Conference Abstracts

Abstract

Test-pumping drawdown curves are not always sufficiently indicative of aquifer characteristics and geometry. In fact, drawdown curves should never be analysed and interpreted alone. The derivative analysis (Bourdet et al., 1983) and flow dimension theory (Barker, 1988) make it possible to infer the regional geometries and flow characteristics of fractured aquifers which are otherwise often unknown or inconclusive when interpreting point-source borehole logs. The propagation of the drawdown and/or pressure front through the aquifer reaches distal hydrogeological objects which influence the flow regime and imprints signatures in the drawdown derivative curves. The conjunctive interpretation of these flow regime sequences and geological data results in a robust, well-informed conceptual model which is vital for resource management.

A methodology similar to that of A. Ferroud, S. Rafini and R. Chesnaux (2018) was applied to the test-pumping data of 14 confined and unconfined Nardouw Aquifer boreholes in the Steenbras area, Cape Town, which has been under exploratory investigation since the early 2000’s. The Steenbras wellfield was developed following the major 2017-2018 Western Cape drought. The NE-SW trending open folds and dextral strike-slip Steenbras-Brandvlei Megafault Zone (with crosscutting faults and dykes) make the aquifer hydrogeologically complex. It is due to these complexities that the sequential flow regime analysis was undertaken to enhance the current conceptual understanding.

The analyses reveal domains of flow models which include open vertical fracture, T-shaped channel, double(triple) porosity model, and leaky/recharge boundary amongst others. Poor data quality and noise issues are also highlighted. The outcomes of the sequential flow regime analysis allow for identification of applicable flow models for type curve fitting to avoid erroneous aquifer parameter estimations; improvement of the hydrogeological understanding of the aquifer; enhancements of the current conceptual model in order to inform on subsequent numerical modelling, groundwater resource management and ecological protection.

Abstract

A Case study done in the heterogeneous Tygerberg shales underlying the northern section of the Cape flats aquifer. A well field consisting of five boreholes within a 1.6 Ha area was test pumped to determine aquifer parameters and sustainable yields for the well field. The wellfield located in a highly heterogeneous geological setting, proved to be an interesting scenario for wellfield analysis and determination of sustainable borehole yields. A variety of analytical methods were used to analyse the test pumping data including the Advance FC analysis and the Cooper Jacob Wellfield analysis, both producing different results. Through the test pumping data analysis, the wellfield could be divided into sub wellfield clusters based on drawdown interconnectivity during testing. Sub wellfield clusters were confirmed using groundwater chemistry, providing higher confidence in limiting uncertainty in long term cluster connectivity.

Abstract

Estimating pumping rates for the purpose of equipping boreholes with suitable pumps that will not over abstract either the boreholes or the aquifer(s) that are intersected is often assessed through test pumping of the boreholes prior to pump selection. While the South African National Standard has guidelines on the methodologies and durations of these tests (SANS 10299-4:2003), many production boreholes in the agricultural and industrial sectors are still equipped based upon so called Farmer Tests or Pump Inlet Tests (PIT), often of a short (6-24 hour) duration. These tests are also frequently and incorrectly confused with a Constant Head Test (CHT), both of which are different in methodology to SANS 10299-4:2003 testing, which relies to a high degree on data collected during a Constant Discharge/Rate Test (CDT or CRT) and recovery thereafter. The study will assess differences in test pumping methodology, data collection, analysis methodology and final recommendations made between Farmer Tests and SANS 10299-4:2003 methodology tests for 20 boreholes in which both tests were performed. The selected sites cover a variety of geological and hydrogeological settings in the Western Cape. Test comparisons include boreholes drilled into the Malmesbury Group, Table Mountain Group and Quaternary alluvial deposits, with tested yields ranging from 0.5 – 25 L/s.

Abstract

Underground coal gasification (UCG) is a chemical process that converts coal in-situ into a gaseous product at elevated pressures and temperatures. Underground coal gasification produces an underground cavity which may be partially filled with gas, ash, unburned coal and other hydrocarbons. In this study we assessed the stratification down the length of the boreholes. This was done by comparing the Electrical Conductivity (EC) profile of background boreholes to the verification borehole that were drilled after gasification was complete. Stratification was seen in all boreholes including the cavity borehole. The EC levels were lower in the cavity which may be due to the dilution factor induced by injecting surface water during quenching of the gasifier. The thermal gradient shows a steady increase in temperature with depth with higher temperatures measured in the verification boreholes. This increase in temperature may suggest that heat is still being retained in the cavity which is expected. This study serves as the preliminary investigation on the stratification of temperature and EC and will be proceeded with in depth surveys that covers all the groundwater monitoring wells that monitor different aquifers identified on site proceed.

Abstract

The advent of the 'Big Data' age has fast tracked advances in automated data analytics, with significant breakthroughs in the application of artificial intelligence (AI). Machine learning (ML), a branch of AI, brings together statistics and computer science, enabling computers to learn how to complete given tasks without the need for explicit programming. ML algorithms learn to recognize and describe complex patterns and relationships in data - making them useful tools for prediction and data-driven discovery. The fields of environmental sciences, water resources and geosciences have seen a proliferation of the use of AI and ML techniques. Yet, despite practical and commercial successes, ML remains a niche field with many under-explored research opportunities in the hydrogeological sciences. Currently physical-process based models are widely applied for groundwater research and management, being the dominant tool for describing and understanding processes governing groundwater flow and transport. However, they are limited in terms of the high data requirements, costly development and run time. By comparison, ML algorithms are data-driven models that establish relationships between an input (e.g. climate data) and an output (e.g. groundwater level) without the need to understand the underlying physical process, making them most suitable for cases in which data is plentiful but the underlying processes are poorly understood. Combining data-driven and process-based models can provide opportunities to compensate for the limitations of each of these methodologies. We present applications of ML algorithms as knowledge discovery tools and explore the potential and limitations of ML to fill in data gaps and forecast groundwater levels based on climate data and predictions. Results represent the first step in on-going work applying ML as an additional tool in the study and management of groundwater resources, alongside and enhancing conventional techniques such as numerical modelling.

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

In recent years there has been renewed interested in identifying and understanding groundwater resources. Airborne electromagnetic (AEM) surveys can provide useful, cost effective information about the geometry of aquifers and their host rocks. TEMPEST is a fixed wing AEM system which has been used extensively for groundwater applications. The system possesses many attributes which aid in groundwater exploration including: broad operational bandwidth; multifaceted software approach; and, a distinctive calibration technique. These features allow both shallow and deep subsurface features to be imaged which aid in mapping groundwater aquifers along with the broader groundwater subsystem. This paper will review TEMPEST surveys flown for the Western Australian Department of Water (DoW) for the purpose of groundwater characterisation. The surveys were focussed on the identification of geological contacts, subsurface aquifers and seawater intrusion extents. The survey data was interpreted using an integrated approach which involved reviewing the newly acquired geophysical data, identifying contacts and anomalous features in the acquired data, reviewing existing geological and geophysical data in the area and correlating features identified in acquired data to known geology. The first case study was flown over the North Gnangara area of the Perth Basin with the primary aim of defining the spatial distribution of clay and silty layers that impede recharge to the groundwater table. The survey succeeded in achieving its primary aim of identifying the distribution of clay layer targets. Through the integrated interpretation approach it was also successful in achieving its secondary aims by clearly defining the contact between superficial units and the underlying stratigraphy, identifying key structures within the basin, outlining the top of the seawater intrusion, and mapping confining strata within the deeper aquifer systems in the Perth Basin. The second case study was flown over the lower reaches of four river systems in the North Pilbara coast with the aim of understanding the aquifer geometries and groundwater salinity distribution within the region. The primary aims of the survey were achieved and provided a basement geology map, relative porosity maps, approximate weathered and unweathered bedrock surfaces as well as the approximate geometry of the seawater intrusion within all survey areas. It was also possible to map the interpreted extents of alluvial aquifers within two of the river systems as well as the contact between two sandstone aquifers present in one of the river systems. These case studies show that the TEMPEST AEM system can provide valuable information about the geometry of aquifers and their host geology. AEM surveys should be used as an initial method for determining broad aquifer geometry and the identification of priority areas prior to further less cost effective water bore drilling.

