Masters Degrees (Institute for Groundwater Studies (IGS))

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Open Access
Salinity in the Struisbaai aquifer
(University of the Free State, 1998-05) Weaver, John M. C.; Van Tonder, G.
English: The water-supply for Struisbaai has a historical reputation for its high salinity. Like most of the coastal holiday resorts along the Cape South Coast there are a number of permanent residents. For Struisbaai these comprise owners of small businesses servicing the holiday trade, fishermen and their families and retired folk. However, unlike other coastal resort-towns, Struisbaai is notable for the lack of houses with attractive gardens. This is a direct reflection of the relatively high salinity of the water-supply which in the past was not suitable for irrigation, having salinities of over 100 mS/m and sometimes over 500 mS/m. For example a sample of town water-supply was collected in June 1990 from a tap at Struisbaai Hotel and the EC was found to be 658 mS/m (4150 mg/L of dissolved salts). In 1990 a replacement wellfield was developed which has an EC of about 90 mS/m. With this relatively low salinity attractive gardens may become a feature of the future for Struisbaai. Three previous groundwater investigations have taken place, and in all of these the high salinities have been ascribed to over-pumping with resulting seawater intrusion. However, none of these authors gave any conclusive evidence for their theories. All of these reports gave field observations and then formulated theories for the origin of the salinity but in none of these reports were the two linked by logical arguments. This thesis thus considered the various possible sources of salinity and made conclusions as to the most likely source. The three sources of salinity that were considered are: HH. Salinity derived from sea-spray causing high salinity recharge. H'. Geological factors which yield high salinity groundwater. H'. Hydrogeological factors which result in sea-water intrusion. Field work consisted of drilling of four new boreholes, geophysical down-hole logging of six boreholes, establishing rainwater sampling points, collecting of groundwater samples and processing water samples for isotopic analysis. The methodology used to analyse the data was to closely consider the water quality of rainwater and groundwater samples as well as the isotopic composition of the groundwater. By considering ratios of the chemical composition, ratios of isotopic composition and using graphical plots the conclusion made was that the source of salinity is due to sea-spray which causes rain recharging to the aquifer to have a high salinity. This rain was measured to have a salinity of 10.5 and 12.5 mS/m respectively for the two rain collector stations. When a recharge to the aquifer of about 10% is allowed the resultant salinity is similar to that measured for groundwater at that site. Using the same methodology it was concluded, except for two individual boreholes, that geological and hydrogeological factors are not the source of salinity. For these two individual boreholes it was shown that overpumping and seawater intrusion was the probable cause of salinity. The decision to replace the old wellfield with the new wellfield has been a fortuitous decision. By doing so two positive effects have occurred. Firstly the wellfield is now in an area where the local recharge is less saline due to it being further away from the sea and thus receiving less sea-spray. Secondly the possibility of over-pumping and inducing seawater intrusion is minimal. This thesis has contributed to South African hydrogeology in that as far as can be ascertained this is the first documentation of the contribution that sea-spray makes towards causing salinity in South African coastal aquifers.
Open Access
Environmental impact of point pollution sources
(University of the Free State, 1999-07) De Lange, Stephanus Steyn; Van Tonder, G. J.
English: Due to the importance of groundwater as an alternative for supplementing existing sources of this precious fluid, any study that may help in understanding the complexity of the groundwater environment is an asset. Therefore this dissertation was written with the sincerest hope that the people and organisations involved with groundwater will gain a better understanding of it. The need to protect our groundwater sources has become very important and therefore a different, more practical approach to delineate borehole protection zones was considered based on the existing standards set by Germany and other European nations. As part of the study, emphasis was placed on the effect of the unsaturated (vadose) zone on the migration of pollutants before it reaches the groundwater environment. Field tests on the saturated as well as unsaturated zones were conducted with a conservative tracer (Fluorecein) as well as microbial tracers (bacteriophages), to assist in the delineation process. Thereafter it was decided to propose that three protection zones should be assigned depending on i) the size of the population and ii) the vulnerability and importance of the aquifer. The effect of a pollutant on human health and the possibility of fatalities were the criteria for deciding which protection zone is applicable under given circumstances. Protection zone I involves fencing off the immediate area around the borehole (a radius of 5 m is proposed) as well as the necessity of a well-constructed sanitary seal. Where a borehole supplies water to less than 20 people, a sanitary seal will be sufficient. To determine the extent of protection zone II, the idea was to protect the drinking water from microbial (bacteria and viruses) and nitrate pollution. Emphasis was placed on these two parameters because of their association with pitlatrines and septic tanks. Methods to estimate the fracture extent are proposed and, depending on the estimation of the nitrate and bacterial travel times and loads, a guideline to use i) half the fracture extent, ii) the whole extent of the fracture or iii) double the fracture extent, is proposed. Only if there is the possibility of a hazardous substance that may pollute the groundwater, it is proposed that protection zone III be assigned. The use of the word "hazardous" could make the decision more complex and therefore the issue of risk assessment and management is also addressed very generally in this dissertation. The proposed extent for protection zone III is the whole catchment area of the borehole. A programme called Borehole Protection Zone (BPZONE) was developed by making use of Microsoft Excel to assist the person(s) responsible in the decision making processes of delineating borehole protection zones. Information gathered during the field tests conducted at the Campus Test Site of the University of the Free State as well as the Meadhurst Test Site outside Bloemfontein, yielded very positive results, in terms of delineating protection zones.
