like. 

 To address foreseeable changes to discharges, such as planned changes to process, products, or 

raw materials that could affect discharge characteristics. 

 To incorporate compliance schedules to provide the time necessary to comply with permit conditions. 

 To incorporate other NPDES programmatic requirements (e.g., pretreatment, sewage sludge). 

 To impose additional monitoring requirements that provide the permit writer with data to evaluate 

the need for changes in permit limitations. 

 To increase or decrease monitoring requirements, depending on monitoring results or changes in 

processes or products. 

 To impose requirements for special studies such as ambient stream surveys, toxicity identification 

evaluations (TIEs) and toxicity reduction evaluations (TREs), bioaccumulation studies, sediment 

studies, mixing or mixing zone studies, pollutant reduction evaluations, or other such 

information-gathering studies. 

Section 9.1 below addresses several types of special conditions that apply to both municipal and nonmunicipal facilities. Section 9.2 addresses special conditions unique to municipal facilities. 

9.1 Special Conditions Potentially Applicable to Any Type of 

Discharger 

This section discusses several types of special conditions that could be included in any NPDES permit 

(i.e., municipal or non-municipal). Those special conditions can be thought of as the ABCs of special 

conditions and include the following: 

 Additional monitoring and special studies. 

 Best management practices (BMPs). 

 Compliance schedules. 
September 2010 NPDES Permit Writers’ Manual 

A summary of the use of those special conditions follows. 

9.1.1 Additional Monitoring and Special Studies 

Additional monitoring requirements, beyond those required under the effluent limitations section of the 

permit, and special studies are useful for collecting data that were not available to the permit writer for 

consideration during permit development. Additional monitoring requirements and special studies 

generally are used to supplement numeric effluent limitations or support future permit development 

activities. Examples of the types of special studies that could be required in an NPDES permit include the 

following: 

 Treatability studies: Might be required in a permit when insufficient treatability information for 

a pollutant or pollutants would hinder a permit writer from developing defensible TBELs. 

Treatability studies can also be required when the permit writer suspects that a facility might not 

be able to comply with an effluent limitation. 

 Toxicity identification evaluation/toxicity reduction evaluation (TIE/TRE): Could be 

required in a permit when wastewater discharges are found to be toxic using whole effluent 

toxicity (WET) tests. The purpose of those evaluations is to identify and control the sources of 

toxicity in an effluent. Further guidance related to U.S. Environmental Protection Agency (EPA) 

recommended TIE/TRE procedures and requirements is found in the following guidance 

manuals: 

− Toxicity Reduction Evaluation Guidance for Municipal Wastewater Treatment Plants1

<www.epa.gov/npdes/pubs/tre.pdf>. 

− Clarifications Regarding Toxicity Reduction and Identification Evaluations in the National 

Pollutant Discharge Elimination System Program2

 <www.epa.gov/npdes/pubs/owmfinaltretie.pdf>. 

− Generalized Methodology for Conducting Industrial Toxicity Reduction Evaluations3

 

(No link—see the endnote for ordering instructions). 

− Methods for Aquatic Toxicity Identification Evaluations: Phase I Toxicity Characterization 

Procedures. 2nd ed4

 <www.epa.gov/npdes/pubs/owm0330.pdf>. 

− Toxicity Identification Evaluation: Characterization of Chronically Toxic Effluents, Phase I5

<www.epa.gov/npdes/pubs/owm0255.pdf>. 

− Methods for Aquatic Toxicity Identification Evaluations: Phase II Toxicity Identification 

Procedures for Samples Exhibiting Acute and Chronic Toxicity6

<www.epa.gov/npdes/pubs/owm0343.pdf>. 

− Methods for Aquatic Toxicity Identification Evaluations: Phase III Confirmation Procedures 

for Samples Exhibiting Acute and Chronic Toxicity7

 <www.epa.gov/npdes/pubs/owm0341.pdf>. 

 Mixing or mixing zone studies: Might be required in a permit to assist in determining how 

effluent and receiving water mix and in establishing a regulatory mixing zone that can be applied 

when developing WQBELs. 

 Sediment monitoring: Could be included in a permit if a permit writer suspects that pollutants 

contained in wastewater discharges accumulate in the sediments of the receiving water. 

 Bioaccumulation studies: Might be required in a permit to determine whether pollutants 

contained in wastewater discharges bioaccumulate in aquatic organisms (e.g., fish, invertebrates). 

Such studies could be required when water quality criteria are expressed in terms of fish tissue 

levels. Additional guidance related to evaluating the bioaccumulation potential of a pollutant can 

9-2 Chapter 9: Special Conditions 
September 2010 NPDES Permit Writers’ Manual 

be found in the EPA Great Lakes Water Quality Initiative Technical Support Document for the 

Procedure to Determine Bioaccumulation Factors8 (No link—see the endnote for ordering instructions). 

When establishing additional monitoring or special studies, permit writers must ensure that any 

requirements related to the study (e.g., special sampling or analytical procedures) are specified in the 

appropriate permit condition. In addition, permit writers should establish a reasonable schedule for 

completion and submission of the study or monitoring program. If the anticipated timeline is longer than 

one year, an interim progress report during the study is advisable. 

9.1.2 Best Management Practices (BMPs) 

In general, BMPs are actions or procedures to prevent or reduce the discharge of pollution to waters of the 

United States. Title 40 of the Code of Federal Regulations (CFR) section 122.2 includes the following in 

the definition of BMPs: 

 Schedules of activities. 

 Prohibitions of practices. 

 Maintenance procedures. 

 Treatment requirements. 

 Operating procedures and practices to control 

− Plant site runoff. 

− Spillage or leaks. 

− Sludge or waste disposal. 

− Drainage from raw material storage areas. 

9.1.2.1 When to Use BMPs 

Clean Water Act (CWA) section 304(e) authorizes EPA to require BMPs as part of effluent limitations 

guidelines and standards (effluent guidelines) to control plant site runoff, spillage or leaks, sludge or 

waste disposal, and drainage from raw material storage that it determines are associated with or ancillary 

to the industrial manufacturing or treatment process and can contribute significant amounts of pollutants 

to navigable waters. Where effluent guidelines require specific control measures, including BMPs or 

development of a BMP plan, permit writers must include such requirements in permits. In addition, CWA 

section 402(p)(3)(B)(iii) states that permits for discharges from municipal storm sewers must require 

controls, including management practices, to reduce the discharge of pollutants. Finally, CWA sections 

402(a)(1) and (2) give the permitting authority the ability to include BMPs in permits on a case-by-case 

basis to carry out the provisions of the CWA. 

The NPDES regulations at § 122.44(k) track the statutory provisions cited above. This section of the 

regulations provides that permits must contain BMPs (when applicable) to control or abate the discharge 

of pollutants when any of the following are true: 

 They are authorized under CWA section 304(e). 

 They are authorized under CWA section 402(p) for the control of stormwater discharges. 

 Numeric effluent limitations are infeasible. 

 The practices are necessary to achieve effluent limitations and standards or carry out the purpose 

and intent of the CWA. 

Chapter 9: Special Conditions 9-3
September 2010 NPDES Permit Writers’ Manual 

Circumstances under which numeric effluent limitations might be infeasible include the following: 

 Regulating a pollutant for which limited treatability or aquatic impact data are available to allow 

development of numeric TBELs or WQBELs. 

 Regulating discharges when the types of pollutants vary greatly over time. 

In addition, a permit writer should consider using BMPs under any of the following circumstances: 

 When chemical analyses are inappropriate or impossible. 

 When there is a history of leaks and spills or when housekeeping is sloppy. 

 When a complex facility lacks data for a pollutant or pollutants. 

9.1.2.2 BMPs in NPDES Permits 

Permit writers include BMP requirements in permits using two approaches: (1) site-, process-, or 

pollutant-specific BMPs, or (2) a requirement to develop a BMP plan. Site-, process-, or pollutant-specific 

BMPs might be appropriate in the case of an individual permit where a permit writer has the opportunity 

to review the circumstances at the facility. On the other hand, it might not be appropriate to include site-, 

process-, or pollutant-specific BMPs as conditions in a general permit, a permit for a particularly complex 

facility, or a permit for a facility with operations not familiar to the permit writer. Instead, complicated 

facilities and discharges covered under a general permit could be required to develop a BMP plan that 

requires the permittee to determine appropriate BMPs on the basis of circumstances at its facility. 

Specific BMPs 

Specific BMPs are designed to address conditions particular to a type of facility or to a specific site, 

process, or pollutant. Specific BMPs might be used in a permit when 

 They are needed to address ancillary activities that could result in the discharge of pollutants to 

waters of the United States. 

 Numeric effluent limitations for a specific process are otherwise infeasible and BMPs serve as 

effluent limitations for that process. 

 They are required to supplement and ensure compliance with effluent limitations in the permit. 

To select a specific BMP, the permit writer could 

 Review the industry profiles or the specific facility to determine the applicable and appropriate 

management practices. 

 Evaluate whether the BMP would help to achieve effluent limitations or other environmental 

objectives for that facility. 

 Use information from other permits, pollution prevention sources, and EPA guidance documents 

to identify applicable and appropriate BMPs. 

Specific BMPs frequently are required for certain types of dischargers such as concentrated animal 

feeding operations (CAFOs), combined sewer overflows (CSOs), and stormwater discharges. 

9-4 Chapter 9: Special Conditions 
September 2010 NPDES Permit Writers’ Manual 

BMP Plans 

The Guidance Manual for Developing Best Management Practices9

 <www.epa.gov/npdes/pubs/owm0274.pdf> 

describes the activities and materials at an industrial or municipal facility that are best addressed by 

BMPs. The manual also describes how BMPs work and gives examples of types of BMPs. 

If a permit writer requires a BMP plan, it is the facility’s responsibility to develop, implement, and 

evaluate the success or shortfalls of its own plan. Often, a BMP committee (i.e., a group of individuals 

within the plant organization) is responsible for developing the BMP plan and assisting the plant 

management in implementing and updating the BMP plan. 

EPA has identified several recommended components of effective BMP plans and detailed each 

component in the Guidance Manual for Developing Best Management Practices. The minimum 

suggested components of a general BMP plan are presented below: 

 General Provisions 

− Name and location of facility. 

− Statement of BMP policy and objective. 

− Review by plant manager. 

 Specific Provisions 

− BMP committee. 

− Risk identification and assessment. 

− Reporting of BMP incidents. 

− Materials compatibility. 

− Good housekeeping. 

− Preventive maintenance. 

− Inspections and records. 

− Security. 

− Employee training. 

BMP plans used to supplement effluent limitations or to describe how the discharger plans to meet 

effluent limitations can be submitted to the regulatory agency or be kept on-site and made available to the 

permitting authority upon request. A general schedule for BMP plan development can be included in the 

permit (e.g., complete and submit the plan within six months of permit issuance and begin implementing 

the plan within nine months of permit issuance). 

Exhibit 9-1 presents example permit text for a requirement to develop and implement a BMP plan and 

should be adapted as necessary to reflect conditions at the individual facility. 

Chapter 9: Special Conditions 9-5
September 2010 NPDES Permit Writers’ Manual 

Exhibit 9-1 Example BMP plan requirement 

The following is example text for requiring development and implementation of a BMP plan through an NPDES 

permit. The text should be crafted and changed as necessary to meet the individual facility's needs and the 

permitting authority’s goals. The bracketed text should be updated to be specific to the permit. 

1. Implementation.

[IF A BMP PLAN DOES NOT EXIST:] 

The permittee, must develop and implement a best management practices (BMP) plan that achieves the 

objectives and the specific requirements listed below. A copy of the plan must be submitted to the U.S. 

Environmental Protection Agency (EPA) [AND/OR STATE AGENCY] within six months of the effective date 

of this permit. The plan must be implemented as soon as possible but no later than nine months from the 

effective date of the permit. The permittee must update and amend the plan as needed. 

[IF A BMP PLAN ALREADY EXISTS:] 

The permittee must during the term of this permit operate the facility in accordance with the BMP plan [CITE 

EXISTING PLAN] and in accordance with subsequent amendments to the plan. The permittee must amend 

the plan to incorporate practices to achieve the objectives and specific requirements listed below, and a copy 

of the amended plan must be submitted to the U.S. Environmental Protection Agency (EPA) [AND/OR STATE 

AGENCY] within three months of the effective date of this permit. The amended plan must be implemented as 

soon as possible but not later than six months from the effective date of the permit. 

2. Purpose 

Through implementation of the BMP plan the permittee must prevent or minimize the generation and the 

potential for the release of pollutants from the facility to the waters of the United States through normal 

operations and ancillary activities. 

3. Objectives 

The permittee must develop and amend the BMP plan consistent with the following objectives for the control 

of pollutants. 

a. The number and quantity of pollutants and the toxicity of effluent generated, discharged, or potentially 

discharged at the facility must be minimized by the permittee to the extent feasible by managing each 

influent waste stream in the most appropriate manner. 

b. Under the BMP plan, and any Standard Operating Procedures (SOPs) included in the plan, the permittee 

must ensure proper operation and maintenance of the treatment facility as required by § 122.41(e). 

c. The permittee must establish specific objectives for the control of pollutants by conducting the following 

evaluations. 

1. Each facility component or system must be examined for its waste minimization opportunities and its 

potential for causing a release of significant amounts of pollutants to waters of the United States 

because of equipment failure, improper operation, and natural phenomena such as rain or snowfall, 

etc. The examination must include all normal operations and ancillary activities including material 

storage areas, plant site runoff, in-plant transfer, process and material handling areas, loading or 

unloading operations, spillage or leaks, sludge and waste disposal, or drainage from raw material 

storage. [NOTE THAT ONLY THE APPLICABLE AREAS SHOULD BE INCLUDED IN THE PREVIOUS LIST.]

2. Where experience indicates a reasonable potential for equipment failure (e.g., a tank overflow or 

leakage), natural condition (e.g., precipitation), or other circumstances that may result in significant 

amounts of pollutants reaching surface waters, the program should include a prediction of the 

direction, rate of flow and total quantity of pollutants that could be discharged from the facility as a 

result of each condition or circumstance. 

4. Requirements

The BMP Plan must be consistent with the objectives in the Objectives section above and the general 

guidance contained in the publication entitled Guidance Manual for Developing Best Management Practices 

(BMPs), EPA 833-B-93-004, <www.epa.gov/npdes/pubs/owm0274.pdf> or any subsequent revisions to the 

guidance document. The BMP plan must 

a. Be documented in narrative form, must include any necessary plot plans, drawings or maps, and must be 

developed in accordance with good engineering practices. The BMP plan must be organized and written 

with the following structure: 

1. Name and location of the facility. 

2. Statement of BMP policy. 

3. Structure, functions, and procedures of the BMP Committee. 

4. Specific management practices and standard operating procedures to achieve the above objectives, 

including the following:

9-6 Chapter 9: Special Conditions 
September 2010 NPDES Permit Writers’ Manual 

Exhibit 9-1 Example BMP plan requirement (continued) 

a. Modification of equipment, facilities, technology, processes, and procedures. 

b. Reformulation or redesign of products. 

c. Substitution of materials. 

d. Improvement in management, inventory control, materials handling or general operational 

phases of the facility. 

5. Risk identification and assessment. 

6. Reporting of BMP incidents. 

7. Materials compatibility. 

8. Good housekeeping. 

9. Preventative maintenance. 

10. Inspections and records. 

11. Security. 

12. Employee training. 

b. Include the following provisions concerning BMP plan review: 

1. Review by plant engineering staff and the plant manager. 

2. Review and endorsement by the permittee's BMP Committee. 

3. A statement that the above reviews have been completed and that the BMP plan fulfills the 

requirements set forth in this permit. The statement must include the dated signatures of each BMP 

Committee member as certification of the reviews. 

c. Establish specific BMPs to meet the objectives identified in the Objectives section above, addressing 

each component or system capable of generating or causing a release of significant amounts of 

pollutants, and identifying specific preventive or remedial measures to be implemented. 

d. Establish specific BMPs or other measures that ensure that the following specific requirements are met: 

1. Ensure proper management of solid and hazardous waste in accordance with regulations 

promulgated under the Resource Conservation and Recovery Act (RCRA). Management practices 

required under RCRA regulations must be referenced in the BMP plan. 

2. Reflect requirements for Spill Prevention, Control, and Countermeasure (SPCC) plans under Clean 

Water Act (CWA) section 311 and 40 CFR Part 112 and may incorporate any part of such plans into 

the BMP plan by reference. 

3. Reflect requirements for stormwater control under CWA section 402(p) and the regulations at 40 

CFR 122.26 and 122.44, and otherwise eliminate to the extent practicable, contamination of 

stormwater runoff. 

etc. 

[NOTE: SECTION d. ABOVE COULD BE TAILORED TO EACH FACILITY BY THE PERMIT WRITER AND MAY 

INCLUDE PROCESSES OR AREAS OF THE FACILITY WITH HOUSEKEEPING PROBLEMS, NONCOMPLIANCE, 

SPILLS/LEAKS, OR OTHER PROBLEMS THAT COULD BE REMEDIED THROUGH A BMP. IF THERE IS A KNOWN 

SOLUTION TO THE PROBLEM (E.G., MORE FREQUENT INSPECTIONS, PREVENTIVE MAINTENANCE, ETC.), THIS 

REMEDY COULD ALSO BE INCLUDED AS A PART OF THE BMP PLAN REQUIREMENTS. TO GATHER IDEAS FOR 

SUCH REQUIREMENTS, THE PERMIT WRITER MAY WANT TO CONTACT THE PERMITTEE, COMPLIANCE 

PERSONNEL, FACILITY INSPECTORS, OPERATIONS OFFICE PERSONNEL, AND STATE AGENCY 

COUNTERPARTS. THE PERMIT WRITER MIGHT ALSO WANT TO CHECK REQUIREMENTS IN OTHER PERMITS 

AND BMP PLANS FOR SIMILAR FACILITIES.] 

5. Documentation 

The permittee must maintain a copy of the BMP plan at the facility and must make the plan available to EPA 

[AND/OR STATE AGENCY] upon request. All offices of the permittee, which are required to maintain a copy 

of the NPDES permit, must also maintain a copy of the BMP plan. 

6. BMP Plan Modification 

The permittee must amend the BMP plan whenever there is a change in the facility, or in the operation of the 

facility, that materially increases the generation of pollutants or their release or potential release to the 

receiving waters. The permittee must also amend the plan, as appropriate, when plant operations covered by 

the BMP plan change. Any such changes to the BMP plan must be consistent with the objectives and specific 

requirements listed above. All changes in the BMP plan must be reported to EPA [AND/OR STATE 

AGENCY] in writing. 

7. Modification for Ineffectiveness 

If at any time the BMP plan proves to be ineffective in achieving the general objective of preventing and 

minimizing the generation of pollutants and their release and potential release to the receiving waters and/or 

the specific requirements above, the permit and/or the BMP plan must be subject to modification to 

incorporate revised BMP requirements. 

Chapter 9: Special Conditions 9-7
September 2010 NPDES Permit Writers’ Manual 

9.1.2.3 Pollution Prevention in BMPs 

BMPs are, by their nature, pollution prevention practices. Traditionally, BMPs have focused on good 

housekeeping measures and good management techniques that attempt to avoid contact between 

pollutants and water as a result of leaks, spills, and improper waste disposal. However, on the basis of the 

authority granted under the regulations, BMPs may include a range of pollution prevention options, 

including production modifications, operational changes, materials substitution, and materials and water 

conservation. 

When developing BMPs, permit writers should be familiar with the fundamental principles of pollution 

prevention: 

 Pollution should be prevented or reduced at the source, whenever feasible (Reduce). 

 Pollution that cannot be prevented should be reused or recycled in an environmentally safe 

manner, whenever feasible (Reuse-Recycle). 

 Pollution that cannot be prevented or recycled should be treated in an environmentally safe 

manner, whenever feasible (Treat). 

 Disposal or other release into the environment should be employed only as a last resort and 

should be conducted in an environmentally safe manner (Dispose of). 

When writing an NPDES permit, a permit writer who has familiarity with a certain type of processes 

might identify pollution prevention practices that are not used at a facility and that would help that facility 

achieve its pollution prevention goals. Where the pollution prevention practices are necessary to carry out 

the purposes and intent of the CWA, the permit writer may develop BMPs to implement those practices. 

9.1.3 Compliance Schedules 

The NPDES regulations at § 122.47 allow permit writers to establish schedules of compliance to give 

permittees additional time to achieve compliance with the CWA and applicable regulations. Schedules 

developed under this provision must require compliance by the permittee as soon as possible, but may not 

extend the date for final compliance beyond compliance dates established by the CWA. Thus, compliance 

schedules in permits are not appropriate for every type of permit requirement. Specifically, a permit 

writer may not establish a compliance schedule in a permit for TBELs because the statutory deadlines for 

meeting technology standards (i.e., secondary treatment standards and effluent guidelines) have passed. 

This restriction applies to both existing and new dischargers. Permit writers should note, however, that 

§ 122.29(d)(4) allows a new source or new discharger up to 90 days to start-up its pollution control 

equipment and achieve compliance with its permit conditions (i.e., provides for up to a 90-day period to 

achieve compliance). 

Examples of requirements for which a compliance schedule in an NPDES permit might be appropriate 

include: 

 Pretreatment program development. 

 Sludge use and disposal program development and implementation. 

 BMP plan development and implementation. 

 Effluent limitations derived from new or revised water quality standards. 

9-8 Chapter 9: Special Conditions 
September 2010 NPDES Permit Writers’ Manual 

An EPA Administrator’s decision specifically addresses compliance schedules for effluent limitations 

derived from new or revised water quality standards. In the decision In the Matter of Star-Kist Caribe, 

Inc., documented in the memorandum Order Denying Modification Request With Respect to the 

Administrator’s 1990 Decision in Star-Kist Caribe, Inc. (NPDES Appeal No. 88-5)10

<www.epa.gov/npdes/pubs/owm0121.pdf>, the EPA Administrator interpreted CWA section 301(b)(1)(C) to 

mean that 1) after July 1, 1977, permits may not contain compliance schedules for effluent limitations 

based on water quality standards adopted before July 1, 1977, and 2) compliance schedules are allowed 

for effluent limitations based on standards adopted after that date only if the state has clearly indicated in 

its water quality standards or implementing regulations that it intends to allow them. 

In May 2007, the Director of EPA’s Office of Wastewater Management issued a memorandum to EPA 

Region 9 that clarified the requirements of § 122.47 as they relate to WQBELs [see Compliance 

Schedules for Water Quality-Based Effluent Limitations in NPDES Permits11

<www.epa.gov/npdes/pubs/memo_complianceschedules_may07.pdf>. Permit writers should consider the principles 

outlined in this memo when assessing whether a compliance schedule for achieving a WQBEL is 

consistent with the CWA and its implementing regulations and when documenting the basis for a 

compliance schedule in a permit. Considerations outlined in the memo include the following: 

 Demonstrate that the permittee cannot immediately comply with the new effluent limitation on 

the effective date of the permit. 

 Include an enforceable final effluent limitation and a date for achievement in the permit. 

 Justify and document the appropriateness of the compliance schedule; factors relevant to a 

determination that a compliance schedule is appropriate include how much time the discharger 

had to meet the WQBEL under prior permit(s), whether there is any need for modifications to 

treatment facilities, operations, or other measures and, if so, how long it would take to implement 

such modifications. 

 Justify and demonstrate that compliance with the final WQBEL is required as soon as possible; 

factors relevant to a determination that a compliance is required as soon as possible include the 

steps needed to modify or install treatment facilities, operations, or other measures and the time 

those steps would take. 

 Include an enforceable sequence of events leading to compliance with interim milestones for 

schedules longer than one year. 

 Recognize that a schedule solely to provide time to develop a total maximum daily load (TMDL) 

or to conduct a use attainability analysis (UAA) is not appropriate. 

Many of the principles outlined in the memo could be more generally applied to compliance schedules for 

requirements other than WQBELs. 

9.2 Special Conditions for Municipal Facilities 

This section explains several common special conditions that are applicable only to municipal facilities. 

These conditions reflect requirements for publicly owned treatment works (POTWs) to implement and 

enforce local pretreatment programs for their industrial users; biosolids (sewage sludge) disposal 

requirements; CSO requirements; SSO requirements; and municipal separate storm sewer system (MS4) 

requirements. 

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9.2.1 The National Pretreatment Program 

CWA section 402(b)(8) requires that certain POTWs receiving pollutants from significant industrial 

sources (subject to CWA section 307(b) standards) establish a pretreatment program to ensure compliance 

with these standards. The implementing regulations at § 403.8(a) state that: 

Any POTW (or combination of POTWs operated by the same authority) with a total design flow 

greater than 5 million gallons per day (mgd) and receiving from industrial users pollutants which pass 

through or interfere with the operation of the POTW or are otherwise subject to pretreatment 

standards will be required to establish a POTW pretreatment program unless the NPDES state 

exercises its option to assume local responsibilities as provided in § 403.10(e). 

As specified in § 403.8(a), the Regional Administrator or Director of an authorized state may require a 

POTW with a design flow of 5 mgd or less to develop a POTW pretreatment program. Program 

development could be determined to be necessary to prevent interference with or pass through of the 

POTW based on the nature, or volume, of the industrial influent, a history of treatment process upsets and 

violations of POTW effluent limitation(s), and contamination of municipal sludge. 

Since 1978, approximately 1,500 POTWs have been required to develop and implement pretreatment 

programs through special conditions of NPDES permits. The pretreatment program was developed to 

control industrial discharges to POTWs and to meet the following objectives: 

 To prevent pass through of pollutants. 

 To prevent interference with POTW processes, including interference with the use or disposal of 

municipal sludge. 

 To improve opportunities to recycle and reclaim municipal and industrial wastewater and sludges. 

The pretreatment program also helps ensure POTW personnel health and safety. 

As authorized by the pretreatment regulations at §§ 403.8(c), 403.8(d) and 403.8(e) and the NPDES 

regulations at § 122.44(j)(2), the requirements to develop and implement a POTW pretreatment program 

are included as enforceable conditions in the POTW's NPDES permit. NPDES permits drive the 

development and implementation of pretreatment programs by requiring the following: 

 Adequate legal authority. 

 Maintenance of an industrial user inventory. 

 Development and implementation of local limits. 

 Control mechanisms issued to significant industrial users (SIUs). 

 Compliance monitoring activities. 

 Swift and effective enforcement. 

 Data management and recordkeeping. 

 Reporting to the approval authority (EPA or state). 

 Public participation. 

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Through the NPDES permit, the POTW is required to develop and implement a pretreatment program. 

The POTW is required to submit an approvable program that meets the requirements in § 403.9(b). A 

more detailed description of these required program elements is in § 403.8(f). The POTW must have the 

legal authority enabling it to do the following: 

 Deny or condition new or increased contributions of pollutants, or changes in nature of pollutants, 

to the POTW by industrial users. 

 Require compliance with applicable pretreatment standards and requirements by industrial users. 

 Control through a permit, order, or similar means the contribution to the POTW by each 

industrial user to ensure compliance with applicable pretreatment standards and requirements. 

These control mechanisms must have certain conditions as laid out in § 403.8(f)(1)(iii) and be 

enforceable. 

 Require the development of compliance schedules where necessary by each industrial user for the 

installation of technology required to meet applicable pretreatment standards and requirements, 

and submission of all notices and self-monitoring reports to assess and ensure compliance. 

 Carry out all inspection, surveillance, and monitoring procedures necessary to determine 

compliance with applicable pretreatment standards and requirements independent of information 

submitted by the industrial user (including the authority to enter the premises of the industrial 

user). 

 Obtain remedies for noncompliance (e.g., injunctive relief, penalties). 

 Comply with confidentiality requirements. 

Further, at a minimum, the POTW must have procedures to do the following: 

 Identify and locate all possible industrial users that might be subject to the POTW pretreatment 

program. 

 Identify the character and volume of pollutants contributed to the POTW by the industrial users. 

 Notify industrial users of applicable pretreatment standards and applicable requirements under 

CWA sections 204(b) and 405 and RCRA Subtitles C and D. 

 Receive and analyze self-monitoring reports. 

 Conduct sampling, inspections and other surveillance activities to determine compliance with 

applicable pretreatment standards and requirements independent of information supplied by the 

industrial user. 

 Investigate instances of noncompliance. 

