Conference Abstracts

Abstract

The demand on fresh water has increased to such an extend that supply cannot keep up with demand, especially in areas where desalination of seawater is not an option. There is a large gap between the water user, the water supplier and the capacity of the resource/s. The water user sees it as his/her right to be provided with clean water in sufficient volumes to sustain their most basic needs.At the same time people want higher levels of service, especially where sanitation is concerned. The recent droughts in Cape Town and in Port Elizabeth have put significant focus on groundwater and we've seen uncontrolled drilling for groundwater reaching new heights, which is a problem on its own. We can no longer afford not to bring the groundwater user into the water planning cycle, so that the users, on all levels of society, can be educated to understand that the quantity and quality of fresh water (ground -and surface water) is limited and dependent on recharge from rainfall, size of the catchment, topography and all that takes place on the surface. This education must be specific to a target audience and must take into account the existing knowledge and understanding of the user profile. As an example, a case study will be discussed where there are large groundwater users operating within the upper parts of a catchment, followed by municipal abstractions and private abstractions within the central parts of the same catchment. Four profiles of users are therefore present: (1) large-scale irrigation by farmers, (2) large-scale municipal abstractions, (3) private residents and (4) formal / informal settlements, with the latter probably competing for top pot in terms of water use, with the irrigation. They key deliverable of the presentation / paper will be to (1) make people aware of the problem/challenge, and (2) suggest ways to bridge gaps and get all users and service providers to work together to save water and to understand that there are limits to the quantities available.

Abstract

Groundwater is an important resource for multiple uses in South Africa. Hence, setting limits to its sustainable abstraction while assuring basic human needs is required. Due to prevalent data scarcity related to groundwater replenishment, which is the traditional basis for estimating groundwater availability, the present article presents a novel method for determining allocatable groundwater in quaternary catchments through information on streamflow. Using established methodologies for assessing baseflow, recession flow, and instream ecological flow requirement, the methodology develops a combined stepwise methodology to determine annual groundwater storage volume using linear reservoir theory, essentially linking low flows proportionally to upstream groundwater storages. The approach was trialled for twenty-one perennial and relatively undisturbed quaternary catchments with longterm and reliable streamflow records. Using the Desktop Reserve Model, maintenance low instream flow requirements necessary to meet present ecological state of the streams were determined, and baseflows in excess of these flows were converted into allocatable groundwater storages on an annual basis. Results show that groundwater development potential exists in nineteen of the catchments, with upper limits to allocatable groundwater volumes (including present uses) ranging from 0.02 to 2.60 Mm3/a over the catchments. With a secured availability of these volumes 75% of the years, variability between years is assumed to be manageable. A significant (R2 = 0.86) correlation between baseflow index and the drainage time scale for the catchments underscores the physical basis of the methodology and also enables the reduction of the procedure by one step, omitting recession flow analysis. The method serves as an important complementary tool for the assessment of the groundwater part of the Reserve and the Groundwater Resource Directed Measures in South Africa.

Abstract

With increasing pressure on Cape Town’s potable water supply, the responsibility of diversifying supply for small, medium and large volume water users has fallen to the user to ensure sustainable use of potable water, and utilising all feasible non-potable sources where available.

With estate and sectional title living becoming more common in South Africa, it is possible to develop holistic groundwater development models and strategies for the implementation of mini wellfields within these, in general, more densified living areas. This is well aligned with the Water Conservation and Water Demand Management Strategy of the City of Cape Town, where conjunctive use of groundwater for non- potable uses such as irrigation is implemented, as well as aligning itself with the current water restrictions within the Cape Metropole.

Unlike standard residential neighbourhoods, estate development allows for the implementation of well- managed abstraction and monitoring of groundwater levels, as well as the possibility of shared groundwater usage in situations where legislation allows. The installation of fewer higher yielding boreholes (versus individual wellpoints on each residential section) to supply water to all communal areas and private gardens, allows for targeted data collection, interpretation and reporting.

Implementation of shared water use from a single water use licence (likely issued to the legal entity of the body corporate) within sectional title property has its own complications, where licensed water use would generally be restricted to communal areas.

The multi-phase assessment, implementation and licensing of groundwater supply for a life-rights retirement estate is presented as a case study. This enabled the investigation into shared water usage for irrigation of communal areas, as well as gardens of individual dwellings, eliminating the installation of dozens of wellpoints on estate properties thus ensuring sustainable usage and continued monitoring of the groundwater.

Concurrent development of the groundwater infrastructure during the housing estates development brings its own challenges, and requires special consideration during early phases of the project, where infrastructure damage is commonplace on large construction sites. Holistic water conservation strategies were implemented, such as the construction of permeable pavements to increase the amount of recharge to the underlying aquifer storage below the estate instead of trying to store rainwater in the limited surface space.

Utilising installed borehole equipment, an Aquifer Stress Test (AST) was undertaken to determine the aquifer parameters, sustainable yield of the individual boreholes and the wellfield as a whole, as well as inter borehole interactions. An AST allows for real world scenario aquifer testing to prove sufficient groundwater availability.

Abstract

Environmental isotope techniques have been successfully applied in the field of hydrogeology over the last couple of decades and have proved useful for understanding groundwater systems. This paper describes a study of the environmental isotopes for Oxygen (18O) and Hydrogen (1H, 2H-Deutrium, 3H-Tritium) obtained from various points in and around the underground coal gasification (UCG) site in Majuba, South Africa. UCG is an alternative mining method, targeting deep coal seams that are regarded as uneconomical to mine. The process extracts the energy by gasifying the coal in-situ to produce a synthetic gas that can be used for various applications. The site consists of shallow, intermediate and deep aquifer systems at a depth of 70m, 180 and 300m respectively. The intermediate aquifer is further divided into the upper and lower aquifer systems.
Samples were taken from each aquifer system together with supplementary samples from the Witbankspruit and an on-site water storage dam. A total of 15 samples were submitted for isotope analyses. By investigating the various isotopic signatures from all the samples taken, it will be possible to determine if there are similar or contrasting isotopic compositions by deducing possible water source for each sample due to isotopic fractionation caused by physical, chemical and biological processes. This will also be supported by deducing the mean residence time (MRT) for each water source sampled based on the Tritium data as well as the chemistry data already available for different sources. The chemistry data established linkages between the upper and lower intermediate aquifers.{List only- not presented}
Key words: Environmental isotopes, UCG, Water source, Isotope fractionation

Abstract

Burning of coal for electricity production has resulted in vast amounts of ash being deposited in ash dumps. Rain water and ash water conditioning results in the wetting of ash dumps and if the water retention capacity is exceeded there is a possibility of leaching to soil and underlying aquifers. In this study two different coal ash are used to determine the water retention as excess amount of process water at power stations ash dumps can lead to impeding the desired water balance, which can be critical for maintain various plant processes. The nonlinear relationship between soil water content and matrix suction of a porous material under unsaturated conditions is described by the soil water characteristic curve (SWCC). The SWCC for a given material represents the water storage capability enabling the determination of varying matric suction such as prediction of important unsaturated hydraulic processes including soil permeability, shear strength, volume change with respect to the water content changes. This paper presents an alternative, cost effective and rapid method for measuring and subsequent estimating of the soil-water characteristics of any soil type. Several methods are available to obtain the measurements required for defining soil-water characteristics. However, obtaining the required measurements for a SWCC is generally difficult since there is no laboratory or field instrument, capable of measuring a typical complete plant available water suction range accurately. Due to high methodological effort and associated costs of other methods, a simplified evaporation method which was implemented in the HYPROP (Hydraulic Property analyzer, UMS, 2012) becomes a possible alternative. It relies on the evaporation method initially proposed Schindler (1980). A typical work range for a HYPROP system is 0 to 100 KPa as read out from the two high capacity tensiometers installed at different heights within a saturated sample column. For a dry coal ash dump to be optimally used as sinks, input water applications should be matched with evaporation rates and capillary storage. This will ensure the moisture storage of the ash dump is not exceeded and consequently avert leachate generation at the base of the ash dump. The field capacity of waste materials is of critical importance in determining the formation of leachate in landfills which in this case is the coal ash dump facility. It is the field capacity limit when exceeded which give rise to leachate generation consequently promoting a downward movement of generated leachate.he study found that it is possible to use the Hyprop together with an empirical based fitting model to define a complete SWCC along a dewatering path. The study found the Brooks-Corey model as the suitable representative of the Hyprop measured data, confirmed by AICc and RMSE analysis. The Brooks-Corey estimated retention function parameters within +/- 1% error. A mean value of 35.3% was determined as the water retention or field capacity value for Matimba Coal ash. If the ash dump is operated in excess of this value, chances of groundwater pollution are high.

