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Draft Supplemental Environmental Impact Report Page VIII-16 Forward Inc.Landfill 2018 Expansion Project value is below the threshold of 20 cancers per million and thus, the impact would be 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 OEHHA has established a significance threshold for non-cancer health risk based on concentrations that would result in a Hazard Index (HI)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 0.013 0.9447. The maximum non-cancer chronic hazard risk would be an HI of 0.0056 0.09046. The increased non-cancer acute and chronic hazard risk from the Project(increase in hazard risk from the Current Actual to the Project scenario Landfill Gas Flare)would be less than these maximum Project values.Maximum non-cancer hazard risk values (acute and chronic) are below the threshold of 1.0 and thus,the impact would be less than significant. Table 2-Revised HRA Results Cancer Cancer Project Project Project Risk Risk Increase Chronic Increase Acute Increase (Max- (Occu- in Cancer Hazard in Acute Hazard in Acute imum pied Rec- Risk Index Hazard Index Hazard Scenario Receptor Impact) eptor) Index Index Current 9.30E-06 9.70E-07 1.27E-05 0.0022 0.00340 0.0015 0.0115 Actual Maximum Current 2.10E-05 3.19E-06 1.00E-06 0.0043 0.00130 0.0100 0.0030 Permitted Maximum Project Maximum 2.20E-05 3.30E-06 0.0056 0.013 B-7. SCS Engineers(SCS)prepared the Air Quality Impact Assessment(AQIA)and disagrees with this recommendation.SCS has used the methodology developed by the U.S. Environmental Protection Agency (EPA)and presented in its "Compilation of Air Pollutant Emissions Factors" (AP-42)guidance document. That emission calculation method was developed specifically for landfills and landfill gas combustion sources, which is directly related to the sources considered herein.Where they are not derived from AP-42, the factors available from the District were developed for combustion of natural gas in flares and engines. Combustion properties (e.g.,heat content)of landfill gas (LFG) and natural gas differ significantly, and combustion process design(e.g., retention time, downturn, air/fuel ratio)may differ significantly for LFG and natural gas combustion sources.As such,emission factors derived from natural gas combustion are not representative of LFG sources.