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Ms. Lori Duncan <br /> March 31, 2008 <br /> Page 2 of 7 <br /> The lateral extent of soil contamination was also defined. Soil contamination in the vadose zone <br /> appears to be limited to a small area in the immediate vicinity of the former UST, and soil <br /> contamination in the capillary fringe zone appears to extend no more than 25 feet north, 20 feet <br /> west, 10 feet south, and 5 feet east of the former UST. <br /> Table 2 summarizes soil analytical results and Table 3 summarizes "grab" groundwater analytical <br /> results. Figure 2 presents soil boring locations. <br /> Groundwater Monitoring Wells <br /> Ground Zero directed the installation and sampling of four groundwater monitoring wells (MW 1- <br /> MW4) in December 2000 to further investigate the lateral extent of dissolved contaminants in <br /> shallow groundwater beneath the site. Groundwater beneath the site has been measured at depths <br /> ranging from approximately 21 to 28 feet below the tops of the casings (btoc) of site monitoring <br /> wells. Groundwater has consistently flowed northeast. Based upon analytical results of <br /> groundwater samples collected from soil borings and groundwater monitoring wells MW1 <br /> through MW4 the extent of petroleum hydrocarbon contamination in the groundwater does not <br /> extend more than approximately 40 feet downgradient from the source. Various chlorinated <br /> solvents were also detected in all site wells, however, and free product was noted in well MW3. <br /> Subsequent quarterly groundwater sampling at the site confirmed that the lateral extent of <br /> petroleum hydrocarbon contamination is within close proximity to the former UST. Groundwater <br /> analytical results and the periodic presence of free product in well MW3 indicate that petroleum <br /> hydrocarbon contamination is present in groundwater in the immediate vicinity of the former <br /> UST but does not extend to wells MWl, MW2, or MW4. Various chlorinated solvents are <br /> present in groundwater at low levels; however, only tetrachloroethene (PCE) routinely exceeds <br /> its Maximum Contaminant Level (MCL) of 5 parts per billion (ppb) in more than one site well. <br /> Three additional groundwater monitoring wells (MW5-MW7) were installed in May 2003 to <br /> further investigate the lateral extent of contaminants in shallow groundwater beneath the site. <br /> PCE was detected at very low levels in upgradient well MW5 and at moderate levels in <br /> downgradient well MW6 and cross gradient well MW7. The highest concentration of PCE was <br /> detected in cross gradient well MW7, which is located at the northwest corner of the property, <br /> near the intersection of N. El Dorado and Park Streets. <br /> Monitoring well locations are shown in Figure 2. Table 4 summarizes groundwater analytical <br /> results from site monitoring wells. <br /> Investigation of Potential Vertical Migration Pathways <br /> In May 2003 Ground Zero directed the drilling and sampling of three continuous-core borings <br /> (SB9, SB10 and SB11) using a "direct-push" drilling rig for lithologic logging and subjective <br /> G:\GROUNDZE\GABBARD\workplms\wp_0308.doe <br />