(1) A major stationary source or major modification shall meet each applicable emissions limitation under the Montana State Implementation Plan and each applicable emission standard and standard of performance under ARM 17.8.340 and 17.8.341.

(2) A new major stationary source shall apply BACT for each pollutant subject to regulation under the FCAA that it would have the potential to emit in significant amounts, excluding hazardous air pollutants, except to the extent that such hazardous air pollutants are regulated as constituents of more general pollutants listed in section 108(a) (1) of the FCAA. In evaluating the environmental impacts of any control technology option, the BACT analysis shall consider all pollutants, including hazardous air pollutants.

(3) A major modification shall apply BACT for each pollutant subject to regulation under the FCAA for which it would be a significant net emissions increase at the source, excluding hazardous air pollutants, except to the extent that such hazardous air pollutants are regulated as constituents of more general pollutants listed in section 108(a) (1) of the FCAA. In evaluating the environmental impacts of any control technology option, the BACT analysis shall consider all pollutants, including hazardous air pollutants. This requirement applies to each proposed emissions unit at which a net emissions increase in the pollutant would occur as a result of a physical change or change in the method of operation in the unit.

(4) For phased construction projects, the determination of BACT will be reviewed and modified as appropriate at the latest reasonable time which occurs no later than 18 months prior to commencement of construction of each independent phase of the project. At such time, the owner or operator of the applicable stationary source may be required to demonstrate the adequacy of any previous determination of BACT for the source.