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Lindstrom, K., K. Marini, and D. Dahlstrom.
10th International Conference on the Remediation and Management of Contaminated Sediments, 11-14 February, New Orleans, LA, 24 slides, 2019

Complex features, including a partially penetrating river controlled by a dam and uncertain future operation of the dam in a developed urban setting, necessitated a modeling tool to aid in evaluation of remedial alternatives at a former manufactured gas plant in Flint, MI, An existing MODFLOW-SURFACT™ model was updated and calibrated with site characterization data to create a robust tool for evaluating past, current, and potential future conditions. Remedial alternative scenarios were run with the fifty parameter sets, and concentration, and mass flux results were compared between scenarios using the range of results to quantify the uncertainty of model estimates. Based on the modeled groundwater flow and solute concentrations from Null Space Monte Carlo (NSMC) uncertainty analysis, two dredging and capping alternatives were carried forward in a feasibility study, and a uniform, impermeable cap was ultimately selected for design. Modeling results indicated the impermeable cap would be effective at limiting groundwater discharge to surface water from the areas of greatest groundwater impacts, and groundwater flow paths to post-remedy surface water discharge locations would be lengthened after cap installation. Concentrations are expected to attenuate along the lengthened flow paths prior to discharge to surface water. Informed by the NSMC analysis, a monitoring plan was developed to assess compliance with cleanup criteria following the sediment response action and included areas of greatest uncertainty.

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