SITE INFORMATION AND CORRESPONDENCE

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`. .i INFORMATION SHEET 3_ CITY OF STOCKTON REGIONAL WATER QUALITY CONTROL PLANT SAN JOAQUIN COUNTY and ammonia concentrations of 10 mg/l and 2 mg/1, respectively, will likely provide an effluent of 5 mg/l and 0.5 mg/1 for CBOD and ammonia much of the time, will be more cost effective to build and operate, and will significantly improve water quality over existing conditions. As the existing low dissolved oxygen conditions in the San Joaquin River near Stockton are partially the result of waste water discharges and flow conditions beyond the control of the Discharger, and as the Discharger will make a significant reduction in the magnitude of its contribution to the dissolved oxygen problem by implementation of these tighter effluent limitations, the Board does not believe it is reasonable to require action by the Discharger to further reduce its impact on the river dissolved oxygen concentration until such time as a full study has been conducted of all sources of oxygen demanding substances impacting this reach of the San Joaquin River, and appropriate corrective action is taken against other parties contributing to the problem. Accordingly, until such time as this study is completed and appropriate action is taken against other contributing parties, the Board will not find the Discharger in violation of the receiving water dissolved oxygen limitations as long as the Discharger consistently achieves compliance with the new effluent Carbonaceous Biological Oxygen Demand and Ammonia effluent limitations in this permit. After completion of such a study, the Board may reconsider the Discharger's relative contribution to any remaining dissolved oxygen problem, and may make further adjustments in the Discharger's effluent limitations as is appropriate for the then-existing conditions. Actions to improve water quality in the vicinity of Stockton may occur in the future, including: (1) Improvements in non-point source controls being implemented in agricultural and urban areas; (2) Phase II Hearings on Delta Salinity Standards, which may lead to increased water flow in the river; (3) Additional requirements placed on water projects to provide increased wildlife and fisheries water flows; and (4) Elimination of severe flow reversals at or near the City of Stockton. These actions may significantly improve water quality in the vicinity of Stockton. Effluent and Receiving Water Limitations BOD/Ammonia/TSS/Dissolved Oxygen- The water quality objective for dissolved oxygen in the San Joaquin River in the vicinity of Stockton is now 6 mg/l from 1 September to 30 November, as outlined in the Water Quality Control Plan for Salinity, San Francisco Bay/Sacramento-San Joaquin Delta Estuary, dated May 1991, and 5 mg/l during the rest of the year. The river model found that existing treatment processes contributed to excursions of the water quality objective in the fall and spring, due to high mass loading of BOD and ammonia. It also showed that addition of activated sludge/nitrification units to provide a CBOD (Carbonaceous Biochemical Oxygen Demand) of 5 mg/1 and ammonia of 0.5 mg/l will significantly improve water quality by raising the dissolved oxygen level during critical periods by 2.5 to 3.0 mg/l, and increasing the overall dissolved oxygen in the summer by an additional 1.0 mg/l. The Discharger is unable to