Conference Abstracts

Abstract

Agriculture in Citrusdal is dominated by citrus fruit farms with the majority of freely available land been occupied by citrus crops. However, agriculture uses large amounts of water, which is often in short supply. During periods of stress where rainfall is low and surface water sources are not recharged and increase in demand for the citrus crops due to global economy has lead farmers to seek alternative sources of water to augment current sources for irrigation. One source in particular is groundwater. Groundwater has become the primary alternative source of water as building dams is an expensive exercise and has inherent limitations, such as faulty dam walls and inflow streams drying up. The development of groundwater sources is relatively cheaper and can be spatially convenient. The Citrusdal valley is located in the Western Cape province of South Africa, the valley is located between latitudes 18o15’ and 19°10’ and longitudes 32o20’ and 32°52’. It is composed of the Precambrian Table Mountain Group (TMG) consisting of sequences of arenites and subordinate argillites overlain by extensive cover of Tertiary to Quaternary sediments. The Citrusdal valley TMG overlies the basement Malmesbury shales at great depth. The Citrusdal Valley is primarily composed of the Peninsula sandstone, Cedarberg shale Formations and the topmost Nardouw Subgroup sandstone. Groundwater is located within two units within the Citrusdal basin, the Nardouw aquifer and Peninsula aquifer. Groundwater in the basin is constrained by large faults, small-scale fracture networks, lithologies, and topography. This project uses groundwater chemistry, exploration drilling and pumping tests to examine the groundwater system in the region to understand the complex geometric and hydraulic properties of the syncline basin. Understanding the geometric and hydraulic properties plays a significant role in developing agriculture in the region and to help manage the groundwater so that it is sustainable.

Abstract

The Saldanha / Langebaan area is expanding at a significant rate, increasing the water demand for the area. The expansion comes from the industrial, residential and tourism sector. In addition there are economically viable deposits of silica and phosphate in the area. Ecosystem functioning in the area is also to a degree dependent on groundwater. All of these factors require an improved understanding of the geohydrology of the area. The geology of the area consists of basement Cape Granite and Malmesbury Group rocks that underlie the sediments of the Sandveld Group. The unconsolidated formations present, are (in order of oldest to youngest) as follows: - Elandsfontyn Formation (oldest): This formation overlies the bedrock in depressions and palaeo-channels in the bedrock. This formation is about 40 m thick and is composed of upward fining quartz sediments. - Varswater Formation: This formation is composed of marine deposits and is restricted to the western (seaward) parts of a bedrock depression to the east of the Langebaan Lagoon and Saldanha. The formation is characterized by rounded quartz grains. - Langebaan Formation: This formation consists of calc-arenites. The sediments are generally grey to cream coloured and consist of quartz and shell fragments, the grain size ranges from coarse to fine and the consolidation is variable. - Witzand Formation (youngest). This formation consists of light-coloured, calcareous, coastal dune sand that can be distinguished from the underlying consolidated Langebaan Formation. The Elandsfontyn Aquifer System (EAS) and the Langebaan Road Aquifer System (LRAS) are the main aquifer systems in the area. These aquifer systems are defined by palaeo-channels that have been filled with gravels of the Elandsfontyn Formation and represent preferred groundwater flow paths. Within each of these aquifer systems (EAS and LRAS) two aquifer units are present. Namely, the confined Lower Aquifer Unit (LAU) geologically consisting of the basal gravels of the Elandsfontyn Formation and the Upper Aquifer Unit (UAU) composed of consolidated sands and calcrete. The two units are separated by a clay aquitard. A numerical model has been established for the area, and extends from the Berg River to the Langebaan Lagoon. Granite outcrop and river system define the other boundaries of the model. Extensive logging of groundwater levels by the Department of Water and Sanitation (DWS) has enabled the accurate establishment of a model. In addition extensive field work and a detailed hydrocensus, as well as the capture of a lot of historical information has resulted in a comprehensive GIS which assists with the refinement of the numerical model. The model provides a valuable tool in modelling potential impacts whether they been from planned groundwater abstraction or artificial recharge. {List only- not presented}

Abstract

The Council for Geoscience has a corporate responsibility in rural development projects as part of the South African government initiative in food and water security. Geophysical surveys were carried out at Elizabeth Conradie School in Kimberley, Northern Cape Province South Africa aimed on siting production boreholes to supply the school with water. Traditional geophysical techniques including magnetic, electromagnetic and resistivity were used to locate groundwater bearing structures. The magnetic method was used to locate intrusive magnetic bodies (i.e. Dolerites), while electromagnetic and resistivity were used to map conductivity and resistivity distribution associated with the subsurface geology.

The magnetic method delineated possible groundwater bearing structures which may be related to dolerite dykes and sills. The electromagnetic method appears to have identified shallow fresh dolerite sill. The resistivity method was good in identifying areas of low resistivity which might be related to fractures and/or faults. The high resistivity values might be related to dolerite dykes or sill.

The results of the study showed that geophysical methods are useful non-intrusive tools for mapping groundwater resource. The 1:250 000 scale geological reconnaissance map used to constrain the geophysical interpretation is at a bigger scale when compared to the geophysical interpretation resolution. Considering this and also the ambiguity and none uniqueness in geophysical interpretation, results need to be consolidated by a local scale hydrogeological mapping and drilling results.

Abstract

Two numerical simulations using Feflow® software were conducted to demonstrate the utility of geophysical data to accurately determine groundwater levels and provide additional data to the groundwater modelling community to improve the model’s accuracy. One simulation is based on regional piezometric data, and the other uses geophysical data acquired through transient electromagnetic (TEM), electrical resistivity (ERT), and ground-penetrating radar (GPR) surveys. After both numerical analyses, the root mean square errors (RMS) obtained from the piezometric data and the multiple geophysical techniques to confirm the correlation between observed and simulated water levels were similar at 3.81 m and 2.76 m, respectively. Through a discrete modelling approach, this study shows that groundwater levels estimated using geophysical tools and methods and those determined by direct observation are comparable. In addition, before the 3D numerical flow model, a 3D geological model was built to fully represent this highly complex, heterogeneous, and anisotropic hydrological environment of the Saint-Narcisse moraine glacial deposits in eastern Mauricie, Québec. This stratigraphic reconstruction with Leapfrog software was necessary to provide a more detailed and realistic representation of this complex aquifer system. This study illustrates how geophysical data can complement direct observations to provide additional hydraulic information to hydrologic modellers. Geophysical surveys provide an extensive set of soft data that can be leveraged to improve groundwater flow models and determine water-table heights, particularly in areas characterized by limited direct piezometric information.

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

Periodic climate variability, such as that caused by climate teleconnections, can significantly impact groundwater, and the ability to predict groundwater variability in space and time is critical for effective water resource management. However, the relationship between climate variability on a global scale and groundwater recharge and levels remains poorly understood due to incomplete groundwater records and anthropogenic impacts. Moreover, the nonlinear relationship between subsurface properties and surface infiltration makes it difficult to understand climate variability’s influence on groundwater resources systematically. This study presents a global assessment of the impact of climate teleconnections on groundwater recharge and groundwater levels using an analytical solution derived from the Richards equation. The propagation of climate variability through the unsaturated zone by considering global-scale climate variability consistent with climate teleconnections such as the Pacific-North American Oscillation (PNA) and the El Niño/Southern Oscillation (ENSO) is evaluated, and it is shown when and where climate teleconnections are expected to affect groundwater levels. The results demonstrate the dampening effect of surface infiltration variability with depth in the vadose zone. Guidance for predicting long-term groundwater levels and highlighting the importance of climate teleconnections in groundwater management is provided. The obtained insights into the spatial and temporal variability of groundwater recharge and groundwater levels due to climate variability can contribute to sustainable water resource management.

