Conference Abstracts

Abstract

A groundwater assessment was conducted to identify and predict the contamination and transport properties of a groundwater system. The motivation for the study was the rising concern of a farm owner about the deteriorating water quality of the aquifer system. An investigation of the surface and groundwater quality indicated that two fertilizer dumpsites were the sources of pollution. Water analyses revealed elevated concentrations of Ca, Mg, K, F, NO3, SO4, Mn and NH4 within boreholes near the pollution sources. The NH4 and NO3 concentrations were exceptionally high: 11 941 mg/L and 12 689 mg/L, respectively. These high concentrations were the direct result of the dumping of fertilizer. The rise in these concentrations may also have been catalysed by the nitrogen cycle and the presence of the Nitrosomonas bacterium species. Due to the high solubility of NO3, and because soils are largely unable to retain anions, NO3 may enter groundwater with ease, and could migrate over large distances from the source. Elevated NO3 in groundwater is a concern for drinking water because it can interfere with blood-oxygen levels in infants and cause methemoglobinemia (blue-baby syndrome). A geophysical study was undertaken within the area of investigation to gain insight on the underlying geological structures. The survey indicated preferential flow paths within the aquifer system along which rapid transport of contaminant is likely to occur.
Key words: aquifer system, groundwater quality analyses, fertilizer, nitrogen cycle, Nitrosomonas species, geophysics.

Abstract

The hydrogeological setting of a proposed mine site can significantly influence the viability of the mining venture. The management of groundwater inflows, costs of the dewatering technology, construction and maintenance of storage facilities, discharge strategies and anticipated environmental impacts are vital factors for consideration. It is fundamental to assess the hydrogeological setting at an early stage of the mine life cycle and should involve the collection of sufficient hydrogeological data, conceptualisation of the hydrogeological setting and an assessment of planned mine operations and anticipated impacts. Ambient hydrogeological conditions at the deposit area may be identified by conducting a hydrocensus and utilising existing ore exploration drilling data. Information from the hydrocensus and ore exploration drilling can provide valuable preliminary data on groundwater risks, dewatering and available groundwater resources. Potential groundwater/surface water interactions and receptors sensitive to environmental impacts can be identified during a hydrocensus. Similarly, water strikes and fracture density recorded during exploration drilling provide valuable insight to the subterranean environment. It is also possible to obtain aquifer hydraulic properties through packer testing of exploration boreholes. Geochemical test work on exploration borehole-cores could provide valuable information regarding contamination risks from ore deposit and waste material storage. The installation of piezometers within available and accessible exploration holes that extend below the regional groundwater level can pioneer the collection of monitoring data crucial for consideration during the mine life cycle and provide an understanding of the interaction between hydrogeological units and recharge characteristics. Ultimately, mine operations and associated potential impacts on the surrounding groundwater environment can be simulated with the application of numerical hydrogeological flow and contaminant transport models. The numerical models can simulate the regional groundwater flow system and complexities of the mine environment, the accuracy of which is influenced by the type, spatial and temporal distribution of the data collected. It is accordingly suggested that the collection of hydrogeological data and information during the exploration phase would facilitate the timely conceptualisation of potential groundwater risks and effective planning of hydrogeological investigations required during upcoming phases while assisting in the budget optimisation of these future studies.

Abstract

Water stress is frequently experienced in many parts of South Africa. To ensure the longevity of the country’s water resources, particularly groundwater, accurate quantification of the resource and prediction of the responses of each water resource unit to natural and anthropogenic stresses are necessary. To this endeavour, Simbithi Eco-Estate, located at Shaka’s Rock, KwaZulu-Natal requires the implementation of a Water Management Plan that includes a hydrogeological investigation. A hydrogeological conceptual model was developed for the eco-estate, based on which a numerical groundwater flow model was calibrated to simulate the impacts of different rates of groundwater abstraction within the estate. Hydrometeorological information, subsurface geology, hydraulic head, hydraulic characteristics of the aquifer units and hydrochemical data were analysed to develop a two-layer hydrogeological conceptual model. The conceptual model was used as the main input to the numerical groundwater flow model. The calibrated steady-state numerical model, developed using the finite-difference groundwater modelling code, MODFLOW, was used to determine the sustainability of groundwater abstraction within the eco-estate. During calibration, the hydraulic conductivities of the hydrostratigraphic units, and recharge were varied. The Model calibrated recharge was 5.5 % of the mean annual precipitation (MAP). The five abstraction scenarios considered were: Scenario 1, which is the sustainable abstraction rate determined from the analysis of pumping test data, and Scenario 2 to 5 which are assigned progressively increasing abstraction rates of Scenario 1, by a factor of 20%, 50%, 100%, and 1000%, respectively. The numerical model simulations indicate that Scenario 1 is most sustainable in terms of groundwater level drawdown and saltwater intrusion. The simulated groundwater drawdown progressively increased throughout the succeeding four scenarios.

The simulation results of the 5th scenario indicate that part of the model domain within the vicinity of the northern boreholes becomes dry and subsequent application of forward particle tracking on the simulation results predicts saltwater intrusion from the Indian Ocean towards the south eastern boreholes. It is accordingly recommended that groundwater resource development should be limited to below the abstraction rates of Scenario 4. Additionally, continuous monitoring of all boreholes within the eco-estate is recommended to generate time-series groundwater level information, which would be used to improve the predictive capabilities of the current steady-state model through a transient numerical groundwater flow model. To that end, an immediate establishment of a groundwater level and specific electrical conductivity (EC) monitoring network, equipped with data loggers, is recommended.

Abstract

Top-down governance systems are not well designed to secure the protection, use and management of groundwater at the local level and, on the contrary, perpetuate ‘wicked’ problems of poor groundwater management and protection. Citizen science promises solutions to these ‘wicked’ problems. We present findings from a project in the Hout Catchment, Limpopo, where citizen scientists monitor water in wells in remote rural settings. We redress the bias towards the natural sciences and pay attention to human systems as it is through engaging with people’s ‘ordinary’ citizens that they will protect their environment for better planetary health. To better understand these human systems that impact groundwater, we emphasise diversity and difference and argue for a HOPE model (heralding optimal participatory equity). HOPE has intrinsic and extrinsic value (equity) (addressing a hydrological void and understanding groundwater features). To achieve this, we open up a toolkit providing very practical methods. Using these tools, we propose that citizen science - taking science away from remote institutions, out of libraries and laboratories - and bringing it close to people is emancipatory and addresses new ways of understanding polycentric governance. Citizen science is transformative; citizens move from a passive state of non-engagement with science to acting as scientists. Disempowered people now have a sense of being part of the betterment of their world and improved water resources management. Narrowing the natural and social sciences divide is crucial for improved polycentric governance.

Abstract

The 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.

Abstract

Maphumulo B; Mahed G

Disastrous droughts sweeping across South Africa has led to the population turning towards groundwater as their primary source of water. This groundwater movement has increased the need for proper groundwater management in terms of both quality and quantity. Groundwater sampling is a crucial, and yet often overlooked, component of water quality assessment and management. This thesis evaluated the various groundwater sampling methods used within fractured rock aquifers in the Beaufort West region. Each sampling method was evaluated in terms of their precision and accuracy according to their hydrochemical results. Historical hydrochemical data from past reports was utilised to determine how various groundwater sampling techniques influence results. This helped gained a better understanding of the requirements required to correctly and accurately sample different water sources such as boreholes and windmills. These requirements include the importance of purging in order to remove stagnant water from windmills. By understanding these sampling techniques, it is possible to create a groundwater sampling protocol which should be followed when sampling fractured rock aquifer in order to ensure best possible results.

