Approval and Promulgation of State Implementation Plans; State of Colorado; Interstate Transport of Pollution Revisions for the 1997 8-Hour Ozone NAAQS: “Interference With Maintenance” Requirement

EPA is partially approving State Implementation Plan (SIP) revisions submitted by the State of Colorado on June 18, 2009. Specifically, EPA is approving the portions of the "State of Colorado Implementation Plan to Meet the Requirements of Clean Air Act (CAA) Section 110(a)(2)(D)(i)(I)--Interstate Transport Regarding the 1997 8- Hour Ozone Standard" addressing the "interference with maintenance" requirement of section 110(a)(2)(D)(i)(I) for the 1997 8-hour ozone National Ambient Air Quality Standards (NAAQS) by any other state. The "interference with maintenance" requirement of section 110(a)(2)(D)(i)(I) prohibits a state's emissions from interfering with maintenance of the NAAQS by any other state. This action is being taken under section 110 of the CAA.