(Slip Opinion) OCTOBER TERM, 2006 1
Syllabus
NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
being done in connection with this case, at the time the opinion is issued.
The syllabus constitutes no part of the opinion of the Court but has been
prepared by the Reporter of Decisions for the convenience of the reader.
See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.
SUPREME COURT OF THE UNITED STATES
Syllabus
ENVIRONMENTAL DEFENSE ET AL. v. DUKE ENERGY
CORP. ET AL.
CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
THE FOURTH CIRCUIT
No. 05–848. Argued November 1, 2006—Decided April 2, 2007
In the 1970s, Congress added two air pollution control schemes to the
Clean Air Act (Act): New Source Performance Standards (NSPS) and
Prevention of Significant Deterioration (PSD), each of which covers
modified, as well as new, stationary sources of air pollution. The
NSPS provisions define “modification” of such a source as a physical
change to it, or a change in the method of its operation, that in
creases the amount of a pollutant discharged or emits a new one. 42
U. S. C. §7411(a)(4). The PSD provisions require a permit before a
“major emitting facility” can be “constructed,” §7475(a), and define
such “construction” to include a “modification (as defined in [NSPS]),”
§7479(2)(C). Despite this definitional identity, the Environmental
Protection Agency’s (EPA) regulations interpret “modification” one
way for NSPS but differently for PSD. The NSPS regulations require
a source to use the best available pollution-limiting technology, see
Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467
U. S. 837, 846, when a modification would increase the discharge of
pollutants measured in kilograms per hour, 40 CFR §60.14(a), but
the 1980 PSD regulations require a permit for a modification only
when it is a “major” one, §51.166(b)(2)(i), and only when it would in
crease the actual annual emission of a pollutant above the actual av
erage for the two prior years, §51.166(b)(21)(ii).
After respondent Duke Energy Corporation replaced or redesigned
the workings of some of its coal-fired electric generating units, the
United States filed this enforcement action, claiming, among other
things, that Duke violated the PSD provisions by doing the work
without permits. Petitioner environmental groups intervened as
plaintiffs and filed a complaint charging similar violations. Duke
2 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Syllabus
moved for summary judgment, asserting, inter alia, that none of its
projects was a “major modification” requiring a PSD permit because
none increased hourly emissions rates. Agreeing, the District Court
entered summary judgment for Duke on all PSD claims. The Fourth
Circuit affirmed, reasoning that Congress’s decision to create identi
cal statutory definitions of “modification” in the Act’s NSPS and PSD
provisions affirmatively mandated that this term be interpreted iden
tically in the regulations promulgated under those provisions. When
the court sua sponte requested supplemental briefing on the rele
vance of this Court’s decision in Rowan Cos. v. United States, 452
U. S. 247, 250, that the Government could not adopt different inter
pretations of the word “wages” in different statutory provisions,
plaintiffs injected a new issue into the case, arguing that a claim that
the 1980 PSD regulation exceeded statutory authority would be an
attack on the regulation’s validity that could not be raised in an en
forcement proceeding, see 42 U. S. C. §7607(b)(2), since judicial review
for validity can be obtained only by a petition to the District of Colum
bia Circuit, generally within 60 days of EPA’s rulemaking, §7607(b)(1).
The Fourth Circuit rejected this argument, ruling that its interpretation
did not invalidate the PSD regulations because they can be interpreted
to require an increase in the hourly emissions rate as an element of a
major “modification.”
Held: The Fourth Circuit’s reading of the PSD regulations in an effort
to conform them with their NSPS counterparts on “modification”
amounted to the invalidation of the PSD regulations, which must
comport with the Clean Air Act’s limits on judicial review of EPA
regulations for validity. Pp. 8–17.
(a) Principles of statutory interpretation do not rigidly mandate
identical regulation here. Because “[m]ost words have different
shades of meaning and consequently may be variously construed,
[even] when [they are] used more than once in the same statute or
. . . section,” the “natural presumption that identical words used in
different parts of the same act are intended to have the same mean
ing . . . is not rigid and readily yields whenever there is such varia
tion in the connection in which the words are used as reasonably to
warrant the conclusion that they were employed in different parts of
the act with different intent.” Atlantic Cleaners & Dyers, Inc. v.
United States, 286 U. S. 427, 433. A given term in the same statute
may take on distinct characters from association with distinct statu
tory objects calling for different ways of implementation. The point is
the same even when the terms share a common statutory definition,
if it is general enough. See Robinson v. Shell Oil Co., 519 U. S. 337,
343–344. Robinson is not inconsistent with Rowan, where the
Court’s invalidation of the differing interpretations of “wages,” 452
Cite as: 549 U. S. ____ (2007) 3
Syllabus
U. S., at 252, turned not on the fact that a “substantially identical”
definition of that word appeared in each of the statutory provisions at
issue, but on the failure of the regulations in question to serve Con
gress’s manifest “concern for the interest of simplicity and ease of
administration,” id., at 255. In fact, in a case close to Rowan’s facts,
the Court recently declined to follow a categorical rule of resolving
ambiguities in identical statutory terms identically regardless of
their surroundings, United States v. Cleveland Indians Baseball Co.,
532 U. S. 200, 213, but instead accorded “substantial judicial defer
ence” to an agency’s “longstanding,” “reasonable,” and differing inter
pretations of the statutory term at issue, id., at 218–220. It makes
no difference here that the Clean Air Act does not merely repeat the
same definition in its NSPS and PSD provisions, but that the PSD
provisions refer back to the section defining “modification” for NSPS
purposes. Nothing in the text or legislative history of the statutory
amendment that added the NSPS cross-reference suggests that Con
gress meant to eliminate customary agency discretion to resolve
questions about a statutory definition by looking to the surroundings
in which the defined term appears. EPA’s construction need do no
more than fall within the outer limits of what is reasonable, as set by
the Act’s common definition. Pp. 9–12.
