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 630 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 the 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 630 acres of polishing ponds. The overall plant capacity will not exceed 55 mgd (average dry weather flow) 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 (average dry weather flow). The dissolved oxygen standards applicable to this reach of the San Joaquin River are as follows: a. The Basin Plan prescribes a minimum dissolved oxygen concentration in the San Joaquin River of 5.0 mg/I. This standard is applicable throughout the year. b. The Salinity Plan prescribes a minimum dissolved oxygen concentration of 6.0 mg/l in the San Joaquin River inside of the reach from Turner Cut to Stockton during the period 1 September through 30 November. This higher dissolved oxygen concentration was imposed to enhance aquatic conditions during critical migration periods for salmon, and supersedes the 5.0 mg/l standard prescribed by the Regional Board. The San Joaquin River in the vicinity of the Stockton Waste Water Treatment Plant discharge seasonally experiences violations of the 5.0 and 6.0 mg/ dissolved oxygen standards. In 1978 the Board adopted Waste Discharge Requirements Order No. 78-105 which prescribed tighter effluent BOD and Total Suspended Solids effluent limitations for the Discharger with the intent of reducing or eliminating the low dissolved conditions in the San Joaquin River in the vicinity of Stockton. The City constructed the necessary additional treatment facilities and has complied with the tighter effluent limitations. Despite the City's efforts, the low dissolved oxygen conditions persist.