EPA is taking direct final action partially approving and partially disapproving State Implementation Plan (SIP) revisions submitted by the Governor of Montana on September 19, 1997; December 10, 1997; April 14, 1999; December 6, 1999; and March 3, 2000. These revisions recodify and modify the State's air quality rules so that they are consistent with Federal requirements, minimize repetition in the air quality rules, and clarify existing provisions. In addition, we are also approving into the SIP Yellowstone County's Local Regulation No.002--Open Burning. Finally, we are also announcing that we delegated the authority for the implementation and enforcement of the New Source Performance Standards (NSPS) to the State. EPA is either not acting on or disapproving certain provisions of the State's air quality rules that should not be in the SIP because they are not generally related to attainment of the National Ambient Air Quality Standards (NAAQS) or they are inconsistent with our SIP requirements. Finally, some provisions of the rules will be acted on at a later date. This action is being taken under sections 110 and 111 of the Clean Air Act.