Full opinion text
TABLE OF CONTENTS I. BACKGROUND A. The Statute B. The Regulations 1. The General Pretreatment Regulations 2. The Categorical Electroplating Standards I. BACKGROUND — Continued C. The Consolidated Cases D. The Standard of Review II. THE GENERAL PRETREATMENT REGULATION A. The Definitions of “Interference" and “Pass Through" 1. Interference 2. Pass Through B. Definition of “New Source” C. The Fundamentally Different Factor Variance 1. Variances from Pretreatment Standards 2. Variances for Toxic Pollutants D. The Removal Credits Provision 1. EPA Approval and Authorization 2. Unworkability E. The Combined Wastestream Formula 1. Process Categories 2. Moving Target 3. Attainability and Cost of Combined Pré-, treatment III. THE CATEGORICAL ELECTROPLATING STANDARDS A. Methodology of the Standards 1. The Regression Analysis 2. Lead and Cadmium B. The Cost to Segregated Facilities 1. The NAMF Settlement Agreement 2. The Cost-Benefit Analysis C. The Compliance Deadline for Integrated Facilities IV. CONCLUSION TABLE OF ABBREVIATIONS AISI American Iron and Steel Institute BAT Best Available Technology Economically Achievable BDT Best Available Demonstrated Control Technology BPT Best Practicable Control Technology Currently Available CACI Chicago Association of Commerce and Industry CMA Chemical Manufacturing Association EPA Environmental Protection Agency FDF Fundamentally Different Factor GM General Motors Corp. IIPEC Institute for Interconnecting and Packaging Electronic Circuits J. App. Joint Appendix Legis. Hist. Legislative History Me° Regulated Metal in Influent MFASC Metal Finishing Association of Southern California NAMF National Association of Metal Finishers NPDES National Pollutant Discharge Elimination System NRDC Natural Resources Defense Council PM Precipitable Metals in Influent POTW Publicly Operated Treatment Works R. Add. Addendum of Respondent TSS Total Suspended Solids TTO Total Toxic Organics USBA United States Brewers Association Xme Ratio of Me° to PM Before: GIBBONS, HUNTER and BECKER, Circuit Judges. OPINION OF THE COURT JAMES HUNTER, III, Circuit Judge: Section 307 of the Clean Water Act directs the Administrator of the Environmental Protection Agency (“EPA”) to promulgate regulations requiring industrial facilities to pretreat the pollutants that they discharge into public sewage treatment systems. The Administrator has promulgated both general pretreatment regulations and regulations establishing categorical pretreatment standards for existing electroplating sources. The petitioners in these consolidated cases seek review of the Administrator’s actions in promulgating certain provisions of those regulations. Under section 509 of the Clean Water Act we have jurisdiction to exercise a limited review of the Administrator’s actions. We may overturn those actions only if they are arbitrary, capricious or otherwise contrary to law. Under that standard of review, we find invalid certain provisions of the general pretreatment regulations. Because it is not for us to rewrite those provisions, we will remand them to the Administrator. I. BACKGROUND A. The Statute In 1972 Congress amended the Federal Water Pollution Control Act (“the Act” or “the Clean Water Act”), setting as a national goal the elimination, by 1985, of the discharge of pollutants into navigable waters, 33 U.S.C. § 1251(a)(1) (1976). To reach that goal the Act directed the Administrator of EPA to promulgate regulations setting limits on the pollution that can be discharged by three general types of “point sources,” see id. § 1362(14) (1976 & Supp. I 1977). First, the Administrator was to establish effluent limitations for point sources which discharge pollutants directly into navigable waters (“direct dischargers”). The Administrator had to define effluent limitations for categories or classes of point sources which would require existing direct dischargers to employ by 1977 the best practicable control technology currently available (“BPT”), id. §§ 1311(b)(1)(A), 1314(b)(1) (1976), and to use by 1983-87 the best available technology economically achievable (“BAT”), id. §§ 1311(b)(2) (1976 & Supp. I 1977), 1314(b)(2) (1976). For newly-constructed direct dischargers the Administrator had until 1974 to establish “new source” performance standards requiring the application of the best available demonstrated control technology (“BDT”). Id. § 1316. The Administrator had to set the BPT, BAT, and BDT limitations by considering the factors specified in sections 304(b) and 306(b) of the Act, id. §§ 1314(b), 1316(b). He was to apply those limitations to individual direct dischargers through the National Pollutant Discharge Elimination System (“NPDES”) permit issued to the dis-charger under section 402 of the Act, id. § 1342 (1976 & Supp. I 1977). Second, the Act mandated that the Administrator set effluent limitations for publicly owned treatment works (“POTWs”) engaged in the treatment of municipal sewage or industrial wastewater. See id. § 1292(2) (1976 & Supp. 1 1977). Under the Act the Administrator had to establish effluent limitations, based on “secondary treatment,” which POTWs had to meet by 1977. Id. §§ 1311(b)(1)(B), (C), 1314(d)(1) (1976). The limitations thus established were to be applied to each individual POTW through its NPDES permit. Id. § 1342 (1976 & Supp. I 1977). Third, section 307 of the Act addressed the “indirect dischargers,” point sources which discharged their pollutants not directly into navigable waters but into POTWs. Congress recognized that the pollutants which some indirect dischargers release into POTWs could interfere with the operation of the POTWs, or could pass through the POTWs without adequate treatment. To prevent such discharges by existing sources, Congress directed in section 307(b)(1) of the Act: (b)(1) The Administrator shall ... publish proposed regulations establishing pretreatment standards for introduction of pollutants into [POTWs] for those pollutants which are determined not to be susceptible for treatment by such treatment works or which would interfere with the operation of such treatment works.... Pretreatment standards under this subsection ... shall be established to prevent the discharge of any pollutant through [POTWs], which pollutant interferes with, passes through or otherwise is incompatible with such works. 33 U.S.C. § 1317(b)(1) (1976); see also id. § 1314(g) (Supp. I 1977). The Administrator had to designate the categories of existing sources to which each such standard would apply, promulgate the standards by 1973, and revise the standards as control technologies and industrial processes changed. Id. § 1317(b). For newly-constructed indirect dischargers the Act directed that by 1974 the Administrator had to promulgate pretreatment standards for each category of new sources which “shall prevent the discharge of any pollutant into such treatment works, which pollutant may interfere with, pass through, or otherwise be incompatible with such works.” Id. § 1317(c). New and existing indirect dis-chargers did not need to obtain NPDES permits, but instead had pretreatment standards imposed directly upon them. In 1977 Congress amended the Act by passing the Clean Water Act of 1977, Pub.L. No. 95-217, 91 Stat. 1566 (“the 1977 Amendments”). Section 54 of the 1977 Amendments added a sentence to section 307(b)(1) permitting a POTW to modify the pretreatment requirement of an existing indirect discharger if the POTW could successfully remove all or part of the toxic pollutants released by that discharger. Id. § 54(a), 91 Stat. 1591 (amending 33 U.S.C. § 1317(b)(1) (Supp. I 1977)). B. The Regulations The Administrator elaborated his regulatory approach to indirect dischargers in his National Pretreatment Strategy, 43 Fed. Reg. 27,759 (1978), and in the consent decree in NRDC v. Train, 8 Env’t Rep.Cas. (BNA) 2110 (D.D.C.1976), modified sub nom. NRDC v. Costle, 12 Env’t Rep.Cas. (BNA) 1833 (D.D.C.1979), aff’d in part sub nom. Environmental Defense Fund v. Costle, 636 F.2d 1229 (D.C.Cir.1980), modified on remand sub nom. NRDC v. Gorsuch, Nos. 2153-73 et al. (D.D.C. Oct. 26, 1982). The Administrator announced that he would promulgate two types of pretreatment standards. The first type, “categorical” pretreatment standards, would establish numerical limits on the discharge, by twenty-one specific categories of industrial sources, of particular toxic pollutants which could cause interference with or pass through POTWs. 