KLEPPE v. SIERRA CLUB

MR. JUSTICE POWELL delivered the opinion of the Court.

Section 102(2)(C) of the National Environmental Policy Act of 1969 (NEPA) requires that all federal agencies include a detailed statement of environmental consequences — known as an environmental impact statement — "in every recommendation or report on proposals for legislation and other major Federal actions significantly affecting the quality of the human environment." 42 U.S.C. § 4332 (2)(C). The United States Court of Appeals for the District of Columbia Circuit held that officials of the Department of the Interior (Department) and certain other federal agencies must take additional steps under this section, beyond those already taken, before allowing further development of federal coal reserves in a specific area of the country. For the reasons set forth, we reverse.

83 Stat. 852, 42 U.S.C. § 4321 et seq.

I

Respondents, several organizations concerned with the environment, brought this suit in July 1973 in the United States District Court for the District of Columbia. The defendants in the suit, petitioners here, were the officials of the Department and other federal agencies responsible for issuing coal leases, approving mining plans, granting rights-of-way, and taking the other actions necessary to enable private companies and public utilities to develop coal reserves on land owned or controlled by the Federal Government. Citing widespread interest in the reserves of a region identified as the "Northern Great Plains region," and an alleged threat from coal-related operations to their members' enjoyment of the region's environment, respondents claimed that the federal officials could not allow further development without preparing a "comprehensive environmental impact statement" under § 102(2)(C) on the entire region. They sought declaratory and injunctive relief.

Respondents asserted jurisdiction under 5 U.S.C. § 701-706, 28 U.S.C. § 1331 (a), and 28 U.S.C. § 1361.

The District Court, on the basis of extensive findings of fact and conclusions of law, held that the complaint stated no claim for relief and granted the petitioners' motions for summary judgment. Respondents appealed. Shortly after oral argument but before issuing an opinion on the merits, the Court of Appeals in January 1975 issued an injunction — over a dissent — against the Department's approval of four mining plans in the Powder River Coal Basin, which is one small but coal-rich section of the region that concerns respondents. 166 U.S.App.D.C. 200, 509 F.2d 533. An impact statement had been prepared on these plans, but it had not been before the District Court and was not before the Court of Appeals. In June 1975 the Court of Appeals ruled on the merits and, for reasons discussed below, reversed the District Court and remanded for further proceedings. 169 U.S.App.D.C. 20, 514 F.2d 856. The court continued its injunction in force.

Prior to ruling on motions for summary judgment, the District Court permitted intervention as defendants by several public utilities, coal mining companies, and natural gas companies, by an Indian tribe, and by an individual rancher. Most of these intervenors have joined in a separate petition for certiorari in No. 75-561, which is decided together with this case.

The federal officials petitioned for writ of certiorari on October 9, 1975. On November 7, the Court of Appeals refused to dissolve its injunction, and a week later petitioners moved this Court for a stay. On January 12, 1976, we stayed the injunction and granted the petitions for certiorari. 423 U.S. 1047. We have been informed that shortly thereafter the Secretary of the Interior (Secretary) approved the four mining plans in the Powder River Coal Basin that had been stayed by the injunction.

On the same date the Court of Appeals remanded to the District Court respondents' motion for modification of the injunction to prohibit the Secretary from approving a new mining plan submitted by a coal company, not then a party to the suit, that had been mining coal on leased federal land since 1972. The new mining plan was covered by an impact statement. The Secretary of the Interior approved the plan on November 11. On November 14, the District Court partially enjoined the company from mining under the approved plan.

II

The record and the opinions of the courts below contain extensive facts about coal development and the geographic area involved in this suit. The facts that we consider essential, however, can be stated briefly.

