1. Whole Effluent Toxicity NPDES Program
Laura Phillips
USEPA - Office of Wastewater Management ,

2. What is Whole Effluent Toxicity (WET) Testing & Why Do it?
What is it? -
WQ-based toxics control method that directly measures the total or aggregate toxic effect (additive, synergistic and antagonistic) of an aqueous sample through the response(s) of exposed aquatic organisms.
Why do it? -
Protects Narrative Criterion (“no toxics in toxic amounts”) & was designed to predict the impact and toxicity of effluents to determine “safe effluent discharge concentrations” with respect to WQS (criteria).

3. EPA Whole Effluent Toxicity (WET) Program
WET - Component of the WQ Integrated Approach
WQ WET Criteria & Standards
NPDES Regulations: 40 CFR Part 122
(i.e., 40 CFR Part (d)(1)(iv) & (v))
WET Methods (40 CFR Part 136)
NPDES Permit & EPA Regions, Permitting Authorities (45 NPDES States) and Permittees
Consultants (i.e., Labs)

4. Whole Effluent Toxicity Criteria
Applying toxicity criteria
with allowable dilution
Narrative - “no toxics in toxic amounts”
Numeric TSD recommendations or numeric interpretation of Narrative
Acute = 0.3 TUa (e.g., 100/LC50)
Chronic = 1.0 TUc (e.g., 100/NOEC)
Outfall
0.3 TUa
1.0 TUc

5. Major Components of a NPDES Permit
Cover Page
Effluent limitations
Monitoring & Reporting Requirements
Special Conditions
Standard Conditions

6. With Regard to WET - - NPDES Permits Must Specify
Test Species and Method
(Fathead Minnow, Acute or Chronic)
Testing Frequency
(Representative of the Effluent)
Statistical Endpoints
(Acute: LC50 or IWC, Chronic: NOEC, ICp)
Steps to Address Toxicity
(Accelerated WET testing, TREs/TIEs)

7. WET Test Method Selection
Approved acute and chronic methods (40 CFR Part 136)
Must determine:
Acute or chronic toxicity (based on calculated
limits or available dilution)
Freshwater or marine discharge
Most appropriate species (e.g., 3 species quarterly
for 1 year)

8. WET Monitoring
WET Monitoring Representative of Effluent Discharge: Important for WET reasonable potential determinations & evaluating WET NPDES permit limit compliance
USEPA NPDES Regulations:
 40 CFR (g)(11)  40 CFR Part (j)(5)
 40 CFR Part (i)  40 CFR Part (b)
USEPA Guidance:
Technical Support Document (TSD) (1991, OWM)
Interim Guidance for Performance-Based Reductions of NPDES Monitoring Frequencies (4/19/96, OW/OECA)

9. WET Reasonable Potential (RP) Determinations
No WET Data: Use EPA Technical Support Document’s (TSD) statistical approaches to determine if RP exists.
Fewer than ten valid WET data points (per species): EPA’s TSD provides recommended coefficients of variation.
Ten or more valid WET data points: With ten or more valid and representative effluent data points a robust WET RP determination can be done.

10. TSD Steps in Developing WET Permit Limitations
WLA = Wasteload Allocation, LTA= Long Term Average
Acute & Chronic Wasteload Allocations
Step 1: Convert Acute WLA to Chronic WLA
(WET only)
Step 2: Calculate LTA for Both
Step 3: Select Lowest LTA
Step 4: Calculate Maximum Daily Load & Average Monthly Limits

11. NPDES Program Resources
USEPA OWM Catalog of Publications (EPA 830/B )
Basic Permit Writers’ Manual (EPA/833-B , 12/96)
Technical Support Document (EPA/ , 3/91)
USEPA Basic Permit Writer’s Course - Ca (1/03)
OWM Web site: or
SETAC WET Training Courses
Web site: setac.org

12. NPDES Program Resources Under Development
NPDES Permit Development Tool (NPDES/PDT):
Electronic tool that will allow permit writers to interactively calculate water quality-based effluent limitations for large number of pollutants. Future versions will include the ability to calculate technology-based limits.
Permit Application Software System (PASS):
Phase I: Electronic system which allows permittees to electronically prepare NPDES permit applications, print, & mail it to their NPDES permitting authorities. Phase II: System will be enhanced to allow electronic submission to the NPDES permitting authority. (

13. WET National Program Technical Resources
Information/Assistance:
EPA OW/OWM Web site:
EPA OW/OST Web site:
EPA Regional Contacts
SETAC Web site: including “Frequently Asked Questions” Bulletin Board
SETAC WET Expert Advisory Panel:
USEPA WET Document Compendium

14. USEPA WET Document Compendium - Sample List
WET Requirements in Municipal Permits (7/85)
WET Sample Permitting & Enforcement Guidance (2/89)
WET Control Policy (7/94)
National Policy Regarding WET Enforcement (8/95)
Clarifications Regarding Flexibility in WET Methods (4/96)
Clarifications Regarding WET Test Methods & Guidance on Implementing WET Toxicity in Permits (7/97)
TRE Municipal Guidance (8/99)
WET Variability Guidance (6/00)
WET Test Methods Guidance (7/00)
TRE/TIE Clarifications Document (5/01)
WET Test Methods Proposed Rule (9/01)

15. Where Do We Go From Here?
Critical Crossroads - Require careful consideration of the issues, maintaining the NPDES base program, & identifying possibilities for appropriate flexibility within existing NPDES regs and the CWA.
Review the Facts - Use facts to cull out non-productive issues so remaining issues are prioritized in a manner that produces results.
Pursue Strategic Pathways or Decisions - To overcome ongoing barriers to effectively implementing the NPDES WET program.

16. Closing Remarks Move Program Forward
Where possible, reduce controversies and implement the WET program in a manner that fulfills CWA objectives, complies with USEPA NPDES regulations, and is endorsed by stakeholders through their actions and support to the program.