Groundwater impact assessment in a coal mine area of Witbank, Mpumalanga

Erasmus, Cobus Abraham
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A groundwater impact assessment was compiled of an operational coal mine situated in the Witbank region of Mpumalanga, South Africa. This was done by evaluating the existing groundwater level and groundwater chemistry datasets (2016 - 2012) from the groundwater monitoring programme of the mine. The study area is located within the Witbank coalfield with the local geology dominated by the Vryheid Formation of the Karoo Supergroup. A conceptual hydrogeological site model and a conceptual hydrogeological cross-section were produced using the results obtained from the data evaluation. The mine contains a shallow weathered zone aquifer, fractured aquifer and disturbed groundwater system (opencast coal mine). The 2013 groundwater level and groundwater chemistry dataset provided the most accurate representation of the actual conditions present within the study area (as it contains the most complete datasets). The regional groundwater flow trend appears to be radially inwards towards the central portions of the mine site (over the current mine workings). The regional groundwater trend differs from what would be expected from a natural groundwater system within the region. The variations in the regional groundwater trend were most probably caused by active mine dewatering and groundwater abstraction within the study area. Acid mine drainage reactions influenced most of the groundwater quality issues within the study area. Lowered pH coupled with high concentrations of sulphate and dissolved metals (iron, aluminium and manganese) were encountered within: the current (and rehabilitated) mine workings, the north of the mine site (over the old underground workings and near old mine dumps) and adjacent to, or downstream from, the mine discard stockpile (south-east portion of the mine site). High chloride concentrations in some monitoring boreholes were caused by runoff from agricultural areas and from the mine site within the region. Substantial mixing between contaminated water and fresh water was evident from all of the groundwater chemistry datasets evaluated.
A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Hydrogeology, August 2018
Erasmus, Cobus Abraham, (2018) Groundwater impact assessment in a coal mine area of Witbank, Mpumalanga, University of the Witwatersrand, Johannesburg,