Open Access
A geohydrological situation analysis for the construction of a groundwater management plan for the Sasolburg industrial and mining area
(University of the Free State, 1999-12) Cowley, Jennifer Anne; Van Tonder, Gerrit
English: The Department of Water Affairs in South Africa has recently moved towards the management of regions on a catchment and subcatchment scale. The Taaibos and Leeu Spruit catchments were identified as catchments where groundwater research was needed. The final objective of this work would be the implementation of a Catchment Management Plan These catchments house several influences on groundwater quality. These include the urban area of greater Sasolburg, several chemical industries (petrochemical, fertilizers, plastics ete), mining activities, power stations and agriculture. A groundwater situation analysis was therefore undertaken to highlight all relevant groundwater components. To achieve this, the study included a literature study, the creation of a database, fieldwork including sampling of 101 sites in the catchment for inorganic analysis, sampling of 10 sites for toxicity testing to indicate true toxicity of the water, aerial geophysics over a portion of the catchment and resistivity soundings at points surrounding the industries. Based on information gathered by this work it was possible to identify the principal aquifers in the area and classify them according to methods set out by Parsons (1995). The chief controls on groundwater movement and pollution sources on each site were identified. It was found that a dolerite sill of variable depth and thickness was the main control of groundwater movement underlying the industrial areas. The collected data and sampling highlighted the most important pollution sources. Use of toxicity testing showed the potential of these tests in indicating the true toxicity of samples. These results with, simplified numerical modelling in the area gave an indication of pollution migration and areas of concern. The area was subdivided into groundwater management areas based on the activities in each area. Three zones were defined representing the industrial and mining areas, a buffer zone and the areas to be protected respectively. In each zone different quality guidelines were proposed. A Threat Action Guide spreadsheet was developed to identify and prioritize areas of concern. It uses water quality data for different parameters, the aquifer classification, the water quality guideline for the zone and the distance to the nearest area of concern as inputs. A threat index is thereby calculated using various empirical equations and this index then suggests different generalized management options to be followed. The situation analysis has provided an overview of this heterogeneous area and put a basic framework in place on which the eventual Groundwater Management Plan will be based.
Open Access
Estimation of the preliminary groundwater reserve using numerical models
(University of the Free State, 2000-06) Zhang, Jinhui; Chiang, Wen-Hsing
English: The Water Act requires the determination of the Groundwater Reserve to secure the basic human needs and to protect the environment (aquatic ecosystems in terms of the Act). In other words, it is necessary to determine the allocatable groundwater resources and its use may not cause unacceptable negative impacts. As numerical models have been greatly developed in assessing groundwater resources in recent years, it is used to estimate the Groundwater Reserve. An investigation into existing groundwater numerical models has been done in order to select the suitable numerical model for determining the Groundwater Reserve. The MODFLOW program is selected for the present work because of the widespread of applications and the existence of user-friendly graphical interfaces, e.g. Chiang and Kinzelbach (in press). The procedure of estimating the allocatable groundwater resources can generally be divided into two steps: The first step is to estimate the total accessible groundwater resources by means of the regional groundwater balance. Groundwater fluxes, recharge, abstraction, and leakage to/from surface water bodies are balanced over the whole catchment. The methodology is used for the Pienaars River catchment, where the groundwater recharge is the only inflow term to the aquifer and its determination will directly affect the result. The interaction (water exchange) between groundwater and surface water (rivers and wetland) cannot be quantified without additional data, especially river flow rate and evaporation measurements in proper positions. To date, most available computer models are unable to compute the dynamic interaction between river stages and the groundwater levels. As a result, in most MODFLOW (or other groundwater models) applications, the river stages are often assumed to be known. This is, however, not applicable in many cases, where the change of the surface water profiles (river stages) due to groundwater or surface water abstractions must be predicted. A computer program which is able to couple the groundwater and surface water flow models, will be useful for computing and predicting both the groundwater and surface water levels and their interactions. The second step is to estimate possible negative environmental impacts due to groundwater abstractions. The estimated impacts are scales for decision-makers to give allowances to future abstractions. There are many possibilities to perform the second step, for example post-auditing or by using numerical models. The former is often not appreciated, because most groundwater systems are difficult or impossible to restore once they are damaged or contaminated. The latter is superior due to its predictive capability and its flexibility at the price of the data requirement. Because of the complexity of the saltwater intrusion processes, the program SEAWATER is developed to solve the steady-state salt-/freshwater sharp interface for using with MODFLOW. SEAWATER calculates the interface by means of an iterative process, which uses the Ghyben-Herzberg approximation to determine the location of the interface. The results of the program are compared with several analytical solutions.
Open Access
Manual on pumping test analysis in fractured rock aquifers
(University of the Free State, 2000-11) Van Bosch, Izak Jacobus; Van Tonder, G. J.
