Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2007. / Two–thirds of South Africa, including more than 280 towns and settlements are largely dependent on groundwater for their drinking water supply and development. However, groundwater resources in South Africa are limited both in terms of quantity and quality, especially in the semi–arid parts of the country (Sililo et al., 2001, p. i). Therefore, the importance of protecting groundwater resources from pollution has been recognized. The first objective of this research was to investigate the attenuation capacity of a selection of soil horizons and materials representing major types of diagnostic horizons and materials in the South African soil classification in order to validate their chemical attenuation ratings as provisionally specified by Sililo et al. (2001, p. 4.6). The second objective was to assess the pollutant attenuation capacity of South African soil horizons and materials as well as describe the diagnostic value of key chemical properties of soils for conveying information on their contaminant transport/attenuation potential. The third objective was to investigate whether it is possible to apply acid/base priming using H2SO4 and Ca(OH)2 to a bulk quantity of soil in order to reduce the mobility of contaminants.

Organic contamination is associated with inorganic contamination in a plume resulting from acidic mine drainage water in an area of copper mining, Globe, Arizona. The level of dissolved organic carbon (DOC) is low, but is eight times the 0.5 mgC/l background. The source is probably organic reagents used in mineral processing. DOC fractionation using XAD-8 resin sorption chromatography gave a hydrophobic acid fraction (humic substances) of 1.0 mgC/l, and the hydrophobic neutral fraction was also anomalous, being as high as 49% of DOC. The fractionation data matched that for a waste-solution lake, believed to be a source of the aquifer contamination. Loss of DOC is occurring downgradient in the aquifer, based on comparison of DOC/chloride ratios. Loss occurs as the pH increases to over 4 or 5. Sorption onto metal precipitates being formed, particularly of the hydrophilic fraction, may be occurring.

Metal contamination in groundwater aquifers poses risks to human health as well as other life forms. Previous laboratory experiments have demonstrated that bacteria found in geologic settings like aquifers are likely to adsorb metal contaminants and attenuate metal migration. However, as bacteria can also migrate through the groundwater aquifer a better understanding of the combined effect of these two processes is required. The aim of this laboratory study was to a) explore the affinity bacteria exhibit towards metals and porous media of varying composition, b) investigate the effect of mineral and solution composition on the bacterial filtration and c) use the combined data to predict the impact of microbes on metal mobility in porous media. Pantoea Agglomerans was used as a model bacterium while column materials consisted of quartz sand and iron-oxide coated sand (IOCS). Bacteria were characterised using potentiometric titrations to identify the type and concentration of sites present on their bacterial wall. Particular attention was paid to the effect of kinetics of proton and metal adsorption due to the variable contact times that solutions have with bacteria in columns. It was found that increasing the contact time between cell surfaces and protons during potentiometric titrations resulted in less reproducible results. This was due to the release of cell exudates under high pH conditions rather than cell death. Exudates were also found to adsorb protons. Moreover, zinc adsorption onto cell surfaces is higher after 60 to 90 minutes of contact time, while there is a decline in adsorption for longer contact times due to release of cell exudates in the solution. Stability constants for the adsorption of zinc onto cell surface sites, quartz and IOCS materials were determined through batch adsorption experiments, providing a mechanistic explanation of the adsorption process. Reactive transport models incorporating kinetics and surface complexation are developed to describe zinc movement through packed columns. Batch kinetic studies showed that significant Zn sorption to IOCS takes place gradually during the first two hours of contact time. Adsorption continues to take place at a slower rate for an additional 10 hours. This kinetic effect is manifested also during flow-through experiments (column dimensions: length 0.12 m, diameter 0.025 m) with a Darcian velocity 6.1·10-3 cm s-1, which is comparable to natural groundwater flow rates through sand porous media. A pseudo-second order kinetic adsorption model is combined with a numerical advection dispersion model for the first time to predict Zn transport. Model output results are of mixed quality as the model cannot successfully describe contaminant arrival time and breakthrough curve shape simultaneously. Moreover, a mechanistic surface complexation reactive transport model is capable of predicting Zn sorption under varying pH conditions demonstrating the versatility of mechanistic models. However, these models do not account for kinetics and therefore they are not intended to fit the dispersion of the contaminant due to kinetic effects of adsorption. Experiments in mixed zinc/cell systems demonstrate that transport through IOCS is dominated by the adsorption to the porous medium. This is consistent with the batch surface complexation predictions for the system. Adsorption to bacteria is reversible and zinc is stripped from the cells and redistributed onto the IOCS. Adsorption onto cells becomes significant and plays a role in mobile metal speciation only once the column is saturated with zinc.