Abstract

Water management is a difficult and complex business requiring appropriate institutional arrangements as well as guidance and support from government, which is often unable to act effectively to address day-to-day water resource management (WRM) issues. Theoretically, water as a 'common pool resource' is best managed by users self-organised at a local level and within a basin framework. Water users and other stakeholders have detailed and up-to-date local knowledge as well as an interest in ensuring effective management to share water equitably between different users and to control pollution. This approach is supported by South Africa's National Water Act (NWA), which provides for the establishment of Catchment Management Agencies (CMAs) to perform a range of WRM activities within the framework of a National Water Resource Strategy (NWRS).
Hence, water resource management in general and conjunctive use in particular requires cross sector and cross level cooperative governance. Relevant institutions include the DWA at national and regional level, the CMA, if established, provincial departments that might impact on the water resources, water user associations, water services authorities, water services providers, water boards, and individual water users. These institutions are responsible for various activities and often require some level of inter- and intra-institutional cooperation. Ideally, multiple organisations, policies, legislation, plans, strategies and perspectives should be involved in water-related decision-making, which in turns creates complex leadership challenges. Globally, the lack of sustainable groundwater management can be ascribed to poor governance provisions. These include, but are not limited to, institutional arrangements and political will, including fragmented and overlapping jurisdictions and responsibilities, competing priorities, traditional approaches, rights and water pricing systems, diverging opinions, incomplete knowledge, data as well as uncoordinated information systems. Adding the poor operational and maintenance issues, decision-makers often view groundwater as an unreliable resource and are hesitant to make significant investments in groundwater infrastructure and capacity.
The recent Worldbank and WRC report on groundwater governance in South Africa revealed that the technical, legal, institutional and operational governance provisions were found to be reasonable at the national level but weak concerning cross-sector policy coordination. At the local level, basic technical provisions such as hydrogeological maps and aquifer delineation with classified typology are in place but other governance provisions such as institutional capacity, provisions to control groundwater abstraction and pollution, cross-sector policy coordination and the existence and implementation of groundwater management action plans are weak or non-existent.
It appears from this review that the major hindrances for sustainable groundwater governance and more so for integrated water resource management and conjunctive use scenarios are the discrepancy between groundwater and surface water provisions in the relevant legislation, associated guidelines and their implementation at regional and local, and the lack of skills and clear responsibilities for implementing water resource management actions at municipal level. This is demonstrated with several case studies.

Abstract

POSTER About 97% of the earth's freshwater fraction is groundwater, excluding the amount locked in ice caps (Turton et al 2007) and is often the only source of water in arid and semi-arid regions and plays a critical role in agriculture, this dependency results in over-exploitation, depletion and pollution (Turton et al 2007). Groundwater governance helps prevent these issues. CSIR defines governance as the process of informed decision making that enables trade between competing users of a given resource, as to balance protection and use in such a way as to mitigate conflicts, enhance security, ensure sustainability and hold government officials accountable for their actions (Turton et al 2007). Realising the issues of groundwater governance is a requirement for developing policy recommendations for both national and trans-boundary groundwater governance. Groundwater level decline has led to depletion in storage in both confined and unconfined aquifer systems (Theesfeld 2010). There are about six institutional aspects, namely voluntary compliance, traditional and mental models, administrative responsibility and bureaucratic inertia, conflict resolution mechanisms, political economy and information deficits (Theesfeld 2010). Each of these aspects represents institutional challenges for national and international policy implementation. Traditional local practices should not be disregarded when new management schemes or technological innovations are implemented. The types of policies that impact governance include regulatory instruments, economic instruments and voluntary/advisory instruments. Regulatory or command and control policy instruments such as ownership and property right assignments and regulations for water use are compulsory. Economic policy instruments make use of financial reasons such as groundwater pricing, trading water right or pollution permits, subsidies and taxes. Voluntary /advisory policy instruments are those that influence voluntary actions or behavioural change without agreement or direct financial incentives. These are ideal types though no policy option ever relies purely on one type of instrument. The aim of these policies is to have an impact on governance structures (Theesfeld 2010). The national water act (1998) of the Republic of South Africa is not widely recognized as the most comprehensive water law in the world even though it is the highlight of socio-political events; socially it is still recent in most sites although the law was implemented 15 years ago (Schreiner and Koppen 2002). Regulations for use include quantity limitations, drilling permits and licensing, use licenses, special zone of conservation and reporting and registering requirement. In general when drilling and well construction are done commercially they increasingly fall under the scope of regulatory legislation. This paper will focus mostly on traditional and mental models; procedures that a certain community is dependent on should be taken into account before replacing with technological advanced tools. Consultation of the public can cause conflicts which lead to poor groundwater management.

Keywords: Groundwater governance, policy, policy instruments.

Abstract

Groundwater is increasingly being exploited in South African cities as a drought crisis response, yet there is poorly coordinated regulation of increasing urban users and usage and fragmented management of aquifers. Designing interventions and innovations that ensure sustainable management of these resources requires systems thinking, where the city is understood as an integrated, interdependent set of actors and flows of water. This paper presents a study that applied and integrated an urban water metabolism (UWM) analysis with a governance network analysis for two major South African cities facing severe drought risk, Cape Town and Nelson Mandela Bay. ‘Learning Laboratories’ in each city brought together stakeholders from various groundwater-related domains to build a shared understanding of how groundwater fits into the larger system and how various actors shape urban groundwater flows and the health of local aquifers. The UWM quantified all hydrological and anthropogenic flows into and out of each city (or urban system) to conduct an integrated mass balance. How this mass balance changes under varying climate change scenarios and land use was used as a focal point of stakeholder discussions. The governance network analysis highlighted that many state and non-state actors have a stake in shaping the quantity and quality of urban groundwater, such as regulators, service providers, water users, knowledge providers, investors in infrastructure, and emergency responders.

Abstract

Water scarcity is a growing issue in South Africa. The consumption of water is rising and as such, water is becoming a scarce and valuable resource. Given the circumstances that South Africa is facing, improving the use of ground water could help tackle water scarcity in South Africa. Groundwater has been an important source of water and it can bring socio-economic benefits if properly used. Studies have proved that groundwater resources play a fundamental role in the security and sustainability of livelihoods and regional economies throughout the world. However, in South Africa, groundwater still remains a poorly managed resource and this hinders socio-economic development. This paper examines the current state of ground water management in South Africa. The paper also examines how ground water in South Africa is currently allocated and used, and explores some of the consequences of current water management arrangements. {List only- not presented}

Abstract

Hydraulic behaviour of an aquifer is defined in terms of the volumes of water present, both producible and not (specific yield and specific retention), and the productivity of the water (hydraulic conductivity). These parameters are typically evaluated using pumping tests, which provide zonal average properties, or more rarely on core samples, which provide discrete point measurements. Both methods can be costly and time-consuming, potentially limiting the amount of characterisation that can be conducted on a given project, and a significant measurement scale difference exists between the two. Borehole magnetic resonance has been applied in the oil and gas industry for the evaluation of bound and free fluid volumes, analogous to specific retention and specific yield, and permeability, analogous to hydraulic conductivity, for over twenty years. These quantities are evaluated continuously, allowing for cost-effective characterisation, and at a measurement scale that is intermediate between that of core and pumping tests, providing a convenient framework for the integration of all measurements. The role of borehole magnetic resonance measurements in hydrogeological characterisation is illustrated as part of a larger hydrogeological study of aquifer modeling. Borehole magnetic resonance has been used for aquifer and aquitard identification, and to provide continuous estimates of hydraulic properties. These results have been compared and reconciled with pumping test and core data, considering the scale differences between measurements. Finally, an integrated hydrogeological description of the target rock units has been developed.

Abstract

Groundwater boreholes are a key element of many mining projects, as part of dewatering and water supply  systems,  and  must  achieve  high  levels  of  operational  efficiency  and  service  availability. Outside of the mining industry, planned borefield maintenance programmes have become a key part of professional well-field management, with proven benefits in terms of operational cost savings and continuity of pumping. However, the benefits of proactive planned maintenance of groundwater boreholes on mine sites have only recently been widely recognised. Potential operational problems are described, including water quality issues which can result in mineral contamination leading to deposits and scale build-up which can clog screens and pumps, reduce water flow and yield, and eventually cause pump breakdowns and mine stoppages. Best practice methodologies to remove or minimise the contamination are described and the benefits of implementing a planned maintenance programme are discussed. Case studies are described from two significant mines in Australia, where boreholes suffered from mineral contamination, including calcium carbonate and iron bacteria contamination. Both mines suffered  from  increased  pump  breakdowns,  groundwater  yields  consistently  below  target  and serious cost overruns. Borehole rehabilitation treatment plans were implemented to resolve the immediate contamination problems followed by an ongoing maintenance programme to prevent or minimise their reoccurrence. Treatment programmes included a downhole camera survey, use of a bespoke software program to review the results of the survey and the available water quality data, and a purpose built rehabilitation rig that included the use of specialist chemical treatments to remove and control the existing encrustation and clogging deposits.

