The Environmental Protection Agency (EPA) is finalizing approval of Montana's Regional Haze Progress Report ("Progress Report"), submitted by the State of Montana through the Montana Department of Environmental Quality (MDEQ) on November 7, 2017, as a revision to the Montana Regional Haze State Implementation Plan (SIP). Montana's Progress Report addresses requirements of the Clean Air Act (CAA or Act) and the Federal Regional Haze Rule that require each state to submit periodic reports describing progress towards reasonable progress goals (RPGs) established for regional haze and a determination of the adequacy of the state's existing SIP addressing regional haze (regional haze plan). The EPA is finalizing approval of Montana's determination that the State's regional haze plan is adequate to meet these RPGs for the first implementation period covering through 2018.