2020-10-27_PERMIT FILE - C1981035 (23)

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ENVIRONMENTAL ASSESSMENT 3.4.1.1 Affected Environment The affected area for the air quality analysis of the direct effects of the Proposed Action includes La Plata and Montezuma counties, although most direct air quality impacts would be limited to the vicinity of the mine.The Cumulative Effects study area is consistent with the area analyzed in the Colorado Air Resources Management Modeling Study(CARMMS). Indirect effects associated with coal transport and combustion occur at numerous locations. Most of the coal produced(approximately 83 percent)would be transported by truck to a rail terminal in Gallup, New Mexico.The exact rail transportation routes are not known due to the various coal consumers and potential routes that could be used. The climate of the area is typical of a semi-arid, continental, mid-latitude region: warm summers and cold winters are characterized by high diurnal and seasonal temperature variations. The flow of Pacific air dominating the climate descends into the area as a warming and drying mass after depositing most of its moisture over the western slopes of the Sierra Nevada and Cascade Mountains. This generally creates a large rain shadow effect over Nevada, Utah, and western Colorado. Typically, severe storms and low- pressure systems bypass the region by deflecting north or south over lower elevations of the Rocky Mountains in Wyoming and New Mexico.The predominant air mass over the Rocky Mountains during the winter is usually continental polar and produces cold, dry air during storm-free periods. High pressure systems that result in fine, light, powdery snow tend to become established in winter over the region which lies within the mean winter storm track. During the summer months, the air masses are generally maritime polar. This region is usually south of the main storm track in the summer; however, localized thundershowers do occur primarily during the afternoon, if a moisture supply is available either locally or in the air mass. Regulatory requirements include both state and federal ambient air quality standards. The Clean Air Act also regulates air pollution in classes which are governed by the Prevention of Significant Deterioration (PSD) regulations(40 CFR 52.21).The Project Area is in a Class II area as codified in the Colorado State PSD permitting rules. Detailed quantitative and qualitative discussion pertaining to the PSD rules, increment thresholds as well as ambient air quality standards are described in the associated TRR(OSMRE and BLM 2019). Regional air quality monitors were also evaluated for all applicable standard averaging periods in the counties of Colorado surrounding the Project Area. These include data from 2012-2017 demonstrating that the regional area associated with the Proposed Action meets all applicable air quality standards and is considered in attainment. The primary natural and synthetic greenhouse gases (GHGs) in the Earth's atmosphere are water vapor, carbon dioxide (CO2), methane, nitrous oxide, and fluorinated gases. GHGs allow heat from the sun to pass though the upper atmosphere and warm the earth by blocking some of the heat that is radiated from the earth back into space. As GHG concentrations increase in our atmosphere they impact the global climate by further decreasing the amount of heat that can escape back into space. Many GHGs are naturally occurring in the environment; however, human activity has contributed to increased concentrations of these gases in the atmosphere. CO2 is emitted from the combustion of fossil fuels (i.e., oil, natural gas, and coal), solid waste,trees and wood products, and because of other chemical reactions Dunn Ranch Area Coal Lease by Application COC-78825 and Mine Plan Modification EA 3-7