Mo. Rev. Stat. § 444.358
No later than six months after August 28, 1989, for active metallic minerals waste management areas presently operating under a National Pollutant Discharge Elimination System (NPDES) permit, or dam safety registration, or both, or within ninety days after filing an application for an NPDES construction permit or dam safety construction permit, whichever is applied for first, the operator shall apply to the director for a metallic minerals waste management area permit. The application shall contain, but is not limited to, a schedule and plan for closure and inspection-maintenance of the waste management area, which is to be implemented when the useful operating life of the waste management area is complete or when there is permanent cessation of the operation.
§ 444.358, RSMo