The lower basin of Coeur D’Alene River is an active Superfund site where bed sediment is contaminated by tailings runoff from historic mining operations upstream. Lead is a key index contaminant for the site. DHI assisted Jacobs with the development of a MIKE 21C morphological model for the United States Environmental Protection Agency (EPA), where the model is capable of describing the complex flows, sediment transport (including lead-contaminated sediment) and morphology in the river, lakes and floodplain. The model was calibrated to observe developments over five years and is used in the testing of various scenarios, such as hydraulic measures, sills, source control and riverbed capping.

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Challenge

The lead contamination in the lower basin of Coeur D’Alene River is a challenge for mitigation and cleanup. The reach is around 60 km long. While the river is only 80 m wide, the floodplain and lakes expand up to 1 km away from the river path with a complex flow network connecting them. The river flows into Lake Coeur D’Alene. The lead contamination, originating from mine tailings, is found over as much as 5 m of substrate in the riverbed (recreation area), in the lakes (where black swans and other migratory birds feed) and in the floodplain (where people live). The Coeur D’Alene River lower basin is classified as one of the Superfund sites – polluted locations in the United States where long-term response is needed to clean up hazardous material contamination. The EPA, responsible for managing the site, needed to test different remediation strategies.

Solution

Using MIKE 21C to test solutions before implementation

Testing remedial actions in the MIKE 21C morphological model is cheap compared to the implementation cost. Solutions could involve capping of the riverbed, construction of sills along the river to induce sedimentation of clean sediment coming from the upstream catchments, hydraulic and source control.

The hydro-morphological problem is extremely complex with eddies forming over large scour holes, small tie channels flowing to and from lakes, and floodplain flow. The problem also has large time and spatial scale variations, requiring an efficient numerical model.

The sedimentation is modelled as a graded problem with 14 sediment fractions consisting of four cohesive and three sand fractions mirrored by contaminated counterparts, with the bed substrate described by five layers. The hydro-morphological models are required to run several years when testing solutions.

Results

Identification of the most cost-effective remediation strategy among potential solutions

Better understanding of the morphology of Coeur D’Alene River lower basin

Easy-to-use tool for planning additional remedial actions until objectives are met

‘The Coeur D’Alene River lower basin required a hydro-morphological model capable of handling the inherent complexities, including hydrodynamics with flow separation, secondary flow, small tie channels connecting the river and adjacent lakes, as well as floodplain. The sediment spectrum ranges from clay to medium sand and includes clean and contaminated partitions. The hydro-morphological problem is characterised by large scale variations. MIKE 21C was deemed the best tool for the model due to its ability to handle the complexities and the run speed of the model allowed handling the long timescales that are necessary to simulate for morphological problems.’

Steve Demus, Project Manager
Jacobs (Portland, Oregon)

About the client

Jacobs Engineering Group Inc. is an American international technical professional services firm. The company provides technical, professional and construction services, as well as scientific and specialty consulting for a broad range of clients globally including companies, organisations and government agencies.

Software used

MIKE 21C

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Lead contamination cleanup at Bunker Hill Superfund site

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