A contaminant fate and transport computer model, Bioplume II, which allows simulation of bioremediation in ground water systems, was used to compare the effects of 11 remediation scenarios on a benzene plume. The plume was created in three different hydrogeologic settings from the simulation of an underground gasoline storage tank leak.

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. Johannesburg, South Africa, 2015. / Unable to load abstract

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements of the degree of Master of Science in Geology Johannesburg, 1998 / This study determines the potential of prerncting pollution to ground water by sanitary landfills. The tracing capabilities of both stable and radioactive environmental isotopes are also evaluated. Four landfills were selected, the Linbro Park and Waterval sites in Johannesburg, and the Bloemfontein northern and southern landfill sites. The sites all differ in geological environment, size. age and physiographic setting. [Abbreviated Abstract. Open document to view full version] / MT2017

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. September 2014, Johannesburg. / Aims: The adsorptive removal of Cu, Mn, Hg and U by silica and maghemite nanoparticles (NPs) under acid mine drainage (AMD) conditions was investigated with the aim of assessing the applicability of NPs for remediation of AMD-contaminated water. The effect of NPs on metal uptake by algae, an increasingly popular remediation alternative, was also investigated. Methods: NP and algal metal removal were quantified by batch experiments using commercially prepared, bare and amine-functionalised silica-carbon hybrid NPs characterised for size, surface area, porosity, crystallinity, elemental composition and hydrodynamic size. Metal uptake by algae was quantified in the presence and absence of NPs. Results: Silica and maghemite NPs can be used for the adsorptive removal of Cu, Mn, Hg and U from AMD-contaminated surface and ground water. NP metal uptake was rapid and equilibria were attained within 5 minutes with silica and maghemite NPs, and within 45 minutes with amine-functionalised hybrid NPs. Adsorption efficiencies for Cu, Mn, Hg and U at pH 3 were 52, 56, 56 and 49%, respectively with silica and 56, 52, 75 and 50%, respectively, with maghemite NPs. Metal removal was enhanced by >10% in solutions containing ferric, manganese or sulphate ions, although Cu removal was inhibited in solutions with a >1 Mn:Cu ratio. Despite the presence of high affinity amine groups in hybrid NPs, Cu removal was only 52% due to the low surface area of the adsorbent. The comparative study with Hg, however, showed that surface area was not the only determinant of adsorption efficiency: maghemite NPs with a specific surface area ~15 times less than silica adsorbed 21% more Hg. Metal removal by Scenedesmus sp. was enhanced by 12-27% in solutions containing NPs due to the greater sorption surface areas. NPs also modified metal partitioning in algal cells: intracellular concentrations were lower and extracellular concentrations higher in solutions containing NPs relative to controls (no NPs). Conclusion: Silica and maghemite NPs can be applied for the adsorptive removal of Cu, Mn, Hg and U from AMD-contaminated water and to improve the efficiency of phycoremediation by Scenedesmus sp. These findings also point to the possibility of retardation of metals by NPs during their transportation from tailings and contaminated sites. Their partitioning to NPs and the strength of the interactions thereof can determine the prevalence of the metals in solution or in the solid phase.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand in fulfilment of the requirements for the degree of Master of Science Johannesburg 2017. / The development of the economy of South Africa and many other countries has been highly dependent on mining industries. Minerals such as gold, platinum, diamond and many others have been mined and continue to be mined. Despite the importance of these minerals, their processing comes with social and environmental problems. During the processing of these minerals, trace elements such as copper, chromium, nickel, mercury, uranium, molybdenum and many others are released as wastes into the environment either, directly or indirectly. The release of the elements into the soil is of concern due to the possibility of groundwater system contamination. The presence of these elements in the groundwater system poses serious challenges to the wellbeing of