In April and July 1977, the Environmental Protection Agency (EPA), acting under the Federal Water Pollution Control Act (Act), as amended, 86 Stat. 816, 33 U.S.C. § 1251 et seq., promulgated pollution discharge limitations for the coal mining industry and for that portion of the mineral mining and processing industry comprising the crushed-stone, construction-sand, and gravel categories.1 Although the Act does not expressly authorize or require variances from the 1977 limitation, each set of regulations contained a variance provision.2 Respondents sought review of the regulations in various Courts of Appeals, challenging both the substantive standards and the variance clause.3 All of the petitions for review were transferred to the Court of Appeals for the Fourth Circuit. In National Crushed Stone Assn. v. EPA, 601 F.2d 111 (1979), and in Consolidation Coal Co. v. Costle, 604 F.2d 239 (1979), the Court of Appeals set aside the variance provision as "unduly restrictive" and remanded the provision to EPA for reconsideration.4

To obtain a variance from the 1977 uniform discharge limitations a discharger must demonstrate that the "factors relating to the equipment or facilities involved, the process applied, or other such factors relating to such discharger are fundamentally different from the factors considered in the establishment of the guidelines." Although a greater than normal cost of implementation will be considered in acting on a request for a variance, economic ability to meet the costs will not be considered.5 A variance, therefore, will not be granted on the basis of the applicant's economic inability to meet the costs of implementing the uniform standard.

The Court of Appeals for the Fourth Circuit rejected this position. It required EPA to "take into consideration, among other things, the statutory factors set out in § 301(c)," which authorizes variances from the more restrictive pollution limitations to become effective in 1987 and which specifies economic capability as a major factor to be taken into account.6 The court held that

" 'if [a plant] is doing all that the maximum use of technology within its economic capability will permit and if such use will result in reasonable further progress toward the elimination of the discharge of pollutants . . . no reason appears why [it] should not be able to secure such a variance should it comply with any other requirements of the variance.' " 601 F.2d, at 124, quoting from Appalachian Power Co. v. Train, 545 F.2d 1351, 1378 (CA4 1976).

We granted certiorari to resolve the conflict between the decisions below and Weyerhaeuser Co. v. Costle, 191 U.S.App.D.C. 309, 590 F.2d 1011 (1978), in which the variance provision was upheld. 444 U.S. 1069, 100 S.Ct. 1011, 62 L.Ed.2d 750.

* We shall first briefly outline the basic structure of the Act, which translates Congress' broad goal of eliminating "the discharge of pollutants into the navigable waters," 33 U.S.C. § 1251(a)(1), into specific requirements that must be met by individual point sources.7

Section 301(b) of the Act, 33 U.S.C. § 1311(b) (1976 ed. and Supp. III), authorizes the Administrator to set effluent limitations for categories of point sources.8 With respect to existing point sources, the section provides for implementation of increasingly stringent effluent limitations in two steps. The first step, to be accomplished by July 1, 1977, requires all point sources to meet standards based on "the application of the best practicable control technology currently available [BPT] as defined by the Administrator. . . ." § 301(b)(1)(A). The second step, to be accomplished by July 1, 1987, requires all point sources to meet standards based on application of the "best available technology economically achievable [BAT] for such category or class. . . ."9 § 301(b)(2)(A). Both sets of limitations-BPT's followed within 10 years by BAT's-are to be based upon regulatory guidelines established under § 304(b).

Section 304(b) of the Act, 33 U.S.C. § 1314(b), is again divided into two sections corresponding to the two levels of technology, BPT and BAT. Under § 304(b)(1) the Administrator is to quantify "the degree of effluent reduction attainable through the application of the best practicable control technology currently available [BPT] for classes and categories of point sources. . . ." In assessing the BPT the Administrator is to consider

"the total cost of application of technology in relation to the effluent reduction benefits to be achieved from such application, . . . the age of equipment and facilities involved, the process employed, the engineering aspects of the application of various types of control techniques, process changes, non-water quality environmental impact (including energy requirements), and such other factors as the Administrator deems appropriate." 33 U.S.C. § 1314(b)(1)(B).

