Kentucky Energy and Environment Cabinet (23-3225) v. United States Environmental Protection Agency

RECOMMENDED FOR PUBLICATION
Pursuant to Sixth Circuit I.O.P. 32.1(b)
File Name: 24a0265p.06
UNITED STATES COURT OF APPEALS
FOR THE SIXTH CIRCUIT
COMMONWEALTH OF KENTUCKY (23-3216); KENTUCKY
ENERGY AND ENVIRONMENT CABINET (23-3225),
Petitioners,
v.
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY;
MICHAEL S. REGAN, Administrator, United States
Environmental Protection Agency,
Respondents.
┐
│
│
│
│
│
│
│
│
│
│
│
┘
Nos. 23-3216/3225
On Petition for Review of a Final Agency Action
of the United States Environmental Protection Agency.
Nos. EPA-HQ-OAR-2021-0663; EPA-R04-OAR-2021-0841.
Argued: May 8, 2024
Decided and Filed: December 6, 2024
Before: BOGGS, KETHLEDGE, and MURPHY, Circuit Judges.
_________________
COUNSEL
ARGUED: Matthew F. Kuhn, OFFICE OF THE KENTUCKY ATTORNEY GENERAL,
Frankfort, Kentucky, for Petitioner Commonwealth of Kentucky. Jarrod L. Bentley,
KENTUCKY ENERGY AND ENVIRONMENT CABINET, Frankfort, Kentucky for Petitioner
Kentucky Energy and Environment Cabinet. Jeffrey T. Hammons, UNITED STATES
DEPARTMENT OF JUSTICE, Washington, D.C., for Respondents. Claiborne E. Walthall,
OFFICE OF THE ATTORNEY GENERAL OF THE STATE OF NEW YORK, Albany, New
York, for Amici Curiae. ON BRIEF: Matthew F. Kuhn, OFFICE OF THE KENTUCKY
ATTORNEY GENERAL, Frankfort, Kentucky, for Petitioner Commonwealth of Kentucky.
Jarrod L. Bentley, Joseph A. Newberg, II, KENTUCKY ENERGY AND ENVIRONMENT
CABINET, Frankfort, Kentucky for Petitioner Kentucky Energy and Environment Cabinet.
Jeffrey T. Hammons, UNITED STATES DEPARTMENT OF JUSTICE, Washington, D.C., for
>

-- 1 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 2
Respondents. Claiborne E. Walthall, Elizabeth A. Brody, OFFICE OF THE ATTORNEY
GENERAL OF THE STATE OF NEW YORK, Albany, New York, Deena Tumeh, Kathleen
Riley, Neil Gormley, EARTHJUSTICE, Washington, D.C., Shaun A. Goho, Hayden W.
Hashimoto, CLEAN AIR TASK FORCE, Boston, Massachusetts, for Amici Curiae.
MURPHY, J., delivered the opinion of the court in which BOGGS and KETHLEDGE,
JJ., joined. MURPHY, J. (pp. 34–41), also delivered a separate concurring opinion.
_________________
OPINION
_________________
MURPHY, Circuit Judge. After the Environmental Protection Agency (EPA) changed its
air-quality standard for ozone under the Clean Air Act, the States needed to amend their state
plans to implement the new standard. To help the States with their plan revisions, the EPA
issued two guidance memoranda. It told the States that they could use specific modeling to
identify their emissions that cross state lines. And it told them that they presumptively need not
worry about any interstate emissions that fall below a specific minimum threshold. This
guidance led Kentucky to propose a plan that did not reduce its emissions further. But the EPA
sat on Kentucky’s proposed plan for some two years—well past the Clean Air Act’s deadline for
the agency to act. It then belatedly disapproved the plan. To Kentucky’s surprise, this
disapproval rested on different modeling that came out after the EPA’s deadline and on a lower
threshold than the one the EPA told Kentucky it could use. Kentucky petitioned our court to
vacate the EPA’s disapproval. In response, the EPA sought to transfer Kentucky’s challenge to
the D.C. Circuit because the EPA had disapproved Kentucky’s plan in a rule that also rejected 20
other state plans.
We deny the EPA’s motion to send this case to the D.C. Circuit. Kentucky properly sued
in this court because the EPA’s disapproval was not a “nationally applicable . . . final action” or
one “based on a determination of nationwide scope or effect[.]” 42 U.S.C. § 7607(b)(1). The
EPA’s view that a rule touching less than half the country can qualify as “nationally applicable”
conflicts with that phrase’s ordinary meaning and would create much confusion over where to
sue. At any rate, the EPA cannot turn the quintessential “local” action (a state-plan decision)
into a national one merely by combining it with others. To fend off legal challenges on the

-- 2 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 3
merits, the EPA’s final rule also clarified that its decision to disapprove Kentucky’s plan rested
on Kentucky’s unique facts. So its action was not “based on a determination of nationwide
scope or effect.”
We next hold that the EPA’s disapproval of Kentucky’s plan violated the Administrative
Procedure Act (APA). The EPA acted in an “arbitrary” way by telling Kentucky one thing and
then doing another. 5 U.S.C. § 706(2)(A). It recommended that Kentucky use certain modeling
and a certain threshold. Yet it denied Kentucky’s plan using different modeling and a different
threshold. Ralph Waldo Emerson might have approved of this approach, since he once opined
that “[a] foolish consistency is the hobgoblin of little minds[.]” Antonin Scalia, Assorted
Canards of Contemporary Legal Analysis, 40 Case W. Res. L. Rev. 581, 587 (1989) (quoting
Ralph Waldo Emerson, Self-Reliance, in Essays and English Traits 66 (C.W. Eliot ed. 1909)).
But this “canard” has no place in legal reasoning because “[c]onsistency is the very foundation
of the rule of law.” Id. at 588. Congress thus kept it out of our administrative law by passing the
APA. Because the EPA has not justified its inconsistencies here, we vacate its disapproval of
Kentucky’s plan.
I
A
Like most laws, the Clean Air Act represents a compromise of competing interests.
Cf. Luna Perez v. Sturgis Pub. Schs., 598 U.S. 142, 150 (2023). Congress sought to reduce
pollution. 42 U.S.C. § 7401(a)(1)–(2). But it also sought to respect state authority. Id.
§ 7401(a)(3)–(4). The Act thus seeks to improve air quality in a specific way: through “a model
of cooperative federalism.” Sierra Club v. Korleski, 681 F.3d 342, 343 (6th Cir. 2012) (quoting
Ellis v. Gallatin Steel Co., 390 F.3d 461, 467 (6th Cir. 2004)).
The cooperative process begins at the federal level. The EPA must impose and
periodically revise “national ambient air quality standards” for each air pollutant. 42 U.S.C.
§ 7409(a)(1), (d). The EPA should set these standards at a level that will “protect the public
health.” Id. § 7409(b)(1).

-- 3 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 4
When the EPA adopts a revised air-quality standard for a pollutant, the regulatory process
shifts to the States. Each State must develop an “implementation plan” (or “[s]tate plan” for
short) that will maintain and enforce this standard within its borders. Id. §§ 7407(a); 7410(a). A
State must submit its plan to the EPA for approval within three years of the revised air-quality
standard. Id. § 7410(a)(1). Its plan must satisfy many statutory criteria. See id. § 7410(a)(2).
The plan, for example, must contain the emissions limits required to meet the new standard. Id.
§ 7410(a)(2)(A).
Once the State submits its plan, the EPA must approve or disapprove it within 18 months.
Id. § 7410(k)(1)–(3). The EPA must evaluate the plan only against the statutory criteria. If the
plan meets the criteria, the EPA cannot reject it on the ground that the State has chosen an
unwise method to attain the air-quality standard. See Ohio v. EPA, 603 U.S. 279, 284 (2024).
If the EPA disapproves a state plan, the agency must issue a “[f]ederal implementation
plan” that meets the revised air-quality standard within the State. 42 U.S.C. § 7410(c)(1)(B).
The agency may issue this federal plan “at any time within 2 years” from its disapproval of the
state plan. Id. § 7410(c)(1). But if the State timely revises its plan to correct the original’s
deficiencies and the EPA approves that revised plan, the EPA need not issue its own federal plan.
Id. § 7410(c)(1)(B); see also EPA v. EME Homer City Generation, L.P., 572 U.S. 489, 507–10
(2014).
B
This case concerns a specific requirement that state plans must meet: the “Good Neighbor
Provision.” EME Homer, 572 U.S. at 495. Pollutants emitted from a source (say, a power plant)
in one State often do not stop at that State’s borders. Rather, the wind can carry the pollutants
“over hundreds of miles” to one or more States. Id. at 496. This fact creates a classic “negative
externality”: an upwind State can shift some of the cost of its activities (such as energy
production) to downwind States. See id. at 495. Without national regulation, upwind States
would have little incentive to take these external costs into account. See id. So downwind States
might have to impose greater limits on their own activities to achieve acceptable pollution levels.
See id.

-- 4 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 5
Congress adopted the Good Neighbor Provision to create the national coordination
required for States to “internalize” these harms. See 42 U.S.C. § 7410(a)(2)(D). This provision
requires a state plan to include terms that prohibit “any source or other type of emissions activity
within the State from emitting any air pollutant in amounts which will . . . contribute
significantly to nonattainment in, or interfere with maintenance by, any other State with respect
to” an air-quality standard. Id. § 7410(a)(2)(D)(i). How will States know whether their
emissions will have these interstate effects? To help them identify emissions that they may have
to reduce, the EPA must classify all areas as “nonattainment” (if an area does not meet an air-
quality standard) or “attainment” (if it does). See id. § 7407(d); EME Homer, 572 U.S. at 498.
The Supreme Court has addressed the Good Neighbor Provision once when evaluating
the “Cross-State Air Pollution Rule” (or “Transport Rule”) that the EPA issued in 2011. EME
Homer, 572 U.S. at 500. The Transport Rule adopted a “two-step approach” for determining
whether pollution sources in an upwind State “contribute[d] significantly to nonattainment” in a
downwind State. Id. (citation omitted). First, the EPA asked whether the upwind State had
sources linked to a downwind State’s “receptor[s]” (places where the EPA measures air quality).
Id. At this “screening” step, if an upwind State’s sources contributed only a small part of the
total pollutant at a downwind receptor (less than 1% of the air-quality standard for that
pollutant), the Transport Rule decided that the State did not “contribute[] significantly” to the
downwind State’s pollution problems. Id. at 501. Second, the Transport Rule relied on a cost-
benefit analysis to control emissions from States whose pollution contributions at a receptor
exceeded this 1% threshold. Id. at 500–01. Ultimately, the Court relied on the now-overruled
review scheme from Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S.
837 (1984), to hold that the Good Neighbor Provision’s text permitted this approach. See EME
Homer, 572 U.S. at 495–96; cf. Loper Bright Enters. v. Raimondo, 144 S. Ct. 2244, 2273 (2024).
C
This case also concerns a specific pollutant: ozone. Although ozone in the atmosphere
helps protect us “from the sun’s radiation,” the pollutant at ground levels can harm human health
(for example, by inflaming our lungs) and the earth’s vegetation (for example, by reducing crop
yields). Ohio, 603 U.S. at 284; National Ambient Air Quality Standards for Ozone, 80 Fed. Reg.