Abstract

Carbon Capture and Storage (CCS) in deep saline aquifers is a viable option for Green House Gas (GHG) mitigation. However, industrial-scale scenarios may induce large-scale reservoir pressurization and displacement of native fluids. Especially in closed systems, the pressure buildup can quickly elevate beyond the reservoir fracture threshold and potentially fracture/ reactivate existing faults on the cap rock. This can create pathways, which could act as conduits for focused leakage of brine and/or CO2 up-dip and mobilization of trace elements into capture zones of freshwater wells. Careful pressure management can ensure the reservoir’s hydraulic integrity. This can theoretically be achieved through simulation with appropriate mathematical tools. This research aims to quantify pressure buildup at a CO2 injection well by applying fractional derivatives to the pressure diffusivity Differential Equation (PDE). A numerical solution has been developed to (1) predict and assess the consequence of pressure buildup within the storage formation on groundwater flow in shallow aquifers and (2) assess the impact of pressure-mobilized contaminants (CO2 , brine and/or trace elements) on the quality of usable groundwater, if there is a leakage. The efficiency of each derivative is shown to depend on the type of reservoir heterogeneity. The Caputo derivative captured the long tail dependence characteristic of fracture flow, while the ABC derivative was able to model the cross-over from matric into the fracture flow. The numerical tools presented here are useful for successful risk assessments during geo-sequestration in basins with freshwater aquifers.

Abstract

Aquifer Thermal Energy Storage (ATES) is increasingly utilised to optimise the efficiency of Ground Source Heat Pump (GSHP) systems. However, the criteria for selecting ATES over Unidirectional GSHP is not well-defined. Inappropriate selection of AETS can adversely impact the long-term viability and the GSHP system itself, as well as regional hydraulic and thermal sustainability due to adverse groundwater levels and temperature change. This is a concern in urban aquifers, where GSHP systems are increasingly common. There is a perception that ATES is always the most efficient; however, there is no clear definition of efficiency and how it can be readily assessed at the GSHP design stage. It is proposed and demonstrated herein that GSHP efficiency can be assessed by modelling borehole pumping in lieu of complex Coefficient of Performance calculations for the whole GSHP system. Borehole pumping is a more readily definable modelling outcome for comparing options at an individual site but is also a suitable proxy for comparing efficiency at different sites when given as a flow per unit rate of pumping. Operational efficiencies for ATES versus Unidirectional systems are presented using the pumping rate criteria for modelled scenarios. Here, three model inputs are varied: 1) the balance of heating and cooling, 2) the configuration of a single borehole pair across a hydraulic gradient and 3) the hydraulic gradient itself. These were assessed using coupled groundwater flow and heat transport modelling in Feflow to refine the Goldilocks Zone, the perfect balance, for these variables.

Abstract

The abstract presents a 2D modelling approach alternative to a 3D variable saturated groundwater model of solute or heat transport at the regional scale. We use FEFLOW to represent processes in the saturated zone, coupled with various models describing the unsaturated zone. The choice of the latter depends on modelling needs, i.e. simulation of the movement of seepage water and nitrate fate with respect to crop rotation patterns and dynamic characteristics of heat gradients, respectively. The flexibility of coupling specialized models of different subsurface compartments provides the opportunity to investigate the effects of land use changes on groundwater characteristics, considering the relevant drivers in sufficient detail, which is important in regions with intensive anthropogenic activities. The coupling can be operated either with (direct coupling) or without (sequential coupling) including the feedback between the saturated and the unsaturated zones depending on the depth of the groundwater table below the surface. Thus, the approach allows for reasonable computational times. The Westliches Leibnitzer Feld aquifer in Austria (43 km²; Klammler et al., 2013; Rock and Kupfersberger, 2018) will be presented as an example highlighting the needed input data, the modelling workflow and the validation against measurements.

Abstract

The National Park Plitvice Lakes (NPPL) in the Republic of Croatia was declared in 1949 due to its exceptional natural beauty. However, in addition to its attraction, the NPPL also encompasses an area of significant karstic water resources in the Dinaric karst region, on the border between the Black Sea and the Adriatic Sea catchment. In some parts, groundwater connections to the Klokot Spring and Una River in Bosnia and Herzegovina have been assumed by hydrogeological research and proven by tracing tests, which confirm transboundary aquifer. Assessing transboundary aquifer systems already presents challenges in managing this area, considering not only the well-defined physical catchment. Therefore, comprehensive protection is necessary, which must reconcile people’s aspirations for spatial development with the sustainability of natural systems. Protecting karstic water resources can be achieved through separate analyses of the natural vulnerability of surface and groundwater and their integration into a comprehensive protection system. Protection should be layered through three levels: (1) protecting the area from the impact of the upstream catchment, (2) protecting surface water in the catchment that is most affected by anthropogenic influences, and (3) protecting the surrounding area from the impact of the NPPL, which with numerous visitors every year and tourist facilities, also represents significant pressure on downstream catchments. The ultimate goal is a scientifically based proposal for sustainable development of the protected area, in line with the needs of protection and spatial use, and based on an assessment of the overall risk to water resources.

Abstract

The geochemical study of deep aquitard water in the southern Golan-Heights (GH), Israel, reveals the complex paleo-hydrological history affected by the intensive tectonic activity of the Dead Sea Rift (DSR). The sampled water collected from new research boreholes exhibits relatively high salinities (2,000-10,000 mg Cl/L), low Na/Cl ((HCO3 +SO4 )). δ18OV-SMOW and δDV-SMOW values are relatively depleted (~-7‰ and ~-42‰, respectively), while 87Sr/86Sr ratios are enriched compared to the host rocks. Lagoonary brines with similar characteristics (excluding the water isotopic compositions) are known to exist along the DSR. These brines formed 10-5 Ma ago from seawater that transgressed into the DSR and subsequently underwent evaporation, mineral precipitation and water-rock interactions. These hypersaline brines intruded into the rocks surrounding the DSR and based on the current study, also extended as far as the southern GH. Further, following their subsurface intrusion into the GH, the brines have been gradually diluted by isotopically depleted freshwater, leaving only traces of brines nowadays. The depleted isotopic composition suggests that the groundwater system is recharged at high elevations in the north. It is also shown that variable hydraulic conductivities in different formations controlled the dilution rates and subsequently the preservation of the entrapped brines. The paleo-hydrological reconstruction presented here shows that the flow direction has reversed over time. Brines that initially intruded from the rift have since been gradually flushed back to the rift by younger fresh groundwater.

Abstract

Groundwater is an essential source of water worldwide. The increased reliance on groundwater has caused the mining of many aquifers, a situation compounded by climate change, rising surface-air temperature, declining precipitation, and reduced groundwater recharge in many regions. The global annual intensity of groundwater use rose from 128 to 155 m3 per capita between 1950 (when the world population was 2.5 billion people) and 2021 (when the population was 7.9 billion people) and is herein projected to rise to 178 m3 per capita by 2050 as the world’s population is projected to increase (to 9.7 billion people by 2050) throughout the rest of the 21st century and beyond. This study projects a global annual groundwater depletion of 1,008 km3 by 2050, representing a 256% rise from the estimated 2010 depletion. This projection is most likely a lower bound of the actual groundwater depletion that would be realized considering environmental flows, historical trends of global economic growth, and climate-change impacts, thus being a harbinger of rising environmental degradation (e.g., land subsidence, seawater intrusion, streamflow reduction, aridification). Measures to achieve groundwater sustainability are herein identified.

