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would be necessary, and the success of the measures could not be guaranteed. The geographic area of analysis for impacts to air quality was defined as the airshed in the immediate area of the project site. Affected Environment The park is in a sparsely populated area on the western slope of the Rocky Mountains and is within the Western Slope Region for air quality planning (CDPHE 2003a}. The park is classified as a Class II air quality area, an area in which some degradation is allowed. Low population levels and lack of large industries have meant high standards of air quality and good visibility on a year-round basis. High winds occasionally generate dust storms in the park when the reservoir is low (NPS 1997). The Air Quality Control Commission of the CDPHE is responsible for monitoring and evaluating air quality in the state. The CDPHE has adopted the federal National Ambient Air Quality Standards (NAAQS) except for sulfur dioxide (SOZ). Current standards are set for SOZ, carbon monoxide (CO), nitrogen dioxide (NOZ), ozone (03), particulate matter equal to or less than 10 microns in size (PM,o), fine particulate matter equal to or less then 2.5 microns in size (PM2,5), and lead (Pb}. These pollutants are collectively referred to as criteria pollutants. Areas are classified under the federal Clean Air Act as either "attainment" or "nonattainment" areas for each criteria pollutant based on whether the NAAQS have been achieved or not. When an area has been designated as an attainment area after having been nonattainment, it is also classified as a maintenance area. Colorado has experienced a decline in air pollutants over the past 15 to 20 years. to 1995, Colorado had 12 areas of nonattainment; today there are no areas of nonattainment. However, areas of concern in Colorado are ozone levels in the Denver metropolitan area and PM,o and PM2.5 levels in mountain communities (CDPHE 2003a). The nearest air quality monitoring station is in Gunnison, 8 miles east of Curecanti. The CDPHE operates PM,o monitoring sites in Gunnison, Delta, Crested Butte, and Mt. Crested Butte. In the past few years, there have also been PM,o monitoring sites in Montrose, Olathe, Paonia, and Hotchkiss. CO, PM,o, and PM2.5 are also monitored at a site in Grand Junction. EPA operates an ozone monitor at Gothic, near Crested Butte. No exceedances of any NAAQS were reported for these stations in 2001-2002, according to a Report to the Public prepared by the Air Pollution Control Division of the CDPHE and published by the Colorado Air Quality Control Commission in October 2002. Data from the National Air Quality and Emissions Trend Report (EPA 2003) indicate that PM,o levels in Gunnison County are in the normal range for the state (CDPHE 2003b). Air quality standards are shown in Table 3.1. Table 3.1 -National Ambient Air Quality Standards e .. ...' . .. 8-hour 9.0 ppm 9.0 ppm Carbon Monoxide 10 m Im3 10 m /m3 (C0) 1-hour 35 ppm _ 35 PPm 3 40 m /m a 40 m /m Lead Pb Calendar Quarter 1.5 !m Same as rima standard -- Nitrogen Dioxide Annual Average 0.053 ppm s Same as primary standard 0.053 m Pm' NO 100 /m 100 1-hour 2 52 pPm Same as primary standard 2 pP ' O 0 3 35 m zone ( 3) 8-hour 0.08 ppm 157 Imp Same as primary standard - 36