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i 3 0 RESULTS OF THE INVESTIGATION r 31 Geology and Hydrogeology rSods observed during the drilling of the three monitoring well borings consisted mostly of silt and sand mixtures with some clay The uppermost 15 to 18 fleet of sod consists of a mostly well- graded sand and silty sand sequence This sand sequence is laterally continuous and overlies a silty sand, silt, clayey silt, or silty clay sequence Soils observed during the five Geoprobe soil ' borings included a laterally discontinuous sand sequence at a depth of approximately 30 feet bgs, overlying a well-graded sandy gravel at the maximum drilling depth of 43 feet bgs Detailed soil descriptions are included on the monitoring well logs (Appendix C) During drilling on December 12, 2000, saturated soil and groundwater were first encountered between 19 9 and 20 8 feet bgs On December 20, 2000, the static depth to the groundwater table, as measured in the three groundwater monitoring wells, ranged from 18 47 feet bgs in MW- ' 2 to 18 56 feet bgs in MW-1 As such, groundwater does not appear to present under significant confining conditions Groundwater recharge was observed to be moderately strong The groundwater surface elevation ranged from a high of 18 18 feet above mean sea level (msl) at MW-2 to a low of 18 10 feet above msl at MW-1 The resulting groundwater surface appears ' as a regular plane dipping to the west at a gradient of approximately 0 0013 foot/foot A groundwater surface contour map is included as Figure 3 The well construction details, wellhead elevations and groundwater monitoring data are summarized in Table 3 32 Analytical Results ' The soil samples collected at 20 and 25 feet from the soil borings for MW-1 and MW-2 were laboratory analyzed The soil samples collected at 20 feet in both soil borings contained the ' highest concentrations of petroleum hydrocarbons The soil sample collected at 20 feet from the soil boring for MW-1 contained 240 mg/kg of TPH-as-diesel, 470 mg/kg of TPH-as-gasoline, 6 8 ' mg/kg of ethylbenzene, and 3 0 mg/kg of xylenes The sod sample collected at 20 feet from the sod boring for MW-2 contained 46 mg/kg of TPH-as-diesel, 17 mg/kg of TPH-as-gasoline, and 0 0058 mg/kg of MTBE In the soil samples collected at 25 feet, only the sample from MW-1 contained detectable concentrations of petroleum hydrocarbons (4 6 mg/kg of TPH-as-diesel and 0 028 mg/kg of ethylbenzene) These soil sample results are summarized in Table 1 and the ' laboratory reports are included in Appendix D 11 i 1