Groundwater Recovery Since the End of Dewatering in 2019 at the Former Victor Diamond Mine

The former Victor Diamond Mine is situated in the James Bay Lowlands of northern Ontario, approximately 90 km west of the community of Attawapiskat and 120 km east of the Ring of Fire. Mining the diamond-bearing kimberlite pipe necessitated the creation of an open pit through approximately 270 m of largely permeable sedimentary bedrock down to the top of the crystalline basement. Open pit mining through this layered and occasionally karstic bedrock was only feasible thanks to the operation of a ring of large-diameter dewatering wells encircling the open pit. These dewatering wells operated continuously from 2007 to 2019, pumping an average of about 75,000 m³/day to maintain dry working conditions in the pit. After reaching the intended mining depth, the dewatering wells were decommissioned, and the pit began to passively fill with groundwater. Passive pit lake development was initially swift but was projected to take 15 years to achieve equilibrium. To meet the ambitious closure goals for the mine and overcome various project constraints, existing pumping infrastructure was repurposed to actively fill the open pit with water sourced from a nearby river, thereby accelerating the development of the pit lake and the recovery of the aquifer. With the implementation of the rapid filling system, the lake attained the predicted steady-state elevation by late 2022. In 2025, groundwater levels in the region will be nearly fully recovered, and reclamation activities at the mine will be complete. This paper follows on from a paper describing dewatering at the mine from 2007 to 2018 (Gautrey, 2018) and will detail the aquifer recovery and the return of the natural groundwater flow patterns around the former mine.