Institute for Groundwater Studies (IGS)

Permanent URI for this community

http://hdl.handle.net/11660/103

Browse

Now showing 1 - 20 of 120

Open Access
Acid-base potential characterisation in the Southern highveld coalfield of Mpumalanga
(University of the Free State, 2017-07) Ntwaeaborwa, Gaonkile Molly; Deysel, Lore-Mari
Pyrite, iron disulphide is the most common mineral in the metal sulphite and coal deposit. The oxidation of Pyrite and other metal-sulphide minerals by oxygen has a large environmental impact and plays a key role in Acid Mine Drainage (AMD). Environmental impact shows that soil acidity, toxic metal concentrations and vegetation damage are the predominant negative impact of AMD. AMD is a major concern for the mining industry because mining activities tend to increase the amount of rock surface exposed to air and water. Mining companies are increasingly required to evaluate the AMD potential at future mine sites and provide detailed plans to prevent or minimise AMD at all phases of mine operation as part of the environmental Impact assessment (EIA) process. An investigation was conducted in two mine (Mine 1 and Mine 2) areas in the Southern Highveld Coalfield of Mpumalanga. Mine 1 is an underground coal mine and is situated 10 km outside Trichardt on the road to Bethel. It was established in May 2012 and its shaft supply coal to Sasol Synfuels. Mine 2 is an open-cast coal mine and is situated between 2 towns, amely Trichardt and Kriel. Construction activities started in 1990 and the mine reached full production in September 1992. Both Mines fall in the Karoo Supergroup which comprises of Ecca group formation and consist dominantly of sandstone, siltstone, shale and coal. The aim of this study was to investigate the acid-base potential of these two Mines. 118 samples were collected from Mine 1 borehole core and 71 samples were collected from Mine 2 borehole core to conduct mineralogical and Acid Base Accounting (ABA) analysis. Acid- base potential leachate were further analysed for major and trace elements using Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). Most of the samples analysed for Mine 1 have been found to have High AMD risk at the interburden and these samples have low NNP values, all these samples consisted of coal and they contained pyrite mineral as indicated in the mineralogical analysis. These samples must be taken into consideration to minimise oxidation. Samples (Mine 1) that contained layers of sandstone, siltstone and shale have the highest NNP values and these layers can be used as a buffer to neutralise the AMD. Therefore Mine 1 will produce an AMD at the coal seam once exposed during mining. Mine 2 shows that 3 samples have High AMD risk at the interburden while 2 boreholes show the risk between 20m and 60m, and these samples were coal samples and others were sandstone samples and they contained pyrite. These samples that have coal showed low NNP. Therefore most of the acid generation would be mainly found at the coal seams. Layers that show high NNP values consisted of sandstone, siltstone and shale. They showed no indication of acid generation, therefore they will work as buffers to neutralise the any AMD that will be produced. Mine 2 also indicate that AMD will be produced at the interburden at layers that contains coal, therefore more consideration is needed when these layers are exposed during mining. With such condition it is possible for the mines to predict the types of situations that might arise concerning groundwater quality, and implement proper prevention or remediation programs.
Open Access
Analysis of a post-closure safety assessment methodology for radioactive waste disposal systems in South Africa
(University of the Free State, 2000) Van Blerk, J. J.; Botha, J. F.
𝑬𝒏𝒈𝒍𝒊𝒔𝒉 Radioactive waste in South Africa is generated through the nuclear fuel cycle and the application of radioactive materials in industry, science and medicine. The radioactive waste is presently disposed at Vaalputs in Bushmanland and Thabana at Pelindaba in near-surface disposal facilities. No strategy exists at present for the disposal of high level waste. The objective of radioactive waste management and its underlying principles is to ensure that human health and the environment are protected at all times, without imposing an undue burden on future generations. This implies that, before any long-term management strategy of radioactive waste disposal can be implemented, the impact of the disposed waste must be determined as a function of time-a procedure referred to as post-closure safety assessment. In this thesis, a methodology to perform post-closure safety assessments of radioactive waste disposal systems in South Africa and other parts of Africa is described. Not only will it contribute significantly to reassess the suitability of current waste disposal practices, but also lays the foundation for future disposal practices. The proposed methodology-an integrated approach to radioactive waste management-is aimed at: (a) ensuring the safety of the present public and future generations, (b) enhancing the public acceptance of the methodology, (c) keeping the expenditure associated with the implementation of the methodology at a minimum. The methodology recognises the interdependence between operational phase activities and the post-closure behaviour of the disposal system. It is an iterative process that considers site-specific, prospective evaluations of the post-closure phase to ensure that the disposal system will comply with internationally accepted criteria, within reasonable limits. Provision is therefore made to identify the data, design and other needs that will contribute towards the achievement of this objective. The first step in this procedure is to identify those internal and external features, events and processes that can be used to predict how radioactive material may escape from the disposal facility, along which paths will it migrate and how it may impact humans. Various conceptual and mathematical models that can be used to develop appropriate scenarios of these processes and to compare the results with site specific data are discussed in the thesis. The cost to develop a waste disposal system, the disposal of the waste and the pre- and post closure assessments of the system, or so-called nuclear liabilities, can be astronomically high. Combining the post-closure assessment of the system with the decision analysis framework discussed in the thesis can reduce these costs considerably. Post-closure assessments of radioactive waste disposal systems have in the past often been interpreted as an exercise to predict the exact behaviour of the system far into the future. However, as pointed out in the thesis this is not possible, even with the technology available today. The more pragmatic approach, advanced in the thesis, is that modem technology is able to demonstrate to reasonable members of the public that such a system will be safe. Nevertheless it is recognized that the methodology cannot be implemented without the active participation of the public. It is therefore envisaged that the proposed methodology will be implemented with the close co-operation of the public, particularly those living near the site where the disposal system will be implemented.
Open Access
Analysis of dissolution trapping mechanisms on CO₂ plume: Carbon capture and storage
(University of the Free State, 2022) Kholotsa, Mathapelo Emely; Atangana, A.