The Northern Great Plains region identified in respondents' complaint encompasses portions of four States — northeastern Wyoming, eastern Montana, western North Dakota, and western South Dakota. There is no dispute about its richness in coal, nor about the waxing interest in developing that coal, nor about the crucial role the federal petitioners will play due to the significant percentage of the coal to which they control access. The Department has initiated, in this decade, three studies in areas either inclusive of or included within this region. The North Central Power Study was addressed to the potential for coordinated development of electric power in an area encompassing all or part of 15 States in the North Central United States. It aborted in 1972 for lack of interest on the part of electric utilities. The Montana-Wyoming Aqueducts Study, intended to recommend the best use of water resources for coal development in southeastern Montana and northeastern Wyoming, was suspended in 1972 with the initiation of the third study, the Northern Great Plains Resources Program (NGPRP).

While the record does not reveal the degree of concern with environmental matters in the first two studies, it is clear that the NGPRP was devoted entirely to the environment. It was carried out by an interagency, federal-state task force with public participation, and was designed "to assess the potential social, economic and environmental impacts" from resource development in five States — Montana, Wyoming, South Dakota, North Dakota, and Nebraska. Its primary objective was "to provide an analytical and informational framework for policy and planning decisions at all levels of government" by formulating several "scenarios" showing the probable consequences for the area's environment and culture from the various possible techniques and levels of resource development. The final interim report of the NGPRP was issued August 1, 1975, shortly after the decision of the Court of Appeals in this case.

Department of Interior News Release (Oct. 3, 1972), App. 132.

NGPRP outline, App. 136.

In addition, since 1973 the Department has engaged in a complete review of its coal-leasing program for the entire Nation. On February 17 of that year the Secretary announced the review and announced also that during study a "short-term leasing policy" would prevail, under which new leasing would be restricted to narrowly defined circumstances and even then allowed only when an environmental impact statement had been prepared if required under NEPA. The purpose of the program review was to study the environmental impact of the Department's entire range of coal-related activities and to develop a planning system to guide the national leasing program. The impact statement, known as the "Coal Programmatic EIS," went through several drafts before issuing in final form on September 19, 1975 — shortly before the petitions for certiorari were filed in this case. The Coal Programmatic EIS proposed a new leasing program based on a complex planning system called the Energy Minerals Activity Recommendation System (EMARS), and assessed the prospective environmental impact of the new program as well as the alternatives to it. We have been informed by the parties to this litigation that the Secretary is in the process of implementing the new program.

Department of Interior News Release (Feb. 17, 1973), App. 125-127.

The petitioners in No. 75-561 have included in their brief a press release by the Secretary announcing the new program, and a detailed description of the program. Pending full operation thereof, the short-term leasing policy remains in effect.

Against this factual background, we turn now to consider the issues raised by this case in the status in which it reached this Court.

III

The major issue remains the one with which the suit began: whether NEPA requires petitioners to prepare an environmental impact statement on the entire Northern Great Plains region. Petitioners, arguing the negative, rely squarely upon the facts of the case and the language of § 102(2)(C) of NEPA. We find their reliance well placed.

In the District Court respondents also contended that petitioners had failed to comply with §§ 102(2)(A) and (D), 42 U.S.C. § 4332 (2)(A) and (D), which require an agency to use a specified Page 399 approach to decisionmaking and to describe alternatives when a proposal involves unresolved conflicts concerning uses of resources. (Subparagraph (D) was redesignated subparagraph (E) by Pub.L. 94-83, 89 Stat. 424.) The District Court ruled against respondents on the count based on these subparagraphs, and it has dropped out of the case.

As noted in the first sentence of this opinion, § 102(2)(C) requires an impact statement "in every recommendation or report on proposals for legislation and other major Federal actions significantly affecting the quality of the human environment." Since no one has suggested that petitioners have proposed legislation on respondents' region, the controlling phrase in this section of the Act, for this case, is "major Federal actions." Respondents can prevail only if there has been a report or recommendation on a proposal for major federal action with respect to the Northern Great Plains region. Our statement of the relevant facts shows there has been none; instead, all proposals are for actions of either local or national scope.

