Document ID: s3://data.kl3m.ai/documents/govinfo/USCOURTS/USCOURTS-caDC-15-01271/USCOURTS-caDC-15-01271-0/pdf.json

Parties Involved:
Environmental Protection Agency
Respondent
State of Tennessee
Petitioner

Document Text:

United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued March 25, 2022 Decided March 1, 2024 

No. 15-1239 

ENVIRONMENTAL COMMITTEE OF THE FLORIDA ELECTRIC 

POWER COORDINATING GROUP, INC., 

PETITIONER

v. 

ENVIRONMENTAL PROTECTION AGENCY AND MICHAEL S.

REGAN, 

RESPONDENTS

CITIZENS FOR ENVIRONMENTAL JUSTICE, ET AL., 

INTERVENORS

Consolidated with 15-1256, 15-1265, 15-1267, 15-1268, 

15-1270, 15-1271, 15-1272 

On Petitions for Review of a Final Action 

of the Environmental Protection Agency 

USCA Case #15-1271 Document #2043030 Filed: 03/01/2024 Page 1 of 96
Evan M. Ezray, Deputy Solicitor General, Office of the 

Attorney General for the State of Florida, argued the cause for 

state petitioners. On the briefs were Ashley Moody, Attorney 

General, Henry C. Whitaker, Solicitor General, Daniel W. Bell, 

Chief Deputy Solicitor General, Jason H. Hilborn, Deputy 

Solicitor General at the time the brief was filed, Steve Marshall, 

Attorney General, Office of the Attorney General for the State 

of Alabama, Edmund LaCour, Solicitor General, Tim Griffin, 

Attorney General, Office of the Attorney General for the State 

of Arkansas, Nicholas Bronni, Solicitor General, Vincent M. 

Wagner, Deputy Solicitor General at the time the brief was 

filed, Kris Mayes, Attorney General, Office of the Attorney 

General for the State of Arizona, Drew C. Ensign, Deputy 

Solicitor General at the time the brief was filed, Kathy 

Jennings, Attorney General, Office of the Attorney General for 

the State of Delaware, Valerie Satterfield Edge, Deputy 

Attorney General, Kris Kobach, Attorney General, Office of 

the Attorney General for the State of Kansas, Jeffrey A. 

Chanay, Chief Deputy Attorney General, Christopher M. Carr, 

Attorney General, Office of the Attorney General for the State 

of Georgia, Stephen J. Petrany, Solicitor General, Russell 

Coleman, Attorney General, Office of the Attorney General for 

the Commonwealth of Kentucky, Matthew F. Kuhn, Solicitor 

General, Brett R. Nolan, Principal Deputy Solicitor General at 

the time the brief was filed, Jeff Landry, Attorney General, 

Office of the Attorney General for the State of Louisiana, 

Elizabeth B. Murrill, Solicitor General, Lynn Fitch, Attorney 

General, Office of the Attorney General for the State of 

Mississippi, Mary Jo Woods, Special Assistant Attorney 

General, Andrew Bailey, Attorney General, Office of the 

Attorney General for the State of Missouri, D. John Sauer, 

Deputy Attorney General, Sam M. Hayes, David Yost, Attorney 

General, Office of the Attorney General for the State of Ohio, 

Benjamin M. Flowers, Solicitor General at the time the brief 

was filed, Gentner Drummond, Attorney General, Office of the 

Attorney General for the State of Oklahoma, P. Clayton 

Eubanks, Assistant Attorney General, Marty Jackley, Attorney 

USCA Case #15-1271 Document #2043030 Filed: 03/01/2024 Page 2 of 96
3 

General, Office of the Attorney General for the State of South 

Dakota, Steven R. Blair, Deputy Attorney General, Alan 

Wilson, Attorney General, Office of the Attorney General for 

the State of South Carolina, J. Emory Smith, Jr., Deputy 

Solicitor General, Jonathan Skrmetti, Attorney General, Office 

of the Attorney General for the State of Tennessee, Wilson S. 

Buntin, Senior Assistant Attorney General, Ken Paxton, 

Attorney General, Office of the Attorney General for the State 

of Texas, Priscilla M. Hubenak, Chief, Environmental 

Protection Division, Kellie E. Billings-Ray, Assistant Attorney 

General, Patrick Morrisey, Attorney General, Office of the 

Attorney General for the State of West Virginia, Lindsay S. 

See, Solicitor General. Christopher J. Baum, Deputy Solicitor, 

Office of the Attorney General for the State of Florida, Aaron 

S. Farmer, Principal Assistant Attorney General, Office of the 

Attorney General for the State of Ohio, Phillip R. Hilliard, 

Assistant Attorney General, Office of the Attorney General for 

the State of Tennessee, Thomas T. Lampman, Assistant 

Attorney General, Office of the Attorney General for the State 

of West Virginia, Justin L. Matheny, Deputy Solicitor, Office 

of the Attorney General for the State of Mississippi, Joseph A. 

Newberg, II, Assistant Attorney General, Office of the 

Attorney General for the Commonwealth of Kentucky, James 

H. Percival, II, Chief Deputy Solicitor General, Office of the 

Attorney General for the State of Florida, Andrew A. Pinson, 

Solicitor General, Office of the Attorney General for the State 

of Georgia, Lee P. Rudofsky, Solicitor, Office of the Attorney 

General for the State of Arkansas, and Megan K. Terrell, 

Assistant Attorney General, Office of the Attorney General for 

the State of Louisiana, entered appearances. 

Russell S. Frye argued the cause for industry petitioners. 

With him on the briefs were Lauren E. Freeman, C. Max 

Zygmont, C. Grady Moore, III, Randy E. Brogdon, Robert A. 

Manning, Joseph A. Brown, Margaret C. Campbell, Carroll W. 

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McGuffey, III, M. Brant Pettis, Melissa Horne, Terese T. Wyly, 

P. Stephen Gidiere, III, Gary V. Perko, Leslie Sue Ritts, J. 

Michael Showalter, Patrick F. Veasy, Matthew Kuryla, Devi 

Chandrasekaran, and Samara L. Kline. Amy C. Antoniolli and 

Hahnah Williams entered appearances. 

David J. Kaplan and Sarah A. Buckley, Attorneys, U.S. 

Department of Justice, argued the causes for respondents. With 

them on the briefs were Todd Kim, Assistant Attorney General, 

Andrew S. Coghlan, Attorney, Seth Buchsbaum, Attorney, U.S. 

Environmental Protection Agency, and Paul Bangser, Sheila 

Igoe, and Jan Tierney, Attorneys. 

Andrea Issod argued the cause for environmental 

intervenors. With her on the briefs were Joshua D. Smith, Seth 

L. Johnson, James S. Pew, Patton Dycus, John Walke, Emily 

Davis, and Paul Cort. Eric Schaeffer entered an appearance. 

Before: SRINIVASAN, Chief Judge, PILLARD and WALKER, 

Circuit Judges. 

Opinion of the Court filed PER CURIAM. 

Opinion concurring in part and dissenting in part filed by 

Circuit Judge PILLARD. 

 

 PER CURIAM: The Clean Air Act requires the federal 

government and the states to work together to protect the 

nation’s air. First, the Environmental Protection Agency 

identifies pollutants that endanger public health and welfare 

and sets air-quality standards that the states must meet. Then, 

the states develop state implementation plans to meet and 

enforce those standards. Those plans are called SIPs. 

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 EPA’s role goes beyond simply making sure that SIPs will 

enable states to meet the air-quality standards. Before a SIP 

can go into effect, EPA also makes sure that it complies with 

specific requirements that the Clean Air Act imposes for SIPs. 

Then, after a SIP is approved, EPA must call for the state to 

revise it if the SIP is substantially inadequate to comply with a 

requirement of the Act. 

 In this case, EPA called for 35 states and the District of 

Columbia to revise their SIPs, though it has since withdrawn 

its calls to three of those states. Two sets of petitioners, a group 

of about half the states whose SIPs EPA called and a set of 

companies that are subject to those SIPs, level an array of 

challenges against EPA’s SIP Calls. 

We grant their petitions in part and deny them in part. 

BACKGROUND 

We first explain the relevant parts of the Clean Air Act. 

Then, we provide background on the types of SIP provisions at 

issue in this case. Last, we describe the underlying EPA action 

and this case’s winding path to our decision today.

I. 

 Congress passed the Clean Air Act in 1963. Pub L. No. 

88-206, 77 Stat. 392 (1963). But until 1970, states “generally 

retained wide latitude to determine both the air quality 

standards which they would meet and the period of time in 

which they would do so.” See Train v. NRDC, 421 U.S. 60, 64 

(1975). That year, frustrated with the states’ lack of progress 

toward cleaner air, Congress enacted the 1970 Amendments to 

the Act. Id. 

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The 1970 Amendments changed the regulatory paradigm, 

replacing the old, state-centered model with “an exercise in 

cooperative federalism.” Dominion Transmission, Inc. v. 

Summers, 723 F.3d 238, 240 (D.C. Cir. 2013). The 

Amendments empowered the newly created EPA to set airquality standards to protect public health and welfare. Train, 

421 U.S. at 64-65. And they required the states to implement, 

maintain, and enforce those standards in a timely manner. Id. 

Among other things, SIPs set rules to limit the emissions 

that a source can release. Those rules are often source-specific 

and sometimes take the form of a formula. See, e.g., GA.COMP.

R. & REGS. 391-3-1.02(2)(c)-(z). Emission-control rules may 

also include, for example, technological control requirements 

or work practice requirements. 

 In addition to enabling states to meet the air-quality 

standards that EPA sets, SIPs have to comply with a number of 

the Clean Air Act’s specific legal requirements. Among the 

most important is a requirement that SIPs: 

include enforceable emission limitations and other 

control measures, means, or techniques (including 

economic incentives such as fees, marketable permits, 

and auctions of emissions rights), as well as schedules 

and timetables for compliance, as may be necessary or 

appropriate to meet the applicable requirements of this 

chapter. 

42 U.S.C. § 7410(a)(2)(A). SIPs also must, for example, 

provide for monitoring systems, set up a permitting scheme, 

and “include a program to provide for the enforcement of the” 

emission-control measures. Id. § 7410(a)(2)(C); see also id. 

§ 7410(a)(2)(B), (a)(2)(L).

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 Congress tasked EPA with ensuring that SIPs comply with 

the Act’s requirements. If a SIP submission meets “all of the 

applicable requirements” of the Act, EPA must approve it. Id.

§ 7410(k)(3). If a state wants to revise its SIP, EPA reviews 

the proposed revision and may only approve it if it does not 

interfere with attainment of the national ambient air quality 

standards (NAAQS) “or any other applicable requirement” of 

the Act. Id. §§ 7410(k)(2)-(3), 7410(l); see also id. § 7515.

Then, when EPA signs off on a new or revised SIP, it 

incorporates the SIP into the Code of Federal Regulations, 

which makes it a federally enforceable regulation. Dominion 

Transmission, Inc., 723 F.3d at 244. Once the SIP is approved 

and incorporated, EPA, state and local governments, and 

citizens can all sue to enforce it. Nat’l Mining Ass’n v. EPA, 

59 F.3d 1351, 1363 (D.C. Cir. 1995); 42 U.S.C. §§ 7413(b), 

7602(e), 7604(a). In those suits, courts can award injunctive 

relief or monetary damages. 42 U.S.C. §§ 7413(b), 7602(e), 

7604(a). 

 If that system works, that can sometimes be the end of the 

story. But if problems arise, EPA must address them. 

Specifically, the Act mandates that: 

Whenever the Administrator finds that the applicable 

implementation plan for any area is substantially 

inadequate to attain or maintain the relevant national 

ambient air quality standard, to mitigate adequately 

the interstate pollutant transport described in section 

7506a of this title or section 7511c of this title, or to 

otherwise comply with any requirement of this 

chapter, the Administrator shall require the State to 

revise the plan as necessary to correct such 

inadequacies. 

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Id. § 7410(k)(5). 

When EPA uses that authority to require states to revise 

their SIPs, it is referred to as a SIP Call. If the EPA issues a 

SIP Call, it must identify the SIP’s substantial inadequacies and 

set a deadline that affords the state no more than 18 months to 

“revise the [SIP] as necessary to correct such inadequacies.” 

Id. The state need not undergo “a wholesale revision of its 

entire plan,” but must make revisions necessary to correct the 

substantial inadequacies EPA identified. Virginia v. EPA, 108 

F.3d 1397, 1410 (D.C. Cir. 1997), modified on reh’g on other 

grounds, 116 F.3d 499. Should a state fail to timely revise its 

SIP, or should EPA disapprove the state’s submission, EPA 

must timely promulgate a federal implementation plan for that 

state. See 42 U.S.C. § 7410(c)(1). 

II. 

 During periods when a source starts up, shuts down, or 

malfunctions—SSM periods—Petitioners say the source may 

not be able to comply with the emission rules that apply during 

regular operation. See Restatement and Update of EPA’s SSM 

Policy Applicable to SIPs, 80 Fed. Reg. 33,840, 33,843 (June 

12, 2015) (defining “SSM”). Some SIPs thus include a variety 

of SSM provisions that can insulate sources from liability for 

emissions during SSM periods that exceed the emission levels 

permitted under the regular rule.

Four types of SSM provisions are at issue in this case. 

First, some SIPs include “automatic exemptions,” which 

exclude SSM periods from otherwise applicable emission 

rules. 

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Second, other SIPs include “director’s discretion” 

provisions, which allow state officials to independently and 

conclusively decide that excess emissions are not violations 

during SSM periods. 

 Third, at least one SIP includes provisions that EPA 

believes could be read to allow state officials to excuse 

emission violations during SSM periods in a way that 

forecloses EPA or citizen-suit enforcement. EPA called those 

“overbroad enforcement discretion” provisions. Unlike 

director’s discretion provisions—which let state officials 

determine that there is no violation—overbroad enforcement 

discretion provisions let state officials recognize that a 

violation happened but bar enforcement. 

Fourth, many SIPs include affirmative defenses for excess 

emissions that occur during SSM periods. Some affirmative 

defenses protect sources against all liability, while others 

protect only against certain forms of relief. E.g., 118-01-19 

ARK. CODE § 602 (all liability); ARIZ. ADMIN. CODE § 18-2-

310(B)-(C) (providing an affirmative defense except in a 

“judicial action seeking injunctive relief”). 

III. 

 This case’s origins date back over a decade. In June 2011, 

Sierra Club filed a petition for rulemaking. Among other 

requests, it identified 39 SIPs that it believed included SSM 

provisions that made the SIPs unlawful, and it asked EPA to 

call them. 

Twenty months later, EPA published a proposed rule in 

response to Sierra Club’s petition. It initially indicated its 

intent to grant Sierra Club’s petition as to all types of SSM 

provisions except affirmative defenses to monetary damages 

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for excess emissions during malfunctions. Then, in NRDC v. 

EPA, we vacated a similar affirmative defense in a federal 

emission standard. 749 F.3d 1055, 1058, 1064 (D.C. Cir. 

2014). So EPA published a supplemental notice in which it 

proposed to grant Sierra Club’s petition as to those affirmative 

defenses as well. 

Comments flowed in. Sixty-nine thousand different 

commenters offered their thoughts on the original proposed 

rule, and twenty thousand commenters responded to the 

supplemental notice. 

In 2015, after considering those comments, EPA published 

its Final Action. It called SIPs from 35 states and the District 

of Columbia. 

EPA began by explaining why it was now calling SIPs it 

had previously approved. When Congress enacted the 1970 

Clean Air Act amendments, it set an ambitious timetable for 

implementing the cooperative-federalism framework. It gave 

EPA 30 days (plus a 90-day notice-and-comment period) to 

develop the first air-quality standards. Train, 421 U.S. at 65. 

Then, the states had nine months from EPA’s promulgation of 

air-quality standards to submit SIPs. Id. From there, EPA had 

four months to verify that each SIP complied with the Clean 

Air Act and, if so, to approve it. Id. That timetable was a tall 

order for an EPA that had been created less than a month 

earlier. Reorganization Plan No. 3 of 1970, reprinted in 5 

U.S.C. app. 1 (creating EPA effective December 2, 1970); Pub. 

L. No. 91-604, 84 Stat. 1676 (Dec. 31, 1970) (1970 

Amendments). 

In the SIP Calls here, EPA explained that the timetable 

proved too tall an order: “[B]ecause the EPA was inundated 

with proposed SIPs and had limited experience in processing 

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them, not enough attention was given to the adequacy, 

enforceability and consistency of” SSM provisions. 80 Fed. 

Reg. 33,840, 33,843/3 (June 12, 2015). 

 

 On the merits of its call, EPA first explained its view that 

it can call any SIP that “contains a provision that is inconsistent 

with fundamental requirements of the” Clean Air Act. Id. at 

33,926/3. As EPA reads the Act, it does not need to 

demonstrate that the substantial legal infirmity has had any 

demonstrated ill effects; its existence is enough. 

 EPA then identified the aspects of the Act that it believes 

the SSM provisions are inconsistent with. 

 It started with automatic exemptions. Because EPA reads 

the Act to “require that SIPs contain ‘emissions limitations’ to 

meet CAA requirements” and “those emissions limitations 

must be continuous,” 80 Fed. Reg. 33,927/2, it argues that 

automatic exemptions bring SIPs out of compliance with the 

Act. The Act defines an emission limitation as a requirement 

that limits emissions “on a continuous basis.” 42 U.S.C. 

§ 7602(k). According to EPA, an exemption would make the 

limitation discontinuous and thus violate the Act’s definition of 

an emission limitation. 

 Next, EPA applied the same logic to director’s discretion 

provisions. It determined that allowing state officials to decide 

that excess emissions during SSM periods were not a violation 

makes an emission limitation as discontinuous as simply 

having a categorical exemption. In addition, EPA thought that 

if a state official can decide to waive an emission limitation’s 

application, such waivers would amount to “de facto revisions 

of the approved emission limitations” without EPA approval. 

80 Fed. Reg. at 33,928/1. 

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 After that, EPA explained that overbroad enforcement 

discretion provisions unlawfully blocked the Act’s 

enforcement scheme by allowing a state to unilaterally bar an 

EPA or citizen suit. 

 Finally, EPA concluded that affirmative defense 

provisions similarly interfere with the Act’s enforcement 

scheme. EPA’s reasoning tracked the logic of the NRDC 

decision that had persuaded EPA to revise its interpretation and 

issue the supplemental notice of proposed rulemaking. See 

NRDC, 749 F.3d at 1063-64. 

 Three sets of petitioners sought our review: Texas and a 

coalition of Texas companies and trade groups; a group of other 

states that petitioned together; and a group of industrial 

companies and organizations. The Sierra Club and other 

environmental groups intervened to support EPA. The many 

parties completed extensive briefing, and we scheduled an oral 

argument for May 8, 2017. Then, less than a month before 

argument, EPA asked us to postpone the argument as the new 

administration reconsidered the SIP Calls. We agreed, and the 

case remained in abeyance for more than four years. 

 During those four years, EPA withdrew its calls to Iowa, 

North Carolina, and Texas—leaving 32 states and the District 

of Columbia subject to the SIP Calls. That mooted the Texans’ 

petitions for review and meant that the SIP Calls issued to 

North Carolina and Iowa are not before this court, nor are the 

SIP Calls directed at states that never joined the petition. That

leaves sixteen State Petitioners and the Industry Petitioners. 

 In November 2021, EPA reaffirmed the original SIP Calls 

as to the remaining states and moved to reopen this case. We 

granted the motion and now resolve the case as follows. 

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In part I of the analysis, we evaluate EPA’s SIP-call 

authority. In part II, we evaluate EPA’s specific objections to 

the four types of SSM provisions. 

ANALYSIS 

We set aside an EPA SIP Call if it is “arbitrary, capricious, 

an abuse of discretion, or otherwise not in accordance with 

law” or if it is “in excess of [EPA’s] statutory jurisdiction, 

authority, or limitations.” 42 U.S.C. § 7607(d)(9)(A), (C); see 

also Maryland v. EPA, 958 F.3d 1185, 1196 (D.C. Cir. 2020). 

We employ the traditional tools of statutory interpretation to 

determine what the Clean Air Act requires. Sierra Club v. 

EPA, 551 F.3d 1019, 1026-27 (D.C. Cir. 2008). Courts, like 

EPA, “must give effect to the unambiguously expressed intent 

of Congress.” Id. at 1026 (quoting Chevron U.S.A., Inc. v. 

NRDC, 467 U.S. 837, 844 (1984)). If, however, the Clean Air 

Act is ambiguous on a particular issue, we defer to the agency’s 

reasonable interpretation of the Act. Id. 

