An agency shall issue an environmental impact statement with respect to a proposed agency action requiring an environmental document that has a reasonably foreseeable significant effect on the quality of the human environment.
An agency shall prepare an environmental assessment with respect to a proposed agency action that does not have a reasonably foreseeable significant effect on the quality of the human environment, or if the significance of such effect is unknown, unless the agency finds that the proposed agency action is excluded pursuant to one of the agency’s categorical exclusions, another agency’s categorical exclusions consistent with section 4336c of this title, or another provision of law. Such environmental assessment shall be a concise public document prepared by a Federal agency to set forth the basis of such agency’s finding of no significant impact or determination that an environmental impact statement is necessary.