Full opinion text
Opinion for the court filed by Chief Judge J. SKELLY WRIGHT. J. SKELLY WRIGHT, Chief Judge: A group of companies, in the chemical, petroleum, rubber, and steel industries and an industry association (collectively “the Companies”) appeal from a District Court order denying their motion to vacate a settlement agreement (the Agreement) previously adopted by the court, and granting a motion for modification of the settlement agreement filed by the signatories to the Agreement-five environmental groups and the Environmental Protection Agency (EPA or Agency). Natural Resources Defense Council, Inc. v. Costle, 12 ERC 1833 (D.D.C.1979). The Companies contend that the settlement agreement must be vacated both because it has been superseded by legislation enacted by Congress in 1977, and because each of the lawsuits that were resolved by the Agreement is now moot and must be dismissed. The Companies further contend that in proposing the modifications to the settlement agreement approved by the District Court EPA violated rulemaking and public participation requirements of the Administrative Procedure Act, the Clean Water Act, and its own regulations, as well as requirements of constitutional due process. I. Between 1973 and 1975 five environmental groups (collectively “NRDC”) brought four separate lawsuits against EPA to rectify the Agency’s alleged failure to implement several provisions of the statute then known as the Federal Water Pollution Control Act (FWPCA). 33 U.S.C. § 1251 ef seq. (1976). The first lawsuit challenged the criteria EPA was using to decide which pollutants to include in a list of toxic pollutants the Agency was required to compile by Section 307(a) of the FWPCA, and also sought to expand EPA’s then existing list of toxic pollutants (the toxic criteria case). The second and third lawsuits were aimed at compelling EPA to promulgate effluent discharge standards for the substances already on the Agency’s list of toxic pollutants (the deadlines cases). The fourth lawsuit sought an order requiring EPA to promulgate pretreatment standards under Section 307(b) of the FWPCA covering approximately 35 industries and a wide variety of pollutants (the pretreatment case). While these lawsuits were pending EPA officials conducted a thorough review of the Agency’s strategy for controlling toxic pollutant emissions. They concluded that there was a need to replace the Agency’s then existing approach with a new strategy calling for an integrated program for controlling toxic pollutants. Furthermore, EPA officials felt that development of the new approach could provide a basis for resolving the controversies between the environmental groups and the Agency. After the general outlines of the new program were developed EPA and NRDC, joined by four industry intervenors in one of the lawsuits, began settlement negotiations. After tentative agreement was reached between EPA and NRDC a proposed settlement agreement was submitted to the District Court. The District Court held several hearings on the proposed agreement and allowed interested parties to file comments on it. The Companies intervened in the proceedings in the District Court and filed comments vigorously opposing the proposed agreement. After requiring several modifications the District Court approved the settlement agreement, finding it a “just, fair, and equitable resolution of the issues raised.” Natural Resources Defense Council, Inc. v. Train, 8 ERC 2120, 2122 (D.D.C.1976). No appeal was taken from the court’s order adopting the settlement agreement. The settlement agreement outlined a comprehensive strategy for regulation of toxic pollutant discharges under the FWPCA, including details concerning the timing, scope, and nature of the regulatory programs EPA agreed to initiate. Insofar as is relevant to the instant case, EPA proposed to regulate discharge of toxic pollutants by developing effluent limitations, guidelines, and performance standards for new and existing emission sources, as well pretreatment standards regulating introduction of pollutants into treatment works. These limitations, guidelines, and standards were to cover 21 major industries and 65 specified pollutants or groups of pollutants. In promulgating effluent limitations and guidelines EPA agreed that it would employ technology-based controls such as “best available technology” (BAT) performance standards for existing emission sources, and performance standards reflecting the “best available demonstrated control technology” (BADCT) for new sources. The pretreatment standards EPA undertook to promulgate were to apply to any of the 65 pollutants listed in the Agreement and any other pollutants that proved to be “incompatible” with “publicly owned treatment works” (POTWs). Promulgation of the regulations envisaged by the Agreement was to take place according to a phased schedule running through December 31, 1979 and compliance with the regulations by affected industries was to be achieved by June 30, 1983. Adoption of the industry-by industry, technology-based approach, using statutory authority conferred by various sections of the FWPCA, marked a change in EPA’s regulatory strategy. Its previous efforts to control discharge of toxic pollutants had relied on authority conferred by Section 307 of the FWPCA in developing health-based standards on a pollutant-by-pollutant basis. The new strategy offered substantial advantages over the old. First, it allowed EPA to cover far more substances and emission sources than could have been handled under the old approach. Second, it allowed the Agency to develop a single regulatory package which would apply to all of the problem pollutants in the discharge of a particular industry, enabling the industry to predict the entire cost of pollution control. Third, the Agency could allow considerations of cost and technology to enter into its decisionmaking and industry was allowed a longer compliance period Finally, EPA also expected that the new program would be easier to administer. After the Agreement was adopted by the District Court Congress began a review of the FWPCA and EPA’s progress toward implementing its provisions. Committees of both Houses of Congress held hearings at which various difficulties EPA was experiencing under the then existing statutory scheme were discussed and the new regulatory framework and strategy established by the settlement agreement was explored. In testimony before the congressional committees NRDC’s representatives emphasized that the Agreement was working well, and EPA’s spokesman, while acknowledging that the Agency was having trouble meeting the deadlines set by the Agreement, strongly supported the Agreement. The outcome of these hearings was the enactment in December 1977 of several amendments to the FWPCA which was renamed the Clean Water Act (CWA). We shall discuss the nature and importance of those provisions of the 1977 Amendments that are pertinent to this case later. At this point we simply note that the Companies and NRDC disagree about the effect of the 1977 Amendments on the settlement agreement. Meanwhile, NRDC’s monitoring of EPA’s implementation of the Agreement’s provisions convinced it that the Agency would not meet any of the deadlines for proposing and promulgating regulations. Accordingly, on September 26, 1978 NRDC moved for an order to show cause why EPA should not be held in contempt of the District Court’s order approving the