SITE INFORMATION AND CORRESPONDENCE_1993-2003

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WASTE DISCHARGE REQUIREMENTS ORDER NO.R5-2002-0213 • 9 U.S.DEPARTMENT OF DEFENSE DEFENSE LOGISTICS AGENCY DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN SHARPE GROUNDWATER REMEDIATION SYSTEM SAN JOAQUIN COUNTY CWA. Regulations promulgated at 40 CFR 122.44 (a) require technology-based effluent limitations to be placed in NPDES permits based on national effluent limitations guidelines and standards, best professional judgment (BPJ), or a combination of the two. 16. Previous Order No. 95-258 included daily maximum and monthly median effluent limitations for total volatile organic compounds (total VOCs) (1.0 µg/L(ppb) and<0.5µg/L (ppb), respectively) based upon technically achievable treatment levels for air strippers. These technology based effluent limitations still apply to the discharge, and total VOC constituents have been detected in influent groundwater,prior to treatment, at concentrations up to 57.7 µg/L (ppb). Therefore, the daily maximum and monthly median effluent limitations for total VOCs have been retained and included in this Order. 17. Where technology-based effluent limitations are inadequate to ensure compliance with water quality standards applicable to the receiving water,more stringent effluent limits based upon applicable water quality standards are imposed. 18. Federal regulations, 40 CFR Part 122.44 (d)(1)(i), require that NPDES permit effluent limitations must control all pollutants which are or may be discharged at a level which will cause or have the reasonable potential to cause or contribute to an in-stream excursion above any State water quality standard, including any narrative criteria for water quality. Beneficial uses, together with their corresponding water quality objectives, constitute the state water quality standards for purposes of compliance with the Clean Water Act. In determining whether a discharge has the reasonable potential to contribute to an in-stream excursion (reasonable potential analysis), the dilution of the effluent in the receiving water may be considered where areas of dilution are defined. The available dilution may also be used to calculate protective effluent limitations by applying water quality criteria at the edge of the defined mixing zone. These calculations include receiving water pollutant concentrations that are typically based on worst-case conditions for flow and concentration. If limited or no dilution is available, effluent limitations are set equal to the applicable water quality criteria which are applied at the point of discharge so the discharge will not cause the receiving stream to exceed water quality objectives established to protect the beneficial uses. In situations where receiving water flows are substantially greater than effluent flows, dilution may be considered in establishing effluent limitations. However, when a receiving water is impaired by a particular pollutant or stressor, limited or no pollutant assimilative capacity may be available in spite of the available dilution. In these instances, and depending upon the nature of the pollutant, effluent limitations may be set equal to or less than the applicable water quality criteria that are applied at the point of discharge such that the discharge will not cause or contribute to the receiving stream excursion above water quality objectives established to protect the beneficial uses.