Conference Abstracts
Title | Presenter Name | Presenter Surname | Area | Conference year Sort descending | Keywords | ||||||
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Complexity versus Simplicity: A comparative analysis of complex geology in hydrogeological modelling | Anton | Lukas | 2012 | modelling, FEFLOW | |||||||
AbstractThis paper was presented at the GWD Central Branch Symposium, Potchefstroom in 2012 Numerical modelling of hydrogeological systems has progressed significantly with the evolution of technology and the development of a greater understanding of hydrogeology and the underlying mathematical principles. Hydrogeological modelling software can now include complex geological layers and models as well as allow the pinching out of geological features and layers. The effects of a complex geology on the hydraulic parameters determined by numerical modelling is investigated by means of the DHI-WASY FEFLOW and Aranz Geo Leapfrog modelling software packages. The Campus Test Site (CTS) at the University of the Free State in Bloemfontein, South Africa was selected as the locale to be modelled. Being one of the most studied aquifers in the world, the CTS has had multiple research projects performed on it and as a result ample information is available to construct a hydrogeological model with a high complexity. The CTS consists primarily of stacked fluvial channel deposits of the Lower Beaufort Group, with the main waterstrike located on a bedding-plane fracture in the main sandstone aquifer. The investigation was performed by creating three distinct hydrogeological models of the CTS, the first consists entirely of simplified geological strata modelled in FEFLOW by means of average layer thicknessand does not include the pinching out of any geological layers. The second model was created to be acopy of the first, however the bedding-plane fracture can pinch out where it is known to not occur. The third and final model consisted of a complex geological model created in Leapfrog Geo which was subsequently exported to FEFLOW for hydrogeological modelling. |
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The Complexity Of Baseline Monitoring In Unconventional Gas Projects | Richard | O'Brien | Karoo | 2013 | anthropogenic influence, groundwater monitoring | ||||||
AbstractThe monitoring of groundwater to detect changes resulting from anthropogenic activities requires an understanding of the particular aquifer system, release mechanisms and migration pathways which form the basis of a conceptual hydrogeological model. This conceptual hydrogeological model illustrates the connections between sources, pathways and receptors. The objective of a monitoring programme implemented in the context of shale gas exploration activities in the Karoo would be the detailed monitoring of groundwater quality for the protection of groundwater users. This objective requires a defensible baseline dataset so that changes in water quality can be investigated. In selecting parameters to monitor, cognisance must be taken of parameters which occur in multiple sources, those naturally present in the shallow potable aquifer, potential tracers representing the deeper groundwater and additives arising from the exploration activities. Sodium, potassium and chloride are all likely to be present in both deep and shallow groundwater and are potential additives. Given the expected higher salinity of deep connate groundwater, the use of aggregate parameters such as electrical conductivity might be of particular importance. Lithium, fluoride, strontium and uranium, while constituents of both the shallow and deep groundwater, are likely to be present at higher concentrations in the deeper groundwater, and could be indicators of deeper groundwater. Geochemical analysis of cores may provide initial clues as to such indicator parameters. Methane, which is known to occur in some existing Karoo boreholes, is potentially one of the more mobile tracers which could indicate migration from potential future production zones to shallow aquifers. The viability of using methane and other dissolved gasses (for example ethane) as indicators would require the use of stable isotope analyses to elucidate the origin of the gases.
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Towards The Effective Management Of Groundwater Resources During Unconventional Gas Mining | Surina | Esterhuyse | National | 2013 | Unconventional gas | ||||||
AbstractUnconventional gas mining is a new and unprecedented activity in South Africa that may pose various risks to groundwater resources. According to legal experts, South Africa does not currently have the capacity to manage this activity effectively due to various lacunae that exist in the South African legislation. The possible impacts of unconventional gas mining on groundwater, as well as governance strategies that are used in countries where unconventional gas mining is performed; have been analysed and will be discussed. Based on possible impacts and strategies to manage and protect groundwater internationally, possible governance options for the management of South Africa’s groundwater resources are proposed |
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The Geohydrological Status Of The Vanrhynsdorp Karst Aquifer | Jana | Brits | Vanrhynsdorp | 2013 | Geohydrological, Aquafer | ||||||
AbstractThe aim of this study was to determine the geohydrological status of the aquifer within the boundaries of the Vanrhynsdorp Water User Association with emphasis on the central catchment, E33F. This will assist the Department of Water Affairs with the introduction of compulsory groundwater-use licensing and empowerment of the Vanrhynsdorp Water User Association to manage the resource. In this study emphasis was given to the determination of the water balance and groundwater reserve of the central catchment and the designing of a representative groundwater monitoring network. A literature study of five projects conducted since 1978 was done. Comparisons were made between the data and results of these studies. All the historical data from these studies, as well as the data from the current monitoring programme up until December 2012, were put together and analysed. A conceptual model and groundwater reserve determination, as well as a representative monitoring network, were produced. The study showed a general decline in groundwater levels over a 34-year period. It also showed an increase in rainfall over the last 20 years. Based on the reserve determination and the declining groundwater level in spite of increased rainfall and thus recharge, it was concluded that over-abstraction of groundwater in the study area is taking place. It is recommended that compulsory licensing should be put in place as soon as possible and that no additional groundwater-use licences should be granted in the study area. The installation of flow meters on all production boreholes should be stipulated in the licensing condition. This will assist the monitoring and regulation of groundwater abstraction volumes. |
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Investigation Of Possible Contaminant Plumes Emanating From Residual Mine Deposits In The Mpumalanga Province Of South Africa, Results From Geophysical Surveys | Emmanuel | Sakala | Mpumalanga | 2013 | contamination, plumes, geophysical methods | ||||||
AbstractAcid-mine drainage (AMD) has received considerable media coverage in South Africa as of late. This have caused a considerable increase in researches, most of them with emphasis on decanting of contaminated water from the old gold mines in Witwatersrand basins and fewer on mine residue contamination from coal and gold mines in the Mpumalanga Province. The paper outlines results of ground geophysical surveys that were carried out along the perimeter of two mine residual deposits (dumps) in the Barberton Greenstone Belt, Mpumalanga Province. The aim of the study was to generate a 3D geoelectric model of the subsurface showing possible acid-mine drainage contaminant pathways. Two geophysical methods, namely Frequency Domain Electromagnetic Profiling (FDEM) and Electrical Resistivity Tomography (ERT) were applied in order to investigate the variation of electrical conductivity in the subsurface. The ERT method was done over frequency domain electromagnetics anomalies. FDEM electrical conductivity values ranging between 40 mS/m to 60 mS/m were considered as anomalous in that geological terrain. These areas were then surveyed by the ERT method to check the depth extent of these FDEM anomalies. On the resistivity section, between station 40 m and 80 m of Dump 1 – ERT1, a discontinuity in the bedrock was identified. The area could act as a pathway for contaminants to flow from the dump to groundwater. The FDEM survey identified an area with high conductivity values to the north of Dump 1. The ERT results also showed a shallow plume at 30 m depth which is consistent on two parallel sections on Dump 1. The area could be a possible AMD pathway of a mine dump residue to a Komati tributary on the north. The bedrock is generally characterised by high resistivity values; a break in the bedrock exists on this high resistivity zone on ERT 6. This break could be a fault zone which can act as possible pathway of (AMD) from a mine dump residue to a shallow aquifer. Potential contaminant recharge pathways were delineated using geophysical, electrical and electromagnetic methods. Potential groundwater recharge pathways and sub-vertical low resistivity zones with values <100Ohm.m were delineated using the ERT method. Investigation of contaminant plume migration is recommended over the anomalies that were generated from geophysics data in the Barberton areas. New technologies (artificial neural networks (ANN), fuzzy logic, etc.) combined with laboratory studies is recommended for development of a software platform that accepts 3D geoelectric data (present study), constrained with geology, geochemistry (soil and water), hydrology and hydrogeology data. |
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Hydrogeological Characterisation Of The Fountains East And Fountains West Karst Aquifer Compartments | Vevanya | Naidoo | Gauteng | 2013 | fountains | ||||||
AbstractThe Fountains East and Fountains West groundwater compartments (by means of the Upper and Lower Fountain springs) have been supplying the City of Pretoria with water since its founding in 1855. These adjacent compartments which are underlain by the Malmani dolomites of the Chuniespoort Group are separated by the Pretoria syenite dyke and are bounded to the north by the rocks of the Pretoria Group (Timeball Hill Formation). Inorganic chemistry data (2007-2012), as well as spring discharge volumes (2011-2012) for the Upper and Lower Fountain springs, supplied by the City of Tshwane Municipality, is being used to characterise the two compartments. This is done by means of piper diagrams, bar graphs and temporal plots. Interpretation of the combined chemical and discharge volume data as well as geotechnical and isotope data (in progress) will aid in understanding the karst aquifer and the controls on groundwater system within and possibly between these compartments. |
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Numerical modelling of mine dewatering and flooding in the Evander Gold Basin, South Africa | Kai T | Witthueser | Witwatersrand | 2013 | gold mining, mine water rebound | ||||||
AbstractThe assessment and prediction of mine water rebound has become increasingly important for the gold mining industry in the Witwatersrand basin, South Africa. The cessation of dewatering lead to large volumes of contaminated surface discharges in the western parts of the basin. Towards the eastern extremity of the Witwatersrand basin the detached Evander Goldfield basin has been mined since the early 1950s at depths between 400 and 2000 metres below ground, while overlain by shallower coal mining operations. The hydrogeology of the Evander basin can be categorised by a shallow weathered-fractured rock aquifer comprising of the glacial and deltaic sediments of the Karoo Supergroup, while the deeper historically confined fractured bedrock aquifer consist predominantly of quartzite with subordinate lava, shale and conglomerate of the Witwatersrand Supergroup. The deep Witwatersrand aquifer has been actively been dewatered for the last 60 years with a peak rate of 60 Ml per day in the mid late 1960s. Modelling the impacts of mine dewatering and flooding on a regional scale as for the Evander basin entails challenges like the appropriate discretisation of mine voids and the accurate modelling of layered aquifer systems with different free groundwater surfaces on a regional scale. To predict the environmental impacts of both the historic and future deep mining operations, the detailed conceptual model of the aquifers systems and a 3-dimensional model of the mine voids were incorporated into a numerical groundwater model to simulate the dewatering and post-closure rebound of the water tables for the basin. The presented model could serve as an example for the successful modelling of mine dewatering and flooding scenarios for other parts of the Witwatersrand basin. |
