Masters Degrees (Institute for Groundwater Studies (IGS))

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Open Access
Geohydrological modelling to determine cumulative impact on groundwater at the Letšeng Diamond Mine, Lesotho
(University of the Free State, 2023) Theko, Thato; Allwright, Amy
Letšeng diamond mine (LDM) uses the split-shell open-pit mining method. The method includes excavation from the surface to access the ore at depth. Material from excavation and that separated during diamond extraction form primary mine waste. Approximately 20 million tonnes of waste is produced as fine-grained waste deposited into Tailings Storage Facilities (TSF) and coarse-grained waste deposited onto Waste Rock Dumps (WRDs). The waste can contain toxic chemical substances that can seep into groundwater or flow into surface water, contaminating it. For this reason, the study aims to determine the cumulative impacts of mining on groundwater quality. To achieve this, groundwater modelling techniques were employed to simulate groundwater flow and groundwater travel times and travel paths for contaminant transport. Geological, hydrological, hydrogeological and hydrochemical data were collected, analysed, and integrated to conceptualise the hydrogeology of LDM to provide a better understanding of the hydrogeological system. The conceptual model also indicated possible sources of contamination and their possible receptors incorporating the Source Pathway Receptor concept. This was achieved by collecting and analysing the water quality data. Mine water sampling results show that most constituents are within the acceptable limits, while nitrates and sulphates were elevated above limits at locations down gradient from the Old Slimes Dam, WRDs and Patiseng TSF suggesting these areas are potential on-site sources of contamination. The conceptual model formed the basis of the groundwater model. Based on the prevailing hydrogeological conditions in the mining area, a groundwater flow model was developed using MODFLOW 6. Due to data limitations, instead of simulating the contaminant from the source to the receptor using transport modelling, particle tracking with MODPATH was used to simulate the pathway and travel time of contaminants in groundwater. Particle tracking results show that the simulated extent of contaminant movement is generally in line with the water quality sampling results, where sampling points beyond the mine lease areas show acceptable water quality as opposed to samples closer to potential sources which show elevated levels of contamination, suggesting contamination is mostly contained within the mine lease area. Similarly, MODPATH results indicate that most particles do not exceed the lease area, also indicating that contamination from potential sources is mostly limited within the mine lease area. Over a five-year simulation period, there is very limited movement of contaminants, although some particles from the Old Slimes Dam are released into the Mothusi Dam, thus posing a risk on its quality. Based on these findings, the Dam was identified as the most sensitive receptor. Over a 10-year period, there is further movement of particles, and some start to move beyond the lease area as some boreholes start showing increased nitrate concentrations such as borehole L_WE_010 down-gradient from the WRD east, suggesting groundwater contamination from the WRD. Over 20 years, a maximum travel distance of 5 km from the eastern WRD is observed, however no sensitive receptor was reached. While the calculated extent of the cumulative migration from the Old Slimes Dam is contained on- site over the 20 years, there is potential impact on the quality of groundwater as some particles intercept the boreholes downstream of the Mothusi Dam, borehole L_WE_015 and borehole L_WE_016. More boreholes are also intercepted over the 20 years. Over time, contaminants will migrate off-site into the weathered shallow layer through the streams therefore reaching some of the receptors in the surrounding environment, either by percolation or conveyed as surface contaminants into the weathered layer. Due to low hydraulic conductivity in the types of rocks in the area, the migration of contaminates is very slow and is mostly limited within the first layer. The results show that there is some seepage of contaminants from potential sources, mostly affecting surface water compared to groundwater. However, the groundwater modelling results also indicate that over long-term evaluations, mining activities at LDM have significant impacts on the groundwater quality, where contaminant particles from different sources are observed at monitoring boreholes suggesting groundwater contamination. This study clarifies the slow but significant effects of mining operations on groundwater and surface water resources over time at Letšeng diamond mine. The results highlight the need for ongoing monitoring and mitigation measures to reduce cumulative effects on vulnerable receptors including the Khubelu, Qaqa Rivers and Mothusi Dam. The conclusion of this assessment emphasizes the critical need for ongoing environmental management within mining practices to protect the quality of nearby water resources. This is achieved by addressing the sources and pathways of contamination that have been identified, putting in place rigorous monitoring, and strengthening mitigation measures.
