Missouri Risk-Based Corrective Action (MRBCA) - PUB2187

In 2006, the Missouri Department of Natural Resources adopted a risk-based corrective action process, detailed in the Missouri Risk-Based Corrective Action Technical Guidance. This process provides a framework for remediation decisions at contaminated sites. It protects human health and the environment, while allowing constructive current and future site use. The adoption of risk-based decision-making was initiated when the department decided to move away from using drinking water standards as the cleanup criteria for contaminated groundwater when the groundwater was not and will not be used as drinking water.

Using a risk-based process, site remediation is based on site-specific human health and environmental risk from exposure to contamination rather than the traditional application of generic standards to all sites.

If determined to be safe based on an evaluation of exposure pathways and receptors, contamination may be left in place with appropriate controls, whether engineering or institutional controls or both, to ensure long-term protection.

A risk-based framework can streamline decision making and the process of site cleanup and closure, clearly define endpoints, and focus finite resources (both private and public) on sites with the highest current or potential risks. By adopting a departmental risk-based process, the department is able to provide greater consistency in its decision-making.

Beginning in 1999 and ending in 2006, the department worked with stakeholders in the Risk-Based Remediation Rule Workgroup to develop several products to put risk-based decision-making into practice in Missouri. These products are:

Departmental Missouri Risk-Based Corrective Action (MRBCA) Technical Guidance

This guidance provides a framework for environmental professionals, both in the public and private sectors, for the process, methodologies, and key elements of risk-based corrective action.

Departmental MRBCA Rules

In 2009, the Department, with the assistance of certain stakeholders, developed a risk-based corrective action rule to codify the process and its key elements and methodologies. The rulemaking process involved both the Clean Water Commission and the Hazardous Waste Management Commission. The rule, 10 CSR 25-18.010 Risk-Based Corrective Action Process, was adopted in June 2009 and became effective on Oct. 31, 2009.

Missouri Risk-Based Corrective Action Process for Petroleum Storage Tanks and Tanks MRBCA Rule

In 2004, the department published a separate risk-based corrective action (RBCA) technical guidance for petroleum storage tank sites. The guidance was updated in Missouri Risk-Based Corrective Action (MRBCA) Process for Petroleum Storage Tanks (2013) to include updated tier 1 risk-based target levels. Both guidance documents are incorporated into rule by reference in rules 10 CSR 26-2.062, 2.078, and 2.082.

History of RBCA in Missouri

In 1995, the General Assembly passed House Bill 251, which directed the Clean Water Commission to use risk-based corrective standards to remediate underground storage tank sites. In 1999, the General Assembly passed Senate Bill 334, which directed the Clean Water Commission to develop a process to determine if risk-based remediation of groundwater was appropriate for any particular site. Although separate actions, both directives aimed to facilitate Department decisions based on a consideration of site-specific risk. Later, Senate Bill 901 (signed in 2004) gave regulatory authority for tanks, including authority for risk-based remediation rules, from the Clean Water Commission to the Hazardous Waste Management Commission.

Prior to MRBCA, the Department’s Environmental Remediation Program (ERP) used Cleanup Levels for Missouri (CALM) Guidance for voluntary cleanups of contaminated sites. The CALM guidance established a risk-based procedure for site remediation.

In response to the legislative directives and widespread stakeholder interest, the department formed the Risk-Based Remediation Rule Workgroup. External stakeholders in this group represented key sectors of Missouri’s citizenry, such as industry, private contractors and consultants, citizen organizations and state, federal and local agencies. Before developing a rule, the workgroup decided to first develop a policy approach and technical guidance. ERP coordinated this effort with input from the department’s Water Protection Program, Environmental Services Program, Missouri Geological Survey (then known as the Division of Geology and Land Survey), Missouri Department of Health and Senior Services, the U.S. Environmental Protection Agency and the RAM Group, a private contractor.

What is the MRBCA process?

A site must first be characterized, which includes identifying what contaminants are on the site, where they are located and in what amounts. This information is used to identify any risk to human or ecological receptors by comparing contaminant concentrations detected on the site to risk-based target values. The process can include up to three steps or tiers. At tiers one and two of the process, if contaminants pose unacceptable risk, the remediating party may choose to remediate by reducing contaminant concentrations to at or below applicable target levels or by controlling access and exposure to the contamination through engineering and institutional controls, or the remediating party may conduct further assessment to better define potential risks.

For site remediation, the remediating party has the option of reducing contaminant concentrations to safe levels or managing the risks through engineering or institutional controls (both of which are used to prevent people from exposure to contaminants). Although the remediating party chooses how to address excess risk, ultimately the department must guarantee the remediation is protective of human health and the environment.

What is Tiered Evaluation?

Tiered evaluations allow for increasingly refined assessments of site-specific risk. At the tier 1 level, target levels are calculated based upon various default or generic exposure scenarios. The department uses reasonable exposure scenarios to develop the tier 1 levels, rather than the most stringent and conservative scenarios. At the end of a tier 1 risk assessment, if contaminant concentrations at the site exceed the calculated target values (called risk-based target levels[RBTLs]), then the remediating party has the following options: develop a risk management plan to reduce contaminant concentrations to below the RBTLs, manage the risk through the use of engineering or institutional controls (or both) or perform a tier 2 or tier 3 risk assessment to better define the risk and develop site-specific target levels.

• A tier 2 risk assessment allows the development of site-specific target levels based on actual site characteristics.
• A tier 3 risk assessment allows more flexibility in managing risk at a contaminated site and in developing target levels.

What are the Default Target Levels?

Default target levels (DTLs) are contaminant concentrations that are the lowest of the tier 1 RBTLs for soil and groundwater for all exposure pathways and below which human receptors are protected from all complete exposure pathways for residential or other unrestricted land use. Therefore, the remediating party need not determine exposure pathways and receptors if full and complete site characterization shows the maximum contaminant concentrations at the site are below the DTLs.

What is the policy framework behind MRBCA?

• Provide default target levels
• Employ a three-tiered approach, with the first tier providing standard cleanup levels and approaches and progressing to more site-specific assessment at tiers two and three
• Applies to all environmental media - surface water, ground water, surface and subsurface soil and indoor and outdoor air
• Determine all current and future exposure pathways, including an evaluation of current and potential future groundwater use
• Provide for an evaluation of risk posed by contaminants to ecological receptors
• Use institutional controls and activity and use limitations for long-term stewardship and, by that, long-term protection from all remaining contamination
• Provide technical guidance on the process, methodologies and key elements of the risk-based corrective action framework
• Allow for existing administrative requirements under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), Resource Conservation and Recovery Act (RCRA) and other federally mandated programs

Additional Information

Departmental Missouri Risk-Based Corrective Action Technical Guidance
Missouri Risk-Based Corrective Action (MRBCA) Process for Petroleum Storage Tanks: 2013 Guidance Document Update - PUB2933
Missouri Risk-Based Corrective Action (MRBCA) Process for Petroleum Storage Tanks January 2004 (Updated March 8, 2005)
Missouri Code of State Regulations for Department of Natural Resources