The local actions are the decisions by the various petitioners to issue a lease, approve a mining plan, issue a right-of-way permit, or take other action to allow private activity at some point within the region identified by respondents. Several Courts of Appeals have held that an impact statement must be included in the report or recommendation on a proposal for such action if the private activity to be permitted is one "significantly affecting the quality of the human environment" within the meaning of § 102(2)(C). See, e. g., Scientists' Institute for Public Information, Inc. v. AEC, 156 U.S.App.D.C. 395, 404-405, 481 F.2d 1079, 1088-1089 (1973); Davis v. Morton, 469 F.2d 593 (CA10 1972). The petitioners do not dispute this requirement in this case, and indeed have prepared impact statements on several proposed actions of this type in the Northern Great Plains during the course of this litigation. Similarly, the federal petitioners agreed at oral argument that § 102(2)(C) required the Coal Programmatic EIS that was prepared in tandem with the new national coal-leasing program and included as part of the final report on the proposal for adoption of that program. Tr. of Oral Arg. 9. Their admission is well made, for the new leasing program is a coherent plan of national scope, and its adoption surely has significant environmental consequences.

In an affidavit submitted in support of the application for a stay of the Court of Appeals' injunction, the Secretary described four impact statements completed by the petitioners on coal-related activity in Montana and Wyoming. One was the multiproject statement on the Powder River Coal Basin that was the subject of that injunction. See supra, at 395-396. Another was on the single mining plan subsequently brought under the injunction as modified by the District Court. See n. 4, supra. A third covered one leased tract, and apparently was occasioned by an application for approval of a new mining plan on the tract. The fourth, on another single mining plan, has been the subject of litigation, on the merits of which we intimate no view. See Cady v. Morton, 527 F.2d 786 (CA9 1975).

But there is no evidence in the record of an action or a proposal for an action of regional scope. The District Court, in fact, expressly found that there was no existing or proposed plan or program on the part of the Federal Government for the regional development of the area described in respondents' complaint. It found also that the three studies initiated by the Department in areas either included within or inclusive of respondents' region — that is, the Montana-Wyoming Aqueducts Study, the North Central Power Study, and the NGPRP — were not parts of any plan or program to develop or encourage development of the Northern Great Plains. That court found no evidence that the individual coal development projects undertaken or proposed by private industry and public utilities in that part of the country are integrated into a plan or otherwise interrelated. These findings were not disturbed by the Court of Appeals, and they remain fully supported by the record in this Court.

The Secretary's affidavit in support of the application for a stay of the Court of Appeals' injunction confirms that the situation regarding regional planning or a regional development program has not changed. See App. 195-196.

Quite apart from the fact that the statutory language requires an impact statement only in the event of a proposed action, respondents' desire for a regional environmental impact statement cannot be met for practical reasons. In the absence of a proposal for a regional plan of development, there is nothing that could be the subject of the analysis envisioned by the statute for an impact statement. Section 102(2)(C) requires that an impact statement contain, in essence, a detailed statement of the expected adverse environmental consequences of an action, the resource commitments involved in it, and the alternatives to it. Absent an overall plan for regional development, it is impossible to predict the level of coal-related activity that will occur in the region identified by respondents, and thus impossible to analyze the environmental consequences and the resource commitments involved in, and the alternatives to, such activity. A regional plan would define fairly precisely the scope and limits of the proposed development of the region. Where no such plan exists, any attempt to produce an impact statement would be little more than a study along the lines of the NGPRP, containing estimates of potential development and attendant environmental consequences. There would be no factual predicate for the production of an environmental impact statement of the type envisioned by NEPA.

