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Opportunity for Comment on Proposed Dispersion Modeling Data and Guidance Updates

The DNR is proposing updates to the pre-processed meteorological data for AERMOD, new default background concentrations, updated guidance, and a new air resource availability summary. There will be a 2-week informal comment period from November 19 through December 3. At the end of the comment period the DNR will consider any comments that are received and then finalize the data and documentation.

The updates are summarized below, and are available for review on the Air Quality Bureau’s Stakeholder Involvement webpage under “Public Input.” Please send any comments or questions to Brad Ashton at Brad.Ashton@dnr.iowa.gov, or by phone at (515) 725-9527, by 4:30 pm on December 3.

Meteorological Data
New data has been processed covering the time period 2010-2014. The meteorological sites being used are the same as the previous 2005-2009 dataset, but some counties will be represented by different sites. A sensitivity analyses was conducted which shows very minimal effect on predicted model concentrations.

Background Concentrations
The DNR is proposing to revise the default background concentrations used in dispersion modeling. The default background concentrations are a conservative estimate of the observations across the statewide monitoring network, and are intended to provide applicants with pre-approved data that can be used in any modeling analysis. The background concentrations are trending down in most cases, but there are a few increases. The DNR is also proposing additional data and guidance to assist applicants in proposing alternate background concentrations.

Modeling Guidance Updates
Proposed updates have been made to the PSD and non-PSD modeling guidelines, as well as the modeling checklist. The proposed updates include revisions to web links for the new website, references to the updated meteorological data and background concentrations, as well as several other changes.

Air Resource Availability Summary
The DNR has created a new draft document that is intended to provide information that will assist applicants when filling out Form MD, as well as inform facilities when changes in the amount of available resource occur due to air quality impacts from projects at their facility or at neighboring facilities. This will allow facilities to better plan for future projects by informing them of the amount of air resource currently being utilized by themselves and their neighbors. 

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