McGOWAN, Circuit Judge:

Under the aegis of the Federal Water Pollution Control Act Amendments of 1972 (the Act), Pub.L. No. 92-500, 86 Stat. 816, 33 U.S.C. §§ 1251- 1376, as amended, Clean Water Act of 1977, Pub.L. No. 95-217, 91 Stat. 1566, the Environmental Protection Agency has embarked upon a step-by-step process of issuing effluent limitations for each industry that discharges pollutants into the waters of the United States. By these consolidated petitions, members of one such industry, American pulp and paper makers, challenge the validity of EPA regulations limiting the 1977-83 effluent discharges of many pulp, paper, and paperboard mills. See 42 Fed.Reg. 1398-426 (1977). We are satisfied that EPA properly construed and rationally exercised the authority delegated to it by Congress — and that, with one exception, it did so according to the appropriate procedures. Accordingly, we uphold the resulting effluent limitations in all but one instance.

I. THE STATUTE

After several years of judicial experience with the Federal Water Pollution Control Act Amendments of 1972, and, in particular, with industry-wide challenges to effluent limitations promulgated thereunder, little further explanation of the statutory framework is necessary. See, e.g., E. I. duPont de Nemours Co. v. Train (duPont), 430 U.S. 112, 116-21, 97 S.Ct. 965, 51 L.Ed.2d 204 (1977); American Paper Inst. v. Train, 177 U.S.App.D.C. 181, 186-89, 543 F.2d 328, 333-36, cert. dismissed, 429 U.S. 967, 97 S.Ct. 398, 50 L.Ed.2d 335 (1976); American Frozen Food Inst. v. Train, 176 U.S.App.D.C. 105, 113-122, 539 F.2d 107, 115-24 (1976). As now authoritatively interpreted by the Supreme Court in duPont, supra, 430 U.S. at 126-36, 97 S.Ct. 965, section 301(b) of the Act, 33 U.S.C. § 1311(b), authorizes the Environmental Protection Agency (EPA or the Agency), after orchestrating a process of study, proposal, notice, and comment, to issue two sets of progressively more stringent regulations precisely limiting the effluent discharges of every "category [or] class of [existing] point sources," i.e., generally, every industry that pollutes the Nation's waters. According to section 301(b), the first set of regulations must limit discharges between July 2, 1977 and July 1, 1983, inclusive, to levels characteristic of point sources utilizing "BPCTCA," i.e., the "best practicable control technology currently available." Section 301(b)(1)(A). The second set applies thereafter and is defined in terms of the more restricted levels of discharges from point sources using "BATEA," i.e., the "best available technology economically achievable." Section 301(b)(2)(A).

Section 304 of the Act, 33 U.S.C. § 1314, establishes the minimum cross-industry criteria that EPA must use in developing each of the two sets of industry-specific limitations, and requires EPA to identify other factors as well as the model technology (BPCTCA for 1977, BATEA for 1983) relevant to each affected industry. Jurisdiction to review both the 1977 and 1983 sets of industry-wide regulations is conferred upon the United States Courts of Appeals by section 509(b)(1) of the Act, 33 U.S.C. § 1369(b)(1).

Meanwhile, the permit-issuing system established by section 402 of the Act, 33 U.S.C. § 1342, provides a procedure whereby the general effluent limitations for each class of point sources are transformed by EPA, or some EPA-approved state agency, into an authorization for a specific plant or mill to discharge effluents up to specified limits. The statute contemplates a very close correlation between the general effluent limitations promulgated by EPA and the specific discharge authorizations allowed each mill by the permit-issuing agency. The only exception to this rule is the Act's provision of a "modification" or variance procedure under which EPA may relax the general standards somewhat in individual permits under certain limited circumstances. Section 301(c), 33 U.S.C. § 1311(c). See duPont, supra, 430 U.S. at 128, 97 S.Ct. 965. These permit-related proceedings are also judicially reviewable under the Act. Section 309(b)(1)(F), 33 U.S.C. § 1369(b)(1)(F).

Finally, the regulatory circle is closed by stringent criminal and civil penalties — the latter of which are enforceable both by the government and by private citizens — for any effluents discharged in excess of those provided for in the permit. Sections 301(a), 309 of the Act, 33 U.S.C. §§ 1311(a), 1319.

II. THE PAPER INDUSTRY REGULATIONS A.

The regulations at issue in this case are the result of a rulemaking process developed by the Agency over the past six years for promulgating industry-wide effluent limitations under sections 301(b) and 304(b) of the Act. See notes 1 and 2 supra. See generally, La Pierre, Technology-Forcing and Federal Environmental Protection Statutes, 62 Iowa L.Rev. 771, 810-13 (1977). The procedures for these regulations began in early 1973 when EPA divided the American pulp and paper industry into two segments for purposes of establishing 1977 and 1983 effluent limitations. In "Phase I" of its rulemaking effort for the industry, it proposed, received several tiers of comments on, and promulgated 1977 and 1983 limitations for the "unbleached" segment of the industry, which produces unbleached pulp and paper. 39 Fed.Reg. 18742 (1974). This Court reviewed and upheld those regulations in full in 1976, and they are not in issue here. See American Paper Inst., supra.

Promulgation of "Phase II" regulations for the apparently larger, "bleached" segment of the paper industry did not proceed with the same dispatch as in Phase I. Accordingly, along with many of EPA's responsibilities under the Act, its rulemaking for Phase II of the paper industry became the subject of law suits and settlement agreements between environmental action groups and the Agency, resulting in the establishment of court-enforced time-tables for the promulgation of each industry's limitations. See Natural Resources Defense Council (NRDC) v. Train, 6 E.R.C. 1033 (D.D.C. 1973), rev'd in part remanded, 166 U.S.App.D.C. 312, 510 F.2d 692 (1975), timetable extended on remand, see NRDC v. Costle, 183 U.S.App.D.C. 11, 17, 561 F.2d 904, 910 n. 32 (1977). These efforts apparently put EPA under a judicially enforceable obligation to issue the 1977 limitations by January 30, 1976 which it chose to accomplish by promulgating those limitations separately and more quickly than their 1983 counterparts. Consequently, it is only the 1977-related regulations that are before us.

The actual promulgation procedures used in devising the challenged regulations were not unlike those used in Phase I and delineated in American Paper Inst., supra, 543 F.2d at 334-36. EPA commenced the 1977 part of the Phase II rulemaking process by commissioning two consulting firms in July 1973 to prepare a draft study suggesting possible industrial subcategories, as well as BPCTCA and achievable effluent reduction levels for each. About a year later, in August 1974, EPA made the draft study public and some 22 organizations, including many of the petitioners now before us, made it the target of comment and criticism. Another year passed as the Agency responded to this new wave of solicited information by revising the draft report and by appending it, described as a "draft Development Document," to an advance notice of proposed regulations. That notice was issued in the fall of 1975, and comments were again solicited. 40 Fed.Reg. 41300 (1975). It was followed a few months later by the issuance of a third contractor's study of the economic impact of the proposed regulations ("Economic Analysis").

Comments on this complete package of proposals and supporting analyses were processed and reflected in "Interim Final" regulations published on February 19, 1976 and accompanied by revised drafts of the Development Document and Economic Analysis. The Agency's obligation to comply with the January 30, 1976 deadline accounted for this quasi-final format as well as for the relatively quick turn-around time between this and the preceding public notices. See NRDC v. Train, supra, 510 F.2d at 711. This procedure also allowed petitioners in these consolidated cases to set the judicial review mechanism in motion even as they were provided — and utilized — one final opportunity to urge the Agency on its own to revise the limitations before their final issuance.

The Agency's efforts during these intermediate stages attracted thousands of pages of public comment. The industry, moreover, was offered the opportunity to introduce further testimony at a formal hearing, but it declined. The "Final Limitations" issued on January 6, 1977, with final Development Document and Economic Analysis attached. These regulations, like each of the Agency's intermediate proposals during the rulemaking process, reflected significant changes — generally favorable to industry — in response to comments received.

The present litigation commenced in early 1976 with a petition for review filed in the United States Court of Appeals for the Third Circuit by petitioners in No. 76-1675. Subsequently, other review petitions were also filed in the Ninth Circuit but were transferred by that court to the Third Circuit under 28 U.S.C. § 2112(a). EPA then convinced the Third Circuit to transfer all of the cases to this Circuit in light of its experience with the related issues raised in the Phase I litigation, American Paper Inst., supra. This court consolidated the petitions and established briefing and oral argument schedules providing for a single presentation of the issues raised in common by all of the petitioners, as well as for supplemental presentations by individual petitioners, or groups thereof, on specialized issues.

Although for ease of discourse we will generally refer collectively to the challengers before us as "petitioners", it is important to note that the limitations have somewhat different impacts on, and accordingly have elicited some separate challenges from, different segments of the industry. In order to understand the challenges as they reflect both the common concerns of all members, and the separate concerns of individual subcategories, of the American paper industry, we turn next to a brief discussion of the manufacturing and pollution control processes typical of the industry.

B.

To make paper from trees is an old art; to do it without water pollution is a new science. In papermaking, logs or wooden chips must be ground up or "cooked" in one of several processes until only cellulose pulp is left. The pulp is bleached and made into various types and grades of paper. The cooking solutions and wash water that are left contain a variety of chemicals produced during "cooking" and other processes, including acids and large quantities of dissolved cellulose-breakdown products. Indeed, in some pulping processes, more of the wood is discarded in the waste water than is used to make paper. Appendix (App.) 2116. EPA has selected three parameters for measuring the pollutant content of the industry's effluent, all of which have been used extensively in this and other industries' measurements: total suspended solids (TSS), biochemical oxygen demand (BOD), and pH. TSS reflects the total amount of solids in solution, while BOD reflects the amount of biodegradable material in solution, and pH measures the acidity of the solution.

EPA has divided this segment of the industry into 16 subcategories, and further subdivided it into 66 subdivisions, for the purposes of its rulemaking effort. As noted, some of petitioners' challenges concern all of the regulations for the whole industry, while other challenges are directed to regulations for particular industry subcategories. Actually, of the 16 subcategories in the whole industry, only three — the three that use some form of the "sulfite process" — have evoked particularized challenges. The reaction of sulfite mill operators stems from the limitations' greater economic impact on them. That impact in turn results from the fact that the sulfite process creates one of the highest pollution loads of any industrial process, and certainly the highest within the pulping industry. In fact, the Act's legislative history focused in particular on injury to shellfish in rivers and bays caused by sulfite wastes. A Legislative History of the Water Pollution Control Act Amendments of 1972 718-21 (1973) [hereinafter referred to as Legislative History]. Because the sulfite process is central in this case, we describe it in greater detail.

In the sulfite process, wooden chips are "cooked" in hot solutions of sulphurous acid and other chemicals. The cooking dissolves the binding agent in the wood (lignin) and also a good deal of the cellulose. The end product is cellulose pulp and an acid solution called spent sulfite liquor (SSL). There are two types of sulfite processes. In the papergrade sulfite process, which produces cellulose pulp for paper, the cellulose does not need to be very pure, and moderate steps suffice for cooking and separating pulp from SSL. In the dissolving sulfite process, aimed at making the raw cellulose base for materials such as cellophane and rayon, the cellulose must be pure, so the cooking and separation of the SSL are more complete and extra bleaching of the pulp is performed.

The sulfite process results in SSL and other potential pollution solutions containing acids, dissolved cellulose break-down products, and many types of organic compounds. These solutions receive various kinds of waste treatment. SSL is evaporated and burned in "SSL recovery," eliminating the water pollution potential and producing usable heat and sometimes reusable chemicals. The non-SSL waste solutions are pumped into sedimentation tanks where some of the suspended solids settle out of solution. The solutions are then pumped into other tanks and lagoons for secondary or "biological" treatment, in which bacteria are grown in the solutions to feed on and break down the waste. Eventually, the water is drained from the bacteria-laden solutions by a variety of methods. After draining, the caked solid or "sludge" that is left is incinerated or used for landfill.

III. SCOPE OF REVIEW

Before turning to the merits of petitioners' challenges to the 1977 effluent limitations, some mention must be made of the appropriate scope of review under the circumstances of this case. Generally, informal rulemaking such as produced the regulations involved herein is reviewed under section 10(e)(2) of the Administrative Procedure Act (APA), 5 U.S.C. § 706(2). Pursuant to this provision, we must "set aside" any portion of the 1977 effluent limitations that is "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law," is "in excess of statutory . . authority . . . or short of statutory right," or is "without observance of procedure required by law." See American Paper Inst., supra, 543 F.2d at 338; American Frozen Food Inst., supra, 176 U.S.App.D.C. at 130-31, 539 F.2d at 132-33. See generally Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 415-17, 91 S.Ct. 814, 28 L.Ed.2d 136 (1971).

