(Slip Opinion)              OCTOBER TERM, 2008                                       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

     ENTERGY CORP. v. RIVERKEEPER, INC., ET AL.

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
                 THE SECOND CIRCUIT

    No. 07–588.      Argued December 2, 2008—Decided April 1, 2009*
Petitioners’ powerplants have “cooling water intake structures” that
  threaten the environment by squashing against intake screens (“im
  pingement”) or suctioning into the cooling system (“entrainment”)
  aquatic organisms from the water sources tapped to cool the plants.
  Thus, the facilities are subject to regulation under the Clean Water
  Act, which mandates that “[a]ny standard established pursuant to
  section 1311 . . . or section 1316 . . . and applicable to a point source
  shall require that the location, design, construction, and capacity of
  cooling water intake structures reflect the best technology available
  for minimizing adverse environmental impact.” 33 U. S. C. §1326(b).
  Sections 1311 and 1316, in turn, employ a variety of “best technology”
  standards to regulate effluent discharge into the Nation’s waters.
  The Environmental Protection Agency (EPA) promulgated the
  §1326(b) regulations at issue after nearly three decades of making
  the “best technology available” determination on a case-by-case basis.
  Its “Phase I” regulations govern new cooling water intake structures,
  while the “Phase II” rules at issue apply to certain large existing fa
  cilities. In the latter rules, the EPA set “national performance stan
  dards,” requiring most Phase II facilities to reduce “impingement
  mortality for [aquatic organisms] by 80 to 95 percent from the calcu
  lation baseline,” and requiring a subset of facilities to reduce en
  trainment of such organisms by “60 to 90 percent from [that] base
  line.” 40 CFR §125.94(b)(1), (2). However, the EPA expressly
  declined to mandate closed-cycle cooling systems, or equivalent re
——————
   * Together with No. 07–589, PSEG Fossil LLC et al. v. Riverkeeper,
Inc., et al., and No. 07–597, Utility Water Act Group v. Riverkeeper, Inc.,
et al., also on certiorari to the same court.
2               ENTERGY CORP. v. RIVERKEEPER, INC.

                                  Syllabus

    ductions in impingement and entrainment, as it had done in its
    Phase I rules, in part because the cost of rendering existing facilities
    closed-cycle compliant would be nine times the estimated cost of
    compliance with the Phase II performance standards, and because
    other technologies could approach the performance of closed-cycle op
    eration. The Phase II rules also permit site-specific variances from
    the national performance standards, provided that the permit-issuing
    authority imposes remedial measures that yield results “as close as
    practicable     to     the   applicable    performance     standards.”
    §125.94(a)(5)(i), (ii). Respondents—environmental groups and vari
    ous States—challenged the Phase II regulations. Concluding that
    cost-benefit analysis is impermissible under 33 U. S. C. §1326(b), the
    Second Circuit found the site-specific cost-benefit variance provision
    unlawful and remanded the regulations to the EPA for it to clarify
    whether it had relied on cost-benefit analysis in setting the national
    performance standards.
Held: The EPA permissibly relied on cost-benefit analysis in setting the
 national performance standards and in providing for cost-benefit
 variances from those standards as part of the Phase II regulations.
 Pp. 7–16.
    (a) The EPA’s view that §1326(b)’s “best technology available for
 minimizing adverse environmental impact” standard permits consid
 eration of the technology’s costs and of the relationship between those
 costs and the environmental benefits produced governs if it is a rea
 sonable interpretation of the statute—not necessarily the only possi
 ble interpretation, nor even the interpretation deemed most reason
 able by the courts. Chevron U. S. A. Inc. v. Natural Resources
 Defense Council, Inc., 467 U. S. 837, 843–844. The Second Circuit
 took “best technology” to mean the technology that achieves the
 greatest reduction in adverse environmental impacts at a reasonable
 cost to the industry, but it may also describe the technology that most
 efficiently produces a good, even if it produces a lesser quantity of
 that good than other available technologies. This reading is not pre
 cluded by the phrase “for minimizing adverse environmental impact.”
 Minimizing admits of degree and is not necessarily used to refer ex
 clusively to the “greatest possible reduction.” Other Clean Water Act
 provisions show that when Congress wished to mandate the greatest
 feasible reduction in water pollution, it used plain language, e.g.,
 “elimination of discharges of all pollutants,” §1311(b)(2)(A). Thus,
 §1326(b)’s use of the less ambitious goal of “minimizing adverse envi
 ronmental impact” suggests that the EPA has some discretion to de
 termine the extent of reduction warranted under the circumstances,
 plausibly involving a consideration of the benefits derived from re
 ductions and the costs of achieving them. Pp. 7–9.
                     Cite as: 556 U. S. ____ (2009)                   3

                               Syllabus

     (b) Considering §1326(b)’s text, and comparing it with the text and
  statutory factors applicable to parallel Clean Water Act provisions,
  prompts the conclusion that it was well within the bounds of reason
  able interpretation for the EPA to conclude that cost-benefit analysis
  is not categorically forbidden. In the Phase II rules the EPA sought
  only to avoid extreme disparities between costs and benefits, limiting
  variances from Phase II’s “national performance standards” to cir
  cumstances where the costs are “significantly greater than the bene
  fits” of compliance. 40 CFR §125.94(a)(5)(ii). In defining “national
  performance standards” the EPA assumed the application of tech
  nologies whose benefits approach those estimated for closed-cycle
  cooling systems at a fraction of the cost. That the EPA has for over
  thirty years interpreted §1326(b) to permit a comparison of costs and
  benefits, while not conclusive, also tends to show that its interpreta
  tion is reasonable and hence a legitimate exercise of its discretion.
  Even respondents and the Second Circuit ultimately recognize that
  some comparison of costs and benefits is permitted. The Second Cir
  cuit held that §1326(b) mandates only those technologies whose costs
  can be reasonably borne by the industry. But whether it is reason
  able to bear a particular cost can very well depend on the resulting
  benefits. Likewise, respondents concede that the EPA need not re
  quire that industry spend billions to save one more fish. This con
  cedes the principle, and there is no statutory basis for limiting the
  comparison of costs and benefits to situations where the benefits are
  de minimis rather than significantly disproportionate. Pp. 9–16.
475 F. 3d 83, reversed and remanded.

  SCALIA, J., delivered the opinion of the Court, in which ROBERTS,
C. J., and KENNEDY, THOMAS, and ALITO, JJ., joined. BREYER, J., filed
an opinion concurring in part and dissenting in part. STEVENS, J., filed
a dissenting opinion, in which SOUTER and GINSBURG, JJ., joined.
                         Cite as: 556 U. S. ____ (2009)                              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
                                    _________________

                       Nos. 07–588, 07–589 and 07–597
                                    _________________


          ENTERGY CORPORATION, PETITIONER
07–588                  v.
              RIVERKEEPER, INC., ET AL.

          PSEG FOSSIL LLC, ET AL., PETITIONERS
07–589                     v.
               RIVERKEEPER, INC., ET AL.

     UTILITY WATER ACT GROUP, PETITIONER
07–597                v.
            RIVERKEEPER, INC., ET AL.
ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
           APPEALS FOR THE SECOND CIRCUIT
                                  [April 1, 2009]

  JUSTICE SCALIA delivered the opinion of the Court.
  These cases concern a set of regulations adopted by the
Environmental Protection Agency (EPA or agency) under
§316(b) of the Clean Water Act, 33 U. S. C. §1326(b). 69
Fed. Reg. 41576 (2004). Respondents—environmental
groups and various States1—challenged those regulations,
and the Second Circuit set them aside. Riverkeeper, Inc. v.
——————
  1 The  EPA and its Administrator appeared as respondents in support
of petitioners. See Brief for Federal Parties as Respondents Supporting
Petitioners. References to “respondents” throughout the opinion refer
only to those parties challenging the EPA rules at issue in these cases.
2          ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of the Court

EPA, 475 F. 3d 83, 99–100 (2007). The issue for our deci
sion is whether, as the Second Circuit held, the EPA is not
permitted to use cost-benefit analysis in determining the
content of regulations promulgated under §1326(b).
                               I
   Petitioners operate—or represent those who operate—
large powerplants. In the course of generating power,
those plants also generate large amounts of heat. To cool
their facilities, petitioners employ “cooling water intake
structures” that extract water from nearby water sources.
These structures pose various threats to the environment,
chief among them the squashing against intake screens
(elegantly called “impingement”) or suction into the cool
ing system (“entrainment”) of aquatic organisms that live
in the affected water sources. See 69 Fed. Reg. 41586.
Accordingly, the facilities are subject to regulation under
the Clean Water Act, 33 U. S. C. §1251 et seq., which
mandates:
      “Any standard established pursuant to section 1311
    of this title or section 1316 of this title and applicable
    to a point source shall require that the location, de
    sign, construction, and capacity of cooling water in
    take structures reflect the best technology available
    for minimizing adverse environmental impact.”
    §1326(b).
Sections 1311 and 1316, in turn, employ a variety of “best
technology” standards to regulate the discharge of efflu
ents into the Nation’s waters.
   The §1326(b) regulations at issue here were promul
gated by the EPA after nearly three decades in which the
determination of the “best technology available for mini
mizing [cooling water intake structures’] adverse envi
ronmental impact” was made by permit-issuing authori
ties on a case-by-case basis, without benefit of a governing
                    Cite as: 556 U. S. ____ (2009)                   3