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

The increase in awareness of environmental issues and the desire for a cleaner environment by the public has caused mining companies to place greater emphasis on the continuous rehabilitation of harmful effects caused by mining operations. Ongoing rehabilitation is also a requirement of the government departments involved in mining in South Africa. The biggest concern for the relevant government departments is the possible uncontrolled pollution of water resources in the vicinity of mines, after they have closed. In  the  compilation  of  this  paper,  the  unique  nature  of  the  South  African  situation  has  been considered – this refers to a legally acceptable approach towards current legislation and policies. This study leads to the construction of a logical approach towards mine closure, specifically to understand issues around costs and financial liability. The final product of this approach should ultimately give more clarity on: 

the principles followed to identify objectives for mine closure and groundwater assessment;

key steps to follow when assessing site hydrogeology and to determine related impacts, risks, closure costs and liabilities; and an overview of methods that could be used for the mitigation of polluted aquifers and a brief site-specific application.

Abstract

The increase in awareness of environmental issues and the desire for a cleaner environment by the public has caused mining companies to place greater emphasis on the continuous rehabilitation of harmful effects caused by mining operations. Ongoing rehabilitation is also a requirement of the government departments involved in mining in South Africa. The biggest concern for the relevant government departments is the possible uncontrolled pollution of water resources in the vicinity of mines, after they have closed.

In  the  compilation  of  this  paper,  the  unique  nature  of  the  South  African  situation  has  been considered – this refers to a legally acceptable approach towards current legislation and policies. This study leads to the construction of a logical approach towards mine closure, specifically to understand issues around costs and financial liability. The final product of this approach should ultimately give more clarity on:

the principles followed to identify objectives for mine closure and groundwater assessment;

key steps to follow when assessing site hydrogeology and to determine related impacts, risks, closure costs and liabilities; and

an overview of methods that could be used for the mitigation of polluted aquifers and a brief site-specific application.

Abstract

Groundwater is the water that is found beneath the surface of the ground in a saturated zone (Bear 1979). Groundwater contamination refers to the groundwater that has been polluted commonly by human activities to the extent that it has higher concentrations of dissolved or suspended constituents. The scale of the potential supply of groundwater from the Cape Flats Aquifer Unit (CFAU) is very significant due to the increase of the population in Cape Town that leads to limited water resources (Maclear 1995). Groundwater contamination is a threat in the Cape Flats. This is because sand is more susceptible to pollution as a result of urbanisation, industrialisation, intense land use area for waste disposal and agricultural activities (Adelana 2010). The aim of this paper is to evaluate groundwater contamination and assess possible prevention and treatment measures in the CFAU. Pumping tests were done in UWC site in Borehole 5 (pumping borehole) and Borehole 4 (observation borehole) for six hours; three hours was for the pumping and the other three hours for recovery. This was done in order to see how the aquifer recovers after pumping. Water samples were also taken and analysed in the lab. This was done to find the type of contamination, whether it is degradable or non-degradable. The Borehole 5 drawdown plot is showing a straight line. This suggests a linear flow and that there is no confining bed beneath. This is because straight lines are showing the Cooper-Jacob type curve, which is for unconfined aquifers. The curve of Borehole 4 can be fitted to a Theis-type curve. This suggests a radial flow pattern indicating homogeneous characteristics in the deeply weathered zone and that there is a confining bed beneath. This is because aquifers responding in the same manner as the Theis-type curve, are confined aquifers (Hiscock 2005).The groundwater samples are showing a TDS range of 260 to 1 600 mg/l. This could be the result of the waste water treatment plant that is near UWC and the industries that are near the airport and at Bellville South. In conclusion, the geology of the CFAU is very susceptible to groundwater contamination, which is due to agricultural, industrial and human activities.

Abstract

The interaction between groundwater and wetlands is poorly understood, even though it has been the topic of many research projects, like the study done at the Langebaan Lagoon. This interaction is complex as it lies at the intersection between groundwater and surface water, but each situation is unique, with different conditions regulating the interaction. Wetlands can be the source of water that recharges groundwater systems on the one hand, while the other is dependent on the groundwater systems. This interaction became part of the project looking at how to implement Managed Aquifer Recharge for Saldanha Bay Local Municipality without having a negative impact on the groundwater-dependent ecosystems, such as the springs and wetlands in the area. Ten wetlands were identified on the Langebaan Road Aquifer Unit, and a monitoring programme was developed. The purpose of the monitoring was to determine the status of the wetlands as a baseline before the implementation of managed aquifer recharge and to determine the level of groundwater dependence. The latter was done by hydrochemical analysis of rainwater, groundwater and water from the wetlands and stable isotope analysis. The ability of the wetlands to act as a recharge point to the groundwater system will be investigated through column experiments and lithostratigraphic analysis of soil columns taken at the wetlands. Groundwater levels will also be plotted as contour lines to determine the intersection of the water table with the wetlands in the area.

Abstract

The Western Cape has experienced a drought since 2015 and one of the regions most adversely affected by this drought was the Swartland. Towns in this region make use of water supplied by the Vo?lvlei Dam, which is the Swartland Municipality's bulk and only source of water. Groundwater exploration was undertaken to find alternative sources of water which would be used to relieve some of the pressure on surface water resources. A total of seven towns and communities were identified as high risk and most vulnerable. These include Abbotsdale, Koringberg, Malmesbury, Moorreesburg, Riebeek Kasteel, Riebeek West and Riverlands. This project posed several challenges, namely: available land, proximity to infrastructure and unfavourable geology (in terms of groundwater potential). The project had mixed results in terms of quality and yield. This paper presents the approach and results of the groundwater development.

Abstract

The original City of Cape Town (CCT) Table Mountain Group (TMG) Aquifer Feasibility Study and Pilot Project was initiated in 2002, the purpose being to evaluate the feasibility of augmenting the CCT's bulk water supply using groundwater from the TMG (specifically the fractured Peninsula and Nardouw Aquifers). CCT TMG groundwater exploration/development was fast tracked under the "New Water Programme" (NWP; from 2017-present) as a result of two interrelated water scarcity/demand factors, namely periodic drought (including the major 2015-2017 1:590-year event) and rapid urban growth. Initial NWP TMG groundwater development (including additional exploration via detailed geological mapping and heliborne geophysics) has occurred in the vicinity of the CCT-operated Steenbras Dam, in the form of a minimum 15-20 Ml/day wellfield scheme. The planned "Steenbras Wellfield" targets both TMG aquifers along the Steenbras-Brandvlei Megafault Zone on the southeastern limb of the Steenbras Syncline (which regionally occurs within the high groundwater potential Cape Fold Belt Syntaxis). Current drilling activities have included ultra-deep (up to 975 m depth, representing the deepest groundwater-specific boreholes outside of mining/resource activities in South Africa), wide diameter abstraction (using rotary air percussion, reverse circulation and hydraulic/water hammer techniques) and core exploratory boreholes into both TMG aquifers. Tested abstraction borehole yields range between 10-70 l/s, while artesian-discovery core holes into the Peninsula Aquifer from Steenbras towards Theewaterskloof Dam have surface pressures and flows of up to 800 kPa and 4 l/s respectively (from BQ-sized holes intersecting water strikes between 840-910 m). Further CCT TMG groundwater exploration and wellfield scheme development (potential total combined supply of ~50-150 hm3/a or ~140-400 Ml/day) is planned along major TMG structures within the Grabouw-Eikenhof and Theewaterskloof basins, Wemmershoek, Voelvlei, Berg River and the CCT South Peninsula region. This has, and will continue to include, monitoring of surface/groundwater-dependent ecosystems as a geo-ethical approach to minimise ecological/environmental impact.

Abstract

POSTER The Department of Transport and Public Works has been involved with the building and upgrading of schools in the Western Cape, as well as providing green areas for sports fields. Due to the excessive costs of using municipal water the option of using groundwater for irrigation was investigated by SRK Consulting. A number of successful boreholes have been scientifically sited, drilled and tested since 2011. The boreholes have been equipped with pumps and data loggers have been installed in several. These data loggers measure time-series water levels and temperature while the flow meters measure the discharge rate and the quantity of groundwater used. Currently groundwater is being abstracted to irrigate the sports fields. Initially some problems were encountered. Boreholes were not operating optimally due to incorrect pump sizes resulting in water levels to be at pump inlet depths and pumps were not being switched off for recovery. However, due to continuous monitoring, the pumping rates and times were adjusted accordingly. It is imperative that all boreholes are equipped with loggers and continuously monitored to ensure that the boreholes are being optimally and sustainably used. Monitoring groundwater abstraction and aquifer water levels provides critical information for proper groundwater resource management. It is envisaged that schools will become proactive and participate in the groundwater monitoring. The latter will assist with groundwater awareness and assist in the use of alternative water sources and ease the burden on already stretched conventional sources.