In form, section 10(e)(2) embodies a list of various adjectives or adjectival phrases — any one of which, if found applicable, requires our disapproval of the administrative action in question. These formulations are far from being entirely discrete as a matter of the ordinary meaning of language, and, indeed, are in some respects cumulative rather than differential in their applicability. This is especially true of the words "arbitrary," "capricious," and "abuse of discretion." In its totality, at all events, section 10(e)(2) is indicative of a multifaceted review function committed to the courts. In the present context, for example, that function is divisible into three categories — statutory, procedural, and substantive.

In the case before us, we first must determine whether the EPA regulations involved herein are "not in accordance with law," or, more particularly, whether they are "in excess of statutory . . . authority." APA §§ 10(e)(2)(A), (C), 5 U.S.C. § 706(2)(A), (C). We must also consider whether the process used in arriving at those regulations afforded those affected in their procedural due. More specifically, in the informal rulemaking context involved herein, this inquiry asks whether the agency gave "interested persons an opportunity to participate in the rule making through submission of written [or other] data" and whether it "incorporate[d] in the rule adopted a concise general statement of their basis and purpose." 5 U.S.C. § 553. See Vermont Yankee Nuclear Power Corp. v. National Resources Defense Council, 435 U.S. 519, 98 S.Ct. 1197, 1202, 55 L.Ed.2d 460 (1978). Finally, we are charged by section 10(e)(2) of the APA to consider whether the agency "abuse[d its] discretion" (or was "arbitrary" or "capricious") in exercising the quasi-legislative authority delegated to it by Congress, or, on the other hand, whether its "decision was based on a consideration of the relevant factors and [was not the product of] a clear error of judgment." Citizens to Preserve Overton Park, Inc., supra, 401 U.S. at 416, 91 S.Ct. at 824. See also Vermont Yankee, supra, at 1214.

Due concern both for the intent of Congress in drafting the particular statute at issue, and, more generally, for the "boundaries between the legislative and the judicial function," Industrial Union Dep't v. Hodgson, 162 U.S.App.D.C. 331, 339, 499 F.2d 467, 475 (1974), often demands that we exercise certain aspects of our review function with more circumspection than is appropriate to others. Turning to the case at hand, therefore, we are initially confronted with a "complicated and lengthy statute," American Frozen Food Inst., supra, 176 U.S.App.D.C. at 111, 539 F.2d at 113, aimed at achieving the monumental "national goal" of eliminating "the discharge of pollutants into the [nation's] navigable waters" within the short span of 13 years. Section 101(a)(1) of the Act, 33 U.S.C. § 1251. The immensity of the planning task thrust upon the Agency by Congress was heightened by the drafters' insistence upon industry-by-industry uniformity of effluent limitations and control techniques. E.g., Legislative History, at 170 (statement of Sen. Muskie). Not only would the Agency's regulations have to work almost immediately, but they also would have to achieve cross-industry applicability despite the geographical, technological, and economic diversity that characterizes almost every discrete sector of manufacturing and agriculture in this country.

Yet, ambitious as was their goal, the drafters of the Act labored under no illusions about the uncertain state of current knowledge concerning the creation, effects, and control of water pollution. E.g., Legislative History, at 1332 (remarks of Sen. Buckley). Their intent, therefore, was to rely on EPA's ingenuity, see, e.g., C H Sugar Co. v. EPA, supra note 6, 553 F.2d at 286-87 — backed up by the Act's comprehensive system of administrative rulemaking and stiff penalties — to force each industry on its own to develop the technology necessary to achieve the Act's aspiring goal. See generally La Pierre, supra. Congress's commitment to that goal, as well as the severe impact its achievement may have on those immediately affected, is further illustrated by the drafters' realization that enforcement of the Act would probably shut down some plants around the nation. E.g., Legislative History, at 231 (remarks of Rep. Jones). See American Iron Steel Inst. v. Train, 526 F.2d 1027, 1052 (3d Cir. 1976).

In light of the structure and aims of the Act, and the breadth of authority delegated by it to the EPA to identify highly sophisticated control technology in an area fraught with scientific uncertainty, our review function encounters significant limitations in the substantive aspect where the given statutory standards are "arbitrary," "capricious," or "abuse of discretion." First, it is elementary that our function is not to weigh de novo the available evidence and to substitute our judgment for that of the Agency. Second, an expansive concept and exercise of the review power in the eleven Courts of Appeals charged with that function could easily impede accomplishment of the Act's ambitious pollution-ending aspiration as well as its goal of industry-by-industry uniformity. See generally, Currie, Judicial Review Under Federal Pollution Laws, 62 Iowa L.Rev. 1221, 1261-71 (1977). This problem looms larger in the substantive area of review than it does in those areas involving statutory interpretation and procedural integrity because of the technological and scientific uncertainty that EPA must overcome as best it can in making the discretionary judgments delegated to it by Congress. There are also obvious limitations upon the capacity of courts to deal meaningfully with arcane areas of knowledge of this kind.

EPA has taken its responsibility quite seriously, employing no less than three highly qualified private consulting firms to augment its own technological expertise. Accordingly, we must not be too quick to draw conclusions, differing from those of the Agency, in this necessarily imprecise area of knowledge. E.g., Industrial Union Dep't, supra, 162 U.S.App.D.C. at 338-39, 499 F.2d at 474-75 n. 18 ("Where existing methodology or research in a new area of regulation is deficient, the agency necessarily enjoys [a] broad discretion to attempt to formulate a solution to the best of its ability on the basis of available information"). See Permian Basin Area Rate Cases, 390 U.S. 747, 811, 88 S.Ct. 1344, 20 L.Ed.2d 312 (1968); Ethyl Corp. v. EPA, 176 U.S.App.D.C. 373, 396, 399, 541 F.2d 1, 24, 27 ( en banc), cert. denied, 426 U.S. 941, 96 S.Ct. 2663, 49 L.Ed.2d 394 (1976); id. 176 U.S.App.D.C. at 438-439, 541 F.2d at 66-67 (Bazelon, C.J., concurring); Society of the Plastics Indus., Inc. v. OSHA, 509 F.2d 1301, 1308 (2d Cir.), cert. denied, 421 U.S. 992, 95 S.Ct. 1998, 44 L.Ed.2d 482 (1975). Indeed, the mere fact that the counsel on both sides in this suit could draw upon the opinions of diverse experts sitting virtually at their elbows during preparation of their briefs, while we are forced to decide between their resulting arguments on the basis of our "generalist" judicial backgrounds, argues for restraint on our part. In sum, unless we are quite certain of our basis for doing so, we must be slow to overturn the Agency's judgment, whichever way it may incline, when Congress has required it to act quickly and decisively despite the lack of exact data.

The likelihood of that degree of certainty on our part, we might add, almost inevitably decreases when our review is based on the record of informal rulemaking before the Agency. Because of the nature of such rulemaking, again exaggerated in this case by the complexity of the subject matter, the record's portrayal of facts is essentially unsystematic ( i.e., unaffected by any rules of evidence, or by face-to-face adversarial presentation). See Vermont Yankee, supra, 98 S.Ct. at 1217. Moreover, the greater part of the record will often transcend even an eclectic collection of facts and will instead be oriented towards aiding the Agency in making "pure[ly] legislative judgments." Industrial Union Dep't, supra, 162 U.S.App.D.C. at 338, 499 F.2d at 474. As such, it is relatively unhelpful to judges who have no way of testing the veracity of its "extensive and often conflicting" contents, or of analyzing it in the light of the neutral principles in which judicial decisionmaking is grounded. Id. 162 U.S.App.D.C. at 338-340, 499 F.2d at 474-76; accord FCC v. National Citizens Comm. for Broadcasting, 436 U.S. 775, 813-814, 98 S.Ct. 2096, 2121-2122, 56 L.Ed.2d 697 (1978); see Ethyl Corp. v. EPA, supra, 176 U.S.App.D.C. at 392, 541 F.2d at 20; Society of Plastics Indus., Inc., supra, 509 F.2d at 1304; Automotive Parts Accessories Ass'n v. Boyd, 132 U.S.App.D.C. 200, 208, 407 F.2d 330, 338 (1968).

In these circumstances, therefore, we will be content in carrying out our substantive review (that is, assuming the statute and the requisite procedures have been followed) first, to insist upon an explanation of the facts and policy concerns relied on by the Agency in making its decision; second, to see if those facts have some basis in the record; and finally, to decide whether those facts and those legislative considerations by themselves could lead a reasonable person to make the judgment that the Agency has made. See Citizens to Preserve Overton Park, Inc., supra, 401 U.S. at 416, 91 S.Ct. 814; Amoco Oil Co. v. EPA, 163 U.S.App.D.C. 162, 180-81, 501 F.2d 722, 740-41 (1974); Industrial Union Dep't, supra, 162 U.S.App.D.C. at 339-40, 499 F.2d at 475-76.

On the other hand, the Act — its history, intent, and the nature of the duties it delegates to the Agency and the judiciary — does not imply any derogation of the courts' traditional primacy in interpreting statutory directives and enforcing procedural rectitude. Although calling upon the Agency to make technical judgments, the provisions of the Act that are controlling in this case use common-sense terms that are thoroughly treated in the legislative history, so that their meaning is not inherently more accessible to the Agency than to ourselves. See Texas Gas Transmission Corp. v. Shell Oil Co., 363 U.S. 263, 270, 80 S.Ct. 1122, 4 L.Ed.2d 1208 (1960); Lubrizol Corp. v. EPA, 562 F.2d 807, 816-17 n. 23 (1977). Accordingly, in this statutory area of review, and particularly in the absence of some special indication that the Agency interpretation may coincide with that of Congress, cf. Udall v. Tallman, 380 U.S. 1, 16-18, 85 S.Ct. 792, 13 L.Ed.2d 616 (1965), we are less hesitant to reject the decision of the Agency, if the latter does not comport with the conclusion dictated by established principles of statutory construction. See Adamo Wrecking Co. v. United States, 434 U.S. 275, 98 S.Ct. 566, 570 n. 5, 54 L.Ed.2d 538 (1978); ASARCO, Inc. v. EPA, 188 U.S.App.D.C. 77, 83, 578 F.2d 319, 325 (1978), discussing Train v. Natural Resources Defense Council, 421 U.S. 60, 75, 95 S.Ct. 1470; 43 L.Ed.2d 731 (1975).

Even more so than our review of EPA's statutory interpretations, our review of its procedural integrity in promulgating the regulations before us is the product of our independent judgment, and our main reliance in ensuring that, despite its broad discretion, the Agency has not acted unfairly or in disregard of the statutorily prescribed procedures. E.g., National Asphalt Pavement Ass'n v. Train, 176 U.S.App.D.C. 296, 304-5, 539 F.2d 775, 783-84 (1976). Our assertion of judicial independence in carrying out the procedural aspect of the review function derives from this country's historical reliance on the courts as the exponents of procedural fairness. E.g., Hurtado v. California, 110 U.S. 516, 4 S.Ct. 111, 28 L.Ed. 232 (1884); Palko v. Connecticut, 302 U.S. 319, 58 S.Ct. 149, 82 L.Ed. 288 (1937); Goldberg v. Kelly, 397 U.S. 254, 90 S.Ct. 1011, 25 L.Ed.2d 287 (1970); Goss v. Lopez, 419 U.S. 565, 95 S.Ct. 729, 42 L.Ed.2d 725 (1975). Recently, this reliance has transcended cases arising under either of the due process clauses and has infused modern notions of administrative law, in particular in the area of informal rulemaking. E.g., Rodway v. Department of Agriculture, 168 U.S.App.D.C. 387, 391-95, 514 F.2d 809, 813-18 (1975); Portland Cement Ass'n v. Ruckelshaus, 158 U.S.App.D.C. 308, 326, 486 F.2d 375, 393 (1973), cert. denied, 417 U.S. 921, 94 S.Ct. 2628, 41 L.Ed.2d 226 (1974); see Independent Broker-Dealers' Trade Ass'n v. SEC, 142 U.S.App.D.C. 338, 350, 442 F.2d 132, 144, cert. denied, 404 U.S. 828, 92 S.Ct. 63, 30 L.Ed.2d 57 (1971).

