United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued October 24, 2013 Decided April 18, 2014

No. 10-1371

NATURAL RESOURCES DEFENSE COUNCIL,

PETITIONER

v.

ENVIRONMENTAL PROTECTION AGENCY AND GINA 

MCCARTHY, IN HER OFFICIAL CAPACITY AS ADMINISTRATOR,

U.S. ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENTS

CEMEX, INC., ET AL.,

INTERVENORS

Consolidated with 10-1378, 13-1112

On Petitions for Review of Final Actions of the 

United States Environmental Protection Agency

James S. Pew and Seth L. Johnson argued the causes for 

petitioners. With them on the briefs were John Walke, 

Meleah Geertsma, and Avinash Kar. 

Matthew R. Oakes, Attorney, U.S. Department of Justice, 

argued the cause for respondents. With him on the brief were 

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Robert G. Dreher, Acting Assistant Attorney General, and 

Steven E. Silverman, Attorney, U.S. Environmental Protection 

Agency. Daniel R. Dertke and T. Monique Peoples, 

Attorneys, U.S. Department of Justice, entered appearances.

Carter G. Phillips argued the cause for intervenors. With 

him on the briefs were Roger R. Martella Jr., Timothy K. 

Webster, Ryan C. Morris, William M. Bumpers, Debra J. 

Jezouit, Michael B. Schon, Deborah E. Jennings, Chet M. 

Thompson, Beth S. Ginsberg, Jason T. Morgan, Ashley C. 

Parrish, Cynthia A.M. Stroman, and Richard G. Stoll. 

Russell S. Frye and Richard G. Stoll were on the brief for 

amici curiae SSM Coalition, et al. in support of respondents.

Before: KAVANAUGH and SRINIVASAN, Circuit Judges, 

and EDWARDS, Senior Circuit Judge.

Opinion for the Court filed by Circuit Judge 

KAVANAUGH.

KAVANAUGH, Circuit Judge: Portland cement is the key 

ingredient in concrete. The basic process for making Portland 

cement is much the same today as it was when the material 

was first developed nearly 200 years ago. Cement 

manufacturers pulverize limestone and minerals, and then 

heat those raw materials to several thousand degrees. The 

resulting substance, called clinker, is then cooled and ground 

into a fine gray powder. This powder – called Portland 

cement – is later combined with sand, rocks, and water to 

make concrete. 

The grinding and heating involved in cement 

manufacturing has an unfortunate side effect: It releases into 

the air a number of hazardous air pollutants, most notably 

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mercury, hydrochloric acid, hydrocarbons, and particulate 

matter. This case concerns EPA’s efforts to develop rules 

under the Clean Air Act to limit emissions of those pollutants

from cement plants. 

In a previous decision, we considered EPA’s first attempt

to create emission standards for the cement industry, and we

found the agency’s action arbitrary and capricious. See

Portland Cement Association v. EPA, 665 F.3d 177 (D.C. Cir. 

2011). Following our ruling, EPA went back to the drawing 

board and developed the emission standards at issue here, the 

2013 Rule. 

Several environmental organizations, including the 

Natural Resources Defense Council and the Sierra Club, have 

petitioned for review of the 2013 Rule, arguing primarily that 

certain aspects of the Rule contravene the Clean Air Act. 

They also challenge EPA’s decision to create an affirmative 

defense for private civil suits in which plaintiffs sue sources 

of pollution and seek penalties for violations of emission 

standards. EPA’s affirmative defense would be available to 

defendants in cases where an “unavoidable” malfunction had 

resulted in impermissible levels of emissions. 

We conclude that the emissions-related provisions of 

EPA’s 2013 Rule are permissible but that the affirmative 

defense for private civil suits exceeds EPA’s statutory 

authority. We therefore grant the petitions in part and vacate 

the portion of the Rule pertaining to the affirmative defense. 

We deny the petitions in all other respects. 

