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RESPONSE TO WRITTEN COMMENTS � -14- 10 City Of Stockton-Regional Wastewater Control Facility NPDES No. CA0079138 26 April 2002 Board Meeting the record is insufficient to justify the imposition of stringent limitations without accounting for the available assimilative capacity, at least on a seasonal basis. RWQCB Response: The Basin Plan contains a narrative toxicity objective and requires the Regional Board to consider relevant numerical criteria and guidelines developed by other agencies in implementing the objective. In March 2000, the California Department of Fish and Game (CDFG) finalized water quality criteria for diazinon (reference: Water Quality Criteria for Diazinon and Chlorpyriphos, Administrative Report 00-3, 2000). The Regional Board used these criteria in implementing the narrative toxicity objective. Monitoring of the delta by the Regional Board finds recurring OP pesticides concentrations exceeding the CDFG criteria, affirming that no assimilative capacity exists for OP pesticides. Stockton Comment No. IV.D(2) (Lindane Endrin aldehvde and DDT): The proposed limits for these parameters are based on concerns regarding fish tissue levels. However, no such information is presented in the record. Moreover, the tentative permit states that the effluent limitations for certain pesticides are based on a narrative water quality objective from the Basin Plan. The Basin Plan states that certain pesticides shall not be present at"concentrations detectable within the accuracy of analytical methods approved by the [EPA] or the Executive Officer." (Basin Plan at 111.6-00.) The permit thus refers to a non-detect limit for various pesticides, based on the Basin Plan objective. The Regional Board would effectively establish, as a numeric limit, whatever concentration could be detected as a result of technological advances. This would occur without consideration of the relevant factors in Water Code section 13241, which must be addressed in applying any narrative criteria. (Wat. Code, § 13263.) The use of a detection limit for lindane by application of the narrative criteria is particularly inappropriate as the CTR established less restrictive numeric limits than the detection level incorporated by the Board. Where a numeric objective is available, narrative procedures should not be applied (cite 40 CFR § 122.41). RWOCB Response: Information regarding the concerns of high levels of pesticides in fish tissue is discussed in the Fact Sheet, Section 11.1, "Health advisories by the Department of Health Services remain in effect for human consumption offish in the Delta, including the SJR at Stockton, due to excessive concentrations of mercury in fish flesh. These current warnings and available fish tissue data confirm that there is currently no assimilative capacity for these pollutants. Therefore, water quality based effluent limitationsfor thesepollutants thatproperly address bioaccumulation and the non-detect Basin Plan objective are required." The Basin Plan contains a water quality objective that prohibits concentrations of"persistent chlorinated hydrocarbon pesticides" in the receiving water"detectable within the accuracy of analytical methods approved by the [EPA] or the Executive Officer". Lindane is a persistent chlorinated hydrocarbon pesticide. Given that there is no dependable dilution in the receiving water, effluent concentrations are effectively receiving water concentrations. To implement the "non-