What to Do When You Fail a NPDES Whole Effluent Toxicity Test in California
- joe15219
- May 22
- 3 min read
Failing a Whole Effluent Toxicity (WET) test as part of your NPDES permit in California can be a stressful and confusing experience. But it’s also an important opportunity to correct potential problems before they lead to more significant regulatory or environmental consequences. This guide breaks down what to do step by step if your WET test results indicate a failure under the California NPDES program.
What is a Whole Effluent Toxicity (WET) Test?
Whole Effluent Toxicity (WET) tests measure the aggregate effect of wastewater effluent on aquatic organisms. These tests are designed to ensure that discharges do not cause unacceptable harm to receiving waters and are a core part of compliance for NPDES (National Pollutant Discharge Elimination System) permits in California.
There are two main types of WET tests:
Acute Toxicity Tests: Short-term exposure, assessing immediate harmful effects.
Chronic Toxicity Tests: Longer exposure, looking at effects on growth, reproduction, or survival.
Step 1: Confirm the Failure
First, validate that the test was conducted correctly and that the results are indeed valid. Review:
Test conditions (temperature, pH, salinity, etc.)
Chain of custody records
Lab certifications
QA/QC data and control organism performance
If there are errors or anomalies, you may be able to invalidate the test and avoid a formal violation.
Step 2: Notify the Regional Water Board
If the test results are confirmed and represent a true failure, you are generally required to notify the appropriate California Regional Water Quality Control Board (RWQCB) promptly—typically within 24 hours of learning of the result. Check your permit for specific timelines and reporting requirements.
Failure to notify can lead to further penalties or regulatory enforcement.
Step 3: Review Your Permit Requirements
California’s NPDES permits typically include a Toxicity Reduction Evaluation (TRE) Trigger. If your WET test exceeds this trigger level, you may be required to:
Conduct a Toxicity Identification Evaluation (TIE) to determine the cause.
Initiate a Toxicity Reduction Evaluation (TRE) to mitigate the issue.
The response process is usually outlined in your permit, including the timelines for initiating and reporting progress on TIE/TRE activities.
Step 4: Start a TIE or TRE (if required)
A TIE helps isolate the toxicant(s) in your effluent using lab procedures such as chemical manipulations or fractionations. If a toxicant is identified, you can take direct corrective action.
A TRE is a more comprehensive, long-term strategy that may include:
Process audits
Treatment system adjustments
Source control programs
Chemical substitution
Additional monitoring
Consulting a specialist in wastewater toxicology is highly recommended at this stage.
Step 5: Maintain Communication and Documentation
Throughout the investigation and correction process, maintain regular communication with the Regional Water Board and keep detailed documentation of:
All test results
Investigative steps taken
Corrective actions implemented
Monitoring data post-correction
This transparency helps demonstrate good faith compliance and may prevent enforcement actions.
Step 5: Maintain Communication and Documentation
Throughout the investigation and correction process, maintain regular communication with the Regional Water Board and keep detailed documentation of:
All test results
Investigative steps taken
Corrective actions implemented
Monitoring data post-correction
This transparency helps demonstrate good faith compliance and may prevent enforcement actions.
Conclusion
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