The Environmental Protection Agency (EPA) is taking final action to re-approve a State Implementation Plan (SIP) revision submitted by the State of Montana. On September 19, 2016, the Governor of Montana submitted to the EPA a Clean Air Act (CAA) section 175A(b) second 10-year maintenance plan for the Missoula, Montana area for the carbon monoxide (CO) National Ambient Air Quality Standard (NAAQS). This limited maintenance plan (LMP) addresses maintenance of the CO NAAQS for a second 10-year period beyond the original redesignation. This action is being taken under sections 110 and 175A of the CAA.