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The United States Environmental Protection Agency (“EPA”) has issued a July 2024 document titled:

National Pollutant Discharge Elimination System Whole Effluent Toxicity Permit Writer’s Manual (“Manual”).

See EPA-833-B24-001.

The Manual was developed by the Water Permits Division of EPA’s Office of Wastewater Management.

The EPA imposes on certain Clean Water Act National Pollutant Discharge Elimination System (“NPDES”) permittees a requirement to pass “whole effluent toxicity” (“WET”) test.

See 40 C.F.R. 122.44(d)(1)(iv).

This test measures the aggregate effect “evaluating the integrated effects of all chemicals in the aqueous sample” of a discharge on aquatic organisms. It is one of the ways the EPA and states implement the Clean Water Act’s prohibition of the discharge of toxic pollutants in toxic amounts.

WET tests measure wastewater’s effects of specific organism’s abilities to survive, grow, and reproduce. For example, a test population of minnows may be exposed to a permittees wastewater effluent. The number of organisms that die or become immobilized will then be counted to determine whether the wastewater is “toxic”.

EPA states that the purpose of the manual is to provide the NPDES permit writer with information and resources that support writing NPDS permit WET requirements. The Manual is stated to have been designed for:

• New NPDES permit writers.
• Experienced NPDES writers.
• Anyone else interested in learning about the regulatory, programmatic, and technical aspects of developing and implementing WET provisions in an NPDES permit.

The Manual summarizes recommendations and requirements related to NPDES WET permit requirements are premised on:

• EPA guidance.
• EPA policy.
• Clean water Act regulations.
• Clean Water Act itself.

Nevertheless, EPA states that the Manual is not intended to a stand-alone reference document. Instead, it is built to be supplemental to the NPDES permit Writer’s Manual “U.S. EPA 2010a”.

Key sections of the Manual include:

• Section 1 - Introduction to the Manual
• Section 2 - NPDES WET program background
• Section 3 – Toxicity testing
• Section 4 – NPDES permit conditions for WET monitoring.
• Section 5 – Regional potential analysis for evaluating the need for NPDES WET permit limits.
• Section 6 – Developing NPDES WET permit limits.
• Section 7 – Evaluating NPDES compliance for WET and enforcement considerations.

A copy of the Manual can be downloaded here.