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5.ENVIRONMENTAL CHECKLIST MOUNTAIN HOUSE NEIGHBORHOODS K AND L INITIAL STUDY 3.AIR QUALITY AND GREENHOUSE GAS EMISSIONS thresholds of significance, so this impact would be significant and unavoidable, as was stated in the 1994 MEIR. c) Would the project result in a cumulatively considerable net increase of any criteria pollutant for which the project region is non-attainment under an applicable federal or State ambient air quality standard(including releasing emissions which exceed quantitative thresholds for ozone precursors)? Cumulative impacts can result from individually minor but collectively significant impacts, meaning that the project's incremental effects are considerable when viewed in connection with the effects of past,current,and probable future projects. Notably, any project that would individually have a significant air quality impact would also be considered to have a significant cumulative air quality impact.As discussed above under Item (b), project operations for the entire Mountain House community would result in significant emissions of ROG, NOx, and PM 10 and would thus be considered cumulatively significant. d) Would the project expose sensitive receptors to substantial pollutant T concentrations? Localized Criteria Pollutants. Project traffic would increase concentrations of carbon monoxide along streets providing access to the project. Carbon monoxide is a local pollutant(i.e., high concentrations are normally only found very near sources). The major source of carbon monoxide,a colorless, odorless, poisonous gas, is automobile traffic. Elevated concentrations,therefore, are usually only found near areas of high traffic volume and congestion. Both the Guide for Assessing and Mitigating Air Quality Impacts(SJVAPCD, 2002)and statewide Transportation Project-Level Carbon Monoxide Protocol(Garza et al., 1997) recommend that carbon monoxide impacts be quantified for signalized intersections at Level of Service E or worse,as these locations represent"hot spots"for carbon monoxide and are the locations where violations of an ambient air quality standard are most likely. The traffic impact analysis prepared by TJKM for the project examined Level of -- Service(LOS)for affected intersections. No existing or future signalized intersection is forecast to operate at LOS E or worse through the year 2035 with the proposed project. Since the project is within an attainment area for carbon monoxide(ambient air quality standards are currently attained)and in an area with low background concentrations,changes in carbon monoxide levels resulting from the project would not result in violations of the ambient air quality standards and would represent a less-than-significant impact. Construction would result in numerous activities that would generate fugitive dust particulate matter,which is another localized pollutant. The fine, silty soils in the project area and often strong afternoon winds exacerbate the potential for dust, particularly in the summer months. Clearing, grading, leveling, earthmoving, and excavation are the activities that generate the most PM10 emissions. Impacts (snn 1) 540