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III. ENVIRONMENTAL SETTING,IMPACTS AND MITIGATION MEASURES B. AIR QUALITY affecting a substantial number of people. Additionally,the SJVUAPCD has established thresholds of significance for construction impacts,project operations and cumulative impacts. For construction impacts,the pollutant of greatest concern to the District is PM-10.1 The SJVUAPCD recommends that significance be based on a consideration of the control measures to be implemented during project construction (SJVUAPCD, 1998b). Compliance with Regulation VIII, Rule 8010,and implementation of appropriate mitigation measures to control respirable particulate matter(PM-10)emissions are considered to be sufficient to render a project's construction-related impacts less than significant. The SJVUAPCD Guide for Assessing and Mitigating Air Quality Impacts (GAMAQI)contains a list of feasible control measures for construction-related PM-10 emissions. The SJVUAPCD's GAMAQI also includes significance criteria for evaluating operational-phase emissions from direct and indirect sources associated with a project. Indirect sources include motor vehicle traffic associated with the project and do not include stationary sources covered under permit with the SJVUAPCD. For this analysis, the project would be considered to have a significant effect on the environment if it would exceed the following thresholds: • Cause a net increase in pollutant emissions of reactive organic gases(ROG)or NO, 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 on-site operations and thereby violate SJVUAPCD Regulation VIII.2 Stationary sources that comply,or that would comply, with SJVUAPCD Rules and Regulations generally would not be considered to have a significant air quality impact. The operation of any project with the potential to expose sensitive receptors to substantial levels of toxic air contaminants would be deemed to have a potentially significant impact. More specifically,proposed development projects that have the potential to expose the public to toxic air contaminants 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 (MEI)exceeds 10 in one million. ® Ground-level concentrations of non-carcinogenic toxic air contaminants would result in a Hazard Index greater than 1 for the MEI. 1 Construction equipment emits carbon monoxide and ozone precursors. The SJVUAPCD has determined that these emissions would cause a significant air quality impact only in the case of a very large or very intense construction project(SJVUAPCD, 1998b). 2 Visible dust is defined by the SJVUAPCD as"visible dust of such opacity as to obscure an observer's view to a degree equal to or greater than an opacity of 40 percent,for a period or periods aggregating more than three minutes in any one hour." Stockton Scavenger Transfer Station Expansion III.B.10 ESA/990190