CORRESPONDENCE_2003-2004 - Laserfiche WebLink

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District(APCD)Rule 4642 requires that surface emissions be controlled by extending the LFG system into other landfill areas, and monitoring surface emissions as an indication of proper LFG system maintenance and adjustment. Maintenance of surface emissions below 500 ppm indicates proper operation. The final design features will be prepared by the consultants selected for the work. In general, the LFG system will be subject to the approval of a request for Authority to Construct submitted to the APCD by the County. Design criteria contemplated at this time are: A. Location of Collectors • Vertical wells will be installed on flat areas where landfill roads allow drill rig access and on not where Module 1 liner extension will be placed. • Horizontal collectors will be installed under Module 1 liner extension,based on the Module 1 liner design including an HDPE membrane or equivalent. B. Vertical Well Depth • Two-thirds of the depth of refuse fill in deep areas, not less than 65 feet deep • Under no circumstances closer than 10 feet from the bottom of the refuse fill C. Vertical Well Spacing: Radius of influence assumed to be not less than three times the well depth; therefore, spacing between wells will be approximately six times well depth. Spacing of wells will be adjusted to conform to landfill configuration. D. Minimizing Air Intrusion at Vertical Wells: Vertical wells will be provided with aplastic "well skirt" extending at least four feet from the well bore to minimize intrusion of air through the disturbed refuse adjacent to the well riser. Note that 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 gas is air pulled into the landfill). 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 use of LFG as an energy source will be considered, such consideration to include seeking proposals from private firms to install "turn key LFG-to- a Foothill Sanitary Landfill-Site Improvement Strategy 3 Department of Public Works/Solid Waste February 2,2004 County of San Joaquin