(b) The Fourth Circuit’s construction of the 1980 PSD regulations
to conform them to their NSPS counterparts was not a permissible
reading of their terms. The PSD regulations clearly do not define a
“major modification” in terms of an increase in the “hourly emissions
rate.” On its face, the definitional section specifies no rate at all,
hourly or annual, merely requiring a “physical change in or change in
the method of operation of a major stationary source that would re
sult in a significant net emissions increase of any” regulated pollut
ant. 40 CFR §51.166(b)(2)(i). But even when the regulations men
tion a rate, it is annual, not hourly. See, e.g., §51.166(b)(23)(i).
Further at odds with the idea that hourly rate is relevant is the man
date that “[a]ctual emissions shall be calculated using the unit’s ac
tual operating hours,” §51.166(b)(21)(ii), since “actual emissions”
must be measured in a manner looking to the number of hours the
unit is or probably will be actually running. The Court of Appeals’s
reasons for its different view are no match for these textual differ
ences. Consequently, the Court of Appeals’s construction of the 1980
PSD regulations must be seen as an implicit invalidation of those
regulations, a form of judicial review implicating the provisions of
§7607(b), which limit challenges to the validity of a regulation during
enforcement proceedings when such review “could have been ob
tained” in the Court of Appeals for the District of Columbia within 60
days of EPA rulemaking. Because the Court of Appeals did not be
4 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Syllabus
lieve that its analysis reached validity, it did not consider the appli
cability or effect of that limitation here. The Court has no occasion
itself at this point to consider the significance of §7607(b). Pp. 12–17.
(c) Duke’s claim that, even assuming the Act and the 1980 regula
tions authorize EPA to construe a PSD “modification” as it has done,
EPA has been inconsistent in its positions and is now retroactively
targeting 20 years of accepted practice was not addressed below. To
the extent the claim is not procedurally foreclosed, Duke may press it
on remand. P. 17.
411 F. 3d 539, vacated and remanded.
SOUTER, J., delivered the opinion of the Court, in which ROBERTS,
C. J., and STEVENS, SCALIA, KENNEDY, GINSBURG, BREYER, and ALITO,
JJ., joined, and in which THOMAS, J., joined as to all but Part III–A.
THOMAS, J., filed an opinion concurring in part.
Cite as: 549 U. S. ____ (2007) 1
Opinion of the Court
NOTICE: This opinion is subject to formal revision before publication in the
preliminary print of the United States Reports. Readers are requested to
notify the Reporter of Decisions, Supreme Court of the United States, Wash
ington, D. C. 20543, of any typographical or other formal errors, in order
that corrections may be made before the preliminary print goes to press.
SUPREME COURT OF THE UNITED STATES
_________________
No. 05–848
_________________
ENVIRONMENTAL DEFENSE, ET AL., PETITIONERS v.
DUKE ENERGY CORPORATION ET AL.
ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
APPEALS FOR THE FOURTH CIRCUIT
[April 2, 2007]
JUSTICE SOUTER delivered the opinion of the Court.
In the 1970s, Congress added two air pollution control
schemes to the Clean Air Act: New Source Performance
Standards (NSPS) and Prevention of Significant Deterio
ration (PSD), each of them covering modified, as well as
new, stationary sources of air pollution. The NSPS provi
sions define the term “modification,” 42 U. S. C.
§7411(a)(4), while the PSD provisions use that word “as
defined in” NSPS, §7479(2)(C). The Court of Appeals
concluded that the statute requires the Environmental
Protection Agency (EPA) to conform its PSD regulations
on “modification” to their NSPS counterparts, and that
EPA’s 1980 PSD regulations can be given this conforming
construction. We hold that the Court of Appeals’s reading
of the 1980 PSD regulations, intended to align them with
NSPS, was inconsistent with their terms and effectively
invalidated them; any such result must be shown to com
port with the Act’s restrictions on judicial review of EPA
regulations for validity.
I
The Clean Air Amendments of 1970, 84 Stat. 1676,
2 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
broadened federal authority to combat air pollution, see
Chevron U. S. A. Inc. v. Natural Resources Defense Coun
cil, Inc., 467 U. S. 837, 845–846 (1984), and directed EPA
to devise National Ambient Air Quality Standards
(NAAQS) limiting various pollutants, which the States
were obliged to implement and enforce, 42 U. S. C. §§7409,
7410. The amendments dealing with NSPS authorized
EPA to require operators of stationary sources of air pol
lutants to use the best technology for limiting pollution,
Chevron, supra, at 846; see also 1 F. Grad, Environmental
Law §2.03, p. 2–356 (2006), both in newly constructed
sources and those undergoing “modification,” 42 U. S. C.
§7411(a)(2). Section 111(a) of the 1970 amendments de
fined this term within the NSPS scheme as “any physical
change in, or change in the method of operation of, a sta
tionary source which increases the amount of any air
pollutant emitted by such source or which results in the
emission of any air pollutant not previously emitted,” 42
U. S. C. §7411(a)(4).
EPA’s 1975 regulations implementing NSPS provided
generally that “any physical or operational change to an
existing facility which results in an increase in the emis
sion rate to the atmosphere of any pollutant to which a
standard applies shall be considered a modification within
the meaning of [S]ection 111.” 40 CFR §60.14(a) (1976).