Our reliance on careful procedural review, moreover, derives from an expectation that if the Agency, in carrying out its "essentially legislative task," has infused the administrative process with the degree of openness, explanation, and participatory democracy required by the APA, it will thereby have "negate[d] the dangers of arbitrariness and irrationality in the formulation of rules . . .," Automotive Parts Accessories Ass'n, supra, 132 U.S.App.D.C. at 208, 407 F.2d at 338, quoted in National Asphalt Pavement Ass'n, supra, 176 U.S.App.D.C. at 304-05, 539 F.2d at 783-84. See Ethyl Corp. v. EPA, supra, 176 U.S.App.D.C. at 438, 541 F.2d at 66 (Bazelon, C.J., concurring). quoting International Harvester Co. v. Ruckelshaus, 155 U.S.App.D.C. 411, 448, 478 F.2d 615, 652 (1973) (Bazelon, C.J., concurring). Furthermore, such procedures will maximize the susceptibility of the record to judicial review. Dry Colors Mfrs. Ass'n v. Department of Labor, 486 F.2d 98, 105-07 (3d Cir. 1973). In short, we are willing to entrust the Agency with wide-ranging regulatory discretion, and even, to a lesser extent, with an interpretive discretion vis-a-vis its statutory mandate, so long as we are assured that its promulgation process as a whole and in each of its major aspects provides a degree of public awareness, understanding, and participation commensurate with the complexity and intrusiveness of the resulting regulations. See American Frozen Food Inst., supra, 176 U.S.App.D.C. at 133, 539 F.2d at 135; note 11 supra. Even here, however, beyond the notice, comment, and explanation requirements of section 553 of the APA, it is generally up to the Agency to select among the myriad available techniques to accomplish the goal of public understanding and participation. Vermont Yankee, supra, 98 S.Ct. at 1211-17. Cf. duPont, supra, 430 U.S. at 131-32 nn. 22-23, 97 S.Ct. 965; Texaco Inc. v. FEA, 531 F.2d 1071, 1082 (Em.App.), cert. denied, 426 U.S. 941, 96 S.Ct. 2662, 49 L.Ed.2d 394 (1976).

IV. THE AGENCY'S PROCEDURES

Turning first, then, to our procedurally oriented review task, we note that in general the Agency appears to have bent over backwards to accommodate public participation in, and understanding of, the promulgation of the effluent limitations before us. No less than four opportunities for public comment on parts or all of the proposed regulations and supporting data were provided by the Agency and liberally utilized by the industry. That EPA made the hoped-for use of these procedures is evidenced by its willingness at each stage to reflect the comments in revisions of its conclusion, and by the fact that members of the industry apparently exhausted most of their comments and criticisms before the Agency exhausted its procedures. Hence, the industry's trade association rejected EPA's offer to hold a formal hearing.

The one procedural inadequacy attributed to EPA in this case is of very limited scope. It concerns EPA's derivation of one effluent limitation (out of three in all) for one subdivision of the industry (out of 66 in all): the BOD limitation for acetate grade dissolving sulfite mills. The genesis of this challenge is complicated and somewhat obscure. It revolves around EPA's computation of the "secondary waste load" that must be treated by typical acetate grade dissolving sulfite mills using BPC-TCA. To derive a typical secondary waste load, the Agency was forced to adjust the limited data available to it, see note 70 infra, to make it representative of the appropriate mills. The dispute has arisen out of the Agency's identification and computation of the appropriate adjustments. Petitioners contend that, properly adjusted, the figures would show that these mills produce large amounts of waste that are costly to treat. Consequently, they urge that a high cost figure must be utilized in the Agency's cost-benefit balancing. EPA responds that there is not so much waste to treat at a typical mill, and thus that it justifiably used a lower cost estimate than the one argued for by petitioner.

EPA originally computed the secondary waste load for these mills at 487 pounds of waste to be treated per ton of product (lbs/ton), App. 1514, a figure to which the industry did not object. Between the publication of the Interim Final Limitations and the Final Limitations, however, the Agency apparently secured new data and recalculated the waste load as lower, i.e., 404 lbs/ton. EPA purportedly arrived at the latter figure after it (1) studied two other factors that it realized would require adjusting the figure upwards and downwards respectively, but then (2) decided to disregard the two factors on the assumption that they cancelled each other out. We say "purportedly" because the record includes no mention of the two factors, much less of their mode of being considered. Finally, in making its cost calculations, EPA took the 404 lbs/ton figure and reduced it to 314 lbs/ton on a further assumption that it now admits is erroneous.

Because the industry had no opportunity to comment on either the 314 or 404 lbs/ton figures after the Final Limitations were issued, it made its objection to them in its brief on appeal. It concluded these objections by recalculating secondary waste load and arriving at a figure close to the Agency's original 487 lbs/ton calculation. Brief for Petitioners in Nos. 76-1688 and 76-1690, at Appendix F. Included in its recomputations were some new data that had not been placed in the record. Although counsel for EPA conceded in response that petitioners' objections to the secondary waste load figures were partly correct, they also noted that petitioners' new data were favorable to EPA's conclusions. Counsel asserted that if EPA recalculated secondary waste load based on both the new data, and on the two factors previously disregarded because they were assumed to cancel out, see note 21 supra and accompanying text, it would arrive at secondary waste load figure of 292 lbs/ton — even below its earlier computations. In sum, EPA conceded some errors and deletions but urged that by remaking its computations from scratch, it could justify the figures used in the Final Limitations.

The labyrinthine trail that must be followed merely to set forth this dispute — without even venturing a guess as to how to resolve it — amply illustrates the inadequacy of the procedures followed by the Agency. Most obviously, the defect stems from the inadequacy of the Agency's final published explanation. That explanation includes, and we presume the Agency relied upon, computations now admitted to be erroneous. See note 22 supra and accompanying text. Further, it deletes mention of a phantom set of not-quite-offsetting adjustments that Agency attorneys now deem crucial to the viability of the EPA's cost determination. See note 21 supra and accompanying text.

Absent a coherent discussion — in the record — of the factual "basis" and legislative "purpose" underlying EPA's conclusion, see 5 U.S.C. § 553, we are unable to rely on our usual assumption that the Agency, when relying on supportable facts and permissible policy concerns and when obligated to explain itself, will rationally exercise the duties delegated to it by Congress. It is for this reason that we take no solace in the fact that the Agency's counsel, after the fact, may be able convincingly to rationalize the Agency's decision. E.g., Dry Color Mfrs. Ass'n, supra, 486 F.2d at 106. See Vermont Yankee, supra, 98 S.Ct. at 1214, quoting Camp. v. Pitts, 411 U.S. 138, 143, 93 S.Ct. 1241, 36 L.Ed.2d 106 (1973).

Moreover, the Agency's procedures in this limited instance improperly denied petitioners the opportunity to comment on a significant part of the Agency's decisionmaking process as required by section 553. See American Frozen Food Inst., supra, 539 F.2d at 135, 176 U.S.App.D.C. at 133. Thus, the 404 and 314 lbs/ton figures variously relied upon by the Agency must be validated, if at all, by reference (1) to certain data on two mills obtained by the Agency after the opportunity for public comment had lapsed; (2) other data from one mill that is not reflected in the record at all but was included by petitioners in their brief; and (3) calculations, also not reflected in the record, based on information scattered throughout the record. This denial of an opportunity for comment on these facts further undermines our usual assumption that notice and comment rulemaking, by virtue of its accessibility to public scrutiny, will achieve rational results.

Our conclusion does not imply any dissatisfaction with the rule that the Agency need not subject every incremental change in its conclusions after each round of notice and comment to further public scrutiny before final action. E.g., International Harvester Co. v. Ruckelshaus, 155 U.S.App.D.C. 411, 424, 478 F.2d 615, 632 n. 51 (1973); South Terminal Corp. v. EPA, 504 F.2d 646, 659 (1st Cir. 1974). But in this case, the Agency's final conclusions are far from the "logical outgrowth" of the preceding notice and comment process, id., and instead are the result of a complex mix of controversial and uncommented upon data and calculations. Given the lengths that the Agency must travel to justify its revisions between the interim and final stages, we cannot be sure that further and ultimately convincing public criticism of those changes would not have been forthcoming had it been invited by the Agency. See Marathon Oil Co. v. EPA, 564 F.2d 1253, 1271-72 n. 54 (9th Cir. 1977).

For all of the foregoing reasons, therefore, we must remand the regulation setting forth the BOD limitation for acetate grade dissolving sulfite mills. On remand, the Agency should conduct notice and comment proceedings aimed at reassessing and more fully explaining its conclusions concerning that limitation's validity in light of the cost of complying therewith. See id. at 1271-72.

V. THE AGENCY'S INTERPRETATION OF THE STATUTE

Petitioners raise two major statutorily premised arguments in challenging these effluent regulations. First, they claim that the Act, as interpreted by the Supreme Court in duPont, requires a greater degree of flexibility to vary the general effluent limitations in individual permits than the regulations allow. Second, it is contended that EPA has too severely narrowed the group of factors relevant in determining allowable effluent limitations and in so doing has contravened the will of Congress as expressed in section 304(b)(1)(B), quoted in note 2 supra. These two arguments merge to the extent that EPA refuses to allow variances based on the same factors that it also refuses to consider in setting the overall limitations. We find the Agency's statutory interpretation correct in both instances.

A.

The Act explicitly includes a variance procedure for use by the permit-granting agencies in deciding how to reflect the EPA's overall 1983 limitations in the effluent permits of specific mills. Section 301(c). No similar variance clause with reference to the 1977 limitations is explicit in the Act. Nonetheless, the Agency consistently has included variance provisions in its regulations setting 1977 limits for the various industries, see United States Steel Corp. v. Train, 556 F.2d 822, 844-45 (7th Cir. 1977), and recently the Supreme Court held that under its understanding of the Act, such a variance provision is legally required:

We conclude that the statute authorizes the 1977 limitations as well as the 1983 limitations to be set by regulation, so long as some allowance is made for variations in individual plants, as EPA has done by including a variance clause in its 1977 limitations.

duPont, supra, 430 U.S. at 128, 97 S.Ct. at 975 (emphasis added and footnote omitted). See United States Steel Corp., supra, 556 F.2d at 844-45.

Despite the Court's closing phrase, which seems to validate the Agency's actual variance practice, that question was left open in a footnote:

We agree with the Court of Appeals, [ E. I. duPont de Nemours Co. v. Train, 541 F.2d 1018, at 1028 (4th Cir. 1976)], that consideration of whether EPA's variance provision has proper scope would be premature.

duPont, supra, 430 U.S. at 128 n. 19, 97 S.Ct. at 975. Thus, while duPont clearly establishes the necessity of including some provision for variances in the 1977 limitations, it raises a question as to the justiciability of the provision's specific validity in the context of review of the general set of limitations.

Our reading of duPont and of the cited portion of the lower court opinion in that case leads us to conclude that, while final review of the variance provision must await individual permittees' attempts to utilize it, see note 29 infra, a threshold review of the provision is a prerequisite to validation of the general limitations.

This conclusion is mandated by the narrowness of the rationale relied upon by the Fourth Circuit, and adopted by the Supreme Court, as a basis for avoiding the specifics of the variance question in duPont:

The administration of these [variance] provisions in practice is a matter of speculation at the present. The question will arise when a claim for a variance is made in a permit application.

541 F.2d at 1028. Accord, Natural Resources Defense Council, Inc. v. EPA, 537 F.2d 642, 647 (2d Cir. 1976). In the three years that have now elapsed since duPont was briefed and argued in the Fourth Circuit, however, enough indicia of the Agency's attitude toward the 1977 variance provision under the Act has accumulated so that its administration is anything but "a matter of speculation." See especially In re Louisiana-Pacific Corp., 10 E.R.C. 1841 (1977) (Decision of the Administrator of EPA).

Petitioners have alleged that these recent indicia contradict the rebuttable presumption of administrative regularity that motivated the Supreme Court and Fourth Circuit in duPont to allow the limitations to go into effect in advance of final proof that the variance provision was meaningful. In petitioner's view, the indicia point to the complete emasculation by the Agency of its 1977 variance provision. Accordingly, because the Supreme Court premised the Agency's power to set 1977 limitations by regulation on the availability of a meaningful variance provision, see pp. ___-___ of 191 U.S.App.D.C., pp. 1033-1034 of 590 F.2d infra, and because the presumption that its variance will be applied meaningfully is no longer necessitated by a lack of concrete information, we cannot approve the regulations without finding that they include a sufficiently flexible variance provision. Since its own decision in duPont, the Fourth Circuit has reached a similar conclusion and has undertaken to review the variance clause in certain effluent limitations for electric generating plants. Appalachian Power Co. v. Train, 545 F.2d 1351, 1358-60 n. 22, modified, 545 F.2d 1380 (4th Cir. 1976).

