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4.Environmental Analysis odors from the project is expected to be less than significant. If complaints are received regarding — odor emissions from the asphalt plant,the applicant may use odor counteractants, which are to be introduced into the stack flue gas. Mitigation: No mitigation required. Impact 4.6.4: Project DPM Impact. Implementation of the project may lead to increases in chronic exposure at nearby sensitive receptors to certain toxic air contaminants from operation of the combination of stationary and mobile sources.This impact is potentially significant. DPM emissions would be released from the on-site equipment and from haul trucks associated with the project. CARB has declared that DPM from diesel engine exhaust is a TAC. Additionally,the California Office of Environmental Health Hazard Assessment(OEHHA)has — determined that chronic exposure to DPM can cause carcinogenic and non-carcinogenic health effects. OEHHA has specified an acceptable exposure level(AEL) of DPM as a non-carcinogen of 5 gg/m3 (annual average). OEHHA has also established a unit risk value for DPM,which is the — probability of contracting cancer if exposed to an average concentration of 1 µg/m3 for 70 years. The unit risk value established for DPM is 300 in a million per microgram per cubic meter. The carcinogenic and non-carcinogenic health risks from the project were estimated by conducting dispersion modeling of DPM emissions from all sources associated with the project. For the on-site activities, it was assumed, as a worst case,that all equipment would use diesel fuel,even though some of the future equipment may be required to reduce DPM emissions by using alternative fuels or alternative engine technologies. It should be noted that on-site _ equipment would move within the property as different phases of the quarrying become operational. Thus, DPM exposure would increase or decrease as on-site equipment moves closer or further from sensitive receptors. The dispersion modeling and health risk analyses were based _ on the worst-case results. The estimated DPM emissions from the project(during 2008)are 2.74 tons per year(1.47 tons from on-site equipment and 1.27 tons from haul trucks. Based on information submitted to the County, onsite equipment would operate near the plant site and at the mining extraction area. Modeling accounted for the duration(in years) and location of each phase of operations (see Project Description). The operation would occur in nine phases over the course of 26 to 60 years. Operation was assumed to be 12 hours a day(during periods of peak demand)throughout the year, excluding Sundays. DPM emissions were modeled using U.S. EPA-approved dispersion models to estimate ambient air concentrations at nearby residences and sensitive receptors from all operations. Modeling results for the various production levels are reported in Table 4.6-6. Detailed modeling methodology and background data are contained in Appendix D. RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.6-26 ESA/203015 Draft Environmental Impact Report May 2006