-- 5 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 6
65292, 65302–11, 65369–73 (Oct. 26, 2015). In October 2015, the EPA lowered the air-quality
standard for ozone from 75 to 70 parts per billion (or ppb). 80 Fed. Reg. at 65330, 65365. This
revision required the States to submit revised implementation plans within three years. See
42 U.S.C. § 7410(a). To help States develop plans that would meet the Good Neighbor
Provision, the EPA released two memoranda in 2018.
March 2018 Memorandum. The EPA issued its first guidance in March 2018. It told the
States that it planned to determine each State’s good-neighbor obligations using the same
approach from the Transport Rule (but the agency now divided this approach into four steps).
Mar. Mem., J.A. 76–77. At Step 1, the relevant federal or state regulator should “identify
downwind” locations that will struggle to attain or maintain the air-quality standard. Id. At Step
2, the regulator should identify the upwind States whose pollution sources “contribute enough to
those downwind air quality problems to warrant further review[.]” Id. at 76. At Step 3, the
regulator should rely on cost considerations (among other things) to calculate the amount of
emissions reductions (if any) that an upwind State must make so that it does not contribute to the
“downwind air quality problems[.]” Id. at 77. At Step 4, the regulator should identify
“permanent and enforceable measures” to achieve these reductions. Id. The EPA told States that
their plans could follow this approach or “alternative frameworks” that comported with the Good
Neighbor Provision. Id.
This March 2018 Memorandum also included “modeling” data to predict ozone problems
in downwind States in 2023 and to identify the upwind contributors. Id. The EPA suggested
that the States could “consider using this national modeling to develop” their plans. Id. at 80.
The modeling relied on data centered on pollution from 2011, so we will call it the “2011
modeling.” Id. at 77–80. It identified two types of downwind “receptors”: those showing that a
location would not attain the ozone standard in 2023 (“nonattainment receptors”) and those
showing that a location would struggle to maintain that standard in 2023 (“maintenance
receptors”). Id. at 78.
August 2018 Memorandum. Five months later, the EPA issued more “recommendations”
for state plans. Aug. Mem., J.A. 98. These recommendations addressed “Step 2”—the
“screening” step at which the EPA eliminates the upwind States that contribute only a small

-- 6 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 7
amount to downwind receptors. Id. at 99. As with the Transport Rule, the EPA historically
screened out States that contributed less than 1% of an air-quality standard. See EME Homer,
572 U.S. at 500 & n.3. If the EPA applied this rule to the ozone standard of 70 ppb, it would set
a .7 ppb “threshold” that a State’s contributions must exceed. Aug. Mem., J.A. 100. The August
2018 Memorandum compared this 1% rule (.7 ppb) to a larger threshold: 1 ppb. Id. It found that
“the amount of upwind collective contribution” under both thresholds was “generally
comparable[.]” Id. at 101. The EPA thus told States that they could use the higher 1 ppb
threshold. Id. According to the EPA, if a State’s ozone contributions fell below 1 ppb at a
receptor, the State could find that it did not contribute enough pollutants to warrant further
review at Steps 3 and 4. Id. at 99. Yet the EPA also refused to guarantee approval of a state plan
that followed this recommendation because the recommendation might “not apply to the facts
and circumstances” of all States. Id. at 98.
D
Kentucky relied on these memoranda to draft its plan. It used the 2011 modeling from
the March 2018 Memorandum and the 1 ppb threshold from the August 2018 Memorandum.
State Plan, J.A. 151–52. At Step 2, these choices showed that Kentucky exceeded the screening
threshold at only one maintenance receptor in Harford County, Maryland. Id. at 152; Mar.
Mem., J.A. 89. Kentucky contributed 1.52 ppb of ozone to this location. State Plan, J.A. 152.
Turning to Step 3, Kentucky decided that it need not impose further emissions reductions
despite the link to the Maryland receptor. Id. Kentucky gave several reasons for this conclusion.
To begin with, the Maryland receptor was a “maintenance” receptor, so the pollution there was
less severe than the pollution at a “nonattainment” receptor. Id. Kentucky’s ozone-producing
emissions also would continue to decrease in future years because of other regulations and
because of the expected “retirement of several” power plants. Id. at 163–66, 177–78. Kentucky
also opined that “local” emissions in Maryland (such as local car traffic) contributed far more
than Kentucky emissions to ozone in the area. Id. at 173–77. The Commonwealth believed that
the EPA should compel “local sources” to reduce their emissions before requiring far-away
sources to “over-control” their emissions. Id. at 173.

-- 7 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 8
During Kentucky’s notice-and-comment process, the EPA commented on its state plan.
EPA Comments, J.A. 124–28. Among other things, Kentucky’s plan used an “intricate
combination” of the 2011 modeling from the March 2018 Memorandum and additional modeling
from a Kentucky contractor. Id. at 126. The EPA recommended that Kentucky simply use the
EPA’s 2011 modeling and its 1 ppb screening threshold as an “alternative, more straightforward
approach[.]” Id. The agency added that this approach would still connect Kentucky only to the
Maryland monitor. Id. The EPA separately noted that Kentucky should specifically identify the
power-plant closures that EPA’s 2011 modeling failed to capture. Id.
After this feedback, Kentucky formally submitted its plan in January 2019. State Plan,
J.A. 129. When discussing the EPA’s comments, Kentucky “concur[red] with EPA’s” simplified
proposal. Id. at 454. Despite the link to the Maryland monitor, Kentucky also continued to find
that it need not reduce emissions. Id. at 178. In that respect, it identified the planned power-
plant “shutdown” that the 2011 modeling had not considered. Id. at 454.
Under the Act, the EPA had until July 2020 to rule on Kentucky’s plan. 42 U.S.C.
§ 7410(k)(1)(B), (2). That date came and went without a ruling.
Nearly 20 months after the deadline, the EPA proposed a rule to disapprove Kentucky’s
plan. Air Plan Disapproval, 87 Fed. Reg. 9498, 9498 (Feb. 22, 2022). This rule included two
surprises. As for the first, the EPA used different modeling than the modeling in its March 2018
Memorandum. See id. at 9500–01. The new modeling centered on pollution in 2016, so we will
call it the “2016v2 modeling.” Id. As for the second, the EPA rejected the 1 ppb threshold that
its August 2018 Memorandum had recommended to screen out small upwind contributions. Id.
at 9502–03. The agency proposed returning to the lower threshold that the Transport Rule had
used: 1% of the air-quality standard (.7 ppb for the ozone standard). Id. These changes affected
Kentucky in different ways. On the one hand, the new modeling no longer linked Kentucky to
the Maryland receptor because that receptor was now adequately attaining the air-quality
standard. Id. at 9507, 9509. On the other hand, the .7 ppb threshold linked Kentucky to three
nonattainment receptors in Connecticut and one maintenance receptor in Pennsylvania. Id.

-- 8 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 9
A year later, the EPA disagreed with Kentucky’s objections and issued a final rule
disapproving its plan. Air Plan Disapprovals, 88 Fed. Reg. 9336, 9356 (Feb. 13, 2023). This
rule combined the EPA’s denial of Kentucky’s plan with its denial of 20 others. See id. at 9336–
38 & n.8. The rule contained two fresh surprises. The EPA again switched to new modeling: the
“2016v3 modeling.” See id. at 9339, 9344. Although this modeling contained similar data as the
2016v2 modeling, it included “models, methods, and source datasets that became available in
calendar years 2020 through 2022[.]” Id. at 9345. Further, the EPA now identified a third type
of “receptor”—what it called a “violating monitor”—in addition to maintenance and
nonattainment receptors. Id. at 9342. It chose this third group as a cautionary matter. Fresh
information from 2021 and 2022 showed that certain locations were not attaining the ozone
standard even though the EPA’s modeling predicted that these areas would meet the standard.
Id. at 9349. At the same time, the EPA used these new monitors only on a “confirmatory basis”
and chose not to rely on them as a sole ground to deny a state plan. Id.
How did these fresh changes affect Kentucky? The 2016v3 modeling and 1% threshold
continued to link Kentucky to three Connecticut receptors. 2016v3 Modeling, J.A. 577. The
EPA also linked Kentucky to four new violating monitors in Connecticut, New York, Michigan,
and Ohio. Id. at 578; see 88 Fed. Reg. at 9356. Relying on these links at Step 2, the EPA found
Kentucky’s proposal inadequate at Step 3. See 88 Fed. Reg. at 9356.
E
The EPA’s disapproval of these 21 state plans triggered a flood of litigation. Many States
sought review of the EPA’s denials in their regional circuit courts. Kentucky and its Energy and
Environment Cabinet (collectively, Kentucky) filed petitions for review in our court, asking us to
vacate the EPA’s disapproval of their plan. The EPA responded by moving to transfer
Kentucky’s case to the D.C. Circuit. Meanwhile, the Commonwealth moved to stay the EPA’s
disapproval of its plan pending our full review. In May 2023, a motions panel granted a short
administrative stay while it considered these motions. The same month, other circuit courts also
stayed the denials of other state plans. See Ohio, 603 U.S. at 288–89.

-- 9 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 10
A few days after we granted our administrative stay, the EPA imposed its own federal
implementation plan on Kentucky and 22 other States for the 2015 ozone standard. Federal
“Good Neighbor Plan” for the 2015 Ozone National Ambient Air Quality Standards, 88 Fed.
Reg. 36654, 36654 (June 5, 2023). States challenged that plan in the D.C. Circuit. See Ohio,
603 U.S. at 290.
As litigation over the federal plan progressed, regional circuits continued to stay the
EPA’s disapproval of state plans. See id. In July 2023, we turned our administrative stay into a
stay pending our full review. Kentucky v. EPA, 2023 WL 11871967, at *5 (6th Cir. July 25,
2023) (order). We also denied the EPA’s motion to transfer the suit to the D.C. Circuit. See id.
at *1–3.
A short time later, the EPA stayed its federal plan for the States that had obtained judicial
stays. Federal “Good Neighbor Plan” for the 2015 Ozone National Ambient Air Quality
Standards, 88 Fed. Reg. 49295, 49295 (July 31, 2023). These stays grew to cover “12 of the 23”
States subject to the federal plan. Ohio, 603 U.S. at 289–90. Yet this plan’s emissions
reductions rested on the premise that all States would participate. See id. at 287–88, 293–94.
The Supreme Court thus stayed the federal plan pending judicial review of that plan’s validity.
See id. at 300.
* * *
The Supreme Court’s decision completes the backdrop against which we must review
Kentucky’s petitions here. Those petitions raise three questions. Did Kentucky sue in the right
court? If so, did the EPA lawfully deny Kentucky’s plan? If not, what is the proper remedy?
Our short answers: Yes, No, and Vacatur. We will fill in the details to each answer in turn.
II. Did Kentucky Sue in the Right Court?
The EPA has renewed its request to transfer Kentucky’s petitions to the D.C. Circuit.
Kentucky responds that we should reject this request based solely on the motions panel’s earlier
order denying the EPA’s motion to transfer. See Kentucky, 2023 WL 11871967, at *1–3.
According to Kentucky, we must “defer[]” to “the decisions of motions panels” and “cannot

-- 10 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 11
simply” reject them. Wallace v. FedEx Corp., 764 F.3d 571, 583 (6th Cir. 2014). Yet we have
never explained the amount of deference due these decisions. Indeed, why should we defer at
all? We can (and sometimes do) depart from unpublished opinions. See Bell v. Johnson, 308
F.3d 594, 611 (6th Cir. 2002). And other circuits do not defer to similar interlocutory rulings.
See Tex. Democratic Party v. Abbott, 978 F.3d 168, 176 (5th Cir. 2020); United States v. Lopez-
Armenta, 400 F.3d 1173, 1175 (9th Cir. 2005); Am. Fed’n of Grain Millers, Loc. 24 v. Cargill
Inc., 15 F.3d 726, 727 (7th Cir. 1994); 16AA Charles A. Wright et al., Federal Practice and
Procedure § 3973.3, at 256–60 (5th ed. 2023). Still, we may save that question for another day.
Even reviewing the EPA’s motion de novo, we agree with the motions panel that it lacks merit.
A. Background Law
The Clean Air Act allows a party injured by an EPA action to file a “petition for review”
challenging the action in a circuit court of appeals. 42 U.S.C. § 7607(b)(1). The Act’s (lengthy)
judicial-review provision contains three basic parts. First, the provision gives the D.C. Circuit
the authority to review the EPA’s “nationally applicable” “regulations” or “final action”:
A petition for review of action of the Administrator in promulgating any national
primary or secondary ambient air quality standard, any emission standard or
requirement under section 7412 of this title, any standard of performance or
requirement under section 7411 of this title,[] any standard under section 7521 of
this title (other than a standard required to be prescribed under section 7521(b)(1)
of this title), any determination under section 7521(b)(5) of this title, any control
or prohibition under section 7545 of this title, any standard under section 7571 of
this title, any rule issued under section 7413, 7419, or under section 7420 of this
title, or any other nationally applicable regulations promulgated, or final action
taken, by the Administrator under this chapter may be filed only in the United
States Court of Appeals for the District of Columbia.
Id. Second, the provision gives the appropriate regional circuit court the authority to review the
EPA’s “locally or regionally applicable” actions:
A petition for review of the Administrator’s action in approving or promulgating
any implementation plan under section 7410 of this title or section 7411(d) of this
title, any order under section 7411(j) of this title, under section 7412 of this title,
under section 7419 of this title, or under section 7420 of this title, or his action
under section 1857c-10(c)(2)(A), (B), or (C) of this title (as in effect before
August 7, 1977) or under regulations thereunder, or revising regulations for
enhanced monitoring and compliance certification programs under section

