(a) The North Dakota plan, as submitted, is approved as meeting the requirements of Part C, Title I, of the Clean Air Act, except that it does not apply to sources proposing to construct on Indian Reservations.

(b) Regulation for preventing of significant deterioration of air quality. The provisions of § 52.21 except paragraph (a)(1) are hereby incorporated and made a part of the North Dakota State implementation plan and are applicable to proposed major stationary sources or major modifications to be located on Indian Reservations.