The legislative history of NEPA fully supports our reading of § 102(2)(C) as to when an impact statement is required. The bill passed by the House contained no provision comparable to § 102(2)(C) of the Act. The bill that was reported to and, as amended, passed by the Senate did contain the forerunner of § 102(2)(C). The committee report made clear that the impact statement was required in conjunction with specific proposals for action. S. Rep. No. 91-296, p. 20 (1969). After the House-Senate Conference, the managers on the part of the House, in a separate statement, explained § 102(2)(C) in language that tracks the statute on the requirement of a proposal. H.R. Conf. Rep. No. 91-765, p. 8 (1969). See also 115 Cong. Rec. 40420 (1969).

Section 102(2)(C) states that the statement must be a detailed statement on —
"(i) the environmental impact of the proposed action,
"(ii) any adverse environmental effects which cannot be avoided should the proposal be implemented,
"(iii) alternatives to the proposed action,
"(iv) the relationship between local short-term uses of man's environment and the maintenance and enhancement of long-term productivity, and
"(v) any irreversible and irretrievable commitments of resources which would be involved in the proposed action should it be implemented." (Emphasis added.)

In contrast, with both an individual coal-related action and the new national coal-leasing program, an agency deals with specific action of known dimensions. With appropriate allowances for the inexactness of all predictive ventures, the agency can analyze the environmental consequences and describe alternatives as envisioned by § 102(2)(C). Of course, since the kind of impact statement required depends upon the kind of "`federal action' being taken," Aberdeen Rockfish R. Co. v. SCRAP, 422 U.S. 289, 322 (1975), the statement on a proposed mining plan or a lease application may bear little resemblance to the statement on the national coal-leasing program. Nevertheless, in each case the bounds of the Page 403 analysis are defined, which is not the case with coal development in general in the region identified by respondents.

IV A

The Court of Appeals, in reversing the District Court, did not find that there was a regional plan or program for development of the Northern Great Plains region. It accepted all of the District Court's findings of fact, but concluded nevertheless that the petitioners "contemplated" a regional plan or program. The court thought that the North Central Power Study, the Montana-Wyoming Aqueducts Study, and the NGPRP all constituted "attempts to control development" by individual companies on a regional scale. It also concluded that the interim report of the NGPRP, then expected to be released at any time, would provide the petitioners with the information needed to formulate the regional plan they had been "contemplating." The Court therefore remanded with instructions to the petitioners to inform the District Court of their role in the further development of the region within 30 days after the NGPRP interim report issued; if they decided to control that development, an impact statement would be required.

We conclude that the Court of Appeals erred in both its factual assumptions and its interpretation of NEPA. We think the court was mistaken in concluding, on the record before it, that the petitioners were "contemplating" a regional development plan or program. It considered the several studies undertaken by the petitioners to represent attempts to control development on a regional scale. This conclusion was based on a finding by the District Court that those studies, as well as the new national coal-leasing policy, were "attempts to control development by individual companies in a manner consistent with the policies and procedures of the National Environmental Policy Act of 1969." But in context, that finding meant only that the named studies were efforts to gain background environmental information for subsequent application in the decisionmaking with respect to individual coal-related projects. This is the sense in which the District Court spoke of controlling development consistently with NEPA. Indeed, in the same paragraph containing the language relied upon by the Court of Appeals, the District Court expressly found that the studies were not part of a plan or program to develop or encourage development. See supra, at 400-401.

Moreover, at the time the Court of Appeals ruled there was no indication in the record that the NGPRP was aimed toward a regional plan or program, and subsequent events have shown that this was not its purpose. The interim report of the study, issued shortly after the Court of Appeals ruled, described the effects of several possible rates of coal development but stated in its preface that the alternatives "are for study and comparison only; they do not represent specific plans or proposals." All parties agreed in this Court that there still exists no proposal for a regional plan or program of development. See Tr. of Oral Arg. 48.

