The Environmental Protection Agency (EPA) is promulgating a Federal Implementation Plan (FIP) containing emission limits and compliance determining methods for several sources located in Billings and Laurel, Montana. EPA is promulgating a FIP because of our previous partial and limited disapprovals of the Billings/Laurel Sulfur Dioxide (SO2) State Implementation Plan (SIP). The intended effect of this action is to assure attainment of the SO2 National Ambient Air Quality Standards (NAAQS) in the Billings/Laurel, Montana area. EPA is taking this action under sections 110, 301, and 307 of the Clean Air Act (Act).