Hydrochemical characterisation of Northern KwaZulu-Natal historic coal mining districts, Northeastern South Africa.

Abstract

This M.Sc. dissertation reports the results of a hydrogeochemical study undertaken on historical coal mining districts of northern KwaZulu-Natal (KZN) Province, South Africa. The research catchment covers an area of about 12945 km2, located in the head waters of the Tugela River Basin or the uThukela Water Management Area (WMA). The main aim of the study was to assess the effectiveness of the rehabilitation undertaken by the South African Government on the various defunct/abandoned historical coal mines in northern KZN in improving surface water and groundwater quality in the region. Characterisation of surface water and groundwater water in terms of their interconnection, flow and hydrochemistry were undertaken. Primary (original data) and secondary data and information were collected, collated and analysed to understand the hydrogeochemical conditions of the region. The original data collected through a series of field campaigns within the study area, were complimented with secondary data from the Department of Water Affairs and Sanitation (DWS) monitoring programme, the KZN Groundwater Recourse Information Project (GRIP), the National Groundwater Archives (NGA) and borehole logs, hydrochemical and borehole yield data from various reports. The results of the study reveal that since the beginning of groundwater monitoring in 2010, the groundwater has been characterised by circumneutral waters. Time series EC, SO42- and Fe2+ data reveal no incongruities apart from a few episodes of elevated concentrations. Surface water hydrochemical analyses revealed peaks in EC coupled with low pH at varied sampling points which are presumed to be impacts from Acid Mine Drainage (AMD). Time series saturation states of groundwater with respect to calcite and dolomite indicate that groundwater remains oversaturated with respect to these minerals but under saturated with respect to gypsum as a result of carbonate AMD neutralization reactions. Trace metal data reveal no anomalous concentrations both in surface water and groundwater samples as a result of the circumneutral hydrogeochemical conditions. Major ion hydrochemical data show two main groundwater hydrochemical facies in the study area, namely most upstream boreholes are characterized by Na-Ca-HCO3-SO4 and most downstream boreholes are characterised by Ca-Mg-HCO3-SO4 hydrochemical water types. All surface water and groundwater samples have δD and δ18O isotopic values that plot on or below the Local and Global Meteoric Water Lines, indicating recharge from meteoric source with some evaporation mainly within the rehabilitated mine dumps. The detectible tritium signal in the shallow aquifers reflect recent active recharge taking place.