Even had the record justified a finding that a regional program was contemplated by the petitioners, the legal conclusion drawn by the Court of Appeals cannot be squared with the Act. The court recognized that the mere "contemplation" of certain action is not sufficient to require an impact statement. But it believed the statute nevertheless empowers a court to require the preparation of an impact statement to begin at some point prior to the formal recommendation or report on a proposal. The Court of Appeals accordingly devised its own four-part "balancing" test for determining when, during the contemplation of a plan or other type of federal action, an agency must begin a statement. The factors to be considered were identified as the likelihood and imminence of the program's coming to fruition, the extent to which information is available on the effects of implementing the expected program and on alternatives thereto, the extent to which irretrievable commitments are being made and options precluded "as refinement of the proposal progresses," and the severity of the environmental effects should the action be implemented.

The Court of Appeals thought that as to two of these factors — the availability of information on the effects of any regional development program, and the severity of those effects — the time already was "ripe" for an impact statement. It deemed the record unclear, however, as to the likelihood of the petitioners' actually producing a plan to control the development, and surmised that irretrievable commitments were being avoided because petitioners had ceased approving most coal-related projects while the NGPRP study was underway. The court also thought that the imminent release of the NGPRP interim report would provide the officials with sufficient information to define their role in development of the region, and it believed that as soon as the NGPRP was completed the petitioners would begin approving individual projects in the region, thus permitting irrevocable commitments of resources. It was for this reason that the court in its remand required the petitioners to report to the District Court their decision on the federal role with respect to the Northern Great Plains as a region within 30 days after issuance of the NGPRP report.

The Court's reasoning and action find no support in the language or legislative history of NEPA. The statute clearly states when an impact statement is required, and mentions nothing about a balancing of factors. Rather, as we noted last Term, under the first sentence of § 102(2)(C) the moment at which an agency must have a final statement ready "is the time at which it makes a recommendation or report on a proposal for federal action." Aberdeen Rockfish R. Co. v. SCRAP, 422 U.S. 289, 320 (1975) ( SCRAP II) (emphasis in original). The procedural duty imposed upon agencies by this section is quite precise, and the role of the courts in enforcing that duty is similarly precise. A court has no authority to depart from the statutory language and, by a balancing of court-devised factors, determine a point during the germination process of a potential proposal at which an impact statement should be prepared. Such an assertion of judicial authority would leave the agencies uncertain as to their procedural duties under NEPA, would invite judicial involvement in the day-to-day decisionmaking process of the agencies, and would invite litigation. As the contemplation of a project and the accompanying study thereof do not necessarily result in a proposal for major federal action, it may be assumed that the balancing process devised by the Court of Appeals also would result in the preparation of a good many unnecessary impact statements.

This is not to say that § 102(2)(C) imposes no duties upon an agency prior to its making a report or recommendation on a proposal for action. The section states that prior to preparing the impact statement the responsible official "shall consult with and obtain the comments of any Federal agency which has jurisdiction by law or special expertise with respect to any environmental impact involved." Thus, the section contemplates a consideration of environmental factors by agencies during the evolution of a report or recommendation on a proposal. But the time at which a court enters the process is when the report or recommendation on the proposal is made, and someone protests either the absence or the adequacy of the final impact statement. This is the point at which an agency's action has reached sufficient maturity to assure that judicial intervention will not hazard unnecessary disruption.

B

Assuming that the Court of Appeals' theory about "contemplation" of regional action would permit a court to require preproposal preparation of an impact statement, the court's injunction against the Secretary's approval of the four mining plans in the Powder River Basin nevertheless would have been error. The District Court had found that respondents would not have been entitled to an injunction against any individual projects even if their claim of the need for a regional impact statement had been valid, because they had shown no irreparable harm that would result absent such an injunction and the record disclosed that irreparable harm would result to the intervenors who sought to carry out their business ventures and to the public who depended upon their operations. The Court of Appeals made no finding as to the equities at the time it originally entered the injunction; when it continued the injunction following its decision on the merits, it stated only that the "harm" justifying an injunction "matured" whenever an impact statement is due and not filed. But on the Court of Appeals' own terms there was in fact no harm. First, the Court of Appeals itself held that no regional impact statement was due at that moment, and it was uncertain whether one ever would be due. Second, there had been filed a comprehensive impact statement on the proposed Powder River Basin mining plans themselves, and its adequacy had not been challenged either before the District Court or the Court of Appeals in this case, or anywhere else. Thus, in simple equitable terms there were no grounds for the injunction: the District Court's finding of irreparable injury to the intervenors and to the public still stood, and there were — on the Court of Appeals' own terms — no countervailing equities.