Abstract

The purpose of this study was to determine the optimal sampling methods for the analysis of radioactive material in fractured rock aquifers. To achieve this a number of data sets were used which span a 40 year period in and around Beaufort West. Well purging requires the pumping out of stagnant water. This step is crucial as the idle well water may not be representative of the entire aquifer. This step was found to be critical in the studies analysed and had a direct impact on the results. It is necessary to pump out the entire well volume and recommended to pump out at least two well volumes before sampling commences. Samples may also be taken prior to well-purging as a means of checking the effects of purging. Another important aspect for sampling is that of multi-level sampling, particularly in the case of boreholes which feature multiple fracture or aquifer interception points. Prior to sampling, sampling containers should be well washed and cleaned using HCl and rinsed with deionised water. This is done to remove any contaminants which may hinder laboratory analysis. It was found that the multilevel sampling method yielded the best results. Furthermore, the samples stemming from windmills also had good results. The evolution of sampling as a science has improved over the past 40 years, but a fundamental understanding of sampling as a science needs to be incorporated

Abstract

Vermaak, N; Fourie, F; Awodwa, A; Metcalf, D; Pedersen, PG; Linneberg, MS; Madsen, T

The Strategic Water Sector Cooperation (SSC) between Denmark and South Africa is a long-term bilateral cooperation, which amongst others are contributing to the South African water sector by demonstrating and testing different Danish groundwater mapping methodologies in South Africa in order to add long term value to the South African work on optimizing the utilization of groundwater and to increase the resilience against drought. One key aspect is to develop a South African groundwater mapping methodology, based on the detailed Danish methodology and South African specialized knowledge of the South African hydrogeology. In this case, the SSC has contributed to the work done by Umgeni Water in The District Municipality of uThukela in the KwaZulu-Natal (KZN) province of South Africa. The methodology that has been used is integrated modelling using 3-geological models built in GeoScene3D and groundwater modelling, which was based on existing data from Umgeni Water and Department of Water and Sanitation (DWS). Based on the outcome of the 3-D geological voxel model both known aquifers where the boundary has been adjusted, as well as new aquifers has been outlined. Good places for drilling production boreholes have been identified, followed by groundwater modelling of sustainable abstraction rates from existing and new potential well fields. Finally, recommendations were made for new data collection and how to modify the Danish mapping approach for use in South Africa, taking the differences in geology and water management into consideration. The Danish methodology for groundwater mapping is adaptable to South African conditions but it requires Danish and South African experts works closely together. The project has also shown that integrated 3-D geological modeling and hydrological modelling can contribute to a sustainable development of groundwater in South Africa, as well as the Danish methodology for modelling and monitoring sustainable abstraction rates.4

Abstract

Surface water has traditionally been the primary resource for water supply in South Africa. While relatively easy to assess and utilise, the surface water resource is vulnerable to climatic conditions, where prolonged periods of drought can lead to an over-exploitation and eventually water shortness and supply failure. Following the drought in 2018, more focus has been given to the groundwater resource to supplement the water supply in South Africa.

In the Saldanha Bay municipality the water supply is based on a combination of surface water and groundwater, with plans to supplement this with desalination and managed aquifer recharge (MAR) in the future. For an efficient and sustainable utilisation of the different water resources, a Water Supply Management System is developed that can be used to manage water mix from multiple resources. The system builds on top of a flexible WaterManager system developed for operation of complex water supply infrastructures, which in the study is extended by implementing operational rules for optimal management.

The operational rules provide recommendations for the day-to-day management, but also consider seasonal and long-term utilisations. To achieve this, the rules will rely on real-time monitoring data combined with results from hydrological modelling, providing estimated system response to selected scenarios to which the water supply must be resilient. In the present study the combined Water Supply Management System is developed and tested using synthetic data, which will be presented in the paper.

Abstract

Extensive geological, mineralogical and geochemical research have been done on the Insizwa layered mafic sill intrusion, located in the northern part of the Eastern Cape province, South Africa. This focus is understandable in the light of its potential for Cu, Ni and PGM extraction. However, the complex is also linked to a potentially significant groundwater reserve, and is located in a populated rural area with numerous communities residing on or in close proximity to the intrusion. These communities rely on local groundwater sources and recent groundwater development projects have suggested that groundwater yield potential is higher in its host Karoo sedimentary rocks adjacent to the intrusion than farther away. The proposed research will endeavour to investigate the structural geological features that influence groundwater yield, quality and community water supply potential in the Insizwa and surrounding area to provide a baseline for integrated quantified groundwater management, to meet community needs and awareness.

Abstract

Electromagnetic (EM) techniques were used to map groundwater salinity and clay layers in the Netherlands. The EM method used the so-called time domain system, is towed behind an ATV and is therefore called towed TEM. The results revealed a detailed 3-dimensional insight into the subsurface’s sequence of clay and sandy layers. Also, shallow saline groundwater, far from the coast, has been detected related to a subsurface salt dome. The rapid, non-destructive data acquisition makes the tTEM a unique tool. Electromagnetic (EM) techniques detect electrical conductivity contrasts in the subsurface with depth. EM data can often be interpolated into a 3D model of electrical conductivity. Expert knowledge of the regional geohydrologist, together with existing (borehole) data, is paramount for the interpretation. The towed Transient Electro-Magnetic system (tTEM) is developed to acquire data up to 60-80m depth by driving a transmitter and a receiver behind an ATV. With a speed of 10-15 km/h, measurements are collected every 5m. On fields, the distance between lines is typically 20m, resulting in a dense network of data that is inverted into 1D resistivity models, showing the variation of conductivity with depth. Interpolating 1D resistivity models into a 3D model allows for further interpretation in terms of geology, lithology, and groundwater quality. The tTEM technique bridges the gap between point measurements and more expensive and lower-resolution airborne EM data collection. The technique is sensitive to disturbance by man-made conducting infrastructure.

Abstract

The 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.

Abstract

The current Grahamstown/Makhanda drought has once again highlighted the vulnerability of the local surface water resources. The two local dams supplying the western part of town (and the university) are fed by a typical Eastern Cape river which requires a very large amount of rainfall to generate runoff into the dam. Rainfall records since 1860 indicate that statistically, the current drought is not the worst drought the town has endured and there have been many similar droughts in the past, most recently in the mid-1990s, and early 1980s. The severe drought in the 1980s led to the municipality commissioning a groundwater feasibility study carried out by Dr Andrew Stone, employed by Rhodes University at the time. The study included the drilling and testing of 13 boreholes, as well as a report on incorporating groundwater into the town's water infrastructure. All but two of these boreholes are destroyed, and they, along with the report were forgotten about. Around 4 years ago, we discovered the report at the university and began building on the work undertaken by Andrew Stone by monitoring 31 of the town's boreholes and carrying out a detailed analysis of the towns local groundwater fed spring, which many of the town's residents rely on. The current drought reignited the interest in groundwater, particularly with the arrival of Gift of the Givers who drilled a further 15 boreholes in town. The renewed focus on groundwater development came with its own complexities since the western part of town that the university resides in and the historically white area, is the only part of town to yield good quality groundwater. The local synclinal fold structure has resulted in a bowl type landscape in which much of the town is situated. Resistant Witteberg quartzitic sandstone rocks are observed as high-lying ridges which border the south-western margin of the town. The less resistant Dwyka tillite and Witteberg shales are generally found in the low-lying areas. This paper discusses the current water crisis, and how groundwater could be used on an on-going basis to relieve the water deficit in drier times caused by the vulnerable local dams.

