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r <br /> ®® <br /> SAM <br /> June 26, 1992 <br /> . ARCO Service Station No. 549, Stockton, California <br /> Evaluation of round-Water Conditions <br /> Dissolved,benzene, total xylene_isomers,,and a-unknowm hydrocarbon_(2.1,--0-907, nd 150? <br /> `parts perJbillion'[ppb];respectively);were-identified in the-ground wafer samples collected} <br /> from monitoring_well~'MW-f The ground-water quality is presented on plate 29. Total oil <br /> and grease was not detected in the water sample collected from well MW-1. A bailer blank <br /> is, collected before sampling well MW-1 was analyzed, and results indicated that hydrocarbons <br /> were not detected. Laboratory results of samples collected from wells MW-2, MW-3, and <br /> MW-4 indicated TPHg and BTEX compounds were not detected. The analytical results are <br /> summarized in Table 4. Appendix C contains the laboratory reports and Chain of Custody <br /> It <br /> Records. <br /> SUMMARY <br /> i � <br /> The following summarizes the results of this investigation: <br /> o Residual gasoline hydrocarbons have been analytically detected in soil <br /> samples collected near the tank cavity and dispenser island with higher <br /> concentrations detected near the tank cavity. <br /> o The ground-water surface beneath the site occurs approximately 49 to 51 feet <br /> below grade. At the time of measurement, the groundwater flow direction <br /> was slightly south of west with a hydraulic gradient of 0.004. <br /> o Relatively low concentrations of dissolved gasoline hydrocarbons (2.1 ppb` <br /> benzene and 0.96 ppb total xylene isomers) were analytically detected in the <br /> ,_ground-water sample collected from monitoring well .MW-1: TPHg and <br /> BTEX compounds were not detected in groundwater samples collected from <br /> wells:MW-2, MW-3, and MW-4. <br /> • V004-4 10 <br />�k <br />