I

Section 112 of the Clean Air Act, 42 U.S.C. § 7412, 

requires EPA to establish technology-based emission 

standards for major sources of certain hazardous air 

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pollutants. Emission standards must reflect “the maximum 

degree of reduction in emissions” that EPA determines is 

“achievable,” taking into consideration “the cost of achieving 

such emission reduction, and any non-air quality health and 

environmental impacts and energy requirements.” 42 U.S.C. 

§ 7412(d)(2). The resulting standards are commonly known 

as the “maximum achievable control technology,” or 

“MACT” standards. See National Lime Association v. EPA, 

233 F.3d 625, 630 (D.C. Cir. 2000).

EPA uses a two-step process for establishing MACT 

standards. The agency begins by setting a minimum 

stringency level, or “floor,” based on the results achieved by

the best-performing similar sources. See 42 U.S.C. 

§ 7412(d)(3). Once EPA sets the statutory floor, it then 

determines, considering cost and the other factors listed in 

Section 112(d)(2), whether a more restrictive standard is

“achievable,” and if so then adopts that standard. EPA calls

these stricter requirements “beyond-the-floor” standards. 

Sierra Club v. EPA, 479 F.3d 875, 877 (D.C. Cir. 2007).

When EPA sets an emission standard, it also determines a 

schedule for compliance with that standard. For existing 

sources, EPA must “provide for compliance as expeditiously 

as practicable, but in no event later than 3 years after the 

effective date” of the emission standard. 42 U.S.C. 

§ 7412(i)(3)(A). 

In 2010, pursuant to its Section 112 authority, EPA 

promulgated National Emission Standards for Hazardous Air 

Pollutants from the Portland Cement Manufacturing Industry 

and Standards of Performance for Portland Cement Plants, 75 

Fed. Reg. 54,970 (Sept. 9, 2010). That 2010 Rule set or 

revised emissions limits for mercury, hydrogen chloride, total 

hydrocarbons (a surrogate for organic hazardous air pollutants 

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such as benzene and formaldehyde), and particulate matter (a 

surrogate for certain non-mercury metals). Cement plants 

would be required to comply with the new standards 

beginning in September 2013. 75 Fed. Reg. at 54,993. 

In addition to establishing emission standards, the 2010 

Rule created an affirmative defense in private civil suits when

violations of the standards occurred because of “unavoidable” 

malfunctions. See id. at 54,993, 55,053. The affirmative 

defense replaced a previous EPA policy creating an 

exemption from emissions limitations during malfunction 

events. In a prior decision, this Court struck down that

exemption because it was inconsistent with the requirement 

that emission standards apply continuously. See Sierra Club 

v. EPA, 551 F.3d 1019, 1027-28 (D.C. Cir. 2008).

Industry groups petitioned this Court for review and we

found the 2010 Rule arbitrary and capricious and remanded to 

EPA. We ruled specifically that, in calculating the floor for 

MACT purposes, EPA had arbitrarily included in its dataset 

information from cement kilns properly classified as 

commercial incinerators, which are regulated under a separate

provision of the Act. See Portland Cement Association v. 

EPA, 665 F.3d 177, 186-89 (D.C. Cir. 2011).

In our 2011 decision, however, we did not vacate the 

emission standards set forth in the 2010 Rule or stay its 

implementation pending EPA’s reconsideration process, 

stating that “it is unlikely that significant changes will be 

made to the standards upon reconsideration.” Id. at 189. 

On remand, however, EPA made several relevant 

changes to the Portland cement emission standards. See

National Emission Standards for Hazardous Air Pollutants for 

the Portland Cement Manufacturing Industry and Standards of 

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Performance for Portland Cement Plants, 78 Fed. Reg. 10,006 

(Feb. 12, 2013) (the 2013 Rule).

First, consistent with our Portland Cement opinion, EPA 

revised its dataset to exclude commercial incinerators. When 

recalculated using the revised data, the maximum emissions 

level for particulate matter – the floor – was ultimately 

revised from 0.04 lb/ton to 0.07 lb/ton of clinker for existing 

kilns. See id. at 10,017-19. And EPA declined to re-adopt the 

more stringent, 0.04 lb/ton limit of the 2010 Rule as a 

beyond-the-floor standard. The agency reasoned that 

achieving that additional increment of particulate reduction 

would not be cost effective on a cost-per-ton basis. See id. at 

10,020-21.

