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�--" City of Stockton A68108.01B <br /> July 18, 1997 Page 8 <br /> ti— <br /> TABLE 4 <br /> Summary of Groundwater Analytical Results <br /> Soil Probe Location SP-1 <br /> December 20, 1996 <br /> Results in wacrogmms per liter OAgIL) <br /> �- sampk <br /> Location Benzene Toluene Ethyl- Xylenes MTBE TPH-G <br /> bcncene <br /> SP-1 18 100 it 110 46 5,700 <br /> MTBE = methyl tertiary-butyl ether <br /> TPH-G = total petroleum hydrocarbons-gasoline range constituents <br /> —. \iD = not detected at or above detection limit for reporting purposes <br /> Detection limits for these analyses are reported on the attached laboratory reports. <br /> r <br /> 6.0 EVALUATION <br /> 6.1 Soil Characterization: Gasoline range constituents were detected in soil samples <br /> collected at soil probe location SP-1 at depths of 16, 20, 24, and 28 feet BSG. The greatest <br /> �r concentrations of PPCs were detected in the soil sample collected at 20 feet BSG. The <br /> vertical extent of PPC migration is presumed to extend no deeper than 32 feet based on the <br /> analytical results of the soil sample collected at that depth. PPC impacted soils are <br /> presently separated from the current water table level (approximately 45 feet BSG) by at <br /> least 13 feet. <br /> The lateral extent of PPC migration appears to be less than 5 feet from the former UST <br /> location as indicated by the analytical results of soil samples collected from soil probe <br /> location SP-3. <br /> 6.2 Groundwater Characterization: The analytical results for the groundwater sample <br /> collected from the soil probe SP-1 suggest that groundwater has been impacted by PPCs. <br /> ,r It is possible, although not likely, that some or all of the contaminants detected in the water <br /> sample may have resulted from soil cross-contamination. Soils penetrated by the probe <br /> prior to collecting the groundwater sample contained relatively high concentrations of PPCs. <br /> The concentrations of benzene detected in groundwater (18 micrograms per kilogram) <br /> exceeds the maximum contaminant level (MCL) for drinking water standards as published <br /> +� in the California Code of Regulations, section 64444. <br /> 6.3 Additional Investigation and Proposed Corrective Action: Based on the results of <br /> '-" the soil sample analyses, it would appear that there is a PPC impacted soil volume of <br /> �••.� approximately 55 cubic yards. Drawing 3 shows the estimated lateral extent of the PPC <br />