Abstract

One-third of the world faces water insecurity, and freshwater resources in coastal regions are under enormous stress due to population growth, pollution, climate change and political conflicts. Meanwhile, several aquifers in coastal regions extending offshore remain unexplored. Interdisciplinary researchers from 33 countries joined their effort to understand better if and how offshore freshened groundwater (OFG) can be used as a source of potable water. This scientific network intends to 1) estimate where OFG is present and in which volumes, 2) delineate the most appropriate approaches to characterise it, and 3) investigate the legal implications of sustainable exploitation of the offshore extension of transboundary aquifers. Besides identifying the environmental impact of OFG pumping, the network will review existing policies for onshore aquifers to outline recommendations for policies, action plans, protocols and legislation for OFG exploitation at the local to international levels. Experienced and early-career scientists and stakeholders from diverse disciplines carry out these activities. The Action leads activities to foster cross-disciplinary and intersectoral collaboration and provides high-quality training and funded scientific exchange missions to develop a pool of experts to address future scientific, societal, and legal challenges related to OFG. This interaction will foster new ideas and concepts that will lead to OFG characterisation and utilisation breakthroughs, translate into future market applications, and deliver recommendations to support effective water resource management. The first exchange mission explored the Gela platform carbonate reservoir (Sicily), built a preliminary 3D geometrical model, and identified the location of freshened groundwater

Abstract

Environmental isotope and hydrochemical analyses were employed to improve existing understanding of groundwater flow dynamics in the defunct mine for assessing the source of water at a pumping shaft located near Stilfontein Town, Northwest Province, South Africa. Currently pumping is done using the shaft at an average rate of 37,000 m3 /day to prevent flooding of downstream mines. The current findings point out that the source of water at the shaft comes from a much narrow area than previously reported and that the contribution of seepage water from a nearby return water dam is significant enough to compensate groundwater flow from the upper dolomite aquifer and limit northerly expansion of the cone-of-depression. Hydrochemical data reveals that shaft-water at deeper levels (950 m bgl) exhibit evidence of mine seepage originating from the nearby tailings dam. The isotope data also show that up to 45% of water is recycled between shaft water and the surface water. Tritium values of the shaft-water samples are above 4 TU suggesting recent recharge is taking place at deeper levels through open fractures and mine underground haulages. The information from the hydrochemical and environmental isotope data was used to improve an earlier understanding that the source of water as coming dominantly from dolomite aquifer. Finally, the results highlight the relevance of coupling various methods to check the result of numerical modelling, and indeed the centralized pumping is key to controlling subsurface water flooding in downstream mines, a successful implementation of regional mine water management.

Abstract

PMWIN5.3 has been one of the most commonly used software for groundwater modeling because of its free source and the adoption of popular core program MODFLOW. However, the fixed formats required for data input and lack of GIS data support have posted big challenges for groundwater modelers who are dealing with large areas with complicated hydrogeological conditions. In South Africa, most geological and hydrogeological data have been captured and stored in GIS format during various national research projects such as WR2005, NGA and etc. Therefore, a proper linkage between PMWIN and ArcGIS is expected to do the preprocessing for modeling in PMWIN. Visual Basic for Application (VBA) embedded in ArcGIS 9.3 was used to develop the linkage. Based on the conceptualization of the study area, the model dimension, discretization and many value setting processes can be easily carried out in ArcGIS other than directly in PMWIN. Then the grid specification file and other input files can be exported as the PMWIN-compatible files. The functions of move, rotation, refinement, sub-model, deleting and inserting row(s) or column(s) of the model have also been developed to avoid the inconvenience aroused from model modification. The linkage can be used with a higher version of PMWIN or ArcGIS. It has been applied to several gold fields in the Witwatersrand gold basin to simulate the groundwater flow and mass transportation for various conditions and scenarios. One of the applications will be presented in this paper. It has been proved that the linkage is efficient and easy to use. {List only- not presented}

Abstract

PMWIN5.3 has been one of the most commonly used software for groundwater modelling because of its free source and the adoption of the popular core program MODFLOW. However, the fixed formats required for data input and lack of GIS data support have posted big challenges for groundwater modellers who are dealing with large areas with complicated hydrogeological conditions. In South Africa, most geological and hydrogeological data have been captured and stored in GIS format during various national research projects such as WR2005, NGA, etc. Therefore, a proper linkage between PMWIN and ArcGIS is expected to do the pre-processing for modelling in PMWIN. Visual Basic for Application (VBA) embedded in ArcGIS 9.3 was used to develop the linkage. Based on the conceptualisation of the study area, the model dimension, discretisation and many value-setting processes can be easily carried out in ArcGIS other than directly in PMWIN. Then the grid specification file and other input files can be exported as the PMWIN-compatible files. The functions on the modification of model geometrics have also been integrated with the toolbar. The linkage can be used with a higher version of PMWIN or ArcGIS. It has been applied to several gold fields in the Witwatersrand gold basin to simulate the groundwater flow and mass transportation for various conditions and scenarios. One of the applications will be presented in this paper. It has been proven that the linkage is efficient and easy to use.

Abstract

Water scarcity has driven many countries in arid regions, such as Oman, to desalinate seawater for freshwater supply. Episodic problems with seawater quality (e.g., harmful algae), extreme weather events that affect energy supply and hence the desalination process have nurtured the urgent need to store desalinated seawater (DSW) in the aquifers for use during emergency and peak demand time. Aquifer Storage and Recovery (ASR) using injection wells is a possible strategic option for Oman Water and Wastewater Services Company (OWWSC) to augment aquifer storage using excess desalinated water during low demand times. ASR strategically serves as a water supply backup to optimize production capacities against seasonal demand patterns. The technical-economic feasibility of implementing ASR schemes was investigated in Jaalan, Oman, using hydrogeological and geophysical field measurements, groundwater flow and hydraulic modelling, and economic analysis. Analysis of modelled scenarios results revealed that the Jaalan aquifer is suitable for storing and recovering about 4,000 m3 /hr in 2045. Various well field designs have been tested and optimized numerically using MODFLOW 6, showing that with 160 dual-purpose wells, 7.9 Mm3 can be injected and abstracted within the constraints defined for a robust and sustainable ASR system. Simulations with the density-dependent flow model (MF6 BUY) show that the injected volume can be fully recovered considering the drinking water quality standard. Other sites were also studied. ASR capacity was found to be site-specific, and the groundwater developments near the ASR site governed its feasibility

Abstract

The 'maintainable aquifer yield' can be defined as a yield that can be maintained indefinitely without mining an aquifer. It is a yield that can be met by a combination of reduced discharge, induced recharge and reduced storage, and results in a new dynamic equilibrium of an aquifer system. It does not directly or solely depend on natural recharge rates. Whether long-term abstraction of the 'maintainable aquifer yield' can be considered sustainable groundwater use should be based on a socio-economic-environmental decision, by relevant stakeholders and authorities, over the conditions at this new dynamic equilibrium.
This description of aquifer yields is well established scientifically and referred to as the Capture Principle, and the link to groundwater use sustainability is also well established. However, implementation of the Capture Principle remains incomplete. Water balance type calculations persist, in which sustainability is linked directly to some portion of recharge, and aquifers with high use compared to recharge are considered stressed or over-allocated. Application of the water balance type approach to sustainability may lead to groundwater being underutilised.
Implementation of the capture principle is hindered because the approach is intertwined with adaptive management: not all information can be known upfront, the future dynamic equilibrium must be estimated, and management decisions updated as more information is available. This is awkward to regulate.
This paper presents a Decision Framework designed to support implementation of the capture principle in groundwater management. The Decision framework combines a collection of various measures. At its centre, it provides an accessible description of the theory underlying the capture principle, and describes the ideal approach for the development operating rules based on a capture principle groundwater assessment. Sustainability indicators are incorporated to guide a groundwater user through the necessary cycles of adaptive management in updating initial estimations of the future dynamic equilibrium. Furthermore, the capture principle approach to sustainable groundwater use requires a socio-economic-environmental decision to be taken by wide relevant stakeholders, and recommendations for a hydrogeologists' contribution to this decision are also provided. Applying the decision framework in several settings highlights that aquifer assessment often lags far behind infrastructure development, and that abstraction often proceeds without an estimation of future impacts, and without qualification of the source of abstracted water, confirming the need for enhanced implementation of the capture principle.