Second, citing additional compliance strategies afforded

cement manufacturers by the revised particulate standard, 

EPA established a new compliance date of September 2015

for that standard. See id. at 10,014. EPA further concluded

that although the emissions limits for mercury, hydrochloric 

acid, and hydrocarbons remained the same as in the 2010 

Rule, the new September 2015 compliance date would also 

apply to those emission standards. According to EPA, 

coordinating the compliance date for particulate matter, 

mercury, hydrochloric acid, and hydrocarbons was essential

because the latter standards “all typically involve some 

element of [particulate matter] generation and capture and so 

the controls must be integrated with [particulate matter]

control strategies.” Id. at 10,022.

The 2013 Rule also retained the affirmative defense for 

private civil suits when the defendant violated emission 

standards due to an unavoidable malfunction. EPA explained 

that in its view, the affirmative defense was necessary to 

resolve a “tension” between the Clean Air Act’s requirement 

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that emission standards apply at all times and the fact that 

emission limits may sometimes be exceeded for reasons 

beyond the control of the source. See id. at 10,014.

NRDC, the Sierra Club, and other environmental 

organizations have petitioned for review of various aspects of 

the 2013 Rule. In Part II of this opinion, we address 

petitioners’ arguments regarding the emission standards for 

particulate matter. In Part III, we address petitioners’ 

challenge to the compliance schedule implementing some of 

the 2013 Rule’s emission standards. In Part IV, we consider

whether EPA’s decision to create the affirmative defense to

civil penalties for certain malfunction-related events exceeds 

the agency’s statutory authority.

II

We first consider petitioners’ challenges to the emission 

standards for particulate matter. 

A

The 2013 Rule ultimately set the emissions level for 

particulate matter at 0.07 lb/ton of clinker for existing kilns. 

The 2010 Rule had set the level at 0.04 lb/ton of clinker. 

Petitioners argue that the 2013 Rule weakens the particulate 

matter standard in violation of Section 112(d)(7) of the Clean 

Air Act, 42 U.S.C. § 7412(d)(7). That provision, titled “Other 

requirements preserved,” states:

No emission standard or other requirement 

promulgated under this section shall be interpreted, 

construed or applied to diminish or replace the 

requirements of a more stringent emission limitation

or other applicable requirement established pursuant to 

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section 7411 of this title, part C or D of this 

subchapter, or other authority of this chapter or a 

standard issued under State authority. 

(emphases added). Petitioners maintain that EPA violated 

Section 112(d)(7) because the 2013 Rule’s particulate matter

standards “diminish or replace” the more stringent standards 

in the 2010 Rule. 

EPA responds that such a reduction does not violate 

Section 112(d)(7). In EPA’s view, the most natural reading of 

Section 112(d)(7) is that “other authority” refers to authority 

other than Section 112 and other than the parts of the Clean 

Air Act specifically enumerated in Section 112(d)(7). Stated 

another way, EPA suggests that Section 112(d)(7) is simply a 

savings clause that makes clear that Section 112 does not 

supersede the requirements of other, more restrictive 

provisions of the Act. 

By contrast, petitioners say that “other authority” of the 

Act includes Section 112 itself, as well as other provisions in

the Act. Petitioners read the statute as an anti-backsliding

restriction on EPA’s ability to voluntarily reduce the 

stringency of any emission standard issued under Section 112. 

As EPA points out, however, when Congress has sought

to include that sort of anti-backsliding provision in the Clean 

Air Act, it has done so directly and explicitly. Cf., e.g., 42 

U.S.C. § 7410(l) (“The Administrator shall not approve a 

revision of a [State Implementation Plan] if the revision 

would interfere with any applicable requirement concerning 

attainment and reasonable further progress”); id. § 7502(e) 

(specifying pollution control requirements if “the 

Administrator relaxes a national primary ambient air quality 

standard”). Section 112(d)(7) contains no such language. 