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 The Jeffreys Bay Municipal borehole field is located in the coastal town of Jeffreys Bay, Eastern Cape Province, South Africa. It is underlain by the Jeffreys arch domain which features the Skurveberg and Baviaanskloof formations of the Table Mountain Group. The Jeffreys arch has been subject to groundwater exploration, targeting its characteristic faults and folds. The investigation was intended to establish five (5) high yielding boreholes with good water quality. Geophysical surveys, drilling and pump tests were conducted in succession. Ground surveys were carried out across the study area using the electromagnetic method to identify subsurface geological structures through anomalies in the earth's magnetic field. The interpretation of the data revealed significant anomalies within an anticlinorium. Drilling through quartz and quartzitic sandstone posed considerable difficulties mostly along zones of oxidation. The main water strikes with airlift yields of 9 - 35 L/s were intersected within quartzitic sandstone at depths of about 120m and greater. Chemical sampling results revealed adherence of iron and manganese concentrations to the drinking water recommended limits as per SANS 241-1 (2011). Two (2) of the five (5) boreholes revealed higher than recommended of iron and manganese concentrations. The aquifer test data was processed using the Flow Characteristic programme, the recommended abstraction rates range between 4-17 L/s/24 hrs. Results observed during different exploration phases revealed high yields and good water quality with greater depths as compared to the existing shallow boreholes with high iron, conductivity and manganese concentrations. Treatment of borehole water with high concentrations is necessary. It is recommended that drilling for groundwater resources within the anticlinorium of the Jeffreys arch be done at great depths.

Abstract

In this study the groundwater resource in the Tsineng area in the Northern Cape Province was assessed in terms of the volumes of water that may be sustainably removed from the aquifer system, and the quality of the available groundwater. A strong emphasis was placed on the use of airborne and ground geophysical techniques to gain a better understanding of the geological and geohydrological conditions in the study area. The airborne geophysical technique employed during the current investigation was the time-domain electromagnetic (TDEM) method employing the SkyTEM system, while the ground geophysical surveys consisted of gravity, magnetic, frequency-domain electromagnetic and electrical resistivity tomography surveys. The geophysical techniques were used to provide information on physical changes in the subsurface conditions that may be related to the presence of geological structures associated with potential groundwater resources.

The TDEM data revealed well-defined resistivity anomalies which correlated with two known prominent fault zones. Resistivity anomalies were also identified at the locations of mapped dolerite dykes known to intersect the study area. The ground geophysical investigations were conducted across preliminary targets defined from the airborne TDEM data and confirmed the presence of the identified structures. Based on the results of the geophysical investigations and the known geological conditions, drilling targets were selected at positions deemed promising for the installation of successful production boreholes. A total of 78 exploration boreholes were drilled of which 60 had water strikes. Forty of the boreholes had blow-yields in excess of 2 L/s, with a combined total blow-yield of 409 L/s. These boreholes were selected for hydraulic tests to assess the hydraulic parameters of the intersected aquifer systems. From the estimated hydraulic parameters the total sustainable yield from the boreholes was estimated at more than 7 500 m 3 /day.

Chemical analyses of water samples from the 40 high-yielding boreholes showed that the water in the study area is generally of very good quality, suitable for human consumption. The results of the current research demonstrate that the use of geophysical techniques could greatly contribute to an understanding of the geological and geohydrological conditions in a study area, which could in turn lead to a higher success rate during groundwater exploration programmes.

Abstract

This paper presents the results of groundwater flow modelling studies that were conducted within the scope of the PRIMA RESERVOIR project. The project’s main goal is to develop an innovative methodology to mitigate land subsidence due to excessive groundwater exploitation in water-stressed Mediterranean watersheds. This objective is achieved by integrating earth-observation-derived land subsidence rates with a coupled implementation of numerical groundwater flow and geomechanical modelling. MODFLOWbased 3-D transient flow models were constructed for the four pilot sites (the coastland of Comacchio in Italy, the Alto Guadalentín aquifer in Spain, the Gediz River basin alluvial aquifer in Turkiye and the Azraq basin in Jordan) that have different hydrogeological properties and pose different challenges concerning water management. Models were calibrated and run for similar simulation periods (2013-2021) to obtain hydraulic head drawdowns and changes in groundwater storage. Land subsidence at these sites was evaluated using Advanced Differential Radar Interferometry (A-DInSAR) on image stacks from the Sentinel-1 satellite. Subsidence rates were then compared to hydraulic head drawdown rates to identify groundwater pumping-induced subsidence areas. The comparison for all study areas suggested that locations of maximum displacements do not necessarily coincide with areas that display the largest head drawdown calculated by the flow models. Other triggering factors, such as the thickness of compressible materials, are also related to high subsidence areas.

Abstract

Evidence suggests that physical availability of groundwater may be only one of many factors in determining whether groundwater-based rural water supply schemes in South Africa are reliable or "sustainable". Other factors include budgetary constraints, community preferences, policy decisions, operation and maintenance procedures, and the availability of skilled staff. These factors and others combine to create "complex problems" around the issue of rural water supplies that require a multidisciplinary approach if they are to be effectively resolved. This work is an on-going part of Water Research Commission Project K5/2158, “Favourable Zone Identification for Groundwater Development: Options Analysis for Local Municipalities”, due to be completed in March 2014.

Abstract

South Africa has an energy crisis. The country requires 53 Gigawatt of new capacity by 2030. The exploitation  of  unconventional  gas  is  a  potential  game-changer  to  meet  South  Africa’s  current energy deficit to fuel economic growth and development. Water management, both in terms of abstraction and disposal, has emerged as a critical issue in the development of unconventional gas reservoirs. This presentation focuses on a high-level, qualitative analysis of the groundwater-related institutional and governance challenges associated with unconventional gas exploration and production. The findings represent a synthesis of information sourced from regulatory and legislative documents as well as international experience. The analysis maps the current groundwater institutional and governance landscape in South Africa and lessons learned from other regimes such as the United Kingdom and United States of America. Good governance entails ensuring that there is compliance with policy and legislation, effective decision-making, appropriately allocated accountability, transparency and that stakeholder interests are considered and balanced. This forms the basis of a preliminary gap analysis.

Abstract

South Africa has committed to achieving the United Nations Sustainable Development Goals (SDG's) by 2030. But what does this mean and how does groundwater fit in to this? SDG 6 in particular focuses on ensuring universal access to safe and affordable drinking water for all by 2030. SDG 6 requires that the country protects and restores water-related ecosystems such as forests, mountains, wetlands, aquifers and rivers which are essential if we are to mitigate water scarcity. To accomplish this, South Africa has proceeded to align various plans, strategies, and policies to encompass the targets of the SDG's. This paper will focus on SDG sub-goal 6.3 which incorporates improvement of water quality and sub-goal 6.6 which involves protection and restoration of ecosystems. The methodology given by the UN for the groundwater in indicator 6.3.2 stipulates that countries are required to report on "proportion of water with good ambient water quality", in South Africa however we had to domesticate the indicator i.e. render it suitable for South African conditions so we changed the methodology to "proportion of water the conforms to the Water Quality Objectives (WQO's)" but there are virtually no WQO's developed for groundwater. Four core groundwater quality parameters (Electrical Conductivity, pH, Nitrate and Sulphate) are available through ZQM stations categorized through 65 hydrogeological (Vegter) regions. Groundwater water quality baseline is calculated as a reference period/range per hydrogeological region. For SDG 6.6, the indicator required for groundwater is "Quantity of groundwater within aquifers" The methodology received by the UN for "Quantity of groundwater within aquifers" required a baseline (average reference period of five years) in meters per hydrogeological region. This indicator is again domesticated for South Africa and based on the 40-60 percentiles of groundwater levels per hydrogeological region. There are a number of future indicators that can be included for aquifers under SDG 6.6, but the groundwater sector needs to come together and decide what is important to report on. These SDG targets reporting has given the Water and Sanitation sector a new look at data. It has forced us to critically think of concepts such as baseline and performance monitoring. We now know where our data gaps and targets are, and we have to provide an action plan to address these.

