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' t' { � r 15 April 1996 E '• AGE-NC Project No 95-0121 Page 2,of 9 , r 23 ASSESSMENT OF HYDROCARBON-IMPACTED SOIL AND GROUND WATER A total of nineteen soil bonngs were advanced at the site between May 1989 and December 1994, nine of the borings were completed as two-inch diameter monitoring wells (MW-1 through MW-9) Extensive hydrocarbon-impacted soil and ground water;including free product, was encountered ' during assessment of the site In July 1995, one dual-purpose soil vapor extraction/ground water extraction well (EW-1), and two soil vapor extraction wells(VW-1, VW-2) were installed at the site In August 1995, an 8-hour soil ` vapor extraction (SVE)test was conducted at the site The pilot test was performed to provide vapor extraction data for proper system design of a remediation system Details of the S VE pilot test were ' included in the Corrective Action Plan (CAP), dated 14 November 1995, prepared by AGE Recommendations in the CAP included installation of an SVE system to remediate hydrocarbon- ' impacted soil and an in-situ air sparging (IAS) system to remediate hydrocarbon-impacted around water 24' REGIONAL GEOLOGIC,SETTING ' The subject site is located in the eastern portion of the Great Valley geomorphic province of California The valley is a nearly flat, elongate trough trending northwest and southeast for approximately 450 miles The Valley is enclosed by the igneous Sierra Nevada to the east and the ' sedimentary and metamorphic Coast Ranges to the west The surficial and upper several hundred feet of subsurface layers consists of a great thickness of predominantly unconsolidated alluvial and ' floodplain deposits (dominantly sands, silts, and clays) of Quaternary age, which are derived from the predominantly granitic mountains of the Sierra Nevada Beneath the upper sedimentary deposits ire a thick sequence of marine deposits of Mesozoic age These units are further underlain by a pre- Jurassic complex of igneous and metamorphic basdment rock 3 2 5 GROUND WATER DEPTH AND FLOW DIRECTION The water-table surface beneath the site; has fluctuated from 'approximately 21 feet bsg to approximately, 33 feet bsg between 1991 'and 1996 The uppermost ground water flows in a unconfined aquifer With increasing depth, the aquifer becomes semi-confined due to the presence , of mixed heterogeneous layers of sediments ` Ground water surface elevation contour maps published by the San Joaquin County Flood Control and Water Conservation District indicate thataregronal ground water flow is towards the northeast r r ,