A recent review sheds light on best-practice water quality assessments for mine design, operations and closure.
The 2019-20 Black Summer bushfires inspired Bronwen Forsyth to write a paper on the implications of climate change on mine-waste management and water-quality prediction.
Dr Forsyth, a senior environmental geochemist at SRK Consulting, wanted to start a conversation in mining about the effects of climate change on Acid Metalliferous Drainage (AMD) assessment and water-quality prediction.
She identified a lack of Australian-based literature that address climate-change impacts on AMD – and believed more could be done to inform mining companies on this issue.
“When I saw the devastation from the bushfires, I considered how climate change is affecting my everyday work in AMD and water quality assessment,” Forsyth says. “I wanted to encourage new thinking on how I could help mining companies with AMD issues to better adapt to climate change.”
Forsyth presented her paper – Climate Change and the Assessment of Acid Metalliferous Rock Drainage: What are the Considerations for Our Technical Discipline? – at the 10th AMD Australia workshop in June. The virtual workshop was held through the Sustainable Minerals Institute at the University of Queensland, where Forsyth completed her PhD in 2014.
The paper is timely. Climate change in Australia is expected to bring more hot days and shifting rainfall patterns, including longer droughts followed by floods. This uncertainty has implications for AMD assessment and water-quality predictions that should be factored in mine design, operations and closure.
“There’s a natural tendency to avoid uncertainty in AMD assessments,” Forsyth says. “But climate science has come a long way. We need to embrace climate uncertainty and factor it into AMD and water-quality predictions. And better communicate those risks to executives and boards, so they can make informed decisions.”
The risks are substantial. In her paper, Forsyth cited research from the devastating 2010/11 Queensland floods that closed or restricted production in 40 of Queensland’s 50 coal mines, costing more than $2 billion in lost production.
Several coal or coal-seam gas mines had uncontrolled water discharges during that wet season. Environmental groups raised questions about whether the run-off from those mines led to elevated salinity in downstream environments.
Practical implications
For her paper, Forsyth analysed local and international research on AMD and climate change, across government, academia and industry. In addition, she drew on personal observations from more than a decade of work in Australian and Canadian mining.
She had two goals. First, to identify the practical implications of higher temperatures and more variable rainfall on mine waste and water management. Second, to offer suggestions for the pursuit of best practice for AMD assessment in response to climate change.
“Australian mining needs a framework for AMD assessment that incorporates climate change,” she says. “More research can raise awareness of this issue, encourage industry debate, and help AMD practitioners and mining companies better respond to climate-change risk.”
Forsyth’s paper outlines the potential impacts of climate change on mine waste and management – and provides a range of suggestions. Chief among them is developing a new approach to determining “first-flush” concentrations to account for longer dry periods followed by intense rainfall. First flush refers to pollutant concentration or mass loadings associated with the initial portion of run-off water.
During drought, soluble minerals, as by-products of sulphide mineral oxidation, accumulate in the mine waste rock. If heavy rainfall follows a dry season, the soluble minerals dissolve and can be transported from the waste facility in runoff to local waterways, or as seepage into groundwater. The discharge from a mine’s waste-rock dump, for example, could have a high concentration of solutes within an intense first flush, followed by a “long tail” of lower concentrations.
“AMD assessments typically focus on long-term averages or mean annual precipitation rates,” Forsyth says. “We need to better account for extreme lows and highs in precipitation brought on by climate change, and how that can affect first-flush concentrations, in AMD assessments.”
Creating value
Enhanced AMD assessments can create significant value for mining companies by better understanding the environmental risks and identifying appropriate mitigation measures. A robust understanding of AMD potential is a critical input into the design of mine pits, waste-rock dumps, tailings storage facilities, covers, water-management structures and water treatment.
Moreover, AMD assessments that better incorporate climate change can help mining companies identify and manage risks prior to closure. These include: the unintended exposure of potentially AMD-forming wastes following extreme weather events; and unforeseen closure costs, such as water treatment and longer periods of care and maintenance to achieve mine waste landform rehabilitation objectives before mine lease relinquishment.
She says some mine closures underestimate AMD risks. “It can be very costly if a mine gets its closure wrong and has to provide water treatment in perpetuity. Mining companies need to understand how climate change will affect discharge flow, seepage or underground transport at mine closure, many decades after production stops.”
Risk management
Forsyth says executive teams and boards should view AMD assessments (in the context of climate change) as part of their organisation’s risk-management strategy.
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