Conference Abstracts

Abstract

Groundwater discharge is crucial for transporting terrestrial carbon into streams and rivers, but the effects of groundwater flow paths on terrestrial carbon inputs are poorly understood. Here, we investigated environmental tracers (EC, Cl-, 2H, 18O, 220Rn, and 222Rn) and carbon concentrations in riparian groundwater, streambed groundwater, and stream water over six groundwater-stream monitoring sites. Significantly high 220Rn and 222Rn activities in the stream and endmember analysis results of the environmental tracers reveal that vertical groundwater discharge from the streambed (VGD) and lateral groundwater discharge from the riparian zone (LGD) is of equal importance for the stream. We quantified VGD by modelling the detailed 222Rn and Cl- profiles at the streambed and then combined differential flow gauging to estimate LGD. VGD (2.9 ± 1.4 m2 d-1) prevailed in relatively wide and shallow channels, while LGD (2.6 ± 2.6 m2 d-1) dominated narrow and deep channels. Carbon measurements indicate that LGD had the highest CO2, CH4, DIC, and DOC, while VGD had relatively higher CO2 but lower CH4, DIC, and DOC than stream water. Our findings suggest that LGD is the primary carbon source for the stream, while VGD mainly dilutes the stream (except CO2). Finally, we observed that groundwater discharge and temperature overrode metabolism in controlling stream carbon dynamics, implying the importance of groundwater discharge for understanding stream carbon cycling. Overall, this study identified the impacts of groundwater flow paths on carbon exchanges between terrestrial and stream ecosystems.

Abstract

Advances in groundwater age dating provide key information for groundwater recharge history and rates, which is of great significance for groundwater sustainable development and management. By far the, radioisotope 14C is the most frequently used in routine investigations. However, groundwater age can be misinterpreted given its dating range of up to 40 ka and its chemically active in nature. In comparison, 81Kr is less frequently used but chemically inert with a dating range of up to 1,300 ka, which overcomes the limit of 14C. Although it is not as precise as 14C when the groundwater age is younger than 40 ka, it may be helpful to determine the reliability of 14C dating results. In this study, we collected eight field samples from coastal aquifers in Nantong, China and analyzed them for 81Kr, 85Kr, and 14C. The 14C results show that all groundwater ages range from 2,400 to 35,300 years, with different correction methods yielding uncertainties of 1,500 to 3,300 years. Four of the 81Kr ages provided upper bounds, while three yielded groundwater ages which are consistent with the 14C dating results within measurement uncertainties. Interestingly, one 81Kr result gave an age of 189+11 - 12ka, whereas the corresponding corrected 14C age was less than 29,200 years. The great difference may indicate modern contamination in the sampling process or mixing between young and old groundwaters. Further investigation is needed to shed more lights in this case. Moreover, it shows the benefits of introducing 81Kr in routine hydrogeological investigations and the groundwater studies.

Abstract

To explore the sources of pollution and health risk profile of heavy metal elements in groundwater,41 sets of representative groundwater samples from the southwest subbasin of the Shiqi River were examined for 10 heavy metal elements, correlation analysis and principal component analysis were used to resolve the possible sources of heavy metal contamination in groundwater. The concentration characteristics and health risk levels of the 10 heavy metals were assessed using the single factor contamination index (Pi), the Nemerow comprehensive contamination index (PN) and the health risk model. The results show that: 1) The average values of heavy metal elements of the groundwater in the study area all met the limit of class III water standard in the quality standard for groundwater; only the maximum value of Al was exceeded, followed by a large variation in the concentrations of Al, Mn and Cr. The heavy metal element with the largest average contribution was Al (65.74%). 2) The results of the single factor contamination index evaluation show that only the heavy metal element Al exceeds the level, and the results of the Nemerow comprehensive contamination index evaluation show that the study area is basically at low pollution levels and the quality of groundwater is good. 3) The results of the multivariate statistical analysis show that Zn, Co and Mn are mixed sources of geological formation and domestic waste, Al, As, and Cu are agricultural sources, Cd, Cr and Ni are industrial sources, and Hg comes from long-range atmospheric transport.

Abstract

Since 2018, the North China Plain has started a large-scale ecological water replenishment project for rivers and lakes, with 17.5 billion cubic meters total from the South–North Water Transfer Project and other water sources. It is a key question of how much water infiltration into aquifers will affect groundwater and how to characterize and evaluate this effect quantitatively. The groundwater numerical model of the Beijing-Tianjin- Hebei region as the main part of the North China Plain was established using a numerical simulation method, and the groundwater level variation under the replenishment condition was simulated and predicted. By comparing the two scenarios, the relative rise method of groundwater level was proposed to characterize the influence of river water infiltration on groundwater level, and the unstructured grid method was used to refine cells near the river to improve simulation accuracy. Simulation results show that the groundwater level around some rivers has risen significantly in the past four years, especially in the alluvial fan regions with better infiltration properties. Accordingly, at the Piedmont alluvial fan region, there is also a large influence range on groundwater level. The maximum influence distance is more than 10km (0.1m relative rise of groundwater level was taken as the influential boundary). According to the prediction, if the water replenishment project continues, the range of influence can continue to expand, but the expansion rate will slow down due to the reduction of the hydraulic gradient.

Abstract

This study aims to investigate the groundwater circulation and hydrogeochemical evolution in the coastal zone of Xiamen, southeast China, which can provide a reference for the development of water resources and the protection of soil and water environment in the coastal areas. A close connection between mountains and the sea characterizes the southeast coast of China. Although rainfall is abundant, the topography limits it, and water resources quickly run into the sea. Coupled with a concentrated population, water is scarce. In addition, this area’s water and sediment environment are influenced by human activities and geological conditions. Its changing trend also needs further study. Therefore, using hydrochemical analysis, isotope technology, numerical simulation and other techniques, this study took Xiamen City on the southeast coast as an example to study the groundwater circulation and the environmental evolution of water and sediment. The results show that although the aquifer is thinner, there is still deep groundwater circulation, and the seawater intrusion range of deep aquifer is much further than that of shallow aquifer. In addition to geological causes, human activities have become the main factors affecting groundwater quality, especially nitrate and lead. The nitrate content even exceeds the content of the major ionic components. Introducing land-based pollutants has also contributed to declining seawater and sediment quality in the Bay area. In general, the main pollutants in coastal areas include nutrients, heavy metals and new pollutants.

