The April 2006 Departmental MRBCA technical guidance document was updated in June 2006 and June 2008. Information about any additional updates, revisions and rulemaking will be provided below when they become available.
Current Updates
The MRBCA Tier 1 RBTLs were initially published in June 2006, and 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. EPA also made changes to some of the generally applicable methods and equations used to develop EPA's regional screening levels (RSLs). The 2006 RBTLs were developed using some, but not all, of the EPA data evaluation methods and equations.
This update of RBTLs relies on EPA current methods and equations, as well as the EPA input values for toxicity and exposure factors. As a result, the updated RBTLs will be much more consistent with EPA RSLs. However, the RBTLs for carcinogenic chemicals will be based on an individual excess lifetime cancer risk (IELCR) level of one in 100,000 (1x10-5) rather than the one in one million (1x10-6) IELCR level used by EPA. This effort will ensure RBTLs are based on current science and are accurate, protective and defensible. Updating RBTLs also 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 corrects historical errors and inconsistencies, clarifies certain provisions, expands on issues not adequately addressed in the 2006 guidance, eliminates redundant text and is restructured to improve readability. Certain issues in the updated guidance were updated by the department’s Environmental Remediation Program (ERP), such as ecological risk screening/ assessment, hot spot identification and management and collection of soil geotechnical data. Certain other issues were updated by ERP in coordination with the Department of Health, with consideration of the MRBCA Stakeholder Group comments previously received on initial draft updates to the guidance. This includes issues such as updating the RBTLs, selecting COCs for risk assessment, evaluating cumulative risk and various vapor intrusion-related issues.
Updating the RBTLs was a cooperative effort between the Department of Natural Resources and the Department of Health. The Department of Health had the main knowledge and expertise to calculate the updated target levels for risk assessment purposes. The Department of Natural Resources had the knowledge and expertise needed to appropriately apply the target levels for risk management. These complimentary functions help to ensure the updated guidance is useful for both risk assessment and risk management.
As part of the MRBCA update process, the Department of Health is preparing software that can be used in Tier 2 and Tier 3 assessments when changes to default assumptions are proposed by eligible Brownfields/ Voluntary Cleanup Program facilities. This software will be made available on this webpage when completed. The draft updated RBTLs and associated tables of input parameters and equations will be available as part of the revised guidance.
For questions regarding the RBTL update, guidance revision, rulemaking project, please contact the Department of Natural Resources' Brownfields/ Voluntary Cleanup Program at 573-526-8916 or by email at MissouriBrownfields@dnr.mo.gov. To receive MRBCA update email notifications, please use the green “Get Updates on this Issue” button on this webpage.
