When is a supplemental environmental review needed?
After FTA’s completion of an environmental review with a Record of Decision (ROD), Finding of No Significant Impact (FONSI), or Categorical Exclusion (CE) determination, a supplemental environmental review is needed in the following situations:

There are three levels of evaluation and documentation for supplemental environmental reviews:

• re-evaluations
• supplemental EAs
• supplemental EISs

*  CEs and dCEs are generally re-written or modified as needed and signed a new.

As with the original NEPA review, the level of supplemental review depends on the proposed change or new information, and the significance of the impacts associated with the change or new information. The supplemental environmental document does not need to be the same level of documentation as the original finding; the level of review depends on the new project impacts. For example, if a CE determination was made originally and now there are changes to the project that require the use of U.S. Department of Transportation Section 4(f) resource with greater than de minimis impact, a supplemental EA may be needed to consider alternatives that avoid the Section 4(f) resource. 

When is a re-evaluation needed?
A re-evaluation of the original NEPA review can occur at any time, and is conducted to:

• Determine if proposed changes to the project would have significant new or changed environmental impacts not evaluated in the original NEPA review (23 CFR § 771.130)
• Determine if new information or circumstance (for example, the discovery of an intact archaeological site originally thought to be previously destroyed) reveals significant new or changed impacts not evaluated in the original NEPA document (23 CFR § 771.130)
• Verify that, despite the passage of time, the original NEPA review is still valid; such as the project has not changed, the affected environment has not changed, and applicable federal environmental laws and regulations have not changed (23 CFR § 771.129)

What information should be included in a re-evaluation?
The information provided by the grant applicant in a re-evaluation would normally include the information below. Some FTA regional offices use a particular form or reporting format to organize these documents.

• A description of the changes to the project;
• The reasons for the project changes;
• The changed circumstance or new information available about the project;
• The source of the new information;
• Changes to the affected environment since the original document was issued;
• The new or changed impacts resulting from the project change;
• The new or changed impacts resulting from the changes in the affected environment; The new or changed impacts resulting associated with the new information; and
• Mitigation for any new or changed impacts.

What if the re-evaluation determines there are no potentially significant new or changed impacts?
The re-evaluation process should be completed with a written FTA determination that a supplemental NEPA document is not needed with a reference made to the re-evaluation document. 

What if the re-evaluation determines there are potentially significant new or changed impacts?
One potential impacts have been identified, FTA and the grant applicant should determine what level of supplemental NEPA document, either a supplemental EA or supplemental EIS, is appropriate to address the newly identified impacts. 

When is a supplemental EA needed?
A supplemental EA is authorized by 23 CFR Part 771.130(c) and would be prepared when:

• The proposed change to the project or the new information about it are of such public interest or controversy that it warrants public review and comment; or
• The change or new information involves substantial new use or increased use of a resource such as a parkland, wetlands, or historic site, and the development and evaluation of alternatives to avoid the resource are required.
• If the new or changed impacts are clearly significant, then FTA would immediately require a supplemental EIS rather than an EA.

What information should be included in a supplemental EA?
A supplemental EA would discuss:

• A very brief description of the original project and the original NEPA documents that led to that project;
• A description of the proposed change or new information that results in the need for this supplemental EA;
• A statement that the scope of this review does not cover the entire project but only covers the limited area in which the change or new information applies;
• A description of the alternatives within this area of limited scope including, at a minimum, the originally approved alternative and the proposed change;
• The new or changed environmental impacts associated with the change, and a comparison to the impacts of the originally approved alternative within the area of the change; and
• Any new or changed mitigation measures associated with the new or changed impacts.

After FTA approval of the supplemental EA, it would be announced in local newspapers and be made available for 30-day public review and comment in the same way that an original EA is publicized and distributed. It would also be sent, in some form (hardcopy, electronic copy, or web address) to the agencies whose interests are affected by the change.

If the supplemental EA and the public and agency comments on that EA do not reveal any significant new or changed impacts, the FTA finding would be documented as follows:

• The supplemental EA would be referenced as the basis for this finding;
• New or changed mitigation presented in the supplemental EA would be committed to;
• Public and agency comments on the supplemental EA would be summarized and responses would be provided in the same way that comments on an original EA are dealt with; and
• Any additional actions or changes precipitated by the public or agency comments but not presented in the supplemental EA, would be specified.

When is a supplemental EIS needed?
A supplemental EIS is needed when the NEPA process has been completed and final design of the project results in a proposed change to the project with significant new or changed impacts. It is rare that, after NEPA completion, the affected environment changed so much during a 3-year lull in project activity that significant new impacts would result and a supplemental EIS would be needed, though such a situation is conceivable. In each of these cases, a supplemental draft EIS and supplemental final EIS would be prepared.

Is scoping required for a supplemental EIS?
Although scoping is not required for a supplemental EIS (40 CFR Part 1502.9), early coordination with cooperating agencies and participating agencies whose interests would be affected by the proposed change is appropriate. Otherwise, the process is the same as it is for an original EIS.

What information should be included in a supplemental EIS?
The supplemental EIS would discuss the same topics listed above for a supplemental EA. 

The supplemental EIS is documented in an addendum or amendment to the original ROD. The ROD addendum is of limited scope and states that it does not override the original ROD except where the project change or new information is located.

Additional Resources:
CEQ Regulations Implementing NEPA, 40 CFR Part 1500

FTA/ FHWA Environmental Impact and Related Procedures in 23 CFR Part 771