Abstract

Collecting groundwater information close to the ocean often raises the question whether a tidal effect could be influencing the data. Sometimes this issue leads to speculation that is counterproductive and sometimes it is overlooked thereby causing judgement errors when interpreting data. This paper looks at the theoretical background of tidal influences in coastal aquifers to identify the screening factors to consider when deciding whether a contaminated site assessment needs to take tidal influences into account. The rising and falling of the tides cause a standing wave with varying frequency that is dampened by the neighbouring aquifer as the wave travels into it. Unconfined aquifers generally tend to be affected over a short distance, while the pressure wave can travel significant distances in a confined aquifer. There are indications that the rise and fall of the tides prevent discharge of the LNAPL, but it could cause lateral spreading due to the head changes in the aquifer. The tidal fluctuation also causes uncertainties in the LNAPL measurements. The case study presents data from a site where tidal variation directly influences the distribution of LNAPL in monitoring holes, while the variation in total fluid level is slight. In this specific case the tidal variation has to be accounted for, otherwise skewed measurement data will be collected.

Abstract

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

Abstract

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

Abstract

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

Abstract

Open pit mines often experience problems related to groundwater inflows. To perform mineral extractionin safe conditions with high productivity, it is essential to have dry working conditions. For this reason, the groundwater table is often lowered below the elevation of the floors of the pits by using various dewatering schemes. Numerical groundwater models are powerful tools that can be used to simulate the behaviour of aquifers during dewatering operations. However, these models typically require a lot of geohydrological data which are often expensive and time-consuming to collect. When geohydrological input data are limited, artificial neural networks (ANNs) provide an alternative approach of predicting the behaviour of the groundwater system during dewatering. This study investigated the possibility of predicting the impacts of pit dewatering on the aquifer system in the vicinity of open pit mines where geohydrological inputs are limited, using ANNs. First, the performance of the ANNs in predicting hydraulic head responses was evaluated by using synthetic data sets generated by a numerical groundwater model developed for a fictional mine. The synthetic data sets were then used to both train and evaluate the performance of the ANNs. The ANN found to give the best predictions of the hydraulic heads had an architecture of 2-6-1 (input-hidden-output layers) and was based on the hyperbolic tangent transfer function. This network was selected to predict the hydraulic heads at a number of piezometers installed at two open pit mines in the Democratic Republic of the Congo. The only input to the ANN was the recorded hydraulics heads and the time of recording. A portion of the real data set was used to train the ANN, while the remaining portion was used to evaluate the performance of the ANN in predicting the hydraulic heads. The results of the performance analyses indicated that the ANN successfully predicted the general behaviour of the aquifer system under dewatering conditions, using only limited input data. The results of this investigation therefore illustrate the great potential of using ANNs to predict aquifer responses during dewatering operations in the absence of comprehensive geohydrological data sets. Since these networks recognise patterns in the training data sets without considering the underlying physical principles that govern the processes, the responses of complex systems that are dependent on numerous parameters may be predicted.

Abstract

Modern societies rely heavily on subsurface resources and need open access to accurate and standardized scientific digital data that describe the subsurface’s infrastructure and geology, including the distribution of local and regional aquifers up to a depth of five kilometres. These data are essential for assessing and reducing climate change’s impact and enabling the green transition. Digital maps, 3D and 4D models of the subsurface are necessary to investigate and address issues such as groundwater quality and quantity, flood and drought impacts, renewable geo-energy solutions, availability of critical raw materials, resilient city planning, carbon capture and storage, disaster risk assessment and adaptation, and protection of groundwater-dependent terrestrial and associated aquatic ecosystems and biodiversity. For over a decade, EuroGeoSurveys, the Geological Surveys of Europe, has been working on providing harmonized digital European subsurface data through the European Geological Data Infrastructure, EGDI.

These data are invaluable for informed decision-making and policy implementation regarding the green transition, Sustainable Development Goals, and future Digital Twins in earth sciences. The database is continuously developed and improved in collaboration with relevant stakeholders to meet societal needs and facilitate sustainable, secure, and integrated management of sometimes competing uses of surface and subsurface resources.

Abstract

The North-European country Denmark is in many ways different from the Republic of South Africa. Similarities also exist, for example the common ownership of underground resources. In Denmark, like in South Africa, groundwater forms a strategic resource for water utilization, and a coherent management approach is needed in both countries in order to secure a sustainable and balanced use, in which the wishes of different stakeholders are optimized. Denmark is solely depending on the use of groundwater for domestic, industrial and agricultural use. Therefore, an effective management scheme and new technologies have been developed in order to make groundwater assessments, delineating groundwater protection zones, water preservation, leakage detection, well field monitoring systems etc. This expertise forms the basis of the bilateral Strategic Water Sector Cooperation Programme (SSC), initiated in 2015. The programme consists of three main tracks, respectively focusing on urban water services and NRW, groundwater management, and water efficiency in industries. In addition to these, two cross-cutting tracks focus on water sector financing and the potential for research and innovation cooperation. The preliminary findings of the programme indicate that some of the Danish management approaches and technologies can be used in South Africa, either adapted or directly. In exchange, the South African experiences, amongst others, in how to handle drought, may be relevant in a future Danish context, where extreme weather situations, induced by climate change, is to be expected. 

Abstract

Globally, losses of excess nitrogen (N) from agriculture are affecting our air and water quality. This is a well-known environmental threat and is caused by food production for an ever-growing population. Since the 1980s, many European countries, such as Denmark, have successfully combatted N pollution in the aquatic environment by regulating and introducing national agricultural one-size-fits-all mitigation measures. However, further reduction of the N load is still required to meet the demands of, e.g., the EU water directives. Scientifically and politically, implementing additional targeted N regulation of agriculture is a way forward. A comprehensive Danish groundwater and modelling concept has been developed to produce high-resolution groundwater N retention maps showing the potential for natural denitrification in the subsurface. The concept’s implementation aims to make future targeted N regulation successful environmentally and economically. Quaternary deposits, formed by a wide range of glacial processes and abundant in many parts of the world, often have a very complex geological and geochemical architecture. The results show that the subsurface complexity of these geological settings in selected Danish catchments results in large local differences in groundwater N retention. This indicates a high potential for targeted N regulation at the field scale. A prioritization tool is presented that has been developed for cost-efficient implementation at a national level to select promising areas for targeted N regulation.