English: With the depletion of surface water resources in South Africa the utilisation of groundwater as the only potable water resource for communities in some rural areas is quickly becoming a reality. Failure of this resource will cause serious problems and it may even lead to loss of life. To prevent failure and to ensure the sustainability of this new resource, pumping tests are performed to determine the long-term sustainable yield of bore hole. This is the main reason why pumping tests are performed in South Africa, but in some instances pumping tests are performed to determine parameter values for aquifers. This research focussed on presenting guidelines on the proper planning and execution of the different types of pumping tests. To perform a proper pumping test involves big financial costs and therefor it is important to ensure that the correct information is obtained during such a test. Recommendations regarding the lengths of pumping tests as well as the abstraction rates during pumping tests are also made in this research. Before the interpretation of pumping test data it is important to obtain a better understanding of the basic concepts and characteristics involved in groundwater hydraulics. These concepts, together with the interpretation of diagnostic and derivative data plots are discussed in detail and it will provide the reader with enough knowledge to identify and understand the different flow regimes present in an aquifer. This research looks at the different steps involved in the interpretation of pumping test data and these steps are illustrated by means of worked examples. The different analytical methods to determine parameter values for an aquifer are also discussed in this thesis and the assumptions made in developing these methods are pointed out to the reader. In most cases these assumptions result in incorrect parameter value estimates. Numerical models, developed for the unique aquifer systems of South Africa, yielding the correct parameter values, are also discussed. Well losses can be divided into linear and non-linear losses. Non-linear well losses are mainly caused by turbulent flow inside the aquifer and borehole. This research however shows a non-linear relationship between drawdown and abstraction rate while the flow inside the aquifer is still linear. The non-linearity between drawdown and abstraction rate is corroborated by means of several examples and this nonlinearity can only be the result of the unique composition of aquifers in this country. Different abstraction rates result in different fractures being dewatered and fracture extents that are reached, causing a smaller effective T-value. The consequence of this non-linearity is that it is very difficult to extrapolate the future water levels in an aquifer. To estimate a sustainable yield in the case of non-linearity this research recommends a revised step drawdown test. This l00-minute test, conducted without constant time intervals, will also point out the positions of the main water strikes. A method, developed in South Africa, with which the long-term sustainable yield can be determined, is also discussed in detail and it is explained by means of a step by step worked example. Included in this method is the effect of boundary conditions as well as a risk analysis.
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
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
Evaluation of groundwater resource potential of Pallisa district in eastern Uganda
(University of the Free State, 2003-09) Nyende, Jacob; Hodgson, F. D. I.
This study aimed at assessing the ground water resources potential in Pallisa district, which is found in the eastern part of Uganda. The aims of the investigation can be Iisted as follows: ~ To determine the reliability and applicability ofVES in Pallisa district; ~ To evaluate the potential for sustainable harvesting of groundwater resource; ~ To determine the hydrogeological properties of the aquifer and make recommendations; ~ To suggest improved management strategies of water resource in Pallisa district in order to provide basic water services to the rural population and; ~ To propose a monitoring programme in the area that will include boreholes to determine the variation of water quality and quantity with time. The majority of the population of Pallisa district mainly uses groundwater as a source of supply for potable water. Groundwater is increasingly on demand in Pallisa district due to: (i) Population growth, (ii) Modem agricultural practices (iii) Livestock demands. Though springs and shallow wells are a source of groundwater in Pallisa, many of them have not been developed. There is need to have many of them developed to provide clean water and increase in the number of deep wells also in case of consistent droughts. The geological environment covered by this study consists of a Gneissic Complex Formation or Gneiss and granitic formations of the Pre-Cambrian origins. The study shows that Gneiss complex forms the principal source of ground water supplies while fresh metamorphic rocks are impermeable. From the hydrogeological investigations, it is clear that among the three water bearing zones (the upper, the middle and the lower), the metamorphic formations are widely weathered as you go deeper the earth, meaning that the lower zone of fresh geological granitic material are of a fractured bedrock. The study further revealed that the fracture zones have higher hydraulic conductivity with low storage coefficients and are generally confined. The hydrogeological investigation shows that groundwater in Pallisa district lies right below 30 - 70 m from the surface topography. This was shown by the hydrogeological profiles constructed through the underlying aquifer of the wells around Pallisa town. Higher transmissivity values were observed in the crystalline rock aquifer which related to the western and north - western of Pallisa district, with an average of 13.5 m2/d, due to the presence of open waters of Lake Kyoga, Mpologoma and Dodoi rivers. Such transmissivity values typically corresponded to drawdowns in order of a few meters at pumping yields of about 1 m3/hr. The recharge rate of 110 mm/a, taken as uniform throughout Pallisa district, had the total amount of groundwater recharged being l.956*109*0.11 m3/a = 215.2 million m3/a. The amount of water demanded by both the rural and urban is 35.7-million m3/a, which represents 17% of the groundwater currently used. The rest 83% of groundwater is unutilised. The hydro-chemical characterisation of waters in the study area show that the groundwater from the bedrock aquifers of Pallisa district represent regimes where there are predominantly calcium enrichment, which is typical of lime dosing to neutralize acid waters and both the regolith and bedrock groundwaters are dominated by the carbonate ions. This diversity of bedrock types is as a result of weathering of the underlying material. However, groundwater from many of the boreholes in Pallisa district is generally acceptable for human and livestock consumption. Stable isotopes of oxygen and hydrogen has been extensively used to investigate the rainfall and seasonal patterns of deuterium and 180 content of rainfall in the study area i.e. Pallisa district. This was inferred from historical observations at Entebbe, approximately 180 km to the south. The average monthly rainfall and 018 clearly demonstrates a relationship between the amount of rainfall and depletion in 180. As. part of the present study, monitoring of the groundwater resource in terms of yield aquifers with respect to drawdowns and water quality, consumption at water using production boreholes and management of these boreholes play important roles that can never be underestimated as per the recommendations made.
