43 CFR 46.300 - Purpose of an environmental assessment and when it must be prepared.
The purpose of an environmental assessment is to allow the Responsible Official to determine whether to prepare an environmental impact statement or a finding of no significant impact.
(a) A bureau must ensure that an environmental assessment is prepared for all proposed Federal actions, except those:
(1) That are covered by a categorical exclusion;
(2) That are covered sufficiently by an earlier environmental document as determined and documented by the Responsible Official; or
(3) For which the bureau has already decided to prepare an environmental impact statement.
(b) A bureau may prepare an environmental assessment for any proposed action at any time to:
(1) Assist in planning and decision-making;
(2) Further the purposes of NEPA when no environmental impact statement is necessary; or
(3) Facilitate environmental impact statement preparation.