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Informal Comment Requested on Proposed Modeling Guidance Updates
Friday, January 04, 2013
The Iowa DNR invites the public to provide informal input on proposed changes to several modeling guidance documents, including the “Air Dispersion Modeling Guidelines For Non-PSD, Pre-Construction Permit Applications,” “Air Dispersion Modeling Checklist,” “Air Dispersion Modeling Guidelines For PSD Projects,” and the “Modeling Protocol Template.” These documents are used to assist in the completion of dispersion modeling analyses conducted by applicants and by the DNR that are associated with construction permitting projects.
Additionally, the DNR invites the public to provide informal input on a new guidance document on “Rounding Conventions.”  The new “Rounding Conventions” document provides guidance on truncation criteria and rounding conventions that can be applied to modeled concentrations when comparing values with the National Ambient Air Quality Standards (NAAQS). This guidance is intended to improve consistency in how the rounding conventions are applied to modeled concentrations.

Purpose of the Proposed Changes

The DNR is proposing changes to the modeling guidance documents to incorporate a new streamlined modeling determination process for non-Prevention of Significant Deterioration (non-PSD) projects. The new modeling determination process was previously provided for informal public comment and has been incorporated into the Form MD. Updates to the modeling guidance documents also provide for the implementation of the 2006 fine particulate (PM2.5) and 2010 1-hour nitrogen dioxide (NO2) and sulfur dioxide (SO2) NAAQS as applicable.

Need for Guidance Changes
The proposed changes to the modeling guidance documents are needed to incorporate the revised modeling determination process for non-PSD projects and to provide guidance for modeling required in conjunction with the DNR’s implementation of the PM2.5 and 1-hour NO2 NAAQS. Review of minor projects for the PM2.5 NAAQS and the 1-hour NO2 NAAQS is scheduled to begin January 22, 2013.  Review of major (PSD) projects for the PM2.5 NAAQS and the 1-hour NO2 and SO2 NAAQS is already required by EPA.
Summary of Guidance Changes

For non-PSD projects, the modeling guidance has been updated to reflect the new streamlined modeling determination process. More information on the revised determination process is available in the list serve article dated December 3, 2012. The modeling guidance documents have been updated to include significant impact levels for the new NAAQS to be evaluated, the new NAAQS, and specific guidance related to the new NAAQS including the 3-tiered screening approach for NO2 and evaluation of the 1-hour NAAQS for intermittent use sources. The modeling guidance documents also reflect updated default background concentrations. 

Information available for review

The proposed modeling guidance documents are available on the DNR’s website at Air Quality Public Input (scroll down to the Other Air Quality Items section). Or, click here: (scroll down to Other Air Quality Items). 

How to Provide Input

Please provide any informal comments or suggestions to Lori Hanson, Iowa DNR Air Quality Bureau, by Monday, January 14, 2013, as follows:

Fax: (515) 242-5094
Mail or Hand-delivery: DNR Air Quality Bureau, 7900 Hickman Road, Suite 1, Windsor Heights, Iowa 50324

For questions, please contact Lori Hanson at the e-mail address noted above or by phone at (515) 281-8911.

This list serve article is intended for consultants, industries, environmental groups, general public, and other entities regulated under the Clean Air Act. It was written by the DNR Air Quality Bureau to share regulatory news, program updates and technical guidance.