settlement agreement. EPA responded on October 20,1978 with a motion to amend the Agreement to extend the deadlines for promulgating regulations, to allow the Agency additional discretion to exclude certain pollutants and industry categories from regulation, and to extend the deadline for compliance with the guidelines to June 30, 1984. In its accompanying opposition to NRDC’s motion EPA explained why it had not been able to meet the original deadlines specified by the Agreement. Also on October 20, 1978 the Companies filed a motion to vacate the settlement agreement, arguing that Congress had intended the 1977 Amendments which produced the CWA to supplant the settlement agreement, that the Agreement was in conflict with the congressional program, and that continuation of the settlement agreement would inevitably involve the court in questions of analytical chemistry. On October 30, 1978 NRDC served detailed interrogatories and requests for documents on EPA. Thereafter, NRDC and EPA began discussions on a possible settlement of the controversy. On November 28, 1978 EPA officials met with representatives of the Companies to announce that a tentative agreement with NRDC had been reached, and to distribute copies of a proposed joint motion to modify the settlement agreement that EPA and NRDC had agreed to. The Companies were given ten days in which to submit written comments on the proposal. NRDC and EPA considered the suggestions made in the Companies’ comments and made some changes in the proposed modifications to reflect these suggestions. EPA and NRDC filed their joint motion to modify the settlement agreement on December 15, 1978. At the same time they withdrew all their pleadings relating to the motion for a show cause order. The Companies, however, declined to withdraw their motion to vacate the settlement agreement. By agreement of the parties the Companies were given until January 5, 1979 to file with the court any response or objections to the proposed modifications. The Companies filed a memorandum opposing the motion to modify the Agreement. In addition to repeating their contention that the Agreement must be vacated because it had been superseded by the 1977 Amendments, the Companies raised two new arguments. First, they argued that the Agreement also must be vacated because each of the four cases which underlie the Agreement had been mooted by the Amendments and must be dismissed. Second, they maintained that the proposed modification would violate public notice and comment requirements of the Administrative Procedure Act (APA), the Clean Water Act, EPA regulations, and an Executive Order, as well as constitutional requirements of due process. The District Court heard oral argument on both motions and permitted additional briefs on the new issues raised by the Companies. On March 9, 1979 the District Court issued its order denying the Companies’ motion to vacate the settlement agreement and granting NRDC’s and EPA’s motion to modify the Agreement. In its memorandum opinion accompanying the order the District Court addressed each of the Companies’ arguments. First, it rejected the Companies’ claim that Congress intended the 1977 Amendments to the FWPCA to supplant the Agreement. The court concluded that neither the terms of the Amendments nor the legislative history support this claim. Instead, it found that Congress intended the Agreement “to remain in effect to supply the. missing details of a cohesive strategy for controlling toxic water pollution.” Natural Resources Defense Council, Inc. v. Costle, supra, 12 ERC at 1836. Second, the court ruled that two of the four cases that were resolved by the settlement agreement were not moot, and that these two cases provided an adequate basis for continuing the Agreement. Id. at 1837,1838. Finally, the court dismissed the Companies’ statutory and constitutional objections to the modifications to the settlement agreement proposed by NRDC and EPA. The court found that the modifications were not “rules” within the meaning of the APA for which notice and comment were required, and that appellants’ constitutional rights to effective notice were not violated because the modifications would have no direct or immediate effect on them. Id. at 1838-1840. These appeals followed. II. On appeal the Companies raise essentially the same three arguments that they presented to the District Court. We will examine these arguments separately. A. The Effect of the 1977 Amendments Appellants contend that the District Court erred in rejecting their claim that Congress intended the 1977 Amendments to supersede the settlement agreement. Appellants maintain that these Amendments were a direct response to the problems EPA had faced in attempting to implement the provisions of the FWPCA, the same problems that were responsible for the shortcomings in the Agency’s fulfillment of its statutory obligations that NRDC’s lawsuits were aimed at rectifying. The Companies point out that Congress devoted a significant amount of time to studying these problems. The outcome of this detailed review, appellants contend, was a congressional acknowledgement that EPA’s failure to accomplish much in terms of realizing the objectives and goals of the FWPCA was largely a result of deficiencies in both substantive and procedural provisions of the Act. Appellants argue that the toxic pollutant provisions of the 1977 Amendments-were designed to replace the unworkable provisions of the FWPCA with a comprehensive and workable statutory framework for regulation of toxic pollutants that would eliminate the need for continued court supervision of the toxic pollutants programs. In particular, Congress abandoned the requirement that EPA develop health-based standards regulating discharge of toxic pollutants on a pollutant-by-pollutant basis, substituting in its place an industry-by-industry, technology-based BAT approach to controlling emission sources. In addition, Congress resolved the controversy over how many pollutants should be included in EPA’s list of toxic pollutants by specifying 65 pollutants that had to be included in the list and granting EPA’s Administrator authority to add pollutants to or delete them from this list. While acknowledging that these two changes merely adopted the regulatory framework established by the settlement agreement, appellants point to other provisions in the Amendments which they contend show that Congress did more than merely ratify the settlement agreement. In appellants’ view, the breadth and detail of these other changes demonstrate that Congress “went beyond mere ratification of the [settlement agreement] and tinkering with its toxics program and instead devised a comprehensive program to control the discharge of toxic pollutants to replace the old section 307(a) and the [Agreement].” Appellants find further support for their view that Congress intended the Amendments to supersede the settlement agreement in the legislative history of the Amendments. In this the Companies largely rely on a statement made by Congressman Roberts while explaining the toxic pollutant provisions of the House-Senate Conference Report to his colleagues. Congressman Roberts said: In summary, the revisions to the toxics regulatory program contained in the conference report * * * simplify the procedures for identifying toxic pollutants and promulgating regulations according to their characteristics. The discretion exercised by the Administrator is broadened, the procedures less formally structured, and burdens of proof modified to the point where the program may proceed in a more rapid and orderly fashion without further recourse to the courts. Crisis-by-crisis reaction to the problem of toxics must no longer be the norm, but must be replaced by an orderly program for adding compounds to the list, with the Administrator fully in charge. It, therefore, would be entirely appropriate for the United States to petition the courts to relinquish jurisdiction over toxic pollutant control under Public Law 92-500, now that the statutory basis has been laid for a workable regulatory program the lack whereof led to the litigation resulting in the consent decree. This is particularly appropriate in view of the large number of potentially toxic chemicals to be addressed by the program and the need for administrative discretion within the revised regulatory framework to carry out the provisions of law enacted herein. This is the intent of this legislation, an outgrowth of House initiatives by the House conferees. 