Table 3. Summary of the National Environmental Policy Act (NEPA) and its key provisions.

Provision Description
Overall policy:
(42 U.S.C. § 4332)
Passed into law in 1970, the NEPA is one of the most influential environmental laws in the United States. It requires all federal agencies that propose a “major federal action significantly affecting the quality of the human environment” to first assess the potential impacts of the proposed action.
Environmental impact statement:
42 U.S.C. § 4332(1)(C)
All major federal actions require the development of an environmental impact statement (EIS) “that informs both the agency and the public regarding possible environmental consequences. An EIS generally comprises several elements, including: (i) the environmental impact of the proposed action, (ii) any adverse environmental effects which cannot be avoided should the proposal be implemented, (iii) alternatives to the proposed action, (iv) the relationship between local short-term uses, [the] environment, and the maintenance and enhancement of long-term productivity, and (v) any irreversible and irretrievable commitments of resources which would be involved in the proposed action should it be implemented.”
42 U.S.C. § 4332(1)(C):
40 CFR 1502.9(c). Supplemental environmental impact statement
Additional NEPA analysis is required when significant new circumstances or information relevant to environmental concerns or substantial changes in the proposed action that are relevant to environmental concerns may necessitate the preparation of a supplemental EIS. Increasingly, the supplemental NEPA process is becoming important to adaptive management efforts in order to integrate new information back into the management process (Benson 2010a).