The practice of carbon capture and storage effectively lowers greenhouse gas emissions and mitigates climate change and global warming. To determine whether long-term geological CO₂ sequestration is safe and practical, scientists have increasingly relied on model-based predictions of CO₂ behavior beneath the earth's surface in recent years. This investigation aims to get a firm grasp of the CO₂ dissolution trapping process and mathematical models depicting the behavior of the CO₂ convective dissolution process (Fingering) in saline aquifers. This comprehension will eventually help to ensure that the CO₂ plume stays inside the designated locations of CO₂ storage. The approach involved employing the concept of fractional differentiation by replacing the classical time derivative with the Caputo, Caputo Fabrizio, and Atangana Baleanu fractional derivative. To analyze the finger development process using three non-local operators: Power law, exponential law, and Mittag-Leffler function. Equally important, through performing linear stability analysis, we considered the stability evolution equation for the perturbation, which incorporated the exponential law and thus resulted in a memoryless function. We then replaced the exponential kernel with the Mittag-Leffler kernel to the perturbation equation to modify it into a process that has memory. By incorporating the Mittag-Leffler kernel into the perturbation equation, we suggest a new approach that provides a more accurate, robust, and efficient solution algorithm to capture finger development. In conclusion, we demonstrated some numerical simulations obtained using MATLAB.
Open Access
Application of artificial neural networks in the field of geohydrology
(University of the Free State, 2009-03) Steyl, Gideon; Dennis, S. R.
English: Groundwater has been identified as a viable alternative for future freshwater production in South Africa. The management thereof is steadily gaining more recognition from governmental institutions. A significant obstacle in the development of this resource is the conceptual understanding of surface water and groundwater interaction. The availability of reliable data for rainfall, flow volumes in rivers and water levels in boreholes have prompted an investigation into patching incomplete data sets. This study also focused on predicting the influence of rainfall and flow volumes in a river on the surrounding groundwater levels. Neural networks have been used to investigate both data patching and forward prediction of water levels in selected data sets.
Open Access
Application of electroseismic techniques to geohydrological investigations in Karoo rocks
(University of the Free State, 2003-11) Fourie, Francois Daniel; Botha, J. F.
English: The possibility of using surface electroseismic (ES) methods for groundwater exploration in fractured Karoo rocks is studied by investigating the criteria of vertical and lateral resolution of surface ES data and the ES thin bed response. The ES Fresnel zones for monochromatic excitation are found to be larger than their seismic equivalents and the lateral resolution of surface ES data is consequently poorer. Seismic velocity increases with depth result in larger ES Fresnel zones and poorer lateral resolution. As in seismics, only a single Fresnel zone can be identified for broadband excitation. Higher dominant frequencies and broader bandwidth result in higher lateral resolution. Rayleigh's criterion for vertical resolution applied to ES data requires that the imbedded layer has a thickness of at least λ/2 to be deemed resolvable, where λ is the wavelength of the seismic wave under consideration. There are, however, two wavelengths to consider for ES phenomena − those of the Biot fast pressure and slow pressure waves. Since the wavelength of the slow pressure wave in saturated Karoo rocks may be a couple of orders of magnitude smaller than the wavelength of the fast pressure wave, the theoretical limit of resolution is determined by the slow pressure wave. This wave is, however, strongly dissipative and the practical limit of resolution seems to depend more strongly on the wavelength of the fast pressure wave. A simplified approach to examine the ES thin bed response suggests that imbedded layers with thicknesses smaller than λ/2, where λ is the wavelength of the fast pressure wave, may be classified as electroseismically thin. Investigations by means of a full waveform approach that simultaneously takes the influence of the different wave types into consideration, supports the above observation. The results of an ES field survey on a site where a localised fracture is known to occur, supports the idea, but does not conclusively proof, that the lateral and vertical resolution of surface ES data is insufficient to detect fractures with apertures in the millimetre to centimetre range. The influence of porosity contrasts on ES reflection is studied by examining the change in the magnitude of the reflection coefficients when varying the porosity (and all porositydependent parameters, such as permeability) of a Karoo sandstone overlain by a Karoo mudstone. Increases in the sandstone porosity results in larger reflection coefficients, and consequently, stronger reflection. The possibility therefore exists to map porosity contrasts in a certain geological environment and thus identify zones more likely to be suitable as aquifers. The possibility of using ES techniques as a non-invasive means of obtaining information on the elastic properties of the rock matrix is investigated by examining the electroseismic and magnetoseismic transfer functions at positions in boreholes. The transfer functions are dependent on various physical and chemical parameters, including the elastic parameters and none of these parameters can be determined unambiguously from the evaluation of the different transfer functions. The shear modulus of the porous frame may be estimated from measurements of the shear wave velocity in a fluidsaturated porous system. Since an approximate linear relation exists between the shear and bulk moduli of the porous frame, the bulk modulus may be estimated once the shear modulus is known. Porosity changes due to aquifer deformation may lead to detectable changes in the transfer functions. The electroseismic transfer function of the fast pressure wave is insensitive to porosity changes in consolidated material. Although the electroseismic transfer function of the slow pressure wave is very sensitive to porosity changes, this wave is strongly dissipative and is notoriously difficult to measure. The magnetoseismic transfer function is sensitive to porosity changes and is likely to yield the most useful information on aquifer deformation.
Open Access
Application of the Mixing Cell Model to the quantification of groundwater – surface water interaction
(University of the Free State, 2013-07) Matthews, Amy Jane; Witthüser, K. T.; Van Tonder, G. J.
English: The significance of a reliable groundwater resource assessment is of growing importance as water resources are stretched to accommodate the growing population. An essential component of a groundwater resource assessment is the quantification of surface water – groundwater interaction. The insufficient amount of data in South Africa and the apparent lack of accuracy of current estimates of the groundwater component of baseflow lead to the investigation of a new methodology. The applicability of the Mixing Cell Model (MCM) to quantify the groundwater contribution to baseflow is examined to determine whether the method would be of use in groundwater resource assessments. The MCM simultaneously solves water and solute mass balances to determine unknown inflows to a system, in this application the groundwater component of baseflow. The incorporation of water quality data into the estimation of the surface water – groundwater interaction increases the use of available data, and thus has the ability to decrease the uncertainty of the estimation process. The balance equations are equated to an error term which is used in the quadratic programming solution of minimizing the square error sums in order to determine the unknown inflows. The mixing cell model is applied to datasets from the surface water – groundwater interaction test site developed by the University of the Free State, in addition to data collected along the middle Modder River during a fieldwork survey. The MCM is subsequently applied to a set of quaternary catchments in the Limpopo Province for which there are available calibrated estimates of the groundwater component of baseflow for the Sami and Hughes models. The MCM is further applied to the quaternary catchment D73F, located in the semi-arid Northern Cape, to assess the applicability of the mathematically based MCM in terms of a flow system located within a regionally-defined zero groundwater baseflow zone. The MCM results for each study area are assessed in comparison to groundwater baseflow volumes determined by the Pitman, Sami and Hughes models. A chemical hydrograph separation method which also incorporates water quality data is additionally reported for the study areas to further validate the MCM. The results indicate that the mixing cell model can reliably estimate the groundwater component of baseflow to a river. This application of the mixing cell model could contribute to increase and evaluate the accuracy of current groundwater baseflow estimates in South Africa, which will in turn ensure the responsible and sustainable use of the countries water resources.