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Effects Of Dolerite Intrusions On The Geohydrology Of Upper Karoo Sediments In The Elundini Area, South Africa | Jakobus | Prinsloo | The Elundini Area, South Africa | 2013 | Geohydrology | ||||||
AbstractThe Karoo Supergroup has a hydrogeological regime which is largely controlled by Jurassic dolerite dyke and sill complexes. The study area is located in the north-eastern interior of the Eastern Cape Province, close to the Lesotho border. The sedimentary rocks of the upper Karoo constitute fractured and intergranular aquifers, due to relatively hydro-conductive lithologies. The main groundwater production targets within the upper-Karoo are related to dolerite intrusions that have a number of characteristics that influence groundwater storage and dynamics. Magnetic, electromagnetic and electrical resistivity geophysical techniques are used to determine the different physical characteristics of the dolerite intrusions, such as size, orientation and the level of weathering. Trends in the data collected from a large-scale development programme can provide evidence that intrusion characteristics also play a role in determining the hydrogeological characteristics of the area. Interpreted geophysical borehole drilling, aquifer testing and water chemistry data can be used to indicate hydrogeological differences between dolerite intrusion types. Observed trends could be used for more accurate future well-field target areas and development. |
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Comparison Of Analytic And Numerical Estimations Of Groundwater Drawdown Evolution For Open Pit Dewatering | Jaco | Nel | Kolwezi, Democratic Republic of the Congo | 2013 | dewatering, Drawdown | ||||||
AbstractA new mining site situated near Kolwezi in the Democratic Republic of the Congo plans to develop a pit in phases over a period of six years. The mine requires dewatering volume estimates of the pit as well as a constant water supply to the plant. Hydrogeologic data available at the site during the scoping phase was limited to a few water level measurements and blowout yields from only five hydrological boreholes. Hydraulic properties from reports at neighbouring sites were extrapolated to the geological units at the site. The depth to water level at the site is about 20 m, with a planned final pit depth of approximately 180 m below surface. Based on the limited data available an analytical approach to estimate the inflow into the mine was adopted. Analytical calculations proposed by Marinelli and Niccoli (2000) were used to estimate the inflow into the Pumpi mine pits. The analytical calculations consider recharge, depth of mining vertical and horizontal hydraulic conductivities. Drawdown evolution of pit dewatering are obtained by using different mining depths at different mine stages. The output results from the analytical calculations are the maximum extent of influence of the pit as well as the volume of water inflow into the pit. Limitations of the analytical equations are that they, amongst others, cannot consider complex boundaries. Drilling and pump testing to obtain local hydraulic properties and boundary conditions are planned during the first quarter of 2013. The numerical model will be set up after the drilling and pumping tests, using the new data for calibration. The numerical model will contain as much of the physical layer definitions and potential internal boundaries as possible with model boundaries incorporated along far field fault zones and hydraulic boundaries. The numerical model should improve the reliability of estimates of pit inflow and water supply to the plant. The results between the analytical and numerical approaches can then be compared to improve future dewatering estimates with limited data. It is expected that the reliability of the analytical predictions will reduce after year 4, where the role of boundaries are expected to influence the drawdowns and related flow towards the pit. |
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Establishing An Aquifer Protection Policy For Co2 Geological Storage Utilising Hydrogeological Numerical Modelling, Bela-Bela (South Africa). | Tshegofatso | Mophatlane | Bela-Bela, Limpopo | 2013 | aquifer protection, Hydrogeological, geological storage | ||||||
AbstractSouthern Africa hosts over 93% of the continent's energy, which has been conserved in coal seams deposited in various Karoo age sedimentary basins. Carbon dioxide geological storage (CGS) is proving to be an emerging greenhouse gas technology (GHGT), that global governments have elected to mitigate the projected coal use in Southern Africa. One of the major challenges of successfully introducing CGS to the public and world leaders is the significant risk the technology poses to groundwater resources. Lack of public confidence is further coupled by the poor knowledge of the subsurface behaviour of injected media, such as CO2, in South African potential lithological reservoirs. The study has utilised data from a current MSc research, in which the Springbok Flats Coal Basin (SFCB) has been used as the problem set-up. The aim of this study is to determine which FELOW™ mesh geometry would be the most suitable to simulate a CO2 ingress plume within a regional aquifer. The study has utilised principals of dense vegetation zones (DVZ) and density- variable fluid flow (DVFF) when simulating the ingression. The specific objective is to utilise the simulation results to guide amendments of water legislature, towards accommodating CO2 geological injection and storage operations. Results indicate that a combination of high-quality triangular meshes of various geometries, created with the FEFLOW compatible mesh generator, TRIANGLE, produced the best 3D model and simulation results. The basic matrice unit for the DTZ was defined as a quad mesh composed of two right-angled triangles and one equi-angualar triangle (five nodes), while the unit for modelling springs was defined as a quad mesh with four-equi-angular triangles, both used in various scales. The results were used to amend the Stream Flow Reduction Activities (SFRA) policy and thus the aquifer licensing procedure of the National Water Act, in order to accommodate the allocation of aquifer use licenses for CO2 geological storage operations. The amendments illustrate the significance of finite element simulation codes for integrated water resources management policy. |
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Setting Water Quality Compliance Limits For Contaminated Groundwater In Fractured Rock Aquifers | Morne | Burger | National | 2013 | Water quality, fractured rock (504, aquifer, contamination | ||||||
AbstractIndustrial facilities and mining activities represent a potential contamination hazard to down gradient surface water and groundwater environments. The assessment of the risks posed by such contaminant sources should facilitate regulators to determine set compliance limits. These limits should, however, take in consideration the heterogeneous nature of fractured rock aquifers. This paper will focus on the limitations or technical feasibility of applying single groundwater quality compliance limits for fractured rock aquifers. It will also aim to describe how groundwater contamination limits could be determined in a more feasible manner. |
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Towards The Effective Management Of Groundwater Resources During Unconventional Gas Mining | Surina | Esterhuyse | South Africa | 2013 | Unconventional gas | ||||||
AbstractUnconventional gas mining is a new and unprecedented activity in South Africa that may pose various risks to groundwater resources. According to legal experts, South Africa does not currently have the capacity to manage this activity effectively due to various lacunae that exist in the South African legislation. The possible impacts of unconventional gas mining on groundwater, as well as governance strategies that are used in countries where unconventional gas mining is performed; have been analysed and will be discussed. Based on possible impacts and strategies to manage and protect groundwater internationally, possible governance options for the management of South Africa’s groundwater resources are proposed. |
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Groundwater Closure Cost Estimation For The Mining Industry | Pieter F | Labuschagne | National | 2013 | Mining , Environment, Rehabilitation | ||||||
AbstractThe increase in awareness of environmental issues and the desire for a cleaner environment by the public has caused mining companies to place greater emphasis on the continuous rehabilitation of harmful effects caused by mining operations. Ongoing rehabilitation is also a requirement of the government departments involved in mining in South Africa. The biggest concern for the relevant government departments is the possible uncontrolled pollution of water resources in the vicinity of mines, after they have closed. In the compilation of this paper, the unique nature of the South African situation has been considered – this refers to a legally acceptable approach towards current legislation and policies. This study leads to the construction of a logical approach towards mine closure, specifically to understand issues around costs and financial liability. The final product of this approach should ultimately give more clarity on: the principles followed to identify objectives for mine closure and groundwater assessment; key steps to follow when assessing site hydrogeology and to determine related impacts, risks, closure costs and liabilities; and an overview of methods that could be used for the mitigation of polluted aquifers and a brief site-specific application. |
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Implementation Of Protection Zoning | Shuaib | Dustay | National | 2013 | Protection, development | ||||||
AbstractCurrently limited progress is made in South Africa (and Africa) on the protection of groundwater quality. To achieve the objective of water for growth and development and to provide socio- economic and environmental benefits of communities using groundwater, significant aquifers and well-fields must be adequately protected. Groundwater protection zoning is seen as an important step in this regard. Till today, only one case study of groundwater protection zoning exists in Africa. Protection zone delineation can be done using published reports and database data. However, due to the complexity of the fractured rock at the research site, more data are required. This data can be collected by conducting a hydro census and through aquifer tests. An inventory of the activities that can potentially impact water quality was done and aquifer characteristics such as transmissivity and hydraulic conductivity were determined through various types of aquifer testing. Fracture positions were identified using fluid-logging and fracture flow rates were also measured using fluid-logging data. A conceptual model and basic 3D numerical model were created to try to understand groundwater movement at the research site. The improved information will be used to build a more detailed numerical model and implement a trustworthy groundwater protection plan, using protection zoning. The expected results will have applicability to groundwater management in general. The protection plan developed during this project can be used as case study to update and improve policy implementation. |
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An Updated Hydrogeology Concept Within The Kruger National Park Southern Supersite | Ashton | van Niekerk | The Kruger National Park, Limpopo, Mpumalanga | 2013 | Hydrogeological, ERT | ||||||
