Water is inseparable from mining. Environmental water around the mine can impact mine operations and safety. Conversely, the mine and its associated water can profoundly impact the surrounding environment, including non-mining water. Managing the water that both goes into the mine and comes out of the mine is essential for protecting the mine’s functions and workers, as well as the surrounding communities, infrastructure, ecosystems, and people. Managing ‘water balance’ is a key element.
Water balance in mining can be either negative or positive. In a water-negative mine site, usage and evaporation can keep excess water from accumulating. In a water-positive mine site, water accumulates at a rate faster than it’s removed, and that can cause problems. Mines can accumulate water from the atmosphere (rainfall), from surface sources, or seepage from the water table where the mine reaches beneath it. Mines also pull huge amounts of water from other sources to be used in mining operations, which creates a large supply of polluted water with the potential to do great damage.
Dealing with all that water, bringing in what’s needed, getting rid of excess (de-watering), handling its use, storage, transport, characteristics, cleaning, and reclamation, ensuring its availability, preventing negative impacts, and controlling costs are all elements of successful mine water management.
Failed tailings dams have been an especially dangerous consequence of inadequate mine water management, causing massive economic and environmental devastation and substantial human injury and death. Tailings dam failures in Brazil at mines in Mariana in 2015 and in Brumadinho in 2019 killed nearly 300 people and polluted hundreds of square miles. In 2008, China’s Shanxi province saw two disasters just one month apart: 276 people died when a tailings dam at an iron ore mine failed; soon after, 43 people died in a similar incident. A tailings spill in 2020 in Heilongjiang, China, allowed over 660 million gallons (2.5 million cubic meters) of ore-contaminated wastewater to spread ecological havoc up to 68 miles (110 km) from the mining site.
Settlement costs alone for the Brazilian mine disasters reached billions of dollars, not to mention the cost of lost production and repairs. Effective mine water management can help deter similar occurrences and protect the mine’s workers and the surrounding environment and water supply. It will also ensure a mine has sufficient water for continued operations and the mine’s long-term economic benefit.
In addition to determining the hydrology of the land under and surrounding a mine in the early phases, it’s important to allocate sufficient financial, technological, and human resources to handle mine water management effectively.
Human resources will include expertise in hydrology, geochemistry, seismology, engineering, and other fields. Mine operators may find an advantage in working with consultants to provide expertise that may be lacking in-house.
Technology requirements include pumping systems, filtration, transport, sensing, and other devices. Financially, there needs to be a commitment on the part of mine operators to make the necessary funds available to support effective and environmentally safe mine water management.
Integrated drainage systems (IDS) can be used to manage the flow of water through the mine in a manner that prevents contamination of outside water sources. The system would generally include a centrifugal pump and motor, numerous valves, monitoring devices, and a drainage pipe.
As water moves through the mine, collecting in ditches, pits, channels, and other points, pumps are used to move it into the drainage system, away from operational areas of the mine. From there, the water might be processed and cleaned for reuse by the mine. Based on regulations and the quality of the re-processing, it may also be released back into the environment or stored in retention ponds, where contaminants have a further chance to settle out of the water.
Mines often generate tailings (liquid or slurry holding toxic mine waste) faster they can dispose of it and store it in dams or waste pits for far longer than is safe. The situation has long plagued mine operators, not to mention the people who live downstream.
The impact of tailings in water management and mine operations will vary based on the disposal methods. Technological advances have provided methods to remove liquid from tailings (dewater them) so they are solid enough for dry stacking. The water itself can be cleaned, processed, and reused to reduce the amount of new water the mine has to bring in to maintain operations.
Mine water may contain a range of contaminants that any effective treatment system would have to filter out, such as high acid content from dissolved rock, high saline levels, heavy metals, and chemicals used in processing. Treating the water often requires more than one approach.
Various chemicals can be used to restore pH to normal levels, so acid is less of a problem. Coagulants can be used to gather suspended solids and combine them into clumps, into bigger clumps using agents known as flocculants, so that subsequent filtration is more effective. Electric current can perform the same function through electrocoagulation. Additives can soften the water, inhibit corrosion, and kill algae or other biological agents.
