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tA� PRELIMINARY HYDROGEOLOGIC ASSESSMENT WORK PLAN 1999 E.Yosemite Avenue,Manteca,California Delta Project No.40-88-480 Page 9 3,4 Lyell Inventgr_y There are no known domestic wells in the vicinity of the site. However, in order!o more thoroughly document the presence of wells near the site, a well inventory has been initiated at the Department e.a of Water Resources in Sacramento, California. Results of this inventory will be reported in the Preliminary Hydrogeologic Assessment Report that will be suhmitted following completion of the activities described in this work plan. �.5 LAIlties The location of any city utilities located adjacent to or at the sitc- will be verified with the City of Manteca Public Works Department prior to commencement of field activities at the site. 3.6 Regional Geology Manteca,California,is located within the Great Central Valley Geomorphic Province of California. The Central Valley Province is bordered to the east by the Sierra Nevada Mountains and to the west r . by the Coast Ranges. Surficial geology in the Manteca area consiats primarily of recent alluvium and the Victor Formation, Both units consist of discontinuous lenses of gravel, sand, and clay. The combined thickness of both units typically does not exceed about 150 feet. T The Victor Formation underlies recent alluvium(where present)and occurs as a band approximately 15 miles wide in the east central portion of the county and extends the entire length of the county. The Victor Formation dips gently to the west, where it interfingers and blends with the flood basin "' deposits about 3 miles west of Manteca. A generalized stratigraphic column of the geologic units present in San Joaquin County is presented in.Table 4. 3.7 Site Geoloev Based on information provided by the four soil borings drilled by ETS (Section 2.1), subsurface materials at the site consist primarily of medium- to coarse-grained and silty sand with minor amounts of micaceous silt. Following completion of the activities described in this work plan k� hydrogeologic cross-section(s) of the site will be prepared and presented in the Pre.'iminary Hydrogeologic Assessment Report. 3.8 round bVater Flow The direction of ground water flow within the uppermost water-bearing zono at the site has not been �. defined at this time. However, because of the change in elevation from about 45 feet above mean sea Ievel(ft ms1)at the site to less than 15 ft msl at the San Joaquin River, located about five miles K,