AbstractPOSTER Electrical Resistivity Tomography (ERT) surveys were conducted in the Kruger National park (KNP) as part of a recent Water Research Commission project (titled: Surface water, groundwater and vadose zone interactions in selected pristine catchments in the Kruger National Park). The surveys were carried out in a pristine ephemeral third-order supersite catchment, namely the southern granite (Stevenson Hamilton). This supersite is representative of the southern granite region of KNP as it covers part of the dominant geology, rainfall gradient and dominant land system. Electrical resistivity profiling provided valuable data on the subsurface geological material distribution and results depended on soil/rock properties, water content and salinity. The purpose of electrical surveys was to characterise the hydrogeological components of weathering and depth to water level using the subsurface resistivity distribution. The ground resistivity is related to various geological parameters such as the mineral and fluid content, porosity and degree of water saturation in the rock. Based on the initial ERT survey interpretations, boreholes were drilled providing actual subsurface results in the form of borehole drilling logs, water levels, hydraulic data and in situ groundwater quality parameters. Integrating the ERT survey data with the results from the intrusive survey enabled an updated conceptualisation of groundwater flow characteristics and distribution across the southern granite supersite. |
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The Challenges Facing Delineation Of Integrated Units Of Analysis Within Context Of The Groundwater Resources Directed Measures | Sagadevan | Kisten | National | 2013 | groundwater resource directed measures | ||||||
AbstractThe Department of Water Affairs (DWA), Chief Directorate: Resource Directed Measures has developed guidelines over the past decade in order to facilitate proper implementation of the Groundwater Resource Directed Measures (GRDM) (also known as determination of the groundwater component of the Reserve). An intrinsic component of the GRDM is delineation of Integrated Units of Analysis (IUAs) from which the allocatable groundwater and surface water components are calculated, which essentially drives the allocation of water use licenses. Delineation typically follows a three-tiered approach, namely primary, secondary and tertiary level. Primary delineation is based on quaternary boundaries (considered to be the basic building block of the IUA); secondary follows geological, hydrogeological and hydrological boundaries, groundwater abstraction zones and baseflow contribution; and tertiary is dependent on management criteria. How then, do we undertake this challenging task of delineating IUAs to a level where it can be better managed and monitored? Complexities arise when hydrogeological data are scarce, hydrological and hydrogeological systems are not in sync, aquifers extend across a quaternary, water management area, provincial and administrative boundaries, surface water and groundwater interactions are not well understood, and legislation on protection of water resources differs greatly from one country to the next. Having undertaken delineation of IUAs in the Waterval Catchment (Upper Vaal WMA), Olifants WMA and Mvoti to Umzimkhulu WMA with the available datasets, the key criteria for the respective WMAs have ultimately been management class, significant aquifers, groundwater– surface water interaction and groundwater stressed areas, and secondary catchment boundaries, followed by other hydrogeological, geological and management considerations. |
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Numerical groundwater flow model for the Palla Road wellfield, Botswana | Martin | Holland | Botswana | 2013 | numerical groundwater flow model | ||||||
AbstractThe Palla Road well-field is located in the Central District of Botswana approximately 160 km from Gaborone and 50 km from Mahalapye. The aim of this project was to review and update the existing groundwater model developed in the late 1990s of the Palla Road well-field in order to assess the viability of long-term groundwater abstraction due to the increasing water demands in the region. The main hydrogeological units recognised in the project area comprise of aquifer systems developed in the Ntane Sandstone Formation and formations of the Middle Ecca Group with minor aquifers developed in Mosolotsane Formation and the Stormberg Basalt. The finite-difference model boundary covers an area of 3 702 km2 and was set-up as a three-dimensional semi-uniform grid comprising of four layers. Eight recharge and 14 hydraulic conductivity zones in accordance with the geological model were distinguished. Steady state calibration was accomplished by varying the hydraulic conductivity values, while keeping the recharge rates constant in order to achieve a unique solution. Transient calibration of the model covered three larger stress periods namely: (1) initial condition (pre-1988), (2) abstraction period (1988 to 2012) and (3) predicted model simulations (2013 to 2036). The calibrated groundwater flow model was used to assess the impacts associated with the proposed abstraction scenarios for the Palla Road and Chepete well-fields with consideration of potential cumulative impacts due to the Kudumatse well-field. Three basic scenarios comprising certain sub-scenarios based on the future water demand for the Palla Road and Kudumatse region were considered. The model simulations show that the abstraction scenario 2a, namely simultaneous abstractions from the Chepete/Palla Road and Kudumatse well-fields, poses a risk to the sustainability of downstream water resources. The maximum simulated drawdown in the central and southern parts of the Palla Road well-field reach 14 m after six years of pumping. Although outflow diminishes after a six-year period, it is restored to approximately 80-90% after the simulated recovery period. The presented 3-D multi-layer model can be used as a tool to determine the optimal abstraction rates while giving cognisance to the sustainability of the resource. |
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The Use Of Vegetable Oil Substrates In The Treatment Of Contaminated Groundwater | M | Pienaar | National | 2013 | prevention strategies, contamination, Water treatment | ||||||
AbstractEdible vegetable oil (EVO) substrates have been successfully used to stimulate the in situ anaerobic biodegradation of groundwater contaminated with chlorinated solvents, as well as numerous other anaerobically biodegradable contaminants like nitrates and perchlorates at many commercial, industrial and military sites throughout the world. EVO substrates are classified as a slow release fluid substrate, and comprise of food-grade vegetable oil such as canola or soya bean oil. The EVO substrate serves as an easily biodegradable source of carbon (energy) used to create a geochemically favourable environment for the anaerobic microbial communities to degrade specific contaminants of concern. EVO substrate’s can either be introduced into the subsurface environment as pure oil, in the form of light non-aqueous phase or as an oil/water emulsion. The emulsified vegetable oil substrates has several benefits over non-emulsified vegetable oil as the fine oil droplet size of the commercially manufactured emulsified oils can more easily penetrate the heterogeneous pore and fracture spaces of the aquifer matrix. The use of this technology to stimulate in situ biodegradation of groundwater contaminants is still relatively unknown in South Africa. This paper gives an overview of the EVO technology and its application, specifically looking at the advantages of using this relatively inexpensive, environmentally-friendly based technology to remediate contaminated groundwater within fractured rock environments commonly encountered in South Africa. |
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In Situ Iron Removal: Innovative Option For Preventing Production Borehole Clogging | Kate | Robey | International | 2013 | Borehole clogging, prevention strategies, Iron Removal | ||||||
AbstractMany aquifer systems worldwide are subject to hydrochemical and biogeochemical reactions involving iron, which limit the sustainability of groundwater schemes. This mainly manifests itself in clogging of the screen and immediate aquifer with iron oxyhydroxides resulting in loss of production capacity. Clogging is caused by chemical precipitation and biofouling processes which also manifests in South African well-fields such as in Atlantis and the Klein Karoo. Both well-fields have the potential to provide a sufficient, good quality water supply to rural communities; however, clogging of the production boreholes has threatened the sustainability of the schemes as quality and quantity of water is affected. Rehabilitation of the affected boreholes using techniques such as the Blended Chemical Heat Treatment method does not provide a long-term solution. Such treatments are costly with varying restoration of original yields achieved and clogging recurs with time. Currently the research, management and treatment options in South Africa have focused on the clogging processes which are complex and site-specific, making it extremely difficult to treat and rectify. This project attempts to eliminate elevated concentrations of dissolved iron, the cause of the clogging. High iron concentrations in groundwater are associated with reducing conditions in the aquifer allowing for the dissolution of iron from the aquifer matrix. These conditions can be natural or human-induced. Attempts to circumvent iron clogging of boreholes have focussed on increasing the redox potential in the aquifer, by injection of oxygen-rich water into the system, to prevent dissolution and to facilitate fixation of iron in the aquifer matrix. Various in situ treatment systems have been implemented successfully overseas for some time. In South Africa thus far in situ treatment of iron has only been proposed as a solution for production borehole clogging. Based on experience from abroad the most viable option to research the elimination of ferrous iron in South African aquifer systems would be through the in situ iron removal treatment. Different techniques of increasing the dissolved oxygen concentration in the injected water to intensifying the redox change in the aquifer can be applied; however, the use of ozone as the oxidant is a new approach. Its effectiveness is evaluated by the results in iron removal in surface water treatment for drinking water supply. |
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Characterisation Of A Large Light Non-Aqueous Phase Liquid (Lnapl) Plume Over A Fractured Gneiss Aquifer In Limpopo Province, South Africa; With Reference To An Ongoing Pump-And- Treat Remediation Technology | Mahlogonolo | Phahlamohlaka | Limpopo | 2013 | LNAPLS | ||||||
AbstractWork is being conducted in Limpopo province following a large volume release of petroleum hydrocarbons that took place from a leaking underground pipeline, resulting in significant groundwater contamination. This is considered to be the largest petroleum hydrocarbon release recorded to date in South Africa. The leak took place for 15 years before it was discovered 13 years ago in 2000. From the pressure tests that were performed, 10-15 ML of A-1 Jet fuel is considered to have been released to the subsurface. Product bailing was the first method employed for the recovery of the free product, and was later replaced with a P&T system which was considered to be more effective. The village located about 6 km to the north of the spillage depends mostly on groundwater. This paper presents a progress update of works that have been conducted in support of developing a conceptual model which aims to determine the areal extent of the plume. |
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Groundwater Asset Management In The Mining Industry | Mike | Deed | National | 2013 | groundwater management, Mining , Boreholes | ||||||
AbstractGroundwater boreholes are a key element of many mining projects, as part of dewatering and water supply systems, and must achieve high levels of operational efficiency and service availability. Outside of the mining industry, planned borefield maintenance programmes have become a key part of professional well-field management, with proven benefits in terms of operational cost savings and continuity of pumping. However, the benefits of proactive planned maintenance of groundwater boreholes on mine sites have only recently been widely recognised. Potential operational problems are described, including water quality issues which can result in mineral contamination leading to deposits and scale build-up which can clog screens and pumps, reduce water flow and yield, and eventually cause pump breakdowns and mine stoppages. Best practice methodologies to remove or minimise the contamination are described and the benefits of implementing a planned maintenance programme are discussed. Case studies are described from two significant mines in Australia, where boreholes suffered from mineral contamination, including calcium carbonate and iron bacteria contamination. Both mines suffered from increased pump breakdowns, groundwater yields consistently below target and serious cost overruns. Borehole rehabilitation treatment plans were implemented to resolve the immediate contamination problems followed by an ongoing maintenance programme to prevent or minimise their reoccurrence. Treatment programmes included a downhole camera survey, use of a bespoke software program to review the results of the survey and the available water quality data, and a purpose built rehabilitation rig that included the use of specialist chemical treatments to remove and control the existing encrustation and clogging deposits. |
