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DNR to Delay Implementation of Revised PM2.5 SILs

  • 7/30/2018 8:29:00 AM
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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 significant impact level (SIL) of 1.2 µg/m3 for particulate matter less than or equal to 2.5 microns in diameter (PM2.5), 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 planned to incorporate EPA’s recommended SILs into modeling guidance for PSD projects. However, Sierra Club has filed a petition for review in the U.S. Court of Appeals for the District of Columbia Circuit in response to EPA’s guidance. Due to the uncertainty of this ongoing litigation the DNR has decided against implementing the proposed changes to the PSD Modeling Guidelines at this time. The DNR may implement the changes at some future date. For now, the PSD Modeling Guidelines will remain unchanged. However, applicants who wish to use the lower annual PM2.5 SIL included in EPA’s guidance will be allowed to do so.

Please send any questions to Jim McGraw at, or by phone at (515) 725-9543.