A coupled hydrodynamic-biogeochemical model for the prediction of mine pit lake water quality
- Lorax Environmental Ltd., Canada (maryam.zarrin@lorax.ca)
Pit lakes are a common feature of the post-closure landscape at mine sites where mining voids are allowed
to fill with surface runoff, direct precipitation, and groundwater. Pit lakes also commonly serve as focal points
for post-closure water management, often serving as a receptacle for various mining-related drainages and
the final point of discharge for mine effluents. Therefore, an accurate and acceptable numerical model
capable of predicting pit lake water balance, mixing characteristics, and water quality is needed to support
post-closure management. In this paper, a coupled hydrodynamic-biogeochemical model (PitMod) for water
quality prediction is described. The model, described in Crusius et al. (2002) and Dunbar (2013), simulates
the physical and geochemical evolution of pit lakes over pit filling times ranging from monthly to century time
scales. Within PitMod, the pit lake is approximated based on a one-dimensional, horizontally averaged
vertical layer scheme. PitMod calculates the time-dependent vertical distribution of physical and geochemical
pit lake properties, including temperature, salinity, conductivity, and dissolved oxygen. In this regard, the
physical component of PitMod considers the effects of pit morphology, climate data, multiple surface and
sub-surface (groundwater) inflows/outflows, precipitation/evaporation, surface ice formation/melting, vertical
mixing due to surface wind stress, convective circulation, and turbulent mixing. The geochemical portion of
PitMod utilizes a customized version of PHREEQC, capable of a wide variety of aqueous geochemical
calculations, including speciation, saturation index calculations, mineral equilibria, surface complexation
(adsorption) reactions, ion exchange, and redox processes. The model can also incorporate predictions of
dissolved metal scavenging by biogenic particles in response to lake primary production.
PitMod, which has been applied at over 50 mine projects since 2002, incorporates physical processes like
those found in other lake models such as DYRESM (Imerito, 2007), and has been validated against field
observations. However, unlike DYRESM, PitMod offers the advantage of being able to incorporate various
non-conservative geochemical and biological processes that are relevant to predictions of long-term water
quality.
How to cite: Zarrinderakht, M., Salvador, S., and Martin, A.: A coupled hydrodynamic-biogeochemical model for the prediction of mine pit lake water quality, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1188, https://doi.org/10.5194/egusphere-egu23-1188, 2023.