43 Fed.Reg. 27,760, 27,771-73 (1978); NRDC v. Train, 8 Env’t Rep.Cas. (BNA) at 2130-36. Categorical pretreatment standards would be set to require the application of similar levels of control technology as the Act mandated for direct dischargers. 43 Fed.Reg. 27,760-63 (1978); 42 Fed.Reg. 6480 (1977). The Administrator agreed to promulgate categorical pretreatment standards “generally analogous to best practicable control technology currently available” (BPT) for eight industries by May 15, 1977. NRDC v. Train, 8 Env’t Rep.Cas. (BNA) at 2128 ¶ 13. For all twenty-one industrial categories the Administrator would then promulgate categorical pretreatment standards based on BAT for existing sources and BDT for new sources. 43 Fed.Reg. 27,760 (1978); see NRDC v. Gorsuch; NRDC v. Train, 8 Env’t Rep.Cas. (BNA) at 2123-26. The second type of pretreatment standard, the “prohibited discharge” standard, would not set numerical limits on the discharge of particular pollutants by specified sources. 43 Fed.Reg. 27,759-60 (1978). Rather, the prohibited discharge standard would establish a general prohibition on the release of any pollutants by any nondomestic source if those pollutants interfere with or pass through a POTW. Id. 1. The General Pretreatment Regulations The General Pretreatment Regulations for Existing and New Sources of Pollution, 40 C.F.R. § 403.1.-16 (1982), serve to implement the two types of pretreatment standards. First, the general pretreatment regulations themselves contain the prohibited discharge standard generally forbidding interference and pass through, id. § 403.5, and define the terms “interference” and “pass through,” id. § 403.3(i), (n). Second, the general pretreatment regulations establish the mechanisms and procedures governing the separately promulgated categorical pretreatment standards. The general regulations define whether a source is a “new source” under the standards. Id. § 403.-3(k). The general regulations contain a mechanism through which the existing industrial user of a POTW can obtain a variance from a categorical discharge limit if the user can show that during the development of the standard EPA had considered “fundamentally different” factors than those relating to the user’s operation (“the FDF variance provision”). Id. § 403.13. The regulations set up the procedure by which a POTW can revise an industrial user’s categorical discharge limit to reflect the POTW’s removal of the user’s pollutants (“the removal credit provision”). Id. § 403.7. Finally, the regulations provide a formula to calculate an adjusted categorical discharge limit where the industrial user mixes the effluent from the regulated process with other wastewaters prior to pretreatment (“the combined wastestream formula”). Id. § 403.6(e). The Administrator first proposed the general pretreatment regulations on February 2, 1977. 42 Fed.Reg. 6476 (1977). He promulgated the regulations on June 26, 1978. 43 Fed.Reg. 27,736 (1978). On October 29, 1979, the Administrator proposed amendments to the regulations, 44 Fed.Reg. 62,260 (1979), which he promulgated on January 28,1981, 46 Fed.Reg. 9404 (1981). The Administrator then attempted to postpone indefinitely the effective date of first all and later part of the general pretreatment regulations. 47 Fed.Reg. 4518 (1982); 46 Fed.Reg. 19,936, 50,502, 50,503 (1981). After we declared that indefinite postponement invalid in NRDC v. EPA, 683 F.2d 752 (3d Cir.1982), the Administrator reinstated the regulations’ effective date of March 30, 1981. 47 Fed.Reg. 42,688 (1982); see 46 Fed.Reg. 11,971 (1981). On October 4,1982, we granted the petitioners’ unopposed motion to extend the regulations’ effective date until June 30, 1981. 48 Fed.Reg. 2774 (1983). 2. The Categorical Electroplating Standards The categorical pretreatment standards for the Electroplating Point Source Category, 40 C.F.R. §§ 413.01.-84 (1982), are BPT-level pretreatment standards set pursuant to the NRDC v. Train consent decree. 44 Fed.Reg. 52,592, 52,608 (1978); see 8 Env’t Rep.Cas. (BNA) at 2128 ¶ 13(b). The categorical electroplating standards cover 7752 existing firms with electroplating operations, the firms falling in three broad groups: independent “job shops,” firms performing electroplating as their primary line of business; independent manufacturers of printed circuit board; and “captive operations,” electroplating sections of firms which' perform electroplating as part of their manufacture of another product. See 44 Fed.Reg. 52,593 (1979); 43 Fed.Reg. 6561-62 (1978). The electroplating standards divide those firms into seven subcategories, based on the electroplating process employed. For each subcategory the standards, inter alia, set numerical limits on the dischargeable concentrations of cyanide and several metals (e.g., cadmium, chromium, copper, lead, nickel, and zinc). 40 C.F.R. §§ 413.14.-84 (1982). Electroplating sources discharging less than 10,000 gallons per day of electroplating process wastewater have to meet limits for only lead, cadmium and amenable cyanide. Id. “Integrated” facilities, which combine the process wastestream from their captive electroplating operations with other wastewaters prior to pretreatment, are instructed to adjust their discharge limits using the combined wastestream formula. Id. § 413.04; see id. § 413.02(h). The Administrator proposed the categorical electroplating standards on February 14, 1978, 43 Fed.Reg. 6560 (1978), and promulgated them on September 7, 1979, 44 Fed. Reg. 52,590 (1979), corrected, id. at 56,360. Following promulgation petitioners National Association of Metal Finishers and Institute for Interconnecting and Packaging Electronic Circuits filed petitions for review in this court. Nos. 79-2256, 79-2443. On March 7, 1980, those parties and EPA reached a settlement agreement (“the NAMF Settlement Agreement”). Addendum to Respondent’s Brief at D-l [hereinafter cited as “R.Add.”]. Pursuant to that agreement the Administrator on July 3, 1980, proposed several amendments to the 1979 electroplating standards. 