Abstract

Historically Finsch Diamond Mine has experienced groundwater inflow in the underground workings of the mine. The inflow results in unsafe and undesirable working conditions. Sampling was conducted over a three month period in order to determine the source of the groundwater inflow. The sampling consisted of various underground samples, monitoring borehole samples as well as surficial water body samples. The samples were analysed for major and minor chemical constituents as well as O18 and H2 isotopes. In order to determine the source of inflow in the underground workings the samples were compared to that of the South African drinking water standard (SANS), graphically interpreted via Piper, expanded Durov and Stiff Diagrams as well as isotopically analysed by comparison to the Global Meteoric Water Line (GMWL). Geochemical modelling was employed in order to determine the typical chemical constituents where groundwater interacts with tailings material and to calculate mixing ratios. Comparison to SANS and the geochemical modelling indicated that elevated sulphate and sodium is associated with fine residue deposit (FRD) water. The Piper and expanded Durov diagrams indicated the presence of three major water types namely: calcium-magnesium-bicarbonate, calcium-magnesium-sulphate and sodium-sulphate types. The isotope analysis indicated the presence of three major water types namely: samples which correspond well with the GMWL, samples which do not correspond well with the GMWL but fall along a mixing line and water which does not correspond with the GMWL. From the analyses, it was clear that water with a sodium-sulphate signature and an evaporated nature, as seen from the isotope data occurred in the underground workings of the mine. These samples corresponded well with water from a nearby FRD and indicate that the FRD is responsible for inflow on shallow levels of the mine.

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

New Vaal Colliery (NVC) is an opencast mine in the northern Free State, located within a meander of the Vaal river and underlain by the Transvaal Supergroup dolomitic aquifer. Dewatering of the pits results in high-sulphate water that needs to be stored in the Maccauvlei dam, the main unlined pollution control dam. In 2011 the mine was issued a water use license containing challenging conditions, one of which was the requirement for all water pollution dams on site to be lined. The conditions were viewed as impractical and unnecessary as the mine impacted water did not pose a risk to the surrounding environment, in particular to the underlying dolomitic aquifer. In order to motivate for the amendment of the license conditions, a hydrogeological conceptual site modelling (CSM) process was initiated in order to identify and quantify the groundwater balance and assess the extent of interaction between the dolomite aquifer and the mine.

The CSM formed the basis for the development of a detailed and robust numerical model and triggered the re-evaluation of the mine’s land rehabilitation plan. The results were to be used to ensure the risks associated with water management on site were addressed and for submission of a water use license amendment application. This paper summarises the CSM development. A history of hydrogeological studies provided the initial understanding of the hydrostratigraphy which is characterised by three main units, namely the shallow weathered and mine aquifers, the Karoo aquifers and aquiclude as well as the pre-Karoo aquifer and aquiclude. The available site data indicated that while the Maccauvlei dam may have a hydraulic connection to the shallow artificial mine aquifer, it was unlikely that water from the dam impacted on the dolomitic aquifer.

This was supported by water levels measured in boreholes targeting the dolomite aquifer, which generally recorded an elevation above that of the Vaal River, confirming the confined or semi-confined nature of the aquifer. The pressure heads suggested that water flow is from the dolomitic aquifer to the mine and not the other way around. Of significance to the mine’s water management were the findings that 1) a geological graben forming the boundary between NVC and the defunct Cornelia mine could provide substantial groundwater flow into the mine and 2) that the flooded old underground mine working still to be mined are likely to exceed the site’s infrastructure capacity for water storage and limit coal production. The CMS was sufficient to illustrate that it is not likely that the mine water has an impact on the dolomitic aquifer water quality, a finding later supported by the numerical model. The modelling process provided the necessary platform to negotiate a progressive implementation of license conditions that are specific to the mine and cost effective over the life of mine, despite the gaps identified.

Abstract

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

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

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

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

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

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

Abstract

In the wake of the ongoing water restrictions in South Africa, the issue of groundwater potential for drought relief has been debated on many environmental and socio-economic platforms, nationally. Consequently, the development of groundwater and its related vulnerabilities has become a key topic to the decision makers and stakeholders. Currently, the recruitment of water professionals into government and private water sectors adds substantial value to understanding the importance of protecting this precious resource. This has allowed the monitoring of groundwater to gain ever increasing momentum. Groundwater monitoring has become an essential scientific tool for role-players to achieve robust and verifiable data used for modelling aquifer potential and vulnerability to pollution and over-abstraction. The data is generally sourced from various hydrogeological and environmental investigations which include groundwater development, vulnerability assessment and remediation projects. Groundwater and environmental consulting firms are tasked with imperative roles for implementing groundwater monitoring programmes to the ever growing industrial, commercial, agricultural and public sectors in South Africa. However, groundwater monitoring data, especially in the private sector, are reliable but remains mostly inaccessible due to confidentiality clauses. This does limit our accuracy and comprehensive understanding for determining aquifer potential and vulnerability risks at large. The conceptualisation and modelling of vast monitoring datasets has been recognised as an important contributing factor to enhance groundwater sustainability. This research emphasises the significance of groundwater monitoring for development, protection and remediation of aquifers. Comparing monitoring results from typical sites and methods, provides scientific validation to support good governance of water. Deterioration of groundwater potability in the sight of an existing drought can have irreversible environmental and economic implications for South Africa.

Abstract

POSTER Water resources are not just lakes, glaciers and polar ice caps and rivers; however one of the largest water resources is underground water well-known as Groundwater. Groundwater is one of the most important source of water as it the huge reservoir for freshwater. Groundwater can be defined as water existing underneath the earth surface in rock bodies known as aquifers. Approximately 140 communities in South Africa depend on groundwater as the source of water (Department of water affairs and forestry, 1998). Nevertheless groundwater is vulnerably to pollutants resulting from surrounding environmental effects which lead to poor groundwater quality. Numerous environmental effects have a huge impact in polluting groundwater such as pesticides, seawater encroachment, sewage effluent discharges to the ground and storage tanks underground; hence one need to identify, evaluate and come up with solutions on eradication of all these environmental effects that lead to groundwater pollution ( Hearth 1983).

The objectives of the report will be based on minimizing the groundwater pollution at the source and to restore groundwater quality to extent that the beneficial users recognise its suitability. Inspection in University of the Western Cape (UWC) campus site and Rawsonville site will be conducted by BSc Environment and Water Science students of UWC in June using various tools in order to identify and monitor surrounding environmental effects towards groundwater pollution. UWC campus research site is located on top of the Cape Flats primary aquifer (unconfined sand aquifer); Cape Flat aquifer is overlain by an impermeable bedrock Malmesbury (shale) secondary fractured aquifer. Generally this borehole test will be based on testing on how the surrounding environmental impacts with various aquifer properties affect the groundwater quality or whether the surrounding environment interrupts the groundwater quality in Cape flats aquifer and Rawsonville site. The UWC campus site has low infiltration compared with Rawsonville site as it is surrounded by vegetation that plays role in trapping water from infiltrating therefore this aquifer is less likely to be contaminated by pollutants from the land surface, however with it being surrounded by residential areas and industries it is likely to be polluted. Rawsonville on the other hand is located in the grape farm which makes it easier for the site to be contaminated by fertilisers used for agricultural practice. The pumping test will further enable one in knowing the quantity of groundwater in UWC campus site and Rawsonville site thus extraction levels for municipal works, irrigation and so forth will be monitored in a correct manner (Department of water affairs and forestry, 1998). Finally groundwater models will be used to further investigation on the behaviour of groundwater systems.

Abstract

The use of the integrated geographic information system and remote sensing technologies have not been widely demonstrated as one of the efficient techniques in facilitating better data analysis to enhance the interpretations of groundwater potential controlling parameters for sustained utilization and management of groundwater resources. This paper discuss the results of the study that aimed at showcasing the application of the integrated geographic information system and remote sensing techniques to delineate and classify possible groundwater potential zones in the Bilate River catchment, South Ethiopian Rift valley Escarpment. Thematic layers of lithology, geomorphology, drainage, lineament, rainfall, soil, slope and land use/land cover were prepared in Landsat ETM+ imagery and ArcGIS software. Weights assigned based on thematic layers relative importance in groundwater occurrence. In addition, corresponding normalized weights obtained based on the Saaty's analytical hierarchy process. Lastly, linear summation equation used weights to obtain a unified weight map containing due weights of all input variables. Thematic layers further reclassified to arrive at groundwater potential map using ArcGIS and IDRIS software. Key results included four different groundwater potential zones that classed as high, moderate, low and poor based on pair wise comparison of Satty’s importance scale criteria. The resulted groundwater potential zoning map validated based on existing water sources point data of the study area. The results provide important information, with the groundwater potential zone suitable for use by local authorities and decision makers responsible for groundwater resource management in the study area. Finally, integrated geographic information system and remote sensing technologies have provided an efficient tool for the identification of groundwater potential zones.

