Clarification of definition of a modification: emission rate increases, pollution control, efficiency, safety, and reliability projects

Paragraph (4) of section 111(a) of the Clean Air Act (42 U.S.C. 7411(a)) is amended— (1) by inserting (A) before The term; (2) by adding at the end the following: For purposes of the preceding sentence, a change increases the amount of any air pollutant emitted by such source only if the maximum hourly emission rate of an air pollutant that is achievable by such source after the change is higher than the maximum hourly emission rate of such air pollutant that was achievable by such source during any hour in the 10-year period immediately preceding the change.; and (3) by adding at the end the following: (B) Notwithstanding subparagraph (A), the term modification does not include a change at a stationary source that is designed— (i) to reduce the amount of any air pollutant emitted by the source per unit of production; or (ii) to restore, maintain, or improve the reliability of operations at, or the safety of, the source, except, with respect to either clause (i) or (ii), when the change would be a modification as defined in subparagraph (A) and the Administrator determines that the increase in the maximum achievable hourly emission rate of a pollutant from such change would cause an adverse effect on human health or the environment..