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Acid-Mine Drainage And Its Potential Impact On The Water Resources In The Waterberg Coalfield | Vanessa | Aphane | Limpopo | 2013 | Water resource | ||||||
AbstractSouth Africa currently ranks number nine in the world of the proved coal reserves that has been estimated to last for over 200 years. Coal constitutes about 77% of the primary energy needs in the country, with the Waterberg Coalfield estimated to host about 40% of the remaining South African coal resources. Coal deposits in the study area largely consist of shales, mudstones, siltstones and sandstones which host coal-containing clay minerals; quartz, carbonates, sulphides and the most abundant sulphide mineral is pyrite. Once mining begins, the sulphide minerals are exposed to surface which allows contact with atmospheric oxygen and water causes oxidation to take place, therefore causing acid-mine drainage (AMD). Acid-base accounting (ABA) was used to determine the balance between the acid-producing potential (AP) and acid-neutralising potential (NP). From the analysis the Net Neutralising Potential (NP-AP) was determined, which is one of the measurements used to classify a sample as potentially acid or non-acid-producing. Mineralogical analyses will be done by x-ray defraction (XRD) to define and quantify the mineralogy of the geological samples which can help in the management plan to minimise generation of acid. AMD does not only result in the generation of acid, but as well as in decreased pH values and increased values of specific conductance, metals, acidity, sulphate, and dissolved and suspended solids. Inductively coupled plasma analysis was done to determine the release of the heavy metals which can be detrimental to the environment. Sample analysis was done on the interburden, overburden as well as the coal samples. From results obtained, over 35% to 50% of the samples have an excess of acid potential which classifies the samples as having a higher risk for acid generation. About 30% to 40% of the samples have a higher neutralising potential; the rest of the samples have a medium acid risk generation. The water demand will increase as developments continue in the area, with inter- catchment transfers identified as the answer to fill the gap of water scarcity. Acid mine drainage poses a big threat on water resources, both groundwater and surface water nationally, which might be less of a problem in the Waterberg because of the cycle of low rainfall in the area, but the potential of AMD cannot be neglected. |
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Multi-Data Integration Approach In Groundwater Resource Potential Mapping: A Case Study From The North West Province, South Africa | A | Tessema | Naledi Local Municipality, North West Province | 2013 | case study, Groundwater | ||||||
AbstractA multi-data integration approach was used to assess groundwater potential in the Naledi Local Municipality located in the North West Province of South Africa. The geology comprised Archaean crystalline basement, carbonate rocks (dolomite and limestone) and windblown sand deposits of the Kalahari Group. The main objective of the study is to evaluate the groundwater resource potential using multi-data integration and environmental isotope approaches. Prior to data integration, weighting coefficients were computed using principal component analysis. The results of integration of six layers revealed a number of groundwater potential zones. The most significant zone covers ~14% of the study area and is located within carbonate rocks in the southern part of the study area. The localisation of high groundwater potential within carbonate rocks is consistent with the results of principal component analysis that suggests that lithology significantly contributed to the total data variance corresponding to principal component 1. In other words, carbonate rocks consisting of dolomite and limestone largely account for groundwater occurrence in the southern part of the area. In addition, the relatively elevated isotopic signature of tritium (≥1.0 TU) in groundwater samples located in the southern part of the area suggests a groundwater recharge zone. Furthermore, moderate-to-good groundwater potential zones within the Ventersdorp lava coincide with maximum concentration of fractures, which is consistent with the results of statistical correlation between borehole yield and lineament density. The multi-data integration approach and statistical correlation used in the context of evaluating groundwater resource potential of the area provided a conceptual understanding of hydrogeological parameters that control the development of groundwater in crystalline and carbonate rocks. Such approach is crucial in light of the increasing demand for groundwater arising from municipal water supply and agricultural use. The two approaches are very effective and can be used as a sound scientific basis for understanding groundwater occurrence elsewhere in similar hydrogeological environments. |
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A Summary Of Wetland Legislation In South Africa Over The Past Fifty Years | Nelda | Breedt | National | 2013 | wetland legislation | ||||||
AbstractThe deterioration of wetlands due to human activity has been a problem for many years. Under the old Water Act 36 of 1956 no provision of water was made for managing the environment. This idea was only introduced in the 1970s and focussed mainly on maintaining the floodplains and estuaries in the Kruger National Park, with small amounts being allocated to drinking water for wildlife. This was followed by the Conservation of Agricultural Resources Act, 43 of 1983, the first legislation under which wetlands could be protected, and which today still provides an important legal platform for the protection of wetlands, through integrated conservation of the soil, water resource and vegetation. South Africa became a signatory to the Ramsar Convention in 1975, but until the late 1990s not much was done to enforce wetland conservation. With the introduction of the National Water Act, 36 of 1998, and the National Environmental Management Act, 107 of 1998, South African legislation became the first to balance human, environmental and economic interests, for the purpose of sustainable development. As part of this review I refer to case studies in Gauteng and discuss some of the challenges we still face. |
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Ecosystems In Fractured Aquifer Groundwater Can Treat Contamination | Willem J | van Biljon | National | 2013 | Ecosystems, aquifer, contamination | ||||||
AbstractGroundwater is not often regarded as ecosystems and especially fractured aquifer systems are seen as organism free. Conventional tests show very little to no presence of micro-organisms in groundwater. However, these micro-organisms are ubiquitous and can be detected by using sophisticated methods. In this specific case study where petroleum hydrocarbon contamination exists in a fractured rock aquifer, the presence of micro-organisms has been for years inferred by means of monitoring for secondary lines of evidence that prove attenuation of the contaminants, not only by means of dilution, adsorption or diffusion into the matrix, but through metabolism. The sampling evidence is clear that the preferential sequence of metabolism is taking place whereby electron acceptors are reduced as predicted for such biodegradation. Specifically sulphate is consumed and mostly manganese is reduced, with some iron reduction also being observed. Monitoring has shown that groundwater recharge bringing in new nutrients effected increased biodegradation. In order to definitively identify the contribution made by micro-organisms, DNA testing was performed. The results support the secondary lines of evidence. Outside of the contaminated zone very low population numbers of organisms were detected in the groundwater. Inside the contaminated zone elevated population numbers were observed indicating that active biodegradation is taking place. Furthermore, the edges of the plume, where contaminant levels are mostly below detection, contained a more diverse population of micro-organisms than the central area. Conditions on the edge of the plume probably represent an ideal nutrient environment for the organisms as opposed to the high concentration source, which might be toxic to some organisms. Better understanding of the bio-dynamics of this fractured aquifer presents a unique opportunity to better manage and enhance the remediation of the contaminants. Possible strategies include the addition of nutrients when necessary and the cultivation of the naturally occurring organisms to augment the population. The data shows that aquifers are ecosystems even in fractured environments. |
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Community Involvement In Groundwater Management In The Western Cape: The Sandveld Case Study | Ayuk Juveta | Nchoung | Western Cape | 2013 | groundwater management, case study, Groundwater, Water treatment | ||||||
AbstractGroundwater is a reliable freshwater resource. Its location underground prevents it from evaporative forces. Thus it serves as storage of most of the world’s liquid fresh water. Being enclosed in the ground it is not also easily contaminated. Since groundwater can be used wherever it exists without costly treatments, there is over-dependence on the resource. Though in the past it was mainly used by rural dwellers for domestic water supply, presently, due to effects of climate change on surface water resources, pressures of population growth leading to expansion of towns and cities, groundwater is also supplied for agriculture and industrial purposes. But, the resulting effect from these additional users is the vulnerability of groundwater resources to reduction and pollution. Its importance in sustaining livelihood and development has been highly credited and its management is looked upon as a prerogative. To enhance groundwater management in the Sandveld, a qualitative content analysis approach was used to evaluate six factors considered to be highly needed in groundwater management. This background was used to find out how institutional arrangement in South Africa facilitates or constraints groundwater management in the Sandveld, a highly groundwater dependent area in the West Coast of the Western Cape. The results showed that all six factors are present, but three facilitate groundwater management while three others constrain management. The community involvement which ranked first, is deficient. Thus, institutional weaknesses that need to be strengthened have been identified. |
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Petroleum Hydrocarbon Contamination In Soil And Groundwater: Case Study On The Coastal Tank Farm, Southern Africa | Pieter | Badenhorst | The Coastal Tank Farm, Southern Africa | 2013 | petroleum, Hydrocarbon, contamination, Groundwater, case study | ||||||
AbstractIn this study, a petroleum hydrocarbon contamination assessment was conducted at a cluster of petroleum products storage and handling facilities located on the Southern African Indian Ocean coastal zone. The Port Development Company identified the need for the assessment of the soil and groundwater pollution status at the tank farms in order to develop a remediation and management plan to address hydrocarbon related soil and groundwater contamination. Previous work conducted at the site consisted of the drilling and sampling of a limited number of boreholes. The current investigation was triggered by the presence of a free-phase product in the coal-grading tippler pit located ~350 m down gradient and south-east and east of the tank farms, rendering the operation thereof unsafe. The assessment intended identifying the source of product, distribution and mobility, the extent of the contamination, and the human health risks associated with the contamination. To achieve these, the investigation comprised site walkover and interviews, drilling of 76 hand auger and 101 direct push holes to facilitate vertical soil profile VOC screening and sampling (soil and groundwater), as well as granulomeric analysis to understand grain size distribution within the soil profile. The highest concentrations were associated with the coarse sand layers with the highest permeability. Free-phase hydrocarbons product was found in holes adjacent to the pipeline responsible for the distribution of the product from the jetty to the different tanks farms. Of the 57 soil samples, 21 had high values of GRO and DRO, with 22 below Detection Limit and 14 can be described having traces of hydrocarbon. Both TAME and MTBE were detected in most of the water samples, including from wells located far down gradient. The groundwater sink, adjacent to the pipeline running from west to east, resulted in the limited lateral spread of MBTE in this area, with limited movement towards the sea. The depth of the soil contamination varies over the sites. Based on the site assessment results it was concluded that most of the groundwater contamination, which is a mixture of different product types, is associated with the pipeline responsible for transporting product from the jetty to the different petroleum companies. |
