SITE INFORMATION AND CORRESPONDENCE

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WASTE DISCHARGE REQUIREMENTS -4- CITY OF STOCKTON REGIONAL WATER QUALITY CONTROL PLANT SAN JOAQUIN COUNTY mg/l. These treatment system improvements will decrease the discharge's contribution to 20% or less of the oxygen demand to the river during critical low river dissolved oxygen periods, without actions from other sources. Even with the treatment plant improvements, the water quality objective will still not be met; (6) The San Joaquin River in the vicinity of Stockton would not meet the receiving water dissolved oxygen standards even if the Stockton discharge were eliminated; (7) Delta water management, particularly the Clifton Court and Tracy pumping facilities have a strong influence on river flows and water quality; (8) When the rock barriers are installed at the Old River confluence, river flow is predominantly downstream, and the dissolve) oxygen sag occurs in the Deep Water Channel. Without the rock barriers, Delta pumping draws river flows upstream and the dissolved oxygen sag occurs upstream of the treatment plant discharge; and (9) The installation of a flow gage at the Stockton outfall will greatly improve the accuracy of the model. 15. These waste discharge requirements contain a further tightening of the Discharger's effluent limitations based on the results of the City's model to reduce the impact of the City's discharge on the receiving water. Based on the model, the tightened effluent limitations will result in a decrease in River dissolved oxygen as the direct result of the City's discharge. However, as previously stated, the River will seasonally not achieve compliance with the Dissolved Oxygen standards even if the discharge is totally eliminated. 16. 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. 17. The Discharger has submitted information showing that treatment to consistently achieve 30-day average effluent limits for CBOD and ammonia of 5 mg/1 and 0.5 mg/l, respectively, is not cost effective at this time. Treatment units designed to achieve 30-day average effluent limits for CBOD and ammonia concentrations of 10 mg/l and 2 mg/1, respectively, will likely provide an effluent of 5 mg/1 and 0.5 mg/l 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. 18. 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, beyond the requirements