ARCHIVED REPORTS LEC APPLICATION FOR CERTIFICATION

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5.1 AIR QUALITY Where: Hg=Good Engineering Practice stack height,measured from the ground-level elevation at the base of the stack H=height of nearby structure(s) measured from the ground-level elevation at the base of the stack L= lesser dimension,height or maximum projected width, of nearby structure(s) In using this equation,the guidance document indicates that both the height and width of the structure are determined from the frontal area of the structure,projected onto a plane perpendicular to the direction of the wind. For the LEC,the nearest influencing structure is the HRSG,which is 105 feet above ground level. Therefore,GEP stack height is 2.5 times that height, or 262.5 feet.The proposed stack height of 150 feet will not exceed GEP stack height, so the full physical stack height may be used in the modeling analysis. For regulatory applications, a building is considered sufficiently close to a stack to cause wake effects when the downwind distance between the stack and the nearest part of the building is less than or equal to five times the lesser of the height or the projected width of the building. Building dimensions for the buildings analyzed as downwash structures were obtained from plot plans. The building dimensions were analyzed using the Lakes Environmental Building Profile Input Program (BPIP) to calculate 36 wind-direction-specific building heights and projected building widths for use in building wake calculations. The building dimensions used in the GEP analysis are shown in Appendix 5.113,Table 5.113-1. As the existing power plant structures will remain in place,those structures are reflected in the downwash analysis. 5.1.5.4 Receptor Grid Selection and Coverage Receptor and source base elevations were determined from USGS Digital Elevation Model (DEM) data using the 71/2-minute format (10-to 30-meter spacing between grid nodes). All coordinates were referenced to UTM North American Datum 1927(NAD27),Zone 10.The AERMOD receptor elevations were interpolated among the DEM nodes according to standard AERMAP procedure. For determining concentrations in elevated terrain,the AERMAP terrain preprocessor receptor-output (ROU) file option was chosen. Hills were not imported into AERMOD for CTDM-like processing. Cartesian coordinate receptor grids were used to provide adequate spatial coverage surrounding the project area for assessing ground-level pollution concentrations, to identify the extent of significant impacts, and to identify maximum impact locations.A 250-meter resolution coarse receptor grid was developed,which extend outwards at least 10 km from the location of the new turbine stack. In addition,more refined nested grids were developed to efficiently identify the maximum impact areas. These nested grids had the following resolutions: • 25-meter resolution along the facility fence line in a single tier of receptors composed of four segments extending out to 100 meters from the fence line; • 100-meter resolution from 100 meters to 1,000 meters from the fence line; and SAC/371322/082410013(LEC_5.1_AIR_QUALITY.DOC) 5.1-35