Numerical modeling and environmental isotope methods in integrated mine-water management: a case study from the Witwatersrand basin, South Africa

Mengistu, Haile; Tessema, Abera; Abiye, Tamiru; Demlie, Molla; Lin, Haili

Numerical modeling and environmental isotope methods in integrated mine-water management: a case study from the Witwatersrand basin, South Africa | Modélisation numérique et méthodes des isotopes environnementaux pour la gestion intégrée de l’eau des mines: une étude de cas sur le Bassin du Witwatersrand, Afrique du Sud Métodos de modelado numérico e isótopos ambientales en el manejo integrado del agua de mina: un caso de estudio de la cuenca de Witwatersrand, Sudáfrica 数值模拟与环境同位素方法在矿水综合管理中的应用:南非金山矿区实例研究 Modelação numérica e métodos de isótopos ambientais na gestão integrada mina-água: estudo de caso da Bacia de Witwatersrand, na África do Sul

2015

Mengistu, Haile | Tessema, Abera | Abiye, Tamiru | Demlie, Molla | Lin, Haili

Improved groundwater flow conceptualization was achieved using environmental stable isotope (ESI) and hydrochemical information to complete a numerical groundwater flow model with reasonable certainty. The study aimed to assess the source of excess water at a pumping shaft located near the town of Stilfontein, North West Province, South Africa. The results indicate that the water intercepted at Margaret Shaft comes largely from seepage of a nearby mine tailings dam (Dam 5) and from the upper dolomite aquifer. If pumping at the shaft continues at the current rate and Dam 5 is decommissioned, neighbouring shallow farm boreholes would dry up within approximately 10 years. Stable isotope data of shaft water indicate that up to 50 % of the pumped water from Margaret Shaft is recirculated, mainly from Dam 5. The results are supplemented by tritium data, demonstrating that recent recharge is taking place through open fractures as well as man-made underground workings, whereas hydrochemical data of fissure water samples from roughly 950 m below ground level exhibit mine-water signatures. Pumping at the shaft, which captures shallow groundwater as well as seepage from surface dams, is a highly recommended option for preventing flooding of downstream mines. The results of this research highlight the importance of additional methods (ESI and hydrochemical analyses) to improve flow conceptualization and numerical modelling.

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