Even had the Court of Appeals determined that a regional impact statement was due at that moment, it still would have erred in enjoining approval of the four mining plans unless it had made a finding that the impact statement covering them inadequately analyzed the environmental impacts of, and the alternatives to, Page 408 their approval. So long as the statement covering them was adequate, there would have been no reason to enjoin their approval pending preparation of a broader regional statement; that broader statement, when prepared, simply would have taken into consideration the regional environmental effects of the four mining plans once they were in operation, in determining the permissibility of further coal-related operations in the region. See Part V. infra.

V

Our discussion thus far has been addressed primarily to the decision of the Court of Appeals. It remains, however, to consider the contention now urged by respondents. They have not attempted to support the Court of Appeals' decision. Instead, respondents renew an argument they appear to have made to the Court of Appeals, but which that court did not reach. Respondents insist that, even without a comprehensive federal plan for the development of the Northern Great Plains, a "regional" impact statement nevertheless is required on all coal-related projects in the region because they are intimately related.

There are two ways to view this contention. First, it amounts to an attack on the sufficiency of the impact statements already prepared by the petitioners on the coal-related projects that they have approved or stand ready to approve. As such, we cannot consider it in this proceeding, for the case was not brought as a challenge to a particular impact statement and there is no impact statement in the record. It also is possible to view the respondents' argument as an attack upon the decision of the petitioners not to prepare one comprehensive impact statement on all proposed projects in the region. This contention properly is before us, for the petitioners have made it clear they do not intend to prepare such a statement.

Petitioners lodged with this Court a copy of the massive six-volume impact statement on the projects in the Powder River Coal Basin, but it is not part of the record.

We begin by stating our general agreement with respondents' basic premise that § 102(2)(C) may require a comprehensive impact statement in certain situations where several proposed actions are pending at the same time. NEPA announced a national policy of environmental protection and placed a responsibility upon the Federal Government to further specific environmental goals by "all practicable means, consistent with other essential considerations of national policy." § 101(b), 42 U.S.C. § 4331 (b). Section 102(2)(C) is one of the "action-forcing" provisions intended as a directive to "all agencies to assure consideration of the environmental impact of their actions in decisionmaking." Conference Report on NEPA, 115 Cong. Rec. 40416 (1969). By requiring an impact statement Congress intended to assure such consideration during the development of a proposal or — as in this case — during the formulation of a position on a proposal submitted by private parties. A comprehensive impact statement may be necessary in some cases for an agency to meet this duty. Thus, when several proposals for coal-related actions that will have cumulative or synergistic environmental impact upon a region are pending concurrently before an agency, their environmental consequences must be considered together. Only through comprehensive consideration of pending proposals can the agency evaluate different courses of action.

The term "action-forcing" was applied to the provisions of what became § 102(2) throughout their consideration by the Senate. See, e. g., S. Rep. No. 91-296, p. 9 (1969); 115 Cong. Rec. 40416, 40419 (1969).

The legislative history of the provision in the Senate, where it originated and where it received the most attention, supports this interpretation. See S. Rep. No. 91-296, supra, at 2, 20-21; 115 Cong. Rec. 29052-29053, 29055, 29058, 40416 (1969). The Conference Report to the House is consistent. See id., at 40923-40928.