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.10

Section 402 authorizes the establishment of the National Pollutant Discharge Elimination System (NPDES), under which every discharger of pollutants is required to obtain a permit. The permit requires the discharger to meet all the applicable requirements specified in the regulations issued under § 301. Permits are issued by either the Administrator or state agencies that have been approved by the Administrator.11 The permit "transform[s] generally applicable effluent limitations . . . into the obligations (including a timetable for compliance) of the individual discharger. . . ." EPA v. California ex rel. State Water Resources Control Board, 426 U.S. 200, 205, 96 S.Ct. 2022, 48 L.Ed.2d 578 (1976).

Section 301(c) of the Act explicitly provides for modifying the 1987 (BAT) effluent limitations with respect to individual point sources. A variance under § 301(c) may be obtained upon a showing "that such modified requirements (1) will represent the maximum use of technology within the economic capability of the owner or operator; and (2) will result in reasonable further progress toward the elimination of the discharge of pollutants." Thus, the economic ability of the individual operator to meet the costs of effluent reductions may in some circumstances justify granting a variance from the 1987 limitations.

No such explicit variance provision exists with respect to BPT standards, but in E. I. du Pont de Nemours & Co. v. Train, 430 U.S. 112, 97 S.Ct. 965, 51 L.Ed.2d 204 (1977), we indicated that a variance provision was a necessary aspect of BPT limitations applicable by regulations to classes and categories of point sources. Id., at 128, 97 S.Ct., at 975. The issue in this case is whether the BPT variance provision must allow consideration of the economic capability of an individual discharger to afford the costs of the BPT limitation. For the reasons that follow, our answer is in the negative.12

The plain language of the statute does not support the position taken by the Court of Appeals. Section 301(c) is limited on its face to modifications of the 1987 BAT limitations. It says nothing about relief from the 1977 BPT requirements. Nor does the language of the Act support the position that although § 301(c) is not itself applicable to BPT standards, it requires that the affordability of the prescribed 1977 technology be considered in BPT variance decisions.13 This would be a logical reading of the statute only if the factors listed in § 301(c) bore a substantial relationship to the considerations underlying the 1977 limitations as they do to those controlling the 1987 regulations. This is not the case.

The two factors listed in § 301(c)-"maximum use of technology within the economic capability of the owner or operator" and "reasonable further progress toward the elimination of the discharge of pollutants"-parallel the general definition of BAT standards as limitations that "require application of the best available technology economically achievable for such category or class, which will result in reasonable further progress toward . . . eliminating the discharge of all pollutants. . . ." § 301(b)(2). A § 301(c) variance, thus, creates for a particular point source a BAT standard that represents for it the same sort of economic and technological commitment as the general BAT standard creates for the class. As with the general BAT standard, the variance assumes that the 1977 BPT standard has been met by the point source and that the modification represents a commitment of the maximum resources economically possible to the ultimate goal of eliminating all polluting discharges. No one who can afford the best available technology can secure a variance.

There is no similar connection between § 301(c) and the considerations underlying the establishment of the 1977 BPT limitations. First, § 301(c)'s requirement of "reasonable further progress" must have reference to some prior standard. BPT serves as the prior standard with respect to BAT. There is, however, no comparable, prior standard with respect to BPT limitations.14 Second, BPT limitations do not require an industrial category to commit the maximum economic resources possible to pollution control, even if affordable. Those point sources already using a satisfactory pollution control technology need take no additional steps at all. The § 301(c) variance factor, the "maximum use of technology within the economic capability of the owner or operator," would therefore be inapposite in the BPT context. It would not have the same effect there that it has with respect to BAT's, i. e., it would not apply the general requirements to an individual point source.

More importantly, to allow a variance based on the maximum technology affordable by the point source, even if that technology fails to meet BPT effluent limitations, would undercut the purpose and function of BPT limitations. Rather than the 1987 requirement of the best measures economically and technologically feasible, the statutory provisions for 1977 contemplate regulations prohibiting discharges from any point source in excess of the effluent produced by the best practicable technology currently available in the industry. The Administrator was referred to the industry and to existing practices to determine BPT. He was to categorize point sources, examine control practices in exemplary plants in each category, and, after weighing benefits and costs and considering other factors specified by § 304, determine and define the best practicable technology at a level that would effect the obvious statutory goal for 1977 of substantially reducing the total pollution produced by each category of the industry.15 Necessarily, if pollution is to be diminished, limitations based on BPT must forbid the level of effluent produced by the most pollution-prone segment of the industry, that segment not measuring up to "the average of the best existing performance." So understood, the statute contemplated regulations that would require a substantial number of point sources with the poorest performances either to conform to BPT standards or to cease production. To allow a variance based on economic capability and not to require adherence to the prescribed minimum technology would permit the employment of the very practices that the Administrator had rejected in establishing the best practicable technology currently in use in the industry.

