(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 (“impingement”) 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 facilities. In the latter rules, the EPA set “national performance standards,” requiring most Phase II facilities to reduce “impingement

mortality for [aquatic organisms] by 80 to 95 percent from the calculation baseline,” and requiring a subset of facilities to reduce entrainment of such organisms by “60 to 90 percent from [that] baseline.” 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 operation. 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 various 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 consideration of the technology’s costs and of the relationship between those

costs and the environmental benefits produced governs if it is a reasonable 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. 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 precluded by the phrase “for minimizing adverse environmental impact.” 

Minimizing admits of degree and is not necessarily used to refer exclusively 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 environmental impact” suggests that the EPA has some discretion to determine the extent of reduction warranted under the circumstances, 

plausibly involving a consideration of the benefits derived from reductions 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 reasonable 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 circumstances where the costs are “significantly greater than the benefits” of compliance. 40 CFR §125.94(a)(5)(ii). In defining “national

performance standards” the EPA assumed the application of technologies 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 interpretation 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 Circuit held that §1326(b) mandates only those technologies whose costs 

can be reasonably borne by the industry. But whether it is reasonable to bear a particular cost can very well depend on the resulting 

benefits. Likewise, respondents concede that the EPA need not require that industry spend billions to save one more fish. This concedes 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, Washington, 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. 

—————— 

1The 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 decision 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 cooling 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, design, construction, and capacity of cooling water intake 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 effluents into the Nation’s waters. 

The §1326(b) regulations at issue here were promulgated by the EPA after nearly three decades in which the 

determination of the “best technology available for minimizing [cooling water intake structures’] adverse environmental impact” was made by permit-issuing authorities 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 requirements 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 implementing §1326(b)’s requirements via site-specific permit decisions 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 available 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 waterintake flow greater than 10 million gallons per day to,

among other things, restrict their inflow “to a level commensurate with that which can be attained by a closedcycle recirculating cooling water system.”2 §125.84(b)(1).

New facilities with water-intake flow between 2 million 

—————— 

2Closed-cycle cooling systems recirculate the water used to cool the

facility, and consequently extract less water from the adjacent waterway, 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 facilities, accounting for approximately 53 percent of the Nation’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 entrainment 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 

—————— 

3The 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 economically practicable,” id., at 41602. 

In its Phase II rules, however, the EPA expressly declined to mandate adoption of closed-cycle cooling systems

or equivalent reductions in impingement and entrainment, 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. Moreover, 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]lthough not identical, the ranges of impingement and

entrainment reduction are similar under both options. . . .

[Benefits of compliance with the Phase II rules] can approach 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 compliance 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 authority must impose remedial measures that yield results “as

close as practicable to the applicable performance standards.” §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 permissibly 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 costbenefit analysis, which “compares the costs and benefits of 

various ends, and chooses the end with the best net benefits,” 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 analysis 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 environmental 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 technology’s costs, 69 Fed. Reg. 41626, and of the relationship 

between those costs and the environmental benefits produced, id., at 41603. That view governs if it is a reasonable 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 

—————— 

4The 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 contradicting 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 greatest 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 environmental 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 quantity of that good than other available technologies. 

Respondents contend that this latter reading is precluded 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 environmental 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 procedures implementing the Act “shall encourage the drastic

minimization of paperwork and interagency decision

procedures.” 33 U. S. C. §1251(f). If respondents’ definition 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 technologically 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 “minimizing adverse environmental impact” suggests, we think,

that the agency retains some discretion to determine the

extent of reduction that is warranted under the circumstances. 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 impact,” 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 

—————— 

5Respondents 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 discharge 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.) Subsequent amendment limited application of this standard to

toxic and nonconventional pollutants, and for the remainder established a (presumably laxer) test of “best conventional-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 effluents but to cooling water intake structures, requires, as we

have described, “the best technology available for minimizing 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 factors, “the total cost of application of technology in relation 

