(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 to assist agency planning and decision making.

(c) An environmental assessment shall:

(1) Briefly provide sufficient evidence and analysis for determining whether to prepare an environmental impact statement or a finding of no significant impact;

(2) Briefly discuss the:

(i) Purpose and need for the proposed agency action;

(ii) Alternatives as required by section 102(2)(H) of NEPA; and

(iii) Environmental effects of the proposed action and alternatives;

(3) List the Federal agencies; State, Tribal, and local governments and agencies; or persons consulted; and

(4) Provide a unique identification number for tracking purposes, which the agency shall reference on all associated environmental review documents prepared for the proposed action and in any database or tracking system for such documents.

(d) For applications to the agency requiring an environmental assessment, the agency shall commence the environmental assessment as soon as practicable after receiving the application.

(e) If an agency publishes a draft environmental assessment, the agency shall invite public comment and consider those comments in preparing the final environmental assessment.

(f) Agencies shall involve the public, State, Tribal, and local governments, relevant agencies, and any applicants, to the extent practicable in preparing environmental assessments (see § 1501.9).

(g) The text of an environmental assessment shall not exceed 75 pages, not including any citations or appendices.

(h) Agencies:

(1) Should supplement environmental assessments if a major Federal action is incomplete or ongoing, and:

(i) The agency makes substantial changes to the proposed action that are relevant to environmental concerns; or

(ii) There are substantial new circumstances or information about the significance of the adverse effects that bear on the analysis to determine whether to prepare a finding of no significant impact or an environmental impact statement.

(2) May also prepare supplements when the agency determines that the purposes of the Act will be furthered by doing so.

(i) Agencies may reevaluate an environmental assessment to determine that the agency does not need to prepare a supplemental environmental assessment and a new finding of no significant impact or an environmental impact statement.

(j) Agencies generally should apply § 1502.21 of this subchapter to environmental assessments.

(k) As appropriate to improve efficiency and effectiveness of environmental assessments, agencies may apply the other provisions of part 1502 and 1503 of this subchapter, including §§ 1502.4, 1502.22, 1502.24, and 1503.4, to environmental assessments.