FIELD DOCUMENTS AND WORK PLANS 1992-1999

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INFORMATION SHEET -2- MARLEY COOLING TOWER COMPANY STOCKTON, SAN JOAQUIN COUNTY River below Bellota. From 1 October to 1 April every year, the East Stockton Water District dams the Calaveras River at its fork with Upper Mormon Slough, thus diverting all flows through Upper Mormon Slough and the Stockton Diverting Canal . From 1 April to 1 October every year, flows are split between the Calaveras River and Upper Mormon Slough. A series of check dams are installed along the Calaveras River, Upper Mormon Slough, and the Stockton Diverting Canal to provide irrigation water for adjacent farmers. During this time, there are periods of no flow in the Stockton Diverting Canal . MCTC submitted a Report of Waste Discharge (RWD) which requested an increase in the treated water flow from the treatment plant. MCTC proposed in the RWD an expansion of the on-site ground water treatment facility to control contaminant movement. An electrochemical reduction and precipitation treatment plant will be expanded and used in parallel with the existing ion exchange treatment system. Flows have been proposed to be increased to a maximum of 1 .01 mgd (0.72 mgd average) . Ground water treatment will consist of various combinations of the following unit processes: flow equalization, reduction, precipitation, settling, filtration, pH adjustment and ion exchange. A Remedial Investigation / Feasibility Study has been conducted and in August 1990, the final Remedial Action Plan (RAP) was adopted by the DHS. The recommended ground water remedial action in the RAP included an increase to 0.72 mgd in the discharge of the treated ground water and/or storm water. A revised monitoring program has been prepared for the new plant. The adoption of the modified waste discharge requirements will expedite ground water cleanup by increasing flows. Basis for Effluent Limitations Effluent limits on the discharge to the Stockton Diverting Canal are based on water quality objectives established by the "California Inland Surface Waters Plan" . Limits were set at 6.5 pg/l for Copper, 11 pg/l for Hexavalent Chromium, and 10 pg/1 for Arsenic, for protection of freshwater aquatic life. Limits were set at 50 Ng/l for Total Chromium for protection of human health and the recommended upper level for protection of human health for Total Dissolved Solids at 1000 pg/l . The TDS of the natural groundwater extracted ranges from 330 - 860 mg/l and an increase of approximately 300-500 mg/l can be attributed to the treatment process. Although an effluent concentration of 500 mg/l TDS is the Basin Plan Objective, it is believed to be in the best interest of the people of California to allow a higher discharge concentration in order to facilitate the cleanup of the contaminated ground water.