Open Access
Appraisal of geophysical methods used for groundwater exploration in South Africa
(University of the Free State, 2023) Kolobe, Libuseng T.; Fourie, F. D.
Groundwater is a crucial resource that has been a means of survival for humans for many years, as seen in the tendency to settle near springs (Fitts, 2013). Interestingly, groundwater was extracted from dry mountain basins by Persians in what is now modern Iran (Fitts, 2013). Indeed, many methods have been developed over time to explore groundwater, as has been done with other resources of the Earth that are not readily visible. According to Arefayne 𝘦𝘵 𝘢𝘭. (2016), groundwater exploration is “the investigation of underground formations to understand the hydrologic cycle, know the groundwater quality, and identify the nature, number, and type of aquifers”. Numerous exploration methods are employed and are often used in conjunction with one another to ensure the most accurate estimation of groundwater potentiality in a given area. These exploration methods may be direct or indirect (Balasubramanian, 2017), with surface methods often indirect. These include esoteric techniques, which are the most ancient, also known as water witching or dowsing. Here, operators using a forked stick or an egg (Balasubramanian, 2017) claim to be able to detect water underground, the accuracy of which is fairly unproven (Arefayne and Abdi, 2016). Geomorphological methods study the landforms in the area of interest to show where the groundwater is likely to occur (Balasubramanian, 2017). Features such as pediplains or valley flats often show good groundwater potential (Sedhuraman et al., 2014). The slope and drainage density are also particularly important features as there is more infiltration in gently sloping areas, and a higher drainage density indicates more runoff and, hence, less potential for recharge (Sedhuraman et al., 2014). Other surface exploration methods may be geological in nature (Balasubramanian, 2017). Such methods first collect and analyse topographic maps, aerial photographs, geological maps, and core logs. This is then supplemented by geological field reconnaissance and evaluation of hydrological data on stream flows, springs, well yields, groundwater recharge levels, and water quality (Balasubramanian, 2017). Faults, joints, and lineaments are also noted, as these may form preferential flow paths for groundwater (Van Tonder 𝘦𝘵 𝘢𝘭., 2001). The structure of the water-bearing strata can also give indications for groundwater occurrence (Balasubramanian, 2017). Contacts between permeable rock overlying impermeable strata along the sides of valleys are suitable locations for groundwater (Balasubramanian, 2017). Quartz veins and dykes can be linear and form ridges (Nel, 2017). There, erosion-prone rock types may form depressions and are connected with structures ideal for water storage (Nel, 2017). Geobotany, which is the study of how plants are related to the subsurface, can also be used in the exploration of groundwater (Odhiambo, 2016). This means observing any anomaly in the growth of vegetation or trees growing in a straight line can be an indicator of subsurface moisture changes (Nel, 2017). The presence of phreatophytes can also allude to the presence of groundwater (Nel, 2017). Halophytes and white efflorescence of salt on the ground may also be an indication of shallow brackish or saline groundwater (Balasubramanian, 2017). Playas and precipitation of salt are also good indicators of possible groundwater occurrence (Balasubramanian, 2017). Photogeology, which is the use of aerial photography to study geology, can also provide valuable information for targets of a groundwater exploration exercise (Mekel, 1988). Another manner through which groundwater exploration can be conducted is through the use of geophysical methods. There are a variety of geophysical methods used in groundwater exploration employed for several reasons. However, the main objective of geophysical surveys in hydrogeology is to provide parameters for the creation of models essential for decision-making in groundwater exploration and protection (Mpofu 𝘦𝘵 𝘢𝘭., 2020). Geophysical survey methods can be airborne, conducted on the surface, or even conducted down boreholes (Balasubramanian, 2017). These methods operate primarily by detecting anomalies or contrasts in the physical properties of the Earth (Balasubramanian, 2017). These properties include but are not limited to density, elasticity, magnetism, and electrical resistivity. Such anomalies indicate the potential zones which can be exploited for groundwater. The use of geophysics in groundwater exploration is very important as it removes the need to drill many boreholes before the target is reached (Mpofu 𝘦𝘵 𝘢𝘭., 2020). Geophysical tools are invaluable in groundwater exploration; therefore, this study will be primarily based on the use of geophysics for groundwater exploration in South Africa.
Open Access
Aquaponics as a productive rehabilitation alternative in Mpumalanga Highveld coalfields
(University of the Free State, 2016-03-11) Botha, Ilse; Weaver, Alex.
The Mpumalanga Highveld Region is commonly known for its coal mining activities, especially surface mines. South Africa is still reliant on coal as its main energy source. A dilemma identified is that most of the coal reserves in Mpumalanga are (or were) located below highly productive arable land formerly used for food production such as maize. With a growing energy demand, these valuable areas of land are being impacted negatively. The post-mining land is predominantly rehabilitated to a grazing land capability instead of the pre-mining arable land capability, hindering the production of crops on those areas when mining ceases. This adds to the food security threat which South Africa is currently facing. The National Development Plan 2030 indicated the intentions to diversify the national economy. It was identified that agricultural activities should be expanded to relieve the high levels of poverty in rural areas, and that sustainable agriculture should be the main focus. With the prevailing trends of surface coal mines expanding on available arable land, the realization of this goal might not be possible. This study looked at aquaponics as a possible environmental management alternative that will enhance the agricultural productivity of rehabilitated mine land. An experimental site located close to Middelburg and Emalahleni was used as the base for this study to determine the financial feasibility of such a venture. Five chosen mines within a 20km radius were investigated to understand their rehabilitation practices and to prove that the sites are rehabilitated to a grazing land standard. These sites were all identified as favourable for the initiation of aquaponics. The two post-mining land use alternatives were compared with one another to understand what the benefits and constraints are. The economic driver was a main focus, followed with a brief overview of environmental and social aspects that can be kept in mind when these land uses are established.
