16 U.S.C. § 460l–21

As used in this part: (a) The term “project” shall mean a project or any appropriate unit thereof. (b) The term “separable costs,” as applied to any project purpose, means the difference between the capital cost of the entire multiple-purpose project and the capital cost of the project with the purpose omitted. (c) The term “joint costs” means the difference between the capital cost of the entire multiple-purpose project and the sum of the separable costs for all project purposes. (d) The term “feasibility report” shall mean any report of the scope required by the Congress when formally considering authorization of the project of which the report treats. (e) The term “capital cost” includes interest during construction, wherever appropriate.