The Environmental Protection Agency (EPA) is approving elements of a state implementation plan (SIP) submission from Montana regarding the infrastructure requirements of the Clean Air Act (CAA) for the 2015 8-hour ozone National Ambient Air Quality Standards (NAAQS). The infrastructure requirements are designed to ensure that the structural components of each state's air quality management program are adequate to meet the state's responsibilities under the CAA. Additionally, EPA is finalizing approval of Montana's request to update their SIP to incorporate the most recent version of EPA's "Guidelines on Air Quality Models." EPA is taking this action pursuant to the CAA.