In 1974, when Oskar Steffen, Andy Robertson, and Hendrik Kirsten established SRK in Johannesburg, South Africa, mine water quality management acid mine drainage (AMD) was emerging as a major concern for sustainably managing mine sites. A few years after SRK established its office in Vancouver, British Columbia in 1979, SRK became very involved in helping the provincial government develop technical guidance for prediction, prevention, control and treatment of AMD, or acid rock drainage (ARD) as it was recoined by Andy Robertson to reflect that acidic drainage can develop under conditions when sulphidic mine waste is exposed. A major push at the time was to prevent ARD at new mines by incorporating the technical solution of water covers into mine design, often by the construction of earthen impoundments. This resulted in nearly stopping oxidation of sulphide minerals due to the low concentration of oxygen in water compared to air but also led to the need for permanent management of structures to ensure the water cover remained intact forever.
However, since the mid-2010s, the mining industry has experienced several high-profile failures of dams which has highlighted the risk of using impoundments to permanently manage saturated mine wastes. This has resulted in the commitment of the industry to phase out permanent water covers and renewed focus on mine waste management to prevent ARD and related metal leaching (ML) without relying on saturation to limit oxygen availability. The preferred technology of dry covers has become very well developed to the point now where covers can achieve very low oxygen concentrations in wastes. Nonetheless, the question needs to be asked whether this approach achieves permanent prevention of the need for active management of water quality rightfully demanded by the long term users of the lands impacted by mines. In many cases, there is confidence covers will be intact for decades to centuries but these time frames do not consider use of the lands and geological processes in landscapes which span thousands to millions of years. The real solution to mine waste management to limit the potential for long term water quality effects is to adopt technologies that result in the perpetual slow release of potential contaminants of concern (PCOCs) or result in substantial depletion of the PCOC in parallel with slow failure of the technology. It is possible that covers can achieve this objective but there are greater opportunities with co-disposal technologies, optimization of mine workings to allow saturated disposal, and appropriate use of natural water bodies without dams.
As an example, SRK has been working with several clients for over a decade to implement blending of acid generating and acid consuming waste rock such that the resulting mixture not only is non-acid generating on balance but also limits accelerated weathering associated with the acid generating components such that PCOC leaching occurs slowly. Properly implemented, this technology can achieve the goal of slow steady leaching without long term active management.
