Stratos Inc. was retained by the Mine Environment Neutral Drainage (MEND) program to assess the impacts of climate change on acid rock drainage (ARD) at Canadian mines. Stratos retained the technical expertise of Brodie Consulting Ltd. for this project.
Climate change poses a number of risks to mining operations. Extreme weather events and changes in precipitation patterns may lead to interruptions in production and damage to mining infrastructure. Permafrost degradation and increases in precipitation may compromise the integrity of waste containment structures such as dams and tailings covers. Drought conditions may lead to a shortage of water required for processing and waste management (e.g. water covers). Climate change may also affect energy and transportation infrastructure on which the mining sector depends to deliver electricity, labour, supplies, and to ship product.
This assessment focuses on risks associated with acid rock drainage and metal leaching (ARD/ML) produced by mining activities. ARD/ML occurs when minerals containing metals and sulphur (sulphides) come in contact with both air and water. At mine sites, the prevention and management of ARD includes the management of water, tailings and waste rock. Therefore, the climate change risks related to ARD arise from the impacts that a changing climate has on water management structures and activities, on waste impoundment structures, and on the hydrologic/hydrogeologic/ geochemical conditions affecting the flow of water and contaminants at mine sites.
Mining activity occurs across Canada, so mining operations will be exposed to the broad range of regional impacts that are projected by climate models, including more pronounced impacts in the north (due to arctic amplification). Previous studies on climate change impacts in Canada identified a range of potential impacts for the mining sector, including impacts related to ARD. This assessment builds on previous work by looking more closely at the impacts for specific infrastructure elements and determining which of these impacts are most likely and significant for mining operations and for society.
This assessment is a high-level risk analysis and not a detailed technical study. The findings are based on the professional judgment of a multi-disciplinary team (engineering, sustainability, finance). A small set of interviews with technical experts was also conducted. The assessment included a review of recent reports on the impacts of climate change in Canada, and more specifically on climate change and the mining sector. Risks were identified by imposing climate change conditions (2050s projections) onto the mining infrastructure and activities most relevant to the prevention and management of ARD. Indicative estimates of cost impacts were developed for some relevant and more likely scenarios – presented in terms of net present value.
The following conclusions arise from our review and analysis:
Operations – Impact on Activities and Infrastructure
Many of the effects of climate change, with the notable exception of extreme weather events, will be incremental – small changes over long periods of time. Based on current climate change projections for Canada, mining operations that are active today or that are being planned or constructed today will be able to adapt, through changes in management practices or modest capital investments, to most of these incremental environmental changes over the next 25 to 30 years. This observation is based on our view that during the operation phase of these mines, changes in the environmental parameters (temperature, precipitation, permafrost) that inform the design of key structures relevant to ARD (i.e. covers, dams, treatment systems, and other water management structures) will not change sufficiently to increase ARD or lead to significant changes in the strategies to prevent ARD. As the impacts of climate change will vary between regions, mines will be impacted differently and to varying degrees.
More frequent heavy precipitation events are projected for Canada (NRCan, 2008; NRTEE, 2010). There is a risk that hydraulic structures at mine sites (dams, ditches, spillways, holding ponds) will have insufficient capacity for such events resulting in more contaminated runoff from the mine site or in other temporary measures being taken, such as flooding pits, which could result in shutdowns. Based on our analysis of the net present value of a hypothetical copper mine in Canada, such shutdowns alone would not make the mine uneconomical but could have a significant impact on the bottom line. While new dams are designed using the most recent climate projections (which include climate change impacts), existing dams may be vulnerable over the long term. The literature reviewed for this assessment suggests that more research is required to determine the impacts of climate change on probable maximum precipitation (PMP) and probable maximum flood (PMF) values that are used in dam design.
Closure – Impact on Activities and Infrastructure
Of greater concern are the impacts of climate change on post-closure infrastructure required for the long-term or ‘perpetual’ storage and containment of tailings and other contaminants – including tailings covers and dams. These impacts add to the existing policy and technical challenges of ensuring the long-term integrity of mine sites post closure.
