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4.Environmental Analysis — The operation of any project with the potential to expose sensitive receptors to substantial levels of TACs would be deemed to have a potentially significant impact. More specifically, the following thresholds would be considered to have a significant air quality impact: • Probability of contracting cancer for the Maximally Exposed Individual (MEI)4 exceeds 10 in one million. • Ground-level concentrations of non-carcinogenic TACs would result in a Hazard — Index greater than 1. These standards are typically applied to the results of a health risk assessment based on a detailed — air dispersion modeling effort. Lastly, any project that would individually have a significant air quality impact would also be — considered to have a significant cumulative air quality impact. Emissions of local pollutants(e.g., CO and TACs)are cumulatively considerable and thus significant when modeling shows that the _ combined emissions from the project and other existing and planned projects in the area would exceed air quality standards. Impact 4.6.1: Project Construction-Related Impact.Project construction emissions would result in intermittent,temporary increases in air pollutant emissions.This impact is considered potentially significant. Construction-related dust emissions5 would vary from day to day,depending on the level and type of activity, silt content of the soil, and the weather. In the absence of mitigation,construction — activities may result in significant quantities of dust, and as a result, local visibility and PMio concentrations may be adversely affected on a temporary and intermittent basis during the construction period. In addition,the fugitive dust generated by construction would include not only PMio, but also larger particles, which would fall out of the atmosphere within several hundred feet of the site and could result in nuisance-type impacts. Increased emissions of PMio could adversely affect local visibility. Combustion emissions from heavy equipment and construction worker commute trips would also vary from day to day, and would contribute incrementally to regional ozone concentrations during the construction period. Estimates of construction emissions are not required by the Valley Air District for purposes of CEQA documentation and thus have not been prepared. The Valley Air District requires implementation of effective and comprehensive control measures rather than detailed — quantification of emissions. Implementation of feasible control measures can be reasonably expected to reduce PMio emissions during construction. The Valley Air District has determined that compliance with its Regulation VIII constitutes sufficient mitigation to minimize adverse construction-related air quality impacts to less-than-significant impact levels. The following control measures are required under Regulation VIII: 4 The MEI is the off-site receptor that is exposed to the highest average concentration of TACs. — 5 Fugitive dust emissions related to the construction phase of the project;that is,the initial period when site grading and construction of the processing operations are to occur,but before excavation and production begins. RMC Pacific Vernalis Quarry Mining and Reclamation PrqecF_4.6-1 8 ESA 1203015 Draft Environmental Impact Report May 2006