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1 12 October 1999 AGE-NC Project No 98-0497 Page 6 of 7 ' • Review of regional ground water elevation maps published by the SJCFCD suggested the prevailing ground water flow direction in southeast Stockton is generally toward the northeast, review of regional depth to ground water maps published by the SJCFCD suggests ' that ground water near the site is first encountered between 65 and 70 feet bsg General Iithology beneath the site is depicted in cross sectional view on Figures 3 and ' consists of a dark brown, moist, fine sandy, clayey silt was encountered from 5 feet bsg to depths of approximately 14 feet bsg Between 10 feet bsg and 35 feet bsg, a gray/brown, damp, silty fine sand was encountered Between 35 feet bsg and 40 feet bsg, a brown, damp ' silty fine sand was encountered At depths in excess of 40 feet bsg, a brown, damp to moist, fine sandy silt was encountered ' • Faint to moderate hydrocarbon vapor and odor was noted in duplicate soil samples collected from P-1 at depths between 15 feet bsg and 65 feet bsg • TPH-g was detected in soil samples collected from probe boring P-1 at concentrations ' ranging as high as 1,900 mg/kg, the laboratory reported the sample chromatogram to be representative of a strongly aged gasoline or that diesel range compounds were significant • • TPH-d was detected in soil samples collected from P-1 at concentrations ranging as high as 10,000 mg/kg, the laboratory reported the diesel range chromatograms as unmodified or weakly modified • Further laboratory review of the gasoline and diesel range chromatograms indicated the sample chromatograms to be more indicative of a diesel impact ' • BTEX compounds were detected in soil samples collected from P-1 at concentrations ranging as high as 8 3 mg/kg, benzene was detected from the P-1 sample at 65 feet bsg at a ' concentration of 0 047 mg/kg • MTBE was detected in soil samples collected from P-1 utilizing EPA Method 8260 Modified at concentrations ranging as high as 0 055 mg/kg ' 6.0. CONCLUSIONS • The soil horizon at the site consists of approximately 10 feet of sandy, clayey silt overlain ' _ _ by approximately 30 feet of silty fine-sand, which in turn is underlain by a sandy silt of - _-- undetermined thickness • The soil underlying the former UST pit has been significantly impacted by petroleum . hydrocarbons to depths as great as 70 feet below surface grade ' • The mayor portion of the petroleum hydrocarbon soil-impact at the site appears to have been Adh anced GeoEn%ironmental,Inc