We stress, however, that our view of the variance provision in the paper industry limitations before us, while indispensable in reviewing those limitations, is quite narrow. It seeks only to establish that the provision can be applied with enough flexibility to support the general rulemaking effort. We consequently take no position on its application in specific cases, or on its precise interpretation, beyond insisting that it meet this minimum-flexibility requirement.

The limited question before us, therefore, is whether the variance provision included in the 1977 paper industry limitations now under review has a capacity for the degree of flexibility that duPont deemed crucial to the legality of any general set of industrywide effluent limitations under the Act. Answering that question requires an examination of the Court's analysis in duPont.

Prior to that case, the circuits had disagreed over whether the Act even permitted EPA to bind individual point sources with general regulations under section 301 or whether the binding limits were to be set in every case by the permit-issuing agencies with jurisdiction in each of the 50 states. Compare CPC Int'l, Inc. v. Train, 515 F.2d 1032, 1038 (8th Cir. 1975), with, e.g., American Frozen Food Inst., supra. The Supreme Court upheld the Agency's assertion of authority to issue binding, general limitations. It started with the observation that as to the 1983 limitations, section 301 of the Act "leaves no doubt that these [general] limitations are to be set by regulation." duPont, supra, 430 U.S. at 126, 97 S.Ct. at 974.

Noting, however, that "[d]ifferent language is used in § 301 with respect to the 1977 limitations," id. at 127, 97 S.Ct. at 9741, see id. at 133-34 n. 24, 97 S.Ct. 965, the Court nonetheless decided that two sets of limitations could be established by the same procedures, "so long as some allowance is made for variations in individual plants" in the 1977 limitations. Id. at 127-28, 97 S.Ct. 965. The Court apparently insisted upon reading a variance requirement into section 301's provisions with respect to the 1977 limitations in order to make those provisions coextensive with the section's 1983 provisions — which do include a variance requirement, section 301(c) — and to "unambiguously" invest the Agency with rulemaking authority. 430 U.S. at 127, 97 S.Ct. 965.

The importance that the Court assigned to a meaningful variance as a prerequisite to valid general limitations may be seen first in its use of the mandatory phrase "so long as." Moreover, in the same case the Court unequivocally refused to read a variance requirement into the Act's provisions governing effluent regulations for newly built plants. 430 U.S. at 137-39, 97 S.Ct. 965. Here the Court found "that Congress intended these regulations to be absolute prohibitions," id. at 138, 97 S.Ct. at 980 — a finding it did not make with respect to the 1977 limitations despite the Act's failure explicitly to provide for variances therefrom. Finally, the Court emphasized the need for a meaningful variance when it argued that giving EPA the power to set general regulations would not undermine the Act's intent to give the states, through the permit-granting agencies, an important role in administering the Act. The Court subscribed to the view that, by leaving the granting of variances to the state agencies in the first instance, the significance of their role would be preserved. Id. at 134 n. 24, 97 S.Ct. 965, citing American Meat Inst. v. EPA, 526 F.2d 442, 452 (7th Cir. 1975). Accord, American Paper Inst., supra, 177 U.S.App.D.C. at 190, 543 F.2d at 337. See generally Train v. Natural Resources Defense Council, Inc., 421 U.S. 60, 78-87, 95 S.Ct. 1470, 43 L.Ed.2d 731 (1975). Because the states can only grant variances that conform to EPA's interpretation of its variance provision, see In re Louisiana-Pacific Corp., supra, the states' role could still be severely undercut if the Agency were to interpret the variance allowance so narrowly as to remove its effect.

The motivating force in duPont was the Court's desire to overcome the "highly anomalous" result that would attend a reading of section 301 to require a different pattern of promulgation for the 1977 limitations than the one so clearly laid out for the 1983 limitations. Hence, the Act was read, despite its nonparallel language, to establish the same promulgation procedures for both sets of limitations and, accordingly, to require a variance provision under both. At minimum, therefore, duPont indicates that the Agency must give permittees the ability to secure variances from the 1977 limitations analogous to their statutorily provided ability to secure the same with respect to the 1983 standards.

Section 301(c) of the Act allows a modification of the general 1983 limitations in section 301(b)(2)(A)

upon a showing . . . that [a variance] (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.

The crucial language here appears to be "technology within the economic capability of the owner." This language clearly harks back to the "best available technology economically achievable for such category [of point sources]" language in section 301(b)(2)(A) which provides for the establishment of general 1983 limitations. In other words, section 301(c) (if properly invoked) authorizes the Agency to relieve a particular point source operator from any demands that the Act does not allow the Agency to make of the industry generally. That is to say, it may relieve him from the requirement of using more than the best available technology economically achievable (BATEA). Even the second qualification in section 301(c), that the variance may not halt progress toward eliminating pollution, tracks language in section 301(b)(2)(A) requiring that BATEA "result in reasonable further progress toward the national goal of eliminating the discharge of all pollutants." See note 32 supra.

Furthermore, the Act quite explicitly lays out the minimum factors that the Agency must consider in identifying BATEA. Those factors, referred to in section 301(b)(2)(A), are found in section 304(b)(2)(B). As such, it seems clear that in deciding under section 301(c) whether the variance sought by a mill owner "represent[s] the maximum use of technology within the economic capability of [that] owner," the permit-granting agency, and the EPA in supervising that agency, must consider the factors laid out in section 304(b)(2)(B).

Analogously, the 1977 variance provision must at minimum allow a petitioning mill operator to seek a dispensation from any limitation that, as a whole, demands more of him than section 301(b)(1)(A), the 1977 limitation provision, allows EPA to demand of the industry as a whole. Although this formulation ensures a meaningful variance, it should be noted that it is not a license for avoidance of the Act's strict pollution control requirements. It simply allows individual operators to argue, that, given the overall impact of an effluent limitation on their operations, they are faced with stricter requirements than the Act authorizes EPA to place on the industry as a whole.

More specifically, section 301(b)(1)(A), as interpreted in duPont, requires "the application of the best practicable control technology currently available" (BPCTCA) for each industrial subcategory. See note 1 supra. Moreover, it, too, refers to a portion of section 304 that enumerates the factors relevant in setting BPCTCA. Section 304(b)(1)(B); see note 2 supra. Under duPont, therefore, a variance provision should allow the state agencies and EPA to excuse mill operators from making more than the maximum use of technology practicably available to them. Pursuant to section 304(b)(1)(B), the outlines of practicability in each case depend upon "the total cost [to the operator] of application of technology in relation to the effluent reduction benefits to be achieved" by that technology as well as upon "the age of [the mill operator's] equipment . . . the process employed [by him], the engineering aspects of the application [at the mill] of various types of control techniques, process changes [and] non-water quality environmental impact [of the technology specified for his mill] (including energy requirements)." The precise interrelationship of these factors in making variance decisions, moreover, basically should track the scope and interrelationship that we have assigned them in developing the general, industry-wide limitations. See pp. ___ -___ of 191 U.S.App.D.C., pp. 1041-1053 of 590 F.2d infra.

As will be explained more thoroughly infra, this approach clearly rules out the necessity of considering local receiving water quality in making variance decisions. See In re Louisiana-Pacific, supra; pp. ___-___ of 191 U.S.App.D.C., pp. 1041-1044 of 590 F.2d infra. A more difficult question surrounds the relevance and importance of economic hardship. This issue is crucial, of course, because those mill operators who are most hard pressed economically will be the most likely to pursue vigorous variance demands. Moreover, when faced with the ultimate threat of economic hardship — plant closure, with attendant unemployment and regional economic dislocation — the local permit-granting agency will find it difficult to resist a plea for a variance.

We have explored this issue carefully, and we express our conclusion emphatically: Although the "total cost" of pollution control at the petitioning mill must be considered under a satisfactory variance provision, it is only relevant "in relation to the effluent reduction benefits to be achieved" at that mill, section 304(b)(1)(B); so long as those costs relative to the pollution reduction gains are not different from those that may be imposed on the industry as a whole, the difficulty, or in fact the inability, of the operator to absorb the costs need not control the variance decision.

We reach this conclusion under the statute only after satisfying ourselves that the legislative intent is as clear as the result is harsh. Most prominently, the Act's supporters in both Houses acknowledged and accepted the possibility that its 1977 requirements might cause individual plants to go out of business. E.g., Legislative History, at 231 (remarks of Rep. Jones); id. at 1282 (remarks of Sen. Bentsen). They self-consciously made the legislative determination that the health and safety gains that achievement of the Act's aspirations would bring to future generations will in some cases outweigh the economic dislocation it causes to the present generation. See American Iron Steel Inst., supra, 526 F.2d at 1052. They accordingly authorized EPA to impose effluent restrictions that they knew might shut down parts of regulated industries — including, specifically, paper mills. See Legislative History, at 718-21 (statement of Rep. Meeds). The Agency, in turn, has projected that its limitations for the paper industry may shut down eight marginal mills, see p. ___ of 191 U.S.App.D.C., p. 1047 of 590 F.2d infra, and the variance provision need not protect these or other individuals from impacts authorized for the industry as a whole.

Even more specifically, at least one legislator considered and rejected "giving variances to pollution controls based on [such purely] economic grounds" as

[w]hen the otherwise healthy small independent firm is forced to close, the tax base of the community is further weakened, and workers and families are forced back into already congested metropolitan areas . . ..

Legislative History, at 1355 (remarks of Sen. Nelson). Despite the appeal of economic hardship variances in circumstances such as those described, Senator Nelson argued, they could become "a tool used by powerful political interests to obtain so many exemptions on the flimsiest of pretenses [that] tragic delay in stopping the destruction of our environment" would result. Id. Hence, he opposed such variances and chose to rely on other means of protecting businesses from effluent-control-induced bankruptcy. See id., discussing section 8 of the Act, amending Small Business Act, § 7, 15 U.S.C. § 636, now codified in 15 U.S.C. § 636(g) (authorizing low interest loans to aid small businesses in meeting the Act's requirements).

We come, then, to the question of whether the actual variance provision included in the Phase II paper industry limitations, as interpreted, is capable of the minimum degree of flexibility just described. That provision notes that the EPA was at pains to account for all available data "such as age and size of plant . . energy requirements and costs" relevant to effluent levels but acknowledges the inevitable possibility "that data which would affect these limitations" have not been considered (emphasis added). It accordingly allows a discharger to secure a permit containing less stringent limitations than those established by the EPA, if the discharger can show "that factors related to the equipment or facilities involved, the process applied, or other such factors related to such discharger are fundamentally different from the factors considered in the establishment of the guidelines" (emphasis added).

Not surprisingly, EPA's likely interpretation of these terms, and particularly the parts of it italicized above, have occasioned some dispute. The Agency itself at one point accepted public comments on this type of 1977 variance under the Act, looking toward a regulation definitively interpreting it. 39 Fed.Reg. 28926 (1974). No such regulation has been forthcoming, however.

Nonetheless, in 1974, the Agency's General Counsel instructed Agency personnel that the "other such factors" language in the typical 1977 variance provision quoted above did not envision the consideration of any economic factors. He accordingly limited the provision's application to cases involving fundamentally different "factors of a technical and engineering nature." Memorandum to Regional Administrators of EPA, 39 Fed.Reg. 30073 (1974) (emphasis added). It was this interpretation that the Fourth Circuit disapproved of in Appalachian Power Co., supra, discussed in notes 30 35 supra. Because the General Counsel's 1974 opinion relied exclusively on Congress's failure to include a variance procedure for the 1977 limitations we, too, would be inclined to find the opinion inconsistent with the Act, as now authoritatively interpreted in duPont to include a meaningful variance requirement. See Currie, Congress, The Court, and Water Pollution, 1977 S.Ct.Rev. 39, 53-56. Nonetheless, we need not reach that question in light of the Agency's recent reinterpretation and expansion of the variance provision.

