Ukeiley v. U.S. Envtl. Prot. Agency, 896 F.3d 1158

Robert Ukeiley, a Colorado resident with a lung condition, sued to challenge EPA’s 2016 approval of Colorado’s PM-10 maintenance plan for the Lamar area after the EPA concurred with Colorado’s request to exclude certain exceedances as "exceptional events."
Lamar (eastern Colorado plains) historically experienced wind-driven fugitive dust (PM-10); EPA redesignated it attainment in 2005 after Colorado submitted a 10-year maintenance plan; Colorado submitted a revised plan in 2013 covering through 2025.
Colorado asked the EPA to exclude 55 PM-10 exceedances (high-wind events); the EPA concurred on 34 after reviewing meteorological, soil, and controls data and soliciting comment, then approved the plan in 2016.
The statutory and regulatory framework: the Clean Air Act allows exclusion of monitoring data influenced by "exceptional events" (42 U.S.C. § 7619); EPA’s Exceptional Events Rule and high-wind guidance set technical elements (e.g., not reasonably controllable, clear causal relationship, outside historical fluctuations).
Ukeiley argued the exclusions were unlawful because frequent windy days in Lamar are not "exceptional" (i.e., not rare), so the EPA arbitrarily and capriciously applied the statute and rule.
The Tenth Circuit reviewed under the APA (arbitrary-and-capricious standard) and Chevron deference, evaluated statutory text, EPA rule and guidance, and the administrative record, and denied the petition.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether "exceptional event" excludes recurring natural high-wind events	Ukeiley: "Exceptional" requires rarity; frequent windy days cannot qualify	EPA/Colorado: statute distinguishes human-caused (must be unlikely to recur) from natural events (no recurrence limit); guidance requires events be outside normal historical fluctuations	The statute is unambiguous: natural events may recur; EPA’s interpretation and application were reasonable; exclusion upheld
Whether EPA’s application to exclude 34 exceedances was arbitrary or capricious	Ukeiley: EPA relied on flawed, insufficient evidence and misapplied criteria	EPA: relied on extensive meteorological, soil, and causal analyses per its Rule and guidance	Court: EPA’s decision was supported by technical data and reasoned analysis; not arbitrary or capricious
Scope/timing of challenge (timeliness)	Ukeiley: challenge targets EPA’s 2016 decision and statutory interpretation	EPA: contention that Ukeiley should have challenged Rule in 2007	Court: challenge is to EPA’s application and statutory interpretation in this decision, not an untimely attack on the Rule itself; merits considered
Standard of review / deference to EPA technical judgments	Ukeiley: urges stricter reading of "exceptional"	EPA: invokes Chevron and deference to agency technical expertise	Court: applied Chevron framework; found statute clear re: natural events and in any ambiguity would defer to EPA; upheld agency expertise

Sinclair Wyoming Ref. Co. v. EPA, 887 F.3d 986 (10th Cir.) (describing APA §706 review scope)
US Magnesium, LLC v. EPA, 690 F.3d 1157 (10th Cir. 2012) (arbitrary-and-capricious standard for EPA action)
Maier v. EPA, 114 F.3d 1032 (10th Cir. 1997) (narrow but searching review of agency factfinding)
Chevron U.S.A., Inc. v. Natural Resources Defense Council, 467 U.S. 837 (1984) (two-step test for agency statutory interpretation)
Stenberg v. Carhart, 530 U.S. 914 (2000) (follow explicit statutory definition over ordinary meaning)
City of Albuquerque v. Browner, 97 F.3d 415 (10th Cir.) (deference to agency technical determinations)
Oklahoma v. EPA, 723 F.3d 1201 (10th Cir.) (applying Chevron deference to EPA interpretations)