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Report on Additional Site Assessment and Sod Vapor Extraction Testing 3 7-Eleven Store No 20632,4627 Da Vinci Drive Stockton,CA August 14 2002 Q13 Soil Sample Collection Soil samples from soli boring SB-1 were collected continuously from 5 to 30 feet bg Samples from 20, 25, and 30 feet bg were submitted for analysis With the (verbal) approval of Mr Harlin Knoll of the SJCPHS, soil samples were not collected from MW-4R, due to the close proximity of the well to boring SB-1 Soil samples from wells MW-6, MW-7, SPV-1, and SPV-2 were collected continuously from 5 to 15 feet bg, and samples from the 10- and 15-foot bg depth intervals were analyzed All samples to be analyzed were sealed using Teflon septum caps, labeled with the job identification number, the sample number, date, and sampler name The samples were stored on ice and transported with a chain-of-custody record to a state-certified laboratory for analysis Soil samples were analyzed for BTEX, and TPH-G using EPA Method 8015/8020 and for MTBE, TBA, DIPS, ETRE, TAME, ethylene dibromide (EDB), and 1,2-dichloroethane (1,2-DCA) using EPA Method 8260 Copies of the drilling logs can be found in Appendix A 34 Groundwater Sample Collection Groundwater samples at depths of 30 and 40 feet bg were collected from boring SB-1 using a hydropunch to vertically delineate the hydrocarbon plume in the source area Groundwater samples were collected into 40-milliliter vials, filled to zero headspace, acidified to a pH of 2, capped, labeled, and placed on ice for transport to a state-certified laboratory under legal chain-of-custody The samples were analyzed for BTEX and TPH-G by EPA Method 8015/8020 and for MTBE, TBA, DIPS, ETBE, TAME, EDB, and 1,2-DCA by EPA Method 8260 40 RESULTS 41 Geology aThe relatively level site is located at an elevation of approximately 2 feet above mean sea level According to the California Division of Mines and Geology (Jennings, 1977), the site is underlain by Quaternary alluvial deposits The material encountered during recent drilling at the site generally consisted of alluvial clayey silts and silty clays with lenses of clayey silt and very fine-grained sand at about 12 to 15 feet bg and below 28 feet bg During drilling, groundwater was encountered at aapproximately 12 feet bg Historically, groundwater levels have fluctuated between about 5 and 8 feet bg 20632sardoc