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COMMENTARY: Revisions to the Guideline on Air Quality Models

NSR Law Blog is pleased to have Gale F. Hoffnagle, Senior Vice President and Technical Director at TRC Environmental Corporation, share his views on EPA's recently finalized, and now delayed, Appendix W changes to the Guideline to Air Quality Models. Mr. Hoffnagle has worked with NSR modeling since the 1977 Clean Air Act Amendments. He prepared the following comments for NSR Law Blog....

A recent blog “EPA Delays 30 Rules –Including Appendix W Modeling Update” suggested that more commentary was in order.

The revised Guideline will make permitting more difficult. The primary reasons are:

  1. The requirement that any alternatives to the straight use of AERMOD (and even some of AERMOD’s switches) will require agreement from EPA headquarters (disguised as the Clearinghouse). This consolidates all decisions on modeling and may create artificial logjams in the approval process for modeling protocols (the plan for modeling required before permit modeling begins). The nearly complete reliance on AERMOD to provide all model evaluations out to 50 kilometers, continues a history of highly conservative (over estimation of air quality impacts) which continues to require over control of emissions.

  2. By withdrawing the preference for the use of CALPUFF at distances beyond 50 kilometers (called long range transport) the guideline leaves open the question of what is the acceptable modeling method. The applicants proposed protocol will need to address the scientific issues of which model to pick as opposed to just the issues of what input to use and switches to set in CALPUFF. Modeling beyond 50 kilometers is an alternative that requires headquarters agreement.

  3. By requiring that the applicant address the chemical formation (called “secondary formation”) of particulate matter (PM2.5) and ozone after release of VOCs, NOx or SOx from the stack, the Guideline increases the workload for the modeling, maybe by a substantial amount. EPA voluntarily added this because of a petition form the Sierra Club. The Guidance does not specify any specific model to use in this evaluation, thereby increasing the time to develop a protocol, defend the protocol, getting the protocol approved and then actually performing what is significant modeling work which can only be classified as “academic”. Modeling for secondary formation is an alternative that requires headquarters agreement.

  4. EPA has attempted to soften the “secondary formation” requirement by issuing draft Guidance on minimum emission rates below which such modeling would not be required (MERPS Guidance). But even that Guidance is sufficiently non-specific to leave in doubt the results of any protocol offer of proof that the modeling is not needed. That Guidance is also based on Significant Impact Limits (SIL) which EPA issued for comments (not a proposed Guideline or Rule). Those SILs were much lower than past SILs.

In summary, the Guideline as promulgated would increase the time, cost and expense needed to obtain an NSR permit. Never mind that the modeling result is more likely to result in more emissions controls beyond BACT.

The promulgated Guideline is the antithesis of The Presidential memorandum of January 24, 2017, “Streamlining Permitting and Reduce Regulatory Burdens for Domestic Manufacturing”. That memorandum requires the Secretary of Commerce to “conduct outreach to stakeholders on the actions that would streamline the permitting process”. The Administrator of EPA is to coordinate with the secretary in this process and prepare an Action Plan. Reversing the effects of the promulgated Guideline would be a good place to start.

Gale Hoffnagle

TRC Environmental Corporation

21 Griffin Road North, Windsor, CT 06095

Tel. (860) 298-6247

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