As of September 13, 1977, when EPA filed its brief in this case, the Agency still adhered to its 1974 interpretation of the variance provision to exclude consideration of economic factors. Brief for Respondent at 17-20. Moreover, that brief suggested that the provision's "fundamental difference" language required that the applicant demonstrate a qualitatively different factor than any considered by the Agency in its rulemaking before a variance could be granted. Id. at 12-17. That is to say, if the Agency had considered data relevant, for example, to climate, or to energy needs for sludge disposal, the brief indicated that no variance based on those factors could subsequently issue, even if the climate or energy situation facing the applicant was quantitatively different from the range of such situations considered by the Agency.

Nonetheless, two days after the brief was filed in this case, the Administrator of the EPA handed down a decision in In re Louisiana-Pacific, supra, which seems significantly to have liberalized the Agency's approach to the variance provision. In essence, this decision tracked the analysis in duPont and thereby expanded the range of factors recognized by EPA as relevant to the granting of a variance to include all of those factors listed in section 304(b)(1)(B):

My authority to provide for variances from [BPCTCA] flows from, and is inherent in, my authority to promulgate effluent limitations guidelines under Sections 301(b)(1)(A) and 304(b)(1) . . .. Variances can only be based on fundamental differences in factors which are appropriate to [the general] technology-based regulations and limitations derived through the variance process must still meet the congressional definition of best practicable control technology.

. . . . This does not mean that where a fundamental difference can be shown with respect to a factor other than [one not listed in section 304(b)(1)] a variance may not be appropriate.

Id. at 1851. See also id. at 1847 (describing section 304(b) of the Act as the source of "factors which must be taken into account in developing [the general] industrial effluent limitations . . ..").

Consistent with his reliance on section 304(b), the Administrator clearly broke with the 1974 opinion of the General Counsel and cited such nontechnical factors relevant to the 1977 variances as energy requirements, id. at 1851, raw materials, id. at 1846 n. 9, non-water quality environmental impacts, such as land and air pollution from sludge disposal or burning, id. at 1850-51 n. 22, 1852-53 n. 30, and even such economic factors as compliance costs, id. at 1051-52 n. 27. As a matter of the potentially relevant factors, therefore, the Agency's interpretation has been brought into line with what we believe are the dictates of duPont, and on that score we find the variance clause capable of the requisite minimum degree of flexibility.

The Louisiana-Pacific decision also clarifies the Agency's position with respect to the meaning of the "fundamentally different" language in the variance clause. First, it makes clear that, if an individual operator demonstrates a "substantial" id. at 1851, or "fundamental" difference in a section 304(b)(1)(B) factor vis-a-vis the Agency's regulatory findings about the factor "on a national basis," a variance will be allowed. Id. at 1851 n. 25, 1852-53. Since EPA must, and claims that it did, consider all of the section 304(b)(1)(B) factors in setting the general limitations, the Administrator's decision indicates that factors already considered during rulemaking can, and in fact must, be considered during variance proceedings, so long as the requisite difference is shown. Here again, the degree of flexibility necessary to justify EPA in setting general 1977 limitations is achieved, and variances are not restricted to qualitatively different circumstances from those considered by EPA during rulemaking.

The remaining question, therefore, concerns the requirement that the difference between the individual and national situations (whether qualitative or quantitative) is fundamental. None of the petitioners in this case takes issue with the "fundamental difference" language so long as it is not used to preclude consideration of any of the section 304(b)(1)(B) factors. Petitioners realize that such a requirement, along with the allocation of the burden of proof to the variance applicant, assures that the pin-hole safety valve envisioned in the Act and duPont does not become a yawning loophole. E.g., Joint Brief for Petitioners Addressing Common Issues, at 24.

We agree with the parties to these petitions that the fundamentality requirement does not deprive the variance provision before us of the minimum potential for flexibility required by duPont. Although the variance must prevent the regulations from having a greater overall impact on an individual mill than the Act authorizes the general regulations to have on the industry, the one designed by EPA for use in its industry-wide limitations for 1977 accomplishes this goal. Because EPA, in devising the limitations, undertook a meticulous effort to obtain all relevant information from all available sources including the industry itself, and attempted to account for that information in all its diversity, the Agency has built a significant degree of flexibility into the regulations themselves. This flexibility is reflected in the 16 subcategories and 66 subdivisions thereof, as well as in the establishment of maximum single-day, and 30-day-average, limits that are much higher than the yearly-average limits that the Agency has found within the technological reach of the industry.

Thus, to a great degree, the Agency has accounted for cross-industry, and even "cross-subcategory," differences in establishing the limits. Allowing for variances based on slight or moderate differentials at individual plants would accordingly ignore the liberality that is already built into the system. It would allow for variances, when the impact on an individual did not exceed the range of impacts considered by the Agency for the industry generally.

Moreover, without the fundamentality requirement the rulemaking process could be shortcircuited. As discussed earlier, Congress has placed EPA under the burden of almost instantaneously establishing comprehensive regulations aimed at achieving a monumental goal. That effort must proceed in advance of the availability of much relevant data. If the regulations could be ignored every time a mill owner — who did not produce data from his operation during rulemaking — suddenly develops the facts and finds them somewhat different from the ones available to the Agency, the achievement of the congressional goals would be pushed far beyond the time periods established in the Act.

Finally, the Agency, without destroying the necessary flexibility, may insist upon a fundamental difference as to one or even several individual factors, in order to account for the fact that each limit is the product of consideration of myriad factors, each of which may be expected to vary from plant to plant. As noted earlier, a variance only need be granted when the overall situation facing an individual operator differs from the overall situation of the industry. See note 34 supra and accompanying text. The Agency has properly adopted an approach that focuses on only one or a few of the relevant factors — but sets a high differential standard therefor — in order to relieve itself of having to analyze all of the relevant factors in every variance case to achieve the overall differential picture.

In sum, the most recent delineation by the Agency of its 1977 variance policy under the Act convinces us that its policy is capable of sufficient flexibility to buttress its claim of authority to limit 1977 effluent discharges by way of general regulations. We emphasize, once more, however, that this conclusion is inextricably linked to the Agency's current interpretation of its variance provision, and that, while crucial to our affirmance of the regulations as a whole, it implies no opinion on the specifics of individual variance applications.

B.

EPA's consideration of the factors bearing on "the best practicable technology currently available" (BPCTCA) has inspired several challenges from petitioners. Some of these challenges concern the Agency's refusal to consider receiving water quality, while others concern EPA's manner of assessing the factors that all agree must be considered: cost and nonwater environmental impacts. We uphold the Agency's interpretation and application of the statute against both sets of challenges.

1.

Some of the paper mills that must meet the effluent limitations under review discharge their effluents into the Pacific Ocean. Petitioners contend that the ocean can dilute or naturally treat effluent, and that EPA must take this capacity of the ocean ("receiving water capacity") into account in a variety of ways. They urge what they term "common sense," i.e., that because the amounts of pollutant involved are small in comparison to bodies of water as vast as Puget Sound or the Pacific Ocean, they should not have to spend heavily on treatment equipment, or to increase their energy requirements and sludge levels, in order to treat wastes that the ocean could dilute or absorb.

EPA's secondary response to this claim was that pollution is far from harmless, even when disposed of in the largest bodies of water. As congressional testimony indicated, the Great Lakes, Puget Sound, and even areas of the Atlantic Ocean have been seriously injured by water pollution. Even if the ocean can handle ordinary wastes, ocean life may be vulnerable to toxic compounds that typically accompany those wastes. In the main, however, EPA simply asserted that the issue of receiving water capacity could not be raised in setting effluent limitations because Congress had ruled it out. We have examined the previous legislation in this area, and the 1972 Act's wording, legislative history, and policies, as underscored by its 1977 amendments. These sources, which were thoroughly analyzed in a recent opinion of the administrator of the Agency, fully support EPA's construction of the Act. They make clear that based on long experience, and aware of the limits of technological knowledge and administrative flexibility, Congress made the deliberate decision to rule out arguments based on receiving water capacity.

The earliest version of the Federal Water Pollution Control Act was passed in 1948 and amended five times before 1972. Throughout that 24 year period, Congress attempted to use receiving water quality as a basis for setting pollution standards. W. Rodgers, Environmental Law 355-57 (1977). At the end of that period, Congress realized not only that its water pollution efforts until then had failed, but also that reliance on receiving water capacity as a crucial test for permissible pollution levels had contributed greatly to that failure. EPA v. State Water Resources Control Board, 426 U.S. 200, 202, 96 S.Ct. 2022, 48 L.Ed.2d 578 (1976).

Based on this experience, Congress adopted a new approach in 1972. Under the Act, "a discharger's performance is . . . measured against strict technology-based effluent limitations — specified levels of treatment — to which it must conform, rather than against limitations derived from water quality standards to which it and other polluters must collectively conform." Id. at 204-05, 96 S.Ct. at 2024 (footnotes omitted). See Save the Bay, Inc. v. EPA, 556 F.2d 1282, 1284 (5th Cir. 1977); American Frozen Foods Inst., supra, 176 U.S.App.D.C. at 113, 539 F.2d at 115.

This new approach reflected developing views on practicality and rights. Congress concluded that water pollution seriously harmed the environment, and that although the cost of control would be heavy, the nation would benefit from controlling that pollution. Yet scientific uncertainties made it difficult to assess the benefits to particular bodies of receiving water. Even if the federal government eventually could succeed at the task at which had failed for 24 years and thus could determine benefits and devise water quality standards, Congress concluded that the requisite further delay was too long for the nation to wait. Note, The Federal Water Pollution Control Act Amendments of 1972: Ambiguity as A Control Device, 10 Harv.J.Legis. 565, 571-72 (1973).

Moreover, by eliminating the issue of the capacity of particular bodies of receiving water, Congress made nationwide uniformity in effluent regulation possible. Congress considered uniformity vital to free the states from the temptation of relaxing local limitations in order to woo or keep industrial facilities. In addition, national uniformity made pollution clean-up possible without engaging in the divisive task of favoring some regions of the country over others.

More fundamentally, the new approach implemented changing views as to the relative rights of the public and of industrial polluters. Hitherto, the right of the polluter was pre-eminent, unless the damage caused by pollution could be proven. Henceforth, the right of the public to a clean environment would be pre-eminent, unless pollution treatment was impractical or unachievable. The Senate Committee declared that "[t]he use of any river, lake, stream or ocean as a waste treatment system is unacceptable" — regardless of the measurable impact of the waste on the body of water in question. Legislative History at 1425 (Senate Report). The Conference Report stated that the Act "specifically bans pollution dilution as an alternative to waste treatment." Id. at 284. This new view of relative rights was based in part on the hard-nosed assessment of our scientific ignorance: "we know so little about the ultimate consequences of injection of new matter into water that [the Act requires] a presumption of pollution. . . ." Id. at 1332 (remarks of Sen. Buckley). It also was based on the widely shared conviction that the nation's quality of life depended on its natural bounty, and that it was worth incurring heavy cost to preserve that bounty for future generations.

The Act reflects the new approach in a number of provisions. As noted, its goal was zero discharge of pollutants by 1985, section 101(a)(1), 33 U.S.C. § 1251(a)(1), not discharges at acceptable or tolerable levels for receiving water. The rest of the statute "authorize[s] a series of steps to be taken to achieve [that] goal," duPont, supra, 430 U.S. at 116, 97 S.Ct. at 969. It defines "pollution," "pollutant," "discharge of a pollutant," and "effluent limitation" in terms of any addition to water that alters its "chemical, physical, biological, [or] radiological integrity;" it does not specify additions that diminish the quality of the receiving water. In only one limited instance, thermal pollution, is receiving water capacity to be considered in relaxing standards, and the section allowing such consideration was drafted as a clear exception. Section 316(a) of the Act, 33 U.S.C. § 1326(a). Otherwise, receiving water quality was to be considered only in setting " more stringent" standards than effluent limitations otherwise would prescribe. Section 301(b)(1)(C) of the Act, 33 U.S.C. § 1311(b)(1)(C) (emphasis added).

The Act was passed with an expectation of "mid-course corrections," Legislative History, at 175 (statement of Sen. Muskie), and in 1977 Congress amended the Act, although generally holding to the same tack set five years earlier. Pub.L. No. 95-217, 91 Stat. 1584. Notably, during those five years, representatives of the paper industry had appeared before Congress and urged it to change the Act and to incorporate receiving water capacity as a consideration. See, e.g., Hearings before the Subcomm. on Environmental Pollution of the Senate Comm. on Environment and Public Works, 95th Cong., 1st Sess., pt. 3, at 193, 195, 540. Nonetheless, Congress was satisfied with this element of the statutory scheme. Except for a provision specifically aimed at discharges from "publicly owned treatment plants," section 301(h) of the Act, 33 U.S.C. § 1311(h), it resolved in the recent amendments to continue regulating discharges into all receiving waters alike.

