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Mr. Robert McClellon <br />October 20, 2010 <br />Page 4 of 4 <br />CONCLUSIONS AND RECOMMENDATIONS <br />Ten metals (arsenic, barium, chromium, cobalt, iron, lead, manganese, nickel, vanadium and zinc) and <br />TDS were detected above the analytical reporting limits in the groundwater samples collected on <br />September 14, 2010. Of these constituents, five (arsenic, barium, iron, manganese, and TDS) were <br />above their established regulatory levels. Because four of the metal results and TDS were above their <br />established regulatory 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 <br />historically exceeded 5% by volume within the following probes: VW -4, VW -5S, VW -5D, VW -6S, <br />and VW -6D. Since the passive soil vapor extraction trench installation in September 2006, the methane <br />concentration has decreased within these probes to less than 5% by volume during the following quarter <br />and has continued to be less than 5% during the subsequent quarters. Methane concentrations measured <br />within all probes during the 3Q10 were less than 5 percent by volume. Based on the results during this <br />quarter, compared to the results prior to the passive soil vapor extraction installation, the passive soil <br />vapor extraction trench appears to be effective at controlling methane from leaving the site. URS, on <br />behalf of RadioShack, plans to continue monitoring activities for measuring landfill gas concentrations <br />within the probes, 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 />Table 1 <br />Table 2 <br />Summary of 2010 Field Measurement Results <br />Dissolved Metals Results, Total Dissolved Solids Results, and Field <br />Measurement Results Summary in Groundwater <br />Figure 1 Site Plan <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\Quartcrly Rpt\2010\3Q 10\102010.doc <br />