CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE NINTH CIRCUIT.
Stevens, J., delivered the opinion for a unanimous Court. Brennan, J., filed a concurring statement, post, p. 359.
JUSTICE STEVENS delivered the opinion of the Court.
We granted certiorari to decide two questions of law.*fn1 As framed by petitioners, they are:
"1. Whether the National Environmental Policy Act requires federal agencies to include in each environmental impact statement: (a) a fully developed plan to mitigate
environmental harm; and (b) a 'worst case' analysis of potential environmental harm if relevant information concerning significant environmental effects is unavailable or too costly to obtain.
"2. Whether the Forest Service may issue a special use permit for recreational use of national forest land in the absence of a fully developed plan to mitigate environmental harm." Pet. for Cert. i.
Concluding that the Court of Appeals for the Ninth Circuit misapplied the National Environmental Policy Act of 1969 (NEPA), 83 Stat. 852, 42 U. S. C. § 4321 et seq., and gave inadequate deference to the Forest Service's interpretation of its own regulations, we reverse and remand for further proceedings.
The Forest Service is authorized by statute to manage the national forests for "outdoor recreation, range, timber, watershed, and wildlife and fish purposes." 74 Stat. 215, 16 U. S. C. § 528. See also 90 Stat. 2949, 16 U. S. C. § 1600 et seq. Pursuant to that authorization, the Forest Service has issued "special use" permits for the operation of approximately 170 Alpine and Nordic ski areas on federal lands. See H. R. Rep. No. 99-709, pt. 1, p. 2 (1986).
The Forest Service permit process involves three separate stages. The Forest Service first examines the general environmental and financial feasibility of a proposed project and decides whether to issue a special use permit. See 36 CFR § 251.54(f) (1988). Because that decision is a "major Federal action" within the meaning of NEPA, it must be preceded by the preparation of an Environmental Impact Statement (EIS). 42 U. S. C. § 4332. If the Service decides to issue a permit, it then proceeds to select a developer, formulate the basic terms of the arrangement with the selected party,
and issue the permit.*fn2 The special use permit does not, however, give the developer the right to begin construction. See 36 CFR § 251.56(c) (1988). In a final stage of review, the Service evaluates the permittee's "master plan" for development, construction, and operation of the project. Construction may begin only after an additional environmental analysis (although it is not clear that a second EIS need always be prepared) and final approval of the developer's master plan. This case arises out of the Forest Service's decision to issue a special use permit authorizing the development of a major destination Alpine ski resort at Sandy Butte in the North Cascade Mountains.
Sandy Butte is a 6,000-foot mountain located in the Okanogan National Forest in Okanogan County, Washington. At present Sandy Butte, like the Methow Valley it overlooks, is an unspoiled, sparsely populated area that the District Court characterized as "pristine." App. to Pet. for Cert. 20a. In 1968, Congress established the North Cascades National Park and directed the Secretaries of the Interior and Agriculture to agree on the designation of areas within, and adjacent to, the park for public uses, including ski areas. 82 Stat. 926, 930, 16 U. S. C. §§ 90, 90d-3. A 1970 study conducted by the Forest Service pursuant to this congressional directive identified Sandy Butte as having the highest potential of any site in the State of Washington for development as a major downhill ski resort.*fn3 App. to Pet. for Cert. 23a.
In 1978, Methow Recreation, Inc. (MRI), applied for a special use permit to develop and operate its proposed "Early Winters Ski Resort" on Sandy Butte and an 1,165-acre parcel of land it had acquired adjacent to the National Forest. The proposed development would make use of approximately 3,900 acres of Sandy Butte; would entice visitors to travel long distances to stay at the resort for several days at a time; and would stimulate extensive commercial and residential growth in the vicinity to accommodate both vacationers and staff.
In response to MRI's application, the Forest Service, in cooperation with state and county officials, prepared an EIS known as the Early Winters Alpine Winter Sports Study (Early Winters Study or Study). The stated purpose of the EIS was "to provide the information required to evaluate the potential for skiing at Early Winters" and "to assist in making a decision whether to issue a Special Use Permit for downhill skiing on all or a portion of approximately 3900 acres of National Forest System land." Early Winters Study 1. A draft of the Study was completed and circulated in 1982, but release of the final EIS was delayed as Congress considered including Sandy Butte in a proposed wilderness area. App. to Pet. for Cert. 26a. When the Washington State Wilderness Act of 1984 was passed, however, Sandy Butte was excluded from the wilderness designation,*fn4 and the EIS was released.
