## Facts

- Dakota Access Pipeline (DAPL) is a 1,168-mile crude-oil pipeline; a key segment crosses Lake Oahe, a federally regulated Missouri River reservoir.
- Lake Oahe provides important water and related resources for the Standing Rock Sioux Tribe and other Sioux tribes.
- The U.S. Army Corps of Engineers issued a federal easement for the Lake Oahe crossing under the Mineral Leasing Act.
- Rather than preparing an Environmental Impact Statement (EIS), the Corps prepared an Environmental Assessment (EA) and issued a mitigated Finding of No Significant Impact (FONSI).
- The Standing Rock Sioux Tribe, joined by other tribal parties, challenged the post-remand EA/FONSI, arguing the Corps failed to take a hard look at spill risk and consequences, leak detection and response, operator safety history, and environmental justice impacts.
- After earlier litigation and a remand for additional analysis, the Corps reaffirmed its decision that an EIS was unnecessary, prompting renewed NEPA challenges.

## Issues

1. Whether the Corps’ post-remand EA and mitigated FONSI satisfied NEPA’s “hard look” requirement for the Lake Oahe easement.
2. Whether unresolved disputes about spill risk and consequences made the environmental effects “highly controversial,” requiring an EIS under NEPA regulations.
3. Whether other NEPA significance factors—such as impacts to unique resources and environmental justice concerns—supported requiring an EIS.

## Decision

- The court held the Corps violated NEPA by issuing the Lake Oahe easement without preparing an EIS.
- The court found the effects were “highly controversial” because there were substantial, unresolved technical disputes about the size, nature, and effect of spill risks and consequences.
- The court concluded the Corps’ EA/FONSI was arbitrary and capricious for inadequately responding to material critiques concerning worst-case discharge, leak detection and response, operator safety record, and environmental justice.
- The court remanded to the Corps to prepare an EIS and reserved remedy questions (such as vacatur or operational relief) for later proceedings.

## Legal Principles

- NEPA requires an agency to prepare an EIS when a proposed federal action may significantly affect the quality of the human environment; an EA must supply sufficient analysis to support a reasoned significance determination.
- “Highly controversial” under NEPA refers to a substantial dispute over the size, nature, or effect of environmental impacts, not mere public opposition.
- When faced with credible technical disagreement on key risk questions, an agency must give a reasoned explanation that engages the substance of the critiques; conclusory responses do not satisfy the “hard look” standard.
- Significance analysis may require consideration of low-probability, high-consequence risks where potential harm is severe.
- Environmental justice effects and distribution of risk are relevant considerations in evaluating whether impacts may be significant.

## Conclusion

The court ruled that the Corps’ reliance on an EA and mitigated FONSI for DAPL’s Lake Oahe crossing did not satisfy NEPA because unresolved technical disputes and inadequately addressed criticisms made the impacts potentially significant, requiring preparation of a full EIS on remand.


Standing Rock Sioux Tribe v. U.S. Army Corps of Eng’rs, 440 F. Supp. 3d 1 (D.D.C. 2020)