life forms, due to their toxicity, when they exceed threshold limits. From the processing plants, these elements could be released onto the soil, and mobilise to groundwater, increasing the already existing environmental crisis due to water pollution. Once these elements are in the water, access to living organisms becomes easier through the food chain. Some of these elements are not biodegradable and thus persist in the environment as well as in the bodies of living organisms. They can cause serious health problems because of their toxicity effect. In humans, these elements can be carcinogenic, and also cause chronic disorders, kidney failures, defects in infants, bone and vascular diseases which could also be lethal. It is therefore of importance that these elements are neither bioavailable nor bioaccessible to living organisms. When these elements are mobile in the soil, the probability of reaching groundwater increases. Water, an important natural resource should always be protected from such pollutants. The demand for unpolluted water has been rising every year in the world due to increasing population, extended droughts and improper disposal. This research was dedicated to determining the behaviour of elements in an agricultural soil impacted by mining activities. Agricultural soils are sometimes exposed to pollutants that could originate from dust fallout or precipitation; fertilisers and manure; pesticides; and water used for irrigation. Understanding the iv processes that control the distribution of these pollutants in agricultural soils is an important risk assessment measure, considering that such pollutants have the potential of being taken up by crops and vegetables or transported to groundwater. In this study, a soil on a farm that grows vegetables for commercial purpose. Cabbage, spinach, carrots and potatoes are some of the vegetables grown on the plot and sold to markets in Pretoria and Johannesburg. The plot is in the vicinity of smelting operations in the North West Province. The mobility of trace elements in the soil can be controlled, depending on the type and properties of soil. Hence in this research, the ability of the soil to adsorb elements entering the soil is studied. The batch experimental work was performed to determine the effect of pH, initial concentration (5 - 100 mg/L), competing ions (Fe3+, Ca2+, Co2+, Mg2+, K+, Ni2+ and Zn2+), fertilisers (ammonium nitrate, ammonium phosphate and calcium chloride) and plant exudates (acetic acid, citric acid and oxalic acid as well as ethylenediaminetetraacetic acid (EDTA) which is often used as proxy organic ligand (found in manure)) on the adsorption of cadmium (Cd), copper (Cu) and chromium (Cr) onto an agricultural soil. The PHREEQC geochemical modelling code was used to complement experimental methods in predicting processes and to further assess the leaching behaviour of the elements. Powder X-ray diffraction (PXRD) and X-ray fluorescence (XRF) were used to determine the mineralization of the soil. The structural features of the soil were determined using Fourier Transform Infrared spectroscopy (FTIR) and the element content was determined using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The point of zero charge (PZC) of the soil was found to be 8.3 and the cation exchange capacity (CEC) of 51.6 meq/ 100g. In the absence of fertilisers and plant exudates, the soil exhibited a similar high adsorption for elements at all initial concentrations by all the elements. Most (> 90%) of the elements were adsorbed within the first 3 minutes of contact with the soil. Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms were used to describe the experimental data for the elements. Kinetic rates were modelled using pseudo first-order and pseudo second-order equations. Pseudo v second-order gave the best fit for all the elements (R2 >0.999) indicating chemisorption. The effect of pH on Cd and Cu was insignificant however, the adsorption of Cr decreased with pH. The presence of competing ions decreased the adsorption of cadmium more than that of the other analyte elements. The soil was generally effective in adsorbing and retaining the elements. However, the retention was highly dependent on elemental speciation and prevailing conditions e.g. pH (as in the case of Cu and Cr). Such changes in conditions would have implications for groundwater quality. The effect of plant exudates and EDTA was studied and the results showed that low molecular weight organic acids (LMWOAs) viz acetic acid (AA), citric