                         Opinion of the Court

regulation. The EPA’s initial attempt at such a regulation
came to nought when the Fourth Circuit determined that
the agency had failed to adhere to the procedural require
ments of the Administrative Procedure Act. Appalachian
Power Co. v. Train, 566 F. 2d 451, 457 (1977). The EPA
withdrew the regulation, 44 Fed. Reg. 32956 (1979), and
instead published “draft guidance” for use in implement
ing §1326(b)’s requirements via site-specific permit deci
sions under §1342. See EPA, Office of Water Enforcement
Permits Div., {Draft} Guidance for Evaluating the Adverse
Impact of Cooling Water Intake Structures on the Aquatic
Environment: Section 316(b) P. L. 92–500, (May 1, 1977), at
http://www.epa.gov/waterscience/316b/files/1977AEIguid.pdf,
(all Internet materials as visited Mar. 30, 2009, and avail
able in Clerk of Court’s case file); 69 Fed. Reg. 41584
(describing system of case-by-case permits under the draft
guidance).
  In 1995, the EPA entered into a consent decree which,
as subsequently amended, set a multiphase timetable for
the EPA to promulgate regulations under §1326(b). See
Riverkeeper, Inc. v. Whitman, No. 93 Civ. 0314 (AGS),
2001 WL 1505497, *1 (SDNY, Nov. 27, 2001). In the first
phase the EPA adopted regulations governing certain new,
large cooling water intake structures. 66 Fed. Reg. 65256
(2001) (Phase I rules); see 40 CFR §§125.80(a), 125.81(a)
(2008). Those rules require new facilities with water
intake flow greater than 10 million gallons per day to,
among other things, restrict their inflow “to a level com
mensurate with that which can be attained by a closed
cycle recirculating cooling water system.”2 §125.84(b)(1).
New facilities with water-intake flow between 2 million
——————
  2 Closed-cycle cooling systems recirculate the water used to cool the

facility, and consequently extract less water from the adjacent water
way, proportionately reducing impingement and entrainment.
Riverkeeper, Inc. v. EPA, 358 F. 3d 174, 182, n. 5 (CA2 2004); 69 Fed.
Reg. 41601, and n. 44 (2004).
4             ENTERGY CORP. v. RIVERKEEPER, INC.

                          Opinion of the Court

and 10 million gallons per day may alternatively comply
by, among other things, reducing the volume and velocity
of water removal to certain levels. §125.84(c). And all
facilities may alternatively comply by demonstrating,
among other things, “that the technologies employed will
reduce the level of adverse environmental impact . . . to a
comparable level” to what would be achieved by using a
closed-cycle cooling system. §125.84(d). These regulations
were upheld in large part by the Second Circuit in
Riverkeeper, Inc. v. EPA, 358 F. 3d 174 (2004).
   The EPA then adopted the so-called “Phase II” rules at
issue here.3 69 Fed. Reg. 41576. They apply to existing
facilities that are point sources, whose primary activity is
the generation and transmission (or sale for transmission)
of electricity, and whose water-intake flow is more than 50
million gallons of water per day, at least 25 percent of
which is used for cooling purposes. Ibid. Over 500 facili
ties, accounting for approximately 53 percent of the Na
tion’s electric-power generating capacity, fall within Phase
II’s ambit. See EPA, Economic and Benefits Analysis for
the Final Section 316(b) Phase II Existing Facilities Rule,
A3–13, Table A3–4 (Feb. 2004), online at http://www.
epa.gov/waterscience/316b/phase2/econbenefits/final/a3.pdf.
Those facilities remove on average more than 214 billion
gallons of water per day, causing impingement and en
trainment of over 3.4 billion aquatic organisms per year.
69 Fed. Reg. 41586.
   To address those environmental impacts, the EPA set
“national performance standards,” requiring Phase II
facilities (with some exceptions) to reduce “impingement
mortality for all life stages of fish and shellfish by 80 to 95
——————
  3 The EPA has also adopted Phase III rules for facilities not subject to

the Phase I and Phase II regulations. 71 Fed. Reg. 35006 (2006). A
challenge to those regulations is currently before the Fifth Circuit,
where proceedings have been stayed pending disposition of these cases.
See ConocoPhillips Co. v. EPA, No. 06–60662.
                  Cite as: 556 U. S. ____ (2009)            5

                      Opinion of the Court

percent from the calculation baseline”; a subset of facilities
must also reduce entrainment of such aquatic organisms
by “60 to 90 percent from the calculation baseline.” 40
CFR §125.94(b)(1), (2); see §125.93 (defining “calculation
baseline”). Those targets are based on the environmental
improvements achievable through deployment of a mix of
remedial technologies, 69 Fed. Reg. 41599, which the EPA
determined were “commercially available and economi
cally practicable,” id., at 41602.
   In its Phase II rules, however, the EPA expressly de
clined to mandate adoption of closed-cycle cooling systems
or equivalent reductions in impingement and entrain
ment, as it had done for new facilities subject to the Phase
I rules. Id., at 41601. It refused to take that step in part
because of the “generally high costs” of converting existing
facilities to closed-cycle operation, and because “other
technologies approach the performance of this option.” Id.,
at 41605. Thus, while closed-cycle cooling systems could
reduce impingement and entrainment mortality by up to
98 percent, id., at 41601, (compared to the Phase II targets
of 80 to 95 percent impingement reduction), the cost of
rendering all Phase II facilities closed-cycle-compliant
would be approximately $3.5 billion per year, id., at
41605, nine times the estimated cost of compliance with
the Phase II performance standards, id., at 41666. More
over, Phase II facilities compelled to convert to closed-cycle
cooling systems “would produce 2.4 percent to 4.0 percent
less electricity even while burning the same amount of
coal,” possibly requiring the construction of “20 additional
400–MW plants . . . to replace the generating capacity
lost.” Id., at 41605. The EPA thus concluded that “[a]l
though not identical, the ranges of impingement and
entrainment reduction are similar under both options. . . .
[Benefits of compliance with the Phase II rules] can ap
proach those of closed-cycle recirculating at less cost with
fewer implementation problems.” Id., at 41606.
6          ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of the Court

   The regulations permit the issuance of site-specific
variances from the national performance standards if a
facility can demonstrate either that the costs of compli
ance are “significantly greater than” the costs considered
by the agency in setting the standards, 40 CFR
§125.94(a)(5)(i), or that the costs of compliance “would be
significantly greater than the benefits of complying with
the applicable performance standards,” §125.94(a)(5)(ii).
Where a variance is warranted, the permit-issuing author
ity must impose remedial measures that yield results “as
close as practicable to the applicable performance stan
dards.” §125.94(a)(5)(i), (ii).
   Respondents challenged the EPA’s Phase II regulations,
and the Second Circuit granted their petition for review
and remanded the regulations to the EPA. The Second
Circuit identified two ways in which the EPA could per
missibly consider costs under 33 U. S. C. §1326(b): (1) in
determining whether the costs of remediation “can be
‘reasonably borne’ by the industry,” and (2) in determining
which remedial technologies are the most cost-effective,
that is, the technologies that reach a specified level of
benefit at the lowest cost. 475 F. 3d, at 99–100. See also
id., at 98, and n. 10. It concluded, however, that cost
benefit analysis, which “compares the costs and benefits of
various ends, and chooses the end with the best net bene
fits,” id., at 98, is impermissible under §1326(b), id., at
100.
   The Court of Appeals held the site-specific cost-benefit
variance provision to be unlawful. Id., at 114. Finding it
unclear whether the EPA had relied on cost-benefit analy
sis in setting the national performance standards, or had
only used cost-effectiveness analysis, it remanded to the
agency for clarification of that point. Id., at 104–105.
(The remand was also based on other grounds which are
not at issue here.) The EPA suspended operation of the
Phase II rules pending further rulemaking. 72 Fed. Reg.
                     Cite as: 556 U. S. ____ (2009)                     7

                          Opinion of the Court

37107 (2007). We then granted certiorari limited to the
following question: “Whether [§1326(b)] . . . authorizes the
[EPA] to compare costs with benefits in determining ‘the
best technology available for minimizing adverse envi
ronmental impact’ at cooling water intake structures.”
552 U. S. ___ (2008).
                              II
  In setting the Phase II national performance standards
and providing for site-specific cost-benefit variances, the
EPA relied on its view that §1326(b)’s “best technology
available” standard permits consideration of the technol
ogy’s costs, 69 Fed. Reg. 41626, and of the relationship
between those costs and the environmental benefits pro
duced, id., at 41603. That view governs if it is a reason
able interpretation of the statute—not necessarily the only
possible interpretation, nor even the interpretation
deemed most reasonable by the courts. Chevron U. S. A.
Inc. v. Natural Resources Defense Council, Inc., 467 U. S.
837, 843–844 (1984).4
  As we have described, §1326(b) instructs the EPA to set
standards for cooling water intake structures that reflect
“the best technology available for minimizing adverse
environmental impact.” The Second Circuit took that