Open Access
Quantification of the impact of irrigation on the aquifer underlying the Vaalharts irrigation scheme
(University of the Free State, 2003-11) Ellington, R. G.; Usher, B. H.
Abstract not available
Open Access
Site characterization and risk assessment of organic groundwater contaminants in South Africa
(University of the Free State, 2004-11) Hohne, Surina; Usher, B.
English: South Africa has only recently realized that organic groundwater contamination occurs in this country and that it can have a serious effect on the groundwater quality. The Water Research Commission (WRC) recently launched studies to investigate Non Aqueous Phase Liquid (NAPL) pollution, and Dense NAPL in specific. The understanding of NAPL pollution problems, is however, still very limited. Hence groundwater practitioners confronted with NAPL pollution problems have burning questions regarding amongst others the characterization of the pollution, which is much more sophisticated than in the case of inorganic pollution. While in this phase, groundwater practitioners can not even begin to consider remedial efforts for contaminated sites, which continue to pollute the groundwater. It is therefore of paramount importance to get up to speed with technologies and practices accepted worldwide for characterization. Much improvement is still needed on these characterization methods, but South Africa can learn from past mistakes made by other countries in addressing NAPL pollution. In order to begin contemplating addressing NAPL characterization, it is important to understand the nature of the problem, which is why Chapter 2 describes the current situation of organic groundwater pollution and the associated vulnerability of aquifers in South Africa. The general understanding of groundwater pollution by NAPL is distorted, not only in the eyes of the public, but also in the eyes of experts in the groundwater field. A general misconception is that NAPL pollution only occurs at heavy industries such as ISCOR and SASOL, but Chapter 2 clearly shows that organic pollution is much more widespread and sinister in nature than would have been thought before. Smaller urban activities and small industries have been identified to be just as large a contributor towards organic pollution as the heavy industries. Shortcomings in the current understanding of NAPL pollution have been highlighted in Chapter 2 and further studies can be focused on determining the current impact of various industries on groundwater in South Africa, as well as delineating towns in which leaking underground storage tanks may be a problem. In order to address the NAPL pollution problem, legislative tools have to be in place. Gaps in legislation have therefore also been highlighted, of which several are listed in Chapter 3. These concerns need to be addressed by making the applicable policies and regulations, and implementing these regulations. In order to shed light on how site assessment and characterization can be performed in South Africa, Chapters 4, 5, 6 and 7 address issues associated with site assessment and characterization. Risk assessment has also been addressed (Chapter 8) and several shortcomings, to be addressed by toxicologists and groundwater practitioners, have been highlighted. It was clear from the investigations performed throughout this thesis, that several shortcomings exist in association with site assessment, site characterization and risk assessment, which will need to be addressed in the near future.
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
Managing the impact of irrigation on the Tosca-Molopo groundwater resource
(University of the Free State, 2005-05) Van Dyk, Gabriel Stephanus Du Toit; Van Tonder, G. J.