acid (CA) and oxalic acid (OA) and EDTA significantly (p < 0.05) decreased the adsorption capacity of the elements onto the agricultural soil. AA had the least effect on the adsorption capacity of the elements whereas OA and EDTA strongly prevented the adsorption of the elements. Moreover, some of the elements which were already in the soil including those which were not under study such as Ca and Mg were desorbed from the soil by OA and EDTA. Thus, the mobility of the elements was increased by the presence of plant exudates, increasing groundwater contamination and consequently threatening the health of living organisms. Agrochemicals such as fertilisers, stabilizers and pesticides are constantly applied to agricultural soils to improve the fertility of the soil for better crop production however; their presence may affect the mobility and bioavailability of elements in the soil. The effect of ammonium nitrate and ammonium phosphate as well as calcium chloride on the adsorption of Cd, Cu and Cr onto an agricultural soil was studied. The effects of initial concentrations of the elements (5 – 50 mg/L), concentrations of fertilisers (0.01 – 0.1 mol/L) and pH (3 - 8) on the adsorption of Cd, Cu and Cr were studied. The initial concentration of the elements and the concentration of fertilisers had no significant effect (p > 0.05) on the adsorption capacities of Cu and Cr at pH 5. But, ammonium nitrate and calcium chloride decreased the adsorption capacity of Cd. The adsorption of Cd onto the soil was reduced as the concentration of fertilisers increased. The adsorption of Cd was lower than that of Cu and Cr at all pH values. The agricultural soil was found to vi be an effective adsorbent in preventing the mobility of Cu and Cr in the presence of fertilisers but not for Cd whose adsorption was significantly affected by the presence of ammonium nitrate and calcium chloride. A continuous flow fixed-bed column script with specified conditions simulating the natural environment was utilised in PHREEQC for column studies. The geochemical computer model PHREEQC can simulate solute transport in soil surfaces. The effect of initial concentration (100 and 300 mg/L) of the elements, column bed depth (5 and 10 cm) and pH (3, 5, 7 and 10) were considered in this study. The adsorption capacity was affected by initial concentration of the elements since the breakthrough curves at higher analyte concentrations were reached at lower pore volumes than at low concentrations. This can be attributed to the fast occupation of active sites of the soil at higher concentrations. The results from PHREEQC indicated that the conditions used would lead to the oxidation of Cr3+ to Cr6+ leading to the formation of HCrO4- and Cr2O72- which were not favoured for adsorption by soil surfaces due to high solubility. This could have potential implications on the quality of groundwater in regions with similar conditions. Thus, the leaching of Cr6+ onto the agricultural soil will be high in areas where remediation techniques are not applied. The changing of bed depth from 5 to 10 cm did not have an effect on the adsorption of the elements. The ability of the soil surfaces to adsorb Cd and Cu even at lower bed depth implies that the soil will be effective in preventing the leaching of the elements to groundwater due to strong surface interactions of the elements with the soil. The results from PHREEQC showed that the adsorption of Cd and Cr onto the soil surface was not affected by pH. The results for Cr were contradicting with those obtained from laboratory experiments which could be due to the conditions used in PHREEQC. The change in the speciation of Cu at basic conditions decreased the ability of Cu adsorption onto the soil surfaces. The Cu2+ was converted to Cu(OH)2 which were large in size and thus only a small amount could be adsorbed since the other adsorption sites were covered by the large species. This research had notable outputs in the form of publications which will form an important repository of information. / LG2017