123 Cong.Rec. H12927-H12928 (daily ed. Dec. 15, 1977). Appellants maintain that Congressman Roberts’ views must be given significant weight, pointing out that he was chairman of the House Subcommittee that drafted the Amendments, chairman of the House conferees, vice-chairman of the House-Senate Conference Committee, and floor manager of the Conference Report in the House. Appellants suggest that Congressman Roberts’ statement takes on added significance because the toxic pollutant provisions of the Amendments were drafted by the Conference Committee and the Conference Report is silent on the issue of congressional intent. Claiming to have demonstrated that Congress intended the 1977 Amendments to supplant the settlement agreement, appellants then note that courts have vacated settlement agreements where an intervening Act of Congress has changed the relevant law in such a manner as to eliminate the right which the settlement agreement was designed to safeguard. The Companies find illustrations of the operation of this principle in two Supreme Court cases, System Federation No. 91 v. Wright, 364 U.S. 642, 81 S.Ct. 368, 5 L.Ed.2d 349 (1961), and Pennsylvania v. Wheeling & Belmont Bridge Co., 59 U.S. (18 How.) 421, 15 L.Ed. 435 (1855). In Wheeling & Belmont Bridge the Court examined the effect of subsequent legislation on an outstanding injunction. The State of Pennsylvania had earlier obtained an injunction barring the company from constructing or maintaining a bridge across the Ohio River on the ground that the bridge in question obstructed navigation in such a manner as to be in conflict with certain Acts of Congress regulating navigation. A subsequent statute declared the bridge to be a lawful structure in its existing position and elevation. The Supreme Court dissolved the injunction, pointing out that the later Act of Congress had eliminated the public right the injunction had served to protect by resolving the question whether the bridge was an unlawful obstruction. In System Federation the Court relied on Wheeling & Belmont Bridge in holding that a District Court had abused its discretion in refusing to modify a consent decree after an Act of Congress changed the relevant law. The District Court had earlier approved a consent decree resolving litigation brought by non-union employees against a railroad and a number of unions representing its employees. The plaintiffs had charged the defendants with violating Section 2 of the Railway Labor Act which forbade discrimination against non-union employees. As part of the settlement agreement the court enjoined the defendants from discriminating against non-union employees because of their refusal to join a union. After Congress amended the Railway Labor Act to permit contracts requiring union shops the unions petitioned the District Court for a modification of the consent decree to permit negotiation of union shop contracts. The District Court denied the petition and the Sixth Circuit affirmed. In reversing the Supreme Court pointed out that “the District Court’s authority to adopt the consent decree comes only from the statute which the decree is intended to enforce” since “[i]t was the Railway Labor Act, and only incidentally the parties, that the District Court served in entering the consent decree.” System Federation No. 91 v. Wright, supra, 364 U.S. at 651, 81 S.Ct. at 373. The Court then noted that a “court must be free to continue to further the objectives of [an] Act when its provisions are amended” by “modify[ing] the terms of a consent decree when a change in law brings those terms in conflict with statutory objectives.” Id. The Companies argue that since the terms and legislative history of the 1977 Amendments indicate that Congress intended the toxic pollutant provisions of the Amendments to supersede the framework established by the settlement agreement, application of the settled principles announced by the Supreme Court in Wheeling & Belmont Bridge and System Federation requires that the judgment of the District Court in the instant case be reversed and the settlement agreement vacated. The power of a District Court sitting as a court of equity to modify the terms of a settlement agreement it previously adopted cannot be drawn into question. See System Federation No. 91 v. Wright, supra, 364 U.S. at 642-647, 81 S.Ct. at 368; Chrysler Corp. v. United States, 316 U.S. 556, 62 S.Ct. 1146, 86 L.Ed. 1668 (1942); United States v. Swift & Co., 286 U.S. 106, 52 S.Ct. 460, 76 L.Ed. 999 (1932). The decision to grant or deny a request to modify the terms of a consent decree rests with the discretion of the District Court. See System Federation No. 91 v. Wright, supra, 364 U.S. at 646-647, 81 S.Ct. at 371; Chrysler Corp. v. United States, supra, 316 U.S. at 562, 62 S.Ct. at 1149. However, sound exercise of judicial discretion may require that terms of a consent decree be modified when there has been a significant change in the circumstances obtaining at the time the consent decree was entered. This change in circumstances may result from a change in controlling law, including changes brought about by subsequent legislation. See, e. g., System Federation No. 91 v. Wright, supra; Pennsylvania v. Wheeling & Belmont Bridge Co., supra; Daylo v. Administrator of Veterans’ Affairs, 501 F.2d 811, 816 (D.C.Cir.1974); McGrath v. Potash, 199 F.2d 166, 167-168 (D.C.Cir.1952). Application of these settled principles does not, however, provide a ready answer to the case at bar. One of the issues we must resolve is whether in fact Congress intended the 1977 Amendments to supplant the settlement agreement. Our starting point, of course, is the language and provisions of the Amendments. Clearly, the strongest evidence of a congressional intent to supersede the settlement agreement would be an explicit declaration of such an intention in the language of the Amendments. In the instant case we do not understand appellants to be suggesting that any such declaration of congressional intent appears in the language of the 1977 Amendments. Nor have we found any such statements. The silence of the Amendments on the issue of Congress’ intent with regard to the settlement agreement is not necessarily fatal to appellants’ claim, however. As the District Court pointed out, if a congressional intent to supplant the Agreement is a “necessary implication” of the provisions of the Amendments, we