-- 11 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 12
7414(a)(3) of this title, or any other final action of the Administrator under this
chapter (including any denial or disapproval by the Administrator under
subchapter I) which is locally or regionally applicable may be filed only in the
United States Court of Appeals for the appropriate circuit.
Id. Third, the provision redirects even a locally or regionally applicable action to the D.C.
Circuit if the action is “based on a determination of nationwide scope or effect” and the EPA
notes that the action has this scope or effect:
Notwithstanding the preceding sentence a petition for review of any action
referred to in such sentence may be filed only in the United States Court of
Appeals for the District of Columbia if such action is based on a determination of
nationwide scope or effect and if in taking such action the Administrator finds and
publishes that such action is based on such a determination.
Id.
Our court has yet to decide on the nature of this provision. Does it impose a
(nonwaivable) jurisdictional ban on the wrong circuit’s adjudication of a petition or instead a
(waivable) limit on the proper venue in which to sue? See Wachovia Bank v. Schmidt, 546 U.S.
303, 315–16 (2006). Other courts have read § 7607(b) as granting jurisdiction to all circuit
courts, and they have added that its circuit-specific rules identify only the proper venue. See
Texas v. EPA, 829 F.3d 405, 418 (5th Cir. 2016); Dalton Trucking, Inc. v. EPA, 808 F.3d 875,
879–80 (D.C. Cir. 2015); Clean Water Action Council of Ne. Wis., Inc. v. EPA, 765 F.3d 749,
751–52 (7th Cir. 2014). But the parties did not brief this distinction. And our holding that
Kentucky sued in the right court eliminates the need to decide it. Cf. Jaber v. Gonzales, 486
F.3d 223, 228 n.3 (6th Cir. 2007).
B. Application
The EPA offers two reasons why this suit belongs in the D.C. Circuit. It first argues that
its disapproval of the 21 state plans qualifies as a “nationally applicable . . . final action.” And
even if the disapproval of Kentucky’s plan was “locally or regionally applicable,” the EPA next
argues that it was “based on a determination of nationwide scope or effect.” These claims have
created a circuit split. Apart from Kentucky, several States have challenged the disapprovals of
their plans in regional circuits. And most circuit courts have held that they (not the D.C. Circuit)

-- 12 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 13
represent the proper tribunal for the suits. See West Virginia v. EPA, 90 F.4th 323, 331 (4th Cir.
2024) (citing cases). The Tenth Circuit, by contrast, has sent challenges to the denial of
Oklahoma’s plan to the D.C. Circuit. See Oklahoma ex rel. Drummond v. EPA, 93 F.4th 1262,
1266–69 (10th Cir. 2024), cert. granted, 2024 WL 4529798 (U.S. Oct. 21, 2024). We agree with
the courts that have rejected the EPA’s two arguments for D.C. Circuit review.
1. Did the EPA take a “nationally applicable” action when denying Kentucky’s plan?
The EPA argues that its rule disapproving the state plans qualifies as a single “nationally
applicable . . . final action” rather than many “locally or regionally applicable” actions.
42 U.S.C. § 7607(b)(1). This claim misreads the phrases “nationally applicable” and “final
action.”
Nationally Applicable. The EPA first misconstrues the phrase “nationally applicable” in
§ 7607(b)(1). As with any case, we start with the “ordinary meaning” of the words Congress
used. Engine Mfrs. Ass’n v. S. Coast Air Quality Mgmt. Dist., 541 U.S. 246, 252 (2004) (quoting
Park ‘N Fly, Inc. v. Dollar Park & Fly, Inc., 469 U.S. 189, 194 (1985)); see Nat’l Ass’n of Mfrs.
v. Dep’t of Def., 583 U.S. 109, 127 (2018). The key words—“nationally applicable regulations
promulgated, or final action taken,” by the EPA—convey that the challenged regulations or
action must apply to the entire country. 42 U.S.C. § 7607(b)(1). Because the phrasal adjective
“nationally applicable” modifies the nouns “regulations” and “action,” the regulations or action
must “have reference to” (“applicable”) the “nation as a whole” (“nationally”). 1 Oxford English
Dictionary 575 (2d ed. 1989); 10 Oxford English Dictionary, supra, at 235; Webster’s Third New
Int’l Dictionary 105, 1505 (1976). We doubt that we need dictionaries for this point. Would
anyone say that Congress passed a “nationally applicable” law if the law formally applied to only
40% of the country? No, the word “‘[n]ational’ contemplates an activity with a nationwide
scope.” Black’s Law Dictionary 923 (5th ed. 1979). And here, all agree that the EPA’s rule
formally applies to just 21 States—not the whole country.
Two canons of construction confirm this reading. The sentence in § 7607(b)(1) that
contains the “nationally applicable” clause triggers the “ejusdem generis” canon. That canon
applies to a catchall clause following a list of items. See Bissonnette v. LePage Bakeries Park

-- 13 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 14
St., LLC, 601 U.S. 246, 252 (2024). It instructs courts to interpret the catchall as falling within
the same class as the specific items that precede it. See id. So, for example, the phrase “seamen,
railroad employees, or any other class of workers” covers only transportation workers—not all
workers. 9 U.S.C. § 1; see Bissonnette, 601 U.S. at 252–53. The catchall clause here—“any
other nationally applicable regulations promulgated, or final action taken, by the” EPA—also
follows a list of specific actions that parties must challenge in the D.C. Circuit. 42 U.S.C.
§ 7607(b)(1). And as far as we can tell, those actions have nationwide applicability. See id. For
example, challengers must sue in the D.C. Circuit over “any national primary or secondary
ambient air quality standard[.]” Id. Likewise, they must sue in the D.C. Circuit over the EPA’s
“standards” for stationary sources, hazardous pollutants, motor vehicles, fuels, and aircraft under
42 U.S.C. §§ 7411, 7412, 7521, 7545, and 7571. Id. § 7607(b)(1). And they must sue in that
court over the general “rules” that govern enforcement (or similar) proceedings under §§ 7413,
7419, and 7420. Id. § 7607(b)(1). Given that the list in § 7607(b)(1) includes several national
regulations, we read the catchall to have a similar breadth. See Bissonnette, 601 U.S. at 252.
Next, courts presume that Congress means to adopt “clear boundaries” in “jurisdictional
statutes” to avoid wasteful litigation over the proper forum. Direct Mktg. Ass’n v. Brohl, 575
U.S. 1, 11 (2015); see Miss. ex rel. Hood v. AU Optronics Corp., 571 U.S. 161, 172–73 (2014);
Hertz Corp. v. Friend, 559 U.S. 77, 94 (2010). Even if § 7607(b)(1) is a mere venue provision,
the Supreme Court would likely extend this “clear boundaries” principle to § 7607(b)(1). See
New York v. EPA, 133 F.3d 987, 990 (7th Cir. 1998). And our reading has “administrative
simplicity” because it asks an objective question: Does the action formally apply to the nation?
Hertz, 559 U.S. at 94. The EPA’s view, by contrast, would engender perpetual litigation over the
actions that are “nationally applicable.” The agency says its rule here falls within that phrase
because the rule covers 21 States in different parts of the country. Would this logic reach an
action that covered only California, Maine, and Alabama because they fall in different parts of
the country? If not, how many more States are needed? The EPA does not even try to answer
these questions.
Final Action. The EPA also misconstrues the phrase “final action” in § 7607(b)(1). It
argues that its disapprovals of the 21 state plans all qualify as a single consolidated action rather

-- 14 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 15
than 21 separate actions. It thus advocates for a “rulemaking approach” that treats as a single
“action” any regulatory decisions that the EPA combines into a single rule in the Federal
Register. According to Kentucky, by contrast, the phrase “final action” adopts a “statutory
approach” that treats each activity the Clean Air Act allows the EPA to take as a distinct
“action”—whether the EPA announces these activities in a single rule or separate rules in the
Federal Register.
We side with Kentucky in this debate. This time, though, the ordinary meaning of
“action” does not help all that much. That word means simply a “thing done” or “something
done.” Webster’s Third, supra, at 21; Black’s, supra, at 26. So these (circular) definitions leave
the critical question unanswered: Did the EPA do 21 “things” or a single “thing” in the rule?
That said, Kentucky’s approach better fits the “structure” of the judicial-review
provision. Engine Mfrs. Ass’n, 541 U.S. at 252. As a general matter, § 7607(b)(1) focuses on
the statute (not the rulemaking) to distinguish the EPA actions that parties must challenge in the
D.C. Circuit from those they must challenge in regional circuits. See Texas v. EPA, 2023 WL
7204840, at *4 (5th Cir. May 1, 2023) (per curiam). The provision ties the proper tribunal to the
activity taken “under this chapter” (that is, under the Clean Air Act). 42 U.S.C. § 7607(b)(1).
For example, § 7409(a)(1) requires the EPA to issue a national air-quality standard “for each air
pollutant,” and § 7607(b)(1) sends a challenge to “any” such “standard” to the D.C. Circuit. On
the other hand, § 7419(a)(1)(A) allows the EPA to issue a “primary nonferrous smelter order” for
a specific smelter, and § 7607(b)(1) sends a challenge to such an “order” to a regional circuit.
Nothing in § 7607(b)(1)’s text would allow the EPA to obtain D.C. Circuit review of the smelter
order simply by combining it with the air-quality standard. Rather, the standard and the order
represent distinct “actions” even if the EPA publishes them in the same rule in the Federal
Register.
Congress also knows how to refer to rules in the Federal Register when it wants to.
Section 7607(b)(1) makes the “notice” of an EPA action “in the Federal Register” relevant to the
60-day limit for suing. Id. Congress also required a “promulgated rule” to go through several
procedures. Id. § 7607(d)(6)(A). Yet Congress used “final action” (not “promulgated rule”)
when deciding where parties must sue. Id. § 7607(b)(1), (d)(6)(A). And courts normally

