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Former Canteen Facility January 13,2005 Qu_agterly Groundwater Monitoring Report Page 4 I • 1,2-DCA was detected at a concentration of 77 gg/L, in MW-11, which exceeds the CAMCL of 0 5 gg/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 Ishallow 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 INVESTIGATIONUMMARY and CONCLUSIONS CLUSIONS 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, and MW-11 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- ie DCA concentrations are located offsite in monitor well MW-11 Well MW-11 also has detectable concentrations of TPH(g), although the laboratory flagged the result as I estimated The majority of the groundwater impacts are centered on the MW-3 and MW-13 series wells IREMEDIATION SYSTEM OPERATION and MAINTENANCE Delta installed an approved soil and groundwater remediation system at the site during the period Ifrom 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 ISVE SYSTEM OPERATIONS SVE operations continued with only wells VE-1 and VE-3 For the majority of the quarter, these I two wells continued to produce enough hydrocarbon vapors for efficient ICE unit power Only at the very end of September, were there any indications of significant decline in hydrocarbon concentrations from the two SVE wells IOperation 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 Ivapor extraction wells and overall inlet manifold were measured and recorded, along with total I