would have to find that appellants are correct in arguing that the Agreement must be vacated. Alternatively, evidence of congressional intent may be provided by clear statements in the legislative history. After reviewing the changes made in the toxic pollutant provisions of the FWPCA by the 1977 Amendments, as well as the legislative history of the Amendments, we are unable to accept appellants’ contention that they show that Congress clearly intended the 1977 Amendments to supersede the settlement agreement. First, this case does not present an instance of the type of situation that confronted the Supreme Court in System Federation and Wheeling & Belmont Bridge -a situation in which there is a clear conflict between the terms of a settlement agreement and the provisions of a subsequent Act of Congress. As appellants concede the two major substantive changes in the toxic pollutant provisions of the FWPCA that were made by the 1977 Amendments merely ratified the settlement agreement. Both Congress’ sub-, stitution of an industry-by-industry, technology-based BAT approach for the pollutant-by-pollutant, health-based approach required by Section 307 of the FWPCA, and its decision to specify a list of 65 pollutants-the same pollutants listed in the Agreement-that were to be included in EPA’s revised list of toxic pollutants under Section 307(a), amounted to little more than an “attempt to conform the statute to the reality of [the] program” EPA had been developing under the terms of the settlement agreement. Natural Resources Defense Council, Inc. v. Costle, supra, 12 ERC at 1836. See Hercules, Inc. v. EPA, 598 F.2d 91, 101 (D.C.Cir.1978). Only in two relatively minor aspects did the amended statute depart from the framework established by the settlement agreement. First, Section 307(a) of the Act was amended to allow EPA’s Administrator to add to or delete from the list of 65 toxic pollutants. Second, the Agreement’s deadline for promulgation of BAT regulations was extended to July 1, 1980. These minor departures from the terms of the settlement agreement cannot be interpreted as evidence of a congressional rejection of the Agreement, or as signs of an intention to supersede all its provisions. If instead of endorsing the strategy and framework set out in the settlement agreement the Amendments had required EPA to adopt a different regulatory approach, we might be inclined to agree with the Companies that a congressional intention to supersede the Agreement is a “necessary implication.” But as we have already indicated, this is not such a case. Indeed, if any inferences are to be drawn from Congress’ actions, it would appear that the District Court’s conclusion that “Congress intended for the Agreement to remain in effect to supply the missing details of a cohesive strategy for controlling toxic water pollution” is the more plausible inference. We are also not persuaded by the Companies’ claim that the legislative history of the Amendments offers clear evidence of a congressional intent to supplant the settlement agreement. First, we, like the District Court, have some difficulty understanding why if, as appellants maintain, Congress wanted to supplant the Agreement, it did not bother to say so in any of the reports-House, Senate, or Conferenee-that accompanied the legislation; this in spite of the fact that it also failed to express this intent in the Amendments themselves. The absence of any indications of such congressional intent in the various reports could not have been inadvertent since both House and Senate Committees heard testimony from NRDC and EPA about the terms of the settlement agreement. Moreover, the silence of the committee reports on this issue of congressional intent stands in marked contrast to the clarity with which these reports dealt with other court decisions which Congress chose to supersede. For example, in amending Sections 313 and 404 of the FWPCA to make it clear that the dredging activities of the Army Corps of Engineers are subject to state water quality laws, the Senate Report explained that these amendments were intended to overrule a contrary holding by the Eighth Circuit in Minnesota v. Hoffman, 543 F.2d 1198 (8th Cir. 1976), cert. denied, 430 U.S. 977, 97 S.Ct. 1672, 52 L.Ed.2d 373 (1977). S.Rep. No.95-370, 95th Cong., 1st Sess. 68 (1977) U.S.Code Cong. & Admin.News 1977, p. 4326. The only real support for their interpretation of congressional intent the Companies have pointed to is the statement by Congressman Roberts quoted above. It is, of course, well established that courts give considerable weight to the views of sponsors and floor managers of legislation in determining congressional intent. See NLRB v. Fruit & Vegetable Packers & Warehousers, Local 760,377 U.S. 58, 66-67, 84 S.Ct. 1063, 1068, 12 L.Ed.2d 129 (1964); Schwegmann Bros. v. Calvert Distillers Corp., 341 U.S. 374, 394-395, 71 S.Ct. 745, 750, 95 L.Ed. 1035 (1954); United States v. United Mine Workers of America, 330 U.S. 258, 278-284, 67 S.Ct. 677, 688, 91 L.Ed. 884 (1947). However, not even Congressman Roberts’ statement offers such clear support for appellants’ claim. Congressman Roberts did not suggest that it was Congress’ intention (as he understood it) that the 1977 Amendments would automatically supersede the Agreement. Rather, he merely indicated that inasmuch as Congress had amended the procedural provisions of the FWPCA that were responsible for EPA’s difficulties with implementing the statute, EPA should consider “petition[ing] the courts to relinquish jurisdiction over toxic pollutant control * * Thus the most that appellants can claim is that Congressman Roberts thought it “entirely appropriate” for EPA to ask the court to relinquish jurisdiction. This is not quite the same as a suggestion that Congressman Roberts believed that the Amendments would automatically supersede the settlement agreement. Moreover, there are other statements in the legislative history of the Amendments, including a statement by Congressman Roberts, which indicate a different view-' of congressional intent from that suggested by appellants. The Senate Report on the 1977 Amendments had this to say about the regulatory framework established by the settlement agreement: During the course of its hearings the committee examined in detail EPA’s proposal and strategy for controlling the discharge of toxic pollutants primarily through the development of effluent guidelines for the best available technology economically achievable under section 301(b)(2)(A) and the subsequent reissuance of permits under section 402 to require the application of such technology by dischargers by July 1,1983. The Committee approves of and endorses this strategy. S.Rep.No.95-370, supra, at 56, U.S.Code Cong. & Admin.News, 1977, p. 4380 (emphasis added). Similarly, in explaining the reasoning behind the toxic pollutant provisions of the Conference Report to his Senate colleagues Senator Muskie noted: Another, and possibly more important, reason for maintaining the BAT requirements is that the Agency currently has a major program underway of using BAT to control toxics. Technology-based effluent limitations are being developed which will place limits on toxic pollutants which pose or are likely to pose human health and ecological hazards. The conference agreement was specifically designed to codify the so-called “Flannery decision,” which set forth 65 families of pollutants which are to be regulated by BAT, and EPA has been implementing this consent decree. To take a different course for dealing with toxics at this point would require a major reprogramming of EPA resources. Such a delay, whether it be to allow utilization of a different section of the act or in order to implement this section, would only cause confusion and add still more delay to efforts to solve the toxics problem. The discharge of toxic pollutants should be eliminated as soon as possible. Because EPA is already embarked upon a program to control toxics using a proven mechanism, technology-based effluent limitations, and because of the urgency to control toxics, prudent public policy demands that the strategy be maintained. 