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D. Minimizing Air Intrusion at Vertical Wells: Vertical wells will be provided with a plastic "skirt" extending at least four feet from the well bore to minimize intrusion of air through the disturbed refuse adjacent to the well riser. E. Horizontal Collector Spacing: Because the horizontal wells in this project will be installed under a HDPE liner, each collector will have the potential to collect landfill gas from under the entire Module 1 liner extension. In general, it is anticipated that the collectors will be located towards the base of the liner extension where maximum vacuum can be exerted. As with all the design features, this feature will also be developed by the consultant selected for the work. F. Piping will be above-ground as much as possible to reduce cost. Materials will be recommended by the selected consultant and selected by the County. G. LFG Collection: Each collector(vertical well or horizontal collector)will be provided with an adjustment valve and sampling ports to measure LFG quality. H. Treatment of Collected LFG: The County will attempt to use LFG as an energy source. This work will include seeking proposals from private firms to install "turn key" LFG-to- electricity system at the site. An energy project will be pursued at the County's discretion, based on economic benefit. If an LFG-to-energy project is found to be beneficial to the County,then LFG treatment will be by combustion in electrical generation equipment. This equipment will be operated in accordance with the APCD operating permit, and sufficient in size for the landfill. If an LFG-to-energy project is not found to be beneficial to the County,then collected LFG will be treated by combustion in a temperature-controlled flare in accordance with an APCD operating permit. I. LFG System Operation: The methane content of LFG is 55%to 60%unless diluted by air pulled into the landfill by the LFG system. In general,methane concentration of 40% indicates that most or all of the LFG is being collected(and that approximately 25%of the collected "LFG" is actually air pulled into the landfill by the LFG system). To ensure a significant collection of LFG without overdrawing the landfill,operation of the LFG system will attempt to maintain the methane content between 40%and 45%,which will allow the use of the collected LFG as an energy resource. Successful operation of the LFG system will be indicated by the collection of most or all of the LFG produced, in turn indicated by: Reduction of surface emissions to the AQMD surface emissions limits Reduction of methane concentration in LFG by approximately one-fourth(to between 40%and 45%methane) Continued non-detection of VOCs in groundwatwer. Foothill Sanitary Landfill Site Improvement 4 Department of Public Works/Solid Waste Revised March 12,2004 County of San Joaquin