ARCHIVED REPORTS_QUARTERLY REPORT - SECOND QUARTER 2008

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l � Metcalf & Eddy, Inc. conducted a comprehensive groundwater investigation in June 1999, consisting of groundwater hydropunch sampling at 14 locations across the site. Groundwater samples were collected at depths ranging from 27 feet to 105 feet bgs. Twenty-eight of these samples were analyzed for carbon tetrachloride and chloroform at an on-site mobile laboratory, utilizing EPA method 8010. Four samples were shipped to an off-site laboratory and analyzed by EPA method 8260B. Data from this investigation showed carbon tetrachloride to be localized in two discrete zones of groundwater impact: one zone in the center of the property and one zone in the southern portion of the property. The results of the investigation were presented in a letter report submitted to the Regional Water Quality Control Board (RWQCB) in July 1999 (Metcalf & Eddy, 1999a). Additional soil and groundwater investigation was conducted at the site in September 1999. This investigation consisted of cone penetrometer testing (CPT) at six locations, soil sampling at seven locations, and hydropunch sampling at one location. The results provided data related to hydrogeologic conditions at the site and were summarized in a November 19, 1999 letter report to the RWQCB (Metcalf&Eddy, 1999b). CGC undertook another round of site work in early 2000 to establish a groundwater monitoring network. This phase of work consisted of installation of five pairs of monitoring wells (total of ten wells). These wells are labeled MW-lA/MW-1B through MW-5A/MW-5B. The "A" wells are screened across a shallow water-bearing zone at approximately 25 feet bgs, whereas the `B" wells are screened across an intermediate water-bearing zone at approximately 75 feet bgs (see Table 1). In February 2000, carbon tetrachloride and chloroform were detected in the shallow wells at concentrations up to 220 pg/L and 150 µg/L, respectively. Carbon tetrachloride and chloroform were detected in the intermediate wells at concentrations up to 1100 µg/L and 80 µg/L, respectively. No vadose zone contamination was detected during drilling and installation of the new wells. Results of this work were presented in the Site Characterization Report submitted to the RWQCB (Metcalf& Eddy, 2000a). A soil vapor survey was conducted and four new monitoring wells were installed between March and May, 2001 (Haley & Aldrich, 2001a). A deep well, MW-3C, was installed to delineate the vertical extent of groundwater impact at the site. The location of this well was selected to coincide with the highest known concentration of carbon tetrachloride in the intermediate water- bearing zone. MW-3C was screened to intersect a water-bearing zone at a depth of approximately 125 feet bgs (see Table 1). The well cluster, MW-7A/MW-7B, was designed to explore the eastern extent of groundwater impact in both the shallow and intermediate water- bearing zones. Well MW-8B was designed to better map the northern extent of groundwater impact in the intermediate water-bearing zone. The 2001 soil vapor survey consisted of samples from 39 gridded locations evenly spaced across the site. Of the 39 samples, 33 contained no detectable VOCs. The highest concentration of carbon tetrachloride detected in soil vapor was 12 gg/L near the center of the site. The soil vapor survey identified no potential source areas in the vadose zone that could affect underlying groundwater. 3