-- 15 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 16
presume Congress acts intentionally with such different word choices. See Burlington N. &
Santa Fe Ry. Co. v. White, 548 U.S. 53, 63 (2006); Gen. Motors Corp. v. United States, 496 U.S.
530, 541 (1990).
As a specific matter, § 7607(b)(1) clarifies that the disapproval of each state plan
qualifies as a distinct “action” that falls on the local side of this divide. The Clean Air Act
requires the EPA to “act” on each State’s “submission” on a plan-by-plan basis within a specific
time. 42 U.S.C. § 7410(k)(2); see West Virginia, 90 F.4th at 330. The judicial-review provision
then indicates that the EPA’s “action in approving . . . any implementation plan” (in the singular)
belongs in a regional circuit. 42 U.S.C. § 7607(b)(1). And while the EPA denied Kentucky’s
plan, this decision falls within the catchall for “locally or regionally applicable” actions (which
includes a “denial or disapproval”). Id. As then-Judge Kavanaugh explained, EPA action on a
state plan qualifies as the “prototypical” decision that belongs in a regional circuit because of its
local character. Am. Rd. & Transp. Builders Ass’n v. EPA, 705 F.3d 453, 455 (D.C. Cir. 2013).
So each state-plan denial in the EPA’s rule qualifies as a distinct “action” under the Clean Air
Act. This reading makes this case easy: the EPA’s disapproval of Kentucky’s plan is a locally
applicable action.
The EPA’s contrary arguments do not convince us otherwise. The agency offers no
textual theory for its view that the phrase “nationally applicable” can reach an action applying to
a hodgepodge of States that make up less than half the nation. It instead jumps to precedent,
suggesting that courts have treated EPA actions as “nationally applicable” if they affect a large
(unidentified) number of States. See S. Ill. Power Coop. v. EPA, 863 F.3d 666, 671 (7th Cir.
2017); ATK Launch Sys., Inc. v. EPA, 651 F.3d 1194, 1197 (10th Cir. 2011); Texas v. EPA, 2011
WL 710598, at *3–4 (5th Cir. Feb. 24, 2011); W. Va. Chamber of Com. v. Browner, 1998 WL
827315, at *2, *6–8 (4th Cir. Dec. 1, 1998) (per curiam). But the Fifth Circuit has since clarified
that the EPA misread its precedent. See Calumet Shreveport Refin., L.L.C. v. EPA, 86 F.4th
1121, 1131 (5th Cir. 2023), cert. granted, 2024 WL 4529794 (U.S. Oct. 21, 2024). True, a
regulation can be “nationally applicable” if its “legal effect” applies to the whole country—even
if its practical effect is felt only by a subset of States. Id. The EPA could, for example, adopt a
universal regulation imposing requirements that practically apply to only some States

-- 16 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 17
(say, because of their different geographies or because the remaining States already satisfy the
regulation). But the EPA seeks to go well beyond that valid principle because it makes no claim
that a rule disapproving 21 state plans formally applies everywhere.
As for the remaining circuits, we disagree with their view that a regulation need not
regulate the nation as a whole to be “nationally applicable.” Take the Tenth Circuit’s decision in
ATK Launch Systems, 651 F.3d at 1197. It did not try to interpret the phrase “nationally
applicable.” Rather, it merely concluded that a regulation’s reach “from coast to coast and
beyond” suffices even if the regulation does not formally apply to the whole nation. Id. But the
court did not say why. And it left many questions unanswered. How many States must a rule
cover? How spread out must the covered States be? Nothing in the statute can answer these
questions.
Next, the EPA suggests that we must consider the “face of [its] rule”—not the rule’s
“practical effect” as applied to Kentucky—to decide whether it is “nationally applicable.”
Respondents’ Br. 32 (quoting ATK Launch Sys., 651 F.3d at 1197). This argument conflates the
rule issued in the Federal Register (the EPA’s words) with the “final action” that the EPA takes
(the statute’s words). 42 U.S.C. § 7607(b)(1). Those phrases do not mean the same thing. And
the relevant final action (the denial of Kentucky’s plan) applies only to Kentucky on its face.
The EPA also argues that its disapprovals of the 21 plans represent a single “nationally
applicable” action because the disapprovals rested on a “uniform legal interpretation and
common, nationwide analytical methods[.]” Respondents’ Br. 35 (quoting 88 Fed. Reg. at 9380–
81). This theory conflicts with § 7607(b)(1)’s text and structure. Starting with text, the phrase
“nationally applicable” modifies the action that the EPA takes—not the reasons for it. And here,
the action was a “prototypical” local decision. Am. Rd. & Transp. Builders Ass’n, 705 F.3d at
455. Turning to structure, Congress recognized that local actions might rest on national
decisions. So it allowed D.C. Circuit review if the EPA showed that a local action was “based
on a determination of nationwide scope or effect[.]” 42 U.S.C. § 7607(b)(1). We would unravel
this layered scheme if we looked to an action’s justification at the start to decide whether the
action is national or local.

-- 17 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 18
The EPA ends with policy. It suggests that Kentucky’s view inefficiently requires many
courts to “concurrently” review actions that rest on the “same legal interpretations, policy
decisions, and analytical methodology,” which could generate “inconsistent” results.
Respondents’ Br. 37. Yet we see competing “wisdom” in “allowing difficult issues to mature
through full consideration” by different courts. E.I. du Pont de Nemours & Co. v. Train, 430
U.S. 112, 135 n.26 (1977). This expanded review increases the likelihood that the Supreme
Court will have all arguments before it when it resolves the issue. See id. Regardless, the axiom
that “no legislation pursues its purposes at all costs” applies just as much to procedural
provisions as it does to substantive ones. CTS Corp. v. Waldburger, 573 U.S. 1, 12 (2014)
(quoting Rodriguez v. United States, 480 U.S. 522, 525–26 (1987) (per curiam)). We thus must
enforce the judicial-review provision as written even if it conflicts with the EPA’s views of
“sound policy.” Nat’l Ass’n of Mfrs., 583 U.S. at 132 (quoting Florida Power & Light Co. v.
Lorion, 470 U.S. 729, 746 (1985)). And the written text makes clear that the EPA took a locally
applicable action when disapproving Kentucky’s plan.
2. Is the denial of Kentucky’s plan “based on a determination of nationwide
scope or effect”?
The EPA alternatively claims that, even if its disapproval of Kentucky’s plan was
“locally or regionally applicable,” that disapproval was “based on a determination of nationwide
scope or effect” under § 7607(b)(1). 88 Fed. Reg. at 9380. The EPA said as much in the final
rule itself, so it met the separate requirement that it “publish” this finding. Id.; 42 U.S.C.
§ 7607(b)(1). The agency reasoned that all 21 disapprovals were “based on a common core of
nationwide policy judgments and technical analysis concerning the interstate transport of
pollutants throughout the continental U.S.” 88 Fed. Reg. at 9380. The EPA then listed three
examples. First, the agency used the same four-step “framework” when disapproving all 21
plans. Id. Second, the disapprovals rested on the 2016v3 modeling and a uniform approach to
identifying maintenance and nonattainment receptors. Id. at 9380–81. Third, the EPA
considered requests to use “alternative approaches or alternative sets of data” under the same
standards. Id. at 9381. This interpretation misreads two other phrases in § 7607(b)(1):
“determination” and “based on.”

-- 18 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 19
Determination. The EPA argues that each analytical step in the chain of reasoning to its
ultimate decision for a “final action” qualifies as an independent “determination” that triggers
review in the D.C. Circuit if at least one step (considered in isolation) has a “nationwide scope or
effect.” 42 U.S.C. § 7607(b)(1). To give the obvious example, the EPA reasons that every
approval or disapproval of a state plan includes the choice to follow its four-step “framework”
for applying the Good Neighbor Provision. 88 Fed. Reg. at 9380. Because this framework
applies everywhere, the EPA says that every one of its actions on a state plan will be “based on a
determination of nationwide scope or effect” about the Good Neighbor Provision’s meaning.
This broad reading of “determination” lacks merit. We again start with the “ordinary
meaning” of the text. Engine Mfrs. Ass’n, 541 U.S. at 252. Admittedly, “determination” in the
abstract could mean what the EPA says because it can refer to any academic resolution of a
“question by argument or reasoning.” Webster’s Third, supra, at 616. But the EPA’s reading
does not fit the context. When used to describe a ruling from an “administrative agency,”
Black’s Law Dictionary, supra, at 405, “determination” has a more precise “legal meaning” that
refers to the agency’s ultimate decision—not each preliminary step on the road to that decision.
Smith v. Spizzirri, 601 U.S. 472, 477 (2024); United States v. Hansen, 599 U.S. 762, 774 (2023).
In other words, the word “implies an ending or finality of a controversy or suit,” Black’s Law
Dictionary, supra, at 405, and directs us to look to the “authoritative decision” of the “matter at
issue,” 4 Oxford English Dictionary, supra, at 548; Webster’s Third, supra, at 616; see also
McQuillin v. Hartford Life & Accident Ins. Co., 36 F.4th 416, 420 (2d Cir. 2022). This
understanding shows that courts should ask whether the ultimate decision underlying the EPA’s
“final action” has a “nationwide scope or effect.” 42 U.S.C. § 7607(b)(1); see West Virginia, 90
F.4th at 328–29.
The EPA’s “unbounded interpretation,” by contrast, would upset Congress’s “careful
delineation” of the actions that parties should challenge in the D.C. Circuit and those that they
should challenge in regional circuits. Fischer v. United States, 603 U.S. 480, 493 (2024). If
“determination” covered each discrete choice the EPA makes en route to a final decision, every
“final action” rests on a nationwide “determination.” After all, the EPA always must ground its
actions in a “national rule or standard” in the Clean Air Act or its regulations. West Virginia, 90

-- 19 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 20
F.4th at 328. The agency cannot haphazardly regulate parties by adopting one view of the law
for some States and the opposite view for others. The EPA’s reading thus would allow it to send
every action to the D.C. Circuit despite Congress’s presumptive choice to keep local actions
local.
To be sure, the EPA’s reading would not make Congress’s choice entirely “superfluous.”
Fischer, 603 U.S. at 493. Even if all local actions rest on nationwide determinations (as the EPA
implies), the agency still must “publish[]” a finding to that effect. 42 U.S.C. § 7607(b)(1). If it
opts not to, parties could sue in regional circuits. The EPA thus asks us to give it total discretion
to decide where parties should sue. But this fact confirms its error because § 7607(b)(1) does not
grant it this discretion. Recall that the relevant sentence sends a local action to the D.C. Circuit
only if both the action “is based on a determination of nationwide scope or effect and” the EPA
“publishes that such action is based on such a determination.” Id. (emphasis added). So the
action must rest on a nationwide determination (the first requirement) independent of the EPA’s
published views (the second requirement). Congress would not have written this sentence in the
conjunctive if it meant to give the EPA complete discretion. It would have simply said that a
local action belongs in the D.C. Circuit if the EPA finds that it rests on a national determination.
All told, then, “determination” refers to the EPA’s “authoritative” answer to the question it
resolves when taking an action. 4 Oxford English Dictionary, supra, at 548.
This definition proves the EPA’s error here. The agency suggests that its preliminary
choices (such as its use of the four-step framework for the Good Neighbor Provision) were
independent “determination[s]” under § 7607(b)(1). But those choices did not “end[]” the
“controversy”: whether the EPA should approve Kentucky’s plan. 4 Oxford English Dictionary,
supra, at 548. Instead, the “determination” underlying the EPA’s disapproval was its ultimate
decision that Kentucky did not satisfy the Good Neighbor Provision. See 88 Fed. Reg. at 9356.
We thus must ask whether this decision about Kentucky’s plan had a “nationwide scope
or effect” under § 7607(b)(1). It did not. Like “nationally applicable,” the word “nationwide”
shows that a determination’s “scope or effect” must exist “throughout [the] entire nation.”
Webster’s Third, supra, at 1505; West Virginia, 90 F.4th at 328. And the phrase “scope or
effect” shows that this provision reaches EPA decisions that apply to the entire country as a legal