In this work two inverse methodologies are developed based on the Green element method for the recovery of contaminant release histories and reconstruction of the historical concentration plume distribution in groundwater. Unlike direct groundwater contaminant transport simulations which generally produce stable and well-behaved solutions, the solutions of inverse groundwater contaminant transport problems may exhibit non-uniqueness, non-existence and instability, with escalation in computational challenges due to paucity of data. Methods that can tackle inverse problems are of major interest to researchers, and this is the goal of this work. Basically, the advection dispersion equation which governs the transport of contaminants can be handled by analytical or numerical methods like the Finite element method, the Finite difference method, the Boundary element method and their many variants and hybrids. However, if a numerical method is used to solve an inverse problem the resulting matrix is ill-conditioned requiring special techniques to be employed in order to obtain meaningful solutions. In view of this we explore the Green element method, which is a hybrid technique, based on the boundary element theory but is implemented in an element by element manner. This method is attractive to inverse modelling because of the fewer degrees of freedom that are generated at each node. We develop two approaches, in the first approach inverse Green element formulations are developed, the ill-conditioned matrix that results is decomposed with the aid of the singular value decomposition method and solved using the Tikhonov regularized least square method. The second approach utilizes the direct Green element method and the Shuffled complex evolutionary (SCE) optimization method. Finally, the proposed approaches are implemented to solve typical problems in contaminant transport with analytical solutions besides those that have appeared in various research papers. An investigation on the capability of these approaches for the simultaneous recovery of the source strength and the contaminant concentration distribution is carried out for three types of sources and they include boundary iv sources, instantaneous point sources and continuous point sources. The assessment accounts for different transport modes, time discretization, spatial discretization, location of observation points, and the quality of observation data. The numerical results demonstrate the applicability and limitations of the proposed methodologies. It is found in most cases that the solutions with inverse GEM and the least squares approach are of comparable accuracy to those with direct GEM and the SCE approach. However, the latter approach is found to be computationally intensive.

Este trabalho apresenta os resultados obtidos no processo de remediação de uma área impactada pelo composto tetracloroeteno através do emprego da tecnologia de oxidação química in situ (ISCO). O teste de bancada realizado em uma amostra de água subterrânea da área de estudo tratada com uma solução de 5% de permanganato de potássio resultou em um percentual de remoção da massa de tetracloroeteno e seus produtos de degradação natural (tricloroeteno, dicloroeteno e cloreto de vinila) superior a 99%. Ao todo, foram injetados em subsuperfície 2950 kg de permanganato de potássio a uma concentração de 6% para o tratamento de 20000 m³ de um aqüífero impactado pelo composto tetracloroeteno e os seus produtos de degradação natural. A injeção de permanganato potássio resultou na destruição de aproximadamente 70% das concentrações de tetracloroeteno e seus produtos de degradação natural na área alvo de remediação dentro de um período de 30 dias após o término da aplicação do oxidante em subsuperfície, comprovando a eficiência do processo de oxidação química in situ para o tratamento de águas subterrâneas impactadas pelo composto tetracloroeteno. / This work presents the results obtained during the remediation process of an area impacted by the compound tetrachloroethene applying the technology of in situ chemical oxidation (ISCO). The bench test performed in a groundwater sample from the study area treated with a 5% potassium permanganate solution resulted in a percentage removal of tetrachloroethene mass and its natural degradation products (trichloroethene, dichloroethene and vinyl chloride) superior than 99%. In total, it was injected in the subsurface 2950 kg of potassium permanganate with a concentration of 6% in order to treat 20000 m³ of an aquifer impacted by the compound tetrachloroethene and its natural degradation products. The potassium permanganate injection resulted in the destruction of approximately 70% of the tetrachloroethene concentration and its natural degradation products in the target area within a period of 30 days after finishing the oxidant application in the subsurface, confirming the efficiency of the in situ chemical oxidation process for treating groundwater impacted by tetrachloroethene.