SITE INFORMATION AND CORRESPONDENCE 1980-1999

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STAFF REPORT • -4- WHITE SLOUGH WATER POLLUTION CONTROL PLANT SAN JOAQUIN COUNTY mercury (30-day average, chronic criteria) is 0.77 gg/l, and the proposed California Toxics Rule concentration is 0.050 µg/1. Effluent monitoring for mercury has shown the median concentration to be non-detectable at <0.2 Itg/l, which is questionable without implementing "clean technique" (EPA Method 163 1) for sample collection, handling, and analyses. In view of the uncertainty of applicable water quality criteria, and the accuracy of existing sampling results, the proposed permit does not contain a water quality-based effluent limitation for mercury. The proposed permit requires "clean-technique" monitoring for mercury. If mercury is found to be detectable, or if the California Toxic Rule is implemented, or if a TMDL program is adopted for the Sacramento-San Joaquin Delta, the permit may be reopened and effluent limits and/or mass loading limitations imposed. In the interim, the proposed permit requires the Discharger to develop a program for identification and control of mercury discharges within the collection system. 8. Pesticides and Unknown Toxicity The Sacramento-San Joaquin Delta has been listed as an impaired water body pursuant to Section 303(d) of the Clean Water Act because of: (1) diazinon and chlorpyrifos (organophoshate pesticides), (2) aldrin, dieldrin, chlordane, endrin, heptachlor, heptachlor epoxide, hexachlorocyclohexane (including lindane), endosulfan and toxaphene (chlorinated hydrocarbon pesticides), (3)DDT, and (4) unknown toxicity. The Basin Plan requires that; total chlorinated hydrocarbon pesticide concentrations shall not be present in the water column at detectable concentrations and pesticide concentrations shall not exceed those allowable by applicable antidegradation policies. The Basin Plan's requirement that persistent chlorinated hydrocarbon pesticides shall not be present in the water column in detectable concentrations is the most stringent criteria for the regulation of the detected persistent organochlorine pesticides. Lindane (an organochlorine pesticide) was detected in 7 of 19 sampling events. The detectable concentrations of lindane were less than EPA's freshwater ambient water quality criteria. However, per the Basin Plan requirements, the proposed permit applies a non- detectable limitation to each individual pesticide at any detection level. Based on review of the effluent monitoring, a maximum acceptable detection level of 0.02 µg/1 has been proposed as an effluent limitation. The Discharger is not currently capable of meeting this requirement and a CDO for organochlorine pesticides has also been proposed. This proposed permit requires the Discharger to monitor for all 303(d) listed pesticides including diazinon and chlorpyrifos, as outlined in the monitoring and reporting program. The Discharger will be required by the permit to determine whether the level of diazinon and chlorpyrifos in the discharge cause or contribute to an in-stream excursion above water quality objectives, and allows the Board to reopen the permit and include effluent limitations for these specific pesticides which are not addressed by the Basin Plan.