COMPLIANCE INFO_FINAL INITIAL STUDY/MITIGATED NEGATIVE DECLARATION 5/25

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Memorandum March 25, 2025 Page 4 21202-23 North County Landfill_AQ_0307 ambient air quality standards but are regulated through state and local risk management programs. Unlike criteria air pollutants, which generally affect regional air quality, TAC emissions are evaluated based on estimations of localized concentrations and risk assessments. The adverse health effects a person may experience following exposure to any chemical depend on several factors, including the amount (dose), duration, chemical form, and any simultaneous exposure to other chemicals. For risk assessment purposes, TACs are separated into carcinogens and non-carcinogens. Carcinogens are assumed to have no safe threshold below which health impacts would not occur, and cancer risk is expressed as excess cancer cases per 1 million exposed individuals over a lifetime of exposure. Non-carcinogenic substances are generally assumed to have a safe threshold below which health impacts would not occur. Acute and chronic exposure to non- carcinogens is expressed as a hazard index, which is the sum of expected exposure levels divided by the corresponding acceptable exposure levels. Landfill Gas Methane (CH4) and carbon dioxide (CO2) are the primary constituents of LFG and are produced by the natural process of bacterial decomposition of organic material within the landfill under anaerobic conditions. By volume, LFG is typically 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. Some of these compounds have strong, pungent odors (for example, hydrogen sulfide). Volatile organic compounds (VOC), including approximately 30 TACs, have been identified in uncontrolled LFG, including benzene, toluene, ethyl benzene, and vinyl chloride. Exposure to these pollutants can lead to adverse health effects. Existing regulations under the Federal Clean Air Act, as discussed below under Regulatory Setting, require landfills of a certain size to install and operate a gas collection and control system. These regulations target municipal solid waste (MSW) landfill emissions. The regulations require NMOCs to be measured as a surrogate for LFG and owner/operators to collect and combust their LFG. The rate of LFG generation is influenced by the amount of bioavailable carbon, the type of material containing it, and the environmental conditions that support anaerobic bacterial activity. As waste is continuously deposited in the landfill, LFG production gradually increases throughout the landfill’s operational life, reaching its highest level on the final day of waste disposal, often referred to as the landfill’s closure. After closure and capping, LFG generation may decline further due to reduced moisture infiltration.