51.857—Frequency of conformity determinations.
(a)
The conformity status of a Federal action automatically lapses 5 years from the date a final conformity determination is reported under § 51.855, unless the Federal action has been completed or a continuous program has been commenced to implement that Federal action within a reasonable time.
(b)
Ongoing Federal activities at a given site showing continuous progress are not new actions and do not require periodic redeterminations so long as such activities are within the scope of the final conformity determination reported under § 51.855.
(c)
If, after the conformity determination is made, the Federal action is changed so that there is an increase in the total of direct and indirect emissions above the levels in § 51.853(b), a new conformity determination is required.