Abstract

Currently limited progress is made in South Africa (and Africa) on the protection of groundwater used for drinking water. To achieve the objective of water for growth and development and to provide socio-economic and environmental benefits of communities using groundwater, significant aquifers and well fields must be adequately protected. Groundwater protection zoning is seen as an important step in this regard. Till today, limited case studies of groundwater protection zoning exists in Africa. A case study at the Rawsonville research site is conducted in this research project. Generic protection zones can be delineated at the site using published reports and database data. However, due to the complexity of the fractured rock at the research site, these would be of limited value and would not provide adequate protection for the well field Baseline data was collected by conducting a hydro census and through aquifer tests. An inventory of the activities that can potentially impact water quality was done and aquifer characteristics such as transmissivity and hydraulic conductivity were determined through various types of aquifer testing. Fracture positions were identified using fluid logging and fracture flow rates were also measured using fluid logging data. A conceptual model and preliminary 3D numerical model were created to try to understand groundwater movement at the research site. The knowledge gained will be used to guide information gathering and monitoring that can be used to build a more detailed numerical model and implement a trustworthy groundwater protection plan at a later stage. The expected results will have applicability to groundwater management in general. The protection plan developed during this project can be used as a case study to update and improve policy implementation. {List only- not presented}

Abstract

The quality of groundwater is, in part, controlled by the character of the rock in which it is stored and the water - rock contact time. Rainfall (or recharge) is also a contributing factor as the mineralisation of groundwater increases from east to west across South Africa. It is well established that groundwater is more mineralised than surface water, and with most of South Africa's domestic supplies being sourced from dams, municipal water supplies are generally of low salinity. The exception to this is where water supplies are sourced from groundwater - such as in the Karoo and along the West Coast. The assessment of water potability is based on both the South African National Standard 241 and the Department of Water and Sanitation guidelines, with the former being a legal requirement. Previously, SANS 241 had two classes of water with the lower class only being allowed for a limited period. In 2015, Class II water was done away with and only a single class of water is now specified. While this may have been done to conform to World Health Organisation standards, it disregarded the realities of a resource-strapped South Africa where in large parts the municipal water supplies simply cannot meet the SANS241 standard. This paper examines the implications of the SANS 241 standard on efforts to establish emergency groundwater supplies during the drought impacting the Western Cape Province.

Abstract

Gold mining  activities over  the  past 60 years  in the Klerksdorp  goldfield produced  saline mine drainage that polluted water. Oxidation of sulphide material in tailings storage facilities, waste rock dumps and extraction plants is mobilised to produce saline mine drainage with sulphate, minor salts and  metals  that  seep  to  the  groundwater  and  ultimately  into  surface  water  resources.  Water regulation requires mines to prevent, minimise/reduce or eliminate pollution of water resources. The waste philosophy has matured from tolerate and transfer to treat and termination of pollution sources.  The  impact  of  the  pollution  was  determined  and  possible  technologies  to  treat  the impact   were   evaluated.   Source   controls   with   proper  water  management  by  storm  water management,  clean  dirty  water  separation,  lined  water  conveyance  structures  and  reduced deposition of water on waste facilities are crucial. The aquifer character determines the possible remediation technology. From the possible technologies phytoremediation, physical interception and  re-use  of  this  water  was  selected.  In  future  possible  treatment  of  the  water  would  be considered. This paper explain the strategy and report on the phased implementation of these plans and the expected results. The establishment of 500 ha of woodlands as phytoremediation, interception trenches of 1 000 m, 38 interception boreholes and infrastructure to re-use this water is planned. The total volume of 15 Ml/day would be abstracted for re-use from the boreholes and trenches. The woodlands can potentially attenuate and treat 5 Ml/day. The established woodlands of 150 ha prove to be successful to intercept diffused seepage over the area of establishment and reduce  the  water  level  and  base  flow.  The  two  production  interception  well- fields  that  are abstracting  50  and  30 l/s,  respectively  , indicate  a  water  level decline of between 2 to 14 m, with regional cones of depression of a few hundred meters to intercept groundwater flow up to a 20 m depth. Predictions from groundwater modelling indicate that these schemes can minimise pollution during the operational phase and protect downstream water resources. Predictions from modelling indicate that the pollution sources need to be removed to ensure long-term clean-up to return the land to safe use. The gold and uranium prize is securing the removal of the sources through  re-processing  of  the  tailings  and  waste  rock  dumps.  After  removal  of  the  sources  of pollution,  the  remediation  schemes  would  have  to  be  operated  for  20  years  to  return  the groundwater to an acceptable standard  of  stock  watering  and  industrial  water  use.  The  water quality is observed by a monitoring network of approximately 100 observation boreholes.

Abstract

The Heuningvlei pipeline scheme was built in the 1980s to supply water to rural communities in a low rainfall area (<300 mm/annum) – Northern Cape Province. In 2008, the Joe Morolong Local Municipality identified the need to refurbish and upgrade the pipeline scheme for socio-economic reasons. The safe yield and water quality information of existing sources supplying the scheme was unreliable. This was investigated by borehole test pumping and water quality sampling, which indicated reduced yields and deteriorating water quality since 1989.

Water demands, which includes supply to communities for domestic use, schools, clinics and stock watering in the Heuningvlei area, was estimated at 2 380 m3/day or 868 700 m3/annum. The potable groundwater  supply  recommended  from  11  existing  boreholes  is  316 937 m3/annum,  leaving  a deficit of 551 763 m3. The aquifers utilised for the existing water supply comprise fractured banded iron formations (BIF) and dolomite bedrock. Kalahari sedimentary and dolomite aquifers to the east of the pipeline scheme contain high saline water not suitable for domestic use.

No surface water sources exist in the area and the feasibility of the socio-economic development project depends on establishing local groundwater resources that would not impact on existing sources. A target area was identified which is approximately 10 km south from the pipeline. This area is covered by the thick Kalahari sediments (up to 130 m) underlain by dolomite bedrock with a potable groundwater balance of 2.3 million m3/a. Both the associated primary (Kalahari) and secondary (Dolomite) aquifers contain potable water. The target area was not investigated in the past due to perceived poor water quality (elevated salinity) conditions, very low (<10 %) borehole exploitability prospect and difficult drilling conditions.

The paper will discuss the importance of recharge estimate and understanding of flow regime at sub-catchment and local scale, use of an airborne magnetic survey in conjunction with ground geophysics, mapping of Kalahari sediment thickness, and successful drilling of exploration boreholes to exploit the deeper Kalahari sedimentary and dolomite bedrock aquifers. The successful development of localised potable water in a low rainfall area made it feasible to implement the Heuningvlei socio-economic development project.

Abstract

The 2011 Olifants River Water Supply Scheme (ORWSS) Reconciliation Strategy recommended that the Malmani Subgroup dolomites along the Limpopo-Mpumalanga escarpment be investigated as a potential groundwater resource for input into the ORWSS. The Department of Water and Sanitation - Directorate: Water Resource Planning Systems (DWS D: WRPS) in turn initiated a 2-year project that began in mid- 2016 to develop a feasibility plan for the groundwater resource development of the Malmani Subgroup dolomites within the ORWSS, with the main aims of the project being: 1) to secure groundwater as a long- term option to augment the water supply to the ORWSS by optimising surface water-groundwater conjunctive use; and 2) to determine the artificial recharge potential of the dolomitic (and/or other) aquifers within the ORWSS. The ~2000 m thick, Late Archaean (~2.6-2.5 billion year old) Malmani Subgroup is comprised of stromatolite-bearing dolomites and limestones (i.e. chemical sediments including chert, with some local clastic shale and quartzite), and forms part of the Chuniespoort Group (lower Transvaal Supergroup) with the overlying banded ironstones of the Penge Formation, and mudstones, dolomites and limestones of the Duitschland Formation. The Malmani Subgroup dolomites (and Transvaal Supergroup as a whole) have undergone deformation, fracturing/faulting and dyke intrusion by a range of tectonic events (including the Bushveld Complex intrusion and slumping, Vredefort meteorite impact, “Transvaalide fold-and-thrust belt”, Pan African Orogeny, Gondwana breakup and current East African Rift development), which have resulted in the development of a high yielding (>10 l/s sustainable yields and transmissivities of ~500-2500 m2 /day per borehole in the vicinity of large regional faults/fractures or dolerite intrusions) fractured dolomitic karst aquifer. Quaternary alluvial deposits (of up to 30-40 m thickness) also occur within valleys incised into the Malmani Subgroup at Fertilis (Mohlapitse River), Penge (Olifants River and associated tributaries), Ga-Maditsi (Steelpoort River), and along the Ohrigstad, Blyde and Treur River valleys. Groundwater quality within the Malmani Subgroup dolomitic aquifers in the ORWSS area is generally good (EC of <70 mS/m), however poorer water quality can be present (e.g. elevated EC, nitrates and trace metals) as a result of contamination from human settlements, agricultural irrigation, mining, and recharge from contaminated surface water e.g. the Olifants and Steelpoort Rivers. Current work completed/being undertaken as part of the project includes: identification of two preliminary regional hydrogeological targets and twelve related wellfield target zones (WFTZ); hydrocensus of selected DWS NGA and GRIP boreholes within these two preliminary targets; re-testing of selected high yielding GRIP boreholes at constant discharge rates of 20-25 l/s, and re-analysis of existing GRIP Malmani Subgroup data; macrochemical and dissolved trace metal analysis of groundwater chemistry from tested and drilled boreholes; development of a regional groundwater balance model to determine the groundwater potential per WFTZ; surface-groundwater interaction and artificial recharge assessments (the latter focusing on alluvial deposits overlying the Malmani Subgroup dolomites); identification of potential wellfield sites within the WFTZs based on structural analysis, measured aquifer parameters, groundwater potential and geophysics; numerical groundwater modelling; and drilling/testing of exploration/monitoring boreholes within selected wellfield sites.

