Cleaning a contaminated lake with DOP150

In the Canadian Northwest Territories, a large-scale sediment clean-up project has started. The project aims to remove contaminated sediment from a lake. Mill Lake and its surroundings were polluted by mining activities in the middle of the last century. The contractor opted for a DOP150 submersible dredge pump, which cleans the lake bottom and pumps the contaminated material into Geotubes.

Uranium mining site

The location of the dredge project is a remote, abandoned mining site, situated on the lands of the First Nation Tłı̨chǫ people. In the late 1950s the area was used to mine uranium. The mining activities were short-lived, but the contamination remains. The Canadian Government has started a large clean-up operation; the Kwetı̨ı̨ɂaà (Rayrock) Mine Remediation Project. Part of this project is to remove the sediments of the lake and store them responsibly. The project started in early 2023 with the construction of a winter road to the Rayrock sites, followed by site organisation and commissioning, and gradually moving on to the remediation works.

Dredge pump set-up

The contractor has an excavator with DOP pump on site, located on a pontoon. The DOP150 is a hydraulically driven submersible dredge pump, fitted with a flat bottom head. The DOP slurry pump is powered by a separate hydraulic power pack, located on the pontoon behind the excavator. The excavator, a John Deere 300G, lowers the DOP pump to the correct dredging depth and moves the sub pump onboard when required.

Natural area

The main challenge of the dredging operations is not the sediment removal itself – dredging at a maximum of 5 metres is no real challenge for a DOP dredge pump. The removal of contaminated sediment is well-monitored for both layer depth and resuspension. The real challenge is the debris at the bottom of the lake; branches of all sizes have accumulated at the bottom over the years. When the suction head passes, the branches get stuck in its suction openings. This slows down the cleaning operation. Yet, as the mesh size of the drag head grid is smaller than the ball passage of the dredge pump, the vast majority of the debris can be removed from the grid.

DOP pumps fills Geotubes

The DOP dredge pump is connected to an approximately 350-meter length discharge pipeline. This discharge line leads to a dedicated storage area, the so-called Confined Disposal Facility. Here, dozens of Geotubes are filled with the contaminated sediments and the process water is captured and treated before being returned to the environment. When the lake has been cleaned, the Geotubes will be covered and capped, ensuring the contamination is effectively contained. The Mill Lake basin will be reclaimed using strategies jointly developed with the Tłı̨chǫ Government, with the overall objective of returning the area (as much as possible) to pre-development conditions to allow future Tłı̨chǫ generations to carry out traditional activities in this area of outstanding natural beauty.