Abstract
Pit lakes are an end product of open pit mining and may contain saline or acidic water that can create environmental damage if left unmanaged. Pit lakes are characterized by large depth and a low surface area which creates favourable conditions for meromictic (non-mixing) systems.
This study presents a pit lake located in Northern Canada that initially filled with runoff and groundwater in the late 1990s upon closure of a lead-zinc mine, forming a two-layer freshwater-brackish water meromictic system. The pit lake currently serves as a common collection point of mine-impacted water that is then treated and discharged into the environment. Of interest in this study is the evolution of the pit lake since formation and new efforts to continually manage the pit waters.
18 years of CTD profiles (2004-2022) and two years of measurements with thermistor and conductivity chains (2020-2022) follow the evolving structure of the pit lake. Initially a meromictic system, active management of the pit lake through water treatment and pumped saline inflows eroded the chemocline in 2014 resulting in a complete mixing event. This mixing event transformed the pit lake into a brackish dimictic system, typically mixing in October and again in April-May after ice-off. As salinity continues to increase and acidification of the pit waters intensifies, treatment of the pit water becomes more complex and has garnered interest to re-establish meromixis to isolate saline water
Author and Presenter:
Mark Sumka | SRK Consulting Vancouver, Canada
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