—————— 

6The statute does not contain a hyphen between the words “conventional” 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 costbenefit 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 pollutants.” 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 dissent’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 “costeffectiveness” 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 factors. If silence here implies prohibition, then the EPA

could not consider any factors in implementing §1326(b)—

an obvious logical impossibility. It is eminently reasonable 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, “interpreted in its statutory and historical context . . . unambiguously 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 proposition 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 statute’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 conclude that cost-benefit analysis is not categorically forbidden. 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 systems 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 impingement and entrainment of 1.4 billion aquatic organisms, id., at 41661, Exh. XII–6, with annualized usebenefits of $83 million, id., at 41662, and non-use benefits 

of indeterminate value, id., at 41660–41661—when compared to annual costs of $389 million, demonstrates quite 

clearly that the agency did not select the Phase II regulatory 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 legitimate 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 Environmental 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 reasonable 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 demonstrate 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 estimated 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 restrictions would be “‘wholly disproportionate to any environmental 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 substantial 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 recognize 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 

—————— 

7Dry 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 costbenefit analysis in setting the national performance standards 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 costbenefit 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 permissibility of cost-benefit analysis. See id., at 108, 110, 113, 115, 

117, 120.8 The judgment of the Court of Appeals is reversed, and the cases are remanded for further proceedings 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 question 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). 
Opinion of the Court 

Cite as: 556 U. S. ____ (2009) 17 

Appendix to opinion of the Court 

APPENDIX TO OPINION OF THE COURT 

Statutory

Standard 

Statutorily Mandated

Factors 

Entities 

Subject to

Regulation 

BPT: 

“[E]ffluent limitations 

. . . which shall require 

the application of the 

best practicable control 

technology currently

available.” 33 U. S. C. 

§1311(b)(1)(A) (emphasis added). 

“Factors relating to the 

assessment of best practicable 

control technology currently 

available . . . shall include 

consideration of the total cost 

of application of technology in 

relation to the effluent 

reduction benefits to be 

achieved.” 33 U. S. C. 

§1314(b)(1)(B). 

Existing point 

sources during

the Clean Water 

Act’s initial 

implementation

phase. 

BCT: 

“[E]ffluent limitations 

. . . which shall require 

application of the best 

conventional pollutant 

control technology.” 33 

U. S. C. §1311(b)(2)(E) 

(emphasis added). 

“Factors relating to the 

assessment of best conventional pollutant control 

technology . . . shall include 

consideration of the reasonableness of the relationship 

between the costs of attaining

a reduction in effluents and 

the effluent reduction benefits 

derived.” 33 U. S. C. 

§1314(b)(4)(B). 

Existing point 

sources that 

discharge 

“conventional 

pollutants” as 

defined by the 

EPA under 33 

U. S. C. 

§1314(a)(4). 

BATEA: 

“[E]ffluent limitations 

. . . which . . . shall 

require application of 

the best available 

technology economically 

achievable . . . which 

will result in reasonable 

further progress toward

the national goal of

eliminating the discharge of all pollutants.” 33 U. S. C. 

§1311(b)(2)(A) (emphasis added). 

“Factors relating to the 

assessment of best available 

technology shall take into

account . . . the cost of achieving such effluent reduction.” 

33 U. S. C. §1314(b)(2)(B). 

Existing point 

sources that 

discharge toxic 

pollutants and 

nonconventional 

pollutants. 
Opinion of the Court 

18 ENTERGY CORP. v. RIVERKEEPER, INC. 

Appendix to opinion of the Court 

Statutory

Standard 

Statutorily Mandated

Factors 

Entities 

Subject to

Regulation 

BADT: 

“[A] standard for the 

control of the discharge 

of pollutants which 

reflects the greatest 

degree of effluent 

reduction with the 

Administrator determines to be achievable 

through application of 

the best available 

demonstrated control 

technology.” 33 U. S. C. 

§1316(a)(1) (emphasis 

added). 

“[T]he Administrator shall 

take into consideration the 

cost of achieving such effluent 

reduction, and any non-water 

quality environmental impact

and energy requirements.” 33 

U. S. C. §1316(b)(1)(B). 

New point 

sources within 

the categories of 

sources identified by the EPA 

under 33 

U. S. C. 

§1316(b)(1)(A). 

BTA: 

“Any standard . . . 

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). 

