Model-supported decision-making at a contaminated sediment site: Post-audit and site closure

Computer simulation models have been used to support decision-making at contaminated sediment sites for decades. Nonetheless, their reliability in remedial decision-making has been questioned, and there is a need for retrospective studies of the accuracy of model predictions, that is, post-audits. The Neal's Landfill site near Bloomington, Indiana, provides an example of the successful use of a mathematical simulation model in the selection of a remedy for a site that includes streams with polychlorinated biphenyl (PCB)-affected sediment, water, and fish. A chemical fate and transport and bioaccumulation computer simulation model was developed to compare the effectiveness of alternative remediation plans in reducing fish total PCB concentrations. A post-audit of the model, using several years of data collected after remediation, demonstrates that the model successfully predicted declines in surface water and fish tissue PCB concentrations over a decade, including those associated with longer term natural recovery processes as well as the response to remedial actions. The model predicted, and the post-audit bore out, that risk-based goals would be met using an alternative less extensive than others under consideration. An uncertainty analysis, based on bounding model calculations, provided important support for decision-making, as did the inclusion of a statistical Remedy Confirmation Clause in the Consent Decree for the site. This study demonstrates the utility of a computer simulation model to guide remedial decision-making at a contaminated sediment site. Integr Environ Assess Manag 2022;18:1233-1245. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).