Open Access
Investigating groundwater abstraction impacts on surface water levels and surface water – groundwater interaction with analytical and numerical models
(University of the Free State, 2023) Maluleke, Ntsako Victor; Allwright, Amy
Groundwater is an important source of water for many human needs, including agriculture, water supply and industry. However, the use of groundwater may have adverse consequences. Various studies have been conducted to analyse the effect of groundwater pumping on nearby streams, and many analytical models and numerical models have been developed for various aquifer and stream conditions. Numerical models are time-consuming and require a significant amount of data input but can simulate complex systems. On the other hand, analytical models are suitable to use since they are ease to use, and have minimum data requirements and exact solutions, but they are limited to less complex problems. Streamflow impacts from groundwater pumping continue to be one of the main issues with groundwater resource development. The primary objective of this dissertation is to investigate GW-SW interaction and the impact of groundwater abstraction on surface water bodies. A secondary objective is to then develop a conceptual model that highlights the natural system behaviour of groundwater abstraction in nearby streams to evaluate alternative approaches for managing and understanding streamflow depletion. The developed hypothetical model of an abstraction borehole near the stream is incorporated by realistic available data from the previous UFS/WRC test site along the Modder River, Free State, South Africa. Four analytical solutions, namely Jenkins (1968), Hantush (1965), Hunt (1999) and Hunt (2003) have been simulated using the developed hypothetical models (simple stream-aquifer conceptualisation to improved stream-aquifer conceptualisation) which aid in the quantification of streamflow depletion rates. To identify parameters that greatly influence streamflow depletion, parameters are varied to understand their sensitivity and effect on the rate of streamflow depletion. Furthermore, statistical analysis is used to visualise parameters that greatly influence streamflow depletion using ANOVA (Analysis of Variance). Groundwater abstraction is found to be the most sensitive parameter that greatly affects the streamflow depletion; therefore, groundwater abstraction rates should be monitored, and data collection should be accurately acquired to give out the best recommendation as this can greatly impact the surface water. Distance separation is also considered sensitive and greatly influences streamflow depletion. The period of pumping is less sensitive due to the fact that only time simulation is being extended with no variation of any parameter. The sensitivity analyses improve the understanding of how the analytical models simulate streamflow depletion rates and provide information to water managers on which parameters are most sensitive and require focused data collection. Numerical models are applied and designed to represent the analytical solutions to assess how the solution would be implemented in a numerical model. Two approaches have been used within this dissertation namely, 1) analytical model condition which aims at creating a numerical model to simulate analytical condition as closely as possible to understand the implication of the analytical model assumptions and 2) complex numerical model conditions considering a real-world complex numerical model and assess how analytical solutions are able to represent streamflow depletion. The approximation in the numerical model, limited aquifer extent of the numerical model domain, and differences in parameter and boundary condition applied are the most significant factors that cause differences between the analytical and numerical model results. Analytical solutions overestimate and underestimate streamflow depletion when addressing a complex setting, although they fail to address complex hydrogeological settings, these analytical solutions can act as conservative tools which aid water managers in decision-making on the quantification of streamflow depletion and its mitigation. This study's thorough investigation using different models highlights the complexities of groundwater pumping's impact on streamflow. By examining factors like borehole distance, aquifer hydraulic parameters, and model conceptualisations, it exposes limitations in simplistic analytical models while emphasising the complex nature of aquifer-stream dynamics. Understanding time delays, geological variations, and model assumptions provides crucial insights for water resource management. These findings offer valuable guidance for balancing groundwater use and preserving streamflow, urging a holistic approach integrating the strengths of numerical simulations. This research advocates sustainable strategies to address streamflow depletion, promoting responsible groundwater utilisation for the future.
Open Access
Numerical groundwater modelling as a tool to quantify shallow aquifer water ingress through mining-related open voids
(University of the Free State, 2023) van Dyk, George Pieter; Allwright, Amy
The quantification of water ingress volumes and rates from different aquifer systems through open voids can aid in related studies concerning water quality, decanting potential, and stability evaluations especially in areas where historic mining has played a significant role in altering the groundwater environment. The objective of the research and approach is to evaluate if numerical groundwater modelling can be used as a tool to quantify ingress rates from shallow aquifer systems during rapid recharge events when these aquifer systems become saturated and water seeps through individual mine related open voids on a regional scale, eventually reaching historic mining infrastructure and deeper hard rock aquifers. A case study that focused on the East Rand Basin was used to evaluate if numerical modelling can be used to produce quantified ingress rates from shallow aquifer systems through mine-related open voids. The East Rand Basin has a rich history of mine related activities which still has a large influence on the regional aquifer systems. The research included gathering spatial and site-specific data required to construct and represent a numerical groundwater model in FEFLOW groundwater modelling software. The representative model was used to simulate a scenario that included monthly rainfall records that indicated elevated rainfall events and applied as time dependant recharge to the shallow aquifer systems identified along the Blesbokspruit and associated tributaries. The mapped mine-related open voids that fell within the shallow aquifers systems were assigned as discrete features to represent open voids leading to the mapped historic underground mine workings. The simulation included hydraulic head raises with each consecutive rainfall event to saturate the shallow aquifer systems and the ingress rates were recorded at each individual open void. The outcome of the numerical modelling assessment proved that ingress rates can be quantified with results indicating that a maximum of 12 000 m³/d can flow from the shallow aquifer systems during heavy rainfall events through 33 (out of 69) mapped open voids. The results were compared to a similar study (Waal, 2013), that indicated a good comparison in inflow rates. The model illustrated that roughly 16% of surface-related water (including ingress through shallow aquifer systems) could come from 46% of mine related open voids. Numerical groundwater modelling proved to be a valuable tool to quantify ingress rates from aquifer systems through open voids, however data availability and data quality add major limitations to the result accuracy and model confidence.