The Early Winters Study is a printed document containing almost 150 pages of text and 12 appendices. It evaluated five alternative levels of development of Sandy Butte that might be authorized, the lowest being a "no action" alternative and the highest being development of a 16-lift ski area able to accommodate 10,500 skiers at one time. The Study considered the effect of each level of development on water resources, soil, wildlife, air quality, vegetation, and visual quality, as well as land use and transportation in the Methow Valley, probable demographic shifts, the economic market for skiing and other summer and winter recreational activities in the Valley, and the energy requirements for the ski area and related developments. The Study's discussion of possible impacts was not limited to on-site effects, but also, as required by Council on Environmental Quality (CEQ) regulations, see 40 CFR § 1502.16(b) (1987), addressed "off-site impacts that each alternative might have on community facilities, socio-economic and other environmental conditions in the Upper Methow Valley." Early Winters Study 1. As to off-site effects, the Study explained that "due to the uncertainty of where other public and private lands may become developed," it is difficult to evaluate off-site impacts, id., at 76, and thus the document's analysis is necessarily "not site-specific," id., at 1. Finally, the Study outlined certain steps that might be taken to mitigate adverse effects, both on Sandy Butte and in the neighboring Methow Valley, but indicated that these proposed steps are merely conceptual and "will be made more specific as part of the design and implementation stages of the planning process." Id., at 14.
The effects of the proposed development on air quality and wildlife received particular attention in the Study. In the chapter on "Environmental Consequences," the first subject discussed is air quality. As is true of other subjects, the discussion included an analysis of cumulative impacts over several
years resulting from actions on other lands as well as from the development of Sandy Butte itself. The Study concluded that although the construction, maintenance, and operation of the proposed ski area "will not have a measurable effect on existing or future air quality," the off-site development of private land under all five alternatives -- including the "no action" alternative -- "will have a significant effect on air quality during severe meteorological inversion periods." Id., at 65. The burning of wood for space heat, the Study explained, would constitute the primary cause of diminished air quality, and the damage would increase incrementally with each of the successive levels of proposed development. Ibid. The Study cautioned that without efforts to mitigate these effects, even under the "no action" alternative, the increase in automobile, fireplace, and wood stove use would reduce air quality below state standards, but added that "[t]he numerous mitigation measures discussed" in the Study "will greatly reduce the impacts presented by the model." Id., at 67.
In its discussion of air-quality mitigation measures, the EIS identified actions that could be taken by the county government to mitigate the adverse effects of development, as well as those that the Forest Service itself could implement at the construction stage of the project. The Study suggested that Okanogan County develop an air quality management plan, requiring weatherization of new buildings, limiting the number of wood stoves and fireplaces, and adopting monitoring and enforcement measures.*fn5 In addition, the
Study suggested that the Forest Service require that the master plan include procedures to control dust and to comply with smoke management practices.*fn6
In its discussion of adverse effects on area wildlife, the EIS concluded that no endangered or threatened species would be affected by the proposed development and that the only impact on sensitive species was the probable loss of a pair of spotted owls and their progeny. Id., at 75. With regard to other wildlife, the Study considered the impact on 75 different
indigenous species and predicted that within a decade after development vegetational change and increased human activity would lead to a decrease in population for 31 species, while causing an increase in population for another 24 species on Sandy Butte. Ibid. Two species, the pine marten and nesting goshawk, would be eliminated altogether from the area of development. Ibid.
In a comment in response to the draft EIS, the Washington Department of Game voiced a special concern about potential losses to the State's largest migratory deer herd, which uses the Methow Valley as a critical winter range and as its migration route. Id., at Appendix D (letter of November 18, 1982). The state agency estimated that the total population of mule deer in the area most likely to be affected was "better than 30,000 animals" and that "the ultimate impact on the Methow deer herd could exceed a 50 percent reduction in numbers." Ibid. The agency asserted that "Okanogan County residents place a great deal of importance on the area's deer herd." Ibid. In addition, it explained that hunters had "harvested" 3,247 deer in the Methow Valley area in 1981, and that, since in 1980 hunters on average spent $1,980 for each deer killed in Washington, they had contributed over $6 million to the State's economy in 1981. Because the deer harvest is apparently proportional to the size of the herd, the state agency predicted that "Washington business can expect to lose over $3 million ...