Our experience with litigation under the Act, and particularly with this case, emphasizes the weight of Congress' policies. Even without receiving water capacity as an issue to delay it, EPA was late in promulgating these regulations. See pp. ___-___ of 191 U.S.App.D.C., pp. 1020-1024 of 590 F.2d supra. We have wrestled with the problems of weighing technological imponderables and can understand the greater difficulties that would have arisen if the receiving water issues involving even greater imponderables had also been involved. Historically, the paper industry itself, and particularly the sulfite process sector, avoided the impact of regulation because of the difficulty of proving that its discharges adversely affected receiving water.

Under the new statutory scheme, Congress clearly intended us to avoid such problems of proof so that a set of regulations with enforceable impact is possible. The dangers of ignoring this congressional mandate are clearly revealed by the one experiment in the Act with allowing consideration of receiving water capacity. As we have noted, thermal pollution regulation is the only area where the 1972 Act explicitly allowed receiving water capacity to continue as an issue. In reviewing the results of that experiment during consideration of the recent amendments to the Act, Congress found that the water capacity issue had led to a regulatory breakdown. "Heat has thus become an unregulated pollutant, clearly not the intent of the Congress. . . . That limited exemption has been turned into a gaping loophole." S.Rep. No. 370, 95th Cong., 1st Sess. 8, reprinted in U.S. Code Cong. Admin. News, pp. 4326, 4334. Given the clarity of Congress' desire not to allow the receiving water capacity loophole to engulf its overall regulatory efforts in this area, we affirm the Agency's refusal to consider water quality in setting its limitations.

2.

Petitioners also challenge EPA's manner of assessing two factors that all parties agree must be considered: cost and nonwater quality environmental impacts. They contend that the Agency should have more carefully balanced costs versus the effluent reduction benefits of the regulations, and that it should have also balanced those benefits against the non-water quality environmental impacts to arrive at a "net" environmental benefit conclusion. Petitioners base their arguments on certain comments made by the Conferees for the Act, see notes 52 67 infra, and on the fact that the Act lists non-water quality environmental impacts as a factor the Agency must "take into account."

In order to discuss petitioners' challenges, we must first identify the relevant statutory standard. Section 304(b)(1)(B) of the Act, 33 U.S.C. § 1314(b)(1)(B), identifies the factors bearing on BPCTCA in two groups. First, the factors 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 second, they

shall also take into account 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 appropriated[.]

See note 2 supra.

The first group consists of two factors that EPA must compare: total cost versus effluent reduction benefits. We shall call these the "comparison factors." The other group is a list of many factors that EPA must "take into account:" age, process, engineering aspects, process changes, environmental impacts (including energy), and any others EPA deems appropriate. We shall call these the "consideration factors." Notably, section 304(b)(2)(B) of the Act, 33 U.S.C. § 1314(b)(2)(B), which delineates the factors relevant to setting 1983 BATEA limitations, tracks the 1977 BPCTCA provision before us except in one regard: in the 1983 section, all factors, including costs and benefits, are consideration factors, and no factors are separated out for comparison.

Based on our examination of the statutory language and the legislative history, we conclude that Congress mandated a particular structure and weight for the 1977 comparison factors, that is to say, a "limited" balancing test. In contrast, Congress did not mandate any particular structure or weight for the many consideration factors. Rather, it left EPA with discretion to decide how to account for the consideration factors, and how much weight to give each factor. In response to these divergent congressional approaches, we conclude that, on the one hand, we should examine EPA's treatment of cost and benefit under the 1977 standard to assure that the Agency complied with Congress' "limited" balancing directive. See note 52 supra. On the other hand, our scrutiny of the Agency's treatment of the several consideration factors seeks to assure that the Agency informed itself as to their magnitude, and reached its own express and considered conclusion about their bearing. More particularly, we do not believe that EPA is required to use any specific structure such as a balancing test in assessing the consideration factors, nor do we believe that EPA is required to give each consideration factor any specific weight.

Our conclusions are based initially on the section's wording and apparent logic. By singling out two factors (the comparison factors) for separate treatment, and by requiring that they be considered "in relation to" each other, Congress elevated them to a level of greater attention and rigor. Moreover, the comparison factors are a closed set of two, making it possible to have a definite structure and weight in considering them and preventing extraneous factors from intruding on the balance.

By contrast, the statute directs the Agency only to "take into account" the consideration factors, without prescribing any structure for EPA's deliberations. As to this latter group of factors, the section cannot logically be interpreted to impose on EPA a specific structure of consideration or set of weights because it gave EPA authority to "upset" any such structure by exercising its discretion to add new factors to the mix. Instead, the listing of factors seems aimed at noting all of the matters that Congress considered worthy of study before making limitation decisions, without preventing EPA from identifying other factors that it considers worthy of study. So long as EPA pays some attention to the congressionally specified factors, the section on its face lets EPA relate the various factors as it deems necessary.

The legislative history reveals that clear congressional policies support the section's facial structure. The original House and Senate versions of the section differed significantly. A major point of contention between the two versions involved the House's stronger concern over the economic effects of imposing stringent effluent limitations. Ultimately a compromise was reached at Conference and accepted by both houses. It provided, first, that the Agency must use "limited" cost-benefit balancing in deriving 1977 standards, but not in arriving at the 1983 standards. Legislative History, at 170 (statement of Sen. Muskie). A "midcourse" evaluation was then to occur in the mid- to late-1970's, after the Act had been in effect for several years but before full implementation of the 1983 standards. Id. at 175. The latter step was designed to allow Congress to rewrite the 1983 standards in order to continue the cost-benefit balancing during that period as well, if Congress found after early experience that such a course was necessary. Section 315 of the Act, 33 U.S.C. § 1325 (establishing a National Study Commission to consider mid-course changes).

Thus the fact that Congress indicated its greater concern for cost-benefit calculation in the short run by making cost and benefit "comparison factors" for 1977, but only "consideration factors" for 1983, demonstrates the more relaxed view it took of EPA's treatment of consideration factors relevant to both the 1977 and 1983 standards. Indeed, after studying the need for mid-course correction, Congress decided to retain the 1972 arrangement, which, except for limited modifications not germane here, gives the Agency more complete discretion in considering the relevant factors in the future.

Judicial decisions have carefully observed that the cost and benefit factors require more rigorous EPA consideration of cost versus benefit in the 1977 standards than in the 1983 standards. American Paper Inst., supra, 177 U.S.App.D.C. at 191, 543 F.2d at 338 (cost-benefit balancing in 1977, not in 1983); accord American Frozen Food Inst., supra, 176 U.S.App.D.C. at 117, 539 F.2d at 119; American Meat Inst., supra, 526 F.2d at 462-63; see W. Rodgers, supra at 466. But see Appalachian Power Co., supra, 545 F.2d at 1361, criticized in La Pierre, supra, 62 Iowa L.Rev. at 819-20. Since the consideration factors specified in the 1977 provision track the language of all of the factors — including cost and benefit — in the 1983 provision, these cases support a lower level of administrative rigor and judicial review with respect to the 1977 consideration factors than with respect to the costs and benefit factors relevant to that year's limitations. We are fortified in this view by its coincidence with the Agency's interpretation. As the Supreme Court held last year, the EPA's construction of this Act is entitled to some deference. duPont, supra, 430 U.S. at 134-35, 97 S.Ct. 965.

Consequently, we must review the comparison factors to determine if EPA weighed them through the "limited" balancing test as intended by Congress. On the other hand, we may review the consideration factors only to determine if EPA was fully aware of them and reached its own express conclusions about them. Since the two types of factors are separate, we divide our discussion accordingly.

a.

Petitioners do not challenge the cost-benefit analysis for the whole industry. They do, however, challenge the analysis for the sulfite sector, contending that EPA used an "overall" instead of an "incremental" method of balancing, and that its figures on the cost of BPCTCA for the dissolving sulfite subcategory were underestimates. We uphold EPA's determination against both contentions.

EPA's approach was similar to the one we upheld in American Paper Inst., supra, 177 U.S.App.D.C. at 191-92, 543 F.2d at 338-39. The Agency assessed the costs of internal and external effluent treatment measures, not only for the industry, but also for each subcategory. This included a separate cost assessment for the sulfite subcategories. App. 2380-83. An economic analysis was prepared to determine the impact of the costs on the industry. App. 1211-448. It found that the industry as a whole would readily absorb the cost of compliance with the 1977 standards, estimated at $1.6 billion. Out of 270 mills employing 120,000 people, eight mills would likely be closed and 1800 people laid off. The Agency noted that the impact on the three heavily polluting sulfite subcategories would be the greatest. Of less than 30 sulfite mills, three would probably close, resulting in 550 people being laid off.

Against these costs, EPA balanced the main effluent reduction benefit: overall 5,000 fewer tons per day of BOD discharged into the nation's waters. EPA refined this balance by calculating the cost per pound of BOD removed for each subcategory. App. 2478-79. Although sulfite mills must make large investments in waste treatment facilities, the cost-benefit balance is favorable for the limitations on these mills, because of the large volume of waste they produce and thus the greater treatment efficiency. See note 8 supra.

Petitioners' first contention is that EPA not only should have calculated the overall cost-benefit balance, but also should have made an "incremental" calculation of that balance. More precisely, they contend that EPA must undertake to measure the costs and benefits of each additional increment of waste treatment control, from bare minimum up to complete pollution removal. In support of this contention, they point to Senator Muskie's description of cost-benefit balancing, which suggests a focus on the "additional degree" or "marginal" amount of effluent reduction. See note 52 supra. Petitioners concede that we accepted EPA's calculation of the overall cost-benefit balance, without any further marginal or incremental analysis, in American Paper Inst., supra, 177 U.S.App.D.C. at 191, 543 F.2d at 338. Nonetheless, they suggest that the present case can be distinguished, because in these proceedings, unlike in American Paper Inst., industry representatives submitted an incremental breakdown of costs and benefits to the Agency.

The failure of American Paper Inst. to require EPA to perform its own incremental analysis is justified for a number of reasons beyond some oversight on the part of paper industry petitioners in that case. While EPA has no discretion to avoid cost-benefit balancing for its 1977 standards, it does have some discretion to decide how it will perform the cost-benefit balancing task. "[E]ven with th[e] 1977 standard, the cost of compliance was not a factor to be given primary importance," American Iron Steel Inst., supra, 526 F.2d at 1051, and, as such, cost need not be balanced against benefits with pinpoint precision. A requirement that EPA perform the elaborate task of calculating incremental balances would bog the Agency down in burdensome proceedings on a relatively subsidiary task. Hence, the Agency need not on its own undertake more than a net cost-benefit balancing to fulfill its obligation under section 304.

However, when an incremental analysis has been performed by industry and submitted to EPA, it is worthy of scrutiny by the Agency, for it may "avoid the risk of hidden imbalances between cost and benefit." Id. at 1076 n. 19 (Adams, J., concurring). If such a "hidden imbalance" were revealed here, and if the Agency had ignored it, we might remand for further consideration. But in this case the incremental analysis proffered by industry showed that the last and most expensive increment of BOD treated in sulfite mills cost less than $.15 per pound of BOD removed, which is below the average cost of treatment in most of the industry's subcategories. App. 3545-51B. See note 8 supra. We would be reluctant to find that EPA had ignored a "hidden imbalance" when the most unfavorable incremental cost-benefit balance that is challenged falls well within the range of averages for the industry as a whole.

Petitioners' next contention is that EPA underestimated the cost of BPCTCA for the dissolving sulfite subcategory, by misfiguring the cost of SSL recovery. We have examined petitioners' contention, bearing in mind that we do not review EPA's cost figuring de novo, but accord EPA discretion to arrive at a cost figure within a broad zone of reasonable estimate. See Permian Basin Area Rate Cases, 390 U.S. 747, 88 S.Ct. 1344, 20 L.Ed.2d 312 (1968). Petitioners' complaint revolves around the Agency's refusal to include the capital cost of installing SSL recovery in some of its cost calculations. As EPA notes, five out of six dissolving sulfite mills have already installed SSL recovery. Where, as here, most of a cost element has been incurred already, or will be incurred for a purpose other than meeting federal effluent limitations, EPA may exclude that element from the cost of BPCTCA. Accordingly, we uphold EPA's estimate of the cost of BPCTCA.

b.