Additional contaminants can be removed by filtration systems such as sand, multimedia, or cartridge filters, while membrane filtration methods such as micro, ultra, and nanofiltration can remove suspended particles. Activated carbon can also be used.
The term “dewatering” simply means that water is being removed from something. In mining, active and reactive dewatering are methods of removing water that has infiltrated the mine and interferes with operations. The function of process dewatering removes water from the mine waste that it gets mixed with as part of the mining process.
When the depth of a mine descends past the water table, water will seep in constantly. It may be infiltrated with suspended solids and highly acidic or highly alkaline and will corrode equipment, interfere with operations, and endanger the miners. The USGS notes the most acidic waters ever measured were found coursing through a mine in Iron Mountain, CA.
Reactive dewatering is used in underground mines, as well as some open pit mines. Reactive essentially means that as water seeps into the mine and collects in sumps (or hollows) at the base of the mine, it’s pumped back out using various pump technologies.
In open pit mines, active dewatering is the preferred process. Open pit mines are literally big deep pits that get deeper as work progresses and drop even further below the water table. One part of the process is similar to reactive, removing collected water with sump pumps placed around the mine floor. But active goes a step further, taking measures to lower the water table to keep water from seeping back in. In active dewatering, a second set of pumps, either borehole or wellpoint pumps (borehole for deeper mines), are used around the mine to actually lower the water table into which the mine is intruding.
Mineral mining uses huge quantities of water to process the mined materials. By dewatering, the mined materials become easier to transport, and storing the waste becomes easier and safer. Available methods include filtration, thickener and centrifugal technologies, and drying. Some situations may require a combination of methods.
Once water is removed from either the mine or materials, it can be stored in pits, reused in mining, or returned to the environment, depending on the success of the treatment methods used.
Consistent monitoring of mine water is essential for safety and continued mine operations. Monitoring would include the location, movement, and chemical characteristics of the water.
Various local and remote sensing technologies can provide a steady flow of data on water levels in the mine and the effectiveness of pumping systems; on the speed at which water is moving through conduit and where the conduit may be leaking; and on the quality of the water, including its pH level, contaminants, and oxygen levels. Local GPR (ground penetrating radar) or seismic surveys can assess the location and movement of underground water, while satellite-based monitoring can assess soil moisture and its characteristics quickly and frequently over vast mining installations. Drones have also been incorporated into mine water monitoring.
Regardless of the type of data collected or the methods used, timely analysis should be applied to help mine operators locate or anticipate problems and initiate corrective actions.
Satellite-based remote monitoring of soil moisture by ASTERRA EarthWorks is a more recent advance that supports mine water management. EarthWorks uses synthetic aperture radar on satellites orbiting 390 miles (627 km) above the Earth. It deploys a band of the spectrum (the L-band) that is able to penetrate the surface to about 10’ (3 m), where it can detect moisture in the soil and determine certain chemical characteristics. EarthWorks can spot excess moisture around conduit to locate possible leaks and under mine roads and hillsides that might precede lead to failure of the structure.
Most importantly, it can locate moisture that would indicate seepage from tailings and water retention dams that could lead to collapse if not remediated. It even has the ability to issue alerts for critical zones such as these so that decision-makers and engineers can move to prevent disaster.
A recent test in Northern Europe of EarthWorks for monitoring tailings dams clearly demonstrated its value. In this test, the mine operator directed the team a to a specific area of interest covering a total of .079 sq km (.03 sq miles). Of this, EarthWorks determined that .016 km2 (.006 sq mi2) had mid-level moisture, .0028 km2 (.0006 mi2) had mid-high level moisture, and .0015 km2 (.0006 mi2) had high moisture. Thus, 1.91% of the area of interest was highlighted as having high soil moisture.
By combining this data with topographic features for moisture behavior analysis and corroborating with data from other sensors on known points of interest the mine operators collect, they can make a significant leap forward in their dam monitoring capabilities.
Effective mine water management is essential for safe and profitable mine operations. It can help prevent a mine’s costliest problems, such as interruptions to operations or the failure of tailings or retention dams, as well as reduce the amount of new water that must be brought into the mine.
Learn more about ASTERRA EarthWorks and how it can contribute to safe, effective mine water management.