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The Environmental Impacts Of Groundwater On The St Lucia Wetland | Claudia | Brites | Myalazi Plantation, KwaZulu-Natal | 2013 | Environment, Groundwater | ||||||
AbstractThis paper has been based on a study conducted at the Nyalazi plantation in KwaZulu-Natal, South Africa. The study was conducted in order to determine the impacts of the different timber species planted on the groundwater levels associated with the site area. Commercial timber plantations are widespread throughout the country and form an essential component of the South African economy. The site is located 200 km north of the port of Durban and approximately 20 km north of the town of St Lucia in the KwaZulu-Natal Province. The study area, the Nyalazi plantation, is located on the western shores of Lake St Lucia, situated on a peninsula between the Nyalazi River, west of the site and Lake St Lucia to the east. The two main tree species which are located in the Nyalazi plantation are Pinus elliottii and Eucalyptus grandis Camaldulensis. The geological units which influence the hydrogeological regime of the site area include the recent deposits of cover sands and the Port Durnford Formation. These geological successions are the most influential on the groundwater environment as these are the units closest to the surface. The study area is located on the Maputuland coastal plain, also referred to as the Zululand coastal plain, which is classified as a primary aquifer and is the largest of its kind in South Africa. High recharge is experienced within the upper formations of the coastal plain which are unconfined aquifers (Mkhwanazi, 2010). This aquifer consists of unconsolidated clays and sands, which may be defined as an alluvial or primary aquifer (Rawlins & Kelbe, 1991). The monitoring network was initiated by SAFCOL (South African Forest Company, Ltd) in 1995, now known as SiyaQubeka. In total 21 monitoring points were installed, which includes piezometers and deeper boreholes. The trends of the groundwater level data collected over the 17-year period was analysed. Limited historical information was available for the Pinus elliottii plantation; however, based on the data it was evident that the mature pine plantations had minor effects on the groundwater environment of the study area. Conversely, the Eucalyptus species indicated a significant impact with the lowering of the groundwater table between 10 and 16 m over a period of 13 years within the plantation area, which equates to an average decline of one metre per year. |
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Effects Of Dolerite Intrusions On The Geohydrology Of Upper Karoo Sediments In The Elundini Area, South Africa | J | Prinsloo | The Elundini Area, South Africa | 2013 | Dolerite Intrusions, Geohydrology, Groundwater | ||||||
AbstractThe Karoo Supergroup has a hydrogeological regime which is largely controlled by Jurassic dolerite dyke and sill complexes. The study area is located in the north-eastern interior of the Eastern Cape Province, close to the Lesotho border. The sedimentary rocks of the upper Karoo constitute fractured and intergranular aquifers, due to relatively hydro-conductive lithologies. The main groundwater production targets within the upper-Karoo are related to dolerite intrusions that have a number of characteristics that influence groundwater storage and dynamics. Magnetic, electromagnetic and electrical resistivity geophysical techniques are used to determine the different physical characteristics of the dolerite intrusions, such as size, orientation and the level of weathering. Trends in the data collected from a large-scale development programme can provide evidence that intrusion characteristics also play a role in determining the hydrogeological characteristics of the area. Interpreted geophysical borehole drilling, aquifer testing and water chemistry data can be used to indicate hydrogeological differences between dolerite intrusion types. Observed trends could be used for more accurate future well-field target areas and development. |
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Arsenic In The West-African Water Reserves: Investigation Into Sources Of The Contaminant Through Case Studies In The Region | AA | van Coller | Western Africa | 2013 | Contaminant, investigations, Groundwater reserve | ||||||
AbstractThe mineral-rich basin of the West African region has vast reserves of gold, diamond as well as iron ore deposits. Throughout the regional geological setting characterised by structural variations and intrusive belts with metamorphic mineral-rich sequences covered by saprolite soils, one common chemical constituent remains a constant in the water reserves. Arsenic is in high concentrations throughout the region with chemical ranges commonly above the various country guidelines as well as international IFC and WHO standards. The aqueous chemical species is associated with arsenopyrite-rich mineralogy of the regional greenstone belts and highly weathered soils. This conference presentation investigates the natural source of the arsenic through baseline data, as well as the effect of mining on the already high concentrations of arsenic in both the groundwater and surface water. Natural levels of various chemical species in the regional area are already high at baseline level. One of the main research questions is thus whether mining and other anthropogenic activities will have an impact on the environment or will the changes to concentrations be so insignificant to allow the ecosystems and water users to continue in their current ways without any effect. Various case studies in Burkina Faso, Liberia, Sierra Leone and other countries have been combined to investigate the arsenic-rich resources of the West African region through groundwater specialist investigative methods with emphasis on geochemical modelling of the fluid–rock and fluid–fluid interactions leading to the aqueous chemical conditions in the region. |
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Hydraulic Tests Of Strong Artesian Boreholes: Well-Head Construction And Test Design | Kornelius | Riemann | National | 2013 | hydraulic tests, artesian conditions, aquifer | ||||||
AbstractArtesian boreholes are a common feature worldwide in confined aquifers. However, the hydraulic testing of these boreholes and estimation of aquifer properties from such tests still pose a challenge for hydrogeologists. Common hydraulic tests, such as step-drawdown or constant discharge rate tests require a static water level at the start of the test, and the measurement of drawdown (increasing over time) and abstraction rate (fixed for a period of time). Usually, when undertaking a pumping test in an artesian borehole, the drawdown is measured from ground level, and the drop in hydraulic head between static pressure and ground level is often ignored. This also implies that the starting time of the test is not at the static water level. A constant head test, set at ground level, is the other option. However, the decrease in flow rate is not only dependent on the hydraulic properties of the aquifer, but also masked by pipe hydraulic effects within the well. This kind of test would also limit the available drawdown to be utilised for the test. Hence, it was required to develop a method for undertaking hydraulic tests in strong artesian boreholes allowing for the drawdown to fluctuate between above and below ground and avoiding the pitfalls described above. The solution is a specially designed and constructed well-head for the installation of the pump and monitoring equipment prior to the hydraulic test. The standard tests are slightly modified and will only be carried out after sealing the well-head and reaching static hydraulic pressure. The recommended well-head construction and subsequent hydraulic tests were carried out at a strong artesian borehole in the Blossoms Well-field, south of Oudtshoorn in the Western Cape of South Africa. |
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The Thermal Springs Of Swaziland – A Review | Nicholas | Robins | Swaziland | 2013 | thermal springs, hydrochemical | ||||||
AbstractThe thermal springs of Swaziland and adjacent KwaZulu-Natal have, over the years, attracted attention from hydrogeologists, hydrochemists and structural geologists. While some of the springs in Swaziland are well known amenities, others are less well-visited and some difficult to access. There are eleven warm springs in Swaziland, discharging between 1 and 10 l/s from Precambrian age rocks; all are situated at or near valley bottoms. The springs have surface discharge temperatures of between 25 and 52 oC and total dissolved solids concentrations of less than 400 mg/l. In all cases the water is meteoric in origin. Geothermometry indicates that maximum temperatures up to 100 oC are achieved during circulation. If the average geothermal gradient is about 20 oC/km as recorded in a deep mine at Barberton, then this would require circulation up to a depth of several kilometres. However, it is likely that circulation bottoms at about 1 km, as pressure of overburden inhibits dilation of fractures at such depths, and the excess temperature may derive from a locally enhanced geothermal gradient. The discharge water is young, with 14C ages of between 4 000 and 5 000 years. |
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An Evaluation Of The Physical Parameters That Affect Evaporation Rates On Multi-Component Hyper-Saline Effluents In A Controlled Environment | D | Bent | National | 2013 | Evaporation rates, Hyper-Saline Effluents, Controlled environment | ||||||
AbstractThe effluent at the eMalahleni water reclamation plant is being processed through reverse osmosis which improves the quality of the mine water to potable standards. Brine ponds are generally used for inland brine disposal and this option has been selected for the eMalahleni plant. Limited capacity to store the brines requires enhanced evaporation rates and increased efficiency of the ponds. This study aims to establish the physical behaviour of the brine from the eMalahleni plant in an artificial evaporation environment. This includes the actual brine and synthetic salts based on the major components. An experimental unit was designed to accommodate and manipulate the parameters that affect the evaporation rate of brines and distilled water under certain scenarios. Two containers, the one filled with 0.5M of NaCl and the other with distilled water were subjected to the same environmental conditions in each experimental cycle. Each container had an area of a 0.25 m² and was fitted with identical sensors and datalogger to record the parameter changes. The energy input was provided by infra-red lights and wind-aided electrical fans. This equipment used in these experiments was to simulate actual physical environmental conditions. The rate of evaporation was expected to be a function of humidity, wind, radiation, salinity and temperature. The experiments showed the type of salt and thermo-stratification of the pond to be significant contributors to the evaporation rate. The results also showed that the NaCl solution absorbed more heat than the water system. The difference in evaporation observed was ascribed to a difference in the heat transfer rate, which resulted in a higher temperature overall in the brine container than in the water container under similar applied conditions. This effect remained despite the introduction of 2 m/s wind flow over the tanks as an additional parameter. The wind factor seemed to delay evaporation due to its chilling effect upon the upper layers of the ponds, initially hindering the effective transfer of radiative heat into the ponds.