 Comply with public participation requirements, including annual public notice of industrial users 

determined to be in significant noncompliance during the previous 12-month period. 

Also, as part of the POTW pretreatment program, POTWs must have adequate resources and funding to 

implement the program, evaluate the need for and, as necessary, develop local limits and develop an 

enforcement response plan. 

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The NPDES permit should include the conditions specified in § 403.9, including that the POTW be 

required to submit the program documentation, detailing the authority and procedures to be implemented, 

along with other information about the program. The permit will allow the POTW up to one year, from 

the time when written notification from the approval authority determined the need for a pretreatment 

program, to develop and submit a program for approval as stated in § 403.8(b). Once the permitting 

authority reviews and approves the program, the requirement to implement the approved program is then 

incorporated into the permit. 

The permit writer generally incorporates the requirement to develop a pretreatment program at the time of 

permit reissuance. The requirement, however, may also be incorporated through a modification of the 

permit if there is cause, as defined in detail in § 403.8(e), to make such a modification. The permit writer 

must follow procedures outlined by § 122.62 related to modifications when including the requirement to 

develop a pretreatment program in an NPDES permit 

During the life of the permit, it might be necessary for the POTW to modify its approved pretreatment 

program (changes to local limits, changes to the ordinance, and such). The changes can be brought about 

by the POTW’s desire to change the way the program operates, or they can be the result of changes that 

are necessary to address deficiencies in the program found during inspections or audits done by the 

permitting authority. Whatever the reason for the modification, the permitting authority must review and 

approve any modification to the approved program that is considered substantial, as required by § 403.18. 

All substantial program modifications to the POTW’s approved pretreatment program require minor 

modifications to the NPDES permit and are subject to the procedural requirements in §§ 122.63(g) and 

403.18. In addition, incorporating the requirement for a previously approved pretreatment program for the 

purpose of making the implementation of the program an enforceable part of the permit is also considered 

a minor modification to the NPDES permit. 

The majority of POTWs that need pretreatment program requirements in their permits currently have 

them in place. In addition, an NPDES state or an EPA region will often designate a pretreatment 

coordinator to serve as the pretreatment expert to review the annual report from the POTW and 

recommend any action to be taken. The state or EPA regional pretreatment coordinator is a key resource 

on pretreatment issues, particularly at the time of NPDES permit reissuance. EPA regions and approved 

states have developed standard pretreatment development or implementation conditions (with minor 

modifications made to tailor the conditions to the specific discharger) that are placed in all applicable 

NPDES permits in that region or state. The permit writer can usually obtain examples of these NPDES 

pretreatment conditions from the EPA or state pretreatment coordinators. The permit writer might need to 

update or modify pretreatment implementation language or initiate corrective action related to the 

pretreatment program. 

EPA has developed the Pretreatment Program Website <www.epa.gov/npdes/pretreatment> and prepared a 

number of guidance manuals for POTWs on how to implement their local pretreatment programs that are 

accessible through this website. In addition, EPA prepared the Introduction to the National Pretreatment 

Program12 <www.epa.gov/npdes/pubs/final99.pdf> as a reference for anyone interested in understanding the 

basics of pretreatment program requirements and to provide a roadmap to additional and more detailed 

guidance materials for those trying to implement specific elements of the pretreatment program. 

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Pretreatment program information and monitoring data obtained through the POTW’s pretreatment 

program are useful to the permit writer in identifying possible modifications to the pretreatment 

program’s local limits or procedures, or the need for water quality-based controls. The permit writer 

should obtain such data with the aid of the pretreatment coordinator. Permits must include conditions 

requiring a POTW to provide a written technical evaluation of the need to revise local limits under 

§ 403.5(c)(1) following permit issuance or reissuance [§ 122.44(j)(2)(ii)]. In addition, POTWs with a 

design flow greater than or equal to one mgd and with an approved pretreatment program or required to 

develop a pretreatment program must sample and analyze their effluent for priority (toxic) pollutants 

listed in Part 122, Appendix J, Table 2 as part of the permit application process [see § 122.21(j)(4)(iv)]. 

Those data and information also are useful for determining the need for WQBELs. 

9.2.2 Biosolids (Sewage Sludge) 

CWA section 405(d) requires that EPA regulate the use and disposal of sewage sludge to protect public 

health and the environment from any reasonably anticipated adverse effects of these practices. In the 

CWA, Congress directed EPA to develop technical standards for municipal sludge use and disposal 

options and enacted strict deadlines for compliance with these standards. Within one year of promulgation 

of the standards, compliance was required unless construction of new pollution control facilities was 

necessary, in which case compliance was required within two years. 

EPA promulgated Part 503, Standards for the Use or Disposal of Sewage Sludge in 58 Federal Register

(FR) 9248, February 19, 1993, with amendments in 59 FR 9095, February 19, 1994 and 60 FR 54764, 

October 25, 1995. These regulations address four sludge use and disposal practices: land application, 

surface disposal, incineration, and disposal in a municipal solid waste landfill. The standards for each end 

use and disposal method consist of general requirements, numeric effluent limitations, operational 

standards, and management practices, as well as monitoring, recordkeeping, and reporting requirements. 

Unlike technology standards, which are based on the ability of treatment technologies to reduce the level 

of pollutants, EPA’s sewage sludge standards are based on health and environmental risks. Part 503 

imposes requirements on four groups: 

 Persons who prepare sewage sludge or material derived from sewage sludge. 

 Land appliers of sewage sludge. 

 Owners/operators of sewage sludge surface disposal sites. 

 Owners/operators of sewage sludge incinerators. 

Details of that rule are described in A Plain English Guide to the EPA Part 503 Biosolids Rule13

<www.epa.gov/owm/mtb/biosolids/503pe/>. 

The risk assessment for the Part 503 rule that governs the land application of biosolids took nearly 10 

years to complete and had extensive rigorous review and comment. The risk assessment evaluated and 

established limitations for a number of pollutants. These limitations are in chapter 4 of A Guide to the 

Biosolids Risk Assessments for the EPA Part 503 Rule14 <www.epa.gov/owm/mtb/biosolids/503rule/>. 

The regulation is largely self-implementing, and anyone who engages in activities covered by the 

regulation must comply with the appropriate requirements on or before the compliance deadlines. A 

person who violates Part 503 requirements is subject to administrative, civil, and criminal enforcement 

actions. 

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CWA section 405(f) requires the inclusion of sewage sludge use or disposal requirements in any NPDES 

permit issued to a Treatment Works Treating Domestic Sewage (TWTDS) and authorizes the issuance of 

sewage sludge-only permits to non-discharging TWTDS. In response, EPA promulgated revisions to the 

NPDES permit regulations at Parts 122 and 124 in 54 FR 18716, May 2, 1989, to address inclusion of 

sewage sludge use and disposal standards in NPDES permits and NPDES permit issuance to treatment 

works that do not have an effluent discharge to waters of the United States, but are involved in sewage 

sludge use or disposal as preparers, appliers, or owners/operators. TWTDS includes all sewage sludge 

generators and facilities, such as blenders, that change the quality of sewage sludge. 

EPA recognizes that implementation of Part 503 requirements is a source of confusion for permit writers 

and permittees who might already have NPDES permits with special conditions addressing sewage sludge 

requirements. EPA has provided several guidance documents to help clarify NPDES permitting 

expectations, and explain the requirements of Part 503: 

 Part 503 Implementation Guidance15 <www.epa.gov/npdes/pubs/owm0237.pdf>. 

 Land Application of Sewage Sludge—A Guide for Land Appliers on the Requirements of the 

Federal Standards for the Use or Disposal of Sewage Sludge Management in 40 CFR Part 50316

<www.epa.gov/npdes/pubs/sludge.pdf>. 

 Surface Disposal of Sewage Sludge—A Guide for Owners/Operators of Surface Disposal 

Facilities on the Monitoring, Recordkeeping, and Reporting Requirements of the Federal 

Standards for the Use or Disposal of Sewage Sludge in 40 CFR Part 50317 <No Link–see the endnote 

for ordering instructions>. 

 Preparing Sewage Sludge for Land Application or Surface Disposal—A Guide for Preparers of 

Sewage Sludge on the Monitoring, Record Keeping, and Reporting Requirements of the Federal 

Standards for the Use or Disposal of Sewage Sludge in 40 CFR Part 50318 <No Link–see the endnote 

for ordering instructions>. 

 Domestic Septage Regulatory Guidance, A Guide to the EPA 503 Rule19

<www.epa.gov/npdes/pubs/owm0026.pdf>. 

 Control of Pathogens and Vector Attraction in Sewage Sludge20

<www.epa.gov/nrmrl/pubs/625r92013/625R92013.pdf>. 

The permit writer should refer to the Part 503 Implementation Guidance and EPA Region and state 

guidelines or policies for instructions on how to implement the applicable Part 503 standards into the 

permit. The permit writer will need to determine the type of sewage sludge use or disposal practice(s) 

used by the discharger and apply the appropriate Part 503 standards. In general, conditions will need to be 

established to address the following: 

 Pollutant concentrations or loading rates. 

 Operational standards (such as pathogen and vector attraction reduction requirements for land 

application and surface disposal and total hydrocarbons (THC) concentrations for incinerators). 

 Management practices (e.g., siting restrictions, design requirements, operating practices). 

 Monitoring requirements (e.g., pollutants to be monitored, sampling locations, frequency, and 

sample collection and analytical methods). 

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 Recordkeeping requirements. 

 Reporting requirements (e.g., contents of reports and frequency or due dates for submission of 

reports). 

 General requirements (e.g., specific notification requirements before land application, submission 

of closure and post closure plan for surface disposal sites). 

In addition to any specific applicable Part 503 standards, three boilerplate conditions must be written in 

the NPDES permit where applicable. These consist of the following: 

 Text requiring the POTW/TWTDS to comply with all existing requirements for sewage sludge 

use and disposal, including the Part 503 standards [see § 122.44(b)(2)]. 

 A reopener clause, which authorizes reopening a permit to include technical standards if the 

technical standards are more stringent or more comprehensive than the conditions in the permit 

[see § 122.44(c)]. 

 A notification provision requiring the permittee to give notice to the permitting authority when a 

significant change in the sewage sludge use or disposal practice occurs (or is planned) [see 

standard conditions in § 122.41(l)(1)(iii)]. 

If permit conditions based on existing regulations are insufficient to protect public health and the 

environment from adverse effects that could occur from toxic pollutants in sewage sludge, permit 

conditions should be developed on a case-by-case basis using best professional judgment (BPJ) to fulfill 

the statutory requirement. The Part 503 Implementation Guidance contains information to assist permit 

writers in developing effluent limitations and management practice requirements on a case-by-case basis 

to protect public health and the environment from adverse effects that could occur from toxic pollutants in 

sewage sludge. For more information on biosolids, see section 2.3.1.3 of this manual and the Biosolids 

Website <www.epa.gov/owm/mtb/biosolids/index.htm> 

9.2.3 Combined Sewer Overflows (CSOs) 

Combined sewer systems were designed and built in the 19th and early 20th centuries to collect sanitary 

and industrial wastewater and stormwater runoff. During dry weather, combined sewers carry sanitary 

wastes and industrial wastewater to a treatment plant. In periods of heavy rainfall, however, stormwater is 

combined with untreated wastewater, which can overflow and discharge directly to a waterbody without 

being treated. These overflows are called combined sewer overflows (CSOs). 

EPA published a CSO Control Policy in 59 FR 18688, April 19, 1994. That policy represents a 

comprehensive national strategy to ensure that municipalities, permitting authorities, water quality 

standards authorities, and the public engage in a comprehensive and coordinated planning effort to 

achieve cost-effective CSO controls that ultimately meet appropriate health and environmental objectives. 

The CSO Control Policy includes expectations for NPDES permitting authorities. In general, EPA 

envisioned a phased permit approach, including initial requirements to implement Nine Minimum CSO 

Controls (NMC) and develop a Long-Term CSO Control Plan (LTCP), followed by requirements to 

implement the controls in the approved LTCP. The Wet Weather Water Quality Act of 2000 amended the 

CWA to add section 402(q), which required that CSO permits be issued in conformance with the CSO 

Control Policy. 

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CSOs are point source discharges subject to both the technology-based requirements of the CWA and 

applicable state water quality standards. Under the CWA, CSOs must comply with Best Available 

Technology Economically Achievable (BAT) for nonconventional and toxic pollutants and Best 

Conventional Technology (BCT) for conventional pollutants. However, there are no promulgated BAT or 

BCT limitations in effluent guidelines for CSOs. As a result, permit writers must use BPJ in developing 

technology-based permit requirements for controlling CSOs. Permit conditions also must achieve 

compliance with applicable water quality standards. 

The 1994 CSO Control Policy contains the recommended approach for developing and issuing NPDES 

permits to control CSOs. In addition, EPA has developed the following CSO guidance documents to help 

permit writers and permittees implement the CSO Control Policy: 

 Combined Sewer Overflows–Guidance for Long-Term Control Plan21

<www.epa.gov/npdes/pubs/owm0272.pdf>. 

 Combined Sewer Overflows–Guidance for Nine Minimum Controls22

<www.epa.gov/npdes/pubs/owm0030.pdf>. 

 Combined Sewer Overflows–Guidance for Screening and Ranking23 <www.epa.gov/npdes/cso>. 

 Combined Sewer Overflows–Guidance for Monitoring and Modeling24

<www.epa.gov/npdes/pubs/sewer.pdf>. 

 Combined Sewer Overflows–Guidance for Financial Capability Assessment and Schedule 

Development25 <www.epa.gov/npdes/pubs/csofc.pdf>. 

 Combined Sewer Overflows–Guidance for Funding Options26

<www.epa.gov/npdes/pubs/owm0249.pdf>. 

 Combined Sewer Overflows–Guidance for Permit Writers27 <www.epa.gov/npdes/cso>. 

 Combined Sewer Overflows–Guidance: Coordinating Combined Sewer Overflow Long-Term 

Planning with Water Quality Standards Reviews28 <www.epa.gov/npdes/pubs/wqs_guide_final.pdf>. 

Combined Sewer Overflows–Guidance for Permit Writers24 contains guidance and example permit 

language that permit writers can use. Controlling CSOs typically requires substantial long-term planning, 

construction, financing and continuous reassessment; therefore, the implementation of CSO controls will 

probably occur over several permit cycles. The guidance explains a phased permitting approach to CSOs. 

Exhibit 9-2 depicts this phased permitting approach and the types of permit conditions that should be 

developed for each phase. 

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Exhibit 9-2 Categories of CSO permitting conditions 

NPDES permit Phase I Phase II Post phase II 

A. Technology-based  NMC, at a minimum  NMC, at a minimum  NMC, at a minimum 

B. Water Quality-based  Narrative  Narrative + performancebased standards 

 Narrative + performancebased standards + 

numeric WQBELs (as 

appropriate) 

C. Monitoring  Characterization, 

monitoring, and 

modeling of CSS 

 Monitoring to evaluate 

water quality impacts 

 Monitoring to determine 

effectiveness of CSO 

controls 

 Post-construction 

compliance monitoring 

D. Reporting  Documentation of NMC 

implementation 

 Interim LTCP 

deliverables 

 Implementation of CSO 

controls (both NMC and 

long-term controls) 

 Report results of postconstruction compliance 

monitoring 

E. Special conditions  Prohibition of dry 

weather overflows 

(DWO) 

 Development of LTCP 

 Prohibition of DWO 

 Implementation of LTCP 

 Reopener clause for 

water quality standards 

violations 

 Sensitive area 

reassessment 

 Prohibition of DWO 

 Reopener clause for 

water quality standards 

violations 

Depending on the permittee’s situation, a permit may contain both Phase I and Phase II elements. Phase I 

permits require demonstration of implementation of the NMC, shown in Exhibit 9-3. 

Exhibit 9-3 Nine minimum CSO controls 

1. Proper operation and regular maintenance programs for the sewer system and the CSOs 

2. Maximum use of the collection system for storage 

3. Review and modification of pretreatment requirements to ensure that CSO impacts are minimized 

4. Maximization of flow to the POTW for treatment 

5. Prohibition of CSOs during dry weather 

6. Control of solid and floatable materials in CSOs 

7. Establishment of pollution prevention programs 

8. Public notification to ensure that the public receives adequate notification of CSO occurrences and 

CSO impacts 

9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls 

In the Phase I permit issued/modified to reflect the CSO Control Policy, the NPDES authority should at 

least require permittees to 

 Immediately implement BAT/BCT, which at a minimum includes the NMC, as determined on a 

BPJ basis by the permitting authority. 

 Develop and submit a report documenting the implementation of the NMC within 2 years of 

permit issuance/modification. 

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September 2010 NPDES Permit Writers’ Manual 

 Comply with applicable water quality standards, no later than the date allowed under the state’s 

water quality standards expressed in the form of a narrative limitation. 

 Develop and submit, consistent with the CSO Control Policy and based on a schedule in an 

appropriate enforceable mechanism, an LTCP, as soon as practicable, but generally within 2 years 

after the effective date of the permit issuance/modification. Permitting authorities may establish a 

longer timetable for completion of the long-term CSO control plan on a case-by-case basis to 

account for site-specific factors that could influence the complexity of the planning process. 

Exhibit 9-4 shows the minimum elements of the LTCP. 

Exhibit 9-4 Elements of the long-term CSO control plan 

1. Characterization, monitoring, and modeling of the combined sewer system 

2. Public participation 

3. Consideration of sensitive areas 

4. Evaluation of alternatives 

5. Cost/performance considerations 

6. Operational plan 

7. Maximizing treatment at the existing POTW treatment plant 

8. Implementation schedule 

9. Post-construction compliance monitoring program 

Phase II permits require the implementation of an LTCP. The Phase II permit should contain the 

following: 

 Requirements to implement the technology-based controls including the NMC determined on a 

BPJ basis. 

 Narrative requirements that ensure that the selected CSO controls are implemented, operated and 

maintained as described in the LTCP. 

 Water quality-based effluent limits under §§ 122.44(d)(1) and 122.44(k), requiring, at a 

minimum, compliance with, no later than the date allowed under the state’s water quality 

standards, the numeric performance standards for the selected CSO controls, based on average 

design conditions specifying at least one of the following: 

− A maximum number of overflow events per year for specified design conditions consistent 

with II.C.4.a.i of the CSO Control Policy. 

− A minimum percentage capture of combined sewage by volume for treatment under specified 

design conditions consistent with II.C.4.a.ii of the CSO Control Policy. 

− A minimum removal of the mass of pollutants discharged for specified design conditions 

consistent with II.C.4.a.iii of CSO Control Policy. 

− Performance standards and requirements that are consistent with II.C.4.b of the CSO Control 

Policy. 

 A requirement to implement, with an established schedule, the approved post-construction water 

quality assessment program including requirements to monitor and collect sufficient information 

to demonstrate compliance with water quality standards and protection of designated uses as well 

as to determine the effectiveness of CSO controls. 

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 A requirement to reassess overflows to sensitive areas in those cases where elimination or 

relocation of the overflow is not physically possible and economically achievable. 

 Conditions establishing requirements for maximizing the treatment of wet-weather flows at the 

POTW, as appropriate, consistent with section II.C.7. of the CSO Policy. 

 A reopener clause authorizing the NPDES authority to reopen and modify the permit upon 

determination that the CSO controls fail to meet water quality standards or protect designated 

uses. 

Reviewing the permittee’s LTCP and consultations with other staff involved in the CSO control process 

and the permittee are important steps in the process of determining the appropriate Phase II permit 

conditions. Water quality-based controls in Phase II generally are expressed as narrative requirements and 

performance standards for the combined sewer system. Finally, post Phase II permit conditions would 

address continued implementation of the NMC, long-term CSO controls, and post-construction 

compliance monitoring. There may also be numeric WQBELs when there are sufficient data to support 

their development. 

LTCP implementation schedules were expected to include project milestones and a financing plan for 

design and construction of necessary controls as soon as practicable. The CSO Control Policy expected 

permitting authorities to undertake the following: 

 Review and revise, as appropriate, state CSO permitting strategies developed in response to the 

National CSO Control Strategy. 

 Develop and issue permits requiring CSO communities to immediately implement the NMC and 

document their implementation and develop and implement an LTCP. 

 Promote coordination among the CSO community, the water quality standards authority, and the 

general public through LTCP development and implementation. 

 Evaluate water pollution control needs on a watershed basis and coordinate CSO control with the 

control of other point and nonpoint sources of pollution. 

 Recognize that it might be difficult for some small communities to meet all the formal elements 

of LTCP development, and that compliance with the NMC and a reduced scope LTCP might be 

sufficient. 

 Consider sensitive areas, use impairment, and a CSO community’s financial capability in the 

review and approval of implementation schedules. 

Communities must develop and implement LTCPs to meet water quality standards, including the 

designated uses and criteria to protect those uses for waterbodies that receive CSO discharges. The CSO 

Control Policy recognized that substantial coordination and agreement among the permitting authority, 

the water quality standards authority, the public, and the CSO community would be required to 

accomplish this objective. The CSO Control Policy also recognized that the development of the LTCP 

should be coordinated with the review and appropriate revision of water quality standards and their 

implementation procedures. 

In developing permit requirements to meet technology-based requirements and applicable state water 

quality standards, the permit writer, in conjunction with staff involved in water quality standards and the 

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permittee, should identify the appropriate site-specific considerations that will determine the CSO 

conditions to be established in the permit. EPA believes that the following information will be 

particularly relevant in developing the appropriate conditions: 

 CSO Discharge 

− Flow, frequency, and duration of the CSO discharge. 

− Available effluent characterization data on the CSO discharge. 

− Available information and data on the impacts of the CSO discharge(s) (e.g., CWA section 

305(b) reports, ambient survey data, fish kills, CWA section 303(d) lists of impaired waters). 

− Compliance history of the CSO owner, including performance and reliability of any existing 

CSO controls. 

− Current NPDES permit and NPDES permit application. 

− Facility planning information from the permittee that addresses CSOs. 

 Technologies 

− Performance data (either from the manufacturer or from other applications) for various CSO 

technologies that may be employed, including equipment efficiency and reliability. 

− Cost information associated with the installation, operation and maintenance of CSO 

technologies. 

− Reference materials on various types of CSO. 

For more information on CSOs, see section 2.3.1.4 of this manual and the Combined Sewer Overflows 

Website <www.epa.gov/npdes/cso>. 

9.2.4 Sanitary Sewer Overflows (SSOs) 

EPA’s Report to Congress on the Impacts and Control of CSOs and SSOs29

<www.epa.gov/npdes/csossoreport2004> shows that NPDES permit requirements establishing clear reporting, 

recordkeeping and third party notification of overflows from municipal sewage collection systems, as 

well as clear requirements to properly operate and maintain the collection system, are critical to effective 

program implementation. NPDES authorities should be improving NPDES permit requirements for SSOs 

and sanitary sewer collection systems, which could lead to improved performance of municipal sanitary 

sewer collection systems and improved public notice for SSO events. 

The NPDES regulations provide standard conditions that are to be in NPDES permits for POTWs as 

discussed in Chapter 10 of this manual. Standard conditions in a permit for a POTW apply to portions of 

the collection system for which the permittee has ownership or has operational control. When reissued, 

permits for POTW discharges should clarify how key standard permit conditions apply to SSOs and 

sanitary sewer collection systems. On August 20, 2007, EPA circulated a draft fact sheet, NPDES Permit 

Requirements for Municipal Sanitary Sewer Collection Systems and SSOs

<www.epa.gov/npdes/pubs/sso_fact_sheet_model_permit_cond.pdf>, which explains the ways NPDES permitting 

authorities should be improving implementation of NPDES permit requirements to address SSOs and 

sanitary sewer collection systems. 

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The draft fact sheet indicates that clarifications should address the particular application of standard 

permit conditions to SSOs and municipal sanitary sewer collection systems as discussed below. 

 Immediate reporting. Permits should clarify that the permittee is required to notify the NPDES 

authority of an overflow that could endanger health or the environment from portions of the 

collection system over which the permittee has ownership or operational control as soon as 

practicable but within 24 hours of the time the permittee becomes aware of the overflow. 

[See § 122.41(l)(6)]. 

 Written reports. Permits should clarify that the permittee is required to provide the NPDES 

authority a written report within 5 days of the time it became aware of any overflow that is 

subject to the immediate reporting provision. [See § 122.41(l)(6)(i).] In addition, permits should 

clarify that any overflow that is not immediately reported as indicated above, should be reported 

in the discharge monitoring report. [See § 122.41(l)(7)]. 

 Third party notice. Permits should establish a process for requiring the permittee or the NPDES 

authority to notify specified third parties of overflows that could endanger health because of a 

likelihood of human exposure; or unanticipated bypass and upset that exceeds any effluent 

limitation in the permit or that could endanger health because of a likelihood of human exposure. 

Permits should clarify that the permittee is required to develop, in consultation with appropriate 

authorities at the local, county, or state level (or any combination), a plan that describes how, 

under various overflow (and unanticipated bypass and upset) scenarios, the public, and other 

entities, would be notified of overflows that may endanger health. The plan should identify all 

overflows that would be reported, to whom they should be reported, the specific information that 

would be reported, a description of lines of communication, and the identities of responsible 

officials. [See § 122.41(l)(6)]. 

 Recordkeeping. Permits should clarify that the permittee is required to keep records of 

overflows. Clarified permit language for recordkeeping should require the permittee to retain the 

reports submitted to the NPDES authority and other appropriate reports that could include work 

orders associated with investigation of system problems related to an overflow, that describes the 

steps taken or planned to reduce, eliminate, and prevent reoccurrence of the overflow. 

[See § 122.41(j)]. 

 Capacity, management, operation and maintenance programs. Permits should clarify 

requirements for proper operation and maintenance of the collection system. [See §§ 122.41(d) 

and 122.41(e)]. This may include requiring the development and implementation of capacity, 

management, operation and maintenance (CMOM) programs. EPA’s Region 4 has developed 

materials and guidance that can help a municipality with its CMOM program on the 

Management, Operation and Maintenance (MOM) Programs Project Website

<www.epa.gov/region4/water/wpeb/momproject/>. The CMOM program may use a process for selfassessment and information management techniques for ongoing program improvement and may 

develop and implement emergency response procedures to overflows. In addition, the CMOM 

permit condition may specify appropriate documentation requirements, including the following: 

− CMOM program summary. Permittees may be required to develop a written summary of their 

CMOM programs, which would be available to the NPDES authority and public on request. 

The program summary would give an overview of the management program and summarize 

major implementation activities. 

Chapter 9: Special Conditions 9-21
September 2010 NPDES Permit Writers’ Manual 

9-22 Chapter 9: Special Conditions 

− Program audit report. Permittees may be required to conduct comprehensive audits of their 

programs during the permit cycle, and submit a copy of the audit report to the NPDES 

authority with the application for permit renewal. EPA’s Sanitary Sewer Overflow Toolbox 

Website <www.epa.gov/npdes/sso/ssotoolbox> provides information on CMOM. 

− System evaluation and capacity assurance plan. Capacity assurance refers to a process to 

identify, characterize and address hydraulic deficiencies in a sanitary sewer collection system. 

The permit may require the permittee to implement a program to assess the current capacity 

of the collection system and treatment facilities that they own or over which they have 

operational control to ensure that discharges from unauthorized locations do not occur. Where 

peak flow conditions contribute to an SSO discharge or to noncompliance at a treatment 

plant, the permittee may be required to prepare and implement a system evaluation and 

capacity assurance plan. In some instances, the permittee may already be under an 

enforceable obligation and schedule, in which case this permit provision would be redundant 

and, thus, unnecessary. 

Section 2.3.1.5 of this manual and EPA’s Sanitary Sewer Overflows Website <www.epa.gov/npdes/sso> 

provide more information on SSOs. 

 

1

 U.S. Environmental Protection Agency. 1999. Toxicity Reduction Evaluation Guidance for Municipal Wastewater Treatment 

Plants. EPA/833B-99/002. U.S. Environmental Protection Agency, Office of Wastewater Management, Washington, DC. 

<www.epa.gov/npdes/pubs/tre.pdf>.

2

 U.S. Environmental Protection Agency. 2001. Clarifications Regarding Toxicity Reduction and Identification Evaluations in the 

National Pollutant Discharge Elimination System Program. U.S. Environmental Protection Agency, Office of Wastewater 

Management and Office of Regulatory Enforcement, Washington, DC. <www.epa.gov/npdes/pubs/owmfinaltretie.pdf>. 

