• What are the water quality concerns at mines?

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    The use of water in mining has the potential to affect the quality of surrounding surface water and groundwater. In response to environmental concerns and government regulations, the mining industry worldwide increasingly monitors water discharged from mine sites, and has implemented a number of management strategies to prevent water pollution. Water issues and management vary from site to site and must be addressed locally, but in general, the mining industry seeks to minimize its impact on water quality and availability.

    How mines use water

    Mining operations use water for mineral processing and metal recovery, controlling dust, and meeting the needs of workers on site. [1] The amount of water required by a mine varies depending on its size, the mineral being extracted, and the extraction process used. For instance, metal mines that chemically process ore to concentrate metals such as copper and gold use much more water than non-metal mines such as coal, salt, or gravel mines. [2]

    Although a large mining operation may use a considerable amount of water, the minerals industry overall consumes a relatively small quantity of water at national and global levels. [3] Mining accounted for 4% of the water used in Canada in 2005, versus 60% for coal and nuclear electric power generation, 18.5% for manufacturing , 9.5% for municipal water supplies, and 8% for agriculture. [4] Mining accounts for 1% of water used in the U.S., and 2-3% of the total water consumed in Australia. [3, 5]

    The rate of water reuse and recycling in mineral processing is often very high at mine sites, especially in areas with arid climates. [3] A number of innovative water conservation practices are being developed and implemented to reduce water use.

    Types of mine water

    There are a number of classifications of mine water, which can vary in their quality and potential for contamination: [1, p. 9]

    • Mine water: refers to any surface or groundwater present at the mine site
    • Mining water: water which has come into contact with any mine workings
    • Mill water: water used to crush and grind ore, may contain dissolved minerals and/or metals
    • Process water: water used in the chemical extraction of metals, commonly contains process chemicals
    • Leachate: water which has trickled through solid mine wastes and may contain dissolved minerals, process chemicals, and/or metals
    • Effluent: Mining, mill, or process water which is being discharged into surface water, often after being treated
    • Mine drainage water: Surface or groundwater which flows or has the potential to flow off the mine site

    Typically, all the mine water at metal mines is collected and stored in tailings ponds (see below) before being treated and released to surface water if necessary. [1, 3]

    Extent of water contamination from mines

    Water pollution from mines is often cited as a major concern among stakeholders. [6] In the past, mines operated without the environmental management strategies and control technologies that are standard practice among larger mining companies today, contributing to environmental concerns over proposed mines. [7] For instance, a survey of mine waste management in California in 1992 found that mines that had started operations after new mine waste disposal regulations were introduced in 1984 had satisfactory waste containment systems, whereas some tailings ponds built before 1984 leaked unacceptably. [8]

    Although regulated mines have greatly improved their environmental performance, the use of liquid mercury in informal or artisanal mining (ASM) continues to pose a serious threat to water quality in some areas of the world. [7] ASM produces approximately 20-30% of the world’s gold (500-800 tonnes per year). [9] At least 650 to 1000 tonnes of mercury are released into the environment every year by ASM as a result of poor management practices, which accounts for about a third of all human-released mercury. [9] Other environmental problems associated with ASM include the direct dumping of tailings and effluents into rivers, improperly constructed tailings dams, acid rock drainage from mining areas, and absent or improper mine closure. [10] Monitoring environmental violations and enforcing the rules that combat those violations has been difficult due to a lack of resources and the widely scattered and inaccessible nature of ASM. [10]

    Water quality regulations in Canada

    In Canada, provincial governments have primary jurisdiction over mining operations within their borders and control water pollution from mines on a case-by-case basis through permit and licence conditions. [11, 12] The federal government also has regulations covering water quality control under the Fisheries Act and the Canadian Environmental Protection Act. [11] The federal government introduced the Metal Mining Effluent Regulations (MMER) under the Fisheries Act in 2002, which replaced the 1977 Metal Mining Liquid Effluent Regulations. The new regulations include a limit on releases of cyanide, a more stringent requirement for total suspended solids, an upper pH limit, and minimum toxicity requirement for effluent in addition to the other water quality parameters defined in the 1977 regulations. [13] Between 2003 and 2008, over 92% of discharge water sampled at mining facilities contained total suspended solids below the new regulatory limit, 95% of samples were below the limit for fish toxicity, and 99% of the samples were below the limits for dissolved metals and pH. [13]

    Potential for water contamination

    The potential for water contamination at a mine site depends on a number of factors: [1]