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Natural methane in the Karoo: Its occurrence and isotope clues to its origin | Siep | Talma | Karoo | 2013 | Methane concentration | ||||||
AbstractThe possible future exploitation of methane in the Karoo has stimulated work from various disciplines to examine its occurrence, exploitability and exploitation risks. Groundwater issues are vital in this context because of its possible use during exploration and exploitation, and more important, to understand the risks of its pollution during and after all these activities. This paper presents the experiences of the authors to document the presence of methane in the Karoo based on data from boreholes, springs, tunneling and deep drilling. There have been frequent anecdotal reports of explosive gas in boreholes, both dry and wet, in the Karoo. In some cases the gas is identified as methane. Thermal spring waters in the Karoo invariably contain some amounts of methane. Methane pockets have been found in the Karoo during tunneling projects and in some deep Soekor boreholes. A groundwater study in the vicinity of the Gariep Dam indicated substantial quantities of methane in warm groundwater and an association with helium. The isotope concentrations of carbon and hydrogen in methane characterise the methane-forming processes. Such analyses in samples from the central Karoo basin are consistent with that of thermogenic gas found elsewhere in the world. Towards the edges of the basin, lower 13C-values indicate that methane there is produced by microbial processes at shallower depths. The presence of thermogenic methane together with helium on the surface is likely to give clues to pathways from depth. |
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A Numerical Simulation Of Solute Transport In The Unsaturated Zone Of Dry Coal Ash Dumps With A Case Study In South Africa | Innocent | Muchingami | Mpumalanga | 2013 | unsaturated zone, Simulations, waste disposal | ||||||
AbstractAn understanding of the movement of moisture fluxes in the unsaturated zone of waste disposal sites play a critical role in terms of potential groundwater contamination. Increasing attention is being given to the unsaturated or vadose zone where much of the subsurface contamination originates, passes through, or can be eliminated before it contaminates surface and subsurface water resources. As the transport of contaminants is closely linked with the water flux through the unsaturated zone, any quantitative analysis of contaminant transport must first evaluate water fluxes into and through this region. Mathematical models have often been used as critical tools for the optimal quantification of site-specific subsurface water flow and solute transport processes so as to enable the implementation of management practices that minimize both surface water and groundwater pollution. For instance, numerical models have been used in the simulation of water and solute movement in the subsurface for a variety of applications, including the characterisation of unsaturated zone solute transport in waste disposal sites and landfills. In this study, HYDRUS 2D numerical simulation was used to simulate water and salt movement in the unsaturated zone at a dry coal ash disposal site in Mpumalanga, South Africa. The main objective of this work was to determine the flux dynamics within the unsaturated zone of the coal ash medium, so as to develop a conceptual model that explains solute transport through the unsaturated zone of the coal ash medium for a period of approximately 10 year intervals. Field experiments were carried out to determine the model input parameters and the initial conditions, through the determination of average moisture content, average bulk density and the saturated hydraulic conductivity of the medium. A two-dimensional finite-element mesh of 100 m × 45 m model was used to represent cross section of the ash dump. Two-dimensional time lapse models showing the migration of moisture fluxes and salt plumes were produced for the coal ash medium. An explanation on the variation of moisture content and cumulative fluxes in the ash dump was done with reference to pre-existing ash dump data, as well as the soil physical characteristics of the ash medium. |
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Characterisation Of Hydrochemical Facies And Water Quality Of The Coastal Plain-Sand Aquifers Of Parts Of Eastern Niger Delta, Nigeria | AN | Amadi | Nigeria | 2013 | hydrochemical, Water quality, coastal aquifers | ||||||
AbstractSoil and water pollution are major environmental problem facing many coastal regions of the world due to high population, urbanisation and industrialisation. The hydrofacies and water quality of the coastal plain-sand of part of Eastern Niger-Delta, Nigeria, was investigated in this study. Hydrogeological investigations show that the aquifers in the area are largely unconfined sands with intercalations of gravels, clay and shale which are discontinuous and, however, form semi-confined aquifers in some locations. Pumping test results show that the transmissivity ranged between 152.0 m2/day and 2 835.0 m2/day with an average value of 1 026.0 m2/day, while the specific capacity varied between 828.0 m3/day and 15 314.0 m3/day with a mean value of 6 258.0 m3/day. Well-discharge ranged between 1 624.0 m3/day and 7 216.0 m3/day with an average value of 3 218.0 m3/day, while hydraulic conductivity varied between 3.2 m/day and 478.4 m/d with a mean value of 98.6 m/day. These findings indicate that the aquifer in the area is porous, permeable and prolific. The observed wide ranges and high standard deviations and mean in the geochemical data are evidence that there are substantial differences in the quality/composition of the groundwater within the study area. The plot of the major cations and anions on Piper, Durov, and Scholler diagrams indicated six hydrochemical facies in the area: Na-Cl, Ca-Mg-HCO3, Na-Ca-SO4, Ca-Mg-Cl, Na-Fe-Cl and Na-Fe-Cl-NO3. Heavy metal enrichment index revealed 12 elements in the decreasing order of: Fe > Ni > Cu > Zn > Mn > Cd > V > Co > Pb > Cr > As > Hg. The study identified salt intrusion, high iron content, acid-rain, hydrocarbon pollution, use of agrochemicals, industrial effluents and poor sanitation as contributors to the soil and water deterioration in the area. Saltwater–freshwater interface occurs between 5 m to 185 m, while iron-rich water is found between 20 m to 175 m. The first two factors are natural phenomenon due to the proximity of the aquifer to the ocean and probably downward leaching of marcasite contained in the overlying lithology into the shallow water table, while the last four factors are results of various anthropogenic activities domiciled in the area. The DRASTICA model, a modification of the DRASTIC model, was developed and used in the construction of the aquifer vulnerability map of the area. Modern sanitary landfill that ensures adequate protection for the soil and groundwater was designed and recommended to replace the existing open-dumpsites. Owing to the monumental and devastating effects of hydrocarbon pollution in the area, the need to eradicate gas-flaring and minimise oil spills in the area was advocated. Bioremediation and phytoremediation techniques were recommended to be applied in the clean-up of soils and water contaminated with hydrocarbon in the area.
