SITE INFORMATION AND CORRESPONDENCE

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INFORMATION SHEET -2- CITY OF STOCKTON REGIONAL WATER QUALITY CONTROL PLANT SAN JOAQUIN COUNTY The City recently completed a river model to assess the impact of the discharge on the receiving water. Water quality parameters considered include TDS, BOD, ammonia, nitrate, and dissolved oxygen. The model provided the following information: (1) Initial dilution, not taking into account recirculation of effluent, is 10:1; (2) Long-term average dilution, taking into account recirculation of effluent, is 4:1; (3) Critical water quality conditions occur in the fall and spring, due to a high mass loading of BOD and ammonia; (4) The current discharge contributes up to 43% of the oxygen demand to the river during critical low river dissolved oxygen periods, under current Delta flow conditions, as simulated in the model over the calibration period; (5) Addition of activated sludge/nitrification units to provide a CBOD (Carbonaceous Biochemical Oxygen Demand) of 5 mg/1 and ammonia of 0.5 mg/1 will significantly improve water quality by raising the dissolved oxygen level during critical periods from 2.5 to 3.0 mg/l, and increasing the dissolved oxygen in the summer by an additional 1.0 mg/I. 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 dissolved 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. 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 still 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. 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) 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. 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/I, respectively, is not cost effective at this time. Treatment units designed to achieve 30-day average effluent limits for CBOD