Whole Effluent Toxicity (WET) limits have been added to Kentucky Pollutant Discharge Elimination System (KPDES) permits since 1988. The program has grown to the point that now approximately 160 facilities have WET as a permit condition requiring self-monitoring. In the permit, the limit is expressed on the limits page as a toxicity unit (TU), either acute or chronic. The specific requirements are written under Part IV, Biomonitoring.
Almost all major discharge facilities are required to perform WET, as well as some minor industries or municipalities with pretreatment requirements. Both acute and chronic limits based on stream flow versus volume of discharge are used for testing.
When a KPDES permit is issued, the facility is required to test using both the fathead minnow, Pimephales promelas, and the daphnid, Ceriodaphnia dubia. Monthly testing is required for the first year. After a period of six months, the permittee may request to test only with the most sensitive species. After the first year, the facility may request reducing testing frequency to once per quarter.
Upon permit renewal, the facility is required to return to testing both species for four tests to re-establish the most sensitive species. If the facility is currently testing monthly, then both species may be tested monthly. If quarterly testing was in effect at renewal, both species are tested quarterly.
The most recent minor modifications were made to the generic permit language for biomonitoring in Kentucky in 1999. The changes cleared up confusion that had arisen over the years concerning interpreting specific language. To get a copy of a specific permit, please submit a written Freedom of Information request to the Surface Water Permits Branch.
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