——————
   4 The dissent finds it “puzzling” that we invoke this proposition (that

a reasonable agency interpretation prevails) at the “outset,” omitting
the supposedly prior inquiry of “ ‘whether Congress has directly spoken
to the precise question at issue.’ ” Post, at 6, n. 5 (opinion of STEVENS,
J.) (quoting Chevron, 467 U. S., at 842). But surely if Congress has
directly spoken to an issue then any agency interpretation contradict
ing what Congress has said would be unreasonable.
   What is truly “puzzling” is the dissent’s accompanying charge that
the Court’s failure to conduct the Chevron step-one inquiry at the
outset “reflects [its] reluctance to consider the possibility . . . that
Congress’ silence may have meant to foreclose cost-benefit analysis.”
Post, at 6, n. 5. Our discussion of that issue, infra, at 11, speaks for
itself.
8          ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of the Court

language to mean the technology that achieves the great
est reduction in adverse environmental impacts at a cost
that can reasonably be borne by the industry. 475 F. 3d,
at 99–100. That is certainly a plausible interpretation of
the statute. The “best” technology—that which is “most
advantageous,” Webster’s New International Dictionary
258 (2d ed. 1953)—may well be the one that produces the
most of some good, here a reduction in adverse environ
mental impact. But “best technology” may also describe
the technology that most efficiently produces some good.
In common parlance one could certainly use the phrase
“best technology” to refer to that which produces a good at
the lowest per-unit cost, even if it produces a lesser quan
tity of that good than other available technologies.
   Respondents contend that this latter reading is pre
cluded by the statute’s use of the phrase “for minimizing
adverse environmental impact.” Minimizing, they argue,
means reducing to the smallest amount possible, and the
“best technology available for minimizing adverse envi
ronmental impacts,” must be the economically feasible
technology that achieves the greatest possible reduction in
environmental harm. Brief for Respondents Riverkeeper,
Inc. et al. 25–26. But “minimize” is a term that admits of
degree and is not necessarily used to refer exclusively to
the “greatest possible reduction.” For example, elsewhere
in the Clean Water Act, Congress declared that the proce
dures implementing the Act “shall encourage the drastic
minimization of paperwork and interagency decision
procedures.” 33 U. S. C. §1251(f). If respondents’ defini
tion of the term “minimize” is correct, the statute’s use of
the modifier “drastic” is superfluous.
   Other provisions in the Clean Water Act also suggest
the agency’s interpretation. When Congress wished to
mandate the greatest feasible reduction in water pollution,
it did so in plain language: The provision governing the
discharge of toxic pollutants into the Nation’s waters
                     Cite as: 556 U. S. ____ (2009)                    9

                          Opinion of the Court

requires the EPA to set “effluent limitations [which] shall
require the elimination of discharges of all pollutants if
the Administrator finds . . . that such elimination is tech
nologically and economically achievable,” §1311(b)(2)(A)
(emphasis added).       See also §1316(a)(1) (mandating
“where practicable, a standard [for new point sources]
permitting no discharge of pollutants” (emphasis added)).
Section 1326(b)’s use of the less ambitious goal of “mini
mizing adverse environmental impact” suggests, we think,
that the agency retains some discretion to determine the
extent of reduction that is warranted under the circum
stances. That determination could plausibly involve a
consideration of the benefits derived from reductions and
the costs of achieving them. Cf. 40 CFR §125.83 (defining
“minimize” for purposes of the Phase I regulations as
“reduc[ing] to the smallest amount, extent, or degree
reasonably possible”). It seems to us, therefore, that the
phrase “best technology available,” even with the added
specification “for minimizing adverse environmental im
pact,” does not unambiguously preclude cost-benefit
analysis.5
  Respondents’ alternative (and, alas, also more complex)
argument rests upon the structure of the Clean Water Act.
The Act provided that during its initial implementation
period existing “point sources”—discrete conveyances from
which pollutants are or may be discharged, 33 U. S. C.
§1362(14)—were subject to “effluent limitations . . . which
shall require the application of the best practicable control
technology currently available.” §1311(b)(1)(A) (emphasis
——————
   5 Respondents concede that the term “available” is ambiguous, as it

could mean either technologically feasible or economically feasible. But
any ambiguity in the term “available” is largely irrelevant. Regardless
of the criteria that render a technology “available,” the EPA would still
have to determine which available technology is the “best” one. And as
discussed above, that determination may well involve consideration of
the technology’s relative costs and benefits.
10           ENTERGY CORP. v. RIVERKEEPER, INC.

                        Opinion of the Court

added). (We shall call this the “BPT” test.) Following that
transition period, the Act initially mandated adoption, by
July 1, 1983 (later extended to March 31, 1989), of stricter
effluent limitations requiring “application of the best
available technology economically achievable for such
category or class, which will result in reasonable further
progress toward the national goal of eliminating the dis
charge of all pollutants.” §1311(b)(2)(A) (emphasis added);
see EPA v. National Crushed Stone Assn., 449 U. S. 64,
69–70 (1980). (We shall call this the “BATEA” test.) Sub
sequent amendment limited application of this standard to
toxic and nonconventional pollutants, and for the remain
der established a (presumably laxer) test of “best conven
tional-pollutant control technology.” §1311(b)(2)(E).6 (We
shall call this “BCT.”) Finally, §1316 subjected certain
categories of new point sources to “the greatest degree of
effluent reduction which the Administrator determines to
be achievable through application of the best available
demonstrated control technology.” §1316(a)(1) (emphasis
added); §1316(b)(1)(B). (We shall call this the “BADT”
test.) The provision at issue here, applicable not to efflu
ents but to cooling water intake structures, requires, as we
have described, “the best technology available for minimiz
ing adverse environmental impact,” §1326(b) (emphasis
added). (We shall call this the “BTA” test.)
   The first four of these tests are elucidated by statutory
factor lists that guide their implementation. To take the
standards in (presumed) order of increasing stringency,
see Crushed Stone, supra, at 69–70: In applying the BPT
test the EPA is instructed to consider, among other fac
tors, “the total cost of application of technology in relation
——————
   6 The statute does not contain a hyphen between the words “conven

tional” and “pollutant.” “Conventional pollutant” is a statutory term,
however, see 33 U. S. C. §1314(a)(4), and it is clear that in
§1311(b)(2)(E) the adjective modifies “pollutant” rather than “control
technology.” The hyphen makes that clear.
                  Cite as: 556 U. S. ____ (2009)           11

                      Opinion of the Court

to the effluent reduction benefits to be achieved.”
§1314(b)(1)(B). In applying the BCT test it is instructed to
consider “the reasonableness of the relationship between the
costs of attaining a reduction in effluents and the effluent
reduction benefits derived.”        §1314(b)(4)(B) (emphasis
added). And in applying the BATEA and BADT tests the
EPA is instructed to consider the “cost of achieving such
effluent reduction.” §§1314(b)(2)(B), 1316(b)(1)(B). There
is no such elucidating language applicable to the BTA test
at issue here. To facilitate comparison, the texts of these
five tests, the clarifying factors applicable to them, and the
entities to which they apply are set forth in the Appendix,
infra.
   The Second Circuit, in rejecting the EPA’s use of cost
benefit analysis, relied in part on the propositions that (1)
cost-benefit analysis is precluded under the BATEA and
BADT tests; and (2) that, insofar as the permissibility of
cost-benefit analysis is concerned, the BTA test (the one at
issue here) is to be treated the same as those two. See 475
F. 3d, at 98. It is not obvious to us that the first of these
propositions is correct, but we need not pursue that point,
since we assuredly do not agree with the second. It is
certainly reasonable for the agency to conclude that the
BTA test need not be interpreted to permit only what
those other two tests permit. Its text is not identical to
theirs. It has the relatively modest goal of “minimizing
adverse environmental impact” as compared with the
BATEA’s goal of “eliminating the discharge of all pollut
ants.” And it is unencumbered by specified statutory
factors of the sort provided for those other two tests, which
omission can reasonably be interpreted to suggest that the
EPA is accorded greater discretion in determining its
precise content.
   Respondents and the dissent argue that the mere fact
that §1326(b) does not expressly authorize cost-benefit
analysis for the BTA test, though it does so for two of the
12          ENTERGY CORP. v. RIVERKEEPER, INC.

                      Opinion of the Court

other tests, displays an intent to forbid its use. This
surely proves too much. For while it is true that two of the
other tests authorize cost-benefit analysis, it is also true
that all four of the other tests expressly authorize some
consideration of costs. Thus, if respondents’ and the dis
sent’s conclusion regarding the import of §1326(b)’s silence
is correct, it is a fortiori true that the BTA test permits no
consideration of cost whatsoever, not even the “cost
effectiveness” and “feasibility” analysis that the Second
Circuit approved, see supra, at 6, that the dissent would
approve, post, at 1–2, and that respondents acknowledge.
The inference that respondents and the dissent would
draw from the silence is, in any event, implausible, as
§1326(b) is silent not only with respect to cost-benefit
analysis but with respect to all potentially relevant fac
tors. If silence here implies prohibition, then the EPA
could not consider any factors in implementing §1326(b)—
an obvious logical impossibility. It is eminently reason
able to conclude that §1326(b)’s silence is meant to convey
nothing more than a refusal to tie the agency’s hands as to
whether cost-benefit analysis should be used, and if so to
what degree.
   Contrary to the dissent’s suggestion, see post, at 3–4,
our decisions in Whitman v. American Trucking Assns.,
Inc., 531 U. S. 457 (2001), and American Textile Mfrs.
Institute, Inc. v. Donovan, 452 U. S. 490 (1981), do not
undermine this conclusion. In American Trucking, we
held that the text of §109 of the Clean Air Act, “inter
preted in its statutory and historical context . . . unambi
guously bars cost considerations” in setting air quality
standards under that provision. 531 U. S., at 471. The
relevant “statutory context” included other provisions in
the Clean Air Act that expressly authorized consideration
of costs, whereas §109 did not. Id., at 467–468. American
Trucking thus stands for the rather unremarkable propo
sition that sometimes statutory silence, when viewed in
                 Cite as: 556 U. S. ____ (2009)           13

