Impact assessment of mining projects on groundwater resources can be a challenging task due to uncertainty on groundwater flow regime, the complex numerical tools to successfully simulate stresses on groundwater resources posed by the mining projects, timeframe and budget of EIAs.

In this article, we will call EIA the document issued before the mine begins for regulatory official approval and social license.

Before a mining project begins and along mine life, there is a huge interest in describing the general groundwater flow condition and predict project impacts along the mine’s life and when closure. Regulatory officials are deeply focused on the predictive simulation of all mining aspects relevant to the flow and quality on groundwater resources.

Data available for an EIA is limited, as well as the quality of the predictive simulations. From the numerical modeling perspective, it is even a misuse of resources to have a high complexity on the simulations based on short records of groundwater levels and hydraulic tests.

Some predictive simulations are feasible to be performed before the start of the mining operation on a standard EIA, while others can be only assessed along the mine’s life, and few will rely on scientific research.

Predictive Simulation Checklist

We wanted to propose a checklist of a common EIA predictive simulations. The proposed simulations are not mandatory, and mining projects will require to consider specific impacts, however this list is a starting point to plan the numerical modeling work. These simulations are listed below with a brief scope.

Pit Development

Pit inflows and predrainage flow rates: From the calibrated model, a transient simulation of mine inflows must be simulated to predict flow to the mine work, this simulation can include the planned predrainage schemas. Total inflows have to be separated in contribution from regional flow and storage. Results from this simulation include also the water table by end of the mine and cone of depression for different mine years (minimum 4).

Pit rebound: After the end of the mine and upon climate conditions, the pit will be flooded. The pit flooding simulation is iterative and interacts with a surface water model. Results from this simulation should include the final water table distribution and the final water level on the pit. It is important to analyze pit lake overflow and related groundwater flows coming from the pit lake.

Impact to surface water and groundwater flow regimes

Baseflow impact: Most of the new mining projects involve short mine life (less than 20 years). The related baseflow maximum impact will occur after the end of mine, therefore it is important to consider long transient simulations. The simulation should include the water table and cone of depression related to the maximum decrease on the baseflow.

Groundwater storage: Mine pit will take water from groundwater storage along its life. The groundwater will fill up some years after the end of the mine. Numerical simulation should provide the plot and charts of water extracted/refilled to groundwater storage till groundwater flow regimen reaches steady flow conditions again.

Waste Dumps and Tailing Deposits

Seepage flowpaths: As first glance of the impact posed by seepage, a particle tracking simulation will be needed. This simulation will provide a panorama of the flowpath distribution, basins, water courses involved and arrival times.

Contaminant transport modeling: With the predicted concentration of key contaminant on waste dumps and tailing deposits, a contaminant transport model should be run.

Project Management

Since the EIA is a collaborative work, it is important for the hydrogeological team to have an agreement on the numerical simulation that will be included on the report as soon as the conceptual model is finished. This practice will optimize the time dedicated to the numerical modeling work.

It is important to safe modeling hours for the observation phase, since the regulatory officials/stakeholders can require more simulations or further simulation on the reported impacts.