40 CFR § 1501.5 - Environmental assessments.
(a) An agency shall prepare an environmental assessment for a proposed action that is not likely to have significant effects or when the significance of the effects is unknown unless the agency finds that a categorical exclusion (§ 1501.4) is applicable or has decided to prepare an environmental impact statement.
(b) An agency may prepare an environmental assessment on any action in order to assist agency planning and decision making.
(c) An environmental assessment shall:
(2) Briefly discuss the purpose and need for the proposed action, alternatives as required by section 102(2)(E) of NEPA, and the environmental impacts of the proposed action and alternatives, and include a listing of agencies and persons consulted.
(e) Agencies shall involve the public, State, Tribal, and local governments, relevant agencies, and any applicants, to the extent practicable in preparing environmental assessments.
(f) The text of an environmental assessment shall be no more than 75 pages, not including appendices, unless a senior agency official approves in writing an assessment to exceed 75 pages and establishes a new page limit.
(g) Agencies may apply the following provisions to environmental assessments:
(1) Section 1502.21 of this chapter - Incomplete or unavailable information;
(2) Section 1502.23 of this chapter - Methodology and scientific accuracy; and
(3) Section 1502.24 of this chapter - Environmental review and consultation requirements.