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CE Former Canteen Facility July 1,2004 Quarterly Groundwater Monitoring Report Page 4 I • MTBE was detected in monitor wells MW-3, MW-3A, MW-3D, MW-11, and MW-13 at concentrations of 85, 200, 8 0, 15, and 1,500 µg11, respectively The ICAMCL for MTBE is 13 µg11, exceeded in MW-3, MW-3A, MW-11, and MW-13 • 1,2-DCA was detected at a concentration of 95 µg/L in MW-11, which exceeds the CAMCL of 0 5 µg/L I Historical groundwater analytical results are summarized on Table 2 Figures 3 and 4 illustrate the isoconcentration contours for benzene and TPH(g) concentrations, respectively, in the shallow aquifer wells Figures 5 and 6 illustrate the concentrations for benzene and TPH(g), 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 GROUNDWATER INVESTIGATION SUMMARY and CONCLUSIONS Sampling and analysis was performed in May 2004 to evaluate the current concentrations of • petroleum hydrocarbons of Site groundwater monitoring wells Based on the results, AES has developed the following conclusions I • Monitor wells MW-3, MW-3A, MW-3D, MW-11, MW-13, and MW-13A 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 The only detectable 1,2-DCA concentrations are located offsite in monitor well MW-11 Well MW-11 also has detectable concentrations of TPH(g) The majority of the groundwater impacts are centered on the MW-3 and MW-13 series wells ' REMEDIATION SYSTEM OPERATION and MAINTENANCE AES installed an approved soil and groundwater remediation system at the site during the period from February 23 to March 23, 2004 (Figure 7) The remediation system consisted of air sparging (AS) in conjunction with soil vapor extraction (SVE) The SVE system was put into operation on March 24, 2004 For the first five weeks of operation all five of the SVE wells (designated VE-1 through VE-5) were operating After this initial period of operation the levels of extracted hydrocarbon vapors decreased due to dilution from the SVE wells located outside ' the source area The vapor extraction system was then optimized to increase the flow in the • source area wells by shutting off the down-gradient SVE wells (VE-4, and VE-5) Starting on April 30, 2004, only SVE wells in the vicinity of the former tankpit source area (VE-1, VE-2, ' and VE-3)were operating as this area had the highest concentrations of hydrocarbons detected in I