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1 <br /> 13 <br /> 3 GEOLOGIC AND HYDROGEOLOGIC SETTING <br /> i <br /> Geologic and hydrogeologic conditions at this facility were originally described in <br /> ACG's December 19, 1991, Problem Assessment Report ACC's geologic descriptions, <br /> summarized below, are supplemented with information from installation of these new <br /> monitoring wells <br /> ' 3.1 Regional Geologic Setting <br /> ' The Earth Grains facility is situated within the north-central portion of the Central <br /> Valley geomorphic province, which is bounded to the west by the Coast Range province and <br /> by the Sierra Nevada province to the east Thousands of feet of sedimentary strata in the <br />' Central Valley, resulting from erosion of the adjacent mountain ranges, overly Mesozoic- <br /> aged granitic basement rock <br /> Surficial material at Earth Grains consists of Holocene (less than 10,000-years old) <br /> fluvial deposits that formed in accordance with erosional and depositional processes related to <br />' the San Joaquin River Holocene sediments are generally flat-lying, unconsolidated, and <br /> fine-grained Holocene sediments, approximately several hundred feet thick in the middle of <br /> the Central Valley, overlie Pleistocene alluvium <br /> 3.2 Site Geology <br />' The near-surface geology at this facility, to the maximum explored depth of 75 feet <br /> BGS, consists of interbedded, discontinuous sequences of fine-grained sand, silt, and clay <br /> Subsurface strata are detailed on the geologic borehole logs (Appendix A), and illustrated on <br /> Geologic Cross Sections AW, B-B', A-B, and C-C' that are on Figures 4, 5, b, and 7, <br />' respectively The cross section locations are shown on Figure 3 <br /> 04/94/121382/125997/STOCKREP REP/1 <br />