3

 U.S. Environmental Protection Agency. 1989. Generalized Methodology for Conducting Industrial Toxicity Reduction 

Evaluations (TREs). EPA-600/2-88-070. U.S. Environmental Protection Agency, Water Engineering Research Laboratory, 

Cincinnati, OH. Publication available on NEPIS Website <www.epa.gov/nscep/> as document 600288070. 

4

 U.S. Environmental Protection Agency. 1991. Methods for Aquatic Toxicity Identification Evaluations: Phase I Toxicity 

Characterization Procedures. Second Edition. EPA-600/6-91-003. U.S. Environmental Protection Agency, Office of Research 

and Development, Washington, DC. <www.epa.gov/npdes/pubs/owm0330.pdf>. 

5

 U.S. Environmental Protection Agency. 1992. Toxicity Identification Evaluation: Characterization of Chronically Toxic 

Effluents, Phase I. EPA-600/6-91-005F. U.S. Environmental Protection Agency, Environmental Research Laboratory, Duluth, 

MN. <www.epa.gov/npdes/pubs/owm0255.pdf>. 

6

 U.S. Environmental Protection Agency. 1993. Methods for Aquatic Toxicity Identification Evaluations: Phase II Toxicity 

Identification Procedures for Samples Exhibiting Acute and Chronic Toxicity. EPA-600/R-92-080. U.S. Environmental 

Protection Agency, Environmental Research Laboratory, Duluth, MN. <www.epa.gov/npdes/pubs/owm0343.pdf>. 

7

 U.S. Environmental Protection Agency. 1993. Methods for Aquatic Toxicity Identification Evaluations: Phase III Confirmation 

Procedures for Samples Exhibiting Acute and Chronic Toxicity. EPA-600/R-92-081. U.S. Environmental Protection Agency, 

Environmental Research Laboratory, Duluth, MN. <www.epa.gov/npdes/pubs/owm0341.pdf>. 

8

 U.S. Environmental Protection Agency. 1995. Great Lakes Water Quality Initiative Technical Support Document for the 

Procedure to Determine Bioaccumulation Factors. EPA-820/B-95-005. U.S. Environmental Protection Agency, Office of 

Science and Technology, Washington, DC. Publication available on NEPIS Website <www.epa.gov/nscep/> as document 

820B95005. 

9

 U.S. Environmental Protection Agency. 1993. Guidance Manual for Developing Best Management Practices. EPA 833-B-93-

004. U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/owm0274.pdf>.

Endnotes for this chapter continued on the next page. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 9: Special Conditions 9-23

 

10 King, Ephraim S. 1992. Order Denying Modification Request With Respect to the Administrator’s 1990 Decision in Star-Kist 

Caribe, Inc. (NPDES Appeal No. 88-5). U.S. Environmental Protection Agency, Office of Water. Memorandum, May 27, 1992. 

<www.epa.gov/npdes/pubs/owm0121.pdf>. 

11 Hanlon, James. A. 2007. Compliance Schedules for Water Quality-Based Effluent Limitations in NPDES Permits.

U.S. Environmental Protection Agency, Office of Wastewater Management. Memorandum, May 10, 2007. 

<www.epa.gov/npdes/pubs/memo_complianceschedules_may07.pdf>. 

12 U.S. Environmental Protection Agency. 1999. Introduction to the National Pretreatment Program. EPA-833-B-98-002. 

U.S. Environmental Protection Agency, Office of Wastewater Management, Washington, D.C. 

<www.epa.gov/npdes/pubs/final99.pdf>. 

13 U.S. Environmental Protection Agency. 1994. A Plain English Guide to the EPA Part 503 Biosolids Rule. EPA/832/R-93/003. 

U.S. Environmental Protection Agency, Office of Wastewater Management, Washington, DC. 

<www.epa.gov/owm/mtb/biosolids/503pe/>. 

14 U.S. Environmental Protection Agency. 1995. A Guide to the Biosolids Risk Assessments for the EPA Part 503 Rule. EPA/832-

B-93-005. U.S. Environmental Protection Agency, Office of Wastewater Management, Washington, DC. 

<www.epa.gov/owm/mtb/biosolids/503rule/>. 

15 U.S. Environmental Protection Agency. 1995. Part 503 Implementation Guidance. EPA-833-R-95-001. U.S. Environmental 

Protection Agency. Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/owm0237.pdf>. 

16 U.S. Environmental Protection Agency. 1994. Land Application of Sewage Sludge—A Guide for Land Appliers on the 

Requirements of the Federal Standards for the Use or Disposal of Sewage Sludge in 40 CFR Part 503. EPA-831/B-93-002b. 

U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/sludge.pdf>. 

17 U.S. Environmental Protection Agency. 1994. Surface Disposal of Sewage Sludge—A Guide for Owner/Operators of Surface 

Disposal Facilities on the Monitoring, Record Keeping, and Reporting Requirements of the Federal Standards for the Use or 

Disposal of Sewage Sludge in 40 CFR Part 503. EPA-831/B-93-002c. U.S. Environmental Protection Agency, Office of Water, 

Washington, DC. Publication available on NEPIS Website <www.epa.gov/nscep/> as document 831B93002c. 

18 U.S. Environmental Protection Agency. 1993. Preparing Sewage Sludge for Land Application or Surface Disposal—A Guide 

for Preparers of Sewage Sludge on the Monitoring, Recordkeeping, and Reporting Requirements of the Federal Standards for the 

Use or Disposal of Sewage Sludge in 40 CFR Part 503. EPA-831/B-93-002a. U.S. Environmental Protection Agency, Office of 

Water, Washington, DC. Publication available on NEPIS Website <www.epa.gov/nscep/> as document 831B93002a. 

19 U.S. Environmental Protection Agency. 1993. Domestic Septage Regulatory Guidance—A Guide to the EPA 503 Rule. 

EPA-832/B-92-005. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/owm0026.pdf>. 

20 U.S. Environmental Protection Agency. 1992, Rev. 2003. Control of Pathogens and Vector Attraction in Sewage Sludge. 

EPA-625/R-92-013. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC. 

<www.epa.gov/nrmrl/pubs/625r92013/625R92013.pdf>. 

21 U.S. Environmental Protection Agency. 1995. Combined Sewer Overflows–Guidance for Long-Term Control Plan. 

EPA-832/B-95-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/owm0272.pdf>. 

22 U.S. Environmental Protection Agency. 1995. Combined Sewer Overflows–Guidance for Nine Minimum Controls. 

EPA-832/B-95-003. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/owm0030.pdf>. 

23 U.S. Environmental Protection Agency. 1995. Combined Sewer Overflows–Guidance for Screening and Ranking. EPA-832/B95-004. U.S. Environmental Protection Agency, Office of Wastewater Management, Washington, DC. 

<www.epa.gov/npdes/cso>. 

24 U.S. Environmental Protection Agency. 1995. Combined Sewer Overflows–Guidance for Monitoring and Modeling. EPA832/B-99-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC. 

<www.epa.gov/npdes/pubs/sewer.pdf>. 

25 U.S. Environmental Protection Agency. 1995. Combined Sewer Overflows–Guidance for Financial Capability Assessment and 

Schedule Development. EPA-832/B-97-004. U.S. Environmental Protection Agency, Office of Water and Office of Wastewater 

Management, Washington DC. <www.epa.gov/npdes/pubs/csofc.pdf>. 

26 U.S. Environmental Protection Agency. 1995. Combined Sewer Overflows–Guidance for Funding Options. EPA-832/B-95-

007. U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/owm0249.pdf>. 

Endnotes for this chapter continued on the next page. 
September 2010 NPDES Permit Writers’ Manual 

9-24 Chapter 9: Special Conditions 

 

27 U.S. Environmental Protection Agency. 1995. Combined Sewer Overflows–Guidance for Permit Writers. EPA-832/B-95-008. 

U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/cso>. 

28 U.S. Environmental Protection Agency. 2001. Combined Sewer Overflows–Guidance: Coordinating Combined Sewer 

Overflow (CSO) Long-Term Planning with Water Quality Standards Reviews. EPA-833/R-01-002. U.S. Environmental 

Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/pubs/wqs_guide_final.pdf>. 

29 U.S. Environmental Protection Agency. 2004. Report to Congress on the Impacts and Control of CSOs and SSOs. EPA 833-R04-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC. <www.epa.gov/npdes/csossoreport2004>. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 10: Standard Conditions of NPDES Permits 10-1

CHAPTER 10. Standard Conditions of NPDES Permits 

This chapter describes standard conditions, sometimes called boilerplate conditions, that must be 

incorporated in National Pollutant Discharge Elimination System (NPDES) permits. Standard conditions, 

specified in Title 40 of the Code of Federal Regulations (CFR) 122.41 and 122.42, play an important 

supporting role to effluent limitations, monitoring and reporting requirements, and special conditions 

because they delineate various legal, administrative, and procedural requirements of the permit. Standard 

conditions cover various topics, including definitions, testing procedures, records retention, notification 

requirements, penalties for noncompliance, and other permittee responsibilities. The conditions provided 

in § 122.41 apply to all types and categories of NPDES permits and must be included in all permits (see 

§ 123.25 for applicability to state NPDES permits). The conditions provided in § 122.42 apply only to 

certain categories of NPDES facilities. Any permit issued to a facility in one of the categories listed in 

§ 122.42 must contain the additional conditions, as applicable. 

The use of standard conditions helps ensure uniformity and consistency of all NPDES permits issued by 

authorized states or the U.S. Environmental Protection Agency (EPA) Regional Offices. Permit writers 

need to be aware of the contents of the standard conditions because it might be necessary to explain 

portions of the conditions to a discharger. The permit writer should keep abreast of any changes in EPA’s 

standard conditions set out in §§ 122.41 and 122.42. According to § 122.41, standard conditions may be 

incorporated into a permit either expressly (verbatim from the regulations) or by reference to the 

regulations. It generally is preferable for permit writers to attach the standard conditions expressly 

because permittees might not have easy access to the regulations. Some states have developed an 

attachment for NPDES permits that includes the federal standard conditions. 

10.1 Types of Standard Conditions 

A brief summary of the § 122.41 standard conditions that must be included in all types of NPDES permits 

follows: 

 Duty to Comply § 122.41(a): The permittee must comply with all conditions of the permit. 

Noncompliance is a violation of the Clean Water Act (CWA) and is grounds for enforcement 

action, changes to or termination of the permit, or denial of a permit renewal application. 

 Duty to Reapply § 122.41(b): A permittee wishing to continue permitted activities after the 

permit expiration date must reapply for and obtain a new permit. 

 Need to Halt or Reduce Activity not a Defense § 122.41(c): The permittee may not use as a 

defense in an enforcement action the reasoning that halting or reducing the permitted activity is 

the only way to maintain compliance. 

 Duty to Mitigate § 122.41(d): The permittee is required to take all reasonable steps to prevent 

any discharge or sludge use or disposal in violation of the permit that has a reasonable likelihood 

of adversely affecting human health or the environment. 

 Proper Operation and Maintenance § 122.41(e): The permittee must properly operate and 

maintain all equipment and treatment systems used for compliance with the terms of the permit. 
September 2010 NPDES Permit Writers’ Manual 

The permittee must provide appropriate laboratory controls and quality assurance procedures. 

Operation of backup systems is required only when needed to ensure compliance. 

 Permit Actions § 122.41(f): The permit may be modified, revoked and reissued, or terminated 

for cause. A request by the permittee for a permit modification, revocation or reissuance, 

termination, or a notification of planned changes or anticipated noncompliance does not suspend 

the permittee’s obligation to comply with all permit conditions. 

 Property Rights § 122.41(g): The permit does not convey any property rights of any sort, or any 

exclusive privilege. 

 Duty to Provide Information § 122.41(h): The permittee must furnish, within a reasonable time, 

any information needed to determine compliance with the permit or to determine whether there is 

cause to modify, revoke and reissue, or terminate the permit. The permittee also must furnish, on 

request, copies of records that must be kept as required by the permit. 

 Inspection and Entry § 122.41(i): The permittee must, upon presentation of valid credentials by 

the Director or his or her representative, allow entry into the premises where the regulated activity 

or records are present. The Director must have access to and be able to make copies of any 

required records; inspect facilities, practices, operations, and equipment; and sample or monitor at 

reasonable times. 

 Monitoring and Records § 122.41(j): Samples must be representative of the monitored activity. 

The permittee must retain records for 3 years (5 years for sewage sludge activities) subject to 

extension by the Director. Monitoring records must identify the sampling dates and personnel, the 

sample location and time, and the analytical techniques used and corresponding results. 

Wastewater and sludge measurements must be conducted in accordance with Parts 136 or 503 or 

other specified procedures. Falsification of results is a violation under the CWA. 

 Signatory Requirement § 122.41(k): The permittee must sign and certify applications, reports, 

or information submitted to the Director in accordance with the requirements in § 122.22. 

Knowingly making false statements, representations, or certifications is punishable by fines or 

imprisonment. 

 Planned Changes § 122.41(l)(1): Notice must be given to the Director as soon as possible of 

planned physical alterations or additions to the facility (or both) that could meet the criteria for 

determining whether the facility is a new source under § 122.29(b); result in changes in the nature 

or quantity of pollutants discharged; or significantly change sludge use or disposal practices. 

 Anticipated Noncompliance § 122.41(l)(2): The permittee must give advance notice of any 

planned changes that could result in noncompliance. 

 Permit Transfers § 122.41(l)(3): The permit is not transferable except after written notice to the 

Director. The Director may require modification or revocation and reissuance, as necessary. 

 Monitoring Reports § 122.41(l)(4): Monitoring results must be reported at the frequency 

specified in the permit and be reported on a discharge monitoring report (DMR) or forms 

provided or specified by the Director for reporting results of monitoring sludge use or disposal 

practices. Monitoring for any pollutant that occurs more frequently than is required by the permit 

and uses approved test procedures or test procedures specified in the permit must also be 

reported. Calculations requiring averaging must use an arithmetic mean unless otherwise 

specified in the permit. 

10-2 Chapter 10: Standard Conditions of NPDES Permits 
September 2010 NPDES Permit Writers’ Manual 

 Compliance Schedules § 122.41(l)(5): Reports of compliance or noncompliance or any progress 

report must be submitted no later than 14 days following the interim or final compliance date 

specified in a compliance schedule. 

 Twenty-Four Hour Reporting § 122.41(l)(6): The permittee must orally report any 

noncompliance that might endanger human health or the environment within 24 hours after 

becoming aware of the circumstances. Within 5 days of becoming aware of the circumstances, the 

permittee must provide a written submission including a description of the noncompliance and its 

cause; the period of noncompliance, including exact dates and times; the anticipated time the 

noncompliance is expected to continue (if not already corrected); and steps taken to reduce, 

eliminate, or prevent reoccurrence unless the Director waives the requirement. In addition, 24-

hour reporting is required for an unanticipated bypass exceeding effluent limits; an upset 

exceeding effluent limits; and a violation of a maximum daily effluent limitation for pollutants 

listed in the permit for 24-hour reporting. 

 Other Noncompliance § 122.41(l)(7): The permittee must report all instances of noncompliance 

not reported under other specific reporting requirements at the time monitoring reports are 

submitted. 

 Other Information § 122.41(l)(8): If the permittee becomes aware that it failed to submit any 

relevant facts in its application, or submitted incorrect information in its application or other 

reports, it must promptly submit such facts or information. 

 Bypass § 122.41(m): The intentional diversion of wastestreams from any portion of a treatment 

facility. Bypass is prohibited unless the bypass does not cause the effluent to exceed limits and is 

for essential maintenance to assure efficient operation (no notice or 24-hour reporting is required 

in such a case). All other bypasses are prohibited, and the Director of the NPDES program may 

take enforcement action against a permittee for a bypass, unless the bypass was unavoidable to 

prevent loss of life, personal injury, or severe property damage, there was no feasible alternative, 

and the proper notification was submitted. 

 Upset § 122.41(n): An upset (i.e., an exceptional incident in which there is unintentional and 

temporary noncompliance with technology-based effluent limits because of factors beyond the 

permittee’s control) can be used as an affirmative defense in actions brought against the permittee 

for noncompliance. An upset does not include noncompliance to the extent caused by operational 

error, improperly designed or inadequate treatment facilities, lack of preventative maintenance, or 

careless or improper operation. The permittee (who has the burden of proof to demonstrate that an 

upset has occurred) must have operational logs or other evidence that shows 

− When the upset occurred and its causes. 

− The facility was being operated properly. 

− Proper notification was made. 

− Remedial measures were taken. 

10.2 Other Standard Conditions 

In addition to standard conditions specified in § 122.41 that are applicable to all permittees, § 122.42 

includes additional conditions applicable to certain categories of NPDES permits. Below are summaries 

of these additional standard conditions applicable to various types of NPDES permits. 

Chapter 10: Standard Conditions of NPDES Permits 10-3
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10-4 Chapter 10: Standard Conditions of NPDES Permits 

Non-Municipal (Industrial) Permits: Additional standard conditions applicable to non-municipal 

permits are found in § 122.42(a) and specify that the permittee must notify the Director as soon as it 

knows or has reason to believe that the discharge has or will exceed certain notification levels specified in 

§§ 122.42(a)(1) and (2). In addition, § 122.44(f) allows the Director to establish alternate notification 

levels upon petition by the permittee or by his or her own initiative. 

Publicly Owned Treatment Work (POTW) Permits: Additional standard conditions applicable to 

POTWs are found in § 122.42(b). The standard conditions specify that the permittee must provide 

adequate notice to the Director of the new introduction of certain pollutants into the POTW from an 

indirect discharger and of substantial changes in the volume or character of pollutants introduced into the 

POTW. That notice must include information on the quality and quantity of effluent introduced to the 

POTW and information on the impact to the quality and quantity of the POTW’s effluent. 

Municipal Separate Storm Sewer Systems: Additional standard conditions applicable to large, medium 

or EPA-designated municipal separate storm sewer systems are in § 122.42(c). Those standard conditions 

require that the permittee submit an annual report addressing the status, and changes to, the stormwater 

management program, water quality data and other information specified in §§ 122.42(c)(1)-(6). 

Individual Stormwater Permits: Initial permits for discharges composed entirely of stormwater and 

permitted under § 122.26(e)(7) must require compliance no later than 3 years after permit issuance. 

Concentrated Animal Feeding Operations (CAFO) Permits: The regulations at § 122.42(e) specify 

conditions that must be included in all permits for CAFOs. 
September 2010 NPDES Permit Writers’ Manual 

Chapter 11: NPDES Permit Administration 11-1

CHAPTER 11. NPDES Permit Administration 

Previous discussions in this manual focused on the process of developing National Pollutant Discharge 

Elimination System (NPDES) permit conditions and effluent limitations. This chapter describes the 

administrative process associated with the issuance of an NPDES permit including a discussion of the 

other federal laws that might affect the development or issuance of NPDES permits. 

11.1 Other Federal Laws Applicable to NPDES Permits 

This section addresses other federal laws, besides the Clean Water Act (CWA), that permit writers should 

consider when drafting an NPDES permit. The requirements imposed under these statutes only apply to 

federal actions (i.e., U.S. Environmental Protection Agency [EPA] issuance of permits). Permits issued by 

states authorized to administer the NPDES program are not subject to the requirements of these statutes. 

However, many states may have enacted state legislation that is modeled on federal law and, therefore, it 

is prudent to review state law in these areas before preparing an NPDES permit. 

The following sections briefly discuss the other federal laws and contain links to other websites for more 

information. Because these laws are implemented by other federal agencies, many of the links provided 

below are to websites outside EPA, and EPA is not responsible for the information provided on those 

websites. The NPDES regulations at Title 40 of the Code of Federal Regulations (CFR) 122.49 also 

include a discussion of how some of the laws relate to the federal NPDES program. Exhibit 11-1 presents 

the other federal laws that are applicable to NPDES permits and includes the legislative citations from the 

United States Code (U.S.C.) and the implementing regulations in the CFR. 

Exhibit 11-1 Other federal laws applicable to NPDES permits 

Federal law Year 

Federal 

agency 

Legislative 

citations 

Implementing 

regulations 

Endangered Species Act (ESA) 1973 FWS, NMFS 16 U.S.C. 1531 et seq. 50 CFR Part 402

National Environmental Policy Act (NEPA) 1969 CEQ 42 U.S.C. 4321 et seq. 40 CFR Part 6 

National Historic Preservation Act (NHPA) 1992 ACHP 16 U.S.C. 470 et seq. 36 CFR Part 800

Coastal Zone Management Act (CZMA) 1972 NOAA 16 U.S.C. 1451 et seq. 15 CFR Part 930

Wild and Scenic Rivers Act 1968 Various 16 U.S.C. 1271 et seq. 36 CFR Part 297

Fish and Wildlife Coordination Act (FWCA) 1934 FWS 16 U.S.C. 661 et seq. -- 

Essential Fish Habitat Provisions (EFH) 1996 NOAA 16 U.S.C. 1855(b)(2) 50 CFR Part 600

11.1.1 Endangered Species Act 

This section discusses procedures intended to protect endangered species that apply only to permits issued 

by EPA. The 1973 Endangered Species Act (ESA) <www.fws.gov/endangered/esa-library/pdf/ESAall.pdf>, 

16 U.S.C. 1531 et seq., was enacted to protect and conserve endangered and threatened species and 

critical habitat. The Fish and Wildlife Service (FWS) <www.fws.gov/endangered/> of the Department of the 

Interior and the National Marine Fisheries Service (NMFS) <www.nmfs.noaa.gov/pr/> of the National 
September 2010 NPDES Permit Writers’ Manual 

Oceanic and Atmospheric Administration (NOAA) within the Department of Commerce (collectively the 

Services) share primary responsibility for administration of the ESA. 

ESA section 7 requires that federal agencies consult with the Services to ensure that any action 

authorized, funded, or carried out by the agencies that could affect a listed species or critical habitat and 

to ensure that their actions are not likely to jeopardize the continued existence of any endangered species 

or threatened species, or result in the destruction or adverse modification of critical habitat of such 

species. The ESA section 7 regulations are in 50 CFR Part 402. FWS/NMFS published the ESA Section 7 

Consultation Handbook <www.fws.gov/endangered/esa-library/pdf/TOC-GLOS.PDF> to address the major 

consultation processes pursuant to ESA section 7. 

Consultation may be either informal or formal. An informal consultation determines if an action is or is 

not likely to adversely affect the species. A formal consultation is required if the findings from the 

informal consultation show that there is a likelihood for adverse impacts and evaluates whether the 

proposed action is likely to jeopardize the continued existence of the species. It is EPA’s responsibility to 

ensure that consultation occurs; however, a nonfederal representative (i.e., the discharger) may be 

designated for the informal consultation. 

On February 22, 2001, EPA entered into a National Memorandum of Agreement (National MOA)

<www.epa.gov/fedrgstr/EPA-SPECIES/2001/February/Day-22/e2170.pdf> with the Services that outlines the process 

for consulting on federally issued NPDES permits. In addition, because consultation is not required for 

state-issued permits, the National MOA includes a process for coordinating with the Services on stateissued permits. EPA permit writers should review the ESA consultation regulations and the ESA section 7 

Consultation Handbook, and coordinate with the Region’s ESA coordinator (if such a position has been 

established in a Region) and the Service office(s) nearest to the site. 

11.1.2 National Environmental Policy Act 

This section discusses environmental review procedures that apply only when EPA issues permits to new 

sources (dischargers subject to New Source Performance Standards). The 1969 National Environmental 

Policy Act (NEPA) <www.epa.gov/compliance/basics/nepa.html>, 42 U.S.C. 4321 et seq., requires that agencies 

perform environmental impact reviews and prepare an Environmental Impact Statement (EIS) for major 

federal actions significantly affecting the quality of the human environment [see section 102(2)(C)]. The 

President’s Council on Environmental Quality (CEQ) <www.whitehouse.gov/ceq/> coordinates federal 

environmental efforts to comply with NEPA. 

Within EPA, the Office of Federal Activities under the Office of Enforcement and Compliance Assurance 

(OECA) is responsible for EPA’s implementation of NEPA <www.epa.gov/compliance/nepa/>. EPA’s NEPA 

regulations are at 40 CFR Part 6. With respect to NPDES permits, CWA section 511 establishes that only 

EPA-issued permits to new sources are subject to NEPA’s environmental review procedures before 

permit issuance. States may have their own state law versions of NEPA. Federal permit writers should 

coordinate efforts with the Office of Federal Activities and document all NEPA activities in the permit 

file and fact sheet. 

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11.1.3 National Historic Preservation Act Amendments 

Section 106 of the 1992 National Historic Preservation Act (NHPA) <www.achp.gov/nhpa.html>, 16 U.S.C. 

470 et seq., as amended, and implementing regulations 36 CFR Part 800 require the Regional 

Administrator, before issuing a license (permit), to identify the area of potential effect of a permitted 

discharge and, if historic or cultural resources within that area would be adversely affected by the 

discharge, to adopt measures when feasible to mitigate potential adverse effects of the licensed activity 

and properties listed or eligible for listing in the National Register of Historic Places. 

The Act’s requirements are to be implemented in cooperation with State Historic Preservation Officers

<www.achp.gov/shpo.html>, and upon notice to, and when appropriate, in consultation with the Advisory 

Council on Historic Preservation <www.achp.gov/>, which provides national oversight for the NHPA. A 

decision by the D.C. Circuit in 2003 concluded that NHPA consultation is not required for state-issued 

permits (National Mining Ass’n v. Fowler, 324 F.3d 752 (D.C. Cir. 2003) <caselaw.findlaw.com/us-dccircuit/1169695.html>). 

Federal permit writers should evaluate potential effects of NHPA and submit written documentation of 

the evaluation to the State Historic Preservation Office and to the permit file. 

11.1.4 Coastal Zone Management Act 

The 1972 Coastal Zone Management Act (CZMA) <www.coastalmanagement.noaa.gov/czm/czm_act.html>, 

16 U.S.C. 1451 et seq., was enacted to manage the nation’s coastal zone and is implemented through a 

state-federal partnership. Section 307 of the CZMA (16 U.S.C. 1456 and 15 CFR Part 930) prohibits the 

issuance of federal NPDES permits for activities affecting land or water use in coastal zones unless the 

permit applicant certifies that the proposed activity complies with the state Coastal Zone Management 

Program and the relevant state either concurs with the applicant’s certification or the state’s concurrence 

is conclusively presumed as a result of the state’s failure to concur or non-concur. Coastal States, 

according to the CZMA, include those states and territories adjacent to the Atlantic, Pacific, or Arctic 

oceans; the Gulf of Mexico; or one or more of the Great Lakes. Any of those states that have completed 

the development of its management program is required, as a condition of receipt of federal grant money 

under the CZMA, to adopt coastal management plans, which designate boundaries, identify areas of 

particular concern, and establish inventories of permitted uses and enforcement policies. Beach access, 

emergency planning, and erosion control also must be addressed in such plans. 

The Office of Ocean and Coastal Resource Management <www.coastalmanagement.noaa.gov/>, which is part 

of NOAA within the Department of Commerce, oversees the CZMA. The CZMA implementing 

regulations are at 15 CFR Part 930. EPA and other federal agencies must coordinate their activities on 

coastal lands with state CZMA plans. Federal permit writers should document all activities relating to 

CZMA in the permit file. 

11.1.5 Wild and Scenic Rivers Act 

The 1968 Wild and Scenic Rivers Act (WSRA) <www.rivers.gov/publications/wsr-act.pdf>, 16 U.S.C. 1271 et 

seq., established a National Wild and Scenic Rivers System (System) and prescribed the process by which 

additional rivers may be added to this System. Rivers may be added by act of Congress [WSRA section 

2(a)(i)] or by the Secretary of the Interior at the initiative of a state governor [WSRA section 2(a)(ii)]. 

Under WSRA section 7(a), EPA is prohibited from assisting, by license or otherwise, in the construction 

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of any water resources project that would have a direct and adverse effect on the values for which a 

national wild and scenic river was established. The WSRA regulations are codified at 36 CFR Part 297. 