45 Fed.Reg. 45,322 (1980). In response to the petition for review of Ford Motor Co., No. 80-1008, EPA proposed other changes, 45 Fed.Reg. 19,245 (1980). Ford later filed a petition for reconsideration of the 1979 standards. J.App. at 2082. On January 28, 1981, the Administrator denied Ford’s petition for reconsideration, 46 Fed.Reg. 9476 (1981), and promulgated the amendments to the electroplating standards, id. at 9462, corrected, id. at 30,625. The deadline for compliance with the electroplating standards for integrated facilities was set at three years from the effective date of the combined wastestream formula, while non-integrated facilities had a compliance date of May 12,1982, 46 Fed.Reg. 9462 (1981), later modified to April 27, 1984, 48 Fed.Reg. 2775 (1983); 46 Fed.Reg. 43,973 (1982). On August 31, 1982, the Administrator published the proposed Metal Finishing regulations, which established BAT pretreatment standards for most of the indirect dischargers presently covered by the electroplating standards. 47 Fed.Reg. 38,462-63 (1982). Only existing job shops and printed circuit board manufacturers would remain under the electroplating standards, which would be amended to restrict the discharge of toxic organic pollutants. Id. at 38,464, 38,468. On July 15, 1983, the Administrator promulgated the Metal Finishing regulations. 48 Fed.Reg. 32,462 (1983) (to be codified at 40 C.F.R. § 433.10.-17). C. The Consolidated Cases As noted above, National Association for Metal Finishers (“NAMF”), Institute for Interconnecting and Packaging Electronic Circuits (“IIPEC”), and Ford Motor Co. (“Ford”) filed petitions for review of the 1979 electroplating standards. Nos. 79-2256, 79-2443, 80-1008. Ford, NAMF, General Motors Corp. (“GM”), and Metal Finishing Association of Southern California (“MFASC”) petition for review of the 1981 electroplating amendments. Nos. 81-1279, 81-1351, 81-1712, 81-2119. Ford also petitions for review of the Administrator’s denial of its petitions for review' of the Administrator’s denial of its petition for reconsideration of the 1979 electroplating standards, No. 81-1214. We address that appeal in Ford Motor Co. v. EPA, 718 F.2d 55 (3d Cir.1983). Petitioners Natural Resources Defense Council (“NRDC”), United States Brewers Association (“USBA”), and Chemical Manufacturing Association (“CMA”) petition for review of the 1978 general pretreatment regulations. Nos. 81-1977, 81-1978, 81-1979. Petitioners Ford, NAMF, CMA, NRDC, Interlake, Chicago Association of Commerce and Industry (“CACI”) and others seek review of the 1981 general pretreatment regulations. Nos. 81-1210, 81-1981, 81-1982, 81-1983, 81-1984, 81-1985, 81-2150, 81-2151. Consideration of the cases was necessarily held pending our resolution in NRDC v. EPA of the challenge to the Administrator’s indefinite postponement of the 1981 general pretreatment amendments. Judge Becker of this Court then presided over a series of conferences in which he consolidated the cases, set a briefing schedule, and, on October 29, 1982, limited the subjects of briefing. D. The Standard of Review Under section 10(e) of the Administrative Procedure Act, we may not invalidate agency actions unless we find them to be “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law.” 5 U.S.C. § ■ 706(2)(A) (1976). This standard sets the level of deference with which we must review the agency’s actions for their statutory authority, substantive validity and procedural regularity. See Weyerhaeuser Co. v. Costle, 590 F.2d 1011, 1024 (D.C.Cir.1978). We must extend “great deference to the interpretation given the statute by the officers or agency charged with its administration.” EPA v. National Crushed Stone Association, 449 U.S. 64, 83, 101 S.Ct. 295, 307, 66 L.Ed.2d 268 (1980) (quoting Udall v. Tallman, 380 U.S. 1, 16, 85 S.Ct. 792, 801, 13 L.Ed.2d 616 (1965)); American Iron & Steel Institute v. EPA (“AISI I”), 526 F.2d 1027, 1041-42 (3d Cir.1975), mandate recalled in part, 560 F.2d 589 (3d Cir.1977), cert. denied, 435 U.S. 914, 98 S.Ct. 1467, 55 L.Ed.2d 505 (1978). If an act is susceptible to more than one reasonable interpretation, we must accept any reasonable interpretation chosen by the agency. Udall v. Tallman, 380 U.S. 1, 16, 85 S.Ct. 792, 801, 13 L.Ed.2d 616 (1965); see NRDC v. Train, 421 U.S. 60, 75, 95 S.Ct. 1470, 1479, 43 L.Ed.2d 731 (1975). If the agency rejects the reasonable interpretation of the statute, however, we must “honor the clear meaning of a statute, as revealed by its language, purpose and history.” International Brotherhood of Teamsters v. Daniel, 439 U.S. 551, 556 n. 20, 99 S.Ct. 790, 800 n. 20, 58 L.Ed.2d 808 (1979); see FEC v. Democratic Senatorial Campaign Committee, 454 U.S. 27, 32, 37, 102 S.Ct. 38, 42-45, 70 L.Ed.2d 23 (1981). Our inquiry into the substantive basis for the agency’s actions must be searching and careful, but our review is a narrow one. As the Supreme Court has recently stated: The scope of review under the arbitrary and capricious standard is narrow and a court is not to substitute its judgment for that of the agency. Nevertheless, the agency must examine the relevant data and articulate a satisfactory explanation for its action including a “rational connection between the facts found and the choice made.” Burlington Truck Lines v. United States, 371 U.S. 156, 168 [83 S.Ct. 239, 246, 9 L.Ed.2d 207] (1962). In reviewing that explanation, we must “consider whether the decision was based on a consideration of the relevant factors and whether there has been a clear error of judgment.” Bowman Transp. Inc. v. Arkansas-Best Freight System, [419 U.S. 281, 285, 95 S.Ct. 438, 442, 42 L.Ed.2d 447 (1974) ], Citizens to Preserve Overton Park v. Volpe, [401 U.S. 402, 416, 91 S.Ct. 814, 823, 28 L.Ed.2d 136 (1971)]. Normally, an agency rule would be arbitrary and capricious if the agency has relied on factors which Congress has not intended it to consider, entirely failed to consider an important aspect of the problem, offered an explanation for its decision that runs counter to the evidence before the agency, or is so implausible that it could not be ascribed to a difference in view or the product of agency expertise. The reviewing court should not attempt itself to make up for such deficiencies: “We may not supply a reasoned basis for the agency’s action that the agency itself has not given.” SEC v. Chenery Corp., 332 U.S. 194, 196 [67 S.Ct. 1575, 1577, 91 L.Ed. 1995] (1947). We will, however, “uphold a decision of less than ideal clarity if the agency’s path may reasonably be discerned.” Bowman Transp. Inc. v. Arkansas-Best Freight Systems, [419 U.S. at] 286 [95 S.Ct. at 442], Motor Vehicle Manufacturers Association v. State Farm Mutual Automobile Insurance Company, - U.S. -, ---, 103 S.Ct. 2856, 2865-66, 77 L.Ed.2d 443 (1983). Our review of an agency’s “observance of procedure required by law,” 5 U.S.C. § 706(2)(D) (1976), is more exacting. NRDC v. EPA, 683 F.2d 752, 760 (3d Cir. 1982); see Weyerhaeuser, 590 F.2d at 1027-28. Under section 4 of the Administrative Procedure Act, an agency initiating informal rulemaking must first publish a general notice which includes “either the terms or substance of the proposed rule or a description of the subjects and issues involved.” 5 U.S.C. § 553(b)(3) (1976). Such notice must “fairly apprise interested persons” of the subjects and issues dealt with in the rule ultimately promulgated. American Iron & Steel Institute v. EPA (“AISI II”), 568 F.2d 284, 290-98 (3d Cir.1977); see Ethyl Corp. v. EPA, 541 F.2d 1, 48 (D.C.Cir.1976) (en banc), cert. denied, 426 U.S. 941, 96 S.Ct. 2663, 49 L.Ed.2d 394 (1976). The agency must then give interested persons an opportunity to participate in the rulemaking through the submission of written comments. 