Especially significant here is the identification of an NSPS
“modification” as a change that “increase[s] . . . the emis
sion rate,” which “shall be expressed as kg/hr of any pol
lutant discharged into the atmosphere.” §60.14(b).1
——————
1 EPA’s 1975 NSPS regulations did not specify that the “rate” means the
maximum rate possible for the technology, see 40 CFR §§60.14(a)–(b)
(1977), but the parties all read the regulations this way. See Brief for
Petitioners 2; Brief for United States 7; Brief for Respondent Duke 32.
At another point in the NSPS regulations, a different definition of “modifi
cation” appeared: “ ‘Modification’ means any physical change in, or change
in the method of operation of, an existing facility which increases the
Cite as: 549 U. S. ____ (2007) 3
Opinion of the Court
NSPS, however, did too little to “achiev[e] the ambitious
goals of the 1970 Amendments,” R. Belden, Clean Air Act 7
(2001) (hereinafter Belden), and the Clean Air Act Amend
ments of 1977, 91 Stat. 685, included the PSD provisions,
which aimed at giving added protection to air quality in
certain parts of the country “notwithstanding attainment
and maintenance of” the NAAQS. 42 U. S. C. §7470(1).2
The 1977 amendments required a PSD permit before a
“major emitting facility” could be “constructed” in an area
covered by the scheme. §7475(a). As originally enacted,
PSD applied only to newly constructed sources, but soon a
technical amendment added the following subparagraph:
“The term ‘construction’ when used in connection with any
source or facility, includes the modification (as defined in
[S]ection 111(a)) of any source or facility.” §14(a)(54), 91
Stat. 1402, 42 U. S. C. §7479(2)(C); see also New York v.
EPA, 413 F. 3d 3, 13 (CADC 2005). In other words, the
“construction” requiring a PSD permit under the statute
was made to include (though it was not limited to)
a “modification” as defined in the statutory NSPS
provisions.
In 1980, EPA issued PSD regulations,3 which “limited
the application of [PSD] review” of modified sources to
——————
amount of any air pollutant (to which a standard applies) emitted into the
atmosphere by that facility,” §60.2(h); see also New York v. EPA, 413 F. 3d
3, 11–12 (CADC 2005) (per curiam) (“[N]either the 1975 regulation nor its
preamble explained why EPA found it necessary to offer these two sepa
rate glosses on ‘modification’ ”).
2 Statutory PSD superseded a regulatory PSD scheme established by
EPA in 1974. See 39 Fed. Reg. 42510. Under the regulations, the term
“modification” was defined as “any physical change in, or change in the
method of operation of, a stationary source which increases the emis
sion rate of any pollutant for which a national standard has been
promulgated.” Id., at 42514.
3 Although EPA had promulgated an earlier set of PSD regulations in
1978, 43 Fed. Reg. 26380, none of the parties argues that they govern
the conduct at issue in this case.
4 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
instances of “ ‘major’ modificatio[n],” Belden 46, defined as
“any physical change in or change in the method of opera
tion of a major stationary source that would result in a
significant net emissions increase of any pollutant subject
to regulation under the Act.” 40 CFR §51.166(b)(2)(i)
(1987). Further regulations in turn addressed various
elements of this definition, three of which are to the point
here. First, the regulations specified that an operational
change consisting merely of “[a]n increase in the hours of
operation or in the production rate” would not generally
constitute a “physical change or change in the method of
operation.” §51.166(b)(2)(iii)(f ). For purposes of a PSD
permit, that is, such an operational change would not
amount to a “modification” as the Act defines it. Second,
the PSD regulations defined a “net emissions increase” as
“[a]ny increase in actual emissions from a particular
physical change or change in the method of operation,” net
of other contemporaneous “increases and decreases in
actual emissions at the source.” §51.166(b)(3). “Actual
emissions” were defined to “equal the average rate, in tons
per year, at which the unit actually emitted the pollutant
during a two-year period which precedes the particular
date and which is representative of normal source opera
tion.” §51.166(b)(21)(ii). “[A]ctual emissions” were to be
“calculated using the unit’s actual operating hours [and]
production rates.” Ibid. Third, the term “significant” was
defined as “a rate of emissions that would equal or exceed”
one or another enumerated threshold, each expressed in
“tons per year.” §51.166(b)(23)(i).
It would be bold to try to synthesize these statutory and
regulatory provisions in a concise paragraph, but three
points are relatively clear about the regime that covers
this case:
(a) The Act defines modification of a stationary
source of a pollutant as a physical change to it, or a
change in the method of its operation, that increases
Cite as: 549 U. S. ____ (2007) 5
Opinion of the Court
the amount of a pollutant discharged or emits a new
one.
(b) EPA’s NSPS regulations require a source to use
the best available pollution-limiting technology only
when a modification would increase the rate of dis
charge of pollutants measured in kilograms per hour.
(c) EPA’s 1980 PSD regulations require a permit for
a modification (with the same statutory definition)
only when it is a major one and only when it would in
crease the actual annual emission of a pollutant above
the actual average for the two prior years.
