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1 Draft Environmental P Impact Report Page IV.D-25 Forward Landfill Expansion CARB's EMFAC2007, while landfill gas emission estimates are based on EPA's Landfill Gas Emissions Model (LandGEM). As identified in Standards of Significance, the significance of air toxic emissions depends upon the chance of contracting cancer from exposure to TACs, or upon having adverse health effects from exposure to non-carcinogenic TACs. Cancer risks would be significant if the incremental risk equals or exceeds 10 in a million for the Maximally Exposed Individual.1s Exposure to non-carcinogenic substances would be significant if the Hazard Index (HI)exceeds 1.0.19 The standards are typically applied to the results of a health risk assessment (HRA) r through a detailed air dispersion modeling effort using the US EPA's AERMOD dispersion model. This assessment is intended to provide a worst-case estimate of the increased exposure by employing a standard emission estimation program and an accepted pollutant dispersion model. Conservative health risk methodologies were used in the risk assessment in order to r estimate maximum potential health risks. These methodologies are anticipated to �! overestimate both non carcinogenic and carcinogenic health risk, possibly by an order of magnitude or more. For carcinogenic risks, the actual probabilities of cancer formation in the populations of concern due to exposure to carcinogenic pollutants are likely to be lower than the risks derived using the risk assessment methodology. In accordance with OEHHA guidelines, the HRA was accomplished by applying the highest estimated concentrations of TAC at the receptors analyzed to the established cancer potency factors and acceptable reference concentrations for non-cancer health effects. The HRA for this project utilized the CARB Hotspot Analysis and Reporting Program (HARP)20 to determine both cancer risks and non-cancer health effects. HARP is a computer software package that combines the tools of emission inventory database, facility prioritization, air dispersion modeling, and risk assessment analysis. The incremental carcinogenic risk(increase in cancer risk from the Current Permitted to ' the Project scenario) is estimated to be 0.73 cancer occurrences per million persons at the maximally exposed residential receptor21. This value are below the threshold of 10 cancers per million and thus, the impact is less than significant. This analysis is based on conservative (overestimated) assumptions, and can be considered a worst-case analysis. The maximum incremental cancer risk is relatively small compared with the overall lifetime cancer incidence of 200,000 to 250,000 per million in the United States. The Hazard Index is an expression used to describe the potential for non-cancer health effects.The OEHHA has established a significance threshold for non-cancer health risk based on concentrations that would result in a Hazard Index greater than 1.0. Based on the modeling,the non--cancer health risks would be well below the Hazard Index of 1.0 at all receptors. The maximum non--cancer acute hazard risk would be an HI of 0.0032. The " The Maximally Exposed osed Individual represents the worst-case risk estimate,based on a theoretical person continuously exposed for 70 years at the point of highest compound concentration in the air. " The Hazard Index is the ratio of a hazardous air pollutant concentration to its Reference Concentration, or safe exposure level. If this "hazard index" exceeds one, people are exposed to levels of hazardous air pollutants that may pose non-cancer health risks. 2°HARP(Version 1.4a). zi 9.7 cancer occurrences per million persons at the maximally exposed individual(an unoccupied receptor)