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4.6 WATER RESOURCES Water in Tracy Lakes provides beneficial uses such as groundwater recharge and seasonal wetlands for wildlife habitat. Water in Tracy Lakes is currently not used for water supply. In fact, since 1940, any accumulated runoff in the lakes has been drained and/or pumped from the lakes into the Mokelumne River to allow dry farming of the lake bed. The nearby Mokelumne River is a proposed water source for the development. Water from this river is used primarily for agricultural and drinking water supplies, as well as supporting in-stream fisheries wildlife habitat, and recreational uses. Diversions upstream of the project site provide water for the San Francisco Bay Area and for numerous farmers in the Central Valley. Drinking water supplies are stored in Camanche Dam and agricultural water is diverted from the river at numerous locations;the closest is at Woodbridge,a few miles upstream of the project site. The water quality of the Mokelumne River is ve ry good and is suitable for all existing and potential beneficial uses as shown in the recent water quality test data (Table 4.6-2). Groundwater Resources Groundwater is a major source of water in San Joaquin County. Groundwater supplies farmers and other users with a reliable source of water from year-to-year. However, this resource is not inexhaustible; there is a limit to the amount of water available for consumption. Currently the aquifer in San Joaquin County is undergoing an overdraft of approximately 200,000 acre-feet per year (Pulver, 1991). There are two existing wells on the project site, one immediately adjacent to the Mokelumne River and another along the northern border of the project site. Groundwater on the site is currently used for agriculture and/or livestock. The historical use of these wells is roughly estimated at 130 to 190 acre-feet per year, based on irrigation requirements for 65 acres at two to three acre-feet/acre of irrigation (Verdegaal, 1992). Little or no groundwater data, with respect to quantity or quality, are available for the project site and surrounding areas of the County (Beatermann, 1991). However, according to well drillers in the area, groundwater can usually be found at depths of 40 to 50 feet in areas away from the Mokelumne River, and 10 to 15 feet deep immediately adjacent to the river. Twelve to fourteen-inch diameter wells drilled in the area commonly produce 600 to 800 gallons per minute from a 200-to 260-foot well. Although site specific yields may differ, these are general trends for the area. Due to the agricultural land uses in the vicinity of the project, there is a concern of possible high concentrations of nitrates and Dibromochrolopropane(DBCP). Nitrate concentrations in groundwater are often increased by the use of land-based wastewater disposal, and by the application of nitrogen-based fertilizers. DBCP is an agricultural pesticide which is no longer in use, and it has contaminated the groundwater in numerous areas within San Joaquin County. 4.6-5