Abstract

Large parts of the City of Cape Town overlie a significant aquifer. Urban development proceeded without acknowledgement of the importance of this aquifer causing contamination in some areas and a lack of protection of recharge areas. Use of the aquifer for private domestic and industrial purposes has also largely continued unchecked. With the recent drought in Cape Town use of the aquifer dramatically increased, as did the City's understanding that the aquifer is a strategic resource to them. This paper presents the pros and cons of decentralised groundwater use. The current status quo of decentralised groundwater use in Cape Town, from basements to garden irrigation boreholes and to large-scale industrial users is presented, along with an assessment of the impact of the drought on groundwater availability. Recommendations are provided for how best to manage the challenges of decentralised groundwater use.

Abstract

The benefits of numerical groundwater modelling in resource management and scenario-testing are well known; it provides quantitative predictions of aquifer responses to stresses not yet experienced, albeit with uncertainties. Modelling is hence a widely used tool in Environmental Impact Assessment (EIA), in which prior to project commencing, the likely impacts must be assessed quantitatively to determine their significance. Based on these results mitigation measures can be proposed such that the residual impact is deemed acceptable.

At the stage of an EIA there is often very little data on which to base a model. Generally one is required to predict timescales in the order of hundreds of years with only very short-term time series data, and required to predict the response to stresses far beyond those used in the calibration. The very nature of the problems posed at EIA stage therefore render the accuracy of most modelling conducted at EIA phase severely limited. Recognising this, an appropriate model for the problems at hand can still be constructed and provide useful results.

The model results need to  be seen  as  the first phase  in  an  adaptive management cycle, rather than  a standalone prediction which a mine can use for future operation. To strengthen the resulting predictions, the cycle in which monitoring results are used to update the model, and thus update predictions and update future requirements for monitoring repeating the cycle, needs to be entrenched into the mine phases by ensuring the recommendation as detailed in the Environmental Management Plan. Thus, what started as a useful demonstrative tool, but with large uncertainties, becomes an accurate quantitative prediction tool for operation, closure and post-closure planning.

This paper outlines a case study of a proposed open-pit zinc mine on an inselberg in South Africa, within which these themes are explored. Limited initial data was sufficient to build a useful yet simplified model. The purpose and known limitations of the model approach dictated the spatial discretisation of the model, its dimensions, and the geometry of the aquifer units, yet the simplification of the aquifer systems into the numerical model was only feasible once the complexity of the aquifer systems had been recognised, else over- or unjustified simplification is a risk.

The paper concludes with a framework for integrating the adaptive groundwater management into the mine life cycle through applying appropriate models at each phase, which would strengthen the use of groundwater models in mining.

Abstract

POSTER Investigations have shown that receiving water bodies, which mainly include rivers, streams and the more complicated geohydrological system, are part of the primary end receivers of harmful contaminants from identified coal mining waste bodies. Some of these potential dangers include acid mine drainage (AMD) and sulphur mine drainage (SMD) which have dire effects on the surroundings. The need for a cost effective methodology to assess site hydrology and geohydrology, to understand the associated legal responsibility of contaminated streams and aquifers, is recognised. In the compilation of this paper the unique nature of South African legislation and policies are implemented in the development of a logical approach towards mine closure specifically in the field of groundwater assessments. Furthermore, this paper explores co-disposal of discard and slurry material and the environmental impact of co-disposed wastes is assessed. The unique geological attributes of the KZN coal fields and the geochemical research results found indicates that on its own discard has great potential to produce long term SMD and that slurry has lower SMD potential. Co-disposed results are promising and buffering against long term chemical changes are noted. The final product of this approach constantly considered site hydrogeology, related impacts, risks and liabilities. This gave more clarity on aspects related to the principles followed to identify objectives for sustainable mine closure and to adopted a philosophy of mine closure as a hydrogeological concept. Overview of methods that could be used for mitigation of polluted aquifers and a brief site specific application is discussed with the aim to achieve the key deliverable which focuses on methods to scientifically assess sources, pathways and receivers. Ultimately this process has led to the development of a logical approach towards mine closure for groundwater assessment and remediation in the typical anthracite mine environment.

Abstract

The main purpose of this paper is to present a case study where soil moisture and rainfall data were evaluated for engineered tree plantations, to understand the potential impact on vertical groundwater recharge. Soil moisture for probes within the tree plantation root zones and reference sites within the same soil types were evaluated, in context to site rainfall patterns. Water transfer from shallow to deeper soil zones for a dataset of 2 years are presented. Observations in terms of water movement in the root zone are made. A water balance is presented in the effort to conceptualise the impact on water transfer through the upper vadose zone and to quantify the significance in terms of potential vertical groundwater recharge reduction.

Abstract

The main purpose of this paper is to present a case study where a water balance concept was applied to describe the expected groundwater safe yield on a sub-catchment scale. The balance considers effective recharge based on local hydrogeology and land cover types, basic human needs, groundwater contribution to baseflow, existing abstraction and evaporation. Data is derived from public datasets, including the WRC 90 Water Resources of South Africa 2012 Study, 2013-2014 South African (SA) National Land Cover and Groundwater Resource Assessment Ver. 2 (GRAII) datasets. The result is an attempt to guide a new groundwater user regarding the volume of groundwater that can be abstracted sustainably over the long-term.

Abstract

Since the first decant of acid mine drainage in the West Rand in 2002, a great deal of effort has gone into researching the challenges which it poses there and in the adjacent Central Rand and East Rand Gold Fields. Short-term interventions have been implemented to maintain water at conservatively-determined safe levels and remove the worst contaminants from the water pumped from the mined. A feasibility study, looking at the long-term options has proposed treatment of water to a much higher standard, identifying a number of potential end-users of the treated water and highlighted the extremely high costs involved in responsible management. During the second half of 2010, a team of experts was convened to assess problems related to acid mine drainage in the Witwatersrand and propose solutions. A number of recommendations were made and the most urgent - the need for a short-term intervention to bring things under control and the the feasibility study for long-term management of the problems were undertaken. Nevertheless, despite the intense focus on the problem, a number of questions have remained unanswered. Throughout the period of min flooding, no detailed systematic monitoring of surface water flow has been undertaken, preventing the detailed apportionment of pollution between underground and surface sources. Ingress control measures have been proposed, but funding mechanisms, regulatory hurdles and challenges relating to long-term management have not all been comprehensively addressed. On a more positive note, the installation and operation of pumps to control the water level in the Western and Central Basins will start to provide valuable data regarding the response of the flooded mine workings to pumping, assisting in the characterisation of the hydraulic properties and behaviour of the large voids. This will facilitate the optimisation of pumping strategies and the refinement of environmental critical levels and assist in the development of more sustainable management options.

Abstract

In order to obtain a better understanding of a groundwater system, it is very important to understand the recharge mechanisms of such a system. Several intensive investigations have been done, documenting the different methodologies to derive recharge. Most of these studies have been centred on the detailed analysis and description of isotopes, which are either a characteristic of the water, the rock, or both. The isotopes of strontium, in particular the isotopic 87Sr/86Sr ratio, is one of such methodologies applied to drive the sources of recharge. The Oshivelo management area is part of the greater Owambo Basin, with no major rivers flowing through the project area, while the Omuramba Owambo, which crosses the area from east to west, bears water only rarely. This rural area therefore heavily relies on groundwater resources. Towards the end of the 20th century, through exploratory drillings an artesian aquifer in the southern part of the Owambo basin was discovered. Several investigation and water supply boreholes have been drilled, with the major findings summarised: - In the late 1990s DWA (DWA, 1999) drilled 12 exploration boreholes and six observation boreholes, showing high yields ranging between 40 and 200 m?/h. One of the boreholes yielded saline water, classified under the Oshivelo Artesian Aquifer and it was recognized that there may be a risk of saltwater intrusion when beginning to exploit the aquifer. It was assumed that the aquifer receives local recharge from the Etosha Limestone Member aquifer in the order of 3.75 MCM/a and additional unquantified recharge from the Otavi Dolomite Aquifer. - In the early 2000s KfW funded a study of the Tsumeb area, including the development of a groundwater flow model according to which an amount of 31 MCM/a would be leaving the Tsumeb area at the northern model boundary, i.e. flow into the Oshivelo Region. - The DWA plans to supply the north-western Oshikoto Region with water from the KOV2 aquifer via a pipeline in order to overcome water shortages there and to become more independent from surface water supplies from Angola. Though, through the groundwater model, a first estimate of groundwater resources availability has been established, the source of recharge is yet to be determined, including the flow mechanisms. Without, this vital piece of information, a valuable groundwater resource may be eventually utilized unsustainably. This presentation will focus primarily on the determination of groundwater recharge mechanisms, which would produce additional input to refine the existing groundwater flow model, concentrating on the Oshivelo Aquifer system. Upon the successful completion of this investigation, the next step would then be to evaluate the groundwater flow model and use it for a proper groundwater management plan. {List only- not presented}

