De-risking Mining Projects with Acid and Metalliferous Drainage (AMD) Characterization

Acid and metalliferous drainage (AMD), or acid rock drainage, remains one of the most persistent and costly environmental risks associated with mining. When mine materials are poorly characterized, or characterization data is not interpreted correctly, it leads to inadequate management of AMD risks, which can drive impacts that extend well beyond operations, often lasting decades after closure. These impacts can include long-term—and sometimes—perpetual water treatment obligations, increased closure and reclamation costs, and decreased trust and confidence from regulators, rightsholders, and community members.

As weathering and geochemical reactions of mined materials are natural processes, it is critical for mine operations, as land users, to conduct material characterization to effectively identify and manage potential geochemical risks. AMD characterization collects critical information on the geochemical properties of mine materials to help inform and develop plans, actions, costs, and resources required to minimize potential adverse impacts resulting from AMD (EGBC, 2026).

Some jurisdictions, including those in Australia and Canada, have advanced guidance on material characterization. This includes a recent update to the Western Australian Government’s updated Guideline for Preparing Mining Development and Closure Proposals (MDCP) and the publication of the Engineers and Geoscientists British Columbia (EGBC) Practice Advisory for Metal Leaching and Acid Rock Drainage (ML/ARD) Characterization and Prediction.

In alignment with Western Australia’s Mining Act and Regulations, the MDCP guideline has strengthened expectations regarding detailed physical and geochemical characterization of all mine waste and subsurface materials, as well as the early identification of potentially problematic materials (Government of Western Australia, 2025).

As for the EGBC practice advisory, the guide reinforces accountability and defensibility by providing guidance on the expectations and obligations of professional practice for developing characterization and prediction programs for mining-related produced or disturbed materials with AMD potential (EGBC, 2026).

Both guidance documents underscore the importance of material characterization in identifying and managing geochemical risks that may affect operations and closure. In this month’s Conversation on Closure, we outline how an early, practical approach to AMD characterization can help de-risk mining projects and facilitate responsible closure.

A Practical Approach to AMD Characterization

Material characterization for AMD can generally be structured around a defined flow path.

1. The process typically begins with identifying and understanding site geology, including material composition, climate (drainage and weathering conditions), mineral reactivity, and types of mine domains (e.g., mine rock stockpiles, tailings facilities, pit walls, underground workings, etc.). This provides information that is representative of the site and its conditions, and sets the framework for developing reliable predictions and AMD management recommendations (EGBC, 2026).
2. Developing a sampling program should aim to assess the spatial and geochemical variability of all rock types within the mine footprint. The number of samples required depends on the project, including the nature and volume of the mined material, the variability of critical geochemical properties within the material, and the availability of previous studies at the site (Government of Western Australia, 2025).
3. Based on the results of the sampling program, site-specific characterization tests and prediction plans can be developed to identify risks and define management criteria. Tests can include elemental analysis, mineralogy, static leach testing, kinetic leach testing, and acid-base accounting (Government of Western Australia, 2025). At this stage, it is important to conduct a well-informed sensitivity analysis on factors that contribute to uncertainties and provide contingency plans to minimize potential site-specific risks (EGBC, 2026).
4. Finally, as the project transitions into operations, monitoring and active management programs are required to validate predictions and refine controls. This should include recommended monitoring schedules and objectives for further studies related to project milestones, such as the pre-construction of a mine rock storage facility (EGBC, 2026).

This approach allows for adaptability, as it can be tailored to integrate water, closure, and geotechnical considerations to inform landform design, water management, and long-term closure performance.