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reduce predicted pollutant concentrations, and is therefore valuable for use by an industrial <br />facility when required to perform dispersion modeling as part of a regulatory action. Where <br />appropriate, MMA would pursue regulatory approval for the adjust u* option when modeling <br />impacts for industrial clients. MMA processed the meteorological data in AERMET first using <br />the default settings and then with the adjust u* option, creating AERMET output files for both <br />cases. <br />AERMOD <br />AERMOD combines the receptor file output from AERMAP, the two AERMET files (surface <br />and vertical profile data), and user-specified emission source data to calculate pollutant <br />concentrations at each receptor. The emission source data includes source locations, pollutant <br />emission rates, and various physical characteristics of the sources (release heights and <br />dimensions). Emission sources and receptors used in this study are described below. <br />Emission Source Representation <br />AERMOD allows the user to select from a number of different source configurations to <br />represent the emission sources being modeled (area, point, volume, etc.). For this study, <br />a series of volume sources were placed along County Road 120 and configured as <br />recommended by EPA's Haul Road Workgroup7. A total of 869 volume sources were <br />modeled (526 on the unpaved section of the road, 343 on the paved section). Daily PMlo <br />emissions (as calculated below) from both sections of the road were divided by the <br />respective number of volume sources, converted to an emission rate in grams per second <br />(g/sec), and applied to each of the sources. <br />Receptors <br />Model receptors were placed at 24 area resident/structure locations, as identified through <br />the Google Earth program and La Plata County map files. A total of 1,044 receptors <br />were also placed along both sides of County Road 120 to generate predicted <br />concentration isopleths. These receptors were placed at the following distances from the <br />road and spacing between receptors. <br />Distance from Spacing Between <br />Road Edge <br />Receptors <br />10 meters <br />50 meters <br />50 meters <br />100 meters <br />150 meters <br />100 meters <br />250 meters <br />100 meters <br />6 Qian, W., and A. Venkatram. Performance of Steady -State Dispersion Models Under Low Wind -Speed <br />Conditions. Boundary -Layer Meteorology 138:475-491. (2011) <br />U.S. EPA. Memorandum from Tyler Fox, March 2, 2012, Subject: Haul Road Workgroup Final Report <br />Submission to EPA-OAQPS. <br />9250 East Costilla Avenue 1 Suite 630 1 Greenwood Village, Colorado 80112 4 <br />303/790-1332 1 Fax 303/790-7820 <br />www.mevehil-monnett.com <br />