Abstract

Groundwater is vulnerable to contamination from various anthropogenic sources. The degree of groundwater vulnerability can be assessed using various methods, which are grouped into three major categories: index-and-overlay methods, process-based computer simulations and statistical analyses. This study attempts to produce a groundwater vulnerability map of the eThekwini Metropolitan District Municipality using the index-and-overlay method of DRASTIC in a GIS environment for the first time. The advantage of this method is that it provides relatively simple algorithms or decision trees to integrate large amount of spatial information into maps of simple vulnerability class es and indices. The main objective of the study is to identify areas of high groundwater contamination potential based on hydrogeological conditions so that management interventions are undertaken timely. DRASTIC is a groundwater vulnerability assessment method based on the intrinsic property of groundwater systems to human or natural impacts. It uses seven hydrogeological parameters, namely, Depth to groundwater, net Recharge, Aquifer media, Soil media, Topography, Impact of the vadose zone and hydraulic Conductivity of the aquifer. These DRASTIC parameters characterize the hydrological setting and are known to control the vulnerability of aquifers to surface derived pollutants. Various studies show that depth to groundwater and impact to vadose zone impose larger impact on aquifer vulnerability followed by recharge, topography and soil media. The application of DRASTIC to the greater Durban area resulted in vulnerability index values in the range from 71 to 168. Based on these index values, greater Durban area is classified into zones of low, moderate and high vulnerability of groundwater to pollution. The low vulnerability areas (Drastic Index. DI: 71-114) are located in the northern region around Magangeni which are underlain by the intergranular and fractured aquifer due to essentially deep groundwater table (>25 m), vadose zone sediments, low hydraulic conductivity and recharge rate. The moderately vulnerable areas (DI: 114-127) cover more than 50% of the study area that is underlain by fractured and Intergranular, and fractured aquifers. The moderate vulnerability areas are located in the western region (Hammarsdale and Kloof), northern region (Mount Edgecombe and Tongaat) and southern region (Amanzimtoti). The moderate vulnerability pattern is mainly due to variation in the hydraulic conductivity of the aquifer and the vadose zone and less by the recharge and the depth to groundwater. The region around central Durban, the Bluff area, Yellowwood Park and areas along the coast that are underlain by intergranular aquifer are mapped as "hotspots" characterized by high vulnerability to groundwater pollution (DI: 127-168) and needs immediate management intervention.

Abstract

The way in which groundwater is utilized and managed in South Africa is currently being reconsidered, and injection wells offer numerous possibilities for the storage, disposal and abstraction of the groundwater resource for municipalities, rural communities, mining, oil and gas, and a multitude of other industries. This presentation is about the North Lee County Reverse Osmosis Water Treatment Plant Injection Deep Injection Well project in southwest Florida in the United States. Water is plentiful in Florida, but it is not drinking water quality when it comes out of the ground. As such, treating water from wells is an important part of water supply in the coastal regions of the state. One form of treatment is reverse osmosis (RO), which generates a brine concentrate waste. The concentrate must then be disposed of, and a preferred method of disposal is an injection well because the disposal is not visible to the general public. The injection well project was associated with the construction of a large water treatment plant. The emphasis of this presentation is on the drilling and technical work in the field for this injection well, and to illustrate the rigorous requirements of drilling, constructing and testing a Class I injection well. Class I injection wells are permitted by the United States Environmental Protection Agency (US EPA) for injecting hazardous waste, industrial non-hazardous liquid, and/or municipal wastewater beneath the lowermost Underground Source of Drinking Water (USDW). Aquifer storage and recovery (ASR) wells are permitted as Class V injection wells by the US EPA. The permitting of an injection well is rigorous and requires state and federal approval before, during and after the field portion of the project. {List only- not presented}

Abstract

Noble gases are used in this study to investigate the recharge thermometry and apparent groundwater residence time of the aquifers on the eastern slope of the Wasatch Mountains in the Snyderville Basin of Summit County, Utah. Recharge to and residence time for the basin aquifer in the Salt Lake Valley, Utah, from the western slope of the Wasatch Mountain range by 'mountain-block recharge' (MBR), is a significant source of subsurface flow based on noble gas and tritium (3H) data. The Snyderville Basin recharge thermometry from 15 wells and 2 springs indicates recharge temperatures fall within the temperature "lapse space" defined by the recharge thermometry determined in the study of MBR for the Salt Lake Valley and the mean annual lapse rate for the area. Groundwater residence times for the Snyderville Basin were obtained using tritium and helium-3 (3He). The initial 3H concentrations calculated for the samples were evaluated relative to the 3H levels in the early 1950s (pre-bomb) to categorize the waters as: (1) dominantly pre-bomb; (2) dominantly modern; or (3) a mixture of pre-bomb and modern. Apparent ages range from almost 6 years to more than 50 years. Terrigenic helium-4 (4He) is also used as a groundwater dating tool with the relationship between terrigenic 4He in Snyderville Basin aquifers and age based on the apparent 3H/3He ages of samples containing water from only one distinct time period. The 4He is then used to calculate groundwater residence times for samples that are too old to be dated using the 3H/3He method. The mean groundwater residence times calculated with both methods indicate the water yielded by wells and springs in the Snyderville Basin generally ranges from 6 to more than 50 years. In addition, the calculated terrigenic 4He age for the pre-bomb component of many samples was found to exceed 100 years. While terrigenic 4He residence times are not as definitive as those calculated with the 3H/3He method, or chlorofluorocarbons (CFCs), age dating with terrigenic 4He allows initial estimates to be made for groundwater residence times in the Snyderville Basin, and is an important tool for establishing groundwater residence times greater than 50 years. Historic water levels from production wells indicate a declining water table. This trend in conjunction with precipitation data for the area illustrates the decline in the water levels to be a function of pumping from the aquifers. Groundwater residence times in the Snyderville Basin and declining water levels support the need for a groundwater management program in the Snyderville Basin to effectively sustain the use of groundwater resources based on groundwater age. {List only- not presented}

Abstract

Studies have shown that the use of natural water (drinking and bathing) with high level of 222Rn concentration may contribute to negative health effect in human beings. Thermal springs located in Limpopo province were sampled for the determination of 222Rn concentration by gamma ray spectrometry. The spring water has been used for domestic purposes: drinking and bathing, and for recreation bathing mainly. 19 samples were collected between thermal springs emanation points and swimming facilities (out and in doors). Radon-222 concentration found in these water ranges from 0.2 to 624 Bq/l. These results indicate that 7 thermal springs may represent increasing risk on bathing or inhalation of radon gas, leading to an increased risk of healthy.

Abstract

The hydrochemical, water stable isotopes of groundwater have been determined around Evander Goldfields Mine in Mpumalanga. Based on the stratigraphy of the study area four major aquifer systems can be identified namely Karoo Supergroup, Transvaal Supergroup, Ventersdorp Supergroup and Witwatersrand Supergroup. Hydrochemical and isotope in groundwater were assessed for Karoo and Witwatersrand Supergroup aquifer systems. The results show that in Karoo, groundwater chemistry evolve in two ways: the shallower recently recharged groundwater depicts Ca-Mg-HCO3 water type and the relatively deeper circulation and older governed by ionic exchange present Na-HCO3 water type. In the study area boreholes around tailing facilities constructed to monitor groundwater in the immediate vicinity of these structures show Na-Cl and Ca-Mg-Cl, and this is highly mineralized groundwater. Water samples collected underground mine workings between 1500 and 2080 mbgl in Wtwatersrand Supergroup aquifer system present Na-Cl water type. All groundwater samples analysed for isotopes ?18O and ?2H plot on and/or close to the Global Meteoric Water and Pretoria Meteoric Water Lines. However, groundwater from the deeper part of the underground workings in the Evander mine plot shifting toward negative values of ?18O in relation to the rest of the groundwater in this study. This fraction of groundwater may originate from precipitation isotopically different from the present day rainfall as suggested by deuterium excess values which are above 21.75?. However, the probability that the shifting of ?18O signature may result from groundwater exchange with CO2 gas has to be considered. Hence, analysis of ?18O and ?13C in groundwater CO2 gas has to be performed in order to clarify the hydrochemical processes evolving groundwater in the study area.

