To amend section 111 of the Clean Air Act to clarify when a physical change in, or change in the method of operation of, a stationary source constitutes a modification, and for other purposes.

This bill amends the Clean Air Act to provide that a modification of a stationary source results in an increase in air pollution only when the maximum achievable hourly emissions rate from the source is higher than: (1) the rate of the source as it was originally designed, and (2) the rate that was actually achieved during the 10 years before the change.