Open Access
Aquifer parameter estimation in fractured-rock aquifers using a combination of hydraulic and tracer tests
(University of the Free State, 2002-08) Riemann, Kornelius; Van Tonder, G. J.
English: Water resources in South Africa are already being stressed and the country is slowly becoming a water-scarce country. This presents a challenge to all water resource managers to ensure that the basic water needs of every South African are met. A good estimation of the aquifer parameters is the basis of managing groundwater resources and understanding groundwater flow and transport processes. Because most of the suitable groundwater resources in Southern Africa occur in fractured rock aquifers, this thesis focuses on aquifer parameter estimation in fractured rock aquifers. A guideline for aquifer parameter estimation in fractured rocks is derived, based on a combination of hydraulic and tracer tests. The methods included account for the unknown flow geometry and the resulting uncertainty by introducing the non-integer flow dimension, which can be calculated from hydraulic and / or tracer test data. The guideline includes: o New methods for conducting and analysing tracer tests accounting for non-integer flow dimension prevailing during the tests in fractured aquifers. G A new method for estimating the kinematic porosity from single-well tracer tests. • Description and comparison of the use of a three-dimensional numerical model for aquifer parameter estimation . • The software TRACER-PLAN to enable the geohydrologist to conduct effective tracer tests. Depending on the type of test and the geological structure the test setup, such as discharge rates, amount of tracer and duration of the test, can be optimised. • To simplify and unify the analysing procedure the software TRACER enables the user to choose the correct analysing method depending on the test set-up and the conceptual model of groundwater flow. Most of the analysing procedures mentioned in this thesis are included. While the approaches for estimating the hydraulic parameters from pumping test data are commonly used methods, which are adapted to the situation in Southern Africa, new approaches to analyse tracer test data are developed, which account in a more general way for the unknown geometry. A combination of hydraulic and tracer tests including analysing procedure is proposed, which enables the hydrogeologist to estimate important hydraulic and transport parameters from the results of one test rather than conducting different tests. Depending on the purpose of the investigation, two types of combined tests are developed. As minimum requirement conducting and analysing a single-well test is suggested. If an observation borehole in the vicinity is available, a multiple-well test should be conducted. The proposed methods were used in case studies with different geological settings and compared to each other. From the results of the case studies and theoretical models it can be concluded that G analytical methods for estimating the hydraulic properties of fractured rock aquifers must be used with precaution, even when the correct conceptual model is chosen, I) for more accurate estimation numerical models, preferable a three-dimensional numerical model, should be used, Q the developed methods for analysing tracer test data, using the concept of fractional flow dimension, will yield more accurate and normally higher values for the flow velocity than the common methods, using the length of the tested section and a flow dimension of2, lil the developed methods for analysing tracer test data, using the concept of fractional flow dimension, are applicable in different geological settings, o the developed method for estimating the kinematic porosity from a single-well tracer test is generally applicable in both the fracture zone and the matrix, but the accuracy depends upon the correct conducting procedure, e the validity and accuracy of the results depends mainly on the quality of the conducting procedure and the correct conceptual model for the analysing procedure. The requirement for the analysing procedure can be summarised as: • From the hydraulic test data the conceptual model should be derived, using diagnostic plots and derivatives, as integrated in the software TRACER or in other software programs such as FC and TPA • The hydraulic data should be analysed applying the approach of non-integer flow dimension, as integrated in the software TRACER. • If necessary numerical models should be used for complete parameter estimation. lil The tracer test data should be analysed, applying the approach of non-integer flow dimension, as integrated in the software TRACER. The effect of matrix diffusion on solute transport in fractured aquifers is immanent, but no existing method is able to simulate it properly. Further research in estimating the impact of matrix diffusion on the plume movement and in developing a suitable method to simulate and quantify its effect is therefore strongly recommended.
Open Access
Aquifer test interpretation with special emphasis on the drawdown evaluation for wells within fracture networks smaller than the representative elementary volume (rev)
(University of the Free State, 2002-05) Bardenhagen, lngo; Van Tonder, G. J.