To put the matter another way, under § 304, the Administrator is directed to consider the benefits of effluent reductions as compared to the costs of pollution control in determining BPT limitations. Thus, every BPT limitation represents a conclusion by the Administrator that the costs imposed on the industry are worth the benefits in pollution reduction that will be gained by meeting those limits. To grant a variance because a particular owner or operator cannot meet the normal costs of the technological requirements imposed on him, and not because there has been a recalculation of the benefits compared to the costs, would be inconsistent with this legislative scheme and would allow a level of pollution inconsistent with the judgment of the Administrator.16

In terms of the scheme implemented by BPT limitations, the factors that the Administrator considers in granting variances do not suggest that economic capability must also be a determinant. The regulations permit a variance where "factors relating to the equipment or facilities involved, the process applied, or such other factors relating to such discharger are fundamentally different from the factors considered in the establishment of the guidelines." If a point source can show that its situation, including its costs of compliance, is not within the range of circumstances considered by the Administrator, then it may receive a variance, whether or not the source could afford to comply with the minimum standard.17 In such situations, the variance is an acknowledgment that the uniform BPT limitation was set without reference to the full range of current practices, to which the Administrator was to refer. Insofar as a BPT limitation was determined without consideration of a current practice fundamentally different from those that were considered by the Administrator, that limitation is incomplete. A variance based on economic capability, however, would not have this character: it would allow a variance simply because the point source could not afford a compliance cost that is not fundamentally different from those the Administrator has already considered in determining BPT. It would force a displacement of calculations already performed, not because those calculations were incomplete or had unexpected effects, but only because the costs happened to fall on one particular operator, rather than on another who might be economically better off.

Because the 1977 limitations were intended to reduce the total pollution produced by an industry, requiring compliance with BPT standards necessarily imposed additional costs on the segment of the industry with the least effective technology. If the statutory goal is to be achieved, these costs must be borne or the point source eliminated. In our view, requiring variances from otherwise valid regulations where dischargers cannot afford normal costs of compliance would undermine the purpose and the intended operative effect of the 1977 regulations.

The Administrator's present interpretation of the language of the statute is amply supported by the legislative history, which persuades us that Congress understood that the economic capability provision of § 301(c) was limited to BAT variances; that Congress foresaw and accepted the economic hardship, including the closing of some plants, that effluent limitations would cause; and that Congress took certain steps to alleviate this hardship, steps which did not include allowing a BPT variance based on economic capability.18

There is no indication that Congress intended § 301(c) to reach further than the limitations of its plain language. The statement of the House managers of the Act described § 301(c) as "not intended to justify modifications which would not represent an upgrading over the July 1, 1977, requirements of 'best practicable control technology.' " Leg.Hist. 232. The Conference Report noted that a § 301(c) variance could only be granted after the effective date of BPT limitations and could only be applied to BAT limitations. Similarly, the Senate Report on the Conference action emphasized that one of the purposes of the BPT limitation was to avoid imposing on the "Administrator any requirement . . . to determine the economic impact of controls on any individual plant in a single community." Leg.Hist. 170.

Nor did Congress restrict the reach of § 301(c) without understanding the economic hardships that uniform standards would impose. Prior to passage of the Act, Congress had before it a report jointly prepared by EPA, the Commerce Department, and the Council on Environmental Quality on the impact of the pollution control measures on industry.19 That report estimated that there would be 200 to 300 plant closings caused by the first set of pollution limitations. Comments in the Senate debate were explicit: "There is no doubt that we will suffer some disruptions in our economy because of our efforts; many marginal plants may be forced to close." Leg.Hist. 1282 (Sen. Bentsen).20 The House managers explained the Conference position as follows:

"If the owner or operator of a given point source determines that he would rather go out of business than meet the 1977 requirements, the managers clearly expect that any discharge issued in the interim would reflect the fact that all discharges not in compliance with such 'best practicable technology currently available' would cease by June 30, 1977." Id., at 231.

