(a) Activities that require Corps authorization under 33 U.S.C. 1344, 33 U.S.C. 401, 33 U.S.C. 403, and 33 U.S.C. 1413 are reviewed (and when applicable, permitted) on a site-specific basis based upon an application containing a complete description of the proposed activity, and all activities which the applicant plans to undertake which are reasonably related to the same project and for which a Corps permit will be required. See 33 CFR 325.1(d)(1)-(2). However, only for reviews of activities under 33 U.S.C. 408, the District Engineer may prepare tiered environmental documents when conducting multi-phased reviews of proposed alterations or in other appropriate circumstances. Multi-phased reviews under 33 U.S.C. 408 evaluate proposed alterations in multiple successive iterations of progressively greater detail. Each successive review must be accompanied by a NEPA document that considers the potential impacts of the alteration at the level of detail of the given phase of review to help inform the development of the proposed alteration. The analysis in each environmental document will reflect the level of planning in each tier. For example, the first tier may consider the differing impacts of selecting different sites for the alteration, the second tier may consider different project configurations, and the final tier may consider the impacts from different construction methods. Each successive analysis should build off the previous analysis, formally incorporating the prior environmental documents.

(b) After completing a programmatic environmental assessment or environmental impact statement for a review under 33 U.S.C. 408, the District Engineer may rely on that document for 5 years if there are not substantial new circumstances or information about the significance of adverse effects that bear on the analysis. After 5 years, as long as the District Engineer reevaluates the analysis in the programmatic environmental document and any underlying assumption to ensure reliance on the analysis remains valid and briefly documents its reevaluation and explains why the analysis remains valid considering any new and substantial information or circumstances, the District Engineer may continue to rely on the document.