State and Industry Petitioners challenge EPA’s SIP Calls 

on two fronts. First, they argue that EPA misinterpreted its 

SIP-call authority under section 7410(k)(5) of the Clean Air 

Act. Second, they claim that EPA incorrectly interpreted the 

Act, as well as the SIPs in question, when it called the SIPs for 

containing at least one of four types of SSM provisions that 

EPA deemed impermissible: (1) automatic exemption 

provisions, (2) director’s discretion provisions, (3) overbroad 

enforcement discretion provisions, and (4) affirmative defense 

provisions. We consider each challenge in turn. 

I. 

We begin by addressing Petitioners’ crosscutting 

challenges to EPA’s statutory authority to issue any of these 

disputed SIP Calls. Section 7410(k)(5) of the Clean Air Act 

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sets out EPA’s SIP-call authority. It states, as relevant here, 

that whenever EPA “finds” that a SIP is “substantially 

inadequate” to “comply with any requirement of this chapter,” 

then EPA “shall” require the state to “revise the [SIP] as 

necessary to correct such inadequacies.” 42 U.S.C. 

§ 7410(k)(5). State and Industry Petitioners advance four 

arguments why EPA misinterpreted its SIP-call authority. 

First, they assert that EPA lacked authority to call the SIPs 

without making factual findings about the real-world effects of 

the inadequate SIPs, even when calling SIPs as substantially 

legally inadequate to “comply with any requirement” of the 

Act. Second, Petitioners insist that, when issuing a SIP Call, 

EPA must consider each SIP “as a whole,” rather than object 

to individual provisions in isolation. Third, they maintain that 

ambiguity in a SIP provision—that is, where it is unclear 

whether a SIP provision conflicts with the Act—can never be 

a sufficient basis for issuing a SIP Call. Fourth, and finally, 

they argue that EPA must engage in a cost-benefit analysis 

whenever it calls a SIP and that failure to do so renders the 

challenged action arbitrary and capricious. We consider each 

of those arguments and conclude that, in its Final Action, EPA 

abided by the strictures of its SIP-call authority under section 

7410(k)(5). 

A. 

Petitioners contend that, before EPA issues any SIP Call 

under section 7410(k)(5), it must make factual findings about 

adverse effects resulting from the SIP’s deficiencies—for 

example, by identifying instances in which the SSM provisions 

at issue prevented or will prevent attainment of the national 

ambient air quality standards (NAAQS). That argument is at 

odds with the statutory text and structure. While factual 

findings about the effects of SIP inadequacies may be needed 

to support some types of SIP Calls, section 7410(k)(5) does not 

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categorically require them. The Act obligates EPA to issue a 

SIP Call whenever it determines that a SIP does not comply 

with the Act’s legal requirements, so long as the legal 

deficiencies are “substantial[].” 42 U.S.C. § 7410(k)(5). A SIP 

Call based on failure to comply with the Act’s legal 

requirements need not be withheld until the agency is able to 

document actual or anticipated damage to the environment, to 

human health or welfare, or to any other objective of the Act. 

Requiring such a factual showing would impermissibly 

“place[] an information submission obligation on EPA [that] 

Congress did not impose,” EPA v. EME Homer City 

Generation, L.P., 572 U.S. 489, 510 (2014). 

We start with the statutory source of EPA’s authority to 

call a SIP. Section 7410(k)(5) of the Act compels the agency 

to call a SIP whenever it “finds” that the SIP is “substantially 

inadequate” for one of three reasons: (1) “to attain or maintain 

the relevant national ambient air quality standard,” (2) “to 

mitigate adequately the interstate pollutant transport,” or (3) 

“to otherwise comply with any requirement” of the Act. 42 

U.S.C. § 7410(k)(5). Those three distinct grounds for issuing 

a SIP Call are stated as alternatives, separated by the word “or.” 

In using that conjunction, Congress made clear that a 

substantial inadequacy to “otherwise comply with any 

requirement” of the Act (per the third stated ground) is by itself 

sufficient to require EPA to call the SIP. Id. EPA need not 

also show the SIP meets the standard to be called under the first 

ground for failure to attain or maintain the NAAQS, or under 

the second ground for failure to mitigate interstate pollutant 

transport. 

EPA might call a SIP for failure to comply with the Act 

(i.e., under the third ground) in a variety of circumstances. To 

provide a few examples, a SIP might be challenged as 

inadequate under the third ground if the state fails to provide 

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for the operation of air quality monitoring devices, id. 

§ 7410(a)(2)(B), to ensure personnel to carry out the plan, id. 

§ 7410(a)(2)(E), to require periodic reporting of emissionsrelated data from stationary sources, id. § 7410(a)(2)(F)(ii), to 

provide for consultation with local governments, id. 

§§ 7410(a)(2)(J), 7421, to submit air quality modeling data to 

EPA, id. § 7410(a)(2)(K)(ii), or to address non-NAAQS 

pollutants in new source review permit programs, id. §§ 7470-

79, 7503. 

In the action under review, EPA relied on that third ground 

for issuing a SIP Call. 80 Fed. Reg. 33,840, 33,925/3 (June 12, 

2015). EPA concluded that the SIPs were substantially 

inadequate to comply with the Act’s requirements for emission 

limitations, its remedial and enforcement provisions, and its 

procedural requirements for revising a SIP. See, e.g., id. at 

33,874/2-75/2, 33,957/2-74/2. The inadequacies EPA 

identified were legal in nature—that is, the SIPs on their face 

conflicted with the Act’s legal requirements vis-à-vis SIPs. 

We first consider what findings, if any, the plain text of 

section 7410(k)(5) requires when EPA calls a SIP for legal 

inadequacies. Under the third ground, EPA plainly must find 

that a SIP is substantially inadequate to “comply with any 

requirement” of the Act. 42 U.S.C. § 7410(k)(5). That is, EPA 

must determine that a SIP provision has not conformed to 

“those statutory and regulatory requirements that are germane 

to the SIP provision at issue.” 80 Fed. Reg. at 33,925/3. 

The shortcoming EPA identifies must also be one that 

renders the SIP “substantially inadequate” to comply with the 

Act. 42 U.S.C. § 7410(k)(5). In the SIP Calls, EPA noted that 

“section 110(k)(5) [i.e., 42 U.S.C. § 7410(k)(5)] does not 

specify a particular form of analysis or methodology that the 

EPA must use to evaluate SIP provisions for substantial 

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inadequacy.” 80 Fed. Reg. at 33,926/1. EPA noted that, for 

some SIP Calls, a “technical evaluation” of the inadequacy 

might be warranted. Id. at 33,937/1. But calling a SIP that on 

its face violates key legal requirements of the Act “does not 

require that type of technical analysis and does not require a 

‘quantification’ of the extent of the deficiency.” Id. To 

determine that a SIP is “substantially inadequate,” EPA need 

conclude only that it is materially deficient, or falls short in a 

meaningful, nontrivial way. See, e.g., WEBSTER’S NINTH NEW 

COLLEGIATE DICTIONARY 1176 (1990) (“substantial” includes 

“being largely but not wholly that which is specified”); 

WEBSTER’S NEW WORLD DICTIONARY 1336 (3d. coll. ed. 

1988) (“substantial” includes “with regard to essential 

elements; in substance”); id. at 680 (“inadequate” means “not 

adequate; not sufficient; not equal to what is required”). The 

Final Action abides by that ordinary understanding of 

“substantially inadequate”: Where SIPs threaten to undermine 

the “fundamental integrity of the [Clean Air Act]’s SIP process 

and structure” and allow the Act’s emission rules to be 

“violated without potential recourse,” 80 Fed. Reg. at 33,926/3, 

they readily clear the threshold of substantial inadequacy. 

Beyond determining that the SIP is deficient and that such 

deficiency is material, EPA need not invariably make factual 

findings about the effects of that asserted legal deficiency—for 

example, on air quality. Section 7410(k)(5)’s third ground 

imposes no such limitation. Under that clause, EPA is 

obligated to call a SIP that is substantially inadequate for 

purposes of “any” Clean Air Act requirement, 42 U.S.C. 

§ 7410(k)(5), no matter the degree to which that requirement is 

shown to impair the SIP’s ability to protect the environment or 

human health and welfare. In some cases, as here, the 

requirement will be legal in nature—for example, a 

requirement about what SIPs must contain, not what emission 

reductions the state must achieve. Under those circumstances, 

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noncompliance may be readily apparent from the statutory text 

and the SIP itself. As EPA recognized, “it is not necessary to 

establish that these deficiencies literally caused a specific 

violation of the NAAQS on a particular day or undermined a 

specific enforcement case.” 80 Fed. Reg. at 33,937/1. Failure 

to comply with the Clean Air Act’s legal requirements “does 

not become legally permissible merely because there is not 

definitive evidence” of adverse environmental or other effects 

caused by that noncompliance. Id. at 33,926/2. 

Our conclusion that EPA need not, as a blanket rule, make 

factual findings about the effects of a legal inadequacy accords 

with section 7410(k)(5)’s requirement that EPA “find” a 

substantial inadequacy. Because Congress has not defined the 

term “find” as used in section 7410(k)(5), we “construe [that] 

statutory term in accordance with its ordinary or natural 

meaning.” FDIC v. Meyer, 510 U.S. 471, 476 (1994); see also 

Food Mktg. Inst. v. Argus Leader Media, 139 S. Ct. 2356, 2363 

(2019). The ordinary meaning of “find” is “to settle upon and 

make a statement about (as a conclusion).” WEBSTER’S NINTH 

NEW COLLEGIATE DICTIONARY 464 (1990); see also Find, 

BLACK’S LAW DICTIONARY (6th ed. 1990) (“to determine”). 

To be sure, in legal usage, “find” sometimes connotes 

factfinding, as distinct from reaching a legal conclusion. See, 

e.g., FED.R.CIV. P. 52 (requiring courts in a bench trial to make 

findings of fact and state conclusions of law separately); Find, 

BLACK’S LAW DICTIONARY (6th ed. 1990) (defining “find” to 

include “[t]o announce a conclusion upon a disputed fact or 

state of facts”). But the word “find” “easily admits of multiple 

meanings,” Schiller v. Tower Semiconductor Ltd., 449 F.3d 

286, 300 (2d Cir. 2006), and is not limited to that particular 

legal usage. “And it is normal usage that, in the absence of 

contrary indication, governs our interpretation of texts.” 

Freeman v. Quicken Loans, Inc., 566 U.S. 624, 634 (2012). 

EPA’s reading—that it may “find” a SIP provision inadequate 

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where the SIP “does not meet applicable legal requirements,” 

even “without definitive proof that this legal deficiency caused 

a specific outcome,” 80 Fed. Reg. at 33,934/2—is faithful to 

the ordinary, popular meaning of the word “find.” 

In short, the text of section 7410(k)(5) instructs that EPA 

shall issue a SIP Call whenever it concludes that a SIP is 

materially deficient to comply with any requirement of the Act. 

In the Final Action, EPA did exactly that, explaining why in its 

view the SIPs were deficient to comply with the Act’s 

requirements for emission limitations, its remedial and 

enforcement provisions, and its procedural requirements for 

revising a SIP. See, e.g., id. at 33,874/2-75/2, 33,957/2-74/2. 

EPA further explained why those asserted deficiencies were 

“substantial.” See, e.g., id. at 33,926/3, 33,927/1-29/3. At least 

where EPA calls a SIP for substantial legal inadequacies, 

section 7410(k)(5) requires nothing more. 

Statutory structure and context confirm that EPA need not 

in all cases make factual findings about the practical effects of 

asserted inadequacies before calling a SIP for substantial legal 

inadequacies. 

First, our reading comports with section 7410(a)(2)(H)(ii), 

which requires SIPs to “provide for revision” of their own 

terms “whenever [EPA] finds on the basis of information 

available to [EPA] that the plan is substantially inadequate . . . 

to otherwise comply with any additional requirements 

established under this chapter.” 42 U.S.C. § 7410(a)(2)(H). 

Sections 7410(a)(2)(H)(ii) and 7410(k)(5) “complement[]” one 

another. Virginia, 108 F.3d at 1410. The former describes 

what the states must include in their SIPs—that is, they must 

reserve the legal authority to revise their SIPs in the event EPA 

deems them substantially inadequate, see 42 U.S.C. 

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§ 7410(a)(2)(H)(ii)—while the latter codifies EPA’s SIP-call 

authority, see id. § 7410(k)(5). 

Petitioners home in on the phrase “on the basis of 

information available,” which appears only in section 

7410(a)(2)(H)(ii), to assert that EPA must make factual 

findings. They read EPA’s SIP-call authority in section 

7410(k)(5) to incorporate language from section 

7410(a)(2)(H)(ii) requiring EPA to find substantial inadequacy 

“on the basis of information available.” That claim fails. For 

one, we agree with EPA that, unlike section 7410(k)(5), 

“section 110(a)(2)(H)(ii) [42 U.S.C. § 7410(A)(2)(H)(ii)] does 

not on its face directly address the scope” of EPA’s authority 

to call SIPs. 80 Fed. Reg. at 33,934/2. We thus do not interpret 

section 7410(a)(2)(H)(ii)’s “listing of specific structural or 

program requirements” for SIPs “in a way that contradicts or 

curtails the broad [SIP-call] authority” that Congress codified 

in section 7410(k)(5). Id. at 33,934/2-3. 

Even if one were to consider section 7410(a)(2)(H)(ii) in 

isolation, Petitioners overread the phrase “on the basis of 

information available.” By its own terms, section 

7410(a)(2)(H)(ii) does not specify any particular type of 

supportive material for an EPA determination of substantial 

inadequacy. It demands only that a SIP Call be based on 

available “information,” which ordinarily refers to “data,” 

“facts,” or “knowledge acquired in any manner.” WEBSTER’S 

NEW WORLD DICTIONARY 222 (2d. coll. ed. 1974). It is well 

within EPA’s authority under section 7410 to base a finding of 

substantial inadequacy on the agency’s knowledge acquired 

through comparing a SIP’s provisions to the relevant Clean Air 

Act requirements. By allowing EPA to decide to call a SIP 

based on “available” information, Congress made clear that 

EPA does not need to gather new information or set forth 

factual findings. Put otherwise, EPA has the authority to 

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21 

request additional information from the states as needed, see 42 

U.S.C. § 7410(p), but is under no obligation to do so. 

Second, our reading respects that section 7410(k)(5), 

governing EPA’s SIP-call authority, suggests the agency 

should evaluate states’ earlier-approved SIPs with a degree of 

leeway not afforded when EPA reviews states’ initial SIP 

submissions or their proposed revisions. When a state submits 

a SIP or SIP revision for approval, EPA may not approve it 

unless “it meets all of the applicable requirements” of the Act. 

Id. § 7410(k)(3). Moreover, EPA may not approve a SIP 

revision if it “would interfere with any applicable requirement” 

of the Act, id. § 7410(l)—that is, if it would cause the state to 

backslide or come out of compliance with the Clean Air Act’s 

requirements, see 80 Fed. Reg at 33,941/3. Those standards 

governing EPA’s approval of SIPs and their revisions appear 

to require EPA to ensure absolute or near-absolute compliance 

with the Act. 

In contrast, Congress directed EPA, when calling an 

earlier-approved SIP, to apply a more forgiving compliance 

standard. Under section 7410(k)(5), a SIP’s failure to comply 

with the Act’s requirements must be “substantial[],” 42 U.S.C. 

§ 7410(k)(5), thereby preventing EPA from calling an 

approved SIP based on slight variations from the Act’s 

requirements. The higher bar on SIP Calls than on initial 

approvals makes sense: While Congress sought to ensure strict 

compliance with the Act in the first instance, it did not want 

EPA calling long-approved implementation plans for minimal 

forms of noncompliance too insubstantial to justify a re-do. 

 There may well be provisions of the Act, then, with which 

a SIP’s failure to ensure compliance should prevent the SIP’s 

initial approval but, if only identified later, would not justify a 

SIP Call. To the extent that those provisions exist, Petitioners 

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do not argue that the main provision at issue in the Final 

Action—section 7410(a)(2)(A), specifying some of the key 

required contents of SIPs—is among them. And for good 

reason. That section, which directs that each SIP “shall” 

include “emission limitations” and “other control measures, 

means, or techniques” as “necessary or appropriate” to meet 

the Act’s requirements, goes to the heart of SIPs’ role in EPA’s 

and states’ implementation and enforcement of the Act. See id.

§ 7410(a)(2)(A). 

We now turn to a third and final reason why the statutory 

context and structure demand only an EPA determination of 

substantial legal inadequacy and not necessarily factual 

findings about the adverse effects resulting from the SIP’s 

deficiencies: Namely, an across-the-board obligation for EPA 

to make such factual findings would perturb the federal-state 

balance Congress struck in the Clean Air Act. 

The Clean Air Act is an exercise in cooperative federalism. 

One of the core obligations it imposes on EPA is to identify air 

pollutants that endanger public health and welfare, and to set 

standards for permissible ambient concentrations of those 

pollutants. See id. §§ 7408-09. Congress then obligates states 

to determine how they will meet those air-quality standards, 

affording each state leeway to select means consistent with its 

particular circumstances and priorities, and to accordingly 

develop its own implementation plan for EPA’s approval. See 

id. § 7410(a)(2). EPA cannot require states to adopt a 

particular emission-control measure, see Virginia, 108 F.3d at 

1408, and did not do so in the challenged SIP Calls, giving 

states a range of options to correct their deficient SIPs, see, e.g., 

80 Fed. Reg. at 33,947/1; see also id. at 33,976/2-82/2. But, 

while states generally have “the power to determine which 

sources w[ill] be burdened by regulation and to what extent,” 

Union Elec. Co. v. EPA, 427 U.S. 246, 269 (1976), the Act 

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“‘subject[s] the states to strict minimum compliance 

requirements’ and gives EPA the authority to determine a 

state’s compliance with the requirements,” Michigan v. EPA, 

213 F.3d 663, 687 (D.C. Cir. 2000) (quoting Union Elec. Co., 

427 U.S. at 256-57). 

By requiring a determination of “substantial[] 

inadequa[cy]” before EPA must issue a SIP Call, Congress 

ensured that EPA cannot call states’ already-approved SIPs for 

slight or immaterial noncompliance with the Act. 42 U.S.C. 

§ 7410(k)(5). At the same time, Congress recognized EPA’s 

need to act prophylactically to protect air quality and entrusted 

EPA to ensure states achieve the Act’s objectives. See 

generally id. §§ 7401(a)(3)-(4), (c), 7410(k)-(l). Mandating 

that EPA factually demonstrate observed adverse effects on air 

quality or enforcement, as State Petitioners urge, would 

contravene the statutory text and undercut the role that 

Congress reserved for EPA in the Clean Air Act. Just as EPA 

cannot force the states to adopt a particular control measure, 

the states cannot force EPA to wait for air quality to deteriorate, 

or for human health and welfare to suffer, before seeking 

corrections to SIPs with substantial legal deficiencies. After 

all, “[a]n agency need not suffer the flood before building the 

levee.” See Stilwell v. Off. of Thrift Supervision, 569 F.3d 514, 

519 (D.C. Cir. 2009). 

Finally, we disagree with Industry Petitioners that the 

Act’s legislative history shows Congress intended EPA to 

make factual findings before calling a SIP, even when the SIP’s 

inadequacy is a legal shortcoming discernible from the text of 

the statute and the SIP itself. Industry Petitioners rely on a 

Senate report from 1970 that describes EPA’s job to “find[] 

from new information developed after a plan is approved that 

the plan is not or will not be adequate to achieve promulgated 

ambient air quality standards” and “notify the appropriate 

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States and give them an opportunity to respond to the new 

information.” Ind. Pet. Br. at 31-32 (emphasis omitted) 

(quoting S. REP. NO. 91-1196, at 55-56 (1970)). That report 

has little relevance here and, in any case, does not support 

Petitioners’ argument. It speaks to the first ground for issuing 

a SIP Call, i.e., where a SIP is substantially inadequate “to 

attain or maintain the relevant national ambient air quality 

standard.” 42 U.S.C. § 7410(k)(5). The report does not 

address EPA SIP Calls under the third ground for failure to 

“comply with any requirement” of the Act, id.; indeed, in 1970 

when the report was written, the Act did not yet include the 

third ground for a SIP Call. Only in 1977 did Congress expand 

section 7410(a)(2)(H)(ii) to recognize that a SIP may be 

substantially inadequate to otherwise comply with the Act’s 

legal requirements. See Clean Air Act Amendments of 1977, 

Pub. L. No. 95-95, § 108(a)(6)(A), 91 Stat. 685, 693-94. And 

only in 1990 did Congress codify the section 7410(k)(5) SIPcall authority. See Clean Air Act Amendments of 1990, Pub. 

