State facility permits are issued to facilities that are not considered to be major (as defined in the department's regulations), but that meet the criteria of Subpart 201-5. These are generally large facilities with the following characteristics: ... They require the use of permit conditions to limit emissions below thresholds that would make them subject to certain state or federal requirements ...
So I see it as a minor project being treated as major by virtue of meeting criteria in Subpart 201-5. That is met by virtue of the CO, NOx, and SO2 emissions (at minimum) that are defined as criteria pollutants and therefore regulated air pollutants.