Furthermore, EPA argues that petitioners’ interpretation of 

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Section 112(d)(7) would mean that any change to a rule 

issued under Section 112 – even a necessary change made just 

for technical reasons or because there was a calculation error 

– would be impermissible if the change made the standard 

less stringent. EPA says that it would be extraordinary if the 

statute precluded that kind of necessary change. 

In wading through this back-and-forth, we ultimately 

need not decide whether EPA’s reading is the better or only 

reading of this statutory provision, but simply whether it is a 

permissible reading. EPA administers the Clean Air Act, and

we must defer to its reasonable interpretation of any 

ambiguities in the statute. See Chevron U.S.A. Inc. v. NRDC, 

467 U.S. 837, 843-44 (1984). Here, even if the statute does 

not compel EPA’s reading, and indeed even if EPA’s reading 

is not the better reading, the statute at a minimum is 

sufficiently ambiguous on this point to permit EPA’s reading

of “other authority.” Because EPA’s reading is at least 

reasonable, we reject petitioners’ argument and rule for EPA 

at Chevron step two. 

B

Petitioners also contend that EPA should have set a more 

restrictive particulate matter standard when considering 

whether to set “beyond-the-floor” standards. Petitioners 

argue in particular that EPA misinterpreted the statute to 

allow it to consider cost-effectiveness when setting beyondthe-floor standards. 

Under Section 112(d), EPA must require “the maximum 

degree of reduction in emissions” that EPA determines is 

“achievable.” 42 U.S.C. § 7412(d)(2). To determine that 

emission level, EPA first establishes a minimum stringency 

level, or “floor,” based on the emission results achieved by 

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the best-performing sources in the category at issue. See id.

§ 7412(d)(3). Once EPA sets the statutory floor, it then 

determines, based on cost and the other factors listed in 

Section 112(d)(2), whether a more restrictive, beyond-thefloor standard is achievable.

1

 

When it promulgated the 2013 Rule, EPA rejected 

petitioners’ argument to set a 0.04 lb/ton limit as a beyondthe-floor standard. 78 Fed. Reg. at 10,020. EPA estimated 

that a beyond-the-floor standard set at the 0.04 lb/ton level 

would result in a reduction of 138 tons of particulate matter 

per year, at a cost of $37 million. Id. Based on those 

estimates, EPA noted that the cost-effectiveness of the 

potential beyond-the-floor standard – $268,000 per ton of 

particulate matter removed – was substantially lower than the 

cost-effectiveness of other emission standards previously 

rejected by EPA. See 78 Fed. Reg. at 10,021.

Petitioners take issue with EPA’s consideration of costeffectiveness as a component of the Section 112(d)(2) cost

analysis. Petitioners contend that “cost” for purposes of the 

statute only concerns whether “the standard is too expensive 

for industry to achieve,” in essence, whether the standards 

would bankrupt the industry. Pet’rs Br. 34. 

 1 In relevant part, the statute reads: “Emissions standards 

promulgated under this subsection and applicable to new or existing 

sources of hazardous air pollutants shall require the maximum 

degree of reduction in emissions of the hazardous air pollutants 

subject to this section (including a prohibition on such emissions, 

where achievable) that the Administrator, taking into consideration 

the cost of achieving such emission reduction, and any non-air 

quality health and environmental impacts and energy requirements, 

determines is achievable for new or existing sources in the category 

or subcategory . . . .” 42 U.S.C. § 7412(d)(2) (emphasis added).

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EPA says that Congress afforded it wide latitude in 

deciding how to balance cost and other considerations when 

determining that maximum achievable reduction in emissions. 

According to EPA, Section 112 does not command EPA to 

use a particular form of cost analysis. In taking cost into 

account, EPA contends that it may determine whether the 

proposed emission levels would be cost-effective. Indeed, 

EPA notes that this Court has previously recognized EPA’s 

authority to consider cost-effectiveness in setting standards 

under nearly identical provisions of the Clean Air Act. See, 

e.g., Husqvarna AB v. EPA, 254 F.3d 195, 200 (D.C. Cir. 

