Mo. Rev. Stat. § 260.573

If the provisions set forth in sections 260.565 to 260.575 and any rules promulgated thereunder are met, and the applicant has remitted all applicable participation fees, the department shall issue, to the applicant, a letter stating that no further action need be taken at the site related to any contamination identified in the environmental assessments and for which remedial action has been taken in accordance with the approved remedial action plan. Such letter, however, shall provide that the department of natural resources may require the person to conduct additional environmental site assessments or remedial actions in the event that any monitoring conducted at or near the real property or other circumstances indicate that additional contamination is present which was not identified by the environmental site assessments or for which remedial action was not taken according to the remedial action plan.