Abstract

In the recent drought of the Cape, Drakenstein Municipality sought to improve its water security and supply through including groundwater into the municipal water supply network. After a desktop assessment of the geology and hydrogeology of the municipal area, it was initially proposed that groundwater development target the Table Mountain Group Aquifer (TMGA), which lies along and within the eastern boundary of the municipal border and is expected to yield 2 - 5 L/s/borehole. The alternate aquifers of the area are in the bedrock shales of the Malmesbury Group and the crystalline granites of the Cape Granite Suite. These are both categorized to have expected yields of 0.1 - 0.5 L/s/borehole. It was then decided that despite the substantially higher estimate potential of targeting the TMGA further away from the towns, investigations would focus on exploration on municipal land closer to local infrastructure, to limit on the costs of the additional infrastructure that would be required to get the water to the towns. This resulted in the exploration being predominantly focused on inferred bedrock faulting in the Malmesbury Group within Paarl; and the contact of the Malmesbury Group to the Wellington Pluton granite in Wellington, as well as part of the Wellington- Piketberg Fault. While several boreholes drilled in exploration in both the Malmesbury Group and the Cape Granite Suite confirmed the generally low yield expectations (< 1 L/s), surprisingly high yielding boreholes were drilled in the town of Paarl. Initial exploration of the potential fault was done in 2017 with electromagnetic and resistivity profiling to look for subsurface changes that may be associated with fracture zones. After the results of these surveys seemed to show some change in geophysical properties in the subsurface where a fault was inferred, exploration drilling along some of these profiles was conducted. In particular, exploration drilling at the Boy Louw Sportsfield in Paarl intersected water strikes from 60 - 90 mbgl in excess of 20 L/s blow yields. After a 3-day yield test with a further day for recovery in early 2018, a production wellfield was planned. Production drilling involved drilling larger diameter boreholes that would allow for higher flow rate pump installations than the typical 127 mm (PVC sleeved) to 165 mm inner diameter boreholes found in the region. Drilling depths of 100 - 150 mbgl were reached, by which depths airlift yields were exceeding 20 L/s as expected from the initial exploration drilling. Wellfield testing of the boreholes was performed by conducting two separate simultaneous borehole pumping tests at 38 L/s and 44 L/s, during which all available boreholes in the wellfield were monitored for water level changes. Based on the data analyses of these tests, the sustainable yield of the wellfield was initially estimated to be up to 60 L/s. As there was still some uncertainty regarding the high yields in a geological environment which was typically much lower yielding, two operational recommendations were put in place. The first was that the boreholes be equipped with pumps capable of adjusting flow rates as well as water level monitoring infrastructure to allow for informed management of the resource. The water level monitoring was also to be installed in the exploration boreholes to monitor the drawdown outside of the production boreholes. The second was that a one-month step-wise start to production should occur. During this period the wellfield was to start with a week of continuous pumping at a lower rate than estimated as sustainable, with increasing rates each week. This was recommended in such a way as to bridge the gap between the cumulative wellfield test rates and the cumulative wellfield recommended rate of abstraction and allow for any final optimizations to be made to this rate.While the first recommendation of monitoring infrastructure and variable rate pump installations was adhered to, in May 2019 the wellfield was abstracted from at the full initial recommendation of 60L/s. After a week of abstraction, three of the production boreholes were performing as expected fromthe wellfield test results, while one of the production boreholes had begun to drawdown more rapidly than expected. It was noted that this began to occur at a lower depth than what was reached during the 2018 wellfield tests. The rate of the individual borehole was reduced and abstraction continued for another two weeks with the new wellfield total of 54 L/s. The drawdown data of the borehole in question during the May 2019 abstraction was then re-analysed within the context of the wellfield, and with the increased drawdown data, to produce final wellfield production recommendations. As with all sustainable yield testing of boreholes, the choice of available drawdown is critical to the success of the analysis. In the Boy Louw Wellfield, it is likely that had higher abstraction rates been used during the wellfield testing, greater drawdowns may have revealed the inflection point in one of the production boreholes. Accounting for this in the initial analyses would have resulted in a more accurate initial wellfield recommendation. Additionally, the recommendations of a step-wise start to production would have likely revealed the same thing. While one of the production boreholes is now recommended to be operated at less than 50% of its initial recommendation due to the more recent identification of an inflection point, the total abstraction rate is still 90% of the initial wellfield tests' analyses recommendation. Against all odds, this allows an abstraction rate of 54 L/s from 4 production boreholes within a geological setting previously characterized as 0.1 - 0.5 L/s/borehole. Based on these results, it is recommended that future wellfield developments can adopt a similar methodology of iteratively increasing the development of a wellfield through scientific principles and testing. Wellfield testing should aim to cause sufficient drawdown in the production boreholes, as well as identify and quantify the cumulative interactions between adjacent boreholes within the wellfield. Should this not be achieved, a step-wise start to production with the ability to optimize flow rates is strongly recommended.

Abstract

The response of an alluvial and estuarine deposit aquifer, locally known as the Harbour Beds Formation, located in the coastal area of the Durban Metropolitan District to 48 hours of group well pumping is studied to understand its potential for groundwater supply and consequent seawater intrusion. Groundwater levels were monitored from the three pumped boreholes and piezometers. Similarly, EC, TDS and pH were monitored every hour from the boreholes and piezometers. Hydrochemical and water isotopes (2H and 18O) samples of groundwater were taken at 12, 18, 24, 36, 42 and 48 hours during pumping. The results indicate that the aquifer has a transmissivity, hydraulic conductivity and storativity of 48.97 m2/d, 1.7 m/day and 0.0032, respectively. The generally monitored EC, TDS, and pH have been fairly constant during the pumping period and didn’t show any seawater intrusion. Similarly, the hydrochemical data monitored for the three boreholes show general Na-CaHCO3-Cl-dominated groundwater throughout the pumping duration. However, uneven drawdown distribution and complex groundwater flow conditions indicate that the aquifer structure and hydraulic properties are heterogeneous. The water isotopes (2H and 18O) monitoring during the test pumping suggests spatial variability regarding water recharging the Harbour Beds aquifer. Though limited in area extent, the Harbour Beds Formation aquifer is a productive aquifer with acceptable water quality and can be a viable water source for domestic and industrial uses. However, continuous long-term monitoring of water quality and groundwater levels using data loggers is recommended to prevent induced seawater intrusion and contamination.

Abstract

Stable isotopes of the water are widely used in volcanic contexts to identify the recharge area, thanks to a strong orographic effect. Such data help improve the study areas’ conceptual model, especially to identify flow paths through the volcanic edifice. The most common pattern considered is a high to medium-elevation recharge area on a flank of the volcano, feeding both local perched aquifers and a deep basal aquifer. This is quite common for “shield volcanoes”, with the flank comprising a thick accumulation of lava flows. On composite volcanoes, especially in a volcanic arc context, the large diversity of lithologies (effusive/ destructive events dynamics) along the flanks may create a compartmented aquifers system. The Arjuno-Welirang-Ringgit volcanic complex (East Java) has been studied to elaborate a hydrogeological conceptual model. Stable isotopes of the water show significant results in identifying the recharge areas of several aquifers that are outflowing at a similar range of elevation. These results help to propose a water flow pattern from the recharge areas to the main springs with juxtaposed and superposed aquifers. This also leads to constraining the geometry of the aquifers and concluding that one volcanic complex with several recharge areas can feed juxtaposed aquifers. These results also highlight the need to adapt the study scale to each “point of interest” in the volcanic context, as each spring shows a different flowing pattern, preferential recharge elevation, and surface area. These are mandatory data to propose an adapted groundwater management.

