1 CFR 601.17: Supplemental Environmental Assessments.

(a) The NCPC shall prepare a supplemental EA if five or more years have elapsed since adoption of the EA and:

(1) There are substantial changes to the proposed action that are relevant to environmental concerns; or

(2) There are significant new circumstances or information that are relevant to environmental concerns and have a bearing on the proposed action or its impacts.

(b) The NCPC may supplement a Draft or Final EA at any time to further the purposes of NEPA.

(c) The NCPC shall prepare, circulate, and file a supplement to a Draft or Final EA, and adopt a FONSI in accordance with the requirements of §§ 601.15 and 601.16. If NCPC is not the Lead Agency, it shall proceed as outlined in § 601.16(b) and (c).