The Court of Appeals held that Congress’s provision
defining a PSD modification by reference to an NSPS
modification caught not only the statutory NSPS defini
tion, but also whatever regulatory gloss EPA puts on that
definition at any given time (for the purposes of the best
technology requirement). When, therefore, EPA’s PSD
regulations specify the “change” that amounts to a “major
modification” requiring a PSD permit, they must measure
an increase in “the amount of any air pollutant emitted,”
42 U. S. C. §7411(a)(4), in terms of the hourly rate of
discharge, just the way NSPS regulations do. Petitioners
and the United States say, on the contrary, that when
EPA addresses the object of the PSD scheme it is free to
put a different regulatory interpretation on the common
statutory core of “modification,” by measuring increased
emission not in terms of hourly rate but by the actual,
annual discharge of a pollutant that will follow the modifi
cation, regardless of rate per hour. This disagreement is
the nub of the case.
II
Respondent Duke Energy Corporation runs 30 coal-fired
electric generating units at eight plants in North and
South Carolina. United States v. Duke Energy Corp., 411
F. 3d 539, 544 (CA4 2005). The units were placed in ser
6 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
vice between 1940 and 1975, and each includes a boiler
containing thousands of steel tubes arranged in sets. Ibid.
Between 1988 and 2000,4 Duke replaced or redesigned 29
tube assemblies in order to extend the life of the units and
allow them to run longer each day. Ibid.
The United States filed this action in 2000, claiming,
among other things, that Duke violated the PSD provi
sions by doing this work without permits. Environmental
Defense, North Carolina Sierra Club, and North Carolina
Public Interest Research Group Citizen Lobby/Education
Fund intervened as plaintiffs and filed a complaint charg
ing similar violations.
Duke moved for summary judgment, one of its positions
being that none of the projects was a “major modification”
requiring a PSD permit because none increased hourly
rates of emissions. The District Court agreed with Duke’s
reading of the 1980 PSD regulations. It reasoned that
their express exclusion of “[a]n increase in the hours of
operation” from the definition of a “physical change or
change in the method of operation” implied that “post
project emissions levels must be calculated assuming” pre-
project hours of operation. 278 F. Supp. 2d 619, 640–641
(MDNC 2003). Consequently, the District Court said, a
PSD “major modification” can occur “only if the project
increases the hourly rate of emissions.” Id., at 641. The
District Court found further support for its construction of
the 1980 PSD regulations in one letter and one memoran
——————
4 The United States argues that some of Duke’s projects were gov
erned by EPA’s PSD regulations promulgated in 1992 rather than the
1980 PSD regulations. Brief for United States 20, n. 4. Duke disputes
this. Brief for Respondent Duke 14, n. 4. Because the United States
acknowledges that the two sets of regulations “did not materially differ
with respect to the legal question at issue here,” Brief for United States
20, n. 4, we will assume, as did the Court of Appeals and the District
Court, that the 1980 PSD regulations control. 411 F. 3d, at 543, n. 1;
United States v. Duke Energy Corp., 278 F. Supp. 2d 619, 629 (MDNC
2003).
Cite as: 549 U. S. ____ (2007) 7
Opinion of the Court
dum written in 1981 by EPA’s Director of the Division of
Stationary Source Enforcement, Edward E. Reich. Id., at
641–642.
The United States and intervenor-plaintiffs (collectively,
plaintiffs) subsequently stipulated “that they do not con
tend that the projects at issue in this case caused an in
crease in the maximum hourly rate of emissions at any of
Duke Energy’s units.” App. 504. Rather, their claim “is
based solely on their contention that the projects would
have been projected to result in an increased utilization of
the units at issue.” Ibid. Duke, for its part, stipulated to
plaintiffs’ right to appeal the District Court’s determina
tion that projects resulting in greater operating hours are
not “major modifications” triggering the PSD permit re
quirement, absent an increase in the hourly rate of emis
sions. The District Court then entered summary judg
ment for Duke on all PSD claims.
The Court of Appeals for the Fourth Circuit affirmed,
“albeit for somewhat different reasons.” 411 F. 3d, at 542.
“[T]he language and various interpretations of the PSD
regulations . . . are largely irrelevant to the proper analy
sis of this case,” reasoned the Court of Appeals, “because
Congress’ decision to create identical statutory definitions
of the term ‘modification’ ” in the NSPS and PSD provi
sions of the Clean Air Act “has affirmatively mandated
that this term be interpreted identically” in the regula
tions promulgated under those provisions. Id., at 547,
n. 3, 550. The Court of Appeals relied principally on the
authority of Rowan Cos. v. United States, 452 U. S. 247,
250 (1981), where we held against the Government’s differ
ing interpretations of the word “wages” in different tax
provisions. 411 F. 3d, at 550. As the Court of Appeals saw
it, Rowan establishes an “effectively irrebuttable” pre
sumption that PSD regulations must contain the same
conditions for a “modification” as the NSPS regulations,
8 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
including an increase in the hourly rate of emissions.5 411
F. 3d, at 550.
As the Court of Appeals said, Duke had not initially
relied on Rowan, see 411 F. 3d, at 547, n. 4, and when the
Court sua sponte requested supplemental briefing on
Rowan’s relevance, plaintiffs injected a new issue into the
case. They argued that a claim that the 1980 PSD regula
tion exceeded statutory authority would be an attack on
the validity of the regulation that could not be raised in an
enforcement proceeding. See 42 U. S. C. §7607(b)(2). Un
der §307(b) of the Act, they said, judicial review for validity
can be obtained only by a petition to the Court of Appeals
for the District of Columbia Circuit, generally within 60
days of EPA’s rulemaking. 42 U. S. C. §7607(b).
The Court of Appeals rejected this argument. “Our choice
of this interpretation of the PSD regulations . . . is not an
invalidation of those regulations,” it said, because “the
PSD regulations can be interpreted” to require an increase
in the hourly emissions rate as an element of a major
“modification” triggering the permit requirement. 411 F. 3d,
at 549, n. 7. To show that the 1980 PSD regulations are
open to this construction, the Court of Appeals cited the
conclusions of the District Court and the Reich opinions.
