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Revised Modeling Guidance Available for Use

  • 6/8/2017 1:53:00 PM
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The DNR has updated various modeling guidance documents to incorporate the latest changes to federal modeling requirements.  The updates were reviewed with stakeholders at the May 25, 2017, AQ Client Contact meeting.  The guidance updates were also posted for a two week informal comment period that ended on June 7.  No comments were received so the documents were finalized as drafted.

The updated guidance is being implemented in response to revisions to air dispersion modeling requirements in Appendix W of 40 CFR Part 51.  The final rule became effective on May 22, 2017 and includes several new or updated model options that help alleviate model over-prediction or allow for more appropriate source characterization.  Of particular importance to applicants in Iowa are the updates to the Nitrogen Dioxide Tier 2 and Tier 3 screening techniques, the optional adjustment of the surface friction velocity (Adjust-u*), and regulatory options to address plume rise for horizontal and capped stacks.

For additional information about the 2017 Appendix W final rule please visit EPA’s Support Center for Regulatory Atmospheric Modeling (SCRAM) website.

The revised guidance documents are available on the Dispersion Modeling webpage.

Please send any questions to Brad Ashton at, or by phone at (515) 725-9527.