Our assessment indicates that most types of covers (simple soil covers, store and release, water, permafrost, geo-synthetic) are vulnerable to climate change to various degrees. Geo-synthetics are the least susceptible to the direct effects of climate change . Permafrost degradation in permafrost covers could lead to increased percolation into the waste layer. Changes in rainfall patterns, evapotranspiration, and temperature will impact vegetation on covers. More precipitation and wetter conditions may result in increased percolation into the waste layer of store and release covers and compromised permafrost covers leading to increased flushing of contaminants (ARD) and release to the environment. In regions in which more periods of drought are projected, there is an increased risk of exposure of tailings to air and increased ARD, although this can be managed with minor adjustments to the depth of a water cover. In regions where positive water balances are projected with climate change, water covers may be no more vulnerable to climate change than geo-synthetic covers.
Based on our analysis the scenario with the greatest cost impact for a mining operation involves the use of a geo-synthetic cover instead of a more conventional cover to avoid potential impacts due to climate change. The magnitude of this cost increase would depend on the size of the mine and of the tailings impoundment. Based on our analysis of the net present value of a hypothetical copper mine in Canada, the incremental cost of adaptation could represent on the order of a 20% reduction in NPV.
Cost and risk implications for mine operators and regulators/society will vary depending on how the vulnerabilities of waste covers or other structures are addressed. If the selected cover design is poorly adapted to climate change, other and possibly more expensive remedial measures, such as perpetual water treatment, may be required. After planned closure, many mining sites will be left with engineered structures and activities (dams, waste piles, treatment plants) that will require long-term site monitoring and maintenance, possibly in perpetuity. Unless sound long-term financial provisions are in place, it is likely that orphaned or abandoned mines will be created, with financial liability falling to the taxpayer. The increased likelihood of this scenario, or perceptions thereof, may present a risk to a mining proponent’s license to operate, especially in jurisdictions where there is already concern about closure plans that involve perpetual water treatment. This represents a near-term risk for mining companies.
For mines located near the southern boundary of the permafrost zone, or in other areas where significant permafrost degradation is projected, the design of permafrost covers, or the decision to use permafrost cover, should be informed by thermal analysis that takes future climate change scenarios into account. It is important to note that while northern mines may experience more climate change impacts that other mines in Canada, engineering practice in cold climates is already factoring in climate change into designs. However, mines that were closed before these practices were adopted are more likely to be at risk.
Climate change impacts on the ARD Process
Based on the temperature increases anticipated for the timeframe considered in this study (2.5C to 3.5C) (NRTEE, 2010), the impacts of increased temperature on sulphide oxidation rates is not anticipated to have a significant impact on a mine during operation. Where ARD is treated, more treatment reagents may be required but this change alone is not expected to represent a large increase in operating costs or to threaten the business case for the mine.
Similarly, following closure, an increase in the sulphide oxidation rate may lead to an increase in long-term treatment costs. However, this impact is estimated to be less than other potential impacts of climate change (e.g. tailings cover failure) and non-climate related factors that could lead to a change in approach in managing the site.
Others have reported that there are still gaps in understanding of how cold temperatures, ice, and permafrost degradation affect acid generation and dynamics of acid generating potential. (Stratos, 2009). MEND Report 1.61.6 (SRK, 2006) reported that limited research has been completed on the effect of low temperature on the performance of mine waste management facilities and recommended that more research in this area be conducted.
It is important to note that mine sites that are already problematic with respect to ARD, due to inadequate design, management, or regulatory oversight, may also be more vulnerable to climate change impacts.
In general, more options and more effective options for minimizing ARD are available earlier in the mine life. Similarly, climate change adaptation measures are more effective and less costly when developed and integrated at the planning and design phase. Anticipatory adaptation would involve adapting infrastructure designs, especially for covers, at the design stage to withstand long-term climate change conditions.