At some points in their brief respondents appear to seek a comprehensive impact statement covering contemplated projects in the region as well as those that already have been proposed. The statute, however, speaks solely in terms of proposed actions; it does not require an agency to consider the possible environmental impacts of less imminent actions when preparing the impact statement on proposed actions. Should contemplated actions later reach the stage of actual proposals, impact statements on them will take into account the effect of their approval upon the existing environment; and the condition of that environment presumably will reflect earlier proposed actions and their effects. Cf. n. 26, infra.

Neither the statute nor its legislative history contemplates that a court should substitute its judgment for that of the agency as to the environmental consequences of its actions. See Scenic Hudson Preservation Conference v. FPC, 453 F.2d 463, 481 (CA2 1971), cert. denied, 407 U.S. 926 (1972). The only role for a court is to insure that the agency has taken a "hard look" at environmental consequences; it cannot "interject itself within the area of discretion of the executive as to the choice of the action to be taken." Natural Resources Defense Council v. Morton, 148 U.S.App.D.C. 5, 16, 458 F.2d 827, 838 (1972).

Agreement to this extent with respondents' premise, however, does not require acceptance of their conclusion that all proposed coal-related actions in the Northern Great Plains region are so "related" as to require their analysis in a single comprehensive impact statement. Respondents informed us that the Secretary recently adopted an approach to impact statements on coal-related actions that provides:

"A. As a general proposition, and as determined by the Secretary, when action is proposed involving coal development such as issuing several coal leases or approving mining plans in the same region, such actions will be covered by a single EIS rather than by multiple statements. In such cases, the region covered will be determined by basin boundaries, drainage areas, areas of common reclamation problems, administrative boundaries, areas of economic interdependence, and other relevant factors." Brief for Respondents 20a.

At another point, the document containing the Secretary's approach states that a "regional EIS" will be prepared "if a series of proposed actions with interrelated impacts are involved . . . unless a previous EIS has sufficiently analyzed the impacts of the proposed action(s)." Id., at 20a-21a. Thus, the Department has decided to prepare comprehensive impact statements of the type contemplated by § 102(2)(C), although it has not deemed it appropriate to prepare such a statement on all proposed actions in the region identified by respondents.

The document is an "Executive Summary and Decision Document" signed by the Secretary and dated December 16, 1975. The decision as to impact statements is part of the implementation of the new coal-leasing policy based on staff recommendations following release of the Coal Programmatic EIS. See supra, at 397-398.
Respondents contend that this document represents a significant shift in Department policy since the start of this litigation, but we disagree. Early in the litigation the Department and three other agencies prepared the comprehensive impact statement on proposed actions in the Powder River Coal Basin, see supra, at 395; its preface — quoted by the District Court — states that it evaluated "the collective impact of the proposed actions and, insofar as now possible, the impacts of potential future coal mining within the geographic area." Moreover, the Secretary's consistent position, in affidavits dating back to the District Court, has been that statements might be prepared on regions or "subregions" once the Coal Programmatic EIS was completed. While the affidavits did not, until the application for a stay of the injunction, expressly predicate preparation of such statements upon the pendency of several proposals within the region or subregion, neither are they inconsistent with such predication.

Respondents conceded at oral argument that to prevail they must show that petitioners have acted arbitrarily in refusing to prepare one comprehensive statement on this entire region, and we agree. Tr. of Oral Arg. 67. The determination of the region, if any, with respect to which a comprehensive statement is necessary requires the weighing of a number of relevant factors, including the extent of the interrelationship among proposed actions and practical considerations of feasibility. Resolving these issues requires a high level of technical expertise and is properly left to the informed discretion of the responsible federal agencies. Cf. SCRAP II, 422 U.S., at 325-326. Absent a showing of arbitrary action, we must assume that the agencies have exercised this discretion appropriately. Respondents have made no showing to the contrary.