    • Type of ore being mined: Some ores, such as sulphide ores, are more chemically reactive than others, and have a greater tendency to dissolve and contaminate water. Common contaminants that are present naturally in metal ores include metals, metalloids, and salts.
    • Chemicals used in the mineral preparation and metal extraction processes: Chemicals used to process metal ores include cyanide, sulphuric acid, and organic chemicals. A single mine may use a combination of physical and chemical processes to separate metals from ore.
    • Climate: The amount of water available and potential for contamination at a mine site can vary depending on the climate. For instance, mines in permafrost regions where the groundwater could be frozen would not have the same concerns for groundwater contamination as mines in warmer regions.
    • Life stage of the mine: Whether a mine is under construction, operating, or closed can affect its potential to contaminate water. For example, the potential for water contamination from process chemicals is minimal following the closure of a mine, but if the mine workings were to be subjected to natural flooding, minerals could dissolve and mix with the surrounding groundwater.
    • Environmental management practices in place: Modern water management practices and mine designs greatly reduce the potential for water contamination at mine sites. In general, old abandoned mine sites have a higher potential to pollute nearby waterways because the water control techniques that modern environmental regulations now require were not in place when the mine was opened or closed. Knowledge of water management and impact reduction has greatly increased over time, and the prevention of water contamination is now an important component of mine operation and closure plans.

    Environmental impact assessments (EIAs), required in more than 100 countries including Canada, identify potential sources of water contamination at proposed mine sites, and the environmental management strategies that the mining companies intend to use to limit or prevent water contamination. [1, 14] While some form of EIA exists in many developing countries, their implementation tends to fall short of international standards. [15] However, there have been international efforts by the United Nations, the U.S. Environmental Protection Agency, and the World Bank to encourage the adoption of EIAs in developing countries by providing training and capacity-building programs. [15] Enforceable effluent regulations and permit conditions are often used to ensure compliance with EIAs.

    Tailings ponds

    Tailings are finely ground rock and mineral waste products from mineral processing operations. [8] Tailings are usually deposited in the form of a water-based slurry into tailings ponds, which are sedimentation lagoons enclosed by dams built to capture and store the tailings. [7] Tailings ponds were first introduced in order to prevent the direct discharge of mine water into surface waters. [7] There are a number of cases in drier climates where no water is directly discharged from tailings ponds because evaporation is the major water removal process. [16] In wetter climates, mines may be permitted to discharge water that meets water quality guidelines into surface waters. Water management and water level monitoring are very important components of mine design, and are used to avoid tailing dam failures such as the one at Baia Mare. [7]

    Heap leach residue

    Heap leach piles are piles of crushed ore that are sprayed with a dilute solution containing process chemicals such as cyanide to dissolve or leach valuable metals out of the rock. [8] The metal-bearing solution or leachate is captured by liners and drains, and processed to remove the metals. The solution is often reused and recycled. [1] Where heap leach piles are used, all leachate is captured, both for environmental and economic reasons.

    Negative impacts of water contamination

    Water contaminated with high concentrations of metals, sulphide minerals, dissolved solids, or salts can negatively affect surface water quality , aquatic ecosystems, and groundwater quality. [1] Impacts on aquatic life can include increased mortality, health or reproductive problems, and a reduction in the number of species present. [17] Impacts on human health can occur where the quality of water supplies used for irrigation, drinking, and/or industrial applications is affected. Water contamination can result in a need for water treatment or the adoption of a different water source. [1] Environmental monitoring programs and water management strategies are increasingly used by large and medium-sized mining companies worldwide to assess and minimize the impacts of water contamination.

    Beneficial uses of mine water

    The majority of mine waste is inert or benign, and therefore is unlikely to contaminate water. [1] There are a number of cases where mine water is considered to be of high enough quality that it requires little to no treatment before it is released into the environment. [7, 18] Shibdon Pond in England is one example where drainage from an abandoned coal mine has supported the development of a wetland, which is now home to a thriving ecosystem. [7] Treated mine water has been used as an additional drinking water source in Africa and England. [7, 19] In addition, dissolved metals in some mine waters are sufficiently valuable to be extracted at a profit . Iron-rich mine waters have been used in water treatment plants to remove other contaminates, and mineralized mine waters are occasionally used in spas . [7, 20]