Abstract

Year-round water security is at risk as socio-economic developments lead to increasing water demands, while climate change affects water availability through higher-intensity rainfall and prolonged periods of drought. Coastal zones and deltas with often high population densities experience additional risks of salinisation and land subsidence. These developments ask for creative solutions to secure sustainable and year-round access to fresh water. The subsurface provides storage capacity to actively infiltrate freshwater, bridging the time-gap between demand and supply. Combining infiltration with extraction and desalination of brackish water prevents the salinisation of aquifers whilst providing an additional water source. We call this COASTAR. A Dutch research consortium with partners like water companies and water boards develops COASTAR. Among COASTAR results are suitability maps for Aquifer Storage and Recovery (ASR) and Brackish Water Extraction (BWE) in the coastal zone of the Netherlands. The maps are based on geohydrological factors. A quick-scan analysis was also performed to quantify the nation-wide potential extractable ASR and BWE volumes. COASTAR develops case study models and local scale pilots on ASR and BWE. For two water supply regions, an analysis has been made to geographically match development in water demand with suitability for ASR and BWE as a step in the search for strategic locations to develop ASR and BWE. The suitability maps provide guidance for initiatives’ development and practical experiences from pilot projects; this provides important information for further upscaling of COASTAR approaches.

Abstract

Due to technical, social, and economic limitations, integrated groundwater management presents a significant challenge in developing countries. The significance of this issue becomes even more pronounced in groundwater management, as this resource is often overlooked and undervalued by decision-makers due to its status as a “hidden resource,” despite the fact that it provides multiple ecosystem services. This study aims to establish the technical hydrogeological foundation in rural basins of central Bolivia through alternative, simplified, and cost-effective methods and tools. The study includes applying geophysical techniques, such as Electrical Resistivity Tomography, to determine the conceptual hydrogeological model of a micro-basin. In addition, a soil water balance approach was applied, characterizing 24 biophysical variables to identify groundwater recharge zones, while global circulation models provided a substitute for unreliable meteorological data. Furthermore, a participatory model was developed to identify recharge areas in upper basin areas within the framework of developing a municipal policy for their protection. The participatory model included local knowledge in all stages of methodology development, considering the characteristics of the local plant communities and the spatial distribution of local rainfall. The research findings have already contributed to resolving socio-environmental conflicts in Bolivia and establishing a foundation for effective water governance by empowering local rural communities. This study has demonstrated the feasibility of using alternative, simplified, and low-cost methods and tools to establish the technical hydrogeological basis, which can inform public policies to promote sustainable groundwater management in developing countries.

Abstract

Integrated geophysical methods can be useful tools in mapping the subsurface characteristics likely to control groundwater occurrence and hence are useful in identifying potential drill targets in different aquifer formations in Southern Africa. This study applied hydrogeophysical methods (natural, electrical, and electromagnetic) to identify potential groundwater-bearing targets within the Kalahari sand aquifers in Namibia and the crystalline basement aquifer system in Namibia and South Africa. The results suggest that hydrogeophysical assessments in Kalahari sandstone aquifers could clearly show that the system exhibits a well-defined layered aquifer formation likely recharged from surface water. On the other hand, crystalline basement formations could be combined with geological observations and used to identify groundwater controls like lineaments and depths to fractured zones. The magnetic method, horizontal and vertical frequency domain electromagnetic geophysical methods presented herein managed to delineate the main dykes and lineament features associated with groundwater occurrence in typical crystalline basement aquifers, while the natural magneto telluric investigations managed to delineate the deep and shallow aquifer formation in Kalahari sandstone aquifer formation. The study also advocates for integrating geophysical methods with local and regional geology for groundwater evaluation to provide a more detailed approach to resource assessment in some of the vulnerable aquifer systems in Southern Africa. Results from this study are useful for technical groundwater management and promoting the utilization of groundwater as a climate-resilient strategy in Southern Africa.

Abstract

The alluvial aquifer in the Varaždin region has a long-standing problem with high groundwater nitrate concentrations, mainly from agricultural activities. Since groundwater is used in public water supply networks, it is important to ensure its sustainable use. The aquifer is also used to exploit gravel and sand, and the increased demand for this valuable construction material causes the excavation of gravel pit lakes, making groundwater more vulnerable. Although engineered processes can remove nitrate from groundwater, natural attenuation processes should be investigated to understand the nitrogen behaviour and additional mechanisms for groundwater remediation. Previous research has shown nitrate is a conservative contaminant in the critical zone. Aerobic conditions within an aquifer system prevent significant denitrification. Thus, nitrification is the main process controlling nitrogen dynamics in groundwater. Since groundwater and gravel pit lakes are hydraulically connected, and natural nitrate attenuation exists in these lakes, an additional mechanism for groundwater remediation is possible. This work used isotope hydrochemistry and groundwater modelling to investigate gravel pit lakes as possible sites to reduce nitrate concentration in groundwater. Based on the isotopic composition of groundwater and nitrate concentrations, water balance and solute mass balance were calculated, which made it possible to estimate the nitrate attenuation rate in gravel pit lakes. The gained retardation factor was applied to the groundwater flow and nitrate transport model through several scenarios to evaluate the contribution of gravel pit lakes in reducing the groundwater nitrate concentrations

Abstract

Introduction: Verlorenvlei catchment in the renowned potato Sandveld area is shared by three main towns where agriculture is a primary economic activity. This semi-arid catchment, receives low winter rainfall, but has a dynamic groundwater system providing almost all water services in the catchment and sustaining the acclaimed Verlorenvlei RAMSAR site. There have been recurring concerns of land use as a potential threat to water resources and the sustainability of Verlorenvlei RAMSAR site. The Minister of Water and Sanitation as custodian of water resources requires that surface water use less than 18 250 m3 and ground water use less than 3 650 m3/a to be granted under general authorization. All water use above such general authorization volumes is to be registered (Government Gazette No. 20526 of 1999). Water use registration, is identified as a tool used to achieve the effective management and governance of water resources. Water use above general authorization, is associated with larger scale land use activity, which may have an impact on water resources and the environmental at large. The following study, seeks to examine and compare catchment water use for land uses, to catchment water availability using water use registration data. Comparing water allocation and catchment capacity, this study further seeks to explore the effectiveness of water use registration in achieving good governance of water resources. Purpose: The purpose of this study was to determine effectiveness of water use registration in promoting good governance in the Verlorenvlei catchment Results: Of 124 registered water users identified in the Verlorenvlei catchment, only two of these water users are within the legislative limit outlined by Government Gazette No. 20526 of 1999. Overall, permissible water use is 447 547 259.5 m3/a, over 10 times the catchment capacity of 40 000 000 m3/a. Conclusion: Overall, excessive water use for land use activity is observed within the catchment, despite provision of legislature guiding against excessive water use. Increased water use registration, does however correlate with improved land use practices for agricultural production (Potato SA, 2014) suggesting probability of good governance. Lastly, there is a need for monitoring; improved water and land use efficiency, Integrated Water Resources Management and good governance in the catchment.

