S.D. Codified Laws § 34A-10-2
If administrative, licensing, or other proceedings, and judicial review thereof are available by law, the agency may permit the attorney general, any political subdivision of the state, any instrumentality or agency of the state or of a political subdivision thereof, any person, partnership, limited liability company, corporation, association, organization, or other legal entity to intervene as a party on the filing of a pleading with the agency asserting that the proceeding or action for judicial review involves conduct which has the effect of polluting, impairing, or destroying the air, water, or other natural resources or the public trust therein. Such pleading shall be filed at least three days before the last agency evidentiary hearing conducted before the issuance of a final decision.
SDCL 34A-10-2