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4.6 Air Quality f. in Impact 4.6.4(DPM Impacts of On-Site Equipment),the Project's DPM impact from on-site it equipment would be significant after mitigation for receptors adjacent to the site. As discussed under Impact 4.6.4, the health effect from long-term exposure to DPM is considered to be serious and both the state and federal governments are enacting stringent measures to reduce the levels of DPM generated by heavy trucks in the near future. These measures will help to further reduce DPM exposure statewide and in the vicinity of the project site. Mitigation: No mitigation required. Impact 4.6.7: Project TACs Impact from Asphalt Operations.Implementation of the project may lead to increases in chronic exposure of nearby sensitive receptors to certain toxic air contaminants from the asphalt batching operations.This impact is less than significant. Emission points within the asphalt plant includes a natural-gas fired burner on the drying drum, i.. the mixing drum,natural gas-fired hot oil heater in the asphalt oil storage tanks,other asphalt plant handling such as truck loadout and silo filling, and storage piles. The drying drum and mixing drum are ducted to a fabric filter stack to the atmosphere.The hot oil heater is vented directly to the air. The California OEHHA has determined the chronic exposure to TACs can cause carcinogenic and non-carcinogenic health effects as documented in their Risk Assessment Guidelines. The OEHHA has specified AEL for specific TACs. An AEL is the probability of acquiring some health effects. OEHHA has also established a unit risk value for specific TACs. A unit risk value is the probability of contracting cancer if exposed to an average concentration of 1 ttg/m'for 70 years. The carcinogenic and non-carcinogenic health risks due to the asphalt batching r operations were estimated by conducting dispersion modeling of TAC emissions from asphalt operations;both the hot mix plant and fugitive emissions from loadout, silo filling,and storage. The primary exposure pathway was identified as inhalation. Operation was assumed to be ` 24 hours a day (during periods of peak demand)throughout the year,excluding Sundays. TAC emissions were modeled using U.S. EPA-approved dispersion models to estimate ambient air concentrations at nearby residences. Detailed modeling methodology and background data is contained in Appendix D.Using the unit risk factors,as established by OEHHA, the maximum incremental carcinogenic risk is estimated to be less than 0.05 in a million. The maximum annual average concentration is less than the non-carcinogenic AEL, thus leading to a hazard index much r less than the significance threshold of 1. Therefore,the carcinogenic and non-carcinogenic risk from TAC due to asphalt operations, when added to the other project components, would be less than significant. r Mitigation: No mitigation required. RMC Pack Vernalis Quarry Mining and Reclamation Project 4.6-31 ESA 1203015 Draft Environmental Impact Report May 2006 V