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Update of Tier 1 Risk-Based Target Levels - 2014

In 2014, the department’s Hazardous Waste Program (HWP) will be updating 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. The update pertains only to departmental MRBCA RBTLs and not to the RBTLs in the Missouri Risk-Based Corrective Action Process for Petroleum Storage Tanks guidance document (Tanks RBCA). 

The Tanks RBCA RBTLs are being updated as part of a separate effort. That effort involves updating the Tanks RBCA guidance and incorporating the updated guidance, including the updated RBTLs, into rule by reference through a formal rulemaking. For more information regarding the guidance update and rulemaking, refer to the HWP’s Rules in Development webpage.

The MRBCA Tier 1 RBTLs were initially published in June 2006. Those RBTLs were developed based on data and methods in place at that time. Since then, the 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 1 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.

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 DHSS, 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, and the HWP will notify stakeholders and establish a schedule for a 60-day comment period during which stakeholders will be able to review and comment on the RBTLs and all associated information (e.g., toxicity, fate and transport and exposure factors; methods and equations). The notification as well as information on this page will stipulate the beginning and ending dates of the comment period and explain how stakeholders may submit their comments.

Direct questions regarding the RBTL update project to 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.