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
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
The investigation of groundwater transport in a geological formation: West Park Cemetery, Johannesburg, South Africa
(University of the Free State, 2023) Vava, Bomkazi; Atangana, Abdon
Groundwater is a source of fresh water for many people who live in communities with little surface water around the world. The major sectors of groundwater use are municipal; rural; agricultural irrigation; agricultural-livestock watering; industry and mining. The amount and quality of groundwater have nevertheless decreased because of anthropogenic activities, global climate change, and poor groundwater management. The use of fertilizers and pesticides, urban development, the dumping of household waste on the land, municipal waste discharge and laboratory waste disposal, the aquifer close to contaminated streams, mining operations, and the discharge of effluents with high concentrations of industrial chemicals and sludge on the land pose a concern on groundwater. Due to the migration of solutions from leachate to the soil, dumpsites are also regarded as important sources of groundwater pollution. Pollution from naturally existing toxins, such as arsenic or fluoride, should not be overlooked. Historically, contaminated drinking water has been known to be capable of transmitting dangerous chemicals and deadly diseases. In this thesis, we have considered contamination from cemeteries because they also contribute to contaminating groundwater, which spreads infectious diseases and dangerous substances. Many lives are lost because of the spread of some infectious diseases, resulting in a large number of burials that could pollute groundwater. The Johannesburg West Park Cemetery was selected as our case study location. We gathered a variety of data regarding the cemetery expect for water samples as the boreholes were dry. The collected data were subjected to numerous analyses, and a detailed presentation of the geological structure under the cemetery was made. A high rate of burials was seen between 2020 and 2022, primarily because of the spread of COVID-19. We presented evidence to support our claim that the crossover seen during the decay process cannot be replicated by the decay model with the classical derivative. To simulate the transition from fast decay to slow decay, a fractional model was utilized using a Mittag-Leffler function as the solution. The acquired results assisted us in choosing an appropriate mathematical formulation of the advection-dispersion equation, which was also numerically examined. Under certain hypotheses, we ran some numerical simulations utilizing the mass released within the geological formation as the beginning concentration. The cemetery's boreholes should be checked monthly to improve the environment, and additional boreholes should be dug to figure out the type of aquifer beneath the cemetery and the direction of flow since these details aren't currently known. This will help to ensure that the cemetery does not contaminate the environment, or the water supplies nearby.
Open Access
Delineation of groundwater protection zones: Towards a groundwater management plan in the Sutherland area, South Africa
(University of the Free State, 2022) Mulder, Daniél; Fourie, F. D.
The water resources of the largely groundwater-dependent Central Karoo region have been put under much strain as a result of continuous drought over the past seven years (DWS, 2021a). Rainfall patterns have been erratic, with the lowest recorded rainfall in decades. Hence, there has been limited recharge to the respective aquifers, resulting in declining groundwater levels and a decrease in borehole yields. The town of Sutherland relies solely on groundwater for its water supply. It was reported by the DWS (2021a) that in the long term, continuous water level monitoring of the production boreholes has indicated a general drop in water levels and a correlating decline in yields. In addition to dropping water levels, there has been a large increase in the number of privately owned boreholes drilled within the town area. Previously, these boreholes mostly targeted shallow water strikes within the fractured aquifer. However, with the declining water levels noted above, these boreholes have become increasingly low yielding and, in some cases, even dry. The response to this has been private drilling continuing past the shallow fractures to deeper water strikes in the aquifer, likely contributing towards a general drop in water levels within production boreholes close to town. The existing water supply boreholes are located within a 1-km radius of the town where the significant increase in groundwater use is occurring. Furthermore, historically, other than wellhead protection, the supply boreholes have been unprotected against contamination and the impact of other groundwater users. Figure 1 depicts one of the existing production boreholes and wellhead protection with a residential area in the background. In 2021, the expansion of the existing town supply with newly developed boreholes and wellfields targeted relatively undeveloped and undisturbed areas. This presented the opportunity to delineate protection zones and to develop standard operating procedures for sustainable aquifer management that will prevent the deterioration of groundwater quality and the aquifer itself through contamination and over-abstraction.
