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 significant drawdown of the water table in the surrounding countryside. This drawdown can impact on 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.

mine-dewatering

Visual MODFLOW can be used with MODFLOW and ZONEBUDGET to estimate the amount of water that must be extracted in order 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 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 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.

mine-dewatering2

Online References using Visual MODFLOW for Mine Dewatering

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

TitleRegion
Applying numerical groundwater modelling for mine dewatering projects around the worldVarious
Effects of dewatering methods on seepage and deformation of foundation pits
P
ublished in: Chinese Journal of Geotechnical Engineering
China
Oregon Department of Geology and Mineral Industries – Mine Dewatering and Ground Water ProtectionUSA
Application of Visual Modflow to Dewatering Design of Foundation PitChina
Yandicoogina 2013 Groundwater model Setup and Calibration
K
eywords: MODFLOW-SURFACT
Australia
Preliminary Dewatering Assessment – Mining Operations
K
eywords: Preliminary Dewatering Assessment – Mining Operations
Australia
Pumping well optimization in the Shivee-Ovoo coal mineMongolia
Nullagine Gold Project – Mine DewateringAustralia
NovaGold, Galore Creek Project – Open Pit Slope Design – Feasibility Geotechnical Report
K
eywords: MODFLOW-SURFACT
Canada
Use of Numerical Groundwater Modelling for Mine Dewatering Assessment
Keywords: MODFLOW-SURFACT
 Various

 

Sample Visual MODFLOW Flex Models

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