On May 22, 2017, the revisions to air dispersion modeling requirements in Appendix W of 40 CFR Part 51 became effective. The final rule includes several new or updated model options to help alleviate model over-prediction or allow for more appropriate source characterization. The IDNR has incorporated these changes in their modeling guidance documents. Brad Ashton of the IDNR is accepting informal comments on the modeling guidance documents through June 7, 2017. Also with the Appendix W effective date, the IDNR has released new meteorological data (Version D) for immediate use.