Federal permit writers should verify whether the receiving water is part of the System and document all 

activities related to the Act in the permit file and fact sheet. For detailed explanation of WSRA section 7, 

refer to Wild and Scenic Rivers Act: Section 7 <www.rivers.gov/publications/section-7.pdf>, a technical report 

of the Interagency Wild and Scenic Rivers Coordinating Council. Permit writers may also refer to 

Water Quantity and Quality as Related to the Management of Wild and Scenic Rivers

<www.rivers.gov/publications/water.pdf>, a technical report of the Interagency Wild and Scenic Rivers 

Coordinating Council. 

11.1.6 Fish and Wildlife Coordination Act 

The 1934 Fish and Wildlife Coordination Act (FWCA) <www.fws.gov/habitatconservation/fwca.html>, 

16 U.S.C. 661 et seq., requires mitigation for the loss of wildlife habitat due to the construction of federal 

water resources projects. The FWCA requires designers of federal dams, reservoirs, and irrigation works 

to include the costs and benefits to fish and wildlife when determining the benefit/cost ratio of a project 

and requires that EPA and other federal agencies consult with state and federal wildlife and fisheries 

agencies to minimize the impacts of the activity on fish and wildlife. The FWCA specifically calls for 

ongoing studies by the U.S. Department of the Interior on the effects of domestic sewage and industrial 

wastes on fish and wildlife (16 U.S.C. 665). 

No implementing regulations directly related to the FWCA and NPDES permits exist. However, the FWCA 

describes actions taken or compelled by the affected federal agencies. The Water Resources Development 

under the Fish and Wildlife Coordination Act manual <www.fws.gov/habitatconservation/fwca.pdf> provides the 

FWS guidance on implementing the FWCA. Federal permit writers should note any FWCA consultation 

activities in the permit file. 

11.1.7 Essential Fish Habitat Provisions 

The 1996 Essential Fish Habitat (EFH) provisions of the Magnuson-Stevens Fishery Conservation and 

Management Act (Magnuson-Stevens Act or MSA) promote the protection of essential fish habitat in any 

federal action authorized, funded, or undertaken, or proposed to be authorized, funded, or undertaken, by 

such agency that might adversely affect such habitat identified under the MSA [16 U.S.C. 1855(b)(2)]. 

The MSA requires that federal agencies, such as EPA, consult with the NMFS for any EPA-issued 

permits that might adversely affect essential fish habitat identified under the MSA. The regulations 

applicable to federal agencies’ coordination and consultation under the MSA are codified at 50 CFR 

600.905 through 600.930, and other EFH information can be found on the NMFS EFH Website

<www.habitat.noaa.gov/protection/efh/index.html>. Federal permit writers should note any EFH determinations 

and consultation activities in the permit file. 

11.2 Documentation for Development of the Draft Permit 

EPA regulations at 40 CFR 124.2 define a draft permit as a document that indicates the Director’s 

tentative decision to issue or deny, modify, revoke and reissue, terminate, or reissue a permit. After the 

permit is issued, the fact sheet and supporting documentation (administrative record) are the primary 

support for defending the permit in the administrative appeals process. Documenting the permit requires 

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the permit writer to be organized and logical throughout the permit development process. Some of the 

content of the fact sheet and administrative record is specified by federal and state regulation, and the 

remainder is dictated by good project management. Permit writers should recognize the importance of 

 Developing a thorough permit in a logical fashion. 

 Meeting legal requirements for preparation of an administrative record, fact sheet, and statement 

of basis. 

 Substantiating permit decisions and providing a sound basis for the derivation of permit terms, 

conditions, and limitations if challenges are made. 

 Establishing a permanent record of the basis of the permit for use in future permit actions. 

Exhibit 11-2 presents reasons for good documentation in the permit file and fact sheet. 

Exhibit 11-2 Reasons for good documentation 

 Streamlines the permit reissuance/ compliance monitoring process 

 Establishes a permanent record of the basis for the permit 

 Explains the legal and technical basis of the permit 

 Provides a sound basis for future modifications and permits 

 Requires the permit writer to be organized and logical throughout permit development process 

Exhibits 11-3 and 11-4 provide flow diagrams of the NPDES permit administrative process. In general, 

the administrative process includes the following: 

 Documenting all permit decisions. 

 Coordinating EPA and state review of the draft (or proposed) permit. 

 Providing public notice, conducting hearings (if appropriate), and responding to public 

comments. 

 Defending the permit and modifying it (if necessary) after issuance. 

Note that Exhibit 11-3 provides the general framework for the administrative process where EPA is the 

NPDES permitting authority and Exhibit 11-4 provides a typical framework for the administrative process 

where a state is the permitting authority. State requirements need not be identical to federal regulatory 

requirements, provided they are at least as stringent. Some authorized states have slightly different 

processes for developing and issuing NPDES permits. The same holds true for the appeal process. This 

manual presents EPA’s procedure; state procedures for NPDES permit hearings and appeals vary 

according to state law. 

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Exhibit 11-3 Administrative process for EPA-issued NPDES permits 

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Exhibit 11-4 Typical administrative process for state-issued NPDES permits* 

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11.2.1 Administrative Record 

The administrative record should be considered the foundation that supports the NPDES permit. If EPA 

issues the permit, the contents of the administrative record are prescribed by regulation, with § 124.9 

identifying the required content of the administrative record for a draft permit and § 124.18 describing the 

requirements for final permits. Regardless of whether a state or EPA issues the permit, all supporting 

materials must be made available to the public at any time and may be examined during the public 

comment period and any subsequent public hearing. The importance of maintaining the permit records in 

a neat, orderly, complete, and retrievable form cannot be over emphasized. The record allows personnel 

from the permitting agency to reconstruct the justification for a given permit and defend the permit during 

any legal proceedings regarding the permit. 

The administrative record for a draft permit consists, at a minimum, of the specific documents shown in 

Exhibit 11-5. Materials that are readily available in the permit issuing office or published material that is 

generally available do not need to be physically included with the record as long as they are specifically 

referred to in the fact sheet or statement of basis. If EPA issues a draft permit for a new source, the 

administrative record should include any EISs or Environmental Assessments (EAs) performed in 

accordance with § 122.29(c). 

Exhibit 11-5 Elements of the administrative records for a draft permit 

 Permit application and supporting data 

 Draft permit 

 Statement of basis or fact sheet 

 All items cited in the statement of basis or fact sheet, including calculations used to derive the 

permit limitations 

 Meeting reports 

 Correspondence with the applicant and regulatory personnel 

 All other items in the supporting file 

 For new sources, any EA, draft/final EIS, or other such background information, such as a 

Finding of No Significant Impact (only applies if EPA issues the permit) 

The administrative record should include all meeting reports and correspondence with the applicant and 

other regulatory agency personnel, trip reports, and records of telephone conversations. All 

correspondence, notes, and calculations should be dated and indicate the name of the writer and all other 

persons involved. Because correspondence is subject to public scrutiny, references or comments that do 

not serve an objective purpose should be avoided. Finally, the presentation of calculations and 

documentation of decisions should be organized in such a way that they can be reconstructed and the 

logic supporting the calculation or decisions can easily be found. 

11.2.2 Fact Sheets and Statements of Basis 

A fact sheet is a document that briefly sets forth the principal facts and the significant factual, legal, 

methodological, and policy questions considered in preparing the draft permit. When the permit is in the 

draft stage, the fact sheet and supporting documentation serve to explain the rationale and assumptions 

used in deriving the limitations to the discharger, the public, and other interested parties. 

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The NPDES regulations at § 124.8(a) stipulate that every EPA and state-issued permit must be 

accompanied by a fact sheet if the permit 

 Involves a major facility or activity. 

 Incorporates a variance or requires an explanation under § 124.56(b) (toxic pollutants, internal 

waste stream, and indicator pollutants and for privately owned waste treatment facilities). 

 Is an NPDES general permit. 

 Is subject to widespread public interest. 

 Is a Class I sludge management facility. 

 Includes a sewage sludge land application plan. 

A well-documented rationale for all permit decisions reduces the work necessary to reissue a permit by 

eliminating conjecture concerning the development of those permit conditions that are being carried 

forward to the next permit. That is also true if a modification is initiated during the life of the permit. The 

required contents of a fact sheet, as specified in §§ 124.8 and 124.56, are listed in Exhibit 11-6. 

Exhibit 11-6 Required elements of a fact sheet 

Required element 

Regulatory 

citation 

(40 CFR) 

General facility information 

 Description of the facility or activity

 Sketches or a detailed description of the discharge location

 Type and quantity of waste/pollutants discharged

§ 124.8

§ 124.56

§ 124.8

Summary rationale of permit conditions 

 Summary of the basis for the draft permit conditions

 References to the applicable statutory or regulatory provisions

 References to the administrative record

§ 124.8 

Detailed rationale of permit conditions 

 Explanation and calculation of effluent limitations and conditions

 Specific explanations of 

- Toxic pollutant limitations 

- Limitations on internal wastestreams 

- Limitations on indicator pollutants 

- Case-by-case requirements 

- Decisions to regulate non-publicly owned treatment works (POTWs) under a separate 

permit

 For EPA-issued permits, the requirements of any state certification

 For permits with a sewage sludge land application plan, a description of how all required 

elements of the land application plan are addressed in the permit

§ 124.56

 Reasons why any requested variances do not appear justified, if applicable § 124.8

Administrative Requirements

 A description of the procedures for reaching a final decision on the draft permit, including 

- Public comment period beginning and ending dates 

- Procedures for requesting a hearing 

- Other procedures for public participation 

 Name and telephone number of the person to contact for additional information 

§ 124.8

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The fact sheet should include detailed discussions of the development of permit limitations for each 

pollutant, including the following: 

 Calculations and assumptions related to production and flow. 

 Type of limitations (i.e., limitations based on secondary treatment standards, effluent limitations 

guidelines and standards (effluent guidelines), case-by-case determinations, or water quality 

standards). 

 Whether the effluent guidelines used were Best Practicable Control Technology Currently 

Available (BPT), Best Available Technology Economically Achievable (BAT), Best 

Conventional Pollutant Control Technology (BCT), or New Source Performance Standards 

(NSPS). 

 The water quality standards or criteria used. 

 Whether any parameters were used as indicators for other pollutants. 

 Citations to appropriate wasteload allocation or total maximum daily load studies, guidance 

documents, other references. 

Often, decisions to include certain requirements lead to a decision to exclude other requirements. It is just 

as important to keep a thorough record of items that were not included in the draft permit as it is to keep a 

record of included items. Such records might include the following: 

 Why were secondary treatment standards, case-by-case determinations, or effluent guidelines 

used as the basis for final effluent limitations rather than water quality standards (i.e., 

demonstrate that the limitations checked to see that water quality standards would be attained)? 

 Why was biomonitoring not included? 

 Why were pollutants that were reported as present in the permit application not specifically 

limited in the permit? 

 Why is a previously limited pollutant no longer limited in the draft permit? 

Finally, the fact sheet should address the logistics of the permit issuance process, including the beginning 

and ending dates of the public comment period, procedures for requesting a hearing, and other means of 

public involvement in the final decision. 

A statement of basis, as described in § 124.7, is required for EPA-issued permits that are not required to 

have a fact sheet. A statement of basis describes the derivation of the effluent limitations and the reasons 

for special conditions. However, a prudent permit writer will develop the detailed rationale required in a 

fact sheet for any permit that includes complex calculations or special conditions (e.g., case-by-case 

effluent limitations based on best professional judgment [BPJ]) even if a fact sheet is not required by 

regulation. 

11.3 Items to Address before Issuing a Final Permit 

This section describes the public participation activities that must be conducted in the permit issuance 

process. These include providing public notices, collecting and responding to public comments, and 

holding public hearings as necessary. 

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11.3.1 Public Notice 

The public notice is the vehicle for informing all interested parties and members of the general public of 

the contents of a draft NPDES permit or other significant actions with respect to an NPDES permit or 

permit application. The basic intent of this requirement is to ensure that all interested parties have an 

opportunity to comment on significant actions of the permitting agency with respect to NPDES permits. 

The exact scope, required contents, and methods for effecting public notices are found in § 124.10. The 

NPDES permit-related actions for which public notice is required are shown in Exhibit 11-7. 

Exhibit 11-7 Actions for which public notice is required 

 Tentative denial of an NPDES permit application (not necessarily applicable to state programs) 

 Preparation of a draft NPDES permit, including a proposal to terminate a permit 

 Scheduling of a public hearing 

 An appeal has been granted by the Environmental Appeals Board 

 Major permit modifications (after permit issuance) 

 New Source determinations (EPA only) 

The permit writer should be particularly concerned with the first three items in Exhibit 11-7. It is 

important to note that no public notice is required when a request for a permit modification, revocation, 

reissuance, or termination is denied. 

Public notice of NPDES permit-related activities should be provided using the following methods: 

 For major permits, publication of a notice in daily or weekly newspaper within the area affected 

by the facility or activity. 

 For general permits issued by EPA, publication in the FR. 

 For all permits, direct mailing to various interested parties. This mailing list should include the 

following: 

− The applicant. 

− Any interested parties on the mailing list. 

− Any other agency that has issued or is required to issue a Resource Conservation and 

Recovery Act (RCRA), Underground Injection Control (UIC), Prevention of Significant 

Deterioration (PSD) (or other permit under the Clean Air Act), NPDES, CWA section 404, 

sludge management, or ocean dumping permit under the Marine Research Protection and 

Sanctuaries Act for the same facility or activity. 

− Federal and state agencies with jurisdiction over fish, shellfish, and wildlife resources and 

over coastal zone management plans, the Advisory Council on Historic Preservation, State 

Historic Preservation Officers, including any affected states and tribes. 

− State agencies conducting area-wide and continuing planning under CWA sections 208(b)(2), 

208(b)(4) or 303(e) and the FWS, NMFS, and the U.S. Army Corps of Engineers. 

− Users identified in the permit application of a privately owned treatment work. 

− Persons on any mailing lists developed by including those who request inclusion in writing 

and persons solicited for area lists from participants in past permit proceedings in the area. 

− Any local government having jurisdiction over the locality of the facility. 

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A public notice must contain the information shown in Exhibit 11-8. 

Exhibit 11-8 Contents of the public notice 

 Name and address of the office processing the permit action 

 Name and address of the permittee or applicant and, if different, of the facility or activity regulated by 

the permit 

 A brief description of the business conducted at the facility or activity described in the permit 

 Name, address, and telephone number of a contact from whom interested persons can obtain 

additional information 

 A brief description of the comment procedures required, the time and place of any hearing to be held 

including procedures to request a hearing 

 For EPA-issued permits, the location and availability of the administrative record and the times at 

which the record will be open for public inspection and a statement that all data submitted by the 

applicant is available as part of the administrative record 

 A description of the location of each existing or proposed discharge point and the name of the 

receiving water and the sludge use and disposal practice(s) and the location of each sludge treatment 

works treating domestic sewage and use or disposal sites known at the time of permit application 

 Requirements applicable to a thermal variance under CWA section 316(a) 

 Requirements applicable to cooling water intake structures under CWA section 316(b) 

 Any additional information considered necessary 

The regulatory agency preparing the permit must provide public notice of the draft permit (including a 

notice of intent to deny a permit application), and it must provide at least 30 days for public comment. 

The draft permit is usually submitted for public notice after it has undergone internal review by the 

regulatory agency that is issuing the permit. State-issued permits typically undergo public notice after 

EPA has reviewed and commented on the draft permit. In the special case of those EPA-issued permits 

that require an EIS, public notice is not given until after a draft EIS is issued. 

11.3.2 Public Comments 

Public notice of a draft permit might elicit comments from concerned individuals or agencies. Frequently, 

such comments are simply requests for additional information. However, some comments are of a 

substantive nature and suggest modifications to the draft permit or indicate that the draft permit is 

inappropriate for various reasons. In such cases, commenters must submit all reasonable arguments and 

factual material in support of their positions and comments by the close of the public comment period, 

and the permitting authority must consider those comments in making final decisions. If the approach is 

technically correct and clearly stated in the fact sheet, it will be difficult for commenters to find fault with 

the permit. Commenters can always suggest alternatives, however. In addition, an interested party may 

also request a public hearing. 

To the extent possible, it is desirable to respond to all public comments as quickly as possible. In some 

cases, it might be possible to diffuse a potentially controversial situation by providing further explanation 

of permit terms and conditions. Additionally, permit writers should also consider notifying commenters 

that their comments have been received and are being considered. 

The permitting agency must respond to all significant comments, in accordance with § 124.17, at the time 

a final permit decision is reached (in the case of EPA-issued permits) or at the same time a final permit is 

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actually issued (in the case of state-issued permits). The response should incorporate the following 

elements: 

 Changes in any of the provisions of the draft permit and the reasons for the changes. 

 Description and response to all significant comments on the draft permit or the permit application 

raised during the public comment period or during any hearing. 

If any information is submitted during the public comment period raises substantial new questions about 

the draft permit, one of the following actions can occur: 

 A new draft permit with a revised fact sheet or statement of basis is prepared. 

 A revised statement of basis, a fact sheet, or revised fact sheet is prepared, and the comment 

period is reopened. 

 The comment period is reopened but is limited to new findings only. 

If any of those actions is taken, a new public notice, as described earlier, must be given. 

For EPA-issued permits, any documents cited in the response to comments must be included in the 

administrative record. If new points are raised or new material is supplied during the public comment 

period, EPA may document its response to these new materials by adding new materials to the 

administrative record. 

11.3.3 Public Hearings 

Any interested party may request a public hearing. The request should be in writing and should state the 

nature of the issues proposed to be raised during the hearing. However, a request for a hearing does not 

automatically necessitate that a hearing be held. A public hearing should be held when there is a 

significant amount of interest expressed during the public comment period or when it is necessary to 

clarify the issues involved in the permit decision. 

Thus, the decision of whether to hold a public hearing is actually a judgment call. Such decisions are 

usually made by someone other than the permit writer. However, the permit writer will be responsible for 

ensuring that all the factual information in support of the draft permit is well documented. 

Public notice of a public hearing must be given at least 30 days before the public meeting. Public notice 

of the hearing may be given at the same time as public notice of the draft permit, and the two notices may 

be combined. The public notice of the hearing should contain the following information: 

 Brief description of the nature and purpose of the hearing, including the applicable rules and 

procedures. 

 Reference to the dates of any other public notices relating to the permit. 

 Date, time, and place of the hearing. 

Scheduling a hearing automatically extends the comment period until at least the close of the hearing 

[§ 124.12(c)] and the public comment period may be extended by request during the hearing. Anyone may 

submit written or oral comments concerning the draft permit at the hearing. A presiding officer is 

responsible for scheduling the hearing and maintaining orderly conduct, including setting reasonable time 

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limitations for oral statements. Note that a transcript or recording of the hearing must be available to 

interested persons. 

11.3.4 Environmental Justice Considerations 

Environmental justice (EJ) is the fair treatment and meaningful involvement of all people regardless of 

race, color, national origin, or income with respect to the development, implementation, and enforcement 

of environmental laws, regulations, and policies. EPA has this goal for all communities and persons 

across U.S. It will be achieved when everyone enjoys the same degree of protection from environmental 

and health hazards and equal access to the decision-making process to have a healthy environment in 

which to live, learn, and work. 

In NPDES permits, the public participation process provides opportunities to address EJ concerns by 

providing appropriate avenues for public participation, seeking out and facilitating involvement of those 

potentially affected, and including public notices in more than one language where appropriate. 

11.3.5 EPA and State/Tribal Roles in Reviewing Draft Permits 

The CWA and the NPDES regulations include review roles for EPA and for states, tribes, and territories 

(states) depending on whether EPA or a state is issuing an NPDES permit. 

11.3.5.1 State-issued Permits 

Each authorized state administering an NPDES program must transmit to the EPA Region copies of 

permit applications received and copies of draft or proposed permits [§ 123.43(a)]. The state and the EPA 

Region execute a Memorandum of Agreement (MOA) under § 123.24 that addresses administration and 

enforcement of the state’s regulatory program. The MOA may specify that EPA will review draft permits 

rather than proposed permits [§ 123.44(j)] and specify the classes or categories of permit applications and 

draft or proposed permits that the state will send to the EPA Region for review, comment, and, where 

applicable, objection. In addition, the MOA specifies classes or categories of permits for which EPA will 

waive its right to review the draft or proposed permit. EPA cannot waive its right to review classes or 

categories of permits for the following: 

 Discharges into the territorial seas. 

 Discharges that could affect waters of a state other than the one in which the discharge originates. 

 Discharges proposed to be regulated by general permits. 

 Discharges from a POTW with a daily average discharge exceeding 1 million gallons per day. 

 Discharges of uncontaminated cooling water with a daily average discharge exceeding 500 

million gallons per day. 

 Discharges from any major discharger or from any NPDES primary industry category. 

 Discharges from other sources with a daily average discharge exceeding 500,000 gallons per day 

(however, EPA may waive review for non-process wastewater). 

The MOA provides a period up to 90 days from receipt of a permit during which the EPA Region can 

make general comments on, objections to, or recommendations with respect to the permit. If the EPA 

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Region objects to a permit, within 90 days of receiving the permit it must transmit to the state a statement 

of the reasons for the objection and the actions that the state must take to eliminate the objection 

[§ 123.44(a)-(b)]. Specific causes for objection are outlined in the regulations at § 123.44(c). Any 

interested party can request a public hearing on an objection by the EPA Region. After such a hearing, the 

Region can affirm the objection, modify the terms of the objection, or withdraw the objection and notify 

the state of that decision. If the EPA Region does not withdraw the objection, the state then has 30 days to 

resubmit a permit revised to meet the objection. If the state does not do so, exclusive authority to issue the 

permit passes to the EPA Region. If no public hearing on the objection is held, the time frame for the state 

to resubmit a revised permit is 90 days from receipt of the objection. 

11.3.5.2 EPA-issued Permits 

Permits issued by EPA require an opportunity for state review and certification under CWA section 401. 

The state in which a discharge originates or will originate is provided the opportunity to review an 

application or a draft permit and certify that the discharge will comply with the applicable water quality 

standards. This process also has the benefits of ensuring that state initiatives or policies are addressed in 

EPA-issued NPDES permits and promoting consistency between state-issued and EPA-issued permits 

where not all permits within the state are issued by the same agency. 

Regulations at §§ 124.53 (State Certification) and 124.54 (Special provisions for state certification and 

concurrence on applications for CWA section 301(h) variances) describe procedures an EPA permit 

writer should follow to obtain state certification. Under CWA section 401(a)(1), EPA may not issue a 

permit until a certification is granted or waived. If EPA is preparing the draft permit, state certification 

can be accomplished by allowing states to review and certify the application before draft permit 

preparation. Under § 124.53, if EPA has not received a state certification by the time the draft permit is 

prepared, EPA must send the state a copy of the draft permit along with a notice requesting state 

certification. 

If the state does not respond within a specified reasonable time, which cannot exceed 60 days, it is 

deemed to have waived its right to certify. If the state chooses to certify the draft permit, it may include 

any conditions more stringent than those in the draft permit necessary to ensure compliance with the 

applicable provisions of the CWA or state law, and must cite the CWA or state law references that 

support the changes. In addition, the state is required to include a statement of the extent to which each 

condition of the draft permit can be made less stringent without violating the requirements of state law, 

including water quality standards. Failure to provide this statement for any condition waives the right to 

certify or object to any less stringent condition that might be established during the EPA permit issuance 

process. When a permit applicant requests a CWA section 301(h) variance (§ 124.54), the state 

certification process is very similar to the process described above. For more on CWA section 301(h) 

variances, see section 5.1.3.5 of this manual. 

11.3.6 Schedule for Final Permit Issuance 

The final permit may be issued after the close of the public notice period and after state certification has 

been received (for permits issued by EPA). The public notice period consists of the following: 

 A 30-day period that gives notice of intent to issue or deny the permit. 

 A 30-day period advertising a public hearing (if applicable). 

 Any extensions or reopening of the comment period. 

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Final EPA permit decisions are effective immediately upon issuance unless comment were received on 

the draft permit, in which case, the effective date of the permit is 30 days after issuance (or a later date if 

specified in the permit). In addition, permit decisions will not be immediately effective if review is 

requested on the permit under § 124.19. As discussed earlier, any comments that are received must be 

answered at the time of final permit issuance (in the case of NPDES states or tribes) or after a final 

decision is reached (in the case of EPA). The administrative record for the final permit consists of the 

items in Exhibit 11-9. 

Exhibit 11-9 Elements of the administrative records for a final permit 

 All elements for the draft permit administrative record (see Exhibit 11-5) 

 All comments received during the comment period 

 The tape or transcript of any public hearing 

 Any materials submitted at a hearing 

 Responses to comments 

 For NPDES new source permits, the draft or final EIS 

 The final permit 

11.4 Administrative Actions after Final Permit Issuance 

Once the final permit has been issued, the issuing authority should enter the permit limitations and any 

special conditions into the Integrated Compliance Information System for the NPDES program (ICISNPDES) (for more on ICIS-NPDES, see the introduction to this manual and section 11.5.1.1 below). 

Entering permit information into ICIS-NPDES will ensure that the facility’s performance will be tracked 

and the permitting agency will be alerted to the need for corrective action if violations of permit 

limitations, terms, or conditions occur. 

After final permit issuance, interested parties have opportunities to change the permit through permit 

appeals, major/minor permit modifications, termination and revocation, or transfer. Those administrative 

procedures are described below. 

11.4.1 Permit Appeals 

Throughout the process of developing a permit and during the public notice period, the permit writer 

should carefully consider all legitimate concerns of the applicant/permittee and any other interested party. 

Nevertheless, there will inevitably be situations in which a permit is issued in spite of the objections of 

the permittee or a third party. In such instances, the permittee or interested party can choose to legally 

contest or appeal the NPDES permit, as provided in § 124.19. Permit appeals are the process by which 

any person that filed comments on the draft permit may contest the final limitations and conditions in a 

permit. 

Appeals of EPA-issued permits consist of petitioning the Environmental Appeals Board (EAB) for 

review. Such review must be requested within 30 days of issuance of the final permit, and challenges 

must be limited to issues raised during the draft permit’s public comment or hearing processes, although 

persons not participating in these processes may seek review of changes in the permit from draft to final 

permit. During the appeals process, only those conditions of an existing permit that are being contested 

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are stayed. Within a reasonable time following the filing of the petition for review, the EAB must grant or 

deny the petition. Only individual permits may be appealed to the EAB; general permits may be 

challenged in court or an individual permit may be sought and appealed. 

Many states have similar administrative appeal procedures designed to resolve challenges to the 

conditions of a permit. For the sake of convenience, such procedures, which could be known by different 

names (e.g., evidentiary hearing, administrative appeal), are hereafter permit appeals. Permit writers will, 

from time to time, be involved in permit appeals and will need to address the types of issues discussed 

below. 

Aside from preparing the administrative record and notices, the permit writer might not be involved in the 

procedural matters relating to permit appeals. All requests for permit appeals are coordinated through the 

office of the EPA Regional Counsel or the appropriate state legal counsel. The permit writer’s first 

involvement with the appeals process will likely come as a result of designation of the appeals staff, and 

his or her role will be limited to that of a technical advisor to legal counsel and, where a state uses an 

evidentiary hearing procedure, possibly a witness. 

11.4.1.1 Deposition and Testimony 

In a state hearing procedure, a permit writer might be required to give a deposition during which the 

appellant attorney conducts the questioning that would otherwise occur in the hearing. The deposition is 

transcribed and presented as evidence. The appellant attorney may ask some of the same questions at the 

hearing. 

To prepare for a deposition and testimony, the permit writer should first consult with his or her general 

counsel to become familiar with laws, regulations, and policies that could affect the permit. The permit 

writer should also be thoroughly familiar with the technical basis for the permit conditions. For example, 

if final effluent limitations are based on water quality standards, the permit writer should thoroughly study 

the applicable water quality standards, water quality models, and procedures used to develop the effluent 

limitations and be prepared to defend all assumptions and decisions made in the effluent limitation 

calculations. For case-by-case limitations based on BPJ, the permit writer should carefully review all 

applicable data and procedures used to calculate the effluent limitations and should be sure that the 

information on which case-by-case limitations are based is unimpeachable, the limitations were derived 

from the data in a logical manner in accordance with established procedures, and the limitations are 

technically sound and meet applicable standards for economic reasonableness. 

