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REGIONAL BOARD RESPONSE (SRRCB/OCC FILE A-1483) -22- PETITION FOR REVIEW OF WASTE DISCHARGE REQUIREMENTS ORDER NOS. R5-2002-0083 AND R5-2002-0084 CITY OF STOCKTON REGIONAL WASTEWATER CONTROL FACILITY appropriate reductions within the Sacramento River watershed. Offsets do not include sources that, if not controlled, would enter the facility's treatment system. These sources should already be controlled as part of the Discharger's pollutant prevention program, which is also required. In order to assure that offsets will actually reduce the cause of the impairment, an offset feasibility study is required. The study must investigate ratios to express the relationship between the mass of the pollutant from the outfall and the mass discharged at the offset source. These ratios should take into account the relative bioavailability, the likelihood that the pollutant will actually reach the water body, and a factor of safety to account for uncertainty in biological effects and in monitoring. A monitoring program is required to be implemented that measures loadings from the RWCF outfall and provides data to estimate loading reductions from the offsets including possible base-line data collection. The studies performed by the Discharger will provide the Regional Board with site and watershed specific information necessary to prepare terms for the final offset program. Order R5-2002-0083 will be reopened for public comment and Regional Board approval of the final offset program. In addition to the offset program, the interim and/or final effluent limitations would need to clearly indicate how compliance would be assessed. Also details, such as the amount of time for which loads can be banked, will need to be addressed. The approach described above will allow the Discharger to comply with the terms of its permit, allow for growth, and do so in a way that effectively removes the pollutants of concern from the watershed. Group A Pesticides: The Basin Plan 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 and final non-detect effluent limitations have been imposed in Order R5-2002-0083. The RWCF cannot meet the final effluent limitations; therefore, interim performance-based effluent limitations are required. Since Group A pesticides are bioaccumulative constituents, the interim limits are set as mass loadings. The 303(d) listing of Group A pesticides in the Delta is not the basis for the mass limitations. The interim mass loadings have been set to provide a mass cap while not restricting growth. A growth factor,based on population projections by the San Joaquin Council of Governments, was incorporated in the calculations (see Table 11-6 of Order R5-2002-0083). EIGHTH BASIS: NEW GROUNDWATER REOUIREMENTS Stockton requests that the State Board direct the RWQCB to delete the Groundwater Limitation and adopt provisions consistent with the water quality objectives in the Basin Plan. Groundwater Limitation F.2. of Order R5-2002-0083 states, "Any constituent concentration, when compared with background, shall not be incrementally increased beyond the current concentration in downgradient wells."The limitation does not preclude all degradation downgradient,but requires that it not become incrementally increased from that which currently exists,pending completion of studies required by Provision G.10. The requirements are consistent with the Basin Plan, Resolution 68-16, and Water Code section 13263. The Regional Board is not establishing a new water quality objective, rather,