Takeaway
In short, this case holds that agencies must take a hard look at significant post-EIS information, but courts review a reasoned decision not to supplement under the deferential arbitrary-and-capricious standard.
Congress authorized a three-dam flood-control project in Oregon’s Rogue River Basin. The Army Corps of Engineers completed the Lost Creek and Applegate Dams, then pursued construction of the Elk Creek Dam. The planned Elk Creek Dam would control flooding but also affect river temperature, turbidity, fish habitat, fishing, wildlife, and forest land. The Corps prepared an original environmental impact statement in 1971 and a final supplemental EIS in 1980. In 1982, it decided to proceed, and Congress appropriated construction funds in 1985.
Oregon environmental and fishing organizations sued in 1985 to stop construction. They alleged that the Corps had inadequately considered cumulative effects, failed to supply a complete mitigation plan and a worst-case analysis, and failed to prepare another supplemental EIS after receiving later information from Oregon fish-and-wildlife biologists and a federal soil survey. The District Court rejected the NEPA claims, finding the Corps’ actions reasonable. The Ninth Circuit reversed, holding in relevant part that the later materials were significant new information requiring a second supplemental EIS. The Supreme Court reversed that ruling.
Issue #1
Whether a federal agency must prepare a supplemental EIS when post-EIS information raises environmental concerns about a project that remains under construction.
Holding
No. A supplemental EIS is required only when significant new circumstances or information, relevant to environmental concerns and the proposed action or its impacts, show that remaining major federal action may affect the environment significantly in a way not already considered.
Reasoning
Although NEPA does not expressly mention post-decision supplementation, its action-forcing purpose sometimes requires it. NEPA is designed to ensure that agencies and the public confront environmental consequences while there is still time for informed decisionmaking. An agency therefore cannot ignore significant adverse information merely because it has already approved the project.
The governing CEQ and Corps regulations require supplementation when significant new circumstances or information bear on environmental concerns and the proposed action or its impacts. But NEPA does not require a new EIS whenever any new information emerges. Such a rule would make agency decisionmaking endless, because each new assessment could itself become outdated before a decision was completed.
The Court applied a rule of reason focused on the usefulness of the new information to the remaining decisionmaking process. If major federal action remains and the new information shows a significant environmental effect, or a significant extent of an effect, that the original EIS did not already consider, the agency must supplement. The agency must at least take a hard look at the proffered information before deciding that supplementation is unnecessary.
Issue #2
What standard governs judicial review of an agency’s decision not to prepare a supplemental EIS.
Holding
The Administrative Procedure Act’s arbitrary-and-capricious standard governs; courts must defer to an agency’s reasoned scientific judgment unless it reflects a clear error of judgment.
Reasoning
The dispute over the significance of the new materials was primarily factual and scientific, not a pure question of statutory interpretation or application of law to settled facts. It required evaluating competing claims about fish mortality, water temperature, turbidity, scientific methodology, and predictive models—subjects that implicate agency expertise.
Under APA review, a court must carefully examine whether the agency considered the relevant factors and made a reasoned decision. The inquiry is searching and careful, but narrow. A court may not substitute its own preferred scientific judgment simply because it finds contrary expert views more persuasive.
An agency has discretion to rely on the reasonable views of its qualified experts when specialists disagree. At the same time, courts may not accept an agency’s invocation of finality automatically; they must confirm from the record that the agency actually evaluated the significance of the new evidence.
Issue #3
Whether the Corps acted arbitrarily or capriciously in declining to prepare a second supplemental EIS based on the Cramer Memorandum and the Soil Conservation Service survey.
Holding
No. The Corps took the required hard look and reasonably concluded that the materials did not provide significant new and accurate information requiring supplementation.
Reasoning
The Cramer Memorandum suggested that the dam might warm the river enough to reduce chinook-fry survival and might contribute to disease-related prespawning fish mortality. The Corps’ Supplemental Information Report evaluated those concerns, explained weaknesses in the underlying model and causal inferences, accounted for the dam’s capacity to manage temperature and reduce peak flows, and noted that independent experts had criticized important aspects of the underlying fisheries study.
The memorandum was not an official position of the Oregon Department of Fish and Wildlife, and its concerns remained partly speculative. The Corps reasonably found that the predicted temperature increase was smaller and more manageable than the memorandum suggested, and that evidence such as prior fish mortality and the absence of similar events after another dam undercut the proposed disease connection.
The soil survey did not itself purport to predict downstream turbidity or identify changed conditions. Moreover, the Corps’ earlier turbidity conclusions rested on water samples and computer modeling studies, rather than solely on soil-composition assumptions. The Corps could therefore reasonably conclude that the survey did not materially alter the 1980 EIS’s turbidity analysis.
If all the disputed information had been both new and accurate, it could have required a supplemental EIS. But after a careful scientific review, the Corps reasonably concluded that the information that was new was not significant and that the information that might be significant was not new and accurate. That judgment was disputable, but not arbitrary or capricious.
Issue #4
Whether the final supplemental EIS was defective because it lacked a complete mitigation plan and a worst-case analysis.
Holding
No. For the reasons explained in the companion case, Robertson v. Methow Valley Citizens Council, NEPA did not require either a complete mitigation plan or a worst-case analysis.
Reasoning
The Court treated the Ninth Circuit’s contrary holdings as erroneous under Robertson. NEPA requires informed consideration and disclosure of environmental consequences, including mitigation where relevant, but it does not require a fully developed and committed mitigation plan as a condition of approving a project.
Likewise, NEPA did not impose the worst-case-analysis requirement applied by the Ninth Circuit. The Corps’ use of available scientific models and its discussion of anticipated effects did not render the EIS legally deficient on that ground.