Beginning in 2015, the department’s Hazardous Waste Program (HWP) began an effort to:

  • Update the Tier 1 Risk-Based Target Levels (RBTLs) found in Tables B-2 through B-10 of the Missouri Risk-Based Corrective Action (MRBCA) guidance document
  • Revise the MRBCA guidance document
  • Amend 10 CSR 25-18.010 consistent with updating the RBTLs and revising the guidance

The update, revision and rulemaking pertains only to the departmental MRBCA RBTLs, guidance, and rule and not to the Missouri Risk-Based Corrective Action Process for Petroleum Storage Tanks guidance document (Tanks RBCA).

The MRBCA Tier 1 RBTLs were initially published in June 2006. They were developed based on data and methods in place at that time. Since then, the U.S. Environmental Protection Agency (EPA) has updated toxicity data for numerous chemicals. In addition, EPA has made changes to some of the generally applicable methods and equations they use to develop its regional screening levels (RSL). The 2006 RBTLs were developed using some of the EPA methods and equations. This update of RBTLs will rely more strongly on EPA methods and equations as well as the EPA input values for toxicity and exposure factors. As a result, updated RBTLs will be much more consistent with the EPA RSLs, although the RBTLs for carcinogenic chemicals will be based on an individual excess lifetime cancer risk (IELCR) level of one in 100,000 (1x10E-05) rather than the one in one million (1x10E-06) IELCR level used by EPA.

This effort will ensure RBTLs are based on current science and are accurate, protective and defensible. In addition, updating RBTLs is consistent with the department’s intention to periodically revisit and revise MRBCA guidance to ensure the document remains current, as discussed in Appendix A of the guidance.

The MRBCA guidance revision will involve correcting errors and inconsistencies, clarifying certain provisions, expanding on issues not adequately addressed in the 2006 guidance and eliminating redundant text and restructuring the guidance to improve its readability.  In addition, the Missouri Department of Natural Resources' HWP proposes to address various specific technical issues associated with the guidance.  Some of these issues – such as ecological risk assessment, hot spot identification and management and collection of soil geotechnical data – will be addressed by the HWP, while others – for instance, updating the RBTLs, selecting COCs for risk assessment, evaluation of cumulative risk and various vapor intrusion-related issues – will be addressed jointly by the HWP, the Department of Health and a MRBCA stakeholder group.

Updating the RBTLs is a cooperative effort between the department and the Department of Health and Senior Services (DHSS). The knowledge and expertise required to calculate target levels resides within the Department of Health and Senior Services, whereas the knowledge and expertise needed to appropriately apply the target levels resides within this department. These complimentary attributes are beneficial to this project and will help to ensure the resulting products are of the highest quality.

When they become available, the draft updated RBTLs and associated tables of input parameters and equations will be available on this webpage, as will revised guidance. 

To join the stakeholder group or for questions regarding the RBTL update/guidance revision/rulemaking project, please contact Tim Chibnall of the HWP by email or call 573-522-1833. In addition, you may register to receive updates regarding this effort by clicking on the red envelope on the right side of this page and providing the information requested.