Code of Federal Regulations Title 43. Public Lands:  Interior § 43.46.300 Purpose of an environmental assessment and when it must be prepared

(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.

(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.