Abstract

Clogging of existing boreholes due to natural well ageing is the most common cause of decreasing yield worldwide, also in South Africa. Maintenance plans based on systematic monitoring are required including inspection, service and rehabilitation to lengthen production times and to slow down ageing processes. Therefore a prerequisite of economical well operation is to apply the most efficient measures to secure their production capacity at the lowest possible cost. Rehabilitations by mechanical, hydraulic or impulse methods do often not lead to acceptable yield increases. Acids of all kinds have been applied to remove iron(III) and manganese(III,IV) clogging, although pH values of < 1.0 are required before any significant dissolution takes place. This treatment does not only affect substances in adjacent geology but also well construction materials and technical equipment. Alternatives for acidization were researched and developed at the Technical University of Aachen (RWTH) in 1990’s by Prof. Dr. Treskatis and Dr. Houben. Since then iron(III) and manganese(III,IV) are removed by pH-neutral reductants with 50 times greater dissolving capacity than hydrochloric acid at pH 1.0 in identical molar concentration. The closed-circuit injection technique was proved to be the only method to transfer chemical agents as far as the borehole wall in a study by Dresdner Groundwater Center on behalf of German Gas and Water Association in 2003. Low pressure circulation based on large volume flow is accomplished by means of state-of-the-art gravel washers. The application of pH-neutral dissolvers by closed-circuit injection has proved its effectiveness not only in Germany, but also in Switzerland, Austria, Netherlands, Spain, UK, UAE and Peru. Our case study documents its successful introduction in Finland 2020. Until then stand-by acidization had been the only means of battling well ageing. Research funds enabled rehabilitations in different parts of the country resulting in unexpected high yield increases.

Abstract

Given the challenging global water outlook due to climate change and urbanisation, there is a heightened necessity for greater water resilience at critical facilities to tackle water disasters or disasters that lead to water crises. In 2017, the Western Cape Province of South Africa experienced an extended drought with the risk of acute water shortages. The Western Cape Government (WCG) developed business continuity plans and implemented a programme to ensure water supply to certain critical service delivery facilities, utilising the strategy of developing localised groundwater supply systems. The case study research of the WCG program enabled the development of an evaluation framework that assessed this strategy’s effectiveness in improving water resilience levels at critical facilities. From the lessons learnt in the WCG programme, the research also crystallised the critical success factors in sustainably implementing this strategy. The research showed that this is an effective strategy for its purposes and provides both current and future disaster preparedness planners with an improved understanding of the levels of water resilience achievable through this strategy and the methodology to achieve it best.

Abstract

South Africa has a looming water supply crisis, with 98% of its surface water already developed, demand outstripping supply in most catchment areas (WRC, 2015). Based on current usage trends, South Africa is expected to face a water deficit of 17% by 2030, and this shortage will only be worsened by climate change (WWF, 2017) which is mainly characterized by prolonged period of drought. There are many challenges facing the sustainability of groundwater, among others there are issues such as climate change, human errors in data handling, over abstraction due increasing water demand, damage of borehole infrastructure in remote areas and poor groundwater management systems.

Groundwater resources within the D41L quaternary catchment occurs in abundance. Aquifers in the area are classified as karst and fractured dolomite aquifers with a median yield of >5 L/s. These aquifers are compartmentalized by several impervious dykes that sub-divide the D41L area into sub-catchments and smaller sub-compartments. With the probable impacts of extended drought period in the Gasegonyana Local Municipal area, increased water demands and density of abstraction points in some sub-catchments/sub-compartments the water resources have become stressed and at risk of being over-exploited. To sustainably and secure future water supply in the region, it has become essential that a comprehensive assessment is undertaken of the sustainable water supply potential of the D41L and delineate various groundwater resource units (GRU's).

The paper highlights why is it imperative to conduct the groundwater feasibility studies on a regional scale in order to protect the sole aquifer resource for semi-desert areas such as Gasegonyana municipal zone. Secondly, the importance use of appropriate geophysical techniques which include regional gravity surveys on dolomitic aquifers with emphases to sustainability on exploitable resources as these karst aquifers are highly vulnerable to over-abstraction if not properly investigated.

Groundwater water potential and large aquifer zones were delineated explicitly with the regional gravity results and exploration drilling of these zones proved to be sustainable compared to existing boreholes that were drilled in limited/smaller dolomitic compartments. The predictive scenario of the groundwater assessment confirms that the water demand could be achieved with half of the simulated abstraction rates while an increase in water demand should be managed accordingly by distributing the yields of the borehole between the existing boreholes and the newly drilled production boreholes.

The study results will ensure sustainability of water supply in the region and the document will assist the town planners and stakeholders to manage high population growth in a groundwater secure zone, and it will mitigation against climate change impact for the municipality.

Abstract

As populations, agricultural and industrial demands grow with time, increasing attention is placed on developing groundwater resources in a sustainable manner. At the small, local scale, this tends to involve exploration (scientific and otherwise) and test pumping (also subject to more and less scientific methods). While there can be some subjectivity in the analysis of scientific test pumping data (the selection of representative periods of drawdown stability, the inclusion of potential boundary conditions and the estimation of available drawdown), published methodologies such as the FC method (2001) and the Q20 (1959) and R20 (2006) concepts attempt to calculate sustainable abstraction rates based on these tests. At a larger catchment or aquifer scale, water balance estimates of inflows, storage and outflows are also used to estimate the effects of groundwater abstraction within such a “water budget”. This can be done conceptually, but is often also through a numerical model. A drawback of such methods is the difficulty in estimating representative annual inflow volumes, such as groundwater recharge. One such methodology is the Aquifer Firm Yield Model (2012) which assesses sustainable groundwater supplies based on threshold recharge inflows, baseflow and evapotranspiration outflows, and a 5 m aquifer saturated fluctuation limit. While this was intended for use at a preliminary stage of investigations, before sufficient hydrogeological data would be available for a numerical model, it nonetheless provides an estimate of the available groundwater for abstraction based on a water budget concept rather than test pumping data analysis. A comparison of the results of these two approaches is provided for several newly developed municipal production boreholes in the Karoo to compare where the assumptions inherent to each approach may be highlighted by noticeable differences in results.

Abstract

A cycle of research is under way to investigate sustainable farming practices and business development on emerging farms in the lowveld of the Limpopo Province of South Africa. One of the main limiting factors for intensive agricultural production in this region is water availability. The objectives of this study were: i) to determine the spatial extent of occurrence of shallow groundwater (<20 m deep), in particular along dry river beds; and ii) to determine the sustainability of shallow groundwater abstraction for irrigation on emerging farms.

