Statement of Qualifications:
Pit Lake Water Quality Modeling and Risk Assessment
The development and management of pit lakes left behind after mining is one of the most significant issues facing the global mining industry. HydroGeoLogica takes a pragmatic approach to pit lake evaluation and management, evaluating critical paths and drivers to identify potential financial, social, environmental, and regulatory risks and opportunities.
HydroGeologica’s pit lake evaluation begins with developing a conceptual model of the pit and its surroundings.
A pit lake water balance is constructed to predict inflows, outflows, and lake surface elevations through time. Water balance models are typically built using a dynamic systems model such as GoldSim, a state-of-the art stochastic modelling platform (please refer to our Mine Water Balance Modelling SOQ). When necessary, we link the GoldSim water balance model to PHREEQC, the reactive geochemistry model, using a proprietary DLL code.
A geochemical model of the pit lake is constructed to represent the following geochemical mechanisms:
- Chemical mixing and mass balance
- Evaporative concentration
- Mineral equilibria
- Sorption reactions
- Reaction kinetics
- Gas exchange with the atmosphere
- Reduction/oxidation reactions
The pit lake chemistry is simulated through time as it fills, then as it evolves after filling. A screening level risk assessment is conducted to determine if additional management of the pit lake is likely to be required to meet regulatory and closure requirements. Multiple management options can be simulated, such as:
- Pit backfill
- Rapid filling
- Passive treatment
- Water treatment
- Grout curtains
- Forced stratification
- Water disposal
- Alkali amendment
- Ferric amendment
- Organic/nutrient amendment
Cost, risk, and benefit are evaluated for decision making to identify the most cost-effective and sustainable alternative(s). Pit lake monitoring provides real-time feedback to adjust and fine tune the closure plan during the dynamic filling phase to optimize management and long-term costs.