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1 1 4 <br /> iConcentrations of diesel and gasoline hydrocarbons were detected in the groundwater-grab <br /> ' samples collected at each of the five soil boring locations The highest concentrations were <br /> detected in the groundwater-grab sample collected from S13-1, located within the former UST <br /> ' excavation This sample contained 2,700,000 micrograms per liter(µg11) of TPH-as-diesel, 29,000 <br /> µgll of TPH-as-gasoline, 68 µg11 of benzene, 7 5 µg11 of toluene, 130 µg11 of ethylbenzene, 210 µg11 <br /> of xylenes, and 6 5 µg11 of tertiary butanol MTBE, DIPS, ETBE and TAME were not detected in <br /> ' any of the groundwater-grab samples These groundwater-grab sample results are summarized <br /> in Table 2 <br /> ' 1 2 3 Installation of Three Monitoring Wells <br /> ' On March 23, 2001, Ramage Environmental published Monitonng Well Installation Report, which <br /> documented the installation of three on-site groundwater table monitoring wells The objectives of <br /> ' this investigation were to confirm concentrations of petroleum hydrocarbons in groundwater and to <br /> establish a groundwater monitoring capability at the site <br /> ' During drilling, saturated soil and groundwater were first encountered between 19 9 and 20 8 feet <br /> bgs Eight days later, the static depth to the groundwater table, as measured in the three <br /> groundwater monitoring wells, ranged from 18 47 to 18 56 feet bgs The groundwater surface <br /> elevation ranged from a high of 18 18 feet above mean sea level (msl) at MW-2 to a low of 18 10 <br /> feet above msl at MW-1 The resulting groundwater surface appeared as a regular plane dipping <br /> ' to the west at a gradient of approximately 0 0013 foot/foot <br /> ' Soil and groundwater beneath the site are impacted by diesel and gasoline hydrocarbons, in <br /> relatively equal proportion Concentrations of benzene are not present or significant in soil and <br /> are relatively low in groundwater Except for a couple of trace detectable concentrations, MTBE, <br /> ' DIPE, ETBE, TAME, TBA and 1,2-DCA are not present in soil or groundwater <br /> ' The groundwater samples collected from all three of the groundwater monitoring wells contained <br /> detectable concentrations of petroleum hydrocarbons Maximum concentrations in groundwater <br /> include 15,000 µg11 of TPH-as-diesel, 12,000 µg11 of TPH-as-gasoline, 19 µg/l of benzene, 5 6 <br /> ' µg11 of toluene, 1,300 µg11 of ethylbenzene, and 52 µg/l of xylenes The gasoline oxygenate <br /> compounds and 1,2-DCA were not detected in any of the groundwater samples <br /> Petroleum hydrocarbons concentrated in groundwater near the source appear to have migrated <br /> preferentially to the northwest and west, in an apparent downgradient direction <br /> 5 <br /> 1 <br />