A permit appeal before the EAB relies on the information presented in the petitions and briefs, and 

possibly includes oral argument, but typically does not use depositions and direct testimony. 

11.4.1.2 The Permit Writer’s Role in the Appeals Process 

As technical advisor to legal counsel, the permit writer’s most important function is to develop support 

for contested permit conditions. A permit writer should not attempt to support technically indefensible 

conditions. Contested permit conditions that are not technically defensible and are not based on any legal 

requirement should be brought to counsel’s attention, with advice that EPA or the state withdraw those 

conditions. 

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The second most important advisory function of the permit writer is assisting counsel in identifying 

weaknesses in the appellant’s arguments. That process could include developing questions for crossexamination of opposing witnesses in a state permit appeal that involves a hearing. Questions should be 

restricted to the subject material covered by the witness’ direct testimony and should be designed to elicit 

an affirmative or negative response, rather than an essay-type response. 

Finally, the permit writer should remember that when a person petitions for EAB review or requests a 

hearing for a state-issued permit, the permit writer should refrain from any discussion about the case 

without first consulting with legal counsel. 

In the role of technical advisor or witness, the permit writer should do the following: 

 Cultivate credibility. 

 Never imply or admit weakness in his or her area of expertise. 

 Never attempt to testify about subjects outside his or her area of expertise. 

 Always maintain good communication with counsel. 

The EAB generally will attempt to resolve permit appeals in the initial stage of granting review. If that is 

not possible, the EAB conducts formal review of the contested conditions and publishes a written opinion 

(an Environmental Administrative Decision). The result of an EAB or state permit appeal might be relief 

from certain permit conditions, validation or strengthening of contested permit conditions, or a 

combination of these two outcomes. Under certain circumstances, decisions of the EAB can be appealed 

in federal court. Authorized state’s permit appeal procedures typically provide for further appeal of 

administrative decisions regarding contested permit conditions in state court when all administrative steps 

have been fulfilled. 

11.4.2 Modification or Revocation and Reissuance of Permits 

In most cases, a permit will not need to be modified (or revoked and reissued) during the term of the 

permit if the facility can fully comply with permit conditions. However, under certain circumstances, it 

might be necessary to modify the permit before its expiration date. A permit modification could be 

triggered in several ways. For example, a representative of the regulatory agency might inspect the 

facility and identify a need for the modification (i.e., the improper classification of an industry), or 

information submitted by the permittee might suggest the need for a change. Of course, any interested 

person may make a request for a permit modification. 

Modifications differ from revocations and reissuance. In a permit modification, only the conditions 

subject to change are reconsidered while all other permit conditions remain in effect. Conversely, the 

entire permit could be reconsidered when it is revoked and reissued. 

Except where the permittee requests or agrees, permit modifications are limited to specific causes

identified in §§ 122.62(a) and 122.62(b) and summarized in Exhibit 11-10. Most NPDES permit 

modifications require EPA or the state to conduct the public notice and participation activities of Part 124, 

similar to the issuance or reissuance of the permit; however, only those specific conditions being modified 

are open to review and comment. The permitting authority may revoke and reissue a permit during its 

term for the causes identified in § 122.62(b) (i.e., the final two bulleted items in Exhibit 11-10). 

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Exhibit 11-10 Causes for permit modification 

 Alterations: When there are material and substantial alterations or changes to the permitted facility or activity 

occur that justify new conditions that are different from the existing permit. 

 New information: When information is received that was not available at the time of permit issuance. 

 New regulations: Under limited circumstances, when standards or regulations on which the permit was based 

have been changed by the modification, withdrawal or promulgation of amended standards or regulations or by 

judicial decision. 

 Compliance schedules: To modify the compliance schedule when good cause exists, such as an act of God, 

strike, or flood. 

 Variance requests: When requests for variances or fundamentally different factors are filed within the specified 

time but not granted until after permit issuance. 

 Toxics: To insert CWA section 307(a) toxic effluent standard or prohibition. 

 Reopener: Conditions in the permit that require it to be reopened under certain circumstances. 

 Net limits: Upon request of a permittee who qualifies for effluent limitations on a net basis under § 122.45(g) or 

when a permittee is no longer eligible for net limitations, as provided in § 122.45(g)(1)(ii). 

 Pretreatment: As necessary under § 403.8 (e) to put a compliance schedule in place for the development of a 

pretreatment program or to change the schedule for program development. 

 Failure to notify: Upon failure of an approved state to notify another state whose waters may be affected by a 

discharge from the approved state. 

 Non-limited pollutants: When the level of any pollutant that is not limited in the permit exceeds the level that 

can be achieved by the technology-based treatment requirements appropriate to the permit. 

 Notification levels: To establish notification levels for toxic pollutants as provided in §122.44(f). 

 Compliance schedules for innovative or alternative facilities: To modify the compliance schedule in light of 

the additional time that might be required to construct such a facility. 

 Small municipal separate storm sewer system (MS4) minimum control measures: For a small MS4 to 

include required minimum control measures when the permit does not include such measure(s) based on the 

determination that another entity was responsible for implementation and the other entity fails to fulfill its 

responsibility to implement such measure(s).

 Technical mistakes: To correct technical mistakes or mistaken interpretations of law made in developing the 

permit conditions. 

 Failed BPJ compliance: When BPJ technology is installed and properly operated and maintained but the 

permittee is unable to meet its limitations, the limitations may be reduced to reflect actual removal; however, 

they may not be less than the limitations in the effluent guidelines. If BPJ operation and maintenance costs are 

extremely disproportionate to the costs considered in a subsequent effluent guideline, the permittee may be 

allowed to backslide to the limitations in the effluent guideline. 

 Land application plans: When required by a permit condition to incorporate a land application plan for 

beneficial reuse of sewage sludge, to revise an existing land application plan, or to add a land application plan. 

 Cause exists for termination: Cause exists under § 122.64, and the Director determines that modification is 

appropriate.

 Notification of proposed transfer: Director may modify the permit upon receipt of ownership transfer 

notification.

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There are certain minor modifications that, upon consent of the permittee, may be processed by the 

permitting authority without following the procedures for public notice in Part 124. Minor modifications 

are generally non-substantive changes (e.g., typographical errors) and are exempt from the administrative 

procedures; that is, a draft permit and public review are not required. The specific permit changes that can 

be processed as minor modifications, described in § 122.63, are to 

 Correct typographical errors. 

 Incorporate more frequent monitoring or reporting. 

 Revise an interim compliance date in the schedule of compliance, provided the new date is not 

more than 120 days after the date specified in the permit and does not interfere with attainment of 

the final compliance date requirement. 

 Allow for a change of ownership, provided no other change is necessary (see section 11.4.4 

below). 

 Change the construction schedule for a new source discharger. 

 Delete a point source outfall when that outfall is terminated and does not result in discharge of 

pollutants from other outfalls except in accordance with permit limits. 

 Incorporate an approved local pretreatment program. 

11.4.3 Permit Termination 

Situations could arise during the life of the permit that are causes for termination of the permit. Such 

circumstances, described in § 122.64(a), include the following: 

 Noncompliance by the permittee with any condition of the permit. 

 Misrepresentation or omission of relevant facts by the permittee. 

 Determination that the permitted activity endangers human health or the environment, and can be 

regulated to acceptable levels only by permit modification or termination. 

 A change in any condition that requires either a temporary or permanent reduction or elimination 

of a discharge (e.g., plant closure). 

Terminations are used to retract a permittee’s privileges to discharge during the permit term. A notice of 

intent to terminate a permit is a type of draft permit that follows the same procedures as any draft permit 

prepared under § 124.6. Administrative procedures, such as public notice, must be followed in permit 

termination proceedings. If a facility with a terminated permit wishes to obtain permit coverage, it would 

have to submit an application and apply for a new permit. 

The regulations at § 122.64(b) do provide one exception to the more formal permit termination process 

described above. Where the entire discharge is permanently terminated by elimination of the flow or by 

connection to a POTW (but not by land application or disposal into a well) the permit can be terminated 

by notice to the permittee, and the Part 124 administrative process is not required. However, if the 

permittee objects to such an expedited termination, the Permitting Authority must then proceed in 

accordance with the administrative procedures described above. 

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11.4.4 Permit Transfer 

Regulatory agencies occasionally receive notification of a change in ownership of a facility covered by an 

NPDES permit. Such changes require that a permit be transferred by one of two provisions: 

 Transfer by modification or revocation: The transfer may be made during the process of a 

major or minor permit modification. It may also be addressed by revoking and subsequently 

reissuing the permit. 

 Automatic transfer: A permit may automatically be transferred to a new permittee if three 

conditions are met: 

− The current permittee notifies the Director 30 days in advance of the transfer date. 

− The notice includes a written agreement between the old and new owner that contains the 

specific date for transfer of permit responsibility, coverage, and liability between them. 

− The Director of the regulatory agency does not notify the old permittee and the proposed new 

permittee that the subject permit will be modified or revoked and reissued. 

11.5 Permit Compliance and Enforcement 

EPA’s OECA is responsible for nationally managing EPA’s compliance and enforcement programs for all 

media including the CWA and NPDES. EPA uses a mix of tools including compliance assistance, 

incentives, and monitoring and enforcement. EPA and state environmental agencies authorized to 

administer the NPDES program seek to achieve and maintain a high level of compliance with 

environmental laws and regulations. Enforcement provides a powerful incentive for NPDES permittees to 

comply, and the way in which an NPDES permit is written directly affects its enforceability. Each permit 

must be written clearly and unambiguously so that compliance can be tracked effectively and the permit 

can be enforced if violations occur. 

The permit writer could become actively involved with the compliance monitoring and enforcement of 

the terms and conditions of the NPDES permits that he or she has written. The extent of the permit 

writer’s involvement will usually depend on the organizational structure of the regulatory agency. Larger, 

centrally organized agencies typically have separate personnel responsible for enforcing the terms of 

NPDES permits. In other organizations, the individual who writes the permit will also be responsible for 

such enforcement activities as discharge monitoring report (DMR) tracking, facility inspections, and 

enforcement recommendations. If a civil judicial enforcement action occurs, the permit writer might be 

called on to testify regarding the specific requirements of the permit or its basis. 

Regardless of a regulatory agency’s organizational structure, the permit writer should have an 

appreciation for the various aspects of a meaningful NPDES compliance enforcement program. The 

following sections address compliance monitoring reviews and inspections and data in the national ICISNPDES (formerly the Permit Compliance System or PCS) database, which provides the basis for 

evaluating compliance. This section concludes with a brief description of the enforcement actions 

available to facilitate permit compliance. For more information about CWA enforcement, see OECA’s 

Clean Water Act Enforcement Website <www.epa.gov/compliance/civil/cwa/index.html>. 

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11.5.1 Compliance Monitoring 

Compliance monitoring is a broad term that includes all activities that federal or state regulatory agencies 

take to ascertain a permittee’s compliance with the conditions specified in an NPDES permit. Compliance 

monitoring data collected as part of the NPDES program are used to evaluate compliance and support 

enforcement actions. The process includes receiving, reviewing, and entering data into the ICIS-NPDES 

database, conducting on-site inspections, identifying violators, and determining an appropriate response. 

A primary function of the compliance monitoring program is to verify compliance with permit conditions, 

including effluent limitations and compliance schedules. Compliance verification is achieved through 

 Compliance review: A review of all written reports and other material relating to the status of a 

permittee’s compliance. 

 Compliance inspections: Field-related regulatory activities (i.e., facility inspections, effluent 

sampling) to determine compliance. 

11.5.1.1 Compliance Review 

Compliance and enforcement personnel use two primary sources of information to carry out compliance 

reviews: 

 Permit/compliance files. 

 The ICIS-NPDES database. 

Permit/compliance files include the permit, application, fact sheet, compliance schedule reports, 

compliance inspection reports, DMRs, enforcement actions, and correspondence (e.g., summaries of 

telephone calls, copies of warning letters). Compliance personnel periodically review that information and 

use it to determine if enforcement is necessary and, if so, what level of enforcement is appropriate. 

The ICIS-NPDES database <https://icis.epa.gov/icis> is the national database for tracking compliance with 

NPDES requirements and is discussed further in this manual’s introduction. Information in ICIS-NPDES 

includes facility and discharge characteristics, self-monitoring data, compliance schedules, permit 

conditions, inspections, and enforcement actions. Permittees are required to submit effluent monitoring 

data, and compliance and status information, via Compliance Schedule Reports and DMRs. EPA Regions 

and NPDES states enter such information into ICIS-NPDES and evaluate permittees on compliance with 

NPDES permit requirements. Inspection and enforcement information is collected and entered by Regions 

or authorized states or both. Quarterly, EPA reviews the ICIS-NPDES system data and generates a 

quarterly noncompliance report (QNCR) for all major facilities following the requirements of § 123.45. 

ICIS-NPDES supports compliance and enforcement actions and assists EPA staff in evaluation and 

oversight of the NPDES program. The database also promotes national consistency and uniformity in 

permit and compliance evaluations. NPDES permits must be written so that compliance can be tracked 

using ICIS-NPDES. Situations might arise in which permit limitations and monitoring conditions are not 

initially compatible with ICIS-NPDES entry and tracking. In such cases, the permit writer should alert the 

state or EPA Regional staff responsible for entering ICIS-NPDES codes and work with them to resolve 

any coding issues. To assist ICIS-NPDES coders in accurately interpreting and entering the permit into 

ICIS-NPDES and to assist enforcement personnel in reviewing permittee’s self-monitoring data and 

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reports in a timely manner, permit writers should follow the compliance inspection procedures discussed 

in the next section. 

11.5.1.2 Compliance Inspections 

Compliance inspections refer to all field-related regulatory activities conducted to determine permit 

compliance. Such field activities can include compliance evaluation inspections (non-sampling), sampling 

inspections, other specialized inspections, and remote sensing. Certain inspections, such as diagnostic 

inspections and performance audit inspections, aid the regulatory agency in evaluating the facility’s 

problems in addition to providing information to support enforcement action. Biomonitoring inspections 

are specifically targeted at facilities with effluent suspected or identified as causing toxicity problems that 

threaten the ecological balance of the receiving waters. 

Compliance inspections are undertaken to fulfill one or more of the following purposes: 

 Establish a regulatory presence to deter noncompliance. 

 Ensure that permit requirements are being met or determine if permit conditions are adequate. 

 Check the completeness and accuracy of a permittee’s performance and compliance records. 

 Assess the adequacy of the permittee’s self-monitoring and reporting program including on-site 

laboratory functions. 

 Determine the progress or completion of corrective action. 

 Obtain independent compliance data on a facility’s discharge. 

 Evaluate the permittee’s operation and maintenance activities. 

 Observe the status of construction required by the permit. 

11.5.2 Quarterly Noncompliance Reports 

EPA Regional offices and NPDES states are required by the regulations at § 123.45 to report quarterly on 

major facilities that are not in compliance with the terms and conditions of their permit or enforcement 

order (i.e., that meet the criteria for reportable noncompliance [RNC] for effluent limitation, schedules, 

and reporting violations). 

The regulations in § 123.45 establish requirements for listing facility violations and resulting regulatory 

enforcement action on QNCRs. The regulation establishes reporting requirements for violations that meet 

specific, quantifiable reporting criteria, as well as for violations that are more difficult to quantify but are 

of sufficient concern to be considered reportable. The regulation also specifies the format that the reports 

must follow and the schedule for their submission. 

Only major facilities that meet RNC criteria must be reported on the QNCR. RNC consists of several 

general types of violations as established in § 123.45: 

 Effluent limitations 

− Monthly average effluent limitations (see below for more). 

− Other effluent limitations with water quality or health impacts. 

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 Schedule: Violations of compliance schedule milestones by 90 days or more. 

 Reporting: Reports late by 30 days or more. 

A violation of any monthly average limitation should be evaluated for magnitude by comparing the 

measured amount in the DMR to the product of the monthly average limitation times the Technical 

Review Criteria (TRC) for that pollutant or parameter. The TRC is 1.4 for Group I (conventional) 

pollutants and 1.2 for Group II (generally toxic) pollutants. Appendix A to Part 123 contains a list of 

pollutants in each Group. RNC includes violations of a given Group I or Group II pollutant or parameter 

that equals or exceeds the product of the TRC times the monthly average limitation for any 2 or more 

months during a 6-month reporting period. RNC also includes violations of a Group I or Group II 

parameter by any amount (not necessarily TRC times the limitation or greater) for 4 months during the 

6-month reporting period. 

A subset of instances of RNC that appear on the QNCR could be noted as significant noncompliance

(SNC). This distinction is used solely for management accountability purposes as a means of tracking 

trends in compliance and evaluating the relative timeliness of enforcement response toward priority 

violations. 

The definition of SNC is not regulatory and can change as the NPDES program evolves to encompass 

new enforcement priorities. For example, in September 1995, EPA revised the definition of SNC to 

include violations of non-monthly average permit limitations by major facilities. Many permits for 

NPDES major facilities lacked required monthly average limitations and, thus, were not evaluated for 

SNC violations and follow-up formal enforcement action. The new definition became effective as of 

October 1, 1996. EPA’s SNC policy is described in the memorandum Revision of NPDES Significant 

Noncompliance (SNC) Criteria to Address Violations of Non-Monthly Average Limits1

<www.epa.gov/compliance/resources/policies/civil/cwa/revisedsncmemo.pdf>. 

Generally, the designation of SNC indicates a violation is of sufficient magnitude or duration or both to 

be considered among EPA’s priorities for regulatory review or response. The categories of SNC are 

 Effluent limitations: The effluent limitation SNC criteria are the same as for QNCR discussed 

above. 

 Schedule: The schedule SNC criteria are the same as for QNCR discussed above. 

 Reporting: The reporting SNC criteria are the same as for QNCR discussed above. 

 Order requirements: Violation of requirements in administrative or judicial orders. 

The instance of SNC is considered resolved when the SNC criteria are no longer met during the review 

period, or when the permittee formerly in SNC exhibits compliance for all 3 months of the most recent 3-

month reporting period. A permittee with SNC violations under a compliance schedule that is meeting its 

deadlines for corrective actions is in resolved pending status. 

Any major permittee that is listed on the QNCR for two consecutive 3-month reporting periods for the 

same instance of SNC (e.g., same outfall point, same parameter, same category of violation) is expected 

to return to compliance or to be addressed with an appropriate enforcement action before the reporting 

deadline for the second QNCR. If the facility is in SNC after the second QNCR, and no enforcement 

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action has been taken, the facility is placed on the Watch List. The Watch List is a management tool that 

identifies and tracks facilities with serious violations and no apparent formal enforcement response. 

11.5.3 Enforcement 

EPA’s NPDES compliance and enforcement principles and recommendations are described in the NPDES 

Enforcement Management System (EMS)2 <www.epa.gov/compliance/resources/policies/civil/cwa/emscwa-jensenrpt.pdf>. By choosing an appropriate enforcement response to CWA violations, EPA tries to achieve 

several goals: 

 Correction of the violation as soon as possible. 

 Deterrence of future violations by the same permittee or other permittees. 

 Equal treatment of the regulated community through use of a uniform approach to selecting 

enforcement responses (i.e., similar violations are treated similarly). 

 Assessment of an appropriate penalty. 

 Protection of human health and the environment. 

Once a facility has been identified as having potential CWA violations, EPA or the NPDES state reviews 

the facility’s compliance history. The review includes an assessment of the magnitude, frequency, and 

duration of violations. The permitting authority identifies significant violations and makes a 

determination of the appropriate enforcement response. CWA section 309 authorizes the Agency to bring 

civil or criminal action against facilities that discharge pollutants without a permit or discharge in 

violation of NPDES permit conditions and judicial penalties up to $32,500 per day per violation. 

EPA Regions and authorized states have specific procedures for reviewing self-monitoring and inspection 

data and for deciding what type of enforcement action is warranted. EPA recommends an escalating 

response to continuing noncompliance. The range of enforcement responses includes the following: 

 Informal action (e.g., notice of violation [NOV]). 

 Formal action. 

 Administrative compliance order. 

 Administrative order with or without an administrative penalty order (up to $157,500). 

 Civil judicial action that imposes injunctive relief seeking compliance or penalty or both. 

 Criminal prosecution. 

Considerations when making determinations on the level of the enforcement response include the 

following: 

 The duration of the violation. 

 The severity of the violation. 

 The degree of economic benefit obtained through the violation. 

 Compliance history and previous enforcement actions taken against the violator. 

 The degree of culpability. 

 The deterrent effect of the response on similarly situated permittees. 

Equally important considerations may include fairness and equity, national consistency, and the integrity 

of the NPDES program. 

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Citizens can participate in the enforcement process in a number of ways. Under the Freedom of 

Information Act, citizens have the right to request certain facility-specific compliance information from 

EPA’s ICIS-NPDES database. In addition, under NPDES regulations, interested citizens can intervene in 

any federal civil judicial action to enjoin any threatened or continuing violation of program requirements 

or permit conditions, and to recover civil penalties in court. Citizens also have the opportunity to review 

and comment on any proposed consent decree to resolve a state or federal civil judicial enforcement 

action. 

CWA section 505 allows any citizen to begin a civil judicial enforcement action on his or her own behalf. 

In certain circumstances, citizens may not begin suit if EPA or the state is diligently prosecuting a civil or 

criminal judicial action or an administrative action to obtain a penalty under CWA section 309(g) or a 

comparable provision of state law. Citizens must also give EPA, the state, and the alleged violator 

60 days’ notice of the alleged violation before beginning a citizen suit. 

1

 Herman, S.A. 1995. Revision of NPDES Significant Noncompliance (SNC) Criteria to Address Violations of Non-Monthly 

Average Limits. U.S. Environmental Protection Agency, Office of Enforcement and Compliance Assurance. Memorandum, 

September 21, 1995. <www.epa.gov/compliance/resources/policies/civil/cwa/revisedsncmemo.pdf>. 

2

 U.S. Environmental Protection Agency. 1989. The Enforcement Management System: National Pollutant Discharge 

Elimination System (Clean Water Act). EC-G-1998-11b. U.S. Environmental Protection Agency, Office of Water, Washington, 

DC. <www.epa.gov/compliance/resources/policies/civil/cwa/emscwa-jensen-rpt.pdf>. 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-1

Appendix A.

Appendix A. Acronyms, Abbreviations and Glossary 

This appendix contains two tables for permit writers to more easily navigate through the acronyms and 

the terms that are mentioned throughout this manual. The first table, Acronyms and Abbreviations, 

provides the full text of the acronyms and abbreviations used throughout and indicates whether they are 

defined in the Glossary (the second table), which provides definitions of terms used in the Clean Water 

Act and NPDES permit program. It provides a reference to the source of the definitions, where available. 

A.1 Acronyms and Abbreviations 

Exhibit A-1 presents the abbreviations used in the NPDES Permit Writers’ Manual. 

Exhibit A-1 Acronyms and abbreviations 

Acronym or

abbreviation Full phrase Glossary 

1Q10 1-day, 10-year Low Flow 

7Q10 7-day, 10-year Low Flow 

4AAP 4-Aminoantipyrine (used for detecting phenolic compounds colorimetrically) 

ACHP Advisory Council on Historic Preservation 

ACR Acute-to-Chronic Ratio 

AFO Animal Feeding Operation x 

AML Average Monthly Limitation x 

ASR Alternative State Requirement 

AWL Average Weekly Limitation x 

BA Biological Assessment 

BAT Best Available Technology Economically Achievable x 

BCT Best Conventional Pollutant Control Technology x 

BE Biological Evaluation 

BMP Best Management Practice x 

BOD Biochemical Oxygen Demand x 

BOD5 5-day Biochemical Oxygen Demand 

BPJ Best Professional Judgment x 

BPT Best Practicable Control Technology Currently Available x 

CAAP Concentrated Aquatic Animal Production 

CAFO Concentrated Animal Feeding Operation x 

CBOD Carbonaceous Biochemical Oxygen Demand x 

CBOD5 5-day Carbonaceous Biochemical Oxygen Demand 

CEQ Council on Environmental Quality 

CERCLA Comprehensive Environmental Response, Compensation and Liabilities Act 

CFR Code of Federal Regulations x 

cfs Cubic Feet per Second 

CGP Construction General Permit 

CMOM Capacity, Management, Operation and Maintenance 
September 2010 NPDES Permit Writers’ Manual 

Exhibit A-1 Acronyms and abbreviations (continued) 

Acronym or 

abbreviation Full phrase Glossary 

COD Chemical Oxygen Demand x 

CSO Combined Sewer Overflow x 

CSS Combined Sewer System x 

CV Coefficient of Variation 

CWA Clean Water Act x 

CWIS Cooling Water Intake Structure 

CZMA Coastal Zone Management Act 

DMR Discharge Monitoring Report x 

DWO Dry Weather Overflow 

EA Environmental Assessment 

EAB Environmental Appeals Board 

EC Effect Concentration 

EFH Essential Fish Habitat 

EIS Environmental Impact Statement 

ELG Effluent Limitations Guidelines or Effluent Guidelines x 

EMS Enforcement Management System 

eNOI Electronic Notice of Intent 

EPA U.S. Environmental Protection Agency 

ESA Endangered Species Act 

FDF Fundamentally Different Factors x 

FR Federal Register 

FWCA Fish and Wildlife Coordination Act 

FWPCA Federal Water Pollution Control Act 

FWS U.S. Fish and Wildlife Service 

GC/MS Gas Chromatography/Mass Spectroscopy 

gpd Gallons per Day 

HEM Hexane Extractable Material 

IC Inhibition Concentration 

ICIS Integrated Compliance Information System 

I/I Infiltration/Inflow 

LA Load Allocation 

lbs/day Pounds per Day 

LC50 Lethal Concentration to 50% of test organisms 

LOEC Lowest Observed Effect Concentration 

LTA Long-Term Average 

LTCP Long-Term Control Plan 

MDL Method Detection Limit x 

MDL Maximum Daily Effluent Limitation x 

MEP Maximum Extent Practicable 

μg/L Micrograms per Liter 

mg/L Milligrams per Liter 

mgd Million Gallons per Day x 

ML Minimum Level x 

A-2 Appendix A. Acronyms, Abbreviations and Glossary 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-3

Exhibit A-1 Acronyms and abbreviations (continued) 

Acronym or 

abbreviation Full phrase Glossary 

MOA Memorandum of Agreement 

MS4 Municipal Separate Storm Sewer System x 

MSA Magnuson-Stevens Act 

MSGP Multi-Sector General Permit 

N/A Not Applicable 

NAICS North American Industrial Classification System x 

NEMI National Environmental Methods Index 

NEPA National Environmental Policy Act 

NHPA National Historic Preservation Act 

NMC Nine Minimum CSO Controls 

NMFS National Marine Fisheries Service 

NMP Nutrient Management Plan 

NOAA National Oceanic and Atmospheric Administration 

NOEC No Observable Effect Concentration 

NOI Notice of Intent 

NOV Notice of Violation 

NPDES National Pollutant Discharge Elimination System x 

NRDC Natural Resources Defense Council 

NSCEP National Service Center for Environmental Publications 

NSPS New Source Performance Standards 

NTIS National Technical Information Service 

O&G Oil and Grease 

OCPSF Organic Chemicals, Plastics, and Synthetic Fibers Point Source Category 

OECA EPA Office of Enforcement and Compliance Assurance 

ONRW Outstanding National Resources Waters 

OTIS Online Tracking Information System 

OW Office of Water 

OWRC Office of Water Resource Center 

PCS Permit Compliance System 

POTW Publicly Owned Treatment Works x 

PSD Prevention of Significant Deterioration 

PSES Pretreatment Standards for Existing Sources 

PSNS Pretreatment Standards for New Sources 

QNCR Quarterly Noncompliance Report 

RAPP Refuse Act Permit Program 

RCRA Resource Conservation and Recovery Act 

RNC Reportable Noncompliance 

SIC Standard Industrial Classification x 

SIU Significant Industrial User x 

SNC Significant Noncompliance 

SOP Standard Operating Procedure 

SPCC Spill Prevention Control and Countermeasure x 

SS Suspended Solids x 
September 2010 NPDES Permit Writers’ Manual 

Exhibit A-1 Acronyms and abbreviations (continued) 

Acronym or 

abbreviation Full phrase Glossary

SSO Sanitary Sewer Overflow x 

STORET EPA Storage and Retrieval Database x 

SWPPP Stormwater Pollution Prevention Plan 

TBEL Technology-Based Effluent Limit(s) x 

TCDF Tetrachlorodibenzofuran 

TEC Transportation Equipment Cleaning Point Source Category 

THC Total Hydrocarbons 

TIE Toxicity Identification Evaluation 

TMDL Total Maximum Daily Load x 

TOC Total Organic Carbon x 

TRC Technical Review Criteria 

TRE Toxicity Reduction Evaluation x 

TRI Toxic Release Inventory 

TSD Technical Support Document [for Water Quality-based Toxics Control] 

TSS Total Suspended Solids x 

TTO Total Toxic Organics 

TU Toxic Units 

TUa Toxic Units – Acute 

TUc Toxic Units – Chronic 

TWTDS Treatment Works Treating Domestic Sewage x 

UAA Use Attainability Analysis 

UIC Underground Injection Control 

U.S.C. United States Code 

WET Whole Effluent Toxicity x 

VGP Vessel General Permit 

WLA Waste Load Allocation x 

WPD EPA Water Permits Division 

WQA Water Quality Act of 1987 

WQBEL Water Quality-Based Effluent Limit(s) x 

WQS Water Quality Standard(s) x 

WSRA Wild and Scenic Rivers Act 

A.2 Glossary 

Exhibit A-2 includes definitions of terms used in the NPDES Permit Writers’ Manual. For terms that have 

a definition in the federal regulations, that definition is included with an appropriate citation. The citations 

also indicate where this guidance manual has paraphrased or modified the regulatory definitions for 

consistency with the format of the glossary. For terms that do not have a regulatory definition, but that are 

defined in another published EPA document, the citation to the relevant EPA document is provided. 