L. No. 101-549, § 101(c), 104 Stat. 2399, 2407. Even if that 

legislative history were relevant, it is not nearly as illuminating 

as Petitioners make it out to be. As EPA recognized, the 

legislative history does not require Industry Petitioners’ 

reading of “find” or “information” any more than does the 

statute itself. See 80 Fed. Reg. at 33,935/1. 

In sum, we hold that when EPA calls a SIP for a substantial 

legal inadequacy, it need only identify the deficiency and 

explain why it is substantial. Whether a SIP is “substantially 

inadequate” to comply with the Act may depend on the 

particular circumstances of the SIP Call at issue, including the 

nature of the Clean Air Act provisions the SIP violates, as well 

as the extent of its noncompliance. We further hold that the 

Act does not categorically require EPA, when calling a SIP for 

a substantial legal inadequacy, to make specific factual 

findings of actual or projected harm to the Act’s objectives as 

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a result of that deficiency. In so holding, we note that the Tenth 

Circuit came to a similar conclusion in U.S. Magnesium, LLC 

v. EPA, 690 F.3d 1157 (10th Cir. 2012). There, the court 

explained that because section 7410(k)(5) “says nothing about 

whether the agency is required to make a specific factual 

finding” before calling a SIP, EPA reasonably interpreted its 

authority not to require factual findings when calling a SIP for 

failure to comply with the Act’s legal requirements. Id. at 

1167; see id. at 1167-68. In reaching a similar bottom line, we 

see no need to resort to deference. The statute itself is clear: 

Factual findings about the knock-on effects of a SIP’s 

deficiencies are not categorically required when EPA calls a 

SIP for substantial inadequacies to comply with the Act. 

B. 

We next consider Industry Petitioners’ assertion that EPA 

cannot base a SIP Call on legal deficiencies in specific SIP 

provisions so long as the SIP “as a whole” is adequate to 

comply with the Act. We conclude that we need not decide 

whether section 7410(k)(5) requires EPA to review SIPs “as a 

whole,” because even if EPA were subject to such a 

requirement, the agency clearly satisfied it here. 

Industry Petitioners seem to argue that EPA cannot object 

to particular SIP provisions, even if inconsistent with the Act’s 

explicit requirements, so long as the SIP as a whole ultimately 

complies with the NAAQS. To the extent this argument 

reprises Petitioners’ contention that EPA must make factual 

findings about a SIP’s overall effectiveness in attaining the 

NAAQS before calling it, we have already explained why no 

such factual findings are necessary when EPA calls a SIP for 

substantial legal inadequacies. See pp. 14-25, supra. In any 

event, Petitioners’ argument is belied by the text of section 

7410(k)(5). Recall that section 7410(k)(5) identifies three 

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distinct grounds for calling a SIP. Congress expressly 

recognized that some SIPs might be deficient in ways that 

interfere with the NAAQS and thus could be called under the 

first ground, or that fail to curtail interstate pollution and so 

could be called under the second. Acknowledging, however, 

that SIPs can be substantially inadequate in other ways, 

Congress conferred on EPA the third type of SIP-call authority, 

the power to call SIPs that are “otherwise” legally deficient. 42 

U.S.C. § 7410(k)(5). Requiring EPA to demonstrate adverse 

effects on the NAAQS for all SIP Calls—even those under the 

third ground—would contravene the plain text of section 

7410(k)(5) and would render the third ground surplusage. 

Industry Petitioners further claim that EPA overlooked 

other provisions in the called SIPs that bring the SIPs “as a 

whole” into compliance with the Act’s enforcement scheme 

and its specification of continuous emission limitations. In 

particular, commenters pointed to SIP provisions that confer a 

“general duty” on sources to limit emissions at all times, 

including during SSM periods. Those general-duty provisions, 

Petitioners argue, resolve any perceived violations of the Act’s 

requirements vis-à-vis emission limitations. Setting aside 

whether those general-duty provisions satisfy the Act’s 

definition of emission limitation, see Sierra Club, 551 F.3d at 

1027-28, the record demonstrates that EPA did in fact consider 

those general-duty provisions, see 80 Fed. Reg. at 33,889/1-

90/1, 33,903/1-04/2, 33,979/3-80/1; see also EPA Br. at 68-84, 

129-31. The agency explained in detail why, in its view, the 

general-duty provisions failed to bring the SIPs into 

compliance. See 80 Fed. Reg. at 33,903/1-04/2. On appeal, 

Petitioners do not cite any other SIP provisions they claim EPA 

overlooked and that they assert obviate the need for a SIP Call. 

Thus, whether or not EPA was required to consider the SIPs 

“as a whole,” it plainly did so. 

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C. 

State Petitioners argue that EPA impermissibly called SIPs 

to address ambiguous SIP provisions—that is, provisions that 

could be read as incompatible with the requirements of the 

Clean Air Act. According to State Petitioners, ambiguous 

provisions have only the “mere potential for” inadequacy. 

State Pet. Br. at 19. Thus, say the states, EPA has arbitrarily 

lowered the standard for calling SIPs from “substantial[] 

inadequa[cy]” to potential substantial inadequacy. For its part, 

EPA explained that ambiguous SIPs undermine the Act’s 

effectiveness: Because ambiguous provisions leave the 

regulated community, public, regulators, and courts uncertain 

as to what the SIP does—and does not—require, such 

provisions dilute the Clean Air Act’s compliance requirements 

and enforcement scheme. See 80 Fed. Reg. at 33,885/1-2, 

33,886/2, 33,926/3-27/1. In other words, the inadequacy is not 

merely “potential” because lack of clarity on its own hinders 

enforcement. 

We reject Petitioners’ claims that ambiguity cannot 

support a SIP Call. Nothing in section 7410(k)(5) requires 

substantial inadequacies to be unambiguous. Rather, 

consistent with the Tenth Circuit’s decision in U.S. 

Magnesium, we conclude that section 7410(k)(5) empowers 

EPA to call SIPs to clarify language that may be read to violate 

the Act. See 690 F.3d at 1169-70. By calling SIPs for 

ambiguous provisions, EPA fulfills its role within the statutory 

scheme. Congress charged EPA with ensuring that SIPs meet 

the requisites of the Clean Air Act and fulfill the Act’s purpose 

of improving air quality. See 42 U.S.C. § 7410(k)(5); id.

§ 7410(k)(3); id. § 7410(l); see generally id. §§ 7401, 

7410(a)(2). Ambiguous SIP provisions leave unclear what 

regulated parties must do to conform to the SIP’s requirements 

and hamstring EPA in its efforts to police compliance with the 

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Act. As the agency observed, if EPA is “unable to ascertain” 

what a SIP provision requires, then courts, regulated entities, 

and the public “will have the same problem.” 80 Fed. Reg. at 

33,943/3. By seeking clarification or revision of ambiguous 

SIP provisions, EPA dispels any uncertainties as to the SIP’s 

demands, enabling SIP provisions to fulfill their role in 

achieving the mandates of the Clean Air Act. 

State Petitioners advance a distinct argument against 

EPA’s stance on ambiguous provisions. EPA’s position is 

especially vexing, they say, because EPA will not consider 

states’ post hoc interpretive letters—i.e., letters submitted after 

EPA’s approval of the SIP—to clarify ambiguous provisions. 

See id. at 33,888/1. Instead, if states wish to rely on interpretive 

letters to cure material ambiguities in their SIPs, EPA requires 

that the letters be provided during notice and comment. That 

ensures that EPA approval rests on a shared EPA and state 

understanding, appropriately memorialized in the public 

rulemaking docket. Id. at 33,885/2-88/3. Whatever its merit, 

EPA’s decision not to rely on after-the-fact interpretive letters 

to resolve any ambiguity in SIPs is beside the point: Petitioners 

did not challenge in the period for public comment EPA’s 

policy against reliance on post hoc interpretive letters. See id.

at 33,887/1-9/1. 

Thus, under section 7410(k)(5), if EPA reasonably 

determines that a SIP provision could reasonably be understood 

to conflict with the Act, that can suffice to warrant a finding of 

substantial inadequacy. 

D. 

Last, Industry Petitioners maintain that EPA did not fulfill 

its duty to consider the economic costs and benefits of the SIP 

Calls. They assert that a finding of “substantial[] 

inadequa[cy]” requires consideration of costs and benefits, and 

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that EPA’s decision not to carry out such an analysis 

necessarily renders the Final Action arbitrary and capricious. 

According to Petitioners, EPA should have evaluated not just 

the “direct costs” to states of editing the violative SIP 

provisions, see 80 Fed. Reg. at 33,883/3-84/2, but also the costs 

to revise other portions of their SIPs that refer to the violative 

provisions and/or to create new, compliant emission rules, as 

well as the cost to industry to meet revised SIP provisions. 

Contrary to EPA’s contention, Industry Petitioners timely 

objected during the period for public comment to EPA’s lack 

of cost-benefit analysis. Several commenters critiqued EPA 

for failing to conduct a cost-benefit analysis and cautioned that 

the SIP Calls would impose outsized costs on states and 

industry without commensurate benefits. See SSM Coalition 

Comments, J.A. 598 (“EPA failed to perform such an 

assessment of the costs and benefits.”), 595 (“EPA Unlawfully 

Failed To Assess the Undoubtedly High Costs the Proposed 

SIP Calls Would Impose on States and Regulated Sources . . . 

The SIP Call Notice is totally lacking in any analysis of what 

this EPA action would cost the states, stationary sources, and 

the public.”), 579 (“The SIP Call Notice would impose 

tremendous resource demands . . . and costly new constraints 

on [source] operations.”), 580 (“The proposed SIP Calls would 

impose huge administrative burdens on state agencies, as well 

as significant costs for regulated facilities, without any clear 

environmental benefit.”); Southern Company Comments, J.A. 

506-12 (section titled “EPA Has Arbitrarily and Capriciously 

Failed To Consider the Significant Cost, Technical, and 

Operational Burden of This Rule”). Because Petitioners 

objected “with reasonable specificity during the period for 

public comment,” we consider their objections. 42 U.S.C. 

§ 7607(d)(7)(B). 

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Contrary to Industry Petitioners’ contention, however, 

section 7410(k)(5) does not impose an across-the-board 

obligation on EPA to quantify and weigh costs and benefits 

before calling a SIP. In calling for cost-benefit analysis, 

Industry Petitioners principally rely on Michigan v. EPA, 576 

U.S. 743 (2015). Michigan and other states challenged EPA’s 

disregard of costs when the agency first considered whether to 

regulate power plants’ emissions of hazardous air pollutants 

under Clean Air Act section 112. Id. at 750. Interpreting 

section 112’s instruction that the agency regulate power plants 

only if it found such regulation “appropriate and necessary,” 42 

U.S.C. § 7412(n)(1)(A), the Supreme Court held that EPA had 

unreasonably ignored costs in its threshold determination 

whether to regulate. Michigan, 576 U.S. at 753. The Court 

reasoned that the word “appropriate” was the “classic broad 

and all-encompassing term that naturally and traditionally 

includes consideration of all the relevant factors,” including 

cost. Id. at 752. Because cost is a “centrally relevant factor 

when deciding whether to regulate,” it was unreasonable under 

the circumstances to read the phrase “‘appropriate and 

necessary’ as an invitation to ignore cost.” Id. at 752-53. 

Furthermore, in section 112, there was an express statutory 

directive for EPA to study “the costs of [available] 

technologies” to control hazardous mercury emissions from 

power plants. 42 U.S.C. § 7412(n)(1)(B). That statutorily 

mandated consideration of cost bolstered the Michigan Court’s 

decision that EPA was required to conduct a cost-benefit 

analysis under the circumstances presented there. 576 U.S. at 

753. Even as it recognized a cost-benefit analysis requirement 

in that context, however, the Court acknowledged that “[t]here 

are undoubtedly settings in which the phrase ‘appropriate and 

necessary’ does not encompass cost.” Id. at 752. 

Seeking support from Michigan, Petitioners insist the 

phrase “substantially inadequate” signals the need for costUSCA Case #15-1271 Document #2043030 Filed: 03/01/2024 Page 30 of 96
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benefit analysis, just as the phrase “appropriate and necessary” 

did with respect to EPA’s decision whether to regulate certain 

hazardous air pollutants. That analogy proves too much. 

Unlike the provision at issue in Michigan, section 7410(k)(5) 

does not prompt EPA to consider all relevant factors (including 

cost). To the contrary, section 7410(k)(5) puts significant 

bounds on EPA’s duty to call a SIP. For starters, EPA is neither 

required nor authorized to call a SIP whenever the agency 

decides it would be “appropriate and necessary” to do so. 

Instead, to call a SIP, EPA must determine it to be substantially 

inadequate—that is, materially deficient. See pp. 16-18, supra. 

And not every substantial inadequacy suffices: The 

inadequacy must also be on one of three statutorily defined 

grounds. See 42 U.S.C. § 7410(k)(5). 

None of the other considerations in Michigan has any 

bearing on this challenge to EPA’s SIP-call authority. Unlike 

section 112, the provisions governing EPA’s SIP Call authority 

contain no “express reference to cost.” Michigan, 576 U.S. at 

753. Nor is EPA’s duty to call for revision of a substantially 

inadequate SIP akin to the agency action at issue in Michigan

of “first deciding whether to regulate” an industry’s hazardous 

emissions. Id. at 756. Far from it. By the time a SIP Call 

occurs, EPA has already identified air pollutants that endanger 

public health and welfare and has promulgated the NAAQS, 42 

U.S.C. §§ 7408-09; states have already submitted SIPs as 

required to meet the NAAQS, id. § 7410(a)(1), and other 

obligations of the Act; EPA has already approved those plans, 

id. § 7410(k)(3)-(4); and states may have even revised those 

plans with further EPA approval, id. § 7410(l). 

The cooperative federalism required by the Clean Air Act 

makes it especially anomalous in the SIP-call context to read 

an implied cost-benefit mandate into the statutory authorization 

for EPA to call a substantially inadequate SIP. When calling a 

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SIP, EPA cannot dictate, or even predict, the particular 

measures states will adopt to rectify the SIP’s deficiencies. 80 

Fed. Reg. at 33,883/3; see Train, 421 U.S. at 78-79; Virginia, 

108 F.3d at 1409-10, 1414-15. In response to the SIP Calls 

under review, for instance, states might decide to remove 

legally deficient provisions. Or they could adopt alternative 

numerical emission limits. Or perhaps they would seek to put 

in place technological controls or work practices. Or they 

might refashion their applicable emission rules altogether. See 

80 Fed. Reg. at 33,974/2-82/2. Requiring consideration of 

costs in every SIP Call would thus upset the federal-state 

balance Congress established in the Clean Air Act. Because 

the states retain broad discretion in crafting SIP provisions so 

long as they comply with the Act, balancing the benefits and 

burdens of a particular SIP revision is best left to the state 

agency tasked with revising the implementation plan. After all, 

“[p]erhaps the most important forum for consideration of 

claims of economic and technological infeasibility is before the 

state agency formulating the implementation plan.” Union 

Elec. Co., 427 U.S. at 266. 

That said, nothing in our decision prevents EPA from 

choosing to consider costs to the extent feasible and not 

prohibited by the Act. See Entergy Corp. v. Riverkeeper, Inc., 

556 U.S. 208, 222-26 (2009); see also Michigan, 213 F.3d at 

674-79. We hold only that section 7410(k)(5) does not 

invariably require EPA to assess costs and benefits when 

calling SIPs for failure to comply with the Act’s legal 

requirements. EPA’s decision not to do so here is no ground 

for invalidating the challenged action. 

II. 

 In addition to Petitioners’ overarching challenges to EPA’s 

statutory authority to call the SIPs at issue, Petitioners also 

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33 

more particularly challenge EPA’s decision to call four specific 

categories of SIP provisions: (1) automatic exemptions, (2) 

director’s discretion provisions, (3) overbroad enforcement 

discretion provisions, and (4) affirmative defense provisions. 

We now take up those specific challenges. 

With respect to automatic exemptions and director’s 

discretion provisions, we agree with Petitioners and set aside 

the SIP Calls insofar as they rest on those provisions. With 

respect to overbroad enforcement discretion provisions, we 

reject that challenge and uphold EPA’s Final Action. And with 

respect to affirmative defense provisions, we agree with 

Petitioners as to certain types of affirmative defense provisions 

but reject Petitioners’ challenge as to other types. 

A. 

We first consider automatic exemptions. We cannot 

sustain EPA’s rationale for concluding that automatic 

exemptions are substantially inadequate to comply with the 

CAA. See 42 U.S.C. § 7410(k)(5). We thus vacate the SIP 

Calls insofar as they are predicated on that conclusion. 

1. 

Automatic exemptions exclude SSM periods from 

otherwise applicable emission restrictions. In calling SIPs on 

the basis that they contain automatic exemptions, EPA relied 

on its authority to call SIPs that are “substantially inadequate 

to . . . comply with any requirement of [the CAA].” Id. 

The centerpiece of EPA’s belief that automatic exemptions 

violate a requirement of the CAA is that, by excluding SSM 

periods from an emission restriction, an automatic exemption 

impermissibly renders the limitation discontinuous. The 

agency’s analysis proceeds in three steps. 

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First, EPA starts with the premise that it “interprets CAA 

sections 110(a)(2)(A) and 110(a)(2)(C) [i.e., 42 U.S.C. 

§§ 7410(a)(2)(A) and (C)] to require that SIPs contain 

‘emission limitations.’” State Implementation Plans, 80 Fed. 

Reg. at 33,927/2. Second, EPA reasons that the “emission 

limitations” that SIPs ostensibly must contain are defined by 

the CAA as restrictions that apply on a “continuous” basis. Id.

(citing 42 U.S.C. § 7602(k), which defines “emission 

limitation”). Third, EPA concludes that, because automatic 

exemptions from “otherwise applicable emission limitations” 

render limitations “less than continuous” in that they need not 

apply during SSM periods, automatic exemptions are 

“inconsistent with a fundamental requirement of the CAA”—

i.e., the statute’s definition of an “emission limitation” as a 

“continuous” measure. Id.

That rationale begins with—and rests on—an essential 

premise at the first step: that SIPs must contain “emission 

limitations.” From that premise, EPA builds its argument that: 

(a) The CAA defines an “emission limitation” as a measure that 

operates “on a continuous basis,” 42 U.S.C. § 7602(k); and 

(b) automatic exemptions conflict with the CAA because they 

render an emission limitation discontinuous, contravening the 

statutory definition of “emission limitation.” Even if we 

assume the correctness of the last step of the analysis—i.e., that 

an automatic exemption renders a given measure incompatible 

with the statutory definition of “emission limitation”—EPA’s 

rationale breaks down if the measure need not qualify as an 

“emission limitation” in the first place. In that event, the fact 

that the statute defines an “emission limitation” as operating 

“on a continuous basis,” id., would not matter: If the measure 

in question need not qualify as an “emission limitation,” then 

it need not satisfy the CAA’s definition of an “emission 

limitation” (including the requirement that it apply “on a 

continuous basis”). 

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35 

A great deal turns, then, on EPA’s starting premise that 

SIPs invariably must contain “emission limitations.” Indeed, 

because EPA views automatic exemptions to be inconsistent 

with the CAA as a categorical matter, and because the agency 

thus called every automatic exemption in any SIP, the essential 

premise of EPA’s Final Action is still broader: The premise is 

not just that SIPs must contain “emission limitations,” but that 

every emission restriction in a SIP that is subject to an 

automatic exemption (and hence was called by EPA) must 

qualify as an “emission limitation.” 

What is the basis for that essential premise of EPA’s 

rationale for calling automatic exemptions as a blanket matter? 

In its brief, EPA at one point states, without elaboration, that 

“[i]t is indisputably a ‘requirement[] of this chapter’ that SIPs 

include ‘enforceable emission limitations.’” EPA Br. 48-49 

(quoting 42 U.S.C. § 7410(a)(2)(A)). That assertion, it bears 

noting, does not even purport to support the full breadth of the 

essential premise of EPA’s categorical call of automatic 

exemptions—i.e., that every emission restriction in a SIP that 

is subject to an automatic exemption must qualify as an 

“emission limitation.” At any rate, even on the narrower 

question whether SIPs must include at least some “emission 

limitations,” that assertion in EPA’s brief still falls short. 

In stating that it “is indisputably a ‘requirement[] of this 

chapter’ that SIPs include ‘enforceable emission limitations,’” 

id., EPA quotes from and relies upon 42 U.S.C. 

§ 7410(a)(2)(A). As Petitioners emphasize, though, that 

provision does not state that any SIP, no matter the 

circumstances, must include “emission limitations.” Rather, it 

states that a SIP “shall— 

(A) include enforceable emission limitations and 

other control measures, means, or techniques . . . , as 

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well as schedules and timetables for compliance, as 

may be necessary or appropriate to meet the 

applicable requirements of this chapter.” 