123 Cong.Rec. S19647-S19648 (daily ed. Dec. 15, 1977) (emphasis added). Inasmuch as Senator Muskie was chairman of the Senate Subcommittee which reviewed EPA’s implementation of the FWPCA, was a member of the House-Senate Conference Committee on the 1977 Amendments, and served as floor manager of the Conference Report in the Senate, his views are entitled to significant weight in fathoming congressional intent. Nothing in Senator Muskie’s statement suggests that he viewed the settlement agreement as being superseded by the Amendments. If anything, his statement seems to confirm the District Court’s conclusion that Congress intended the settlement agreement to supply the details of the toxics program. Further evidence that Congress intended the settlement agreement to continue in force, subject to modifications to conform it to the amended statute, is provided by a statement made by Senator Randolph in discussing the toxic pollutant provisions of the Conference Report. He stated: In the requirements for the control of toxic pollutants adopted by the conferees, the measure before us largely follows the strategy presently being used by the Environmental Protection Agency under the settlement agreement in the case of Natural Resources Defense Council against Train. That important case required the development of a minimum degree of control for a specified list of pollutants to be achieved on a definite schedule. The principal way in which the conference report modifies the settlement agreement is to require the publication of effluent limitations based on best available technology at a minimum for the listed pollutants by July 1, 1980, and to specify July 1, 1984, as the latest date for compliance with those effluent limitations. 123 S19663 (daily ed. Dec. 15, 1977) (emphasis added). Senator Randolph was chairman of the Senate Committee that drafted the 1977 Amendments and a member of the House-Senate Conference Committee. Insofar as Senator Randolph viewed the 1977 Amendments as “modifying” the settlement agreement, it is difficult to believe that he understood Congress’ intention to be that the Agreement would be completely superseded by the Amendments. Finally; as we have already indicated, a statement by Congressman Roberts suggests that he too assumed that EPA would continue to be bound by the terms of the Agreement. In describing the BAT-toxic pollutants provisions of the Conference Report to the House, Congressman Roberts said the following about the statutory provision authorizing EPA to add to or delete from the list of 65 toxic pollutants specified by the statute: [T]he Administrator, in his discretion, may determine that certain toxic pollutants-or subclasses of pollutants-are not appropriate for regulation in certain circumstances. For example, the Administrator may use his discretion when equal or more effective protection is already provided with respect to that pollutant by an effluent limitation and guideline promulgated pursuant to other sections of the act or, when the discharge of [a] specific pollutant results from its presence in intake water; or, where a specific pollutant is present in either insignificant or trace quantities and does not cause or is not likely to cause toxic effects to identifiable organisms affected by the discharge. 123 Cong.Rec. H12927 (daily ed. Dec. 15, 1977). However, Congressman Roberts did not describe decisionmaking criteria contained in the statute. Rather, these decisionmaking criteria are contained in paragraph 8 of the settlement agreement. Section 307(a)(1) merely directs the Administrator to “take into account toxicity of the pollutant, its persistence, degradability, the usual or potential presence of the affected organisms in any waters, the importance of the affected organisms, and the nature and the extent of the effect of the toxic pollutant on such organisms.” Thus Congressman Roberts’ statement seems to imply that he too expected that the settlement agreement would continue in force to supply missing details for the toxic pollutants program. These indications in the legislative history of the 1977 Amendments that Congress expected the settlement agreement to continue in effect, and the ambiguity of such evidence as the Companies are able to mar-shall in support of their interpretation of congressional intent, lead us to conclude that the District Court properly rejected appellants’ statutory supersession argument. We therefore turn to the Companies’ claim that the Agreement should be vacated because each of the four cases which provided the basis for the Agreement is now moot and must be dismissed. B. Mootness Appellants begin their discussion by pointing out that Article Ill’s “case or controversy” requirement prevents federal courts from issuing judgments in cases which are moot. Citing Supreme Court decisions in Hall v. Beals, 396 U.S. 45, 90 S.Ct. 200, 24 L.Ed.2d 214 (1969), and Kremens v. Bartley, 431 U.S. 119, 97 S.Ct. 1709, 52 L.Ed.2d 184 (1977), appellants further note that a case may become moot if the statute upon which a claim is based is amended in such a fashion that the facts set forth in the complaint do not present a controversy under the new law. Appellants contend that application of these controlling legal precedents to the facts of the instant cases requires vacation of the settlement agreement and dismissal of the four cases which underlie the Agreement. The Companies suggest that both parties agree (and the District Court found) that two of the four cases are moot. In these two cases-the deadlines cases-NRDC had alleged that EPA had violated Section 307(a) of the FWPCA by failing to promulgate final toxic pollutant effluent standards for nine substances within six months of issuing proposed standards as required by the statute. The complaint requested the court to order EPA to promulgate final standards for the nine substances. The Companies note that the 1977 Amendments repealed both the six — month deadline and the requirement that EPA promulgate toxic pollutant effluent standards, replacing these provisions with a requirement that EPA promulgate effluent guidelines for 65 specified pollutants on an industry-by — industry basis by July 1, 1980 and thereby mooting the deadlines cases. Appellants contend that the mootness question in these cases involves the two remaining cases-the toxic criteria case and the pretreatment case. In the toxic criteria case NRDC alleged that EPA had violated the statute in two respects. First, NRDC contended that EPA had used unlawful and restrictive criteria for selecting substances to include in the list of toxic pollutants required by Section 307(a) of the FWPCA. Second, NRDC alleged that because of its use of these impermissible criteria EPA had illegally