Open Access
Geophysical investigations in the Khakhea-Bray Transboundary Aquifer
(University of the Free State, 2022) Ngobe, Thandeka Fortunate; Gomo, M.
A limited number of transboundary aquifers (TBAs) in the Southern African Development Community (SADC) region have been subjected to investigations that will improve the hydrogeological understanding of the shared groundwater resource. The Khakhea-Bray transboundary aquifer, shared between Botswana and South Africa, is one of the TBAs that lacks a conceptual understanding of the groundwater systems. Therefore, this study aims to contribute to filling this research gap by conducting a geophysical investigation in the Khakhea-Bray TBA. The study applied the magnetotelluric approach to understanding the factors influencing groundwater occurrence in the dolomite of the Khakhea-Bray TBA. An ADMT-300S groundwater detectors of the ADMT series products was used to conduct the geophysical survey. This equipment measures the electric potential difference of the subsurface geology for 300 m below the surface measured at a 5 m depth interval. The magnetotelluric geophysical survey was carried out by targeting existing boreholes with accessible drilling data within the TBA. The survey stations were spaced at 3 to 5 Km intervals in areas with no boreholes. The integrated analysis approach used lithology data and water strike information from seven boreholes. The lithology data provided insight into the subsurface geology of the study area. The water strikes information of boreholes was used to calibrate the geophysical data of the dolomite aquifer system. This was done to identify the electrical properties of the water strike zones within the aquifer system, establishing the factors influencing groundwater occurrence. The geophysical data from survey stations on the same transverse line was processed into electric potential difference cross section models using RockWorks 2021 software. The distance weighting anisotropic method was applied to interpolate the data between the survey stations. The results show that the weathered-fractured zone is the main factor influencing the groundwater occurrence in the dolomite rock. The weathered-fractured zone was characterized by electric potential difference values varying between 0.02 mV to 0.065 mV. The weathered fractured zones in the dolomite were observed at shallow depths ranging between 7.5 m and 90 m. These dolomite aquifers were confirmed by the water strikes of the existing boreholes that were drilled targeting the dolomite aquifer zones. Another zone exhibiting the electric potential difference values ranging between 0.02 mV and 0.065 mV was observed at depths between 165 m and 300 m. The zone below 165 m showing the electric potential difference values between 0.02 mV and 0.065 mV was regarded as an unconfirmed potential weathered-fractured zone that needs to be validated with lithology and water strike data. Since the weathered-fractured zone was identified as the factor for groundwater occurrence in the dolomite of the study area, this suggests that during groundwater exploration for borehole drilling in the study area, the zones showing electric properties of a weathered-fractured aquifer zone must be targeted to increase the success rate of the borehole. The developed models showed the subsurface stratigraphy and the potential zones for groundwater occurrence within the transboundary dolomitic aquifer system of Khakhea-Bray TBA. This implies that the MT has the ability to map the aquifers and delineate the subsurface stratigraphic layers in dolomite settings. The models also revealed that the dolomite aquifers are confined, suggesting that these aquifers are less vulnerable to pollution from surface sources. The confined aquifer also suggests that the aquifer is not recharged directly from the top but through preferential flow paths on the dolomite rock surface.