A case study was investigated in the Molototsi River catchment, a torrential tributary of the Letaba River. The geology consists of well-developed, medium-textured alluvial/colluvial soils overlying predominantly Goudplaats gneiss. Geophysical surveying and mapping was carried out with a Model G5 proton memory magnetometer and an EM-34 electrical resistivity meter. Groundwater level data were collected from the GRIP database (Groundwater Resource Information Project - Department of Water and Sanitation) and selected boreholes were monitored with Solinst water level loggers. Groundwater abstraction data, borehole logs and digital elevation models were also collected.

A methodology was developed to map the extent of shallow groundwater using measured groundwater levels, a National Land Cover map (NLC 2013/14), the wetland map of the National Freshwater Ecosystem Priority Areas (NFEPA), satellite remote sensing (MOD16 evapotranspiration data) and ground-truthing. Groundwater level monitoring indicated that the water bearing features may not be directly connected to the alluvium and sand river bed (alluvial aquifer), resulting in limited baseflow estimated to be ~15 m3 a -1 for a river reach of 100 m. Episodic recharge of the alluvial aquifer occurs predominantly via surface runoff. The hydraulic conductivity of the river sand aquifer was estimated to be >20 m d-1 , and one order of magnitude smaller in the fractured rock aquifers. Groundwater modelling with MODFLOW was done at farms abstracting groundwater from fractured bedrock aquifers and directly from the sand bed of the Molototsi River to investigate how much water can be abstracted for sustainable irrigation. Both modelling and monitoring results indicated that there is limited scope for large scale expansion of irrigation, given the competition for water in the area, in particular for drinking water supply. However, the volume of water stored in the dry river bed could represent a useful reserve during periods of severe drought, with recharge from occasional flood events being essential. Given the porosity of the river bed aquifer of about 40%, it was estimated that a 100 m reach of the Molototsi River would retain about 7,200 m3 of water that could be abstracted if numerous wells are established and recovery periods are allowed. A water volume of 7,200 m3 is sufficient to irrigate 1.8 ha of vegetables for one season. This volume could be augmented to a certain extent by establishing river bed sand dams.

Abstract

With an increasing population, development of the country and a changing climate, an increased demand for fresh water, coupled with negatively impacted natural water resources, are observed. One impacted component of the water resource may have an impact on another, due to the interaction between water resource components in the water cycle. All water resource components need to be well-managed and protected to ensure their availability and sustainability. Studies on water quantities, flow dynamics, quality, and contamination are essential in this regard. Isotopes are used as a tool in these studies to define the interconnection between different water resource components. The information gained from isotope studies is valuable in the planning of activities in areas where interacting water resource components may potentially be affected. A study in Middleburg comprised a literature review and field investigations at and around a cemetery, as part of a Water Research Commission project on impacts on the water resource from large scale burials. A seasonal wetland is located downgradient of the cemetery, between the cemetery and a stream that flows past the cemetery. In order to assess possible flow pathways from the cemetery to the stream, monthly monitoring of surface and groundwater quality and level fluctuations was carried out on the stream, as well as existing and newly installed boreholes at the site. The water samples were analysed for inorganic constituents, tritium, and stable water isotopes. The isotope results - revealed the comparative influence of rainfall and shallow groundwater contributions to streamflow, while groundwater provides base-flows as the stream levels recede. The depth to groundwater reduced with increasing rainfall, indicating direct recharge. The difference in concentrations of some inorganic parameters in the stream compared to the groundwater at the cemetery revealed the effect of natural attenuation and the wetland acting as a filter to improve the water quality of the shallow interflow.

Abstract

POSTER The areas studied in this paper are situated in semi-dry regions of Limpopo and Northern Cape Provinces of South Africa. Groundwater is the only dependable source of water for many local users and farming communities. The growing population is putting immense pressure in the current water resources, hence a need to find new groundwater resources. The areas are most dominated by fractured rock aquifers which accounts to over 90% of South African aquifers. Finding sustainable sources of groundwater in these regions is often a challenge due the complex nature of the fracturing network system of fractured aquifers. This study uses a supervised committee learning with artificial neutral network (SCLANN) model to improve the regional groundwater exploration in granitic basement terrains and valley controlled aquifers in metamorphic terrains of South Africa. The data used in the study was obtained from the national groundwater archive and interpretation of high resolution aeromagnetic data, ground surveys and remote sensing datasets. The artificial neural network (ANN), Fuzzy (F) and Neuro-fuzzy (NF) unsupervised models whose input were groundwater controlling parameters like regolith thickness, lithology, relief, faults, lineament density, lengths of lineaments was used. The results from the ANN, F and NF models were used as inputs to a nonlinear supervised SCLANN framework with the borehole yield as the training and validation outputs. Borehole yield was used as it is one of the measurable parameter that directly related to productivity of groundwater resources. The use of the unsupervised models improved the results significantly as the SCLANN model results as a combined advantage of the individual models to achieve the optimal high performance. The results show that the three models used to build a SCLANN model was able to improve the identification of potential groundwater targets at regional scales. This approach can be incorporated in regional groundwater exploration programs to improving drilling success rate on granitic basement and metamorphic terrains in South Africa. The results show that the SCLANN outperforms individual unsupervised models. However the SCLANN results for granitic basement terrains were far much better than the metamorphic terrains probably showing the limitation of the approach in metamorphic terrains.

Abstract

McGibbon, D; Riemann, K

The Cape Flats Aquifer Management Scheme (CFAMS) includes both abstraction of groundwater and managed aquifer recharge (MAR) as part of the City of Cape Towns (CoCT) New Water Programme to diversify their bulk water supply and build resilience against future droughts. Since the project was initiated in early 2018, over 250 boreholes have been drilled for exploration, monitoring, abstraction, and MAR. Rotary mud drilling was used for most of the drilling due to its suitability in unconsolidated geological material, typical of the CFA. As effective as rotary mud drilling is for large scale development, it lacks in accuracy for detailed geological interpretation used for borehole siting and design (gravel pack and screen aperture size and screen position). This is due to the mixing of material and the circulation of the drilling mud washing away fine sediment which can skew grain size analysis results and obscure the vertical position and thickness of thin confining clay or organic rich lenses. The clay and organic rich layers can cause surface flooding during injection as they act as confining layers which effects borehole design and more importantly siting of MAR boreholes. To overcome this, two additional drilling techniques were explored, sonic and air core. Air core was disregarded early on due to the air creating a cavity in the underlying unconsolidated sediments. Sonic drilling, however, was successful in retrieving a continuous undisturbed core log through high resonant energy that liquefies the sediments, which are then brought to surface in a core barrel. The undisturbed continuous nature of the log allows for accurate grain size analysis and detailed vertical geological logging which can be used for facies analysis to interpret the paleoenvironment and predict the lateral extent of clay or organic rich layers that influence borehole siting, design, and the hydrochemistry.