5 U.S.C. § 553(c) (1976). After considering the relevant comments submitted, the agency must incorporate in the promulgated rules “a concise general statement of their basis and purpose.” Id. To ensure meaningful judicial review, the agency in that statement and in its supporting materials must articulate the rational basis for the choices it has made; however, as stated above, we “should not reverse an agency’s decision that is not fully articulated where we can reasonably discern the basis for the agency’s action." AISI I, 526 F.2d at 1047; see AISI II, 568 F.2d at 295-96. Finally, we note that the Administrator’s actions are entitled to a presumption of regularity. Citizens to Preserve Overton Park v. Volpe, 401 U.S. 402, 415, 91 S.Ct. 814, 823, 28 L.Ed.2d 136 (1971). A party petitioning for review of an agency’s regulations bears the burden of overcoming that presumption. Lewes Dairy v. Freeman, 401 F.2d 308, 316 (3d Cir.1968), cert. denied, 394 U.S. 929, 89 S.Ct. 1187, 22 L.Ed.2d 455 (1969); accord Environmental Defense Fund v. Costle, 657 F.2d 275, 283 n. 28 (D.C.Cir.1981). If after adequate notice and opportunity to comment a petitioner claims on appeal that the agency overlooked technical, factual and policy issues not raised in comments before the agency, that petitioner will have less latitude in its complaints, Weyerhaeuser, 590 F.2d at 1028 n. 15, or in special circumstances will be barred altogether, AISI I, 526 F.2d at 1050; see American Frozen Food Institute v. Train, 539 F.2d 107, 134 (D.C.Cir.1976). II. THE GENERAL PRETREATMENT REGULATIONS NRDC and all the other petitioners (“industrial petitioners”) raise challenges to several provisions of the general pretreatment regulations, 40 C.F.R. §§ 403.1.-16 (1982). We consider those challenges in the following order: (A) the definitions of “interference” and “pass through;” (B) the definition of “new sources;” (C) the FDF variance provision; (D) the removal credits provision; and (E) the combined waste-stream formula. A. The Definitions of “Interference” and “Pass Through” Section 403.3 of the general pretreatment regulations defines “interference” and “pass through.” 40 C.F.R. § 403.3(i), (n) (1982). The industrial petitioners in their joint brief (“joint petitioners”), and USBA contend that the breadth of the definitions of “interference” and “pass through” violates the Act because the definitions subject indirect dischargers to penalties without consideration of fault, causation or consequences. Joint petitioners argue that the definitions were improperly promulgated. We will grant the petitions for review in Nos. 81-1982, 81-1983, 81-1984, 81-2150, and 81-2151, and will remand the definition of both “interference” and of “pass through.” 1. Interference Section 307(b) of the Act directs the Administrator to promulgate pretreatment standards to prevent the discharge of any pollutant through a POTW which “interferes with, passes through or is otherwise incompatible with such works.” 33 U.S.C. § 1317(b)(1) (1976 amended Supp. I 1977). Under that mandate the Administrator not only has promulgated the categorical pretreatment standards setting numerical limits upon discharges from certain regulated categories of industrial sources, but has also established a general prohibition applying to all non-domestic indirect dischargers whether or not they are subject to categorical pretreatment standards. See 40 C.F.R. § 403.5(a) (1982). That “prohibited discharge” standard contains a general prohibition of the introduction into a POTW of pollutants that “Pass Through a POTW or Interfere with the operation or performance of the works.” Id. § 403.5(a). The prohibited discharge standard also specifically prohibits the introduction into a POTW of pollutants that in several specified ways cause interference. Violation of the prohibited discharge standard is unlawful and renders the violator liable to suit by the Administrator, by the State, by the POTW, or by any adversely affected party. 33 U.S.C. §§ 1317(d), 1319(b), (c), (f), 1342(b)(7), 1365(a) (1976 & Supp. I 1977). Violations may carry civil penalties of up to $10,000 per day, and criminal penalties of up to $25,000 per day and two years in prison. Id. § 1319(c)(1), (d). In addition, if the violation is likely to recur the POTW is required to develop and enforce such specific effluent limits for its users as are necessary to ensure the POTW’s future compliance with its NPDES permit. 40 C.F.R. § 403.5(c)(2) (1982). Section 403.3 provides the definition of “interference” as that term is used in the prohibited discharge standard. As originally promulgated in the 1978 general pretreatment regulations, section 403.3 defined “interference” as “an inhibition or disruption of a POTW’s sewer system, treatment processes or operations which contributes to a violation of any requirement of [the POTW’s] NPDES Permit.” 43 Fed.Reg. 27747 (1978) (emphasis added). In 1979 the Administrator proposed to narrow the ambit of the definition by requiring an inhibition or disruption which “causes or significantly contributes” to the violation of the POTW’s permit, and by including a “safe harbor” provision exempting from the definition inhibitions and disruptions caused by an indirect discharger “in compliance with specific prohibitions or standards developed by Federal, State or local governments.” 44 Fed.Reg. 62,260, 62,265 (1979). As promulgated, however, the 1981 general pretreatment amendments omitted the safe harbor provision and defined “significantly contributes” using three numbered categories. 46 Fed.Reg. 9413 (1981). The amended regulations thus redefine “interference” as: an inhibition or disruption of the POTW ... which is a cause of or significantly contributes to either a violation of any requirement of the POTW’s NPDES permit (including an increase in the magnitude or duration of a violation) or to the prevention of sludge use or disposal by the POTW .... An industrial user significantly contributes to such a permit violation or prevention of sludge use or disposal ... whenever such User: (1) Discharges a daily pollutant loading in excess of that allowed by contract with the POTW or by Federal, State or local law; (2) Discharges wastewater which substantially differs in nature or constituents from the User’s average discharge; or (3) Knows or has reason to know that its Discharge, alone or in conjunction with Discharges from other sources, would result in a POTW permit violation or prevent sewage use or disposal .... 40 C.F.R. § 403.3(i) (1982). Joint petitioners allege that the present definition is contrary to the Act because it renders an indirect discharger liable for interference even though its discharges did not cause the POTW’s permit violation or sludge problem. They posit that an industrial user may be held liable if discharging more than average or beyond its contract limit, even though it is the discharge of another user of the POTW, or a malfunction or mistake at the POTW itself, that actually causes the inhibition or disruption. Joint petitioners contend that Congress did not intend to subject indirect dischargers to liability without proof of causation. EPA argues that joint petitioners have misread the definition. EPA urges that the definition requires that causation be shown before liability is established. In its brief EPA emphasizes that an industrial user’s discharge must “lead to” or “give rise to” the inhibition or disruption. Brief for Respondent (No. 79-2256) at 125-27. At oral argument EPA’s counsel asserted that to prove liability the Administrator must show that the discharge both caused the inhibition or disruption and fell within the three categories defining “significantly contributes.” Transcript of Oral Argument at 133, 136. We cannot agree. The words “leads to” and “gives rise to” do not appear in the definition. Instead, the promulgated definition requires only that the discharge “is a cause of or significantly contributes,” and defines “significantly contributes” by substituting three categories of discharger misconduct, at least two of which exclude any necessity for proving that the discharge caused the inhibition or disruption. 