From 1990 to 2000 rapid development of irrigation from groundwater resources in dolomite aquifers took place in the Tosca Molopo area. This abstraction lead to water levels declining 10 to 20m regionally and up to 60m proximate to intensive irrigation. The purpose of this study was to investigate the impact of irrigation on the resource and initiate actions to manage the resource. This thesis reports on the qualification and quantification of the impact, determination of water use and regulating use to ensure sustainable future use. The Tosca Molopo area is located in South Africa proximate to the Botswana border. The area of interest is characterized by a flat topography. From the watershed in the west at 1210 m the elevation gradually decline to 1070 m in the east over a distance of 60 km. A number of non-perennial rivers drain the area, and although insignificant as surface water resources they play a major role in groundwater recharge. A low annual rainfall, varying from 399 mm in the east to 385 mm in the west, characterizes the study area. Evaporation in the area is high at between 2050 – 2250 mm/a (WRC, 1994) with only a small percentage of rainwater available to recharge groundwater. Two distinctive aquifers namely a primary aquifer formed by fine-grained sediments of the Kalahari Group and fractured/ carstified dolomites of the Ghaap Plato formation contribute to the system. The general flow is from the SW to the NE with the Molopo River the base of drainage. From the observed water level reaction the sediments contribute largely towards the storage of the aquifer system with the fractures of the dolomite contributing to high yielding flow. The MODFLOW PMWIN 5.1.7 (Chiang 2000) software was used to construct a 2-layer finite difference flow model. The model covering 80 km east west and 50 km north south or 4000 km2 was divided into cells of 0.5 X 0.5 km generating 100 rows and 160 columns. Based on the conceptual model provision was made for 2 layers namely the unconsolidated primary aquifer and the underlying fractured dolomite with its aquifer characteristics. The first layer ranges from an elevation of 1160 mamsl at a depth of 10 m in the southwest. To the northeast it range from an elevation of 1080 mamsl to a depth 960 mamsl or a thickness exceeding 120 m. The base of the sediments is the top of the fractured dolomite aquifer with its base at 900 mamsl. Of the number of dolerite dykes intruded into the dolomite the Grassbank and Quarreefontein dykes (both 15 m thick) are the most influential on the groundwater flow. Both these dykes act as no-flow boundaries of the Neumann (impervious) type impeding flow from the south and west of the area. Towards the east the Quarreefontein dyke does not seem to be a no-flow boundary as the water level information indicate connection with the dolomite to the south. The surface and groundwater shed formed by the Banded Iron Formation of the Waterberge forms the boundary to the west. The combination of both a geological contact and watershed is a leaking boundary. The Molopo River forms the eastern boundary. Recharge to the aquifer was determined with the chloride mass balance method with groundwater sample analysis and the Cl rain content 0.8mg/l. Recharge zones as determined from this chloride analysis were used for the model. Recharge in each zone was based on seasonal recharge for the winter (ranging from 0.5% or 0.4 mm to 3% or 1.5 mm) and summer (ranging from 0.5% or 1.6 mm to 3% or 8.3 mm) depending on the precipitation. Groundwater is the sole source of water for both agricultural and domestic requirements. As irrigation use is responsible for 99.5 % of the total use no domestic and stock watering abstraction was considered. Irrigation abstraction was calculated from the registration areas, field observations and reports from users. The volume was then averaged over a six-month period (182.5 days) according to crop cultivated to obtain the daily abstraction from the aquifer. The calibrated model was used to test the following 10-year future scenarios of abstraction and recharge in order to assist in decisions regarding management of abstraction from the aquifer system. Scenario 1 was with average precipitation and recharge at the current high abstraction rate of 16.1 Mm3/a. This scenario was not acceptable due to the regional water level declines of 20 to 30m and 60 to 110 m water level declines proximate to irrigation. Scenario 2 was with was with average precipitation and recharge at the restricted abstraction at 11.1 Mm3/a. This scenario would result in regional water level declines of 10 to 20m and 30 to 60m proximate to irrigation. With strong abstraction control this scenario with controllable water level declines was acceptable. Scenario 3 was similar to scenario 2, but with 20 % less than normal precipitation. The water level declines that will result with this scenario were similar to scenario 1, but it was expected that below normal precipitation would be the exception. The 4th scenario tested was if normal precipitation prevailed and all irrigation abstraction was stopped. The regional water level would recover fully after 10 years with only 10 m still to recover proximate to heavily irrigated areas. The model demonstrated that rates as specified by scenario 2 can be sustainable abstracted from the system at average recharge and that these abstractions would still be sustainable at 20 % less than average recharge as in scenario 3. Management of abstraction of the aquifer was consequently structured to ensure that abstraction would not exceed the sustainable yield of 11.1 M m3/a. Based on the evaluation and modeling of the resource the regulating and management of abstraction was addressed within the legal framework provided by the National Water Act (NWA) to obtain sustainable, equitable and fare dispensation of water use. Only water use exercised before Oct 1998 is recognized as existing water use. Potentially unauthorized users were identified with the use of satellite images. These water users were given the opportunity to proof that they are authorized users through a communication process and to submit supporting evidence. Users who could not submit satisfactory evidence were directed to scale their use down to authorized use by a specific time (summer 2003). These water users appealed to the water tribunal against the ruling of the water use authority, but the tribunal ruled in favor of the water use authority. In line with equitable access, application from new users were still processed with only 60 m3/ha of property owned authorized in accordance with General Authorization as prescribed by regulations of the NWA. With these actions the resource was still over allocated with water use still not within the accepted sustainable abstraction. Therefore it was decided that regulations would be implemented to enforce users to restrict their water use to 60 % of authorized water rights. The NWA makes provision for local management structures to be established to manage their local water use. Such a Water User Association (WUA) was established in the Tosca area and would on the long term enhance the capabilities for water use management. The resource is currently over allocated. It is recommended that the irrigation water use be restricted with 40% of authorized water rights. The water rights are not fairly allocated. Although the above actions are aimed at normalizing the critical damage to the resource and eminent conflict in the area compulsory licensing would be the long-term solution in this area. Compulsory licensing is aimed at sustainable and equitable allocation of water rights. The WUA should ensure that all users comply to abstraction control measures and water level monitoring the boreholes in the monitoring network would indicate if the resource would stabilize and recover to within sustainable use.
Open Access
The occurrence and evaluation of LNAPLs contamination in urban areas of South Africa
(University of the Free State, 2005-11) Phophi, Thilivhali Samuel; Usher, B. H.
