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1 <br /> URS <br /> Mr. Robert McClellon <br /> April 24, 2008 <br /> Page 4 of 4 <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> Nine metals (arsenic, barium, chromium, cobalt, iron, manganese, nickel, vanadium and zinc) and TDS <br /> were detected above the analytical reporting limits in the groundwater samples collected on <br /> March 13,2008. Of these constituents, three (iron, manganese, and TDS) were above their established <br /> regulatory levels. Because two of the metal results and TDS were above their established regulatory <br /> levels,URS plans to continue quarterly monitoring of these metals and TDS. <br /> Prior to the installation of the passive soil vapor extraction trench, the methane concentration has <br /> historically exceeded 5 percent by volume within VW-4, VW-5S, VW-5D, VW-6S, and VW-6D. Since <br /> the passive soil vapor extraction trench installation, the methane concentration has decreased within <br /> these probes to less than 5 percent by volume during the following quarter and has continued to be less <br /> than 5 percent during the subsequent quarters.Methane concentrations measured within all probes during <br /> the first quarter of 2008 were less than 5 percent by volume. Based on the results during this quarter, <br /> compared to the results prior to the passive soil vapor extraction installation, the passive soil vapor <br /> extraction trench appears to be effective at controlling methane from leaving the site. URS, on behalf of <br /> RadioShack, plans to continue the monitoring activities for measuring the landfill gas concentrations <br /> within the 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 /> t <br /> mine,P.E. <br /> vil Engineer <br /> Enclosures: Table 1 —Summary of Field Measurement Results <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—March 2008 <br /> Attachment 1 —Non-Hazardous Waste Manifest <br /> Attachment 2—Monitoring Well Sampling Data Logs <br /> Attachment 3—Analytical Report <br /> cc: Judy McCampbell (RadioShack) <br /> John Macanas (CIWMB) <br /> Ross Atkinson (RWQCB) <br /> K:\Wprocess\25532\WorldEntelprise\Quarterly Rpt\2008\I Q08\043008.doc <br />