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IDNR issued updated air dispersion modeling guidance documents on June 5, 2020 for both PSD and non-PSD projects. The notable updates are summarized below.

Non-PSD Guidance Document

  • Construction permit application Form MD is now an optional form but IDNR still recommends including it as this is the method they will use on a case-by-case basis to determine if modeling is needed for an application.
  • Discusses the Ambient Ratio Method 2 (ARM2) option during NO2 modeling rather than the previous ARM option.
  • Clarifies that property boundary changes alone won't trigger modeling, but the new boundary is required to be used in future modeling if triggered by a project.

PSD Guidance Document

  • References the December 2019 EPA Revised Policy on Exclusions from “Ambient Air”.
  • Includes Ozone in the secondary pollutant formation discussion.
  • Discusses the Ambient Ratio Method 2 (ARM2) option during NO2 modeling rather than the previous ARM option.