Mo. Rev. Stat. § 701.035
Sections 701.025 to 701.059 shall not prohibit the enforcement of ordinances of political subdivisions establishing a system for the regulation and inspection of on-site sewage disposal contractors and a minimum code of standards for design, construction, materials, operation and maintenance of on-site sewage disposal systems, for the transportation and disposal of wastes therefrom and for on-site sewage disposal systems servicing equipment, provided such ordinance establishes a system at least equal to state regulation and inspection. Nor shall sections 701.025 to 701.059 be interpreted so as to preempt any private right of action which might otherwise exist. Nothing in sections 701.025 to 701.059 shall be construed to prohibit a political subdivision from enacting and enforcing standards which are more stringent than the provisions of sections 701.025 to 701.059 and rules promulgated pursuant thereto.
§ 701.035, RSMo