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i• 3.0 INVESTIGATION RESULTS 31 Geology and Hydrogeology iSoils observed in the three soil borings consisted mostly of clay and silt sequences to the total drilling depth of 33 feet bgs This sequence appears to be massive and laterally continuous ' across the site Soil boring logs are included in Appendix C / During drilling, the depth to first encountered groundwater ranged from 26 05 to 29 20 feet bgs The depth to the groundwater table, as measured in the four groundwater monitoring wells, ranged from 23 75 feet bgs in MW-1 to 24 94 feet bgs in MW-3 The groundwater surface elevation in the four wells ranged from a high of 12 62 feet below mean sea level (msl) at MW-1 to a low of 13 30 feet below msl at MW-4 The resulting groundwater surface appears as an irregular plane dipping toward the east-southeast at a gradient of approximately 0 0229 foot/foot A groundwater surface contour map is included as Figure 4, and the groundwater monitoring data are summarized in Table 3 - 32 Analytical Results i. In soil, only the sample collected at 25 feet bgs from G-6 contained a detectable gasoline compound concentration (0 018 mg/kg of ethanol) The soil sample analytical results are summarized in Table 1, and the laboratory report is included in Appendix D In the groundwater samples collected from the three soil borings, low concentrations of gasoline compounds were detected at G-4 and G-5 The sample collected from G-4 contained 0 55 micrograms per liter(pg/1) of toluene, 0 79 pg/I of xylenes, 3 8 pgA of MTBE, and 11 pg/I of ethanol The sample collected from G-5 only contained 1 5 pg/I of MTBE These groundwater sample analytical results are summarized in Table 2, and the laboratory report is included in Appendix D Consistent with previous quarterly groundwater sampling results, the groundwater samples collected from MW-1, MW-2 and MW-3 contained detectable concentrations of petroleum hydrocarbons, including TPH-as-gasoline, TPH-as-kerosene, and BTEX compounds The groundwater sample collected from MW-3 also contained 4 7 pg/I of DIPE and 76 gg/l of 1,2-DCA The groundwater sample collected from MW-4 did not contain detectable concentrations of petroleum hydrocarbons These groundwater sample analytical results are also summarized in iTable 2, and the laboratory report is also included in Appendix D r . 10