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

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CHAPTERFOUR Environmental Consequences and Mitigation with established air quality modeling guidance. A screening version of CALPUFF (known as CALPUFF-Cite) was used for the far-field analysis, as a conservative assessment approach. Specific Class I and sensitive Class II areas included in the far-field analysis are: Utah • Arches National Park (Class I Area) • Canyonlands National Park (Class I Area) Colorado • Black Canyon of the Gunnison Wilderness (Class I area) • Flat Tops Wilderness (Class I area). • Maroon Bells - Snowmass Wilderness (Class I area) • Colorado National Park (sensitive Class II area) • Dinosaur National Monument (sensitive Class II area) Five years of data were modeled in both analyses, with the specific years and meteorological data sets recommended by air quality staff at the CDPHE. Both analyses were conducted according to the distinct project phases, since each project phase will occur separately, with the Phase 1 railroad construction occurring first, followed by the Phase 2 mine are/transmission line/haul road construction activities, and finally by the Phase 3 start of ongoing operations (also referred to as "production" in Appendix G). An expected timeline for the three project phases is included as an attachment to Appendix G. Temporary Impacts Temporary impacts will occur from those emissions generated during construction activities. Primarily, construction emissions will consist of fugitive road dust from vehicle traffic, heavy construction vehicles and mobile equipment, and soil disturbance. A small amount of construction-related emissions will be generated by fuel combustion in construction equipment and passenger vehicles. The near-field analysis did not predict any negative air quality impacts due to the two construction phases. However, the far-field analysis indicates a few possible temporary air- quality impacts due to construction activities: Predicted maximum 24-hour concentrations of particulate matter less than 10 micron in diameter (PMio) are higher than PMio 24-hr Class I PSD Significant Impact Levels (SILs) for each year modeled, at each Class I and sensitive Class II area included in the far-field analysis. The SILs do not represent thresholds at which negative impacts occur; rather they are typically employed as screening values to be used in PSD permitting to determine whether additional air quality modeling should be performed. The SILs are established conservatively low, so that larger projects going through the PSD construction permitting process will be required to perform "cumulative" air quality analyses. Often, when modeling results exceed the SILs and additional modeling analyses are required, the final results show no negative air quality impacts. In this case, the SILs are employed as a conservative threshold to determine whether or not air quality impacts will occur. If modeled results are lower than the respective SIC, then it can be asserted that no impacts will occur. However, 4-60 DBMS 615