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
Prefeasibility study for managed aquifer recharge within the Greater Kruger National Park, Limpopo province, South Africa
(University of the Free State, 2022-02) Holloway, Michael Thomas; Lourens, Paul; De Lange, Fanie
The Greater Kruger National Park (GKNP) is located in South Africa, which is a relatively dry country and among the 20 most water-scarce countries in the world. Two study sites for a prefeasibility study are situated along the western borders of the GKNP, located within the private game park boundaries of Olifants West Nature Reserve (Balule) and Timbavati Game Reserve (Motswari), north of Hoedspruit. Warm summer with seasonal rainfall on hot afternoons and winters that are mild and dry with almost no rainfall characterises the climate of the study areas. Except for Water Research Commission (WRC) reports and selected geological reports on regional geology surrounding the study areas, few hydrogeological studies have been conducted in the study areas. This dissertation investigates the prefeasibility of progressing to a full feasibility study for Managed Aquifer Recharge (MAR) through a combination of literature investigations and diagnosis of multiple field visits to collect hydrogeological information within the study areas. National guidelines on MAR have been consulted throughout the dissertation and study to guide the investigation on the potential for success to feasibility within the study area for MAR. The study involved an in-depth hydrocensus of both study sites to identify all possible boreholes, as well as establish a monitoring network of selected boreholes to monitor the effect of regional groundwater use on the hydrogeological setting. Geochemical analysis was conducted on both groundwater sites and surface water sites to class the water quality against water types and drinking water guidelines for usage within communities and game reserves/lodges. Geophysical surveys and available literature were assessed to characterise the hydrogeological flow regimes within the study areas, to develop a conceptual model for further understanding of the study areas hydrogeology, as well as to complete specific elements of a prefeasibility study check-list. In accordance with the prefeasibility check-list, many aspects were investigated to determine the success and need for a MAR scheme. Water level monitoring of selected boreholes indicated that over a period of two-and-a-half years, an overall decrease in the water table for boreholes at a higher elevation. This decrease in water level indicated that the aquifer is dewatering as a result of either below average annual rainfall recharge or over-abstraction of groundwater users of the aquifer. Chemistry results of groundwater and surface water sites indicated that the surface water (or source water) is much more desirable than the groundwater, which is typically characterised by elevated electrical conductivity (EC), fluoride (F) and nitrate (NO3) across both study sites. Surface water was more ideal and only displayed elevated aluminium. Through geophysical methods and literature studies, potential MAR sites were identified for both study areas, whereby an Aquifer Storage Transfer and Recovery (ASTR) method can be implemented for recharging groundwater into dolerite dykes and mapped lineaments, upgradient of abstraction boreholes to increase water security and improve the natural groundwater quality setting. MAR schemes are initially more expensive to establish than conventional methods such as water treatment facilities, however, the annual operating expenses are much lower and can see a faster return on investment than treatment options. The MAR method proposed is non-invasive and opportunistic for flood water runoff from within drainage channels, whereby potential groundwater zones of MAR correlate to. It is recommended that this dissertation complete the purpose of a prefeasibility study and precedes a feasibility study in the future.
Open Access
Evaluation of a training manual for groundwater resource management and groundwater governance for municipalities in South Africa
(University of the Free State, 2021-11) De Lange, Johann; Kotze, Yolanda
Groundwater knowledge is crucial in water scarce countries like South Africa. The management of groundwater resources are often neglected, and there is a lack of proper knowledge in groundwater as a discipline. It is vital that countries such as South Africa enlighten the public and knowledgeable individuals about groundwater. Groundwater resource management and groundwater governance in municipalities is required to improve groundwater management and governance. The enhancement of knowledge and skills will improve groundwater governance and management and educate individuals on groundwater use, sustainability, and protection. These problems can be resolved by developing and providing an easy-access platform. The platform provides individuals from various disciplines with sufficient information to gain general knowledge of groundwater. The development of an easy-access platform (Thinkific) provided an easy gateway to narrow the bridge between groundwater and individuals and was used to determine the effectiveness of the “Training Manual for Groundwater Resource Management and Groundwater Governance for Municipalities in South Africa”. Within this dissertation, the effectiveness of the training manual was significantly proven on a sample of 55 young working adults (participants). The data collected from numerous participants provided a holistic perspective of the effectiveness of the dissertation. Different types of quantitative statistical techniques were used to collect, analyse, and display the data. The main concept revolved around the Kirkpatrick’s evaluation method. Only the first two levels of this evaluation model were utilised. Participants wrote pre- and post-tests and completed evaluation questionnaires. This was done to establish the enhanced level of knowledge within participants and to gather reactions regarding perception and satisfaction of the training manual. These tests indicate the effectiveness of the training manual. The data gathered from this training manual show that it is significant to use the training manual as a foundation for groundwater knowledge. The groundwater content in this training manual is sufficient to use for training.
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
Stochastic groundwater flow models in confined and leaky aquifers
(University of the Free State, 2019-06) Amakali, Sarti Rautia; Atangana, Abdon
This dissertation proposes an application of stochastic modeling of groundwater flow in confined and leaky aquifers. We are estimating that aquifer parameters such as transmissivity, storativity and leakage factor vary, not constant, in space at different period especially in heterogeneous environment. Heterogeneous environment are known to be complex because of their uncertainty. Uncertainty referred in modeling includes errors in dataset, which might be bias or variance (under fitting/over fitting), low or not enough data, or unbalanced data, which all affect the model produced if not captured with appropriate model technique. The groundwater flow equation for confined and leaky aquifers derived by the latest version Atangana and Ramotsho, as well asAtangana and Mathobo, which all include scaling matrix of the soil, are considered and further modified to a new scheme of stochastic models for confined and leaky aquifer. We tried to achieve the capture statistical setting of aquifer parameters using the concept of stochastic modeling technique. The aquifer parameters are replaced by distribution for instance, Gaussian or normal distribution.Due to the complexity of the modified models, it is almost impossible to obtain the exact solution by using analytical solution, thus we opt to numerical analysis, in particular the Newton method used to derive the numerical solutions of the modified models. Detailed analysis of stability and convergences, we used method are presented for both models. Numerical simulations are depicted for different distributions.