Abstract

South Africa is generally a dry country, it receives an average rainfall of approximately 500 mm/a, which is below the global average rainfall of 860mm/a. The annual average temperature in the study area was 25?C from 1995 to 2016. South Africa has made an improvement since 1994 with supplying domestic water of suitable standards, communities in rural areas, mostly have groundwater as the best option for satisfying their water demands. In the study area (Bushveld Igneous Complex), which falls within the Olifants and Limpopo Water Management Area (WMA), groundwater is used in various sectors for various. In both WMA's the irrigation sector is the highest water user. In 2015 irrigation accounted for approximately 72% of the total water requirements in the Limpopo WMA, with 57% of the irrigation requirements fulfilled by groundwater resources. In the Limpopo WMA groundwater resources supply also 44.5% of the domestic water requirements, while surface water resources account for only 21% and water transfer schemes account for 34.5%. In the Olifants WMA the mining sector uses 28 million m3/a of groundwater resources and 58 million m3/a from surface water resources. The aim of this research is to determine the hydrochemical variation and the suitability of groundwater for irrigation and drinking purpose for a sustainable agriculture and basic human needs. There are chiefly five hydro-chemical facies on regional scale identified based on the piper diagrams, namely the Ca-HCO3, mixed Ca-Mg-Cl type followed by Ca-Cl, Na-Cl and mixed Ca-Na-HCO3 water type. The suitability of groundwater is determined based on the water type, the mixed-Ca-Mg-Cl and Ca-HCO3 water types are generally suitable for domestic purposes as per SANS drinking water standards, while the mixed Ca-Na-HCO3, Ca-Cl and Na-Cl water types are mostly not suitable drinking water unless treated.

Abstract

Decades of monitoring, characterising, and assessing nitrate concentration distribution and behaviour in the soil profile and it's pathway into groundwater have resulted in a good understanding of its distribution in the country. While the national distribution is of great importance, site specific conditions determine fate, transport, and ultimately concentration in a specific area. Field experimental work included installation of a barrier containing a cheaply available carbon source to treat groundwater. The "reactor"/ tank with dimensions- 1,37m height, 2.15m diameter used for the experiment was slotted for its entire circumference by marking and grinding through the 5mm thick plastic material. The top section was left open to allow for filling and occasional checking of filled material during the experiment. The tank was packed with Eucalyptus globulus woodchips which was freely available at the site. Concentrations of groundwater nitrate at the site were well over what could be expected in any naturally occurring groundwater systems, and would result only by major anthropogenic activities in unconfined aquifer areas of South Africa. The changes in parameter concentrations with time were measured in order to determine the efficiency and life span of the carbon source used for the experiment. This paper considers 35 months of monitoring at a site where a low technology method was implemented. Field implementation was tested at a site which previously experienced some NH4NO3 spills. Main results from the field work showed that nitrate was totally removed at the treatment zone and surrounding boreholes, and even sulphate and NH4+ were removed during the experiment. This shows that the woodchips were successful in affecting denitrification for 35 months. Data also shows that boreholes further downstream from the tank had reduced NO3-, SO42- and NH4+ levels. Using the available biodegradable carbon for the woodchips based on its composition, a barrier lifespan could be determined. The results of calculations showed that the barrier would be effective for at least another 6.9 years from the period of the last sampling date. A total lifespan of about 10 years can thus be estimated.

Abstract

Huixian Karst National Wetland Park is the most typical karst wetland in the middle and low latitudes of the world and has become an internationally important wetland. The relationship between water quality and aquatic organisms in Huixian Wetland is a hot research topic in wetland ecology. This article focuses on the relationship between the current water quality situation in Guilin Huixian Karst Wetland and the growth of wetland plants. Sixteen sampling points are set up in the wetland to monitor and analyze water quality in wet, normal, and dry seasons. The Kriging index interpolation method is used to obtain a comprehensive water quality interpolation map in the survey area during normal water periods and in combination with the wetland plant survey sample data and the landscape status. A comprehensive analysis of the relationship between wetland plant growth and water quality. The results show that the centre of Huixian Wetland receives recharge from surrounding groundwater, which is greatly affected by the surrounding water quality. The comprehensive water quality is relatively good in the dry season, relatively poor in the normal season, and the worst in the wet season. Agricultural production, non-point source pollution, rural domestic sewage, and human interference affect wetland water quality, which directly affects the structure and function of plant communities and the ecological service function of wetlands.

Abstract

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

Abstract

Governing groundwater in a way that does not deplete the source of water, nor cause any form of degradation is a global challenge. In South Africa, scholarship shows an extensive history of groundwater governance doctrines. Yet, the country’s groundwater remained a poorly governed resource. A recent regulatory regime change culminated in the National Water Act 36 of 1998 (NWA), which was specifically promulgated to ‘provide for fundamental reform of the law relating to water resources’. While the NWA provided an ideal opportunity for the judicious governance of South Africa’s groundwater, groundwater governance remain problematic. The regulatory focus is still very much on surface water. In fact, up to date, no regulations have been made to specifically protect vulnerable aquifers, or aquifers on which communities depend as a source of water supply, or aquifers that supports large scale agriculture. This paper sets out to achieve three objectives: to assess South Africa’s existing regulatory approach to the protection of groundwater; to identify gaps in the regulatory framework; and to explore regulatory opportunities to strengthen groundwater governance. The discussion follows a focussed approach, and hinges on the case of the dolomitic aquifer of Delmas. The Delmas case study is expected to show why policy makers and planners need to be more concerned about groundwater. It will also introduce, explain and propose an established international or foreign legal measure that may be incorporated to strengthen the regulatory status of the Delmas aquifer. The paper concludes with recommendations for strengthening South Africa’s groundwater regulation.

Abstract

Abstract

The continuous increase in demand for water from a growing population and associated additional housing projects in the town of Steytlerville in the Eastern Cape Province has resulted in a shortage in water supply from the existing boreholes. In order to supplement the additional demand, a bulk water augmentation scheme using surface water from the Groot Rivier at a point immediately east of the Hadley crossing was implemented. This was done by drilling two large diameter production boreholes vertically into the alluvium and underlying bedrock of the river to a depth of intersecting the entire thickness of the mapped alluvium. Two boreholes were connected to a network of subsurface drains that allowed for recharge from the open channel to flow into the production boreholes. In addition to the sub-surface drain system connecting the sump boreholes, three recharge drains were constructed upstream of the abstraction boreholes. The purpose of these drains were to recharge the underlying paleo-channel to improve the water quality and yield from the paleo-channel. This was achieved by connecting the sub-surface drainage pipe to a vertical screened recharge borehole. The end result of the study was the successful implementation of a alternate borehole yield of 14l/s from the production wells to the Steytlerville town water reticulation supply.

Abstract

This paper reports the results of groundwater level variability analysis across KwaZulu-Natal (KZN) Province of South Africa and its relationship with rainfall. The study used 32 groundwater level monitoring sites and 15 rainfall stations.

