Application Of Environmental Isotope Tools To Improve Conceptual And Numerical Modeling Of Groundwater Flow In Kosh Goldfields, Witwatersrand Basin, South Africa

Environmental isotope and hydrochemical analyses were employed to improve existing understanding of groundwater flow dynamics in the defunct mine for assessing the source of water at a pumping shaft located near Stilfontein Town, Northwest Province, South Africa. Currently pumping is done using the shaft at an average rate of 37,000 m3 /day to prevent flooding of downstream mines. The current findings point out that the source of water at the shaft comes from a much narrow area than previously reported and that the contribution of seepage water from a nearby return water dam is significant enough to compensate groundwater flow from the upper dolomite aquifer and limit northerly expansion of the cone-of-depression. Hydrochemical data reveals that shaft-water at deeper levels (950 m bgl) exhibit evidence of mine seepage originating from the nearby tailings dam. The isotope data also show that up to 45% of water is recycled between shaft water and the surface water. Tritium values of the shaft-water samples are above 4 TU suggesting recent recharge is taking place at deeper levels through open fractures and mine underground haulages. The information from the hydrochemical and environmental isotope data was used to improve an earlier understanding that the source of water as coming dominantly from dolomite aquifer. Finally, the results highlight the relevance of coupling various methods to check the result of numerical modelling, and indeed the centralized pumping is key to controlling subsurface water flooding in downstream mines, a successful implementation of regional mine water management.

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Haile A
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