Open Access
Modelling reactive pollutant transport in ground water: the case of two species
(University of the Free State, 2019-06) Hans Tah, Mbah; Atangana, Abdon
The locations of a significant number of industrial facilities, landfills and almost all mineral ore bodies are characterised by high in situ stresses and fractures and fissures act as flow paths for fluids underground. Regional scale fracture systems that transport pollution from spatially isolated source locations can cause mixing of chemical pollutants from different source origins due to fracture- fracture flux across two or more intersecting fractures, hence reactive transport. Alerts of groundwater contamination in response to multicomponent pollution transport have been investigated using a mathematical model of the hydrodynamic response of incompressible fluids such as groundwater flow. Fundamental to the model is the conservation of mass associated with the applied source strength and the concentration velocity field redistributions after source has released pollution, assuming the formation is homogenous. Solute distribution depends on the formation porosity and generally, fluids travel faster in fractures than in sedimentary formations. Different variations of the deterministic advection dispersion equation have been employed to predict coupled transport/reactive processes by substitution of a reaction term (retardation factor, etc..) which accounts for the changing concentration of the solid face components through time due to chemical reaction. However, fractured aquifers are inherently heterogeneous due to interconnecting fractures. The results in a non-homogenous mathematical formulation which difficult to solve analytically. As a result, most research endeavours have tended to depend on numerical solutions, increasingly made possible through advanced computational power. Even though it is questionable to what extend numerical models of groundwater reactive transport can be useful in making accurate quantitative predictions, it is still possible for a reactive model to predict the outcome of a particular chemical representation in an aquifer. Nevertheless, the linear, non-homogenous advection dispersion equation can still be solved analytical using the Green’s function method. In this thesis, we show how the advection-dispersion transport equation can be extended to account for geochemical reaction processes in a heterogeneous media. For the hypothetical case study, the system was made of a homogenous and a non-homogenous sub-component. The study’s methodological approach involved coupling of the homogenous transport phase with the non- homogenous system. The solution of the homogenous equation is obtained using Laplace transform and the exact solution of the new non-homogenous equation is obtained analytically using Laplace transform and the Green’s Function method. Both sub-models were solved numerically using the Crank-Nicolson discretization scheme and their stability conditions also established. For the proposed fracture flow system, the linear non-homogenous model was able to approximate the contribution of reactive transport processes in the system. Chemical reactions can attenuate the spread of a contaminant plume due to processes such as sorption and precipitation. The model presented in this thesis was able to predict fate of each species within the system. Mass transfer during and after the reaction resulted in the depletion of one source with respect to another, which the model showed positive results in capturing. The thesis concludes with a chapter on chemical equilibria which is the basis of kinetic modelling and the understanding of the progress of chemical reactions.
Open Access
A new method for modeling groundwater flow problems: fractional-stochastic modeling
(University of the Free State, 2019-06) Mahantane, Mohau L.; Atangana, Abdon
To date, groundwater flow problems are still increasingly becoming a great environmental concern worldwide. This is among some of the reasons that many researchers from various fields of science have focused much of their attention in formulating new mathematical equations and models that could be used to capture and understand the behavior of groundwater flow with respect to space and time. The main aim of this study was to develop a new concept for modeling groundwater flow problems. The approach involved coupling of differential operators with stochastic approach. Literature proves that each of these two concepts has shown a great success in modeling complex real-world problems. But we argued that differential equations with constant coefficient are not fit to capture complexities with statistical setting. Therefore, to solve such a problem in this study, we considered a classical one-dimensional advection-dispersion equation for describing transport in porous medium and then applied stochastic approach to convert groundwater velocity (v), retardation (R) and the dispersion (D) constant coefficients into probability distribution. The next step was to employ the concept of fractional differentiation where we substituted the time derivative with the time fractional differential operator. Thereafter, we applied the Caputo, Caputo-Fabrizio and the Atangana-Baleanu fractional operators and derived conditions under which the exact solution for each derivative can be obtained. We then suggested the numerical solutions using the newly established numerical scheme of the Adams-Bashforth in the case of the aforementioned three (3) different types of differential operators. By combining the two concepts, we developed a new method to capture groundwater flow problems that could not be possible to capture using differential operators or stochastic approach alone. This new approach is believed to be a future technique for modeling complex groundwater flow problems. After solving the new model numerically, the condition for stability was also tested using the Von Neumann stability analysis method. Lastly, we presented numerical simulations using a software package called MATLAB.