Fractured aquifers are characterized by the fact that most of the water flows along fractures, faults, open bedding planes, or other geological features. These features are embedded in a matrix that has either porous nature, like in sandstone, or is almost impermeable (inert), as in the case of granite. It is often observed that in fractured aquifers the measured air lift yield is a strong overestimation of the long-term sustainable yield of the well. The explanation for this effect is that the water extracted initially is provided by a geological feature that is high yielding but limited in its extension, while the long-term sustainable yield is the response of the matrix. Such a geological feature can be among others, a single vertical fracture or a fracture network, which usually acts as a preferential flow path. Pumping tests in primary and secondary aquifers are widely used by the ground water industry because they provide important information on the reservoir and the well performance. Various researches in the oil and ground water industries have found that the presence of single preferential flow paths results in characteristic drawdown curves. However, a lack of research is encountered, when it comes to more complex fracture networks. This work investigates the behavior of drawdown curves in fracture set ups below the representative elementary volume (REV), which is defined as the smallest volume of aquifer that can be considered as a homogeneous fractured unit. Emphasis is given to the importance of a thorough diagnosis of the data to be able to adequately estimate the aquifer properties. Chapter 2 of the present work summarizes the basic knowledge on ground water flow in fractured reservoirs, where the REV, fracture connectivity, and conductivity contrast between fracture and matrix are defined and explained. Thereafter, the flow behavior in fractured media (linear, radial, and spherical) are described. This chapter ends with the review of various well and reservoir boundary effects, such as well bore storage, well bore skin, partial penetration skin, fracture skin, pseudo-skin, fracture dewatering, and reservoir boundaries. Chapter 3 gives practical advice for the planning and performance of pumping tests and stresses the necessity of time correction in the case of variable discharge rate during the test. The importance of the pseudo-skin effect originated by the presence of a single vertical fracture is highlighted. It is shown that pseudo-skin effects are the reason for the apparent dependence of the storage coefficient (S) on the distance between the observation borehole and the single vertical feature, when the common evaluation methods are used for the estimation of S. Furthermore, the radial-acting flow phase and in relation to the REV is explained. This chapter ends with the description of various diagnosis tools, which allow, among others, the determination of the flow phases from pumping test data influenced by preferential flow paths. These tools are included in the computer program Test Pumping Analysis (TPA), which was compiled under the umbrella of this thesis. It is explained that data consistency can be rapidly analysed with the comparison between drawdown and recovery data and any discrepancy must be investigated additionally. The use of straight-lines, especial plots, and curves derivatives is described. Chapter 4 presents the most important analytical and semi-analytical available solutions for the analysis of pumping test data in fractured aquifers, which are included in TPA. For each case, the mathematical solution is first described. The influence of well bore and reservoir effects are explained using TPA, based on theoretical and field examples. Special emphasis is given to the various skin analyses and to the possible misinterpretation of drawdown curves. The solutions presented are: double porosity model of Moeneh (1984) • single vertical fracture with infinite conductivity and finite extent of Gringarten et al. (1974) • single vertical fracture with finite conductivity and finite extent of Cinco-Ley et al. (1978) • single vertical dike with finite conductivity and infinite extent of Boonstra & Boehmer (1986) • bedding plane fracture with infinite conductivity and finite extent of Gringarten & Ramey (1974) • generalized radial flow model for fractured reservoirs of Barker (1988) Chapter 5 investigates more complex fracture situations with help of numerical modelling based on the Darcian law. Synthetic pumping tests are simulated and their drawdown behavior is analysed. The single vertical fracture case is first computed to ensure that the model set up leads to the analytical and semi-analytical solutions of Gringarten et al. (1974) and Cinco-Ley et al. (1978), respectively. To investigate the influence of wider fault zones, which are assumed as a homogeneous fractured zone, faults with increasing width are modelled. It is found that: • for large storage capacities and finite conductivity, the drawdown at early time shows a radial-acting flow phase within the fault, which could be easily misinterpreted as double porosity. However, this effect occurs most likely under unconfined conditions The model is then modified to include parallel vertical fractures. It is found that: • parallel vertical structures with infinite conductivity have no influence on the drawdown at the well • parallel vertical structures with finite conductivity show minor influences at early time, if the dimensionless relative separation Sr (Sr = df/xf) is less than 0.125 Thereafter, the model is modified to represent a crossed fracture case and a bend fracture case, both vertical and with infinite conductivity. The computed drawdown differs significantly from the drawdown measured in the single straight fracture. It is found that: • this drawdown is comparable to that obtained with the uniform flux solution of Gringarten et al. (1974), although the influx along the fracture is not uniform. However, the authors mentioned that some field data from hydraulic fracturing fit better to the uniform flux solution. The results of this work give reasons to believe that such field data are attributed to more complex fracture networks similar to those studied here. The horizontal bedding plane case is also investigated. First, the model is run to compute the infinite and finite flux solutions from Valkó & Economides (1997). The modelled curves fit adequately the data for their solutions, although a labelling error in the published data is identified. Further, the influence of the fracture geometry is analysed. It is found that: • horizontal penny-shape fractures and square features with equivalent influx area have the same drawdown • rectangular horizontal features have a significant influence on the drawdown behavior The investigation of parallel bedding planes shows that: • the shape of the drawdown curve in parallel horizontal fractures is equivalent to that of the single horizontal bedding plane. Therefore, without additional on-site investigations (e.g. fluid logging or flow meter measurements) it is impossible to determine whether the drawdown belongs to a single fracture or to a series of parallel features • The analysis of drawdown curves produced by parallel horizontal fractures using type curves for single horizontal fractures leads to an over estimation of the fracture radius. This effect is important among others, for the design of protection zones Finally, intersections of a single vertical fracture and a single horizontal bedding plane are modelled. It is found that: • the obtained drawdown curves could be misinterpreted with drawdown curves of single cases. Therefore, it is concluded that additional information is necessary to correctly identify the geological set up. This issue is highly important for both the design of well protection zones and the estimation of the transport time
Open Access
Assessing the feasibility of constructing a groundwater contaminant fate and transport model for an LNAPL affected fractured rock aquifer
(University of the Free State, 2011-05) Möhr, Samuel; Dennis, Ingrid
English: Groundwater contamination as a result of Light Non Aqueous Phase Liquid (LNAPL) releases into the subsurface is a widespread occurrence across South Africa which threatens current and future water resources within the country. Groundwater contaminant fate and transport modelling are common elements of hydrogeological investigations and remedial design methodologies in many developed countries where the models are use as management and decision making tools. In South Africa this is not the case, with contaminant flow and transport modelling rarely being employed as part of LNAPL contamination investigations. Over the last 3 years the Beaufort West study area has had extensive investigative work carried with regards to the determination and delineation of LNAPL related groundwater contaminant plumes which are present underneath a significant portion of the town. As a result an extensive data set has been generated with regards to aquifer geometry, fracture network distribution, aquifer parameters and contaminant plume concentrations and extent. The dataset should in theory provide an opportunity to construct a groundwater contaminant fate and transport model for the area as a remedial management tool. By means of collating previously existing data through a comprehensive desktop study, and supplementing this data with a toolkit of field investigations techniques such as diamond barrel core drilling, percussion drilling, electrical conductivity profiling, fluid electrical conductivity profiling, aquifer pump testing, and low flow inorganic and organic groundwater sampling, the conceptual model of the study area was updated and refined to a point where feasibility of constructing a groundwater contaminant fate and transport model could be assessed. Based upon the conceptual understanding of the study area as defined in the conceptual model developed in the study, a groundwater contaminant fate and transport model is not considered feasible for the study area with body of data currently available. This is attributed mainly to the high level of complexity of the observed natural environment and the challenges in acquiring acceptable quality field data such as aquifer parameters given the uncontrolled pumping environment which is present due to the high number of private groundwater users. Potentially an even greater detractor to the construction of a model, is that considering the conceptual understanding of the study area, there are very few questions of significance whose answers could be provided by a model, and this would indicate that a model would not be an effective remedial management or decision making tool in the current scenario.
