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' Additional Site Assessment Report and Request for Closure z 7-Eleven Inc,Store#17547, 1048 W Yosemite Avenue,Manteca,CA August 13,1999 32 Sod Borings On June 18, 1999, IT Corporation supervised the advancement of five GeoprobeTM points (GP-1 ' through GP-5) at the site(Figure 2) Using a truck-mounted hydraulic drill and direct push techniques, one discrete soil sample was collected from each of the soil borings from 15 feet below ground surface ' (bgs) After completion, the borings were backfilled to grade with bentonite chips(saturated in place), and sealed at grade to match the existing surrounding surface ' All drilling equipment was steam cleaned prior to drilling each boring, and sampling equipment was washed in non-phosphate detergent solution and rinsed with water between sampling intervals All soil and rinse water generated during the drilling was placed in labeled Department of Transportation ' (DOT)-approved 55-gallon drums and left on the site pending transportation and disposal by a licensed waste-hauling firm ' 33 Sod Sample Collection ' Sod samples were collected using a 2-inch O D California split-spoon sampler, lined with three 1 5-inch-diameter by 6-inch-long brass tubes The sampler was driven 18 inches ahead of the push rods at each sample point at 4-foot Intervals starting at 2 feet below grade Soil samples were field screened for hydrocarbon vapors using a photo-ionization detector Soil was logged using the Unified Soil Classification System by an IT Corporation field geologist working under the supervision of a ' California registered geologist(Appendix A) One sample tube from each sampling interval was sealed, labeled, and placed on ice in an insulated container for transport under chain-of-custody to a state-certified laboratory The soil samples were selected for laboratory analysis of BTEX and TPH-G using EPA Methods 8020Imodified 8015, and for MTBE and tert-butanol (TBA), di-isopropyl ether(DIPS), ethyl-tert-butyl ' ether(ETBE), and tert-amylmethyl ether(TAME) by EPA Method 8260 r ' 34 Groundwater Sample Collection Grab groundwater samples were collected at the total depth of each borehole using disposable bailers, ' then transferred to 40-milliliter glass vials filled to zero headspace and acidified to a pH of 2 The samples were sealed using Teflon&septum caps, labeled, placed on ice In an insulated container, and ' transported under chain-0f-custody to a state-certified laboratory The groundwater samples were , analyzed for BTEX and TPH-G using EPA Methods 8020/modified 8015, and for MTBE, TBA, DIPS, ETBE, and TAME by EPA Method 8260 The sample from boring GP-5 was also analyzed for ethylene ' dibromide (EDB)and 1,2-dichlorethane (1,2-DCA) by EPA method 8260 r , I I I 1 I I r I II