Abstract

The eastern coastal plain of South Africa has one of the outstanding natural wetland and coastal sites of Africa. The estuaries are complex and dynamic systems sustained by both groundwater and surface water. These systems are driven primarily by changing sea level and fluctuating climatic conditions, especially river runoff and sedimentation rates, which have been heavily affected by land use change. The largest lake, St Lucia, lies at the bottom end of several rivers, some of which have major afforestation within their catchments. Given that there is a strong connection between surface water and groundwater, a significant driver of the reduced river runoff constitutes reduced groundwater baseflows due to the lowering of groundwater levels in the upstream reaches of the lake's catchments. The remaining large lakes (Lake Sibaya and the Kosi Bay Lake system) are largely groundwater driven and are also affected by increasing impacts on the groundwater sustaining the lakes. There is an urgent need to quantify the impact of land use change, particularly increasing plantation forestry, on these coastal estuarine systems. While previous work has been undertaken to better understand the complex environment, this study examines the coastal environment (Lake St Lucia, Lake Sibaya and the Kosi Bay lakes) in an integrated manner and considers the impacts of various land use activities on the system, both in the 'buffer zone' surrounding the lakes and within the upstream reaches of the river catchments. The study builds on previous investigations and utilises results from existing models as well as available field data. The integrated Pitman Model is used to model the groundwater/surface water dynamics and will be validated using existing numerical model results, observed stream flow, groundwater levels and lake level information. While the model has been established at a quaternary catchment scale for the upstream reaches of the rivers, the downstream reaches have been modelled at smaller spatial scales dictated by groundwater flow directions. A wetland sub-model has been established to represent the numerous and varied wetlands while a specific sub-model has been developed to represent the hydrodynamics of Lake St Lucia and its complex connections to the sea. The currently ongoing study aims to quantify the current and future land use change impacts on the groundwater and surface water resources sustaining the lakes.

Abstract

This study explores some of the principle issues associated with quantifying surface  water and groundwater interactions and the practical application of models in a data scarce region such as South Africa. The linkages between the various interdependent components of the water cycle are not well understood, especially in those regions that suffer problems of data scarcity, and there remain  urgent  requirements  for  regional  water  resource  assessments.  Hydrology  (both  surface water and groundwater hydrology) is a difficult science; it aims to represent highly variable and non- stationary processes which occur in catchment systems, many of which are unable to be measured at the scales of interest. The conceptual representations of these processes are translated into mathematical form in a model. Different process interpretations, together with different mathematical representations, result in the development of diverse model structures. These structural uncertainties are difficult to resolve due to the lack of relevant data. Further uncertainty is introduced  when  parameterising  a  model,  as  the  more  complex  the  model,  the  greater  the possibility that many different parameter sets within the model structure might give equally acceptable results when compared with observations. Incomplete and often flawed input data are then used to drive the models and generate quantitative information. Approximate implementations (model structures and parameter sets), driven by approximate input data, will necessarily produce approximate results. Most model developers aim to represent reality as far as possible, and as our understanding of hydrological processes has improved, models have tended to become more complex. Beven (2002) highlighted the need for a better philosophy toward modelling than just a more explicit representation of reality and argues that the true level of uncertainty in model predictions  is  not  widely  appreciated.  Model  testing  has  limited  power  as  it  is  difficult  to differentiate  between  the  uncertainties  within  different  model  structures,  different  sets  of alternative parameter values and in the input data used to run a model. A number of South African case studies are used to examine the types of data typically available and explore the extent to which a model is able to be validated considering the difficulty in differentiating between the various sources of uncertainty. While it is difficult to separate input data, parameter and structural uncertainty, the study found that it should be possible to at least partly identify the uncertainty by a careful examination of the evidence for specific processes compared with the conceptual structure of a specific model. While the lack of appropriate data means there will always be considerable uncertainty surrounding model validation, it can be argued that improved process understanding in an environment can be used to validate model outcomes to a degree, by assessing whether a model is getting the right results for the right reasons.

Abstract

This study explores some of the principle issues associated with quantifying surface and groundwater interactions and the practical application of models in a data scarce region such as South Africa. The linkages between the various interdependent components of the water cycle are not well understood, especially in those regions that suffer problems of data scarcity and there remain urgent requirements for regional water resource assessments. Hydrology (both surface and groundwater hydrology) is a difficult science; it aims to represent highly variable and non-stationary processes which occur in catchment systems, many of which are unable to be measured at the scales of interest (Beven, 2012). The conceptual representations of these processes are translated into mathematical form in a model. Different process interpretations together with different mathematical representations results in the development of diverse model structures. These structural uncertainties are difficult to resolve due to the lack of relevant data. Further uncertainty is introduced when parameterising a model, as the more complex the model, the greater the possibility that many different parameter sets within the model structure might give equally acceptable results when compared with observations. Incomplete and often flawed input data are then used to drive the models and generate quantitative information. Approximate implementations (model structures and parameter sets), driven by approximate input data will necessarily produce approximate results. Most model developers aim to represent reality as far as possible, and as our understanding of hydrological processes has improved, models have tended to become more complex. Beven (2002) highlighted the need for a better philosophy toward modelling than just a more explicit representation of reality and argues that the true level of uncertainty in model predictions is not widely appreciated. Model testing has limited power as it is difficult to differentiate between the uncertainties within different model structures, different sets of alternative parameter values and in the input data used to run a model. A number of South African case studies are used to examine the types of data typically available and explore the extent to which a model is able to be validated considering the difficulty in differentiating between the various sources of uncertainty. While it is difficult to separate input data, parameter and structural uncertainty, the study found that it should be possible to at least partly identify the uncertainty by a careful examination of the evidence for specific processes compared with the conceptual structure of a specific model. While the lack of appropriate data means there will always be considerable uncertainty surrounding model validation, it can be argued that improved process understanding in an environment can be used to validate model outcomes to a degree, by assessing whether a model is getting the right results for the right reasons.

Abstract

Saline groundwater in semi-arid to arid areas is typically ascribed to evaporative concentration of salts on or near the surface followed by dissolution of salts during episodic rainfall events and then percolation of saline downwards. This has been previously postulated for large parts of the west coast of South Africa where groundwater electrical conductivity (EC) ranges between 804 ?S/cm and 21 300 ?S/cm. However, due to the spatial variability of groundwater salt concentrations, it is unlikely that simple evaporation is the only process leading to elevated salinity levels in this region. Palaeo-termite mounds, known as heuweltjies (meaning little hills), are common surface features along the west coast of South Africa, covering an estimated 14 to 25% of the land surface. These structures consisting of aerated and nutrient-rich sediments, containing elevated levels of micro- and macro elements, including salts, compared to the surrounding sediments. For this reason, it is postulated that heuweltjies are an important source of groundwater salts. In the Buffels River valley, exchangeable ions from sediments in the centre of the heuweltjies are up to 20 times higher than in the inter-heuweltjie material and are consistent with elevated heuweltjie salts determined via in-situ EM38 scanning. 36Cl/Cl ratios are highly variable ranging between 25.94 x10-15 and 156.19x10-15, indicating that recharge occurs inland. Groundwater 87Sr/86Sr ratios in the same area are extremely elevated, up to 0.78240, suggesting a direct link to the underlying radiogenic granitic gneisses but decrease to the west suggesting interaction or mixing between different water sources. We propose that in this case, the two water sources are older groundwaters mixing with direct recharge that contains elevated salts but lower 36Cl/Cl and 87Sr/86Sr ratios derived from preferential flow paths through the heuweltjies.

Abstract

An integrated approach involving multivariate statistical analysis combined with graphical methods (Piper trilinear diagram and δ18O-δ 2H plots), and environmental isotope analyses were successfully applied to characterise the spatial distribution of hydrogeochemical parameters and their controlling factors within the Lake Sibayi catchment located in north-eastern South Africa. Bivariate and Multivariate statistical analyses (Factor and Hierarchical Cluster Analyses) were performed on 12 physiochemical parameters (variables) including pH, EC, TDS and major ions of 46 samples collected from various water sources (streams, Lake, shallow and deep boreholes). Bivariate Pearson’s correlation matrix of the measured variables revealed a strong positive correlation between EC and several major elements, which included Na+ , K+ , Mg2+, Ca2+ , Cland HCO3 - indicating their contribution to the salinity. These major ions were also found to be strongly correlated to one another with all correlations found to be significant. Factor analyses in the form of Principal components analyses were performed with the main aim of identifying the underlying factors or processes responsible for the observed hydrochemistry in the study area. The results revealed three principle factors explained about 95% of the hydrochemical variation in the study area. Most of the variance is contained within Factor-1 (69.5%), which has a high positive loading factor associated with EC, TDS, Na+ , Mg+ and Clconcentrations, interpreted in terms of the contribution of these major ions to the salinity of the water (EC and TDS). Factor-2 represents 17.7% of the total variation in the hydrochemistry and has high positive loadings for pH, HCO3 - , K+ , Ca+ and Fe concentrations. The HCO3 - , K+ and Ca+ could be the result of weathering and dissolution of carbonate minerals in calciferous Uloa and Umkwelane Formations and redox processes. The Fe concentrations could be related to leaching of ferricrete layers known to exist in the area and a result of anoxic condition within the aquifer. The variables NO3 - and SO4 - contribute most strongly to Factor-3, which explains 8.01% of the total variance. The loading for NO3 - was positive and could result from anthropogenic pollution of the shallow aquifer and streams, while that of SO4 - being negative and could result from historical marine influences. Hierarchical cluster analysis of hydrochemical data performed using the Ward method with squared Euclidean distance, grouped the water samples into two clusters, representing unique hydrochemical systems, i.e. surface water and groundwater. Each of these two clusters was in turn divided into two sub-clusters, representing stream and lake samples, and shallow and deep aquifers, respectively. These groupings were further supported by characteristic water types; namely, a Na-Cl-HCO3 facies for the river, lake and surrounding boreholes; a Na-Cl hydrochemical facies for shallow boreholes, while deep borehole samples were Na-Ca-Cl to Na-Cl-HCO3 in composition. These clustering were supported by isotopic signals that show a clear distinction between groundwater and lake water samples.

