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4.3.4 Radian Groundwater Investigation <br /> 4.3.4.1 As discussed in Section 2.0, a site investigation was conducted by <br /> Radian Corporation which consisted of a soil gas investigation and the <br /> installation of 16 on-Depot groundwater monitoring wells (LM 27 through LM <br /> 43) , and the sampling of these wells and the groundwater monitoring wells <br /> which existed at the time of the investigation. The location of all <br /> groundwater monitoring wells is included on Figure 2.2-1, and the <br /> analytical results from the groundwater sampling in Appendix H. As <br /> discussed in Section 4.0, the locations of the groundwater monitoring wells <br /> installed by Radian were based primarily upon the results of the soil gas <br /> survey, which identified six Contaminant Areas at the Depot, and previous <br /> sampling data from existing wells. <br /> 4.3.4.2 The Radian wells and those previously installed under the <br /> direction of U.S. Army Environmental Hygiene Agency (USAEHA) (LM 1 through <br /> LM 26) were almost exclusively completed in the uppermost part of the Upper <br /> Tulare HSU, with most wells completed within 50 feet of ground surface. <br /> The results of the Radian investigation focused primarily on the <br /> characterization of the onsite shallow groundwater chemistry and <br /> identification of likely sources of groundwater contamination. Because <br /> monitoring wells were not installed beyond the Depot boundary by Radian, <br /> the off-Depot contamination was not characterized. <br /> 4.3.4.3 The Radian investigation identified the principal groundwater <br /> contaminants to be the purgeable halocarbons TCE and PCE, with the highest <br /> concentration generally located in areas where elevated soil gas <br /> concentrations had been observed. <br /> 4.3.4.4 To evaluate the changes in chemical concentrations which have <br /> occurred since the 1986 Radian investigation, as well as include the most <br /> recent off-site groundwater quality data available and a discussion of the <br /> lateral and vertical extent of contamination, the Radian results are <br /> discussed along with the WCC results in the following section (4.3.5) . <br /> 4-167 <br />