Abstract

The mineral rich Northern Cape Province produces 84% of South Africa's iron ore, while the Kalahari basin holds 92% of the world's high grade manganese deposits, with diamond and lime mining operations to a lesser degree. Mining expansion programs and new mines planned in the Northern Cape drive the region's economic development and growth strategy. The planned mining expansion depend on water being available for mining water needs and related increased demands for domestic water supplies.

Current water supplies consist of local groundwater resources (boreholes and mine dewatering) and bulk water supply from the Vaal Gamagara (VGG) Pipeline Scheme. In 1992 the Kalahari East water supply pipeline was incorporated to supply domestic and stock water to an area of approximately 1.4 million ha.

The VGG scheme consists of 370 km pipes, was built in the late sixties and is nearing its useful life expectancy. Increased water supply interruptions are being experienced while operating at capacity. The pipeline has the capacity to convey and import water of approximately 15 million m3/a into the D41J and D41K quaternary catchments. Water demand projections show an increase to 40.1 million m3/a in 2030.

Various options were investigated to upgrade the VGG water supply scheme. One option considers groundwater resources to augment the water from the Vaal River from four indentified target areas (SD1 to SD4).

Major fault zones in Banded Iron Formations (BIF) are targeted for groundwater resource development in the SD4 area, located east of Hotazel. This area is largely covered by Quaternary age sand and located near the endpoint of the VGG scheme and therefore prioritized as investigation area.

The primary objective of the hydrogeological investigation was to identify the existence of exploitable resources for additional source development. Secondary objectives were to assess the contribution groundwater can make to augmenting pipeline water; providing a source to an area and thus diminish reliance on the pipeline; and providing an independent source, which could prevent the need for pipeline extensions.

The paper will discuss the use of an airborne magnetic and Time Domain Electromagnetic's (TDEM) survey combined with gravity ground surveys as a key success factor in adding to the geological and structural information of the area. The paper will also present the results of exploration drilling (> 60 boreholes) over a large area and related borehole test pumping with water sampling to identify a sustainable and potable water supply of 2.5 million m3/a.

Abstract

Water plays a significant role in the economies of the agricultural, business and industrial sectors. Expanding populations, economies and climate change have put pressure on the quality and availability of water resources in South Africa, therefore water resource protection becomes increasingly important for sustainable water supply management. Hence, a review of the state-of-the-art of water resource protection in South Africa has been undertaken on behalf of the WRC, applying the water resource governance framework. Gaps in scientific understanding and implementation with regards to water resource protection have been identified through literature review and discussions with stakeholders and experts. Aiming to improve the water resource protection in South Africa, a research strategy has been developed to tackle the most relevant of the identified gaps. The legislation in South Africa with respect to water resource protection is state-of-the-art and one of the best in the world. However, there is still space for improvement in that the different acts need to be aligned better to facilitate cooperative governance and improve the implementation of the legislation. Regulations and guidelines are plentiful covering most of the relevant activities and various water resources. The main challenge for implementing the intent of the National Water Act with respect to groundwater resource protection is that the standard methodology for determining Resource Directed Measures (RDM) was developed for surface water resources and is not applicable to groundwater or wetlands. Furthermore, classification and Reserve determination are mostly carried out at a scale that is insufficient for effective groundwater resource protection. The methodology requires update to incorporate potential impacts of climate change, changing land use and changing demographics. The different elements of the RDM methodology need to be aligned. There is also often an insufficient spatial and temporal distribution of monitoring networks to effectively manage groundwater resources. Integrated catchment management can provide a solution to the current state of water resource protection. However, this must be based on a scientific understanding of the complex natural system. The different challenges, research needs and possible solutions are demonstrated on a case study of Stanford Aquifer.

Abstract

Quantification of groundwater is important as it should determine the maximum sustainable use of the resource. The SAMREC Code that is required for mineral resource quantification sets out minimum standards, guidelines and recommendations for public reporting of exploration results for mineral resources and reserves. The code serves as the basis for mineral asset valuation and provides quality assurance to the process and an understanding of the results. In groundwater far too often, various methods are used for resource quantification that leads to various results even should the same resource be investigated by two different hydrogeologists. In far too many cases, the resource is not quantified properly which leads to vast over or under estimations. The result is a lack of trust in groundwater resources. As has been done in the international arena, it is similarly proposed that a code be developed for South Africa to ensure that the sustainability of groundwater resources is determined and the impacts of utilization on the water Reserve and the environment be quantified at a minimum level and that basic hydrogeological principles are followed. A South African Groundwater Regulation Code for sustainable resource quantification and impact assessment (SAGREC) is developed that is proposed to guide groundwater investigations and development processes from planning to baseline assessments, drilling and aquifer testing to resource quantification and sustainability modeling. The aim is to ensure trust being built on groundwater as a resource due to projects that follow a formal process that quantifies the assurance of supply and determines the environmental impacts.

Abstract

The groundwater risk map for the Karoo aquifers has been developed by incorporating the major geological, hydro-geological and uranium concentration factors that affect and control the groundwater contamination using GIS-based DRIST model. This work demonstrates the potential of artificial intelligence to produce a map by using various spatially geo-referenced digital data layers that portray cumulative aquifer sensitivity ratings across the Karoo Uranium Province, South Africa. This provides a relative indication of groundwater risk to uranium contamination. The pollution index used in this analysis was the uranium concentration (expressed as ?g/L). The selection of this index was based not only on the fact that it constitutes the main contaminant that occurs naturally in the geology of the study area but also because it is a prime health hazard and its presence in concentrations that exceed the drinking water guidelines is a representative indicator of groundwater quality degradation. The methodology used for assessment of groundwater risk was based on an approach which was modified specifically for assessment of Uranium pollution at a regional Karoo Uranium Province, where the five DRIST maps were integrated to form an intrinsic vulnerability map. The results show that the high risk for contamination of groundwater by uranium covers the central and northern parts of the study area. The southern part is slightly less risky due to a combination of parameter settings which tend to favour attenuation as compared to transport of uranium in the subsurface. This parameter includes; rocks with good chemical attenuation properties, deeper groundwater table, and less yielding aquifers. The results were validated using the area under the curve approach and a high validation value of 0.737 was obtained. Thus, the groundwater risk map developed can be used for regional environmental planning and predictive groundwater management

Abstract

A hydrogeochemical analysis of multiple samples stemming from two fractured rock aquifers in the Karoo geological formation of South Africa was undertaken. The samples were taken using various sampling methods in numerous locations over varying time frames. The ion error balance for the groundwater samples from the previously mentioned secondary aquifers is further analysed. Graphical representation of the data, which includes a piper plot, gives insight into the groundwater geochemistry. Conclusions drawn highlight the precautionary measures to take into account when sampling in fractured rock aquifers in a South African context. The future recommendations include suggestions related to the entire chain of sampling in the context of the theory of sampling and measurement uncertainty for fractured rock hydrogeology in particular.