Abstract

This study, near Thyspunt between St. Francis and Oyster Bay in the Eastern Cape Province of South Africa, focused on identification and quantification of surface water–groundwater links between the mobile Oyster Bay dune field and the coast. The specific objective was to establish the extent to which important wetlands such as the Langefonteinvlei and the numerous coastal seeps along the coast are directly or indirectly dependent on groundwater as their main water source. A further objective was to establish the extent to which any of the coastal seeps derive their water from the Langefonteinvlei, and are thus interdependent on the integrity of this system. The study also investigated the contribution of the Algoa and Table Mountain Group aquifers to these wetlands. The   monitoring   network   established   as   part   of   this   study   focused   on   unpacking   the interrelationships between surface and groundwater flows, aquifer hydrochemistry and wetland function, as related to the Langefonteinvlei and the coastal seeps in particular. Results indicate that the Langefonteinvlei is fed by groundwater flowing from the mobile Oyster Bay dune field in the north and the water divide in the northeast, which emerges at the foot of the high dune in the north and northeast of the wetland. However, the majority of the vlei area is ‘perched’ above the local water table on a layer of organic-rich sediment. The coastal springs located southwest and west of the Langefonteinvlei are not fed by water from the Langefonteinvlei. They emerge near the coast, where the bedrock lies close to the surface, and are fed by groundwater draining directly from the Algoa and Table Mountain Group aquifers to the Indian Ocean.

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

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Abstract

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

Abstract

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

The Cedarville Flats aquifer located in the Upper Umzimvubu River Basin, Eastern Cape Province is a source of water supply for an important agricultural region in South Africa. The hydrogeology of this important aquifer is investigated to understand the occurrence, circulation, recharge and quality of groundwater. To this end, local and regional geology, borehole lithological logs, borehole yields, aquifer hydraulic characteristics (including aquifer thickness, water level, hydraulic conductivity, transmissivity and storage coefficient), hydrometeorological, hydrochemicaland environmental isotope data were collected and interpreted. The results show that the alluvial aquifer is made up of sand, gravel, boulders and clay and its thickness reaches 51 meters in places. Median hydraulic properties indicate that the Cedarville Flats primary aquifer is the most productive aquifer compared to the underlying Molteno and Burgersdorp Formations. It has an estimated median borehole yield in the order of 6 l/s as compared to 2 l/s for the Burgersdorp and 1.5 liters for the Molteno Formations. The aquifers in the area receive an estimated 7% of rainfall recharge. The groundwaters of the area are characterized by low ionic concentration with EC and TDS ranging from 235 to 285 ?S/cm and from 65 to 151 mg/l, respectively. The hydrochemical data further indicate a groundwater hydrochemical facies of either Ca-Na-Mg-HCO3 or Na-Ca-Mg-HCO3 highlighting a typically less evolved recharge area groundwater having short residence time and hence less water-rock interaction. Springs and artesian wells show a relatively depleted stable isotope and very low to dead tritium signals indicating high altitude recharge and longer circulation path and residence times compared to wells tapping the water table aquifer which indicate young water with recharge coming from the immediate surrounding area. Similarity in hydrochemical and stable isotope signatures between the streams that drain across the alluvial flats and the shallow groundwaters mean that there is a close interconnection between surface water and groundwater in the area.

Abstract

The anticipated exploration and exploitation of Shale Gas in the Eastern Cape Karoo through hydraulic fracturing has raised considerable debate regarding the benefits and risks associated with this process for both the Karoo, and the country as a whole. Major concerns include the potential impact of hydraulic fracturing on ecological, environmental and especially scarce water resources. The Eastern Cape Karoo region is a water stressed area and with further climate change it will become increasingly so. Thus, effective and reliable groundwater management is crucial for sustainable development in this region. This research aims to hydrochemically characterise both the shallow groundwater (<500m) and deeper saline groundwater in the vicinity of the Shale Gas bearing formations, based on major and trace elements, as well as gas isotope analyses. Sampling will include water sampling and gas measurements from shallow boreholes (<300m), SOEKOR drillholes (oil exploration holes drilled in the 60's and 70's up to 4km deep) and thermal springs (source of water >500m).

To-date, a desktop study includes the collation of information determining the areas with the highest potential for Shale Gas Exploration throughout the Eastern Cape Karoo, from which the research area has been determined. This includes the identification of the respective oil companies' exploration precincts. A Hydrocensus has been initiated across this area, which includes slug testing and electrical conductivity profiling of open, unequipped boreholes. Further borehole selection will be finalised from this acquired information. The boreholes will be sampled and analysed a minimum of three times per year, which will occur after summer (April/May) and winter (October/November), after which the hydrochemistry will be analysed. The sampling will be preceded by purging of all inactive boreholes. The possible hydraulic connectivity between the shallow and deep aquifers will be tested, particularly in those areas where dolerite intrusions as well as fault systems may enhance preferential flow of water, using the chemical forensics complemented with passive seismic profiling/imaging and deep penetrating Magneto-Telluric (MT) imaging.

The data collected will form a record against which the impact of fracking can be accurately determined. The research is a critical first step towards the successful governance of groundwater in light of the proposed Shale Gas development. In its absence, effective regulation of the sector will not be possible.

Abstract

A hydrogeological investigation was conducted at a gold mine in the Mandiana region, northeast Guinea. The objectives of the investigation included: 1) Review the efficiency of the current dewatering system and 2) Assess potential dewatering impacts on neighbouring groundwater users. Historical and current hydrogeological information were reviewed and assessed to address the project objectives. The site geological succession contains laterites, saprolites, saprock, dolorite sill and fresh fractured bedrock below. A review of the borehole lithological logs, pump test and monitoring data confirmed that the contact zone between the saprock and the dolorite sill is the major aquifer zone with hydraulic conductivity up to 25 m/d, with a minor alluvial aquifer with hydraulic conductivity ~ 0.05 m/d. The current dewatering system is not as effective as it should be due to electrical issues causing seepage into the current pit floor. A combination of in-pit sumps and dewatering boreholes is recommended to ensure the mine pit’s dry working conditions. The neighbouring groundwater users tap into the alluvial aquifer with water levels ranging between 0-10 mbgl and are not at risk from mine dewatering impacts due to the dewatering boreholes tapping into the deeper saprock-dolorite contact zone. The shallow and deeper aquifers are hydraulically disconnected. The following is recommended: 1) Drilling of replacement dewatering boreholes and implementing continuous water level and abstraction rate monitoring, and 2) Discharge the in-pit sumps (alluvial aquifer inflow and rainfall) into the river downgradient of the mine to supplement recharge to the alluvial aquifer.