Abstract

It has been shown over many years that the efficient management of water resources is almost impossible without a database containing historical and up-to-date information and data of high integrity. When it comes to groundwater the situation is even worse as groundwater was often not seen as a viable resource, and if it was used, then in many cases, it was poorly managed due to the lack of monitoring and poor data collection. This has changed in recent years as groundwater now forms a large part of the used water resources in several communities, towns and metros. Therefore, the need for properly managed groundwater data has increased tremendously, leading to urgent requirements for a water database in whatever form. Unfortunately off-the-shelf groundwater databases relevant to the South African market did not really exist for many years, while international packages are expensive and need a lot of adaptation to work for South African conditions. Therefore, most groundwater practitioners used various forms of database software and/or spreadsheets without much integrity leading to data hosted on various computers around South Africa, but not one central system available to be accessed by groundwater managers, scientists or even the public. The Water Research Commission therefore Initiated a research project for the "Development of an integrated Groundwater Database and visualisation tools for the City of Cape Town and Environs", a system that should be so versatile that it could also be applied in other metros, provincial or national offices. This research project will have a huge impact on water resources decision making for the City of Cape Town, as the recent drought has put the City water managers under immense pressure, which was increased by the need to start using more and more groundwater resources, especially for critical City and province institutions like hospitals, clinics and care centres around the Western Cape. The outcome of the project is a "complete" groundwater resources database with links to surface water and meteorological stations and a number of visualisation tools, including an online web-based mapping tool, which is fed by live data from the database and may be used even by the public for groundwater education purposes.

Abstract

An 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 ?ux in through the unsaturated zone, any quantitative analysis of contaminant transport must ?rst evaluate water ?uxes into and through the this region. Mathematical models have often been used as critical tools for the optimal quantification of site-speci?c subsurface water ?ow and solute transport processes so as to enable the implementation of management practices that minimize both surface 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 characterization 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 100m x 45m 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 preexisting ash dump data as well as the soil physical characteristics of the ash medium.
{List only- not presented}

Abstract

Groundwater exploration in crystalline basement aquifers is often more complex as its occurrence and characteristics are largely a consequence of the interaction of several processes related to recharge and groundwater through-flow within a particular system. An integrated approach of geological mapping and hydrogeophysical investigations can nevertheless be useful in mapping the subsurface characteristics that are likely to control groundwater occurrence in such formation. In this study, multiple geological mapping and hydrogeophysical methods were applied to identify potential groundwater bearing targets as controlled by several geologic structures within the Houtriver gneiss crystalline basement aquifer system in Limpopo province of South Africa. The results from magnetic and frequency domain electromagnetic surveys were combined with geological observations and used to identify anomalous points where vertical electrical resistivity sounding was done in order to infer the thickness and layering of weathered and fractured zones, as well as to assess the area for groundwater potential targets. The magnetic method, horizontal and vertical frequency domain electromagnetic geophysical methods presented herein managed to delineate the main hydrogeological features associated with groundwater occurrence in typical basement aquifers. The vertical electrical sounding (VES) sections done on ten (10) sites suggest that groundwater occurrence is characterized by a multiple layer of varying depths inferred to be caused by different levels of weathering, geology and fracturing within the study area. VES sections are further correlated with the reconstructed drill samples from boreholes drilled within project framework in order to develop a lithological conceptual understanding of weathering and fractured regions that influence groundwater occurrence within the study area. The integration of several geophysical methods for groundwater evaluation in study provided a more detailed approach for the for resource assessment in crystalline basement aquifers as compared to the traditional VES, thereby resulting in increased accuracy in borehole siting.

Abstract

POSTER Most developing urban areas in semi-arid regions of Sub Saharan Africa are often forced to utilise groundwater as an alternate source of domestic water supplies. As such groundwater evaluations strategies often face dual challenges in terms of resource quantification and their quality evaluation. However, groundwater potential assessment and aquifer yield evaluations often present a challenge when the system is of crystalline basement nature where groundwater potential is highly spatially variable and cases of dry holes and seasonal wells have been reported. This study demonstrate the integrated combination of geophysical techniques, (namely, vertical electrical sounding, electrical resistivity tomography, magnetic mapping, and seismic refraction tomography) with both borehole monitoring and infiltration techniques in the groundwater prospecting and spatial yield analysis of the Urban Bulawayo crystalline basement aquifer. The Bulawayo Metropolitan Province of Zimbabwe is located in the semi-arid region of Zimbabwe with an average annual rainfall of below 500 mm and has had a prolonged dry spell has resulted in the dwindling of the existing surface water resources. The aquifer system consists of syenite granite and fractured basaltic greenstone crystalline basement complexes. Provisional geophysical results have shown that the thickness of the fractured zone sharply varies in terms of spatial distribution and often some sections are characterized by shallow surface fractured zone that may only be 20-30 m thick and some sections have a reported regolith of up to 60m in thickness. Borehole yield assessments and chemical analysis techniques will be done on drilled wells in order to come out with detailed spatial variation in the borehole yield and water quality variations across the aquifer system. All the technical evaluations are then integrated to produce a detailed hydro-geophysical map of the system that can be used in the technical groundwater management of the urban Bulawayo aquifer.

Abstract

An 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.

Abstract

Open pit mining operations are located in various, usually complex, geological settings and equally variable climatic regions from arid to extremely high rainfall. Many Southern African open pit mines occur in competent and un-weathered rock masses, and groundwater flow is therefore structurally controlled. Assessing and reducing pit slope pore pressure should be incorporated into pit slope design. Site hydrogeological investigations followed by numerical groundwater modelling is completed to produce predicted pore pressure distributions over the life of a mine and to assess the potential effect of dewatering actions on slope stability. Investigations were completed for two Southern African pits and simulated pore pressure distributions were used in slope stability analysis. In the first case, the simulated slopes are shown to be free draining, and the designed pit slopes are predicted to remain safe and remain so even with the built-up of pore pressure. In the second instance, pore pressure reduction through an aggressive horizontal drill holes programme is demonstrated to improve probability of failure. This has demonstrated the need for collaboration between geotechnical and hydrogeological investigations to improve slope design, reduce likelihood of pit wall failures and reduce mining cost through excavating steeper depressurised slopes.

Abstract

Mabenge B; Famah FIB

Groundwater resources are under increased pressure from population growth, climate change and human activities, leading to widespread groundwater depletion and pollution. It is important, as groundwater professionals to communicate to the younger generation and the broader community, about this vital resource. The Groundwater Kids Educational Program was initiated in November 2020, to educate and share groundwater knowledge amongst primary and high school learners. The program consists of a series of 1 – 2 hour groundwater educational workshops held at schools throughout Gauteng Province. Each workshop comprises a short educational video clip on a selected groundwater topic, followed by an activity that involves the topic of the day, and distribution of groundwater awareness material. Lessons are prepared based on the age group and the level of comprehension of the learners. Learners get the opportunity to engage in activities designed to make learning about groundwater more exciting. These workshops provide a knowledge base for our children participate in efforts to save this resource in generations to come.

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

The joint application of water supply system security, groundwater modelling, and multicriteria analysis (MCA) indicated the potential of Managed Aquifer Recharge (MAR) to increase water supply security in Eastern Botswana substantially. Botswana faces increased water stress due to decreased water availability as climate change exacerbates variability in rainfall and increases evaporation losses and water demand. The water supply for Eastern Botswana is based on the bulk water supply system of the North-South Carrier (NSC) connecting dams in the northeast to the main demand centres, including Gaborone. The potential of MAR to increase the water security of the NSC by storing water that otherwise would have been lost to spillover and evaporation and contribute to the provision of water during droughts was studied. Large-scale MAR in the Ntane sandstone aquifer at a wellfield by the NSC was evaluated in terms of hydrogeology and national water supply perspective. Comprehensive hydrogeological surveys and assessments included borehole injection tests and hydrogeological and geochemical modelling to evaluate risks of losing recharged water and clogging of boreholes. Probabilistic water supply system modelling analysed the impact of different MAR scenarios on the water supply security of the NSC, and an MCA tool assessed the sustainability of the different scenarios. The analysis showed that large-scale MAR is feasible, and a scheme with a capacity of 40,000 m3 /d is the most sustainable from technical, social, economic and environmental perspectives and could potentially reduce the number of months with water shortage by 50% in Gaborone.