The main objective of the study was to understand groundwater level trends for the monitoring period, i.e. from 2004 to 2015 and understand its controls. The Mann-Kendall test was used to explore the presence of trends in groundwater level and rainfall data at 10% statistical significance level. The slope of the trend has been estimated using Sen’s slope estimator. The results revealed that within the Usuthu-Mhlathuzi Water Management Area (WMA), both groundwater level and rainfall have a declining trend for the entire record period. Tembe and Mbazwana areas showed a groundwater level decline of 0.7 and 2.7 m, respectively; while areas around Richards Bay experienced a groundwater level reduction between 0.7 and 6.3 m from 2004 to 2015. During the same period, rainfall was significantly reduced around Tembe, Mbazwana and Richards Bay areas by 26, 6 and 18% from the mean, respectively. The uThukela WMA, around Dundee and Newcastle exhibited an increase in groundwater levels by about 1.5 m between 2004 and 2010 but later declined by 1.2 m in the period from 2014 to 2015. During the period from 2004 to 2010, the rainfall showed increasing trend by 8%, but decreased by 22% in 2015. The central part of the uThukela WMA, around Tugela Ferry and Greytown, showed a decrease in groundwater level and rainfall by 3.2 m and 15%, respectively for the entire record period. The northern Mvoti- uMzimkhulu WMA around Maphumulo showed groundwater level decline by 11 m for the period from 2005 to 2011. However, the groundwater level recovered by 8 m between 2012 and 2013 following an increase in rainfall by 21%. Areas around Durban, groundwater level showed an increasing trend from 2005 to 2008 which coincided with an increasing rainfall amount by about 13%. The rainfall decreased by 21% from 2012 to 2015 resulting in the decline of groundwater level by 0.4 m for the same period. The steady decline in the groundwater level across the province appears to be a response to prolonged reduction in rainfall, which consequently reduced the amount of groundwater recharge reaching the aquifer. The response of the groundwater level to changes in rainfall across KZN has a lag time between 1 to 4 months.

Abstract

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

Abstract

The International Association of Hydrogeologists and UNESCO's International Hydrological Programme have established the Internationally Shared (transboundary) Aquifer Resource Management (ISARM) Programme. This multiagency cooperative program has launched a number of global and regional initiatives designed to delineate and analyze transboundary aquifer systems and to encourage riparian states to work cooperatively toward mutually beneficial, sustainable aquifer development and management. The Stampriet Transboundary Aquifer System was selected as one of the three case studies funded by UNESCO. The Stampriet Aquifer System is located in the arid part of the countries (Botswana, Namibia and South Africa) where groundwater is a sole provider for water resource. The area is characterised by the Kalahari (local unconfined aquifer) and Nossob confined aquifer

Abstract

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

Abstract

To control the impact of nitrate and its sustainable mitigation in groundwater systems used for drinking water production, it is crucial to understand and quantify sources as well as biochemical processes which (permanently) remove nitrate.

In an alluvial aquifer in Germany (Hessian Ried) that serves as major drinking water recourse for the Frankfurt metropolitan area, water quality is challenged by nitrate contamination from intensive agricultural land use locally by far exceeding the drinking water limits of 50 mg/L.

In order to evaluate the capability of the aquifer for natural mitigation of the nitrate contamination, we investigated the denitrification potential with respect to the availability of electron donors and the predominant reduction pathways in different sections of the aquifer. The content of sedimentary sulfide and organic carbon was quantified by solid-phase analyses of drill core samples from aquifer sediments. Water samples from vertical profiles gave access to information on the isotope-hydrochemical composition of the groundwater (multi-parameter profiles, major ions, nitrate isotope signature, sulfate isotope signature). Using this hydrochemical and isotope information in concert with the results of a groundwater flow model allowed determining the nitrate input and the average nitrate reduction kinetics along the flow path upstream of selected groundwater monitoring wells. Batch and column experiments provided detailed information on prevailing reaction pathways and the associated isotope fractionation pattern enabling the recognition and quantification of processes on field scale. Our results suggest that litho-autotrophic denitrification using sedimentary sulfide as an electron donor is preferably responsible for the nitrate degradation in the aquifer. However, due to the low sulfide content (max. 123 mg-S/kg), the potential for autotrophic denitrification is very limited. Consequently, if no active measures reducing the input of fertilizer-derived nitrate will be implemented in the near future, the limited potential for autotrophic denitrification will ultimately exhaust and a severe deterioration of the groundwater quality can be expected.

Abstract

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

Abstract

The work presented in this paper incorporates spring data for further conceptualizing the hydrogeology of northern Namibia’s so-called “Karst Area”, an area around the towns of Tsumeb, Otavi and Grootfontein. Also called the Otavi Mountainland, it can be described as a mountainous highland of parallel, east-west trending elongated valleys and ranges shaped by the underlying folded units of carbonate rocks of the Damara Supergroup. The karst aquifers are a supplementary source to the central areas of the country during drought. Most of these 35 springs are often found near hilltop crests or high up on the mountain flanks rather than lower down at the valley floors. If flows are generated locally as gravity or contact overflow springs, studying them would not add much to conceptualizing the regional groundwater flow. Fundamental insights are provided if flows arise due to hydraulic pressure from deeper down. As artesian boreholes do not occur as a rule in the Karst Area, artesian springs might indicate the presence of deeper aquifers out of reach at normal drilling depth. One such hypothesis is that the bottom of the dolomitic synclines, structurally weaker at the fold axis, had been subjected to deep-seated karstification. The work presented here investigates that possibility and argues for and against it. In addition, established concepts of groundwater flow mechanisms for the area have been revisited. A conclusion has not yet been reached, but the balance of the arguments is presented.

Abstract

The 11 coal-bearing zones currently being mined at Exarro's Grootegeluk mine, discard intraburden onto discard dumps. During mining operations the open pit will be backfilled with plant discards, overburden and interburden on completion of mining. The plant waste will be covered with overburden  and  topsoil.  Intraburden  spoils  consist  of  sandstone,  mudstone  and  shale  rich  in minerals such as pyrite and siderite. These intraburden spoils thus have the capacity to generate acid when exposed to the appropriate conditions. The oxidation of iron sulphides (Pyrite (FeS2)), present within the discard dumps and stockpiles, can influence the hydrochemistry by generating acid-mine drainage, while siderite (FeCO3) can have a basic effect to the immediate surroundings. Acid-base- accounting done on samples gathered from different boreholes in the Waterberg coalfield helped to determine lithological units that can generate acid, with specific regard to the interburden removed and placed on the discard dumps, the interburden used in the pit as backfill, and the acid generation possibility from coal seams in stock piles. This indicated the zones that are more prone to acid- and base-producing potentials. Mineralogical investigations with X-ray diffraction and X-ray fluorescence gave a better record of minerals and elements present in trace amounts within interburden zones that could also have additional problems during storage and use. The areas that possess the highest risk regarding acid generation are the zones enriched in pyrite, as well as the coal seams from stock piles. The management plan for the acid generating spoils of the area has two possibilities: Firstly where acid producing potentials are higher, spoils should not be used where it will be exposed to oxygen and water for long periods of time, as the amount of acid generated cannot be controlled. A second option would entail the immediate compaction and flooding of the mined area so that the amount of acid produced would be controlled and limited.

