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1 EXECUTIVE SUMMARY • The project objectives were to further assess the lateral extent of impacted groundwater and to expand the on-site groundwater monitoring network To achieve these objectives, three additional on-site groundwater table monitoring wells (MW-4, MW-5 and MW-6) were installed, ' on December 1 and 2, 2003 Soils observed during the drilling consisted of massive intervals of clay, silt and fine sand ' mixtures to the total drilling depth of approximately 55 feet Groundwater appears to be present under water table conditions, and recharge appears to be moderately strong On December 19, 2003, the depth to static groundwater across the site ranged from 48 17 feet ' bgs in MW-6 to 50 34 feet bgs in MW-1 The corresponding groundwater surface elevation ranged from a high of 29 45 feet below mean sea level (msl) at MW-6 to a low of 31 13 feet below msl at MW-1 The resulting groundwater surface appears as an irregular plane dipping toward the east-southeast at a gradient of approximately 0 0020 foot/foot A groundwater surface depression at MW-1 does not appear to fit the regional trend, possibly due to the presence of free product All three sod samples collected from the boring for MW-6 contained detectable concentrations of gasoline compounds The maximum concentrations detected included 1 7 milligram per kilogram (mg/kg) of Total petroleum Hydrocarbons (TPH)-as-gasoline, 0 43 mg/kg of benzene, 0 014 mg/kg of ethylbenzene, and 0 059 mg/kg of xylenes Oxygenate compounds and 1,2- dichloroethane (1,2-DCA) were not detected in any of the soil samples analyzed, and no gasoline compounds were detected in the soil samples collected from MW-4 and MW-5 10 The groundwater samples collected from MW-2, MW-4 and MW-6 contained detectable concentrations of gasoline compounds The sample from MW-2 contained 61,000 micrograms per liter (µg11) of TPH-as-gasoline, 17,000 µg/l of benzene, 1,400 µgll of ethylbenzene, 1,900 µg11 of xylenes, and 24,000 µg11 of methyl tertiary butyl ether (MTBE) The sample from MW-4 only contained 0 5 µg11 of MTBE and 24 4g/I of tertiary butanol (TBA) The sample from MW-6 contained 7,800 µg11 of TPH-as-gasoline, 2,100 µg/I of benzene, and 820 µg11 of xylenes In groundwater, gasoline hydrocarbons are concentrated as free product near former UST#3, and concentrations of gasoline compounds appear to decrease with distance from the source area The lateral extent of MTBE in groundwater appears to be mostly defined, and the lateral extents of TPH-as-gasoline and benzene in groundwater remain undefined only to the west of the source area The vertical extent of impacted groundwater has not been investigated Based on these conclusions, Ramage Environmental recommends that the previously-approved remedial feasibility testing tasks be initiated as soon as funding is available The first task should be the installation of the nested soil vapor extraction well and nested air sparge/soil vapor extraction well During this drilling work, another groundwater monitoring well should be installed to the west of MW-6, to further define the lateral extent of impacted groundwater In the meantime, monthly free product removal and quarterly groundwater monitoring should continue 4