Engineered river flow-through to improve mine pit lake and river values.

Area of Science:

• Environmental Science
• Hydrogeology
• Mine Engineering

Background:

• Mine pit lakes can form at closure when voids fill with water, often leading to acid and metalliferous drainage (AMD) and salinity issues.
• Contaminated pit lake water poses risks to communities, ecosystems, and limits beneficial reuse, potentially impacting surface and groundwater.
• Riverine flow-through is an emerging strategy to mitigate pit lake contamination using catchment-scale processes.

Purpose of the Study:

• To present the rationale, processes, and considerations for implementing a flow-through pit lake closure strategy.
• To describe international case studies of pit lakes utilizing or proposing flow-through as a closure component.
• To evaluate the potential of flow-through to remediate contaminated pit lakes and enable end-use opportunities.

Main Methods:

• Review of international case studies and scientific literature on pit lake remediation via flow-through.
• Analysis of chemical and biological processes (dilution, absorption, sedimentation) involved in contaminant reduction.
• Assessment of risks and benefits associated with flow-through strategies for both pit lakes and receiving riverine systems.

Main Results:

• Flow-through strategies can sustainably reduce pit lake contaminant concentrations through natural processes.
• Case studies demonstrate the potential for flow-through to remediate poor water quality and enable beneficial reuse.
• In some cases, flow-through may even improve river water quality, particularly with slightly acidic pit lakes and meso-eutrophic rivers.

Conclusions:

• Flow-through is a potentially valid mine closure strategy for pit lakes with poor water quality, provided riverine system values are prioritized.
• Strategies must be scientifically justifiable, risk-based, and account for potential impacts on surface and groundwater receptors.
• Adaptive management, robust monitoring of biotic and physico-chemical attributes, and stakeholder engagement are crucial for validating flow-through as a sustainable closure approach prior to mine relinquishment.