Abstract

For sustainable water resource management it is crucial to assess the water budget. However, estimating a region's spatiotemporal water budget is fraught with difficulties. The heterogeneous nature of every hydrological system poses major obstacles, particularly at the regional scale where monitoring data are scare. This is further complicated by rapidly changing climatic and land use trends. When estimating water availability and its distribution, the presence and sustainability of groundwater is a vital factor to consider: adequate recharge, whether natural or artificial, can ensure both the productivity of an aquifer as well as the health of its associated aquatic habitats. In order to ameliorate water budget estimates at the regional scale (>1000 km2) we investigate the capability of a multiparameter data-assimilation approach for the Thur catchment in Switzerland, with a focus on the exchange of surface water and groundwater in unconfined aquifers. With a catchment size of ~1700 km2, a dynamic topography (elevation ranging from 356 - 2505 m.a.s.l.), underlain by both consolidated and unconsolidated lithologies, no major barriers along the length of its course (~130 km), naturally variable discharge rates (3 - 1129 m3s-1), an annual average rainfall of 2,701 mm, and 10 operational gauging stations, the Thur River is well suited to this study. We aim to determine 1) the usefulness of multiparameter techniques, particularly when used in conjunction with remotely sensed data, 2) the catchment-wide spatiotemporal water distribution and budget, and 3) the groundwater storage potential within the catchment. Historic and current precipitation data, along with evapotranspiration estimates, a product derived from the MODIS sensor on board the Terra satellite, was used in conjunction with measured long-term hydrological discharge data, groundwater levels, and hydrogeochemical parameters. A remotely sensed water balance was determined for the years 2001 - 2017 and compared to spatiotemporal and statistical geochemical water characteristics from long-term surface water and groundwater monitoring sites. The results are used to determine the primary physical processes involved in regulating the catchment's water distribution. Our working hypothesis suggests that, when coupled with available hydrogeochemical water quality data and geological information, the remotely sensed water budget can be used as a tool to determine the physical processes governing the distribution of a catchment's available water. We aim to determine 1) the usefulness of multiparameter techniques, particularly when used in conjunction with remotely sensed data, 2) the catchment-wide spatiotemporal water distribution and budget, and 3) the groundwater storage potential within the catchment. Historic and current precipitation data, along with evapotranspiration estimates, a product derived from the MODIS sensor on board the Terra satellite, was used in conjunction with measured long-term hydrological discharge data, groundwater levels, and hydrogeochemical parameters. A remotely sensed water balance was determined for the years 2001 - 2017 and compared to spatiotemporal and statistical geochemical water characteristics from long-term surface water and groundwater monitoring sites. The results are used to determine the primary physical processes involved in regulating the catchment's water distribution. Our working hypothesis suggests that, when coupled with available hydrogeochemical water quality data and geological information, the remotely sensed water budget can be used as a tool to determine the physical processes governing the distribution of a catchment's available water. Understanding a catchment's spatiotemporal water distribution will help determine where water bodies could be suitably buffered, either through the rehabilitation and protection of wetlands and river reaches or via managed aquifer recharge, in order to abate the effects of increasing water demand, and climate and land use change on the water budget.

Abstract

POSTER The poster presents the spatial-temporal assessment of groundwater-surfacewater (GW-SW) aspects in Skoonspruit River catchment, North West of South Africa. Despite the common use of quantitative methods to assess various aspects of GW-SW interaction, the use of qualitative methods remains poorly understood in assessing aspects of GW-SW interaction especially in the context of developing countries such as South Africa. While quantitative methods are envisaged to provide reliable and valid results,the use of qualitative methods are exploratory, site specific and more revealing to provide insights for more robust confirmatory methods. Such approach remains fundamental to comprehensive assessments that facilitate relevant generation of information to decision makers to enable them develop and improve interventions for the desired water utilization and management practice. However, the use of such qualitative methods in GW-SW interaction studies has not been applied, a situation which limit the basis for applying quantitative methods and that make quantitative methods not yield the desired results in most studies. The current study argues that the use of quantitative methods should be informed by the results from the qualitative methods and that the poor results from the GW-SW interaction studies is partly due to lack of implementing the qualitative methods prior to using the quantitative methods, especially in the context of developing countries such as South Africa. The current study established spatial variation in the water-type of the upper and lower catchment for both groundwater and surface water. Characterized water-type for several site specific reaches and determined the temporal trends for GW-SW interaction process in order to produce a comprehensive scenario for spatial-temporal pattern for GW-SW interaction in the Skoonspruit River catchment of North West to inform desired interventions for water use and management.
Key Words: Qualitative methods, Quantitative methods, Spatial-temporal assessment, GW-SW interaction, Water use and management, Skoonspruit River catchment, North West

Abstract

The analysis of water chemistry data is widely used to assess groundwater quality and to understand its variability in an area. This study was carried out in the Chókwè district in the Gaza Province located in the south-western part of Mozambique, a downstream area of the Limpopo River basin. A total of twenty[1]seven groundwater samples collected from handpumps, boreholes and wells were analysed with the aim to investigate the groundwater quality and its spatial variability in Lionde, Macarretane and Chókwè city.

The physicochemical parameters such as pH, total dissolved solids, and electrical conductivity, as well as major and minor ions were analysed from the groundwater samples. The data analysis and interpretation of water chemistry were done with the help of the Windows Interpretation System for Hydrogeologists (WISH), version 3.02.188, the Quantum GIS 2.0.1 and Microsoft Excel.

The results showed the cation dominance order of Na⁺>Mg²+>Ca²⁺>K⁺ , while for anions it was Cl−>HCO₃ −>SO₄²⁻ . The groundwater quality in the Macarretane area was classified as unacceptable, and in the Lionde area it was classified as poor for drinking. The average value of the major physicochemical ions in these areas was not within the permissible limits, except for potassium (K⁺), sulphate (SO₄²⁻) and bicarbonate (HCO₃⁻ ). The electrical conductivity values in the district ranged from 241 µS/cm to 12 000 µS/cm, while total dissolved solids ranged from 162.8 mg/L to 7 652.6 mg/L. The spatial analysis of water quality revealed that the groundwater quality is influenced by the local geology, through halite, calcite and dolomite dissolution processes or chemical reactions. The groundwater is highly mineralised in quaternary deposits dominated by alluvium, sand, silt, gravel and eluvial floodplain clayey sand with an average value of 1 621 mg/L and 1 498 mg/L, respectively. The quality of the groundwater is classified as very hard with more than 180 mg/L of CaCO₃ of total hardness.

Abstract

After drilling technology improvements in South Africa in the early 1900s, several deep (>300 m) exploratory drilling programmes were conducted to explore for pressurised groundwater resources. The results were not significant, except for the Cretaceous Uitenhage Artesian Basin and recent investigations in folded Table Mountain Group Aquifer systems. Large sedimentary units in Southern Africa do have the structural geometry to drive regional artesian systems; however, diverse climate and aquifer hydraulic limitations counteract these conditions to such a level that sustainable basin- like  deep  flow mechanisms  are  probably  non-existing,  except where enhanced  by  deep mining activities.

On the contrary, several deep drilling projects in South Africa, Botswana and Namibia have undoubtedly  proven  the  existence  of  pressurised  groundwater  strikes  below  300 m  (northern Kalahari)  to  as  deep  as  3 000 m  (western  Karoo  Basin).  Given  the  regional  hydrogeological characteristics of these systems, the availability of sufficient recharge zones required to drive sustainable artesian flow or semiartesian conditions becomes a challenge. The existence of isolated pressurised compartments as a result of the lithostatic pressurisation in the deeper sections of many of the sedimentary successions may prove to be a more realistic explanation for these pressurised water strikes observed during deep drilling operations in Southern Africa.

