vvEPA FACT SHEET National Pollutant Discharge Elimination System Whole Effluent Toxicity Permit Writers' Manual The National Pollutant Discharge Elimination System (NPDES) Whole Effluent Toxicity (WET) Permit Writers' Manual (hereafter manual) provides the NPDES permit writer with information and resources that support writing NPDES permit WET requirements. The manual was designed for the NPDES permit writer, whether new to or experienced with the NPDES program, or anyone else interested in learning about the regulatory, programmatic, and technical aspects of developing and implementing WET provisions in an NPDES permit. It summarizes recommendations and requirements for developing NPDES WET permit requirements based on EPA guidance, policy, and regulations, as well as the Clean Water Act (CWA). The manual is not intended to be a stand-alone reference document. The manual should be integrated into, as necessary, EPA's, states', territories', and authorized Tribes' regulations, policy, and guidance applicable to specific types of dischargers and site-specific circumstances. What it covers: • An overview of how and why WET requirements in NPDES permits are used. • A list of EPA's NPDES WET references. • A summary and description of EPA's different toxicity test methods (including desk reference sheets) and statistical approaches for analyzing valid toxicity test data used in the NPDES permit program. • A discussion of the recommended and required NPDES permit conditions for WET including compliance monitoring, assessment conditions, dilution water, toxicity test concentration series, types of toxicity tests, quality assurance (QA) and quality control (QC), toxicity test report review, statistical test endpoints, and WET diagnostic approaches (e.g., toxicity reduction evaluations [TREs] and toxicity identification evaluations [TIEs]). • The recommended steps for conducting a reasonable potential analysis to evaluate the need for NPDES WET permit limits and how to develop limits with a link to an EPA spreadsheet calculator. • An overview of evaluating the quality of WET data and other compliance and enforcement considerations for WET permit conditions. For more information: • Contact: Laura Phillips, (202) 564-0741, phillips.laura(5)epa.gov or Jackie Clark, (202) 564-6582, clark.jackie(5)epa.gov • Visit: https://www.epa.gov/system/files/documents/2024-06/npdes-wet-permit-writers-manual.pdf EPA 833-B-24-001 July 2024 ------- |