omitted from the list 25 substances which the Agency would have determined to be toxic pollutants had it used the proper statutory criteria. In the pretreatment case NRDC sought to compel EPA to promulgate pretreatment standards covering over 30 categories of point sources. NRDC alleged that EPA had violated the statute by failing to publish final pretreatment standards for approximately 31 categories of point sources within 90 days of publishing proposed standards as required by the Act, and it noted that proposed standards for 14 of these categories had been pending for more than one year. Appellants argue that NRDC’s claim in the toxic criteria case was based on language in the old Section 307 which was repealed by the 1977 Amendments, noting that the new Section 307(a) only requires EPA to publish a list of 65 specified toxic pollutants, which EPA has done, and further provides that EPA “may revise [this] list” by adding pollutants to or deleting them from it. Appellants maintain that the 1973 EPA decisions at issue in the toxic criteria case are irrelevant to the Agency’s implementation of the new statutory provisions. Appellants further argue that resolution of the issues raised in the toxic criteria case would amount to the court’s rendering an advisory opinion because the decision would not alter either the existing Section 307(a) list or the manner in which EPA has and will implement the new statutory provisions. The Companies then turn to the District Court’s finding that the toxic criteria case is not moot because “[t]o date, EPA has not renounced the alleged arbitrary and unauthorized criteria it used [to compile the list of toxic pollutants under the old Section 307(a) in 1973], nor has it published revised selection criteria.” Natural Resources Defense Council, Inc. v. Cos- tie, supra, 12 ERC at 1837. The Companies maintain that the District Court failed to realize that the 1973 criteria have been effectively repealed by EPA and have been made irrelevant by the 1977 Amendments. The Companies add that when EPA published the list of toxic pollutants in January 1978 as directed by the 1977 Amendments, it omitted any mention of the 1973 criteria in discussing its authority to revise the Section 307 list. Finally, the Companies suggest that events transpiring after the District Court’s decision demonstrate that the 1973 criteria are irrelevant and will no longer be applied by EPA. Appellants first note that on March 27, 1979 EPA published a document entitled “Guidance on Factors to be Addressed in Petitions to Revise” the Section 307(a) toxic pollutant list. 44 Fed.Reg. 18279 (March 27, 1979). Appellants maintain that the list of factors contained in this document effectively repealed the 1973 criteria. Second, appellants maintain that in denying two petitions by Dow Chemical Company to remove two substances from the Section 307 list the Agency made no mention of the 1973 criteria, thereby confirming that the March 27,1979 publication effectively repealed the 1973 criteria. The Companies’ contention that the fourth case-the pretreatment case-is moot is based on their interpretation of the provisions of the settlement agreement. They contend that to settle the pretreatment case EPA and NRDC agreed to paragraph 13 of the settlement agreement pursuant to which EPA undertook to promulgate pretreatment standards covering eight industry categories by May 15, 1977. Appellants point out that EPA has issued regulations establishing pretreatment standards for the eight industrial categories listed in paragraph 13, and they argue that EPA’s fulfillment of its obligations has extinguished the controversy between the parties and rendered the pretreatment case moot. Finally, appellants contend that even if the District Court was correct in finding that the pretreatment and toxic criteria cases are not moot, it still erred by refusing to vacate the Agreement. According to the Companies, the proper procedure to be followed when a court discovers that some of the cases which underlie a settlement agreement have become moot is to vacate the agreement and rehear the remaining cases to determine what, if any, relief is appropriate in light of the issues which remain live controversies. Appellants maintain that this procedure is necessary to avoid adjudication of moot issues, and is mandated by constitutional limitations on the court’s power as well as by the Supreme Court’s decision in Duke Power Co. v. Greenwood County, 299 U.S. 259, 57 S.Ct. 202, 81 L.Ed. 178 (1936). In that case an action was brought by a utility to restrain the County from constructing a power plant and from making contracts for that purpose. The Federal Emergency Administrator for Public Works intervened in the case, revealing that the federal government had entered into a contract with the County to loan it money for the project. The utility challenged the constitutionality of the loan and was upheld by the District Court which entered a final decree enjoining the contract. While the appeal was pending the County and the Administrator terminated the first contract and substituted a new contract which they claimed did not contain the objectionable provisions of the old one. The Court of Appeals remanded the case to the District Court for reconsideration in light of the new contract. Although the pleadings in the District Court were not amended and the court’s term had expired, the District Court nevertheless heard evidence regarding the new contract. On appeal the Supreme Court ruled that the first decree should have been vacated so as to revest the court with jurisdiction over the case. The Court pointed out that “[wjhere it appears upon appeal that [a], controversy has become entirely moot, it is the duty of the appellate court to set aside the decree below and to remand the cause with directions to dismiss. * * * If it appears that supervening facts require a retrial in the light of a changed situation, the appropriate action of the appellate court is to vacate the decree which has been entered and revest the court below with jurisdiction of the cause to the end that the issues may be properly framed and the retrial had.” Id. at 267-268, 57 S.Ct. at 205 (citations omitted). Appellants contend that Duke Power requires a trial court to vacate a settlement agreement to the extent that it is based on mooted issues, arguing that the court has no power to modify such an agreement without making a preliminary determination that the issues, if any, in the remaining “live” controversies will support the modified decree. Appellants claim that the District Court refused to make such a determination in this case. The Companies further argue that as a factual matter the pretreatment and toxic criteria cases do not provide an adequate basis for continuing the settlement agreement. In their view, the remaining controversies in these two cases, assuming that there are some, cannot support even the original settlement agreement, let alone the modifications approved by the District Court. Addressing first the Companies’ claim that both the pretreatment and toxic criteria cases are moot, we agree with the District Court that these two cases remain live controversies. With respect to the pretreatment case, we are unable to agree with the Companies’ suggestion that EPA’s compliance with the requirements of paragraph 13 of the settlement agreement has fulfilled all its obligations relating to that case and therefore