Abstract

The research aims to reveal possible ways of formation of the chemical composition of mineral and fresh groundwater in Quaternary sediments of the coastal plain of Northern Sinai. Statistical assessment of the distribution of various hydrochemical indicators of mineral and fresh groundwater has been carried out according to the following data samples: 1) the general population for all Quaternary deposits (164 wells); 2) the central zone (74 wells); the eastern zone (25 wells); the western zone (65 wells). The following variables were assessed: total dissolved solids (TDS) (in ppm), concentrations of major components (in epm and % epm), pH value and the depth of the sampled well (ds) (in meters). The physicochemical equilibria between the groundwater and rock–forming carbonate and sulfate minerals were calculated using the PHREEQC software. Saturation indices (SI) for groundwater of three zones in relation to various rock-forming minerals were analyzed. Correlation relationships were obtained for TDS, major components and some genetic coefficients ((Requ=(Na++K+)/ (Ca2++Mg2+); Na+/Cl-; SO4 2-/Cl-; Ca2+/SO4 2-). It was concluded that the groundwater chemical composition is defined by infiltration recharge and/or intrusion of Mediterranean seawater.

Most likely, during short-term flood periods, the infiltration into aquifers significantly exceeds the evaporation. Despite the relatively high evaporation rate, the degree of groundwater metamorphization is below the saturation level in relation to sulfates and carbonates. The research is of great practical importance for assessing freshwater resources to provide potable water supply

Abstract

2-D Electrical Resistivity Tomography (ERT) and hydrochemical study have been conducted at El Sadat industrial city. The study aims at investigating the area around the waste water ponds to determine the possibility of water percolation from the wastewater (oxidation) ponds to the Pleistocene aquifer and to inspect the effect of this seepage on the groundwater chemistry. Pleistocene aquifer is the main groundwater reservoir in this area, where El Sadat city and its vicinities depend totally on this aquifer for water supplies needed for drinking, agricultural and industrial activities. In this concern, 7 ERT profiles were measured around the wastewater ponds.

Besides, 10 water samples were collected from the ponds and the nearby groundwater wells. The water samples have been chemically analyzed for major cations (Ca+2, Na+, K+, Mg+2), major anions (Cl-, CO3-2, HCO3-, SO4-2), nutrients (NO2-, NO3-, PO4-3) and heavy elements (Cd, V, Cr, Zn, Ni, Cu, Fe, Mn, Pb). Also, the physical parameters (pH, Alkalinity, EC, TDS) of the water samples were measured. Inspection of the ERT sections shows that they exhibit lower resistivity values towards the water ponds and higher values in opposite sides. Also, the water table was detected at shallower depths at the same sides of lower resistivity. This could indicate a wastewater infiltration to the groundwater aquifer near the oxidation ponds. Correlation of the physical parameters and ionic concentrations of the wastewater (ponds) samples with those of the groundwater samples indicates that; the ionic levels are randomly varying and no specific trend could be obtained. Also, the wastewater samples shows some ionic levels lower than those detected in other groundwater samples. Besides, the nitrate level is higher in samples taken from the cultivated land than the wastewater samples due to the over using of nitrogen fertilizers. Then, we can say that the infiltrated water from wastewater ponds are NOT the main controller of the groundwater chemistry in this area, but rather the variable ionic concentrations could be attributed to local, natural and anthropogenic processes.

Abstract

Natural processes (e.g., El Nio) and anthropogenic activities (e.g., land-use modification and groundwater abstraction) drive local and global hydrological changes. Consequently, these changes threaten the role of wetlands in the hydrological and ecological functioning of a catchment. Verlorenvlei is a vulnerable RAMSAR-listed estuarine lake located on the west coast of South Africa in Elands Bay. Since the 2015-2018 Western Cape drought, Verlorenvlei has experienced drier-than-normal conditions with less rainfall, negatively impacting the surrounding ecology. Seasonal and spatial changes of the water sources (e.g., rainfall, surface water, and groundwater) supporting the wetland and the interconnectivity between these reservoirs were investigated using O/H stable isotopes and hydrochemistry analysis. The study collected event-based rainfall (57 samples), surface water (18 samples), and groundwater (108 samples) in February, April, and June 2022. Stable isotope ratios and hydrochemistry indicate that groundwater outside the watershed (topographically and surface water delineated) supports the wetlands, suggesting that local and regional groundwater flow systems influence the Verlorenvlei. Furthermore, the Verlorenvlei is subjected to high evaporation compared to other surface waters and, in return, is reliant on baseflow supporting its hydrological functioning. The Krom Antonies and Hol sub-catchments exhibit overlapping groundwater isotope ratios and water types compared to the Verloren sub-catchment, suggesting a disproportionately high groundwater contribution from both sub-catchments into the wetland. Understanding Verlorenvlei’s water balance is necessary to improve ecological reserve determination studies to help ensure environmental and socio-economic sustainable water use

Abstract

For 25 years, the UK’s Environment Agency has commissioned groundwater flow models of the main aquifers in England. These regional-scale models are regularly updated, occasionally recalibrated and used for water resources management, regulatory decisions and impact assessment of groundwater abstractions. This range of uses requires consideration of the appropriate scale of data collection and modelling and adaptation of the groundwater models, with refinement where local impacts on individual springs and seasonal streams are considered and combination and simplification for strategic national water resources planning. The Cretaceous Chalk, a soft white limestone, is the major aquifer of southern and eastern England, supplying up to 80% of the drinking water in this densely populated region. Springs and baseflow of good quality groundwater feed Chalk streams, which are a rare and valuable habitat with a high public profile, but face significant challenges in the 21st century, worsened by climate change and population growth. The modelling informs strategic planning and regulatory decisions, but the model’s scale needs to be appropriate for each issue. The presentation defines these issues and presents examples, ranging from the large-scale, strategic Water Resources East to impact assessment for individual groundwater abstractions and more bespoke local investigations, including simulation of groundwater flood risks. As the scale of investigations reduces, there is increasing importance on the accuracy of information, both temporally and spatially. Model refinement made during local investigations can be incorporated into larger-scale models to ensure that this understanding is captured.

Abstract

A conceptual water budget model is required to “make groundwater visible” in the shared transboundary area of Estonia and Latvia, which doesn’t face any significant water management issues. Despite having a water management agreement since 2003, it wasn’t until 2018 that cooperation on groundwater began. In the EU-WATERRES project, the water balance modelling of the ~9,500 km2 transboundary (TB) area with MODFLOW 6 was performed. Based on budget calculations, the area’s average precipitation is 203 m3 /s, with ~50% (102 m3 /s) of it discharging to the sea as surface water. The infiltration share (7%, 14.4 m3/s) is a small fraction of overall precipitation, but as an average, it forms ~14% of surface water flow, with 98% of infiltrated groundwater forming the baseflow. Modelling produced two main conclusions: surface water and groundwater form a joint system in the upper ~150 m cross-section depth, and there is no preferred regional TB flow direction due to flat topography. This makes cross-border flow highly dependent on pumping close to the border area. The results of recent studies provide valuable information on groundwater’s importance in EE-LV TB areas and a basis for simple conceptual models to make groundwater visible to the general audience and decision-makers. These findings are critical for specialists in managing water resources in the region and will inform decisions related to the use and protection of groundwater in transboundary areas.

