For general modeling guidance and procedures, refer to the Colorado Modeling Guideline . The procedures here are intended to be supplemental guidance for new sources and modifications NOT subject to PSD rules. The best way to check for the most recent version is to check for the most recent model change bulletins on EPA's Support Center for Regulatory Air Models website . In addition to the documents cited above, EPA's modeling clearinghouse contains memos that help clarify EPA's guidance on certain issues. For example, it may be necessary to obtain a facility plot plan that shows the spatial relationship between emission points and buildings to determine if it s necessary to include building downwash in the model.
Additional guidance is presented in the sections that follow.
The worst impact will generally occur at the nearest location where the stable plume actually impacts on the terrain. This is found by locating the nearest location where the terrain elevation is at or above the final plume height. For terrain locations closer than the distance to final rise, the plume may impact on the terrain at a lower elevation. As stated earlier, it is not necessary to enter terrain elevations when the building downwash options are used. The exception to this is for sources that have or will have operating schedule restrictions.