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WASTE DISCHARGE REQUIREMENTS 11- '� CITY OF STOCKTON REGIONAL WASTEWATER CONTROL FACILITY SAN JOAQUIN COUNTY LATE REVISIONS Based on calculations presented in the Table 11-6 of the Fact Sheet, interim mass load limitations are being established in this Order for mercury at 0.921bs/year, DDT at 7.5 lbs/year, endrin aldehyde at 12.9 lbs/year, and lindane at 3.2 lbs/year. As described in 4" Effluent Limitations B.1 and B.I I and providing that the Discharger is in compliance with the terms of its compliance schedules in G.1, G.6, G.7, and G.8, actual mass loading above or below the interim mass limitation for mercury can be "banked"until such time as a discharge specific offset program is adopted by the Regional Board into the Order to provide a means for offsetting these loads. The interim mass loadings for Group A Pesticides have been set to provide a mass cap while not restricting growth. A growth factor was incorporated in the calculations. The growth factor is based on population projections by the San Joaquin Council of Governments, which estimates the City of Stockton will grow at a rate of 2.3%per year. This Order contains a compliance schedule for mercury based on the provisions of the SIP. Also, based on the provisions of the Basin Plan, this Order contains a compliance schedule for the Group A pesticides. As part of the compliance schedules for these pollutants, the Discharger shall develop a pollution prevention program in compliance with CWC Section 13263.3(d)(3) and perform engineering feasibility treatment studies as described in Provisions G.6 and G.7. For Mercury, this Order requires the Discharger to develop an offset program as described in Provision G.8, which could be used to offset mercury loads above the interim mass limitation. These plans and studies will provide the Regional Board with site- and watershed-specific information necessary to prepare terms for a final offset program for mercury. This Order will be reopened to provide for public comment and Regional Board approval of the final offset program. A final effluent limitation of non-detect based on the water quality objectives in the Basin Plan for Group A Pesticides is imposed in this Order and must be met at the end of the compliance schedule, which coincides with the time schedule to build the Title 22 tertiary facilities. The final effluent limitation (mass load allocation) for mercury in the RWCF effluent shall come from the TMDL. The interim mass limitations shall remain in effect until that time. Once the TMDL has been adopted, any mass discharge over and above the TMDL shall be banked and addressed by the offset program. If an offset program is determined to be infeasible, the Regional Board will reconsider the interim mass cap on mercury. OP Pesticides 31. Under the direction of the Regional Board, the Discharger began monthly monitoring of the organo-phosphate pesticides (chlorpyrifos and diazinon) in the effluent and receiving water beginning in March 2000. Chlorpyrifos has not been detected above the analytical reporting limit (0.065 µg/1) in the effluent or receiving water samples. Diazinon has been detected three times above the analytical reporting limit at concentrations as high as 0.087 µg/1 in the effluent. Diazinon was also detected once in the downstream receiving water at 0.057 µg/1. There are no CTR or NTR criteria for either of these pollutants. The Basin Plan contains the narrative toxicity objective. The Basin Plan requires the