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1 ENVIRONMENTAL IMPACTS AND MITIGATION MEASURES Significance Criteria According to CEQA, a project will normally have a significant adverse impact on air quality if it will "violate any ambient air quality standard, contribute substantially to an existing or projected air quality violation, or expose sensitive receptors to substantial pollutant concentrations." The project's potential for violating the ambient air quality standards for local pollutants or causing nuisance to neighboring properties is used in this EIR to determine the significance of localized air quality impacts. For regional pollutants, violation of air quality standards cannot be used as a "threshold of significance" since the standards are exceeded in the San Joaquin County. The U. S. Environmental Protection Agency has recently published a proposed rule regarding conformity determination for non -transportation projects that includes annual emission thresholds for non -attainment areas and maintenance areas that trigger the need for a conformity determination, and project impacts have been judged using these thresholds of significance (U.S.E.P.A 1993). These significance thresholds are 54.7 pounds per day for ozone precursors (ROG and NOx), 82 pounds per day for PM -10, and 219 pounds per day for SOx. Impact 4.7-1 Construction activities such as clearing, excavation and grading operations, construction vehicle traffic and wind blowing over exposed earth would generate exhaust emissions and fugitive particulate matter emissions that would affect local and regional air quality. Construction activities are a source of organic gas emissions. Solvents in adhesives, non- waterbase paints, thinners, some insulating materials and caulking materials would evaporate into the atmosphere and would participate in the photochemical reaction that creates urban ozone. Asphalt used in paving is also a source of organic gases for a short time after its application. Construction dust could affect local air quality at various times during construction of the project. The dry, windy climate of the area during the summer months combined with the fine, silty soils of the region create a high potential for dust generation when and if underlying soils are exposed to the atmosphere. The effects of construction activities would be increased dustfall and locally elevated levels of PM 10 downwind of construction activity. Construction dust has the potential for creating a nuisance at nearby properties, although sensitive land uses nearby are limited to two residences located about 600 feet north of the site on the east side of MacArthur Drive. Construction dust is considered to represent a potentially significant localized and temporary impact. Mitigation 4.7-1 The severity of construction impacts can be reduced to a level that is less -than -significant through application of additional mitigation measures. To ensure that construction mitigation is utilized, final approval should not be given until the contractor submits a satisfactory PM -10 Dust Prevention and Control Plan. This plan should specify the methods of control that will be utilized, demonstrate the availability of needed equipment and personnel, and identify a responsible individual who, if needed, can authorize the generation and implementation of additional measures, if needed. The Plan should, at a minimum, include the following: ER -93-1 -87- (9-27-93)