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t.. <br /> 3.0 SITE INVESTIGATION RESULTS <br /> S"' 3.1 Geology and Hydrogeology <br /> In general, soil beneath the site consists of interbedded fine-grained siliciclastic sediments <br /> characteristic of fluvial-deltaic channel and overbank deposits. The soil samples collected from <br /> SB-7 and SB-8 indicate that the shallow subsurface soil is primarily silty sand with some clay. <br /> The deeper soil samples collected from SB-6 indicate that the soil from approximately 20 feet to <br /> 30 feet bgs consists of silt and clay mixtures free of measurable sand. Soil observed at 30 feet <br /> bgs consisted of poorly-graded medium sand with approximately 30% silt and 10% clay. Soil <br /> observed at 35 feet bgs consisted of silty fine sand with approximately 50% silt and 10% clay. <br /> Groundwater was encountered at 36 feet bgs beneath the site. Groundwater was extracted <br /> easily and found to be relatively clear. <br /> w.. <br /> 3.2 Analytical Results <br /> Based on the investigation results, vadose zone soil beneath the site has been impacted by <br /> petroleum hydrocarbons. Soil in the capillary fringe and groundwater beneath the site have not <br /> been impacted by significant concentrations of petroleum hydrocarbons. The soil sample <br /> analytical results are summarized in Table 1 and the groundwater analytical results are <br /> presented in Table 2. The laboratory reports are included as Appendix D. <br /> All three soil samples collected from the vadose zone in SB-6 contained elevated concentrations <br /> of TPH-as-diesel and minor concentrations of TPH-as-gasoline. The highest concentration of <br /> TPH-as-diesel (10,000 ppm) and TPH-as-gasoline (32 ppm)were detected in the soil sample <br /> collected at 30 feet bgs in SB-6. Trace concentrations of toluene, ethylbenzene and xylenes <br /> were also detected in the vadose zone soil samples. Neither benzene nor MTBE were detected <br /> in any of the vadose zone soil samples. The soil sample collected at 35 feet bgs in SB-6 from <br /> w. the capillary fringe did not contain detectable concentrations of TPH-as-diesel, TPH-as-gasoline, <br /> BTEX, MTBE or VOCs. <br /> The two shallow soil samples collected from SB-8 contained a maximum concentration of 51 <br /> ppm of TPH-as-diesel. Napthalene was detected in the soil sample collected at 5 feet bgs at a <br /> concentration of 0.0073 ppm. TPH-as-gasoline, BTEX, MTBE and other volatile organic and <br /> oxygenate compounds were not detected. <br /> two <br /> 9 <br />