SITE INFORMATION AND CORRESPONDENCE

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o�evron Chevron groundwater flow direction beneath the site throughout the monitoring,period indicates that the direction is not consistent and �is .probably .influenced by local domestic well extractions..A complete record of historic grouridwater. .monitoring results is presented in the quarterly groundwater monitoring report issued by Alton Geoscience dated June 2, 1992. In evaluating the above historic data from the subject site-the foliowing observations and comments are offered: Soil samples taken from beneath the fuel,tanks,suggest that a.release or overspill-occurred from the 5000 gallon unleaded tank and the'2000 gallon.supreme tank. This"is supported by the initial groundwater sample analyses from MW-4, 2, and 3. With the exception of the groundwater'data collected from monitoring wel EA-2 on February 18, 1988, the groundwater contamination bene'ath.the site appears to be confined to,the vicinity of the fuel tank pit. This limited areal extent of the groundwater,contamination i5 further supported by the lack of any detectable hydrocarbon concentrations in the soilat depths above .the 2118/88 water level (46.0 feet bgs) in all soil borings-installed outside of the area contained between-MW-1; 2, and 3. The relatively low levels of dissolved hydrocarbon concentrations originally:measured in MW-1; 2, and 3 indicated that the release of fuel to groundwater was .limited in volume.-This argument is supported by the fact that the extent of contamination,was decreased'by several orders of magnitude(as measured in MW 1, 2, and 3 between March,..1987 and February, 1988) in response to the removal of the tanks and.i�mpacted soil.in January, 1987, the tank pit remaining open until - June, 1987, and the chemical adsorption of hydrocarbons-on soil as groundwater levels dropped by 6.0 feet between March,,1987 and February, 1988. All of these had the effects of increasing iii situ.volatilization, biodegradation, and hydrocarbon decay in'the presence of oxygen. Considering the above argument,,further_ .decreases in groundwater contamination would be. expected.'as groundwater levels continued to drop.an additional-31.0 feet since February,-1988. This appears.to be true-since no detectable concentrations of dissolved'hydrocarbons have been measured in EA-1,3-5 4, 5, and 6 since February, 1988: The in situ passive remediation described .above also appears to be very effective. This is recognized by the lack of any detectable hydrocarbon.concentrations measured in all soil borings drilled onsite since-March, 1987.This is mosvconvincing in the case of.soil.boring SB-I which was drilled bcneath.1he location where the-greatest-.amount of soil and groundwater contamination had been previously documented.. Figure 3 is includedJn this work plan-to illustrate.the rationale used in determining the placement of the two proposed .soil this. The:cross section-diagram illustrates -all:,known .soi -and . groundwater contamination at the subject site an&its spatial relationship to former UST's and wells,recent soil borings; and to the:'proposed soil borings (SB=2 and SB-3). 'The objective of soil boring SB-2 is to define the vertical'extent.of arty:residual soil`contamination that may-exist between the deepest-tank bottom satnple beneath the former.-2000 gallon supreme tank and the deepest soil sample obtained informer monitoring'well MW-1: The groundwater.sample to-be obtained from this.boring will also define ihe-levels4 dissolved hydrocarbons that may remain in R110 CEJ