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Apr-14-98 12 .35P Pinnall/EMCON P-03 <br /> 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 photoionization <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 in 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 /> SAC`(';1F1 LES W RC0\2169\ROW R2.D069SNntt:1 <br />