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CONCLUSIONS <br /> The monitoring results show that methane concentrations exceed 5% in only a single probe along <br /> the north side of the secondary site. This is a great improvement over recent quarters, and may <br /> be an indication that the work on the gas system is helping to control gas migration. However, <br /> normal operation of the landfill gas system does not consistently control gas migration, so it is <br /> necessary to modify the system in an attempt to reduce perimeter gas levels to below 5%. The <br /> County is in the process of evaluating which system modifications will be most effective. <br /> Previously, we suggested that we would install a larger motor for a blower to provide more <br /> vacuum. It has since been determined that series operation of both blowers is more efficient, so <br /> we are proceeding with this plan. We are also investigating some significant system <br /> modifications that will improve winter operations. <br /> We believe that vacuum shortage is a major reason for the lack of migration control. The areas <br /> of gas migration are concentrated on the north end of the landfill,where vacuum is lowest. We <br /> have been directing all available vacuum to the north end by closing off vacuum to all wells on <br /> the south half of the site. <br /> Monitoring will continue with the next monitoring event in January 2000. Further monitoring <br /> will help determine if the gas control system is working more efficiently. <br /> N:\WES\HL\GAS\4thg99gas.wpd <br /> 5 <br />