Abstract
A hydrodynamic and water quality model was developed for a pit lake located on a mine site in Northern Quebec, Canada. The purpose of the study was to understand the long-term effects of storing Potentially Acid Generating (PAG) waste rock in the pit that will be flooded as part of the closure plan. During mine closure, the waste rock will be disposed into the open pit and then the pit will be filled with natural runoff and direct precipitation. During initial pit filling, water fills the pore spaces of the waste rock until the waste rock becomes saturated. As filling continues, there are diffusive fluxes between the submerged waste rock and pit water column. The model simulations were completed with timeframes up to 100 years into post closure to determine:
- Whether the pit lake water column will turn over or remain stratified, thereby isolating mine-influenced water from mixing with surface water in the pit lake;
- Upward flux of chemically charged porewater to the pit lake from the submerged waste rock; and
- Pit Lake water quality over time.
The PAG waste rock disposed in the pit presented additional complexity and challenge in developing the hydrodynamic model. This study presents the approach used to overcome this challenge.