42 U.S.C. § 7410(a)(2)(A) (emphasis added). The only 

“enforceable emission limitations” that must be included in a 

SIP, then, are those that “may be necessary or appropriate” to 

enable the state “to meet the applicable requirements of this 

chapter [i.e., the CAA].” Id. Or, as Petitioners articulate the 

point: “[R]egardless of what ‘emission limitation’ means, 

Congress explicitly provided states discretion to impose them 

only as ‘necessary or appropriate’ to meet some other 

applicable requirement of the CAA.” Ind. Pet. Br. 49 

(emphasis added) (citing 42 U.S.C. § 7410(a)(2)(A)). 

Put in the alternative, if it is not “necessary or appropriate” 

that a given measure qualify as an “emission limitation” to 

enable a state “to meet the [CAA’s] applicable requirements,” 

the measure can be included in a SIP even if it does not meet 

the CAA’s definition of an “emission limitation.” Indeed, the 

plain terms of section 7410(a)(2)(A) specifically allow for 

inclusion in a SIP of measures other than “enforceable 

emission limitations”: The provision states that, in addition to 

“enforceable emission limitations,” a SIP can also 

“include . . . other control measures, means, or techniques” as 

“may be necessary or appropriate to meet [the CAA’s] 

requirements.” Id. (emphasis added). So, even if a given 

emission restriction does not qualify as an “emission 

limitation” under the CAA—including, for instance, because it 

does not operate on a “continuous basis,” id. § 7602(k)—it 

could still be part of a SIP. And EPA would lack authority to 

call such a measure solely on the ground that it fails to meet the 

statutory definition of an “emission limitation”—a definition it 

did not need to satisfy. 

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To illustrate the point, consider a hypothetical example of 

a state that submits a SIP containing various measures, some of 

which restrict emissions but none of which satisfies the CAA’s 

definition of “emission limitation.” Under section 

7410(a)(2)(A), as noted, the SIP must “include enforceable 

emission limitations and other control measures, means, or 

techniques . . . as may be necessary or appropriate to meet the 

[CAA’s] applicable requirements.” Id. § 7410(a)(2)(A). The 

most prominent “applicable requirements” are the NAAQS. 

See id. § 7410(a)(1). Suppose that the state concludes it can 

satisfy the NAAQS for a given pollutant through its particular 

combination of other types of control measures (and without 

any “emission limitations,” as defined by 42 U.S.C. § 7602(k)). 

The state might then consider that mix of “other control 

measures” to be “necessary or appropriate” to meet the 

NAAQS. Id. § 7410(a)(2)(A). 

In that situation, EPA could not call the SIP solely on the 

ground that the SIP’s “other control measures” fail to satisfy 

the statutory definition of an “emission limitation.” Even if so, 

the SIP may still “include . . . other control measures . . . as 

[are] necessary or appropriate to meet the [CAA’s] applicable 

requirements.” Id. Indeed, EPA acknowledged at oral 

argument that the agency could as a conceptual matter approve 

“a SIP that doesn’t include an emission limitation at all,” so 

long as that SIP still “would then meet [the] requirements of 

the Clean Air Act.” Oral Arg. 1:34:40-1:34:53. 

To be sure, EPA could determine that the hypothetical 

state is wrong in concluding that its chosen mix of “other 

control measures” is “necessary or appropriate” to meet the 

NAAQS. If so, EPA might decide that, for the state to meet the 

NAAQS, at least one of the “other control measures” must be 

adjusted such that it satisfies the definition of an “emission 

limitation”—including, for instance, by converting it from a 

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38 

discontinuous to a continuous measure. And EPA could call 

the SIP on that basis. 

But EPA, in that event, would not rest its SIP Call solely 

on the ground that the SIP’s “other control measures” do not 

satisfy the statutory definition of an “emission limitation.” 

Rather, EPA would rely on its determination that, for the state 

to meet the NAAQS, it is “necessary or appropriate” that one of 

the SIP’s measures be converted from a non-“emission 

limitation” to an “emission limitation.” EPA’s SIP-call 

authority, that is, would be predicated on that kind of 

“necessary or appropriate” determination. Here, though, EPA 

made no such finding that, for a state to meet the NAAQS (or 

satisfy some other pertinent requirement of the Act), it is 

“necessary or appropriate” for the SIP measures subject to 

automatic exemptions instead to operate during SSM periods. 

Our dissenting colleague protests that the hypothetical 

example of a state whose SIP contains no provisions satisfying 

the statutory definition of “emission limitation” has never in 

fact happened in the real world. Dissenting Op. 22. That may 

well be so; no one contends otherwise. The purpose of the 

hypothetical example is simply to illustrate that, insofar as such 

a SIP runs afoul of the statute, it would be because including 

measures satisfying the statutory definition of “emission 

limitation” is “necessary or appropriate” to enable the state to 

meet the NAAQS or some other CAA requirement. 42 U.S.C. 

§ 7410(a)(2)(A). It would not be merely because the SIP’s 

emission restrictions fail to fit within the statutory definition of 

“emission limitation,” without regard to the implications for 

complying with the Act’s requirements. 

Our colleague posits two reasons, apart from the statutory 

definition, that EPA might believe a SIP’s emission restrictions 

must apply during SSM periods (and thus cannot be subject to 

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39 

automatic exemption provisions). Neither reason she puts 

forward, however, can possibly justify EPA’s blanket call of 

automatic exemptions in this case. EPA does not (and could 

not) claim otherwise. 

Our colleague first surmises that automatic exemptions 

from SSM periods “undercut states’ ability to meet Clean Air 

Act requirements, such as attaining and maintaining the 

NAAQS.” Dissenting Op. 5. If that were so, and if EPA 

reasonably so concluded, we agree that EPA could call a SIP 

on that basis. EPA, though, never made any such 

determination and does not purport to have done so—indeed, 

that is exactly the problem with EPA’s blanket call of 

automatic exemption provisions. EPA instead relied on a 

supposed obligation to satisfy the statutory definition of an 

“emission limitation”—which, for the reasons explained, is not 

itself a requirement of the Act for the emission restrictions in a 

SIP. Rather, those measures must operate during SSM periods 

only if it is “necessary or appropriate” for them to do so to 

enable the state to meet the NAAQS (or comply with the Act’s 

other pertinent requirements). 42 U.S.C. § 7410(a)(2)(A). 

Second, according to our colleague, automatic exemptions 

tend to frustrate accurate tracking of emissions because 

monitoring generally assumes a source’s compliance at all 

times. Dissenting Op. 5-6. The resulting “inaccuracies in 

emission inventories,” our colleague submits, “distort[] 

strategies for attaining the NAAQS and downstream modeling 

of NAAQS attainment.” Id. at 6. Again, though, EPA did not 

rely on that explanation to justify its blanket call of automatic 

exemptions. Quite the opposite: EPA reviewed that precise 

theory, deemed it an “oversimplification,” and expressly 

declined to rest the SIP Calls on “how SSM exemptions may 

or may not negatively impact things like emissions 

inventories.” 80 Fed. Reg. at 33,950/1. 

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Where does this leave us with respect to EPA’s across-theboard call of automatic exemption provisions in this case? 

EPA’s authority to call a SIP is conditioned on the agency’s 

finding that the SIP is “substantially inadequate to attain or 

maintain the relevant [NAAQS] . . . or to otherwise comply 

with any requirement of” the CAA. 42 U.S.C. § 7410(k)(5). 

And here, EPA premised its call of automatic exemption 

provisions on section 7410(a)(2)(A)’s reference to “emission 

limitations” when setting out what a SIP must include. See 80 

Fed. Reg. at 33,927/2. For EPA to justify its call of every 

automatic exemption based on that provision, the agency 

would need to find that, to enable a state to meet the NAAQS 

or some other “applicable requirement[],” it is “necessary or 

appropriate” that emission restrictions subject to automatic 

exemptions satisfy the statutory definition of an “emission 

limitation.” 42 U.S.C. § 7410(a)(2)(A). As a result, EPA 

cannot ground its blanket call of automatic exemptions on 

section 7410(a)(2)(A)’s specification that SIPs must “include 

enforceable emission limitations” in certain situations (when 

“necessary or appropriate to meet the [CAA’s] applicable 

requirements”). 42 U.S.C. § 7410(a)(2)(A). The agency did 

not make—and does not purport to have made—the predicate 

“necessary or appropriate” determination with respect to any

automatic exemption, much less to all automatic exemptions as 

a class. 

To be sure, EPA grounds its authority to call automatic 

exemption provisions not just in section 7410(a)(2)(A) but also 

in section 7602(k), the CAA’s definition of “emission 

limitation.” The latter provision, though, does not say anything 

about when a SIP must include an “emission limitation.” 

Rather, it defines an “emission limitation” as a measure “which 

limits the quantity, rate, or concentration of emissions of air 

pollutants on a continuous basis,” 42 U.S.C. § 7602(k), without 

speaking to the antecedent question of when such a measure 

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must be part of a SIP. That question instead is addressed in 

section 7410(a)(2)(A), which, again, requires a SIP to include 

an “emission limitation[]” only when it is “necessary or 

appropriate to meet the [CAA’s] applicable requirements.” 42 

U.S.C. § 7410(a)(2)(A). 

For that reason, EPA’s reliance on Sierra Club v. EPA, 551 

F.3d 1019, is misplaced. In that case, we considered 42 U.S.C. 

§ 7412(d)(1), which requires EPA to “establish[] emission 

standards” for certain sources and pollutants. The CAA gives 

“emission standard” the same definition as “emission 

limitation.” 42 U.S.C. § 7602(k) (“The terms ‘emission 

limitation’ and ‘emission standard’ mean a 

requirement . . . which limits the quantity, rate, or 

concentration of emissions of air pollutants on a continuous 

basis . . . .”). In Sierra Club, we held that EPA’s establishment 

of an SSM exemption for an “emission standard” was 

inconsistent with the definition’s requirement that an emission 

standard “be continuous.” 551 F.3d at 1027-28. EPA submits 

that, in this case, automatic exemptions for SSM periods are 

likewise inconsistent with the definition of “emission 

limitation[]” and so should also be deemed invalid.

The relevant provision in Sierra Club, however, simply 

required EPA to “establish[] emission standards,” 42 U.S.C. 

§ 7412(d)(1), without any proviso conditioning that obligation 

on a predicate determination that it is “necessary or 

appropriate” for a measure to qualify as an “emission 

standard.” As a result, every measure established by EPA 

under that provision needed to qualify as an “emission 

standard,” including by satisfying the requirement that the 

measure operate on a “continuous basis.” There are also other 

provisions that likewise require the use of “emission 

limitations” without condition. See, e.g., 42 U.S.C. 

§ 7429(a)(1)(A) (requiring EPA to establish performance 

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standards for solid waste incineration units and stating that 

“[s]uch standards shall include emission limitations” 

(emphasis added)). 

Here, by contrast, a SIP must include “emission 

limitations” only when “necessary or appropriate to meet the 

[CAA’s] applicable requirements.” 42 U.S.C. 

§ 7410(a)(2)(A). And EPA has not purported to find that it is 

“necessary or appropriate” for every (or indeed any) emission 

restriction subject to an automatic exemption to qualify as an 

“emission limitation” under the statutory definition. 

Our dissenting colleague stresses that the emission 

restrictions at issue meet at least part of the definition of 

“emission limitation” in that they limit “the quantity, rate, or 

concentration of emissions.” Dissenting Op. 10, 20 (quoting 

42 U.S.C. § 7602(k)). And because they meet part of the 

definition, she suggests, they must satisfy the rest of the 

definition too, by limiting emissions “on a continuous basis.” 

Id. (quoting 42 U.S.C. § 7602(k)). That view could in theory 

have some purchase if the two relevant types of emission 

restrictions referenced in section 7410(a)(2)(A)—“emission 

limitations” and “control measures”—were mutually 

exclusive, such that a limit on “the quantity, rate, or 

concentration of emissions” could fit only in the former 

category. If so, such a limit perhaps would need to meet every 

part of the definition of “emission limitation,” or else it would 

be neither an “emission limitation” nor a “control measure.” 

But the statute makes plain that “emission limitations” are a 

subset of “control measures,” not an entirely distinct category. 

See 42 U.S.C. § 7410(a)(2)(A) (referring to “emission 

limitations and other control measures”) (emphasis added). 

The statute thus contemplates restrictions satisfying only part 

of the definition of “emission limitation”: Such measures, even 

if not “emission limitations,” can be “control measures.” 

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In the SIP Calls, but not in its brief in our court, EPA 

sought to ground its authority to call automatic exemptions in 

one additional provision: 42 U.S.C. § 7410(a)(2)(C). See State 

Implementation Plans, 80 Fed. Reg. at 33,927/2 (“Automatic 

exemptions from otherwise applicable emission limitations 

thus render those limits less than continuous as required by 

CAA sections 302(k), 110(a)(2)(A) and 110(a)(2)(C) . . . .” 

(emphasis added)). That provision does not help the agency. 

It requires SIPs to “include a program to provide for the 

enforcement of the measures described in subparagraph (A),” 

i.e., section 7410(a)(2)(A). 42 U.S.C. § 7410(a)(2)(C). While 

section 7410(a)(2)(C) thus calls for SIPs to provide for the 

“enforcement of the measures” that must be included in a SIP 

under section 7410(a)(2)(A), it does not address which 

measures must be contained in a SIP in the first place. That 

instead is the office of section 7410(a)(2)(A), which requires a 

SIP to include only those measures that are “necessary or 

appropriate to meet the [CAA’s] applicable requirements.” 42 

U.S.C. § 7410(a)(2)(A). 

In the end, then, EPA’s authority to issue a blanket call of 

automatic exemptions must be supported by the terms of 

section 7410(a)(2)(A). And because reliance on that provision, 

under the provision’s plain terms, is conditioned on a 

“necessary or appropriate” determination that EPA has not 

made, the agency’s call of automatic exemptions must be set 

aside. 

2. 

EPA in varying measure floats two alternative reasons for 

why it ostensibly could call automatic exemptions without 

having to make any “necessary or appropriate” determination 

under section 7410(a)(2)(A): (i) The “necessary or 

appropriate” condition in that provision in fact does not apply 

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to “emission limitations” at all; or (ii) EPA had already made 

any required “necessary or appropriate” finding when initially 

approving the SIPs. Neither of those theories withstands 

scrutiny. 

a. 

In its briefing in this case, EPA nowhere disputes that, 

under the text of section 7410(a)(2)(A), SIPs must “include 

enforceable emission limitations” only “as may be necessary or 

appropriate to meet the [CAA’s] applicable requirements.” 42 

U.S.C. § 7410(a)(2)(A). That is, EPA does not contest that, per 

the language of the provision, the “necessary or appropriate” 

condition applies to “enforceable emission limitations.” True, 

EPA, as explained, issued its blanket call of automatic 

exemptions without making the requisite “necessary or 

appropriate” determination. But with respect to construing the 

language of section 7410(a)(2)(A), EPA’s briefing does not 

dispute that the words “as may be necessary or appropriate” 

modify “enforceable emission limitations.” 

In fact, EPA explains in its brief that, “under section 

7410(a)(2)(A), each SIP must contain enforceable emission 

limitations as necessary to meet all applicable CAA 

requirements.” EPA Br. 36-37 (emphasis added). And in the 

Final Action itself, EPA expressly acknowledged that section 

7410(a)(2)(A) “means that a SIP must . . . contain legitimate, 

enforceable emission limitations to the extent they are 

necessary or appropriate ‘to meet the applicable requirements’ 

of the Act.” State Implementation Plans, 80 Fed. Reg. at 

33,879/2 (emphasis added) (quoting 42 U.S.C. 

§ 7410(a)(2)(A)). 

In another part of the SIP Calls, moreover, EPA responded 

to comments supposing that the agency espoused a contrary 

interpretation of section 7410(a)(2)(A) under which “the 

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statutory phrase ‘as may be necessary’ only qualifies what 

‘other control[s]’ are required rather than also qualifying what 

emission limitations are required.” Id. at 33,902/1-2. Under 

such an interpretation, in other words, the “necessary or 

appropriate” clause would modify “other control measures, 

means, or techniques,” but would not trace back to also modify 

“enforceable emission limitations.” 42 U.S.C. 

§ 7410(a)(2)(A). 

EPA, though, did not accept the commenters’ 

understanding of the agency’s interpretation, instead referring 

to it only as “EPA’s purported interpretation.” State 

Implementation Plans, 80 Fed. Reg. at 33,902/1 (emphasis 

added). And in EPA’s response to those comments, the agency 

acted on an understanding that “necessary or appropriate” does

modify “enforceable emission limitations,” and sought to 

explain why its call of automatic exemptions should be upheld 

anyway (an explanation we consider and reject below, see Part 

II.A.2.b, infra). Id. at 33,902/2-3. For the most part, then, EPA 

accepts that under a straightforward reading of the terms of 

section 7410(a)(2)(A), the “necessary or appropriate” clause 

applies to “enforceable emission limitations.” 

In a response to a comment elsewhere in the SIP Calls, 

however, the agency put forward an explanation that appears 

to rest implicitly on a contrary reading of section 7410(a)(2)(A) 

under which the “necessary or appropriate” clause modifies 

only “other control measures, means, or techniques,” not 

“enforceable emission limitations.” The comment contended 

that when an emission restriction in a SIP is subject to an SSM 

exemption, section 7410(a)(2)(A) still allows the measure to be 

included in a SIP as an “other control measure[],” even if it 

does not qualify as an “emission limitation[]” due to its 

discontinuity. See State Implementation Plans, 80 Fed. Reg. at 

33,896/1. EPA rejected that possibility, reasoning that its logic 

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would “theoretically allow a SIP to contain no emission 

limitations whatsoever.” Id. at 33,896/3. EPA then observed: 

“This result is contrary to judicially approved EPA 

interpretations of prior versions of the CAA as requiring all 

SIPs to include continuously applicable emission limitations 

and only requiring ‘other’ additional controls ‘as may be 

necessary’ to satisfy the NAAQS.” Id. at 33,896/3-33,897/1. 

That observation references an interpretation of a “prior 

version[],” id., of section 7410(a)(2)(A) under which the words 

“as may be necessary” were construed to modify only “other 

control measures” and not to modify “emission limitations.” 

Consistent with such an understanding, EPA supported its 

observation by citing an opinion that had adopted such an 

interpretation of section 7410(a)(2)(A)’s predecessor. Id. at 

33,897/1 n.175 (citing Kennecott Copper Corp. v. Train, 526 

F.2d 1149, 1153 (9th Cir. 1975)). 

Even assuming that was the correct interpretation of the 

previous language, however, the language is materially 

different now. The prior version called for approval of a SIP if 

it “includes emission limitations, schedules, and timetables for 

compliance with such limitations, and such other measures as 

may be necessary to insure attainment and maintenance of [the 

NAAQS].” Kennecott Copper, 526 F.2d at 1153 (quoting 42 

U.S.C. § 1857c-5(a)(2)(B) (1970)). The 1990 Clean Air Act 

Amendments changed the language in several ways, including 

by expanding the qualifying phrase “as may be necessary to” 

to “as may be necessary or appropriate to,” and also by 

expanding the ensuing words from “insure attainment and 

maintenance of [the NAAQS]” to “meet the [CAA’s] 

applicable requirements” (including but not limited to the 

NAAQS). 42 U.S.C. § 7410(a)(2)(A). And crucially for our 

purposes, the previous version linked its “necessary” clause 

more closely to “such other measures” by placing them in the 

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same clause while putting “emission limitations” in a separate 

clause, whereas the current version, exhibiting no such 

imbalance, links its “necessary or appropriate” clause with both 

“other control measures” and “emission limitations” to the 

same degree. 

In particular, the previous version, as just noted, called for 

a SIP to “include[] emission limitations, . . . and such other 

measures as may be necessary to insure attainment” of the 

NAAQS. 42 U.S.C. § 1857c-5(a)(2)(B) (1970). Because the 

qualifying phrase “as may be necessary” appeared immediately 

after (and in the same clause as) “such other measures,” 

whereas “emission limitations” appeared in a distinct, previous 

clause set off by a comma, the most natural reading was that 

“as may be necessary” modified only “such other measures,” 

not “emission limitations.” The result of that reading was that 

a SIP always needed to include “emission limitations” 

regardless of their necessity in achieving the NAAQS—i.e., 

regardless of whether “other measures” could render an 

“emission limitation” unnecessary to achieve the NAAQS. See 

Train, 421 U.S. at 67. And a SIP therefore could contain “other 

measures” only if “emission limitations” could not attain the 

NAAQS on their own. See id.

The current provision, by contrast, sets off “as may be 

necessary or appropriate” in a separate clause from both 

“emission limitations” and “other control measures,” while 

pairing the latter two in the same clause: Section 7410(a)(2)(A) 

now calls for SIPs to “include enforceable emission limitations 

and other control measures, . . . , as may be necessary or 

appropriate to meet the applicable requirements of [the CAA].” 

