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EXECUTIVE SUMMARY ' The objectives of this investigation were to confirm concentrations of petroleum hydrocarbons in groundwater and to establish a groundwater monitoring capability at the site To achieve these objectives, three on-site groundwater table monitoring wells were permitted, installed, surveyed, monitored and sampled During drilling, saturated soil and groundwater were first encountered between 19 9 and 20 8 feet below ground surface (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 appears as a regular plane dipping to the west at a gradient of approximately 0 0013 foot/foot Groundwater does not appear to be present under significant confining conditions, and recharge was observed to be moderately strong ' Soil and groundwater beneath the site are impacted by diesel and gasoline hydrocarbons, in relatively equal proportion Concentrations of benzene are not present or significant in soil and are relatively low in groundwater Except for a couple of trace detectable concentrations, MTBE, DIPS, ETBE, TAME, TBA and 1,2-DCA are not present in soil or groundwater The soil samples collected at 20 and 25 feet from the soil borings for MW-1 and MW-2 were laboratory analyzed The soil samples collected at 20 feet in both soil borings contained the highest concentrations of petroleum hydrocarbons, up to 240 mg/kg of TPH-as-diesel, 470 mg/kg of TPH-as-gasoline, 6 8 mg/kg of ethylbenzene, and 3 0 mg/kg of xylenes The groundwater samples collected from all three of the groundwater monitoring wells contained detectable concentrations of petroleum hydrocarbons Maximum concentrations in groundwater include 15,000 µg11 of TPH-as-diesel, 12,000 µg11 of TPH-as-gasoline, 19 µg/I of benzene, 5 6 pg/l of toluene, 1,300 µg/l of ethylbenzene, and 52 µg/I of xylenes The gasoline oxygenate compounds and 1,2-DCA were not detected in any of the groundwater samples The bulk of the petroleum hydrocarbon mass remains concentrated in soil beneath and in close proximity to the former USTs Impacts to soil in the vadose zone are defined to the proximity of the former UST excavation Vertically, the concentrations in soil decline rapidly with depth below the groundwater table, and are defined above 43 feet bgs Impacts to soil at or near the water table and to groundwater are not defined Petroleum hydrocarbons concentrated in groundwater near the source appear to have migrated preferentially to the northwest and west, in an apparent downgradlent direction Based on these conclusions, Ramage Environmental recommends the following 1 Continue to monitor and sample groundwater at the site on a quarterly basis 2 Complete the sensitive receptor survey for the site vicinity 3 Complete project tasks outlined in the PHS/EHD May 16, 2000 letter for each of the six ' county sites, and meet to discuss site information and priorities 4