40 CFR § 1501.3
When to prepare an environmental assessment
June 9, 2020
(a) Agencies shall prepare an environmental assessment (§1508.9) when necessary under the procedures adopted by individual agencies to supplement these regulations as described in §1507.3. An assessment is not necessary if the agency has decided to prepare an environmental impact statement.
(b) Agencies may prepare an environmental assessment on any action at any time in order to assist agency planning and decisionmaking.