HGS RESEARCH HIGHLIGHT – Improving control of contamination from waste rock piles
Broda, S., Aubertin, M., Blessent, D., Hirthe, E., & Graf, T. (2017). Improving control of contamination from waste rock piles. In Environmental Geotechnics (Vol. 4, Issue 4, pp. 274–283). Thomas Telford Ltd. https://doi.org/10.1680/envgeo.14.00023
“The flow simulations presented here were conducted with HydroGeoSphere (Therrien et al., 2010), which is a fully integrated finite element surface and subsurface flow and transport model. The basic method commonly used to numerically model variably saturated flow is the EPM approach, thereby treating the materials as continuous porous media. The main equation to be solved can then be expressed by Richards’ equation.”
Fig. 4. Conceptual layout of the simulated WRP (a) without a cover for a homogeneous representation of the waste rock (dark grey) and with (b) a horizontal cover made of compacted material (light grey) and homogeneous core (dark grey) waste rock zone, (c) an inclined cover (5%) and homogeneous waste rock zone, and (d) an inclined cover and 50 fractures in the core waste rock zone; the free drainage boundary (black line) is applied in all cases. Left and bottom boundary are impervious.
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This study conducted by researchers investigates how well compacted cover layers on waste rock piles can mitigate infiltration into these waste piles, reducing the overall potential for oxidation of sulfidic waste materials and control environmental contamination. The research provides a detailed examination of how different cover configurations and hydrogeological conditions affect the performance of these covers in mitigating risks associated with waste rock piles.
At the core of the study is the application of HydroGeoSphere (HGS), a sophisticated modelling platform, which excels in simulating complex interactions between surface water and groundwater. The HGS platform was used to model various scenarios involving different cover types—both inclined and horizontal— and their influence on water infiltration and contamination management.
The researchers utilized HGS to simulate the impact of diverse cover designs under various hydrogeological settings, focusing on parameters such as air entry values, cover thickness, and slope. This allowed for an analysis of how these factors interact to affect the infiltration of water through the waste rock piles and the subsequent potential for contamination. The study specifically evaluated the role of inclined covers, which direct water flow towards the edges of the pile, and horizontal covers, which provide a uniform barrier to infiltration.
Key findings from the study revealed that covers with higher air entry values will reduce water infiltration, which is crucial for controlling contamination. Inclined covers were shown to be particularly effective, as they guide water towards the edges and away from the core of the waste rock pile, thereby reducing the risk of contamination. The study also demonstrated that well-designed compacted covers can enhance the resilience of waste rock piles by managing runoff and minimizing the leaching of contaminants
In addition to evaluating the immediate effects of different cover designs, the study considered the long-term implications by examining historical recharge events and their impact on water movement within the waste rock piles. This aspect of the research highlighted the importance of designing covers that not only perform well under current conditions but also remain effective over time as environmental conditions change.
The study's insights provide significant value for the mining industry, offering practical guidance for the design and implementation of waste rock pile covers. By understanding how various cover designs and hydrogeological factors interact, the research provides actionable recommendations for improving contamination control and reducing environmental impact of mining operations.
Abstract:
Waste rock piles are made of heterogeneous, coarse-grained rock extracted from mines to reach the ore. The internal structure of a pile has a major impact on water and oxygen movement and hence the production of acid mine drainage or contaminated neutral drainage. This paper illustrates potential avenues to minimize the infiltration of precipitation into the core zone of rock piles by applying a compacted layer on top of each bench, made of finer-grained non-reactive waste rock. Several configurations and characteristics (without and with cover, inclined and horizontal covers, varying hydrogeological properties of the cover material) are evaluated using the numerical three-dimensional fully integrated variably saturated flow model HydroGeoSphere. In these simulations of a single bench, the compacted layer is represented as being homogeneous and isotropic while the loose core waste rock zone is represented using two approaches: (i) the classic equivalent porous media approach and (ii) a medium with randomly generated fractures to represent the effect of macropores on water flow. Short (10 d) and longer-term (1 a) simulations have been conducted with recharge events based on historic observations. The results provide guidelines for the design of efficient compacted layers leading to an improved environmental response of waste rock piles.