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Delineation Of Zones At Risk From Groundwater Inflows At An Underground Platinum Mine In South Africa | A | Stoll | National | 2013 | groundwater inflow | ||||||
AbstractThe subject mine has a policy of avoiding groundwater inflow into the underground workings due to the impact on the mine operations. It has already implemented a significant mitigation measure by excluding shallow mining and a large pillar under the river that is present in the mining area. To assess the potential for groundwater inflows into the underground mine workings as a result of a planned expansion project, Environmental Resources Management (ERM) undertook numerical groundwater modelling based on a detailed geological investigation to define the proposed mining area into high, medium and low mining risk areas with respect to potential groundwater inflow. The conceptual definitions of the mining risk areas are: High Risk – general groundwater seepage and inflow expected in the face and roof of the mining unit from numerous joints and fractures which is regarded as serious enough to permanently halt mining operations. Medium Risk – possibility of limited point source groundwater inflow in the face and roof of the mining unit from sporadic selective joints and fractures. Not expected to halt mining operations. Low Risk – no significant groundwater risk to mining operations expected. The areas identified as being potentially at risk from groundwater inflow were determined using a combination of geological mapping, ground geophysics and percussion drilling that was incorporated into a numerical hydrogeological model. The study undertaken by ERM enabled the mine to incorporate the identified mining risk zones into the early stages of the mine planning, and allowed for a significant reduction in the size of the safety pillar under the river. |
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Flowing Fluid Electrical Conductivity Profiling – An Inventive And Cost-Effective Alternative To Conventional Downhole Hydraulic Profiling Techniques | Samuel D | Möhr | National | 2013 | Electrical conductivity, Hydraulic profiling | ||||||
AbstractFlowing fluid electrical conductivity (FFEC) profiling provides a simple and inexpensive way to characterise a borehole with regards to the vertical location of transmissive zones, the hydraulic properties of the various transmissive zones and the intra-well flow conditions which may be present in the well under ambient conditions. The method essentially involves analysing the time evolution of fluid electrical conductivities in a borehole under pumped and ambient conditions using a down-hole conductivity/temperature data logger. The premise of the method is that the borehole column of water has its electrical conductivity altered by adding saline water into the borehole. This results in a contrast in electrical conductivity (EC) between the water in the borehole and the water in the adjacent formation. At depths where transmissive zones are present, decreases in EC values in the FFEC profile will be observed where formation water with a lower EC (relative to the borehole water column) enters into the well, whilst pumping at low abstraction rates (between 500 ml and 1 liter per minute). By altering the EC of the well-borewater and maintaining a constant pumping rate, the sequence of FFEC profiles depicts the dynamic flow and transport response which is dependent upon the hydraulic properties of the formation. In this paper the authors present several examples where FFEC profiling has been used to identify transmissive zones in boreholes where no information existed with regards to the vertical distribution of transmissive zones. Furthermore, the authors present case studies where FFEC profiling has been employed as an alternative technology to more conventional hydraulic profiling techniques. This includes a comparative technology case study where down-hole impeller flow meter technology was employed in addition to FFEC profiling and a multi-rate FFEC profile test which was used to determine discrete fracture transmissivity values in a borehole where packer testing equipment could not be installed. Within the context of groundwater contamination investigations, the method holds several attractions as it generates minimal waste water to be managed and disposed of, is inexpensive and can be completed within a relatively short time period. |
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Conceptual Modelling Of Lake–Groundwater Interactions For The Lake Sibayi Catchment, North-Eastern South Africa | Jannie | Weitz | Lake Sibayi Catchment, North-Eastern South Africa | 2013 | conceptual model, hydrochemical | ||||||
AbstractLake Sibayi (a topographically closed freshwater lake) and coastal aquifers around the Lake in eastern South Africa are important water resources and are used extensively for domestic water supplies. Both the Lake and groundwater support an important and ecologically sensitive wetland system in the area. Surface and subsurface geological information, groundwater head, hydrochemical and environmental isotope data were analysed to develop a conceptual model of aquifer–lake interaction for further three-dimensional numerical modelling. These local geologic, groundwater head distribution, lake level, hydrochemistry and environmental isotope data confirm a direct hydraulic link between groundwater and the Lake. In the western section of the catchment, groundwater flows to the lake where groundwater head is above Lake stage, whereas along the eastern section, the presence of mixing between Lake and groundwater isotopic compositions indicated that the Lake recharges the aquifer. Stable isotope signals further revealed the movement of lake water through and below the coastal dune cordon and eventually discharges into the Indian Ocean. Quantification of the 14-year monthly water balance for the Lake shows strong seasonal variations of the water balance components. Recent increase in rate of water abstraction from the lake combined with decreasing rainfall and rapidly increasing pine plantations may result in a decrease in lake level which would have dramatic negative effects on the neighboring ecosystem and a potential seawater invasion of the coastal aquifer. |
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Hydrogeochemical Footprint As A Result Of Mining Activities In The Johannesburg Area | Tamiru | Abiye | Johannesburg | 2013 | hydrochemical | ||||||
AbstractThe water quality in the crystalline rocks of the Johannesburg and its environs has been severely altered by the mining activity. Due to freshwater scarcity and dependency of the people on the groundwater, it is important to understand the extent of hydrogeochemical footprint in the area. The water quality characteristic has been thoroughly assessed in the crystalline aquifers based on the input from hydrogeochemical characteristics and environmental isotopes. The results show that the calculated dilution factor for acid-mine decant is in the range of 68% as a result of interaction with surrounding fresh water. The SO4/Cl ratio has a wide range of values that falls between 0 and 306.37, while that of Fe/Ca ratio falls between 0 and 5.59. High SO4/Cl values potentially indicate the interference of acid-mine decant with the groundwater system traced through sulphate concentration. Similarly, a high Fe/Ca ratio also indicates the impact of acid-mine decant on the groundwater system where iron is traced with respect to calcium concentration. In this regard the ratios above 0,25 (with the assumption of 1 to 4 natural abundance for Fe:Ca in water in the area) could potentially represent acid-mine decant source.The results confirm that most of the water- supply wells have heterogeneous chemistry with distinctive hydrogeochemical footprint represented by abnormally high Fe, SO4 and Si as a result of acid-mine decant. |
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Quenching A Thirsty Country | Fanus | Fourie | National | 2013 | Groundwater, strategy, Boreholes | ||||||
AbstractOnly 40% of all the available groundwater resources are developed in South Africa and the development of surface water are becoming more costly and challenging. The Minister of Water and Environmental Affairs acknowledge this and identified the need to increase the use of groundwater as one of the interventions to address the increasing water requirement of towns and communities. Over the last seven years the Department of Water Affairs developed many reconciliation strategies for the area of water management, the big metro municipalities and for the smaller towns and villages in South Africa. The reconciliation strategies entails, among other things, sustainable ways to source additional water supplies for the selected towns/metro’s or villages. Groundwater played a major role in the recommended interventions. The challenges are now the implementation of the groundwater schemes and sustainable management of the groundwater resources. Or differently put: the balancing act between selling of groundwater and the prevention of over-abstraction. The bankability of regional schemes, the credibility of groundwater as a bulk scheme source, poor management of boreholes/well-fields, institutional responsibility, acceptable quality and treatment of groundwater, still challenge the use of groundwater development. Groundwater need to play its role in addressing the future water needs of South Africa, or can it? |
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Estimation Of Representative Transmissivities In Heterogenous Aquifers | Gerrit | van Tonder | National | 2013 | transboundary aquifers, hydraulic conductivity | ||||||
AbstractThe so-called apparent increase of transmisivity (T) or hydraulic conductivity (K) with scale is an artifact and does not exist in the field. The reason for the apparent increase of T with scale is due to the use of the “not applicable” random log Gaussian stochastic models that are used by geohydrologists. In the petroleum field, where deterministic methods are applied, the apparent increase of T with aquifer volume does not occur. Groundwater practitioners have to change their view and use models that do not show this effect. |
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Hydrogeology Of Cedarville Flat Primary Aquifer | Nwabisa | Ndlovu | Cedarville, Eastern Cape | 2013 | Hydrogeology, aquifer, Groundwater, development, hydrogeological conceptual model | ||||||
AbstractPOSTER The study focuses on the primary aquifer in the Cedarville flats. Groundwater extracted from the aquifer is the primary source for domestic and agricultural purposes for farmers and the community in the Cedarville area. The aim of the study is to develop a conceptual hydrogeological model of the primary aquifer in Cedarville flats which may be used as an input to a groundwater flow model that will predict the behaviour of the aquifer. The main objectives of the research are: Characterise the aquifer based on borehole log information, depth to water, hydraulic properties of the aquifer and recharge. Examine the hydrochemistry and environmental isotope composition of groundwater. Develop a conceptual hydrogeological model for the Cedarville primary aquifer. The study area boundary covers a large area including towns like New Amalfi and it goes to Lehlohonolo, but the main focus is in the primary aquifer in the Cedarville flats. The topography varies from predominantly hilly around the escarpment with numerous rivers draining deep valleys to a less mountainous undulating central area like Cedarville flats. Cedarville flats found in the midst of extremely broken ground forming the only considerable extent of plane country in the Eastern Cape territories. They cover about roughly 90 square miles and are hemmed in by ranges of mountains on the south and east and by small hills on the west and north. The aquifer is recharged by Mzimvubu River, which is the largest river in the Mzimvubu river basin; it extends from the Lesotho highlands to the Indian Ocean. It has four main tributaries: the Tsitsa, Tina, Kinira and Mzintlava, all having their headwater in the Drakensberg Mountains. The study area only shows the Tswerika, Riet, Mvenyane, Droewing and non-perennial streams. These streams all flow into the Mzimvubu River and their headwater is from the smaller mountains around the area. The local geology of the area is formed by the Beaufort Group rocks and alluvium rocks which are quaternary in age. The geology that is specifically found in the Cedarville flats aquifer is made of alluvial deposits consisting of clay, sand and gravel. Surrounding the aquifer are Tarkastad subgroup rocks which are predominantly argillaceous rocks, including shale, carbonaceous shale, clay stone, mudstone and siltstone. The primary aquifer in the Cedarville flats is capable of sustaining long-term, large-scale production, and these kinds of aquifers are rarely found in the southern Karoo Basin. Existing boreholes will be used to examine the bore log information, like lithology and thickness of the rocks that form the aquifer. Groundwater hydrographs will be drawn to determine the groundwater level variation. Pumping tests will be conducted to help with hydraulic conductivity, storativity and transmissivity of the aquifer. Water samples will be collected to test the water chemistry and environmental isotopes of the groundwater. Secondary data will be requested from National Groundwater Archives (NGA), Weather SA and the Department of Water Affairs. When all the data is collected, then a conceptual hydrogeological model will be produced.
