HGS RESEARCH HIGHLIGHT - Integrated surface-subsurface water and solute modeling of a reclaimed in-pit oil sands mine: Effects of ground freezing and thawing
Nagare, R.M., Park, Y.-J., Wirtz, R., Heisller, D. & Miller, G. (2022). Integrated surface-subsurface water and solute modeling of a reclaimed in-pit oil sands mine: Effects of ground freezing and thawing. In Journal of Hydrology: Regional Studies (Vol. 39, p. 100975). https://doi.org/10.1016/j.ejrh.2021.100975
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We’re happy to highlight this new study published by our friends at ARKK Engineering and the University of Waterloo. The paper presents the results of integrated hydrologic modeling to demonstrate the role of soil freeze-thaw in hydrological response of reclaimed oil sands landforms. In this case the proposed land-reclamation involved backfilling an open-pit mine with a mixture of tailings materials. The upland portion of the reclaimed land is made-up of a series of hummocks forming a gently sloping hummock/swale system which should direct water flow to a low-lying area connected to the reclaimed landform outlet. The entire system is discretized into 13 numerical layers, and over 1.1 million computational nodes.
Figure 1: Study Area and Conceptual Model of the Reclamation Setting
This model provides a terrific overview of the features offered by HydroGeoSphere in support of water resources challenges in the mining industry, incorporating fully-integrated surface and groundwater flow, solute transport, and thermal energy transport.
The HydroGeoSphere model presented here was able to successfully simulate the water balance and water quality response of the reclaimed landforms, and the results indicate that the impact of winter processes (i.e., pore-water freeze/thaw) on infiltration and surface runoff are significant. Including freeze-thaw resulted in reduced infiltration during spring melt and reduced salt loading during winter. In total, a 20% reduction of chloride mass release (over an 8-year period) was simulated when freeze-thaw processes were included in the simulations. These results provide a strong argument for the inclusion of winter processes and coupled heat dynamics for detailed studies of integrated hydrologic processes in the Athabasca Oil Sands region.
Figure 2: Runoff hydrograph for simulations with and without pore-water freeze/thaw.
Abstract:
Study region: Athabasca Oil Sands, Alberta, Canada.
Study focus: The upland and wetlands substrate in reclaimed oil sands landforms will be constructed of post-mining materials with an objective of replicating the landscape and hydrology of the surrounding boreal systems. Porewater in these materials contain elevated levels of salts and other solutes. Water quality will govern the success and sustainability of the reclaimed landscape. Tightly coupled water and heat dynamics control water and solute movement in boreal systems. We used three-dimensional integrated surface-subsurface flow and chloride transport models with and without ground freezing-thawing to compare performance of an in-pit oil sands mine currently being reclaimed.
New hydrological insights for the region: Transient simulations under wet/dry climate cycles suggest that the reclaimed landform will shed water only during wet years. Annual water balance with and without coupled heat dynamics is identical. However, the three-dimensional representation of ground freeze-thaw results in reduced snowmelt infiltration, summer groundwater table, and solute release during winter. The outcome is increased spring runoff, 20% decrease in chloride mass release over simulated eight-year wet climate cycle and relatively reduced summer runoff. The model results suggest that (1) coupled heat dynamics should be considered for detailed evaluation of reclaimed in-pit landforms at finer time scales, and (2) modeling reclaimed landforms without freeze-thaw provides conservative annual solute release estimates, which is appropriate for coarse site-wide models.