FIELD DOCUMENTS AND WORK PLANS 1988

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INFORMATION SHEET • • MARLEY COOLING TOWER CO. STOCKTON, SAN JOAQUIN CO. -2- The Stockton Diverting Canal is an engineered drainage way connecting Upper Mormon Slough to the Calaveras River near the Southern Pacific Railroad crossing. Upper Mormon Slough is actually the South Fork of the Calaveras 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 . Basis for Effluent Limitations The beneficial uses of the Stockton Diverting Canal are industrial and agri- cultural supply; recreation; esthetic enjoyment; navigation; and preservation of fish and wildlife. These uses are protected by basing effluent limitations on standards to protect aquatic life, human health, agricultural irrigation, and the Regional Board's Basin Plan Objectives. The applicable standards for each of the potential contaminants at MCTC are shown in Table 1. Table 1 standards reflect acceptable levels for instream uses. To determine effluent limits, the most restrictive standard for each constituent was selected. Thus , the respective values used were 6.5 ug/l for Copper, 50 ug/l for Total Chromium, 11 ug/l for Hexavalent Chromium, 10 ug/l for Arsenic, and 500 mg/l for Total Dissolved Solids. Since conditions of no flow do exist in the Stockton Diverting Canal , the initial effluent limits were set without considering any dilution. Thus, the limits require effluent quality equal to instream requirements based on the most stringent standard for each constituent above (Effluent Limit A.1.) . For periods of increased flow, the resultant dilution capacity of the Diverting Canal was afforded Marley' s discharge. Formulas for determining alternative Daily Maximum and Monthly Average limits were developed. Adjusted Daily Maximum limits are based on a 1 :1 dilution ratio of the discharge to the receiving stream flow. This allows some flexibility in day-to-day plant operations without exceeding instream use standards. Adjusted Monthly Average limits use a factor of safety of three times the average monthly discharge rate. This utilizes dilution capacity of the stream while maintaining a margin of safety for instream values. No limits were allowed to exceed drinking water standards since treatment tech- nology exists and to limit the total mass loadings to the Calaveras River and the Delta. Thus, limits were set at 65 ug/l for Copper, 50 ug/l for Total Chromium, 50 ug/1 for Arsenic, and 1000 ng/l for Total Dissolved Solids (Effluent Limitation A.2.) . Additionally, constituent values in the downstream receiving water must not exceed the selected use standards (Receiving Water Limitation D.1.) Revised:GAR:gs:6/0;/88