4. Electronic Theses and Dissertations (ETDs) - Faculties submissions

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Assessing aquifer vulnerability to landfill pollution using drastic method in Gauteng, South Africa
(University of the Witwatersrand, Johannesburg, 2023) Mphaphuli, Idah; Abiye, Tamiru
This study integrated the DRASTIC method and field investigations into mapping the degree of vulnerability of aquifers to landfill pollution in the Gauteng Province, which is one of the most populated provinces in South Africa. In order to investigate the aquifer vulnerability of Gauteng's heterogeneous and complex geology, the DRASTIC method was used to generate intrinsic and specific vulnerability maps. Three vulnerability classes were generated from the DRASTIC index, namely, low vulnerability, moderate vulnerability and high vulnerability, which covered 46%, 37% and 17% of the study area, respectively. The highly-vulnerable areas were associated with the karst aquifer of Malmani dolomite, permeable vadose zone, high hydraulic conductivity and loamy sand/sandy loam soil type, whilst moderately-vulnerable areas were associated with fractured/weathered aquifers, high recharge and low topography. The intrinsic vulnerability was validated using average NO3+NO2-N (nitrate + nitrite as nitrogen) and the results of water samples from field investigations conducted in Marie Louise and Robinson landfill sites. Elevated NO3+NO2-N concentration (9.85-16.03 mg/l) was observed in the highly-vulnerable areas. Water samples were collected, in order to analyse the water chemistry, stable isotopes and radioactive isotopes (tritium). Gibbs and Piper diagrams were used to evaluate the main mechanism controlling the groundwater chemistry and the dominant major ions that influence it. Pollution by leachate was detected in the Marie Louise landfill site, where the groundwater showed high tritium and ammonia concentration. The main hydrochemical facies detected in Marie Louise were Mg SO4, Ca-SO4, Na-SO4 and Na-Cl. The hydrochemical facies detected in Robinson were Na-SO4, Ca-HCO3, Na-Cl and Ca-Cl. The DRASTIC method was shown to be effective in assessing groundwater vulnerability on a regional scale, provided that there is adequate input data.
Baseline Hydrogeology of Dolerite Dykes in Lesotho, Mafeteng District as a Case Study
(University of the Witwatersrand, Johannesburg, 2024-06-10) Monyane, Napo Shadrack; Shakhane, Teboho; Abiye, Tamiru
Groundwater is a vital alternative resource due to the increasing demand for water supply in Lesotho’s rural and urban areas as surface water faces threats from population growth and climate variability. For instance, groundwater serves the demands of Lesotho's growing textile industry and agricultural sectors. The 3D form of the dolerite dykes widespread throughout the Karoo rocks in Lesotho may have an impact on the groundwater occurrence, flow, and yield characteristics of the region. However, specific research on their hydrogeology has not been extensively undertaken. This study aimed at characterising the hydrogeology of the dolerite dykes in the lowlands of Lesotho using selected places namely, Boluma-Tau, Ha Lumisi, Ha Mofota, Ha Maoela, Ha Mofo, Malumeng, Qalabane, Matlapaneng, Thabana Mohlomi, Ha Mohlehli, Malimong, Tsoeneng and Ha Lenonyane as case studies for the research. This research adopted the desktop and walkover survey in developing information on the region’s broad geological and hydrogeological setting within the Karoo lithologies. Included also was the use of ground magnetics in ascertaining the existence and determining the geometry of the dykes, using the D-8 algorithm for flow directions, and drilling and pumping tests for aquifer analysis. The dykes dominating the focal area in the Mafeteng District generally trend NE-SW, NNE-SSW and NW-SE. The magnetic results outlined negative anomalies along the dyke’s contact with the country rocks as surveyed from Qalabane, Mafeteng Lesotho, these magnetic lows imply fracture gaps along the strike of the dyke. A generalised dip, width, and depth could not be easily inferred due to inconsistent magnetic anomaly shapes, but forward modelling indicated a thin (10 m wide) shallow (10°) dyke trending NE-SW intruding both the Burgersdorp and Molteno Formations at Qalabane, Mafeteng. As per the D-8 results, the dolerite dykes in Mafeteng are distributed in the intermediate basin flow values due to a gentle hydraulic gradient. Certain dyke sites exhibit a groundwater flow direction towards the north, whilst others display a radial groundwater flow direction. The derivative analysis revealed the boreholes were drilled in a fractured dyke system, also the dominant radial flow regime and double porosity dip at different pumping durations, and the possible recharge boundary were revealed in some drilled dyke sites. Further analysis from the drawdown versus time curves resulted in average yields of 0.1 – 1.25 l/s with transmissivities ranging from 1 – 14 m2/day, insinuating that a limited extraction of the local water supply is suggested from the dolerite dyke lithologies in the lowlands of Mafeteng Lesotho, given the groundwater yielding capacity and magnitude of the transmissivities. Even though the drilled boreholes from the dyke sites indicated a fractured dyke setting, estimated transmissivity values are variable and low, this is indicative of the inconsistent apertures and lack of interconnectivity of the available secondary hydrogeological features in the lowlands of Lesotho.
Hydrogeological assessments and investigation of inflow sources at Lumwana Copper Mine, Zambia
(University of the Witwatersrand, Johannesburg, 2023) Mbilima, Mike; Abiye, Tamiru
This Research Report presents results of integrated field and desktop-based hydrogeological investigations at the Lumwana Mine, Zambia. Groundwater occurrence in the mine poses challenges with effective mining operations and slope stability. The primary aim of this study was to establish the sources of groundwater inflows and to establish the nature of surface water and groundwater interaction within the Lumwana Mine hydro-geotechnical units. The Lumwana hydrogeological investigation has been achieved through the integration of multi-disciplinary data types, which include geology, structures, hydrochemistry, meteorological data (rainfall, temperature, humidity and evapotranspiration), environmental isotopes, dewatering pumping records, groundwater level monitoring, water temperature, general hydrogeological data and surface hydrology. The investigation has confirmed the presence of hydraulic connections between different surface water bodies such as dams, diversion channels, streams and open pit excavation, and has proven to be a useful approach in tracing the source of mine inflows. Rainfall, groundwater and surface water samples have similar δ18O and δ2H isotopic signatures thus lamenting the existence of a hydraulic link between groundwater and surface water. Recharge estimation through Water Table Fluctuation method (WTF) determined 8% of mean annual precipitation (MAP). The dominant hydrochemical facies are Ca-Mg-HCO3 and Ca-Mg-SO4. The local geology and geochemistry of the tailings are the main controllers of groundwater chemistry through rock-water interaction. The geology of the study area consists of older metamorphosed gneisses, schists, migmatites, amphibolites and granitoids. Integrated assessment of the Lumwana hydrogeological environment has enabled the development of the Lumwana Mine hydrogeological conceptual model. In the shallow, highly to moderately weathered zones, groundwater flows from south towards low topographic regions in the northwest mimicking the general topography. The hydraulic test conducted at Lumwana Mine has revealed the saprock units have higher hydraulic conductivity by several orders compared to the saprolites and the fresh bedrock, where groundwater flow is mainly controlled by the occurrence and distribution of the fracture network.