"[N]on-water quality environmental impact[s] (including energy requirements)" are among the "consideration factors" listed in section 304, and are the sole factors of that kind on which petitioners premise a challenge to the limitations. We have already seen that the Act does not specify a particular structure for EPA's treatment of the consideration factors but instead leaves the Agency with discretion in deciding how they will be "taken into account." In exercising that discretion, it is clear that EPA devoted considerable attention to assessing environmental impact and adequately set forth its conclusions with respect thereto. App. 2360-467 (Development Document). Most crucially, in view of the Act's emphasis in listing "energy requirements" as part of environmental impacts, EPA developed estimates of the new energy demands for the industry as a whole — about 2.4% of the industry's total energy use — and for each industry subcategory. For the sulfite subcategories, with their higher waste loads requiring greater waste treatment, the figure was an 18% increase in energy demand. EPA also developed estimates of the sludge disposal problem, which is the reverse side of effluent reduction benefit, because the waste that is removed from effluent must be disposed of as sludge. We are consequently convinced that EPA took adequately into account the environmental impacts of its regulations.

Petitioners assert, however, that we must impose on EPA a further and special requirement to engage in environmental balancing. They cite allegedly dramatic examples of negative environmental impacts from the air pollution and sludge disposal incident to waste treatment, and contend that EPA failed to give these enough "weight" in the balance. As we have discussed, we believe Congress entrusted the manner of deliberation about all of the "consideration factors" to EPA's discretion, and we are prepared to uphold EPA on that basis alone. Nonetheless, the special policies in the Act with respect to environmental protection warrant some additional comments.

Our consideration begins with the history of the Act, which shows that Congress developed a willingness to entrust EPA with more latitude than other agencies in carrying out programs that affect the environment. In the years immediately prior to the passage of the Act, the federal government had mounted a campaign to control water pollution by a permit program under the Rivers and Harbors Act of 1899, 33 U.S.C. § 407. During that period, Congress also had enacted the National Environmental Policy Act (NEPA), 42 U.S.C. § 4321 et seq., which was designed to force federal decisionmakers to consider the environmental effects of their decisions. Because the water pollution permit program under the Rivers and Harbors Act was aimed at enhancing the environment, some of NEPA's legislative history suggested that the permit program officials might be exempt from the duty under NEPA to prepare environmental impact statements (EIS's). Nevertheless, in December 1971, a court required EIS's for water permits under the Rivers and Harbors Act, Kalur v. Resor, 335 F. Supp. 1 (D.D.C. 1971), and in so doing severely impeded the permit program's administrability. It is not surprising, therefore, that Congress became aware of this threat to the regulation of water pollution and that the legislators took it into account the following year in formulating the successor to that permit program — the 1972 Act. See, e.g., Legislative History, at 260 (remarks of Rep. Dingell).

Accordingly, section 511(d) of the House version of the Act, H.R. 11896, 93d Cong., 1st Sess., excused EPA from complying with NEPA in issuance of water permits. Nonetheless, the House imposed environmental balancing duties on EPA in a different way. Section 101(g) of H.R. 11896 provided generally that "[i]n the implementation of this Act, agencies responsible therefor shall consider all potential impacts relating to the water, land, and air to insure that other significant environmental degradations and damage to the health and welfare of man does not result." The House also included "environmental impact" in the particular section listing the many factors to be "tak[en] into account" in setting effluent limitations. Id. § 304. The Senate version of the Act had no corresponding provisions.

After lengthy deliberations, the Conference Committee knitted the two versions of the Act in a combination that minimized, without entirely omitting, EPA's obligation thereunder explicitly to consider the non-water environment. Like the House bill, the Conference version excused EPA from preparing EIS's. Unlike the House bill, the Conference version completely deleted section 101(g), with its general duty to avoid all significantly adverse environmental impacts. Only section 304 was retained, in a modified and limited form, see note 68 infra, which simply made "non-water quality environmental impacts" one of the many listed factors for EPA to "take into account," along with such other factors as engineering aspects, age, and process changes.

Congress' intent in passing this legislation was obviously not to minimize the importance of protecting the environment. The late 1960's and early 1970's saw the passage of a number of statutes aimed at dramatically increasing the protection given the environment, and the Act involved herein is among the most important. Rather, Congress was resolved to rely on EPA's own internal structure and personnel attitudes to ensure that the net result of all of its programs would be a substantially enhanced natural environment. In essence, Congress was convinced that EPA's internal dynamics and procedures were the "functional equivalent" of the NEPA duties imposed on other agencies. As Senator Muskie declared, "[t]he whole concept of EPA is that environmental considerations are to be determined in one place by an agency whose sole mission is protection of the environment." Based on this conviction about EPA's commitment to environmental goals, the legislators apparently felt that a judicially reviewable environmental balancing duty would serve no purpose except to establish a NEPA duty "as a tactic of litigation and delay" and thus make the EPA program unworkable. Portland Cement Ass'n v. Ruckelshaus, 158 U.S.App.D.C. 308, 317, 486 F.2d 375, 384 (1973), cert. denied, 417 U.S. 921, 94 S.Ct. 2628, 41 L.Ed.2d 226 (1974).

That Section 304 requires EPA to "take into account" non-water quality environmental impacts, therefore, reflects several concerns apart from a fear that the Agency will have an inadequate commitment to protection of the air and land. Perhaps most important, if these factors were not listed, EPA arguably would have no authority to temper its effluent regulations when its own conclusion was that such tempering was needed to protect the land and air. While committing the Agency to lead a comprehensive attack on water pollution, Congress did not intend that attack to prevent the Agency from realizing its other environmental goals. Furthermore, there are some environmental considerations, such as wildlife conservation, that are not within EPA's expertise, but that Congress wanted considered in EPA's deliberations on water pollution. See Legislative History, at 883-84 (letter from Reps. Reuss, Pelly, et al.). Thus, it included a reference to all non-water quality environmental impacts to assure the proper broadening of EPA's environmental impact deliberations. Cf. Sun Enterprises, Ltd. v. Train, 532 F.2d 285, 289-90 (2d Cir. 1976) (EPA required under the Fish and Wildlife Coordination Act to consult with the Interior Department about relevant actions taken under the 1972 Act).

Finally, the requirement of some advertence on the Agency's part to non-water environmental impacts provided a mechanism for assuring that EPA's internal structure and procedures will evolve as expected. The Act's listing of environmental impacts as a factor encourages the Agency, if more incentive is necessary, to seek information from relevant sources outside the Agency and from personnel in sections of the Agency devoted to non-water matters. Once that communication is assured, the likelihood that the expected inter- and intraagency sensitivity to environmental benefits and impacts will not occur is slight indeed.

Thus, since Congress intended EPA's internal structure to protect the non-water environment, the judicial function is completed when we have assured ourselves that EPA expressly considered the probable environmental impacts of its regulations. As we have noted, EPA fully investigated the environmental impacts, and thereby fulfilled this aspect of its statutorily mandated duty.

VI. THE AGENCY'S EXERCISE OF DISCRETION

Petitioners' remaining challenges to the effluent limitations involve attacks solely on the rationality of the Agency's discretionary decisionmaking in various areas. Although we have examined all of petitioners' attacks on the Agency's exercise of discretion and found them wanting, several of them deserve further discussion. Those challenges fall into two major categories: whether EPA has responded adequately to the diversity of the industry in its subcategorization and limit-setting decisions, and whether it has identified "practicable" technology capable of achieving those limitations.

A.

In setting effluent limitations, EPA had to take into account the great diversity among the almost 300 mills subject to Phase II regulation. It did so by two methods: subdivision and averaging. EPA began by subcategorizing the industry on the basis of the major differences in industrial processes and other factors. Further distinctions were made within many subcategories. Industry commented on the earlier subdivision proposals, and EPA accommodated many of industry's concerns, eventually identifying 16 subcategories, divided into 66 subdivisions. On average, that is, EPA tailored one set of limitations to every five mills. This extensive subdivision safeguarded against overzealous standards, increased the confidence that can be placed in the practicability of the regulations, and diminished the need to handle variation through the variance process.

Of course, differences still exist among mills within the same subcategories and subdivisions. EPA took these differences into account by basing its limitations on BPCTCA, i.e., the pollution control achieved at the " average of the best mills." For its averages, EPA drew on the best available data base. That the limitations still impose greater burdens on some mills than others, i.e., on those with below average treatment facilities, is an unavoidable consequence of Congress' goal of uniformity in effluent limitations rather than in treatment expenditures.

Petitioners' specific challenges to EPA's treatment of variability focus on four sources of variability: cold climate, the profitability of SSL recovery, "upset" conditions, and hydraulic flow. At the outset, we note that petitioners have a heavy burden in challenging EPA's treatment of variability. That treatment involves a host of administrative, technical, and statistical considerations as to which we lack the mandate to second-guess the Agency. For the reasons discussed below, we uphold EPA's limitations against all four challenges.

1.

Petitioners argue that EPA inadequately accounted for temperature differences in setting effluent limitations. As all parties agree, cold climates affect biological waste treatment. Bacteria break waste down more slowly at low temperature, and different populations of bacteria predominate at different temperatures, so that mills in cold regions have greater difficulty in using biological treatment. See Tanners' Council v. Train, 540 F.2d 1188, 1194 (4th Cir. 1976); American Meat Inst., supra, 526 F.2d at 455.

EPA considered the climate problem and concluded that northern paper mills could practicably use activated sludge systems as their method of biological treatment. Under this method, waste is treated before it can cool significantly even in cold climates. Although petitioners counter that activated sludge has many drawbacks, including a susceptibility to "shocks" and higher cost, EPA took those drawbacks into account in its deliberations. Thus, it included equalization basins in activated sludge BPCTCA to insulate against "shocks" and, more importantly, it determined that the effluent benefits were worth the extra cost. In light of this latter determination, subcategorization on the basis of climate would be a fruitless act, since the subcategory incurring the higher cost (mills in colder areas) could justifiably be held to the same effluent limitations as the one incurring the lower cost (those in warmer climes). Nor is disapproval of the regulations mandated by prior cases that have discussed temperature subcategorization. The critical issue in those cases has been whether EPA compiled a full record on which it based its decision, and here we find adequate record support for EPA's determination.

2.

Petitioners next contend that EPA acted arbitrarily in refusing to create a separate subcategory for sulfite mills lacking a profitable process for "SSL recovery." As previously noted, the "cooking" of wood with chemicals in the sulfite process leaves behind a waste-laden solution called spent sulfite liquor (SSL). See pp. ___-___ of 191 U.S.App.D.C., pp. 1022-1024 of 590 F.2d supra. SSL can be recovered by collecting, evaporating, and/or burning it. When sodium and magnesium are used in the cooking solution, SSL recovery is profitable because those expensive chemicals may be economically recovered for reuse rather than discharged. When two less expensive chemicals, ammonia and calcium, are used, SSL recovery is less profitable or unprofitable, and SSL recovery is simply useful as a waste treatment method for disposing of SSL without water pollution. See note 10 supra. Petitioners assert that the difference between mills at which SSL is profitable, and those at which it is not, is a more basic process difference than some other such differences that were used as the basis for EPA subcategorization. As such, they assert, the Agency acted arbitrarily in refusing to establish separate subcategories in this instance.

We believe that EPA acted within its broad discretion in regulating all sulfite mills without regard to the profitability of SSL recovery. Process is only one of several factors relevant to subcategorization. Other factors may be influential or decisive. Here, subcategorization would have had a negative effect on the cost and effluent benefit balance, because, then, SSL recovery — a highly cost-efficient pollution-control technique — could have been foregone. By contrast, the other process differences pointed to by petitioners as less drastic but nonetheless the basis for EPA subcategorization do not require that techniques as cost-efficient as SSL recovery be abandoned as BPCTCA.

3.

Waste treatment facilities occasionally release excess pollutants due to such unusual events as plant start-up and shutdown, equipment failures, human mistakes, and natural disasters. EPA accounted for this type of performance variability by using a careful statistical approach. In setting daily and monthly effluent limitations based on performance data from many plants, it made allowance for more than 99% of all the variability in performance. Petitioners contend that this degree of accuracy is insufficient in that the statute's civil and criminal penalties are based on an absolute liability standard. They note that the 99% figure shows that, in the past, fully adequate mill treatment systems have occasionally exceeded the proposed effluent limitations, and they ask the Agency to promulgate an "excursion" or "upset" regulation specifying circumstances in which exceeding the limitations will be excused.