Open Access
Investigation of hydrogeochemical processes and groundwater quality in the Chókwè district, Mozambique
(University of the Free State, 2016-06) Saveca, Paulo Sergio Lourenco; Lukas, Eelco; Juizo, Dinis
Groundwater has been recognised in Sub-Saharan countries as the main source of potable water in rural areas. In semi-arid regions, the climatic and anthropogenic factors both significantly affect groundwater quality. The present study was carried out in the Chókwè district, one of the semi-arid regions in Mozambique within the Limpopo River basin. About 33 water sources (27 groundwater, five surface water and one rainwater) were sampled from July to December 2015 for physicochemical parameters. This study focused on investigating hydrogeochemical processes in groundwater chemistry and their influence on water quality, as well as spatial variability in the Chókwè district. The hydrogeological approaches (WISH) and geospatial tool (Quantum GIS), combined with statistical analyses, were used to assess the groundwater quality. Geochemical ratios, correlation, graphical methods were also applied to understand the local hydrogeology on groundwater hydrochemistry. In addition, the Mozambique standards for drinking water and those of the World Health Organization were used for the assessment of groundwater quality. The analytical results of groundwater chemistry indicated that the order of abundance of cation concentration were Na+ > Mg2+ > Ca2+ > K+, while those of anions were Cl– > HCO3– > SO42–. There is a dominance of Na-Cl hydrochemical facies, and high mineralised groundwater occurs in aquifers underlined by two geological units, namely: alluvium, sand, silt, gravel geological units and eluvial floodplain clayey sand geological units. The alluvium, sand, silt, gravel showed that the content of electrical conductivity (EC) ranged from 603 to 12 000 μS/cm with an average value of 2 364 μS/cm, while for total dissolved solids (TDS) it ranged from 488 to 7 626 mg/L, with an average value of 1 621 mg/L. In the eluvial floodplain clayey sand geological unit the content of EC ranged from 522 to 5 530 μS/cm with an average value of 2 300 μS/cm, while for TDS it ranged from 406 to 3 537 mg/L with an average value of 1 562 mg/L. It was also observed that 15% and 30% of groundwater samples were classified as poor and unacceptable for drinking. For hardness, 7% and 30% of groundwater was hard and very hard, respectively. All parameters in the surface water are within the desirable limits, unlike that of groundwater. Weathering, ion exchange, dissolution and precipitation are the main hydro- geochemical processes. In aquifer mineralogy there is a dominance of sodic plagioclase (Albite), calcic plagioclase (Anorthite), halite, dolomite and calcite. Generally, the groundwater is saline and the land use, chemical evolution, as well as the local hydrogeology, are the factors affecting the spatial variability of water quality. Therefore, groundwater of the Chókwè district would not be safe to use for irrigation over the long term, due to a sodium and salinity hazard.
Open Access
Evaluation of management options for intermine flow and associated impacts in the Central Witbank Coalfield
(University of the Free State, 2003-07) Hough, J. J. H.; Usher, B.
English: Research into the identification, quantification and impact assessment of the intermine flow on the groundwater and surface water quality of the Witbank and Highveld coalfields was undertaken as part of broader research initiatives The study area of this thesis included the coal collieries of the Central Witbank Coalfield. Intermine flow areas were previously identified in studies by Grobbelaar et al., 2001 and Grobbelaar, 2001. The aim of this thesis was to develop a quantitative prediction of long-term intermine flow in the central Witbank coalfield, using the available data collected in the project. From the quantification of these flows and different hydrochemical techniques, likely water quality profiles at these collieries were determined. The quantification on the intermine flow direction as well as the flow volume was predicted through numerical groundwater modelling using Modflow. Local and regional models were compared and it was found that regional models (relative to including the whole extend of the voids in the model area) yielded the most accurate answer of the two models in the study area. The quantification of the predicted impact on water qualities was done through the use of mass balance approximations and an empirical sulphate generation rate method (developed in this study for predicting future sulphate concentrations in underground workings) using available hydrochemical and acid base accounting data. It was calculated that the sulphate generation rate for the underground workings is in the order of 0.1 - 1.5 kg/ha/d depending on the degree to which the void is filled. An evaluation of water management strategies, which will minimise the long-term influence of intermine flow on the groundwater and surface water quality, was also done. A compartmentalization system to mining opencast pits has been suggested for opencast pits with low decant elevations, to inundate a maximum percentage of the spoils to limit AMD reactions. The implementation of artificially created, high recharge areas on opencast pits and underground workings also was investigated to reduce fill-up times of voids as to limit the exposure of oxygen to the acid generating materials. The research indicates that intermine flow can be potentially detrimental to the groundwater- and surface water systems depending on the flow volumes and quality of the intermine flow water in the Central Witbank Coalfield. Flow volumes predicted through numerical modelling was quantified to be considerable enough to be potentially detrimental to mining voids into which the intermine flow water flows. It was also found that the intermine flow could influence the fill up times of the mining voids (both opencast pits and underground workings). The evaluation of different management options identified viable alternatives to manage intermine flow in such a way as to yield future optimal water qualities for the Central Witbank Coalfield.
