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Mr. Robert McClellon <br />February 3, 2010 <br />Page 4 <br />CONCLUSIONS AND RECOMMENDATIONS <br />Twelve metals (arsenic, barium, chromium, cobalt, copper, iron, lead, manganese, nickel, thallium, <br />vanadium and zinc) and TDS were detected above the analytical reporting limits in the groundwater <br />samples collected on December 10, 2009. Of these constituents, six (arsenic, barium, iron, <br />manganese, thallium and TDS) were above their established regulatory levels. Because five of the <br />metal results and TDS were above their established regulatory levels, URS plans to continue <br />quarterly monitoring of these metals and TDS. <br />Prior to the installation of the passive soil vapor extraction trench, the methane concentration <br />historically exceeded 5 percent by volume within the following probes: VW -4, VW -5S, VW -5D, <br />VW -6S, and VW -6D. Since the passive soil vapor extraction trench installation in September 2006, <br />the methane concentration has decreased within these probes to be less than 5 percent by volume <br />during the following quarter and has continued to be less than 5 percent during the subsequent <br />quarters. Methane concentrations measured within all probes during the fourth quarter of 2009 were <br />less than 5 percent by volume. Based on the results during this quarter, compared to the results <br />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 monitoring activities for measuring landfill gas concentrations within the probes, <br />extraction wells, and passive vents on a quarterly basis. <br />Should you have any questions regarding this report, please contact me at (916) 679-2081. <br />Very truly yours, <br />URS <br />Engineer <br />Table 1 Summary of 2009 Field Measurement Results <br />Table 2 Dissolved Metals Results, Total Dissolved Solids Results, and <br />Field Measurement Results Summary in Groundwater <br />Figure 1 Site Plan <br />Figure 2 Groundwater Elevation — December 2009 <br />Attachment 1 Monitoring Well Sampling Data Logs <br />Attachment 2 Analytical Report <br />cc: Jaime Caballero (RadioShack) <br />John Macanas (CIWMB) <br />Ross Atkinson (RWQCB) <br />H:\Wprocess\25532\WorldEnterprise\Quarterly Rpt\2009\4Q09\020310.doc <br />