                     Opinion of the Court

context, is best interpreted as limiting agency discretion.
For the reasons discussed earlier, §1326(b)’s silence cannot
bear that interpretation.
  In American Textile, the Court relied in part on a stat
ute’s failure to mention cost-benefit analysis in holding
that the relevant agency was not required to engage in
cost-benefit analysis in setting certain health and safety
standards. 452 U. S., at 510–512. But under Chevron,
that an agency is not required to do so does not mean that
an agency is not permitted to do so.
  This extended consideration of the text of §1326(b), and
comparison of that with the text and statutory factors
applicable to four parallel provisions of the Clean Water
Act, lead us to the conclusion that it was well within the
bounds of reasonable interpretation for the EPA to con
clude that cost-benefit analysis is not categorically forbid
den. Other arguments may be available to preclude such
a rigorous form of cost-benefit analysis as that which was
prescribed under the statute’s former BPT standard,
which required weighing “the total cost of application of
technology” against “the . . . benefits to be achieved.” See,
supra, at 10. But that question is not before us.
  In the Phase II requirements challenged here the EPA
sought only to avoid extreme disparities between costs and
benefits. The agency limited variances from the Phase II
“national performance standards” to circumstances where
the costs are “significantly greater than the benefits” of
compliance. 40 CFR §125.94(a)(5)(ii). In defining the
“national performance standards” themselves the EPA
assumed the application of technologies whose benefits
“approach those estimated” for closed-cycle cooling sys
tems at a fraction of the cost: $389 million per year, 69
Fed. Reg. 41666, as compared with (1) at least $3.5 billion
per year to operate compliant closed-cycle cooling systems,
id., at 41605 (or $1 billion per year to impose similar
requirements on a subset of Phase II facilities, id., at
14         ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of the Court

41606), and (2) significant reduction in the energy output
of the altered facilities, id., at 41605. And finally, EPA’s
assessment of the relatively meager financial benefits of
the Phase II regulations that it adopted—reduced im
pingement and entrainment of 1.4 billion aquatic organ
isms, id., at 41661, Exh. XII–6, with annualized use
benefits of $83 million, id., at 41662, and non-use benefits
of indeterminate value, id., at 41660–41661—when com
pared to annual costs of $389 million, demonstrates quite
clearly that the agency did not select the Phase II regula
tory requirements because their benefits equaled their
costs.
   While not conclusive, it surely tends to show that the
EPA’s current practice is a reasonable and hence legiti
mate exercise of its discretion to weigh benefits against
costs that the agency has been proceeding in essentially
this fashion for over 30 years. See Alaska Dept. of Envi
ronmental Conservation v. EPA, 540 U. S. 461, 487 (2004);
Barnhart v. Walton, 535 U. S. 212, 219–220 (2002). As
early as 1977, the agency determined that, while §1326(b)
does not require cost-benefit analysis, it is also not reason
able to “interpret Section [1326(b)] as requiring use of
technology whose cost is wholly disproportionate to the
environmental benefit to be gained.” In re Public Service
Co. of New Hampshire, 1 E. A. D. 332, 340 (1977). See
also In re Central Hudson Gas and Electric Corp., EPA
Decision of the General Counsel, NPDES Permits, No. 63,
pp. 371, 381 (July 29, 1977) (“EPA ultimately must dem
onstrate that the present value of the cumulative annual
cost of modifications to cooling water intake structures is
not wholly out of proportion to the magnitude of the esti
mated environmental gains”); Seacoast Anti-Pollution
League v. Costle, 597 F. 2d 306, 311 (CA1 1979) (rejecting
challenge to an EPA permit decision that was based in
part on the agency’s determination that further restric
tions would be “ ‘wholly disproportionate to any environ
mental benefit’ ”). While the EPA’s prior “wholly dispro
                    Cite as: 556 U. S. ____ (2009)                 15

                        Opinion of the Court

portionate” standard may be somewhat different from its
current “significantly greater than” standard, there is
nothing in the statute that would indicate that the former
is a permissible interpretation while the latter is not.
   Indeed, in its review of the EPA’s Phase I regulations,
the Second Circuit seemed to recognize that §1326(b)
permits some form of cost-benefit analysis. In considering
a challenge to the EPA’s rejection of dry cooling systems7
as the “best technology available” for Phase I facilities the
Second Circuit noted that “while it certainly sounds sub
stantial that dry cooling is 95 percent more effective than
closed-cycle cooling, it is undeniably relevant that that
difference represents a relatively small improvement over
closed-cycle cooling at a very significant cost.”
Riverkeeper, 358 F. 3d, at 194, n. 22. And in the decision
below rejecting the use of cost-benefit analysis in the
Phase II regulations, the Second Circuit nonetheless
interpreted “best technology available” as mandating only
those technologies that can “be reasonably borne by the
industry.” 475 F. 3d, at 99. But whether it is “reasonable”
to bear a particular cost may well depend on the resulting
benefits; if the only relevant factor was the feasibility of
the costs, their reasonableness would be irrelevant.
   In the last analysis, even respondents ultimately recog
nize that some form of cost-benefit analysis is permissible.
They acknowledge that the statute’s language is “plainly
not so constricted as to require EPA to require industry
petitioners to spend billions to save one more fish or
plankton.” Brief for Respondents Riverkeeper, Inc. et al.
29. This concedes the principle—the permissibility of at
least some cost-benefit analysis—and we see no statutory
basis for limiting its use to situations where the benefits

——————
  7 Dry cooling systems use air drafts to remove heat, and accordingly

remove little or no water from surrounding water sources. See 66 Fed.
Reg. 65282 (2001).
16             ENTERGY CORP. v. RIVERKEEPER, INC.

                            Opinion of the Court

are de minimis rather than significantly disproportionate.
                         *    *    *
   We conclude that the EPA permissibly relied on cost
benefit analysis in setting the national performance stan
dards and in providing for cost-benefit variances from
those standards as part of the Phase II regulations. The
Court of Appeals’ reliance in part on the agency’s use of
cost-benefit analysis in invalidating the site-specific cost
benefit variance provision, 475 F. 3d, at 114, was therefore
in error, as was its remand of the national performance
standards for clarification of whether cost-benefit analysis
was impermissibly used, id., at 104–105. We of course
express no view on the remaining bases for the Second
Circuit’s remand which did not depend on the permissibil
ity of cost-benefit analysis. See id., at 108, 110, 113, 115,
117, 120.8 The judgment of the Court of Appeals is re
versed, and the cases are remanded for further proceed
ings consistent with this opinion.
                                             It is so ordered.
——————
  8 JUSTICE  BREYER would remand for the additional reason of what he
regards as the agency’s inadequate explanation of the change in its
criterion for variances—from a relationship of costs to benefits that is
“ ‘wholly disproportionate’ ” to one that is “ ‘significantly greater.’ ” Post,
at 7–8 (opinion concurring in part and dissenting in part). That ques
tion can have no bearing upon whether the EPA can use cost-benefit
analysis, which is the only question presented here. It seems to us, in
any case, that the EPA’s explanation was ample. It explained that the
“wholly out of proportion” standard was inappropriate for the existing
facilities subject to the Phase II rules because those facilities lack “the
greater flexibility available to new facilities for selecting the location of
their intakes and installing technologies at lower costs relative to the
costs associated with retrofitting existing facilities,” and because
“economically impracticable impacts on energy prices, production costs,
and energy production . . . could occur if large numbers of Phase II
existing facilities incurred costs that were more than ‘significantly
greater’ than but not ‘wholly out of proportion’ to the costs in the EPA’s
record.” 68 Fed. Reg. 13541 (2003).
                       Cite as: 556 U. S. ____ (2009) 
                         17

                          Opinion of the Court
                     Appendix to opinion of the Court 


         APPENDIX TO OPINION OF THE COURT 


                                                                 Entities
      Statutory              Statutorily Mandated
                                                                Subject to
      Standard                      Factors
                                                                Regulation
           BPT:             “Factors relating to the           Existing point
“[E]ffluent limitations     assessment of best practicable     sources during
. . . which shall require   control technology currently       the Clean Water
the application of the      available . . . shall include      Act’s initial
best practicable control    consideration of the total cost    implementation
technology currently        of application of technology in    phase.
available.” 33 U. S. C.     relation to the effluent
§1311(b)(1)(A) (empha       reduction benefits to be
sis added).                 achieved.” 33 U. S. C.
                            §1314(b)(1)(B).
           BCT:             “Factors relating to the           Existing point
“[E]ffluent limitations     assessment of best conven          sources that
. . . which shall require   tional pollutant control           discharge
application of the best     technology . . . shall include     “conventional
conventional pollutant      consideration of the reason        pollutants” as
control technology.” 33     ableness of the relationship       defined by the
U. S. C. §1311(b)(2)(E)     between the costs of attaining     EPA under 33
(emphasis added).           a reduction in effluents and       U. S. C.
                            the effluent reduction benefits    §1314(a)(4).
                            derived.” 33 U. S. C.
                            §1314(b)(4)(B).
          BATEA:            “Factors relating to the           Existing point
“[E]ffluent limitations     assessment of best available       sources that
. . . which . . . shall     technology shall take into         discharge toxic
require application of      account . . . the cost of achiev   pollutants and
the best available          ing such effluent reduction.”      non
technology economically     33 U. S. C. §1314(b)(2)(B).        conventional
achievable . . . which                                         pollutants.
will result in reasonable
further progress toward
the national goal of
eliminating the dis
charge of all pollut
ants.” 33 U. S. C.
§1311(b)(2)(A) (empha
sis added).
18            ENTERGY CORP. v. RIVERKEEPER, INC.

