ARD/ML Regulatory Decision Tree (GEST v3.1 Integrated)

The ARD/ML Regulatory Decision Tree is grounded in the principle that not all mine waste materials pose equivalent environmental risk, and thus regulatory scrutiny and technical effort should be proportionate to predicted geochemical behavior. It begins with initial field screening (e.g., pH, sulfate, sulfide content, net acid generation potential) and progresses through tiered laboratory testing—including Net Acid Generation (NAG), Acid Base Accounting (ABA), kinetic column tests, and leachate chemistry—based on pass/fail outcomes at each node. GEST v3.1 (Geochemical Evaluation Screening Tool) is embedded as the computational engine for interpreting test data, applying empirically calibrated thresholds (e.g., NAG pH < 4.5 and NAG acidity > 20 kg H₂SO₄/tonne indicates ARD potential), and assigning material categories (e.g., Non-ARD, Potential ARD, ARD). The decision tree explicitly links classification outcomes to statutory obligations: e.g., Potential ARD materials may trigger requirement for long-term water quality modeling using PHREEQC or MINTEQ, while ARD materials mandate engineered cover design and post-closure water treatment planning. Crucially, the integrated version harmonizes GEST’s quantitative outputs with regulatory triggers from instruments such as the Canadian Environmental Protection Act (CEPA), provincial Mines Acts, and the Metal and Diamond Mining Effluent Regulations (MDMER), ensuring defensible, auditable, and legally compliant pathways for permitting and closure planning.