40 C.F.R. § 1506.2 : Protection of Environment — COUNCIL ON ENVIRONMENTAL QUALITY — NATIONAL ENVIRONMENTAL POLICY ACT IMPLEMENTING REGULATIONS — OTHER REQUIREMENTS OF NEPA — Elimination of duplication with State, Tribal, and local procedures

(a) Federal agencies are authorized to cooperate with State, Tribal, and local agencies that are responsible for preparing environmental documents, including those prepared pursuant to section 102(2)(D) of NEPA.
(b) To the fullest extent practicable unless specifically prohibited by law, agencies shall cooperate with State, Tribal, and local agencies to reduce duplication between NEPA and State, Tribal, and local requirements, including through use of studies, analysis, and decisions developed by State, Tribal, or local agencies. Except for cases covered by paragraph (a) of this section, such cooperation shall include, to the fullest extent practicable:
(1) Joint planning processes.
(2) Joint environmental research and studies.
(3) Joint public hearings (except where otherwise provided by statute).
(4) Joint environmental assessments.
(c) To the fullest extent practicable unless specifically prohibited by law, agencies shall cooperate with State, Tribal, and local agencies to reduce duplication between NEPA and comparable State, Tribal, and local requirements. Such cooperation shall include, to the fullest extent practicable, joint environmental impact statements. In such cases, one or more Federal agencies and one or more State, Tribal, or local agencies shall be joint lead agencies. Where State or Tribal laws or local ordinances have environmental impact statement or similar requirements in addition to but not in conflict with those in NEPA, Federal agencies may cooperate in fulfilling these requirements, as well as those of Federal laws, so that one document will comply with all applicable laws.
(d) To better integrate environmental impact statements into State, Tribal, or local planning processes, environmental impact statements shall discuss any inconsistency of a proposed action with any approved State, Tribal, or local plan or law (whether or not federally sanctioned). Where an inconsistency exists, the statement should describe the extent to which the agency would reconcile its proposed action with the plan or law. While the statement should discuss any inconsistencies, NEPA does not require reconciliation.

40 C.F.R. §1506.2

85 FR 43370, 9/14/2020