40 C.F.R. § 403.3(i)(l), (2) (1982). If the Administrator has not written the definition to require causation, we cannot rewrite the definition to match the representations of counsel. Given that section 403.3(i)’s definition of interference does not require causation to establish liability, we must now consider whether liability without causation is within the intent of Congress. We find that neither the language of the Act nor the intent of Congress appears to contemplate liability without causation. First, sections 307(b) and (c) requires that pretreatment standards “prevent the discharge of any pollutant ..., which pollutant interferes with such works.” Id. § 1317(b), (c) (1976 & Supp. I 1977) (emphasis added). Section 307(c) explains that such standards must be promulgated “to insure that any source introducing pollutants into a [POTW] . .. will not cause a violation of the effluent limitations of such treatment works.” Id. § 1317(c) (1976) (emphasis added). Second, Congress made plain its intent that “[i]n no event is it intended that pretreatment facilities be required for compatible wastes as a substitute for adequate municipal waste treatment works.” S.Conf. Rep. No. 1236, 92d Cong., 2d Sess. 130, reprinted in 1972 U.S.Code Cong. & Ad. News 3668, 3776, 3807; accord H.R.Rep. No. 911, 92d Cong., 2d Sess. 113, reprinted in Senate Comm, on Public Works, 93d Cong., 1st Sess., Legislative History of the Water Pollution Control Act Amendments of 1972, at 753, 800 (1973) [hereinafter cited as “1972 Legis.Hist.”]. If the inhibition or disruption is caused not by the industrial user’s discharge but by a mistake or malfunction at the POTW, the industrial user will be punished for failing to substitute its own pretreatment for the POTW’s impaired treatment. We do not think that Congress intended such liability. See also AISI 1,526 F.2d at 1056 (rejecting penalties for circumstances beyond discharger’s control). We conclude that given the language and purpose of the Act, an indirect discharge cannot be liable under the prohibited discharge standard unless it is a cause of the POTW’s permit violation or sludge problem. If the definition of “interference” required that an indirect discharger be both “the cause of” and “significantly contribute to” the POTW’s permit violation, it would be consistent with that causation requirement. As written, however, the definition fails to require such causation, and thus violates the clear meaning of the Act. We will therefore remand the entire definition of interference to the Administrator. 2. Pass Through Joint petitioners allege that the definition of pass through in 40 C.F.R. § 403.3(n) (1982) was promulgated without the notice and comment required under section 4 of the Administrative Procedures Act, 5 U.S.C. § 553(c) (1976). They point out that the amendments proposed in 1979 contained no suggestion that the Administrator intended to use or to define the term “pass through” in the general pretreatment regulations. See 44 Fed.Reg. 62,260-71 (1979). The Administrator nonetheless promulgated the definition of “pass through” in the 1981 general pretreatment amendments, justifying his failure to first propose the definition by saying that it was “almost identical” to the promulgated definition of interference. 46 Fed.Reg. 9416 (1981). EPA now admits that the definition of “pass through” was promulgated without the notice and comment required by the Administrative Procedure Act. Brief for Respondent (No. 79-2256) at 132-33. EPA suggests that for that reason we should remand the definition to the Administrator; nevertheless, it contends that we are not barred from passing on the definition’s substantive validity. Id. at 133 & n. *. We believe that it would be fruitless for us to review the definition before it has been submitted for public comment. We will therefore remand the definition of “pass through” in section 403.3(n) to the Administrator. B. Definition of “New Source” “New source” is defined in section 403.3(k) of the general pretreatment regulations, 40 C.F.R. § 403.3(k) (1982). Under that definition, if the Administrator fails to promulgate a new source pretreatment standard within 120 days of its publication, those sources whose construction began after the publication but before the promulgation of the proposed standard are not considered to be new sources. Petitioner NRDC argues that by excluding those sources the definition is inconsistent with the Act and is contrary to our holding in Pennsylvania Department of Environmental Resources v. EPA, 618 F.2d 991 (3d Cir.1980). We agree, and will accordingly grant NRDC’s petitions for review in Nos. 81-1977 and 81-1985. Under section 307(c) of the Act, the Administrator must promulgate new source pretreatment standards for any indirect dis-charger that would be a “new source” under section 306 of the Act if it were a direct discharger. 33 U.S.C. § 1317(c) (1976). Section 306(a)(2) defines a “new source” as any source, the construction of which is commenced after the publication of proposed regulations prescribing a standard of performance under this section which will be applicable to such source, if such standard is thereafter promulgated in accordance with this section. Id. § 1316(a)(2). Section 306(b)(1)(B) directs the Administrator to promulgate proposed standards of performance within 120 days after the publication of the proposed regulations. Id. § 1316(b)(1)(B). Section 403.3(k) of the general pretreatment regulations defines “new source” as any source whose construction commenced [a]fter proposal of Pretreatment Standards in accordance with section 307(c) of the Act which are applicable to such source, but only if the Standards are promulgated in accordance with section 307(c) within 120 days of their proposal. 40 C.F.R. § 403.3(k)(2) (1982) (emphasis added). If the standards are not promulgated within 120 days of their proposal, only those sources whose construction began after promulgation are considered “new sources.” Id. § 403.3(k)(l); see id. § 403.6(b). In Department of Environmental Resources we considered a similar definition of “new source” promulgated for a category of direct dischargers. We rejected EPA’s definition as inconsistent with the basic policies of the Act. Congress, we found, “intended to subject as many firms as possible to the new source regulations.” 618 F.2d at 999. By its plain meaning the definition of “new source” in section 306(a)(2) achieved that goal by subjecting to new source standards all businesses which initiated new construction after being put on notice by the publication of the proposed standards. We stated that if dischargers wished to limit their period of uncertainty by forcing the Administrator to promulgate proposed standards within section 306(b)(l)(B)’s 120-day deadline, the proper remedy was not the exemption of new construction from new source standards, but was a citizen suit under 33 U.S.C. § 1365 (1976) seeking EPA compliance with the deadline. We therefore held that section 306(a)(2) had to be given its plain meaning, and we struck down the EPA’s definition. 