2001) (“Because section 213 does not mandate a specific 

method of cost analysis, we find reasonable the EPA’s choice 

to consider costs on the per ton of emissions removed 

basis.”); National Association of Clean Water Agencies v. 

EPA, 734 F.3d 1115, 1156-57 (D.C. Cir. 2013) (citing 

Husqvarna; EPA could consider cost-effectiveness in setting 

a beyond-the-floor standard under Section 129(a)(2) of the 

Act).

Again on this issue as with the first, we need not decide 

whether EPA’s reading is the only reading of this provision. 

Even if the statute does not compel EPA’s approach, and even 

if EPA’s reading is not the better reading, we conclude that it 

is still at least a reasonable reading given the various potential

meanings of “cost” in this context. Therefore, we reject 

petitioners’ argument that EPA was required to exclude 

consideration of cost-effectiveness and to set a beyond-thefloor standard of 0.04 lb/ton of clinker. 

III

Next, we consider petitioners’ claim that EPA acted 

unreasonably in setting a compliance date of September 2015 

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for the emission standards for particulate matter, mercury, 

hydrochloric acid, and hydrocarbons.

Under Section 112(i)(3)(A) of the Clean Air Act, EPA 

must require compliance with emission standards for existing 

sources “as expeditiously as practicable, but in no event later 

than 3 years after the effective date of such standard.” 42 

U.S.C. § 7412(i)(3)(A). Petitioners here contend that EPA 

violated this timing provision by “extending” the compliance 

deadline for the 2010 Rule from September 2013 to 

September 2015. 

As applied to the particulate matter standard, there is a

basic flaw in petitioners’ argument: The 2013 Rule did not 

simply “extend” the deadline for complying with the 2010 

Rule. Rather, the 2013 Rule established new particulate 

matter standards with a new effective date of February 2013, 

and a new compliance date of September 2015. EPA 

concluded that any earlier date of compliance would not be 

practicable because of the multi-year timeline for upgrading 

the technology necessary to ensure compliance. See 78 Fed. 

Reg. at 10,024. As we have ruled before, EPA may reset the 

compliance date for an emission standard when it introduces a 

new standard with a new effective date, as was the case for 

particulate matter in the 2013 Rule. See NRDC v. EPA, 489 

F.3d 1364 (D.C. Cir. 2007).

According to petitioners, even if EPA could change the 

compliance date for the particulate matter standard, the 

agency could not do the same for the mercury, hydrochloric 

acid, and hydrocarbon standards. The 2010 Rule set the 

emission levels for those pollutants, and the 2013 Rule did not 

alter the emission levels for those pollutants. This situation 

does indeed present a bit of a conundrum. On the one hand, 

we know under the terms of the statute that EPA has set a 

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compliance date of 2015 as the date that is as expeditious as 

practicable for particulate matter. On the other hand, our 

prior decision did not vacate the prior 2010 Rule, and the 

compliance date for the other pollutants as set forth in that 

Rule would otherwise be 2013.

This conundrum is resolved when one realizes that it 

would be irrational and even absurd to have different 

compliance dates for the different pollutants. EPA explained 

that the technology is such that it would be senseless to have 

different compliance dates. See 78 Fed. Reg. at 10,024. Even 

petitioners do not deny that the compliance date for all the 

pollutants should be the same. To be sure, they want 2013 not 

2015 as the compliance date. But they recognize the general 

undesirability of a compliance date of 2013 for some of the 

pollutants and of 2015 for other pollutants. See Tr. of Oral 

Argument at 10-11. Finally and perhaps most importantly, 

our prior decision in this case also recognized, at least 

implicitly, that there must be a single compliance date for all 

of the pollutants. See Portland Cement Association, 665 F.3d 

at 189. Our decision necessarily relied on an assumption that 

if EPA did not alter the level for any of the pollutants, the date 

would be 2013. But if EPA changed the level for one of the 

pollutants, the compliance date for all the pollutants would 

move together. Petitioners’ argument for a 2013 compliance 

date would be inconsistent with our prior decision.