The excursion issue has troubled EPA and the courts. On the one hand, denying such provisions seemingly asks plants to do the impossible — to handle the most unusual upsets in plant conditions. On the other hand, there are strong policy reasons for denying such provisions and leaving the handling of upsets to EPA's enforcement discretion. Last year, EPA reviewed and elaborated its position on the matter. NPDES Decision of the General Counsel No. 57 (March 16, 1977). Henceforth, EPA will identify "upset conditions" and allow excursion provisions in some industries. In other industries, it will not promulgate such provisions. Instead, it will take variability into account by setting generous daily and monthly effluent limitations and by exercising its discretion not to enforce when appropriate. The proceeding involved in the present case was one of the latter kind. EPA refused to promulgate an excursion provision, stating that it "expects that the performance of the worst cases [ i. e., plants that exceed limitations] will be improved by proper controls and that the effluent limitations can be achieved by properly operated and maintained plants." 42 Fed.Reg. 1420 (1977) (final regulations).

We believe that EPA's position in Decision No. 57 is sound, and we uphold its denial of excursion provisions in this case. A contrary decision might hamper the Agency's ability to "force technology" and hence could impede enforcement. Congress intended effluent limitations to compel plants to improve their performance, even when innovation was required. See pp. ___- ___ of 191 U.S.App.D.C., pp. 1061-1062 of 590 F.2d infra. In this "technology forcing" context, denial of an excursion provision justifiably compels plants to develop monitoring, repair, and back-up capabilities to avoid excessive discharges.

Moreover, depriving EPA of discretion to refuse excursions would interfere with the congressional goal of "swift and direct" enforcement. Excursion provisions cannot be framed in simple numerical terms, as, say, an allowance of four excessive discharges per year, without giving mills a license to dump wastes at will on several occasions annually. American Petroleum Inst. v. EPA, 540 F.2d 1023, 1036 (10th Cir. 1976) (denying excursions). Thus, such provisions must be stated in complex terms, e.g., by specifying plant incidents justifying excessive discharges.

As the Supreme Court has recognized recently, however, there is a major difference in pollution regulation enforcement between simple numerical standards and complex requirements. Once excursion provisions are promulgated, an enforcement case no longer turns on the sharply defined issue of whether the plant discharged more pollutant than it was allowed to, but instead depends on murky determinations concerning the sequence of events in the plant, whether those events would have been avoidable if other equipment had been installed, and whether the discharge was within the intent of the excursion provision. Consequently, what Congress planned as a simple proceeding suitable for summary judgments would become a form of inquest into the nature of system malfunction.

We consequently reject the argument that EPA must promulgate excursion provisions so that the effluent limitations will reflect BPCTCA technology that is effective 100 percent of the time. But see Marathon Oil Co., supra, 564 F.2d at 1273-74. In the nature of things, no general limit, individual permit, or even any upset provision can anticipate all upset situations. After a certain point, the transgression of regulatory limits caused by "uncontrollable acts of third parties," such as strikes, sabotage, operator intoxication or insanity, and a variety of other eventualities, must be a matter for the administrative exercise of case-by-case enforcement discretion, not for specification in advance by regulation. See CPC Int'l, Inc., supra, 540 F.2d at 1338 (denying excursions). A line must be drawn as to what is treated in the general rule and what is handled case-by-case, and we believe it appropriate to defer when EPA, in the interest of preserving an enforcement system based on straightforward numbers, establishes a general rule with better than 99 percent accuracy and leaves the rest to prosecutorial discretion.

We are likewise unpersuaded by an analogy to excursions under the Clean Air Act, and by the threat of citizen suits, and/or of a lack of good faith on the part of government prosecutors. Accordingly, we uphold EPA's decision to deny excursion provisions.

4.

The Agency typically expresses its effluent limitations in terms of pounds of pollutants per ton of goods produced. That figure, in turn, is arrived at by multiplying water flow times pollution concentration — that is to say, by deriving the product of (1) the gallons of water used per ton of goods and (2) the pounds of pollutant per gallon of water:

It is important to note, however, that EPA does not require operators to achieve any specific level of flow, but only that the pollution content in that flow as a whole be below a constant level set relative to tons of product. Hence, EPA does leave industry the option of utilizing a somewhat higher flow but building pollution control technology capable of accommodating it. In light of the nonmandatory nature of the flow determinations made by EPA, we may easily dispose of one of petitioners' contentions. The industry appears to argue that by setting limitations and identifying practicable technology with a given flow in mind, EPA has failed adequately to identify the cost of the required pollution control (or, stated differently, to identify practicable technology) for those plants with higher than average flows. The simple answer to this argument is that EPA studied mills with varying levels of flow and set limitations that it deemed within reach of all of those mills, so long as they installed "practicable" ( i.e., in part, not overly costly) technology. Having found none of the limitations themselves — or the practicable technology determinations — unreasonable, therefore, the fact that some mills use flows different from those considered normal for the purposes of some of EPA's calculations seems irrelevant.

Petitioners further claim, however, that even if reasonable under the normal analysis, the limitations are unsatisfactory because they force any plant with higher than average flows to add internal controls to reduce water usage. In support of their position, petitioners point to the legislative history suggesting that Congress expected most pollution controls to require end-of-pipe, or external, technology, and they repeat the well established rule derived therefrom that internal controls that are not in common use in the regulated industry may not be required by EPA in the 1977 standards. See American Paper Inst., supra, 177 U.S.App.D.C. at 194, 543 F.2d at 341 (citing cases); American Iron Steel Inst., supra, 526 F.2d at 1060-61. Although this rule requires the Agency to make a "common use," rather than "practicability" finding whenever the control technology it identifies is internal, we review its decision for abuse of discretion exactly as we review its other findings.

In this instance, as in most others, EPA has fully explained its methodology so that the bases for its decision on average flow for each subcategory are visible. App. 2073-177, 2478-81 (Development Document). The Agency achieved this series of figures by a careful process. Initially many of its subcategorization divisions were based on characteristic flows within segments of the industry, so that the mills to be compared with each other were fairly uniform to begin with. Next, the Agency measured the average flow within each subcategory — discarding unusually high and, more often unusually low ones. Notably, the Agency based its decision on the average of all mills rather than on the "average of the best," which is its usual — and unchallenged — method of determining practicability. Hence, EPA made a conscious effort to distinguish internal flow controls, which require a "common usage" finding, from other technological requirements, which may be less industrially prevalent so long as they are "practicable."

Moreover, beyond these measurements, the Agency also undertook a detailed study of flow control methods and the cost thereof for each subcategory and found them available and used to one degree or another in all subcategories. App. 2195-242, 2364-97 (Development Document). In fact, it showed, as in American Paper Inst., supra, 177 U.S.App.D.C. 194, 543 F.2d at 341, that some of all internal pollution control measures identified as useful by the Agency are used by no less than 75% of the mills studied within any given subcategory. App. 2214 (Development Document). And, although not all of these controls are aimed at reducing flow, the Agency determined that, overall, more than 50% of all of the mills studied achieved the subcategory flow rate utilized by EPA in setting the limits, which we find sufficiently indicative of the normality of internal flow controls. Accordingly, the Agency's determination of common flow is within the authorized bounds of discretion.

B. 1.

Some of the petitioners have strongly challenged EPA's choice of BPCTCA for the dissolving sulfite subcategory. As discussed above, the intense "cooking" process used in the dissolved sulfite process dissolves most of the wood's cellulose in waste solutions. See pp. ___-___ of 191 U.S.App.D.C., pp. 1022-1024 of 590 F.2d supra. During "biological" treatment this dissolved matter is taken up by bacteria. Disposing of the watery mass of these bacteria, i.e., sludge, is a serious problem, for their tough cell walls make it difficult to drain the water from, i. e., "dewater," them. Moreover, without draining, sludge is difficult to incinerate or use as landfill.

It has long been recognized that the dewatering problem is difficult and that all the available approaches have certain drawbacks. See App. 1515-30 (1969 study). EPA began its consideration of the problem in 1973 with a "state of the art" review of treatment technology, which devoted much attention to alternative dewatering approaches. App. 3693-711. It has since amassed considerable other material on the problem, including the industry's own data and criticism of EPA's dewatering proposals, culminating in discussions in its final Development Document of dewatering technology and the estimated cost and environmental impact thereof. App. 2262-64, 2346-59, 2382-83, 2406-08.

Recognizing the difficulty of the problem, EPA has not promoted a single dewatering technology, but instead has offered diverse approaches — some sequential, some alternative — indicating that each particular dissolving sulfite mill might choose a different approach. In its model, the bacterial solution is chemically prethickened and then mixed with nonbacterial waste, which is easier to dewater and further thickens the mass. The resulting mixture is chemically conditioned and subjected to vacuum filtration, a process in which rotating filters suck a soggy "cake" out of the prethickened waste. This cake, which may still be 20% or less solid, can be used for landfill, either at this point or later after pressing to remove even more water. Alternatively, the sludge can be dried using special boilers, and then burned in those same boilers, with the heat of incineration used to dry more sludge.

Industry pointed out problems and drawbacks with all these proposed steps and alternatives. The Agency responded by pointing to its record support, including the fact that one out of the six dissolving sulfite mills covered by the regulations has already implemented dewatering technology. Although perhaps a closer question than the others reviewed herein, we do not find EPA's choice of BPCTCA in this instance to be an abuse of its broad discretion. EPA has clearly devoted much attention to the problem and has explained its conclusions. In major part it seems to have been motivated by a congressionally mandated policy concern: the determination to push pollution control technology rapidly and decisively forward to the limits of practicability after 1977 and to the limits of achievability after 1983. See Legislative History, at 1460 (Senate Report) (Administrator given 1977 "mandate to press technology and economics to achieve those levels of effluent reduction which he believes to be practicable . . .."). Indeed, even in the earlier set of regulations, Congress expected EPA to press sometimes beyond the most advanced technology currently being used: "In those industrial categories where present practices are uniformly inadequate," Congress has admonished the Administrator to interpret "`best practicable' to require higher levels of control than any currently in place if he determines that the technology to achieve those higher levels can be practically applied." Id. at 169-70 (statement of Sen. Muskie).

To force industry implementation of pollution control technology, EPA has used a number of approaches upheld by the courts. EPA has based its 1977 standards on exemplary facilities, including foreign ones, American Frozen Food Inst., supra, 176 U.S.App.D.C. at 138, 539 F.2d at 140, and has utilized "transfer technology." See note 70 supra. In this case, EPA has used yet another approach — specification of a diverse technological array as BPCTCA — which we uphold in light of the lack of effluent treatment that has traditionally characterized sulfite mills. Under this diversified approach, the Agency has identified a number of alternative dewatering techniques with the expectation that, if several techniques are available, one or another will work at all of the regulated mills. Even if each technique has some drawbacks, together all of them constitute a "practicable technology" suitable to BPCTCA. In sum, because we find that the dewatering methods identified by EPA have had some success in the past and because the judgment as to whether an array of diverse approaches is sufficient in this instance "is best left in the hands of the Agency," Tanners' Council, supra, 540 F.2d at 1192, we accept the Agency's conclusions.

2.

Petitioners also make a broad challenge to all the TSS limitations for the industry. They contend that there are certain "nonsettleable solids" that will not be removed by BPCTCA, and the EPA failed to rely on actual treatment performance data in setting TSS limitations that require removing those solids. We considered and rejected a similar challenge in American Paper Inst., supra, 177 U.S.App.D.C. at 198, 543 F.2d at 345, and we are inclined to do likewise here. Petitioners admit that in the particular subcategory it chose as an example, the bleached kraft subcategory, 10 out of the 32 mills already meet all of EPA's effluent limitations, and even more meet just the TSS limitations. Nonetheless, they complain that these conforming mills, as well as others relied on by EPA, utilize advanced internal and external control technologies that were installed solely to meet stringent state and local water quality standards for particular receiving waters. App. 764. This observation is largely correct but it does not present a cognizable grievance. The mills on which EPA has modeled BPCTCA are without question capable of meeting EPA's effluent limitations, and the Agency accordingly is justified in insisting that all other mills come up to this undoubtedly "practicable" standard.

For all of the foregoing reasons, the 1977 effluent limitations for the bleached segment of the American paper industry are upheld, and the petitions denied, except that the BOD limitation for acetate grade dissolving sulfite mills is remanded to the Agency for further proceedings consistent herewith.

It is so ordered.