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t ; <br /> Quarterly Monitoring Program and Remedial System Report(Q2/2000) 2 <br /> Ranch Market,23569 Santa Fe Road,Riverbank,California May 1,2000 <br /> Soil and Groundwater Assessment <br /> In January 1998 soil boring B-1 was advanced into the former tank pit to a depth of 30 feet bgs <br /> Analyses of soil samples collected from soil boring B-1 at 20, 25 and 30 feet bgs showed a <br /> decline in total purgeable hydrocarbon as gasoline (TPHg) concentrations from 4,140 milligrams <br /> per kilograms (mg/kg) at 20 feet to 6 mg/kg at 30 feet (Table 1) A grab water sample was also <br /> collected from boring B-1 that contained elevated concentrations of benzene, toluene, <br /> ethylbenzene, xylenes and TPHg (Table 2) <br /> In November 1998, four groundwater monitoring wells were installed at the site MW-1 in the <br /> former tank pit and MW-2, MW-3, and MW-4 centered around the former tank pit (Figure 2 and <br /> Table 2) Soil samples collected at 15, 20, 31 and 35 bgs contained reportable concentrations of <br /> BTEX and TPHg Samples collected from MW-2 at 20 feet bgs contained the maximum <br /> concentrations of benzene, 183 mg/kg and TPHg, 28,100 mg/kg The first monitoring and <br /> sampling event conducted in December 1989 revealed all four wells contained reportable <br /> concentrations of dissolved BTEX, TPHg and MtBE (Table 2) No reportable concentrations of <br /> tertiary butanol (TBA), methyl-tert butyl. ether(MtBE), di-isopropyl ether(DIPE), ethyl-tertiary- <br /> butyl ether (ETBE), and tertiary—amyl-methyl ether (TAME) were detected in the water samples <br /> collected in December 1989 <br /> Domestic Wells <br /> Four domestic water supply wells are located within 340 feet of the former tank pit (Figure 2) <br /> Well# Location from Tank Pit Comments <br /> DW-1 90 feet west of tank pit onsite well <br /> DW-2 120 feet south of tank pit Down gradient of tank pit (well idle) <br /> DW-3 245 feet south-southeast Down gradient of tank pit <br /> DW-4 340 feet south of tank pit Down gradient of tank pit <br /> Water samples collected from domestic wells have been analyzed for the presence of BTEX, <br /> TPHg, MtBE, TBA, DIPE, ETBE, TAME, EDB, and 1,2 DCA Since water sample collected <br /> from DW-2 contained reportable concentrations of MtBE, the well was taken out of service <br /> Well DW-1 is now being used to supply water to the site and adjacent residence Notes for <br /> private well survey conducted on April 6, 2000, are attached in Field Notes (Attachment 3) <br /> File Rwoba¢k-00 2Q rpt doc <br />