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Opportunity for Comment: PM2.5 SILs and AAR Summary Web Page

  • 6/8/2018 3:13:00 PM
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The DNR is proposing updates to PSD modeling guidance and is announcing the release of a new web page. Specifically, EPA’s recently released PM2.5 Significant Impact Levels (SILs) have been incorporated into the Prevention of Significant Deterioration (PSD) Modeling Guidelines, and a new web page has been added to assist applicants with filling out Form MD. The DNR is providing this information for a two-week informal comment period.

PM2.5 SILs
On April 17, 2018 EPA released a memo titled “Guidance on Significant Impact Levels for Ozone and Fine Particles in the Prevention of Significant Deterioration Permitting Program.” In this guidance EPA recommended a 24-hour PM2.5 SIL of 1.2 µg/m3, which is the same level as the previously proposed draft SIL. They also recommended an annual PM2.5 SIL of 0.2 µg/m3, which is lower than the previously proposed draft SIL (0.3 µg/m3). Refer to EPA’s Significant Impact Levels for Ozone and Fine Particles web page for additional information regarding their analysis and recommendations.

The DNR plans to incorporate EPA’s recommended SILs into modeling guidance for PSD projects. EPA’s guidance provides flexibility for the use of an annual PM2.5 SIL between 0.2 µg/m3 and 0.3 µg/m3, but requires that justification is provided for whatever value is used. EPA’s guidance provides this justification for the lower 0.2 µg/m3 value. The revised DNR guidance will also allow for this flexibility, but the DNR currently does not have the resources to evaluate an alternate annual SIL. Therefore, applicants will be required to use 0.2 µg/m3 for the annual PM2.5 SIL unless they can provide their own justification for an alternate value. Any such justification will then be provided to EPA for their review during the comment period of the associated draft permits.

For non-PSD projects, the DNR is currently proposing to continue using the higher 0.3 µg/m3 annual PM2.5 SIL.

AAR Summary Web Page
The Air Quality Bureau has added a tool to its web site that will be useful to those applying for a construction air permit.

The DNR uses dispersion modeling to determine the impact that construction projects may have on air quality. The air quality impacts from these projects are compared to the National Ambient Air Quality Standards (NAAQS) to ensure that public health is protected, and this information is summarized for the applicant in the form of an Availability of Air Resources (AAR) Summary. The applicant can then use the AAR Summary for planning purposes and to assist in the preparation of future permit applications.

The Bureau's Availability of Air Resources (AAR) page has been created to assist applicants in completing Section 2 of Form MD. The Availability of Air Resources (AAR) web page includes contact information that can be used to request an AAR Summary, as well as a list of frequently asked questions. AAR Summaries provide the most recent comprehensive modeling results in the vicinity of a facility. Requests sent via the contact information on the AAR web page are forwarded to all DNR modeling staff, allowing requests to be fulfilled even when someone is out of the office.

The updated guidance is available for review on the Air Quality Bureau’s Public Participation web page under “Public Input.”  The AAR Summary web page is available at Please send any comments or questions to Jim McGraw at, or by phone at (515) 725-9543, by 4:30 pm on 6/22/2018.