Abstract

The urban and rural communities sources of water for domestic and other uses come from groundwater in most parts of Ethiopia. But the groundwater is not free from challenge. Fluoride is one of those critical problems which are affecting the health of inhabitants of this corridor. There are places where the fluoride contents reach more than 10mg/l. groundwater Treatment plants, changing the water scheme source from surface water and related efforts have been made so far to alleviation such challenges. Fluoride affects bones and teeth by changing its color and easily affected to a number of health complication in the rift valley of Ethiopia. {List only- not presented}

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

Throughout the world, climate change impact is the main concern for sustainability of water management and water use activities like agricultural production. Climate changes alter regional hydrologic conditions and results in a variety of impacts on water resource systems. Such hydrologic changes will affect almost every aspect of human well-being. The goal of this thesis is to assess the impact of climate change on the hydro climatology of Fincha Sub-basin located in upper Blue Nile Basin of Ethiopia. The GCM derived scenarios (HadCM3 A2a & B2a SRES emission scenarios) experiments were used for the climate projection. The statistical Downscaling Model (SDSM) was used to generate future possible local meteorological variables in the study area. The down-scaled data were then used as input to the Soil and Water Assessment Tool (SWAT) model to simulate the corresponding future stream flow in of Fincha Sub-basin located in upper Blue Nile Basin. A semi distributed hydrological model, SWAT was used to simulate future stream flow. Three benchmark periods simulated for this study were 2020s, 2050s and 2080s. The time series generated by GCM of HadCM3 A2a and B2a and Statistical Downscaling Model (SDSM) indicate a significant increasing trend in maximum and minimum temperature values and a slight decreasing trend in precipitation for both A2a and B2a emission scenarios in both Shambu and Neshe stations for all three bench mark periods. The hydrologic impact analysis made with the downscaled temperature and precipitation time series as input to the SWAT model suggested an overall decreasing trend in annual and monthly stream flow in the study area, in three benchmark periods in the future. This should be considered by policymakers of water resources planning and management. The hydrologic impact analysis made with the downscaled temperature and precipitation time series as input to the hydrological model SWAT suggested for both A2a and B2a emission scenarios. As a result, at the out let of the watershed the projected on average annual flow decrease by 5.59%,9.03%,11% and 2.16%,4.15 and 3.46% for the 2020s,2050s and 2080s for both A2a and B2a emissions scenarios. Potential evapotranspiration in the watershed also will increase annually on average 3 - 16% for the 2020s and 4-19% for the 2050s and 2080s for both A2a and B2a emissions scenarios. {List only- not presented}

Abstract

An investigation of surface and groundwater chemistry was undertaken as part of a resource assessment of water-supply for potash solution-mining in the Danakil Depression of the Afar Rift, situated in northern Ethiopia on the N/S-trending Ethiopia-Eritrean arm of the East African Rift System. Four hydrostratigraphic units are recognised in the area: 1) Basement Tsaliet Group rocks, low yielding and with poor water quality; 2) Adigrat Formation and Antalo Group fractured sandstones and karstic limestones, high yielding with good water quality; 3) Danakil Group and Zariga Formation fine-grained sediments, forming a good regional aquifer; 4) Dogua Formation alluvial fans, forming a major, regional, primary aquifer with high yields and poor water quality (yields of >50 l/s but 3 times the salinity of sea water). In the mining concession area the only available target for groundwater exploration is the Dogua alluvial-fan system that extends off the Dogua Mountain range to the west. During 2015 and 2016, 5 production and 5 exploration/monitoring boreholes were drilled into the fans, thereafter test pumped and sampled for hydrochemical and isotope analysis. The aquifer stress test proved that there is sufficient groundwater available for the life of mining, but that the water quality is poor. The hydrochemical analysis found that in general, water quality is poor (brine with TDS values >100 000 mg/l and a density >1.05 g/cm3 ) and with temperatures of ~50°C. Water quality degrades from south to north, possibly due to recharge of fresh water from the Antalo limestones in the south and lesser quality water from the Tsaliet basement in the north. The high salinity and temperature found throughout the fans is due to hydrothermal influx along rift-boundary faults that extend downwards into the thermally active, volcanic rift zone. Prolonged pumping results in the degradation of the water quality in the southern boreholes and improvement of quality in the northern boreholes; this is likely as the groundwater heads towards equilibrium, with a similar hydrochemical signature to that of the dominant hydrothermal influx. Stable and radiogenic isotope sampling and analysis was undertaken to determine the source of the recharge, the results showing that it is likely a combination of evaporation from fresh water, lateral recharge of ancient sea water along faults from the Red Sea, and hydrothermal recharge from the sub-surface leaching of young Afar and Red Sea Basalts in the active rift zone.

Abstract

The assessment and prediction of mine water rebound has become increasingly important for the gold mining industry in the Witwatersrand basin, South Africa. The cessation of dewatering lead to large volumes of contaminated surface discharges in the western parts of the basin. Towards the eastern extremity of the Witwatersrand basin the detached Evander Goldfield basin has been mined since the early 1950s at depths between 400 and 2 000 m below ground, while overlain by shallower coal mining operations. The hydrogeology of the Evander basin can be categorised by a shallow weathered-fractured rock aquifer comprising of the glacial and deltaic sediments of the Karoo Supergroup, while the deeper historically confined fractured bedrock aquifer consist predominantly of quartzite with subordinate lava, shale and conglomerate of the Witwatersrand Supergroup. The deep Witwatersrand aquifer has been actively dewatered for the last 60 years, with a peak rate of 60 Ml per day in the mid late 1960s. Modelling the impacts of mine dewatering and flooding on a regional scale as for the Evander basin, entails challenges like the appropriate discretisation of mine voids  and  the  accurate  modelling  of  layered  aquifer  systems  with  different  free  groundwater surfaces on a regional scale. To predict the environmental impacts of both the historic and future deep mining operations at Shaft 6, the detailed conceptual model of the aquifer systems and three- dimensional model of the mine voids were incorporated into a numerical groundwater model to simulate the dewatering and post-closure rebound of the water tables for the basin. The presented model could serve as an example for the successful modelling of mine dewatering and flooding scenarios for other parts of the Witwatersrand basin.

