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

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Appendix G Air Quality Analysis Modeling Report 3.1 Model Options The following regulatory default options were run in AERMOD: • Stack-tip downwash, • Elevated terrain effects, • Use calms processing routine, • Use missing data processing routine, and • No exponential decay. The proposed Red Cliff Mine area has little, if any, heavy industrial, light-moderate industrial, commercial, single-family compact residential, or multi-family compact residential land within 3 km. Based on this, the Red Cliff Mine area is considered a rural area and therefore, the rural option was used. Building downwash was not considered for this air quality analysis since all emissions sources were modeled as area sources. Neither wet nor dry deposition was included in the near-field analysis. 3.2 Meteorological Data Five years (1991-1995) of surface meteorology data was obtained from the National Climatic Data Center for the Grand Junction -Walker Field Airport. The same five years of upper air meteorology was obtained from the FSL/NCDC Radiosonde Data Archive. These datasets were processed by AERMET with surface characteristic values obtained from a land use/surface characteristics workbook prepared by the Colorado Department of Public Health and Environment (CDPHE). The AERMET raw meteorology data inputs were determined by CDPHE staff. Figure 3-1 presents a representative wind rose for this processed meteorology. 3.3 Receptor Grid The receptor grid, or network, defines the locations of predicted air concentrations used to assess compliance with the relevant standards or guidelines. The following comprehensive fine and coarse receptor network was used for this analysis: • 25-meter (m) spaced receptors along the project property boundary (defined as a 50 meter buffer from the area sources) • 100-m spaced receptors out to 1 km from the property boundary/land use application area boundary G-4 DBMS 516