    Case Study: Milestone Potash Mine, Lajord, Saskatchewan, Canada

    Potash refers to several forms of potassium salts, an important component of fertilizers. [21] Saskatchewan is the world’s second largest potash producer, where the mineral is mined from buried salts left behind by an ancient inland sea. [21, 22] Most of the mines in Saskatchewan use conventional underground mining to excavate the potash, which is brought to the surface for purification. [22] Where the potash is buried too deeply for the use of conventional mining methods, solution mining can be used to extract the potassium salts via hot or salty water which is pumped below the surface. [23] The water is then evaporated off, leaving behind the salts. Although solution mining is effective for potash, it is usually more expensive than conventional mining because of the large amounts of energy required. [22]

    The Milestone Potash Mine is located approximately 30 kilometers southeast of Regina in Saskatchewan, and is owned by Western Potash Corp., a Vancouver-based junior resource company. [24] The mine is still in the early stages of development, and is expected to start production by 2015. [25] Because the potash resources at Milestone are located 1,600 meters below the surface, solution mining has been proposed for the site. [26] With the use of solution mining, the Milestone mine is expected to yield 2.8 million tonnes per year of potash for more than 40 years. [24]

    In order to meet the water requirements for the solution mining operations, Western Potash has agreed to buy treated wastewater from the City of Regina. [24] The water would be further purified to prevent foaming or scaling. [26] Milestone Mine would be the first potash mine in the world to use treated water, reducing the water demands from the mine in an area where water scarcity is a concern. [24, 27]

    Show References


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    2Canada, Environment Canada. 9. Land-Use Practices and Changes - Mining and Petroleum Production, Threats to Water Availability in Canada. NWRI Scientific Assessment Report Series No.3 and ACSD Science Assessment Series No. 1. 128 p., 2004 [cited 2012 July 3]; Available from: http://www.ec.gc.ca/inre-nwri/default.asp?lang=En&n=0CD66675-1&offset=14&toc=show#table1.
    3Rankin, W.J., Minerals, metals and sustainability : meeting future material needs, 2011, Collingwood, Vic.: CSIRO Pub.
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    7Younger, P.L., S.A. Banwart, and R.S. Hedin, Mine Water: Hydrology, Pollution, Remediation, 2002, Dordrecht, The Netherlands: Kluwer Academic Publishers.
    8Hutchison, I.P.G. and R.D. Ellison, Mine Waste Management, 1992, Chelsea, Michigan: Lewis Publishers, Inc.
    9Telmer, K. Mercury and Small Scale Gold Mining - Magnitude and Challenges Worldwide, International Conference on Managing the International Supply and Demand of Mercury, in Brussels, 2006 [cited 2012 July 31]; Global Mercury Project. Available from: http://www.globalmercuryproject.org/documents/non_country%20specific/Telmer%20Brussels%20ASM%20and%20Mercury%20Magnitude%20and%20Challenges.pdf.
    10McMahon, G., et al. An Environmental Study of Artisanal, Small, and Medium Mining in Bolivia, Chile, and Peru, World Bank Technical Paper No. 429, 1999 [cited 2012 July 31]; Available from: http://www-wds.worldbank.org/servlet/WDSContentServer/WDSP/IB/1999/10/13/000094946_99092905340059/Rendered/PDF/multi_page.pdf.
    11Canada, Environment Canada. Mining, 2012 [cited 2012 June 13]; Available from: http://www.ec.gc.ca/pollution/default.asp?lang=En&n=C6A98427-1.
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    15Lee, J.C. Environmental Impact Assessments in Developing Countries: An Opportunity for Greater Environmental Security?, Working Paper No. 4, 2008 [cited 2012 July 31]; Foundation for Environmental Security and Sustainability. Available from: http://www.fess-global.org/WorkingPapers/EIA.pdf.
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    19International Council on Mining & Metals. Water Management in Mining: A Selection of Case Studies, 2012 [cited 2012 June 12]; Available from: http://www.icmm.com/www.icmm.com/water-case-studies.
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    24Powell, K. Western Potash (WPX) to Buy Recycled Waste Water from City of Regina Mining Insider, 2012 [cited 2012 July 5]; Mining Exploration. Available from: http://www.miningandexploration.ca/mininginsider/blog/western_potash_wpx/.
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    26Grace, K.M. Win Win -- Western Potash Will Buy Regina Waste Water for Giant New Mine, 2012 [cited 2012 July 5]; Small Cap News. Available from: http://business.financialpost.com/2012/06/13/win-win-western-potash-will-buy-regina-waste-water-for-giant-new-mine/.
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