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