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Ms Lori Duncan Page 3 of 4 concentrations of 12 parts per billion (ppb), 11 ppb, 5 9 ppb, 4 4 ppb, 54 ppb, and 150 ppb, respectively No PCE was detected in well MW3 (<2 0 ppb) cis-1,2-Dichloroethene (cis-1,2-13CE) ranged from <0 5 ppb in well MW5 to 17 ppb in well MW3 Chloroform ranged from 1 5 ppb in well MW5 to 2 3 ppb in well MW1, but was not detected in wells MW3 (<2 0 ppb) and MW7 (<0 5) Trichloroethene (TCE) ranged from <0 5 ppb in wells MW2, MW4 and MW5 to 4 4 ppb in well MW7 No petroleum hydrocarbons or gasoline additives were detected above method detection limns in groundwater samples collected from any site well, except well MW3 Well MW3 contained benzene at 10 ppb, toluene at 33 ppb, ethylbenzene at 18 ppb, and xylenes at 92 ppb Well MW3 also contained several additional VOCs associated with petroleum hydrocarbons Groundwater analytical results are summarized on Table 3 Attachment 3 contains laboratory reports and chain of custody documentation The distribution of dissolved PCE, TCE, and cis-1,2-DCE beneath the site are presented on Figures 3, 4, and 5, respectively The figures were created by plotting the average concentration of the target analyte over the last four sampling events, the results of which are noted on each figure Although the contours are based on the composite value, the contours for a given sampling round would be very similar if plotted separately 4.0 DISCUSSION Although groundwater beneath the site has consistently flowed northeast (Figure 2), the highest concentrations of PCE in groundwater were detected in well MW7, which is located northwest (cross-gradient) of the former UST Further, no PCE has been detected in well MW3, which was completed through the former UST's location The distribution of dissolved PCE in site wells (Figure 3) strongly suggests that the primary source of PCE in groundwater is off-site to the northwest The apparent distribution of dissolved TCE (Figure 4) and cis-1,2-DCE (Figure 5) beneath the site suggest that the former UST is a source of contamination for these constituents, but also suggest that a secondary source exist off-site to the northwest, based upon higher concentrations in wells MW6 and MW7 as compared to wells MW1 and MW2 TCE and cis-1,2- DCE are known breakdown products of PCE, and their distribution beneath the site is consistent with an off-site source of PCE 5 0 CONCLUSIONS Although measurable free product remains in well MW3 in the form of oily hydrocarbons, no dissolved petroleum hydrocarbon constituents have been detected in any other site well The concentration of dissolved PCE in all site wells over time is illustrated on Figure 6 Based upon the distribution of PCE, TCE, and cis-1,2-DCE in groundwater beneath the site, we conclude that the primary source of PCE contamination in groundwater beneath the site is an off-site source located northwest of the facility G 1GROUNI]ZEIGABBARDIreportslQMR1200412QM2004 doe