618 F.2d at 1000. In this case EPA has conceded that the “new source” definition in section- 403.3(k) is invalid under our holding in Department of Environmental Resources. Brief for Respondent (No. 81-1977) at 14. Intervenor CMA argues nonetheless that the definition is valid under our holding and under the Act. CMA, however, fails either to distinguish Department of Environmental Re sources, or to proffer any arguments on the proper construction of section 306 which were not considered and rejected in that decision. We hold, therefore, that the definition of “new source” in section 403.-3(k) is invalid. We will remand the definition to the Administrator. C. The Fundamentally Different Factor Variance Section 403.13 of the general pretreatment regulations permits the Administrator to grant a variance from a categorical pretreatment standard to an existing indirect discharger within the category if the Administrator, in establishing the categorical standard, has considered factors “fundamentally different” from the factors relating to that source. 40 C.F.R. § 403.13 (1982). Petitioner NRDC contends that the FDF variance is not authorized by the Act and is specifically prohibited insofar as it would permit the discharge of toxic pollutants. We need not determine whether the Administrator has authority to issue FDF variances, for we agree that such variances may not be issued for toxic pollutants. We will therefore grant NRDC’s petitions for review in Nos. 81-1977 and 81-1985. Section 307(b) of the Act directs the Administrator to promulgate pretreatment standards for existing indirect dischargers by category or categories of sources. 33 U.S.C. § 1317(b)(1), (3) (1976 & Supp. I 1977). As he has chosen to regulate existing indirect dischargers in an analogous manner to direct dischargers, the Administrator bases the categorical pretreatment standards on the BPT and BAT levels of control technology set forth for direct dis-chargers in section 301(b) of the Act. Id. § 1311(b). The Administrator determines those levels for existing indirect dischargers by considering the factors specified in section 304(b). Id. § 1314(b). The fundamentally different factor variance in section 403.13 is also adopted from the regulatory scheme governing direct dis-chargers. Under the Consolidated Permit Regulations, 40 C.F.R. §§ 125.30.-32 (1982), existing direct dischargers may obtain FDF variances from BPT and BAT effluent limitations. Terming the concept equally applicable to pretreatment standards, the Administrator modeled the FDF variance provision for existing indirect dischargers after the FDF variance provision for direct dis-chargers. See 46 Fed.Reg. 9435-36 (1981); 44 Fed.Reg. 62,264-65 (1979); 43 Fed.Reg. 27,738 (1978); 42 Fed.Reg. 6481 (1977). The purpose of the FDF variance provision for indirect dischargers is stated in section 403.13(b): In establishing categorical Pretreatment Standards for existing sources, the EPA will take into account all the information it can collect, develop and solicit regarding the factors relevant to pretreatment standards under section 307(b). In some cases, information which may affect these Pretreatment Standards will not be available or, for other reasons, will not be considered during their development. As a result, it may be necessary on a case-by-case basis to adjust the limits in categorical Pretreatment Standards ... as they apply to a certain Industrial User within an industrial category or subcategory. 40 C.F.R. § 403.13(b) (1982); see id. § 125.-30(b) (near-identical statement of purpose). Indirect dischargers, POTWs and other interested parties may request that an indirect discharger receive a variance. Id. § 403.13(a), (b) (1982). Variances can be used to establish limits more or less stringent than that specified by the applicable categorical pretreatment standard. See id. § 403.13(c)(2), (3). An industrial user seeking to obtain a discharge limit less stringent than required by the categorical standard must establish that the alternative limit is justified by factors relating to the discharge regulated by the categorical pretreatment standard which are fundamentally different from the factors considered by the Administrator in establishing the standard. Id. § 403.13(b), (c)(1)(h), (c)(2). In delineating the factors to be considered fundamentally different, section 403.13 includes most of the factors which section 304(b) directs the Administrator to consider in determining BPT and BAT standards. Id. § 403.13(d); see id. § 403.13(e). 1. Variances from Pretreatment Standards NRDC argues that FDF variances from BPT and BAT pretreatment standards are contrary to the Act. NRDC correctly notes that while Congress expressly provided for modification of other discharge limits, the Act does not explicitly authorize FDF variances from the categorical pretreatment standards. EPA contends that the Act implicitly authorizes FDF variances for indirect dischargers, and relies on the approval given to the FDF variances for direct dis-chargers in E.I. du Pont de Nemours & Co. v. Train, 430 U.S. 112, 97 S.Ct. 965, 51 L.Ed.2d 204 (1978). In du Pont the Supreme Court held that the Administrator had to provide for variances for direct dischargers from BPT effluent limitations. Id. at 128, 97 S.Ct. at 975; see EPA v. National Crushed Stone Association, 449 U.S. 64, 72 & n. 12, 101 S.Ct. 295, 301 & n. 12, 66 L.Ed.2d 268 (1980). The Court found that section 301(b)(1) required that “some allowance [be] made for variations in individual plants” under categorical BPT effluent limitations because that section spoke of “effluent limitations for point sources,” 33 U.S.C. § 1311(b)(1)(A) (1976), rather than “effluent limitations for categories and classes of point sources,” id. § 1311(b)(2)(A) (1976 & Supp. I 1977). 430 U.S. at 128, 97 S.Ct. at 975. As section 307(b) states that pretreatment standards apply to “categories of sources,” id. § 1317(b)(3) (1976), the Administrator is not required under du Pont to make any provision for variances from pretreatment standards. Agreeing that a variance provision is not required, EPA asserts that the Administrator in his discretion may permit FDF variances from the pretreatment standards as an appropriate means to ensure that the categorical standards are not applied inequitably to a particular discharger. See NRDC v. EPA, 537 F.2d 642, 646-47 (2d Cir.1976). We need not consider whether the Administrator possesses the inherent authority to provide for variances from categorical pretreatment standards, however, because we find another of NRDC’s contentions dispositive. NRDC, noting that the FDF variance provision is drawn to permit variances from pretreatment standards for toxic pollutants, argues that variances for toxic pollutants are forbidden by section 301(1) of the Act, 33 U.S.C. § 1311(1) (Supp. I 1977). We agree. 