Institute for Groundwater Studies (IGS)

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Browsing Institute for Groundwater Studies (IGS) by Author "Boshoff, Elida"

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    Comparing model calculated groundwater volumes with alternative methods in a mining enviroment
    (University of the Free State, 2012-09) Boshoff, Elida; Van Tonder, Gerrit; Dennis, Ingrid
    English: A new opencast coal mining operation is proposed in the Belfast region in Mpumalanga, South Africa. This proposed operation is the study site that was investigated in this thesis. The Belfast opencast operation is expected to be operational for 29 years and coal from mainly the number 2 and 3 seams will be mined. The inflow rate of the groundwater was determined by using both analytical and numerical groundwater methods. The rate at which groundwater flows into the mine voids are important to estimate before mining commence since this will determine at what rate groundwater needs to be pumped from the mining pits to ensure dry and safe working conditions. In order to obtain site specific data for the study area, several field investigations have been conducted. These investigations include a geophysical survey, drilling of monitoring boreholes and pump testing of the monitoring boreholes. These investigations are done to obtain a better overview of the aquifer conditions in the study area. For the study area a numerical groundwater flow model was constructed and the groundwater inflow was determined by making use of a water budget function. The analytical approach to determining the inflow included four different methods. A sensitivity analysis was done on the recharge with the numerical and analytical methods. The results from the numerical and analytical approaches were compared to determine whether the analytical approach is in fact a good way of obtaining values that relates with the numerically obtained results. If there is a good correspondence between the analytical and numerical results, the analytical approach can be regarded as a save and representative way to obtain groundwater related values. Especially during the early stages of mine planning analytical methods would be supportive to quickly determine mine related issues as this will assist in decision making and related cost estimates. From the results obtained in this thesis it can be concluded that the analytical approaches used during this study, although giving close to numerical answers, cannot be used in an effective manner in determining groundwater inflows during the early planning of mining. The fact that the analytical approaches did not reveal representative values for the groundwater inflows and also do not correlate with the numerical model results, does not mean that this will be the case at another site with different geohydrological characteristics. It is important to note that assumptions are always made in analytical methods. It is suggested that further research be conducted in relation with analytical and numerical modelling of opencast mines. Research should be performed at several mines to determine whether the relation between the numerical and analytical approaches display similar trends than was found during this study. These mines should preferably be on similar geological areas to compare with each other. The only way to determine whether the analytical methods can in fact be used to get a representative result is by repetition on several mining sites and also comparing these values with the numerical model results and also the actual inflow rates from the mine once mining has started.