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4.5 AIR QUALITY ENVIRONMENTAL IMPACTS AND MITIGATION MEASURES Significance Criteria Project-related air quality impacts can be separated into two categories: short-term impacts due to construction,and long-term impacts due to project operation. Impacts in each category can be classified as having effects on either a regional or local scale. 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 proposed 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. Impacts are judged on their contribution to the regional emission burden, using the following thresholds of significance suggested by the San Joaquin Unit of the San Joaquin Valley Unified Air Pollution Control District: emissions exceeding 550 pounds per day for carbon monoxide, emissions of PM-10 exceeding 80 pounds per day, and emissions of ozone precursors (hydrocarbons or oxides of nitrogen) or other pollutants exceeding 150 pounds per day (Kwong, 1991). Impact 4.5-1 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. The proposed project would have a very long construction period due to the excavation of lakebed materials for engineered fill over a five-year period. During this five-year period, construction activities would be at a maximum and air quality impacts would be greatest. Subsequent development of residences and a golf course would involve a far lower level of activity and resulting air quality impacts. Lakebed excavation would involve a number of activities that would generate air emissions. On-site equipment used to excavate material and load trucks would create vehicle exhausts, as would trucks carrying quarried materials from the site. These vehicles would also be a source of fugitive particulate emissions when operating on the site. Any disturbed areas within the site would also create emissions through wind erosion. 4.5-6 c