                         Opinion of the Court
                    Appendix to opinion of the Court
                                                               Entities
     Statutory              Statutorily Mandated
                                                              Subject to
     Standard                      Factors
                                                              Regulation
          BADT:            “[T]he Administrator shall        New point
“[A] standard for the      take into consideration the       sources within
control of the discharge   cost of achieving such effluent   the categories of
of pollutants which        reduction, and any non-water      sources identi
reflects the greatest      quality environmental impact      fied by the EPA
degree of effluent         and energy requirements.” 33      under 33
reduction with the         U. S. C. §1316(b)(1)(B).          U. S. C.
Administrator deter                                          §1316(b)(1)(A).
mines to be achievable
through application of
the best available
demonstrated control
technology.” 33 U. S. C.
§1316(a)(1) (emphasis
added).
          BTA:           N/A                                 Point sources
“Any standard . . .                                          that operate
applicable to a point                                        cooling water
source shall require                                         intake struc
that the location,                                           tures.
design, construction,
and capacity of cooling
water intake structures
reflect the best technol
ogy available for
minimizing adverse
environmental impact.”
33 U. S. C. §1326(b).
                 Cite as: 556 U. S. ____ (2009)           1

                     Opinion of BREYER, J.

SUPREME COURT OF THE UNITED STATES
                         _________________

                Nos. 07–588, 07–589 and 07–597
                         _________________


         ENTERGY CORPORATION, PETITIONER
07–588                 v.
             RIVERKEEPER, INC., ET AL.

         PSEG FOSSIL LLC, ET AL., PETITIONERS
07–589                    v.
              RIVERKEEPER, INC., ET AL.

     UTILITY WATER ACT GROUP, PETITIONER
07–597                v.
            RIVERKEEPER, INC., ET AL.
ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
           APPEALS FOR THE SECOND CIRCUIT
                        [April 1, 2009]

  JUSTICE BREYER, concurring in part and dissenting in
part.
  I agree with the Court that the relevant statutory lan
guage authorizes the Environmental Protection Agency
(EPA) to compare costs and benefits. Ante, at 7–13. None
theless the drafting history and legislative history of
related provisions, Pub. L. 92–500, §§301, 304, 86 Stat.
844, 850, as amended, 33 U. S. C. §§1311, 1314, make
clear that those who sponsored the legislation intended
the law’s text to be read as restricting, though not forbid
ding, the use of cost-benefit comparisons. And I would
apply that text accordingly.
                            I
  Section 301 provides that, not later than 1977, effluent
2          ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of BREYER, J.

limitations for point sources shall require the application
of “best practicable control technology,” §301(b)(1)(A), 86
Stat. 845 (emphasis added); and that, not later than 1983
(later extended to 1989), effluent limitations for categories
and classes of point sources shall require application of the
“best available technology economically achievable,”
§301(b)(2)(A), ibid. (emphasis added). Section 304(b), in
turn, identifies the factors that the Agency shall take into
account in determining (1) “best practicable control tech
nology” and (2) “best available technology.” 86 Stat. 851
(emphasis added).
   With respect to the first, the statute provides that the
factors taken into account by the Agency “shall include
consideration of the total cost of application of technology
in relation to the effluent reduction benefits to be achieved
from such application . . . and such other factors as the
Administrator deems appropriate.” §304(b)(1)(B), ibid.
With respect to the second, the statute says that the
Agency “shall take into account . . . the cost of achieving
such effluent reduction” and “such other factors as the
Administrator deems appropriate.” §304(b)(2)(B), ibid.
   The drafting history makes clear that the statute re
flects a compromise. In the House version of the legisla
tion, the Agency was to consider “the cost and the eco
nomic, social, and environmental impact of achieving such
effluent reduction” when determining both “best practica
ble” and “best available” technology. H. R. 11896, 92d
Cong., 2d Sess., §§304(b)(1)(B), (b)(2)(B) (1972) (as re
ported from committee). The House Report explained that
the “best available technology” standard was needed—as
opposed to mandating the elimination of discharge of
pollutants—because “the difference in the cost of 100
percent elimination of pollutants as compared to the cost
of removal of 97–99 percent of the pollutants in an effluent
can far exceed any reasonable benefit to be achieved. In
most cases, the cost of removal of the last few percentage
                 Cite as: 556 U. S. ____ (2009)           3

                     Opinion of BREYER, J.

points increases expo[n]entially.” H. R. Rep. No. 92–911,
p. 103 (1972).
    In the Senate version, the Agency was to consider “the
cost of achieving such effluent reduction” when determin
ing both “best practicable” and “best available” technology.
S. 2770, 92d Cong., 1st Sess., §§304(b)(1)(B), (b)(2)(B)
(1971) (as reported from committee). The Senate Report
explains that “the technology must be available at a cost
. . . which the Administrator determines to be reasonable.”
S. Rep. No. 92–414, p. 52 (1971) (hereinafter S. Rep.). But
it said nothing about comparing costs and benefits.
    The final statute reflects a modification of the House’s
language with respect to “best practicable,” and an adop
tion of the Senate’s language with respect to “best avail
able.” S. Conf. Rep. No. 92–1236, pp. 124–125 (1972). The
final statute does not require the Agency to compare costs
to benefits when determining “best available technology,”
but neither does it expressly forbid such a comparison.
    The strongest evidence in the legislative history sup
porting the respondents’ position—namely, that Congress
intended to forbid comparisons of costs and benefits when
determining the “best available technology”—can be found
in a written discussion of the Act’s provisions distributed
to the Senate by Senator Edmund Muskie, the Act’s prin
cipal sponsor, when he submitted the Conference Report
for the Senate’s consideration. 118 Cong. Rec. 33693
(1972). The relevant part of that discussion points out
that, as to “best practicable technology,” the statute re
quires application of a “balancing test between total cost
and effluent reduction benefits.”       Id., at 33696; see
§304(b)(1)(B). But as to “best available technology,” it
states: “While cost should be a factor in the Administra
tor’s judgment, no balancing test will be required.” Ibid.;
see §304(b)(2)(B). And Senator Muskie’s discussion later
speaks of the agency “evaluat[ing] . . . what needs to be
done” to eliminate pollutant discharge and “what is
4           ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of BREYER, J.

achievable,” both “without regard to cost.” Ibid.
   As this language suggests, the Act’s sponsors had rea
sons for minimizing the EPA’s investigation of, and reli
ance upon, cost-benefit comparisons. The preparation of
formal cost-benefit analyses can take too much time,
thereby delaying regulation. And the sponsors feared that
such analyses would emphasize easily quantifiable factors
over more qualitative factors (particularly environmental
factors, for example, the value of preserving non
marketable species of fish). See S. Rep., at 47. Above all,
they hoped that minimizing the use of cost-benefit com
parisons would force the development of cheaper control
technologies; and doing so, whatever the initial inefficien
cies, would eventually mean cheaper, more effective
cleanup. See id., at 50–51.
   Nonetheless, neither the sponsors’ language nor the
underlying rationale requires the Act to be read in a way
that would forbid cost-benefit comparisons. Any such
total prohibition would be difficult to enforce, for every
real choice requires a decisionmaker to weigh advantages
against disadvantages, and disadvantages can be seen in
terms of (often quantifiable) costs. Moreover, an absolute
prohibition would bring about irrational results. As the
respondents themselves say, it would make no sense to
require plants to “spend billions to save one more fish or
plankton.” Brief for Respondents Riverkeeper, Inc., et al.
29. That is so even if the industry might somehow afford
those billions. And it is particularly so in an age of limited
resources available to deal with grave environmental
problems, where too much wasteful expenditure devoted to
one problem may well mean considerably fewer resources
available to deal effectively with other (perhaps more
serious) problems.
   Thus Senator Muskie used nuanced language, which
one can read as leaving to the Agency a degree of author
ity to make cost-benefit comparisons in a manner that is
                  Cite as: 556 U. S. ____ (2009)            5

                      Opinion of BREYER, J.

sensitive both to the need for such comparisons and to the
concerns that the law’s sponsors expressed. The relevant
statement begins by listing various factors that the statute
requires the Administrator to take into account when
applying the phrase “practicable” to “classes and catego
ries.” 118 Cong. Rec. 33696. It states that, when doing so,
the Administrator must apply (as the statute specifies) a
“balancing test between total cost and effluent reduction
benefits.” Ibid. At the same time, it seeks to reduce the
likelihood that the Administrator will place too much
weight upon high costs by adding that the balancing test
“is intended to limit the application of technology only
where the additional degree of effluent reduction is wholly
out of proportion to the costs of achieving” a “marginal
level of reduction.” Ibid.
   Senator Muskie’s statement then considers the “differ
ent test” that the statute requires the Administrator to
apply when determining the “ ‘best available’ ” technology.
Ibid. (emphasis added). Under that test, the Administra
tor “may consider a broader range of technological alterna
tives.” Ibid. And in determining what is “ ‘best available’
for a category or class, the Administrator is expected to
apply the same principles involved in making the deter
mination of ‘best practicable’ . . . except as to cost-benefit
analysis.” Ibid. (emphasis added). That is, “[w]hile cost
should be a factor . . . no balancing test will be required.”
Ibid. (emphasis added). Rather, “[t]he Administrator will
be bound by a test of reasonableness.” Ibid. (emphasis
added). The statement adds that the “ ‘best available’ ”
standard “is intended to reflect the need to press toward
increasingly higher levels of control.” Ibid. (emphasis
added). And “the reasonableness of what is ‘economically
achievable’ should reflect an evaluation of what needs to
be done to move toward the elimination of the discharge of
pollutants and what is achievable through the application
of available technology—without regard to cost.” Ibid.
6          ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of BREYER, J.

