(a) Generally. Except for proposals for legislation as provided in § 1506.8 of this subchapter, agencies shall prepare environmental impact statements in two stages and, where necessary, supplement them as provided in paragraph (d)(1) of this section.

(b) Draft environmental impact statements. Agencies shall prepare draft environmental impact statements in accordance with the scope decided upon in the scoping process (§ 1502.4 of this subchapter). The lead agency shall work with the cooperating agencies and shall obtain comments as required in part 1503 of this subchapter. To the fullest extent practicable, the draft statement must meet the requirements established for final statements in section 102(2)(C) of NEPA and in the regulations in this subchapter. If the agency determines that a draft statement is so inadequate as to preclude meaningful analysis, the agency shall prepare and publish a supplemental draft of the appropriate portion. At appropriate points in the draft statement, the agency shall discuss all major points of view on the environmental effects of the alternatives, including the proposed action.

(c) Final environmental impact statements. Final environmental impact statements shall consider and respond to comments as required in part 1503 of this subchapter. At appropriate points in the final statement, the agency shall discuss any responsible opposing view that was not adequately discussed in the draft statement and shall indicate the agency's response to the issues raised.

(d) Supplemental environmental impact statements. Agencies:

(1) Shall prepare supplements to either draft or final environmental impact statements 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 adverse effects that bear on the analysis.

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

(3) Shall prepare, publish, and file a supplement to an environmental impact statement (exclusive of scoping (§ 1502.4 of this subchapter)) as a draft and final environmental impact statement, as is appropriate to the stage of the environmental impact statement involved, unless the Council approves alternative arrangements (§ 1506.11 of this subchapter).

(e) Reevaluation. An agency may reevaluate an environmental impact statement to determine that the agency does need to prepare a supplement under paragraph (d) of this section. The agency should document its finding consistent with its agency NEPA procedures (§ 1507.3 of this subchapter), or, if necessary, prepare a supplemental environmental assessment and finding of no significant impact.