eliminated the controversy between NRDC and EPA. NRDC’s complaint in the pretreatment case alleged violations and requested relief pertaining to “all pollutants which are determined not to be susceptible to treatment by [publicly owned treatment works] or which would interfere with the operation of such works.” In addition, the complaint specifically listed over 30 categories of point sources for which EPA was required to promulgate pretreatment standards. Paragraph 13 of the settlement agreement, on the other hand, merely required EPA to promulgate pretreatment standards covering eight industries. Given the very broad scope of relief requested by NRDC’s complaint in the pretreatment case and the relatively narrow reach of paragraph 13, it is difficult to accept the Companies’ claim that NRDC exchanged its pretreatment case for the provisions in paragraph 13. Moreover, the Companies’ suggestion that this is the deal that was struck is unsupported by any evidence other than appellants’ bald allegation that this is what happened. As the District Court pointed out other paragraphs of the settlement agreement outline other actions relating to pretreatment standards that EPA agreed to undertake and which it has not yet done. Thus even if we were to accept the Companies’ implicit assumption that only those provisions in the Agreement which deal with pretreatment standards were exchanged for NRDC’s agreement not to prosecute the pretreatment case, we would still reject the suggestion that the case is moot. Finally, inasmuch as the settlement agreement was “a comprehensive interrelated package,” it is reasonable to assume that other provisions of the Agreement, such as the BAT limitations and guidelines, were also part of the quid pro quo NRDC received in return for agreeing not to litigate the pretreatment case. As for the toxic criteria case, it should first be noted that appellants are simply wrong in suggesting that NRDC’s claim in that case was based on language in the FWPCA which was repealed by the 1977 Amendments. In fact, the disagreement between NRDC and EPA revolved around the latter’s interpretation of the statutory criteria for making listing decisions. The 1977 Amendments did not change these criteria in any way. While appellants may be correct in suggesting that the Amendments changed what may have been the Administrator’s mandatory duty to list pollutants into a discretionary duty by explicitly leaving the decision to add to, or delete from, the list specified by Congress to his discretion, the nature of the Administrator’s duty was not central to the controversy between NRDC and EPA. In making the now discretionary listing decisions the Administrator must still use the proper statutory decisionmaking criteria. If in fact EPA has continued to use the 1973 criteria (which NRDC alleges violate the statute), or at the very least has not renounced these criteria, we can hardly conclude that the toxic criteria case is moot. Thus appellants’ contention that the case is moot must ultimately rest on their claim that EPA has abandoned the 1973 criteria. We agree with the District Court that there is no clear evidence indicating that EPA has abandoned the 1973 criteria. Even the EPA publications on which the Companies rely in arguing that EPA has abandoned the 1973 criteria demonstrate that this claim is inaccurate. As NRDC points out, one of the factors listed in these EPA publications as having been considered by the Agency is a pollutant’s usual or potential presence in water, a factor which, NRDC maintains, the statute does not permit the Agency to consider and one of the allegedly illegal criteria mentioned in NRDC’s complaint in the toxic criteria case. We therefore conclude that the District Court correctly found that the toxic criteria case is not moot because there is no clear indication that EPA has abandoned the 1973 criteria. Having determined that the toxic criteria and pretreatment cases are not moot, it remains for us to consider appellants’ contention that the proper procedure for the District Court to follow in these circumstances was to vacate the settlement agreement and rehear the two remaining cases. Appellants have not pointed to any cases that have addressed this precise issue of the procedure to follow when some of the cases underlying a settlement become moot. However, courts have on numerous occasions dealt with the question whether a change in circumstances which moots some of the issues in a particular case thereby eliminates the court’s jurisdiction over the entire case. The usual practice in such situations is for the court to determine whether any remaining controversies in the case provide an adequate basis for continued jurisdiction. An illustration of this is the Supreme Court’s decision in Powell v. McCormack, 395 U.S. 486, 89 S.Ct. 1944, 23 L.Ed.2d 491 (1969). There, Representative Powell had been denied his seat in the House by the 90th Congress, but by the time the case was heard in the Supreme Court he had been reelected and seated by the 91st Congress. Without determining whether his claims for more specific relief had become moot, the Court ruled that his claim for damages on account of past salary required disposition of the merits of the case. The Court pointed out that “[w]here one of the several issues presented becomes moot, the remaining live issues supply the constitutional requirement of a case or controversy.” Id. at 497, 89 S.Ct. at 1951. This disposition of partially moot' cases suggests that even under appellants’ mootness theory a court continues to have jurisdiction over a settlement agreement where some of the cases that underlie the agreement remain live controversies. Thus the District Court had jurisdiction over the Agreement because the pretreatment and toxic criteria cases had not become moot. While it may become necessary to modify the terms of a settlement agreement because some of the cases which provided the basis for it have become moot, we do not agree with appellants’ suggestion that the court must first vacate the settlement agreement and rehear the remaining live cases. Nothing in System Federation No. 91 v. Wright, supra, suggests that this is the required procedure. And as we have previously indicated, the decision whether to modify a settlement agreement in light of changed circumstances is ordinarily left to the discretion of the District Court. As the Supreme Court noted in System Federation No. 91 v. Wright, supra, “A balance must * * * be struck between the policies of res judicata and the right of the court to apply modified measures to changed circumstances. Where there is such a balance of imponderables there must be wide discretion in the District Court.” 