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23 June 1998 - AGE-NC Project No. 97-0349 Page 2 of 5 valley is a nearly flat,elongate trough trending northwest and southeast for approximately 450.miles. e,. The valley is enclosed by the granitic Sierra Nevada on the east and the sedimentary and metamorphic Coast Ranges on the west. The nearly flat-laying 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 frgm the mountains of 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 `y basement rock. ' `y 2.4. GROUND WATER DEPTH AND FLOW DIRECTION The estimated depth to ground water at the site is 50 feet below surface grade (bsg) based on. information from Lines of Equal Depth of Water Wells Fall 1993, published by the San Joaquin County Flood .Control District -.and Water Conservation District and ground water depth �., measurements in monitoring wells located approxim_ately.400 feet north and'200 feet south of the site (Re-Manufacturing). Ground water flow direction, as determined from the Re-Manufacturing site, is south-southeast. . However, due to local seasonal variations flow direction may vary. The uppermost ground water flows in an unconfined aquifer..With increasing depth, the aquifer becomes semi_confined, due to the presence of fine of sediments: 3.0. PROCEDURES 3.1. PROBING AND SAMPLING LM s One soil probe boring (PB 1)was advanced at the site, under the observation of a representative of �. the PHS-EHD..On 21 August.1997,probe boring PB 1 was advanced in the former UST area to a depth of 65 feet bsg. Location of the soil probe boring is illustrated on-Figure 2. Soil samples were collected from each boring at five-foot intervals, beginning at a depth of 5 feet bsg and continuing to a depth'of 50 feet bsg, using a Geoprobe soil sampling assembly and four brass sleeves. Samples were collected using a 2.15-inch diameter,two-foot long;piston-type sampler `y loaded with four pre-cleaned 1.375-inch by 6-inch brass sleeves.'The sampling equipment was washed in an Alconox solution and rinsed with water prior.to,each sampling run to prevent cross- contamination.After collection,the ends of the second brass sleeve were covered with Teflon sheets, capped and sealed with tape. Samples were placed in a chilled container under ice and transported to McCampbell Analytical, Inc, (MAI)under chain-of-custody. Advanced GeoEnvironmental,Inc.