Conference Abstracts

Abstract

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

Abstract

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

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

Abstract

This study assessed aquifer-river interaction using a combination of geological, hydrological, environmental stable isotope, and hydrochemical data in a non-perennial river system in the Heuningnes catchment. Results showed the depth to groundwater levels ranging from 3 to 10 m below ground level and aquifer transmissivity values of 0.17 to 1.74 m2 /day. The analytical data indicated that Na-Cl-type water dominates most groundwater and river water samples. Environmental stable isotope data of river samples in upstream areas showed depleted δ18O (-4.3 to -5.12 ‰) and δ2H (-22.9 to -19.3 ‰) signatures similar to the groundwater data, indicating a continuous influx of groundwater into the river water. Conversely, high evaporative enrichment of δ18O (1.13 to 7.08 ‰) and δ2H (38.8 to 7.5 ‰) were evident in downstream river samples.

It is evident from the local geological structures that the fault in the northeastern part of the study area passing Boskloof most likely acts as a conduit to groundwater flow in the NE-SW direction, thereby supplying water to upstream river flow. In contrast, the Bredasdorpberge fault likely impedes groundwater flow, resulting in hydraulic discontinuity between upstream and downstream areas. Relatively low conductive formation coupled with an average hydraulic gradient of 8.4 × 10−4 suggests a slow flow rate, resulting in less flushing and high groundwater salinisation in downstream areas. The results underscore the significance of using various data sets to understand groundwater-river interaction, providing a relevant water management platform for managing non-perennial river systems in water-stressed regions.

Abstract

South Africa is the leading user of pesticides in Sub-Saharan Africa, but data on pesticide occurrence in (ground)water is limited. Consequently, there is a need to improve knowledge on transport pathways that cause pesticides to enter the aquatic environment. This research monitored pesticide concentrations in three agricultural catchments in the Western Cape, South Africa, including Grabouw (pome fruit), Hex River Valley (table grapes), and Piketberg (wheat). Passive samplers were deployed in rivers from March 2022- March 2023, adding to a 2017-2019 dataset of analytical and pesticide application data. Field and laboratory methods were developed at Stellenbosch University to measure pesticides using Liquid Chromatography-Mass Spectrometry. For quality control, duplicate samples were analyzed at Eawag, Switzerland. 30 compounds were detected, yet two/three comprise most of the total mass, including an analyte not considered in earlier investigations (dimethomorph).

Rainfall-flow relationships and agricultural application could only partially explain detection levels, suggesting that other factors, including non-agricultural application or groundwater input, might influence detections. Two compounds exceeded European Environmental Quality Standards (chlorpyrifos and imidacloprid). Imidacloprid is particularly concerning because it exceeded consistently despite few recorded applications. 2017-2022 imidacloprid data indicates a decreasing concentration trend in Hex River Valley and increasing trends in Piketberg and Grabouw. Consistently high detections during wet and dry periods suggest groundwater input. However, such pesticide transport pathways are poorly understood due to a lack of local evidence. Local authorities must establish a long-term monitoring program to understand better the risk pesticides pose to the aquatic environment and human health.

Abstract

Water resources, including groundwater, are under threat globally from abstraction and pollution, making studies of water flows ever more urgent. South Africa has a growing population, a relatively dry climate and abundant mining activity, all of which increase the importance of water management. Mooiplaas Dolomite Quarry, southeast of Pretoria, has been mining metallurgical grade dolomite since 1969 and is located in the productive karst aquifers of the Malmani Subgroup, Transvaal Supergroup. The site was investigated by sampling precipitation, surface water, groundwater and mine water for hydrochemical and stable isotope analysis from 2011 to 2017, totalling over 400 samples. Nitrate levels in groundwater and mine water were marginally above drinking water limits from explosives residues, and ammonia in the nearby Hennops River was unacceptably high due to municipal sewage outfalls, but otherwise, water quality was very good. Alkalinity from rock weathering, aided by the crushing of dolomite, was the main control on water chemistry. Combined analysis of dissolved matter (TDS, nitrate, Mg, etc.) suggested that the dewatering of the mine and resultant recharge from slime dams caused an aerated zone of groundwater, which mixed with regional groundwater flowing beneath the site. Stable isotopes, with an evaporated signature from mine open water bodies, also showed how mine operations cause recharge to groundwater and subsequent seepage back into the pit lakes. The mine appears not to contaminate the regional groundwater. However, mine designs should avoid situations where process water flows via groundwater back into pits, causing excessive dewatering costs.

Abstract

Transboundary aquifers in Europe are managed according to the Water Framework Directive (WFD) through international river basin districts (IRBD) management plans. Paragraph 11 in the WFD states that each Member State shall ensure the establishment of a programme of measures, PoM, for each river basin district, RBD, or part of an IRBD within its territory. Easy access to harmonized data from neighbouring countries part of the aquifer is essential to analyse the groundwater status and make proper PoMs. The datasets must be available in machine-readable format via an Application Programming Interface (API) and, where relevant, as a bulk download. The metadata describing the data shall be within the scope of the Infrastructure for Spatial Information in the European Community (INSPIRE) data themes set. The datasets must also be described in a complete and publicly available online documentation describing the data structure. Using a questionnaire survey of nine European countries, groundwater sampling and analysis routines are compared to evaluate if data are comparable and accessible across borders.