Petroleum liquids are a basic building block of our modern lives. Uses include fuels, lubricants, and the raw material for manufactured products. The by-product of these uses has been the inadvertent release of petroleum liquids. A result of our utilization of petroleum liquids is a legacy of soil and groundwater impacted by petroleum liquids. The aim of this research is to provide an overview of LNAPLs in South African urban areas, transport mechanism of the LNAPLs in the subsurface, framework for detecting and evaluating LNAPLs under South African conditions. LNAPL is a convenient label for petroleum liquids in soils and groundwater. The acronym stands for Light Non Aqueous Phase Liquid. “Light” highlights the fact that petroleum liquids (i.e., gasoline) are less dense than water; “Non Aqueous” highlights the fact that petroleum is not completely miscible in water. An LNAPL contamination assessment was conducted at a service station after a complaint was raised by a resident who found free product (petrol) in her borehole. A multitude of private boreholes were found during the hydrocensus survey. A petroleum contamination assessment was done through soil vapour survey (SVS), hand auger holes and rotary percussion drilling. No significant petroleum vapours were detected due to clay soil which has low transmission of vapours. Hand auger holes were restricted to shallow depth due to the lack of penetration though the clay soils. Percussion drilling was needed to gather groundwater information (i.e., quality and quantity). Free product (petrol) was found within the percussion and some of the private boreholes. Groundwater samples were collected and analyzed for BTEX (Benzene, Toluene, Ethyl benzene and Xylenes) compounds. No detectable levels of BTEX were found in the soil samples. Risk assessment was done suing the RBCA approach and BP RISC software. BTEX concentrations of groundwater samples have triggered the Tier 1 risk based screening level for the risk values of carcinogenic and non-carcinogenic through groundwater ingestion, indoor and outdoor vapour inhalation exposure pathways. BP RISC was used to conduct Tier 2 evaluation and carcinogenic risk does exist in the receptor borehole through groundwater ingestion risk pathway. AQUA-WIN finite element model was used to determine the abstraction rate that could be used to conduct a pump-and-treat system. Free product could be recovered within two years after commencing with pump and treat system. Due to the lack of South African regulations with regard to petroleum contamination, the pump and treat system was stopped as soon as the product was recovered and monitoring of the dissolved phase hydrocarbons was continued. The establishment of South African guidelines and risk assessment protocols for petroleum hydrocarbons is outlined and strongly recommended for implementation.
Open Access
Groundwater modelling of a phytoremediation area in South Eastern Brazil
(University of the Free State, 2007-05) De Sousa, E. R.; Bernardes, C.; Usher, B. H.
Abstract not available
Open Access
The description of physico-chemical processes in coal mine spoils and associated production of acid mine drainage
(University of the Free State, 2007-05) Fourie, Petrus Johannes; Usher, B. H.
English: In the first part of this study the typical physico-chemical processes involved in Acid Mine Drainage (AMD) generation were discussed. This included a detailed description of mineralogical reactions, oxygen migration processes and heat conduction typically found in coal mine wastes. In the second part of the study the mineralogy as well as the AMD generation potential of coal mine spoils and discard in South Africa was assessed. A geochemical model of the AMD generation at a rehabilitated backfilled open-cast mine was constructed that simulated the oxygen diffusion process. Coal mine wastes produce Acid Mine Drainage (AMD) due to the ingress of oxygen and the subsequent oxidation of pyrite in the waste rock. As coal mine wastes consume oxygen, oxygen molecules will spontaneously diffuse into the coal mine waste rock along the concentration gradient. Oxygen migration into coal mine wastes also occurs through the passive process of advection. Mechanisms for advection include 1) air convection due to heat differences or changes in gas composition, 2) barometric pumping or 3) changes in water saturation. Heat is generated in coal mine waste mostly through pyrite oxidation and spontaneous combustion of coal. Heat flow occurs by means of conduction, convection, radiation and latent heat. Heat has an indirect influence on every aspect of Acid Mine Drainage (AMD) including microbial activity, gas migration, the rate of chemical reactions etc. Coal discard analysed in this study showed a high net acid generation potential, whether subjected to spontaneous combustion or not. Overall it can be concluded that coal discard has a high potential to generate AMD in South Africa. In spoil material it was found that some trace to dominant minerals were present that were also identified in other studies. These minerals include quartz, kaolinite, calcite, dolomite, mica, K-feldspar, plagioclase, siderite, pyrite, illite/smectite, smectite and anatase. The average pyrite content decreased from coal samples to carbonaceous clastic rocks to non-carbonaceous clastic rocks. The net acid generation potential was found to increase upwards from the No. 1 to the No. 4 coal seam. In the case study, one dimensional modelling of oxygen diffusion through waste material was performed using the PYROX 3 model of