On June 8, 2017, the Minnesota Pollution Control Agency (MPCA) published a draft version of the Air Quality Dispersion Modeling Practices Manual (the manual) for 2017-2018. This draft of the manual shows the MPCA's proposed redlined updates, and the MPCA is soliciting comments and input on these updates prior to its finalization later this summer. A draft of the manual can be found online, here. The main updates to the manual include:

  • The removal of the PM10 annual National Ambient Air Quality Standards (NAAQS), Significant Impact Level (SIL), and Prevention of Significant Deterioration (PSD) Class II Increment Level thresholds in order to match the updated Minnesota Ambient Air Quality Standards (MAAQS) found in Minn. R. 7009.0080 and federal NAAQS.
  • The removal of the emissions thresholds for non-PSD permits indicating which type of modeling, if any, will be triggered by a proposed project (i.e., full dispersion modeling, modeling information only, or no modeling required). Additionally, the updated manual now includes language confirming that modeling is determined on a case-by-case basis by the MPCA.
  • The inclusion of updated and additional language explaining fenceline receptors and on-site receptors. Note that this language allows for the MPCA or EPA to approve atypical fencelines (e.g., signage or surveillance in place of a physical barrier), but stresses that the MPCA does not recommend this approach.
  • Updated language on how to select nearby sources for a full impact analysis.
  • Additional language and justification for urban versus rural considerations.
  • Updates to various sections of the manual in order to incorporate the updated version of Appendix W, including:
    • Removing CALPUFF as the only accepted long-range transport model.
    • Adding language regarding the use of ADJ_U* meteorological data and the requirement for some form of justification prior to using the data.
    • Adding POINTHOR and POINTCAP options for horizontal and capped stacks, respectively, as default options (i.e., these options can be used without MPCA approval).
    • Adding and updating language regarding the secondary formation of PM2.5 and ozone to include guidance on the Modeled Emission Rates for Precursors (MERPS).
    • Updating language regarding NO2 modeling to incorporate certain Tier 2 and Tier 3 approaches as regulatory defaults.
  • Various language updates to clarify the intent of various sections of the manual.

While the MPCA will accept comments on the manual year round, comments submitted to the MPCA by July 15, 2017 will be taken into consideration prior to the manual's finalization later this year. Questions or comments on the manual can be submitted to AirModeling.PCA@state.mn.us. In addition, the MPCA is hosting an Air Quality Dispersion Modeling Open House on July 13, 2017 at the MPCA's St. Paul Office to discuss the manual. MPCA is accepting RSVPs to the Open House at the email address listed above.

In addition to the manual updates noted above, the MPCA has recently posted updated meteorological data for the years 2012-2016 on the MPCA website, here. The dataset includes both ADJ_U* and non-ADJ_U* data; however, if ADJ_U* data is used, note that justification on why its use is appropriate must be submitted. Most facilities have seen favorable results (i.e., lower concentrations) with the use of ADJ_U* data, thus the use of this data may be beneficial when modeling your facility. In addition to the updated meteorological data, updated ozone files for years 2012-2016 are also available on the MPCA website, here.

If you have any questions on the updates to the manual, the updated meteorological data, or how these items may affect your facility, please contact Shelley Koehn at (651) 275-9900 X-8.