42 U.S.C. § 7410(a)(2)(A). And when a qualifying phrase like 

“as may be necessary or appropriate” is set off by a comma in 

that manner from both “emission limitations” and “other 

control measures,” the most natural reading is that the 

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48 

qualifying phrase modifies both “emission limitations” and 

“other control measures,” not just the latter. As the Supreme 

Court recently explained: A “qualifying phrase separated from 

antecedents by a comma is evidence that the qualifier is 

supposed to apply to all the antecedents instead of only to the 

immediately preceding one.” Facebook, Inc. v. Duguid, 141 

S. Ct. 1163, 1170 (2021) (quoting W. ESKRIDGE,

INTERPRETING LAW: A PRIMER ON HOW TO READ STATUTES 

AND THE CONSTITUTION 67-68 (2016)). 

In accordance with that reading, a SIP must include 

“emission limitations” only to the extent they are “necessary or 

appropriate to meet the [CAA’s] applicable requirements.” 42 

U.S.C. § 7410(a)(2)(A). EPA does not dispute that 

interpretation to be the most natural reading of section 

7410(a)(2)(A). Rather, EPA, in the referenced part of the SIP 

Calls, invokes only the legislative history, positing that the 

change from the prior to current versions of the statute sought 

merely to “combine and streamline” it rather than alter its 

meaning. 80 Fed. Reg. 33,897/1. But as explained, the 

amendments changed the relationship between the qualifying 

phrase and its potential objects, such that the “necessary or 

appropriate” clause in section 7410(a)(2)(A) is naturally (and 

best) read to modify “emission limitations.” Indeed, as noted, 

EPA itself recognizes exactly that elsewhere in the SIP Calls. 

80 Fed. Reg. 33,879/2 (“With respect to section 110(a)(2)(A), 

this means that a SIP must . . . contain legitimate, enforceable 

emission limitations to the extent they are necessary or 

appropriate ‘to meet the applicable requirements’ of the Act.” 

(quoting 42 U.S.C. § 7410(a)(2)(A)) (emphasis added)). And 

EPA’s brief in this case, we reiterate, says the same about the 

statutory language: “[U]nder section 7410(a)(2)(A), each SIP 

must contain enforceable emission limitations as necessary to 

meet all applicable CAA requirements.” EPA Br. 36-37 

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49 

(emphasis added). We agree with that straightforward reading 

of section 7410(a)(2)(A)’s terms. 

Notably, our dissenting colleague nowhere advances any 

alternate interpretation of the statute’s plain terms. That is 

unsurprising, as there is no sound way to read section 

7410(a)(2)(A) other than to call for a SIP to include “emission 

limitations” only to the extent they are “necessary or 

appropriate to meet the [CAA’s] applicable requirements.” 42 

U.S.C. § 7410(a)(2)(A). While our colleague offers no 

competing interpretation of the provision, she characterizes our 

straightforward reading of it (which is also EPA’s own reading, 

as just noted) as “novel.” Dissenting Op. 3, 19. Insofar as our 

colleague considers that reading to be “novel” in that it differs 

from the provision’s previous understanding, that is because 

the statute has changed, as we have explained. Insofar as she 

deems that reading “novel” because, in her view, Petitioners 

have “never argued” for it “before us,” Dissenting Op. 17, she 

is mistaken: As we set out below, Petitioners plainly argue that 

a SIP needs to include emission limitations only to the extent 

necessary or appropriate to meet the CAA’s applicable 

requirements. See Part II.C, infra. 

In fact, our colleague herself ultimately understands the 

changes to section 7410(a)(2)(A) to mean that the provision’s 

“necessary or appropriate” clause now applies to “emission 

limitations,” even if that was not previously the case. She 

emphasizes that, under the provision, states are charged with 

initially determining whether an “emission limitation” is 

“necessary or appropriate” to meet the CAA’s applicable 

requirements. See Dissenting Op. 26. That of course is true, 

as the language of section 7410(a)(2)(A) sets out in 

enumerating what a state must include in its SIP. See 42 U.S.C. 

§ 7410(a)(2)(A). But if states initially determine whether 

“emission limitations” are “necessary or appropriate” pursuant 

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50 

to that provision, then the provision’s “necessary or 

appropriate” condition necessarily applies to the words 

“emission limitations.” In short, there is no plausible reading 

of the words “enforceable emission limitations and other 

control measures, means, or techniques . . . , as may be 

necessary or appropriate to meet the applicable requirements of 

this chapter” under which “as may be necessary or appropriate” 

modifies only “other control measures, means or techniques” 

without also modifying “emission limitations.” Id. 

b. 

In the SIP Calls (but not in its brief in our court), EPA also 

maintained that it acted consistently with section 7410(a)(2)(A) 

even if the “necessary or appropriate” clause does modify 

“emission limitations.” That argument is grounded in the idea 

that, when EPA initially approved the called SIPs, the agency 

considered measures it regarded as “emission limitations” to be 

“necessary” to meet the CAA’s requirements. See 42 U.S.C. 

§§ 7410(a)(2)(A), (k)(3). EPA explains its reasoning this way: 

“In every state subject to this SIP call, the EPA has previously 

concluded in approving the existing SIP provisions that the 

emission limitations are necessary to comply with the legal 

requirements of the CAA.” 80 Fed. Reg. 33,902/2. 

But whatever may be the potential implications of EPA’s 

initial approval of those so-called “limitations” in the SIPs, the 

SIPs also contained—and EPA thus also approved—the 

exemptions to those limitations. For instance, one of the states 

whose SIP was called for containing automatic exemptions is 

Delaware. And Delaware places its automatic exemptions 

directly alongside the corresponding emission restrictions. See 

7-1100-1104 DEL. ADMIN. CODE § 1.5; 7-1100-1105 DEL.

ADMIN. CODE § 1.7; 7-1100-1109 DEL. ADMIN. CODE § 1.4; 7-

1100-1114 DEL. ADMIN. CODE § 1.3. As an example, 

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Delaware’s emission restriction for “visible emissions” says 

that it “shall not apply to the start-up and shutdown of 

equipment” in specified circumstances, and then immediately 

sets forth the restriction to which the exemption applies—i.e., 

“[n]o person shall cause or allow the emission of visible air 

contaminants or smoke from a stationary or mobile source, the 

shade or appearance of which is greater than 20% opacity for 

an aggregate of more than three minutes in any one hour or 

more than 15 minutes in any 24 hour period.” 7-1100-1114 

DEL. ADMIN. CODE §§ 1.3, 2.0. 

Anyone reading those neighboring provisions (including, 

of course, EPA) would see that Delaware deems the emission 

restriction as a whole—the restriction as tempered by the 

immediately adjacent exemption—to be necessary to comply 

with the CAA. See 7-1100-1101 DEL. ADMIN. CODE § 3.2 

(noting that “emission requirements are selected as minimum 

controls necessary to ensure a reasonable quality of air 

throughout the State”). And EPA thus approved those 

exemptions—no less than the restrictions to which they are 

attached—when it initially approved the SIPs. As a result, 

EPA’s initial approval of the SIPs cannot now somehow justify 

leaving the so-called “limitations” in place but excising the 

interconnected exemptions. The agency approved both as an 

integrated unit. 

That is true of all the automatic exemptions now called by 

EPA: EPA approved all those exemptions when it initially 

approved the associated restrictions. In that light, EPA cannot 

get very far by observing that it “previously concluded in 

approving the existing SIP provisions that the emission 

limitations are necessary to comply with [the] legal 

requirements of the CAA.” 80 Fed. Reg. at 33,902/2. It 

necessarily also approved the exemptions to those “emission 

limitations.” 

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52 

Our dissenting colleague, though, says that we should just 

ignore the agency’s approval of the exemptions because “EPA 

was rushing to approve the SIPs.” Dissenting Op. 26. But to 

the extent that EPA rashly approved the exemptions in the SIPs 

because it was in too much of a hurry, that indictment of EPA’s 

work would also apply to its approval of the restrictions in the 

same SIPs. Once again, there is no sound basis for leaving the 

restrictions in place on the theory that they were initially 

approved by the agency but nonetheless jettisoning the 

interconnected—and also-approved—exemptions. 

At times in the SIP Calls, EPA additionally appears to nod 

at—but never ultimately advances—a somewhat related 

argument also rooted in the states’ submission of the SIPs for 

EPA’s approval. The idea is that the states’ use of the term 

“emission limitations” to describe the emission restrictions in 

their SIPs had the effect of locking the states into satisfying the 

statutory definition of that term (including that an “emission 

limitation” operate “on a continuous basis,” 42 U.S.C. 

§ 7602(k)). Cf. 80 Fed. Reg. 33,879/3 (“Among [the CAA’s] 

requirements are that an emission limitation in a SIP must be 

an ‘emission limitation’ as defined in section 302(k).”). 

Even if EPA never wholeheartedly embraces that sort of 

argument, our dissenting colleague subscribes to it. She 

stresses that “the states have repeatedly told us that their SIPs 

do contain emission limitations as contemplated by the Clean 

Air Act.” Dissenting Op. 20. The apparent upshot of that view 

is that, whenever a state calls an emission restriction in its SIP 

an “emission limitation,” it necessarily buys into the notion that 

the restriction must satisfy the statutory definition of that term. 

That rationale, in other words, essentially tells the states: “You 

at times have referred to the emission restrictions in your SIPs 

as ‘emission limitations.’ Because you did so, you are now 

stuck with those restrictions’ having to meet the statutory 

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53 

definition of that term, regardless of whether meeting the 

definition is in fact necessary or appropriate for you to comply 

with the CAA’s requirements.” 

EPA never adopts that kind of argument. The agency 

understandably may not wish to treat the statute as creating 

what amounts to a semantic “gotcha” game. When a state 

develops and submits a SIP for approval, the SIP includes a 

suite of substantive restrictions that the state—per section 

7410(a)(2)(A)—considers “necessary or appropriate” to 

comply with the CAA. Even if a state uses the words “emission 

limitation” to describe a given emission restriction in its SIP, 

there is no indication that the state thereby means it wants, 

above all else, for the restriction to qualify as an “emission 

limitation” as defined by the CAA, however that term may be 

construed by a court—let alone that the state wants the 

restriction to be an “emission limitation” that operates during 

SSM periods. To the contrary, when the state includes an 

automatic exemption for SSM periods in a measure it might 

describe as an “emission limitation,” that necessarily negates 

any notion that, by using the label “emission limitation,” the 

state somehow accepts that its so-called “emission limitation” 

would have to apply during SSM periods if a court were 

ultimately to decide that the “limitation” would otherwise fail 

to meet the statutory definition. 

A state, in other words, presumably wants the substance of 

the emission restriction it puts in a SIP, including any 

exemption for SSM periods. The state does not simply want to 

satisfy the statutory label “emission limitation,” even if that 

means letting go of the SSM exemption it adopted. Why 

should any state be understood to prize the label over the 

substance—such that the state is somehow deemed to have 

accepted that, even though it made the considered decision to 

adopt an SSM exemption, it would cast aside the exemption 

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54 

just to enable the associated emission restriction to be 

accurately called an “emission limitation” per the statutory 

definition? Why should any state be thought to have accepted 

(let alone desired) that label-over-substance outcome? 

Imagine, for example, a hypothetical state whose emission 

levels comply with the NAAQS and all other applicable CAA 

requirements, but whose emission restrictions are subject to 

automatic exemptions. Why would such a state care (at least 

for purposes of the issue in this case) if its emission restrictions 

amount to “emission limitations” per the statutory definition? 

The state is already complying with the CAA regardless of the 

answer to that question. Our dissenting colleague believes that 

EPA nonetheless could call such a state’s SIP solely on the 

ground that its emission restrictions fail to satisfy the definition 

of an “emission limitation”—apparently because the state at 

one point might have described its restrictions as “emission 

limitations.” Calling a SIP in that situation would serve no 

purpose other than a semantic one: advising the state that it 

cannot accurately refer to its emission restrictions by using the 

statutory term of art “emission limitations.” Nothing in the 

statute supports EPA’s authority to call a state’s SIP for that 

sort of language-policing reason. 

It is irrelevant for these purposes that states first developed 

their SIPs under an older version of section 7410(a)(2)(A) that 

may have required SIPs to contain emission limitations. See 

Dissenting Op. 23. The statute’s text has changed, as 

explained, and EPA must justify its actions under the revised 

version of the statute in effect when it called the SIPs. EPA 

does not suggest otherwise—and in fact, EPA in its briefing in 

our court never once mentions the previous statutory language 

or that the language has changed. 

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Nor does it matter that Petitioners may believe “the SIPs 

at issue here do include emission limitations.” Id. at 10-11. 

True, Petitioners argue that the emission restrictions in the SIPs 

at issue meet the definition of “emission limitations” even 

though they are subject to automatic exemptions. See Ind. Pet. 

Br. 40-51; State Pet. Br. 24-28. But by making that argument, 

Petitioners in no way abandon their position that those 

restrictions need not qualify as “emission limitations” in the 

first place unless their doing so is “necessary or appropriate” to 

enable a state’s compliance with the CAA’s requirements. 

That compliance is ultimately what matters to a state, not 

whether its emission restrictions happen to meet the statutory 

definition of an “emission limitation.” Again, why would a 

state prioritize a restriction’s fitting within the statutory label 

“emission limitation” over retaining the substance of the 

restrictions it adopted (including any SSM exemption)? It 

would not. 

* * * 

Although we set aside EPA’s call of automatic 

exemptions, our decision is necessarily confined to the 

particular “grounds on which the agency acted.” Michigan, 

576 U.S. at 760. The central deficiency in EPA’s rationale is 

that, in relying chiefly on section 7410(a)(2)(A) to support its 

action, the agency did not make the kind of predicate 

“necessary or appropriate” determination required by the 

straightforward language of that provision. We thus do not 

reach the question whether the called SIPs’ relevant emission 

restrictions in fact amount to (or must amount to) “emission 

limitations” per the statutory definition. 

If EPA in the future were to determine that, for states to 

meet the CAA’s applicable requirements, it is “necessary or 

appropriate” for their emission reduction measures to meet the 

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statutory definition of “emission limitations” and operate 

during SSM periods, the agency could explain and implement 

that rationale and its action would be subject to judicial review. 

Here, however, the agency merely reasoned that every 

emission restriction in a SIP needs to be continuous to qualify 

as an “emission limitation” per the statutory definition, without 

explaining why that continuity is “necessary or appropriate” to 

meet any of the CAA’s requirements (beyond the definition 

itself). That rationale cannot be sustained. 

B. 

We next consider EPA’s call of SIPs containing director’s 

discretion provisions. For largely the same reasons that we set 

aside EPA’s call of automatic exemptions, we also set aside 

EPA’s call of director’s discretion provisions. 

Director’s discretion provisions are essentially exemptions 

but with an added step. See State Implementation Plans, 80 

Fed. Reg. at 33,927/3. Whereas automatic exemptions go into 

effect automatically whenever there is an SSM event, director’s 

discretion provisions give state officials discretion to grant 

SSM-related exemptions from otherwise applicable emission 

limitations. According to EPA, the “director’s discretion SIP 

provisions at issue present the same problems and 

inconsistencies with CAA requirements as those that create 

automatic exemptions.” EPA Br. 51. Specifically, director’s 

discretion provisions render “emission limitations less-thancontinuous and preclud[e] enforcement for what would be 

violations absent the discretionary exemptions.” Id. at 68. 

That continuity-based rationale fails as to director’s 

discretion provisions for the same reasons it fails as to 

automatic exemptions: Before concluding that emission 

restrictions in a SIP must apply continuously (including during 

SSM periods), EPA needed to determine that it is “necessary 

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57 

or appropriate” that the restrictions be continuous to enable the 

state to “meet the [CAA’s] applicable requirements.” 42 

U.S.C. § 7410(a)(2)(A). But EPA did not make the requisite 

“necessary or appropriate” finding. And insofar as EPA 

relatedly believes that director’s discretion provisions unduly 

impede enforcement of the CAA, that rationale falls short for 

the same reasons as with automatic exemptions: While SIPs 

must provide for enforcement of their measures, see id. 

§ 7410(a)(2)(C), that requirement does not speak to the content 

of the measures to begin with, including whether they must 

operate continuously. See p. 43, supra. 

EPA also offers one additional rationale in support of its 

call of director’s discretion provisions, this time one that does 

not apply to automatic exemptions. In the agency’s view, a 

director’s discretion provision, by enabling a state official to 

exempt an otherwise applicable emission restriction from SSM 

periods, impermissibly allows the official to modify a SIP 

unilaterally, without going through the CAA’s prescribed 

procedures for revising a SIP. See 42 U.S.C. § 7410(l). We 

find that rationale no more persuasive than the others. 

 A SIP with a director’s discretion provision has built 

within it the possibility that a state official will grant an 

exemption from an otherwise applicable emission restriction. 

And EPA itself, when it initially approved the SIP, authorized 

inclusion of that provision in the SIP. 42 U.S.C. § 7410(k)(3). 

So when a state official exercises the discretion conferred by 

such a provision, that is merely an application of the EPAapproved SIP to a particular situation, not a revision of the SIP. 

To be sure, in granting an exemption, the official alters the 

applicability of an emission restriction. But the official does 

not alter the underlying SIP. Rather, the SIP is what conferred 

the power to grant the exemption in the first place. 

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For those reasons, we conclude that EPA arbitrarily acted 

in excess of its authority in calling director’s discretion 

provisions. In reaching that conclusion, we do not foreclose 

the possibility that EPA in the SIP Calls touched on reasons 

that specific director’s discretion provisions, depending on 

their particulars, might interfere with the CAA. For instance, 

EPA broached whether a provision might be so unbounded as 

to interfere with the agency’s ability to predict the impact on 

compliance with the CAA’s requirements. See State 

Implementation Plans, 80 Fed. Reg. 33,927/3-33,928/1. But 

EPA seeks to sustain its call of director’s discretion provisions 

as a group based either on the same continuity-based rationale 

it offered for calling automatic exemptions or on its distinct 

rationale about SIP revisions. The agency does not argue that 

its call of specific director’s discretion provisions can be 

sustained absent either of those rationales that apply to the full 

group of called provisions. We thus have no occasion to 

address any other reasons that could be offered in support of 

calling specific director’s discretion provisions. 

C. 

As to both automatic exemptions and director’s discretion 

provisions, in short, EPA called the SIPs at issue without 

making the “necessary or appropriate” determination called for 

by the terms of section 7410(a)(2)(A). To the extent our 

dissenting colleague doubts the substantive merits of that 

conclusion, we have explained why we believe any such view 

is groundless. We now address an equally misconceived 

procedural objection she repeatedly presses. 

Our colleague claims that we set aside EPA’s call of 

automatic exemptions and director’s discretion provisions 

based on an argument Petitioners nowhere make. She says that 

“Petitioners did not argue” that “emission limitations are 

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59 

required only as ‘necessary or appropriate.’” Dissenting Op. 

17-18. Or, equivalently: It is a “new reading” of the statute, 

nowhere urged by Petitioners, “that a SIP must include 

‘emission limitations’ only to the extent ‘necessary or 

appropriate to meet the applicable requirements’ of the Clean 

Air Act.” Id. at 18 (quoting 42 U.S.C. § 7410(a)(2)(A)). 

That is a proposition “Petitioners did not argue”? Id. at 17. 

Hardly so. Here is what Petitioners contend in their brief, in 

their own words: “[R]egardless of what ‘emission limitation’ 

means, Congress explicitly provided states discretion to 

impose them only as ‘necessary or appropriate’ to meet some 

other applicable requirement of the CAA.” Ind. Pet. Br. 49 

(emphasis added) (quoting 42 U.S.C. § 7410(a)(2)(A)). That 

is exactly the proposition our colleague insists Petitioners never 

argued. There is no daylight between arguing “that a SIP must 

include ‘emission limitations’ only to the extent ‘necessary or 

appropriate to meet the applicable requirements’ of the Clean 

Air Act,” Dissenting Op. at 19 (quoting 42 U.S.C. 

§ 7410(a)(2)(A)), and arguing that Congress gave “discretion 

to impose them [i.e., emission limitations] only as ‘necessary 

or appropriate’ to meet some other applicable requirement of 

the CAA,” Ind. Pet. Br. 49 (quoting 42 U.S.C. 

§ 7410(a)(2)(A)). Those contentions are self-evidently one and 

the same. 