Congress did not respond to this foreseen economic impact by making room for variances based on economic impact. In fact, this possibility was specifically considered and rejected:

"The alternative [to a loan program] would be waiving strict environmental standards where economic hardship could be shown. But the approach of giving variances to pollution controls based on economic grounds has long ago shown itself to be a risky course: All too often, the variances become a tool used by powerful political interests to obtain so many exemptions for pollution control standards and timetables on the filmsiest [sic] of pretenses that they become meaningless. In short, with variances, exceptions to pollution cleanup can become the rule, meaning further tragic delay in stopping the destruction of our environment." Id., at 1355 (Sen. Nelson).

Instead of economic variances, Congress specifically added two other provisions to address the problem of economic hardship.

First, provision was made for low-cost loans to small businesses to help them meet the cost of technological improvements. 86 Stat. 898, amending § 7 of the Small Business Act, 15 U.S.C. § 636. The Conference Report described the provision as authorizing the Small Business Administration "to make loans to assist small business concerns . . . if the Administrator determines that the concern is likely to suffer substantial economic injury without such assistance." Leg.Hist. 153. Senator Nelson, who offered the amendment providing for these loans, saw the loans as an alternative to the dangers of an economic variance provision that he felt might otherwise be necessary.21 Several Congressmen understood the loan program as an alternative to forced closings: "It is the smaller business that is hit hardest by these laws and their enforcement. And it is that same class of business that has the least resources to meet the demands of this enforcement. . . . Without assistance, many of these businesses may face extinction." Id., at 1359 (Sen. McIntyre).22

Second, an employee protection provision was added, giving EPA authority to investigate any plant's claim that it must cut back production or close down because of pollution control regulations. § 507(e), 86 Stat. 890, 33 U.S.C. § 1367(e).23 This provision had two purposes: to allow EPA constantly to monitor the economic effect on industry of pollution control rules and to undercut economic threats by industry that would create pressure to relax effluent limitation rules.24 Representative Fraser explained this second purpose as follows:

"[T]he purpose of the amendment is to provide for a public hearing in the case of an industry claim that enforcement of these water-control standards will force it to relocate or otherwise shut down operations. . . . I think too many companies use the excuse of compliance, or the need for compliance, to change operations that are going to change anyway. It is this kind of action that gives the whole antipollution effort a bad name and causes a great deal of stress and strain in the community." Leg.Hist. 659.

The only protection offered by the provision, however, is the assurance that there will be a public inquiry into the facts behind such an economic threat. The section specifically concludes that "[n]othing in this subsection shall be construed to require or authorize the Administrator to modify or withdraw any effluent limitation or order issued under this chapter." § 507(e), 33 U.S.C. § 1367(e).

As we see it, Congress anticipated that the 1977 regulations would cause economic hardship and plant closings: "[T]he question . . . is not what a court thinks is generally appropriate to the regulatory process; it is what Congress intended for these regulations." Du Pont, 430 U.S., at 138, 97 S.Ct., at 980.

It is by now a commonplace that "when faced with a problem of statutory construction, this Court shows great deference to the interpretation given the statute by the officers or agency charged with its administration." Udall v. Tallman, 380 U.S. 1, 16, 85 S.Ct. 792, 801, 13 L.Ed.2d 616 (1965).25 The statute itself does not provide for BPT variances in connection with permits for individual point sources, and we had no occasion in Du Pont to address the adequacy of the Administrator's 1977 variance provision. In the face of § 301(c)'s explicit limitation and in the absence of any other specific direction to provide for variances in connection with permits for individual point sources, we believe that the Administrator has adopted a reasonable construction of the statutory mandate.

In rejecting EPA's interpretation of the BPT variance provision, the Court of Appeals relied on a mistaken conception of the relation between BPT and BAT standards. The court erroneously believed that since BAT limitations are to be more stringent than BPT limitations, the variance provision for the latter must be at least as flexible as that for the former with respect to affordability.26 The variances permitted by § 301(c) from the 1987 limitations, however, can reasonably be understood to represent a cost in decreased effluent reductions that can only be afforded once the minimal standard expressed in the BPT limitation has been reached.27

We conclude, therefore, that the Court of Appeals erred in not accepting EPA's interpretation of the Act. EPA is not required by the Act to consider economic capability in granting variances from its uniform BPT regulations.

Reversed.

Justice POWELL took no part in the consideration or decision of these cases.