Respondents' basic argument is that one comprehensive statement on the Northern Great Plains is required because all coal-related activity in that region is "programmatically," "geographically," and "environmentally" related. Both the alleged "programmatic" relationship and the alleged "geographic" relationship resolve, ultimately, into an argument that the region is proper for a comprehensive impact statement because the petitioners themselves have approached environmental study in this area on a regional basis. Respondents point primarily to the NGPRP, which they claim — and petitioners deny — focused on the region described in the complaint. The precise region of the NGPRP is unimportant, for its irrelevance to the delineation of an appropriate area for analysis in a comprehensive impact statement has been well stated by the Secretary:

On the "programmatic" relationship, respondents also rely on the assertion that all of the projects involve similar methods of mining and converting the region's coal. Assuming this to be correct, we do not think it significant.

They rely also on the North Central Power Study and the Montana-Wyoming Aqueducts Study, but each covered an area different from respondents' region and, moreover, it is not clear that either was primarily an environmental study. See supra, at 397.

"Resource studies [like the NGPRP] are one of many analytical tools employed by the Department to inform itself as to general resource availability, resource need and general environmental considerations so that it can intelligently determine the scope of environmental analysis and review specific actions it may take. Simply put, resource studies are a prelude to informed agency planning, and provide the data base on which the Department may decide to take specific actions for which impact statements are prepared. The scope of environmental impact statements seldom coincide with that of a given resource study, since the statements evolve from specific proposals for federal action while the studies simply provide an educational backdrop." Affidavit of Oct. 28, 1975, App. 191.

As for the alleged "environmental" relationship, respondents contend that the coal-related projects "will produce a wide variety of cumulative environmental impacts" throughout the Northern Great Plains region. They described them as follows: Diminished availability of water, air and water pollution, increases in population and industrial densities, and perhaps even climatic changes. Cumulative environmental impacts are, indeed, what require a comprehensive impact statement. But determination of the extent and effect of these factors, and particularly identification of the geographic area within which they may occur, is a task assigned to the special competency of the appropriate agencies. Petitioners dispute respondents' contentions that the interrelationship of environmental impacts is regionwide and, as respondents' own submissions indicate, petitioners appear to have determined that the appropriate scope of comprehensive statements should be based on basins, drainage areas, and other factors. See supra, at 410-411. We cannot say that petitioners' choices are arbitrary. Even if environmental interrelationships could be shown conclusively to extend across basins and drainage areas, practical considerations of feasibility might well necessitate restricting the scope of comprehensive statements.

For example, respondents assert that coal mines in the region are environmentally interrelated because opening one reduces the supply of water in the region for others. Petitioners contend that the water supply for each aquifer or basin within the region — of which there are many — is independent.
Moreover, petitioners state in their reply brief that few active or proposed mines in respondents' region are located within 50 miles of any other mine, and there are only 30 active or proposed mines in the entire 90,000 square miles of the region.

In sum, respondents' contention as to the relationships between all proposed coal-related projects in the Northern Great Plains region does not require that petitioners prepare one comprehensive impact statement covering all before proceeding to approve specific pending applications. As we already have determined that there exists no proposal for regionwide action that could require a regional impact statement, the judgment of the Court of Appeals must be reversed, and the judgment of the District Court reinstated and affirmed. The case is remanded for proceedings consistent with this opinion.

Nor is it necessary that petitioners always complete a comprehensive impact statement on all proposed actions in an appropriate region before approving any of the projects. As petitioners have emphasized, and respondents have not disputed, approval of one lease or mining plan does not commit the Secretary to approval of any others; nor, apparently, do single approvals by the other petitioners Page 415 commit them to subsequent approvals. Thus, an agency could approve one pending project that is fully covered by an impact statement, then take into consideration the environmental effects of that existing project when preparing the comprehensive statement on the cumulative impact of the remaining proposals. Cf. n. 20, supra.

So ordered.

George W. Pring filed a brief for the Environmental Defense Fund, Inc., et al. as amici curiae urging affirmance in both cases.