Our dissenting colleague asserts that Petitioners, in 

arguing that a SIP needs to include emission limitations “only 

as ‘necessary or appropriate’ to meet some other applicable 

requirements of the CAA,” id., assumed the need to satisfy the 

definition of “emission limitations” and disputed only whether 

the definition’s “continuity requirement” is met. Dissenting 

Op. 18. That is incorrect. Far from assuming the definition’s 

applicability, Petitioners argued that, regardless of the 

definition, a SIP must include emission limitations only if 

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necessary or appropriate: “[R]egardless of what ‘emission 

limitation’ means, Congress explicitly provided states 

discretion to impose them only as ‘necessary or appropriate’ to 

meet some other applicable requirement of the CAA.” Ind. Pet. 

Br. 49 (emphasis added) (quoting 42 U.S.C. § 7410(a)(2)(A)).

What is more, after so setting out exactly the interpretation 

of section 7410(a)(2)(A) on which our rejection of the SIP 

Calls rests, Petitioners go on to make several integrally 

associated, follow-on points that we have also found 

persuasive. Petitioners explain that, while “EPA attempts to 

dismiss the ‘necessary or appropriate’ language by interpreting 

the subsequent phrase ‘requirement of this chapter’ to include 

the definition of ‘emission limitation,’” that definition, 

“[w]hatever [it] means,” is “not a standalone ‘requirement’ of 

the Act.” Id. at 50. Precisely so. See pp. 34-38, 40-41, supra. 

That definition, Petitioners elaborate, “says nothing about the 

applicability of emission limitations.” Ind. Pet. Br. 42. True. 

See pp. 40-41, supra. Those points solely make sense in the 

context of Petitioners’ argument that a SIP needs to contain 

“emission limitations” only as necessary or appropriate. 

Petitioners add that “EPA’s interpretation” of section 

7410(a)(2)(A) would “depriv[e] states[] the choice of not 

applying emission limitations to some or all sources during 

SSM (or other) periods.” Ind. Pet. Br. 51. Yes again. See pp. 

52-55, supra. And “[i]f Congress did not want states to have 

discretion to determine how ‘emission limitations’ were 

applied in SIPs, it could have adopted more prescriptive 

measures,” as “it did in CAA § 112,” Ind. Pet. Br. 51, the 

materially different provision we considered in Sierra Club. 

Right once more. See pp. 41-42, supra. 

Tellingly, moreover, EPA fully understands the argument 

that Petitioners are making (and that our colleague nonetheless 

asserts Petitioners have not made). In describing “Petitioners’ 

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61 

arguments” against it, EPA includes the following as a “key 

point” pressed by Petitioners: “EPA misinterprets section 

7410(a)(2)(A).” EPA Br. 43. In particular, EPA explains, 

“Petitioners contend that EPA is trampling the States’ 

discretion under section 7410(a)(2)(A) to determine what 

‘enforceable emission limitations and other control 

measures . . . [are] necessary or appropriate’ to meet CAA 

requirements.” Id. at 48 (alterations in original) (quoting Ind. 

Pet. Br. 50-52; and 42 U.S.C. § 7410(a)(2)(A)). That is indeed 

what Petitioners argue is the upshot of EPA’s mistaken (in 

Petitioners’ view) understanding of the terms of section 

7410(a)(2)(A), particularly the provision’s “necessary or 

appropriate” clause. And as we have explained, we find 

Petitioners’ argument on that score to be persuasive. 

EPA, in attempting to respond to Petitioners’ argument in 

that regard, further confirms that it understands Petitioners to 

be making the argument our colleague professes Petitioners do 

not advance. EPA states: “States do have the discretion not to 

regulate a source or source category entirely if doing so is not 

necessary or appropriate to meet CAA requirements.” Id. at 

50. Why would EPA make it a point to concede that there is

some discretion to refrain from applying an emission limitation 

when it is not “necessary or appropriate” to meet the CAA’s 

requirements, unless EPA understands Petitioners to be 

arguing that emission limitations need only be included in a 

SIP if they are “necessary or appropriate” to meet the CAA’s 

requirements? To be sure, EPA ultimately has no persuasive 

response to Petitioners’ argument on that score; but as to 

whether Petitioners in fact make the argument, EPA plainly 

believes they do. Indeed, EPA, in attempting to respond to 

Petitioners’ argument, cites the exact four pages of the 146-

page Final Action containing the agency’s response to the 

argument that the Action mistakenly overlooks the significance 

of section 7410(a)(2)(A)’s “necessary or appropriate” 

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language—the argument our colleague believes Petitioners do 

not make. See id. at 50 (citing 80 Fed. Reg. at 33,902-03); id.

at 51 (citing 80 Fed. Reg. at 33,896-97). 

All of which is to say: Petitioners absolutely do argue that 

a SIP needs to “include ‘emission limitations’ only to the extent 

‘necessary or appropriate to meet the applicable requirements’ 

of the Clean Air Act.” Dissenting Op. 19 (quoting 42 U.S.C. 

§ 7410(a)(2)(A)). And EPA understands Petitioners to so 

contend. Our colleague might wish that EPA responded more 

fulsomely or in a different way to that argument. EPA, for 

instance, does not rely in its brief on our colleague’s notion that 

the SIPs must contain “emission limitations” as defined by the 

CAA because the states sometimes used those words when 

referring to the emission restrictions in the challenged SIPs. 

Perhaps EPA opted against relying on that notion upon 

recognizing its shortcomings. See pp. 52-55, supra. 

We note, lastly, that even if Petitioners had not made the 

“necessary or appropriate” argument that we ultimately find 

persuasive, we are “not limited to the particular legal theories 

advanced by the parties, but rather retain[] the independent 

power to identify and apply the proper construction of 

governing law.” Kamen v. Kemper Fin. Servs., Inc., 500 U.S. 

90, 99 (1991). After all, because “[o]ur task is to construe what 

Congress has enacted,” we need not “accept an interpretation 

of a statute simply because it is agreed to by the parties.” 

Rumsfeld v. F. for Acad. & Inst. Rts., 547 U.S. 47, 56 (2006) 

(quoting Duncan v. Walker, 533 U.S. 167, 172 (2001)). 

Petitioners of course pointed us to the relevant “governing 

law,” Kamen, 500 U.S. at 99—i.e., the terms of 42 U.S.C. 

§ 7410(a)(2)(A). See EPA Br. 43 (understanding Petitioners to 

argue that “EPA misinterprets section 7410(a)(2)(A)”). And 

once we look at that provision, the significance of its 

“necessary or appropriate” clause to the validity of EPA’s SIP 

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Calls is hardly hidden beneath the surface: It essentially jumps 

off the page upon a scan of the provision’s terms. 

Here, in any event, Petitioners not only directed us to 

section 7410(a)(2)(A), but they also explained precisely how 

the provision’s language undermines EPA’s basic rationale for 

calling the automatic exemption and director’s discretion 

provisions: “[R]egardless of what ‘emission limitation’ means, 

Congress explicitly provided states discretion to impose them 

only as ‘necessary or appropriate’ to meet some other 

applicable requirement of the CAA.” Ind. Pet. Br. 49 (quoting 

42 U.S.C. § 7410(a)(2)(A)). EPA has no persuasive answer to 

that contention. Nor, in our respectful view, does our 

dissenting colleague. 

D. 

EPA (by its own account) called only one SIP, 

Tennessee’s, for containing overbroad enforcement discretion 

provisions. See TENN. COMP. R. & REGS. 1200-3-20-.07-(1), 

.07(3). It found those provisions ambiguous: The provisions 

could be read to limit only Tennessee’s enforcement discretion, 

but EPA thought that they could also be read to allow 

Tennessee officials to foreclose EPA enforcement actions and 

citizen suits. 

The Petitioners do not question that the provision would 

be unlawful if the second reading is correct. Instead, they say 

that EPA cannot call a SIP for being ambiguous, and that EPA 

should have deferred to Tennessee’s construction of any 

potentially ambiguous terms. 

We have already rejected those arguments. We therefore 

deny the petitions for review as to Tennessee’s overbroad 

enforcement discretion provisions. 

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E. 

 We finally turn to EPA’s calls based on affirmative 

defense provisions. 

States have included two kinds of affirmative defenses in 

their SIPs, and each requires a different analysis. 

One kind provides “a complete affirmative defense to an 

action brought for non-compliance” with an emission rule, 

provided the source complies with certain conditions. 118-01-

19 ARK. CODE R. § 602. Those affirmative defenses create an 

exemption from the normal emission rule. So our automaticexemption analysis applies equally to them. 

 

 The other kind precludes certain remedies after a source 

has violated an emission rule. In Arizona, for example, a 

source generally has an affirmative defense for excess 

emissions during SSM period, except in a “judicial action 

seeking injunctive relief.” ARIZ. ADMIN. CODE § 18-2-310(B)-

(C). Those raise a different legal question: whether states can 

limit the relief that Congress empowered federal courts to grant 

for violations of emission rules. We hold that they cannot. 

 As part of its enforcement regime, the Clean Air Act 

authorizes citizens and EPA to seek injunctive relief and 

monetary penalties against sources that violate SIPs’ emission 

rules. 42 U.S.C. §§ 7604(a), 7413(b). Affirmative defenses 

against certain remedies block that aspect of the Act’s 

enforcement regime. 

 That is why, in NRDC v. EPA, we determined that EPA 

could not provide an affirmative defense against monetary 

damages as part of a federal emission rule. 749 F.3d at 1063-

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65 

64. We explained that the Act’s citizen-suit provision “clearly 

vests authority over private suits in the courts, not EPA.” Id.

at 1063. Thus, “the Judiciary, not any executive agency, 

determines the scope—including the available remedies—of 

judicial power vested by statutes establishing private rights of 

action.” Id. (internal quotation marks omitted) (quoting City of 

Arlington v. FCC, 569 U.S. 290, 302 n.3 (2013)). We therefore 

held that once a court finds a violation in a private suit, it is for 

the court alone to determine the appropriate civil penalties. Id. 

Of course, NRDC did not address SIPs. 749 F.3d at 1064 

n.2. But “statutes are not chameleons, acquiring different 

meanings when presented in different contexts.” Maryland, 

958 F.3d at 1202. The enforcement provisions that we 

analyzed in NRDC—sections 113 and 304 of the Act—apply 

to state-created emission rules just as they do to EPA-created 

rules. See 749 F.3d 1055. 

The Petitioners offer three reasons that they believe the 

SIP context is different. Each is unpersuasive. 

First, the Petitioners argue the Act grants states the power 

to alter its enforcement regime through the Act’s requirement 

that SIPs “include a program to provide for the enforcement of 

the” SIPs’ substantive rules. 42 U.S.C. § 7410(a)(2)(C). 

They are incorrect. That provision, § 110(a)(2)(C) of the 

Act, instructs states to “provide for the enforcement” of 

substantive emission rules. To provide is to “furnish” or 

“supply” something—here, enforcement. Provide, THE 

AMERICAN HERITAGE DICTIONARY OF THE ENGLISH 

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66 

LANGUAGE (1976).1

 A duty to supply enforcement does not 

carry with it the power to limit other enforcement efforts that 

the Clean Air Act authorizes. 

That understanding is confirmed when the words in 

section 7410(a)(2)(C) are read “in their context and with a view 

to their place in the overall statutory scheme.” Roberts v. SeaLand Servs., Inc., 566 U.S. 93, 101 (2012) (quoting Davis v. 

Mich. Dep’t of Treasury, 489 U.S. 803, 809 (1989)). That 

section is part of a long list of duties that Congress imposed on 

states. E.g., 42 U.S.C. § 7410(a)(2)(B) (“provide for 

establishment and operation of appropriate devices, methods, 

systems, and procedures necessary to monitor, compile, and 

analyze data on ambient air quality”). None of those other 

duties empowers states to alter other aspects of Congress’s 

scheme. And neither does section 7410(a)(2)(C). 

Second, the Petitioners observe that Congress left it to the 

states “to determine which sources would be burdened by 

regulation and to what extent.” Union Elec. Co., 427 U.S. at 

269. From that premise, they conclude that states’ general 

discretion to determine what types of emission rules are 

“necessary or appropriate” to meet the Act’s requirements 

allows them to decide how those rules should be enforced. 42 

U.S.C. § 7410(a)(2)(A). 

But states’ power to decide whom and how to regulate 

does not carry with it the power to alter the consequences 

Congress chose for violating those regulations. Rather, 

Congress specifically determined how EPA and citizens could 

1 See also Provide, WEBSTER’S NEW WORLD DICTIONARY OF THE 

AMERICAN LANGUAGE (2d ed. 1972) (same); Clean Air Act 

Amendments of 1977, Pub. L. No. 95-95, § 108, 91 Stat. 685, 693 

(adding the provision that is now section 110(a)(2)(C)). 

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67 

enforce the regulations that the states choose to impose. And 

it left it to the courts to determine the appropriate penalties for 

violations. See 42 U.S.C. §§ 7413, 7604(a); NRDC v. EPA, 749 

F.3d at 1063. 

 Third, the Petitioners say that if we agree with EPA, we 

will create a split with the Fifth Circuit’s decision in Luminant 

Generation Co. v. EPA, 714 F.3d 841 (5th Cir. 2013). There, 

the Fifth Circuit’s textual analysis consisted of the following 

sentence: “[S]ection 7413 does not discuss whether a state may 

include in its SIP the availability of an affirmative defense 

against civil penalties for unplanned SSM activity.” Id. at 852. 

It then deferred to EPA’s pre-NRDC view that affirmative 

defenses against monetary damages for unavoidable excess 

emissions were lawful. Id. at 853. 

We “avoid creating circuit splits when possible.” United 

States v. Philip Morris, USA, Inc., 396 F.3d 1190, 1201 (D.C. 

Cir. 2005). But NRDC already rejected the Fifth Circuit’s 

silence-as-delegation logic, and we must follow NRDC. 749 

F.3d at 1064; Ali v. Rumsfeld, 649 F.3d 762, 775 n.20 (D.C. 

Cir. 2011) (“We are of course bound by circuit precedent.”). 

So any disagreement with the Fifth Circuit about the Act’s 

meaning has existed since 2014; we are just applying it now in 

the same context that the Fifth Circuit did. Just as NRDC’s rule 

foreclosed EPA’s affirmative defense, it likewise forecloses 

affirmative defenses in SIPs. NRDC v. EPA, 749 F.3d at 1064. 

 In short, states cannot limit courts’ discretion to determine 

and apply appropriate civil penalties for violations of SIPs. We 

therefore deny the petitions for review as to affirmative 

defenses against monetary damages. 

* * * 

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68 

 As to the calls based on automatic exemptions, director’s 

discretion provisions, and affirmative defenses that are 

functionally exemptions, we grant the petitions and vacate the 

SIP-call order. We deny the petitions as to the calls based on 

the enforcement-discretion provision and affirmative defenses 

against specific relief. 

So ordered. 

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PILLARD, Circuit Judge, concurring in part and dissenting 

in part: 

The majority and I agree on quite a bit. We agree that 

EPA correctly interpreted its SIP-call authority under the 

Clean Air Act and that Petitioners’ crosscutting challenges to 

that authority fail. I also join the majority in denying the 

petitions for review with respect to Tennessee’s overbroad 

enforcement-discretion provisions and those affirmative 

defenses that operate to preclude certain remedies after a 

source has violated an emission rule. I thus join Analysis 

Sections I and II.C in full and Section II.D in part. 

But the majority missteps in vacating EPA’s decision to 

call state implementation plans that are substantially 

inadequate under the Clean Air Act because they include 

automatic exemptions, director’s discretion provisions, or 

affirmative defenses that operate as wholesale exemptions for 

SSM events. As for those provisions, EPA got it right: The 

Clean Air Act requires “emission limitations” (also referred to 

as “emission standards”) to apply continuously, and the 

emission limitations in the SIPs subject to this call violate that 

requirement. 

Reading the majority, one might think this case is about 

whether the SIP provisions challenged as discontinuous are 

emission limitations at all. But make no mistake: No 

challenger pressed before this court that the SIPs at issue did 

not contain emission limitations. No challenger defended on 

the ground that pollution-restricting measures that limit the 

quantity, rate, or concentration of air pollutants were not 

“emission limitations,” or that EPA fell short of establishing 

before issuing its SIP Calls that the measures the states 

included as “emissions limitations” were “necessary or 

appropriate” to their SIPs. Quite the opposite. The states 

have long and repeatedly used the statutorily defined term 

“emission limitations” to refer to their disputed pollution 

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2 

restrictions. And they have defended them as “emissions 

limitations” that they view as appropriate to meet their Clean 

Air Act obligations. The Petitioners’ briefs object only that 

EPA misunderstood what it means for an emission limitation 

to be “continuous” and that, even under EPA’s reading of the 

continuity requirement, the SIPs contain continuous emission 

limitations. See States Br. 7, 22-34; States Reply Br. 1, 8, 11-

12; Indus. Br. 36-52. 

My colleagues nevertheless reject EPA’s SIP Call by 

hypothesizing that the plans at issue may be entirely devoid of 

“emission limitations” as the Act defines them. Positing that 

a discontinuous emission limitation is no emission limitation 

at all, they say that the challenged SIPs cannot be 

substantially legally deficient for failing to meet the 

requirement that “emission limitations” apply on a continuous 

basis. See 42 U.S.C. § 7602(k); Maj. Op. 37. The majority 

also sees the states’ submission and EPA’s approval of these 

SIPs as reason to treat the emission limitations in the SIPs as 

not “enforceable emission limitations” under the Act: Given 

the statutory definition of “emission limitations” as 

continuous, say my colleagues, the states cannot have 

proffered, nor EPA approved, those overtly discontinuous 

measures as “enforceable emission limitations.” 42 U.S.C. 

§ 7410(a)(2)(A); Maj. Op. 50-52. 

But that is wrong for at least three reasons. 

First, EPA has been candid that its initial approval was in 

error to the extent it overlooked the discontinuity of the 

emission limitations when it initially approved them. And 

Petitioners do not argue that EPA’s initial approval of their 

SIPs estops the agency from calling the SIPs to fix its errors. 

Second, Petitioners themselves refer to the disputed 

measures as emission limitations. In legally consequential 

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3 

filings—including their briefs in this very case, comments to 

EPA, and the SIPS themselves—the petitioning states have 

repeatedly referred to their chosen control measures as 

containing “emission limitations.” The majority brushes 

those statements aside as semantic missteps: Because it was 

against the petitioning states’ interests to do so, they must not 

have meant to acknowledge that their discontinuous rules are 

“emission limitations” when, on the majority’s logic, they 

could have avoided the Act’s continuous-applicability 

requirement simply by calling them something else. But that 

cuts the other way. In both law and common sense, 

statements made against a speaker’s own interest are taken as 

more likely to be accurate, not less. 

Third, the statute appears to treat “emission limitations” 

and “other control measures” as distinct categories of 

restrictions. Without briefing on the issue, I would hesitate to 

reduce that distinction to whether a restriction is continuous. 

The crux of my colleagues’ approach is that the discontinuity 

of an emission limitation just redefines it as an “other control 

measure.” In the face of textual and structural reasons to 

doubt Congress intended that workaround, we should not rely 

on it here to excuse the deficiencies EPA identifies. 

I would have answered the questions presented to us—

namely, how to interpret Congress’s direction that emission 

limitations operate on a continuous basis, and whether the 

emission limitations in the SIPs at issue violate that continuity 

requirement. On the issues as to which today’s decision both 

departs from the briefing before us and arrives at a novel 

interpretation of the strictures of the Clean Air Act, I 

respectfully dissent. 

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4 

I. 

This case concerns the difficult task of curbing harmful 

air pollution released by industrial facilities during their 

startup, shutdown, or malfunction. Those so-called SSM 

events may involve, for example, leaks, flares, and even 

explosions. Releases during SSM events often far exceed 

emissions from normal operations because facilities may 

operate less efficiently than during steady-state operation and 

because facilities often bypass controls when they are starting 

up, shutting down, or malfunctioning. See Intervenors’ Br. 1; 

Indus. Br. 7 n.4. Excess emissions from SSM events can be 

regular occurrences: One Georgia facility, for example, 

exceeded applicable emission limits on “thousands of 

occasions” over a four-year period. Sierra Club v. Ga. Power 

Co., 443 F.3d 1346, 1347 (11th Cir. 2006); see id. at 1350. 

The exceedances can be dramatic: Another plant released 

“three times its daily limit” of a pollutant “over a nine-hour 

period.” US Magnesium, LLC v. EPA, 690 F.3d 1157, 1163 

(10th Cir. 2012). 

The pollutants that SIPs must control include particulate 

matter, sulfur dioxide, lead, and others that damage human 

respiratory, cardiac, and neurological health. See 40 C.F.R. 

pt. 50. SSM events can involve bursts of such pollutants in 

high concentrations. Mounting scientific evidence links 

concentrated bursts of pollutants to severe harm to public 

health and welfare. Those harms fall disproportionately on 

industrial facilities’ neighboring communities, many of which 

are socially and economically disadvantaged. For those 

communities, frequent industrial flaring events, for example, 

cause myriad health and welfare problems—from burning 

sensations in the nose and throat to respiratory illness to 

cancer. See generally Intervenors’ Br. 2-3, 7-13. 

