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i Former Canteen Facility June 10, 2002 Quarterly Groundwater Monitoring Report Page 4 • MTBE was detected in MW-3, MW-3A, MW-3D, MW-11 and MW-13 at concentrations ranging from 4 µg/1 to 1,200 µg/l The CAMCL for MTBE is 13 pg/l, exceeded in MW-3, MW-3A, MW-11, and MW-13 • 1,2-DCA was detected at a concentration of 12 pg/]L in MW-11, which exceeds the CAMCL of 0 5 g/L Historical groundwater analytical results are summarized on Table 2 Figures 3 and 4 illustrate the i so concentration contours for benzene and TPH(g) concentrations, respectively, in the shallow aquifer wells Figures 5 and 6 illustrate the isoconcentration contours for benzene and TPH(g) concentrations, respectively, in the one deep aquifer well (MW-13B) The field notes and laboratory reports for this quarterly monitoring event are attached as Appendix A INVESTIGATION SUMMARY and CONCLUSIONS Sampling and analysis was performed in May 2002 to evaluate the current concentrations of petroleum hydrocarbons of Site groundwater monitoring wells Based on the results, AES-RS has developed the following conclusions • Monitor wells MW-3, MW-3A, MW-3D, MW-I1, and MW-13 had detectable concentrations exceeding the CAMCL concentrations of at least one of the following constituents benzene, toluene, ethylbenzene, xylenes, MTBE, and 1,2-DCA • Groundwater impacts appear to be generally confined onsite, although the only detectable 1,2-DCA concentrations are centered offsite on monitor well MW-11 The majority of the groundwater impacts are centered on the MW-3 and MW-13 series wells RECOMMENDATIONS AES-RS recommends the following for the Former Canteen Facility • Continue groundwater monitoring and reporting, including measurement of depth to groundwater in each well, evaluating monitor well status, preparation of a potentiometnc surface contour map containing the calculated gradient and approximate rate of groundwater movement, and preparation of isoconcentration contour maps for benzene and TPH(g) at the two different screened aquifer depths However, AES-RS recommends modifying the monitoring schedule, as noted below AES-RS also recommends modifying the analytical method, using only EPA Method