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SECTIONrTHRE]E Data Evaluation <br /> This section describes the evaluation of the results of the sampling and analysis activities <br /> Leakage of diesel fuel from the former UST has contaminated vadose-zone soil below the tank <br /> location down to groundwater at about 40-ft bgs Samples from below the water table show only <br /> 0 0058 mg/kg xylenes at 51-ft bgs, and no detections at 55 5-ft bgs <br /> Lateral migration of the product plume in the vadose zone appears to have occurred in a loose, <br /> well sorted medium grained sand bed that was encountered at 15-ft and 20-ft bgs in Boring B-5 <br /> This unit was almost devoid of silt and clay and would have provided a pathway for diesel fuel to <br /> move horizontally on top of the underlying silt deposit Elevated concentrations of TPH-diesel <br /> were measured in the silt at 25-ft and 31-ft bgs (Table 2-1) <br /> The measurement of 27 mg/kg TPH-diesel at 10-ft bgs below the gasoline UST may be due to <br /> minor release of gasoline, or lateral migration of diesel fuel from the nearby diesel UST <br /> (Figure 1) <br /> Groundwater has been impacted in the area below the diesel UST The lateral extent of the <br /> groundwater plume is unknown at present <br /> The nearest well is No 1, an industrial well located about 1/4 mile southwest of the site There <br /> are four other wells within a 2,000-foot radius of the site that are at least V4 mile away <br /> URS Greiner Woodward Clyde 1%099670491UST REPORT CHEROKEE DOQ22 SEP 9911OAK 3-1 <br />