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5 

The harms caused by SSM emissions are often avoidable. 

Industrial sources are technologically capable of minimizing 

emissions during startup and shutdown and reducing the 

frequency of, and damage caused by, malfunctions. Id. at 16; 

see also SIP Calls, 80 Fed. Reg. 33,840, 33,874/3 (June 12, 

2015). But they may lack the incentive to do so. After all, 

many state implementation plans simply exempt excess 

emissions during SSM events from the otherwise-applicable 

emission limitations that are designed to curb air pollution. 

As a result, emissions during SSM events that exceed 

otherwise-applicable emission limitations are not treated as 

enforcement risks that should drive compliance. EPA Br. 17-

19. No wonder that many industrial sources have not made 

the investments necessary to protect our air from the harmful 

emissions released during startup, shutdown, and malfunction.

SSM exemptions are regulatory loopholes. In the years 

since EPA initially approved such exemptions, the agency has 

come to recognize that they conflict with the Clean Air Act’s 

requirement that emission restrictions apply continuously. 

SSM exemptions allow sources to emit pollutants causing 

“unacceptable air pollution in nearby communities,” without 

any legal mechanism for state air agencies, EPA, the public, 

or courts to require greater efforts to reduce emissions. 80 

Fed. Reg. at 33,843/3. The exemptions also undercut states’ 

ability to meet Clean Air Act requirements, such as attaining 

and maintaining the NAAQS, preventing significant 

deterioration of air quality in attainment areas, and protecting 

visibility. EPA Br. 18; Memorandum to Docket for 

Rulemaking: Statutory, Regulatory, and Policy Context for 

this Rulemaking, Docket No. EPA-HQ-OAR-2012-0322-

0029, at 23 (Feb. 4, 2013) (J.A. 430). 

EPA has identified these substantial regulatory loopholes, 

but it remains difficult to measure just how damaging 

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6 

uncontrolled SSM emissions are. Because emissions during 

SSM events are exempt from emission limitations, they are 

often not tracked with any precision or regularity. Indeed, 

emission inventories typically “presume compliance by 

sources at all times throughout the year” and are “not adjusted 

to include excess emissions that occur as a result [of] SSM 

events.” Memorandum to Docket for Rulemaking at 23 (J.A. 

430). Those inaccuracies in emission inventories ripple 

throughout the SIP planning process, distorting strategies for 

attaining the NAAQS and downstream modeling of NAAQS 

attainment. See id. at 23-24 (J.A. 430-31). EPA did not “rest 

the SIP Call” on these distortions, Maj. Op. 39, but it did not 

dismiss them either, cf. id. According to EPA, discontinuous 

source compliance with emission limitations has a “negative 

impact” on the accuracy of emissions inventories and SIP 

planning and could “have a larger negative effect” if not 

disallowed. 80 Fed. Reg. at 33,950/1-51/1.

Most of the SSM exemptions are, as EPA put it, “artifacts 

of the early phases of the SIP program, approved before state 

and EPA regulators recognized the implications of such 

exemptions.” 80 Fed. Reg. at 33,957/3. After hurriedly 

approving such SSM exemptions in the wake of the 1970 

Amendments to the Clean Air Act, EPA soon realized that 

they were “not consistent” with the Act. Id. In a series of 

guidance documents dating back to 1982, EPA communicated 

to states that the Clean Air Act bars exemptions from 

emission limitations for SSM events. Id.; see Memorandum 

to Docket for Rulemaking at 8-16 (J.A. 415-23) (describing 

EPA’s longstanding SSM policy). But, while EPA has long 

interpreted the Act to prohibit SSM exemptions, many states 

did not update their SIPs to remove those loopholes. 

Recall that the Clean Air Act sets out requirements for 

SIPs, including that: 

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7 

Each SIP shall— 

(A) include enforceable emission limitations and 

other control measures, means, or 

techniques (including economic incentives such as 

fees, marketable permits, and auction of emissions 

right), as well as schedules and timetables for 

compliance, as may be necessary or appropriate to 

meet the applicable requirements of this chapter.” 

42 U.S.C. § 7410(a)(2)(A). Congress defined an “emission 

limitation” and “emission standard” as: 

a requirement established by the State or the 

Administrator which limits the quantity, rate, or 

concentration of emissions of air pollutants on a 

continuous basis, including any requirement relating 

to the operation or maintenance of a source to assure 

continuous emission reduction, and any design, 

equipment, work practice or operational standard 

promulgated under [the Clean Air Act]. 

42 U.S.C. § 7602(k) (emphasis added). 

That brings us to the SIP Calls at issue here. After 

decades of inaction to correct those deficient SIPs, EPA in 

2015 called SIPs from 35 states and the District of Columbia 

as substantially inadequate to the extent they exempted SSM 

events from emission limitations. EPA explained that, by 

carving out SSM events from otherwise-applicable emission 

limitations, those SIPs violated the Clean Air Act’s 

requirement that emission limitations operate “on a 

continuous basis,” 42 U.S.C. § 7602(k). See, e.g., 80 Fed. 

Reg. at 33,852/1-2, 33,927/1-3, 33,928/3. A subset of the 

states—roughly half of those originally subject to the SIP 

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8 

Calls—and certain industry groups and companies seek 

review in this court. 

II.

Petitioners’ challenges to EPA’s SIP Calls present two 

questions of relevance here: (1) whether emission limitations 

in SIPs must apply at all times to satisfy the Clean Air Act’s 

requirement that emission limitations operate “on a 

continuous basis,” 42 U.S.C. § 7602(k), and (2) whether the 

state plans subject to this SIP Call violated that requirement 

when they exempted SSM emissions from otherwiseapplicable emission limitations. The answer to both questions 

is yes. The Clean Air Act requires that emission limitations 

apply continuously. The called SIPs violated that requirement 

when they included automatic exemptions, director’s 

discretion provisions, and certain affirmative defenses that 

exempt emissions during SSM events from the SIPs’ 

otherwise-applicable emission limitations. 

Perplexingly, the majority answers neither question. 

Rather, my colleagues devote their attention to what they say 

is an “essential premise” of EPA’s SIP Calls—namely, that 

the Clean Air Act invariably requires all SIPs to contain 

emission limitations as the Act defines them. Maj. Op. 34. 

The majority then questions the legitimacy of that premise by 

deciding that the Act does not require every SIP to include 

such a limitation. But that so-called premise is not before us. 

Petitioners do not controvert it, nor does EPA see the need to 

defend it in this case. The position adopted by the majority is 

nowhere to be found in the briefing. That is because the straw 

“premise” it targets is not at all “essential” to the SIP Call 

before us. Even if the majority is correct that the Act does not 

invariably require every SIP to include emission limitations, it 

is enough that as a practical matter the called SIPs in this case 

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9 

all purport to include them. Indeed, States submitted and 

EPA approved them under an earlier version of the Act, when 

“a SIP always needed to include ‘emission limitations.’” Maj. 

Op. 47. Accordingly, the parties all understood the SIPs at 

issue to contain “emission limitations” to which the 

challenged SSM carveouts apply. See infra 20-21. That is 

reason enough not to go down the path taken by the majority. 

A. 

Start with the arguments the parties did bring before this 

court. The Petitioners claim that exemptions for SSM events 

do not violate the Clean Air Act’s requirement that emission 

limitations be continuous. The thrust of their argument 

proceeds in two steps. First, Petitioners argue that an 

emission limitation meets the Act’s continuity requirement so 

long as it is “‘continuous’ over some period of time or 

condition,” even if “not necessarily all periods of time.” 

Indus Br. 42. See Indus. Br. 40-47, 50-52. Under that 

reading, the Act’s continuity requirement merely prohibits the 

use of intermittent emission control technologies, which “vary 

their level of emission control based on air quality.” Indus. 

Br. 46 (emphasis omitted); see also States Br. 25. Second, 

Petitioners claim in the alternative that, even if emission 

limitations must apply at all times, the SIPs comply because 

they “include ‘general duty’ requirements” that obligate 

sources “to minimize emissions either at all times, or as a 

prerequisite to an exception to application of a numeric 

‘emission limitation.’” Indus. Br. 38; see id. at 38-40; States 

Br. 10, 22-28. Neither of those arguments treats the called 

SIPs as devoid of “emission limitations” within the meaning 

of the Act. Rather, they defend as “continuous” the emission 

limitations the states chose to include. Because the emission 

limitations in the called SIPs are not continuous, Petitioners’ 

challenges fail. 

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10 

Start with the text. In the Clean Air Act, Congress 

specified what constitutes an emission limitation. An 

emission limitation is “a requirement” that “limits the 

quantity, rate, or concentration of emissions of air pollutants 

on a continuous basis.” 42 U.S.C. § 7602(k). Recognizing 

the myriad methods by which a state might limit emissions—

from numerical caps to work practice standards to 

technological controls—Congress defined “emission 

limitations” expansively. The statutory definition “includ[es] 

any requirement relating to the operation or maintenance of a 

source” as well as “any design, equipment, work practice or 

operational standard....” Id.

Importantly for our purposes, the Clean Air Act demands 

that, whatever of those various forms it takes, a limitation on 

“the quantity, rate, or concentration of emissions of air 

pollutants” must operate “on a continuous basis,” id.; that is, 

an emission limitation must apply at all times. As EPA 

explained, “the word ‘continuous’ is not separately defined in 

the Act,” but “its plain and unambiguous meaning is 

‘uninterrupted.’” 80 Fed. Reg. at 33,901/1; WEBSTER’S 

THIRD NEW INTERNATIONAL DICTIONARY 493-94 (Phillip 

Babcock ed. 1976) (“operated without interruption”). An 

emission limitation is not continuous if it “provides for any 

period of time when a source is not subject to any requirement 

that limits emissions.” 80 Fed. Reg. at 33,901/1-2. That 

continuity requirement helps protect our nation’s air quality. 

As Congress emphasized when amending the Clean Air Act, 

“[w]ithout an enforceable emission limitation which will be 

complied with at all times, there can be no assurance that 

ambient standards will be attained and maintained.” H.R.

REP. NO. 95-294, at 92 (1977) (emphasis added). 

Against that backdrop, we have interpreted the Clean Air 

Act’s requirement of “continuous” emission limitations to 

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11 

mean that some emission limitation or standard must apply at 

all times. In Sierra Club v. EPA, 551 F.3d 1019 (D.C. Cir. 

2008), we considered a decision by EPA to exempt SSM 

events from compliance with hazardous air pollutant 

standards under section 112 of the Clean Air Act. Id. at 1026. 

We there read section 112, requiring EPA to establish 

emission standards for hazardous air pollutants, alongside 

section 302(k), requiring emission limitations and standards to 

apply “on a continuous basis,” 42 U.S.C. § 7602(k). Sierra 

Club, 551 F.3d at 1027. Interpreting those provisions 

together, we concluded that “Congress has required that there 

must be continuous section 112-compliant standards” and that 

“the SSM exemption violate[d]” that requirement. Id. at 

1027-28. 

Sierra Club’s logic applies with equal force here. In the 

Clean Air Act, Congress required that emission limitations 

included in SIPs be continuous. SSM exemptions violate that 

requirement. The majority attempts to distinguish Sierra 

Club, claiming it does not answer the question the majority 

injects into this case: that is, whether the Clean Air Act 

requires any emission limitations whatsoever in SIPs. See 

Maj. Op. 41-42. That is simply beside the point, because all 

parties before us agreed that the SIPs at issue here do include 

emission limitations. See infra at 20-21. And Sierra Club 

instructs that when SIPs do include emission limitations those 

limitations must be continuous. 551 F.3d at 1027-28. In 

other words, when emission limitations are used, there is no 

option to exempt SSM periods altogether. 

Other circuits have likewise accepted EPA’s 

interpretation that emission limitations must apply 

continuously, including during startup, shutdown, and 

malfunction. In Mont. Sulphur & Chem. Co. v. EPA, 666 

F.3d 1174 (9th Cir. 2012), the Ninth Circuit held that EPA, 

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12 

when promulgating a federal implementation plan to fill gaps 

in a state SIP, “reasonably interpreted the Clean Air Act to 

require continuous limits on emissions,” including during 

SSM events. Id. at 1193; see also Kamp v. Hernandez, 752 

F.2d 1444, 1452-53 (9th Cir. 1985). The Sixth and Tenth 

Circuits, too, have upheld as reasonable EPA’s longstanding 

interpretation of the Clean Air Act to bar SSM exemptions 

from emission limitations. See Mich. Dep’t of Env’t Quality 

v. Browner, 230 F.3d 181, 183-86 (6th Cir. 2000); Ariz. Pub. 

Serv. Co. v. EPA, 562 F.3d 1116, 1129 (10th Cir. 2009). 

In short, there can be little doubt that emission 

limitations, wherever used, must apply continuously. And 

Petitioners do not argue that EPA’s initial approval of a SIP, 

in the earliest days of its statutory role in doing so, should 

estop the agency from calling the SIPs to fix any legal 

deficiencies in such a plan. That then leaves the question 

whether the SSM provisions at issue in these SIP calls—

namely, automatic exemptions, director’s discretion 

provisions, and affirmative defenses—disrupt that continuity. 

EPA correctly found that they do. 

1. Automatic exemptions violate the Act’s requirement 

that emission limitations be continuous. Such provisions 

exempt sources from compliance with emission limitations 

during SSM events or other modes of operation, such that any 

excess emissions are not considered violations of the emission 

limitation. Take West Virginia’s SIP as an example. West 

Virginia provides that limitations on visible emissions “shall 

apply at all times except in periods of start-ups, shutdowns 

and malfunctions.” W. VA. CODE R. § 45-2-9.1. West 

Virginia’s emission limitations thus apply continuously except

during SSM periods. Such carve-outs run afoul of Congress’s 

requirement for continuous emission limitations under section 

7602(k). As in Sierra Club, those automatic exemptions 

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13 

mean that no Clean Air Act-compliant standard governs 

periods of startup, shutdown, and malfunction—i.e., there is 

no continuously applicable emission limitation. See 551 F.3d 

at 1027-28. 

Petitioners claim that, even if the Act requires 

continuously applicable emission limitations, “general duty” 

provisions in SIPs remedy any discontinuity because a general 

duty applies to all periods of source operation. See Indus. Br. 

38-40; State Br. 22-24. General duty provisions require, for 

example, sources to “minimize emissions,” to “use good 

engineering judgment at all times,” to avoid “improperly 

operating or maintaining facilities,” or to avoid “caus[ing] a 

violation of the NAAQS at any time.” 80 Fed. Reg. at 

33,889/3-90/1, 33,903/1. We have held that such general duty 

provisions fail to satisfy the Clean Air Act’s requirement for 

continuous emission standards. See Sierra Club, 551 F.3d at 

1027-28. 

Much as in Sierra Club, the generic general duty 

provisions in the SIPs called by EPA do not meet the Act’s 

requirement for continuous emission limitations. For one, 

where general duty provisions “are not clearly part of or 

explicitly cross-referenced in a SIP emission limitation,” they 

“cannot be viewed as a component of a continuous emission 

limitation.” 80 Fed. Reg. at 33,890/1. And, absent any clear 

indication that general duty provisions are part of a 

continuous emission limitation, they may not be enforceable 

by EPA or citizens. Cf. McEvoy v. IEI Barge Servs., Inc., 622 

F.3d 671, 678 (7th Cir. 2010) (concluding that an Illinois SIP 

provision amounting to a “commandment ‘thou shall not 

pollute’” could not be enforced through the CAA’s citizensuit provision); 80 Fed. Reg. at 33,903-904.

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Moreover, some of the states’ general duty provisions fail 

to meet the Act’s “applicable stringency requirements for 

th[e] type of SIP provision” at issue. 80 Fed. Reg. at 

33,890/1; see id. at 33,904/1; cf. Sierra Club, 551 F.3d at 

1027-28. For example, a generic general duty provision may 

not satisfy the Act’s requirement that stationary sources in 

nonattainment areas use “reasonably available control 

technology,” 42 U.S.C. § 7502(c)(1), that certain sources in 

attainment areas use “best available control technology,” id. 

§ 7475(a)(4), or that certain older sources use “best available 

retrofit technology” as part of the regional haze program, id. 

§ 7491(b)(2)(A). 

For those reasons, EPA rightly determined that the 

generic general duty provisions in the called SIPs “do not 

meet applicable stringency requirements, are not clearly part 

of the emission limitations in the SIP-called provisions, and 

are likely not legally and/or practically enforceable.” EPA 

Br. 69; see 80 Fed. Reg. at 33,903/2-04/2. As such, those 

general duty provisions do not “legitimize exemptions for 

emissions during SSM events” from otherwise-applicable 

emission limitations. 80 Fed. Reg. at 33,890/1. 

2. Automatic exemptions are not the only SIP provisions 

that violate the continuity requirement. So do director’s 

discretion provisions. They allow state air agency personnel 

to make “unilateral decisions on an ad hoc basis” to excuse 

compliance with emission limitations, “up to and including 

the granting of complete exemptions for emissions during 

SSM events.” Id. at 33,917/2. The exercise of a director’s 

discretion thereby has the effect of removing the otherwiseapplicable emission limitation during the SSM event. Just as 

a state cannot automatically exempt SSM emissions from 

emission limitations, it cannot authorize a director’s 

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insufficiently bounded, ad hoc exercise of discretion to do so. 

See id. 

Director’s discretion provisions have another defect: 

They interfere with EPA and citizen enforcement. “[B]y 

granting exemptions for emissions that should be treated as 

violations of the applicable SIP emission limitations,” 

director’s discretion “provisions functionally allow the air 

agency to impose its own enforcement discretion decisions on 

the EPA and other parties.” Id. at 33,917/3. Such provisions 

thus interfere with federal and citizen enforcement of the Act. 

See 42 U.S.C. §§ 7413 (federal enforcement), 7604 (citizen 

enforcement). In that way, director’s discretion provisions 

cannot be squared with the Clean Air Act’s various 

enforcement requirements, including that SIPs generally 

provide for enforcement, see id. § 7410(a)(1), that emission 

limitations be “enforceable,” id. § 7410(a)(2)(A), and that 

SIPs “include a program to provide for the enforcement” of 

their emission limitations, id. § 7410(a)(2)(C). 

3. Last are the SIPs’ affirmative defense provisions. As 

the majority recognizes, some affirmative defenses 

functionally “create an exemption from the normal emission 

rule.” Maj. Op. 64. Therefore, like any other SSM 

exemption, they disrupt an emission limitation’s continuity. 

That discontinuity suffices to justify the SIP Calls for the 

handful of affirmative defense provisions as to which my 

colleagues grant the petitions. 

But there is another reason why EPA correctly called all 

SIPs containing affirmative defenses for SSM events. 

Affirmative defenses interfere with the Act’s enforcement 

structure no matter “what forms of remedy they purport to 

limit or eliminate,” 80 Fed. Reg. at 33,851/3—not just, as the 

majority holds, when they “preclude[] certain remedies” such 

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as civil penalties, Maj. Op. 64. Here is why. The Clean Air 

Act gives federal district courts jurisdiction over EPA 

enforcement actions, 42 U.S.C. § 7413(b), and citizen suits, 

id. § 7604(a), that claim violations of a SIP’s emission 

limitations or standards. Congress vested in the courts the 

authority both “to determine liability” and “to impose 

remedies of various kinds,” including but not limited to civil 

penalties. 80 Fed. Reg. at 33,851/3; see 42 U.S.C. 

§§ 7413(b), (e), 7604(a). That “grant of jurisdiction comes 

directly from Congress,” and EPA is not, nor are the states, 

“authorized to alter or eliminate” it. 80 Fed. Reg. at 33,851/3. 

By including affirmative defense provisions for SSM 

exemptions in their SIPs, states attempt to restrict federal 

courts’ jurisdiction to hold violators liable and fashion 

remedies for noncompliance with emission limitations. Id. at 

33,851/3-52/1. Such defenses usurp the role that Congress 

reserved for courts in the Clean Air Act and so cannot stand. 

See NRDC v. EPA, 749 F.3d 1055, 1062-64 (D.C. Cir. 2014). 

 In short, Petitioners’ challenges to EPA’s SIP Calls of 

automatic exemptions, director’s discretion provisions, and 

affirmative defenses lack merit. Because our review is 

generally confined to the issues presented by the parties, that 

should suffice for this court to deny the petitions in full. 

B.