(emphasis added).
  I believe, as I said, that this language is deliberately
nuanced. The statement says that where the statute uses
the term “best practicable,” the statute requires compari
sons of costs and benefits; but where the statute uses the
term “best available,” such comparisons are not “required.”
Ibid. (emphasis added). Senator Muskie does not say that
all efforts to compare costs and benefits are forbidden.
  Moreover, the statement points out that where the
statute uses the term “best available,” the Administrator
“will be bound by a test of reasonableness.” Ibid. (empha
sis added). It adds that the Administrator should apply
this test in a way that reflects its ideal objective, moving
as closely as is technologically possible to the elimination
of pollution. It thereby says the Administrator should
consider, i.e., take into account, how much pollution would
still remain if the best available technology were to be
applied everywhere—“without regard to cost.” Ibid. It
does not say that the Administrator must set the standard
based solely on the result of that determination. (It would
be difficult to reconcile the alternative, more absolute
reading of this language with the Senator’s earlier “test of
reasonableness.”)
  I say that one may, not that one must, read Senator
Muskie’s statement this way. But to read it differently
would put the Agency in conflict with the test of reason
ableness by threatening to impose massive costs far in
excess of any benefit. For 30 years the EPA has read the
statute and its history in this way. The EPA has thought
that it would not be “reasonable to interpret Section 316(b)
as requiring use of technology whose cost is wholly dispro
portionate to the environmental benefit to be gained.”
In re Pub. Serv. Co. of N. H. (Seabrook Station, Units 1
and 2), 1 E. A. D. 332, 340 (1977), remanded on other
grounds, Seacoast Anti-Pollution League v. Costle, 572
F. 2d 872 (CA1 1978) (emphasis added); see also In re
                  Cite as: 556 U. S. ____ (2009)            7

                      Opinion of BREYER, J.

Central Hudson Gas & Elec. Corp., EPA Decision of the
General Counsel, NPDES Permits, No. 63, p. 371 (July 29,
1977) (also applying a “wholly disproportionate” test); In
re Pub. Serv. Co. of N. H., 1 E. A. D. 455 (1978) (same).
“[T]his Court will normally accord particular deference to
an agency interpretation of ‘longstanding’ duration.”
Barnhart v. Walton, 535 U. S. 212, 220 (2002). And for the
last 30 years, the EPA has given the statute a permissive
reading without suggesting that in doing so it was ignor
ing or thwarting the intent of the Congress that wrote the
statute.
   The EPA’s reading of the statute would seem to permit
it to describe environmental benefits in non-monetized
terms and to evaluate both costs and benefits in accor
dance with its expert judgment and scientific knowledge.
The Agency can thereby avoid lengthy formal cost-benefit
proceedings and futile attempts at comprehensive moneti
zation, see 69 Fed. Reg. 41661–41662; take account of
Congress’ technology-forcing objectives; and still prevent
results that are absurd or unreasonable in light of extreme
disparities between costs and benefits. This approach, in
my view, rests upon a “reasonable interpretation” of the
statute—legislative history included. Hence it is lawful.
Chevron U. S. A. Inc. v. Natural Resources Defense Coun
cil, Inc., 467 U. S. 837, 844 (1984). Most of what the ma
jority says is consistent with this view, and to that extent I
agree with its opinion.
                              II
  The cases before us, however, present an additional
problem. We here consider a rule that permits variances
from national standards if a facility demonstrates that its
costs would be “significantly greater than the benefits of
complying.” 40 CFR §125.94(a)(5)(ii) (2008). The words
“significantly greater” differ from the words the EPA has
traditionally used to describe its standard, namely,
8          ENTERGY CORP. v. RIVERKEEPER, INC.

                     Opinion of BREYER, J.

“wholly disproportionate.” Perhaps the EPA does not
mean to make much of that difference. But if it means the
new words to set forth a new and different test, the EPA
must adequately explain why it has changed its standard.
Motor Vehicle Mfrs. Assn. of United States, Inc. v. State
Farm Mut. Automobile Ins. Co., 463 U. S. 29, 42–43
(1983); National Cable & Telecommunications Assn. v.
Brand X Internet, 545 U. S. 967, 981 (2005); Thomas
Jefferson Univ. v. Shalala, 512 U. S. 504, 524, n. 3 (1994)
(THOMAS, J., dissenting).
  I am not convinced the EPA has successfully explained
the basis for the change. It has referred to the fact that
existing facilities have less flexibility than new facilities
with respect to installing new technologies, and it has
pointed to special, energy-related impacts of regulation.
68 Fed. Reg. 13541 (2003) (proposed rule). But it has not
explained why the traditional “wholly disproportionate”
standard cannot do the job now, when the EPA has used
that standard (for existing facilities and otherwise) with
apparent success in the past. See, e.g., Central Hudson,
supra.
  Consequently, like the majority, I would remand these
cases to the Court of Appeals. But unlike the majority I
would permit that court to remand the cases to the EPA so
that the EPA can either apply its traditional “wholly
disproportionate” standard or provide an adequately
reasoned explanation for the change.
                 Cite as: 556 U. S. ____ (2009)            1

                    STEVENS, J., dissenting

SUPREME COURT OF THE UNITED STATES
                         _________________

                Nos. 07–588, 07–589 and 07–597
                         _________________


         ENTERGY CORPORATION, PETITIONER
07–588                 v.
             RIVERKEEPER, INC., ET AL.

         PSEG FOSSIL LLC, ET AL., PETITIONERS
07–589                    v.
              RIVERKEEPER, INC., ET AL.

     UTILITY WATER ACT GROUP, PETITIONER
07–597                v.
            RIVERKEEPER, INC., ET AL.
ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
           APPEALS FOR THE SECOND CIRCUIT
                        [April 1, 2009]

  JUSTICE STEVENS, with whom JUSTICE SOUTER and
JUSTICE GINSBURG join, dissenting.
  Section 316(b) of the Clean Water Act (CWA), 33
U. S. C. §1326(b), which governs industrial powerplant
water intake structures, provides that the Environmental
Protection Agency (EPA or Agency) “shall require” that
such structures “reflect the best technology available for
minimizing adverse environmental impact.” The EPA has
interpreted that mandate to authorize the use of cost
benefit analysis in promulgating regulations under
§316(b). For instance, under the Agency’s interpretation,
technology that would otherwise qualify as the best avail
able need not be used if its costs are “significantly greater
than the benefits” of compliance. 40 CFR §125.94(a)(5)(ii)
(2008).
2             ENTERGY CORP. v. RIVERKEEPER, INC.

                        STEVENS, J., dissenting

  Like the Court of Appeals, I am convinced that the EPA
has misinterpreted the plain text of §316(b). Unless costs
are so high that the best technology is not “available,”
Congress has decided that they are outweighed by the
benefits of minimizing adverse environmental impact.
Section 316(b) neither expressly nor implicitly authorizes
the EPA to use cost-benefit analysis when setting regula
tory standards; fairly read, it prohibits such use.
                              I
   As typically performed by the EPA, cost-benefit analysis
requires the Agency to first monetize the costs and bene
fits of a regulation, balance the results, and then choose
the regulation with the greatest net benefits. The process
is particularly controversial in the environmental context
in which a regulation’s financial costs are often more
obvious and easier to quantify than its environmental
benefits. And cost-benefit analysis often, if not always,
yields a result that does not maximize environmental
protection.
   For instance, although the EPA estimated that water
intake structures kill 3.4 billion fish and shellfish each
year,1 see 69 Fed. Reg. 41586, the Agency struggled to
calculate the value of the aquatic life that would be pro

——————
  1 To produce energy, industrial powerplants withdraw billions of

gallons of water daily from our Nation’s waterways.            Thermo
electric powerplants alone demand 39 percent of all freshwater with
drawn nationwide. See Dept. of Energy, Addressing the Critical
Link Between Fossil Energy and Water 2 (Oct. 2005), http://
www.netl.doe.gov/technologies/coalpower/ewr/pubs/NETL_Water_Paper
_Final_Oct.2005.pdf (all Internet materials as visited Mar. 18, 2009,
and available in Clerk of Court’s case file). The fish and shellfish are
killed by “impingement” or “entrainment.” Impingement occurs when
aquatic organisms are trapped against the screens and grills of water
intake structures. Entrainment occurs when these organisms are
drawn into the intake structures. See Riverkeeper, Inc. v. EPA, 475
F. 3d 83, 89 (CA2 2007); 69 Fed. Reg. 41586 (2004).
                    Cite as: 556 U. S. ____ (2009)                  3

