Shifting Winds: D.C. Circuit Questions EPA Air Quality Modeling in Good Neighbor Provision Case
See all Insights

Shifting Winds: D.C. Circuit Questions EPA Air Quality Modeling in Good Neighbor Provision Case

Brownstein Client Alert, Oct. 27, 2022

Late last month, the D.C. Circuit Court of Appeals heard oral arguments in Midwest Ozone Group v. EPA, the latest challenge to the Environmental Protection Agency’s (EPA) Cross-State Air Pollution Rule (CSAPR). The Good Neighbor Provision of the Clean Air Act allowed EPA to create the CSAPR in 2011. CSAPR requires fossil fuel-fired power plants in upwind eastern states to reduce their SO2 and NOX emissions so that downwind Eastern Seaboard states can meet their air quality goals. As we discussed in a prior alert, EPA is using that same authority to expand what is known as the “Transport Rule,” which would limit NOX emissions in 25 upwind states—including, for the first time, Western states Wyoming, Utah, and Nevada—whose emissions may impact downwind states’ ability to attain and maintain the 2015 Ozone National Ambient Air Quality Standards (NAAQS).

Questions posed by the panel during the Midwest Ozone Group oral argument may signal skepticism toward EPA’s air quality modeling used in Good Neighbor Provision rules, carrying broader implications for how the D.C. Circuit Court may view other EPA modeling. Midwest Ozone Group alleges EPA deviated from established practice when determining the states on which to impose ozone-season NOX emission limitations. In general, EPA uses photochemical air quality modeling to assess how well control strategies work for regulatory analysis and attainment demonstrations. Due to a court-imposed deadline, EPA was not able to use real data from all of 2021 and instead extrapolated 2021 ozone concentrations from data collected in 2016.

In her first appearance since being confirmed, U.S. Circuit Judge Michelle Childs expressed concern that EPA’s approach could lead to the agency being “more creative” with models in the future. Childs specifically wanted to avoid inadvertently endorsing further deviations from EPA standard practice down the line, wondering “how are you buying [the D.C. Circuit] into that process?” U.S. Circuit Judge Robert L. Wilkins also questioned whether EPA had a response “[g]iven the check that [Plaintiff] did that reveals the model was inaccurate.”

The D.C. Circuit’s questioning of EPA’s modeling approach may signal vulnerability for the agency as it embarks on other regulatory efforts where complex modeling underpins the agency’s actions. Potentially impacted areas include the newly expanded Transport Rule in the Rocky Mountain region and along Denver’s Front Range as the state and EPA continue to grapple with ozone nonattainment. The D.C. Circuit’s potential hesitancy to accept the EPA’s latest modeling choice would also be notable for the lack of deference to EPA on a technical issue and could signal the court’s willingness to question EPA’s methodology and conclusions.

Our attorneys and policy advisors will be tracking this case and its impacts on the CSAPR as well as the Transport Rule and other EPA air quality rulemaking efforts. We would be happy to answer any questions your company may have about how the Good Neighbor Provision’s rules may impact your company or industry.


This document is intended to provide you with general information regarding the implications of Midwest Ozone Group v. EPA. The contents of this document are not intended to provide specific legal advice. If you have any questions about the contents of this document or if you need legal advice as to an issue, please contact the attorneys listed or your regular Brownstein Hyatt Farber Schreck, LLP attorney. This communication may be considered advertising in some jurisdictions. The information in this article is accurate as of the publication date. Because the law in this area is changing rapidly, and insights are not automatically updated, continued accuracy cannot be guaranteed.

Recent Insights