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• May 4, 1993 Working To Restore Nature <br /> Unocal Station No 6981, Stockton, California <br /> ground water gradient, a calculated radius of capture for the pumping test well is 18 feet <br /> The pumping test data and results are presented in detail in the Problem Assessment <br /> Report (RESNA, December 16, 1992, Report No 38032-10) <br /> 43 Distribution of Residual Hydrocarbons <br /> The results of subjective and laboratory analyses of soil samples collected from the onsite <br /> and offsite soil borings and the tank excavation were used to evaluate the lateral and <br /> vertical extent of residual hydrocarbons in soil The sample locations and the concentrations <br /> i of total petroleum hydrocarbons as gasoline (TPHg) are presented on the TPHg <br /> Concentration Maps (Plates 8, 9, and 10) Tables 3, 4, and 5 show the analytical results for <br /> soil samples collected from the tank and product-line excavations and soil borings <br /> Results of laboratory analyses of soil samples indicated that soil with residual gasoline <br /> hydrocarbons remains in place beneath the tank pit and the dispenser islands The lateral <br /> and vertical extent of residual hydrocarbons has been delineated, soil with residual <br /> i hydrocarbons appears to be predominately onsite Soil containing hydrocarbons may extend <br /> offsite northeast and east of the dispenser islands at depths greater than 25 feet below <br /> surface Because of the lowering of ground-water in this area, samples collected from the <br /> 45 to 56 foot depth have probably been within the zone of capillary fringe during the past <br /> i <br /> Using the available data, this trend is shown in Plate 10 as the soil containing TPHg within <br /> this interval is elongate in the approximate direction of the groundwater gradient <br /> 4.3.1 Residual Hydrocarbons In Tank Pit Area <br /> Soil samples collected from the limits of the tank pit and from soil borings drilled near the <br /> pit (B-1, B-5, and B-12) contained gasoline hydrocarbons,TPHg concentrations ranged from <br /> below laboratory detection limits to 1,900 parts per million (ppm) (Tables 4 and 5) <br /> 38032-13 6 <br /> 1 <br />