                       STEVENS, J., dissenting

tected under its §316(b) regulations, id., at 41661. To
compensate, the EPA took a shortcut: Instead of monetiz
ing all aquatic life, the Agency counted only those species
that are commercially or recreationally harvested, a tiny
slice (1.8 percent to be precise) of all impacted fish and
shellfish. This narrow focus in turn skewed the Agency’s
calculation of benefits. When the EPA attempted to value
all aquatic life, the benefits measured $735 million.2 But
when the EPA decided to give zero value to the 98.2 per
cent of fish not commercially or recreationally harvested,
the benefits calculation dropped dramatically—to $83
million. Id., at 41666. The Agency acknowledged that its
failure to monetize the other 98.2 percent of affected spe
cies “ ‘could result in serious misallocation of resources,’ ”
id., at 41660, because its “comparison of complete costs
and incomplete benefits does not provide an accurate
picture of net benefits to society.”3
   Because benefits can be more accurately monetized in
some industries than in others, Congress typically decides
whether it is appropriate for an agency to use cost-benefit
analysis in crafting regulations. Indeed, this Court has
recognized that “[w]hen Congress has intended that an
agency engage in cost-benefit analysis, it has clearly indi
cated such intent on the face of the statute.” American
Textile Mfrs. Institute, Inc. v. Donovan, 452 U. S. 490, 510
(1981). Accordingly, we should not treat a provision’s
silence as an implicit source of cost-benefit authority,
particularly when such authority is elsewhere expressly
granted and it has the potential to fundamentally alter an
——————
  2 EPA, Economic and Benefits Analysis for the Proposed Section

316(b) Phase II Existing Facilities Rule, p. D1–4 (EPA–821–R–02–001,
Feb. 2002), http://www.epa.gov/waterscience/316b/phase2/econbenefits.
  3 EPA, Economic and Benefits Analysis for the Final Section 316(b)

Phase II Existing Facilities Rule, p. D1–5 (EPA–821–R–04–005, Feb.
2004), http://www.epa.gov/waterscience/316b/phase2/econbenefits/final.
htm.
4          ENTERGY CORP. v. RIVERKEEPER, INC.

                    STEVENS, J., dissenting

agency’s approach to regulation. Congress, we have noted,
“does not alter the fundamental details of a regulatory
scheme in vague terms or ancillary provisions—it does
not, one might say, hide elephants in mouseholes.” Whit
man v. American Trucking Assns., Inc., 531 U. S. 457,
467–468 (2001).
  When interpreting statutory silence in the past, we have
sought guidance from a statute’s other provisions. Evi
dence that Congress confronted an issue in some parts of a
statute, while leaving it unaddressed in others, can dem
onstrate that Congress meant its silence to be decisive.
We concluded as much in American Trucking. In that
case, the Court reviewed the EPA’s claim that §109 of the
Clean Air Act (CAA), 42 U. S. C. §7409(a) (2000 ed.), au
thorized the Agency to consider implementation costs in
setting ambient air quality standards. We read §109,
which was silent on the matter, to prohibit Agency reli
ance on cost considerations. After examining other provi
sions in which Congress had given the Agency authority to
consider costs, the Court “refused to find implicit in am
biguous sections of the CAA an authorization to consider
costs that has elsewhere, and so often, been expressly
granted.” 531 U. S., at 467. Studied silence, we thus
concluded, can be as much a prohibition as an explicit
“no.”
  Further motivating the Court in American Trucking was
the fact that incorporating implementation costs into the
Agency’s calculus risked countermanding Congress’ deci
sion to protect public health. The cost of implementation,
we said, “is both so indirectly related to public health and
so full of potential for canceling the conclusions drawn
from direct health effects that it would surely have been
expressly mentioned in [the text] had Congress meant it to
be considered.” Id., at 469.
  American Trucking’s approach should have guided the
Court’s reading of §316(b). Nowhere in the text of §316(b)
                     Cite as: 556 U. S. ____ (2009)                   5

                        STEVENS, J., dissenting

does Congress explicitly authorize the use of cost-benefit
analysis as it does elsewhere in the CWA. And the use of
cost-benefit analysis, like the consideration of implemen
tation costs in American Trucking, “pad[s]” §316(b)’s
environmental mandate with tangential economic effi
ciency concerns. Id., at 468. Yet the majority fails to
follow American Trucking despite that case’s obvious
relevance to our inquiry.
                             II
   In 1972, Congress amended the CWA to strike a careful
balance between the country’s energy demands and its
desire to protect the environment. The Act required in
dustry to adopt increasingly advanced technology capable
of mitigating its detrimental environmental impact. Not
all point sources were subject to strict rules at once. Ex
isting plants were granted time to retrofit with the best
technology while new plants were required to incorporate
such technology as a matter of design. Although Congress
realized that technology standards would necessarily put
some firms out of business, see EPA v. National Crushed
Stone Assn., 449 U. S. 64, 79 (1980), the statute’s steady
march was toward stricter rules and potentially higher
costs.
   Section §316(b) was an integral part of the statutory
scheme. The provision instructs that “[a]ny standard
established pursuant to section 1311 of this title or section
1316 of this title and applicable to a point source shall
require that the location, design, construction, and capac
ity of cooling water intake structures reflect the best tech
nology available for minimizing adverse environmental
impact.”     33 U. S. C. §1326(b) (2006 ed.) (emphasis
added).4 The “best technology available,” or “BTA,” stan
——————
  4 The two cross-referenced provisions, §§1311 and 1316, also establish

“best technology” standards, the first applicable to existing point
sources and the second to new facilities. The reference to these provi
6             ENTERGY CORP. v. RIVERKEEPER, INC.

                         STEVENS, J., dissenting

dard delivers a clear command: To minimize the adverse
environmental impact of water intake structures, the
EPA must require industry to adopt the best technology
available.
   Based largely on the observation that §316(b)’s text
offers little guidance and therefore delegates some amount
of gap-filling authority to the EPA, the Court concludes
that the Agency has discretion to rely on cost-benefit
analysis. See ante, at 11–12. The Court assumes that, by
not specifying how the EPA is to determine BTA, Congress
intended to give considerable discretion to the EPA to
decide how to proceed. Silence, in the majority’s view,
represents ambiguity and an invitation for the Agency to
decide for itself which factors should govern its regulatory
approach.
   The appropriate analysis requires full consideration of
the CWA’s structure and legislative history to determine
whether Congress contemplated cost-benefit analysis and,
if so, under what circumstances it directed the EPA to
utilize it. This approach reveals that Congress granted
the EPA authority to use cost-benefit analysis in some
contexts but not others, and that Congress intend to con
trol, not delegate, when cost-benefit analysis should be
used. See Chevron U. S. A. Inc. v. Natural Resources
Defense Council, Inc., 467 U. S. 837, 842–843 (1984).5
——————
sions in §316(b) merely requires any rule promulgated under those
provisions, when applied to a point source with a water intake struc
ture, to incorporate §316(b) standards.
  5 The majority announces at the outset that the EPA’s reading of the

BTA standard “governs if it is a reasonable interpretation of the stat
ute—not necessarily the only possible interpretation, nor even the
interpretation deemed most reasonable by the courts.” Ante, at 7. This
observation is puzzling in light of the commonly understood practice
that, as a first step, we ask “whether Congress has directly spoken to
the precise question at issue.” Chevron, 467 U. S., at 842. Only later, if
Congress’ intent is not clear, do we consider the reasonableness of the
agency’s action. Id., at 843. Assuming ambiguity and moving to the
                     Cite as: 556 U. S. ____ (2009)                     7

                         STEVENS, J., dissenting

   Powerful evidence of Congress’ decision not to authorize
cost-benefit analysis in the BTA standard lies in the series
of standards adopted to regulate the outflow, or effluent,
from industrial powerplants. Passed at the same time as
the BTA standard at issue here, the effluent limitation
standards imposed increasingly strict technology require
ments on industry. In each effluent limitation provision,
Congress distinguished its willingness to allow the EPA to
consider costs from its willingness to allow the Agency to
conduct a cost-benefit analysis. And to the extent Con
gress permitted cost-benefit analysis, its use was intended
to be temporary and exceptional.
   The first tier of technology standards applied to existing
plants—facilities for which retrofitting would be particu
larly costly. Congress required these plants to adopt
“effluent limitations . . . which shall require the applica
tion of the best practicable control technology currently
available.” 33 U. S. C. §1311(b)(1)(A). Because this “best
practicable,” or “BPT,” standard was meant to ease indus
try’s transition to the new technology-based regime, Con
gress gave BPT two unique features: First, it would be
temporary, remaining in effect only until July 1, 1983.6
Second, it specified that the EPA was to conduct a cost
benefit analysis in setting BPT requirements by consider
ing “the total cost of application of technology in relation
to the effluent reduction benefits to be achieved from such
application.”7     §1314(b)(1)(B).   Permitting cost-benefit
——————
second step reflects the Court’s reluctance to consider the possibility,
which it later laments is “more complex,” ante, at 9, that Congress’
silence may have meant to foreclose cost-benefit analysis.
   6 Congress later extended the deadline to March 31, 1989.
   7 Senator Muskie, the Senate sponsor of the legislation, described the

cost-benefit analysis permitted under BPT as decidedly narrow, assert
ing that “[t]he balancing test between total cost and effluent reduction
benefits is intended to limit the application of technology only where
the additional degree of effluent reduction is wholly out of proportion to
the costs of achieving such marginal level of reduction for any class or
8            ENTERGY CORP. v. RIVERKEEPER, INC.

