On April 23rd, 2026, The US Environmental Protection Agency (EPA) proposed to reconsider and repeal its December 2024 reclassification that moved the Uintah Basin, Utah ozone nonattainment area from Marginal to Moderate under the 2015 8-hour ozone National Ambient Air Quality Standard (NAAQS). If finalized, the area would remain Marginal nonattainment, potentially avoiding Moderate-area planning requirements (e.g., RACT) while keeping key permitting concepts like Nonattainment New Source Review (NA-NSR) front and center for projects that increase Nitrous Oxide (NOx) or Volatile Organic Compounds (VOC).
Utah’s Uintah Basin Background
The Uintah Basin was designated Marginal nonattainment for the 2015 ozone NAAQS effective August 3, 2018. The original attainment deadline was August 3, 2021. Utah and the Ute Indian Tribe requested two independent one-year attainment date extensions based on qualifying ozone monitoring data and certification of compliance with applicable State Implementation Plan (SIP) requirements.
In December 2024, EPA denied the second extension request and reclassified the area to Moderate nonattainment. That decision was challenged and stayed by the courts, prompting EPA to reopen the rulemaking and reevaluate the technical record.
EPA’s Proposed Action to Uintah Basin
After reconsideration, EPA is proposing to:
- Repeal the December 2024 final rule that classified the Uintah Basin as Moderate nonattainment
- Grant the second one‑year attainment date extension, extending the Marginal attainment date to August 3, 2023
- Determine that the area attained the 2015 ozone NAAQS based on certified monitoring data
Key takeaways from EPA’s proposal include:
- Permitting thresholds: Major source threshold for NA-NSR would remain 100 tons per year (tpy) of NOx or VOC (Marginal) for the Uintah Basin ozone nonattainment area.
- Controls and planning: A Marginal-area classification generally avoids Moderate-area planning requirements such as RACT, reducing the likelihood of additional mandatory emissions controls driven solely by reclassification.
- Project reviews: New construction or modifications that increase NOx/VOC should be screened early for ozone Nonattainment New Source Review (NA-NSR) applicability and offset/LAER implications (as applicable).
- Rulemaking timing: EPA is accepting questions through May 26, 2026. Compliance teams should track the final action and align permitting schedules accordingly.
What This Means for Regulated Facilities (Ozone NA-NSR, Major Source Thresholds, RACT)
This proposal would reinstitute the previous Marginal-area compliance framework for sources operating in the Uintah Basin and avoid Moderate nonattainment planning requirements, such as Reasonably Available Control Technology (RACT) and additional emissions control obligations. Additionally, the NA-NSR major source permitting threshold would remain 100 tons per year (tpy) for NOx and VOC per facility. NA-NSR applies to new or modified major sources of NOx or VOC in nonattainment.
TABLE 1. MAJOR SOURCE THRESHOLD BY NONATTIANMENT STATUS
| Nonattainment Status | Major Source Threshold (tpy) of NOx or VOC |
|---|---|
| Marginal | 100 |
| Moderate | 100 |
| Serious | 50 |
| Severe | 25 |
| Extreme | 10 |
Technical Basis
EPA’s proposal is supported by certified ozone monitoring data showing that the two‑year average (2020–2021) fourth‑highest daily maximum 8‑hour ozone concentration met Clean Air Act (CAA) criteria for a second attainment date extension, and the three‑year design value for years 2020–2022 was below 0.070 ppm, supporting attainment by the extended deadline.
Additional certified and preliminary monitoring data reviewed since the 2024 rule further support retaining the Marginal classification as shown below:
Two-year rolling means of the 4th highest daily maximum ozone concentrations across stations trended down over the last decade by 0.1 ppb per year. This decline is essentially negligible.
Regulatory Implications
If finalized:
- The Uintah Basin would return to Marginal-area nonattainment for the 2015 ozone standard.
- Facilities would be subject to Marginal-area requirements, including emissions inventories, emissions statements, and NA-NSR.
- Moderate-area requirements would no longer apply.
This action does not constitute redesignation to attainment. A formal redesignation would require EPA approval of a maintenance plan and additional CAA findings.
Why This Matters
EPA’s proposal provides near‑term regulatory certainty for industry while reinforcing the importance of high‑quality monitoring data and defensible technical analyses in ozone non-attainment decisions. The EPA is accepting comments through May 26, 2026 on this action. Facilities should continue to meet existing Moderate-area obligations and monitor the outcome of this rulemaking as EPA moves toward final action.