Abstract

The City of Windhoek in Namibia has developed wellfields and a managed aquifer recharge scheme within the fractured Windhoek Aquifer to ensure a sustainable potable water supply to the city during drought. A three-dimensional numerical groundwater model of the aquifer was developed using the finite-difference code MODFLOW to determine the potential impacts of varying pump inlet depth elevations and varying production borehole abstraction rates for optimal wellfield and aquifer management. The initial steady-state numerical model was calibrated to September 2011 groundwater levels, representing the best approximation of “aquifer full” conditions (following a good rainfall period and best available data). The subsequent transient numerical model was calibrated against groundwater level fluctuations from September 2011 to August 2019, the period after steady-state calibration for which data was available (and during which monitored groundwater abstraction occurred). The calibrated transient model was used to run various predictive scenarios related to increased emergency groundwater abstraction and estimate potential impacts on the Windhoek Aquifer. These predictive scenarios assessed groundwater level drawdown and recovery, aquifer storage potential, and potential abstraction rates under different pump elevations. Model results indicated a sharp initial groundwater level drop followed by a gradual decrease as groundwater levels approached the 100 m saturated depth mark. Pumping elevations were subsequently updated with recommended abstraction rates and volumes for the entire Windhoek Aquifer. The numerical groundwater model, in association with extensive groundwater monitoring, will be used to assess/manage the long-term sustainable and optimal utilisation of the Windhoek Aquifer.

Abstract

The City of Cape Town (CoCT) metropolitan municipality seeks to identify and develop alternative water resources for the augmentation of surface water to ensure more robust and sustainable water supply to the CoCT and its inhabitants. A 3-D finite-element numerical model of the Atlantis Aquifer was developed using the commercial code FEFlow 7.1 to support the assessment of the impact of groundwater abstraction from the aquifer which has been identified as one of the target zones to develop sustainable alternative water resources as part of the CoCT water reconciliation strategy. The numerical model acts as a decision support tool to assist in planning and management of the rehabilitation and potential expansion of the groundwater abstraction and managed aquifer recharge scheme. The numerical model is to be applied in determining the impact of additional abstraction as well as assess the maximum sustainable yield from the wellfields without negatively impacting on surface water sources and other groundwater dependent users. The model improves upon previous modelling work and represents the latest and most comprehensive knowledge in terms of three-dimensional aquifer geometry, location and rates of anthropogenic groundwater users, spatial distribution of recharge, hydraulic parameters and location of aquifer boundary conditions. Model parameters have been successfully calibrated under steady-state conditions to provide a realistic representation of long-term groundwater levels across the system (R2=98%). Abstraction scenarios and their impact on groundwater levels were assessed using the calibrated numerical model. Scenarios were simulated of three phases of abstraction (approximately 15, 25 and 40 Ml/d) to determine drawdown around the wellfields, the impact on spring discharge, and the possibility of saline intrusion. Model results show drawdown to be mostly confined to the associated wellfields, with minor drawdown experienced in the vicinity of Silwerstroom. Simulated hydraulic heads indicate that seawater intrusion is unlikely to occur under all scenarios.

Abstract

Lake Sibayi (a topographically closed fresh water lake) and coastal aquifers around the lake are important water resources, which the ecology and local community depend on. 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 which would later be integrated into the three dimensional numerical model for the area. 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 feeds the lake as the groundwater head is above lake stage, whereas along the eastern section, the presence of mixing between lake and groundwater isotopic compositions indicates that the lake recharges the aquifer. Stable isotope signals further revealed the movement of lake water through and below the coastal dune cordon before discharging into the Indian Ocean. Quantification of the 9 year monthly water balance for the lake shows strong season variations of the water balance components. Based on lake volume and flow through rate, it was further noted that the average residence time for water in the lake was about 6 years.
A recent increase in the rate of water abstraction from the lake combined with decreasing rainfall and rapidly increasing plantations in the catchment may result in a decrease in lake levels. This would have dramatic negative effects on the neighbouring ecosystem and allow for potential seawater invasion of the coastal aquifer.

Abstract

Modelling of groundwater systems and groundwater-surface water interaction using advanced simulation software has become common practice. There are a number of approaches to simulate Lake-aquifer interactions, such as the LAK Package integrated into MODFLOW, the high conductivity and fixed stage approaches. LAK and the high conductivity approaches were applied and compared in simulating Lake- aquifer interaction in the Lake Sibayi Catchment, north-eastern, South Africa using the finite difference three-dimensional groundwater flow model, Visual MODFLOW Flex under steady state conditions. The steady state model consisted of two layers: an upper layer consisting of the Sibayi, KwaMbonambi, Kosi Bay and Port Durnford Formations which have similar characteristics, and a lower model layer representing the karst, weathered and calcareous Uloa Formation. The bottom model boundary is constrained by the impermeable Cretaceous bedrock. The model area covers the surface and groundwater catchments of Lake Sibayi which is constrained in the east by the Indian Ocean. A no-flow boundary condition is assigned to the northern, western and southern sides and a constant head boundary is assigned to the eastern side. The Mseleni River and neighbouring plantations were modelled using the River and Evapotranspiration boundary conditions respectively. Input parameters for the various boundary conditions were obtained from the previously developed high resolution conceptual model, including recharge

Abstract

Lake  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.

Abstract

Managed aquifer recharge (MAR) has become increasingly popular in Central Europe as a sustainable, clean, and efficient method for managing domestic water supply. In these schemes, river water is artificially infiltrated into shallow aquifers for storage and natural purification of domestic water supply, while the resulting groundwater mound can simultaneously be designed to suppress the inflow of regional groundwater from contaminated areas. MAR schemes are typically not managed based on automated optimization algorithms, especially in complex urban and geological settings. However, such automated managing procedures are critical to guarantee safe drinking water. With (seasonal) water scarcity predicted to increase in Central Europe, improving the efficiency of MAR schemes will contribute to achieving several of the UN SDGs and EU agendas. Physico-chemical and isotope data has been collected over the last 3-4 decades around Switzerland’s largest MAR scheme in Basel, Switzerland, where 100 km3 /d of Rhine river water is infiltrated, and 40 km3 /d is extracted for drinking water. The other 60 km3 /d is used to maintain the groundwater mound that keeps locally contaminated groundwater from industrial heritage sites out of the drinking water. The hydrochemical/isotope data from past and ongoing studies were consolidated to contextualize all the contributing water sources of the scheme before online noble gas and regular tritium monitoring commenced in the region. The historical and the new continuous tracer monitoring data is now used to inform new sampling protocols and create tracer-enabled/assimilated groundwater-surface water flow models, vastly helping algorithm-supported MAR optimization

Abstract

The use of radiogenic isotope tracers, produced through bomb testing (e.g. 3H and 14C), and the application of these isotopes is yet to be fully explored now that atmospheric abundances have returned to background levels. New isotope-enabled institutions and laboratories have recently been established in developing countries to apply isotopes in practical research. This study utilized several laboratories in South Africa and in Europe to compile a robust hydrochemical (major cations and anions) and isotope (d18O, d2H, 3H, 14C, 86Sr/87Sr) dataset of groundwater from 95 sample locations in the Maputo province of Mozambique. Groundwater is hosted in different aquifers and recharged through variable mechanisms ranging from direct infiltration of exposed alluvial soils to inter-aquifer transfer between fractured aquifer systems in the mountainous regions and the weathered bedrock in the lowlands. A combination of hydrochemistry and isotopes provided insight into the heterogeneous nature of recharge, mixing of modern and fossil groundwaters, and aquifer vulnerabilities when combined with other physical parameters in the region. However, it is also clear that grab sampling over a regional spatial extent and two sampling seasons (wet and dry) did not capture all the system variability, and more regular monitoring would uncover details in the system’s behaviour not captured in this study.