                       STEVENS, J., dissenting

analysis in BPT gave the EPA the ability to cushion the
new technology requirement. For a limited time, a tech
nology with costs that exceeded its benefits would not be
considered “best.”
   The second tier of technology standards required exist
ing powerplants to adopt the “best available technology
economically achievable” to advance “the national goal of
eliminating     the     discharge    of    all   pollutants.”
§1311(b)(2)(A). In setting this “best available technology,”
or “BAT,”8 standard, Congress gave the EPA a notably
different command for deciding what technology would
qualify as “best”: The EPA was to consider, among other
factors, “the cost of achieving such effluent reduction,” but
Congress did not grant it authority to balance costs with
the benefits of stricter regulation. §1314(b)(2)(B). Indeed,
in Crushed Stone this Court explained that the difference
between BPT and BAT was the existence of cost-benefit
authority in the first and the absence of that authority in
the second. See 449 U. S., at 71 (“Similar directions are
given the Administrator for determining effluent reduc
tions attainable from the BAT except that in assessing
BAT total cost is no longer to be considered in comparison
to effluent reduction benefits”).
   The BAT standard’s legislative history strongly supports
the view that Congress purposefully withheld cost-benefit
authority for this tier of regulation. See ibid., n. 10. The
House of Representatives and the Senate split over the
role cost-benefit analysis would play in the BAT provision.
The House favored the tool, see H. R. Rep. No. 92–911, p.
107 (1972), 1 Leg. Hist. 794, while the Senate rejected it,
——————
category of sources.” 1 Legislative History of the Water Pollution
Control Act Amendments of 1972 (Committee Print compiled for the
Senate Committee on Public Works by the Library of Congress), Ser.
No. 93–1, p. 170 (1973) (hereinafter Leg. Hist.)
  8 Although the majority calls this “BATEA,” the parties refer to the

provision as “BAT,” and for simplicity, so will I.
                 Cite as: 556 U. S. ____ (2009)            9

                    STEVENS, J., dissenting

see 2 id., at 1183; id., at 1132. The Senate view ultimately
prevailed in the final legislation, resulting in a BAT stan
dard that was “not subject to any test of cost in relation to
effluent reduction benefits or any form of cost/benefit
analysis.” 3 Legislative History of the Clean Water Act of
1977: A Continuation of the Legislative History of the
Federal Water Pollution Control Act (Committee Print
compiled for the Senate Committee on Environment and
Public Works by the Library of Congress), Ser. No. 95–14,
p. 427 (1978).
   The third and strictest regulatory tier was reserved for
new point sources—facilities that could incorporate tech
nology improvements into their initial design. These new
facilities were required to adopt “the best available dem
onstrated control technology,” or “BADT,” which Congress
described as “a standard . . . which reflect[s] the greatest
degree of effluent reduction.” §1316(a)(1). In administer
ing BADT, Congress directed the EPA to consider “the cost
of achieving such effluent reduction.” §1316(b)(1)(B). But
because BADT was meant to be the most stringent stan
dard of all, Congress made no mention of cost-benefit
analysis. Again, the silence was intentional. The House’s
version of BADT originally contained an exemption for
point sources for which “the economic, social, and envi
ronmental costs bear no reasonable relationship to the
economic, social, and environmental benefit to be ob
tained.” 1 Leg. Hist. 798. That this exemption did not
appear in the final legislation demonstrates that Congress
considered, and rejected, reliance on cost-benefit analysis
for BADT.
   It is in this light that the BTA standard regulating
water intake structures must be viewed. The use of cost
benefit analysis was a critical component of the CWA’s
structure and a key concern in the legislative process. We
should therefore conclude that Congress intended to forbid
cost-benefit analysis in one provision of the Act in which it
10            ENTERGY CORP. v. RIVERKEEPER, INC.

                          STEVENS, J., dissenting

was silent on the matter when it expressly authorized its
use in another.9 See, e.g., Allison Engine Co. v. United
States ex rel. Sanders, 553 U. S. ___, ___ (2008) (slip op., at
7–8); Russello v. United States, 464 U. S. 16, 23 (1983)
(“[W]here Congress includes particular language in one
section of a statute but omits it in another . . . , it is gener
ally presumed that Congress acts intentionally and pur
posely in the disparate inclusion or exclusion” (internal
quotation marks omitted)). This is particularly true given
Congress’ decision that cost-benefit analysis would play a
temporary and exceptional role in the CWA to help exist
ing plants transition to the Act’s ambitious environmental
standards.10 Allowing cost-benefit analysis in the BTA
standard, a permanent mandate applicable to all power
plants, serves no such purpose and instead fundamentally
——————
  9 The   Court argues that, if silence in §316(b) signals the prohibition of
cost-benefit analysis, it must also foreclose the consideration of all
other potentially relevant discretionary factors in setting BTA stan
dards. Ante, at 12. This all-or-nothing reasoning rests on the deeply
flawed assumption that Congress treated cost-benefit analysis as just
one among many factors upon which the EPA could potentially rely to
establish BTA. Yet, as explained above, the structure and legislative
history of the CWA demonstrate that Congress viewed cost-benefit
analysis with special skepticism and controlled its use accordingly. The
Court’s assumption of equivalence is thus plainly incorrect. Properly
read, Congress’ silence in §316(b) forbids reliance on the cost-benefit
tool but does not foreclose reliance on all other considerations, such as a
determination whether a technology is so costly that it is not “avail
able” for industry to adopt.
   10 In 1977, Congress established an additional technology-based stan

dard, commonly referred to as “best conventional pollutant control
technology,” or “BCT,” to govern conventional pollutants previously
covered by the BAT standard. See 33 U. S. C. §1311(b)(2)(E). The BCT
standard required the EPA to consider, among other factors, “the
relationship between the costs of attaining a reduction in effluents and
the effluent reduction benefits derived.” §1314(b)(4)(B). That Congress
expressly authorized cost-benefit analysis in BCT further confirms that
Congress treated cost-benefit analysis as exceptional and reserved for
itself the authority to decide when it would be used in the Act.
                     Cite as: 556 U. S. ____ (2009)                   11

                        STEVENS, J., dissenting

weakens the provision’s mandate.11
  Accordingly, I would hold that the EPA is without au
thority to perform cost-benefit analysis in setting BTA
standards. To the extent the EPA relied on cost-benefit
analysis in establishing its BTA regulations,12 that action
was contrary to law, for Congress directly foreclosed such
reliance in the statute itself.13 Chevron, 467 U. S., at 843.
——————
   11 The Court attempts to cabin its holding by suggesting that a “rigor

ous form of cost-benefit analysis,” such as the form “prescribed under
the statute’s former BPT standard,” may not be permitted for setting
BTA regulations. Ante, at 13. Thus the Court has effectively in
structed the Agency that it can perform a cost-benefit analysis so long
as it does not resemble the kind of cost-benefit analysis Congress
elsewhere authorized in the CWA. The majority’s suggested limit on
the Agency’s discretion can only be read as a concession that cost
benefit analysis, as typically performed, may be inconsistent with the
BTA mandate.
   12 The “national performance standards” the EPA adopted were

shaped by economic efficiency concerns at the expense of finding the
technology that best minimizes adverse environmental impact. In its
final rulemaking, the Agency declined to require industrial plants to
adopt closed-cycle cooling technology, which by recirculating cooling
water requires less water to be withdrawn and thus fewer aquatic
organisms to be killed. Riverkeeper, Inc. v. EPA, 358 F. 3d 174, 182,
n. 5 (CA2 2004); 69 Fed. Reg. 41601, and n. 44. This the Agency de
cided despite its acknowledgment that “closed-cycle, recirculating
cooling systems . . . can reduce mortality from impingement by up to 98
percent and entrainment by up to 98 percent.” Id., at 41601. The EPA
instead permitted individual plants to resort to a “suite” of options so
long as the method used reduced impingement and entrainment by the
more modest amount of 80 and 60 percent, respectively. See 40 CFR
§125.94(b). The Agency also permitted individual plants to obtain a
site-specific variance from the national performance standards if they
could prove (1) that compliance costs would be “significantly greater
than” those the Agency considered when establishing the standards, or
(2) that compliance costs “would be significantly greater than the
benefits of complying with the applicable performance standards,”
§125.94(a)(5).
   13 Thus, the Agency’s past reliance on a “wholly disproportionate”

standard, a mild variant of cost-benefit analysis, is irrelevant. See
ante, at 14. Because “Congress has directly spoken to the precise
12            ENTERGY CORP. v. RIVERKEEPER, INC.

                        STEVENS, J., dissenting

Because we granted certiorari to decide only whether the
EPA has authority to conduct cost-benefit analysis, there
is no need to define the universe of considerations upon
which the EPA can properly rely in administering the BTA
standard. I would leave it to the Agency to decide how to
proceed in the first instance.
                              III
   Because the Court unsettles the scheme Congress estab
lished, I respectfully dissent.




—————— 

question at issue,” Chevron, 467 U. S., at 842, longstanding yet imper
missible agency practice cannot ripen into permissible agency practice.

