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S E C 0 R +
<br /> 76(Former BP)Service Station No. 11193
<br /> SJCEHD
<br /> August 30,2007
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<br /> ATTACHMENT A
<br /> PREVIOUS INVESTIGATIONS AND SITE HISTORY SUMMARY
<br /> In April 1987, Kaprealean Engineering, Incorporated (KEI)observed the removal of one 1,000-
<br /> gallon waste oil underground storage tank (UST) in the southwestern portion of the site. One
<br /> soil sample collected from the base of the excavation at approximately 10 feet(ft)below ground
<br /> surface (bgs) contained gravimetric waste oil as petroleum oil at 55 parts per million (ppm,
<br /> EMCON, 1994).
<br /> Between December 3 and 10, 1992, RESNA performed a preliminary site assessment,which
<br /> involved the drilling of four exploratory soil borings (B-1 through B-4)to total depths of 31.5 to
<br /> 36.5 ft bgs, and converting them to wells MWA through MW-4. While gasoline range organics
<br /> (GRO) and diesel range organics(DRO)were not detected above laboratory method reporting
<br /> limits(MRLs),concentrations of benzene,toluene, ethylbenzene, and total xylenes(collectively
<br /> BTEX) were detected in soil. Concentrations of GRO and BTEX were also detected in
<br /> groundwater,with maximum concentrations of GRO(2,200 parts per billion[ppb])and benzene
<br /> (120 ppb)reported in well MW-1. DRO was not detected in groundwater above laboratory MRLs
<br /> (RESNA, 1993). E
<br /> In March 1994, Alisto Engineering (Alisto)conducted a supplemental subsurface investigation,
<br /> which consisted of the installation of three groundwater monitoring wells(MW-5 through MW-7)
<br /> to total depths of 31 to 32 ft bgs. Relatively minor concentrations of benzene,toluene, and total
<br /> xylenes were detected in soil,while GRO and DRO were not detected in soil above laboratory
<br /> MRLs (EMCON, 1994).
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<br /> On November 22, 1994, EMCON conducted a supplemental site assessment to establish
<br /> baseline subsurface conditions during the transfer of ownership of the property from British
<br /> Petroleum (BP)to COP. The investigation consisted of collecting two grab soil samples(TD-2
<br /> and TD-3)below the north and south dispensers,drilling two soil borings(THP-1 and THP-2)to
<br /> total depths of 26.5 ft bgs, and the drilling and installation of vapor extraction well VW-1 to a
<br /> total depth of 17 ft bgs. Soil and Hydropunch® groundwater samples were collected from
<br /> borings THP-1 and THP-2,and analyzed. GRO,toluene, ethylbenzene,and total xylenes were
<br /> detected in soil at maximum concentrations of 2,100 parts per million(ppm), 3.5 ppm, 18 ppm,
<br /> and 110 ppm. Analysis of soil samples from borings THP-1 and THP-2 indicated maximum
<br /> concentrations of DRO at 1 ppm and benzene at 0.03 ppm. Hydropunch groundwater samples
<br /> contained concentrations of GRO, DRO, benzene, and xylenes up to 6,900 ppb, 840 ppb,1,900
<br /> ppb, and 77 ppb, respectively (EMCON, 1994).
<br /> In February 1995,Alisto conducted baildown testing to evaluate aquifer properties beneath the I
<br /> site. Pumping occurred from well MW-1, generating approximately 1.5 ft of drawdown at an
<br /> extraction rate of 6 gallons per minute(gpm). Alisto concluded that the rapid recovery was likely
<br /> I:IBP-ARC0105 BP-COP Sites1111931Work Plans111193 Vertical Delineation WP.doe i
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