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.. .Ole 26 February 1996 AGE-NC Project No. 95-0152 Page 2 of 6 2.3. REGIONAL GEOLOGIC SETTING The subject site is located in the eastern portion of the Great Valley geomorphic province of California. The valley has low topographic relief, and is an elongate 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 surficial and upper several hundred feet of subsurface layers consist primarily of unconsolidated alluvial and floodplain deposits (predominantly sand, silt, and clay) of Quaternary age, which were derived from the Sierra Nevada. Beneath 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. 2.4. GROUND WATER DEPTH AND FLOW DIRECTION According to the San Joaquin County Flood Control and Water Conservation District map entitled �. Lines of Equal Elevation of Water Wells-Fall 1993,ground water depth at the site is approximately 75 feet below surface grade (bsg). Regional ground water flow direction in the area of the site is southwest. 3.0. PROCEDURES v. 3.1. EXCAVATION OF HYDROCARBON-IMPACTED SOIL " On 21 September 1995, approximately 40 cubic yards of hydrocarbon-impacted soil was excavated from the former gasoline UST area. Soil was excavated using an backhoe. The backhoe and operator were provided by Stokley Construction (Stocon) of Tracy, California. The excavated area was ` approximately 10 feet in length, 10 feet in width and extended to a depth of approximately 11 feet bsg. During excavation, soil was screened for the presence of organic vapors (OVs) using a photo- ionization detector(PID: Thermo Environmental 580A; 10.0 eV; calibrated to isobutylene). Based upon field screening techniques, excavated soil was segregated on-site into "clean" and"impacted" stockpiles. ,. Soil samples were collected from the sidewalls and floor of the excavation at the direction of representatives of the PHS-EHD. Each sample was collected from the backhoe bucket using a metric soil sampler preloaded with two clean 2-inch by 3-inch brass sleeves. After collection, the ends of the lead sample sleeve were covered with Teflon sheets, capped and sealed with tape. Each lead sample sleeve was labeled with the following information: boring location, depth, time, date and sampler's initials. Analytical results are summarized in Table 2.