This article provides a legal and regulatory update to articles published in February 2025 and August 2025 related to the “bump-up” of nonattainment areas in Southeast Wisconsin from Moderate to Serious nonattainment for ozone under the 2015 ozone national ambient air quality standard. On September 5, 2025, the U.S. Court of Appeals for the Seventh Circuit stayed the reclassification of ozone nonattainment areas in Southeast Wisconsin from Moderate nonattainment to Serious nonattainment. As a result, these areas are subject to the requirements for Moderate nonattainment areas until the stay is lifted or the judicial review concludes that they should be classified as Serious nonattainment.
2015 Ozone Nonattainment Bump-Up History
On December 17, 2024, the United States Environmental Protection Agency (USEPA) redesignated the existing Moderate ozone nonattainment areas in Southeast Wisconsin as a Serious ozone nonattainment area, with an effective date of January 16, 2025. The affected areas consisted of the entirety of Milwaukee and Ozaukee counties, along with portions of Washington, Racine, Waukesha, Kenosha, and Sheboygan counties. On February 14, 2025, Wisconsin filed suit in the U.S. Court of Appeals for the Seventh Circuit challenging this reclassification and subsequent motion to stay the bump-up pending litigation was filed on August 15, 2025. This stay was granted on September 5, 2025. While the stay is in effect, the rules governing Moderate nonattainment areas will be in place.
Permitting Impacts of the Stay
With the bump-up to Serious nonattainment, the major source and major modification thresholds under the Title V and Nonattainment New Source Review permitting program were lowered (from 100 tons/year to 50 tons/year for the major source threshold and 40 tons/year to 25 tons/year, with 5-year aggregation, for the major modification threshold). However, with the stay in effect, these thresholds will remain at the higher levels as required under the Moderate nonattainment rules and projects are not required to be aggregated over a 5-year period for comparison against the major modification threshold. Additionally, as Registration Operation Permits applicability is based on emissions being a certain percentage of the major source thresholds (i.e., ROPA and ROPC permits are limited to up to 25% of the major source threshold and ROPB are limited to up to 50% of the major source threshold), these permits are also impacted.
When the bump-up became effective on January 16, 2025, the WDNR stated that facilities generally had 12 months (until January 16, 2026) to apply for revised permits as appropriate. However, with the bump-up stayed, facilities likely no longer need to take any action with respect to permitting. If permits applications were submitted, but no permit issued, to comply with the Serious nonattainment requirements, they can be withdrawn. If permits were issued with limits for complying with the Serious nonattainment requirements, a facility may need submit a new application in order to change these limits. Furthermore, should the stay be lifted and the areas be redesignated back to Serious nonattainment, WDNR has indicated that they will communicate a timeframe for any necessary permitting at that time.
Conclusion
The reclassification from Moderate to Serious nonattainment for ozone and the stay of the bump-up to Serious can be confusing to navigate and may or may not require facilities to evaluate which permitting option fits the facility best, now and in the future. Trinity can assist with conducting these evaluations. Please reach out to Trinity’s Wisconsin Office or directly to Steve Tasch or Harrison Rae to discuss the specifics for your facility.
