Water Resources Research Act Program

Details for Project ID 2008MT166B

Modeling the Potential for Transport of Contaminated Sediment

Institute: Montana
Year Established: 2008 Start Date: 2008-03-01 End Date: 2009-02-28
Total Federal Funds: $17,000 Total Non-Federal Funds: $34,386

Principal Investigators: Joel Cahoon

Project Summary: Wetlands associated with Montana hard rock mines play a paradoxical role. The benefit of attenuating flood water and sediment has led to wetlands serving as sinks for metal precipitates and contaminated sediment. However, during high spring runoff or storm events these wetlands may become significant sources of resuspended contaminated sediments. The potential impacts to downstream groundwater, surface water, and sediment quality will affect people, and aquatic and riparian resources. As mine sites and their downstream impacts are remediated, agencies, consulting firms, and watershed groups need a method to assess the potential for mine-impacted wetlands to resuspend contaminated sediments during large spring runoff events.

The gains of removing contamination must warrant the amount of effort, funding, and site disturbance necessary to carry out the remediation. Remediation requires more than knowledge of the metals distribution. It also requires an understanding of the potential for redistribution. We will combine surface water hydrology and hydraulics with groundwater hydrology to assess the potential for resuspension of metals from a mine-impacted wetland.

By using an integrated surface water-groundwater model, we will explore the influence of spring run-off events on fluvial processes and surface water-groundwater interactions and map the probability of erosion of mine-tailings deposits for several flood stages. Our approach aims to determine the potential for resuspension and redistribution from future fluvial events. This task entails estimating the wetland hydrologic response to floods with 10, 25, 50, 100, 200 300 and 500 year recurrence intervals and analyzing output uncertainties. We will simulate runoff and wetland storage using an integrated groundwater-surface water model. The output from modeling will be a distribution of shear stress across the floodplain at each flood stage. Overlaid with metals distributions, we will map the potential for erosion of contaminated areas. The central questions to our project are:.

1. How will the magnitude and power of future spring runoff events impact the role of the wetlands in attenuating contaminated sediment?.

2. How will the fluvial processes and surface water-groundwater interactions during spring runoff events affect the transport of contaminated sediment out of the wetland complex?.

With preliminary data we expect to obtain funding to apply our approach to other mine-impacted wetlands such as those associated with McLaren, Snowshoe, and Bald Butte mines. We will demonstrate a method to assess the potential for a mine-impacted wetland to become a source of heavy metals that can be used by restorationists.