2. Variances for Toxic Pollutants The elimination of the discharge of toxic pollutants has always received special emphasis under the Act. Id. § 1251(a)(3) (1976); see id. § 1362(13). In 1972 Congress directed the Administrator to list and develop effluent limitations for toxic pollutants under section 307(a) of the Act. Id. § 1317(a). The discharge of toxic pollutants generated even greater congressional concern in 1977. E.g., Senate Committee on Environment and Public Works, 95th Cong., 2d Sess., Legislative History of the Clean Water Act of 1977, at 326 (1978) (statement of Cong. Roberts) [hereinafter cited as “1977 Legis.Hist.”]; id. at 454 (statement of Sen. Muskie). In section 53 of the 1977 Amendments, Congress itself added toxic pollutants to the Administrator’s list and required that he promulgate BAT effluent limitations for those pollutants by 1980. Section 53 also added subsection (1) to section 301: (1) The Administrator may not modify any requirement of this section as it applies to any specific pollutant which is on the toxic pollutant list under section 1317(a)(1) of this title. 33 U.S.C. § 1311(1) (Supp. I 1977). EPA does not dispute that the pretreatment standards mandated by section 307(b) are a “requirement” of section 301. Instead EPA argues that “modification” is a term of art in the Act, and that FDF variances are not modifications of a pretreatment standard but are simply the creation of a more appropriate standard based on factors previously overlooked by the Administrator. Under the Administrator’s construction, section 301(7) deprives the Administrator only of his authority to “modify” BAT standards under section 301(c) and (g), 33 U.S.C. § 1311(c), (g) (1976 & Supp. I 1977). The legislative history of section 301(1) does indicate that Congress was primarily concerned with prohibiting modifications under section 301(c) and (g). Nonetheless, it does not appear that Congress used “modification” as a term of art so as to exclude variance provisions from the proscription of section 301(1). Spokesmen for the 1977 Amendments used the terms “waiver” and “modification” interchangeably. 1977 Leg-is.Hist. 328-29 (statement of Rep. Roberts); id. at 458 (statement of Sen. Muskie). More important, Senator Muskie termed section 301(c) a “variance” provision. 1977 Legis. Hist. 461. As “modification” is thus not a term of art, section 301(1) includes variances in its broad prohibition. EPA’s attempt to distinguish the policy behind FDF variances from the policies behind the “modification” provisions is equally unsuccessful. The Supreme Court has stated that section 301(c)’s modifications of BAT limits serve the same function as FDF variances of BPT limits: A § 301(c) variance, thus, creates for a particular point source a BAT standard that represents for it the same sort of economic and technological commitment as the general BAT standard creates for the class. National Crushed Stone, 449 U.S. at 74,101 S.Ct. at 302. If Congress was willing to prohibit section 301(c) modifications where toxic pollutants are concerned, it is difficult to imagine why Congress would have permitted similar FDF variances for those same pollutants. In Appalachian Power Co. v. Train, 620 F.2d 1040 (4th Cir.1980), NRDC argued that section 301(1) prohibited FDF variances from BPT effluent limitations for toxic pollutants. That court deferred to the Administrator’s construction of the Act and upheld the FDF variance provision, remarking that “the best that can be said for § 301(1) is that it is not clear.” Id. at 1046-48. Because we find that section 301(1) is clear, we must disagree. Section 301(1) forbids modifications, and FDF variances are no less modifications than those provisions indisputably prohibited by that section. Given the clear congressional concern throughout the 1977 Amendments for discharges of toxic pollutants, we hold that FDF variances for toxic pollutant discharges are forbidden by the Act. We will therefore remand the FDF variance provision. D. The Removal Credits Provision Section 403.7 of the general pretreatment regulations establishes the criteria and procedures by which a POTW may revise an indirect discharger’s numerical discharge limit for a pollutant, as set in its categorical pretreatment standard, to reflect the POTW’s removal of that pollutant. 40 C.F.R. § 403.7 (1982). Joint petitioners, Interlake and CACI, argue that section 403.7 exceeds the Administrator’s authority under section 307(b)(1) of the Act, is unworkable, and was improperly promulgated. We disagree, and will deny the petitions for review on this issue. Section 307(b) of the Act authorized the Administrator to establish pretreatment standards for any pollutant that “interferes with, passes through, or otherwise is incompatible” with POTWs. 33 U.S.C. § 307(b)(1) (1976). In enacting that section Congress indicated that pretreatment of compatible pollutants may not be necessary, and added that pretreatment should not be required as a substitute for adequate treatment by POTWs. In a further effort “to avoid treatment for treatment’s sake,” 1977 Legis.Hist. 343 (statement of Rep. Roberts), Congress in section 54(a) of the 1977 Amendments to the Act added a sentence to section 307(b)(1): If, in the case of any toxic pollutant under subsection (a) of this section introduced by a source into a publicly owned treatment works, the treatment by such works removes all or any part of such toxic pollutant and the discharge from such works does not violate that effluent limitation or standard which would be applicable to such toxic pollutant if it were discharged by such source other than through a publicly owned treatment works, and does not prevent sludge use or disposal by such works in accordance with section 405 of this Act, then the pretreatment requirements for the sources actually discharging such toxic pollutant into such publicly owned treatment works may be revised by the owner or operator of such works to reflect the removal of such toxic pollutant by such works. Pub.L. No. 95-217 § 54(a), 91 Stat. 1591 (amending 33 U.S.C. § 1317(b)(1) (Supp. I 1977)). The legislative history of the section made clear that “[i]n promulgating national pretreatment standards the Administrator shall include a provision recognizing the option of [a POTW] to modify the requirements to reflect the degree of reduction achieved by the treatment works.” H.R.Conf.Rep. No. 830, 95th Cong., 1st Sess. 88, reprinted in 1977 U.S.Code Cong. & Ad. News 4424, 4463. In the removal credits provision the Administrator has set conditions and procedures for such revision of categorical pretreatment standards. 40 C.F.R. § 403.7 (1982). To be eligible to grant revisions to reflect the toxic pollutants it removes, a POTW must first have a pretreatment program approved by the responsible Approval Authority. Id. § 403.7(b)(2) The POTW must then obtain authorization from the Approval Authority to revise the discharge limits for specific pollutants. Id. § 403.7(b)(1). To obtain authorization the POTW must demonstrate “consistent removal” of each pollutant sufficient to justify the proposed revision. Id. § 403.7(b); see id. at 403.7(a)(1), (2). If once a year or more untreated wastewaters overflow before they reach the POTW and thus bypass the POTW’s treatment process, the POTW either must show that its indirect dischargers compensate for the overflows, or it must reduce the amount of consistent removal claimed. Id. § 403.7(b)(3); see id. § 403.7(a)(3). The POTW must also show that the revision will not prevent it from meeting applicable sludge management requirements. Id. § 403.7(b)(4). Once authorization for the revision has been granted, the POTW must monitor and report semiannually on its capability to remove the specified pollutants. Id. § 403.7(f)(1); see id. §§ 403.7(d), 403.12(i), (j). If the Approval Authority determines that the discharge limit revision no longer meets the requirements of section 403.7, or is significantly contributing to a violation of the POTW’s NPDES permit, the Approval Authority after an opportunity for corrective action may withdraw or modify the revision. Id. § 403.7(f)(5). 