Note that the definitions provided in the Glossary do not constitute EPA’s official use of terms and 

phrases for regulatory purposes, and nothing in this document should be construed to alter or supplant any 

A-4 Appendix A. Acronyms, Abbreviations and Glossary 
September 2010 NPDES Permit Writers’ Manual 

other federal document. Official terminology is in the laws and related regulations as published in such 

sources as the Congressional Record, Federal Register, and elsewhere. 

Exhibit A-2 Glossary 

Term Definition Citation 

401(a) Certification 

A requirement of CWA section 401(a) that all federally issued 

permits be certified by the state in which the discharge occurs. 

The state certifies that the proposed permit will comply with 

state water quality standards and other state requirements. 

1996 U.S. EPA NPDES 

Permit Writers’ Manual

(1996 PWM) 

<www.epa.gov/npdes/pubs/o

wm0243.pdf> 

Acute Effect 

The effect of a stimulus severe enough to rapidly induce an 

effect; in aquatic toxicity tests, an effect generally observed in 

96 hours or less is typically considered acute. When referring to 

aquatic toxicology or human health, an acute effect is not 

always measured in terms of lethality. 

1996 PWM 

Animal Feeding 

Operation (AFO) 

Lot or facility (other than an aquatic animal production facility) 

where the following conditions are met: 

 Animals (other than aquatic animals) have been, are, or will 

be stabled or confined and fed or maintained for a total of 45 

days or more in any 12-month period. 

 Crops, vegetation, forage growth, or post-harvest residues 

are not sustained in the normal growing season over any 

portion of the lot or facility. 

§ 122.23(b)(1) 

Anti-backsliding 

In general, a statutory provision that prohibits the renewal, 

reissuance, or modification of an existing NPDES permit that 

contains effluent limitations, permit conditions, or standards that 

are less stringent than those established in the previous permit. 

For more information on anti-backsliding, see Chapter 7 of this 

manual. 

CWA section 402(o) 

Antidegradation 

A policy developed and adopted as part of a state’s water 

quality standards that ensures protection of existing uses and 

maintains the existing level of water quality where that water 

quality exceeds levels necessary to protect fish and wildlife 

propagation and recreation on and in the water. This policy also 

includes special protection of water designated as Outstanding 

National Resource Waters. 

Adapted from 

1996 PWM

Authorized 

Program or 

Authorized State 

A state, territorial, tribal, or interstate NPDES program that has 

been approved or authorized by EPA under Part 123. 1996 PWM 

Average Monthly 

Discharge 

Limitation 

The highest allowable average of daily discharges over a 

calendar month, calculated as the sum of all daily discharges 

measured during that month divided by the number of daily 

discharges measured during that month. 

§ 122.2 

Average Weekly 

Discharge 

Limitation 

The highest allowable average of daily discharges over a 

calendar week, calculated as the sum of all daily discharges 

measured during a calendar week divided by the number of 

daily discharges measured during that week. 

§ 122.2 

Best Available 

Technology 

Economically 

Achievable (BAT) 

Technology standard established by the CWA as the most 

appropriate means available on a national basis for controlling 

the direct discharge of toxic and nonconventional pollutants to 

navigable waters. BAT limitations in effluent guidelines, in 

general, represent the best existing performance of treatment 

technologies that are economically achievable within an 

industrial point source category or subcategory. 

Adapted from 

1996 PWM 

Appendix A. Acronyms, Abbreviations and Glossary A-5
September 2010 NPDES Permit Writers’ Manual 

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Best Conventional 

Pollutant Control 

Technology (BCT) 

Technology-based standard for the discharge from existing 

industrial point sources of conventional pollutants including 

BOD, TSS, fecal coliform, pH, oil and grease. The BCT is 

established in light of a two-part cost reasonableness test, 

which compares the cost for an industry to reduce its pollutant 

discharge with the cost to a POTW for similar levels of reduction 

of a pollutant loading. The second test examines the costeffectiveness of additional industrial treatment beyond BPT. 

EPA must find limits which are reasonable under both tests 

before establishing them as BCT. 

1996 PWM 

Best Management 

Practice (BMP) 

Schedules of activities, prohibitions of practices, maintenance 

procedures, and other management practices to prevent or 

reduce the pollution of waters of the United States. BMPs also 

include treatment requirements, operating procedures, and 

practices to control plant site runoff, spillage or leaks, sludge or 

waste disposal, or drainage from raw material storage. 

§ 122.2

Best Practicable 

Control Technology 

Currently Available 

(BPT) 

The first level of technology standards established by the CWA 

to control pollutants discharged to waters of the U.S. BPT 

limitations in effluent guidelines are generally based on the 

average of the best existing performance by plants within an 

industrial category or subcategory. 

Adapted from 

1996 PWM 

Best Professional 

Judgment (BPJ) 

The method used by permit writers to develop technology-based 

NPDES permit conditions on a case-by-case basis using all 

reasonably available and relevant data. 

1996 PWM 

Bioassay 

A test used to evaluate the relative potency of a chemical or a 

mixture of chemicals by comparing its effect on a living 

organism with the effect of a standard preparation on the same 

type of organism. 

1996 PWM 

Biochemical 

Oxygen Demand 

(BOD) 

A measurement of the amount of oxygen used by the 

decomposition of organic material, over a specified time (usually 

5 days) in a wastewater sample; it is used as a measurement of 

the readily decomposable organic content of a wastewater. 

1996 PWM 

Biosolids See Sewage Sludge. -- 

Bypass 

The intentional diversion of waste streams from any portion of a 

treatment facility. This definition applies to both direct and 

indirect discharges. 

§ 122.41(m)(1)(i) and 

§ 403.17 

Carbonaceous 

Biochemical 

Oxygen Demand 

(CBOD) 

The biochemical oxygen demand of carbonaceous sources. 

This differs from BOD in that BOD measures both nitrogenous 

and carbonaceous sources, whereas CBOD excludes 

nitrogenous sources (e.g., nitrifying bacteria) from determination 

through the addition of a nitrification inhibitor. 

-- 

Categorical 

Industrial User 

(CIU) 

An industrial user subject to national categorical pretreatment 

standards. 1996 PWM 

Categorical 

Pretreatment 

Standards 

National pretreatment standards , expressed as Pretreatment 

Standards for Existing Sources (PSES) or Pretreatment 

Standards for New Sources (PSNS), specifying quantities or 

concentrations of pollutants or pollutant properties that may be 

discharged to a POTW by existing or new industrial users in 

specific industrial subcategories established as separate 

regulations under the appropriate subpart of 40 CFR chapter I, 

subchapter N. 

Adapted from 

§ 403.6 

A-6 Appendix A. Acronyms, Abbreviations and Glossary 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-7

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Chemical Oxygen 

Demand (COD) 

A measure of the oxygen-consuming capacity of inorganic and 

organic matter present in wastewater. COD is expressed as the 

amount of oxygen consumed in mg/L. Results do not 

necessarily correlate to the biochemical oxygen demand (BOD) 

because the chemical oxidant can react with substances that 

bacteria do not stabilize. 

Adapted from 

1996 PWM 

Chronic Effect 

The effect of a stimulus that lingers or continues for a relatively 

long period, often one-tenth of the life span or more. The 

measurement of a chronic effect can be reduced growth, 

reduced reproduction, and such, in addition to lethality. 

1996 PWM 

Clean Water Act 

(CWA) 

The Clean Water Act is a statute passed by the U.S. Congress 

to control water pollution. It was formerly referred to as the 

Federal Water Pollution Control Act of 1972 or Federal Water 

Pollution Control Act Amendments of 1972 (Public Law 92-500), 

33 U.S.C. 1251 et seq., as amended by: Public Law 96-483; 

Public Law 97-117; Public Laws 95-217, 97-117, 97-440, and 

100-04. 

1996 PWM 

Code of Federal 

Regulations (CFR) 

A codification of the final rules published daily in the Federal 

Register. Title 40 of the CFR contains regulations for the 

protection of the environment. 

1996 PWM 

Combined Sewer 

Overflow (CSO) 

A discharge of untreated wastewater from a combined sewer 

system at a point before the headworks of a publicly owned 

treatment works. CSOs generally occur during wet weather 

(rainfall or snowmelt). During periods of wet weather, these 

systems become overloaded, bypass treatment works, and 

discharge directly to receiving waters at designed overflow 

points. 

1996 PWM 

Combined Sewer 

System (CSS) 

A wastewater collection system that conveys sanitary 

wastewaters (domestic, commercial and industrial wastewaters) 

and stormwater through a single pipe to a publicly owned 

treatment works for treatment before discharge to surface 

waters. 

1996 PWM 

Compliance 

Schedule (or 

Schedule of 

Compliance) 

A schedule of remedial measures included in a permit, including 

an enforceable sequence of interim requirements (for example, 

actions, operations, or milestone events) leading to compliance 

with the CWA and regulations. 

§ 122.2 

Composite Sample 

Sample composed of two or more discrete aliquots (samples). 

The aggregate sample will reflect the average water quality of 

the compositing or sample period. 

-- 

Conventional 

Pollutants 

Pollutants typical of municipal sewage, and for which publicly 

owned treatment works typically are designed to remove; 

defined by Federal Regulation (§ 401.16) as BOD, TSS, fecal 

coliform bacteria, oil and grease, and pH. 

1996 PWM 

Daily Discharge 

The discharge of a pollutant measured during a calendar day or 

any 24-hour period that reasonably represents the calendar day 

for purposes of sampling. For pollutants with limitations 

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

the total mass of the pollutant discharged over the day. For 

pollutants with limitations expressed in other units of 

measurement, the daily discharge is calculated as the average 

measurement of the pollutant over the day. 

§ 122.2 
September 2010 NPDES Permit Writers’ Manual 

A-8 Appendix A. Acronyms, Abbreviations and Glossary 

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Designated Uses 

Those uses specified in water quality standards for each 

waterbody or segment whether they are being attained 

(§ 131.3). Examples of designated uses include cold and warm 

water fisheries, public water supply, and irrigation. 

Adapted from 

EPA. Terms of 

Environment: Glossary, 

Abbreviations, 

Acronyms. 

<www.epa.gov/OCEPAterms/

dterms.html> 

Development 

Document 

A report prepared during development of an effluent guideline 

by EPA that provides the data and methodology used to 

develop effluent guidelines and categorical pretreatment 

standards for an industrial category. 

Adapted from 

1996 PWM 

Director 

The Regional Administrator or the State Director, as the context 

requires, or an authorized representative. When there is no 

approved state program, and there is an EPA-administered 

program, Director means the Regional Administrator. When 

there is an approved state program, Director normally means 

the State Director. In some circumstances, however, EPA 

retains the authority to take certain actions even when there is 

an approved state program. (For example, when EPA has 

issued an NPDES permit before the approval of a state 

program, EPA may retain jurisdiction over that permit after 

program approval, see § 123.1.) In such cases, Director means 

the Regional Administrator and not the State Director. 

§ 122.2 

Discharge 

Monitoring Report 

(DMR) 

The EPA uniform national form, including any subsequent 

additions, revisions, or modifications for the reporting of selfmonitoring results by permittees. DMRs must be used by 

approved states as well as by EPA. EPA will supply DMRs to 

any approved state upon request. The EPA national forms may 

be modified to substitute the state agency name, address, logo, 

and other similar information, as appropriate, in place of EPA's. 

§ 122.2 

Draft Permit 

A document prepared under § 124.6 indicating the Director’s 

tentative decision to issue, deny, modify, revoke and reissue, 

terminate, or reissue a permit. A notice of intent to terminate a 

permit, and a notice of intent to deny a permit, as discussed in § 

124.5, are types of draft permits. A denial of a request for 

modification, revocation and reissuance, or termination, as 

discussed in § 124.5, is not a draft permit. A proposed permit is 

not a draft permit. 

§ 122.2 

Effluent Limitation 

Any restriction imposed by the Director on quantities, discharge 

rates, and concentrations of pollutants which are discharged

from point sources into waters of the United States, the waters 

of the contiguous zone, or the ocean. 

§ 122.2 

Effluent Limitations 

Guidelines (Effluent 

Guidelines or ELG) 

A regulation published by the Administrator under CWA section 

304(b) to adopt or revise effluent limitations. § 122.2 

Existing Uses 

Those uses actually attained in the waterbody on or after 

November 28, 1975, whether they are included in the water 

quality standards. 

§ 131.3 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-9

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Fact Sheet 

A document that must be prepared for all draft individual permits 

for NPDES major dischargers, NPDES general permits, NPDES 

permits that contain variances, NPDES permits that contain 

sewage sludge land application plans and several other classes 

of dischargers. The document summarizes the principal facts 

and the significant factual, legal, methodological and policy 

questions considered in preparing the draft permit and explains 

how the public may comment (§§ 124.8 and 124.56). Where a 

fact sheet is not required, a statement of basis must be 

prepared (§ 124.7). 

1996 PWM 

Fundamentally 

Different Factors 

(FDF) 

Those components of a petitioner’s facility that are determined 

to be so unlike those components considered by EPA during the 

effluent guidelines and pretreatment standards rulemaking that 

the facility is worthy of a variance from the effluent guidelines or 

categorical pretreatment standards that would otherwise apply. 

Adapted from 

1996 PWM 

General Permit 

An NPDES permit issued under § 122.28 that authorizes a 

category of discharges under the CWA within a geographical 

area. A general permit is not specifically tailored for an 

individual discharger. 

1996 PWM 

Grab Sample 

A sample taken from a wastestream on a one-time basis without 

consideration of the flow rate of the wastestream and without 

consideration of time. 

Adapted from 

1996 PWM 

Hazardous 

Substance 

Any substance—as designated under Part 116 pursuant to 

CWA section 311—that presents an imminent and substantial 

danger to the public health or welfare, including fish, shellfish, 

wildlife, shorelines, and beaches, upon discharge to navigable 

waters of the United States. 

Adapted from 

§ 122.2 and 

CWA section 

311(b)(2)(A) 

Indirect Discharger A nondomestic discharger introducing pollutants to a publicly 

owned treatment works. 40 CFR 122.2 

Instantaneous 

Maximum Limit 

The maximum allowable concentration or other measure of a 

pollutant determined from the analysis of any discrete or 

composite sample collected, independent of the flow rate and 

the duration of the sampling event. 

1996 PWM 

Instantaneous 

Minimum Limit 

The minimum allowable concentration or other measure of a 

pollutant determined from the analysis of any discrete or 

composite sample collected, independent of the flow rate and 

the duration of the sampling event. 

-- 

Load Allocation 

The portion of a receiving water's loading capacity that is 

attributed either to one of its existing or future nonpoint sources 

of pollution or to natural background sources. Load allocations 

are best estimates of the loading, which may range from 

reasonably accurate estimates to gross allotments, depending 

on the availability of data and appropriate techniques for 

predicting the loading. Wherever possible, natural and nonpoint 

source loads should be distinguished. 

§ 130.2 

Local Limits 

Where specific prohibitions or limits on pollutants or pollutant 

parameters are developed by a POTW in accordance with § 

403.4(c), such limits must be deemed Pretreatment Standards 

for the purposes of CWA section 307(d). 

Adapted from 

§ 403.4(d) 
September 2010 NPDES Permit Writers’ Manual 

A-10 Appendix A. Acronyms, Abbreviations and Glossary 

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Major Facility 

Any NPDES facility or activity classified as such by the Regional 

Administrator, or in the case of approved state programs, the 

Regional Administrator in conjunction with the State Director (§ 

122.2). Major municipal dischargers include all facilities with 

design flows of greater than one million gallons per day and 

facilities with EPA/state approved industrial pretreatment 

programs. Major industrial facilities are determined based on 

specific ratings criteria developed by EPA or are classified as 

such by EPA in conjunction with the state. 

1996 PWM 

Method Detection 

Limit (MDL) 

The minimum concentration of a substance that can be 

measured and reported with 99% confidence that the analyte 

concentration is greater than zero and is determined from 

analysis of a sample in a given matrix containing the analyte. 

§ 136 - Appendix B 

Maximum Daily 

Effluent Limitation 

(MDL) 

The highest allowable daily discharge of a pollutant. (Chapter 6) -- 

Million Gallons per 

Day (or mgd) 

A unit of flow commonly used for wastewater discharges. One 

million gallon per day is equivalent to 1.547 cubic feet per 

second. 

1996 PWM 

Minimum Level 

(ML) 

The level at which the entire analytical system must give a 

recognizable signal and acceptable calibration point. 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. 

§ 136 - Appendix A 

Mixing Zone 

An area where an effluent discharge undergoes initial dilution 

and is extended to cover the secondary mixing in the ambient 

waterbody. A mixing zone is an allocated impact zone where 

water quality criteria can be exceeded as long as acutely toxic 

conditions are prevented. 

Technical Support 

Document for Water 

Quality-based Toxics 

Control 

<www.epa.gov/npdes/pubs/o

wm0264.pdf> 

Municipal Separate 

Storm Sewer 

System (MS4) 

A conveyance or system of conveyances (including roads with 

drainage systems, municipal streets, catch basins, curbs, 

gutters, ditches, man-made channels, or storm drains): 

a. Owned or operated by a state, city, town, borough, 

county, parish, district, association, or other public 

body (created by or pursuant to state law) having 

jurisdiction over disposal of sewage, industrial wastes, 

stormwater, or other wastes, including special districts 

under state law such as a sewer district, flood control 

district or drainage district, or similar entity, or an 

Indian tribe or an authorized Indian tribal organization, 

or a designated and approved management agency 

under CWA section 208 that discharges to waters of 

the United States. 

b. Designed or used for collecting or conveying 

stormwater. 

c. [That] is not a combined sewer. 

d. [That] is not part of a Publicly Owned Treatment Works 

(POTW) as defined at § 122.2. 

§ 122.26(b)(8) 

Municipal Sludge See Sewage Sludge. -- 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-11

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

National Pollutant 

Discharge 

Elimination System 

(NPDES) 

The national program for issuing, modifying, revoking and 

reissuing, terminating, monitoring and enforcing permits, and 

imposing and enforcing pretreatment requirements, under CWA 

sections 307, 318, 402, and 405. The term includes approved 

program. NPDES permits regulate discharges of pollutants from 

point sources to waters of the United States. Such discharges 

are illegal unless authorized by an NPDES permit. 

Adapted from 

§ 122.2 

National 

Pretreatment 

Standard or 

Pretreatment 

Standard 

Any regulation promulgated by EPA in accordance with CWA 

sections 307(b) and 307(c) that applies to a specific category of 

industrial users and provides limitations on the introduction of 

pollutants into publicly owned treatment works. The term 

includes the prohibited discharge standards under § 403.5. 

Adapted from 

§ 403.3(l) 

New Discharger 

Any building, structure, facility, or installation: 

a. From which there is or may be a discharge of 

pollutants. 

b. That did not begin the discharge of pollutants at that 

site before August 13, 1979. 

c. That is not a new source. 

d. That has never received a finally effective NPDES 

permit for discharges at that site. 

This definition includes an indirect discharger that begins 

discharging into waters of the United States after August 13, 

1979. It also includes any existing mobile point source (other 

than an offshore or coastal oil and gas exploratory drilling rig or 

a coastal oil and gas developmental drilling rig) such as a 

seafood processing rig, seafood processing vessel, or 

aggregate plant, that begins discharging at a site for which it 

does not have a permit; and any offshore or coastal mobile oil 

and gas exploratory drilling rig or coastal mobile oil and gas 

developmental drilling rig that commences the discharge of 

pollutants after August 13, 1979, at a site under EPA's 

permitting jurisdiction for which it is not covered by an individual 

or general permit and which is in an area determined by the 

Regional Administrator in the issuance of a final permit to be an 

area or biological concern. In determining whether an area is an 

area of biological concern, the Regional Administrator must 

consider the factors specified in §§ 125.122(a)(1) - 

125.122(a)(10). 

An offshore or coastal mobile exploratory drilling rig or coastal 

mobile developmental drilling rig will be considered a new 

discharger only for the duration of its discharge in an area of 

biological concern. 

Adapted from 

§ 122.2 
September 2010 NPDES Permit Writers’ Manual 

A-12 Appendix A. Acronyms, Abbreviations and Glossary 

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

New Source 

Any building, structure, facility, or installation from which there is 

or could be a discharge of pollutants, the construction of which 

commenced: 

a. After promulgation of standards of performance under 

CWA section 306, which are applicable to such source; 

or 

b. After proposal of standards of performance in 

accordance with CWA section 306, which are 

applicable to such source but only if the standards are 

promulgated in accordance with CWA section 306 

within 120 days of their proposal. 

Additional Criteria: 

Except as otherwise provided in an applicable new source 

performance standard, a source is a new source if it meets 

the definition in § 122.2; and 

i. It is constructed at a site at which no other source 

is located; or 

ii. It totally replaces the process or production 

equipment that causes the discharge of pollutants 

at an existing source; or 

iii. Its processes are substantially independent of an 

existing source at the same site. In determining 

whether these processes are substantially 

independent, the Director shall consider such 

factors as the extent to which the new facility is 

integrated with the existing plant; and the extent 

to which the new facility is engaged in the same 

general type of activity as the existing source. 

Adapted from 

§ 122.2 and 

§ 122.29(b)(1) 

New Source 

Performance 

Standards (NSPS) 

Technology standards for facilities that qualify as new sources 

under § 122.2 and § 122.29. Standards consider that the new 

source facility has an opportunity to design operations to more 

effectively control pollutant discharges. 

1996 PWM 

Nonconventional 

Pollutants 

All pollutants that are not included in the list of conventional or 

toxic pollutants in Part 401. Includes pollutants such as 

chemical oxygen demand (COD), total organic carbon (TOC), 

nitrogen, and phosphorus. 

1996 PWM 

Nonpoint Source 

Diffuse pollution sources (i.e., without a single point of origin or 

not introduced into a receiving stream from a specific outlet). 

The pollutants are generally carried off the land by stormwater. 

Atmospheric deposition and hydromodification are also sources 

of nonpoint source pollution. 

-- 

North American 

Industrial 

Classification 

System (NAICS) 

The North American Industry Classification System (NAICS) is 

the standard used by federal statistical agencies in classifying 

business establishments for the purpose of collecting, 

analyzing, and publishing statistical data related to the U.S. 

business economy. 

Retrieved from 

<www.census.gov/epcd/www/

naics.html> 

Nutrients 

Chemical elements and compounds found in the environment 

that plants and animals need to grow and survive. Nutrients 

include compounds of nitrogen (nitrate, nitrite, ammonia, 

organic nitrogen) and phosphorus (orthophosphate and others), 

both natural and man-made. 

-- 

Permitting 

Authority 

The agency authorized to issue and enforce specific 

requirements of the NPDES permit program. The permitting 

authority may be EPA, or a state, territorial, or tribal agency that 

has been authorized under CWA section 402(b) to administer 

the NPDES program within its jurisdiction. 

-- 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-13

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

pH 

A measure of the hydrogen ion concentration of water or 

wastewater; expressed as the negative log of the hydrogen ion 

concentration in mg/L. A pH of 7 is neutral. A pH less than 7 is 

acidic, and a pH greater than 7 is basic. 

1996 PWM 

Point Source 

Any discernible, confined, and discrete conveyance, including 

any pipe, ditch, channel, tunnel, conduit, well, discrete fixture, 

container, rolling stock, concentrated animal feeding operation, 

landfill leachate collection system, vessel or other floating craft 

from which pollutants are or may be discharged. The term does 

not include return flows from irrigated agriculture or agricultural 

stormwater runoff. 

Adapted from 

§ 122.2 

Pollutant 

Dredged spoil, solid waste, incinerator residue, filter backwash, 

sewage, garbage, sewage sludge, munitions, chemical wastes, 

biological materials, radioactive materials (except those 

regulated under the Atomic Energy Act of 1954, as amended 

[42 U.S.C. 2011 et seq.)], heat, wrecked or discarded 

equipment, rock, sand, cellar dirt and industrial, municipal, and 

agricultural waste discharged into water. It does not mean 

a. Sewage from vessels. 

b. Water, gas, or other material that is injected into a well 

to facilitate production of oil or gas, or water derived in 

association with oil and gas production and disposed of 

in a well, if the well used either to facilitate production 

or for disposal purposes is approved by authority of the 

state in which the well is located, and if the state 

determines that the injection or disposal will not result 

in the degradation of ground or surface water 

resources. 

§ 122.2 

Pollutant, 

Conservative 

Pollutants that do not readily degrade in the environment and 

that are mitigated primarily by dilution after entering receiving 

waters (e.g., metals, total suspended solids). 

Adapted from 

1996 PWM 

Pollutant, NonConservative 

Pollutants that are mitigated by natural biodegradation or other 

environmental decay or removal processes in the receiving 

water after mixing and dilution have occurred (e.g., biochemical 

oxygen demand, pH, volatile organic compounds). 

Adapted from 

1996 PWM 

Pretreatment 

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. 

§ 403.3(s) 

Primary Industry 

Category 

Any industry category listed in the NRDC settlement agreement 

(Natural Resources Defense Council et al. v. Train, 8 E.R.C. 

2120 [D.D.C. 1976], modified 12 E.R.C. 1833 [D.D.C. 1979]); 

also listed in Appendix A of Part 122. 

§ 122.2 

Primary Treatment 

The practice of removing some portion of the suspended solids 

and organic matter in wastewater through sedimentation. 

Common usage of this term also includes preliminary treatment 

to remove wastewater constituents that may cause maintenance 

or operational problems in the system (i.e., grit removal, 

screening for rags and debris, oil and grease removal, etc.). 

1996 PWM 

Priority Pollutants 

Those pollutants considered to be of principal importance for 

control under the CWA based on the NRDC Consent Decree 

(NRDC et al. v. Train, 8 E.R.C. 2120 [D.D.C. 1976], modified 

12 E.R.C. 1833 [D.D.C. 1979]); a list of the pollutants is 

provided as Appendix A to 40 CFR Part 423. 

1996 PWM 
September 2010 NPDES Permit Writers’ Manual 

A-14 Appendix A. Acronyms, Abbreviations and Glossary 

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Process 

Wastewater 

Any water [that], during manufacturing or processing, comes 

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

any raw material, intermediate product, finished product, 

by-product, or waste product. 

§ 122.2 

Production-Based 

Standard 

A discharge standard expressed in terms of pollutant mass 

allowed per unit of product manufactured or some other 

measure of production. 

1996 PWM 

Proposed Permit 

A state NPDES permit prepared after the close of the public 

comment period (and when applicable, any public hearing and 

administrative appeals) [that] is sent to EPA for review before 

final issuance by the state. A proposed permit is not a draft 

permit.