Abstract

Source protection area delineation has evolved over the last decades from fixed radius, analytical and numerical methods which do not consider uncertainty to more complex stochastic numerical approaches where uncertainties are often considered in a Monte Carlo framework. The representation of aquifer heterogeneity in these studies is typically based on a geostatistical representation of hydraulic properties. This presentation compares results from complex stochastic flow and transport simulations, simple homogeneous models, and existing analytical expressions. As a case study, we use the existing drinking supply wells in West Melton located Canterbury’s Selwyn District in New Zealand. Monte Carlo realisations are parameterised in MODFLOW6 so that the prior knowledge of the aquifer’s effective, large scale flow characteristics is honoured. Homogenous simulations are based on the same grid, using the aquifer’s effective properties to parameterise the numerical flow model. In both cases, conservative transport of pathogens is undertaken using Modpath7, using both forward and backward particle tracking. The numerical results are compared with analytical expressions from the international literature. Our results suggest that aquifer heterogeneity needs to be explicitly addressed in all cases. Homogeneous simulations almost certainly underestimate contamination risk and produce unrealistically small source protection areas. Parameterisation of the stochastic heterogeneous realisations also affects the size and extent of the source protection area, suggesting that these need to be carefully considered for practical applications.

Abstract

Underground mine water rebound prediction in its simplest form can be simulated linearly by comparing the volume of the mined ore with long-term average recharge rate to obtain an estimate of the time which will elapse before the workings are full to their decant elevation.

This type of linear interpolation of rising water levels can lead to an over estimation or an underestimation of the date when mine voids will flood to the critical levels. This is due to the fact that this method cannot account for the variability and interconnection between different mine voids and also does not consider the change in storage over time which is an important factor. In an abandoned underground water environment, water is stored in flooded mine stopes (tanks) and flows through a network of haulages (pipes). Due to the dip and strike of the ore body, the mined stopes are extensively interconnected on multiple levels and bounded by faults and dykes, so that water rising within any one tank will display a common level throughout that tank. At certain elevations, adjoining tanks may be connected via a discrete "overflow point", which may be a holding or permeable geological features. Water level rise during flooding is a function of head-dependent inflows from adjoining mine aquifers and/or other tanks, and the distribution of storage capacity within the tank.

The process of flooding occurs independently in two (or more) adjoining tanks until such time as the water level in one or more of the tanks reaches an overflow point. Inter-tank transfers of water will then occur until the difference in head between the two tanks either side of each overflow point is minimised. To apply the conceptual model stated above, EPANET 2 was used to predict the risk of flooding of a mine shaft, in the Free State Goldfields, if dewatering is discontinued. Considerations on stope volumetric calculations, haulage interconnections, modelling assumptions and predictions, are presented.

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

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

With increasing population growth and a subsequently increased demand for food production, the agricultural sector has had to grow and develop continuously despite drought-stricken water resources in recent years. The expansion in this sector requires increasingly efficient water use management and increases in water supplies, which are often met through groundwater utilization. In the past several years the use of groundwater in the Western Cape has increased exponentially and thus has forced the sharing of resources. The question pertains to how an invisible water resource that is difficult to measure and quantify, can be shared. Issues of varying complexities can arise when submitting a water use licence application (WULA), such as historical water use debates, interactions between groundwater and surface water, seasonal stresses on resources, etc. In one case study in De Doorns, a WULA became side-tracked soon after initiation by a neighbour’s complaint that his production borehole was severely affected by the drilling of the applicant’s boreholes. In the second case study in the Hexriver Valley, a WULA was complicated by a gentleman’s agreement stating that no one in the valley is allowed to abstract groundwater from deeper than 6 m. This gentleman’s agreement stems from past disagreements regarding such practices. The final case study was not a WULA but arose out of concerns for dropping weir levels connected to a new borehole. The borehole was equipped with new casing to case off the alluvium; it was suspected to be the cause of the disturbance. The scientific method was used to evaluate the borehole’s impact on the weir. Case studies such as these will become more prevalent as the demand on water resources will increase. Hydrogeologists needs to more informed of the complexities that can and will arise in the future as a result of shared water resources.

Abstract

Industrial  facilities  and  mining  activities  represent  a  potential  contamination  hazard  to  down gradient surface water and groundwater environments. The assessment of the risks posed by such contaminant sources should facilitate regulators to determine set compliance limits. These limits should, however, take in consideration the heterogeneous nature of fractured rock aquifers. This paper will focus on the limitations or technical feasibility of applying single groundwater quality compliance limits for fractured rock aquifers. It will also aim to describe how groundwater contamination limits could be determined in a more feasible manner.

Abstract

As we look at the legislation set out in the driving policies and its guiding frameworks, the need for able institutions to implement strategies that promise and deliver social growth and development, are highlighted. It is only possible to define an 'able institution' through its ability to fulfil its function and enable stakeholders to be part of the decision-making process. (Goldin, 2013) It is this relationship with the collection of stakeholders, in particular strategic water resource stakeholders, their linkages as well as the identification of specific stakeholder issues, that are critically reviewed. The recent Groundwater Strategy (2010) identified key strategic issues/themes. Each chapter listed a number of well thought out recommended actions that address specific challenges in each theme. It is the need for strategic direction (to put these strategies in place "plans into action") and to articulate the specific vision in the right context to the different stakeholders, (internal as well as external) that requires thinking. It is also the uptake of this information by publics (social action and intervention) and the impact of new learning that will need to be measured. This paper will present on a study where the groundwater sector and all its stakeholders are strategically examined to understand the process of communal thinking in the current environmental conditions. It would draw from current communication practices, style, strengths, sector experiences and trends and also reference specific and unique experiences as with the recent WRC Hydrogeological Heritage Overview: Pretoria project. {List only- not presented}

Abstract

Groundwater resources in Africa face increasing threats of over-exploitation and pollution due to urbanization, agricultural and mining activities, yet monitoring remains challenging. Conventional approaches to monitoring groundwater at the exclusion of communities have not been successful. To overcome this, it is important to fully engage and train local communities in monitoring Groundwater Levels (GWLs), Rainfall and Water Quality (RWQ), which are important for understanding groundwater dynamics in wellfields. In this way, villagers can better understand groundwater issues and convey this information to others to cooperatively manage groundwater. A pilot program to monitor GWLs and RWQ by locals was initiated in two villages each in Botswana and Uganda to learn about its effectiveness. Through continuous stakeholder engagement, the local communities in the two case studies have been facilitated, trained and supported in monitoring groundwater and using the information collected to understand groundwater trends and their sustainability. Preliminary results indicate improvement in understanding the importance of groundwater monitoring by the communities and the implications on groundwater sustainability for improved livelihoods. This has become useful to one of the communities engaged in a village-level irrigation project which depends on groundwater resources. This project builds on a successful village-level participatory approach developed in the MARVI project (www.marvi.org.in ). It seeks to contribute to the United Nation’s 2022 call on “Groundwater: making the invisible visible” to highlight the importance of better monitoring and managing this vital resource.

Abstract

South Africa's water legislation of has often been deemed 'progressive', yet implementation of policies can be weak in terms of groundwater - a resource inherently more difficult to govern than surface water due to its invisibility, difficulties in mapping, the long timescales involved and its ties to land tenure. Furthermore, shallow, hard rock aquifers are frequently perceived as "self-controlling" by their users and thus not requiring active management. This view is however not optimal in areas with a large dependence on groundwater for livelihoods invoking the question what happens between the periods of over-abstraction and the recharge events that replenish them? There is a need for better management, particularly in light of climate variability when recharge episodes can be infrequent and drought can lead to extra calls on aquifers.

