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2.0 GEOLOGY AND HYDROLOGY ' 2.1 Regional Geology The subject site lies west of the city of Lodi, in the Sacramento/San Joaquin Valley (Central ' Valley) The Central Valley is one of the chief geomorphic features in central California, a large, asymmetrical northwest trending trough The Valley's shape controls the occurrence and movement of ground water in the region In the Lodi area, ground water flows generally to the ' Mokelumne River, although flow is greatly affected by pumping for irrigation (San Joaquin County Flood Control, 1990) Regional stratigraphy consists of continentally derived rocks (Tertiary) and Quaternary to Tertiary soil deposits The sediments have been derived from weathering along the western bank of the Sierra Nevada Lodi and the site vicinity lies on older alluvium of Pleistocene age, which ' has been dissected by the present Mokelumne River (Page, 1986) The alluvium is a heterogeneous mix of materials, in the Lodi area chiefly sands, with finer material (silts and clays) and gravel mterbeds In the site and vicinity the sediments form a low terrace that slopes ' gently away from the river's flood plain 2.2 Regional Hydrology ' In the region, ground water flow is to the north, towards the topographic low of the Mokelumne River Data available from San Joaquin County Flood Control District (1990) for spring ' measurements (March 1990) indicate depth to regional ground water at approximately 30 feet 2.3 Local Hydrology, Precipitation, and_Water Usage ' In September 1990 ESE conducted a well survey for wells within an one-mile radius of the site p Y through the California Department of Water Resources (DWR) At that time, a total of fifteen ' wells existed in the one-mile radius of the site Seven of these wells are used for domestic purposes, one is a municipal well, five are irrigation wells, and two of these wells are used for ' unknown purposes The well numbers, addressess, and uses are listed in Table 1 - Vicinity Well Data Their location in relation to the site are presented in Figure 4 - Site Vicinity Wells ' Based on the ground water monitoring wells at the site, ground water flow, at the site, is approximately south-southwest There are no downgradient well locations within one mile of the site Of the canvased well locations, those nearest the site are two on-site AT&T wells; both ' are crossgradient of the former tank excavation and are used for industrial processes The nearest off-site well is located upgradient at the Mainland Nursery ' The climate in the Central Valley is of Mediterranean type (hot summers/mild winters) (Williamson, et al, 1989) Annual precipitation averages between five and 26 inches per year (Bertoldi, et al, 1991) Most of the annual precipitation occurs between November and April, ' making summers hot and winters are moderate allowing a long growing season ' F 164351861CLOSURE RPT 4 Envaromnental Science&Engineering Inc