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URS <br /> Mr. Robert McClellon <br /> January 29, 2016 <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 4Q14 were less than 5%by volume. <br /> Based on a comparison of the results during this most recent monitoring action to the results prior to the <br /> passive soil vapor extraction installation,the passive soil vapor extraction trench appears to be effective <br /> at controlling methane from leaving the site. Because the results of the monitoring activities for <br /> measuring landfill gas concentrations within the probes have been less than 5%by volume since <br /> December 2006(following installation of the passive soil vapor extract trench), URS recommends <br /> continuing monitoring activities on an annual basis. <br /> Should you have any questions regarding this report,please contact me at(916)679-2343. <br /> Very truly yours, <br /> URS <br /> An AECOM Company <br /> Corinne Marks,P.E. <br /> Senior Civil Engineer <br /> Enclosures: Table 1 —Summary of 4Q15 Field Measurement Results <br /> Figure 1 —Site Plan <br /> c: Bill Russum(RSH Liquidating Trust) <br /> Jaime Caballero(RS Legacy Corporation) <br /> Sabra Ambrose(CIWMB) <br />