Abstract
The Canadian Dam Association released its revised Environmental Consequence Classification (ECC) framework in 2023. The revised system represents a significant step forward in the assessment of the environmental consequences associated with hypothetical dam breaches in that it combines the geochemical characterization of the tailings and facility supernatant with ecological variables and restoration timelines in a scientifically based framework. Prior environmental consequence classification systems for hypothetical dam breaches were ambiguous and relied on more value-based judgements than professional judgement.
The 2023 ECC framework incorporates the results of assessments of both the tailings solids in addition to any liquids that are contained within a tailings storage facility. The characterization of the tailings solids relies on the output of static and kinetic geochemical programs to understand if the solids would be expected to leach metal(loids) and/or generate acidic drainage within the timeframe that reclamation and restoration activities would reasonable be expected to occur. The underlying assumption of the ECC that restoration and reclamation activities would be initiated immediately following a dam breach is based on the actual responses to recent dam breaches. The classification of the liquid contents that would be released during a dam breach focuses on the toxicity of the fluid media which may or may not be known in all cases. This paper focuses on how the geochemical aspects of the new system are evaluated and used in the ECC framework.