Abstract

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

Abstract

The uncertainties associated with both the sampling process and laboratory analysis can contribute to the variability of the results. In most cases, it does appear that if the water samples have been analysed by an accredited laboratory, the results are acceptable. While the accreditation of analytical laboratory and therefore its credibility is very important to uphold quality and integrity, the same should be said about the sampling process. The quality and credibility of a sampling process is typically left to the responsibility of the appointed groundwater practitioner without any criteria to evaluate the quality and integrity of the sampling process. Perhaps the quality and integrity of the sampling process is evaluated based on trust or experience of the practitioner. However without any form of scientific criteria to evaluate the quality and integrity of the sampling process, it is difficult for the sampling process to be scrutinized. The quality and integrity of both the sampling process and laboratory analysis must be scientifically evaluated based on the uncertainty of measurements in line with the monitoring goals/requirements. This presentation discusses the aspects of evaluation of measurement uncertainties associated with groundwater sampling as an important component of quality assessment of groundwater sampling processes. The potential implications of the uncertainties on the final results and their use in decision making is also discussed. The credibility of the decisions made also depends on the knowledge about the uncertainties of the final results

Abstract

The Eastern Cape Province has been severely impacted by the current drought period, particularly within the Butterworth town and surrounding communities. This study, conducted within the Mnquma Local Municipality of the greater Amathole District Municipality, presents the approach undertaken in mitigating and augmenting the current water shortage. The area generally experiences annual rainfall of 596 mm and is mostly reliant on surface water with a population of over 250 000 residents. The supply of water to the communities is abstracted from the Gcuwa, Toleni and Xilinxa dams with water levels at 44, 21 and 0.6% respectively. Groundwater source development remained the most feasible solution to alleviate the drought within the area.

The geophysical techniques that were applied include the airborne technique (aeromagnetic and gamma[1]ray spectrometric) and the ground geophysical techniques (magnetic and em34) at the targeted airborne sites to verify the dolerite structures. The airborne method was used to obtain more in-depth knowledge of the geological and hydrogeological conditions within the study area. The total distance in kms’ flown for the airborne survey amounted to ~1200 km. The flight-line pattern was (N-S) and tie-line pattern (E[1]W) of the survey was conducted by AeroPhysX, and the flight-lines were flown at a 200m line spacing and tie-lines at 750m spacing at 60m flying height.

The study area consists of a vast network of E-W trending geological structures such as regional dolerite dyke and sill intrusions, faults and lineaments. Although many dykes are present within the lower Ecca and Dwyka Formations and even the Nama age basement, the bulk of the dykes are strata bound and concentrated in the Upper Ecca and Beaufort Group (Chevallier and Woodford, 1999; Woodford & Chevallier 2002). The airborne geophysical technique assisted by accurately mapping out prominent and inferred dolerite dykes located at inaccessible areas due to steep undulating hills.

 The drilling success rate on the airborne sites is 98% so far with depths ranging from 60 to 300 m with blow yields of between 2 and 50 l/s. A total of 25 prioritized drilling positions have been identified based on the airborne survey.

The hydrochemical status of the successfully developed boreholes is indicative of class 3 water quality according to the SANS 241-1:2015 minimum standards due to turbidity, sodium, chloride, iron and fluoride as common constituents in the developed boreholes. The developed boreholes will be connected  to the existing bulk water supply to the Water Treatment Plant (WTP) for treatment prior human consumption.

Airborne survey has proven to be a useful method in locating new groundwater potential areas as well as identifying unmapped dolerite structures. This paper is based on quantitative and factual findings of actual work conducted on site so far.

Abstract

To date, South Africa has mined approximately 3.2 billion tons of coal from a number of different coal reserves located in various parts of the country. A large number of the mines have reached the end of their productive life, resulting in numerous mine closures. With closures, groundwater levels have rebounded, resulting in decant of mine water into the environment. This paper describes a case study of a closed underground coal mine, the rebound of water levels, the evolution of the groundwater quality and the impact it has had on the management of the potential decant.

On closure of the Ermelo Mines in 1992, initial water quality monitoring indicated that a water treatment plant would be required to treat the mine decant. However, as the groundwater levels in the mine rebounded, the water quality in the mine void evolved from sulphate type water to sodium type water. The evolution of the water quality can be attributed to sulphate reducing bacteria, vertical recharge from the hanging aquifer and stratification. Water level and quality monitoring have shown that the water in the old mine void will not decant to surface due to the depth of the mine void, hydrogeological conditions, a "hanging aquifer"  and the recharge mechanisms. As a result, no water treatment will be required and the mine will not impact on the surface water. The main applications from this paper are:

•  Design  of  a  correct  monitoring  procedure  to  allow  for  monitoring  of  water  quality stratification in rebounding mines.
•  Identifying the role of sulphate reducing bacteria in the evolution of groundwater quality in a methane rich coal mine void.
•  The role of a hanging aquifer in recharging of a coal mine void and resultant stratification. 
• Designing of a mine taking into consideration mine closure.

The main contribution of this paper is the use of hydrogeological information in design of a coal mine so as not to decant on closure.

Abstract

National legislation is the outcome of processes, locally, provincial and nationally. Certain aspects of water management have first been the product of legal initiatives of the South African government, seeking  to  address  local  problems.  As  a  result,  the  National  Water  Act,  36  of  1998,  was promulgated. The Act is in line with the Constitution of the Republic of South Africa, 108 of 1996, which embrace human rights. The Water Services Act, 108 of 1997, regulates the accessibility of water and sanitation by domestic users. Groundwater, in many parts of South Africa, provides the sole  and/or  partial  water  supply  for  meeting  basic  human  needs.  With  an  increase  in  the dependency on groundwater usage, the need to properly and effectively protect, use, develop, conserve,  manage  and  control  groundwater  resources  has  become  a  national  priority  by  the custodian of all water resources: the National Department of Water Affairs. The question arises whether  or  not  the  current  groundwater  allocation  decision-making tools  are  enough  to  make informed  decisions  regarding  the  final  approval,  or  not,  of  groundwater  use  licenses,  and whether  a  proper  framework  that  includes  guidelines  together  with  licensing  conditions  are available  for  decision- making   in   complex  groundwater   scenario   situations   as   part   of   the groundwater license decision process. The current research contributes to answering this question and finding solutions in order to improve and make the groundwater use authorisation process more  effective.  The  groundwater  situation  will  be  discussed  on  a  comparative  basis  from international case studies regarding water legislation and groundwater resource management tools. A full evaluation and analysis of groundwater use authorisation process and decision-making tools on  regional and  national level  in  South  Africa will be done  and a Framework and tool for the evaluation, decision-making and determination of authorisation conditions of groundwater use authorisations, which includes existing lawful water use, general authorisations, and groundwater use licensing, will be developed. Scenarios and case studies are currently implemented.

Abstract

The Dahomey Basin is a transboundary sedimentary basin with its eastern half in south western Nigeria. The vulnerability assessment of the basin was carried out to ascertain the degree of the shallow unconfined aquifers sensitive to groundwater contamination through the investigations of the intrinsic properties of lithology over the unconfined aquifer systems. The basin is a multi-layered aquifer system hosting large population densities particularly in Lagos where nearly half of the population rely on the groundwater for domestics and industrial purposes. The vulnerability evaluation involves determining the protective cover and infiltration condition of the unsaturated zone in the basin. This was achieved using the PI vulnerability method of the European vulnerability approach. The PI method specifically measures the protection cover and the degree to which the protective cover is bypassed. Intrinsic parameters assessed were the subsoil, lithology, topsoil, recharge and fracturing for the protective cover. While, the saturated hydraulic conductivity of topsoil, infiltration processes and the lateral surface and subsurface flow were evaluated for the infiltration bypassed. The results were depicted in vulnerability maps. Map of the protective cover ranges from high to very high. This means a very effective cover over the groundwater resources. The I map revealed a low to very low degree of bypass. The final vulnerability map shows that the Dahomey Basin vulnerability ranges from moderate to very low vulnerability areas. Low vulnerability areas were characterised by lithology with massive sandstone and limestone, sub soils of sandy loam texture, high slopes and high depth to water table. The moderate vulnerability areas were characterised by high rainfall and high recharge, low water table, unconsolidated sandstones and alluvium lithology. The vulnerability map was validated with hydrochemical properties of the groundwater. Chloride and TDS concentration of the groundwater reveals high chloride concentration for low groundwater vulnerability areas while low chloride concentrations were observed for moderate vulnerability areas. Low to moderate groundwater vulnerability areas show low TDS concentrations according to the WHO standards except for the coastal areas with relatively higher TDS concentrations. The groundwater vulnerability maps will be a useful tool for planning land use activities which will minimise groundwater contamination and enhance the protection of the Dahomey Basin groundwater resources.
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Keywords: PI method, Dahomey Basin, aquifer vulnerability, protective cover, groundwater resources.