Better science, advanced technology, more stringent regulations, and active and real-time monitoring and management plans have helped minimize environmental and social impacts from mining. This includes the control and management of all water in and around a site to ensure that no harmful water discharges occur.
Water Use and Management
Mining operations use water for mineral processing and metal recovery, controlling dust, and meeting the needs of workers on site. The amount of water required by a mine varies depending on its size, the mineral being extracted, and the extraction process used.
Modern mining operations are required through state mining laws and permits to treat, and monitor water discharged from mine sites.
In order to comply with regulations and ensure that the quality of water leaving mine sites is not adversely affecting water users downstream, mining companies develop sophisticated water collection systems and management plans to minimize the potential for water contamination, and to prevent the release of polluted water into the environment.
At modern-day mines, all water that contacts mined materials and mine wastes is collected and routed to centralized collection basins. Water from these collection basins is either reused in the mining operation or the water is treated prior to discharge back to the environment. Discharged treated water must comply with permits that contain standards to protect the environment. Permitted standards are developed by the Wisconsin Department of Natural Resources (DNR) and the United States Environmental Protection Agency (EPA), not the mining company.
Water treatment facilities at mines use treatment techniques like those used at other industrial sites and municipal water treatment facilities. Examples of the types of active water treatment systems used at mines includes chemical precipitation, ion exchange, membrane filtration, reverse osmosis, and distillation.
The water treatment system at the Eagle Mine in the Upper Peninsula of Michigan, like most modern-day mines, use a variety of treatment methods to ensure that treated water complies with all permit standards. The choice of which type of water treatment system to use at a particular mine depends on what must be removed from the water, how much water must be treated, and the water quality of the area where the treated water will be returned.
Can a metallic mine produce acidic water that can be treated?
Yes. Many metal-bearing ore deposits contain minerals in which metals are bound to sulfur forming what is sometimes referred to as “sulfide minerals.” When these deposits are mined, the sulfide minerals in the rock may be exposed to water and oxygen. If this happens, the sulfide in the rock undergoes a reaction called oxidation.
This reaction is a natural weathering process that occurs in the environment and is similar to the rusting of metal.
Under certain conditions, the reaction of these sulfide minerals with water and oxygen can lower the pH of water, causing acidity. Over time, the acidic water can cause the release of metals from rock. If not managed properly, these metals can contaminate nearby groundwater and surface water. Modern mines manage this by properly engineering the design of the mine to minimize potential impacts by conducting ongoing waste and water management, treatment and monitoring throughout the life cycle of the mine.
Waste Runoff and Drainage
Through proper engineering and monitoring at every stage in the life of a mine, impacts to the environment can be properly managed. Mines involving sulfide mineral deposits use sustainable mine designs and environmental protection technology to minimize, manage, and treat acidic water and waste throughout the life cycle of a mine – from exploration through closure.
During exploration geologists will carefully note the types and amounts of sulfide minerals in the drill core samples obtained during drilling to define the size and grade of the mineral deposit.
Samples containing sulfide minerals must be collected for short-term and long-term laboratory tests to measure their potential for altering established water pH so that the potential for oxidation of the metals in the rock can be understood.
Mine planners use the results from these tests to develop mine designs to minimize and control acid production. These management techniques use engineered storage facilities to prevent potentially acid-generating waste rock from affecting groundwater and surface water. One technique includes covering the acid-generating wastes with layers of non-acid generating materials and storing them under water to minimize oxidation of the sulfide minerals. Another effective measure for preventing these issues after mining is to cover mine wastes with an engineered cap or cover, minimizing oxidation. All mine designs must address this issue during operation and after the mine has been closed and reclaimed. Mine operators remain financially and legally responsible for maintaining safe and clean environmental conditions for many years following mine closure.
Monitoring and Reporting
The Wisconsin state permits for a mining project include detailed site monitoring requirements to regularly verify that the mine is performing as planned and complying with all environmental protection standards specified in the permits. A mine operator must collect samples at locations approved by the DNR, ensuring the protection of air quality, surface water, groundwater, wetlands, and wildlife.
For example, a Wisconsin Pollutant Discharge Elimination System (WPDES) permit is required for any facility to discharge water to a surface waterbody. This permit will include stringent wastewater discharge limits that regulate the type, quantity, and concentration of various components in the water that can be safely discharged.
The discharge limits are set at levels that will protect beneficial uses of the receiving water, which typically means protecting fish and other aquatic life, allowing for people to continue to use and enjoy waterways.
This permit will stipulate the locations, types, and frequency of monitoring that is required to ensure the facility is complying with the discharge limits.
Monitoring consists of taking water quality samples that are analyzed by an independent, third-party laboratory and can also involve wetlands mapping and sampling, fish tissue tests, sampling and testing other aquatic species, and tests to measure air emissions. The monitoring results are provided to the DNR on a regular basis, as required in each permit.
Project monitoring plays an essential role in safeguarding the environment at mines and at other industrial facilities. First, monitoring provides real-time verification that the facility is complying with its permits. Second, monitoring functions as an early warning system to alert the operator and regulators that there may be the potential for an environmental problem that must be investigated and addressed. If there is a problem, the environmental monitoring system will detect it early.
In the event the monitoring system detects a potential problem, the operator must notify the state immediately. The DNR will require the operator to investigate the problem and develop and implement an appropriate corrective action plan to fix it. This early detection response mechanism minimizes potential risks to the environment and human health and safety by limiting the amount of time that a problem goes undetected and by requiring timely remediation in the event a problem is discovered.
Project monitoring is required for each step of the mining lifecycle. An operating mine site will have on-site environmental staff whose main function is to collect monitoring data in compliance with the permit requirements and to prepare monitoring reports presenting the monitoring data results.
Some mine facilities must be monitored on a continuous basis whereas others are monitored daily, weekly, monthly, or quarterly as specified in the project permits. Different permits will have different requirements for monitoring and reporting. Companies must submit monitoring reports to the DNR on a regular basis defined by the permit. Once the reports are submitted, they become public documents.