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ARCO AM/PM building, two pump islands, and four newly installed, double-wall 10,000-gallon <br /> fiberglass USTs located in the same area as the removed tanks. <br /> 3.0 GEOLOGY AND HYDROGEOLOGY <br /> The Site is located in the San Joaquin Valley ey of California The San Joaquin Valley, which is <br /> ' the southern half of the Central Valley, is a long, narrow basin filled with as much as 13,000 <br /> vertical meters of Cretaceous, Tertiary, and Quaternary marine and continental sediments <br /> ' (Moxon and Graham, 1987). Shallow subsurface deposits in the valley generally consist of a <br /> heterogeneous mixture of clay, silt, sand, and gravel The Site is underlain by Quaternary <br /> ' alluvium mapped as the Lower Member of the Modesto Formation, composed of poorly sorted <br /> stream channel and flood plain deposits which include clay, silt, and sand layers with <br /> conglomerate lenses (Wagner et al , 1987). <br /> Native soils encountered in excavations completed at the Site during tank replacement activities <br /> and previously drilled soil borings at the Site consist predominantly of interbedded silt and sand <br />' to the explored depth of 75 ft. bgs Ground water at the Site occurs at a depth of approximately <br /> 65 ft bgs (RESNA, 1992) <br />' 4.0 TANK EXCAVATION, REMOVAL AND SAMPLING <br /> This section describes the following activities• <br /> • tank removal, <br />' soil sampling below removed tanks, <br />' soil sampling below removed product lines, <br /> • installation of new USTs and conductor casings, and <br /> • laboratory analyses <br /> A chronological summary of Site environmental activities is provided in Appendix A. <br /> ROM assocaTES,mr.. ® 2 Doc #A 158W01 17 <br />