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c l HARNEY LANE SANITARY LANDFILL GAS CONTROL SYSTEM MODIFICATIONS CURRENT CONDITIONS Currently, the landfill gas system uses one blower to apply vacuum to the entire site. One eight inch High Density Polyethylene (HDPE) pipe connects the blower to the six inch header pipes that run along the east and west sides of the landfill. There is also one condensate knockout sump between the landfill and the flare station. One blower produces approximately 15 inches (water column) of vacuum at measured at the blower inlet. Pressure drops caused by pipe elbows and distance results in about 12 inches where the pipe splits. The split cuts the vacuum to each half of the landfill to approximately six inches each. The vacuum drops even further as you move north. The collection wells farthest north on the site on average produce vacuum of less than one inch. The northern area of the landfill contains the most recent and highest methane producing waste, so it is logical that all of the subsurface migration of landfill gas occurs around the north half of the site. PROPOSED MODIFICATIONS The proposed modifications to the landfill gas system are aimed at increasing the available vacuum to the highest gas-producing wells (north half). The modifications will be combined with a strategy of well balancing to direct vacuum to the north. The existing connection from the eight inch header pipe to each six inch header pipe on the landfill will be reconfigured so that it services only the west half of the site. A second eight inch header pipe will be installed parallel to the existing pipe, and it will be connected to the second blower on the flare pad. This pipe will be connected to the six inch header pipe that services the west half of the site. An additional condensate knockout sump will also be installed to service the west half (See Figure 1). By performing these modifications, available vacuum should be at least doubled in all areas. Gas collection wells on the south half of the site will be mostly shut off from vacuum in an effort to direct the vacuum to the critical northern areas. Hopefully, the system modifications and balancing strategy will control the subsurface migration to within regulatory limits. TIME SCHEDULE The County has already begun the process of modifying the gas system. We are currently assessing materials necessary for the project. Trenching for the new pipe will begin during the week of September 27, 1999. The target date for completion of the project is October 28, 1999. s:\wes\hl\gas\wkpings.mem i