We granted the petition for certiorari brought by inter
venor-plaintiffs, 547 U. S. __ (2006), and now vacate.
III
The Court of Appeals understood that it was simply
construing EPA’s 1980 PSD regulations in a permissible
——————
5 The Court of Appeals noted that EPA was free to abandon the re
quirement that a “modification” be accompanied by an increase in the
hourly rate of emissions, provided it did so for both the NSPS and PSD
programs. 411 F. 3d, at 550–551. In other words, the Court of Appeals
raised no question about the reasonableness of the definition of “modifi
cation” in the 1980 PSD regulations, apart from its deviation from the
definition contained in NSPS regulations.
Cite as: 549 U. S. ____ (2007) 9
Opinion of the Court
way that left them in harmony with their NSPS counter
part and, hence, the Act’s single definition of “modifica
tion.” The plaintiffs say that the Court of Appeals was
rewriting the PSD regulations in a way neither required
by the Act nor consistent with their own text.
It is true that no precise line runs between a purposeful
but permissible reading of the regulation adopted to bring
it into harmony with the Court of Appeals’s view of the
statute, and a determination that the regulation as writ
ten is invalid. But the latter occurred here, for the Court
of Appeals’s efforts to trim the PSD regulations to match
their different NSPS counterparts can only be seen as an
implicit declaration that the PSD regulations were invalid
as written.
A
In applying the 1980 PSD regulations to Duke’s conduct,
the Court of Appeals thought that, by defining the term
“modification” identically in its NSPS and PSD provisions,
the Act required EPA to conform its PSD interpretation of
that definition to any such interpretation it reasonably
adhered to under NSPS. But principles of statutory con
struction are not so rigid. Although we presume that the
same term has the same meaning when it occurs here and
there in a single statute, the Court of Appeals mischarac
terized that presumption as “effectively irrebuttable.” 411
F. 3d, at 550. We also understand that “[m]ost words have
different shades of meaning and consequently may be
variously construed, not only when they occur in different
statutes, but when used more than once in the same stat
ute or even in the same section.” Atlantic Cleaners &
Dyers, Inc. v. United States, 286 U. S. 427, 433 (1932).
Thus, the “natural presumption that identical words used
in different parts of the same act are intended to have the
same meaning . . . is not rigid and readily yields whenever
there is such variation in the connection in which the
10 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
words are used as reasonably to warrant the conclusion
that they were employed in different parts of the act with
different intent.” Ibid. A given term in the same statute
may take on distinct characters from association with
distinct statutory objects calling for different implementa
tion strategies.
The point is the same even when the terms share a
common statutory definition, if it is general enough, as we
recognized in Robinson v. Shell Oil Co., 519 U. S. 337
(1997). There the question was whether the term “em
ployees” in §704(a) of Title VII of the Civil Rights Act of
1964 covered former employees. Title VII expressly de
fined the term “employee,” 42 U. S. C. §2000e(f), but the
definition was “consistent with either current or past
employment,” 519 U. S., at 342, and we held that “each
section” of Title VII “must be analyzed to determine
whether the context gives the term a further meaning that
would resolve the issue in dispute,” id., at 343–344.
If Robinson were inconsistent with Rowan (on which the
Court of Appeals relied), it would be significant that Rob
inson is the later case, but we read the two as compatible.
In Rowan, the question was whether the value of meals
and lodging given to employees by an employer for its own
convenience should be counted in computing “wages”
under the Federal Insurance Contributions Act (FICA), 26
U. S. C. §3101 et seq., and the Federal Unemployment Tax
Act (FUTA), 26 U. S. C. §3301 et seq. Treasury Regula
tions made this value “includable in ‘wages’ as defined in
FICA and FUTA, even though excludable from ‘wages’
under the substantially identical” statutory definition of
“wages” for income-tax withholding purposes. 452 U. S.,
at 252. Although we ultimately held that the income tax
treatment was the proper one across the board, we did not
see it this way simply because a “substantially identical”
definition of “wages” appeared in each of the different
statutory provisions. Instead, we relied on a manifest
Cite as: 549 U. S. ____ (2007) 11
Opinion of the Court
“congressional concern for the interest of simplicity and
ease of administration.” Id., at 255 (internal quotation
marks omitted). The FICA and FUTA regulations fell for
failing to “serve that interest,” id., at 257, not for defying
definitional identity.
In fact, in a setting much like Rowan, we recently de
clined to require uniformity when resolving ambiguities in
identical statutory terms. In United States v. Cleveland
Indians Baseball Co., 532 U. S. 200 (2001), we rejected the
notion that using the phrase “wages paid” in both “the
discrete taxation and benefits eligibility contexts” can,
standing alone, “compel symmetrical construction,” id., at
213; we gave “substantial judicial deference” to the “long-
standing,” “reasonable,” and differing interpretations
adopted by the Internal Revenue Service in its regulations
and Revenue Rulings. Id., at 218–220. There is, then, no
“effectively irrebuttable” presumption that the same de
fined term in different provisions of the same statute must
“be interpreted identically.” 411 F. 3d, at 550. Context
counts.
