2008-02-22_APPLICATION CORRESPONDENCE - C2008086 (39)

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CHAPTERFOUR Environmental Consequences and Mitigation since the PMio 24-hr model results are higher than the PMio 24-hr SIC, this assertion cannot be made. In order to state definitely that no temporary PMio 24-hr impacts will occur at the Class I and sensitive Class II areas, additional modeling analysis would be necessary. It should be noted that the highest modeled PMio 24-hr concentration in the far-field analysis (2.64 µg/m3) is less than 2 percent of the PMio 24-hr National Ambient Air Quality Standard (NAAQS) value of 150 µg/m3; therefore, it is reasonable to assume that additional modeling would prove no negative air quality impact. Several days per year, various Class I and sensitive Class II areas are shown to have visibility impacts during the temporary construction period. Specifically, the far-field analysis provides the number of days per year when visibility changes by at least one deciview. A change of one deciview is translates to a "just noticeable" visibility change for most individuals. The majority of the visibility impacts occur at areas close to the proposed mine area, such as the Flat Tops Wilderness and the Colorado National Monument. In a few cases. visibility impacts are noted at Canyonlands National Park, Dinosaur National Monument, and Black Canyon of the Gunnison Wilderness. The maximum visibility impacts were in the Colorado National Monument, during the Phase 1 railroad construction, with 3, 6, 7, 20, and 16 days impacted in the five modeled years, respectively. It should be noted that a conservative approach was used in the CALPUFF-Cite input, to apply the light extinction coefficient for fine particulate matter to all sizes of particulate matter emissions, which may have increased the number of days shown with visibility impacts. • Nitrogen deposition impacts equal to or higher than the threshold of 0.005 kilogram per hectare per year (kg/ha/yr) are shown at the Colorado National Monument for both construction phases. No other nitrogen impacts are shown, and no sulfur impacts for any area, from either construction phase, were modeled. As mentioned earlier, all impacts listed above are from the far-field analysis, which utilized a screening-level version of the CALPUFF model (CALPUFF-Lite). Results from a CALPUFF Cite analysis are considered to be conservative assessments of air quality impacts, because a number of assumptions are made that tend to result in over-predictions of impacts. At times, CALPUFF-Cite can predict much larger impacts that would be predicted from the full version of CALPUFF. If a full version of CALPUFF were used for the far-field analysis, it is possible that some of these temporary impacts would be negated. These impacts are temporary because they are caused by the construction activities associated with the proposed mine. The expected timeline for construction is only 1.5 years. Following the startup of mining operations, the construction emissions will cease, and air quality impacts from the construction activities will cease accordingly. Permanent Impacts Permanent impacts will occur from emissions generated as part of the Phase 3 production activities. These emissions will consist of fugitive dust from vehicles and haul trucks, storage piles, and coal conveyance at the mine site, and other criteria pollutants emitted from fuel burning equipment at the mine site. The emissions will be ongoing and permanent. No negative air quality impacts are associated with the permanent emissions. All modeled criteria pollutants in the near-field and far-field analyses were lower than the respective air 4-61 DBMS 616