SITE INFORMATION AND CORRESPONDENCE_1993-2003

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INFORMATION SHEET 10 WASTE DISCHARGE REQUIRMENTS ORDER NO. R5-2002-0213 U.S. DEPARTMENT OF DEFENSE DEFENSE LOGISTICS AGENCY DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN SHARPE GROUNDWATER REMEDIATION SYSTEM SAN JOAQUIN COUNTY Reasonable Potential Analyses 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. Water Quality Based Effluent Limitations 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. The Porter Cologne Water Quality Control Act defines water quality objectives as "...the limits or levels of water quality constituents or characteristics which are established for the reasonable protection of beneficial uses of water or the prevention of nuisance within a specific area". Water quality objectives designed to protect beneficial uses and prevent nuisances are found in the Basin Plan, and may be stated in either numerical or narrative form. 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. Data Adjustments In most situations, EPA's NPDES regulations require that limits for metals in permit's be stated as total recoverable. Since most water quality criteria are expressed in the dissolved form, it is