There are three types of environmental reviews that may occur for a proposed major federal action: an environmental assessment, an environmental impact statement, or a categorical exclusion. An environmental assessment (EA) is a preliminary step to determine if the action will significantly affect the quality of the environment. If the agency determines that there will be a significant impact, then it must prepare an environmental impact statement (EIS).
An environmental impact statement is an in-depth analysis of the proposed action’s environmental consequences and can take years to finalize. If the agency determines that there will not be a significant impact on the environment, then the agency makes a Finding of No Significant Impact and does not need to prepare an environmental impact statement. These reviews are designed to make an agency consider the environmental consequences of the proposed action, alternative actions the agency could take in lieu of the proposed action, the expected environmental impacts of those alternative actions, and the agency’s rationale for selecting its preferred approach.
Agencies can adopt categorical exclusions which are waivers for categories of certain major federal actions that have been determined not to “individually or cumulatively have a significant effect on the human environment.” If an action falls into a categorical exclusion, no environmental assessment or environmental impact statement is required. Agencies often use categorical exclusions for actions such as routine maintenance, operational activities, and authorization of regularly-occurring actions. An agency’s internal procedures may only require administrative approval to use a categorical exclusion or it may require a documented explanation as to why the proposed action does not require an environmental assessment. Over time, agencies have attempted to expand the reach of their categorical exclusions, which can diminish the impact of NEPA’s procedures for considering environmental impacts.
The Council of Environmental Quality (CEQ), a small agency within the Executive Office of the President, issues implementing regulations for NEPA that outline how federal agencies must comply with NEPA. The CEQ NEPA implementing regulations outline a framework but are designed to provide flexibility to each agency. The CEQ regulations require every agency to adopt its own NEPA implementing procedures to supplement the CEQ regulations, which are reviewed by CEQ.