2008-02-22_APPLICATION CORRESPONDENCE - C2008086 (40)

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Appendix G Air Quality Analysis Modeling Report Estimated impacts from CALPUFF-Cite consider emissions occurring during certain hours of the day and seasons of the year, in accordance with projected daily construction and production hours and the projected construction schedule. Because of the spatial length (approximately 14.5 miles) and relatively longer period of time (approximately 6 months) required to construct the rail spur; the CALPUFF-Cite model assumes that railroad construction begins at the south end (near Interstate 70) during winter months, and continues through the following spring season. Seven of the thirteen "volumes" for the railroad volume source are "turned on" in CALPUFF- Lite during three winter-season months, and the remaining six of thirteen "volumes" are turned on during the three spring-season months. The winter and spring months were included in this analysis because initial modeling indicated the largest visibility impacts will occur during winter months. 4.5 CALPUFF-Cite Results and AQRV Analysis CALPUFF-Cite modeling results for the proposed Red Cliff Mine are presented in Tables 4-5, 4-6, and 4-7. Maximum predicted values are reported for all modeled criteria pollutants, along with maximum nitrogen (N) and sulfur (S) deposition values, and a visibility assessment, for each Class I or sensitive Class II area within the modeling domain. Maximum modeled criteria pollutant concentrations are compared to the Class I increment SILs, and deposition rates are compared to a threshold value of 0.005 l~ilogram per hectare per year (kg/ha/yr). The visibility assessment is expressed in terms of the number of days, for each modeled year, that the deciview change exceeds 1.0 (a change of one deciview is approximately equal to a 10 percent change in atmospheric light extinction). A deciview is a measure of visibility; higher deciview levels represent poorer visibility. A one or two deciview change translates to a "just noticeable" change in visibility for most individuals. None of the maximum modeled NOx or S02 concentrations for any of the three project phases are above their respective SILs. None of the maximum modeled PM10 concentrations during the production phase (Phase 3) are above their respective SILs. However, maximum modeled concentrations of PM10 during the Phase 1 and Phase 2 construction phases are above the 24-hr SIC, for each year, at each Class I or sensitive Class II area modeled. SILs are not thresholds for asserting negative environmental impacts; rather, they are used in PSD permitting to provide a basic screening of potential impacts and justify the need for further analysis. These results do not necessarily indicate that negative PM10 impacts will occur during the construction phases of the project. Instead, the results indicate that further analysis is necessary to predict whether any negative impacts will occur. Visibility changes greater than one deciview are observed for several days across most of the modeled Class I and sensitive Class II areas during the Phase 1 and Phase 2 construction periods. Most of these days occur at the Flat Tops Wilderness, Colorado National Monument, and Black Canyon of the Gunnison Wilderness. The highest number of days with visibility changes occurs at the Colorado National Monument, located less than 25 kilometers from the proposed site. No visibility impacts are observed for any sites after production (Phase 3) begins. Five maximum predicted nitrogen deposition rates during Phase 1 construction and two maximum predicted nitrogen deposition rates during Phase 2 construction are greater than the threshold of 0.005 kg/ha/yr. These predicted rates occur at the Colorado National Monument. No other Class I or sensitive Class II areas are impacted by nitrogen deposition during the G-24 DBMS 536