A bottom line of all these groundwater flow models was the required calculation of the amount of water that flows into the opencast or deep mines in all stages of their existence, including the water inflow after the mine gets closed down. Simulation of water level onset upon the termination of mining was in virtually all cases accompanied by geochemical modelling which was intended to determine quality and stratification of waters inside the mine being flooded. If the quality of water of shallow aquifers or even surface water was threatened, the flow model also aimed at the determination of zones of potential seepage of mine water. The geochemical model defined the potential intensity of impact on the groundwater and surface water due to decanting mine water. Flow models, primarily those applied in deep mines, often had to encounter complicated structural tectonic features in the mining area. They were also frequently required to calculate the amount of water ingressing in the mine if suddenly reached during the mining activity.
All of the below mentioned models were developed using the MODFLOW code. The following is a list of some tasks carried out, with a brief description of the respective issue:
ADP Projects, Namdeb Hydrogeological Investigation – opencast diamond mining in near-shore unconsolidated strata of arenaceous rock, southern coast of Namibia. The modelling focused on the calculation of seawater inflows into the lagoon that emerged during the mining activity, running over the dykes made of (temporarily) unworked material.
Total Coal SA, Dorstfontein West Expansion Project – opencast and deep coal mine in Mpumalanga province, South Africa. Within the impact assessment prepared for the expansion of the existing black coal mine, a numerical model was processed in order to determine the groundwater inflows into the mine. The impact on the water balance and quality of groundwater source within the area concerned was evaluated. Similar projects are as follows:
- Umcebo Mining, Jikama Mines, Kleinfontein, Mpumalanga, JAR;
- NuCoal (Pty) Ltd, Middelburg area, Mpumalanga, JAR.
SGS Environment, Akwaaba Deeps Underground Mine – deep gold mine in Ghana. Within the preparatory work for the extraction of huge gold deposits, a numerical model was processed in order to determine the groundwater inflows into the mine. The impact on the water balance and quality of groundwater source within the area concerned was evaluated.
Bulyanhulu Gold Mine Limited, Bulyanhulu Numerical Model Development – deep gold mine in Shinyanga region, Tanzania. The task of the mathematical modelling was to determine the groundwater inflows into the mining space, including the calculation of the amount of water irruption if the discontinuity zone is reached. The modelling also encompassed a sensitivity analysis for selected parameters of the model (horizontal and vertical hydraulic conductivity, conductivity of bottom sediments in adjacent water flows or infiltration of rainwater, and/or the amount of infiltrating water from the surface water reservoirs).