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• • 6 IMPLEMENTATION OF PREFERRED ALTERNATIVE The preferred corrective action alternative is a passive system likely with carbon filter treatment. This technology was selected because it is capable of controlling offsite migration by releasing methane in a controlled manner. In addition, the use of carbon filtration can prevent the release of regulated VOCs to the atmosphere by capturing them on the carbon. This technology can be implemented with an existing cap and is a relatively low cost alternative because there is no need for electrical power or significant operation/maintenance as would be required by an active system. System implementation details will be determined by: • Test Well Installation • Vapor Testing • Detailed Engineering Each of these activities are summarized in the following subsections. 6.1 TEST WELL INSTALLATION Test wells will be installed adjacent to areas indicating methane concentrations exceeding 5% along the perimeter of the landfill. The lateral spacing for the passive vent network will initially be set at 300 feet. The vent wells will continue on 300 foot spacing until adjacent to a perimeter gas probe that does not exhibit elevated methane. The vent wells will be installed 50 feet from the edge of the landfill. Each vent well will be installed by drilling an 8-inch diameter boring to a depth of 30 feet below ground surface. The boring will be completed as a vent well by installing 2-inch diameter PVC well casing that is screened within the waste. The screened interval will have 0.020-inch slots. The annular space adjacent to the screen will be filled with No. 3 Monterey Sand. The annular space that extends from one foot above the screen to the surface will be filled with a 3-foot layer of hydrated bentonite chips followed by cement bentonite grout. The upper portion of the borehole will be sealed with concrete. The well will be connected to a 200 pound canister of granular activated carbon and a temporary vent riser that will be 10 feet tall and capped with a weather head. Final configurations will be determined after testing and engineering as described below. After installation of the vent wells, a radial influence test will be conducted by extracting landfill gas using a vacuum pump. During extraction, adjacent TGP, PGP, or vent wells, as applicable, will be monitored using differential pressure gauges to evaluate the influence exerted by extraction at the vent well. This test will allow qualitative evaluation of the waste permeability 13 MWXLER BMUCKS Znc, P:\707 Cove Contractors\Feasibility Study and Corrective Action Plan\Corrective Action Plan_Final.doc