Open Access
Assessment of groundwater ingress into mine workings from the deep-seated fractured rock aquifer in the Bushveld Igneous Complex at Dishaba mine
(University of the Free State, 2023) Dumakude, Sbusiso Kwanda; Fourie, Francois D.
Dishaba Mine is reported to experience approximately 16 ML of groundwater ingress daily. The water ingresses occur across the mine, from off-reef haulages to mostly Merensky reef stopes. The water enters the mine workings through fractures, boreholes, and open mining excavations, and poses a risk in terms of mine safety. However, the water entering the mine also presents an opportunity for the mine to reduce its reliance on potable water and potentially use groundwater to meet day to day water requirements for mining and ore processing.
Open Access
Assessment of groundwater resource in the Tsineng area, Northern Cape: a geophysical survey perspective
(University of the Free State, 2016-07) Mokgatle, Tumelo; Fourie, F.
English: In this study the groundwater resource the in Tsineng area, Northern Cape was assessed in terms of the volumes of water that may be sustainably abstracted from the aquifer system, and the quality of the available groundwater. A strong emphasis was placed on the use of airborne and ground geophysical techniques to gain a better understanding of the geological and geohydrological conditions in the study area. The airborne geophysical technique employed during the current investigation was the time-domain electromagnetic method (using the SkyTEM system), while ground geophysical surveys employed the gravity, magnetic, frequency-domain electromagnetic and electrical resistivity tomography methods. The geophysical techniques were used to provide information on physical changes in the subsurface conditions that may be related to the presence of geological structures associated with potential groundwater resources. The results of all the geophysical methods used were collated and correlated to the local geology to make an informed decision during the selection of drilling targets for the installation of production boreholes. From the TDEM data, information on the subsurface distribution of resistivities was obtained. Well-defined resistivity anomalies correlated well with the known presence of two prominent fault zones. Furthermore, resistivity anomalies were also identified at the locations of mapped dolerite dykes known to intersect the study area. The ground geophysical investigations were conducted across preliminary targets defined from the airborne TDEM data. The ground geophysical investigations confirmed the presence of the structures identified from the TDEM data. Based on the results of the geophysical investigations and the known local geological conditions, drilling targets were selected at positions deemed promising for the installation of successful production boreholes. A total of 78 exploration boreholes were drilled during the current investigations. Sixty of these boreholes had water strikes and were thus considered successful. A combined total blow-yield of 409 l/s was measured in the successful boreholes. Forty of the drilled boreholes had blow-yields in excess of 2 l/s. These boreholes were selected for aquifer hydraulic tests to assess the hydraulic parameters of the intersected aquifer systems. From the estimated hydraulic parameters, sustainable yields were determined for the tested boreholes. The total estimated sustainable yield from the boreholes was more than 7 500 m3/day. Water samples from the 40 high-yielding boreholes were submitted for chemical analyses. The results of the analyses showed that the water in the study area is generally of very good quality, suitable for human consumption. It is therefore concluded that groundwater may be successfully used to augment the municipal water supply in the Tsineng area. The results of the current research demonstrate that the use of geophysical techniques could greatly contribute to an understanding of the geological and geohydrological conditions in a study area, which could in turn lead to a higher success rate during groundwater exploration programmes. Keywords: Geophysical Afrikaans: In hierdiestudie is die grondwaterbronne in die Tsineng-area in die Noord-Kaap Provinsiegeëvalueer in terme van die volumes water wat volhoubaaronttrekkan word vanuit die akwifeersisteem, asook die kwalitiet van die beskikbaregrondwater. ‘nSterkklem is geplaas op die gebruik van geofisiesetegnieke om ‘n beterinsig in die geologieseengeohidrologiesetoestande van die studie-area teverkry. Die lug-geofisiesetegniek wat gebruik is gedurende die huidigeondersoek was die tyd-domeinelektromagnetiesemetode (die SkyTEM-sisteem is gebruik), terwyl die grondgeofisieseopnames die gravitasie-, magnetiese-, frekwensie-domeinelektromagnetiese-enelektrieseweerstandtomografie-metodesgebruik het. Die geofisiesetegnieke is gebruik om inligtingtebekomoor die fisieseveranderingeondergronds wat verband mag hou met die teenwoordigheid van geologiesestrukturegeassosieer met potensiëlegrondwaterbronne. Die resultate van al die geofisiesemetodes is gesamentlikbeskouengekorreleer met die plaaslikegeologieomingeligtebesluitete neem tydens die seleksie van boorteikensvir die installering van produksieboorgate. Vanaf die TDEM data is inligtingoor die ondergrondseverspreiding van soortlikeweerstandeverkry. Goed-gedefinieerdeweerstands-anomalië het goedooreengestem met die bekendeteenwoordigheid van twee prominenteverskuiwingsones. Verder is weerstands-anomaliëookgeïdentifiseer by die posisiesvan bekendedolerietgange wat die studie-area deurkruis.Die grondgeofisieseondersoeke is gedoenoorvoorlopigeteikens, soosgedefinieervanaf die TDEM-data.Die grondgeofisieseondersoekehet die teenwoordigheidbevestig van die strukture wat vanaf die TDEM-data geïdentifiseer is. Vanaf die resultate van die geofisieseondersoeke, asook die bekendeplaaslike geologiesetoestande, is boorteikensgekies op plekke wat as belowendbeskou is vir die installering van suksesvolle produksie boorgate. ‘n Totaal van 78 eksplorasie boorgate is geboortydens die huidigeondersoeke.Sestig van hierdieboorgate het water getrefen is gevolglik as suksesvolbeskou.‘n Gekombineerde total eblaaslewering van 409 l/sis gemeet in die suksesvolleboorgate.Veertig van die boorgate het blaaslewerings van meer as 2 l/s gehad. Hierdieboorgate is gekiesvirhidrouliesetoetsing van die akwifeerom die hidrouliese parameters van die akwifeer-sisteemtebepaal. Vanaf die geskattehidrouliese parameters, is volhoubareleweringsvir die getoetsteboorgatebepaal. Die total egeskattevolhoubarelewering van die boorgate was meer as 7 500 m3/day. Watermonsters van die 40 hoë-leweringboorgate is ingedienvirchemieseanalises. Die resultate van die chemieseanalises het getoondat die water in die studie-area oor de algemeen van baiegoeiekwaliteit is, geskikvirmenslikegebruik. Die water kandussuksesvolgebruik word om die munisipalewatertoevoer in die Tsineng-area aantevul. Die resultate van die huidigeondersoek toon dat die gebruik van geofisiesetegniekegrootlikskanbydra tot die begrip van die geologieseengeohidrologiesetoestande in ‘n studie-area, wat weerkan lei tot ‘n hoërsukseskoersgedurendegrondwatereksplorasieprogramme
Open Access
Assessment of the groundwater potential of the Middel Kop/Appleby aquifer, Stella District, Northwest Region
(University of the Free State, 2001-08) Nel, Jacobus Marthinus; Botha, J. F.
