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i <br /> 1 Van Buskirk Park Golf Course TL No. A68101.02 <br /> March 10, 1995 Page 2 <br /> ' 3.1 Site Description <br /> 1 The Van Buskirk Park Golf Course is located at 1740 Houston Avenue in the southwest <br /> portion of the City of Stockton, California. The maintenance yard is located in the south <br /> central portion of the golf course on the north side of Walker Slough (Drawing 1). <br /> 3.2 Geologic and Hydrologic Characteristics <br /> 3.2.1 Geology+ <br /> The site is located in the northern portion of the San Joaquin Valley which comprises the <br /> ' southern segment of the larger Great Valley. The Great Valley is an asymmetrical synclinal <br /> trough interrupted by two major surface cross structures: the Stockton fault in the Stockton <br /> arch and the White Wolf fault in and south of the Bakersfield arch. The Stockton fault is <br /> located approximately 1/4 mile northwest of the site, trending northeast. <br /> The Great Valley has been filled with a sequence of older to younger alluvium of Pliocene <br /> to Holocene age which overlie sedimentary rocks of Cretaceous to Tertiary age. These <br /> sedimentary units, in turn, overlie a crystalline basement of Paleozoic and Mesozoic <br /> metamorphic and igneous rocks. The shallow subsurface geology in the site vicinity consists <br /> of a heterogeneous mix of gravel, sand, silt, and clay (Norris and Webb, 1990). <br /> ' 3.2.2 Hydrolo�v <br /> Sediments containing fresh groundwater are largely unconsolidated silts and sands derived <br /> from river channel, flood plain, and-alluvial fan deposits of Pliocene to Recent age (Davis <br /> and others, 1959). <br /> ' First encountered groundwater in the site vicinity occurs under unconfined (water table) <br /> conditions at a depth of approximately 14 feet below site grade (BSG) and flows to the <br /> north (Twining, 1994a,b,c, 1995). <br /> Local groundwater flow may be influenced by pumping of water wells and recharge from <br /> various sources. The effect of these influences on groundwater beneath the site is beyond <br /> the scope of this investigation. <br /> 3,3 Project History j <br /> ' Twining understands that a 550-gallon gasoline UST was removed from the site in April <br /> 1991 Analysis of a soil sample collected from approximately four feet BSG in the vicinity <br /> of the former dispenser detected 350 milligrams per kilogram (mg/kg) TPH-G and 7,200 <br /> mg/kg TPH-D. Twining also understands that a 1,000-gallon diesel UST was removed in <br /> January 1994. Analysis of a soil sample collected from approximately 11 feet BSG at the <br />