The cut-off wall was one part of the remediation project of the Vale mine in Thompson. To prevent the tailings from producing acid while reacting with the air, water has to cover them. As a result, the tailings dam needed to be raised and impervious to hold a hydraulic water head differential. Instead of a traditional cut-off wall such as sheet piling, a cement bentonite cut-off wall was proposed to create an impervious barrier through the existing tailing dams and the slag beneath, and anchored in the clay below.