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Innovative Insights into Mine Water Flows

The wider use of innovative tracer technology in the Australian mining industry can help miners better understand water flows in legacy and active mines, as well as the environmental parameters of operations.

At a legacy lead-zinc mine in the United Kingdom, SRK Consulting hydrogeologists sought to understand how water flows could affect the placement of a planned remediation facility.

Tracer dye was added to water surface flows entering an open shaft of an underground mine. Monitoring data yielded valuable insights by capturing previously unknown hydraulic discharges from the mine.

The recovery and breakthrough times were used to establish the proportional split of discharges at different monitoring points which, when coupled with water quality data, were used to highlight dominant discharge flow pathways with high metal load.

In Brazil, SRK hydrogeologists have used tracers to delimit the influence area of cavities in limestone and ferriferous formations, springs and pumping wells, and to characterise fractures and hydraulic barriers, providing assistance in the location of dewatering wells and contamination remediation planning at the mine.

In Canada and the US, tracer tests have been used to improve the operation of wellfields and to better understand catchment flow dynamics. Chloride and bromide (natural tracers) have been used to assess residence times in backfill pits and assess the mixing of source waters in waste rock.

SRK hydrogeologists have used a variety of tools and laboratory-based water-quality analyses to interpret tracer data, including the development of in-house analytical and Python models for rapid tracer modelling.

These are just a few examples of how tracer tests are being used to understand water flows in legacy and active mines. New applications of the technology are particularly applicable to Australia, which has thousands of unused mines, some of which can cause public hazards or damage the surrounding environment.

“The insights from tracer testing are invaluable,” Richard Cheal, a senior consultant (hydrogeology) at SRK Consulting Australasia, told Australian Mining.

“The data are particularly valuable in the context of legacy and active mining operations. Understanding water flow dynamics is crucial for refining conceptual models and defining constraints in numerical models.

“The insights developed overseas with the latest tracer testing technology can be applied to many mining operations in Australia.”

Broad application

Cheal says tracer testing has a wide range of applications in mining. By confirming sub-surface flow pathways at a mine, SRK can identify where water from the mine flows to and which waterbodies it affects.

“This information is crucial for developing remediation strategies at a mine,” he said.

In active mines, tracer testing can monitor the effectiveness of water management strategies, provide plume migration data, give insight into contaminant attenuation potential and geochemical mechanisms (such as acid mine drainage and metal loading), aid in the design of tailings storage facilities, and refine conceptual and numerical models.

“Tracer tests can provide insights into hydrogeological conditions, and inform strategies for water management and environmental protection,” Cheal said. “It’s an important part of sustainable resource management.”

Tracer tests assist miners to understand on-site water characteristics and movement.
Tracer tests assist miners to understand on-site water characteristics and movement.

Tracer types

SRK commonly uses fluorescein and rhodamine water tracing fluorescent dyes in tracer tests.

“These are artificial, non-toxic, and conservative because they have limited interaction with the geological media they pass through,” Cheal said.

In some cases, SRK will use natural tracers, such as sodium chloride, or occasionally environmental isotopic tracers. Much depends on the mine-site parameters or the needs of potential stakeholders in the project.

Tracer monitoring, Cheal said, can involve quantitative techniques that use sophisticated equipment, such as the Valeport Hyperion sonde sensor.

“This technology can detect tracers in real-time and at very low concentrations, which provides a detailed picture of tracer movement over time,” he said. “We can also generate breakthrough and mass recoveries, which are essential for understanding the speed and direction of water flows at a legacy or active mine.”

Qualitative monitoring methods for tracer tests typically use granular activated carbon that absorbs any tracer as water passes through.

“While this doesn’t provide exact measurements, it can indicate whether certain pathways contain a tracer, which is particularly useful in complex sub-surface environments,” Cheal said.

Tracer testing is proving increasingly important in understanding water flows in legacy mines.
Tracer testing is proving increasingly important in understanding water flows in legacy mines.

Bright future for tracer testing technology

Cheal expects the latest tracer testing techniques to be used at more legacy and active mines as technology develops, with real-time monitoring technologies for tracer tests to become more prevalent this decade, providing better quality information on water flows.

“We’re seeing significant improvements in tracer testing that is benefiting more mining companies worldwide,” Cheal said. “The integration of technologies will provide a more comprehensive understanding of the hydrogeological impact of mining operations on the environment.”

Also of note are advances in tracer test data analysis, such as SRK’s Python model, which will enable better prediction of sub-surface water flow patterns.

“This is particularly important for complex mine sites with multiple pathways of water movement,” Cheal said.

As mining companies evolve their environmental, social and governance (ESG) standards and the understanding of water flows becomes more and more important, Cheal believes more mining companies will apply tracer tests in new ways in the coming years.

“We’re continuing to use tracer testing technology in innovative ways to inform mine planning, operations and remediation, and to protect the environment,” Cheal said. “A deeper understanding of water flows at a mine can benefit a range of stakeholders.”

Six considerations for mine tracer testing

Regulatory compliance: In Australia, there is no specific requirement for the permitting of groundwater studies using tracers, but regulators should be made aware of their use. Mining companies should be aware that such discussions can take time, depending on the sensitivities of the site.

Tracer selection: Tracer choice should be specific to the unique environmental conditions and the objectives of the study. During test planning, SRK completes an options appraisal to understand the most appropriate tracer type to use.

Environmental stewardship: During pre-test planning, the minimum volume of tracer required for a successful test is estimated based on the expected parameters (distance, travel time, porosity, flow velocity, etc).

Data interpretation: The detail of any interpretation will depend on the type of monitoring data collected (quantitative or qualitative) coupled with the duration and frequency of sampling.

Stakeholder engagement: Keeping local stakeholders aware of the potential for temporary breakthrough of fluorescent tracers into natural surface watercourses will help maintain good stakeholder relationships.

Cost-effectiveness: Tracer tests using dyes or salt tend to require few resources to set up, monitor or analyse and can provide higher value than more intensive investigations. This makes the collection of empirical data from a groundwater system particularly affordable.

This feature appeared in the April 2024 edition of Australian Mining. Read the original here.