324 U.S. at 647-648, 81 S.Ct. at 371. We are of the view that the procedure to follow in circumstances such as those presented by this case is also best left to the discretion of the District Court. Where it deems it appropriate the court may choose to vacate the settlement and rehear the remaining live controversies. Alternatively, the court may simply decide whether modification of the agreement is necessary or appropriate. Nothing in the Supreme court’s decision in the Duke Power case suggests a different rule. Duke Power involved a situation in which the action of the defendants in terminating the contract that had been at issue in the first proceeding before the District Court completely eliminated the controversy in that case. As such the court no longer had jurisdiction over the case. In order to vest the court with jurisdiction over the new controversy created by the existence of the new contract executed by the County and the federal government, the District Court’s decree in the first case had to be vacated and the parties allowed to amend their pleadings in light of the new factual and legal issues that were raised by the second contract. Duke Power has been uniformly interpreted as indicating the procedure to be followed by an appellate court asked to review a decision which has been mooted by events that transpired after the lower court’s decision was rendered. See, e. g., United States v. Munsingwear, 340 U.S. 36, 39-40, 71 S.Ct. 104, 106, 95 L.Ed. 36 (1950); Giumarra Vineyards Corp. v. Farrell, 431 F.2d 923, 925 (9th Cir. 1970); Knapp v. Baker, 509 F.2d 922 (5th Cir. 1975); Narragansett Improvement Co. v. Local Union No. 251, 506 F.2d 715 (1st Cir. 1974); Welch v. Simon, 498 F.2d 1060, 1062 (D.C.Cir.1974). As the Supreme Court explained, “Where it appears upon appeal that [a] controversy has become entirely moot, it is the duty of the appellate court to set aside the decree below and to remand the cause with directions to dismiss.” Duke Power Co. v. Greenwood County, supra, 299 U.S. at 267, 57 S.Ct. at 205. Thus Duke Power does not purport to prescribe a rule to govern situations such as the one in the instant case. All we need decide in this case, then, is whether the District Court abused its discretion by refusing to follow the procedure suggested by the Companies. As a preliminary matter, it should be noted that the Companies do not appear to have urged this procedure on the District Court with as much vigor as they press it on appeal. In these circumstances it is hardly surprising that the court declined to follow this procedure. Be that as it may, the District Court noted that the “Agreement represents a comprehensive, interrelated package of concessions made by EPA in return for plaintiffs’ agreement not to pursue the claims raised in the four lawsuits.” Natural Resources Defense Council, Inc. v. Costle, supra, 12 ERC at 1838. It further noted that “it cannot be said that each portion of the Agreement is specifically responsive to a particular claim contained in one or more of the original complaints.” Id. Finally, the court pointed out that “the [Companies] nowhere have suggested that the two causes of action as to which controversies still survive would not alone have provided a substantial basis for the settlement approved by the court in 1976.” Id. Plainly, the District Court found that these cases do in fact provide an adequate basis for continuing the Agreement. In these circumstances we do not believe that the court abused its discretion by refusing to follow the procedure suggested by the Companies. The court’s conclusion that the two non-moot cases provided an adequate basis for continuing the Agreement obviated any need to vacate the Agreement and rehear the cases. Nor do we think that the District Court was required to make a further determination that the toxic criteria and pretreatment cases could provide an adequate basis for the modifications to the settlement agreement that it approved. Even assuming that the Companies are correct in claiming that the modified settlement agreement “places substantial new burdens and obligations * * * upon EPA,” a claim we will examine in due course, we do not agree that the District Court had to find that these “new burdens” could be supported by the two non-moot cases. The modifications to the settlement agreement were designed to resolve a new controversy that had arisen over EPA’s non-compliance with the court’s 1976 order approving the Agreement. There can be no question that the District Court had the power to enforce the provisions of a settlement agreement it had approved by requiring further action from the offending party. C. Modifications to the Settlement Agreement In contending that EPA contravened public notice and comment requirements of the APA, the Clean Water Act, EPA regulations, an Executive Order, and due process rights guaranteed by the Fifth Amendment in proposing the modifications to the settlement agreement, the Companies focus on two changes made by the modifications. The first is a new paragraph 4(c) which modifies paragraph 4 of the original settlement agreement. Paragraph 4 had required EPA to develop pretreatment standards for any of the 65 pollutants listed in the Agreement which are not susceptible to treatment by, or are otherwise incompatible with, publicly owned treatment works. In addition, EPA was required to promulgate, by December 31, 1979, pretreatment standards for all other incompatible pollutants present in the emissions from any of the 21 industries covered by the Agreement. New paragraph 4(c) requires EPA to initiate a program “to identify and study” pollutants (other than the 65 explicitly covered by the Agreement) which are incompatible with POTWs, and it specifies certain investigatory steps that the Agency is to follow. Second, the Companies focus on the modifications to paragraph 12 of the 1976 Agreement. That provision had required EPA to set up an investigatory program to determine when and if effluent limitations more stringent than the technology-based limitations mandated by the Agreement are necessary to protect human health or aquatic life. EPA agreed to establish “a specific and substantial program” for this purpose by June 30, 1978, and to develop such more stringent limitations whenever the Administrator determined that they were necessary. The modifications to paragraph 12 specify that this program should include processes for identifying seriously contaminated navigable waters and pollutants for which more stringent limitations are necessary, and a process for developing the necessary strategies for limiting discharge of these toxic pollutants. The modifications also set deadlines for EPA to develop and announce these strategies. The Companies and EPA disagree in their characterization of the changes made by these modifications. EPA argues that they provide some fine-tuning of the Agreement, incorporating lessons the Agency has learned in over two years of implementing the Agreement and allowing it greater flexibility and additional time to focus on major environmental problems. In particular, EPA contends that paragraph 4(c) actually increases its rulemaking discretion under the Agreement while merely committing it to specific preliminary investigative action, and that the changes made in paragraph 12 do not reduce the Agency’s discretion. The Companies, on the other hand, maintain that these new provisions require EPA to undertake a new series of programs leading to further regulations that go beyond those mandated by the original Agreement and the requirements of the 1977 Amendments. They argue that these modifications mandate that “EPA undertake specified steps and puts EPA in a straightjacket [s/c] where, by contrast, Congress had left the Agency’s discretion unfettered.” The Companies further argue that, because the modifications place substantial new burdens and obligations on EPA and the industries it regulates, the Agency is required to provide notice and opportunity for public comment prior to taking action of the sort it took in proposing these modifications. In developing this argument the Companies first contend that EPA violated the notice a