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Why we regulate
Learn what types of wastewater discharges are regulated and how
Plan review
The DNR reviews plans for municipal and industrial wastewater treatment plant construction
Discharge permits
Wastewater discharges to surface or groundwaters

WET Guidance Document

The WET Guidance Document is intended to help DNR staff, permittees, and others when making decisions regarding whole effluent toxicity (WET) program issues. The chapters listed below cover numerous topics, from correct sampling procedures to finding a good WET lab, WET enforcement, and others.

Part I of this guidance document was written primarily with DNR staff needs in mind, but others may find those chapters useful, too. Part II is intended as guidance and clarification of existing requirements for permittees, consultants, and others.

The WET Guidance Document is revised as the WET Program changes. The effective date shown in last column of the table below indicates the latest revision date of the chapter in question. Since chapters are regularly updated, users should insure use of the most recent version.

NOTICE: The WET Guidance Document is intended solely as guidance, and does not contain any mandatory requirements except where requirements found in statute or administrative rule are referenced. This guidance does not establish or affect legal rights or obligations, and is not finally determinative of any of the issues addressed. This guidance does not create any rights enforceable by any party in litigation with the State of Wisconsin or the Department of Natural Resources. Any regulatory decisions made by the Department of Natural Resources in any matter addressed by this guidance will be made by applying the governing statutes and administrative rules to the relevant facts.

Contact information
For more information, or if you would like to be notified when the WET Guidance Document is revised, send an email to:
Kari Fleming
Biomonitoring Coordinator

Table of Contents

(click on the chapter number below for PDF version)
Chapter Title Purpose of Chapter Effective Date

Part 1 - WDNR Staff Guidance To Determine Permit Requirements

1.1 Sampling For WET Tests Where to sample; how to insure quality; sampling schedule checklist November 1, 2016
1.2 Receiving Water Used to Make WET Determinations Appropriate RW use in dilution ratios, instream waste concentration, control waters November 1, 2016
1.3 Representative Data, Reasonable Potential and Monitoring Frequencies Determining monitoring frequency and the need for a limit (WET Checklist Instructions) November 1, 2016
1.4 Test Credits When tests may be credited towards future permit terms June 1, 2005
1.5 WET Data Review and Interpretation Describes data review process; discusses concentration-response, confidence intervals, and other information July 1, 2008
1.6 Intermittent Discharges Sampling, retesting intermittent discharges May 15, 2000
1.7 Chapter withdrawn and replaced with Water Quality Review Procedures for Additives (2015)
1.8 Enforcement Strategy Example enforcement situations and appropriate responses to WET violations November 1, 2016
1.9 Reduced Volume Acute Screening (RVAS) Tests Monitoring tool for multiple samples or quick-screen situations June 1, 2005
1.10 Ammonia and Associated WET Requirements Guidance supporting new standards for ammonia. Sample modification when ELS-absent criteria are in effect; WET for pond systems that have been granted a variance. November 1, 2016
1.11 WET Testing of Minor Municipal Dischargers Streamlined procedures for determining WET requirements for a minor municipal discharge November 15, 2002
1.12 WET Limit Compliance Schedules Standard and specialized compliance schedules November 1, 2016
1.13 Spills Toxicity Testing Collecting samples and conducting toxicity tests after a spill November 19, 2012
1.14 Standard Permit Language Provides example WET language found in most WPDES permits November 1, 2016

Part 2 - Guidance For External Customers Clarification of Existing Requirements

2.1 Selection of a WET Laboratory Questions to ask when choosing a WET lab June 1, 2005
2.2 Toxicity Reduction Evaluations Guide for toxicity study design and plan/report submittals July 1, 2008
2.3 WET Testing of Lagoon Systems Why tests are required at WWTPs w/lagoons June 1, 2005
2.4 Toxic Units, LC50 and IC25 Values Uses, definitions, and calculations November 1, 2016
2.5 Relationship Between WET and Chemical Specific Compounds Program differences, when testing for one may replace the other November 1, 2016
2.6 (Chapter withdrawn)
2.7 Dilution Water and Test Controls Why Use RW? Identification of alternate dilution waters June 1, 2005
2.8 The CO2 Entrapment Method pH control/ elimination of artifactual toxicity June 1, 2005
2.9 WET Test Variability Ways to reduce variability in WET tests June 1, 2005
2.10 Chloride and WET Testing What should be done if chloride is believed to be a source of toxicity November 1, 2016
2.11 Dilution Series When and how to choose alternate dilution series June 1, 2005
Last revised: Wednesday November 02 2016