N/A Point sources 

that operate

cooling water 

intake structures. 
_________________ 

_________________ 

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 language authorizes the Environmental Protection Agency

(EPA) to compare costs and benefits. Ante, at 7–13. Nonetheless 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 forbidding, 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 technology” 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 reflects a compromise. In the House version of the legislation, the Agency was to consider “the cost and the economic, social, and environmental impact of achieving such

effluent reduction” when determining both “best practicable” and “best available” technology. H. R. 11896, 92d 

Cong., 2d Sess., §§304(b)(1)(B), (b)(2)(B) (1972) (as reported 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 determining 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 adoption of the Senate’s language with respect to “best available.” 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 supporting 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 principal 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 requires 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 Administrator’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 reasons for minimizing the EPA’s investigation of, and reliance 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 nonmarketable species of fish). See S. Rep., at 47. Above all, 

they hoped that minimizing the use of cost-benefit comparisons would force the development of cheaper control

technologies; and doing so, whatever the initial inefficiencies, 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 authority 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 categories.” 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 “different test” that the statute requires the Administrator to

apply when determining the “‘best available’” technology. 

Ibid. (emphasis added). Under that test, the Administrator “may consider a broader range of technological alternatives.” 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 determination 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 comparisons 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. (emphasis 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 reasonableness 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 disproportionate 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 ignoring 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 accordance with its expert judgment and scientific knowledge. 

The Agency can thereby avoid lengthy formal cost-benefit

proceedings and futile attempts at comprehensive monetization, 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 Council, Inc., 467 U. S. 837, 844 (1984). Most of what the majority 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 costbenefit analysis in promulgating regulations under 

§316(b). For instance, under the Agency’s interpretation, 

technology that would otherwise qualify as the best available 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 regulatory 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 benefits 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-

—————— 

1To produce energy, industrial powerplants withdraw billions of 

gallons of water daily from our Nation’s waterways. Thermoelectric powerplants alone demand 39 percent of all freshwater withdrawn 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 monetizing 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 percent 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 species “‘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 indicated 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 

—————— 

2EPA, 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. 3EPA, 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.” Whitman 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. Evidence that Congress confronted an issue in some parts of a

statute, while leaving it unaddressed in others, can demonstrate 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.), authorized the Agency to consider implementation costs in 

setting ambient air quality standards. We read §109,

which was silent on the matter, to prohibit Agency reliance on cost considerations. After examining other provisions in which Congress had given the Agency authority to

consider costs, the Court “refused to find implicit in ambiguous 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’ decision 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 implementation costs in American Trucking, “pad[s]” §316(b)’s 

environmental mandate with tangential economic efficiency 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 industry to adopt increasingly advanced technology capable 

of mitigating its detrimental environmental impact. Not 

all point sources were subject to strict rules at once. Existing 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 capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental 

impact.” 33 U. S. C. §1326(b) (2006 ed.) (emphasis 

added).4 The “best technology available,” or “BTA,” stan-

—————— 

4The 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 control, 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 structure, to incorporate §316(b) standards. 5The majority announces at the outset that the EPA’s reading of the 

BTA standard “governs if it is a reasonable interpretation of the statute—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 requirements 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 Congress 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 particularly costly. Congress required these plants to adopt 

“effluent limitations . . . which shall require the application 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 industry’s transition to the new technology-based regime, Congress 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 costbenefit analysis in setting BPT requirements by considering “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. 6Congress later extended the deadline to March 31, 1989. 7Senator Muskie, the Senate sponsor of the legislation, described the

cost-benefit analysis permitted under BPT as decidedly narrow, asserting 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 technology with costs that exceeded its benefits would not be 

considered “best.” 

The second tier of technology standards required existing 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 reductions 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.) 8Although 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 standard 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 technology improvements into their initial design. These new 

facilities were required to adopt “the best available demonstrated control technology,” or “BADT,” which Congress 

described as “a standard . . . which reflect[s] the greatest

degree of effluent reduction.” §1316(a)(1). In administering 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 standard 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 environmental costs bear no reasonable relationship to the 

economic, social, and environmental benefit to be obtained.” 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 costbenefit 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 generally presumed that Congress acts intentionally and purposely 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 existing plants transition to the Act’s ambitious environmental

standards.10 Allowing cost-benefit analysis in the BTA 

standard, a permanent mandate applicable to all powerplants, serves no such purpose and instead fundamentally 

—————— 

9The 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 standards. 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 “available” for industry to adopt. 10 In 1977, Congress established an additional technology-based standard, 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 authority 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. 

—————— 

11The Court attempts to cabin its holding by suggesting that a “rigorous 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 instructed 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 costbenefit analysis, as typically performed, may be inconsistent with the

BTA mandate. 12The “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 decided 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). 13Thus, 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 established, I respectfully dissent. 

—————— 

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