-- 20 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 21
matter (de jure) or as a practical one (de facto). That is, a determination might have a nationwide
“scope” if its formal “area” of operation covers the country. 14 Oxford English Dictionary,
supra, at 672; see Webster’s Third, supra, at 2035. And it might have a nationwide “effect” if its
“operative influence” is felt everywhere. 5 Oxford English Dictionary, supra, at 79; see
Webster’s Third, supra, at 724.
Nothing about the EPA’s decision to deny Kentucky’s plan has this scope or effect. To
the contrary, the agency decided that Kentucky’s plan did not satisfy the Good Neighbor
Provision due to “circumstances . . . unique” to that plan. West Virginia, 90 F.4th at 328. To
start, the EPA found that Kentucky wrongly suggested at Step 2 of its framework that the
Commonwealth’s emissions sources were linked only to a Maryland receptor. See 87 Fed. Reg.
at 9509. The EPA decided instead that Kentucky sources were linked to three Connecticut
receptors. 88 Fed. Reg. at 9356; 2016v3 Modeling, J.A. 577. Next, the EPA disagreed with
Kentucky’s “particular arguments” for using the higher 1 ppb threshold (rather than the lower
1% threshold) to weed out the receptors with which it had an insufficient connection. 88 Fed.
Reg. at 9373 (emphasis added). Because Kentucky’s connection to the Connecticut receptors
fell in between these thresholds, the EPA proceeded to Step 3. See id. at 9356. It lastly found
that Kentucky did not adequately show at that step why it need not reduce any emissions to help
the Connecticut receptors attain the ozone standard. Id. This logic applied only to Kentucky and
had, at most, regional effects. So the EPA does not even try to argue that its final
“determination” had any sort of nationwide scope or effect.
Based On. Apart from the EPA’s overbroad reading of “determination,” it disregards that
the final action must be “based on” the identified determinations. 42 U.S.C. § 7607(b)(1). In
ordinary English, one would say that a person’s action (say, taking an umbrella on a trip) is
“based on” a factor (say, the high chance of rain) if the person has “ground[ed]” the action in that
factor. McGraw-Hill’s Dictionary of American Idioms and Phrasal Verbs 34 (2005). When a
statute uses a phrase like “based on” to connect one thing to another in this way, the Supreme
Court has relied on a “traditional background principle[]”—but-for causation—to eliminate
factors that an action could not have been based on. Burrage v. United States, 571 U.S. 204,
213–14 (2014); Safeco Ins. Co. of Am. v. Burr, 551 U.S. 47, 63 (2007); see also Univ. of Tex. Sw.

-- 21 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 22
Med. Ctr. v. Nassar, 570 U.S. 338, 350 (2013). Under this test, the person’s decision to take an
umbrella could not have been based on the chance of rain unless the person would have left the
umbrella at home “but for” this chance. Burrage, 571 U.S. at 212. That is, the chance of rain
must have mattered to that decision. See id. at 211–12. Here, then, if the EPA would have taken
the same “action” without the alleged “determination,” nobody would say the action was “based
on” the determination.
This reading of “based on” independently dooms the EPA’s reliance on two of the
alleged “determinations” identified in the final rule. The agency suggested that its denial of
Kentucky’s plan rested on its decision to rely on the 2016v3 modeling and its use of “uniform”
criteria to evaluate each State’s request to use a 1 ppb threshold rather than a threshold of 1% of
the ozone standard (.7 ppb). 88 Fed. Reg. at 9380. In this court, however, the EPA claims that it
would have denied Kentucky’s plan even if it had allowed Kentucky to use the 2011 modeling
and 1 ppb threshold. Respondents’ Br. 56–57. Under that older modeling and higher threshold,
Kentucky sources were still linked to a Maryland receptor. State Plan, J.A. 152. And the EPA
argues that Kentucky did not adequately explain why it need not cut emissions to allow this
receptor to meet the ozone standard. Respondents’ Br. 57–68. Yet if the EPA would have
denied Kentucky’s plan anyway, that denial could not have been “based on” the agency’s use of
the later modeling and lower threshold. So these decisions cannot allow the EPA to take this
case to the D.C. Circuit.
The EPA’s responses again lack merit. It makes two textual arguments to support its
reading of “determination.” The agency first points out that the statute uses “a” to modify
“determination” (“based on a determination of nationwide scope or effect”). This indefinite
article allegedly implies that an action can rest on multiple determinations and that only one need
have a “nationwide scope or effect.” But the EPA places too much weight on this article.
Because “determination” is a “countable noun[],” basic grammar rules required Congress to use
the article (nobody would say “based on determination”). Niz-Chavez v. Garland, 593 U.S. 155,
162–63 (2021). And the use of “a” says nothing about whether “determination” should reach
each of the EPA’s nonfinal interpretive choices or just its final decision. If anything, the

-- 22 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 23
decision to use a singular noun could just as well convey that the final action must rest on a
“single” decision—not on many separate decisions. Id. at 163.
The EPA also suggests that our reading of “determination” suffers from the same
problem as its reading: we allegedly strike this clause out of the statute because the final
“applying-the-law-to-the-facts” decision that underlies any local action will never have the
required nationwide scope or effect. Yet caselaw existing before Congress amended the key
language in § 7607(b)(1) offers examples of state-plan “determinations” that might have a
“nationwide scope or effect.” Take Dayton Power & Light Co. v. EPA, 520 F.2d 703 (6th Cir.
1975). There, the EPA followed a “unitary rule-making procedure” to adopt regulations that had
“the effect of amending every state’s air quality implementation plan in precisely the same way.”
Id. at 705. Interpreting an earlier version of the statute, we held that the challenges to these
uniform state-plan amendments belonged in the D.C. Circuit. Id. at 706–09. Thus, when the
“automatic application of standard, nation-wide guidelines to all plans simultaneously preordains
wholesale” actions, the EPA “determination” may well have a nationwide scope or effect. Nat.
Res. Def. Council, Inc. v. EPA, 465 F.2d 492, 494 (1st Cir. 1972) (per curiam). But the EPA
makes no such claim here.
Moving away from the text, the EPA argues that the legislative history supports its view.
When discussing this judicial-review provision, a House Report agreed “with the comments” in a
statement accompanying recommended amendments that had been proposed by the
Administrative Conference of the United States. H.R. Rep. 95-294, at 324 (1977) (discussing
Admin. Conf. of the U.S., Recommendations on Judicial Review Under the Clean Air Act, 41
Fed. Reg. 56767, 56769 (Dec. 30, 1976) (Statement of G. William Frick)). These comments
suggested that Congress should send “‘national’ [state-plan] issues” to the D.C. Circuit. 41 Fed.
Reg. at 56769. Yet this meaningless statement says nothing about the key question: Which state-
plan issues are “national”? In fact, this legislative history may well cut the other way. The
statement relied on by the EPA cites decisions like Dayton Power & Light as examples of the
uniform regulations that belong in the D.C. Circuit. See 41 Fed. Reg. at 56769 & n.3. And
again, the EPA’s denial of Kentucky’s plan here looks nothing like the regulations in that case.
In all events, we cannot use (at best) ambiguous legislative history to muddy the unambiguous

-- 23 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 24
meaning of statutory phrases like “nationwide.” See Food Mktg. Inst. v. Argus Leader Media,
588 U.S. 427, 437 (2019). Nothing about the disapproval of Kentucky’s plan has a national
sweep.
The EPA also claims that we should use a “deferential standard” to review whether an
agency action rests on “a determination of nationwide scope or effect” under § 7607(b)(1).
Respondents’ Br. 46. But the Supreme Court has recently told courts that we should no longer
defer to an agency’s answers to legal questions. See Loper Bright, 144 S. Ct. at 2273. And the
EPA resolves a pure question of law when it interprets the key terms in § 7607(b)(1) (such as
“nationally applicable” or “determination”). After Loper Bright, we must review (and correct)
the agency’s mistaken interpretation of those terms without giving it deference.
The EPA lastly makes a big-picture point. It says that any decision about the Good
Neighbor Provision will always involve nationwide issues because this part of the Clean Air Act
concerns pollution that crosses state lines. This argument all but confirms its error: it reads
words like “nationally applicable” and “nationwide” to mean “regionally applicable” or
“regional.” The Good Neighbor Provision regulates pollution as long as it is emitted from one
“State” and travels to “any other State[.]” 42 U.S.C. § 7410(a)(2)(D)(i). It thus would cover
pollution emitted from St. Louis that landed just across the Mississippi River in East St. Louis.
Yet nobody would say that the EPA made a “nationwide” determination when it decided whether
Missouri adequately accounted for this Illinois pollution problem. In the end, the EPA’s fact-
specific denial of Kentucky’s plan belongs in our court, not the D.C. Circuit.
III. Did the EPA Lawfully Disapprove Kentucky’s Plan?
Because Kentucky sued in the right tribunal, we proceed to the merits. Our court has
evaluated the EPA’s disapprovals of state plans using the APA’s general standards. See Navistar
Int’l Transp. Corp. v. EPA, 941 F.2d 1339, 1341 (6th Cir. 1991); Dressman v. Costle, 759 F.2d
548, 555 (6th Cir. 1985); cf. 42 U.S.C. § 7607(d)(1), (9). Under those standards, a court must
“hold unlawful and set aside agency action” that the court finds “arbitrary, capricious, an abuse
of discretion, or otherwise not in accordance with law.” 5 U.S.C. § 706(2)(A).

-- 24 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 25
We need not proceed past § 706(2)(A)’s ban on “arbitrary” and “capricious” actions to
resolve this case. That ban requires agencies to make reasonable decisions in a reasonable way.
See FCC v. Prometheus Radio Project, 592 U.S. 414, 423 (2021); Dep’t of Homeland Sec. v.
Regents of the Univ. of Cal., 591 U.S. 1, 16 (2020). Under this deferential “reasonableness” test,
a court cannot set aside an action simply because it would have made a different choice. See
Prometheus Radio Project, 592 U.S. at 423. But the court must ensure that the agency
considered each “important aspect of the problem” and issued a decision rooted in the law and
facts. Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43
(1983).
When an agency departs from its prior position, the change creates unique “aspect[s] of
the problem” that it must confront. Id.; Encino Motorcars, LLC v. Navarro, 579 U.S. 211, 221–
22 (2016). To start, the agency must “display awareness” that it has, in fact, jettisoned its past
views. FCC v. Fox Television Stations, Inc., 556 U.S. 502, 515 (2009). This requirement does
not compel the agency to meet a “heightened” reasonableness test as compared to when it adopts
a policy from scratch. Id. at 514. Still, the agency must acknowledge the change and explain
why it sees things differently. See Encino Motorcars, 579 U.S. at 221. So while the agency can
make a “U-turn,” it cannot make an unexplained one. Casey v. Berryhill, 853 F.3d 322, 329 (7th
Cir. 2017). Courts thus have found agency action arbitrary and capricious when it rested on an
“[u]nexplained inconsistency” with past practice. Encino Motorcars, 579 U.S. at 222 (citation
omitted).
Next, the agency must address how a change will affect those who have relied on its prior
position. See Fox, 556 U.S. at 515; Smiley v. Citibank (S.D.), N.A., 517 U.S. 735, 742 (1996).
The agency should identify these reliance interests and weigh them against the “policy” reasons
supporting the change. Regents of the Univ. of Cal., 591 U.S. at 33. The Supreme Court has
held, for example, that an agency arbitrarily adopted a more employee-friendly view of the
wage-and-hour laws when the agency ignored that employers had structured their payment
arrangements based on the agency’s past interpretation. See Encino Motorcars, 579 U.S. at 222–
24. And this mandate to address reliance interests applies just as much to an agency’s departure

-- 25 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 26
from informal guidance as it does to its departure from formal regulations. See Perez v. Mortg.
Bankers Ass’n, 575 U.S. 92, 105–06 (2015).
The EPA failed to live up to these standards here. The agency’s denial of Kentucky’s
plan departed from prior guidance in three respects. For one, the EPA’s March 2018
Memorandum told the States (including Kentucky) that they “may consider using” the 2011
modeling to develop their plans for the first two steps of the EPA’s four-step approach to the
Good Neighbor Provision. Mar. Mem., J.A. 80. For another, the EPA’s August 2018
Memorandum told the States that “it may be reasonable and appropriate for [them] to use a 1 ppb
contribution threshold” when identifying the links to downwind receptors that require more
scrutiny at the agency’s later steps. Aug. Mem., J.A. 101. The EPA issued this memo to
“provide[] recommendations” to States but added that this presumption of a 1 ppb threshold may
not fit “the facts” of a particular State. Id. at 98. For a third, the EPA saw nothing about
Kentucky’s unique “facts” that warranted a departure from these recommendations. Id. To the
contrary, the EPA told Kentucky during the Commonwealth’s notice-and-comment process that
it could “rely entirely” on the 2011 modeling and 1 ppb threshold as a “more straightforward
approach” at Step 2. EPA Comments, J.A. 126.
The EPA threw out all this guidance when it disapproved Kentucky’s plan. The EPA
relied on the 2016v3 modeling—not the 2011 modeling that it had recommended—to identify
Kentucky’s links to downwind receptors. 88 Fed. Reg. at 9356. Even worse, this new modeling
showed that Kentucky’s highest contribution to a maintenance or nonattainment receptor was
only “0.84 ppb,” which is below the 1 ppb threshold that the EPA had recommended. Id. Yet
the EPA denied Kentucky’s plan by using a lower threshold: 1% of the ozone standard (.7 ppb).
See id.; see also id. at 9342. The EPA acted arbitrarily because it did not adequately explain
either change.
Threshold Change. The EPA did not even “display awareness” that its switch from a
1 ppb threshold to a .7 ppb threshold changed anything. Fox, 556 U.S. at 515. The EPA’s final
rule reasoned that its August 2018 Memorandum had cautioned that the recommended 1 ppb
threshold might not fit the “facts and circumstances” of all States. 88 Fed. Reg. at 9372. It then
invoked this disclaimer to find that no State “made a sufficient showing” to use this threshold.

