A private developer sought a special-use permit from the U.S. Forest Service to construct a downhill ski resort in the Okanogan National Forest in Washington's Methow Valley. The Forest Service prepared a draft and final EIS evaluating environmental impacts, including wildlife, land use, traffic, socioeconomics, and especially winter air quality concerns tied to temperature inversions and increased vehicular emissions. The EIS identified potential adverse impacts and discussed various mitigation measures—such as phasing development, shuttle and traffic-management strategies, limits on parking, restrictions on wood-burning appliances, and coordination with state and local air quality permitting—but it did not contain a fully specified, enforceable mitigation plan or quantify the effectiveness of each measure. Local citizens and environmental groups challenged the sufficiency of the EIS under NEPA. The district court upheld the EIS, but the Ninth Circuit reversed, holding that NEPA required a complete mitigation plan and a "worst-case" analysis of uncertain air quality effects. The Supreme Court granted certiorari.
Under NEPA, must an agency's EIS include (1) a detailed, fully developed and enforceable mitigation plan for identified harms and (2) a "worst-case" analysis when information is incomplete or uncertain; and, in light of these standards, was the Forest Service's EIS for the proposed ski resort adequate?
NEPA imposes procedural—not substantive—obligations: an agency must take a "hard look" at environmental consequences and disclose them to the public before acting. An EIS must include a reasonably thorough discussion of significant environmental impacts and "possible mitigation measures," but NEPA does not require the adoption of any particular mitigation, nor a fully developed, enforceable mitigation plan at the EIS stage. CEQ's regulations interpreting NEPA are entitled to substantial deference. Under CEQ's 1986 revision of 40 C.F.R. § 1502.22, agencies need not prepare a "worst-case" analysis; instead, they must disclose when information is incomplete or unavailable, explain its relevance, summarize credible scientific evidence, and evaluate reasonably foreseeable significant adverse effects and their likelihood.
No. NEPA does not require a fully developed and enforceable mitigation plan in the EIS, and it does not require a "worst-case" analysis. The Forest Service's EIS, which discussed potential mitigation measures and disclosed uncertainties, satisfied NEPA's procedural requirements. The Ninth Circuit's decision was reversed.
The Court emphasized that NEPA's core is procedural: it ensures that agencies make informed decisions by considering environmental consequences, not that they reach any particular substantive result or guarantee mitigation. Requiring a fully specified mitigation plan at the EIS stage would be incongruous with NEPA's timing and function, because many mitigation details are appropriately developed through later permitting and design processes in coordination with state and local authorities. What NEPA does require is a "reasonably complete" discussion of possible mitigation to inform the decisionmaker and the public. The EIS here identified concrete categories of mitigation—such as phasing, transportation demand management, and emission controls—and explained how further planning and permitting would refine those measures. That level of detail was sufficient to demonstrate the agency took a "hard look." On uncertainty, the Court deferred to CEQ's 1986 revision of § 1502.22, which replaced the earlier "worst-case" analysis requirement with an approach focused on disclosure of data gaps, scientific credibility, and evaluation of reasonably foreseeable adverse effects and their probabilities. The Court found CEQ's interpretation reasonable and entitled to substantial deference. Mandating a worst-case analysis, especially where it could distract from the best available evidence and overwhelm decisionmakers with speculation, was not compelled by NEPA's text or purposes. The Forest Service's EIS acknowledged uncertainties surrounding winter air quality inversions and described potential consequences and mitigation, thus satisfying the governing regulation and NEPA's "hard look" standard. Because NEPA does not require agencies to adopt mitigation, or to demonstrate mitigation's guaranteed efficacy before approval, the adequacy of the EIS turned on the sufficiency of discussion—not on enforceable commitments. The Court concluded the EIS's analysis and mitigation discussion were adequate and that the Ninth Circuit erred in imposing stricter, extra-statutory requirements.
Robertson is a leading case on NEPA's scope. It cements that NEPA is a disclosure statute: agencies must analyze and disclose impacts and mitigation, but NEPA does not require them to select the most environmentally protective alternative or to finalize a mitigation plan in the EIS. The decision also establishes substantial judicial deference to CEQ's NEPA regulations and confirms that a "worst-case" analysis is not required. For students and practitioners, Robertson defines what makes a mitigation discussion adequate, highlights how agencies should handle incomplete information, and frames the "hard look" review that courts apply to EIS adequacy challenges.
Robertson v. Methow Valley Citizens Council is a touchstone for the proposition that NEPA is a procedural statute aimed at informed governmental choices. By rejecting mandates for a fully developed mitigation plan and for worst-case analysis, the Court set practical, disclosure-centered requirements for how agencies address both mitigation and uncertainty in EISs.