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r 1 <br /> •URS <br /> • <br /> Mr. Robert McClellon <br /> January 31, 2008 <br /> Page 4 <br /> Prior to the installation of the passive soil vapor extraction trench,the methane concentration has <br /> historically exceeded 5%by volume within VW-4,VW-5S,VW-5D,VW-6S, and VW-61). Since the <br /> passive soil vapor extraction trench installation,the methane concentration has decreased within these <br /> probes to less than 5% by volume during the following quarter and has continued to be less than 5% <br /> during the subsequent quarters. Methane concentrations measured within all probes during the fourth <br /> quarter of 2007 were less than 5%by volume. Based on the results during this quarter, compared to the <br /> results prior to the passive soil vapor extraction installation,the passive soil vapor extraction trench <br /> appears to be effective at controlling methane from leaving the site. URS on behalf of RadioShack <br /> plans to continue the monitoring activities for measuring the landfill gas concentrations within the <br /> probes, extraction wells,and passive vents once a quarter. <br /> Should you have any questions regarding this report, please contact me at(916) 679-2081. <br /> Very truly yours, <br /> URS <br /> jJa . mine <br /> vil Engineer <br /> Enclosures: Table 1 —Field Measurement Results Summary <br /> Table 2—Dissolved Metals Results,Total Dissolved Solids Results and Field <br /> Measurement Results Summary in Groundwater <br /> Figure 1 —Site Plan <br /> Figure 2—Groundwater Elevation—December 2007 <br /> Attachment 1 —Monitoring Well Sampling Data <br /> Attachment 2—Analytical Report <br /> c: Judy McCampbell (RadioShack) <br /> John Macanas(CIWMB) <br /> Ross Atkinson(RWQCB) <br /> K:\Wprocess\25532\WorldEnterprise\Quarterly Rpt\2007\4Q07\CovLtrRpt.doc <br />