the University of Waterloo. The interaction between the gas, mineral and water phases was modelled using The Geochemist’s Workbench 6 (GWB). Consumption of oxygen by pyrite resulted in a decrease in oxygen concentration towards the bottom of the pit. Oxygen was however present in the saturated zone at the bottom of the pit and oxygen migration into the unsaturated zone was therefore not seen as the rate limiting step for the overall pyrite oxidation process. The pyrite oxidation rate was determined in PYROX after calibrating the oxygen concentration in the model to field conditions. By adjusting the reactive pyrite surface area in GWB the pyrite oxidation rate was calibrated to the rate modelled in PYROX. In the geochemical mass model seven scenarios were run that modelled closed, open and intermediate systems with regard to the oxygen and CO2 buffer. It was found that the geochemical system was nearly open to atmospheric oxygen and CO2, which can be attributed to the shallowness of the pit (average depth of 12 m). During the first few years a near neutral stage (pH 5.5 - 7.5) existed where calcite and dolomite buffered the solution. After depletion of the carbonate minerals an acidic stage (pH 3.0 - 4.0) followed where silicate minerals consumed some of the acidity. These two stages had a significant influence on the mineral reactions in the waste material and the ion concentrations in the pit water. The abiotic rate of pyrite oxidation by oxygen is positively dependent on the dissolved oxygen activity and negatively dependent on the hydrogen activity. As the pH decreased over the model time, the pyrite oxidation rate also decreased. The concentrations of all the major parameters and of iron in the pit water were modelled. It was observed that sulphate reached its peak concentration during the near neutral stage just before the acidification of the pit water and thereafter it decreased steadily before reaching a long-term concentration. During the neutral stage Fe(OH)3 had the highest activity of all iron species. Fe(OH)3 became undersaturated while Fe(OH)2+ and Fe(OH)2+ were the dominant species during the acidic stage. Oxidation of pyrite by ferric iron did however not occur as the ferric iron activity became only high enough at pH levels of below pH 3. This study showed that the AMD process can be successfully modelled using numerical modelling. In South Africa the number of operating coal mines have declined significantly over the past two decades and numerous coal discard dumps are present throughout coalfields. Modelling of AMD at coal mining sites will become increasingly more important for management decisions as more mines close in the Witbank and Highveld coalfields.
Open Access
Geohydrological characteristics of the Msikaba, Dwyka and Ecca groups in the Lisikisiki area, Eastern Cape
(University of the Free State, 2007-11) Nel, Gert Pieter; Van Tonder, G. J.
English: The study focused on the three major geological units, namely the Natal Group Sandstone (NGS or also called Msikaba Sandstone), the Dwyka Formation and the Ecca Group and was aimed at investigation the geohydrological properties of these units and their potential to produce sustainable groundwater supply. The methodology included Landsat lineament mapping, aerial photography mapping, geological mapping, geophysical exploration, drilling and testing. The investigation can be considered successful as various high yielding boreholes were drilled, some of which constituted new records for the Eastern Cape. Although the entire approach can be commented, it was the geophysical exploration that proofed conclusive in the Msikaba Sandstone where the high yields were obtained. Especially the EM-34 produced excellent anomalies where dolerite dykes were targeted and the fracturing on the sides of the dykes were very well defined. Recharge was calculated using the GIS / GRID based approach where a percentage recharge based on lithological properties was used. The percentage recharge seemed high when compared to the Chloride method where the two scenarios, coastal and inland, were considered. When the coastal scenario was used, the percentage recharge was in the same order of magnitude (10 - 12% of rainfall), but if the inland scenario was used the percentage recharge was much lower (<5%). If the pumping test results are considered, it seems that recharge mostly occurs along the fractured zone associated with the dykes on which the boreholes were drilled and not from the host rock in the case of the Msikaba Sandstone. No monitoring boreholes were available to test this theory in the Dwyka and Ecca, but it should be same in the case of the Dwyka. The Ecca produced low yields and poor water quality and hence it is possible that the overlying dolerite sheets have a negative influence on the recharge from rainfall. The fact that dolerite sheets were intersected at shallow depth (30m) without yielding groundwater, substantiate this. The water quality was acceptable in both the Msikaba and Dwyka, but mostly poor to unacceptable in the Ecca. In terms of ranking the three geological units according to their envisaged groundwater potential, they would rank as follows: o Msikaba Sandstone Ranked first o Dwyka Ranked second o Ecca Ranked third Main targets for drilling would include: o Regional dolerite dykes o Faults and larger lineaments o Geological contacts
Open Access
Quantification of the impacts of a domestic waste site on a Karoo aquifer
(University of the Free State, 2008-05) Mndaweni, Sakhile Sibusiso Edwin; Vermeulen, P. D.; Usher, B. H.
