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3.1 Prediction of LFG Generation A significant LFG system design criterion is the LFG production potential of the landfill. The Foothill Landfill is a hillside fill with a nominal depth of 130 feet, receiving nominally 18 inches of rain per year. To evaluate the potential methane and landfill gas generation rate two models were used. The first model used was the spreadsheet version of the United States Environmental Protection Agency (EPA) LandGem Model. The model uses historical and fixture annual refuse tons to estimate the generation curves based on exponential decay of the refuse using decay coefficients published in AP42. Because of the low rainfall at the Foothill Landfill, the decay parameters for and landfills were used (Lo= 100 m3IMg, k=0.02 yr -t). For the purpose of LFG system design, the model considers the refuse tons deposited at the Site through year 2025. Based on these parameters, the peak methane collection rate is estimated to be about 900 SCFM LFG in 2006 (Figure 2). The second model is also an exponential decay model where the decay coefficients have been back -calculated by GC Environmental based on actual methane and LFG flow data from other California landfills. In developing this California model some of the uncertainty in the Lo and k values were evaluated and the results provide a range of estimated methane and landfill gas collection. Based on these analyses, the range of LFG flow rate expected when the LFG system is installed in 2006 is approximately between 800 and 1,300 SCFM. The LFG treatment equipment will be sized to treat up to 2,000 cfm LFG at the time of installation. Based on the projection of LFG production, this system will have sufficient capacity to serve the landfill at least until 2017. Note that this discussion is based on estimates by computer modeling. The LFG system will be expanded as needed based on the actual LFG production, which will be more accurately known after the system is operating. 3.2 LFG Collection and Treatment 3.2.1 Vertical Wells The Radius of Influence (ROI) for vertical wells in and regions of California can be up to 400 ft. To be conservative, vertical wells will be located based on a ROI of 250-300 feet, resulting in a distance between wells of 500-600 ft (Figure 3). Footfall Sanitary Landfill 3 Public Works/Solid Waste LFG CS Design Plan County of San Joaquin - March 10, 2005