-- 26 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 27
Id. at 9373. Yet the EPA’s logic flipped the key presumption. The August 2018 Memorandum
treated the 1 ppb threshold as presumptively acceptable unless a State’s unique facts made the
threshold improper, but the final rule treated the 1 ppb threshold as presumptively unacceptable
unless that threshold fit a State’s facts. The August 2018 Memorandum had presumptively
allowed States to use the 1 ppb threshold because it was “generally comparable” to a .7 ppb
threshold in capturing upwind contributors to downwind receptors. Aug. Mem., J.A. 101. When
departing from this presumption, did the EPA disagree that the thresholds were generally
comparable in this way? Did it change for another reason? The EPA did not even acknowledge
the change, let alone explain it. See Encino Motorcars, 579 U.S. at 221–22.
The EPA instead accused States like Kentucky of “misunderstanding” the August 2018
Memorandum by accepting at face value what it said. 88 Fed. Reg. at 9373. “That’s a bit rich.”
Mingo Logan Coal Co. v. EPA, 829 F.3d 710, 740 (D.C. Cir. 2016) (Kavanaugh, J., dissenting).
It is especially rich in Kentucky’s case. The EPA specifically told Kentucky that it could “rely”
on the 1 ppb threshold. EPA Comments, J.A. 126. So by “disagree[ing] with Kentucky’s
arguments for” that threshold, the agency was disagreeing with itself. 88 Fed. Reg. at 9356.
Modeling Change. When deciding to switch to the 2016v3 modeling, by comparison, the
EPA ignored the “serious reliance interests” that arose from its earlier assurance that States could
use the 2011 modeling. Fox, 556 U.S. at 515. To justify the newer modeling, the EPA reasoned
that it should be able to use “the best information available to it at the time it” decides on a plan’s
validity. 88 Fed. Reg. at 9366. This logic ignored an “important aspect of the problem”:
Kentucky’s reliance on the March 2018 Memorandum. State Farm, 463 U.S. at 43. Indeed, the
EPA’s briefing cites nothing in the rule that even acknowledged this reliance interest.
If the EPA had “considered” Kentucky’s reliance, it might have chosen an alternative to
its flat disapproval. Regents of the Univ. of Cal., 591 U.S. at 32. As Kentucky suggested, the
EPA could have announced in advance that it would use newer data and given States the option
to update their plans. Ky. Comments, J.A. 513–14. In response to comments like this one, the
EPA argued that the Clean Air Act did not require it to give States “specific metrics” to help
them comply with the Good Neighbor Provision. 88 Fed. Reg. at 9363 (quoting EME Homer,
572 U.S. at 510). Yet this generic response ignores the key question: May the EPA affirmatively

-- 27 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 28
give the States one set of “metrics” to draft their plans and then use another set of metrics to
grade them? The EPA’s response thus confirms its utter disregard of Kentucky’s reliance
interest.
The EPA’s defenses of these changes lack merit. First, the EPA rests on the disclaimer
in the August 2018 Memorandum that its recommended 1 ppb threshold might not fit a State’s
facts. But this disclaimer does the EPA no good as applied to Kentucky. Again, the
memorandum proposed the 1 ppb threshold because it captured a “generally comparable”
amount of upwind contributions to downwind receptors as would a .7 ppb threshold. Aug.
Mem., J.A. 101. So if the 1 ppb threshold was not “comparable” to a .7 ppb threshold for a
particular State and receptor, this approach might give way. But the EPA has made no receptor-
specific argument for Kentucky. Indeed, the memorandum itself listed all receptors to which
Kentucky contributed over .7 ppb when finding the two thresholds comparable. Compare Aug.
Mem., J.A. 102–03, with State Plan, J.A. 152. The EPA instead argues that Kentucky did not
provide an adequate “technical justification” for the higher threshold. Respondents’ Br. 70. Yet
the EPA does not explain what “technical” justification Kentucky needed beyond the one in the
EPA’s own prior memorandum.
Second, the EPA suggests that its comments about Kentucky’s draft plan did not promise
that Kentucky could rely on the 2011 modeling or 1 ppb threshold “without conducting further
analysis and offering technical justification.” Respondents’ Br. 70. That is false. When
discussing the modeling data in Kentucky’s plan, the EPA stated: “An alternative, more
straightforward approach would be to rely entirely upon the EPA’s [2011 modeling] and apply
the 1 ppb screening threshold” from the August 2018 Memorandum. EPA Comments, J.A. 126
(emphasis added). The EPA did not then warn that it might still reject the state plan despite this
recommendation.
Third, the EPA says that Kentucky could not have relied on the two memoranda because
the EPA did not have a “longstanding policy” of using only modeling data in existence when a
State submitted a plan or a 1 ppb threshold. Respondents’ Br. 72, 88 (quoting Breeze Smoke,
LLC v. FDA, 18 F.4th 499, 507 (6th Cir. 2021) (order)). This argument misunderstands the law.
While “longstanding policies” suffice to create reliance interests, Encino Motorcars, 579 U.S. at

-- 28 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 29
222, they are not necessary to do so. Such interests can arise in other ways—such as when an
agency tells a party that it can do something during the rulemaking process. See EPA
Comments, J.A. 126. A contrary holding would allow agencies to “pull a surprise switcheroo”
by issuing a final action that flatly contradicts prior guidance, as long as the action does not
depart from some traditional practice. Env’t Integrity Project v. EPA, 425 F.3d 992, 996 (D.C.
Cir. 2005).
The EPA’s support for this alleged “longstanding policy” requirement—our decision in
Breeze Smoke—is not to the contrary. There, we recognized that an agency’s earlier guidance
was not “longstanding,” so a party could not rely on caselaw refusing to defer to agency actions
that inexplicably departed from traditional practice. Breeze Smoke, 18 F.4th at 507. But we did
not uphold the agency action in Breeze Smoke on this basis alone. Rather, we also rejected the
regulated party’s other claim that the agency had told the party one thing during the regulatory
process and then done something different when taking the final action. See id. at 506–07. We
reasoned that the final action comported with the earlier guidance, so the party could not have
relied on anything in that guidance to believe that the agency would act differently. See id.
Here, by contrast, a clear conflict exists. The EPA told Kentucky that it could use the 2011
modeling and 1 ppb threshold and then denied Kentucky’s plan in large part because Kentucky
had done what the EPA told it to do. Because the EPA did not adequately consider Kentucky’s
“reliance interests” when changing course in these ways, it acted arbitrarily. Fox, 556 U.S. at
515.
Fourth, the EPA argues that Kentucky did not prove its reliance because it did not incur
“substantial” monetary “costs” using the 2011 modeling. Respondents’ Br. 93. But Kentucky
wasted the costs it incurred drafting its plan because the EPA evaluated that plan using a
different yardstick from the one the agency promised. Regardless, as a sovereign entity,
Kentucky possesses the “primary responsibility” to regulate pollution emitted from its borders
and the discretion to decide how best to meet air-quality standards. 42 U.S.C. § 7401(a)(3);
Ohio, 603 U.S. at 284. Kentucky placed this important regulatory interest on the line when it
chose to rely on the EPA’s 2011 modeling. And it lost that interest when the EPA used newer
data to disapprove its plan and to impose a federal plan that took the Commonwealth’s

-- 29 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 30
regulatory discretion. See 42 U.S.C. § 7410(c). Given the Clean Air Act’s “cooperative
federalism” design, Sierra Club, 681 F.3d at 343 (quoting Ellis, 390 F.3d at 467), this type of
sovereign reliance interest warrants protection under the APA, see Ohio, 603 U.S. at 291.
* * *
Even if the EPA acted arbitrarily and capriciously in the ways that we have explained, the
agency claims that we should find its mistakes harmless. The EPA opines that it would have
denied Kentucky’s plan even if it had judged the plan using Kentucky’s 2011 modeling and
1 ppb threshold. Under those datapoints, Kentucky still contributed to a Maryland monitor at
Step 2. State Plan, J.A. 152. And the EPA now argues that Kentucky gave inadequate reasons at
Step 3 as to why it need not cut omissions to keep this monitor in attainment. Respondents’ Br.
57–68. The problem? Under basic principles of administrative law, agencies may invoke in
court only the grounds that they relied on at the time they took the challenged action. See
Regents of the Univ. of Cal., 591 U.S. at 20. If those relied-upon reasons cannot sustain an
agency action, neither a court nor an agency may salvage the action by invoking “better” reasons
for it in litigation. See id. at 22–23; see also Calcutt v. FDIC, 598 U.S. 623, 628–29 (2023) (per
curiam).
This principle renders the EPA’s harmless-error arguments premature. The EPA did not
rely on its current Step 3 claims to deny Kentucky’s state plan. To be sure, its rule did state that
Kentucky “did not conduct an adequate Step 3 analysis.” 88 Fed. Reg. at 9356. But the EPA’s
four-part approach raises distinct “steps” for a reason. The validity of a State’s decision on what
emissions to cut at Step 3 depends on the State’s links at Step 2. And the EPA’s rule used the
2016v3 modeling at Step 2 to link Kentucky to Connecticut receptors. See id.; 2016v3
Modeling, J.A. 577. At Step 3, then, the rule analyzed these receptors. The agency noted, for
example, that Kentucky was still linked to them even after the agency considered Kentucky’s
planned power-plant shutdowns. See 88 Fed. Reg. at 9356. The rule, by contrast, did not
suggest that Kentucky’s Step 3 analysis would fall short for the Maryland receptor linked to
Kentucky under the 2011 modeling. Because the EPA abandoned this modeling, it did not even
ask that question.

