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Site No: 11192 930 ppm). All three stockpiles (approximately 1,750 cubic yards) were disposed at the Vasco Road Class IH landfill in Alameda County (IT, 1991a). IT installed three new groundwater monitoring wells (MW-5 through MW-7), two vadose wells (VW-1 and VW-2), and a soil vapor collection system from April through August 1991 (IT, 1991b; Figure C-5). Boring logs indicated that the shallow subsurface beneath the site was composed of clays and silts with lesser amounts of sand and gravel. Groundwater was encountered between 35 and 36 feet bgs. Groundwater was determined to flow north under an approximate hydraulic gradient of 0.005 (IT, 1991b; Figure C-5). Soil samples were collected and analyzed for TPH-G and BTEX. TPH-G (550 ppm) was detected in a sample taken at 11 feet bgs during the drilling of VW-2 (Table C-5). BTEX (up to 0.70 ppm benzene, 0.26 ppm toluene, 9.8 ppm ethylbenzene, and 24 ppm total xylenes) also was detected in soil samples from boring VW-2. Up to 0.03 ppm benzene was detected in soil samples collected during the drilling of well MW-7. Analysis of groundwater samples collected from wells MW-5, MW-6, and MW-7 in August 1991 revealed a concentration of 70 ppb TPH-G in the sample from well MW-7, • located downgradient of the former fuel UST complex (Table C-3). Benzene (19 ppb) was also detected in a groundwater sample from well MW-7. IT collected groundwater samples from wells MW--5 through MW-7 on December 9, 1991, and submitted them for analysis for TPH-G and BTEX (IT, 1991c). IT did not collect samples from MW-1, MW-3, or MW-4 because they had not contained water since February 1991 (IT, 1991c). Benzene (19 ppb) and ethylbenzene (1.2 ppb) were detected in samples taken from well MW-7 (Table C-3). IT attempted HydroPunch"m drilling at eleven locations (HP-1 through HP-11) at the site in February 1992; only three locations. (HP-1, HP-5, and HP-6) yielded water for sampling (Figure C-6; IT, 1992a). These groundwater samples were analyzed for TPH-G and BTEX. TPH-G (380 ppb) was detected in the sample from HP-5, located east of the former fuel UST complex (Table C-6). BTEX (8.4 ppb benzene, 0.90 ppb toluene, 1.4 ppb ethylbenzene, and 5.7 ppb xylenes) was also detected in groundwater samples from HP-1, located southwest of the former fuel UST complex, and from HP-5. IT conducted a soil vapor extraction (SVE) pilot test on January 21, 1992, using horizontal collection piping, vadose wells, and monitoring wells installed during tank backfill and subsequent investigative activities (IT, 1992b). IT concluded that a vapor extraction system connected to the existing perforated pipe stub out would significantly mitigate volatile gasoline hydrocarbons from the soil (IT, 1992b). B/TOSIRP'PI11192RPr.d07-94ILAM116:5 Rev.0, 12127194 0952-090.03 4