(a) On July 8, 1997, the Governor of Montana submitted revisions to the SIP narrative for the Missoula carbon monoxide control plan.

(b) Revisions to the Montana State Implementation Plan, revised Carbon Monoxide Maintenance Plan for Billings, as submitted by the Governor's Designee on July 13, 2011, and the associated Alternative Monitoring Strategy for Billings, as submitted by the Governor's Designee on June 22, 2012.

(c) Revisions to the Montana State Implementation Plan, revised Carbon Monoxide Maintenance Plan for Great Falls, as submitted by the Governor's Designee on July 13, 2011, and the associated Alternative Monitoring Strategy for Great Falls, as submitted by the Governor's Designee on June 22, 2012.

(d) Revisions to the Montana State Implementation Plan, revised Carbon Monoxide Maintenance Plan for Missoula, as submitted by the Governor on September 19, 2016 (as approved by the EPA on February 1, 2018).

[64 FR 68038, Dec. 6, 1999, as amended at 67 FR 7973, Feb. 21, 2002; 67 FR 31150, May 9, 2002; 72 FR 46161, Aug. 17, 2007; 80 FR 16573, Mar. 30, 2015; 80 FR 17333, Apr. 1, 2015; 82 FR 43184, Sept. 14, 2017; 83 FR 4598, Feb. 1, 2018]