§ 122.2 

Publicly Owned 

Treatment Works 

(POTW) 

A treatment works as defined by CWA section 212, which is 

owned by a state or municipality [as defined by CWA section 

502(4)]. 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. The term also means the 

municipality as defined in CWA section 502(4), which has 

jurisdiction over the indirect discharges to and the discharges 

from such a treatment works. 

§ 403.3(q) 

Sanitary Sewer 

A pipe or conduit (sewer) intended to carry wastewater or waterborne wastes from homes, businesses, and industries to the 

POTW. 

1996 PWM 

Sanitary Sewer 

Overflows (SSO) 

Untreated or partially treated sewage overflows from a sanitary 

sewer collection system. 1996 PWM 

Secondary Industry 

Category Any industry category, which is not a primary industry category. § 122.2 

Secondary 

Treatment 

Technology-based requirements for direct discharging POTWs. 

Standard is based on the expected performance of a 

combination of physical and biological processes typical for the 

treatment of pollutants in municipal sewage. Standards are 

expressed as a minimum level of effluent quality in terms of: 

BOD5, total suspended solids (TSS), and pH (except as 

provided by treatment equivalent to secondary treatment and 

other special considerations). 

Adapted from 

1996 PWM 

Section 304(a) 

Criteria 

Developed by EPA under authority of CWA section 304(a) 

based on the latest scientific information on the relationship that 

the effect of a constituent concentration has on particular 

aquatic species and/or human health. This information is issued 

periodically to the states as guidance for use in developing 

criteria. 

§ 131.3(c) 

Self-Monitoring 

Sampling and analyses performed by a facility to determine 

compliance with effluent limitations or other regulatory 

requirements. 

1996 PWM 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-15

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Sewage Sludge 

Any solid, semi-solid, or liquid residue removed during the 

treatment of municipal waste water or domestic sewage. 

Sewage sludge includes solids removed during primary, 

secondary, or advanced wastewater treatment, scum, septage, 

portable toilet pumpings, type III marine sanitation device 

pumpings (33 CFR Part 159), and sewage sludge products. 

Sewage sludge does not include ash generated during the firing 

of sewage sludge in a sewage sludge incinerator or grit and 

screenings generated during preliminary treatment of domestic 

sewage in a treatment works. 

Adapted from § 122.2 

and Part 503 

Significant 

Industrial User 

(SIU) 

An indirect discharger that is the focus of control efforts under 

the National Pretreatment Program. 

SIUs include [with exceptions provided under § 403.3(v)]: 

i. All Industrial Users subject to Categorical Pretreatment 

Standards under § 403.6 and Chapter 1, Subchapter 

N. 

ii. Any other Industrial User that: discharges an average 

of 25,000 gallons per day or more of process 

wastewater to the POTW (excluding sanitary, 

noncontact cooling and boiler blowdown wastewater); 

contributes a process wastestream that makes up 5 

percent or more of the average dry weather hydraulic 

or organic capacity of the POTW; or is designated as 

such by the Control Authority on the basis that the 

Industrial User has a reasonable potential for adversely 

affecting the POTW's operation or for violating any 

Pretreatment Standard or requirement [in accordance 

with § 403.8(f)(6)]. 

Adapted from 

§ 403.3(v) 

Spill Prevention 

Control and 

Countermeasure 

Plan (SPCC) 

A plan prepared by a facility to minimize the likelihood of a spill 

and to expedite control and cleanup activities if a spill occurs. 

Such plans are required for certain facilities under the Oil 

Pollution Prevention Regulations at 40 CFR Part 112. 

Adapted from 

1996 PWM 

Standard Industrial 

Classification (SIC) 

Code 

A code number system used to identify various types of 

industries. A particular industry may have more than one SIC 

code if it conducts several types of commercial or manufacturing 

activities onsite. An online version of the 1987 SIC Manual

<www.osha.gov/pls/imis/sic_manual.html> is available courtesy of the 

Occupational Safety & Health Administration (OSHA). 

Adapted from 

1996 PWM 

Statement of Basis 

A document prepared for every draft NPDES permit for which a 

fact sheet is not required. A statement of basis briefly describes 

how permit conditions were derived and the reasons the 

conditions are necessary for the permit. 

1996 PWM 

STORET 

EPA’s computerized STOrage and RETrieval water quality data 

base that includes physical, chemical, and biological data 

measured in waterbodies throughout the United States. 

1996 PWM 

Storm Water (or 

Stormwater) 

Stormwater runoff, snow melt runoff, and surface runoff and 

drainage. § 122.26(b)(13) 

Technology-Based 

Effluent Limitation 

(TBEL) 

An effluent limit for a pollutant that is based on the capability of 

a treatment method to reduce the pollutant to a certain 

concentration or mass loading level. TBELs for POTWs are 

derived from the secondary treatment regulations in Part 133 or 

state treatment standards. TBELs for non-POTWs are derived 

from effluent guidelines, state treatment standards, or by the 

permit writer on a case-by-case basis using best professional 

judgment. 

Adapted from 

1996 PWM 
September 2010 NPDES Permit Writers’ Manual 

A-16 Appendix A. Acronyms, Abbreviations and Glossary 

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Tiered Permit 

Limits 

Permit limits that apply to the discharge only when a certain 

threshold (e.g., production level), specific circumstance (e.g., 

batch discharge), or time frame (e.g., after 6 months, during the 

months of May through October) triggers their use. 

Adapted from 

1996 PWM 

Total Maximum 

Daily Load (TMDL) 

The sum of the individual wasteload allocations (WLAs) for point 

sources and load allocations (LAs) for nonpoint sources and 

natural background. If a receiving water has only one point 

source discharger, the TMDL is the sum of that point source 

WLA plus the LAs for any nonpoint sources of pollution and 

natural background sources, tributaries, or adjacent segments. 

TMDLs can be expressed in terms of either mass per time, 

toxicity, or other appropriate measure. If best management 

practices (BMPs) or other nonpoint source pollution controls 

make more stringent load allocations practicable, then 

wasteload allocations can be made less stringent. Thus, the 

TMDL process provides for nonpoint source control tradeoffs. 

40 CFR § 130.2(i) 

Total Suspended 

Solids (TSS) 

A measure of the filterable solids present in a sample, as 

determined by the method specified in Part 136. 1996 PWM 

Toxic Pollutant 

Any pollutant listed as toxic under CWA section 307(a)(1) or, in 

the case of sludge use or disposal practices, any pollutant 

identified in regulations implementing CWA section 405(d). 

§ 122.2 

Toxicity Reduction 

Evaluation (TRE) 

A site-specific study conducted in a step-wise process designed 

to identify the causative agent(s) of effluent toxicity, isolate the 

sources of toxicity, evaluate the effectiveness of toxicity control 

options, and then confirm the reduction in effluent toxicity. 

1996 PWM 

Toxicity Test 

A procedure to determine the toxicity of a chemical or an 

effluent using living organisms. A toxicity test measures the 

degree of effect on exposed test organisms of a specific 

chemical or effluent. 

1996 PWM 

Trading (or Water 

Quality Trading) 

An innovative approach to achieve water quality goals more 

efficiently. Trading is based on the fact that sources in a 

watershed can face very different costs to control the same 

pollutant. Trading programs allow facilities facing higher 

pollution control costs to meet their regulatory obligations by 

purchasing environmentally equivalent (or superior) pollution 

reductions from another source at lower cost, thus achieving the 

same water quality improvement at lower overall cost. 

Water Quality Trading 

Fact Sheet: 

<www.epa.gov/owow/watersh

ed/trading/handbook/factsheet.

html>

Treatability Manual 

Five-set library of EPA guidance manuals that contain 

information related to the treatability of many pollutants. The 

manual may be used in developing effluent limitations for 

facilities and pollutants, which, at the time of permit issuance, 

are not subject to industry-specific effluent guidelines. The five 

volumes that comprise this series consist of Vol. I – Treatability 

Data (EPA-600/8-80-042a); Vol. II – Industrial Descriptions 

(EPA-600/8-80-042b); Vol. III – Technologies (EPA-600/8-80-

042c); Vol. IV – Cost Estimating (EPA-600/8-80-042d); and 

Vol. V – Summary (EPA-600/8-80-042e). 

1996 PWM 

Treatment Works 

Treating Domestic 

Sewage (TWTDS) 

A POTW or any other sewage sludge or waste water treatment 

devices or systems, regardless of ownership (including federal 

facilities), used in the storage, treatment, recycling, and 

reclamation of municipal or domestic sewage, including land 

dedicated for the disposal of sewage sludge. This definition 

does not include septic tanks or similar devices. For purposes of 

this definition, domestic sewage includes waste and waste 

water from humans or household operations that are discharged 

to or otherwise enter a treatment works. 

Adapted from 

§ 122.2 
September 2010 NPDES Permit Writers’ Manual 

Appendix A. Acronyms, Abbreviations and Glossary A-17

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Upset 

An exceptional incident in which there is unintentional and 

temporary noncompliance with technology-based permit effluent 

limitations because of factors beyond the reasonable control of 

the permittee. An upset does not include noncompliance to the 

extent caused by operational error, improperly designed 

treatment facilities, inadequate treatment facilities, lack of 

preventive maintenance, or careless or improper operation. 

§ 122.41(n) 

Use Attainability 

Analysis 

A structured scientific assessment of the factors affecting the 

attainment of the use that [can] include physical, chemical, 

biological, and economic factors as described in § 131.10(g). 

§ 131.3 

Variance 

Any mechanism or provision under CWA sections 301 or 316 or 

under 40 CFR Part 125, or in the applicable effluent limitations 

guidelines, which allows modification to or waiver of the 

generally applicable effluent limitation requirements or time 

deadlines of the CWA. This includes provisions, [that] allow the 

establishment of alternative limitations based on fundamentally 

different factors or on CWA sections 301(c), 301(g), 301(h), 

301(i), or 316(a). 

§ 122.2 

Wasteload 

Allocation (WLA) 

The portion of a receiving water’s loading capacity that is 

allocated to one of its existing or future point sources of 

pollution. 

Adapted from 

§ 130.2(h) 

Water Quality 

Criteria 

Elements of state water quality standards, expressed as 

constituent concentrations, levels, or narrative statements, 

representing a quality of water that supports a particular use. 

When criteria are met, water quality will generally protect the 

designated use. 

§ 131.3(b) 

Water Quality 

Limited Segment 

Any segment where it is known that water quality does not meet 

applicable water quality standards, and/or is not expected to 

meet applicable water quality standards, even after the 

application of the technology-based effluent limitations required 

by CWA sections 301(b) and 306. 

§ 131.3 

Water Quality 

Standards (WQS) 

Provisions of state or federal law that consist of a designated 

use or uses for the waters of the United States and water quality 

criteria for such waters based on such uses. Water quality 

standards are to protect the public health or welfare, enhance 

the quality of water, and serve the purposes of the CWA. 

Adapted from 

§131.3 

Water QualityBased Effluent 

Limitation (WQBEL) 

An effluent limitation determined by selecting the most stringent 

of the effluent limits calculated using all applicable water quality 

criteria (e.g., aquatic life, human health, wildlife, translation of 

narrative criteria) for a specific point source to a specific 

receiving water. 

Adapted from 

1996 PWM 
September 2010 NPDES Permit Writers’ Manual 

A-18 Appendix A. Acronyms, Abbreviations and Glossary 

Exhibit A-2 Glossary (continued) 

Term Definition Citation 

Waters of the 

United States 

Means 

a. All waters [that] are currently used, were used in the 

past, or [could] be susceptible to use in interstate or 

foreign commerce, including all waters [that] are 

subject to the ebb and flow of the tide. 

b. All interstate waters, including interstate wetlands. 

c. All other waters such as intrastate lakes, rivers, 

streams (including intermittent streams), mudflats, 

sandflats, wetlands, sloughs, prairie potholes, wet 

meadows, playa lakes, or natural ponds the use, 

degradation, or destruction of which would affect or 

could affect interstate or foreign commerce including 

any such waters 

1. [That] are or could be used by interstate or foreign 

travelers for recreational or other purposes. 

2. From which fish or shellfish are or could be taken 

and sold in interstate or foreign commerce or 

3. [That] are used or could be used for industrial 

purposes by industries in interstate commerce. 

d. All impoundments of waters otherwise defined as 

waters of the United States under this definition. 

e. Tributaries of waters identified in paragraphs (a) 

through (d) of this definition. 

f. The territorial sea and 

g. Wetlands adjacent to waters (other than waters that 

are themselves wetlands) identified in paragraphs (a) 

through (f) of this definition. 

[see additional notes in § 122.2]

§ 122.2 

Whole Effluent 

Toxicity (WET) 

The aggregate toxic effect of an effluent measured directly by a 

toxicity test. § 122.2 
September 2010 NPDES Permit Writers’ Manual 

Appendix B. Index to the CWA and NPDES Regulations B-1

Appendix B.

Appendix B. Index to the CWA and NPDES Regulations 

This appendix provides two tables to help permit writers navigate Clean Water Act (CWA) legislation 

and National Pollutant Discharge Elimination System (NPDES) regulations. The first table provides key 

sections of the CWA and the second table provides an index to NPDES regulations. 

B.1 Index to Sections of the CWA 

Title 33 of the United States Code (U.S.C.) includes the statutes and amendments to the CWA. Exhibit 

B-1 matches key sections of the CWA to the appropriate reference in the U.S.C. This latest version, dated 

December 20, 2004, was provided by the New England Interstate Water Pollution Control Commission. 

Exhibit B-1 Index to sections of the CWA 

33 U.S.C. section Section title CWA section 

Subchapter I Research and Related Programs 

1251 Congressional declaration of goals and policy 101 

1252 Comprehensive programs for water pollution control 102 

1253 Interstate cooperation and uniform laws 103 

1254 Research, investigations, training and information 104 

1255 Grants for research and development 105 

1256 Grants for pollution control programs 106 

1257 Mine water pollution demonstrations 107 

1258 Pollution control in the Great Lakes 108 

1259 Training grants and contracts 109 

1260 Applications for training grants and contracts; allocations 110 

1261 Scholarships 111 

1262 Definitions and authorization 112 

1263 Alaska village demonstration project 113 

1265 In-place toxic pollutants 115 

1266 Hudson River reclamation demonstration project 116 

1267 Chesapeake Bay 117 

1268 Great Lakes 118 

1269 Long Island Sound 119 

1270 Lake Champlain management conference 120 

1273 Lake Pontchartrain Basin 121 

1274 Wet weather watershed pilot projects 121 

Subchapter II Grants for Construction of Treatment Works 

1281 Congressional declaration of purpose 201 

1282 Federal share 202 

1283 Plans, specifications, estimates, and payments 203 

1284 Limitations and conditions 204 

1285 Allotment of grant funds 205 

1286 Reimbursement and advanced construction 206 

1287 Authorization of appropriations 207 

1288 Area wide waste treatment management 208 

1289 Basin planning 209 
September 2010 NPDES Permit Writers’ Manual 

Exhibit B-1 Index to sections of the CWA (continued) 

33 U.S.C. section Section title CWA section 

1290 Annual survey 210 

1291 Sewage collection system 211 

1292 Definitions 212 

1293 Loan guarantees 213 

1294 Wastewater recycling and reuse information and education 214 

1295 Requirements for American materials 215 

1296 Determination of priority 216 

1297 Guidelines for cost-effective analysis 217 

1298 Cost effectiveness 218 

1299 State certification of projects 219 

1300 Pilot program for alternative water source projects 220 

1301 Sewer overflow control grants 221 

Subchapter III Standards and Enforcement 

1311 Effluent Limitations 301 

1312 Water quality-related effluent limitations 302 

1313 Water quality standards and implementation plans 303 

1314 Information and guidelines 304 

1315 Water quality inventory 305 

1316 National standards of performance 306 

1317 Toxic and pretreatment effluent standards 307 

1318 Records and reports, inspections 308 

1319 Enforcement 309 

1320 International pollution abatement 310 

1321 Oil and hazardous substance liability 311 

1322 Marine sanitation devices 312 

1323 Federal facility pollution control 313 

1324 Clean lakes 314 

1325 National study commission 315 

1326 Thermal discharges 316 

1328 Aquaculture 318 

1329 Nonpoint source management program 319 

1330 National estuary study 320 

Subchapter IV Permits and Licenses 

1341 Certification 401 

1342 National pollutant discharge elimination system 402 

1343 Ocean discharge criteria 403 

1344 Permits for dredge and fill materials 404 

1345 Disposal or use of sewage sludge 405 

1346 Coastal recreation water quality monitoring and notification 406 

Subchapter V General Provisions 

1361 Administration 501 

1362 Definitions 502 

1363 Water pollution control advisory board 503 

1364 Emergency powers 504 

1365 Citizen suits 505 

1366 Appearance 506 

1367 Employee protection 507 

1368 Federal procurement 508 

1369 Administrative procedure and judicial review 509 

1370 State authority 510 

B-2 Appendix B. Index to the CWA and NPDES Regulations 
September 2010 NPDES Permit Writers’ Manual 

Appendix B. Index to the CWA and NPDES Regulations B-3

Exhibit B-1 Index to sections of the CWA (continued) 

33 U.S.C. section Section title CWA section 

1371 Authority under other laws and regulations 511 

1251 Note Separability 512 

1372 Labor standards 513 

1373 Public health agency coordination 514 

1374 Effluent standards and water quality information advisory committee 515 

1375 Reports to Congress 516 

1376 Authorization of appropriations 517 

1377 Indian tribes 518 

1251 Note Short Title 519 

Subchapter VI State Water Pollution Control Revolving Funds 

1381 Grants to States for establishment of revolving funds 601 

1382 Capitalization grant agreements 602 

1383 Water pollution control revolving loan funds 603 

1384 Allotment of funds 604 

1385 Corrective actions 605 

1386 Audits, reports, fiscal controls, intended use plan 606 

1387 Authorization of appropriations 607 

B.2 Index to NPDES Regulations 

The index to NPDES regulations table presented in Exhibit B-2 was created by Sylvia Kawabata of EPA 

Region 10 on February 1, 1986, and is maintained by Doug Corb of EPA Region 1. 

Exhibit B-2 Index to NPDES regulations 

Subject 40 CFR section number 

Selected CWA sections 

CWA section 301(c) – Modification of Timetable § 122.21(m)(2) 

Part 125, Subpart E (reserved) 

CWA section 301(g) – Modifications for Certain Nonconventional 

Pollutants 

§ 122.21(m)(2) 

Part 125, Subpart F (reserved) 

Technical Guidance Manual for the 

Regulations Promulgated Pursuant to section 

301(g) of the Clean Water Act of 1977 and 40 

CFR Part 125 (Subpart F); August 22, 1984.

<www.epa.gov/npdes/pubs/owm0008.pdf> 

CWA section 301(h) – Secondary Treatment Waiver § 122.21(n)(1) 

Part 125, Subpart G 

CWA section 301(n) – Timetable for Achievement of Objectives See Fundamentally Different Factors

CWA section 316(a) – Thermal Discharges 

§ 122.21(m)(6) 

Part 125, Subpart H 

§ 124.57 

§ 124.62(a)(2) 

§ 124.66 

NPDES permit subjects 

Administrative Procedures Act Permit Continuance § 122.6 

Administrative Record § 124.9 

§ 124.18 
September 2010 NPDES Permit Writers’ Manual 

Exhibit B-2 Index to NPDES regulations (continued) 

Subject 40 CFR section number 

Alternate Test Procedures 

 Application  § 136.4 

 Approval  § 136.5 

Ambient Monitoring (for Indicator Parameters) § 122.44(d)(1)(vi)(C)(3) 

Anti-backsliding See Backsliding

Antidegradation Policy § 131.12 

Applicability to State NPDES Programs See General Conditions for All Permits (State 

Programs)

Application § 122.21 

 Submittal Deadline (Time to Apply)  § 122.21(c) 

 Permit May Not Be Issued Without Complete Application  § 122.21(e) 

 Completeness  §§ 124.3(c) – 124.3(g) 

Aquaculture § 122.25 

Part 125, Subpart B 

Aquatic Animal Production Facilities § 122.24 

 Application  § 122.21(i)(2) 

 Definition  § 122.24 

Criteria for Determination Part 122, Appendix C 

 General Permit  § 122.28 

Average Monthly (Definition) § 122.2 

 Requirements for use in Non-POTWs  § 122.45(d)(1) 

 Requirements for use in POTWs  § 122.45(d)(2) 

Average Weekly (Definition) § 122.2 

 Requirements for use in POTWs  § 122.45(d)(2) 

Biochemical Oxygen Demand (BOD5) § 133.101(d) 

Backsliding 

§ 122.44(l) 

§ 122.62(a)(15) 

§ 122.62(a)(17) 

 From Water Quality and Technology Based Limits  CWA section 402(o) 

 From Water Quality  CWA section 303(d)(4) 

Best Management Practices 

 Definition 

 § 122.2 

§ 122.44(k) 

§ 130.2(m) 

 In Effluent Limitation Guidelines  CWA section 304(e) 

 Case-by-Case Authority  CWA section 402(a)(1) 

Best Professional Judgment (BPJ) 

 Case-by-Case Authority  §125.3(a)(1) 

 Appropriate Factors  §§125.3(c) and 125.3(d) 

BMP See Best Management Practices

Boilerplate Permit Conditions §§ 122.41 - 122.42 

BPJ See Best Professional Judgment

Bypasses § 122.41(m) 

CAFO See Concentrated Animal Feeding Operations

Calculating NPDES Permit Conditions § 122.45 

Carbonaceous Biochemical Oxygen Demand (CBOD5) § 133.101(e) 

Case-by-Case Limitations 

See also BPJ

§ 122.44(a) 

§ 125.3 

Case-by-Case Permits See also BPJ

§ 124.52 

B-4 Appendix B. Index to the CWA and NPDES Regulations 
September 2010 NPDES Permit Writers’ Manual 

Appendix B. Index to the CWA and NPDES Regulations B-5

Exhibit B-2 Index to NPDES regulations (continued) 

Subject 40 CFR section number 

Clean Water Act (CWA) 

(Public Law 92-500), 33 U.S.C. 1251 et seq., 

as amended by Public Laws 96-483; 97-117; 

95-217, 97-117, 97-440, and 100-04 

Coast Guard (Discharges from Transportation Over Water) § 122.44(p) 

Coastal Zone Management Act § 122.49(d) 

Combined Sewer Overflow Policy 59 FR 18688, April 19, 1994 

<www.epa.gov/npdes/pubs/owm0111.pdf> 

Comments Received During Public Notice Period § 124.13 

Compliance Schedules (in permits) 

§ 122.41(l)(5) 

§ 122.47 

§§ 122.62(a)(4), (a)(9), (a)(13) 

 Allowance by State Water Quality Standards 

 Star-kist Caribe, Inc., NPDES Appeal No. 

88-5 

<www.epa.gov/npdes/pubs/owm0121.pdf> (EAB, 

May 25, 1992) 

Computation of Time § 124.20 

Concentrated Animal Feeding Operations § 122.23 

Concentrated Aquatic Animal Production See Aquatic Animal Production

Conditions Applicable to Specified Categories § 122.42 

Confidentiality of Information § 122.7 

Part 2 

Consolidation of Permit Processing § 124.4 

Continuation of Expired Permits § 122.6 

Continuous Discharge § 122.45(d) 

Conventional Pollutants § 401.16 

Cooling Water Intake Structures [CWA section 316(b)] 

Part 125, Subparts I, J and N 

§ 122.21(r) 

§ 401.14 

DMR See Discharge Monitoring Report

Daily Average See Average Monthly

Daily Maximum See Maximum Daily

Definitions 

§ 122.2 

§ 124.2 

§ 401.11 

Denial of Permit § 124.6(b) 

 Public Notice of Denial  § 124.10(a)(1)(i) 

Design Flow (POTWs) § 122.45(b)(1) 

Dilution, Not A Substitute For Treatment § 122.45(f)(1)(iii) 

§ 125.3(f) 

Discharge Monitoring Report (DMR) § 122.41(l)(4) 

Discharge of a Pollutant (Definition) § 122.2 

Disposal into Wells, into POTWs, or by Land Application § 122.50 

§ 122.45(i) 

Draft Permit § 124.6 

Dredged Materials (Discharge to Waters of the United States) CWA section 404 

Duration of Permits § 122.46 

 Computation of time  § 124.20 

Duty to Comply § 122.41(a) 

Duty to Mitigate § 122.41(d) 

Duty to Provide Information § 122.41(h) 

Duty to Reapply § 122.41(b) 

Effect of a Permit § 122.5 
September 2010 NPDES Permit Writers’ Manual 

B-6 Appendix B. Index to the CWA and NPDES Regulations 

Exhibit B-2 Index to NPDES regulations (continued) 

Subject 40 CFR section number 

Effective Date § 124.15 

Effluent Limitations Guidelines (Effluent Guidelines or ELG) Parts 405-471 

Endangered Species Act § 122.49(c) 

Enforcement Authority § 123.27 

Environmental Impact Statement (EIS) 

 EIS Public Notice of a New Source  § 124.10(b)(1) 

 Final EIS  § 124.61 

 New Source  § 122.29(c) 

 NEPA  Part 6 

Equivalent To Secondary Treatment (for POTWs) § 133.105 

Establishing Limitations, Standards § 122.44 

Establishing Permit Conditions § 122.43 

Evidentiary Hearing Procedures (Eliminated) §§ 124.21 (b) - (c) 

Exclusions § 122.3 

Existing Source (Definition) § 122.29(a)(3) 

Expiration Dates See Duration of Permits

Extension of Public Notice Comment Period § 124.12(c) 

FDF See Fundamentally Different Factors

Fact Sheets § 124.8 

§ 124.56 

Feedlots See Concentrated Animal Feeding Operations

Filter Backwash § 125.3(g) 

Fish and Wildlife Coordination Act § 122.49(e) 

Fish Farms See Aquatic Animal Production Facilities

Flow Augmentation § 125.3(f) 

Flow Limits (POTW - Design Flow) § 122.45(b) 

Flow Monitoring Requirement § 122.44(i)(1)(ii) 

Fundamentally Different Factors (FDF) 

§ 122.21(m)(1) 

§ 122.44(d)(8) 

Part 125, Subpart D 

Frequency of Sampling (Not less than once per year) § 122.44(i)(2) 

General Conditions Applicable to All Permits § 122.41 

General Conditions for All Permits (State Programs) § 123.25 

General Permits § 122.28 

 Public Notice  § 124.10(c)(2)(i) 

 Individual Permit Required  § 122.28(b)(3) 

Great Lakes Water Quality Guidance Part 132 

Indian Tribe (Definition) § 124.2 

Innovative Technology See CWA section 301(k) – Innovative 

Technology

Inspection and Entry § 122.41(i) 

Internal Waste Streams § 122.45(h) 

Interim Dates for Schedules of Compliance § 122.47(a)(3) 

Introduction of New Pollutants (POTW) § 122.42(b) 

Issuance and Effective Date § 124.15 

§ 124.60 

Mass Limitations § 122.45(f) 

§ 122.44(i)(1)(i) 

Maximum Daily (Definition) § 122.2 

 Requirements for Non-POTWs  § 122.45(d)(1) 

Metals (To Be Expressed as Total Recoverable) § 122.45(c) 
September 2010 NPDES Permit Writers’ Manual 

Appendix B. Index to the CWA and NPDES Regulations B-7

Exhibit B-2 Index to NPDES regulations (continued) 

Subject 40 CFR section number 

Method Detection Limit Part 136, Appendix B 

Minor Modifications § 122.63 

Mixing Zones § 131.13 

Modifications § 122.62 

§ 124.5 

Monitoring Results, Requirements for Recording and Reporting § 122.48 

Monitoring and Records § 122.41(j) 

 Monitoring Reports  § 122.41(l)(4) 

 Requirements  § 122.44(h) 

 Recordkeeping  § 122.21(p) 

Municipal Separate Storm Sewer Systems (MS4) 

 When Permit Required  §§ 122.26(a)(3), (4), and (5) 

 Definitions  § 122.26(b) 

 Large and Medium MS4s Application Requirements  § 122.26(d) 

 Small MS4 Requirements  §§ 122.30 and 122.32 - 122.37 

 Tribes  § 122.31 

NPDES (Definition) § 122.2 

National Environmental Policy Act (NEPA) § 122.49(g) 

National Historic Preservation Act § 122.49(b) 