Abstract

During 2017-2018, the City of Cape Town, South Africa faced an unprecedented drought crisis with the six main water storages supplying Cape Town falling to a combined capacity of just under 20%. With the threat of severe water shortages looming, various additional water sources were examined to supplement the municipal water supply network. These were focussed on groundwater, desalination and treated effluent. However, private citizens and businesses also made plans to avoid shortages, resulting in numerous uncontrolled water sources competing with the municipal supply network. Throughout the crisis, groundwater was considered the most important alternative urban water supply source but also the most vulnerable to contamination through accidental and uncontrolled return flows from the municipal network, private residences and agricultural industries. This project aims to constrain the water supply network in the Stellenbosch municipality and monitor the augmentation of groundwater into the network using stable isotopes. Long term monitoring points have been established at 35 tap water sites, 20 private wells as well as at the supply reservoirs that feed the municipal network. Preliminary data show’s distinct isotopic signals associated with each supply reservoir as well as in the local groundwater. The data also shows significant return flow into the alluvial aquifer system during warmer months when private stakeholder’s water consumption is at its highest. Groundwater is expected to supplement this urban supply network in the latter part of 2021 and will likely disrupt the current distribution of stable isotopes in the network, providing further insight into the potential return flow into the local groundwater system.

Abstract

Unicef is the WASH sector lead globally and is, present at the country level, the main counterpart of government, especially regarding the component of the water balance utilised for potable safe water supplies. This mandate means that Unicef then has a role in looking at water resources nationally and not just as individual projects, and in doing so, contributes to good water governance as an integral part of system strengthening. Ensure this is done in partnership with other ministries and stakeholders that support them through advocacy for humanitarian and developmental access and support in technical areas such as groundwater assessments and monitoring. The focus on groundwater is especially linked with the fact that groundwater plays a major role due to its buffering capacity to climate variations, easier access and global coverage. Since groundwater is the most significant component of accessible freshwater resources, it is in the interest of UNICEF to make this resource more visible to meet both development and humanitarian goals, strengthen national systems and ultimately build resilience in mitigating water scarcity to scale or at the National level. Therefore, examples will be presented where Unicef has engaged on this journey with nations such as Afghanistan, Yemen, Mozambique and Rwanda to understand their water resources better. The overall objective at the National level is to adapt the capacity to withstand and recover as quickly as possible from external stresses and shocks or build resilience.

Abstract

The SADC region has vast potential to alleviate water scarcity and promote growth through the responsible development of groundwater resources. To achieve this, it is crucial to understand the resource’s value, implement sustainable abstraction programs, protect its quality, optimize its usage for regional development, and implement innovative aquifer management programs, including artificial recharge. Greenchain Group is a water treatment company that recognizes the value of water and strategically deploys its expertise to maximize the potential of each drop. As membrane technology specialists and local manufacturers of this advanced technology, we understand how to design integrated solutions to safeguard water quality and accessibility. Our wide range of filtration technologies allows us to select the technology suited to the application and regional groundwater context and to produce high-quality water from various sources, including groundwater. Additionally, by removing contaminants/unwanted constituents from groundwater, we enhance the value of each drop of water for local potable consumption, eliminate the need for overwatering in agriculture, and allow for the creation of new agriculture/industries in regions with poor groundwater quality. This same technology can also treat wastewater and remove contaminants (e.g. chemical of emerging concern, PFAS) and thus is critical to water reuse applications and responsible Managed Aquifer Recharge. Greenchain Group’s treatment systems have been used in various industries, including agriculture, mining, energy, medical, food and beverage, and remote and mobile settings.

Abstract

We contend that borehole drilling costs on the Zululand Coastal Plain, South Africa can be much reduced by assisting low cost drillers in drilling 6" diameter boreholes using light weight, maneuverable rigs with trained teams which are more cost-effective and provide optimal value for money invested over the lifespan of the borehole. The improved drilling package will allow local drillers to tap into the deeper more sustainable aquifer identified in the area and provide for better borehole construction. The remoteness of the rural population in the Maputaland area, northern KZN, South Africa, influences the degree of groundwater development. Rural water supply infrastructure is minimal and 40 per cent of the rural community is forced to rely on surface water as well as shallow, low cost drilling for water supply. A number of these low cost drillers were investigated to determine their expertise. Results showed that formal training in drilling technology is unavailable in the area. The inexperience of the drillers results in poor borehole construction. Currently low cost drilling is not cost effective as most of these boreholes collapse after a short time. The correct method of drilling in the area is by Direct Mud Rotary (DMR). Professional DMR drilling and borehole construction costs are in excess of US$ 125/m, unaffordable for poor households. We propose that with limited training and suitable equipment the local drillers can halve existing drilling costs, provide quality work as well as focus on good management practices. This will create jobs as well solve the pending water crisis in the area (and elsewhere in Africa).

Abstract

A groundwater study at Middelburg Colliery was completed with the emphasis on the investigations into water balances on a rehabilitated coal mining environment. Water balance calculations and water scheduling for collieries in Mpumalanga have become important facets of mine planning over the past years. Opencast mining involves the blasting and removal of rocks overlying the coal layer, which is removed completely. The overburden is then replaced (backfilled) and covered with soil and the terrain is rehabilitated. Rainwater penetrating through the soil into the backfill may become acidic by pyrite and sulphides in the backfill material and ultimately decants on the surface. Decanting generally commences a decade or more after mining ceases. Opencast mining impacts the natural groundwater regime and radically alters the nature of groundwater-surface water interactions. The Department of Water Affairs and Forestry in South Africa requires that mines minimise the release of their polluted water. A groundwater balance is the numerical accounting of the annual recharge to a groundwater resource. It can further be described as a quantitative assessment of the total water resources of a basin over a specific period of time. In a groundwater development program, such a budget is necessary to efficiently manage and utilize the resource. Many of the parameters that determine recharge to an aquifer are measured directly and some are computed from hydraulic characteristics and measured field data. The Middelburg Mine Services has been experiencing excess water problems in past years. Because of the lack of space and the concerns of decanting of mine water out of the rehabilitated pit, it was suggested that mine water treatment should be considered. Geohydrological models were created to determine the decant positions and water volumes for the rehabilitated area. The size of the water treatment plant can then be determined using the calculated decant volumes and positions.

