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1 EXECUTIVE SUMMARY 10 The objectives of this investigation were to further assess the lateral extent of impacted groundwater and to expand the on-site groundwater monitoring network to the northeast (downgradient) of the former USTs To achieve these objectives, one additional on-site 1 groundwater table monitoring well (MW-4) was permitted, installed, surveyed, monitored and sampled Groundwater samples were also collected for analysis from the three existing monitoring wells and the on-site domestic water well Soils observed during the drilling of MW-4 consisted of massive intervals of clay, silt and fine sand mixtures to a depth of approximately 70 feet, underlain by a poorly-graded fine sand and ' silty sand interval approximately 15 feet thick This stratigraphy is relatively consistent with soils observed during previous drilling at the site During drilling on November 30, 2001, saturated soil and groundwater were first encountered at approximately 75 5 feet bgs On December 17, 2001, the static depth to the groundwater table at MW-4 was 77 34 feet bgs As such, groundwater does not appear to be present under confining conditions Groundwater recharge was observed to be moderately strong On December 17, 2001, the depth to static groundwater across the site ranged from 76 96 feet bgs in MW-1 to 77 83 feet bgs in MW-3 The corresponding groundwater surface elevation ranged from a high of 23 04 feet (arbitrary datum) at MW-2 to a tow of 22 86 feet (arbitrary datum) at MW-1 The resulting groundwater surface appears as an irregular plane dipping to the north-northeast at a gradient of approximately 0 0031 foot/foot Between September 18 and December 17, 2001, the groundwater surface rose an average of 1 39 feet, and the groundwater flow direction and gradient remained relatively constant The three soil samples collected during the investigation did not contain detectable concentrations of any of the gasoline compounds analyzed Based on the results from previous investigations, most of the petroleum hydrocarbon mass appears to be concentrated in soil immediately below the north end of the former middle UST Vertically, the concentrations of gasoline hydrocarbons appear to decrease rapidly with depth Based on the results from soil samples collected during the drilling of MW-1, MW-2, MW-3 and MW-4, the lateral extent of impacted soil appears to be defined to the area of the former USTs The groundwater samples collected from MW-4 only contained 0 55 µg/l of xylenes No other gasoline compound was detected in the MW-4 sample The groundwater samples collected from MW-1, MW-2 and MW-3, and the on-site domestic water well did not contain detectable concentrations of any of the gasoline compounds analyzed Based on these results, any impact to groundwater appears to be limited to immediately beneath the former USTs Based on these conclusions, Ramage Environmental recommends that the monitoring well network continue to be monitored and sampled on a quarterly basis for at least two additional quarters If, after the next two quarters of sampling, groundwater continues to be free of gasoline compounds, the case should be considered for regulatory closure 4 1