-- 30 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 31
Nor do we find it a forgone conclusion that the EPA would deny Kentucky’s plan on
remand. See Calcutt, 598 U.S. at 629–30. Suppose the EPA kept its 2016v3 modeling but
retained the higher 1 ppb threshold. In that scenario, Kentucky would not be linked to any
maintenance or nonattainment receptors because its “highest-level contribution” to any such
receptor was .84 ppb under that newer modeling. 88 Fed. Reg. at 9356. Or suppose the EPA
relied on the older modeling showing only a single Kentucky link to the Maryland receptor. It
might not make much sense to find Kentucky’s Step 3 analysis inadequate for this receptor.
Kentucky’s plan predicted that its then-existing emissions reductions would allow the Maryland
receptor to maintain the new ozone standard. State Plan, J.A. 177–78. And the EPA’s newer
data may well have proved Kentucky right because Kentucky is no longer linked to this receptor.
2016v3 Modeling, J.A. 577.
In short, we have no idea how the EPA would have acted if it had not committed the legal
errors that we have identified. The agency thus has failed to show that the errors did not
prejudice Kentucky. Yet nothing we have said in this opinion would prohibit the EPA from
properly raising any new concerns in additional administrative proceedings on remand.
IV. What Is the Proper Remedy?
Despite the errors underlying its action, the EPA lastly asks us to remand to the agency
without vacating its disapproval of Kentucky’s plan. Substantial out-of-circuit caselaw underlies
this request. Several courts have held that they may remand an illegal action to an agency
without vacating the action—allowing the action to continue to have binding force in the
meantime. See Black Warrior Riverkeeper, Inc. v. U.S. Army Corps of Eng’rs, 781 F.3d 1271,
1290 (11th Cir. 2015) (collecting cases); see also 33 Charles A. Wright et al., Federal Practice
and Procedure § 8382, at 289–93 (2d ed. 2018). Yet the parties cite only one of our own
decisions that has remanded to an agency without vacating its action. See Sierra Club v. EPA, 60
F.4th 1008, 1021–23 (6th Cir. 2023). There, we did not find the action unlawful and instead
remanded for additional proceedings at the agency’s request. See id. at 1020–21. So the case
says nothing about whether we may refuse to vacate illegal actions. The EPA asks us to break
new ground.

-- 31 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 32
We need not do so to resolve this case. Even assuming that the APA permits this
remand-without-vacatur remedy, it would not apply to the EPA’s errors. The courts that have
permitted remand-without-vacatur relief consider two primary factors when deciding on the
propriety of that relief. See id. at 1022. They first ask how serious of an error the agency made.
See id. If the agency committed a technical error that it could easily fix on remand, courts are
more likely to keep its action in place. See id. If, by contrast, the agency committed a
“fundamental” error—such as taking a substantively illegal action or ignoring notice-and-
comment requirements—these courts will not let the action stand. See Long Island Power Auth.
v. FERC, 27 F.4th 705, 717 (D.C. Cir. 2022); Allina Health Servs. v. Sebelius, 746 F.3d 1102,
1110–11 (D.C. Cir. 2014).
The courts that permit a remand-without-vacatur remedy next ask how disruptive their
vacatur would be. See Sierra Club, 60 F.4th at 1022. If vacatur would, say, upend years of
transactions entered in reliance on the agency’s action, courts are more likely to keep it in place.
See Am. Great Lakes Ports Ass’n v. Schultz, 962 F.3d 510, 518–19 (D.C. Cir. 2020). If,
however, an agency can point to just the normal uncertainty that follows every vacatur of agency
action, courts are more likely to vacate the action. See Sierra Club, 60 F.4th at 1023; Nat. Res.
Def. Council v. Wheeler, 955 F.3d 68, 85 (D.C. Cir. 2020).
Apart from these two factors, courts treat vacatur as the default and remand without
vacatur as the “rare” remedy. United Steel, Paper & Forestry, Rubber, Mfg., Energy, Allied
Indus. & Serv. Workers Int’l Union v. Mine Safety & Health Admin., 925 F.3d 1279, 1287 (D.C.
Cir. 2019); see Am. Great Lakes Ports Ass’n, 962 F.3d at 518. And the two factors merely
structure the inquiry because the proper remedy will depend on all the equities. See Sierra Club,
60 F.4th at 1022.
The EPA has failed to establish that the equities justify remand without vacatur here. For
starters, while the EPA may try to rely on distinct grounds to fix its errors on remand, its current
disapproval contains a “fundamental” defect. Allina Health Servs., 746 F.3d at 1110 (citation
omitted). The agency’s bait-and-switch tactics left Kentucky with the type of “deficient notice”
that has justified vacatur in other cases. Id. If anything, this case warrants that relief even more
because the EPA undercut the Clean Air Act’s “cooperative federalism” structure. Sierra Club,

-- 32 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 33
681 F.3d at 343 (quoting Ellis, 390 F.3d at 467). If we did not vacate its disapproval, the agency
would have every “incentive” to take similar shortcuts in the future. Env’t Def. Fund v. FERC, 2
F.4th 953, 976 (D.C. Cir. 2021).
The EPA has also not shown that vacatur would have any unusually disruptive effects.
See Sierra Club, 60 F.4th at 1023. It asserts that vacatur will bar it from imposing its federal
implementation plan on Kentucky and thus will delay that plan’s emissions reductions. Yet the
Supreme Court has already indefinitely stayed the federal plan. See Ohio, 603 U.S. at 300. So
the agency could not enforce its emissions reductions even if we refused to vacate the
disapproval of Kentucky’s plan. And the EPA’s long delay in acting on this state plan undercuts
any claim that an urgent need exists to compel Kentucky to reduce its emissions. See Texas,
2023 WL 7204840, at *11. Besides, the EPA’s arguments simply assume the conclusion on the
merits: that Kentucky’s current plan falls short of meeting its good-neighbor obligations. But “it
is far from certain” that the EPA will reach that same conclusion on remand. Env’t Def. Fund, 2
F.4th at 976.
All told, we deny the EPA’s motion to transfer. We also grant Kentucky’s petitions for
review, vacate the EPA’s disapproval of Kentucky’s state implementation plan, and remand to
the agency for further proceedings consistent with this opinion.

-- 33 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 34
_________________
CONCURRENCE
_________________
MURPHY, Circuit Judge, concurring. Our holding that the Environmental Protection
Agency (EPA) acted arbitrarily and capriciously and our assumption that the remand-without-
vacatur remedy exists allow us to fully resolve this case. I write this separate concurrence to
highlight two issues that we need not conclusively decide. First, the EPA’s failure to timely act
on Kentucky’s state implementation plan may have provided an independent ground to vacate
the EPA’s disapproval under the Administrative Procedure Act (APA). Second, the validity of
the remand-without-vacatur remedy may depend on the nature of this “vacatur” relief.
I. Did the EPA’s Untimely Disapproval of Kentucky’s Plan Violate the APA?
Apart from barring arbitrary and capricious agency action, the APA also requires
agencies to act “in accordance with law[.]” 5 U.S.C. § 706(2)(A). Kentucky and the EPA have
debated whether the EPA violated this mandate by disapproving Kentucky’s plan in an untimely
manner using data generated after its deadline to act. I think it may well have done so.
Start with some statutory background. The Clean Air Act imposes two deadlines on the
EPA after a State submits a plan. The EPA must first decide whether the plan contains the
“information necessary to enable [the agency] to determine whether the plan submission
complies with the” Act. 42 U.S.C. § 7410(k)(1)(A). The EPA has no duty to “act on” a plan
until it contains this information. Id. Yet the EPA should make this “[c]ompleteness” finding
within 60 days. Id. § 7410(k)(1)(B). And if the EPA has failed to make the finding “6 months
after” the State submitted the plan, the plan “shall on that date be deemed by operation of law to
meet [the] minimum criteria” necessary for the EPA’s review. Id. The second deadline then
identifies when the EPA must approve or disapprove the plan: “[w]ithin 12 months” of the
EPA’s completeness finding (whether made expressly or “by operation of law”). Id.
§ 7410(k)(2)–(3).
The parties agree on how this law applied here. Kentucky submitted its plan in January
2019. But the EPA never expressly found that this plan contained all the required information.

-- 34 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 35
By operation of law, therefore, that finding occurred in July 2019. See id. § 7410(k)(1)(B). This
date, in turn, required the EPA to act on Kentucky’s plan by July 2020. See id. § 7410(k)(2)–(3).
But the EPA missed this deadline. It disapproved the plan more than two years later in February
2023. What consequences should follow from the missed deadline?
Background principles help answer this question. Many statutes command public
officials to act within a certain time. See United States v. James Daniel Good Real Prop., 510
U.S. 43, 63 (1993). The Supreme Court has repeatedly held that officials who miss these
statutory deadlines do not automatically forfeit the power to act belatedly if the statute itself does
not impose that penalty. See id.; Nielsen v. Preap, 586 U.S. 392, 411 (2019) (plurality opinion);
Barnhart v. Peabody Coal Co., 537 U.S. 149, 158–63 (2003); Brock v. Pierce County, 476 U.S.
253, 259–62 (1986); see also McIntosh v. United States, 601 U.S. 330, 337–42 (2024). When a
statute does not identify the consequence for a violation, the Court has explained, courts may not
simply pick the remedy they think best as a common-law matter. See James Daniel Good,
510 U.S. at 63; Gen. Med., P.C. v. Azar, 963 F.3d 516, 526 (6th Cir. 2020) (Murphy, J.,
concurring).
These principles provide the first step in the analysis: The Clean Air Act says nothing
about what should happen if the EPA misses its “[d]eadline for action” on a state plan.
42 U.S.C. § 7410(k)(2). And we cannot create our “own coercive sanction” (say, an automatic
approval of the state plan) to remedy the EPA’s untimely action on the plan. Barnhart, 537 U.S.
at 159 (quoting James Daniel Good, 510 U.S. at 63). Indeed, the Act’s silence stands out
compared to the remedy that applies when the EPA misses the initial deadline to decide whether
the plan contains all required information. In that event, the Act “deem[s]” the plan complete
“by operation of law[.]” 42 U.S.C. § 7410(k)(1)(B). And Congress presumably acted
intentionally with its inclusion of this express remedy for the first deadline and its omission of
the remedy for the second one. See State Farm Fire & Cas. Co. v. United States ex rel. Rigsby,
580 U.S. 26, 34 (2016).
As other background principles show, however, this conclusion does not allow the EPA
to violate the Clean Air Act’s timelines with impunity. Rather, additional sources of law can
allow courts to enforce a statute’s requirements even when the statute itself lacks its own

-- 35 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 36
remedy. As one example from the Supreme Court’s caselaw, Article III gives courts the
“inherent power” to sanction parties for violating court rules—even if no statute gives them this
power. Id. at 37 (citing Chambers v. NASCO, Inc., 501 U.S. 32, 43–46 (1991)). So when a
statute required plaintiffs to file complaints under seal, this background power allowed courts to
punish plaintiffs who violated the sealing requirement despite the lack of a statutory remedy. See
id. If courts rely on these other remedies, however, they must also respect the limitations that
come with the remedies. In criminal cases, for instance, district courts must overlook all errors
that do not harm the defendant. See Fed. R. Crim. P. 52(a); McIntosh, 601 U.S. at 338. This
harmless-error rule covers the failure of courts or prosecutors to meet various statutory deadlines
in criminal cases. See Dolan v. United States, 560 U.S. 605, 617 (2010); United States v.
Montalvo-Murillo, 495 U.S. 711, 722 (1990).
These principles provide the second step in the analysis: Although the Clean Air Act does
not explain what should happen if the EPA acts on a state plan after its deadline, the APA applies
to this untimely action. And this second legal source does allow us to “set aside” (and issue an
“injunction” against) an EPA “action” if it is “not in accordance with” the Clean Air Act’s
timelines. 5 U.S.C. §§ 703, 706(2)(A). The EPA also seemingly violated the Clean Air Act’s
clear command that it “shall act on” Kentucky’s plan within 12 months of its completeness
finding. 42 U.S.C. § 7410(k)(2). The word “shall” suggests that the EPA lacks discretion to
miss this deadline. See State Farm, 580 U.S. at 33–34. In short, courts need not rely on their
“own coercive sanction” to remedy violations of the Clean Air Act’s timelines. James Daniel
Good, 510 U.S. at 63. They need only rely on the APA’s sanction for this violation.
That said, like the harmless-error rule in criminal cases, the APA requires us to give “due
account” to “the rule of prejudicial error.” 5 U.S.C. § 706. If the EPA’s violation of the deadline
when ruling on Kentucky’s plan did not harm Kentucky, the APA would give us no basis to
overturn the untimely disapproval. See Shinseki v. Sanders, 556 U.S. 396, 406–07 (2009). For
several reasons, however, the illegal delay may well have “had a ‘substantial influence’ on the
outcome of the proceeding” in this case. Montalvo-Murillo, 495 U.S. at 722 (quoting Bank of
Nova Scotia v. United States, 487 U.S. 250, 256 (1988)); see Shinseki, 556 U.S. at 407–08.
Those reasons all follow from the EPA’s decision to base its untimely disapproval on data in the