Abstract

Zimbabwe occupies a tectonically stable plateau underlain by ancient Precambrian crystalline basement rocks. These  form a central craton bounded by east-west trending mobile belts; the Zambezi mobile belt to the north and the Limpopo mobile belt to the south. Zimbabwe receives generally low and variable quantities of seasonal rainfall within a semi-arid to savannah type climate characterised by moderate to high temperatures. Evaporation commonly exceeds rainfall so that recharge to the thin near surface aquifers is generally low and in some years non-existent. The groundwater resources of the weathered and fractured basement aquifers that underlie more than 60% of the country are of limited potential, typically sufficient to supply the needs of small villages and cattle ranches. However, within the central plateau area of the African to Post-African erosion surfaces, the weathered and fractured basement may exceed 60 m in thickness. The thickness of this zone diminishes towards the main valley systems where subsequent cycles of erosion have stripped the weathered zone away, leaving only a shallow surface fractured zone that may only be 20-30 m thick. Groundwater resources have been developed extensively in Zimbabwe since the 1920s. During 1991/92 drought abstraction from urban boreholes within the southern Harare area caused yield decline and ultimate failure of numerous boreholes. It is now time to question the long-term viability of groundwater development within the basement aquifers in Zimbabwe given the uncertainty in groundwater resources, the complexities of the climate–groundwater interactions and the projected demands of a growing rural population.

Abstract

The SADC Grey Data archive http://www.bgs.ac.uk/sadc/ provides a chronology of groundwater development within the constituent countries of the SADC region. Early reports show how groundwater development progressed from obtaining water by well digging to the mechanical drilling of boreholes for provision of water for irrigation, township development, transport networks and rural settlement. During the 1930s steam driven drilling rigs were supplanted by petrol engine driven cable tool percussion drilling. Dixey (1931), in his manual on how to develop groundwater resources based on experiences in colonial geological surveys in eastern and southern Africa, describes aquifer properties, groundwater occurrence and resources as well as water quality and groundwater abstraction methods. Frommurze (1937) provides an initial assessment of aquifer properties in South Africa with Bond (1945) describing their groundwater chemistry. South African engineers transferred geophysical surveying skills to the desert campaign during World War II. Paver (1945) described the application of these methods to various geological environments in South Africa, Rhodesia and British colonial territories in eastern and central Africa. Test pumping methods using electric dippers were also developed for the assessment of groundwater resources. Enslin and others developed DC resistivity meters, replacing early Meggar systems, produced data that when analysed, using slide rules with graphs plotted by hand, identified water bearing fractures and deeply weathered zones. Tentative maps were drawn using interpretation of aerial photographs and heights generated using aneroid altimeters. The problems faced by hydrogeologists remain the same today as they were then, even though the technology has greatly improved in the computer era. Modern techniques range from a variety of geophysical surveying methods, automated rest level recorders with data loggers to GPS location systems and a whole host of remotely sensed data gathering methods. Worryingly, using such automated procedures reduces the ability of hydrogeologists to understand data limitations. The available collection of water level time series data are surprisingly small. Surrogate data need to be recognised and used to indicate effects of over abstraction as demand grows. As the numbers of boreholes drilled per year increases the number of detailed hydrogeological surveys undertaken still remains seriously small. Has our knowledge of hydrogeological systems advanced all that much from what was known in the 1980s? Case histories from Malawi, Zimbabwe and Tanzania illustrate a need for groundwater research with well-judged sustainability assessments to underpin safe long-term groundwater supply for the groundwater dependent communities in the region.

Abstract

The hydraulic parameters of heterogeneous aquifers are often estimated by conducting pumping (and recovery) tests during which the drawdown in a borehole intersecting the aquifer is measured over time, and by interpreting the data after making a number of assumptions about the aquifer conditions. The interpreted values of the hydraulic parameters are then considered to be average values that represent the properties of the bulk aquifer without taking into account local heterogeneities and anisotropies. An alternative and more economic approach is to measure streaming potentials in the vicinity of the borehole being tested. The streaming potential method is a non-invasive geophysical method that measures electrical signals generated by groundwater flow in the subsurface through a process known as electrokinetic coupling. This method allows data to be recorded at a high spatial density around the borehole. The interpretation of streaming potential data in terms of aquifer hydraulic parameters is facilitated by a coupled flow relationship which links the streaming potential gradient to the hydraulic gradient through a constant of proportionality called the electrokinetic coupling coefficient. In the current study, field measurements of streaming potentials were taken during the pumping and recovery phases of pumping tests conducted at two sites with dissimilar geological and geohydrological conditions. The recorded streaming potential data were interpreted by calculating the hydraulic head gradient from the streaming potential gradient, and by using the potential field analytical solution for the transient mode, which relates the streaming potential field directly to the average hydraulic conductivity. Hydraulic conductivity values estimated from the streaming potential method were of the same order as values determined from the analysis of drawdown data, with a relative error of 0.2. This study demonstrates that the streaming potential method is a viable tool to compliment pumping tests and provide a spatial representation of the hydraulic parameters.

Abstract

In 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.

Abstract

POSTER Hydraulic fracturing, also known as hydrofracking or fracking, is being engaged in the Karoo region of South Africa in order to enhance energy supplies and improve the economic sector. It will also lead to independence in terms of reduced amount of imports for fuel due to an estimated 13.7 trillion cubic metres of technically recoverable shale-gas reserves in South Africa. 

Fracking is an extraction technique used with the purpose of having access to alternative natural methane gas, which is interbedded in shale deposits deep under the surface of the earth. In this process boreholes are drilled horizontally into shale formations to cover a larger area in the shale and  subsequently  attain  more  natural  gas.  After  these  horizontal  boreholes  are  drilled,  large volumes of water, mixed with chemicals and sand, are pumped into these boreholes under a very high pressure, forcing the natural gas out. This water mixture is referred to as the fracking fluid. Water is the main component in the fracking fluid and the water used for the fluid reaches volumes up to 30 million litres per borehole.

The aim of this study is to present a baseline study of the area and its water resources to ultimately facilitate in resolving the actual impact hydraulic fracturing will have in the area, using a simulation model which will predict the migration of the fracking fluid in the subsurface. In this model, the chemistry of  the fracking fluid  will  be  included  to determine  the impact  it might  have  on the groundwater quality in the area

Abstract

Managed aquifer recharge (MAR), the purposeful recharge of water to aquifers for subsequent recovery, is used globally to replenish over-exploited groundwater resources and to prevent saltwater intrusion. Due to increased water shortage worldwide, there is a growing interest in using unconventional water resources for MAR such as reclaimed water or surface water impaired by wastewater discharges. This, however, raises major concerns related to pollution of our drinking water resources. MARSA is a new Danish-South African research project aiming at developing MAR technologies allowing a broader span of water resources to be used for MAR, including storm water, river water, saline water, and even treated wastewater. It is hypothesised that improved removal of organic pollutants, nitrogen species, antibiotic resistance, and pathogens can be achieved by establishment of reactive barriers or creation of different redox environments through injection of oxidizing agents to anaerobic aquifers during recharge. In MARSA we will carry out feasibility studies, as flow-through columns, first in Denmark and later in South Africa, to investigate the capacity of South African aquifer sediments to remove organic pollutants, nitrogen species, antibiotic resistance genes, and pathogens. Then, based on these studies, MAR options will be further investigated at field conditions in South Africa using real source water from MAR sites. For this presentation we will give an overview of the MARSA-project and show results from previous feasibility studies investigating the potential of reactive barriers to remove organic micropollutants and ammonium. These studies have shown that establishment of reactive barriers will cause oxygen depletion, but also more efficient ammonium and organic micro-pollutant removal. MARSA is funded by the DANIDA fellowship centre, Ministry of Foreign Affairs of Denmark. Project no. 20-M03GEUS.

Abstract

Large scale groundwater abstraction is increasingly being used to support large urban centres particularly in areas of low rainfall but presents particular challenges in the management and sustainability of the groundwater system. The Table Mountain Group (TMG) Aquifer is one of the largest and most important aquifer systems in South Africa and is currently being considered as an alternative source of potable water for the City of Cape Town, a metropolis of over four million people. The TMG aquifer is a fractured rock aquifer hosted primarily in super mature sandstones, quartzites and quartz arenites. The groundwater naturally emanates from numerous springs throughout the cape region. One set of springs were examined to assess the source and residence time of the spring water. Oxygen and hydrogen isotopes indicate that the spring water has not been subject to evaporation and implies that recharge to the spring systems is via coastal precipitation. Although rainfall in the Cape is usually modelled on orographic rainfall, δ18O and δ2H values of some rainfall samples are strongly positive indicating a stratiform component as well. Comparing the spring water δ18O and δ2H values with that of local rainfall, indicates that the springs are likely derived from continuous bulk recharge over the immediate hinterland to the springs and not through large and/or heavy downpours. Noble gas concentrations, combined with tritium activities indicate that the residence time of the TMG groundwater in this area is decadal in age with a probable maximum upper limit of ~40 years. This residence time is probably a reflection of the slow flow rate through the fractured rock aquifer and hence indicates that the interconnectedness of the fractures is the most important factor controlling groundwater flow. The short residence time of the groundwater suggest that recharge to the springs and the Table Mountain Group Aquifer as a whole is vulnerable to climate change and reductions in regional precipitation. Any plans for large-scale abstraction to supplement the City of Cape Town water supply would need to factor this in to models of maximum sustainable yield.

