32 CFR § 775.9 - Documentation and analysis.
(a) Environmental documentation and analyses required by this rule should be integrated as much as practicable with any environmental studies, surveys and impact analyses required by other environmental review laws and executive orders (40 CFR 1502.25). When a cost-benefit analysis has been prepared in conjunction with an action which also requires a NEPA analysis, the cost-benefit analysis shall be integrated into the environmental documentation.
(b) CEQ regulations encourage the use of tiering whenever appropriate to eliminate repetitive discussions of the same issues and to focus on the actual issues ripe for discussion at each level of environmental review (40 CFR 1502.20). Tiering is accomplished through the preparation of a broad programmatic environmental impact statement discussing the impacts of a wide ranging or long term stepped program followed by narrower statements or environmental assessments concentrating solely on issues specific to the analysis subsequently prepared (40 CFR 1508.28).
(1)Appropriate use of tiering: Tiering is appropriate when it helps the lead agency to focus on issues which are ripe for decision and exclude from consideration issues already decided or not yet ripe. (40 CFR 1508.28(b).) The sequence of statements or analyses is:
(i) From a broad program, plan, or policy environmental impact statement (not necessarily site specific) to a subordinate/smaller scope program, plan, or policy statement or analysis (usually site specific) (40 CFR 1508.28 (a)).
(ii) From an environmental impact statement on a specific action at an early stage (such as need and site selection) to a supplement (which is preferred) or a subsequent statement or analysis at a later stage (such as environmental mitigation) (40 CFR 1508.28(b)).
(A) A description of the subsequent stages or sites that may ultimately be proposed in as much detail as presently possible;
(B) All of the implementing factors of the program that can be ascertained at the time of impact statement preparation;
(C) All of the environmental impacts that will result from establishment of the overall program itself that will be similar for subsequent stages or sites as further implementation plans are proposed; and
(D) All of the appropriate mitigation measures that will be similarly proposed for subsequent stages or sites.
(iv) The analytical document used for stage or site specific analysis subsequent to the programmatic environmental impact statement shall also be an environmental impact statement when the subsequent tier itself may have a significant impact on the quality of the human environment or when an impact statement is otherwise required. Otherwise, it is appropriate to document the tiered analysis with an environmental assessment to fully assess the need for further documentation or whether a FONSI would be appropriate.