In short, we reject petitioners’ argument about the 2015 

compliance date. 

IV

We next consider petitioners’ challenge to the affirmative 

defense that EPA created for cases of “unavoidable” 

malfunctions.

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Section 304(a) of the Clean Air Act, 42 U.S.C. § 7604(a), 

allows individuals to file citizen suits in federal district court 

against sources that violate emission standards. Under the 

law as originally enacted, a court could order only injunctive 

relief as a remedy for a violation. But as part of the 1990 

amendments to the Act, Congress expanded the citizen suit 

provision to give district courts authority to impose “any 

appropriate civil penalties,” which may include monetary 

penalties. 42 U.S.C. § 7604(a). 

In the 2010 Rule, EPA created an affirmative defense to 

Section 304(a) for certain emissions violations caused by 

“unavoidable” malfunctions. Under the affirmative defense, 

the district court may assess penalties only if violators “fail to 

meet [their] burden of proving all of the requirements in the 

affirmative defense.” 78 Fed. Reg. at 10,039. EPA retained 

the affirmative defense when it promulgated the 2013 Rule. 

See 40 C.F.R. § 63.1344. 

Petitioners now argue that the affirmative defense 

exceeds EPA’s statutory authority and that it is for the courts 

to decide whether to create an affirmative defense in these 

private civil suits, not EPA. We agree. 

The threshold question is whether petitioners have 

standing to challenge EPA’s adoption of the affirmative 

defense. Petitioners are environmental associations with 

individual members across the country. EPA’s affirmative 

defense would immunize certain emissions that petitioners

contend should be penalized. Some of petitioners’ members 

will suffer from those higher emissions, according to their 

affidavits. A ruling in their favor would prevent those 

emissions and help alleviate that harm. That’s good enough. 

Petitioners have shown injury-in-fact, causation, and 

redressability, and they thus have standing under Article III.

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We turn, then, to the substance of petitioners’ challenge

to the affirmative defense. 

Section 304(a) grants “any person” the right to 

“commence a civil action” against any person “who is alleged 

to have violated (if there is evidence that the alleged violation 

has been repeated) or to be in violation of” an emission 

standard or limitation under the Clean Air Act. 42 U.S.C. 

§ 7604(a). The statute further provides that the federal district 

courts “shall have jurisdiction, without regard to the amount 

in controversy or the citizenship of the parties, to enforce such 

an emission standard or limitation . . . and to apply any 

appropriate civil penalties.” Id. 

When determining whether civil penalties are 

appropriate, district courts look to Section 113(e)(1) of the 

Act, which directs courts to “take into consideration (in 

addition to such other factors as justice may require) the size 

of the business, the economic impact of the penalty on the 

business, the violator’s full compliance history and good faith 

efforts to comply, the duration of the violation as established 

by any credible evidence . . . , payment by the violator of

penalties previously assessed for the same violation, the 

economic benefit of noncompliance, and the seriousness of 

the violation.” 42 U.S.C. § 7413(e)(1). 

Section 304(a) creates a private right of action, and as the 

Supreme Court has explained, “the Judiciary, not any 

executive agency, determines ‘the scope’ – including the 

available remedies – ‘of judicial power vested by’ statutes 

establishing private rights of action.” City of Arlington v. 

FCC, 133 S. Ct. 1863, 1871 n.3 (2013) (emphasis added) 

(quoting Adams Fruit Co. v. Barrett, 494 U.S. 638, 650

(1990)). Section 304(a) is in keeping with that principle. By 

its terms, Section 304(a) clearly vests authority over private

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suits in the courts, not EPA. As the language of the statute 

makes clear, the courts determine, on a case-by-case basis, 

whether civil penalties are “appropriate.” By contrast, EPA’s 

ability to determine whether penalties should be assessed for 

Clean Air Act violations extends only to administrative 

penalties, not to civil penalties imposed by a court. See 42 

U.S.C. § 7413(d)(2)(B) (Administrator may “compromise, 

modify, or remit, with or without conditions, any 

administrative penalty”). To the extent that the Clean Air Act

contemplates a role for EPA in private civil suits, it is only as 

an intervenor. See id. § 7604(c)(2). EPA also of course could 

seek to participate as an amicus curiae. 

