Applying Mental Models to Qualitative Risk Assessment at the Tar Creek Superfund Site

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ABSTRACT Re-suspension of heavy metal residuals generated by former mining activities conducted at the Tar Creek Superfund site may result in exposures of nearby residents. Currently, remediation and mitigation activities include removal of yard soil containing high concentrations of heavy metals, removal of selected chat piles, and providing assistance for families with young children. Although these are important activities to reduce potential risks to Tar Creek residents, a qualitative assessment of the site that uses mental models identifies other potential contaminants of concern, transport, and exposure pathways that may require further investigation. Mental models structure judgments about hazards and risk by visually representing a contaminated site through the use of influence diagrams. A mental model was applied to the Mayer Ranch area of the Tar Creek Superfund site in Ottawa County, Oklahoma, to support a qualitative assessment of the health risks from heavy metals exposure. Documents were reviewed to develop influence diagrams illustrating the processes, interactions, and potential exposures that could subject a hypothetical individual recreating at Mayer Ranch to various health risks. The diagrams were modified to reflect expert judgments. The mental model includes four influence diagrams: source term, fate, and transport processes that may influence human health risks due to exposure to heavy metals; natural wetland processes that could remove heavy metals; net alkaline constructed wetland processes that could remove heavy metals; and potential future impacts from the removal of sediment and land development that could increase risk. Policies, regulations, and technologies that could most reduce the probability of exposures can be determined and evaluated by focusing on the environmental transport pathways and contaminants that pose the greatest potential risks and determining the difference between the risks. Also evident are the knowledge gaps with respect to the processes within wetlands.