The mining industry extracts material that typically contain sulfide minerals, which can lead to metal leaching and acid rock drainage (ML-ARD), also referred to as acid and metalliferous drainage (AMD).
ML-ARD risk arises from the presence of these materials at a mine site within tailings storage facilities (TSFs), mine rock stockpiles (MRSs), ore and low-grade ore stockpiles (LGOs), heap leach pads (HLPs), exposed pit walls, and underground workings[1]. This presentation focuses on application of ‘lived experiences’ in respect of mitigating ML-ARD risk for design, construction, and performance of TSF and MRS landforms, both of which are unsaturated systems. Further, this presentation discusses ‘lived experiences’ for design, construction, and performance of cover systems, which are placed on these landforms, for mitigating ML-ARD risk. These cover systems, also unsaturated systems, are the building blocks for achieving future, or returning, land use, and providing a stable, reliable, and sustainable interface between a mine landform and the environment.

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Two foundational ‘imbalances’ are created when a material that was below surface, is placed on the surface within a TSF or an MRS; a gravitational imbalance and a thermodynamic imbalance. The thermodynamic imbalance results from material that was in a reducing environment for the most part (i.e., a lack of oxidants, such as oxygen), is placed into an oxidizing environment (i.e., in an MRS or TSF). The gravitational imbalance results from meteoric water, as well as groundwater and run-on, landing on, and/or coming
into / on to the mine landform. The system (the landform) continuously works from a state of higher potential energy to lower potential energy. Hence, a cover system ‘works’ in concert with the landform on which it is placed to manage risk from creation of these two foundational imbalances (i.e., manages ingress of oxygen and limits meteoric water and run-on from entering the landform). MRSs and TSFs constructed with a focus on source control also facilitate managing these two foundational imbalances.

The ‘lived experiences’ are summarized in a conceptual model methodology for MRS and TSF landforms, as well as cover systems, which can be applied and updated throughout the mine lifecycle, but ideally, started during project development when key strategic decisions are being made. The conceptual model methodology is incorporated into a repeatable, and formal, decision-making process that allows for transparent reduction of uncertainty, and increase in engineering controls (or both), all in the context of a source-pathway-receptor risk management framework.

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The conceptual model methodology provides an appropriate basis to ensure that numerical modelling is focussed on enhancing the conceptual model’s alignment to site-specific conditions, and comparing designs, to allow the conceptual model to remain as the primary communication tool for performance expectations. Multi-decade performance monitoring of in-service MRS and TSF landforms, as well as monitoring of cover systems on these landforms, is used to illustrate the conceptual model methodology and decision-making framework.

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The field performance data and conceptualization of performance illustrate that risk-based decisions, informed by physical, chemical, and biological mechanisms, which are influenced by site-specific controls, lead to application of proven technology and sustainable landforms for future climate change scenarios.

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Key words: Land Use, Climate and Climate Change, Cover Systems, Proven Technology, Landforms, Water Balance, Water Quality, Risk-Based Decisions, Adaptive Management

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[1]  Senior Technical Advisor, Okane Consultants, Suite 1000, 7 Ave. SW, Calgary, AB T2P 5L5.

[2]  INAP, 2019. International Network fort Acid Prevention (INAP) ARD/AMD Source Control for Mine Rock Stockpiles Phase 1, prepared by Okane Consultants, November 2019.

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