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Southern African Pre-Cretaceous Deep Groundwater Flow Regimes: Evidence And Drivers | Eddie | Van Wyk | South Africa, Botswana, Namibia | 2013 | groundwater flow, deep drilling | ||||||
AbstractAfter drilling technology improvements in South Africa in the early 1900s, several deep (>300 m) exploratory drilling programmes were conducted to explore for pressurised groundwater resources. The results were not significant, except for the Cretaceous Uitenhage Artesian Basin and recent investigations in folded Table Mountain Group Aquifer systems. Large sedimentary units in Southern Africa do have the structural geometry to drive regional artesian systems; however, diverse climate and aquifer hydraulic limitations counteract these conditions to such a level that sustainable basin- like deep flow mechanisms are probably non-existing, except where enhanced by deep mining activities. On the contrary, several deep drilling projects in South Africa, Botswana and Namibia have undoubtedly proven the existence of pressurised groundwater strikes below 300 m (northern Kalahari) to as deep as 3 000 m (western Karoo Basin). Given the regional hydrogeological characteristics of these systems, the availability of sufficient recharge zones required to drive sustainable artesian flow or semiartesian conditions becomes a challenge. The existence of isolated pressurised compartments as a result of the lithostatic pressurisation in the deeper sections of many of the sedimentary successions may prove to be a more realistic explanation for these pressurised water strikes observed during deep drilling operations in Southern Africa. |
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A Methodology To Assess The Movement Of Hydrocarbons And Associated Remediation Thereof | Sascha | Roopa | National | 2013 | Methodology, Hydrocarbon, remediation, contamination | ||||||
AbstractPOSTER Water is an invaluable resource without which life would cease to exist. Supply in South Africa has become limited due to increases in demand brought upon by population growth, urbanisation and industrialisation. In Southern Africa, water systems are considerably degraded by mining, industry, urbanisation and agricultural activity and a large amount of the fresh surface water has already been utilised. The stresses on this resource will unlikely make the current usage sustainable in years to come. In order to provide for basic needs for the future, groundwater as a resource will have to play a major role. It is for this reason that groundwater integrity needs to be preserved. Hydrocarbon contamination is a huge threat to groundwater as it contains toxic substances that are insoluble in water. These toxins are carcinogenic and mutagenic, and have a major impact on human health and ecosystem stability. When spilled, hydrocarbons will move downward through the unsaturated zone under the influence of gravity and capillary forces, trapping small amounts in the pore spaces. Accumulation will result in added weight along the water table, forcing the entire surface to be displaced downward. Some of the components can dissolve in the groundwater and move as a plume of contaminated water by diffusion and advection within the saturated zone. The transport of contaminants from petroleum hydrocarbon spills needs to be described in terms of a multiphase flow system in the unsaturated zone, taking into account contaminant movement in each of the three phases: air, water and free light non-aqueous phase liquid. Petroleum hydrocarbon behaviour in the subsurface is additionally complicated by the presence of multiple compounds, each with different properties. The net result is that some hydrocarbon fractions are transported faster than others and a contamination plume of varying intensity may spread over a large area. The aim of this study is to develop a methodology to map and simulate the movement of groundwater that has been contaminated by hydrocarbons and to determine the fate of the water quality through decomposition. Associated remediation options will be determined thereafter. |
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Sampling Protocol Optimisation Using Fluid Electrical Conductivity Logging | Candice | Lasher | National | 2013 | Electrical conductivity, Sampling Protocol | ||||||
AbstractCharacterisation of fracture positions is important when dealing with groundwater monitoring, protection and management. Fractures are often good conduits for water and contaminants, leading to high flow velocities and the fast spread of contaminants in these conduits. Best practice guidelines related to groundwater sampling suggest that specific depth sampling with specialised bailers or low flow purging are the preferred methodologies to characterise a pollution source. These methods require knowledge about the fracture positions and, more importantly, flow zones in the boreholes. Down-the-hole geophysical and flow logging are expensive, complicated and time consuming. Not all fracture zones identified with geophysical logging seem to contribute to flow through the borehole. An efficient and cost-effective methodology is required for the characterisation of position and flow in individual fractures. This research reviewed the use of Fluid Electrical Conductivity (FEC) logging to assist with the development of a monitoring protocol. FEC logging proved to be beneficial as it provided individual fracture positions, fracture yields and vertical groundwater flow directions. FEC logging proved to be fast, cost-effective and practical in deep boreholes. The technique allows the development of a site-specific sampling protocol. The information so obtained assists with the identification of the appropriate sampling depths during monitoring. |
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An Innovative Application Of The Mixing Cell Model To Quantify Surface Water–Groundwater Interaction | Amy | Allwright | National | 2013 | Innovation, groundwater resource management, baseflow | ||||||
AbstractThe significance of a reliable groundwater resource assessment is of growing importance as water resources are stretched to accommodate the growing population. An essential component of a groundwater resource assessment is the quantification of surface water–groundwater interaction. The insufficient amount of data in South Africa and the apparent lack of accuracy of current estimates of the groundwater component of baseflow lead to the investigation of a new method. This applicability of this new approach, the Mixing Cell Model (MCM), to quantify the groundwater contribution to baseflow is examined to assess whether the method would be of use in further groundwater resource assessments. The MCM simultaneously solves water and solute mass balance equations to determine unknown inflows to a system, in this application the groundwater component of baseflow. The incorporation of water quality data into the estimation of the surface water–groundwater interaction increases the use of available data, and thus has the ability to increase the confidence in the estimation process. The mixing cell model is applied to datasets from the surface water–groundwater interaction test site developed by the University of the Free State, in addition to data collected along the middle Modder River during a fieldwork survey. The MCM is subsequently applied to a set of quaternary catchments in the Limpopo Province for which there are available calibrated estimates of the groundwater component of baseflow for the Sami and Hughes models. The MCM is further applied to the semi-arid quaternary catchment D73F to assess the applicability of the mathematically-based MCM in a flow system within a regionally-defined zero groundwater baseflow zone. The results indicate that the MCM can reliably estimate the groundwater component of baseflow to a river when sufficient data are available. Use of the MCM has the potential to evaluate as well as increase the confidence of currently determined groundwater baseflow volumes in South Africa, which will in turn ensure the responsible and sustainable use of the countries water resources. |
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Hydrocarbon Remediation – Practical Low Cost And Low Maintenance Solutions | Jennifer A | Pretorius | National | 2013 | Hydrocarbon, contamination | ||||||
AbstractIn recent years there is an increased awareness of hydrocarbon contamination in South Africa, and the need for remediating sites affected by these contaminants. Hydrocarbon contamination of groundwater can be caused by a large variety of activities at industrial, mining or residential areas. Once these contaminants are discovered in groundwater where it poses risks to human health and/or the environment, remediation is often required. Remediation of groundwater has become a booming industry for groundwater practitioners and often there is an attitude of more sophisticated and expensive solutions are better. This paper will show that this attitude is not always the best solution, but rather recommend an approach where a combination of low cost/low maintenance system need to be investigated and applied to reach clean-up goals. Determination of natural attenuation potential and on-going monitoring forms an integral part of this type of solution. |
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Groundwater Resource Assessment For Water Supply To The Heuningvlei Socio-Economic Development Area | Collen | Monokofala | Northern Cape | 2013 | groundwater recharge, flow regime analysis, socio-economic development | ||||||
AbstractThe Heuningvlei pipeline scheme was built in the 1980s to supply water to rural communities in a low rainfall area (<300 mm/annum) – Northern Cape Province. In 2008, the Joe Morolong Local Municipality identified the need to refurbish and upgrade the pipeline scheme for socio-economic reasons. The safe yield and water quality information of existing sources supplying the scheme was unreliable. This was investigated by borehole test pumping and water quality sampling, which indicated reduced yields and deteriorating water quality since 1989. Water demands, which includes supply to communities for domestic use, schools, clinics and stock watering in the Heuningvlei area, was estimated at 2 380 m3/day or 868 700 m3/annum. The potable groundwater supply recommended from 11 existing boreholes is 316 937 m3/annum, leaving a deficit of 551 763 m3. The aquifers utilised for the existing water supply comprise fractured banded iron formations (BIF) and dolomite bedrock. Kalahari sedimentary and dolomite aquifers to the east of the pipeline scheme contain high saline water not suitable for domestic use. No surface water sources exist in the area and the feasibility of the socio-economic development project depends on establishing local groundwater resources that would not impact on existing sources. A target area was identified which is approximately 10 km south from the pipeline. This area is covered by the thick Kalahari sediments (up to 130 m) underlain by dolomite bedrock with a potable groundwater balance of 2.3 million m3/a. Both the associated primary (Kalahari) and secondary (Dolomite) aquifers contain potable water. The target area was not investigated in the past due to perceived poor water quality (elevated salinity) conditions, very low (<10 %) borehole exploitability prospect and difficult drilling conditions. The paper will discuss the importance of recharge estimate and understanding of flow regime at sub-catchment and local scale, use of an airborne magnetic survey in conjunction with ground geophysics, mapping of Kalahari sediment thickness, and successful drilling of exploration boreholes to exploit the deeper Kalahari sedimentary and dolomite bedrock aquifers. The successful development of localised potable water in a low rainfall area made it feasible to implement the Heuningvlei socio-economic development project. |
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Aquifer Vulnerability Assessment Of The Molototsi And Middle Letaba Quaternary Catchments, Limpopo Province, South Africa | OT | Makonto | Limpopo | 2013 | aquifer, vadose zone | ||||||
AbstractThe aquifer vulnerability of the Molototsi (B81G) and Middle Letaba (B82D) quaternary catchments was assessed to determine the influence of the vadose zone on the groundwater regime. The aquifer vulnerability was assessed by developing a new method, which evaluates the vadose zone as a pathway for pollutants by using the following four parameters: Recharge, Depth to water table, Soil type (saturated vertical hydraulic conductivity) and Slope (RDSS). Recharge was estimated using the Chloride-mass balance method and the depth to the water table was measured in the field using dipmeter. The seepage behaviour (soil type) was determined as hydraulic conductivity from in situ infiltration and percolation testing (SABS 0252-2:1993 and double ring infiltrometer). The slopes were determined with the digital elevation method using ArcGIS software. The four parameters were overlaid using Weighted Sum, Weighted Overlay and Raster Calculator to produce the vulnerability map. Different weightings were attributed in the methods and the best selected. The results obtained indicated high vulnerability on the lower and upper parts of both catchments. Aquifers in areas which showed high vulnerability are at high risk of contamination. The benefits of the method described are (a) the easy quantification of the parameters through fairly simple methods and (b) the exclusion of arbitrary index values. |