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1 <br /> . April 15, 1993 Working To Restore Nature <br /> ARCO Facility No 6020, Manteca, California <br /> Method 8015 and Method 8020 Ground-water samples were analyzed for TPHg and BTEX <br /> r <br /> using modified EPA Method 8015 and Method 602 Samples from wells MW-1, MW-3, and <br /> MW-4 were also analyzed for nitrates The samples were analyzed at Sequoia Analytical <br /> Laboratory in Sacramento, California (Hazardous Waste Testing Laboratory Certificate <br /> No 1624) Copies of the Analytical Reports and Chain of Custody Records are in Appendix <br /> C <br /> SITE CONDITIONS <br /> Site Geology <br /> Sediments encountered while drilling suggest the site is underlain by three laterally <br /> continuous units The upper unit, Iocated from the surface to approximately 16 feet below <br /> surface grade (bsg), comprises primarily sand The middle unit, located from approximately <br /> 16 to 29 feet bsg, comprise of silt with trace clay The lower unit, located from <br /> approximately 29 to the total depth explored of 39 feet bsg, consists of sand First ground <br /> water beneath the site was encountered at approximately 24 to 28 feet bsg The interpreted <br /> subsurface conditions are shown on geologic cross-sections A-A' and B-B' (Plate 3) The <br /> plan view of the geologic cross-sections is included on Plate 2 <br /> Residual Hydrocarbons in Soil <br /> Results of analyses indicated that gasoline and BTEX compounds were not present in the <br /> soil samples collected from borings B-1, B-2 and B-7 through B-13 TPHg and benzene <br /> were detected near the tank cavity (borings B-3 through B-5) and on the east side of the <br /> station building (boring B-6) TPHg concentrations in these vicinities ranged from below <br /> 30055-5 <br /> 7 <br />