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. May 4, 1993 Working To Restore Nature <br /> Unocal Station No 6981, Stockton, California <br /> occurred during an approximate 4 5 foot decrease in the ground-water elevation (Table 7) <br /> During the first quarter 1993 sampling, ground water elevations were approximately 2 5 feet <br /> P higher compared to the fourth quarter 1992 Associated with this increase in the ground <br /> water elevation is an increase in dissolved concentrations of TPHg and BTEX in MW-7 and <br /> benzene in MW-6 <br /> t <br /> Nitrates and total and fecal coliform bacteria were detected in ground-water samples <br /> collected from monitoring wells during our investigation Specific wells sampled, sample <br /> dates, and concentrations are shown in Table 8 <br /> A <br /> 45 Summa <br /> Based on the field evidence and laboratory results obtained from the Phase II subsurface <br /> 1� investigation, residual gasoline hydrocarbons are not present in soil near borings B-14 <br /> through B-17 and B-19 surrounding the site Soil beneath the dispensers and the <br /> underground storage tank pit, however, contains residual gasoline hydrocarbons at <br /> concentrations that warrant remediation (Plates 8, 9, and 10) <br /> Gasoline-range hydrocarbons have been present in wells MW-1 through MW-5 (when they <br /> contained water in 1990) and have also been reported recently in wells MW-6 through MW- <br /> 1 <br /> 8 and PTW-1 Hydrocarbon concentrations in samples collected from monitoring wells MW- <br /> 9 through MW-13 (surrounding the site) were below the laboratory's limits of detection for <br /> all hydrocarbon analytes The extent of TPHg and benzene in ground water are shown on <br /> 1 Plates 11 through 14 <br /> 1 <br /> 38032-13 9 <br />