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Srte Assessment Report and Request for Closure 2 Sears Auto Center No 1288,5110 Pacific Avenue, Stockton,California February 10,2000 in 1994 (Appendix B), and a Request for Closure was submitted to the PHS/EHD in 1999 (Appendix C) 30 GEOLOGY/HYDROGEOLOGY ' Soil beneath the site consists predominantly of clay with fine sand lenses encountered at various depths to 20 feet bgs, the maximum depth advanced during the investigation Groundwater was not encountered in the borings Boring logs from site activities are provided in Appendix D 40 DRILLING METHODS AND SAMPLING PROCEDURES On November 8, 1999, Vironex Environmental Field Services of Hayward, California, sampled six DPT borings (VA-1 through VA-6) The drilling activities were performed under the supervision of IT Corporation The boring locations are shown on Figure 2 The proposed location of boring VA-6, originally located east of the three gasoline USTs, was relocated west of the USTs at the request of the PHS/EHO Pnor to advancing the borings, subsurface drilling permits were obtained from San ' Joaquin County The boring locations were cleared for underground utilities by Subtronic Corporation Soil samples were collected from the bottom of the six borings, which were located within 10 feet of the former USTs and were advanced to native soil beneath the former UST excavations Around the former 1,000-gallon new/used-oil USTs, the DPT borings VA-1 and VA-2 were advanced at a ' 20-degree angle approximately 6 feet from the center line of the former USTs Boring VA-1 was advanced 16 feet (15 feet true vertical depth) and boring VA-2 was advanced 21 feet (20 feet true vertical depth) The borings were advanced in this way in order to avoid an underground concrete slab ' that had once supported the former USTs. Bonngs VA-3 through VA-6 were vertically advanced to a total depth of 12 to 15 feet bgs around the three former 10,000-gallon gasoline USTs Soil samples were collected from a continuous core using Geoprobe®sampling equipment Soil samples were collected using a 4-foot-long sampler lined with a 1 75-inch-diameter acetate tube From each boring interval, the bottom 6-Inch segment of the acetate tube of soil was first cut and then ' capped at each end with a Teflon sheet and plastic cap Each cap was secured ninth sample tape The soil sample was then labeled and placed on ice in an insulated container pending delivery to a state-certified laboratory The cored soil was described using the Unified Sohl Classification System Dnlling logs are provided in Appendix D All sampling equipment was cleaned between sampling intervals with nonphosphate detergent, ' followed by successive rinses of tap and distilled water This method decontaminates the sampling equipment and prevents cross contamination between sampling intervals All DPT borings were abandoned by backfilling with bentonite grout Because the Geoprobe® produces only a narrow boring (2-inch-diameter) using DPT, there were no soil cuttings produced ' 12eeVAR doc rr CoRPORAnaN