Open Access
Site characterisation of LNAPL-contaminated fractured-rock aquifer
(University of the Free State, 2009-08) Gomo, Modreck; Van Tonder, G. J.; Steyl, G.
English: Site characterisation aims to obtain fundamental data needed to describe the subsurface flow pathways and distribution of contaminants. The study describes the application of various geohydrological techniques as complimentary tools to characterise an LNAPL contaminated fractured - rock aquifer on the Beaufort West study area in South Africa. Field investigations were designed to define and determine the properties of the fracture preferential flow paths responsible for LNAPL transportation in a typical Karoo fractured - rock aquifer system. The research places emphasis on the integration of results to maximise the subsurface geological understanding in particular location of fracture features chiefly responsible for facilitating LNAPL migration and distribution. The core and percussion drilling explorations, cross - correlated with borehole geophysics, were valuable for geological subsurface investigations in particular locations of bedding fractures, which are often associated with high hydraulic conductive flow zones. Tracer and pump tests were conducted to determine hydraulic and mass transport parameters respectively. Hydraulically conductive bedding plane fracture flow zones were identified by integrating results from the geological core logs, borehole geophysics and aquifer tests. The chemical characterisation of the study area was conducted by means of organic hydrocarbon, inorganic water analyses and volatile organic carbon measurements in the soil during air percussion drilling. Based on the findings, the hydrogeological structure of the formation was conceptualised as a fractured sandstone aquifer, characterised by bedding plane fracture preferential flow paths at contact areas, with shale and mudstone formations. The study findings demonstrate the merit and value in the application of various geohydrological tools to complement one another for optimised site understanding. The findings and recommendations of the case study are not necessarily confined to LNAPL contaminated fractured - rock aquifers, but may also be applicable to other types of contaminants in fractured - rock aquifer formations.
Open Access
An investigation into the temporal and spatial mobility of leachate production in a fly-ash dam
(University of the Free State, 2013-07) Marais, Izak Lukas; Steyl, G.
Open Access
Evolution of fluid electrical conductivity (FEC) profiles associated with a contaminant plume in a horizontal single-plane fractured rock aquifer system
(University of the Free State, 2017-07) Moleme, Malefa Florence; Gomo, Modreck
Fluid electrical conductivity (FEC) profiling is a simple and efficient technique used to determine properties such as flow rate, salinity and hydraulic characteristics such as transmissivity. The method is also commonly used to identify and locate high inflow zones intersected by a wellbore, from which groundwater samples can be collected for the purpose of water quality monitoring. Moreover, the identified inflow zones may be targeted for transport and hydraulic tests which may assist in the understanding of groundwater flow and solute mass transport properties of the subsurface. The method primarily involves profiling the FEC with depth in a borehole under either natural or stressed conditions, using a downhole Temperature Level Conductivity probe. Once the FEC tests are conducted and graphs are obtained, observations may be derived from the profiles. Zones where fluid flows into the borehole displays anomalies in the FEC profiles, which may be analysed to infer inflow rate and salinity of the individual fractures. The current challenge with the use of this method is that its application has not yet been studied in a controlled laboratory aquifer environment, in order to understand the typical FEC profile responses in aquifers of different structures and groundwater qualities. Furthermore, no guidelines have been developed to assist in the interpretation of FEC profiles under different hydrogeological conditions. In this study laboratory tests were conducted with the use of a physical model to investigate the evolution of FEC profiles associated with a contaminant plume, in a horizontal single-plane fractured rock aquifer system. To achieve this, two groundwater flow and transport conditions were simulated; one with freshwater flow and the other with saline (contaminated) water. Generally, two distinct profiles associated with a contaminant plume in a borehole drilled in a horizontal single-plane fractured rock aquifer were identified and conceptualised as (1) the conceptual background profile and (2) the conceptual elevated FEC profile. Essentially, within the conceptual background profile three distinct segments (zones) were noted, each which responded differently; the upper segment, transition zone and the lower segment. The conceptual elevated FEC profile was observed when a contaminant associated with increased FEC values reached the monitoring borehole; its anomaly is more or less pronounced (at the fracture position) depending on the stage of the contaminant plume within the system. These profiles were observed under a controlled laboratory environment and were also verified in the field. The profiles which were obtained in the field were comparable to those observed in the laboratory experiment thus increasing the confidence in the accuracy of the laboratory results.