It is true that the Clean Air Act did not merely repeat
the term “modification” or the same definition of that word
in its NSPS and PSD sections; the PSD language referred
back to the section defining “modification” for NSPS pur
poses. 42 U. S. C. §7479(2)(C). But that did not matter in
Robinson, and we do not see the distinction as making any
difference here. Nothing in the text or the legislative
history of the technical amendments that added the cross-
reference to NSPS suggests that Congress had details of
regulatory implementation in mind when it imposed PSD
requirements on modified sources; the cross-reference
alone is certainly no unambiguous congressional code for
eliminating the customary agency discretion to resolve
questions about a statutory definition by looking to the
surroundings of the defined term, where it occurs. See
New York, 413 F. 3d, at 19 (“So far as appears, . . . [this]
12 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
incorporatio[n] by reference [is] the equivalent of Con
gress’s having simply repeated in the [PSD] context the
definitional language used before in the NSPS context”);
compare 91 Stat. 745 (expressly incorporating in an unre
lated provision of the 1977 amendments “the interpreta
tive regulation of the [EPA] Administrator . . . published
in 41 Federal Register 55524–30” with specified excep
tions); New York, supra, at 19 (“Congress’s failure to use
such an express incorporation of prior regulations for
‘modification’ cuts against” any suggestion that “Congress
intended to incorporate” into the Act the “preexisting
regulatory definition” of “modification”). Absent any iron
rule to ignore the reasons for regulating PSD and NSPS
“modifications” differently, EPA’s construction need do no
more than fall within the limits of what is reasonable, as
set by the Act’s common6 definition.
B
The Court of Appeals’s reasoning that the PSD regula
tions must conform to their NSPS counterparts led the
——————
6 Duke argues that the 1977 amendments intended to incorporate
EPA’s definition of “modification” under the 1974 regulatory PSD
program. Brief for Respondent Duke 44; see also n. 2, supra. We find
no support for this argument in the statutory text, which refers to the
statutory NSPS definition rather than the regulatory PSD definition.
Although Duke correctly points out that “Congress instructed that the
bulk of the pre-existing rules ‘shall remain in effect,’ ” Brief for Respon
dent Duke 44 (quoting 42 U. S. C. §7478(a)), this instruction was a
temporary measure “[u]ntil such time as an applicable implementation
plan is in effect,” §7478(a). We therefore do not read this language as a
restriction on EPA’s authority to interpret the statutory PSD provisions
reasonably in a manner that departs from the 1974 regulations. Duke
also invokes Bragdon v. Abbott, 524 U. S. 624, 631 (1998), for the
proposition that “use of the pre-existing term ‘modification’ ‘carries the
implication that Congress intended the term to be construed in accor
dance with pre-existing regulatory interpretations.’ ” Brief for Respon
dent Duke 44. But this reasoning is unavailing here, given the exis
tence of at least three distinct regulatory definitions of “modification” at
the time of the 1977 amendments. See supra, at 2–3, and nn. 1, 2.
Cite as: 549 U. S. ____ (2007) 13
Opinion of the Court
court to read those PSD regulations in a way that seems to
us too far a stretch for the language used. The 1980 PSD
regulations on “modification” simply cannot be taken to
track the agency’s regulatory definition under the NSPS.
True, the 1980 PSD regulations may be no seamless
narrative, but they clearly do not define a “major modifica
tion” in terms of an increase in the “hourly emissions
rate.” On its face, the definition in the PSD regulations
specifies no rate at all, hourly or annual, merely requiring
a physical or operational change “that would result in a
significant net emissions increase of any” regulated pol
lutant. 40 CFR §51.166(b)(2)(i). But even when a rate is
mentioned, as in the regulatory definitions of the two
terms, “significant” and “net emissions increase,” the rate
is annual, not hourly. Each of the thresholds that quan
tify “significant” is described in “tons per year,”
§51.166(b)(23)(i), and a “net emissions increase” is an
“increase in actual emissions” measured against an “aver
age” prior emissions rate of so many “tons per year.”
§§51.166(b)(3) and (21)(ii). And what is further at odds
with the idea that hourly rate is relevant is the mandate
that “[a]ctual emissions shall be calculated using the
unit’s actual operating hours,” §51.166(b)(21)(ii), since
“actual emissions” must be measured in a manner that
looks to the number of hours the unit is or probably will be
actually running. What these provisions are getting at is
a measure of actual operations averaged over time, and
the regulatory language simply cannot be squared with a
regime under which “hourly rate of emissions,” 411 F. 3d,
at 550 (emphasis deleted), is dispositive.
The reasons invoked by the Court of Appeals for its
different view are no match for these textual differences.
The appellate court cited two authorities ostensibly dem
onstrating that the 1980 PSD regulations “can be inter
preted consistently” with the hourly emissions test, the
first being the analysis of the District Court in this case.
14 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
Id., at 549, n. 7. The District Court thought that an in
crease in the hourly emissions rate was necessarily a
prerequisite to a PSD “major modification” because a
provision of the 1980 PSD regulations excluded an “ ‘in
crease in the hours of operation or in the production rate’ ”
from the scope of “ ‘[a] physical change or change in the
method of operation.’ ” 278 F. Supp. 2d, at 640–641 (quot
ing 40 CFR §§51.166(b)(2)(iii)(f) and (3)(i)(a) (1987)). The
District Court read this exclusion to require, in effect, that
a source’s hours of operation “be held constant” when pre-
project emissions are being compared with postproject
emissions for the purpose of calculating the “net emissions
increase.” 278 F. Supp. 2d, at 640.
