ARCHIVED REPORTS_XR0006732 CASE 1

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i 3.0 PROJECT RESULTS � i3.1 Geology and Hydrogeology Based on the CPT data, the subsurface soils to the total drilling depth of 150 feet consist of clay, silt, sand and gravel mixtures The uppermost 15 to 20 feet of soil is mostly silty sand, sand and gravelly sand The first saturated interval is a sand and gravelly sand from approximately 25 to 30 feet bgs Between 30 and 50 feet, the soils consist mostly of interbedded silt and clay mixtures From approximately 50 to 95 feet, soils consist of massive sand and gravelly sand intervals up to 10 feet thick interrupted by thinner intervals of silt and clay mixtures Between approximately 95 and 135 feet, massive silt and clay intervals are interrupted by thin sand and gravelly sand intervals less than 4 feet thick Finally, below 135 feet is a massive gravelly sand interval at least 15 feet thick Gregg's cone penetration test data report is included as Appendix B ' In the four monitoring wells, the depth to the groundwater table, ranged from 22 08 feet below ground surface (bgs) in MW-1 to 23 25 feet bgs in MW-4 The corresponding groundwater ' surface elevation ranged from a high of 15 44 feet above mean sea level (msl) at MW-1 to a low of 14 61 feet msl at MW-4 The resulting groundwater surface appears as a regular plane dipping to the northeast at a gradient of approximately 0 0095 foot/foot A groundwater surface contour map is included as Figure 4 The well construction details and groundwater monitoring data are summarized in Table 1 ' 32 Analytical Results ' From the four groundwater table monitoring wells, only the sample collected from MW-2 contained detectable concentration of gasoline compounds The groundwater sample collected from MW-2 ' contained 480 µg11 of TPH-as-gasoline, 1 8 µg/l of benzene, 2 0 µg/I of ethylbenzene, and 17 µg11 of MTBE The samples collected from MW-1, MW-3, and MW-4 did not contain detectable concentrations of any gasoline compound These groundwater sample analytical results are summarized in Table 2 The distribution of MTBE at the groundwater table is shown on an isoconcentration map (Figure 5) The laboratory reports are included in Appendix C ' The groundwater samples collected from the on-site water supply well and the four residential domestic wells did not contain detectable concentrations of gasoline compounds These ' groundwater analytical results are summarized in Table 3, and the laboratory reports are included in Appendix C 14