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REGIONAL BOARD RESPONSE (SWRCB/OCC FILE A-1483) -14- PETITION FOR REVIEW OF WASTE DISCHARGE REQUIREMENTS ORDER NOS. R5-2002-0083 AND R5-2002-0084 CITY OF STOCKTON REGIONAL WASTEWATER CONTROL FACILITY Diazinon: As described in the response to the Second Basis, above, the Regional Board must include effluent limitations in NPDES permits where there is a reasonable potential for the discharge to cause or contribute to an excursion above a water quality standard. The Regional Board reasonably concluded that with respect to diazinon there is a reasonable potential for the discharge to cause or contribute to an excursion above the Basin Plan narrative toxicity objective9. In implementing the narrative toxicity objective, the USEPA regulations direct the Regional Board to establish an effluent limitation using one or more of three options. In this case, the Regional Board established the effluent limitation based on the explicit policy contained in the Basin Plan for application of water quality objectives as authorized by 40 CFR 122.44(d)(1)(vi)(A). The Basin Plan narrative toxicity objective and the Policy for Application of Water Quality Objectives requires the Regional Board to consider relevant numerical criteria and guidelines developed by other agencies in implementing the objective. The California Department of Fish and Game (CDFG) finalized water quality criteria for diazinon in March 200010. The Regional Board used these criteria in implementing the narrative toxicity objective. Monitoring of the Delta by the Regional Board'1,12 and US GS" found recurring OP pesticide concentrations exceeding the CDFG criteria, including diazinon, in the vicinity of Stockton's discharge, affirming that no assimilative capacity exists for OP pesticides. Oreano-chlorine Pesticides (lindane, endrin aidehvde, and DDT): The Regional Board reasonably concluded that the discharge has the reasonable potential to cause or contribute to an excursion above the water quality objective for organo-chlorine pesticides. The Basin Plan at III-6.00 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, endrin aldehyde, and DDT are persistent chlorinated hydrocarbon pesticides. The discharge contains lindane, endrin aldehyde, and DDT at concentrations that exceed the water quality objective. The Regional Board used the detection limit adopted in the SIP to evaluate compliance with the objective. Given that there is no dependable dilution in the receiving water, the effluent limitations were established at the detection limit. Mercurv: Information regarding the concerns of high levels of mercury in fish tissue is discussed in Order R5-2002-0083 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 indicate that the receiving water has no assimilative capacity for mercury. The health advisories are in the record'". 9 The reasonable potential evaluation for diazinon is described in Order No.R5-2002-0083 (Fact Sheet,pg.39) 10 Water Quality Criteria for Diazinon and Chlorpyriphos,Administrative Report 00-3,2000(Administrative Record, Binder 3,Item 189) Annual Review:Diazinon and Chlorpyrifos in Urban Waterways in Northern California,25 June 1999(Administrative Record,Binder 4,Item 23 8) = Sampling and Analysis Plan: Sacramento-San Joaquin Delta Waterways,25 April 2001 (Administrative Record,Binder 3,Item 109,note:incorrect date in Record Index) 3 San Joaquin River diazinon data near Vernalis(Administrative Record,Binder 1, Item 6,note:incorrect description in Record Index) 14 OEHHA and DHS Sport Fish Consumption Advisories for the San Francisco Bay and Delta Region(Administrative Record,Binder 1,Item 12)