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<br /> <br />Foothill Sanitary Landfill Page 45 of 53 San Joaquin County DPW - Solid Waste <br />Joint Technical Document Revised 6/09/2020 <br /> <br />The waste decomposition process begins with organic waste products undergoing aerobic <br />(presence of free oxygen) decomposition during storage and transport, and for a limited period <br />after placement in the landfill. Aerobic decomposition continues until available oxygen is <br />depleted. When oxygen is depleted, anaerobic (lack of oxygen) decomposition becomes <br />dominant. <br /> <br />Typical byproducts of aerobic decomposition of MSW are carbon dioxide, water, and nitrate. <br />Typical primary products of anaerobic decomposition are methane, carbon dioxide, organic <br />acids, nitrogen, ammonia, iron sulfides, manganese, and hydrogen. These products are the <br />primary factors controlling the quality and quantity of leachate and landfill gas produced. <br />Methane in the gas may range from 50% to 60% and carbon dioxide may range from 30% to <br />50% (Boyle, 1977). <br /> <br />Methane production from MSW will continue from a few years to hundreds of years, in certain <br />environments. The rate of gas production depends on a number of parameters: refuse <br />composition, oxygen present, moisture content, pH, alkalinity, and temperature. <br /> <br />LFG Surface emissions are monitored by a “surface scan” test, in which the methane content of <br />the air immediately above the landfill is measure in accordance with EPA Title V Regulations <br />and the Permit to Operate (Appendix A). This measurement indicates that surface emissions <br />are within the regulatory limits. <br /> <br />Surface emissions are controlled by the LFG collection and treatment system (Figure 15). This <br />system consists of thirty four vertical wells and eighteen horizontal collectors, each of which is <br />provided with an adjustment valve, sampling port, and temperature gauge. The LFG collection <br />rate at each well is adjusted based on the methane content at each well; the vacuum is <br />increased or decreased to maintain the methane content within a prescribed range. <br /> <br />LFG collected from the field is transported to the site’s landfill-gas-to-energy plant (operated by <br />Ameresco Inc.) to generate power. The flare station is maintained as a back-up in the event the <br />LFGTE plant becomes non-operational; in which case the LFG is burned in the flare in <br />accordance with the Permit to Operate issued by the AQMD.