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URS <br /> Mr. Robert McClellon <br /> July 13, 2007 <br /> Page 4 <br /> collected on June 14,2007. Of these constituents,six(arsenic,barium, iron,manganese,thallium,and <br /> TDS)were above their established levels. Since five of the metal results and TDS were above their <br /> established levels,we plan 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%within VW-4,VW-5S,VW-51),VW-6S, and VW-6D. Since the passive soil <br /> vapor extraction trench installation,the methane concentration has decreased within these probes to <br /> less than 5%during the following quarter and has continued to be less than 5% during the subsequent <br /> quarters. Methane concentrations measured within all probes during the second quarter of 2007 were <br /> less than 5 percent.Based on these results during this quarter compared to the results prior to the <br /> passive soil vapor extraction installation,the passive soil vapor extraction trench appears to be <br /> effective at controlling methane from leaving the site. Since the passive soil vapor extraction trench <br /> appears to be effective at controlling methane from leaving the site,we recommend that the monitoring <br /> activities for measuring the landfill gas concentrations within the probes, extraction wells, and passive <br /> vents be continued monthly during the next quarter. If the methane concentrations within all probes are <br /> less than 5%during this next quarter, we plan to recommend that the monitoring activities for <br /> measuring the landfill gas concentrations within the probes, extraction wells,and passive vents be <br /> continued quarterly. <br /> If you have any questions regarding this report,please contact me at(916) 679-2081. <br /> Very truly yours, <br /> URS <br /> amine <br /> S n' Civil Engineer <br /> JK/gng <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—June 2007 <br /> Attachment 1 —Monitoring Well Sampling Logs <br /> Attachment 2—Analytical Report <br /> c: Judy McCampbell(RadioShack) <br /> John Macanas(CIWMB) <br /> K:\Wprocess\25532\WorldEnterprise\Quarterly Rpt\2Q07\CovLtrRpt.doc <br />