Mine Dewatering

Open pits are developed in the mining industry for the extraction of minerals, raw materials, and aggregate. In many circumstances, these pits are excavated below the water table. Depending on the geologic environment and proximity of streams, rivers, ponds, and lakes, significant groundwater inflows may occur. The magnitude of these inflows must be estimated so that pumping systems can be designed to collect and dispose of the water. In addition, these inflows can result in a significant drawdown of the water table in the surrounding countryside. This drawdown can impact water supply wells and baseflow in streams. Because groundwater flow systems are heterogeneous and subject to a variety of influences such as recharge, rivers, and wells, analytical techniques are often insufficient for identifying the critical parameters in these types of analyses.

Visual MODFLOW can be used with MODFLOW and ZONEBUDGET to estimate the amount of water that must be extracted to dewater the open pit at various stages. Mine sites typically pose challenging geological conditions and often have steep hydraulic gradients due to the pit depth and amount of water that must be extracted. For these reasons, you may encounter dry cells in the upper layers of your model which may cause problems with model convergence and stability.  If this is posing a problem, you may want to consider MODFLOW-NWT or MODFLOW-SURFACT, as these versions of MODFLOW have overcome the problem of dry cells. MODFLOW-NWT does this by way of the upstream weighting formulation and the Newton method. MODFLOW-SURFACT does this using pseudo-soil functions.  MODFLOW-NWT will just simulate processes in the saturated zone (unless you add them in the UZF package) where as MODFLOW-SURFACT can do full 3D variably-saturated flow (and transport). Furthermore, MODFLOW-SURFACT includes the Fracture Well package which provides more accurate, representative modeling of pumping wells, which is crucial in dewatering applications. Both MODFLOW-NWT and MODFLOW-SURFACT work with ZoneBUDGET and MODPATH.

Online References using Visual MODFLOW for Mine Dewatering

Note: Waterloo Hydrogeologic does not imply endorsement of software from the authors of these publications/reports.

Sample Visual MODFLOW Flex Models

• Sample Instructions – Mine Dewatering Model
• VMOD Flex Project Files – Mine Dewatering Model

Suggested Reading

• Characterizing, Predicting, and Modeling Water from Mine Sites
• Groundwater modeling for large-scale mine dewatering in Chile: MODFLOW or FEFLOW?