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URS <br /> Mr. Robert McClellon <br /> October 31, 2012 <br /> Page 3 <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> Prior to the installation of the passive soil vapor extraction trench,the methane concentration historically <br /> exceeded 5% by volume within the following probes: VW-4,VW-5S,VW-5D,VW-6S, and VW-6D. <br /> Since the passive soil vapor extraction trench installation in September 2006,the methane concentration <br /> has decreased within these probes to less than 5%by volume during the following quarter and has <br /> continued to be less than 5%by volume during the subsequent monitoring events. Methane <br /> concentrations measured within all probes during 3Q12 were less than 5%by volume. <br /> Based on the results during this quarter,compared to the results prior to the passive soil vapor extraction <br /> installation, the passive soil vapor extraction trench appears to be effective at controlling methane from <br /> leaving the site. Because the results of the monitoring activities for measuring landfill gas concentrations <br /> within the probes have been less than 5%by volume since December 2006(following the installation of <br /> the passive soil vapor extract trench),we recommend that the monitoring activities continue on an annual <br /> basis. <br /> Should you have any questions regarding this report, please contact me at(916) 679-2343. <br /> Very truly yours, <br /> URS <br /> Corinne Marks <br /> Senior Civil Engineer <br /> Enclosures: Table 1 Summary of 3Q12 Field Measurement Results <br /> Figure 1 Site Plan <br /> c: Jaime Caballero(RadioShack) <br /> Sabra Ambrose(CIWMB) <br /> H:\Wurocess\255321WoridEnterprise\Quarterly RptW12\Text doc <br />