Seasonal climate forecasts have the potential to provide information to contribute to groundwater management strategies. This study focuses on the case of Dendron in Limpopo Province. Numerous consultancy reports have been released over the past few decades regarding the over-exploitation of groundwater due to the area's long history of potato cultivation via groundwater-irrigation. The primary aim of this study is to determine the potential contribution of seasonal forecast information in the Dendron area for agricultural groundwater management, given insights to the needs of commercial farmers in the area the dominant users of groundwater. We examine the effectiveness of formal and informal groundwater management strategies in the area and then consider current use of seasonal forecasts and their potential value for decision-making. We also highlight the need for a better understanding of the role of seasonal climate variability in groundwater systems to understand their potential as climate buffers during periods of drought. Insights will be drawn from interviews with farmers and representatives from the Department of Water and Sanitation, and a needs-analysis workshop with the farming community. Constraints and barriers to uptake are also investigated, looking at factors such as data quality and availability, timing of forecasts, perceptions of forecasts, and their communication.

Abstract

The argument in this paper is that improved understanding of science-policy integration, where physical bases of natural science is combined with practice in managing water resource challenges, becomes critical in translating scientific knowledge into effective and sustainability solutions linked to groundwater resource protection. Such hypothesis should be attested at locally relevant scale where water resources reside and where water utilization takes place. This paper provides a practical case-study of how science-policy integration can directly impacts groundwater resource protection practice from a local, and national perspective using strategies of groundwater resources directed measures.

A combination of literature surveys, and desktop record review methods were used for the purpose of data collection from published literature and publicly accessible national databases of the Department of Water and Sanitation (DWS). Collected data were analysed using document analysis, descriptive statistics, and case study analysis methods. Based on the analysis, three types of science-policy nexus theoretical models exist in practice, namely, 1) science-policy integration, 2) policy-science integration, and 3) mixed integration. From a national perspective, the analysis showed that South Africa is able to practically apply science-policy nexus in policy implementation practice for water resources protection, and that such practice depicts a mixed integration model of the nexus. Case study analysis of the Schoonspruit-Koekemoerspruit River Catchment provided insight on how localized operationalization of groundwater resource directed measures facilitates sustained groundwater resources protection for water availability and sustainable utilization. This study provides an exemplary for collaborations between researchers and/or scientists and policy makers to ensure that science research is answering policy-relevant questions and that results from scientific work are readily available for policy implementation. In addition, there is adequate evidence to indicate that science-policy nexus can be designed and prioritized to support sustainable development agenda on groundwater resilience, and visibility at various levels.

Abstract

PFAS and pharmaceuticals in groundwater are two of many synthetic compounds currently under the attention of many researchers and environmental administration in Europe, especially in light of the revision of the EU Groundwater Directive 2006/118/EU. The two types of substances were first included in the voluntary groundwater watch list and were first formally regulated at the EU scale. This regulation implies that they will be obligatory to be monitored within national monitoring programmes for groundwater body status assessment procedures across the EU. While there is no doubt about the need to regulate the presence of these substances in groundwater, sampling procedures and QC/QA protocols may be challenging to implement as no official guidelines exist. Although scientific literature allows us to define protocols usually based on precautionary principle, these may be too difficult and expensive to implement at the national scale monitoring. This article describes a work that the Polish Geological Institute – National Research Institute undertook to define an optimal sampling process for PFAS and pharmaceuticals in groundwater. Experimentally tested factors included cleaning pumps between sampling sites, the need for using protective suits during sampling and the influence of ambient air on sample quality. Results showed that sampling protocols for PFAS and pharmaceuticals do not need to be modified concerning current protocols as these seem to be sufficient to protect groundwater samples from unintentional cross-contamination.

Abstract

Characterisation of fracture positions is important when dealing with groundwater monitoring, protection and management. Fractures are often good conduits for water and contaminants, leading to  high  flow  velocities  and  the  fast  spread  of  contaminants  in  these  conduits.  Best  practice guidelines related to groundwater sampling suggest that specific depth sampling with specialised bailers or low flow purging are the preferred methodologies to characterise a pollution source. These methods require knowledge about the fracture positions and, more importantly, flow zones in the boreholes. Down-the-hole geophysical and flow logging are expensive, complicated and time consuming. Not all fracture zones identified with geophysical logging seem to contribute to flow through   the   borehole.   An   efficient   and   cost-effective   methodology   is   required   for   the characterisation of position and flow in individual fractures. This research reviewed the use of Fluid Electrical Conductivity (FEC) logging to assist with the development of a monitoring protocol. FEC logging  proved  to  be  beneficial  as  it  provided  individual  fracture  positions,  fracture  yields  and vertical groundwater flow directions. FEC logging proved to be fast, cost-effective and practical in deep boreholes. The technique allows the development of a site-specific sampling protocol. The information so obtained assists with the identification of the appropriate sampling depths during monitoring.

Abstract

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

Abstract

The work presented relates to the influence of regional scale dykes in groundwater flow in karst aquifers of northern Namibia’s Otavi Mountainland around the towns of Tsumeb, Otavi and Grootfontein. The aquifers are well studied and are an important water source locally and for populated central areas of the country during drought. The area has parallel, eastwest trending elongated valleys and ranges shaped by the underlying synclines and anticlines of folded carbonate units of the Damara Supergroup. The role of the regional scale dolerite dykes that cut across the dolomitic aquifers has not been fully appreciated till recently. Aeromagnetic data is effective in mapping the dykes in detail. The dykes trend in a north-easterly to northerly direction into the Otavi Platform carbonate rocks. The dykes are normally magnetised with the odd remanent dyke. They consist mainly of dolerite, although in some cases are described as tectonic with hydrothermal magnetite and no dolerite material. The dykes appear to focus southwest of the Otavi Mountainland near the Paresis Alkaline Intrusive (137Ma). Examination of existing hydrogeological data reveals different characteristics of the dykes that influence groundwater flow, forming: a) conduits that enhance flow along contact zones, b) barrier to flow with compartmentalization and c) partial barrier to flow. An advantage has been taken of the understanding gained to manage mines’ dewatering and pumped water management. Future water resources management and contaminant studies will need to recognise the compartmentalised nature of the aquifer

Abstract

The basis of a hydrogeological conceptual model is the comprehensive characterisation of the groundwater system. This ranges from discrete hydraulic feature analysis to local-scale testing to integrated regional-scale aquifer system conceptualisation. Interdisciplinary data integration is critical to each level of characterisation to gain a realistic, yet simplified representation of the hydrogeological system based on various data sources. Incorporation of geological datasets, including (but not limited to) structural and lithological mapping, geotechnical core logs and geophysical surveys, in conjunction with a tailored selection of hydraulic testing techniques, are often underutilised by hydrogeologists. Yet, the contribution of these alternative hydraulic datasets cannot be overstated.

A recent hydrogeological assessment and feasibility study forming part of the planned expansion project for a base-metal mine in the Northern Cape, South Africa, offers an ideal, practical example. The localised nature of the project area and the inherently complex geological setting required a more detailed conceptual model and hydrostratigraphic domaining approach. Highly heterogeneous stratigraphy and strong structural aquifer controls necessitated characterisation by reviewing, testing and analysing various datasets. Exploratory core datasets, hydraulic aquifer tests, geological and downhole geophysical datasets, and statistical Rock Quality Designation—hydraulic conductivity relationships were interpreted to produce meaningful, refined hydraulic process identifications. A comprehensive local groundwater framework, discretised into various hydrostratigraphic units and structural domains with specified hydraulic parameters, was incorporated to provide a novel, more robust conceptual understanding of the unique hydrogeological system.