-- 36 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 37
2016v3 modeling that postdated the EPA’s deadline to act. See Air Plan Disapprovals, 88 Fed.
Reg. 9336, 9345 (Feb. 13, 2023).
For starters, the Clean Air Act notes that the EPA “shall approve” a state plan within the
required timeframe if the plan “meets all of the applicable requirements” of the Act. 42 U.S.C.
§ 7410(k)(3) (emphasis added). So if the information on the date of the EPA’s deadline shows
that the plan complies with the Act, the EPA must approve the plan. See id. The Act does not
give the EPA residual discretion. See Ohio v. EPA, 603 U.S. 279, 284 (2024). Given this
statutory scheme, the EPA’s use of after-the-fact data perhaps shows the required harm to
Kentucky.
A related provision confirms this point. The EPA admits that Kentucky could have sued
back in July 2020 to obtain a court order requiring the EPA to timely act while Kentucky’s plan
remained pending with the EPA. See 42 U.S.C. § 7604(a)(2); 88 Fed. Reg. at 9365; Brock, 476
U.S. at 260 n.7. Yet a court-imposed deadline to rule on the plan in, say, 2021 would likewise
have barred the EPA from relying on “datasets” that did not exist until 2022. 88 Fed. Reg. at
9345. As a result, even the EPA’s preferred remedy shows that its delay harmed Kentucky
because it allowed the EPA to rely on post-deadline data that Congress did not intend for it to
consider. See Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. Auto. Ins. Co., 463 U.S.
29, 43 (1983).
A structural point reinforces the same idea. The Clean Air Act does not leave the EPA
powerless to consider new information. It provides a remedy when new facts show that an
approved state plan “is substantially inadequate to attain or maintain” an air-quality standard. 42
U.S.C. § 7410(k)(5). In a paragraph entitled “[c]alls for plan revisions,” the Act allows the EPA
to “require [a] State to revise” this plan. Id. But such a compelled amendment requires the EPA
to jump through several procedural hoops. The EPA must notify the State of its concerns, and
the State (not the EPA) gets to take the lead in deciding on the revisions that will address those
concerns. See id. This cooperative process also shows that EPA’s unlawful delay likely
prejudiced Kentucky. If the EPA had taken this statutorily contemplated path, Kentucky would
have retained the authority to devise revisions that accounted for the EPA’s post-deadline
modeling. See id. By delaying action on Kentucky’s plan and then disapproving it using this

-- 37 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 38
modeling, the EPA kicked Kentucky out of this process by triggering the power to impose a
federal plan. See Ohio, 603 U.S. at 284–86; Texas v. EPA, 2023 WL 7204840, at *9 (5th Cir.
May 1, 2023) (per curiam).
As far as I can tell, nothing in the EPA’s briefing justifies its unlawful delay and
prejudicial use of post-deadline data. The agency first cites caselaw holding that agencies might
violate the APA’s ban on arbitrary-and-capricious conduct if they “ignore new and better data.”
Dist. Hosp. Partners, L.P. v. Burwell, 786 F.3d 46, 56–57 (D.C. Cir. 2015). The EPA thus
suggests that it would have acted arbitrarily if it overlooked the 2016v3 modeling. Yet this
caselaw has rejected arbitrary-and-capricious challenges when the EPA had good reasons to use
older data. See Sierra Club v. EPA, 356 F.3d 296, 308 (D.C. Cir. 2004); see also Bd. of Cnty.
Comm’rs of Weld Cnty. v. EPA, 72 F.4th 284, 289–90 (D.C. Cir. 2023). The EPA perhaps had
such reasons here: the Act required it to approve or disapprove the plan in a timely manner, not
to wait on constantly updated modeling. See Sierra Club, 356 F.3d at 308. To be sure, I agree
that this fact does not mean that the EPA should “ignore” this newer modeling. Dist. Hosp.
Partners, 786 F.3d at 57. It just means that the EPA should follow the Clean Air Act’s rules for
how to use it: by issuing a call for the revision of an approved plan—not by unlawfully
postponing its decision on a proposed one.
The EPA next relies on a decision that rejected the claim that the agency must rely on
pollution conditions as they existed on the deadline for States to submit their plans. See
Wisconsin v. EPA, 938 F.3d 303, 322 (D.C. Cir. 2019) (per curiam). The EPA places undue
emphasis on Wisconsin. There, the EPA proposed a federal plan in 2016 using data about
expected pollution conditions in 2017. See id. at 312, 321. This data revealed that a downwind
State (Delaware) would have no problematic receptors. Id. at 321. But Delaware argued that the
Good Neighbor Provision required the EPA to consider pollution conditions as they existed in
2011. Id. The State relied on the fact that the Act required upwind States to submit their plans
for meeting the relevant air-quality standard at that time. Id. at 321–22. The D.C. Circuit
rejected this view. Because the Good Neighbor Provision uses the future tense (covering States
that “will” contribute to downwind nonattainment), the court interpreted the provision as
regulating pollution conditions in future years—not as of the plan-submission date. Id. at 322

-- 38 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 39
(quoting 42 U.S.C. § 7410(a)(2)(D)(i)). Nothing I say here conflicts with this logic. Both the
2011 modeling that Kentucky used and the 2016v3 modeling that the EPA used predicted
pollution in a future year: 2023. See Mar. Mem., J.A. 77; 88 Fed. Reg. at 9345. Neither source
modeled pollution existing when Kentucky submitted its plan in 2019. And since Wisconsin
involved a federal plan, it did not discuss what should happen if the EPA violates its statutory
deadline to rule on a state plan. Wisconsin thus did not suggest that the EPA could deny a state
plan using new data generated after its deadline to act.
When the EPA turns to the Clean Air Act’s text, it concedes that the Act imposes a
mandatory deadline for the agency to decide on a plan’s validity. But the EPA calls the statutory
deadline “procedural” and suggests that it is “not ‘central to the regulatory scheme.’”
Respondents’ Br. 80 (quoting Wisconsin, 938 F.3d at 322). The agency adds that it may freely
disregard “procedural” rules in pursuit of achieving the “Act’s central object”: attaining the air-
quality standard. Id. (quoting Wisconsin, 938 F.3d at 316). I see three problems with this ends-
justify-the-means logic. As an initial matter, the Constitution does not give agencies any
prerogative power to “dispense” with statutory requirements that they find “unimportant.” See
Michael W. McConnell, The President Who Would Not Be King 115–19 (2020). Next, because
“no legislation pursues its purposes at all costs,” CTS Corp. v. Waldburger, 573 U.S. 1, 12
(2014) (quoting Rodriguez v. United States, 480 U.S. 522, 525–26 (1987) (per curiam)), the
“limitations” on a statute’s main goals are “often [its] price of passage[.]” Henson v. Santander
Consumer USA Inc., 582 U.S. 79, 89 (2017). So courts must respect those limitations just as
much as the primary provisions. See Kucana v. Holder, 558 U.S. 233, 252 (2010). Finally,
Congress’s findings reveal that it viewed respect for state authority as a central goal of the Clean
Air Act. See 42 U.S.C. § 7401(a)(3). And the EPA’s unlawful delay here did not just run afoul
of a procedural deadline; it also undercut the Act’s primary “cooperative federalism” design.
Sierra Club v. Korleski, 681 F.3d 342, 343 (6th Cir. 2012) (quoting Ellis v. Gallatin Steel Co.,
390 F.3d 461, 467 (6th Cir. 2004)).
All told, the EPA’s untimely disapproval of Kentucky’s plan may have violated the APA
for this independent reason. Given that it acted in an arbitrary and capricious way when
disapproving that plan, though, we need not conclusively resolve the issue.

-- 39 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 40
II. Does the APA Authorize a Remand-Without-Vacatur Remedy?
The EPA has asked us to remand its disapproval of Kentucky’s plan to the agency for
reconsideration without vacating that disapproval. In my view, its arguments about the
availability of this remedy have broader ramifications. The correct answer might turn on a
debate about whether the APA permits vacatur of an agency action as a remedy distinct from an
injunction enjoining the action’s enforcement. Compare Corner Post, Inc. v. Bd. of Governors
of Fed. Rsrv. Sys., 144 S. Ct. 2440, 2460–70 (2024) (Kavanaugh, J., concurring), with United
States v. Texas, 599 U.S. 670, 693–703 (2023) (Gorsuch, J., concurring in the judgment). The
APA instructs courts that they “shall” “set aside” agency action found unlawful. 5 U.S.C.
§ 706(2). What does this text mean? On the one hand, many have read it to create a distinct
vacatur remedy against agency actions (rather than an injunction remedy against their
enforcement). See Corner Post, 144 S. Ct. at 2462–63 (Kavanaugh, J., concurring) (citing
cases); Mila Sohoni, The Power to Vacate a Rule, 88 Geo. Wash. L. Rev. 1121, 1131–37, 1162–
63 (2020). Yet this reading cuts against the notion that courts may refuse to vacate actions found
illegal. Section 706(2) uses the word “shall” and suggests that courts must vacate illegal actions
if the section creates a distinct judicial remedy. See Milk Train, Inc. v. Veneman, 310 F.3d 747,
757 (D.C. Cir. 2002) (Sentelle, J., dissenting) (quoting Checkosky v. SEC, 23 F.3d 452, 491
(D.C. Cir. 1994) (Randolph, J., concurring)).
On the other hand, others have not read § 706(2)’s “set aside” text as creating a
standalone remedy. See Texas, 599 U.S. at 695–97 (Gorsuch, J., concurring in the judgment);
Arizona v. Biden, 40 F.4th 375, 396–97 (6th Cir. 2022) (Sutton, C.J., concurring); John Harrison,
Section 706 of the Administrative Procedure Act Does Not Call for Universal Injunctions or
Other Universal Remedies, 37 Yale J. Reg. Bull. 37, 41–46 (2020). They have instead read it as
codifying an idea first made famous by Marbury v. Madison, 5 U.S. 137 (1803): that a court
need not give effect to an unlawful rule and may “disregard[]” it when deciding on the parties’
legal rights. Id. at 177–78; see Harrison, supra, at 43. Those on this side of the debate have
added that the APA allows courts to grant only traditional remedies like “declaratory judgments
or writs of prohibitory or mandatory injunction[.]” 5 U.S.C. § 703; see Harrison, supra, at 37.
This differing view might make the remand-without-vacatur remedy more defensible. If the

-- 40 of 41 --

Nos. 23-3216/3225 Commonwealth of Ky., et al. v. EPA Page 41
“vacatur” of an action amounts to nothing more than an injunction, the remedy could trigger the
equitable discretion that courts possess when deciding whether to grant that relief. The relief is
never “a matter of right” even for parties with valid claims. Hill v. McDonough, 547 U.S. 573,
584 (2006); see Winter v. Nat. Res. Def. Council, Inc., 555 U.S. 7, 24 (2008). And notably,
courts holding that they may remand without vacatur have justified this remedy on the ground
that vacatur qualifies as an “equitable remedy” subject to their discretion. Black Warrior
Riverkeeper, Inc. v. U.S. Army Corps of Eng’rs, 781 F.3d 1271, 1290 (11th Cir. 2015).
At day’s end, our resolution of this case allows us to avoid these tricky issues. We need
not decide whether we have the power to keep illegal action in place. Even if we did, the EPA
has not justified that remedy on the facts here. So we also need not decide whether “vacatur”
qualifies as a new remedy or as an injunction by another name. Nothing turns on that distinction
here.

-- 41 of 41 --