COMPLIANCE INFO_FINAL INITIAL STUDY/MITIGATED NEGATIVE DECLARATION 5/25

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Memorandum 25 March 2025 Page 4 Landfill Gas LFG is a natural byproduct of the decomposition of organic material in landfills. Methane and carbon dioxide are the primary constituents of LFG and are produced by the decomposition of organic material within the landfill under anaerobic conditions. By volume, LFG is typically comprised of about 50 percent methane and 50 percent carbon dioxide and water vapor. In addition to these main components, LFG contains small amounts of nitrogen, oxygen, and hydrogen, less than 1 percent non-methane organic compounds (NMOCs), and trace amounts of inorganic compounds. Methane emitted from landfills is considered anthropogenic, because it is a direct result of human activities, specifically the disposal of organic waste in oxygen-limited environments where microorganisms break down this waste and produce methane as a byproduct. However, the carbon dioxide emitted from landfills it considered biogenic rather than anthropogenic because it's a natural byproduct of the decomposition of organic matter, which is part of the natural carbon cycle and not solely from human activities. Therefore, the analysis of climate change impacts related to anthropogenic emissions from landfills focuses on methane and not carbon dioxide. The rate of methane generation is influenced by the amount of bioavailable carbon, the characteristics of the waste (e.g., composition and age), and the environmental conditions that support anaerobic bacterial activity. As waste is continuously deposited in the landfill, methane production gradually increases throughout the landfill’s operational life, typically reaching its highest level within several years after the final year of waste disposal, often referred to as the landfill closure year. After closure and capping the landfill, the rate of methane generation typically declines due to reduced moisture infiltration. According to the Title V Permit (N-119-1-12) for the North County Landfill, the flare for the LFG collection system must attain a methane destruction efficiency of at least 99 percent by weight. In other words, flare combustion must convert at least 99 percent of the methane in LFG to carbon dioxide (a less potent GHG) and other compounds. REGULATORY SETTING Federal Regulations On April 2, 2007, the U.S. Supreme Court ruled that CO2 is an air pollutant as defined under the Clean Air Act, and that the Environmental Protection Agency (EPA) has the authority to regulate emissions of GHGs (U.S. Supreme Court, 2007). The EPA made two distinct findings regarding GHGs under Section 202(a) of the Clean Air Act, as follows: