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Ms Lori Duncan Page 3 of 4 3 0 GROUNDWATER ANALYTICAL RESULTS All groundwater samples were analyzed for TPHg and TPHd using EPA method 801513, BTEX using EPA 802113, and VOCs and oxygenated gasoline additives using EPA 8260B Tetrachloroethene (PCE) was detected in wells MW1, MW2, MW4, MW5, MW6, and MW7 at concentrations of 12 parts per billion (ppb), 11 ppb, 6 6 ppb, 5 1 ppb, 44 ppb, and 95 ppb, respectively No PCE was detected m well MW3 (<2 0 ppb) cis-1,2-Dzchloroethene (cis-1,2-DCE) ranged from <0 5 ppb in well MW5 to 19 ppb in well MW3 Chloroform ranged from 0 7 ppb in well MW7 to 3 9 ppb in well MW1, but was not detected in well MW3 (<2 0 ppb) Trichloroethene (TCE) ranged from <0 5 ppb in wells MW4 and MWS to 5 2 ppb in well MW3 No petroleum hydrocarbons or gasoline additives were detected above method detection limits in groundwater samples collected from any site well, except well MW3 Well MW3 contained TPHg at 3,600 ppb, benzene at 20 ppb, toluene at 52 ppb, ethylbenzene at 26 ppb, and xylenes at 140 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 4) strongly suggests that the primary source of PCE in groundwater is off-site to the northwest The apparent distribution of dissolved TCE (Figure 5) and cis-1,2-DCE (Figure 6) 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 Further, the concentration of dissolved PCE in all site wells is decreasing over time, as illustrated on Figure 6 6 1GROUNDZEIGABBARDIreports\QMR1200411QM2004 doc