Abstract

The Verlorenvlei estuarine lake is one of only two freshwater estuarine systems in South Africa. Whilst being important ecologically it is also a critical agricultural region, supporting a significant proportion of South African potato crops as well as a number of other diverse crops. The vlei itself is fed by the Verloren River which is thought to be fed by surface water inflows and baseflow throughout the year along several tributaries, namely the Krom Antonies, Hol, Berg Vallei and Kruismans. Each of these tributaries has a distinct hydrochemical character defined by cation and anion concentrations, as well as O, H and Sr isotopes. Simulated discharge from each tributary suggests that all tributaries contribute to the chemistry of the Verloren River. The Krom Antonies which has the freshest water has the highest discharge at around 50% of surface water inflows, whilst the Hol with the highest EC values contributes around 35% of surface water inflows. In spite of this, the surface water hydrochemistry in the Verloren River, is remarkedly fresh and very similar in character to the surface water of the Krom Antonies. Sr isotopes in each of the tributaries are distinct and support mixing of different components of each tributary above the confluence. However, below the confluence, they drop significantly which indicates mixing with another unidentified Sr-source. This source was thought to be baseflow from the deeper groundwater system, but the Sr isotope composition of deeper groundwater indicates that it is not the contributing component. Recent years have seen dramatic reductions in precipitation, while increases in pumping for agricultural purposes potentially exceeds the long-term sustainable yield of the aquifer system. Identification of this unknown component has therefore become a priority for groundwater management in the area as it is unclear how vulnerable this component will be to climate change and hence what impact climate change will have on the vlei.

Abstract

Understanding the sensitivity of groundwater resources to surface pollution and changing climatic conditions is essential to ensure its quality and sustainable use. However, it can be difficult to predict the vulnerability of groundwater where no contamination has taken place or where data are limited. This is particularly true in the western Sahel of Africa, which has a rapidly growing population and increasing water demands. To investigate aquifer vulnerability in the Sahel, we have used over 1200 measurements of tritium (3H) in groundwater with random forest modelling to create an aquifer vulnerability map of the region.

In addition, more detailed vulnerability maps were made separately of the areas around Senegal (low vulnerability), Burkina Faso (high vulnerability) and Lake Chad (mixed vulnerability). Model results indicate that areas with greater aridity, precipitation seasonality, permeability, and a deeper water table are generally less vulnerable to surface pollution or near-term climate change. Although well depth could not be used to create an aquifer vulnerability map due to being point data, its inclusion improves model performance only slightly as the influence of water table depth appears to be captured by the other spatially continuous variables.

Abstract

Arsenic is a common contaminant typically found in effluent from gold mine operations and copper smelters throughout the world. The geochemical behaviour of arsenic in contact with dolomite underlying an arsenic containing waste rock pile was investigated. The interaction between the arsenic and the dolomite is an important control in the subsequent transport of the arsenic in the dolomitic aquifer. Rocks with varying dolomite content were tested to investigate the interaction between the arsenic and dolomite. From the modelling and test results it was estimated that in the aquifer, between 60 - 90% of arsenic is present in the solid phase under oxidation conditions at >50 mV. At 50 to -25 mV about 40 - 60% of the arsenic is estimated to be present in the solid phase and below -25 mV about 0 - 10% of arsenic will be present in the solid phase. Although some arsenic is removed by the dolomite in the aquifer the arsenic would still be present above acceptable guidelines for drinking water. The arsenic in the solid phase will be in equilibrium with the aquifer water and could be remobilised 1) under more reducing conditions or 2) with a decrease in arsenic in the aquifer.

Abstract

Underground Coal Gasification (UCG) is an emerging, in-situ mining technology that has the advantage to access a low cost energy source that is currently classified as not technically or economically accessible by means of conventional mining methods. As such it offers significant potential to dramatically increase the world's non-recoverable coal resource.

Groundwater monitoring in the South African mining industry for conventional coal mining as an example, is well established, with specific SANS, ASTM and ISO Standards dedicated for the specific environment, location and purposes. In South Africa a major impact of the coal mining industry can be a reduction in the groundwater quantity and quality. South-Africa's groundwater is a critical resource that provides environmental benefits and contributes to the well-being of the citizens and the economic growth. Groundwater supplies the drinking water needs of a large portion of the population; in some rural areas it represents the only source of water for domestic use. Utilization and implementation of groundwater monitoring programs are thus non-negotiable.

The groundwater quality management mission, according to the Department of Water and Sanitation in South-Africa, is set in the context of the water resources mission and is as follows:

"To manage groundwater quality in an integrated
and sustainable manner within the context of the National
Water Resource Strategy and thereby to provide an
adequate level of protection to groundwater resources
and secure the supply of water of acceptable quality."

The scope of this paper is to propose an implemention strategy and a fit-for-purpose groundwater monitoring program for any Underground Coal Gasification commercial operation. It is thus important to pro-actively prevent or minimise potential impacts on groundwater through long-term protection and monitoring plans. A successful monitoring program is one that consists of
(1) an adequate number of wells, located at planned and strategic points;
(2) sufficient groundwater sampling schedules; and
(3) a dedicated monitoring program and quality control standard.

In order to have an efficient monitoring program and to prevent unnecessary analysis and costs, it is also critical to determine upfront what parameters have to be monitored for the specific process and site conditions.

Abstract

Model calibration and scenario evaluations of 2D and 3D groundwater simulations are often computationally expensive due to dense meshes and the high number of iterations required before finding acceptable results. Furthermore, due to the diversity of modelling scenarios, a standardised presentation of modelling results to a general audience is complicated by different levels of technical expertise.

Reducing computational time
In this presentation we look briefly at the use of Reduced Order Models (ROM's), which is one of the recent developments in groundwater modelling. The method allows significant speed-up times in model calibration and scenario evaluation studies. In saturated flow for example, these approaches show speed-up times of >1000 when compared to full models created with Finite Element of Finite Difference methods. These methods are demonstrated to a case study in the Table Mountain Group, in which we show a simplified parameter calibration and scenario evaluation study.

Standardising presentation
In order to present the results to as wide an audience as possible, the use of a web-browser as a GUI is proposed, where the web-page is coupled to a geo-spatial database and data is presented in a spatial and numeric format. The use of the spatial database manager PostgreSQL with PostGIS is proposed. Through a browser interface, users can run modelling scenarios using the ROM, which is evaluated in near real-time. Following the evaluation of the model, we show how PostGIS can spatially present data on a base-map such as google maps. In keeping with the current trends in online map customisation, viewers can interactively choose to overlay the base-map with a data-type (such as pressure or hydraulic head contours or flow direction) that is most intuitive for their level of familiarity with the data.

Conclusion
In using advanced modelling techniques and a simplified browser based presentation of results, high-level decisions in water resource management can be significantly accelerated with the use of interactive scenario evaluations. Furthermore, by reaching a broader audience, public participation will be significantly enhanced.

