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1 <br /> 1110/71-51-1C <br /> 3 4 AREA GEOLOGY <br /> The subject site is located in the Great Valley, also known as the Central Valley, a <br />' California physiographic province It is a nearly flat alluvial plain Elevations of the alluvial <br /> plain are generally just a few hundred feet above sea level The site is in San Joaquin <br /> Valley, a central portion of the Great Valley The area drains to north by San Joaquin <br />' River which, after joining with Sacramento River about 30 miles east of San Francisco, <br /> empties into San Francisco Bay (Hackel, 1966) <br />' The Great Valley has been filled with a thick sequence of sedimentary rocks of Jurassic <br /> to Recent Age The sedimentary sequence rests on a basement floor of metamorphic <br />' and igneous rocks <br /> The site is located in geomorphic unit called the low alluvial plain and fans Low alluvial <br />' plains and fans that border the dissected upland along their valleyward margins are <br /> generally flat to gently undulant and are underlain by undeformed to slightly deformed <br /> alluvial deposits of Pleistocene and Recent Age (Poland and Evenson, 1966) <br /> 3 5 AREA HYDROGEOLOGY <br /> The deposits containing fresh groundwater are principally unconsolidated continental <br /> deposits of Pleistocene to Recent Age that extend to depths ranging from less than a <br />' hundred to more than 3,500 feet The unconsolidated continental deposits consists <br /> chiefly of alluvium but in some areas include widespread lacustrine and marsh or <br /> estuarine sediments Groundwater occurs under both confined (artesian) and unconfined <br />' (water table) conditions in the Central valley The degree of confinement varies widely <br /> because of the heterogeneity of the continental deposits In the big alluvial fans on the <br /> east side of the San Joaquin Valley, the groundwater is unconfined (Poland and Evenson, <br /> ' 1966) <br /> ' 3 6 SITE GEOLOGY AND HYDROGEOLOGY <br /> Woodward Clyde Consultants investigated the site in April 1990 by installing five <br /> monitoring wells labelled as MW-5 through MW-9 and one sod boring tagged as S-5 The <br /> maximum depth of exploration for the monitoring wells was seventy feet Soils <br /> penetrated by drilling consisted primarily of clay, clayey silt and silty clay, with lesser <br /> ' amount of silt, sandy silt, sand and clayey sand to depth 52 to 55 feet From 55 feet to <br /> total depth, the sods consisted generally of poorly graded fine grained sand Groundwater <br /> 9 <br />