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4. ENVIRONMENTAL ANALYSIS 4.6 AIR QUALM — • Cause a net increase in pollutant emissions of ROG or NOx exceeding 10 tons per year. • Cause a violation of state CO concentration standards. The level of significance of CO emissions from mobiles sources is determined by modeling the ambient concentration under project conditions and comparing the resultant 1- and 8-hour concentrations to the respective state CO standards of 20.0 and 9.0 parts per million. • Cause visible dust emissions due to onsite operations and thereby violate Valley Air District Regulation VIII.° 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,proposed development projects that have the potential to expose the public to TACs in excess of the following thresholds would be considered to have a significant air quality impact: • Probability of contracting cancer for the Maximally Exposed Individual 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. Impacts of local pollutants(e.g., CO and TACs)are cumulatively 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 Emissions Impact. Project construction would generate substantial amounts of dust(including PM10 and PM2S)primarily from "fugitive"sources(i.e.,emissions released through means other than through a stack or tailpipe)due to earthmoving and grading and lesser amounts of other criteria air pollutants from operation of heavy equipment construction machinery(primarily diesel operated)and construction worker automobile trips (primarily gasoline operated). This Impact is considered potentially significant. Construction-related dust emissions 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 PM 10 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 PM 10,but also larger particles, which would fall out of the atmosphere within several 4 Visible dust is defined by the SJVUAPCD as"visible dust of sucb opacity as to obscure an observer's view to a degree equal to or greater than opacity of 20 percent,for a period or periods aggregating more than three minutes in any one hour." -- RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.6-18 ESA/203015 Admioisuwve Drati EIR Much 2004