Electronic Theses and Dissertations (Masters)

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Start date: 2020Subject: search.filters.subject.SDG-13: Climate action

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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.
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    The tectonic evolution of the Bredasdorp Basin and its implications for oil and gas formation
    (University of the Witwatersrand, Johannesburg, 2023-10) Tau, Rethabile; Enslin, Stephanie; Manzi, Musa; Saffou, Eric
    The Bredasdorp Basin is an offshore rift basin located in the southernmost tip of Africa, within the larger Outeniqua Basin. Previous studies have indicated the presence of hydrocarbons, as well as structures or evidence that allude to the presence of hydrocarbons, where the basin has not yet been extensively drilled or explored. In this study, seismic attributes applied to high resolution pre-stack time migrated 3D seismic data are analyzed, in conjunction with well logs, specifically the gamma ray logs. By employing these methods, the study aims to delineate the presence of hydrocarbons and their migration, as well as deduce the evolution of the basin based on the structures observed. Using artificial neural network (ANN) to predict the lithologies and analyzing the patterns in the gamma ray logs, the stratigraphic results show that the basin begins with a marine dominated environment from the Valanginian age to Aptian age. From the Aptian to Albian age, there are consistent changes in sea level and sedimentation, caused by thermal sag and uplift. Past the Albian age to present age, the deposition environment is dominated by sandstones and coarse sediments. This is due to the evolving basin moving from a distal to a proximal environment of deposition. Using seismic attributes such as envelope attribute, edge detection and variance attribute, structures such as paleo pockmarks and fluid escape structures are identified. These identified paleo pockmarks have diameters ranging from 400m to 900m. In addition to these structures, erosive features were observed which could be classified as submarine channels or slump structures, with the dominating channel having depths of up to 1585 m. Using variance and ant-tracking, the fault structures observed of the study areas revealed two dominating phases of rifting. The first phase has horsts and grabens bounded by normal faults trending E-W, with implications that the rifting propagated N-S in this phase of rifting. This phase of rifting ends during the Aptian age. The next phase of rifting begins during the Santonian age, with the fault bound horsts and grabens trending N-S, which indicate an E-W rifting direction.