Abstract

Floods result in significant human and economic losses worldwide every year. Urbanization leads to the conversion of natural or agricultural land covers to low-permeability surfaces, reducing the infiltration capacity of the land surface. This amplifies the severity and frequency of floods, increasing the vulnerability of communities. Drywells are subsurface structures built in the unsaturated zone that act as managed aquifer recharge facilities to capture stormwater runoff. They are particularly well-suited for the urban environment because of their low land occupancy. In this study, we utilized an integrated surface-subsurface flow modelling approach to evaluate the effectiveness of dry wells in reducing urban runoff at a catchment scale. We developed a 3D model with HydroGeoSphere, characterizing a synthetic unconfined aquifer covered by a layer of low-permeability materials. Sensitivity analyses of land surface conditions, aquifer properties, dry well designs, and rainfall conditions were performed. Model results indicated that dry wells are more effective in reducing runoff when the land surface has a higher Manning roughness coefficient or the aquifer material has a higher hydraulic conductivity. Dry wells should be situated beneath drainage routes with high runoff flux to achieve optimal performance. Increases in dry well radius or depth enhance the infiltration capacity, but deeper dry wells can contaminate groundwater through infiltrating stormwater. Dry well performance declines with higher rainfall intensity, emphasizing the need for local rainfall intensity–duration–frequency (IDF) data to inform the design level of dry wells in specific catchments.

Abstract

Being extensively available and of high quality, groundwater is the primary source of freshwater in coastal regions globally. However, due to anthropogenic and natural drivers, groundwater salinisation is a growing threat to this resource’s long- and short-term viability. The causes and timescales of aquifer salinisation are complex and difficult to quantify, information essential for suitably timed mitigation strategies. One way to inform these strategies and develop storylines of future freshwater (un)availability is through 3D groundwater salinity modelling. These models can predict current groundwater distributions and quantitatively assess the impacts of a projected increase in groundwater extraction rates and sea-level rise. Until recently, detailed 3D models on this scale have been largely unattainable due to computational burdens and a shortage of in-situ data. Fortunately, recent developments in code parallelization, reproducible modelling techniques, and access to high-performance computing (e.g., via parallel SEAWAT) have made this feasible. Machine learning and data mining developments have also allowed an unprecedented opportunity to constrain and calibrate those models. With this in mind, we present our progress towards global 3D salinity modelling by showcasing a regional-scale model in the Mediterranean Sea area. This test case uses newly developed, automated geological and salinity interpolation methods to create initial conditions while implemented in a parallelized version of SEAWAT. The modelling outcomes highlight the potential of supra-regional scale modelling in the context of global (planetary) processes and localised anthropogenic effects.

Abstract

Worldwide, more than 400 transboundary aquifers (TBAs) have been identified. Only a small number of these aquifers have been assessed in detail. Consequently, little is known about (potential) transboundary impacts. Changes in transboundary groundwater fluxes can indicate potential transboundary impacts as groundwater abstractions can affect such fluxes, indicating potential risks of transboundary contamination. To our knowledge, a quantitative assessment of transboundary aquifer fluxes (TBAFs) is not available because national groundwater models (if existing) often lack a good interaction with surrounding countries. In recent years, a high-resolution global groundwater model (GGM) has been developed as part of the PCR-GLOBWB family of models, having a 5 arcmin (~10*10km2 ) resolution. PCR-GLOBWB has previously been used to quantify environmental flows, assess global droughts, and assess climate impacts on global water resources. Recently the 5 arcmin GGM has been updated to 30 arcsec (~1*1km2 ) using high performance computing (referred to as GLOBGM). We present an application of GLOBGM to assess TBAFs of major TBAs. Results show that even though hydrogeological data are often scarce, a rough order of magnitude of the TBAFs can be assessed. TBA fluxes are compared with groundwater recharge. Although GLOBGM cannot replace assessments of TBAs based on local hydrogeological information and information on groundwater use, the analysis provides valuable information. GLOBGM can be used to quantify the relevance of TBAFs in relation to other fluxes such as from rivers or (future) abstractions. TBAF analyses can also assist in prioritising scarce funds and capacity between TBAs

Abstract

Groundwater level monitoring is essential for assessing groundwater’s availability, behaviour and trend. Associated with a modelling tool, groundwater level fluctuations can be predicted in the short to middle term using precipitation probabilities or meteorological forecasts. This is the purpose of the MétéEAU Nappes tool implemented by BRGM for the City of Cape Town (CoCT) in the Table Mountain Group Aquifer (TMGA). This case study shows how near real-time groundwater level monitoring can support the municipality in managing its future groundwater withdrawals. The TMGA is an important source of groundwater in the Western Cape region of South Africa. The upper Nardouw Sub-Aquifer of the TMGA is an unconfined aquifer recharged by rainfall. It had been monitored in the Steenbras area for over 10 years before CoCT started groundwater production from the Steenbras wellfield in 2021. The MétéEAU Nappes forecasting tool is already implemented on many observation wells of the French national piezometric network, where it is used for decision-making by the French administration. It allows, in particular, to anticipate several threshold levels of drought and take appropriate measures. It combines real-time water cycle measurement data with a groundwater level lumped model (e.g. Gardenia model) and extrapolates observations for the next 6 months from statistical meteorological scenarios completed with abstraction scenarios. This tool can help protect the Steenbras wellfield as a critical water source for CoCT in the TMGA. This study was financed by the French Agency for Development (AFD).

Abstract

This study assessed the chemical and microbial quality of groundwater and potential risks to human health in Siloam Village, South Africa. Due to lack of access to potable water, residents in rural areas drill private boreholes within their homesteads without considering the potential sources of groundwater pollution. This exposes them to health risks associated with groundwater pollution. Water samples from 11 boreholes were collected from August 2013 to January 2014. pH and EC were measured using a multimeter and turbidity was measured using a turbidity meter. Non-metals and metals were analysed using Ion Chromatography and Atomic Absorption Spectroscopy, respectively. Colilert quanti-tray method was used to determine total coliforms and Escherichia coli. Descriptive statistics were used to determine the overall water quality status. Potential risks to human health were inferred based on Department of Water and Sanitation guidelines for domestic use. Water quality parameters found to have serious potential health effects on human beings were correlated with selected water quality parameters at a significance level (α) of 0.05 to understand the nature of correlation and possible sources of contamination. The study determined that nitrates and fluorides were the only parameters with excessively high concentrations in groundwater which are associated with health effects on human beings. Correlation of fluoride with calcium and pH indicated that further investigations are required to identify the local sources and fluoride control mechanisms in the study area. Correlation of nitrate with chloride and potassium indicated that faecal contamination and fertilisers are sources of nitrate pollution in the study area, though faecal contamination was the dominant source. Faecal contamination was confirmed from total coliforms and E.coli in most boreholes. The study identified the need to educate borehole owners in such villages of possible strategies to minimise groundwater pollution. 

Abstract

A fault system may form preferential flow paths for groundwater along fault planes. In an industrial and mining environment, such geological structures pose a geohydrological challenge when delineating and managing groundwater pollution. A geophysical investigation, employing electric resistivity tomography (ERT) and electromagnetics (EM), was conducted along a section of a graben system to improve the geological understanding, define groundwater flow paths and pollution distribution in a mining and industrial setting. Additionally, the geophysical survey assisted in the siting of monitoring boreholes to gain an understanding of the geohydrological properties within the fault system. A total of 35 profiles were completed along a 12 km section of the graben including a refined grid around a water-filled quarry with elevated salinity. The geophysical results confirmed the presence of faults and indicated zones of lower apparent resistivity along the graben. Areas of elevated conductivity were modelled near industrial and mining operations, such as ash tailings, discard dumps and mine-water dams, suggesting that leachate could potentially seep into the underlying aquifers. A refined ERT model around the quarry indicated areas of high conductivity at dolerite contacts, fault planes and within a backfilled area which could form preferential groundwater flow paths from and to the quarry. This study showed that a fault system underlying industrial and mining activities with high conductivity zones could distribute seepage along secondary geological structures but could also aid as a barrier between different aquifer systems. An outstanding groundwater chemistry analysis is expected to provide further insight whether the detected groundwater flow paths along the fault planes contribute to the distribution of pollutants across the industrial site. Overall, the geophysical survey and consequent siting of monitoring boreholes were useful tools to identify groundwater flow paths for pollutants across a large scale structure to implement future water management plans.

Abstract

A 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.