Waste generation is a widespread phenomenon around the world, of which the majority is disposed by landfilling. In landfills, waste constitutes an integral part of the hydrological system, and thus poses a threat to down-gradient groundwater and surface water receptors. This research was undertaken with the purpose of determining the interactions between landfill and the underlying Karoo aquifer, investigating the impacts of a domestic waste landfill on the aquifer and further predicting the magnitude of future contamination. A domestic waste landfill site at Sasol Synfuels (Secunda), located on the Karoo aquifer, was investigated in order to achieve these objectives. This site (Charlie I Landfill) has been used by the refinery to dispose of all non-hazardous/general waste produced for the past twenty years. It is not lined. There is no information available on the type and volume of waste disposed, and the impact on groundwater was not quantified. The landfill is classified as GMB+ (i.e. producing significant amounts of leachate), with the bord-and-pillar mining method taking place underneath the site at the depths of 90- 120m. This implies a lower probability of subsidence at this position. Field investigations indicate that there is a contaminant plume emanating from the landfill, which is mostly concentrated in the upper part of the soil horizon. This horizon is mainly composed of clayey loams and clay, averaging 3m in depth with a laboratory estimated maximum hydraulic conductivity of 0.0128 m/day. It is underlain by the Karoo sediments (sandstones and shales). Regional groundwater levels have been disturbed by the presence of the landfill site, with the higher water table closer to the site and the deeper water table moving away from the site. According to the blow yields obtained, slug tests for boreholes and piezometers, as well as the pumping tests, an average K- value of 10-2 was obtained for the aquifer, except in regions where a dolerite sill or fractures exists. Soil and water quality analyses indicate little contamination to groundwater; while contamination is mainly concentrated in the upper soil zone (i.e. originates from the surface leachate springs at the edge of the landfill). Modelling of the contaminant plume also indicates a slow migration of the plume to the adjacent areas. The physical properties of soils indicate that retardation (by biochemical reactions, sorption, cation-exchange etc.) of contaminants will occur with only very small quantities reaching groundwater. The presence of leachate springs and low levels of contaminant concentrations in groundwater indicates a limited vertical movement of contaminants. Therefore, leachate produced by the landfill site does not infiltrate into the groundwater system.
Open Access
The influence of the irrigation on groundwater at the Vaalharts Irrigation Scheme
(University of the Free State, 2009) Verwey, Philippus Marthinus Jacobus; Vermeulen, P. D.
English: Vaalharts Irrigation Scheme is not only the largest in the country it is known as "The Food Basket". In 1875, Mr Ford, a Government Surveyor got the idea that the Vaalharts area has irrigation scheme possibilities due to the topography of the area. The proposal was approved by government in 1833. Planning, soil tests and more surveys to investigate the possibility were done. A weir was constructed, in the Vaal River, 8.5 km upstream from Warrenton, to deviate water to the Jan Kempdorp/ Hartswater area. In 1938 the first farmers received plots. Today there are almost 1200 plots vary in size from 25 - 75 ha it cover a total area of 35 302 ha. At the start of the irrigation project the water table was 24 mbgl by 1971 it has risen to 1.5 mbgl and waterlogging was experienced. Streutker studied what the cause of the watertabie rising were. The feeder canals were ground canals and it leached to the water table causing the rise, the canals were lined. The water table remained high, in 1976 Gombar & Erasmus investigated the possibility to drain the area with boreholes. It was a solution but to expensive, The water in the Spitskop dam in the Harts River, were all the drain water flow to do not show parallel deterioration and accumulation of salt as the groundwater in the irrigated areas. A research done by Haroldt & Bailey investigated where does the salts and water go. Findings was that there are a "salt sink" present, mainly due to a perched water table and if at some stage the sink will be exhausted it would have severe effects. A 2004 research was done to find the "salt sink". Boreholes were drilled to study the groundwater characteristics, piezometers were installed, to check the possibility of two aquifers. The study concluded that water levels do not differ more than centimetres in the deep and shallow water systems. Water quality as profiled in piezometers indicated no major stratification of groundwater. The deep lying aquifer does not perform separately, thus no "salt sink". This study was done to conclude what is the effect of the irrigation on the groundwater and the following was done: • Planning and Installation of piezometer network • EC profiling of the piezometers • Monitor groundwater levels and EC's • Determine Hydraulic Conductivity • Sample collection and chemical analyses • Monitor flow of drains in the K block • Develop groundwater level contour maps • Develop and run a model to estimate drainage needs • Calculate salt and water balance A Piezometer network consisting of 246 piezometers were installed between Taung in the North and Jan Kempdorp in the south, 208 were surveyed for XYZ coordinates and used for monitoring. The water levels and EC values were measured four times over a period of a year to cover all seasons. The average water level was 1.63 mbgl and the EC average were 191.5 mS/m. Twenty five piezometer sites were selected to cover as much of the soil types present as possible, to determine the hydraulic conductivity. It was between 0.002 and 5.2 m/d. A map was generated to visualize it, and the values were used in the modeling of the drain zones. Water and salt Balance: The leaching requirement to ensure sustainable farming is 611.5 mm/a. According to the water balance it is 562 mm/a. Incoming salts through irrigation water = 4.65 tlha/a. The TDS determined in 1976 averaged 1005 mg/I, in 2004 it was 1350 mg/I, an average increase of 13 mg/I/a. During the research period it were 1476 mg/I, an increase of 96 mg/I in 5 years an average increase of 19.25 mg/I/a. Irrigation salt not drained = 0.8 t/ha/a Upgrading of all infra structure is essential. Internal subsurface drainage should be cleaned and replaced and the spacing should be decreased to drain the area more effective. Effective drainage would minimize the salt loss prevent a salt build up and have a positive influence on farming and crop quality in the area. The drained water can be reticulated to a transpiration pond to recover the salt thus preventing it from influencing nature and activities downstream.
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
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.