English: The importance of groundwater is strongly reflected in the new South African water policy and legislation. All water resources, including groundwater, are now seen as an indivisible asset, with the National Government as its custodian to ensure that the resources are protected, developed and managed properly. Groundwater is the sole source of potable water for the town of Stella in the Lower Vaal Water Management Area of the Northwest Province, but the existing well-field is barely able to supply the present demand. Previous attempts to supply the town with water from groundwater resources have failed, because of the low potential of the aquifers and the poor quality of the groundwater. The proposed resettlement of 2 000 people therefore has to be postponed until sufficient additional water resources can be found for the town. One possible source, not included in previous groundwater explorations of the area, is the granitic aquifer on the farm Middel Kop situated approximately 5 km south-east of Stella. Farmers have used this aquifer extensively since 1990 to irrigate 171 ha of agricultural land. It was consequently decided to investigate this aquifer as a possible additional source of water for Stella. However, farmers have already noticed a continuous decline in the water levels over the years. This meant that the focus of the investigation had to be changed from merely an exploration exercise to an evaluation of the aquifer and the development of a suitable management scheme for the aquifer, as described in this thesis. There are not enough data available to perform a detailed assessment of the aquifer at the moment, a deficiency that should be addressed in future investigations and management of the aquifer. The existing data, however, indicate that the aquifer may be able to sustain a yield of approximately 4 227 m3 d-I in the near future. This volume of water will be able to supply in the needs of the present population and the additional 2 000 resettled people, while allowing 73% of the current irrigated area approximately 8 000 m3 ha-I annually for irrigation. The latter figure can only be achieved if the farmers are allowed to produce one crop per year instead of the two, which is in some cases the practice. This reduction in the water allocated for irrigation may seem harsh, but the decline in the water levels over the last couple of years clearly indicate that the farmers cannot continue with the present practices for much longer. The groundwater quality of the Middel Kop aquifer can be rated as marginal for human consumption. This applies in particular to the relatively high concentrations of fluoride and nitrate in the water, which could affect the health of the population adversely if used untreated for long periods. The conclusion reached in the thesis is that the Middel Kop aquifer can only be used as a source of water for Stella on condition that a detailed monitoring scheme is introduced from the beginning and used to develop a suitable management scheme for the aquifer. This approach will ensure that any impacts on the resource can be properly evaluated and that the quality and quantity of the water can be preserved for future generations.
Open Access
Baseline study of Kendal Power Station
(University of the Free State, 2011-05) Moolman, Dirk; Vermeulen, P. D.
Abstract not available
Open Access
Biobarrier formation for hydraulic control in groundwater remediation in South Africa
(University of the Free State, 2006-11) Van Wyk, A.; Usher, B. H.; Van Heerden, E.
Abstract not available
Open Access
Characterisation and management of a LNAPL pollution site along the coastal regions of South Africa
(University of the Free State, 2009-11) Vermaak, Kevin Harry; Van Tonder, G. J.; Steyl, G.
English: The project site experienced LNAPL spills in the recent past. In the characterisation of the site it was necessary to investigate the physical properties of the vadose and saturated zones. It was found that temperature, saturation, phase-distribution, the hydraulic properties and water levels contributed to the LNAPL being vaporised. The attributes of the soils substantiated the vaporisation model. The geology was found to be dominated by interbedded sandstones and mudstones, underlain by a dolerite sill. The pollution plume was delineated at the study area and an appropriate management plan was proposed for the site. MNA was shown to be an effective management option.
Open Access
Characterisation of the deep aquifers of South Africa - the Karoo Supergroup and Table Mountain Group
(University of the Free State, 2019-06) Makiwane, Nwabisa; Fourie, F. D.; Allwright, A.
Abstract not available
Open Access
Characterisation of the dolomitic aquifer in the Copperbelt Province, Northern Zambia
(University of the Free State, 2005-02) Prinsloo, Martiens; Vermeulen, P. D.
