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EPA NPDES WET Guidance Documents

EPA has developed a variety of Whole Effluent Toxicity (WET) guidance documents. The WET guidance documents below are organized by the following categories: Methodology, Programmatic, and Case Studies.

Methodology: Programmatic:
  • Whole Effluent Toxicity (WET) NPDES Spreadsheet

  • The National Pollutant Discharge Elimination System (NPDES) Whole Effluent Toxicity (WET) Spreadsheet can be used to analyze valid acute or chronic WET test data using statistical approaches recommended in Chapter 1, Section 1.3 of EPA’s Technical Support Document and in EPA’s acute and chronic WET test method documents, as well as using EPA’s Test of Significant Toxicity document (PDF) (73 pp, 522K) . The spreadsheet can be used to analyze valid data for the test endpoints indicated for the selected EPA WET test method (e.g., survival, reproduction, biomass, fertilization), and the results are presented in an easy to read format that can be printed or saved as an Excel file on the user’s computer.

    The results generated by the NPDES WET Spreadsheet can be used by NPDES permit writers for reasonable potential (RP) determinations in accordance with EPA’s TSD (see pages 53-57, Chapter 5) and for NPDES WET compliance determinations (see TSD pages 112-113, Chapter 6). NPDES permittees and WET testing laboratories may also find the spreadsheet helpful when analyzing valid WET test data.

    Disclaimer: Please note that neither the EPA nor any of its employees assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information disclosed. Furthermore, the NPDES WET Spreadsheet is supplied “as-is” without guarantee or warranty, expressed or implied, including without limitation, any warranty of merchantability or fitness for a specific purpose.


    Date Published: 05/24/2012
  • Clarifications Regarding Flexibility in 40 CFR Part 136 Whole Effluent Toxicity (WET) Test Methods (N/A) ()

  • The purpose of this memorandum is to provide clarifications regarding the flexibility in the regulations promulgated at 60 Fed. Reg. 53529 (Oct. 16, 1995), which establish analytical test methods for the determination of whole effluent toxicity (WET). Click on the following link to view this document: http://www.epa.gov/waterscience/WET/wetinfo.html
    Date Published: 04/10/1996
      (This file is not currently available for download)

  • Clarifications Regarding Toxicity Reduction and Identification Evaluations in the National Pollutant Discharge Elimination System Program

  • EPA document developed by the Office of Wastewater Management/Water Permits Division to provide additional clarification on conducting toxicity reduction evaluations and toxicity identification evaluations with respect to whole effluent toxicity (WET) testing. The document clarifies for National Pollutant Discharge Elimination System (NPDES) permit writers and permittees a number of common issues such as: when and under what circumstances a permittee should conduct a TRE and/or a TIE; technical limitations on the TIE process; consideration of persistence and magnitude of toxicity events; ionic imbalances of effluents; the applicability of compliance schedules; and inconclusive TREs/TIEs. The document supplements existing EPA guidance and policies on WET and TREs/TIEs but does not change current policy or legal authority.
    Date Published: 03/27/2001
  • Draft National Whole Effluent Toxicity (WET) Implementation Guidance Under the NPDES Program

  • This draft has been released for public review and comments. This draft document gathers together previous EPA guidance, policy, and other information and organizes it in one comprehensive document. The document also addresses a number of important issues that have been raised by states, regulated industry, and interested stakeholders on the implementation of whole effluent toxicity (WET) limits in NPDES permits. Interested parties may submit comments on the draft guidance until March 31, 2005. (The February 28, 2005 public comment period has been extended to March 31, 2005.)
    Date Published: 12/28/2004
  • EPA Whole Effluent Toxicity (WET) Control Policy (PDF) (1,000K)

  • Policy for the development of effluent limitations in NPDES permits to control whole effluent toxicity for the protection of aquatic life (EPA 833-B-94-002)
    Date Published: 07/01/1994

  • Memorandum: Certification of "Accuracy" of Information Submissions of Test Results Measuring Whole Effluent Toxicity (PDF) (2 pp, 113K)

  • Clarifies that the Agency intends that a certification of "accuracy" occurs in information submissions of testing data for whole effluent toxicity, but as the layperson uses the term, not "accurate" as the term is used to describe the quantifiable performance of a measurement system.
    Date Published: 03/03/2000

  • Method Guidance and Recommendations for Whole Effluent Toxicity (WET) Testing (PDF) (294K)

  • This document provides guidance and recommendations on the conduct of the approved WET test methods and interpretation of WET test results reported under the NPDES program. This guidance partially fulfills the obligations of a legal settlement agreement that resolves a judicial challenge to the WET final rule. The document provides guidance on the following issues: nominal error rate adjustments, confidence intervals, concentration-response relationships, dilution series, and dilution waters.
    Date Published: 07/01/2000

  • National Policy Regarding Whole Effluent Toxicity (WET) Enforcement (PDF) (237K)

  • Memorandum clarifying national enforcement policy related to single exceedances of whole effluent toxicity limits and response when toxicity reduction evaluations are inconclusive.
    Date Published: 08/14/1995

  • National Pollutant Discharge Elimination System Test of Significant Toxicity Implementation Document

  • The transmittal memo and implementation document provides the basis for implementing the Test of Significant Toxicity (TST) approach under the National Pollutant Discharge Elimination System (NPDES) for permitting authorities (states and Regions) and persons interested in analyzing whole effluent toxicity (WET) test data using the traditional hypothesis testing approach as part of the NPDES Program under the Clean Water Act (CWA).
    Date Published: 06/01/2010
  • National Pollutant Discharge Elimination System Test of Significant Toxicity Technical Document (PDF) (116 pp, 2.2MB)

  • This document provides the technical basis for the Test of Significant Toxicity (TST) approach under the National Pollutant Discharge Elimination System (NPDES) for permitting authorities (states and Regions) and persons interested in analyzing valid whole effluent toxicity (WET) test data using the traditional hypothesis testing approach as part of the NPDES Program under the Clean Water Act (CWA).
    Date Published: 06/01/2010

  • Understanding and Accounting for Method Variability in Whole Effluent Toxicity Applications Under the NPDES Program (PDF) (4.6MB)

  • This document was developed by an EPA OWM work group to address questions raised by stakeholders on the issue of analytical variability that might be associated with Whole Effluent Toxicity (WET) testing and how it relates to the NPDES permit program (EPA 833-R-00-003)
    Date Published: 06/01/2010

  • Whole Effluent Toxicity (WET) Control Policy (PDF) (27K)

  • Policy is intended to promote nationwide compliance with statutory and regulatory requirements for the control of WET.
    Date Published: 07/01/1994

Case Studies:
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Last updated on October 28, 2010 5:17 PM
URL:http://cfpub.epa.gov/npdes/wqbasedpermitting/wetdocs.cfm