Water quality prediction is required at various mining stages; permitting, operations, and closure. Typical applications include pit lake water quality, waste rock runoff quality, tailings decant water quality, and treatment requirements and design. Water quality prediction is generally based on site-specific geochemical characterization of mine wastes which is often conducted as part of the baseline work and overall assessment of potential environmental impacts.
Water quality predictions require both hydrologic and geochemical modeling. A hydrologic model is used to predict water flows and/or volumes (e.g. seepage through a waste rock dump or pit lake filling). Once the hydrology is established, geochemical modeling is conducted by applying a chemistry to the various flow components (e.g., groundwater, pit wall runoff, waste rock contact water) and simulating key geochemical processes (e.g., mixing, sorption, reactions, evaporation, etc.).
Basic water balance/mass balance modeling can be completed using a spreadsheet (e.g. Microsoft Excel) or GoldSim. More complex water quality predictions involving chemical precipitation, adsorption, settling of particulate metals etc. are conducted using a combination of applications including GoldSim for hydrology and PhreeqC, and/or Geochemist’s Workbench for the geochemical mixing and reaction simulations.