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d 30 SITE INVESTIGATION RESULTS ' 31 Geology and Hydrogeology ' Sods encountered during drilling generally consisted of a massive sequence of clay and silt soils without significant sandy intervals Some sand was observed in thin, fine sandy silt intervals, less than five feet thick On-site, soils observed below 25 feet at MW-1, MW-2, and MW-3 included discontinuous sandy intervals less than 10 feet thick, interbedded with silty clay and clayey silt On September 26 and 28, 2001, saturated soil was first encountered during drilling between 46 and 47 feet bgs Approximately 30 minutes after encountering saturated soil in each of the soil borings, groundwater was observed between 39 9 and 41 3 feet bgs On November 1, 2001, the static depth-to-groundwater ranged from 40 80 feet bgs in MW-7 to 42 32 feet bgs in MW-1 The corresponding groundwater surface elevation ranged from a high of 22 73 feet below mean sea level (ms]) at MW-6 to a low of 23 51 feet below msl at MW-2 The resulting groundwater surface appears as a plane dipping to the east-southeast at a gradient of approximately 0 0025 foot/foot As shown on the groundwater surface contour map (Figure 4), the groundwater depression observed at MW-2 is not consistent with the regional groundwater surface The well construction details, wellhead elevations and groundwater monitoring data are summarized in Table 2 32 Analytical Results ' All of the soil and groundwater samples collected from the four new wells were free of detectable concentrations of gasoline compounds The soil sample analytical results are summarized in Table 1, and the groundwater sample analytical results are summarized in Table 3 The laboratory reports are included in Appendix E On-site, the groundwater samples collected from MW-2 and MW-3 continued to contain ' concentrations of TPH-as-gasoline, BTEX and 1,2-DCA The highest concentrations of gasoline hydrocarbons were detected in the groundwater sample collected from MW-2 This sample contained 210,000 µg/l of TPH-as-gasoline, 4,600 µg11 of benzene, 37,000 µg/l of toluene, 4,700 µg/l of ethylbenzene, 29,000 µg/I of xylenes, and 500 µg/I of 1,2-DCA The groundwater sample collected from MW-3 contained 1,400 µg/I of TPH-as-gasoline, 0 61 µg11 of benzene, 59 µg/l of ' TBA, and 250 µg11 of 1,2-DCA The groundwater sample collected from MW-1 did not contain detectable concentrations of gasoline hydrocarbons The concentrations of TPH-as-gasoline and benzene and approximate lateral extent of impacted groundwater are posted on Figure 5 13