Under NEPA, when is a federal agency required to prepare an Environmental Impact Statement (EIS)?

A federal agency is required to prepare an Environmental Impact Statement (EIS) under the National Environmental Policy Act (NEPA) when a significant environmental impact is anticipated from a proposed federal action. This requirement is rooted in NEPA's purpose, which is to ensure that environmental factors are weighed alongside economic and technical considerations in decision-making. The EIS process enables thorough examination and public involvement, helping to identify the potential impacts of the proposed action on the environment, as well as alternatives and mitigation strategies.

The significance of this requirement hinges on the need to assess and disclose the potential effects of federal projects, including their influence on natural resources, wildlife, and communities. Preparing an EIS is a way for the agency to transparently communicate its findings to stakeholders and the public and to engage them in the decision-making process.

In comparison, public opposition to a project, the funding source being private, or the mere existence of alternatives does not independently trigger the requirement for an EIS. Instead, the core criterion is the anticipated significance of environmental impacts, which drives the necessity for this comprehensive documentation and analysis.