SITE INFORMATION AND CORRESPONDENCE

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INFORMATION SHEET CITY OF STOCKTON REGIONAL WATER QUALITY CONTROL PLANT SAN JOAQUIN COUNTY The Regional Water Quality Control Plant accepts domestic and industrial wastes from the city and surrounding urbanized county areas. The treatment system includes trickling filters and post secondary treatment in 640 acres of polishing ponds. Tertiary treatment, dissolved air flotation and multi-media filtration, is used when necessary to meet effluent limitations. Sludge is dewatered by belt press and reclaimed off-site. Maximum waste flows occur during tite summer and fall months, with the major volume contributed by the canneries connected to the system. Liquid canning wastes also provide the major organic loading to the plant during this period. During the canning season, the secondary treatment units and sludge handling units are operating at their capacity. The City is upgrading the facility, including expansion of the process units, as well as constructing activated sludge/nitrification units to be operated in lieu of the 640 acres of polishing ponds. The overall plant capacity will not exceed 55 mgd during the term of this permit. Although the current dry weather design flow of the secondary plant is only 38 mgd, the City optimizes the treatment costs of the tertiary plant, which includes the chlorination facilities, by intermittently operating the tertiary plant at close to its design flow. For that reason, this permit allows the discharge flow to be 55 mgd. The City 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) Addition of activated sludge/nitrification units to provide a CBOD of 5 mg/I and ammonia of 0.5 mg/l will significantly improve water quality, however the water quality objective may still not be met; (5) Delta water management, particularly the Clifton Court and Tracy pumping facilities and rock barrier installations at the Old River confluence, have a strong influence on river flows and water quality; and (6) The installation of a flow gage at the Stockton outfall will greatly improve the accuracy of the model. Based on the findings of the river model, and the need to expand the secondary plant, the Discharger plans to upgrade the facility to include activated sludge/nitrification. This Order contains effluent limitations which, when met, will significantly improve the water quality in the receiving water by decreasing the mass loading of CBOD and ammonia. These actions alone may not prevent further excursions below the water quality objective for dissolved oxygen. There are other contributors to the dissolved oxygen deficit in the receiving water. Actions to improve water quality from the other contributors may occur in the future due to: (1) Improvements