EPA argues that its proposed affirmative defense simply 

fleshes out the statutory requirement that penalties be applied 

only when “appropriate.” But under this statute, deciding

whether penalties are “appropriate” in a given private civil 

suit is a job for the courts, not for EPA. When a private suit is 

filed, the defendant can argue that penalties should not be 

assessed, based on the factors in Section 113(e)(1) such as the 

defendant’s “full compliance history and good faith efforts to 

comply.” Id. § 7413(e)(1). EPA can support that argument as 

intervenor or amicus, to the extent such status is deemed 

appropriate by the relevant court. But under the statutory 

scheme, the decision whether to accept the defendant’s 

argument is for the court in the first instance, not for EPA. 

EPA alternatively contends that it is permitted to create 

the affirmative defense because of Section 301(a)(1) of the 

Clean Air Act. See 78 Fed. Reg. at 10,014. That provision 

authorizes EPA’s Administrator to “prescribe such regulations 

as are necessary to carry out his functions under” the Act. 42 

U.S.C. § 7601(a)(1). But we have consistently held that 

EPA’s authority to issue ancillary regulations is not openended, particularly when there is statutory language on point. 

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See, e.g., American Petroleum Institute v. EPA, 52 F.3d 1113, 

1119 (D.C. Cir. 1995) (“the general grant of rulemaking

power to EPA cannot trump specific portions of the CAA”); 

NRDC v. Reilly, 976 F.2d 36, 41 (D.C. Cir. 1992) (EPA 

cannot use its general rulemaking authority as justification for 

adding to a statutorily specified list); Sierra Club v. EPA, 719 

F.2d 436, 453 (D.C. Cir. 1983) (same); see also Gonzales v. 

Oregon, 546 U.S. 243, 264-65 (2006) (“It would 

go . . . against the plain language of the text to treat a 

delegation for the ‘execution’ of [the Attorney General’s] 

functions as a further delegation to define other functions well 

beyond the statute’s specific grants of authority.”). Those 

precedents establish a simple and sensible rule: EPA cannot 

rely on its gap-filling authority to supplement the Clean Air 

Act’s provisions when Congress has not left the agency a gap 

to fill. So it is here. 

On a different tack, EPA notes that Section 304(a)(1) 

does not expressly deny EPA the ability to create an 

affirmative defense, and EPA emphasizes that this Court has 

frequently recognized the need for flexibility in the

administrative process. EPA Br. 46. That’s true. But the 

suggestion implicit in EPA’s argument – that we should 

“presume a delegation of power absent an express

withholding of such power” – is “plainly out of keeping with 

Chevron . . . .” Railway Labor Executives’ Association v. 

National Mediation Board, 29 F.3d 655, 671 (D.C. Cir. 1994) 

(en banc). 

Finally, EPA suggests that an affirmative defense for 

malfunctions is necessary to account for the tension between 

requirements that emissions limitations be “continuous” and 

the practical reality that control technology can fail 

unavoidably. See 78 Fed. Reg. at 10,014. That is a good 

argument for EPA to make to the courts – and for the courts 

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to then consider – in future civil cases when this issue arises. 

But it does not suffice to give EPA authority to create an 

affirmative defense.2 

* * *

We grant the petitions for review with regard to EPA’s 

affirmative defense and vacate those portions of the 2013 

Rule pertaining to the defense. We deny the petitions in all 

other respects.

So ordered. 

 2 The Fifth Circuit recently upheld EPA’s partial approval of 

an affirmative defense provision in a State Implementation Plan. 

See Luminant Generation Co. v. EPA, 714 F.3d 841 (5th Cir. 2013). 

We do not here confront the question whether an affirmative 

defense may be appropriate in a State Implementation Plan. 

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