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INFORMATION SHEET 14 <br /> WASTE DISCHARGE REQUIRMENTS ORDER NO. R5-2002-0213 <br /> U.S. DEPARTMENT OF DEFENSE <br /> DEFENSE LOGISTICS AGENCY <br /> DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN <br /> SHARPE GROUNDWATER REMEDIATION SYSTEM <br /> SAN JOAQUIN COUNTY <br /> concern, mixing zones should not encroach on drinking water intakes. " Before establishing a <br /> mixing zone, the amount of receiving water available to dilute the discharge must be <br /> determined. Dilution credit is a numerical value associated with the mixing zone that <br /> accounts for the receiving water entrained in the discharge, and is a value used in the <br /> calculation of effluent limitations. For continuous discharges and/or year-round mixing <br /> zones, the mixing zone and dilution credit for human health criteria is developed <br /> considering the harmonic mean flow as the critical receiving water flow. <br /> At present, sufficient receiving water information regarding the quality and quantity of <br /> flows in the SSJID Canal and French Camp Slough is not available to adequately assess <br /> ambient dilution water and mixing zone characteristics needed to assess the need for, and <br /> calculate, if necessary, alternative final effluent limitations for arsenic. This Order includes <br /> provisions for completion of a Dilution/Mixing Zone Study that may be appropriate in <br /> developing alternative final effluent limitations for arsenic. Based upon the results of the <br /> study required by this Order, this Order may be reopened, and alternative final effluent <br /> limitations maybe established to include appropriate human health criteria for arsenic <br /> considering pollutant attenuation provided by dilution and a mixing zone. <br /> b. Basin Plan Amendment Process <br /> Concurrent with the Dilution/Mixing Zone Study, the Discharger may provide information <br /> to the Regional Board to support a Basin Plan amendment to de-designate the municipal <br /> and domestic supply(MUN)beneficial use of the SSJID Canal based on the exceptions to <br /> SWRCB Resolution 88-63. If, through this process, the municipal and domestic supply <br /> beneficial use of the SSJID Canal is deemed inappropriate, and is removed through the <br /> basin planning process, receiving water and/or alternative final effluent limits would be <br /> established based upon the results of the Dilution/Mixing Zone Study to ensure protection <br /> of the MUN beneficial use in French Camp Slough. <br /> c. End-of-Pipe'Compliance with new MCL <br /> Without additional information or study,the Discharger can ensure compliance with water <br /> quality standards by meeting the new USEPA primary MCL of 10 µg/L (ppb) at the point <br /> of effluent discharge to SSJID Canal. The compliance date for water purveyors to meet the <br /> new MCL is 23 January 2006. This Order includes a final monthly average effluent <br /> limitation for arsenic of 10 µg/L (ppb) consistent with the new USEPA primary MCL and <br /> effective 23 January 2006. <br /> Considering these options, this Order provides a time schedule for completion of a Dilution/Mixing <br /> Zone Study for arsenic. This study shall be completed prior to the new USEPA MCL compliance <br /> date for water purveyors and effective date of the final monthly average effluent limitation for <br /> arsenic of 23 January 2006. The Discharger may concurrently pursue a Basin Plan Amendment <br /> de-designating the MUN beneficial use of the SSJID Canal,however the Dilution/Mixing Zone <br />