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The Environmental Remediation Program (ERP) has updated the Missouri Risk-Based Corrective Action, or MRBCA, guidance document published in 2006. The draft guidance is being offered here for public comment as provided for in the MRBCA rule (10 CSR 25-18.010).

The MRBCA rule became effective on Oct. 30, 2009.  Both the rule and the guidance are used to guide the investigation, risk assessment, and cleanup of contaminated sites.  Most sites to which the rule and guidance have been and will be applied are enrolled in the ERP’s Brownfields/Voluntary Cleanup Program. 

The MRBCA process includes Risk-Based Target Levels (RBTLs) that are conservative, default cleanup levels used to guide site investigation, determine whether contaminant levels at a particular site require cleanup, and determine when sufficient cleanup has occurred.  The RBTLs published in 2006 were based on information current at the time.  Since that time, certain toxicological properties and data evaluation methods used to develop the RBTLs have changed, and the vapor intrusion exposure pathway has become an even more important aspect of site investigations, risk assessment, and cleanup.  As a result, the RBTLs published in 2006 are out of date and need to be updated.  In addition, since 2006, the ERP has identified needed clarifications in the MRBCA guidance and determined that a revision of the guidance is warranted.

Update and Revision Process
To update the RBTLs and revise the guidance document, the ERP assembled a stakeholder group.  The group was tasked with working with the department to update the RBTLs and revise the guidance.  Starting in December 2015, the stakeholder group met four times to give input on the preliminary revisions to the guidance. An initial draft of the revisions was completed in 2018 and made available to the stakeholders for a 90-day review and comment period. The stakeholder group met a final time in January 2019 to discuss their comments, and a final draft of the revised guidance was completed addressing stakeholder comments and incorporating other relevant information developed during the revision process.

Public Comment, Finalization, and Rulemaking
The final draft will be subject to a 60-day public comment period, which is required for any significant changes to MRBCA  in accordance with 10 CSR 25-18.010(23).  In addition, the updates to the RBTLs and the guidance will require changes to the MRBCA rule (the structure of which closely follows the structure of the guidance), so a formal rulemaking will be required to amend the rule. The ERP anticipates that the rulemaking will be initiated shortly after the 60-day public comment period and any additional guidance revisions made in response to public comments. This schedule should have the updated RBTLs, revised guidance, and amended rule in place and effective in late 2020.

Summary of Major Changes

  • Changes to the Risk-Based Target Levels (RBTLs) due to changes in chemical toxicity, models and inputs
  • The addition of over 450 new potential Constituents of Concern (COC)
  • The elimination of soil types
  • The elimination of RBTLs for the soil to indoor air pathway
  • The definition of surface soil will change from 0-3 feet below ground surface (bgs) to 0-2 feet bgs
  • Additional emphasis and guidance on the vapor intrusion pathway
  • Additional guidance on using separation distances to eliminate the vapor intrusion pathway for petroleum COCs
  • Additional guidance on cumulative risk, expanded application of cumulative risk, and the Missouri Department of Health and Senior Services’ (MDHSS’s) development of a cumulative risk calculation spreadsheet for use by remediating parties
  • The RBTL for trichloroethylene in indoor air is premised on potential chronic health effects, not potential short-term fetal development effects. This will not affect the indoor air RBTL, but will allow more options in response and risk management
  • The hexavalent chromium RBTL will incorporate an alternative toxicity value approved by the MDHSS
  • The RBTLs for protection of construction workers working below ground will be calculated using the State of Virginia Construction Worker Trench Model
  • For sites with sufficiently large data sets, the 95% Upper Confidence Limit (UCL) will be used instead of an arithmetic average for calculating representative concentrations
  • Allow use of certain passive vapor sampling and analysis techniques for quantitative evaluation of vapor intrusion potential and associated risk.
  • Updates to the ecological risk checklists 

Stakeholder Group Documents, Meetings, Agendas and Minutes


  • No announcements at this time