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30 SITE INVESTIGATION RESULTS <br /> 31 Geology and Hydrogeology <br /> In general, the soils beneath the site consist of a fining-upward sequence of fine-grained <br /> siliciclastic sediments The uppermost soil is a light brown silty clay to a depth of approximately <br /> 25 feet bgs Below 25 feet, sandy soils exist in discontinuous intervals less than 10 feet thick <br /> The sandy intervals are interbedded with thin intervals of silty clay and clayey silt <br /> Saturated soil was first encountered during drilling between 42 and 45 feet bgs Approximately 30 <br /> minutes after encountering saturated soil in each of the soil borings, groundwater was observed <br /> between 39 and 41 feet bgs On January 11, 1999, the static depth-to-groundwater ranged from <br /> 39 31 feet bgs in MW-2 to 40 34 feet bgs in MW-1 The corresponding groundwater surface <br /> elevation ranged from a high of 20 99 feet below mean sea level (msl) at MW-3 to a low of 21 49 <br /> feet below msl at MW-2 The resulting groundwater surface appears as a plane dipping to the <br /> south-southeast at a gradient of approximately 0 05 foot/foot A groundwater surface contour <br /> map is included as Figure 4 The well construction details, wellhead elevations and groundwater <br /> monitoring data are summarized in Table 2 <br /> 32 Analytical Results <br /> Soil and groundwater beneath the site have been impacted by significant concentrations of <br /> gasoline hydrocarbons However, oxygenate compounds were not detected in any of the soil or <br /> groundwater samples analyzed The results of the soil sample analyses are summarized in Table <br /> 1 The results of the groundwater monitoring well samples are summarized in Table 3 The <br /> laboratory reports are included in Appendix E <br /> The only soil samples with significant concentrations of gasoline hydrocarbons were those <br /> ' collected directly beneath the former UST excavation from the soil boring for MW-2 The soil <br /> sample collected at 30 feet bgs from MW-2 contained ,4�mg/kgf TPH-as-gasoline, 62 mglkg <br /> of toluene, 54 mg/kg of ethylbenzene and 450 mg/kg of xylenes The concentration of gasoline <br /> hydrocarbons in soil beneath the former USTs declines with depth The soil sample collected <br /> from the capillary fringe (i e , groundwater table interface) at 40 feet bgs from MW-2 contained <br /> 330 mg/kg of TPH-as-gasoline, 1 2 mg/kg of benzene, 31 mg/kg of toluene, 9 0 mg/kg of <br /> ethylbenzene and 57 mg/kg of xylenes Below the water table the concentrations of gasoline <br /> 1 <br /> . 10 <br /> r <br />