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I June 30, 1992 z . Unocal Station No 6981, Stockton, California I Data collected on March 9, 1992 (Table 2) were used to evaluate the direction of ground- water flow and the gradient beneath the site. The ground-water flow direction beneath the site on that date was to the northeast with a gradient of 0.010 to 0.013, as shown on the Potentiometric Surface Map (Plate 22). The direction of ground-water flow and gradient I are similar to those previously evaluated. The average elevation of ground water increased in wells MW-1 through MW-5 from 0 4 to 2 0 feet since the last measurements were taken in November 1991 Vapor-Extraction Test RESNA performed a vapor-extraction test at the site on March 24, 1992, using vapor- extraction wells VW-1, VW-2, VW-3, and VW-4 The test was conducted to evaluate the feasibility of vapor extraction as a soil remediation alternative and to evaluate the off-gas treatment alternatives, if applicable. On the basis of data collected during this test, we conclude that vapor extraction is a feasible method of remediating soil at this site Preliminary evaluation of data obtained during the vapor-extraction test indicates an effective radius of influence of approximately 50 feet for one vapor-extraction well The vapor-extraction test will be described in detail in the Problem Assessment Report (PAR) SUMMARY OF SITE CONDITIONS Sediments beneath the site consist primarily of massive silt with several lenses of sand and clay Soil with the highest concentration of residual hydrocarbons is near the northeast corner of the dispenser islands Residual gasoline hydrocarbons were detected in soil at other locations beneath the site, and extend offsite under Pacific Avenue The lateral and ' vertical extent of residual hydrocarbons has been delineated except along the eastern edge of the property under Pacific Avenue (Plate 2). However, the results of the vapor-extraction test indicate that remediation can be effected by vapor extraction. Dissolved gasoline hydrocarbons are present in ground water underlying the northeast, I southwest, and southeast portions of the site. The highest concentrations occur downgradient of the pump islands and tanks Gasoline hydrocarbons were not detected in the sample from well MW-6, near the northwest corner of the site To date, the lateral extent of dissolved hydrocarbons has not been delineated k h il W32- 3sasz-7 4 i