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1 <br /> GRANITE CONSTRUCTION FACILITY <br /> WKA No 2088 08 <br /> August 18, 1999 <br /> Page 2 <br /> Ph sio�aphic and Hydro�eologic Setting <br />' The site is located in the central portion of the Great Valley geomorphic province of California <br /> The Great Valley is bounded by the mountains and foothills of the Sierra Nevada Range to the <br />' east and the California Coast Ranges to the west The Geologic formations of the Great Valley <br /> are typified by thick sequences of alluvial sediments deposited during the filling of a large <br /> ancient basin. The 1985 United States Geological Survey(USGS) "Geologic Map of the Late <br /> Cenozoic Deposits of the Sacramento Valley and Northern Sierra Foothills, California," shows <br />' the site to be underlain by Holocene age basin deposits These deposits consist primarily of fine- <br /> grained silt and clay These conditions are consistent with those encountered during our drilling <br />' investigations Specifically, subsurface soils at the site primarily consist of silty fine sands to a <br /> depth of approximately 5 feet underlain by clayey silts with lenses of silty sands to the bottom of <br /> the borings <br /> The site lies within the San Joaquin River Ground Water Basin(California Department of Water <br /> Resources, 1985) Groundwater measurements made during our previous field investigations <br /> and quarterly monitoring events have found groundwater depths ranging from 24 to 31 feet <br />' below ground surface (BGS) and a flow direction generally toward the northwest (Plate No 4) <br /> Site History <br /> On April 22, 1992, five USTs consisting of one waste oil (500 gallons), two diesel (12,000- and <br /> i20,000-gallons), and two unleaded gasoline (both 10,000-gallons) with associated dispenser <br /> islands were removed from the site under permit and inspection of the San Joaquin County <br />' Public Health Services (SJCPHS) The waste oil UST was removed from the eastern side of the <br /> construction maintenance facility The remaining diesel and unleaded gasoline USTs were <br />' removed from the central portion of the site (Plate No 2) Analysis of soil samples collected <br /> beneath the USTs revealed detectable concentrations of Total Petroleum Hydrocarbons (TPH) as <br />' gasoline, diesel, motor oil, and BTEX constituents Analysis of samples obtained beneath the <br /> former UST product lines and dispenser islands revealed moderate concentrations of TPH as <br /> gasoline, TPH as diesel, and benzene, toluene, ethylbenzene, and xylenes (BTEX) <br /> `dW <br />' WALLACE KUHL <br /> Re,yded Dat— Cr ASSOCIATES INC <br />