We think this understanding of the 1980 PSD regula
tions makes the mistake of overlooking the difference
between the two separate components of the regulatory
definition of “major modification”: “[1] any physical change
in or change in the method of operation of a major station
ary source that [2] would result in a significant net emis
sions increase of any pollutant subject to regulation under
the Act.” §51.166(b)(2)(i); cf. New York, 413 F. 3d, at 11
(“[The statutory] definition requires both a change—
whether physical or operational—and a resulting increase
in emissions of a pollutant” (emphasis in original)); Wis
consin Electric Power Co. v. Reilly, 893 F. 2d 901, 907
(CA7 1990) (same). The exclusion of “increase in . . . hours
. . . or . . . production rate,” §51.166(b)(2)(iii)(f), speaks to
the first of these components (“physical change . . . or
change in . . . method,” §51.166(b)(2)(i)), but not to the
second (“significant net emissions increase,” ibid.). As the
preamble to the 1980 PSD regulations explains, forcing
companies to obtain a PSD permit before they could sim
ply adjust operating hours “would severely and unduly
hamper the ability of any company to take advantage of
favorable market conditions.” 45 Fed. Reg. 52704. In other
words, a mere increase in the hours of operation, standing
Cite as: 549 U. S. ____ (2007) 15
Opinion of the Court
alone, is not a “physical change or change in the method of
operation.” 40 CFR §51.166(b)(2)(iii).
But the District Court took this language a step further.
It assumed that increases in operating hours (resulting in
emissions increases at the old rate per hour) must be
ignored even if caused or enabled by an independent
“physical change . . . or change in the method of opera
tion.” §51.166(b)(2)(i). That reading, however, turns an
exception to the first component of the definition into a
mandate to ignore the very facts that would count under
the second, which defines “net emissions increase” in
terms of “actual emissions,” §51.166(b)(3), during “the
unit’s actual operating hours,” §51.166(b)(21)(ii); see also
57 Fed. Reg. 32328 (1992) (“[A]n increase in emissions
attributable to an increase in hours of operation or produc
tion rate which is the result of a construction-related
activity is not excluded from [PSD] review . . .”).7
The Court of Appeals invoked one other source of sup
port, the suggestion in the Reich opinions that a physical
or operational change increasing a source’s hours of op
eration, without an increase in the hourly emissions rate,
cannot be a PSD “major modification.” Duke continues to
——————
7 Two Courts of Appeals agree. See United States v. Cinergy Corp.,
458 F. 3d 705, 708 (CA7 2006) (“[M]erely running the plant closer to its
maximum capacity is not a major modification because it does not
involve either a physical change or a change in the method of operation.
If, however, a physical change enables the plant to increase its output,
then, according to the EPA’s interpretation, the exclusion for merely
operating the plant for longer hours is inapplicable” (emphasis in
original)); Wisconsin Electric Power Co. v. Reilly, 893 F. 2d 901, 916,
n. 11 (CA7 1990) (the regulatory exclusion for increases in the hours
of operation “was provided to allow facilities to take advantage of
fluctuating market conditions, not construction or modification activ
ity”); Puerto Rican Cement Co. v. EPA, 889 F. 2d 292, 298 (CA1 1989)
(“[T]here is no logical contradiction in rules that, on the one hand,
permit firms using existing capacity simply to increase their output
and, on the other, use the potential output of new capacity as a basis for
calculating an increase in emissions levels” (emphasis in original)).
16 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
Opinion of the Court
rely on those opinions here, asserting that “there are no
contrary Agency pronouncements.” Brief for Respondent
Duke 28. The Reich letters are not, however, heavy am
munition. Their persuasiveness is elusive, neither of them
containing more than one brief and conclusory statement
supporting Duke’s position. Nor, it seems, are they unem
barrassed by any “contrary Agency pronouncements.” See,
e.g., App. 258 (Memorandum of Don R. Clay, Acting Assis
tant EPA Administrator for Air and Radiation (Sept. 9,
1988) (when “plans to increase production rate or hours of
operation are inextricably intertwined with the physical
changes planned,” they are “precisely the type of change in
hours or rate o[f] operation that would disturb a prior
assessment of a source’s environmental impact and should
have to undergo PSD review scrutiny” (internal quotation
marks and alterations omitted)); see also 57 Fed. Reg.
32328. In any event, it answers the citation of the Reich
letters to realize that an isolated opinion of an agency
official does not authorize a court to read a regulation
inconsistently with its language.8
In sum, the text of the 1980 PSD regulations on “modifi
cation” doomed the Court of Appeals’s attempt to equate
those regulations with their NSPS counterpart. As a
consequence, we have to see the Court of Appeals’s con
struction of the 1980 PSD regulations as an implicit in
——————
8 Duke now offers an alternative argument for applying the hourly
emissions test for the PSD program: before a project can become a “major
modification” under the PSD regulations, 40 CFR §51.166(b)(2)(i) (1987),
it must meet the definition of “modification” under the NSPS regula
tions, §60.14(a). That sounds right, but the language of the regulations
does not support it. For example, it would be superfluous for PSD
regulations to require a “major modification” to be “a physical change in
or change in the method of operation,” §51.166(b)(2)(i), if they presup
posed that the NSPS definition of “modification,” which contains the
same prerequisite, §60.14(a), had already been satisfied. The NSPS
and PSD regulations are complementary and not related as set to
subset.
Cite as: 549 U. S. ____ (2007) 17
Opinion of the Court
validation of those regulations, a form of judicial review
implicating the provisions of §307(b) of the Act, which
limit challenges to the validity of a regulation during
enforcement proceedings when such review “could have
been obtained” in the Court of Appeals for the District of
Columbia within 60 days of EPA rulemaking. See 42
U. S. C. §7607(b); see also United States v. Cinergy Corp.,
458 F. 3d 705, 707–708 (CA7 2006); Wisconsin Electric
Power Co., 893 F. 2d, at 914, n. 6. Because the Court of
Appeals did not believe that its analysis reached validity,
it did not consider the applicability or effect of that limita
tion here. We have no occasion at this point to consider
the significance of §307(b) ourselves.
