Mines And Groundwater: A Pollution Concern?

Mining fuels economies by sourcing minerals, but it is also a leading cause of water pollution. Water pollution from mining affects surface water and groundwater, and it can last for decades, if not centuries, after a mine's closure. There are four main types of mining impacts on water quality: acid mine drainage, heavy metal contamination, seepage from tailings and waste rock impoundments, and sedimentation. The arbitrary discharge of polluted mine water can destroy the ecological environment and affect the utilisation of mine water resources.

Mine drainage

AMD severely degrades water quality and can have detrimental effects on aquatic life and ecosystems. It can also impact infrastructure, causing corrosion and discolouration of water. The rate at which AMD occurs can be accelerated by certain bacteria, such as Thiobacillus ferroxidans, which can further increase the oxidation and acidification processes, leading to even more metal leaching from waste rocks.

The problem of AMD is not limited to abandoned mines. Active mines can also contribute to AMD, especially during heavy rainfall when loosened topsoil is washed away, carrying sediments and contaminants into nearby bodies of water. Additionally, the use of chemical compounds such as sulphuric acid and cyanide in the mining process can further contribute to water pollution if they are leaked or spilled into water sources.

While there have been improvements in mining practices in recent years, the environmental risks associated with mine drainage remain significant. The long-term impact of AMD on water quality and the challenges of treating and managing it effectively continue to be a serious concern for communities and the environment.

Heavy metal contamination

Mining is a highly profitable industry that fuels economies. However, it has long been associated with water pollution, which is a serious environmental concern. Water pollution from mine waste rock and tailings may need to be managed for decades, if not centuries, after a mine's closure.

The Canadian mineral industry, for example, generates one million tonnes of waste rock and 950,000 tonnes of tailings per day, totaling 650 million tonnes of waste per year. After being removed, the waste rock, which often contains heavy metals, is usually stored above ground in large, free-draining piles. This waste rock and the exposed bedrock walls from which it is excavated are the source of most of the metal pollution caused by mining in British Columbia. In other regions of North America, tailings also represent a major source of heavy metal contamination of waterways.

Heavy metal contaminants from mining can remain in ecosystems for centuries and can spread far beyond mining sites into floodplains and rivers. According to a study, more than 23 million people could be living in floodplains contaminated by heavy metals from mines. This is a warning that mining companies and governments need to expand their efforts beyond mines to protect citizens from harm.

Bacteria play a crucial role in the bioremediation of heavy metal-polluted sites. Some bacteria possess inherent biochemical, physiological, and/or genetic mechanisms that enable them to withstand high concentrations of heavy metals. These bacteria can be utilized as potential tools to counteract the toxic effects of heavy metals in the environment.

Acid mine drainage

When a mine is abandoned and pumping ceases, water floods the mine, initiating the acid rock drainage process. Colonies of bacteria and archaea, called extremophiles, accelerate the decomposition of metal ions, although the reactions also occur in an abiotic environment. These microbes occur naturally in rocks, but limited water and oxygen usually keep their numbers low. The oxidation of metal sulfides, often pyrite (iron-sulfide), within the surrounding rock and overburden generates acidity.

The resulting acid can dissolve harmful metals and metalloids, such as arsenic, from the surrounding rock. AMD severely degrades water quality and can kill aquatic life, making water virtually unusable. It can be released anywhere on the mine where sulfides are exposed to air and water, including waste rock piles, tailings, open pits, underground tunnels, and leach pads.

The impact of AMD on water sources is long-lasting. Acidic drainage may be generated for decades or centuries after it is first detected, and water treatment may be required indefinitely. This can impose a significant economic burden on the public, particularly if a mining company files for bankruptcy or refuses to cover water treatment costs. For example, the EPA has spent over $210 million on clean-up after acid runoff from the Summitville Mine in Colorado killed all biological life in a 17-mile stretch of the Alamosa River.

Impact on aquatic life

Mining can have detrimental effects on aquatic life in several ways. Firstly, the process of mining can result in the disturbance and diversion of water bodies, such as streams, rivers, and lakes. This can lead to changes in water flow patterns, affecting aquatic habitats and ecosystems. For example, the Tsolum River in Vancouver, once a thriving source of salmon and trout, faced significant impacts due to mining activities in its watershed, including gravel extraction from its riverbed.

Secondly, mining generates large amounts of waste rock and tailings, which can cause water pollution if not properly managed. This pollution often takes the form of acid mine drainage (AMD) or acid rock drainage (ARD), where sulphides in exposed rocks react with water and oxygen to produce sulphuric acid. This highly acidic water can leach heavy metals such as arsenic, cobalt, copper, cadmium, lead, and zinc from waste rock, resulting in toxic water that can kill aquatic life and render water sources unusable. The acid and dissolved metals are then carried by rainwater or drainage into nearby water bodies, degrading water quality and harming aquatic organisms.

Additionally, mining activities can lead to increased sedimentation in water bodies. Poorly constructed roads and erosion from mining sites can wash sediments into streams, lakes, and rivers, causing disfiguration of stream channels and flooding. This sedimentation can smother aquatic habitats, burying fish eggs and disrupting the balance of ecosystems.

Furthermore, mining operations often require significant water usage, which can lower water tables and dry up rivers and wetlands. This reduction in water availability can directly impact aquatic life, altering habitats and disrupting the natural flow of water that aquatic organisms depend on.

The impacts of mining on aquatic life can be long-lasting and challenging to remediate. Even with modern regulations, the magnitude of the effects depends on factors such as mining technology, the extent of disturbance, and the chemical composition of the mined materials. As a result, aquatic ecosystems may suffer from reduced biodiversity, loss of sensitive species, and changes in the productivity and behaviour of surviving organisms.

Human health concerns

Mining is essential to economies, but the environmental and health risks it poses cannot be understated. Water is essential to life on our planet, and mining activities threaten the water sources on which we all depend.

Acid mine drainage (AMD) is a significant concern, as it severely degrades water quality and can make water virtually unusable. AMD forms when pyrite, an iron sulphide mineral, is exposed to air and water, creating sulphuric acid and dissolved iron. This acid runoff further dissolves heavy metals such as copper, lead, and mercury into groundwater or surface water. These metals are toxic when ingested, even in trace amounts, and can cause serious health problems in humans. For instance, mercury poisoning, which can occur from consuming contaminated fish, impairs the nervous system and is especially harmful to developing fetuses and young children.

Heavy metal pollution, caused by the presence of metals like arsenic, cobalt, copper, cadmium, lead, silver, and zinc in water, poses another serious health risk. These metals are found in excavated rocks or exposed in underground mines and can leach into nearby water sources.

Additionally, there are concerns about the inhalation of fine dust containing lead, zinc, arsenic, asbestos, and other harmful substances from mine tailings, waste rock piles, and other mining-related sources. These constituents are known to cause adverse health effects, depending on the level of exposure and concentration.

The impact of mining on water sources can be long-lasting, requiring management for decades or even centuries after a mine's closure. The vast amount of waste generated by modern mining methods, combined with a lack of environmental consideration in the past, has resulted in a significant legacy of environmental and health issues.

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