Denison
The picture on the left shows the former Denison Mill location and the related Tailings Management Areas (TMA-1 in the top right and TMA-2 in the middle right) in 1997. Quirke Lake is located in the top left.
The Denison Mine closed in 1992. During rehabilitation nearly 2.8 million cubic yards of tailings were hydraulically relocated mostly into deeper areas of TMA-1 while some tailings were placed into the underground workings. All tailings have a 3 foot water cover.
Results
Stanrock
The picture shows the final stages of construction of the Stanrock Dam A as well as the vegetative cover in 1998. A total of four low permeability till core dams were constructed in 1997 and 1998 to replace the four cycloned tailings dams.
As part of the in situ management plan the four new low permeable dams were designed to raise the water table within the tailings thereby reducing the total volume of tailings available to leach acid. A new effluent treatment plant was constructed downstream of the Dam A spillway to treat the acidic tailings water. It is expected that the treatment plant will be required for up to 50 years to treat the inventory of acid.
Improvements are already noted in the tailings water quality as the acidity levels in the influent have decreased.
