40 CFR §52.2178

1. (a)The South Dakota plan, as submitted, is approved as meeting the requirements of part C, subpart 1 of the CAA, except that it does not apply to sources proposing to construct on Indian reservations;
2. (b)Regulations for preventing significant deterioration of air quality. The provisions of § 52.21 except paragraph (a)(1) are hereby incorporated and made a part of the South Dakota State implementation plan and are applicable to proposed major stationary sources or major modifications to be located on Indian reservations.