Navigable Waters (Definition) § 110.1 

Navigation § 122.44(q) 

Need to Halt or Reduce Activity, Not a Defense § 122.41(c) 

Net/Gross - Intake Credits § 122.45(g) 

New Discharger (Definition) § 122.2 

New Source 

 Definition  § 122.2 

 Application Requirements  § 122.21(k) 

 Program Requirements  § 122.29 

 Determination  § 122.29(b) 

 Mitigation Measures  § 122.44(d)(9) 

 Prohibited discharges  § 122.4(i) 

 Public Notice  § 124.10(a)(1)(vi) 

Non-Attainment Waters § 130.10(d) 

Non-Continuous Discharges § 122.45(e) 

Noncompliance 

 Anticipated  § 122.41(l)(2) 

 Other  § 122.41(l)(7) 

Notification Levels 

 General  § 122.62(a)(12) 

 For Existing Manufacturing, Commercial, Mining, and 

Silvicultural Dischargers 

 § 122.42(a) 

 § 122.44(f) 

Ocean Discharge Criteria Part 125, Subpart M 

Offshore Oil and Gas Facilities 

 Requirements Applicable to Cooling Water Intake Structures 

for New Offshore Oil and Gas Extraction Facilities under CWA 

section 316(b) 

 Part 125, Subpart N 

 General Permit Requirements & Application  § 122.28(c) 

Effluent Guidelines and Standards Part 435, Subpart A 

Stormwater Exemption § 122.26(a)(2) 

Oil Pollution Prevention Part 112 
September 2010 NPDES Permit Writers’ Manual 

B-8 Appendix B. Index to the CWA and NPDES Regulations 

Exhibit B-2 Index to NPDES regulations (continued) 

Subject 40 CFR section number 

On-Site Construction (New Source) § 122.29(b)(4) 

Operation and Maintenance § 122.41(e) 

pH Limits with Continuous Monitoring § 401.17 

Planned Changes § 122.41(l)(1) 

Pollutant (Definition) § 122.2 

POTWs, Applications for New and Existing § 122.21(j) 

Pretreatment § 122.44(j) 

Part 403 

Primary Industry Categories Part 122, Appendix A 

Prior Notice of Citizen Suits (Under CWA) Part 135 

Priority Pollutants Part 423, Appendix A 

Privately Owned Treatment Works § 122.44(m) 

Production-based Limitations § 122.45(b) 

Prohibitions § 122.4 

Proper Operation and Maintenance § 122.41(e) 

Property Rights § 122.41(g) 

Public Hearing § 124.12 

 Public Notice for Public Hearings  § 124.10(b)(2) 

§ 124.10(d)(2) 

Public Notice § 124.10 

 Specific Procedures Applicable to NPDES Permits  § 124.57 

Reapplication § 122.21(d) 

Recordkeeping and Reporting 

§ 122.21(p) 

§ 122.41(j)(2) 

§ 122.48 

Reopener Clause 

 Treatment Works Treating Domestic Sewage  § 122.44(c) 

 Other  § 122.62(a)(7) 

Reopening of Public Comment Period § 124.14 

Response to Comments § 124.17 

Reasonable Potential (RP) - Need For A Limit § 122.44(d)(1) 

 Chemical Specific  § 122.44(d)(1)(vi) 

 Whole Effluent Toxicity (WET)  § 122.44(d)(1)(v) 

Retention of Records § 122.41(j)(2) 

Revocation and Reissuance § 122.62 

Sample Type (Composite/Grab) § 122.21(g)(7)(i) 

Sample Holding Times, Containers, and Preservation § 136.3 

Sample, Representative § 122.41(j) 

Schedule of Compliance (Definition) See also Compliance Schedule

§ 124.2 

Secondary Treatment Regulation (POTW) Part 133 

 Definitions  § 133.101 

 Secondary Treatment  § 133.102 

 Special Considerations  § 133.103 

 Treatment Equivalent to Secondary Treatment  § 133.105 

Signatory Requirements § 122.22 

Silviculture § 122.27 
September 2010 NPDES Permit Writers’ Manual 

Appendix B. Index to the CWA and NPDES Regulations B-9

Exhibit B-2 Index to NPDES regulations (continued) 

Subject 40 CFR section number 

Sludge (Definition) § 122.44(o) 

 Sludge Standards  Part 503 

 Land Application  Part 503, Subpart B 

 Surface Disposal  Part 503, Subpart C 

 Pathogens and Vector Attraction Reduction  Part 503, Subpart D 

 Incineration  Part 503, Subpart E 

Sludge, Municipal Co-Disposal Landfills Part 258 

Sludge-Only Facilities (Handlers) § 122.1(b)(3) 

Small Business Exemption § 122.21(g)(8) 

Solid Waste Facilities, Classification of Part 257 

Spill Prevention, Control, and Countermeasures (SPCC) § 112.3 

Standard Conditions §§ 122.41 and 122.42 

State Certification § 124.53 

 Applications for CWA section 301(h) Variances  § 124.54 

 Effect of State Certification  § 124.55 

State Program Requirements Part 123 

Statutory Deadlines 

 For POTWs  § 125.3(a)(1) 

 For Non-POTWs  § 125.3(a)(2) 

Statutory Variances and Extensions § 125.3(b) 

Stays of Contested Permit Conditions § 124.16 

Stormwater § 122.26 

 Discharge Associated with Industrial Activity  § 122.26(b)(14) 

Test Methods, EPA Approved Part 136 

Ten-Year Protection Period See also New Sources and Dischargers

§ 122.29 

Termination of a Permit § 122.64 

Thermal Discharge Variance See CWA section 316(a) – Thermal 

Discharges

Total Maximum Daily Load (TMDL) 

 Definition  § 130.2 

 Which Waterbodies Need TMDLs  § 130.7 

Toxics – Application and Testing 

§ 122.21(g)(7) 

§ 122.21(g)(9) 

§ 122.21(g)(11) 

Toxic Pollutants (Definition) § 122.2 

 Technology-based Controls  § 122.44(e) 

Toxic Pollutant List § 401.15 

Toxicity Based Permit Limits § 125.3(c)(4) 

Transfer of Permit § 122.61 

Treatment Works Treating Domestic Sewage Sludge (TWTDS) 

(Definition) § 122.2 

Twenty-four Hour Reporting § 122.41(l)(6) 

Upset § 122.41(n) 

Variances for 

 Non-POTWs  § 122.21(m) 

 POTWs  § 122.21(n) 

 Appeals of variances  § 124.64 

 Decisions on variances  § 124.62 

 Expedited variance procedures and time extensions  § 122.21(o) 

 Procedures for variances when EPA is the permitting authority  § 124.63 
September 2010 NPDES Permit Writers’ Manual 

B-10 Appendix B. Index to the CWA and NPDES Regulations 

Exhibit B-2 Index to NPDES regulations (continued) 

Subject 40 CFR section number 

Vessel (Definition) § 112.2 

Waste Stabilization Ponds (POTW) § 133.103(c) 

Water Quality Report – CWA section 305(b) § 130.8 

Water Quality Standards (WQS) Part 131 

 Scope  § 131.1 

 Purpose  § 131.2 

 Definitions  § 131.3 

 State Authority  § 131.4 

 EPA Authority  § 131.5 

 Submission, Minimum Requirements  § 131.6 

 Dispute Resolution  § 131.7 

 Establishment of Standards  § 131.10 

 Criteria  § 131.11 

 Antidegradation Policy  § 131.12 

 General Policies on Establishing WQS  § 131.13 

 State Review and Revision of WQS  § 131.20 

 EPA Review and Approval of WQS  § 131.21 

 EPA Promulgation of WQS  § 131.22 

 Federally Promulgated Standards (State-By-State List)  Part 131, Subpart D 

Waters of the United States (Definition) § 122.2 

Wetlands See Waters of the U.S.

§ 122.2 

Whole Effluent Toxicity (WET) Limits § 122.44(d)(1)(iv) 

§ 125.3(c)(4) 

WET Testing With Permit Application (POTWs) § 122.21(j) 

Wild and Scenic Rivers Act § 122.49(a) 

Withdrawal Of State Program §§ 123.63 - 123.64 
September 2010 NPDES Permit Writers’ Manual 

Appendix C.

Appendix C. Priority Pollutants C-1

Appendix C. Priority Pollutants 

Exhibit C-1 presents the list of 126 priority (toxic) pollutants from 40 CFR Part 423 Appendix A, which 

are further discussed in sections 1.2 and 6.1.1.2 of this manual. Note that the list goes up to 129 because 

numbers 017, 049, and 050 were deleted. 

Exhibit C-1 Priority pollutants from 40 CFR Part 423, Appendix A 

# Pollutant name # Pollutant name 

001 Acenaphthene 067 Butyl benzyl phthalate 

002 Acrolein 068 Di-N-Butyl Phthalate 

003 Acrylonitrile 069 Di-n-octyl phthalate 

004 Benzene 070 Diethyl Phthalate 

005 Benzidine 071 Dimethyl phthalate 

006 Carbon tetrachloride (tetrachloromethane) 072 1,2-benzanthracene (benzo(a) anthracene 

007 Chlorobenzene 073 Benzo(a)pyrene (3,4-benzo-pyrene) 

008 1,2,4-trichlorobenzene 074 3,4-Benzofluoranthene (benzo(b) fluoranthene) 

009 Hexachlorobenzene 075 11,12-benzofluoranthene (benzo(b) fluoranthene) 

010 1,2-dichloroethane 076 Chrysene 

011 1,1,1-trichloreothane 077 Acenaphthylene 

012 Hexachloroethane 078 Anthracene 

013 1,1-dichloroethane 079 1,12-benzoperylene (benzo(ghi) perylene) 

014 1,1,2-trichloroethane 080 Fluorene 

015 1,1,2,2-tetrachloroethane 081 Phenanthrene 

016 Chloroethane 082 1,2,5,6-dibenzanthracene (dibenzo(,h) anthracene) 

018 Bis(2-chloroethyl) ether 083 Indeno (,1,2,3-cd) pyrene (2,3-o-pheynylene pyrene) 

019 2-chloroethyl vinyl ether (mixed) 084 Pyrene 

020 2-chloronaphthalene 085 Tetrachloroethylene 

021 2,4, 6-trichlorophenol 086 Toluene 

022 Parachlorometa cresol 087 Trichloroethylene 

023 Chloroform (trichloromethane) 088 Vinyl chloride (chloroethylene) 

024 2-chlorophenol 089 Aldrin 

025 1,2-dichlorobenzene 090 Dieldrin 

026 1,3-dichlorobenzene 091 Chlordane (technical mixture and metabolites) 

027 1,4-dichlorobenzene 092 4,4-DDT 

028 3,3-dichlorobenzidine 093 4,4-DDE (p,p-DDX) 

029 1,1-dichloroethylene 094 4,4-DDD (p,p-TDE) 

030 1,2-trans-dichloroethylene 095 Alpha-endosulfan 

031 2,4-dichlorophenol 096 Beta-endosulfan 

032 1,2-dichloropropane 097 Endosulfan sulfate 

033 1,2-dichloropropylene (1,3-dichloropropene) 098 Endrin 

034 2,4-dimethylphenol 099 Endrin aldehyde 

035 2,4-dinitrotoluene 100 Heptachlor 

036 2,6-dinitrotoluene 101 Heptachlor epoxide (BHC-hexachlorocyclohexane) 

037 1,2-diphenylhydrazine 102 Alpha-BHC 

038 Ethylbenzene 103 Beta-BHC 

039 Fluoranthene 104 Gamma-BHC (lindane) 

040 4-chlorophenyl phenyl ether 105 Delta-BHC (PCB-polychlorinated biphenyls) 
September 2010 NPDES Permit Writers’ Manual 

C-2 Appendix C. Priority Pollutants 

Exhibit C-1 Priority pollutants from 40 CFR Part 423, Appendix A (continued) 

# Pollutant name # Pollutant name 

041 4-bromophenyl phenyl ether 106 PCB-1242 (Arochlor 1242) 

042 Bis(2-chloroisopropyl) ether 107 PCB-1254 (Arochlor 1254) 

043 Bis(2-chloroethoxy) methane 108 PCB-1221 (Arochlor 1221) 

044 Methylene chloride (dichloromethane) 109 PCB-1232 (Arochlor 1232) 

045 Methyl chloride (dichloromethane) 110 PCB-1248 (Arochlor 1248) 

046 Methyl bromide (bromomethane) 111 PCB-1260 (Arochlor 1260) 

047 Bromoform (tribromomethane) 112 PCB-1016 (Arochlor 1016) 

048 Dichlorobromomethane 113 Toxaphene 

051 Chlorodibromomethane 114 Antimony 

052 Hexachlorobutadiene 115 Arsenic 

053 Hexachloromyclopentadiene 116 Asbestos 

054 Isophorone 117 Beryllium 

055 Naphthalene 118 Cadmium 

056 Nitrobenzene 119 Chromium 

057 2-nitrophenol 120 Copper 

058 4-nitrophenol 121 Cyanide, Total 

059 2,4-dinitrophenol 122 Lead 

060 4,6-dinitro-o-cresol 123 Mercury 

061 N-nitrosodimethylamine 124 Nickel 

062 N-nitrosodiphenylamine 125 Selenium 

063 N-nitrosodi-n-propylamin 126 Silver 

064 Pentachlorophenol 127 Thallium 

065 Phenol 128 Zinc 

066 Bis(2-ethylhexyl) phthalate 129 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) 
September 2010 NPDES Permit Writers’ Manual 

Appendix D.

Appendix D. New Source Dates by Effluent Guideline Category D-1

Appendix D. New Source Dates by Effluent Guideline 

Category 

This appendix provides the applicable new source dates used in making new source determinations by 

effluent guideline category as provided in Appendix B of the U.S. Environmental Protection Agency 

(EPA) memorandum New Source Dates for Direct and Indirect Dischargers1

<www.epa.gov/npdes/pubs/newsource_dates.pdf> sent by the directors of EPA’s Water Permits Division and the 

Engineering and Analysis Division to the Regional Water Division Directors on September 28, 2006. 

Section 5.2.2.4 of this manual discusses the determination of whether existing or new source standards 

apply. 

EPA has promulgated regulations under the Clean Water Act (CWA) that establish effluent limitations 

guidelines for existing sources, standards of performance for new sources and pretreatment standards for 

new and existing sources. EPA has codified these regulations at Title 40 of the Code of Federal 

Regulations (CFR) Subchapter N. As discussed in section 5.2.1 of this manual, EPA has published 

effluent guidelines for 56 major industrial categories (over 450 subcategories) since the passage of the 

1972 CWA. Those regulations limit the discharge of pollutants to surface waters by point source 

dischargers (direct dischargers). The regulations also limit the introduction of pollutants into publicly 

owned treatment works (POTWs) by industrial users (indirect dischargers). The CWA and EPA 

regulations define when a source is a new source. A discharger is defined as a new source in CWA 

sections 306(a)(2) and 307(c) and §§ 122.2 (for direct dischargers) and 403.3(m) (for indirect 

dischargers). In general, a facility is a new source if it begins construction after either the date of 

promulgation of new source performance standards applicable to the direct dischargers or the date of 

publication of a proposed new source performance standard applicable to an indirect discharger. 

Exhibit D-1 lists new source dates for direct or indirect dischargers based on regulatory definitions. In 

some cases, effluent guidelines in 40 CFR Chapter I, Subchapter N, specify New Source Dates, and these 

dates are reported in the table below. If dates are not specified in the rule language, EPA based the date on 

the regulatory definitions of new source, which are cited above. EPA’s General Pretreatment Regulations 

provide that an indirect source is a new source if construction of the source began after the publication of 

proposed pretreatment standards for new sources if the proposed standard is later finalized [§ 403.3(m)]. 

For direct dischargers, § 122.2 states that the New Source date is the proposal date if the standard is 

finalized within 120 days after its proposal; otherwise, the New Source date is the promulgation date. 

EPA’s regulations establish the time and date of EPA’s actions for purposes of determining when the 

action is subject to judicial review. The regulations, in the case of the CWA, define the date of an EPA 

promulgation action as two weeks after the rule appears in the Federal Register (see § 23.2). Before 

February 1985, the date on which the final rule was published was considered the promulgation date. 

This document is not a regulation itself, nor does it substitute for any requirements under the CWA or 

EPA’s regulations. Thus, it does not impose legally binding requirements on EPA, states or the regulated 

community. While EPA has made every effort to ensure the accuracy of this table, dischargers’ 

obligations are determined, in the case of direct dischargers, by the terms of their NPDES permit and the 

CWA and EPA’s regulations, and, in the case of indirect dischargers, by permits or equivalent control 
September 2010 NPDES Permit Writers’ Manual 

mechanisms issued to POTW industrial users and the CWA and EPA regulations. Nothing in this 

document changes any statutory or regulatory requirement. If the discussion in this memorandum 

conflicts with any permit or regulation, this document would not be controlling. 

Exhibit D-1 New source dates by effluent category 

40 

CFR 

Part Category 

New source date for 

direct dischargers 

New source date for indirect 

dischargers 

467 Aluminum Forming Subparts A-F: 10/24/83 Subparts A-F: 11/22/82

427 Asbestos Manufacturing Subparts A-K: 10/30/732 Not Applicable 

461 Battery Manufacturing Subparts A-G: 03/09/84 Subparts A-G 11/10/82

407 

Canned and Preserved 

Fruits and Vegetables 

Processing 

Subparts A-H: 03/21/74 Not Applicable 

408 Canned and Preserved 

Seafood Processing 

Subparts A-J, N: 

Subparts O-AG: 

06/26/74 

12/01/75 Not Applicable 

458 Carbon Black Manufacturing Subparts A-D: 01/09/78 Subparts A-D: 05/18/76

411 Cement Manufacturing Subparts A-C: 02/20/74 Not Applicable 

437 Centralized Waste 

Treatment (CWT) Subparts A-D: 01/05/01 Subparts A-D: 01/13/99

434 Coal Mining Subparts B-E, H: 

Subpart G: 

05/04/843

02/22/024 Not Applicable 

465 Coil Coating Subparts A-C: 

Subpart D: 

12/01/82 

11/17/83 

Subparts A-C: 

Subpart D: 

01/12/81

02/10/83

412 Concentrated Animal 

Feeding Operations (CAFO) 

Subparts A-B: 

Subparts C-D: 

02/14/74 

04/14/035 Subpart B: 09/07/73

451 Concentrated Aquatic 

Animal Production Subparts A-B: 09/07/04 Not Applicable 

468 Copper Forming Subpart A: 08/15/83 Subpart A: 11/12/82

405 Dairy Products Processing Subparts A-L: 05/28/74 Not Applicable 

469 Electrical and Electronic 

Components 

Subparts A-B: 

Subparts C-D: 

04/08/83 

12/14/83 

Subparts A-B: 

Subparts C-D: 

08/24/82

03/09/83

413 Electroplating Not Applicable6 See Metal Finishing7

457 Explosives Manufacturing Not Applicable Not Applicable 

424 Ferroalloy Manufacturing Subparts A-C: 02/22/74 Not Applicable 

418 Fertilizer Manufacturing 

Subparts A-D: 

Subpart E: 

Subparts F-G: 

04/08/74 

01/16/76 

10/07/748

Subparts A-D9:

Subpart E: 

Subparts F-G: 

12/07/73

01/16/76

10/07/74

426 Glass Manufacturing 

Subpart A: 

Subparts B-D: 

Subparts E-G: 

Subparts H, J-M: 

01/22/74 

02/14/74 

02/14/74 

01/16/75 

Subparts H, K-M: 08/21/74

406 Grain Mills Subparts A-J: 12/04/7310 Subpart A: 12/04/73

454 Gum and Wood Chemicals Not Applicable Not Applicable 

460 Hospitals Not Applicable Not Applicable 

447 Ink Formulating Subpart A: 07/28/75 Subpart A: 02/26/75

D-2 Appendix D. New Source Dates by Effluent Guideline Category 
September 2010 NPDES Permit Writers’ Manual 

Appendix D. New Source Dates by Effluent Guideline Category D-3

Exhibit D-1 New source dates by effluent category (continued) 

40 

CFR 

Part Category

New source date for indirect 

dischargers 

New source date for

direct dischargers 

415 Inorganic Chemicals 

Subparts B-F, H, K-N, P, 

Q, T, V, W, AJ [CuSO4

manufacturing], AH, AP, 

AU [NiSO4

manufacturing], BB: 

Subparts AJ [except 

CuSO4 manufacturing], 

AU [except NiSO4

manufacturing], BL - BO: 

06/29/82 

08/22/84 

Subparts B-F, H, K-N, P, Q, 

V, AH, AJ [CuSO4

manufacturing], AP, AU 

[NiSO4 manufacturing], BB: 

Subparts T, AA, AC, AE, AI, 

AJ 

[except CuSO4

manufacturing], AL, AN, AQ, 

AR, AU [except NiSO4

manufacturing], AX, BC, BH, 

BK-BO: 

07/24/80

10/25/83 

420 Iron and Steel 

Manufacturing 

Subparts A-B: 

Subpart C: 

Subpart D, Semi-Wet: 

Subpart D, Other: 

Subparts E-L: 

Subpart M: 

11/18/0211

05/27/82 

10/31/02 

05/27/82 

05/27/82 

10/31/02 

Subparts A-B: 

Subpart C: 

Subpart D, Semi-Wet: 

Subpart D, Other: 

Subparts E-F, H-J,L: 

Subpart M: 

11/18/02

12

01/07/81

12/27/00

01/07/81

01/07/81

12/27/00

445 Landfills Subparts A-B: 02/02/00 Not Applicable 

425 Leather Tanning and 

Finishing 

Subparts A, B, D-I: 

Subpart C: 

11/23/82 

04/04/88 

Subpart A, B, D-I: 

Subpart C: 

07/02/79

01/21/87

432 Meat and Poultry Products Subparts A-D, Small 

Facilities: 

Subparts A-D, Other: 

Subparts E-I, Small 

Facilities: 

Subparts E-I, Other: 

Subpart J-L: 

02/28/7413

09/22/04 

01/03/7514

09/22/04 

09/22/04 

Not Applicable 

433 Metal Finishing Subpart A: 07/15/83 Subpart A: 08/31/82

464 Metal Molding and Casting Subparts A-D: 11/13/85 Subparts A-D: 11/15/82

438 Metal Products and 

Machinery Subpart A: 06/12/0315 Not Applicable 

436 Mineral Mining and 

Processing Not Applicable Not Applicable 

471 Nonferrous Metals Forming 

and Metal Powders Subparts A-J: 09/06/85 Subparts A-J: 03/05/84

421 Nonferrous Metal 

Manufacturing 

Subparts B-I (except 

molybdenum acid plants), 

K-M: 

Subparts N-AE, 

molybdenum acid plants 

in subpart I: 

Subpart J: 

03/08/84 

10/04/85 

02/04/88 

Subparts B-I (except 

molybdenum acid plants), 

K-M: 

Subparts N-AE, molybdenum 

acid plants in subpart I: 

Subpart J: 

02/17/83

06/27/84

01/22/87

435 Oil and Gas Extraction16 Subparts C (Onshore), D 

(Coastal), and E 

(Agriculture & Wildlife): 

Subparts A and D 

(Synthetic-Based Drilling 

Fluids): 

03/04/93 

02/05/01 

Subpart D: 02/17/95

440 Ore Mining and Dressing Subparts A-F, J, M: 12/03/82 Not Applicable 
September 2010 NPDES Permit Writers’ Manual 

D-4 Appendix D. New Source Dates by Effluent Guideline Category 

Exhibit D-1 New source dates by effluent category (continued) 

40 

CFR 

Part Category 

New source date for 

direct dischargers 

New source date for indirect 

dischargers 

414 Organic Chemicals, 

Plastics, and Synthetic 

Fibers 

Subparts B-H: 11/19/87 Subparts B-H: 03/21/83 

446 Paint Formulating Subpart A: 07/28/75 Subpart A: 02/26/75

443 Paving and Roofing 

Materials (Tars and Asphalt) Subparts A-D: 07/28/75 Subparts A-D: 01/10/75

455 Pesticide Chemicals Subparts A-B: 

Subparts C, E: 

10/12/93 

11/20/96 

Subparts A-B: 

Subparts C, E: 

04/10/92

04/14/94

419 Petroleum Refining Subparts A-E: 10/18/82 Subparts A-E: 12/21/79

439 Pharmaceutical 

Manufacturing Subparts A-D: 11/20/9817 Subparts A-D: 05/02/95

422 Phosphate Manufacturing Subparts D-F: 06/23/76 Not Applicable 

459 Photographic Not Applicable Not Applicable 

463 Plastics Molding and 

Forming Subparts A-C: 12/17/84 Not Applicable 

466 Porcelain Enameling Subparts A-D: 11/24/82 Subparts A-D: 01/27/81

430 Pulp, Paper, and 

Paperboard 

Subparts B, E: 

Subparts A, C, D, F, G, 

I-L: 

06/15/9818

11/18/82 

Subparts B, E: 

Subparts A, C, D, F, G, I-L: 

12/17/93

01/06/81

428 Rubber Manufacturing Subparts A-D: 

Subparts E-J: 

02/21/74 

01/10/75 Subparts E-K: 08/23/74

417 Soap and Detergents 

Manufacturing Subparts A-S: 4/12/74 Subpart Q: 

Subparts O, P, R: 

12/26/73

02/20/75

423 Steam Electric Power 

Generation 11/19/8219 10/14/80

409 Sugar Processing Subpart A: 

Subparts B, C: 

1/31/74 

12/07/7320 Not Applicable 

 

1

 Boornazian, Linda and Mary Smith. 2006. New Source Dates for Direct and Indirect Dischargers. U.S. Environmental 

Protection Agency, Office of Water Memorandum. September 28, 2006. <www.epa.gov/npdes/pubs/newsource_dates.pdf>. 

2

 The rule was finalized within 120 days of its October 30, 1973, proposal (38 FR 22606). 

3

 The New Source date is specified in 40 CFR 434.11(j)(1). 

4

 The New Source date is specified in 40 CFR 434.11(j)(1). 

5

 New Source date derived from the 10-year protection period [see 40 CFR 412.35(d) and 412.43(d)]. 

6

 Direct dischargers formerly regulated under Part 413 are now regulated under Part 433 (metal finishing). 

7

 Pretreatment categorical standards in Part 413 currently apply only to job shop electroplaters and independent printed circuit

board manufacturers that were in existence before the New Source date for Part 433 (metal finishing). Job shop electroplaters and 

independent printed circuit board manufacturers that are “New Sources” must comply with PSNS in Part 433. Except for these 

“existing” job shop electroplaters and independent printed circuit board manufacturers, all other operations formerly subject to 

Part 413 are now subject to Part 433. 

8

 The rule was finalized within 120 days of its October 7, 1974, proposal. 

9

 Section 41 8.46 (the PSNS under Subpart D) was suspended until further notice, at 40 FR 26275, June 23, 1975, effective July 

20, 1975. 

10 The rule was finalized within 120 days of its December 4, 1973, proposal (38 FR 33438). 

Endnotes for this chapter continued on the next page. 
September 2010 NPDES Permit Writers’ Manual 

Appendix D. New Source Dates by Effluent Guideline Category D-5

 

11 Date specified in 40 CFR 420.14(a)(2), 420.16(a)(2), 420.24(b), and 420.26(a)(2). 

12 See previous footnote. 

13 The 2004 Amendment did not revise NSPSs for small meat products facilities in Subparts A-I, so the 2004 New Source date 

does not affect these facilities. 

14 See previous footnote.

15 Date specified in 40 CFR 438.15.

16 See promulgated standards at 40 CFR 58 FR 12505 and 66 FR 6850 for complete information on the applicability of New 

Source standards. 

17 New Source date derived from the 10-year protection period [see 40 CFR 439.15(c), 439.35(c), and 439.45(b)].

18 Date specified in 40 CFR 430.25(b) and 430.55(b). Refer to these sections for additional information regarding the 

applicability of NSPSs.

19 NSPS promulgated were not removed via the 1982 regulation; therefore wastewaters generated by Part 423-applicable sources 

that were New Sources under the 1974 regulations are subject to the 1974 NSPS. The New Source date for the 1974 regulations 

was 10/8/1974. 

20 The rule was finalized within 120 days of its December 7, 1973, proposal (38 FR 33846).