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01 Mr Michael Infurna July 21, 2006 Page 6 measured at the tyle of vapor sampling As shown in Table 7 and illustrated on Figure 9, total MTBE,benzene, and toluene mass extraction rates decreased over the period of the 13-day total pilot test For MTBE, total mass extraction rates decreased from a maximum of 75 1 pounds per day (lb/day) during the first day of operation to 14 2 lb/day during the 13``' day of operation of the pilot test with a total mass removed of 549 pounds (Table 7) For benzene, total mass extraction rates decreased from 8 91 lb/day to 0 68 lb/day,with a total mass removed of 54 4 pounds Toluene mass extraction rates decreased from a maximum of 34 8 lb/day to 13 7 lb/day,with a total mass removed of 310 4 pounds during the pilot test Conclusions The SVE,AS, and combined AS/SVE pilot test confirmed that AS/SVE is a viable remedial alternative for the Site for both soil and groundwater The VOC concentrations in the SVE system after operation of the AS only test were only slightly higher than during operation of the SVE system only However, the concentration of NME in groundwater decreased from 64,000 µg/L prior to startup to 13,000 following shut down of the combined AS/SVE system Overall concentrations of MTBE in the soil gas and groundwater were reduced by 80 percent during the two-week pilot test In addition, the ROI of the SVE system for VEW-1 was shown to be approximately 22-feet The ROI of VEW-1 covers the former UST area and excavation as shown on Figure 4 Concentrations of MTBE,TPH/g, and tert-butanol increased in MW-2 after the pilot test There was also a small increase in concentrations observed m MW-4, however, the concentrations are still within historical levels The increase of MTBE and TPH/g in both wells may be attributed to mounding of the groundwater table due to air sparging that would essentially push contaminants out radially from the sparging point While groundwater level measurements collected from surrounding groundwater monitoring wells (MW-2,MW-3, and MW-4) during the pilot test did not indicate typical mounding,a steep gradient of 0 02 ft/ft to the northeast did occur prior to breakthrough Once breakthrough occurred, the gradient decreased to 0 004 ft/ft still in the northeast direction Sparging air at a lower flow-rate will prevent such steep gradients,and preventing contanunant migration,while increasing dissolved oxygen levels in groundwater The results of the SVE pilot test suggest that VOC concentrations in soil in the vicinity of monitoring well VEW-1 may continue as a source of petroleum hydrocarbon to groundwater The AS/SVE technology appears to be effective in removing this source and treating the impacted groundwater Therefore, a design P\28000\128253- 1&T Trucl ing SV1.\Documr nts\5VL Rcport umca doc