Section 52.1398 - Control strategy: Sulfur dioxide(a)Redesignation to attainment. The EPA has determined that the Billings 2010 sulfur dioxide (SO2) nonattainment area has met the criteria under CAA section 107(d)(3)(E) for redesignation from nonattainment to attainment for the 2010 1-hour SO2 NAAQS. The EPA is therefore redesignating the Billings 2010 SO2 nonattainment area to attainment.(b) The EPA is approving the maintenance plan for the Billings nonattainment area for the 2010 SO2 NAAQS submitted by the State of Montana on December 14, 2015.(c)Redesignation to attainment. The EPA has determined that the East Helena sulfur dioxide (SO2) nonattainment area has met the criteria under CAA section 107(d)(3)(E) for redesignation from nonattainment to attainment for the 1971 primary and secondary SO2 NAAQS. The EPA is therefore redesignating the East Helena 1971 SO2 nonattainment area to attainment.(d)Maintenance plan. The EPA is approving the maintenance plan for the East Helena nonattainment area for the 1971 SO2 NAAQS submitted by the State of Montana on October 26, 2018. 81 FR 28720 , May 10, 2016, as amended at 84 FR 47899 , Sept. 11, 2019 81 FR 28720 , 5/10/2016; 84 FR 47899 , 10/11/2019; 84 FR 47899 , 10/11/2019