Abstract

Many groundwater models are commissioned and built under the premise that real world systems can be accurately simulated on a computer - especially if the simulator has been "calibrated" against historical behavior of that system. This premise ignores the fact that natural processes are complex at every level, and that the properties of systems that host them are heterogeneous at every scale. Models are, in fact, defective simulators of natural processes. Furthermore, the information content of datasets against which they are calibrated is generally low. The laws of uncertainty tell us that a model cannot tell us what will happen in the future. It can only tell us what will NOT happen in the future. The ability of a model to accomplish even this task is compromised by a myriad of imperfections that accompany all attempts to simulate natural systems, regardless of the superficial complexity with which a model is endowed. This does not preclude the use of groundwater models in decision-support. However it does require smarter use of models than that which prevails at the present time. It is argued that, as an industry, we need to lift our game as far as decision-support modeling is concerned. We must learn to consider models as receptacles for environmental information rather than as simulators of environmental systems. At the same time, we must acknowledge the defective nature of models as simulators of natural processes, and refrain from deploying them in a way that assumes simulation integrity. We must foster the development of modelling strategies that encapsulate prediction-specific complexity supported by complexity-enabling simplicity. Lastly, modelers must be educated in the mathematics and practice of inversion, uncertainty analysis, data processing, management optimization, and other numerical methodologies so that they can design and implement modeling strategies that process environmental data in the service of optimal environmental management.

Abstract

This past drought (summer of 2016/17) in the Western Cape has resulted in a number of boreholes “failing” and desperate farmers calling for more boreholes to be drilled. A closer look shows that many, if not most, of these boreholes were tested by the long-discredited “Maximum drawdown-yield at end of 48 hours x 60% = yield” method. A prime example was a borehole drilled and tested by the “old” method in 1983. This borehole was the main borehole supplying a stud horse farming operation. The borehole was equipped with a large capacity pump set at depth for paddock irrigation, plus a low capacity pump set above for drinking water supply. Using the existing main pump the author carried out a step-test in 2012. The borehole appeared to be sustainable. When re-tested in the middle of the drought of 2017 it hit pump- suction in 8 hours, i.e. it is not sustainable. Two radical examples of water supply boreholes are examined: a borehole with air-lift yield of 10 to 15 L/sec for which the sustainable yield was determined to be 0.5 L/sec, and a borehole with an air-lift yield of 0.5 to 0.7 L/sec for which the sustainable yield was determined to be 7.5 L/sec. Conclusion: In order to determine the sustainable yield of a borehole, especially in the fractured rock environment of Southern Africa, do not rely on the driller’s report of air- lift yield, and use the proper method of test-pumping a borehole. If not you may be in trouble.

Abstract

Well-established engineered systems for depth-discrete monitoring in fractured rock boreholes (referred to as a Multilevel System or MLS) are commercially available and offer much diversity in design options, however, they are used infrequently in professional practice and have seen minimal use in groundwater research. MLSs provide information about hydraulic head and hydrochemistry from many different depths in a single borehole and, therefore, magnify greatly the knowledge value of each borehole. Conventional practice globally is devoted to standard monitoring wells, either alone as longer single screened wells or in clusters or nests with a few wells screened at different depth intervals. These are the mainstay of the groundwater science and engineering community and severely limit prospects for each borehole to provide the information needed to solve the complex problems typically posed by fractured rock. This paper outlines the nature and evolution of MLS technologies and points to recent literature showing how MLSs add important insights that cannot be obtained using conventional wells. Also, it reviews commercially available MLS technologies, which present a range of robust options with each system having different characteristics and niches depending on characterization and monitoring goals and site conditions. The paper also describes refined MLS criteria aimed at improving the cost effectiveness and expanding capabilities of MLSs, so as to improve their accessibility for high resolution data acquisition in the context of both groundwater system characterization and long-term monitoring.

Abstract

A groundwater decision support system (DSS) that incorporates stakeholder participation has been developed for Siloam Village in Limpopo Province, South Africa. Residents of Siloam Village are dependent on groundwater to augment inadequate pipe borne water supply. This creates the need for a DSS that ensures efficient and sustainable management and utilization of water. Such a DSS is constituted of both quantitative and qualitative components. The study further proposes framework for implementation of the DSS which incorporates community participation. This will act as a tool for empowering and educating the communities in rural villages so that they can be able to manage their water resources. The developed DSSs will make it possible for Siloam community to operate their water supply systems efficiently taking into account environmental needs and water quality

Abstract

In South Africa, the use of stochastic inputs in surface water resources assessments has become the norm while this is rarely done for groundwater resources. Studies that have applied multi-site and multi-variate methods that incorporate stochastic generation of groundwater levels are limited. Stochastic based inputs account for uncertainties attributed to inherent temporal and spatial variability of hydrologic variables and climatic conditions. This study applied variable length block (VLB) stochastic generator for simultaneous generation of multi-site stochastic time series of rainfall, evaporation and groundwater levels. In the study, 100 stochastic sequences with record length of 34 years (1980-2013), similar to the historic one were generated. Performance of VLB was assessed by comparing single statistics of historic time series located within box plots of the 100 annual and monthly stochastically generated time series. The statistics used include mean, median, 25th and 75th percentiles, lowest and highest values, standard deviation, skewness, and serial and cross correlation coefficients. Majority (9 out of 10) of the historical statistics were mostly well preserved by VLB, except for skewness. Historic highest groundwater levels were mostly underestimated. Historic statistics below interquartile range (overestimation) is a common problem of weather generators which can be reduced by including additional covariates that influence atmospheric circulation. The generation of multi-site stochastic sequences support realistic assessment of groundwater resources and generation of groundwater operating rules.

Abstract

Communities in the Lower Shire River Valley in the Chikwawa District of southern Malawi face extreme development challenges due to highly variable climate, including floods and droughts, that trap them in poverty and food insecurity. The area has been the focus of numerous studies and data collection campaigns to understand better the causes and processes associated with brackish groundwater (in alluvial aquifers) and dry boreholes. An applied groundwater assessment was performed to evaluate water supply alternatives and solutions to deliver potable water to approximately 15% of the district without water access after a multi-year campaign to reach 100%. The assessment synthesized a significant volume of water quality data collected by researchers and nongovernment organizations, larger scale geological interpretations published in segmented literature, multi-spectral satellite imagery datasets, and combined field reconnaissance to investigate areas of interest further and address pertinent data gaps. Improved understanding of geologic structure and lithology, complex aquifer recharge, and evapotranspiration processes supported identifying areas unsuitable for groundwater development and yielded recommendations for groundwater exploration and other solutions.

A high permeability zone and strong surface-groundwater connection was identified along the Gungu River. Data collected throughout the area of interest corroborated that significant freshwater recharge occurs in the alluvial aquifer, promoting an aquifer zone where freshwater and higher yields are likely. Exploratory drilling resulted in a very high-yielding freshwater well that supported the development of a piped water system serving several villages.

Abstract

This work is part of the AUVERWATCH project (AUVERgne WATer CHemistry), which aims to better characterise some Auvergne water bodies, specifically the alluvial hydrosystem of Allier River (France). Alluvial aquifers constitute worldwide a productive water resource, superficial and easily exploitable. In France, 45% of the groundwater use comes from these aquifers. The study site is a wellfield that withdraws 8.5 million m3 of water annually from an alluvial aquifer to produce domestic water for 80% of the local population. At the watershed scale, precipitations have decreased by -11.8 mm/y, air temperatures have increased by 0.06°C/y and the river flow has declined by 20.8 Mm3 /y on 2000 – 2020. In the summer period, at least 50% of the river flow is ensured by the Naussac dam (upstream catchment part), but the recent winter droughts have not allowed the dam to replenish. Thus, water stakeholders are concerned that the productivity of the wellfield could be soon compromised. Based on geological, geophysical, hydrochemical, and hydrodynamic surveys, a numerical model of the wellfield is being developed using MODFLOW. The calibration in natural flow regime is successful using a range of hydraulic conductivities going from 1×10-3 to 1×10-4 m/s (pilot points method), consistent with the pumping tests. Preliminary results show that the river entirely controls the groundwater levels at all observation points. The perspective is now to calibrate this model in a transient regime by integrating domestic water withdrawals to determine how low the river can go without affecting the wellfield productivity.