An exception granted under this subpart remains in effect until:
(a) Either the State law or the federal standard, requirement, or implementation specification that provided the basis for the exception is materially changed such that the ground for the exception no longer exists; or
(b) The Secretary revokes the exception, based on a determination that the ground supporting the need for the exception no longer exists.
§ 160.204: Process for requesting exception determinations
§ 160.300: Applicability