Indiana Code Title 13. Environment § 13-15-7-2

(1) Additional federal requirements become applicable to a source whose permit allows at least three (3) more years of continued operation.  However, a permit does not have to be revised if the additional requirements will not become effective until after the date the permit expires.  A permit revision to address additional requirements must be completed by the commissioner not more than eighteen (18) months after the adoption of the additional requirements.

(2) Additional requirements become applicable to the permitted source under the acid rain program.  Upon approval by the United States Environmental Protection Agency, an excess offset emissions plan is considered to be incorporated into the permit.

(3) The commissioner or the United States Environmental Protection Agency determines that:

(4) The commissioner or the Administrator of the United States Environmental Protection Agency determines that the permit must be revised or revoked to assure compliance with the applicable federal requirements (as defined in 40 CFR 70.2).