Modeling Guidelines and Modeling Determination Form Revised

The Iowa Department of Natural Resources (DNR) Air Quality Bureau’s non-PSD air dispersion modeling guidelines as well as the non-PSD modeling determination form (Form MD) for construction permits have been updated on the DNR’s website. The updated modeling guidelines can be found at the following website:

www.iowacleanair.com/prof/progdev/modeling.html

The updated non-PSD modeling determination form can be found at the following website:

www.iowacleanair.com/prof/const/conform.html

The updates to the modeling guidelines include clarification of what significant changes at a facility may require a modeling analysis to be reevaluated, as well as a new requirement for AERMAP files to be submitted with all modeling analyses.

The modeling determination flow chart has been modified on both the modeling guidelines as well as Form MD. The emission rate thresholds that would trigger a modeling analysis were originally determined based on the PSD Significant Emission Rates (15 ton/yr for PM10, 40 ton/yr for SO2 and NOX, and 100 ton/yr for CO), but did not consider rounding. Therefore the thresholds have been changed on the flow chart so that they are equivalent to 14.4 ton/yr for PM10, 39.4 ton/yr for SO2 and NOX, and 99.4 ton/yr for CO.

The wording in the modeling determination flow chart was also modified to clarify that the applicant should consider stacks instead of individual emission units when determining if the project needs to be modeled.

In addition, the modeling determination form was updated to clarify that it does not apply to VOC-only sources.

If you have questions about the updated modeling guidance or Form MD, please contact Lori Hanson by email at Lori.Hanson@dnr.iowa.gov, or by phone at (515) 281-8911.