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Ms. Mary Meays December 20, 1995 (9347-3011) Background The following brief discussion of the site background is based, in part, on information from reports prepared by others: Underground Storage Tanks(USTs): One used oil UST and four 4,000-gallon steel gasoline USTs were installed at the site in 1955. In 1963, one 4,000-gallon UST was removed and two 7,500-gallon gasoline USTs were installed at the site. The five remaining gasoline USTs were removed in 1981 (RESNA, 1991x) and the used oil UST was removed in 1991 (SJCPHS/EHD, 1993). Soil Borings: Soil gas samples were collected from 15 sampling points during a soil gas survey performed at the site in May 1990. Petroleum hydrocarbons were detected in the soil gas samples collected in or near the former gasoline UST cluster(Meinfelder, 1990). A total of 1 offsite and 20 onsite soil borings were drilled and sampled at the site between September. 1990 and November 1991. The highest concentrations of total petroleum hydrocarbons as gasoline (TPH-G) were detected at 5,100 and 14,000 parts per million (ppm) in the soil samples collected from borings SB-3 and MW-2, respectively. Benzene was detected at up to 0.9 ppm in the soil sample collected from boring SB-3. The bulk of the adsorbed-phase petroleum hydrocarbon mass in the subsurface soil was detected in the soil samples collected from the borings in the immediate vicinity of the former UST cluster. The subsurface soils beneath the former UST cluster and eastern dispenser island are penetrated by vapor extraction wells connected to the VES (RESNA, 1992a). Nude additional borings were drilled and sampled at the site in September 1992 after the VES had operated continuously for approximately 6 months. TPH-G was detected at up to 4,600 ppm only in soil samples collected from borings CBS and CB9. Benzene was not detected above reported laboratory detection limits in any of the samples collected and analyzed from the nine additional borings. TPH-G and benzene, toluene, ethylbenzene, and total xylenes (BTEX) were not detected above reported laboratory detection limits in the soil samples collected from boring CBI which was drilled approximately 7 feet northwest of well MW-2 (RESNA, 1992a). TPH-G was detected at up to 14,000 ppm in the soil samples collected from boring MW-2 in September 1990. Results of this preliminary investigation indicated that the confirmation boring event was premature, but the VES was effective in reducing the volume of petroleum hydrocarbons in the subsurface soil during the limited duration of VES operation. Soil sampling results are summarized in Table 1. t� 9347301 LBRP -2-