2020-06-25_REVISION - C1981035 (3)

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In addition to PSD AQRV analyses, visibility impacts are also included under a State Implementation Plan for the reduction of Regional Haze. This regulation is used to reduce the visibility impacts from existing facilities and introduce additional emissions controls to a standard known as Best Available Retrofit Technology. Deposition is the process by which pollutants are removed from the atmosphere via mechanical and chemical processes. When air pollutants such as sulfur and nitrogen are deposited into ecosystems,they may cause acidification, or enrichment of soils and surface waters. Atmospheric nitrogen and sulfur deposition may affect water chemistry, resulting in impacts to aquatic vegetation, invertebrate communities, amphibians, and fish. Deposition can also cause chemical changes in soils that alter soil microorganisms, plants, and trees. Although nitrogen is an essential plant nutrient, excess nitrogen from atmospheric deposition can stress ecosystems by favoring some plant species and inhibiting the growth of others. Visibility impairment or haze is caused when sunlight encounters tiny pollution particles in the atmosphere and is either absorbed or scattered which reduces the clarity and color of what can be seen. The ability of a pollutant to cause various degrees of visibility impacts is primarily a function of its physical size, and chemical composition and properties. Visibility can be expressed in terms of deciview (dv) or standard visual range(km).A change of one dv is approximately a 10 percent change in the light extinction coefficient(i.e., light that is scattered or absorbed and does not reach the observer), which is a small, but usually perceptible scenic change. 2.2.1.3 Regional Air Quality The Project Area and vicinity is currently in Attainment or unclassified for all criteria pollutants. Monitoring of criteria pollutants in the region is located near population centers or areas of specific interest. In the late 1990s, the EPA allowed monitoring to cease where pollutants were less than 60 percent of the NAAQS,and as a result the data collected for this analysis is regionally representative but often monitored at some distance from the Project Area. Table 2.2-3 shows recent ambient air quality monitor data for potential pollutants of concern from monitors located in or nearby the affected area. The primary pollutant of concern from the Proposed Action is particulate matter (as determined from the emissions inventory presented below). The area monitors also show that 03 levels are relatively close to the new standard promulgated by EPA in 2015. The 03 NAAQS is the 4t" high averaged over 3 years.There are no 3-year periods that exceed the 70 ppb. A couple of individual years from 2012 to 2017 resulted in a 4t" high greater than 70 ppb, but the highest 3-year average is the La Plata site from 2015 to 2017,which is approximately 99.0 percent of the standard. Therefore,the region remains in attainment for 03.All the monitoring data is from the USEPA's AQS Data Mart (https://www.epa.gov/outdoor-air-quality-data) and excludes exceptional events. The database contains ambient air pollution data collected by USEPA, state, local, and tribal air pollution control agencies,and from various federal land managers from thousands of monitors. Monitoring data is limited, and all pollutants are not monitored at all monitoring locations, and thus data for a pollutant may not be available for all portions of the affected environment. For example, monitoring data for Pueblo County, CO is limited to PM10 and PM2.5.The location of air quality monitoring stations within the Project analysis Dunn Ranch Area LBA and Mining Plan Modification 8 Technical Resources Report