Abstract

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

Abstract

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

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

Abstract

Groundwater represents a crucial source of drinking water in the Lille metropolitan area. Despite its importance, the resource is vulnerable to the potential evolution of land use: recharge, runoff and evapotranspiration processes in a soil-sealing context and changes in cultural practices. As a result, stakeholders emphasized the importance of exploring the influence of land use on groundwater to ensure sustainable resource management and enhance territorial planning. The 3D hydrodynamic model helped manage groundwater resources, but the (MARTHE code) has a significant limitation in that it does not consider the impact of land use evolution. We propose to investigate the contribution of a hydrological distributed numerical approach incorporating land cover data in groundwater modelling compared to a global approach at the scale of a peri-urban territory. To do so, we use the HELP code by considering the temporal and spatial evolution of land use and their associated characteristics, such as vegetation and soil properties, to detail recharge and runoff over more than 20 years that we incorporate into the initial groundwater model.

The two approaches yielded comparable global water balance results. However, at the local scale, the model accounting for land use showed significantly different hydric components. Choosing the appropriate model depends on the specific research question and spatial scale, and considering land use evolution is crucial for accurate urban planning impact assessments, especially at the district level.

Abstract

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

Abstract

The interactions between groundwater and the sewerage networks of the Lens-Liévin urban communities, located in the north of France, locally lead to non-compliance in the operation of the network and the wastewater treatment plants, questioning the city’s economic development policy. Indeed, the infiltration of groundwater inflow in the sewerage network could be the cause. Based on the piezometric measurements carried out in 2022, the surface elevation of the groundwater table is carried out using a kriging approach. The comparison of altitudes between network position and piezometry made it possible to identify the pipes most at risk of the infiltration of groundwater inflow and correspond to those indicated as non-compliant by network managers according to the national decree. Outside this period, the network vulnerability indicators are defined based on simulated piezometry by a 3D hydrodynamic model of the chalky hydrosystem (MARTHE code) established in a transient state. For two past extreme situations, the network would have been flooded at 1.20% in the dry period (1997) and up to 8.30% in the wet period (2001), highlighting the existence of a part of the network systematically flooded. Using the hydrodynamic model according to different prospective scenarios makes it possible to anticipate the actions deployed on the network to guide management and adaptation solutions. However, a modelling methodology that considers the feedback between the dynamics of the groundwater and the flows passing through the networks remains to be developed.

Abstract

This paper describes the results of geohydrological studies conducted at Matsopa Mine, where a shallow bentonite body is mined, to investigate the potential impacts of mining on the groundwater environment. An understanding of such potential impacts is crucial since the communitiesin the area are dependent solely on groundwater for their domestic water supply.

The studies consisted of a) a hydrocensus to investigate the current groundwater quality and use in the vicinity of the mine, b) geophysical surveys to investigate the presence of geological structures that may influence groundwater migration, c) geochemical investigations of the ore body and host rock to predict the character of potential contaminant impacts, and d) groundwater monitoring to determine whether mining has impacted on the groundwater quality.

The hydrocensus found that the groundwater is used for domestic water supply, as well as livestock watering and irrigation, on a number of farms surrounding the mine. The geophysical surveys conducted with the magnetic and electrical resistivity tomography (ERT) methods revealed the presence of dolerite structures adjacent to and in the vicinity of the opencast pits. These structures are likely to be associated with fractures, joints, fissure and cracks which could form preferential pathways for groundwater migration. The results of geochemical analyses using the XRD and XRF methods showed that both the ore and host rock are dominated by SiO2 and contain very low concentrations of trace elements that could pose a threat to the environment and human health. Groundwater monitoring was done on a bimestrial basis. The groundwater quality was found to be good with little or no evidence of contaminant impacts from mining. Elevated nitrate concentrations at a single monitoring site are likely to be due to agricultural activities on the different farms surrounding the mine. During the time spanned by the monitoring events, increasing water level elevations were recorded in the boreholes surrounding the mine. This observation shows that groundwater recharge to the aquifer system was taking place as a result of the higher rainfall experienced as compared to the preceding years. Activities at Matsopa Mine do therefore not appear to have a significant impact on the groundwater levels in the vicinity of the mine. The results of the geohydrological studies therefore indicate that bentonite mining at Matsopa Mine has not had significant detrimental impacts on the groundwater quality and quantity.

Abstract

The city of Bloemfontein is currently entirely dependent on remote surface water sources for its potable water supply. The water is purified at great cost, before being pumped over large distances to the reservoirs of the city. However, the surface water resource is unreliable and susceptible to droughts. In addition, large volumes of the purified water are lost before reaching the users. These losses are due to various factors, including leakages in the pipelines transporting the water to Bloemfontein and illegal connections. To reduce the city's dependence on remote surface water sources, this investigation aims to assess the potential for using groundwater resources to augment the municipal water supply. A prominent ring-dyke underlying the city is thought to be associated with strong aquifers. Our geophysical investigations have shown that this dyke yields large and well-defined magnetic and resistivity anomalies that allow easy interpretation of the geometry of the dyke. Future investigations will include the installation of boreholes at positions as determined from an interpretation of the geophysical data. Hydraulic tests will be performed on the aquifers intersected by the boreholes to determine the hydraulic parameters and sustainable yields. The groundwater quality will be assessed to evaluate its suitability for human consumption.

Abstract

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

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

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

Abstract

The National Water Act (Act 36 of 1996) aims at redressing inequalities in water allocation. Historically, water resources were allocated to few white people who owned land and actively participated in agribusinesses. The need for widening access to water-related business was agreed and water allocation reformed (WAR) model was developed and implemented to re-dress such past inequality. However, limited progress has been registered because there is no real-time model to monitor, evaluate and report the progress of the four water entitlements. The current study focused on groundwater abstraction/use to assess the reported limited progress in WAR. Data report and active groundwater use from WARMS database were collected, filtered and analysed for parameters as set out in the water use license conditions. WARMS database contains information on parameters regarding water use in the water allocation process. Statistical techniques were utilised to establish change detection, trend analyses and correlations including multiple regression analysis in order to establish the magnitude and direction of relationships between factors. Preliminary results showed that several communities did not make significant improvement with regard to WAR. When population groups were compared, results showed that majority of black people lagged behind in accessing water resources for economic use implying that they will continue facing difficulties to participate in agribusiness-related activities. When WAR targets were assessed, findings showed such targets were not achieved. Further analysis showed that water use entitlements and participating in the economic activities are attached to land ownership. The current study recommends that a real-time model is required to monitor, evaluate and report the progress of four water entitlements and to fast tracking land reform tasks which promote the transfer of land from white people to black people because this has been viewed as one of the ways through which progress on water allocation reform process can be fast tracked.

