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1 , Ile 31 October 2005 # AGE-NC Project No 03-1080 ` l Page 9 of 10 6,100 mg/kg, 8,500 mdg, 11 mg/kg, 337 mg/kg,µ0 019 mg/kg, and l 16 mg/kg, ' W respectively However,the extent of contamination appears limited,AGE calculated that an estimated 52 lbs, or 7 8 gallons, of total petroleum hydrocarbons appear to remain in approximately 940 ft3 of predominantly silty sand/silt soil ' In AGE's site conceptual model, the distribution of petroleum hydrocarbons in soil and ground water indicates an apparent release(s)In the area of former dispenser D 1,which then migrated vertically through the upper silty sand/sandy silt until encountering the less permeable clay/silty clay interval at approximately 15 feet bsg Further vertical migration appeared to be retarded by this less-permeable interval, concentrations of COCs were note detected in soil below this Interval, although the underlying ground water was impacted - ' According to the analytical laboratory,the gas chromatograms Indicated that the petroleum 15 V)nor o hydrocarbons were not from a recent release(s),but remnants of aged or degraded fuel AGE ${" speculates that the releases probably occurred prior to 1988, when site subsurface 1 , p ( ) p Y Investigation began for the leaking USTs, when compared to the high concentrations of BTEX compounds In ground water at the time of the UST Investigation between 1992 and ' 1994,there are only xylenes,with occasional occurrences of ethylbenzene,In soil and ground water at the dispenser location Additional evidence of an older release Is the presence of the MTBE degradation product TBA, associated with the low MTBE concentration In sO1 ',• Fate and transport modeling using very conservative site conditions predicts that there should not be any impact to ground water at the dispenser D1 location from the aged petroleum ' hydrocarbon-Impacted soil The high concentrations of TPH-g and TPH-d In ground water beneath the dispenser location may be remnant, degraded fuel left in place at the time of the original site closure In 1998 _ ' One on-site domestic well and one off-site domestic well are located at greater than 100 feet from the dispenser location, after 1997,the original wells were destroyed and the new wells were Installed to deeper depths to avoid any possible contamination from the site UST r release Based on the results of the fate and transport study of remaining petroleum-Impacted soil at the dispenser location, it is unlikely that these wells are contaminated by Impacted r ground water from the site • The nearest surface water feature to the site Is the San Joaquin River, located approximately ' 5 miles west of the site It Is unlikely that water In Smith Canal is contaminated by Impacted ground water from the site r" 9.0. RECOMMENDATIONS ' Based upon petroleum hydrocarbon distribution patterns and migration pathways Identified In the N site conceptual model,AGE recommends no further action In regards to the current Investigation In ' Advanced GeoEnvironmental,Inc