18 C.F.R. § 2.23
The Commission will address and consider cumulative impact issues at original licensing and relicensing to the fullest extent possible consistent with the Commission's statutory responsibility to avoid undue delay in the relicensing process and to avoid undue delay in the amelioration of individual project impacts at relicensing. To the extent, if any, that it is not possible to explore and address all cumulative impacts at relicensing, the Commission will reserve authority to examine and address such impacts after the new license has been issued, but will define that reserved authority as narrowly and with as much specificity as possible, particularly with respect to the purpose of reserving that authority. The Commission intends that such articles will describe, to the maximum extent possible, reasonably foreseeable future resource concerns that may warrant modifications of the licensed project. Before taking any action pursuant to such reserved authority, the Commission will publish notice of its proposed action and will provide an opportunity for hearing by the licensee and all interested parties. Hydropower licenses also contain standard "reopener" articles (see § 2.9 of this part) which reserve authority to the Commission to require, among other things, licensees of projects located in the same river basin to mitigate the cumulative impacts of those projects on the river basin. In light of the policy described above, the Commission will use the standard "reopener" articles to explore and address cumulative impacts only (except in extraordinary circumstances) where such impacts were not known at the time of licensing or are the result of changed circumstances. The Commission has authority under the Federal Power Act to require licensees, during the term of the license, to develop and provide data to the Commission on the cumulative impacts of licensed projects located in the same river basin. In issuing both new and original licenses, the Commission will coordinate the expiration dates of the licenses to the maximum extent possible, to maximize future consideration of cumulative impacts at the same time in contemporaneous proceedings at relicensing. The Commission's intention is to consider to the extent practicable cumulative impacts at the time of licensing and relicensing, and to eliminate the need to resort to the use of reserved authority.
18 C.F.R. §2.23