Abstract

Delineation of groundwater resources of a given area is importance for management of groundwater resources. This is often done manually by combining various geo-scientific datasets in Geographic Information System (GIS) environment, which is time consuming and is prone to subjective bias and also suffers from other human induced uncertainties and difficult to cope with increasing volumes of data. The explosive growth of data leading to ‘rich data, but poor knowledge’ dilemma yet we have challenges to be solved. Artificial Intelligence (AI) has been successfully used in fields such as robotics, process automation in engineering, industry, medical and domestic households. Artificial Intelligence tool have the able to bridge this gap by augmenting the human capabilities in understand science far better than before. Incorporating AI into groundwater potential mapping greatly improves computation speed, reduces the subjectivity nature of manual mapping and lessens human induced uncertainties. The software platform includes artificial intelligence algorithms such as artificial neural networks, support vector machines, random forest, index-overlay and fuzzy logic.

The software platform is semi-automatic to allow the user to control some of the processes yet automating the other processes. The possible inputs to the AI for training includes; aquifer types, topographic slope, lineament and drainage density, land-use / land-cover (LULC), distance to lineaments, distance to streams and soil clay content. Yield values of selected boreholes are used as training outputs.

The software was tested using data gathered for the area surrounding Maluti-a-Phong in the Free State Province of South Africa. The area was chosen because of recent drought which has hit the country and local municipalities are searching for groundwater resources for building wellfields to supply local communities with fresh water. The groundwater potential map of the area was validated using borehole yield values of boreholes which were not used for modelling. Good correlation values as high as 0.85 was obtained between model values and borehole yield. The final groundwater potential map was divided into four zones; very good, good, poor and very poor. Based on this study, it is concluded that the high groundwater potential zones can be target areas for further hydrogeological studies.

The usage of the software proved to be efficient in minimising the time, labour and money needed to map large areas. The results of which can be used by local authorities and water policy makers as a preliminary reference to narrowed down zones to which local scale groundwater exploration can be done. AI should be viewed as augmented intelligence as it aid the decision-making process rather than replacing it. Data-driven approaches should also be knowledge-guided for efficient results.

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

The colliery is situated in the Vereeniging–Sasolburg Coalfield, immediately southwest of Sasolburg in the Republic of South Africa. The stratigraphy of this coal field is typical of the coal-bearing strata of the Karoo Sequence. The succession consists of pre-Karoo rocks (dolomites of the Chuniespoort Group of the Transvaal Sequence) overlain by the Dwyka Formation, followed by the Ecca Group sediments, of which the Vryheid Formation is the coal-bearing horizon. Mainly the lava of the Ventersdorp and Hekpoort Groups underlie the coal. The Karoo Formation is present over the whole area and consists mainly of sandstone, shale and coal of varying thickness.

The underground mine was flooded after mining was ceased at the colliery in 2004. The colliery is in the fortunate position that it has a very complete and concise monitoring programme in place and over 200 boreholes were drilled in and around the mine throughout the life of the mine. To stabilise mine workings located beneath main roads in the area, an ashfilling project was undertaken by the colliery since 1999. A key issue is if the mine will eventually decant, and what the quality of the water will be. This is important for the future planning of the company, as this will determine if a water treatment plant is necessary, and what the specifications for such a plant will be, if needed. Therefore it was decided to do a down-the-hole chemical profile of each available and accessible borehole with a multi- parameter probe with the aim of observing any visible stratification. Ninety-four boreholes were accessible and chemical profiles were created of them.

From the data collected a three-dimensional image was created from the electrical conductivity values at different depths to see if any stratification was visible in the shallow aquifer.  The ash-filling operations disturbed the normal aquifer conditions, and this created different pressures than normally expected at a deeper underground  colliery.  From  the  three-dimensional  image  created  it  was  observed  that  no stratification was visible in the shallow aquifer, which lead to the conclusion that in the event that if decant should occur, the water quality of the decanting water will still be of very good quality unless external factors such as ash-filling activities are introduced. It is not often that it is possible to create chemical profiles of such a large number of boreholes for a single colliery and as a result a very complete and informative three-dimensional electrical conductivity image was created. This image is very helpful in aiding the decision-making process in the future management of the colliery and eventually obtaining a closure certificate, and also to determine whether ash-filling is a viable option in discarding the ash.

Abstract

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

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

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

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

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

Abstract

Despite majority of the terrestrial fresh water resources being groundwater, there still exists a public perception that the only source of potable water is from surface water bodies. Due to this misperception, the general public is often ignorant about the importance of groundwater as a resource. This is evident in the lack of appreciation for the Upper and Lower Fountains in Pretoria as the main reason for various historical events in and around Pretoria, leading to it eventually becoming the capital of South Africa. This project, which introduces a broader Hydrological Heritage Overview programme, is intended to create awareness regarding the history and importance in the development of South Africa, and to improve public understanding of the important role that hydrology and hydrogeology is playing in our day to day lives. Additionally, scientific appraisal of historical data will aid the relevant managements to better manage these valuable resources, while making interesting and important archived data available to the scientific community in the form of trend analyses and conceptual models. The paper will showcase a 10-minute narrated video on the importance of groundwater in the history of Pretoria. As part of a water awareness programme to inform the general public about Pretoria's water supply from springs since its founding in 1855, the video depicts the development of the capital city around these springs from its founding to present.

Abstract

At a regional scale, groundwater recharge is often calculated using surface water models. Precipitation and surface water runoff are easier to measure than groundwater recharge, and evapotranspiration can be estimated with relative accuracy using indirect methods. In modelling, surface water measurements can be used for calibration, and groundwater is the residual term in the water balance of the catchment. This can give a good indication of regional trends, but provides limited scope for the accommodation of groundwater system characteristics and recharge processes. Recently, much research has been focused on the interaction of surface and groundwater models. The coupling of physically based surface and ground water models allows for calibration of the model using both surface and groundwater data while providing scope for improved insight into the processes which define the interaction of groundwater with the rest of the water cycle. For example: stream discharge, interflow, preferential flow through the unsaturated zone and interaction with surface water retained in dams and wetlands. One such model is GSflow (United States Geological Survey), which we are applying to the Upper Vaal Catchment. This model integrates the surface water model PRMS (Precipitation-Runoff Modelling System) with MODFLOW (Modular Groundwater Flow model). The model is initially being calibrated at quaternary catchment scale, starting with the surface water components and later adding the groundwater system. The quaternary catchment is subdivided into smaller, topologically defined hydrological response units. This scaling allows for a better understanding of how well the characteristics of the units are represented in the physical processes incorporated into the model, so that ultimately the sensitivity analysis can incorporate these processes. The results will be compared to current work on recharge being carried out using GRACE data and previous work done in the same area. Once the entire model has been calibrated, there will be scope to calculate future scenarios, allowing for climate and land-use changes. A brief overview of existing work as well as methods and initial results and sensitivity analysis will be presented.