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May 4, 1993 Working To Restore Nature <br /> Unocal Station No 6981, Stockton, Califorrua <br /> Benzene concentrations in these samples ranged from below laboratory detection limits to <br /> 84 ppm The highest TPHg and benzene concentrations were detected in soil from the <br /> I center to the northeast corner of the pit (1,400 and 1,900 ppm TPHg and 24 and 84 ppm <br /> benzene) These concentrations were detected in soil at the base of the tank excavation at <br /> depths of 18 and 22 feet respectively below surface grade However, results of analyses of <br /> soil samples collected from borings drilled southwest and east of the tank pit (B-1 and B-12) <br /> I <br /> and samples collected from the tank excavation indicate that soil with residual gasoline <br /> hydrocarbons adjacent to the tank pit appears to be present primarily near the northern half <br /> of the tank pit <br /> I <br /> 4.3.2 Residual Hydrocarbons In Dispenser Area <br /> Concentrations of TPHg detected in soil samples collected near the dispenser islands and <br /> I0product lines ranged from 5,300 ppm in boring B-11 and 1,407 ppm and 1,726 ppm near the <br /> northeastern dispenser and the southwestern dispenser respectively Soil with residual <br /> hydrocarbons in this area appears to be of limited lateral extent, but results of analysis of <br /> I samples collected from borings B-2, B-6, B-11, and B-13 at depths between 15 and 50 feet <br /> below surface grade indicate that soil with residual hydrocarbons beneath the dispenser <br /> islands extends to ground water <br /> 4 Distribution of Dissolved Hydrocarbons <br /> 4.4.1 Free Hydrocarbons in Ground Water <br /> 1 <br /> Results of subjective analyses of ground-water samples collected during the ground-water <br /> monitoring events indicated floating product has not been present at the site since <br /> monitoring began. <br />/6 <br /> 38032-13 7 <br />