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a a:w DU POW Bi0S\-,tt`11JS Page 9 August 10, 1989 Job No. 211-71-6 A geologic cross section, included in the C-<,fornia Department of Water Resources Bulletin 146 (1967), shows the alluvial deposits are uno, 'yin by a relatively thick sequence of continental- derived sediments which include the Victor Formation (Pleistocene-age) and the Plio-Pleistocene Laguna Formation. The volcanic and volcaniclastie Mehrten Formation of Miocene to Pliocene- age underlies the Laguna Formation at a depth of approximately 800± feet. The U.S.G.S. Open File Report 82-737 (by Harwood and Helley, 1982), showing depth to basement bedrock in the Sacramento Valley, indicates that bedrock beneatl, the project site is located at an elevation of approximately-2,400 meters(-7,870 f feet). U.S.G.S. Water Resources Investigation Report 45- 73 by R.W. Page shows that the base of the post-Eocene continental deposits lies at a depth of approximately 2,500 feet. The Douglas Gas Station is located in the north-central portion of the Eastern San Joaquin County Ground Water Basin as shown in California Department of Water Resources Bulletin 118-80 (1980), The San Joaquia County Ground Water Basin is traversed by the Stanislaus River (southern boundary cf the basin), the Calaveras River, the Mokelumne River(northern boundary of the basin),and several other smaller surface streams which drain in a westerly direction towards the San Joaquin River(the western boundary of the basin). The nearest major sources of ground- water recharge to the project site are the Mokelume River,located about 13/4 miles to the north, and a number of percolation basins and the South Main Canal (located about 1 3/4 miles to the west), c In the Lodi area the large production water wells are screened within the alluvial deposits, the Victor Formation,and the Laguna Formation. The overall permeability of these units is considered fairly high (California (Department of Water Resources Bulletin 146, 1967). Sand and grave! deposits have the highest transmissivities and are the main water-bearing units; the Sat and clay layers generally have lower transmissivities. Ground water in this area is generally unconfined or semi-confined (CDWR Bulletin 146, 1967). The elevation of ground water, as indicated on the Regional Ground-Water Map (Figure 4), is shown to be at approximately mean sea level (MSL). This map was prepared by the California s,. Department of Water Resources for water levels measured during the spring ^f 1980. Earlier potentiometric maps for 1950 and 1964 show the;around water elevation in the site vicinity to be 10 feet MSL and 0 feet MSL,respectively. These three California Department of Water Resources maps show the regional ground-water gradient at the site is directed to the south, towards the City of Stockton where the ground water is subjected to extensive pumping and withdrawal (CDWR Bulletin 146). Water Well Locations We contacted the State Department of Water Resources(Betty Swatsenbarg)regarding production "� wells(domestic and irrigation wells)located in the adjacent area and reviewed well data presented