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I <br /> Mr Ron Rowe <br /> Page 4 of 6 <br /> ' Vapor Sample Analytical Results <br /> Laboratory reports are included in Attachment D and are summarized in Table 4 Based on the <br /> I ' TPPH concentrations, the destruction efficiency of the thermal oxidizer during the April, May, <br /> and June sampling rounds was 92% or better <br /> I ' Overall, analytical results of second quarter 1999 influent samples indicated vapor concentrations <br /> have declined somewhat from the first quarter of 1999 <br /> System Evaluation <br /> The VES has been removing hydrocarbons from subsurface soil since November 19, 1997 at flow <br /> ' rates ranging from 270 to 380 cubic feet per minute including dilution air <br /> i <br /> ' As of June 30, 1999 the system had been in operation for 8,924 hours Based on graphical <br /> interpolation between measured influent vapor concentrations, as of June 30 an estimated 12,000 <br /> pounds of hydrocarbon contamination had been removed from the soil Table 5 summarizes flow <br /> and vapor concentration averages as well as the total hydrocarbon mass removed from the soil <br /> OTHER ACTIVITIES <br /> ' On May 3, 1999 850 gallons of drummed purge water was removed from the site by Evergreen <br /> Environmental Services A copy of the non-hazardous waste manifest is included in Attachment <br /> ' A � <br /> RECOMMENDATIONS <br /> ' Develop Case Closure Criteria and Schedule <br /> In view of the relative success of the soil remediation effort and the static groundwater plume <br /> condition we recommend that site-specific criteria and a tentative schedule for closure be <br /> ' developed for this case <br /> The VES has removed a significant mass of contamination from accessible vadose soils since <br /> ' operation began in November 1997 During this period approximately 12,000 pounds of <br /> hydrocarbons have been removed from the (subsurface The estimated total mass of soil <br /> contaminants prior to instituting vapor extraction was approximately 24,000 pounds, suggesting <br /> ' that approximately 50% of the total has been removed The remaining 50% is comprised for the <br /> most part of contaminated soil which is currently submerged due to high water levels This is not <br /> roek\gmr\29m19W <br />