SITE INFORMATION AND CORRESPONDENCE_CASE 2

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INFORMATION SHEET CITY OF TRACY WASTEWATER TREATMENT PLANT other cities, consideration of recision of Order No. 80-097 will be made after the seven other cities are in compliance. The City discharges treated wastewater to Old River about three miles north- easterly of the City through a diffuser. Recreation in the area consists of fishing and water contact sports of water skiing and swimming, as well as boating. Effluent and Receiving Water Limitations The discharge point is upstream of two major water intake facilities, the Bureau of Reclamation Delta-Mendota Canal and Department of Water Resources Clifton Court Forebay. The major portion of Tracy's diluted discharge is diverted through the Delta-Mendota Canal , which is a domestic water supply source for Tracy. The rest of the discharge is received into the Clifton Court Forebay, which is a domestic water source for much of the State's population. The effluent limits in the permit were developed to protect the use of the surface water as a drinking water supply. The "Water Quality Objectives" for the San Joaquin Delta Basin, contained in the Basin Plan, were reviewed. Compliance with effluent limits and requirements established in this permit will meet those objectives. Effluent limits are based in part on estimates of allowable dilution in Old River, as described in the following paragraph. The permit establishes effluent limits of 20 mg/l each for BODS and suspended matter. The limits are set to protect against the potential for an adverse impact by the discharge on dissolved oxygen in Old River. Seasonal low river flows during July, August, and September, when accompanied by high effluent flows, could impact dissolved oxygen in Old River. Old River flows at Tracy are subject to influences of San Joaquin River flows, local irrigation, municipal , and industrial water demand, pumping at Clifton Court Forebay, and tidal actions. Data on flows in Old River at the City of Tracy diffuser have been estimated using the Department of Water Resources model of the Delta. Effluent limits are partially based on these flow estimates which show a minimum receiving water to wastewater ratio of nearly a 100:1 (monthly basis) . This permit renewal requires the City to monitor the flows in Old River on a daily basis and to report minimum, maximum, and average daily flows. If minimum dilutions are significantly different from the 100:1 estimate, the permit can be reopened and modified. The modifications may include more stringent effluent limits, additional limits not contained in this permit, and the requirement to perform biotoxicity monitoring. In addition, there are proposals to modify the flow regime in the Delta to provide a more complete mix of San Joaquin and Sacramento River waters in the Delta prior to transport of these waters south. These proposals may significantly alter the quantity and quality of water in Old River. The permit contains a provision that allows it to be reopened if flows on which effluent limits have been based are significantly altered.