45 CFR 900.403: Supplemental EIS.

(a) Supplements to either draft or final EISs shall be prepared, as prescribed in 40 CFR 1502.9, when the Commission finds that there are substantial changes are proposed in a project that are relevant to environmental concerns; or when there are significant new circumstances or information relevant to environmental concerns and bearing on the proposed action or its impacts.

(b) Where Commission action remains to be taken and the EIS is more than three years old, the Commission will review the EIS to determine whether it is adequate or requires supplementation.

(c) The Commission shall prepare, circulate and file a supplement to an EIS in the same fashion (exclusive of scoping) as a draft and final EIS. In addition, the supplement and accompanying administrative record shall be included in the administrative record for the proposal. When an applicant is involved, the applicant shall, under the direction of the approving official, provide assistance.

(d) An NOI to prepare a supplement to a final EIS will be published in those cases where a ROD has already been issued.