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C-SHADSOFS91.1/1.10 <br /> 02/10/92 <br /> soil gas and TCE dissolved in groundwater suggests that soil gas is a good <br /> predictive tool for estimating the source areas (contaminated soil) of <br /> TCE-contaminated groundwater. However, no general pattern exists of TCE in <br /> soil gas at the plumes' distal ends. Apparently, soil is a source of VOCs that <br /> migrate by various mechanisms to the groundwater. No evidence has been <br /> discovered that groundwater-transported TCE moves back up through the soil <br /> column. <br /> The second phase of the field investigation to locate sources was intended to <br /> measure VOC concentrations in soil at those locations with the highest <br /> concentrations of soil gas TCE. In a major soil sampling program at SHARPE, <br /> conducted by ESE in 1987, soil samples were collected from discrete vertical <br /> intervals for TCE analysis in 103 soil borings. Other, more limited, soil sampling <br /> programs also have been conducted by Battelle (1983) and, more recently, by <br /> SHARPE personnel. <br /> All areas of significant TCE soil gas concentration were investigated as potential <br /> sources in the 1987 ESE study. The methodology used in the field efforts was to <br /> screen the soils beneath the entire installation for the presence of VOCs in the <br /> soil gas. Areas with high soil gas concentrations were investigated further by . <br /> analyzing split-spoon soil samples for TCE. The combined results of the soil gas <br /> and soils analyses were interpreted to predict the presence of VOCs in the <br /> groundwater and the optimum position of monitor wells and the location(s) of <br /> contaminated soil. <br /> WE is the most prevalent contaminant. This is consistent with the 1987 record <br /> search ESE conducted (1989b) that showed TCE as the predominant solvent used <br /> 1-13 <br />