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Mr Ron Rowe Project 20805-146 010 <br /> April 8, 1998 <br /> Page 2 <br /> After collecting and analyzing the influent data, EMCON shut down the SVE system for a <br /> period of three weeks to allow the vadose soil concentrations to stabilize <br /> Post Shut Down Results <br /> EMCON restarted the SVE system on February 18, 1998 after a three week non- <br /> operational period At this time EMCON, collected influent data using a photwonizatlon <br /> detector and Tedlar bag samples for laboratory analysis Based on field observations <br /> using the PID and confirmed by the laboratory results, that influent concentrations had not ' <br /> rebounded, and had in fact continued to decline, EMCON discontinued any further <br /> sampling of the SVE system for laboratory analysis EMCON proceeded to monitor the <br /> SVE system using the PID to assess any trends The influent concentrations continued to <br /> decline further over the next five hours of first day and over the next few days of <br /> operation The February 18, 1998 analytical results indicated that TPHG had declined to <br /> only 1,176 ppmv and benzene was no longer detected 1n the influent soil vapor <br /> Conclusion <br /> As shown from the analytical and field screening data, there was no rebound in soil vapor <br /> influent concentrations after a three week shut down and benzene continued to decline to <br /> non-detectable levels without SVE operation Based on this data, and the fact that the <br /> SVE system has removed nearly 10,000 pounds of TPHG over the one year life of the <br /> system, EMCON is recommending no further remediation action for the vadose soil at the <br /> site EMCON is aware that further activities will be required for the dissolved <br /> groundwater concentrations beneath the site and that confirmation borings may be <br /> required to substantiate the evidence presented in this letter <br /> • <br /> 5AC\C 1FiLE3WRCO\21681ROWE2 DOC-951mtt 1 <br />