English: External factors that influence the aquifer characteristics of, and sustainable yield from, the dolomitic aquifer include topography, rainfall, surface drainage, evapotranspiration, plant growth, geology, and soils. The topography is gently undulating with a gradient of between 1:400 and 1:800. The low topographical gradients inhibit surface run-off and promote high recharge rates. The annual rainfall will provide the volume of water present in the catchment area that is available for potential recharge to the aquifer. The average rainfall is 1 115mm/annum. Water that leaves the hydrological system of the study area as surface run-off impacts on the volume of water available for recharge to the aquifer in the area. Despite the high rainfall volume and high rainfall intensity only one perennial surface run-off structure exists in the study area. The Kafue River is on average 10 to 20m wide and 3m deep. Only one non-perennial surface run-off feature exists. This feature feeds into the Ipumbu Dam. The volume of water that evaporates from the soil and vegetation before it can reach the underlying aquifer will impact on the volume of water that can be abstracted from the aquifer without negatively impacting on the volume of water in storage in the aquifer. Very little evaporation data is available for the study area. Comparing the calculated potential total evaporation volume with the measured net evaporation and annual rainfall indicates a discrepancy between the evaporation and rainfall data. The rainfall data is considered to be accurate, and based on perceived inaccuracy of the evaporation data, it is recommended that the evaporation data not be used in water balance calculations. The natural plant growth influences the evapotranspiration and in some cases the surface run-off characteristics. Brachystegia Miombo woodlands cover the study area with areas of widespread grass cover between the trees. The main aquifer consists of Upper Roan Formation limestone and dolomite. The main joint set (160º strike direction) controls the strike direction of the solution cavities in the area. Schist and quartzite of the Lower Roan Formation border the limestone and dolomite. Extensive fracturing in the dolomite is found in the geological logs of the high yielding boreholes drilled in the area. The soil in the study area displays infiltration rates higher than the observed rainfall intensity. Combined with the low topographical gradients that retard run-off the high infiltration rate leads to high recharge percentages. The aquifer hydraulic characteristics were determined during the investigation. It is considered that Lake Nampamba forms part of an extensive, well-connected solution cavity network. No compartmentalisation of the dolomite is evident. Three prominent karstic features (Lake Nampamba, Lake Kashiba and the “Chibili Pavement”) occur in the area. Both Lake Nampamba and Lake Kashiba are sinkholes in the dolomite. The author has no scientific evidence to conclude that the solution cavity network stretches as far as the Kafue River. However, analysis of the water level, abstraction and water level data does confirm that Lake Nampamba in the east and the dambo areas in the west that feed Ipumbu dam are interconnected. The groundwater displays a calcium-magnesium dominant character, as is expected from a dolomitic aquifer. Plotting the chemistry data on a trilinear (Piper) diagram indicates that the groundwater recently recharged. This corresponds to the theory of high recharge due to the relatively high rainfall, flat topography, and high soil infiltration rate. Depth to groundwater varies on a seasonal basis due to fluctuations in rainfall and thus recharge, and abstraction volumes. The groundwater level shows an immediate response to recharge, but does indicate a one to two month delay between maximum rainfall and peak groundwater level. A total of 65 boreholes were drilled in the study area between 1978 and 2004. Preliminary aquifer tests were performed on 38 boreholes, and 14 boreholes were identified as high yielding boreholes. Constant rate aquifer tests were performed on these boreholes. The aquifer test data was analysed to obtain the aquifer transmissivity. The aquifer transmissivity ranges between 1 and 6 900m2/day. This wide range is expected in karstic aquifers where the high transmissivity is associated with solution cavities and fractured areas. The low transmissivities are associated with the fine crystalline, competent, unweathered rock. Sustainable yields from the borehole calculated from the aquifer test data range between 5 and 100l/s (432 and 8 640m3/day). Recharge calculations were performed using the Chloride, SVF, Equal Volume and CRD methods. The chloride method is used only as an indication of the recharge percentage. The SVF, Equal Volume, and CRD methods calculated recharge as 25% of the annual rainfall. Aquifer storativity is calculated using the SVF and CRD methods at 0.02 (2%). The total volume of water that can be abstracted from the combined eastern and western aquifers is calculated to be 136Mm3/annum. The current and proposed future annual abstraction volumes are 25.3Mm3 and 44.42Mm3 respectively. This indicates that the combined eastern and western aquifers are capable of sustaining the abstraction volumes. A numerical model was constructed to evaluate the assumptions made, and correlates the calculated values of the manual calculations. The model was initially constructed in steady state without taking the abstraction from the aquifer into account. Once the model was successfully calibrated, the abstraction volumes were incorporated into the numerical model and the model was further calibrated against time series observed rainfall, groundwater levels and abstraction volumes by comparing the groundwater levels with time against those calculated using the numerical model. Once the model was calibrated, the model was applied to evaluate the sustainability of the current and proposed abstraction programs. The numerical model confirms that the combined eastern and western aquifers are capable of sustaining the abstraction programs.
Open Access
Characteristics of fluid electrical conductivity (FEC) profiles associated with a contaminant plume in porous and weathered basement aquifer systems
(University of the Free State, 2023) Moleme, Malefa Florence; Gomo, Modreck
The fluid electrical conductivity (FEC) profiling method has been commonly applied to aid in the compilation of site-specific conceptual models and understanding of the subsurface environment. Although research has recently been conducted to help improve the knowledge and understanding of the evolution of FEC profiles under natural and saline contaminated environments within the fractured-rock aquifer system, a research gap still exists for such studies in other aquifer types. The type of aquifer system plays a significant role in determining the migration patterns and behaviour of contaminants. Therefore, it is expected that the evolution of FEC profiles in different aquifer systems will vary, and this needs to be understood. It is against this background that this research aimed to investigate the behaviour of FEC profiles associated with a saline contaminant plume in typical unconfined porous and weathered basement aquifer systems, using laboratory-based aquifer models. This was done to improve the conceptual understanding of contaminant migration within these aquifer systems, which will essentially improve the interpretation of their FEC profiles. To achieve this, two physical models were developed in the laboratory to represent an unconfined porous aquifer system and a weathered basement aquifer system. The performance of the models was evaluated and tested, and subsequently used to investigate the progression of FEC profiles associated with a saline contaminant plume. The outcome of the laboratory tests was also verified in the field. This study also explored the effects that the distance of a source from a monitoring point would have on the shape of FEC profiles. Unlike previous studies which conducted the FEC profiling technique under induced groundwater flow, this study investigated the efficiency of a non-invasive approach of applying the method under natural gradient conditions. From the analysis of profiles obtained within the two simulated aquifer systems conceptual profiles were developed. Within the unconfined porous aquifer system, FEC profiles recorded from the borehole located closer to the source were notably different from the FEC profiles recorded from a borehole positioned further away from the source, thus it was evident that the distance of a monitoring point from the source influenced the orientation of the plume, and ultimately the resulting FEC profile. This brought to light the phenomenon of “plume orientation”. The orientation of the plume is usually disregarded in groundwater models and assessments, however this research showed that it is an important aspect which can be used to assist with FEC data interpretation and contaminated site characterisation studies. The orientation of the plume was strongly influenced by the magnitude of the forces acting upon it, primarily the gravitational and advection force. Closer to the source, the plume took on a vertical to sub-vertical orientation, whereas as the plume continued to migrate further away from the source it aligned with the flow lines of the system which resulted in a horizontal orientation. From the analysis of the weathered basement aquifer system two distinct signatures were identified and conceptualised: the low FEC profile and the elevated FEC profile. The low FEC profile not only represented a profile captured under natural conditions in the absence of contamination, but also represented a profile that would be observed when the majority of the contaminant has passed the borehole and the system was in the process of re-establishing initial conditions. It had three distinct zones: the weathered zone, transition zone, and the impermeable zone. The elevated FEC conceptual profile was associated with contaminated groundwater conditions within the weathered basement aquifer system. It had two distinct zones: the weathered zone and the impermeable zone.