Managing Mine Water

Managing mine water presents any number of challenges during a mine’s lifespan. Upon closure however, the management of water often continues indefinitely. Managing water sustainably presents an entirely new conundrum: treating ongoing flows in extremely hard to reach locations.

Each year, mining companies spend millions of dollars on operations and maintenance costs to manage water from closed sites. Located in remote areas, without access to a robust workforce, housing, or transportation, managing water flows from closed sites routinely costs companies millions of dollars per year. Mining companies have made significant strides to reduce costs and environmental impact, while complying with legacy regulations, but these residual wastewater streams remain leaky faucets at closed or near-closed sites around the world.

Though the challenge remains, emerging technologies and research are reshaping what it means to close a mine. Between remote sensing technologies and automated treatment processes, nature-based solutions, and creative reuse strategies, there are several avenues companies can explore to put the lid on future spending.

Automating for remote locations

The water industry in general is well-versed in treating millions of gallons per day of wastewater, but many small, rural systems still struggle to manage low flows with a shrinking workforce. Scaling down to residual wastewater streams from closed sites exacerbates the challenge. Skilled labour is hard to find, expensive, and difficult to house in the remote regions where mines once operated.

With the growing use of remote sensing technology and automated systems, companies can look to leveraging these technologies to reduce personnel. The upfront cost of installing sensors and these operating systems would create long-term operations and maintenance savings, reducing the need for in-person labour to emergencies or anomalous events.

Stantec has recently developed a machine learning algorithm, designed to predict influent flows for water resource recovery facilities up to seven days in advance. This information can help operators adjust operations as needed to prepare for potential surges due to wet weather events and storms. While the technology is still being refined and tested with larger scale facilities, using machine learning to help remote operators predict changes or disruptions could be highly beneficial for residual mine water streams as well.

As technology has evolved, Stantec has continued to incorporate automation into treatment designs. By designing robust processes that account for potential process automation drift, and using machine learning to improve process reliability over time, we can optimise active treatment for residual flows. With more data and technology, even sites that require frequent operator attention can gradually transition to longer periods of time between intervention.

Passive and nature-based treatment for residuals

Sustainable mine water management includes evaluating all possible solutions, particularly nature-based solutions. Weaving natural features and processes into mine closure design increases long-term human, ecological, and infrastructure resilience to climate change and other environmental impacts. Additionally, this approach can transform waste streams into assets or reduce the dependence on supplemental resources and equipment. From water quality improvements to slope stabilisation and improved biodiversity, leaning into the natural resources available in a site can reduce the need for O&M, repairs, and reinvestment. By improving public perception and the surrounding environment, nature-based solutions also improve the social license to operate.

In Sudbury, Ontario, Stantec designed a passive bioreactor to treat residual metals (specifically copper) in water stored in the Broken Hammer Mine open pit. Though the mine currently manages metal exceedances with annual lime dosing, water quality modelling predicted the need would remain long-term. As an alternative to active dosing, the team recommended and developed a design for a passive approach using a sulfate reducing bioreactor design. Passive bioreactors are biological treatment systems that clean contaminated water using microorganisms. This approach requires significantly less equipment and in-person maintenance. To fully test the approach, we prepared a pilot scale design and implemented testing on site utilising local materials (i.e. compost and stone) over two years. Positive performance results of the pilot led to the development of a full-scale bioreactor design and permitting.

Exploring reuse amid growing water challenges

Many mature, post-mining sites transitioned decades ago. As the climate has shifted, some regions have become more arid while others have seen increased rainfall. This challenge will inspire significant changes in mine water management.

For example, many post-mining sites in Colorado would be well-positioned to treat their water to reuse standards that could be valuable for recreational purposes, such as streams and water supply for snowmaking. In the agricultural region of eastern Washington state, discharged mine water is actively blended with agricultural water supplies to supplement irrigation systems. Blending the water with another source allows more limited treatment to bring it up to agricultural use standards, and in turn supports crop growth and local farms. At the same time, surface-level integration protects higher-quality groundwater supplies that are necessary to supply potable water to nearby communities.

Similarly, some sites blend treated water from coal mines with fresh water to supply cooling towers for power plants. This reuse strategy presents strong potential for water-intensive data centre development as well. While many mines are not geographically positioned for this option, those that are would be well-suited for reuse conversations.

While these examples illustrate opportunities to transform a costly waste stream into a possible revenue generator and contribute to critical water resource protection in light of a changing climate, there are other avenues for mine water experts to collaborate with nearby municipalities to achieve mutually beneficial outcomes increasing public acceptance. In Peru, Stantec designed a municipal wastewater treatment system that discharges a portion of treated effluent to a local mine for their operations while providing the local municipality with a much-needed treatment facility. This reduces water costs for the mine while also reducing water demand in the region and gaining public and regulatory acceptance and support.

The concept of One Water has taken hold across the global water industry. This approach champions a holistic, watershed level approach to managing water resources. By evaluating the regional impact, use, and need for water resources, communities can better allocate and reuse resources, reducing treatment costs and demands. Similarly, combining water expertise from mining, technology, reclamation, agriculture, and water engineering could deliver game-changing solutions that create a more sustainable future for mine water management.

Read the article online at: https://www.globalminingreview.com/mining/27022026/managing-mine-water/