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National Pollutant Discharge Elimination System (NPDES)

NPDES Permit Limits Additional Resources

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WET Guidance

  • Programmatic

    • Whole Effluent Toxicity (WET) NPDES Spreadsheet -- This spreadsheet can be used to analyze valid acute or chronic WET test data using statistical approaches. The results generated by the 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.
    • Clarifications Regarding Toxicity Reduction and Identification Evaluations in the National Pollutant Discharge Elimination System Program (03/27/2001) -- Provides additional clarification on conducting toxicity reduction evaluations and toxicity identification evaluations with respect to WET testing. The document supplements existing EPA guidance and policies on WET and TREs/TIEs, but does not change current policy or legal authority.
    • Draft National Whole Effluent Toxicity (WET) Implementation Guidance under the NPDES Program (12/28/2004) -- 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 WET limits in NPDES permits.
    • Method Guidance and Recommendations for Whole Effluent Toxicity (WET) Testing (07/01/2000) -- 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.
    • National Pollutant Discharge Elimination System Test of Significant Toxicity Implementation Document (06/01/2010) -- The transmittal memo and implementation document provides the basis for implementing the Test of Significant Toxicity (TST) approach under NPDES for permitting authorities (states and regions) and persons interested in analyzing WET test data using the traditional hypothesis testing approach as part of the NPDES Program.

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Watershed-based Permitting

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Nutrient Permitting

EPA Resources

  • Compilation of Cost Data Associated with the Impacts and Control of Nutrient Pollution -- A compilation of data collected from a range of sources including published, peer-reviewed journals, government-funded research and reports, academic studies and other data sources. This report is a collection of research data from 2000 through 2012 including references to the literature cited. 
  • Nutrient Recycling Challenge -- EPA is partnering with pork and dairy producers, the U.S. Department of Agriculture, and environmental and scientific experts to find affordable technologies that recycle nutrients from livestock manure and create valuable products.
  • Watershed-based Permitting -- Watershed-based permitting is a process that produces NPDES permits that are issued to point sources on a geographic or watershed basis. Since nutrient pollution often has far-field, cumulative impacts on a waterbody, stakeholders may wish to pursue a watershed-based permitting approach to NPDES permits.
  • Water Quality Trading -- Water quality trading under the Clean Water Act is an option for compliance with a water quality based effluent limitation (WQBEL) in a NPDES permit.
  • Discharge Monitoring Report (DMR) Pollutant Loading Tool -- The DMR Pollutant Loading Tool helps determine which facilities are discharging, what pollutants they are discharging and how much, and where they are discharging. The tool calculates pollutant loadings from permit and DMR data from EPA's Integrated Compliance Information System for the National Pollutant Discharge Elimination System (ICIS-NPDES). Data are available from the year 2007 to the present.
  • National Study on Nutrient Control and Water Treatment Technologies -- EPA is considering a national study on nutrient removal at municipal wastewater treatment plants, also called water resource recovery facilities (WRRFs). This study would be a multi-year effort and fill crucial and fundamental information gaps that exist for nationwide nutrient contribution from WRRFs, and the nutrient control measures and practices available for these facilities. In the fall of 2016, EPA plans to collect basic information from all facilities nationwide to identify the secondary treatment facilities that should be surveyed.

Non-EPA Resources

  • Nutrient Modeling Toolkit -- Developed by the Water Environment Research Federation (WERF), the Nutrient Modeling Toolkit is used to quantitatively link nutrient loads to water quality and ecological response indicators on a site-specific basis.

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