Abstract
Mine closure planning for mine-impacted water bodies requires predictive tools capable of defensibly forecasting long-term water quality under evolving hydrologic and geochemical conditions. At the Iron Crown Mine (British Columbia), Canyon Lake provides a case study demonstrating an iterative, closure-focused approach to developing a process-based water quality model to support closure design and risk management. An initial PHREEQC-based model developed in 2019 identified key uncertainties in source loading, sediment reactivity, and seasonal stratification that limited confidence in long-term closure predictions. A subsequent gap assessment informed a targeted characterization program in 2023, including expanded lake profiling, detailed sediment geochemistry, and laboratory batch experiments designed to constrain sediment-water interactions.
Batch experiments on representative shallow and deep sediments, reacted with synthetic low- and circumneutral-pH waters, were coupled with kinetic reaction path modeling to quantify mineral dissolution and precipitation, sulfide oxidation, and adsorption processes. History-matched simulations were used to derive defensible, process-based source terms, replacing empirical assumptions and reducing uncertainty in model inputs critical for closure planning.
The updated, seasonally resolved PHREEQC model incorporates a refined water balance, improved source loading estimates for tailings runoff, seepage, groundwater, and natural inflows, and geochemical controls constrained by experimental results. Model validation demonstrates that the revised configuration reproduces observed stratification and worst-case deep-water conditions. Results confirm that tailings beach runoff is the dominant closure-relevant loading pathway, with secondary contributions from oxidized shallow sediments, while deep sediments remain effectively non-reactive.
This iterative, experiment-informed modeling framework provides a defensible closure tool to evaluate long-term water quality trajectories, prioritize management of key loading pathways, and support closure design decisions to achieve water quality objectives and protect downgradient receptors.
Authors
- Laura Volden | Principal Hydrogeochemist | SRK Canada
- Dirk Kirste | Associate | SRK Canada
- Kelly Sexsmith | Principal Geochemist | SRK Canada
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