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I30 December 1997 • AGE-NC Project No 97-0343 IPage 2 of 6 I TPH-d and xylene were detected in the soil sample at concentrations of 3,000 parts per million(ppili) and 0 188 ppm, respectively Benzene and toluene were not detected above the analytical method reporting limit of 0 010 ppm Based upon results of the soil sample analysis, the PHS-EHD required Iassessment of the lateral and vertical extent of hydrocarbon-impacted soil and/or ground water in the area of the former UST I 2 3 REGIONAL GEOLOGIC SETTING The site is located in the eastern portion of the Great Valley geomorphic province of California The valley is a nearly flat-lying, elongated trough trending northwest and southeast for approximately 450 miles The valley is enclosed by the granitic Sierra Nevada on the east and the sedimentary and metamorphic Coast Ranges on the west The surfieial and upper several hundred feet of subsurface layers consist primarily of unconsolidated alluvial and floodplain deposits (predominantly sand, silt, l and clay) of Quaternary age, which were derived from the mountains of die Sierra Nevada Beneath I the upper sedimentary deposits lie a thick sequence of marine deposits of Mesozoic age, which in turn are underlain by a pre-Jurassic complex of igneous and metamorphic basement rock I • 2 4 GROUND WATER DEPTH AND FLOW DIRECTION The estimated p depth to round water at the site is approximately 60 feet below surface grade (b-,g)) P g based on information from Lines of Equal Depth of Water Wells Fall 1996, published by the San IJoaquin County Flood Control District and Water Conservation District I Based upon data collected from monitoring wells approximately 1/8 mile south of the site in July 1996, ground water was at a depth of approximately 55 feet bsg and had an inferred southerly flow direction, however, flow directions may be both locally and seasonably variable The uppermost I ground water flows in an unconfined aquifer With increasing depth, the aquifer becomes semi- confined, due to the presence of fine-grained strata The Stockton Diverting Canal is located adjacent to the site, however, the canal usually contains little water and does not appear to have a significant effect upon ground water depth or flow direction in the area I I Ads anted GeolEnvironmenlal,Inc I