My colleagues never reach the questions presented by 

Petitioners because, in their view, EPA failed to make a 

“predicate ‘necessary or appropriate’ finding” that they deem 

“required” by the Clean Air Act. Maj. Op. 55. In so holding, 

the majority disposes of the case on an unbriefed theory that 

depends on a blinkered reading of the record. 

My colleagues vacate the SIP Calls because EPA “merely 

reasoned” that emission limitations must be continuous, 

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17 

“without explaining why that continuity is ‘necessary or 

appropriate’ to meet any of the CAA’s requirements.” Maj. 

Op. 56. Their holding hangs on a distinctive reading of the 

Clean Air Act’s section 7410(a)(2)(A). Recall the terms of 

that provision: It instructs that each implementation plan 

shall “include enforceable emission limitations and other 

control measures, means, or techniques (including economic 

incentives such as fees, marketable permits, and auctions of 

emissions rights), as well as schedules and timetables for 

compliance, as may be necessary or appropriate to meet the 

applicable requirements” of the Act. 42 U.S.C. § 

7410(a)(2)(A). The majority says the “necessary or 

appropriate” proviso prevents EPA from faulting the 

discontinuity of a SIP’s emission limitations until it deems it 

at least appropriate to treat them as “enforceable emission 

limitations”—rather than, say, “other control measures, 

means, or techniques.” See Maj. Op. 36, 42. 

But the Petitioners never argued before us that EPA 

needed to make—let alone that it did not make—a predicate 

“necessary or appropriate” determination before accepting 

Petitioners’ own labeling of the subject emission controls as 

“emission limitations.” See generally Indus. Br. 36-60; States 

Br. 22-38. In fact, the Petitioners took issue with the SIP 

Calls in part on the ground that it is up to states when they 

fashion the SIPs, not EPA, to decide what is “necessary or 

appropriate.” See States Br. 4-5; Indus. Br. 21, 36. Likewise, 

the Petitioners do not dispute that the assertedly discontinuous 

control measures subject to these SIP Calls were included in 

SIPs because states believed them “necessary or appropriate” 

for Clean Air Act compliance, and EPA approved them as 

such (albeit in approvals it now says overlooked unlawful 

discontinuities). To the contrary, Petitioners fault EPA for 

“overruling state decisions” about the measures necessary or 

appropriate to comply with the Act. Indus. Br. 20; see States 

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Br. 4-5. The majority’s reliance on the fact that EPA 

“nowhere disputes” that emission limitations are required 

only as “necessary or appropriate,” Maj. Op. 44, is startling 

given that the Petitioners did not argue as much before us. 

The sentence my colleagues quote from the Industry 

Petitioners’ brief as “exactly” making their argument, Maj. 

Op. 59 (quoting Ind. Pet. Br. 49), in fact disputes only EPA’s 

understanding of the continuity requirement. It appears under 

the header “EPA’s Prohibition on So-Called ‘Exemptions’ 

from Emission Limitations Is Not Supported,” Ind. Pet. Br. 

36, where Industry Petitioners argue against EPA’s view of 

the “so-called exemptions,” Ind. Pet. Br. 36-52. Only the 

majority doubts the characterization of the subject SIP 

provisions as (so called) emission limitations per section 

7602(k). 

To be sure, the Industry Petitioners (but not the states) at 

times argued that SSM exemptions were permissible because 

a state could determine that emission limitations were only 

“necessary or appropriate” for particular periods of source 

operation. Indus. Br. 36, 51. They assert that the “necessary 

or appropriate” language gives states discretion to decide that 

an emission limitation will apply only to steady-state 

operation and not to SSM periods. Indus. Br. 49, 51. Under 

that reading, an emission limitation meets the Clean Air Act’s 

requirements if it is “‘continuous’ over some period of time or 

condition,” even if “not necessarily [over] all periods of 

time.” Indus. Br. 42. In short, Industry Petitioners assume 

that the SIPs at issue include emission limitations within the 

meaning of the Act but argue that the challenged SSM 

exemptions permissibly apply because the Act empowers the 

states to decide that fully continuous application is not 

“necessary or appropriate.” Indus. Br. 49.

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All Industry Petitioners argued, then, is that the 

“necessary or appropriate” clause justifies exemptions to 

emission limitations—not that the SIPs might not even, 

technically speaking, include emission limitations at all, see 

Maj. Op. 35-38, nor that EPA needed to determine that 

continuous emission limitations were necessary or appropriate 

before calling the SIPs, see Maj. Op. 48-49. At core, Industry 

Petitioners fought the definition of an emission limitation as 

“continuous” and our construction of that definition in Sierra 

Club, 551 F.3d at 1026-28, not the reality that the SIPs at 

issue do include “emission limitations” that must comply with 

the Act’s definition. 

For us to rule for Industry Petitioners on that theory, we 

would therefore have needed to conclude first that Sierra 

Club was wrong or somehow did not apply. The majority 

instead eschews interpreting the continuity requirement and 

pivots to even more fundamental (and unbriefed) questions: 

must SIPs contain “emission limitations” at all, and must we 

presume they do not unless EPA has made a predicate 

determination that it is “necessary or appropriate” for a 

measure to qualify as an “emission standard”? See Maj. Op. 

34. 

To answer that question the majority deploys a novel 

reading of the Clean Air Act, concluding that a SIP must 

include “emission limitations” only to the extent “necessary 

or appropriate to meet the applicable requirements” of the 

Clean Air Act. Maj. Op. 7-8 (quoting 42 U.S.C. 

§ 7410(a)(2)(A)). Relying on this new reading of section 

7410, my colleagues conclude that, in the absence of an 

explicit EPA categorization of challenged provisions as 

“emission limitations,” we should presume the SIPs at issue 

here do not contain emission limitations at all. Their reading 

seems to require EPA to make a “predicate finding” as to any

USCA Case #15-1271 Document #2043030 Filed: 03/01/2024 Page 87 of 96
20 

SIP provision that it is “necessary or appropriate” to treat it as 

what a state says it is—as opposed to some other measure or 

means—before a court may so treat it. Maj. Op. 36. Consider 

a SIP that transparently announces what appears to be a 

schedule or timetable for compliance as contemplated by 

section 7410. 42 U.S.C. § 7410(a)(2)(A). On the majority’s 

logic, may we no longer take a SIP at its word and treat its 

compliance deadlines and timeframes as “enforceable” 

“schedule[s] and timetable[s] of compliance” under the Act, 

42 U.S.C. § 7602(p), unless EPA finds it “appropriate” or 

“necessary” that the timing requirements be so treated? 

 More to the point, the Petitioners do not dispute that the 

SIPs at issue needed to, and appropriately do, include 

“emission limitations.” Indeed, the states have repeatedly told 

us that their SIPs do contain emission limitations as 

contemplated by the Clean Air Act: 

 In their briefing the states refer to the disputed 

emission limitations as “emission limitations.” See, 

e.g., States Br. 24-29; States Reply Br. 1, 8, 11-12. 

Industry Petitioners even describe the provisions 

subject to the disputed SSM carveouts as “numerical” 

or “numeric emission limitation[s].” Ind. Pet. Br. 37. 

That quantitative descriptor highlights that the 

referenced “emission limitations” are indeed limits on 

the “quantity, rate, or concentration of emissions” 

within the meaning of section 7602(k), and so subject 

to its continuity requirement. 

 In their comments on the SIP Calls the states refer to 

the disputed emission limitations as “emission 

limitations.” See, e.g., Comment of Ohio (J.A. 529-

30) (explaining that Ohio has never taken the position 

that excess emissions are not violations of emission 

limitations); Comment of Georgia (J.A. 575-76) 

USCA Case #15-1271 Document #2043030 Filed: 03/01/2024 Page 88 of 96
21 

(“EPA’s proposal if finalized would likely require that 

Georgia evaluate all of the emission limitations in 

Georgia Rule 391-3-1-.02 . . . .”); Comment of 

Delaware (J.A. 600) (“As such, Delaware’s SIP 

provides for continuous limits; at no time does 

Delaware’s SIP provide for any unit to be ‘exempted’ 

from being covered by an emission limitation.”); 

Comment of West Virginia (J.A. 630) (“Emissions 

that occur during SSM must be subject to a continuous 

limitation, and emissions that occur during regular 

operations may be subject to a different, but also 

continuously applied, limitation.”); Comment of 

Florida (J.A. 746) (“Florida’s rule establishes 

enforceable, alternative emissions limitations and 

measures such that an emission limitation applies 

continuously . . . .”). 

 Even in the enacted SIPs themselves the states refer to 

the disputed emission limitations as “emission 

limitations.” See e.g., S.C. CODE ANN. REGS. 61-62.1 

§§ I(29), V(A) (2016) (explaining that the state 

developed its implementation plan “to provide 

enforceable emission limitations” and that an emission 

limitation “limits the quantity, rate, or concentration of 

emissions of air pollutants on a continuous basis”); 

118-01-19 ARK. CODE. R. § 602 (2022) (providing an 

affirmative defense for exceedances of “emission 

limitation[s]” during emergency conditions); LA.

ADMIN. CODE tit. 33, pt. III, § 103(A) (2023) 

(directing that the SIP’s “emission limitations apply to 

any source of emissions existing partially or wholly 

within the state of Louisiana”). 

There is thus every indication that the states, in submitting 

SIPs to fulfill their legal obligations under the Clean Air Act, 

intended to include “‘emission limitation[s]’ as defined by the 

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CAA.” Maj. Op. 53 (emphasis added). And there is every 

indication the Petitioners are defending those emission 

limitations’ compliance with the Act’s requirement that they 

be continuous. Why not take them at their word? 

 The majority sidesteps those admissions to posit that the 

Clean Air Act could allow for a SIP that contains various 

emission control measures, “none of which satisf[ies] the 

CAA’s definition of ‘emission limitation.’” Maj. Op. 37. 

Assuming the text may be so read, the permissibility of that 

hypothetical is beside the point. As EPA explained at 

argument, “if [a] state[] were to bring a plan to EPA that 

contained just control measures and not emission limitations 

and said that [it] me[t] the requirements of the Clean Air Act, 

then EPA could assess that plan.” Oral Arg. Tr. 68:14-17. 

But here, states “picked emission limitation[s] as one element 

of their plan[s].” Oral Arg. Tr. 68:18-19. That choice is 

reason enough to treat the SIPs under review as containing 

“emission limitations” within the meaning of the Act. 

Moreover, the majority provides no indication (nor is 

there any, as far as I can tell) that any state has ever—in the 

more than fifty years of the Clean Air Act’s existence—

submitted and received approval for a SIP without provisions 

that appear to be (and have been treated as) “emission 

limitations.” That is no accident. Emission limitations are at 

the heart of a state’s responsibilities to reduce emissions 

pursuant to the Clean Air Act. In assigning to the states 

certain responsibilities under the Act, Congress sought to 

ensure that “[e]ach source’s prescribed emission limitation” 

would be “the fundamental tool for assuring that ambient 

standards are attained and maintained.” H.R. REP. NO. 95-

294, at 92. 

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Whatever the case for statutory permissibility of a 

hypothetical SIP devoid of emission limitations, there is 

certainly no basis for concluding that the challenged SIP 

provisions in this case were simply not emission limitations at 

all, nor have the Petitioners so argued. Yet that conclusion is 

the linchpin of the majority’s call for a re-do. 

It makes sense that these state plans, first formulated in 

the early 1970s, all do include “emissions limitations” within 

the meaning of the Clean Air Act. Before the 1990 

amendment of the Act, an earlier version of section 7410 

(then codified at 42 U.S.C. § 1857c-5) instructed that state 

plans shall “include[] emission limitations, schedules, and 

timetables for compliance with such limitations, and such 

other measures as may be necessary . . . .”—a formulation 

that courts read to require “emission limitations.” See 

Kennecott Copper Corp. v. Train, 526 F.2d 1149, 1153-54 

(9th Cir. 1975) (quoting 42 U.S.C. § 1857c-5(a)(2)(B) 

(1970)); see id. at 1153-56 (collecting cases). It was not until 

Congress amended that provision in 1990 that it added “or 

appropriate” and changed the syntax to the current version, on 

which the majority depends for its holding that “emission 

limitations” are optional unless EPA deems them “necessary 

or appropriate.” Given the pre-1990 origins of the relevant 

emission-control measures in the SIPs (and the challenged 

loopholes), it is no wonder that every one of the petitioning 

states treats them as “emission limitations.” 

The states proffered and EPA accepted SIPs that 

purported to include “emission limitations” as defined by the 

Clean Air Act. See 80 Fed. Reg. at 33,902/2. Petitioners seek 

to defend them as “emission limitations” that meet the 

requirement of “continuous emission reduction.” It is entirely 

unsurprising that EPA “never wholeheartedly embraces” my 

emphasis on the states’ own consistent description of the 

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24 

relevant SIP provisions as “emissions limitations.” Maj. Op. 

52; see id. 25. The Petitions never said they were anything 

else. 

Our judicial role is as “neutral arbiter[s] of matters the 

parties present.” United States v. Sineneng-Smith, 140 S. Ct. 

1575, 1579 (2020) (quoting Greenlaw v. United States, 554 

U.S. 237, 243 (2008)). In our adversarial system, “we rely on 

the parties to frame the issues for decision.” Id. (quoting 

Greenlaw, 554 U.S. at 243). So, our “well-established” rule 

is that “we do not consider arguments not presented to us,” 

Diamond Walnut Growers, Inc. v. NLRB, 113 F.3d 1259, 

1263 (D.C. Cir. 1997) (en banc), even if those arguments can 

be supported by citations to the administrative record, see 

NRDC v. EPA, 25 F.3d 1063, 1071 n.4 (D.C. Cir. 1994). And 

we are especially reluctant to consider unbriefed or 

inadequately briefed arguments where they raise “important 

questions of far-reaching significance,” Carducci v. Regan, 

714 F.2d 171, 177 (D.C. Cir. 1983) (quoting Ala. Power Co. 

v. Gorsuch, 672 F.2d 1, 7 (D.C. Cir. 1982)), or implicate a 

complex regulatory scheme, see Time Warner Ent. Co., L.P. 

v. FCC, 56 F.3d 151, 202 (D.C. Cir. 1995). Every reason 

calls for restraint. 

 Today’s decision well illustrates why we ordinarily stick 

to what the parties have argued. Without the benefit of the 

parties’ presentation, it is difficult to say just how wrong or 

damaging the majority opinion might be. What I can say is 

that my colleagues unearth—and, in some cases, answer—a 

host of questions that were not raised in the briefing and that 

we had never resolved before today. 

 Here is the strange upshot of the majority’s interpretation 

of section 7410(a)(2)(A): Provisions that otherwise look like 

and are treated as emission limitations are reviewed as “other 

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control measures,” undefined under the Act, precisely 

because they are discontinuous. See Maj. Op. 37. Under that 

logic, a flawed emission limitation is simply no emission 

limitation at all and so the continuity question that was briefed 

and argued in this case just goes away. For the majority, it 

does not matter whether the called SIPs lack continuous 

protection against harmful emissions, because if the emission 

limitations in the SIPs were actually just “other control 

measures,” the statute does not require them to apply 

continuously. 

 But it is not evident that emission limitations and “other 

control measures” are interchangeable but for the requisite 

continuity of the former, and we lack the benefit of briefing 

on the matter to determine the boundaries of either. In the 

Clean Air Act, Congress gave examples of “other control 

measures, means, or techniques”—namely, “economic 

incentives such as fees, marketable permits, and auctions of 

emissions rights.” 42 U.S.C. § 7410(a)(2)(A). In so doing, 

Congress illustrated the kinds of “other control measures” it 

had in mind. They stand in contrast to an emission limitation, 

“which limits the quantity, rate, or concentration of emissions 

of air pollutants on a continuous basis, including . . . any 

design, equipment, work practice or operational standard 

promulgated under this chapter.” Id. § 7602(k). Indeed, to 

the extent “other” measures are ways of harnessing market 

power to make underlying emission limitations more efficient, 

they seem to presuppose “emission limitations” as a distinct 

but complementary counterpart. 

C. 

Cabining the reach of its holding, the majority notes that, 

going forward, EPA may ensure that states’ pollution 

restrictions are “enforceable emission limitations” for 

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26 

purposes of a SIP by making a predicate “necessary or 

appropriate” finding to that effect. Maj. Op. 37-38, 40, 55. 

Never mind that Petitioners did not argue that the Clean Air 

Act imposes any such predicate, nor did they object that 

provisions in the SIPs failed to meet it. 

In so doing, the majority surmises both who must make a 

necessary-or-appropriate determination (EPA, say my 

colleagues) and when (before calling the SIPs, they say). 

Remember, though, that section 7410(a)(2) describes what 

“[e]ach implementation plan submitted by a State” shall 

include. 42 U.S.C. § 7410(a)(2) (emphasis added). It thus 

appears—as the Petitioners themselves argued—that 

Congress called on the states to determine in the first instance 

what measures they believe are “necessary or appropriate,” 

subject to EPA approval. See Indus. Br. 53; States Br. 4-5.

Perplexingly, though, it is not enough for the majority that the 

states that proffered the SIPs, and EPA when initially 

approving them, concluded that emission limitations are at the 

very least appropriate to comply with the Act. See 80 Fed. 

Reg. at 33,902/2-3. The fact that EPA simultaneously 

approved SSM exemptions, see Maj. Op. 50–51, shows only 

that a newly created EPA was rushing to approve the SIPs on 

too tight a timeline—not that the challenged SIP provisions 

were simply not “emission limitations” at all. 

D. 

 In short, if anyone has manufactured a “semantic ‘gotcha’ 

game,” Maj. Op. 53, it is the majority. According to my 

colleagues, an emission reduction measure that is a “design, 

equipment, work practice or operational standard” that “limits 

the quantity, rate, or concentration of emissions of air 

pollutants,” 42 U.S.C. § 7602(k), that a state labeled an 

“emission limitation” and submitted to EPA to show how it 

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27 

planned to meet the Act’s requirements, that EPA then 

approved as an appropriate way for the state to do what the 

Act necessitates, 80 Fed. Reg. at 33,902/2-3, and that states, 

industry, and EPA all have for decades treated as an emission 

limitation, might not be an emission limitation after all. That 

cannot be right. If it looks like a duck, swims like a duck, and 

quacks like a duck, then it probably is a duck. 

While I believe the majority erred, it helps that its core 

holding is limited. Presumably EPA can re-issue the vacated 

SIP Calls. My colleagues tell the agency simply to show that 

continuous emission limitations are “necessary”—or even just 

“appropriate”—to meet Clean Air Act requirements. That is a 

low bar. No factual showing would necessarily be required. 

See Maj. Op. 14-25. And EPA’s insistence that emission 

limitations operate continuously would simply reiterate its 

longstanding policy, beginning in 1977, that SSM exemptions 

are inconsistent with the Clean Air Act. See J.A. 125. It 

might even be enough for EPA to point out that the called 

SIPs are ambiguous as to whether they do contain “emission 

limitations.” See Maj. Op. 27-28. What is more, nothing in 

today’s decision forecloses EPA from calling SIPs because 

they contain emission limitations that are discontinuous due to 

SSM exemptions, see Maj. Op. 34, or fail to include measures 

that meet the statutory definition of emission limitations, see 

Maj. Op. 37, or interfere with the Clean Air Act’s 

enforcement scheme, see Maj. Op. 39, or interfere with EPA’s 

ability to predict compliance with the Act, see id. The court’s 

opinion also does not categorically preclude EPA, going 

forward, from pointing to its initial approval of SIP provisions 

to establish that those provisions were “necessary or 

appropriate” to meet Clean Air Act requirements. See Maj. 

Op. 55-56. 

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28 

So, while the majority goes down a path that it never 

should have considered, resulting in more years of delay in 

controlling harmful emissions, the fallout may be more 

contained than it appears at first glance. 

* * * 

 In brief, EPA correctly called SIPs for containing SSM 

provisions that violated the Clean Air Act’s requirement of 

continuous emission limitations. This court should have 

acknowledged that the states appropriately included emission 

limitations in their SIPs, the Act says an emission limitation 

must be continuous, and the SIP provisions rendering them 

discontinuous necessitated EPA’s SIP Calls. My colleagues 

provide no practical reason to doubt that the continuous 

applicability of the SIPs’ emission rules is indeed “necessary 

or appropriate.” Yet the majority assigns to EPA a procedural 

step it claims was missed: What everyone refers to as 

emission limitations should not be treated as such under the 

Act unless EPA first finds that it was “necessary or 

appropriate” that they were included as “emission limitations” 

in the SIPs. In vacating EPA’s SIP Calls on that ground, the 

majority strays from the briefing, from our circumscribed 

judicial role, and from the mandates of the Clean Air Act. On 

these issues only, I respectfully dissent. 

USCA Case #15-1271 Document #2043030 Filed: 03/01/2024 Page 96 of 96