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IFormer Canteen Facility October 15,2004 uarterl Groundwater Monitoring Report Pa e 4 I • 1,2-DCA was detected at a concentration of 96 µg/L in MW-I1, which exceeds the CAMCL of 0 5 µg/L 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 IGROUNDWATER INVESTIGATION SUMMARY and CONCLUSIONS I ISampling and analysis was performed in August 2004 to evaluate the current concentrations of petroleum hydrocarbons of Site groundwater monitoring wells Based on the results, Delta has developed the following conclusions • Monitor wells MW-3, MW-3A, MW-3D, MW-11, 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 I • • Groundwater impacts appear to be generally confined onsite The only detectable 1,2- DCA concentrations are located offsite in monitor well MW-i 1 Well MW-I I also has detectable concentrations of TPH(g) The majority of the groundwater impacts Iare centered on the MW-3 and MW-13 series wells REMEDIATION SYSTEM OPERATION and MAINTENANCE IDelta 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 Vacuum for the SVE system has been provided by a trailer- mounted internal combustion engine (ICE) unit In addition to the vacuum for the system, the ' ICE unit also destroys hydrocarbon vapors that are recovered from the subsurface SVE SYSTEM OPERATIONS SVE operations continued with only wells VE-1 and VE-3 For the majority of the quarter, these two wells continued to produce enough hydrocarbon vapors for efficient ICE unit power Only at I the very end of September, were there any indications of significant decline in hydrocarbon concentrations from the two SVE wells Operation and maintenance (O&M) activities for the AS-SVE remediation system were • conducted weekly The weekly O&M activities included vacuum readings from the individual vapor extraction wells and overall inlet manifold were measured and recorded, along with total