IV
Finally, Duke assumes for argument that the Act and
the 1980 regulations may authorize EPA to construe a
PSD “modification” as it has done, but it charges that the
agency has taken inconsistent positions and is now “retro
actively targeting twenty years of accepted practice.”
Brief for Respondent Duke 37; see also Brief for State of
Alabama et al. as Amici Curiae. This claim, too, has not
been tackled by the District Court or the Court of Appeals;
to the extent it is not procedurally foreclosed, Duke may
press it on remand.
* * *
The judgment of the Court of Appeals is vacated, and
the case is remanded for further proceedings consistent
with this opinion.
It is so ordered.
Cite as: 549 U. S. ____ (2007) 1
THOMAS, J., concurring in part
SUPREME COURT OF THE UNITED STATES
_________________
No. 05–848
_________________
ENVIRONMENTAL DEFENSE, ET AL., PETITIONERS v.
DUKE ENERGY CORPORATION ET AL.
ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
APPEALS FOR THE FOURTH CIRCUIT
[April 2, 2007]
JUSTICE THOMAS, concurring in part.
I join all but Part III–A of the Court’s opinion. I write
separately to note my disagreement with the dicta in that
portion of the opinion, which states that the statutory
cross-reference does not mandate a singular regulatory
construction.
The Prevention of Significant Deterioration (PSD) stat
ute explicitly links the definition of the term “modifica
tion” to that term’s definition in the New Source Perform
ance Standard (NSPS) statute:
“The term ‘construction’ when used in connection with
any source or facility, includes the modification (as de
fined in section 7411(a) of this title) of any source or
facility.” 42 U. S. C. §7479(2)(C).
Section 7411(a) contains the NSPS definition of “modifica
tion,” which the parties agree is the relevant statutory
definition of the term for both PSD and NSPS. Because of
the cross-reference, the definitions of “modification” in
PSD and NSPS are one and the same. The term “modifi
cation” therefore has the same meaning despite contextual
variations in the two admittedly different statutory
schemes. Congress’ explicit linkage of PSD’s definition of
“modification” to NSPS’ prevents the Environmental
Protection Agency (EPA) from adopting differing regula
2 ENVIRONMENTAL DEFENSE v. DUKE ENERGY CORP.
THOMAS, J., concurring in part
tory definitions of “modification” for PSD and NSPS. Cf.
IBP, Inc. v. Alvarez, 546 U. S. 21, 34 (2005) (concluding
that an “explicit reference” to a previous statutory defini
tion prohibits interpreting the same word differently).
Section 7479(2)(C)’s cross-reference carries more mean
ing than the mere repetition of the same word in a differ
ent statutory context. When Congress repeats the same
word in a different statutory context, it is possible that
Congress might have intended the context to alter the
meaning of the word. See Atlantic Cleaners & Dyers, Inc.
v. United States, 286 U. S. 427, 433 (1932). No such possi
bility exists with §7479(2)(C). By incorporating NSPS’
definition of “modification,” Congress demonstrated that it
did not intend for PSD’s definition of “modification” to
hinge on contextual factors unique to the PSD statutory
scheme. Thus, United States v. Cleveland Indians Base
ball Co., 532 U. S. 200 (2001), which analyzes the mere
repetition of the same word in a different statutory con
text, carries little weight in this situation.
Likewise, this case differs from the circumstance we
faced in Robinson v. Shell Oil Co., 519 U. S. 337 (1997). In
Robinson, we considered whether “employee,” as used in
§704(a) of Title VII of the Civil Rights Act of 1964, in
cluded former employees. We determined that under the
clear language of the statute, certain statutory provisions
using the term “employee” made sense only with respect to
former employees or current employees, but not both. Id.,
at 342–343. Accordingly, upon analyzing the context of
§704(a), we were compelled to conclude that the term
“employee” included former employees. This case does not
present a similar situation. The statute here includes a
statutory cross-reference, which conveys a clear congres
sional intent to provide a common definition for the term
“modification.” And the contextual differences between
PSD and NSPS do not compel different meanings for the
term “modification.” Robinson is, therefore, inapplicable.
Cite as: 549 U. S. ____ (2007) 3
THOMAS, J., concurring in part
Even if the cross-reference were merely the equivalent
of repeating the words of the definition, we must still
apply our usual presumption that the same words re
peated in different parts of the same statute have the
same meaning. See Atlantic Cleaners, supra, at 433; ante,
at 9. That presumption has not been overcome here.
While the broadly stated regulatory goals of PSD and
NSPS differ, these contextual differences do not compel
different definitions of “modification.” That is, unlike in
Robinson, reading the statutory definition in the separate
contexts of PSD and NSPS does not require different
interpretations of the term “modification.” EPA demon
strated as much when it recently proposed regulations
that would unify the regulatory definitions of “modifica
tion.” See 70 Fed. Reg. 61083, n. 3 (2005) (terming the
proposal “an appropriate exercise of our discretion” and
stating that the unified definition better serves PSD’s
goals).
The majority opinion does little to overcome the pre
sumption that the same words, when repeated, carry the
same meaning. Instead, it explains that this Court’s cases
do not compel identical language to be interpreted identi
cally in all situations. Granting that point, the majority
still has the burden of stating why our general presump
tion does not control the outcome here. It has not done so.