1. EPA Approval and Authorization Joint petitioners challenge the Administrator’s authority under the Act to mandate that POTWs must have approved pretreatment programs before they may grant removal credits. See id. § 403.-7(b)(2). Joint petitioners first correctly observe that section 307(b)(1) does not expressly impose such a condition. They then claim that the Administrator has improperly transplanted that condition from section 402(b)(8) of the Act, 33 U.S.C. § 1342(b)(8) (Supp. I 1977). Section 402(b) sets the terms, conditions and requirements for permits issued under federal and state NPDES permit programs. Id. § 1342(a)(3), (b) (1976 & Supp. I 1977). As amended in 1977, section 402(b)(8) authorizes the Administrator to insure that a POTW’s permit includes conditions to require “a program to assure compliance with [section 1317(b) ] pretreatment standards by each [significant] source” introducing regulated pollutants into the POTW. Pub.L. No. 95-217 § 54(c), 91 Stat. 1591 (amending 33 U.S.C. § 1342(b)(8) (Supp. 1.1977)). The amended section 402(b)(8) and the removal credits provision were both added by section 54 of the 1977 amendments, and the legislative history makes clear that the two provisions are closely related. The conference report and spokesmen in the House stated that the conferees had added the provision to allow a POTW to revise pretreatment standards to reflect removal “in applying these pretreatment standards through its pretreatment program.” H.R.Conf.Rep. No. 830, 95th Cong., 1st Sess. 87, reprinted in 1977 U.S.Code Cong. & Ad.News 4424, 4462; 1977 Legis.Hist. 342-43 (statement of Rep. Roberts); id. at 403 (statement of Rep. Anderson). Senator Muskie, the legislation’s sponsor, informed the Senate that the new provision permitted POTWs to grant removal credits “[w]here a local compliance program is approved.” 1977 Legis.Hist. 461. He explained: Tying local [removal] credits to local compliance programs not only provides an incentive for local participation, but more importantly, it provides assurance that the removal levels which justified the local credits will be maintained by a publicly-owned treatment works committed to a sound pretreatment program. Id. at 462. In light of this persuasive legislative history, we believe that the Administrator may require an approved pretreatment program as a condition upon a POTW’s grant of removal credits. Petitioner CACI, emphasizing that Congress in section 307(b)(1) authorized POTWs, not EPA, to grant removal credits, claims the Administrator may not require that POTWs obtain his authorization for each proposed removal credit. There is support, however, for such an authorization requirement in the legislative history. Senator Muskie stated that “EPA and the [states issuing NPDES permits] may approve case-by-case modifications of the national pretreatment standards,” and listed several conditions the EPA might place on its authorization. 1977 Legis.Hist. 461. Moreover, the Administrator’s authorization fits within the scheme of the Act as established by section 54 of the 1977 Amendments. As noted above, the Administrator may require that a POTW seeking to grant removal credits have an approved pretreatment program to assure compliance by its indirect dischargers with the section 1317(b) pretreatment standards. Section 54 also allowed the Administrator to bring an action to compel the POTW to enforce the pretreatment standards under its program. Pub.L. No. 95-217 § 54(b), 91 Stat. 1591 (adding 33 U.S.C. § 1319(f) (Supp. I 1977)). Together those provisions endow the Administrator with the power to deny authorization to a POTW’s dispensation of removal credits. CACI acknowledges that power, but argues that the Administrator must set the conditions on his authorization by litigation rather than regulation. See Air Reduction Co. v. Hickel, 420 F.2d 592 (D.C.Cir.1968). We find it hard to believe that Congress required such a piecemeal approach. See Weinberger v. Hynson, Westcott & Dunning, Inc., 412 U.S. 609, 624-26, 93 S.Ct. 2469, 2480-81, 37 L.Ed.2d 207 (1973). Section 501(a) of the Act empowers the Administrator “to prescribe such regulations as are necessary to carry out his functions under this chapter.” 33 U.S.C. § 1361(a) (1976); see du Pont, 430 U.S. at 132, 97 S.Ct. at 977; see also 33 U.S.C. § 1251(d) (1976). Since such regulations would not deprive POTWs of the sole ability to grant, and the ultimate power to deny, removal credits, we conclude that under section 501(a) the Administrator may express the conditions on his authorization of removal credits in binding regulations. 2. Unworkability Petitioners place more emphasis on their contention that the removal credits provision is simply unworkable. Joint petitioners raise two specific defects that they claim render the provision unworkable. First, they attack section 403.7(f)(5), which permits the Administrator to withdraw or modify removal credits if semiannual data reveals that the POTW issuing the credits is no longer attaining its predicted removal. Joint petitioners say that due to section 403.7(f)(5) they will be unable to rely on their removal-revised discharge limits and will be forced to install just as much control technology as if there were no removal at all. We agree with EPA, however, that such withdrawn or modified discharge limits, though unfortunate, are merely the recognition of the POTW’s failure to remove the pollutant. By requiring such modifications, the Administrator prevents the granting of removal credits for toxic pollutants which the POTW simply discharges into navigable waters: Such a requirement is consistent with the mandate of section 307(b)(1) that any revision “reflect the removal of such toxic pollutants by such works.” 33 U.S.C. § 1317(b)(1) (Supp. I 1977). It is also consonant with the legislative history requiring “documented pollutant removals” and “a demonstration that the pollutant is degraded or treated,” 1977 Legis.Hist. 461 (statement of Sen. Muskie). Second, joint petitioners challenge the requirement in section 403.7(b)(3) that a POTW unable to prevent toxic overflows must reduce the amount of removal claimed in proportion to the number of hours of overflow. Joint petitioners claim that POTWs will be unable to make verifiable engineering estimates of the hours of overflow, and will thus be unable to grant removal credits. As the Administrator notes, however, section 403.7(b) simply implements the statutory requirement that removal credits be granted only for pollutants actually removed by the POTW. Moreover, a POTW unable to estimate the time, let alone the amount, of untreated wastewater overflow may not be able to accurately predict the proportion of pollutants which it will remove. Requiring such an estimate thus has a rational basis under the Act. Joint petitioners and Interlake also make a generalized claim that the removal credits provision is unworkable. Such a generalized claim is necessarily less persuasive than a claim detailing the alleged errors made by the Administrator. We have nonetheless reviewed the bases cited by petitioners for the