Updated Dispersion Modeling Guidance Documents Available

September 24, 2007

The Iowa Department of Natural Resources (DNR) Air Quality Bureau’s air dispersion modeling guidelines and associated air dispersion modeling checklist have been updated on the DNR’s website at: www.iowacleanair.com/prof/progdev/modeling.html.

The updates to both of these documents were the result of recommendations from a modeling workgroup that the DNR convened earlier this year. The workgroup included representatives from business and industry, consultants, and the DNR. The workgroup reviewed the provisions of the guidance used by the DNR for modeling non-Prevention of Significant Deterioration (PSD) construction permitting projects. The recommendations from the workgroup’s review of the modeling guidance resulted in several updates to non-PSD modeling guidance, including the addition of EPA’s AERMOD dispersion model as the preferred model for use in non-PSD construction permitting projects; clarifications on the use of potential emissions and actual emissions; and new guidance regarding the placement of receptors on rail lines that transverse a plant property.

Criteria for determining when a construction permit project is modeled have been updated to include current DNR practices. The criteria are presented in a new, easier-to-use flow chart. The Non-PSD Modeling Determination Form (Form MD) has also been updated.

If you have questions about the updated modeling guidance, please contact Lori Hanson at (515) 281-8911.