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URS 0 <br /> Mr. Robert McClellon <br /> January 31, 2012 <br /> Page 3 <br /> with approximately 3%bentonite powder. An area of approximately 2 feet in diameter(measured from <br /> the well casing)and approximately 2 feet deep was excavated and backfilled with the cement slurry to <br /> create a mushroom cap. No solid waste was observed in the soil cuttings generated from the excavated <br /> area. <br /> Investigation-Derived Waste.Because no solid waste was observed in the soil cuttings,the soil cuttings <br /> were spread at each decommissioned well as per the requirements of the approved work plan. <br /> Annual Monitoring Activities <br /> Landfill gas concentrations were measured within the gas migration monitoring probes, extraction wells, <br /> and passive vents were completed on December 13, 2011. <br /> Using a handheld portable landfill gas monitor,a GEM 2000, each gas-migration monitoring probe, each <br /> extraction well, and each passive vent was measured for methane, oxygen, and carbon dioxide. These <br /> measurements were recorded in a field logbook. <br /> RESULTS <br /> The methane concentrations measured during the quarter were 0%in all gas-migration monitoring <br /> probes. Methane concentrations measured in the vapor extraction wells were 4.3%in EW-1 and 6.0%in <br /> EW-2. Methane concentrations measured in the passive vents were 0%in VP-land VP-2,0.4%in VP-3, <br /> and 2.3%in VP-4. Oxygen concentrations measured at all sample locations during the quarter ranged <br /> from 0.3%to 22.3%. Carbon dioxide concentrations measured at all sample locations during the quarter <br /> ranged from 0.1%to 26.4%. Table 1 summarizes results for each probe, each extraction well, and each <br /> passive vent. <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> Prior to the installation of the passive soil vapor extraction trench,the methane concentration historically <br /> exceeded 5%by volume within the following probes: VW-4,VW-5S,VW-5D,VW-6S, and VW-6D. <br /> Since the passive soil vapor extraction trench installation in September 2006,the methane concentration <br /> has decreased within these probes to less than 5%by volume during the following quarter and has <br /> continued to be less than 5%by volume during the subsequent monitoring events. Methane <br /> concentrations measured within all probes during 4Q11 were less than 5%by volume. <br /> Based on the results during this quarter,compared to the results prior to the passive soil vapor extraction <br /> installation,the passive soil vapor extraction trench appears to be effective at controlling methane from <br /> leaving the site. Because the results of the monitoring activities for measuring landfill gas concentrations <br /> within the probes have been less than 5%by volume since December 2006(following the installation of <br /> the passive soil vapor extract trench),we recommend that the monitoring activities continue on an annual <br /> basis. <br /> H:\Wprocess\25532\WorldEnterprise\Radio Shack0ecomm_Annual Rpffext.doc <br />