Abstract

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

Abstract

The Kavango West and East regions are situated in a semi-arid area northeast of Namibia and bounded by the perennial Okavango River on the northern border. Groundwater in the area is the main source of water supply for the inhabitants living further from the river. In addition, most bulk water users along the river have boreholes for their water supply. With a semi-arid climate, drought in the regions is common and inflicts devastating effects on local communities. More drought relief boreholes are being drilled to sustain communities, increasing the dependency of the inhabitants on groundwater. The complexity of the behaviour and nature of the groundwater in the regions is poorly understood, and there are no strategies to manage these aquifers properly. As a result, an attempt was made to better understand the groundwater potential by examining several hydrogeological factors involved. A basic water-balance approach was used in determining the groundwater potential of the middle and lower Kalahari aquifers. The total resource potential for the entire region is estimated at 144 447.16 x 106 m3 /a, demonstrating great resource potential with significant storage space.

The greatest potential is shown in the middle Kalahari aquifers, comprising about 94% of the total resource. Groundwater recharge, as one of the hydrogeological factors, was determined using the chloride mass balance method, giving an average of 6.03 mm/a for the entire study area. If utilized sustainably, the Kalahari aquifers can sustain most communities within the two regions, especially those further from the Okavango River.

Abstract

The interaction between dryland hydrological fluxes and the high spatial and seasonal climate variability is inherently complex. Groundwater recharge is episodic, and rivers are ephemeral. When flow occurs in the river network, water is lost through the riverbed, giving rise to focused recharge, which could be a significant part of total recharge. We have used the integrated and physically based MIKE SHE modelling system to analyze the hydrological processes and fluxes in the 7,715 km2 Hout-Sand catchment in the South African part of the Limpopo River Basin. The discharge hydrograph measured at the outlet station is highly episodic, with a small baseline flow component superimposed by high flow events in response to intense rainfall. Likewise, the groundwater hydrographs from the area are characterized by rapid increases in groundwater levels in response to high rainfall events with recurrence intervals of several years. Due to the scarcity of basic measurements and information, we used data products from satellite platforms to supplement the information on rainfall, evapotranspiration, soil moisture, land use and irrigated areas. We applied MIKE SHE to test different conceptual flow models of the catchment by calibrating the different models against direct measurements of river discharge and groundwater levels and indirect estimates of evapotranspiration and soil moisture from satellite products. By analyzing the simulated model dynamics and the resulting values for the calibration parameters, we identified the most plausible conceptual model, which then forms the basis for water resources assessment and management recommendations for the Hout-Sand catchment.

Abstract

Previous studies have shown that river-aquifer connectivity exists. However, an integrated approach that consists of multiple measuring methods to quantify and characterise such connectivity still needs improved scientific understanding due to the underlying principles and assumptions of such methods, mainly when such methods are applied in a semi-arid environment. Three techniques (hydrogeochemistry, stable water isotopes, and baseflow separations) were applied to quantify and characterize river-aquifer interactions. The study’s objective was to improve knowledge and understanding of the implications of the results from the three methods. Field measurement, laboratory assessment, and record review were used to collect primary and secondary data. Results showed that Na- HCO3 water type dominated the upper stream, discharging onto the surface and forming stream sources. Na-HCO3 water type was an outlier when the area’s geology and land use activities were assessed. The isotope results showed that the studied aquifer had 9% recently recharged water. Being the upstream, the freshwater in such a mountainous aquifer was expected. The baseflow index (BFI) results showed that the dependency of the total river flow to aquifer discharge contributed 7.24 % in the upper stream, 7.31% in the middle stream, and 7.32% in the lower stream. These findings provided empirical evidence that hydrochemistry, stable isotopes, and baseflow separation methods provide key insights into aquifer-stream connectivity. Such findings inform choosing appropriate and relevant measures for protecting, monitoring, and allocating water resources in the catchments.

Abstract

Urban karst terrains can experience geotechnical issues such as subsidence or collapse induced/accelerated by groundwater withdrawal and civil works. Sete Lagoas, Brazil, is notable for overexploiting a karst aquifer, resulting in drying lakes and geotechnical issues. This study aims to evaluate the progression of geotechnical risk areas from 1940 to 2020 and to simulate future scenarios until 2100. Historical hydraulic head data from the 1940s (when the first pumping well was installed) to the 2000s, a 3D geological model, and a karst-geotechnical risk matrix for defining risk levels were employed to develop a calibrated Feflow numerical model. The results indicate that, before the first well in 1942, the groundwater flow direction was primarily towards the northeast. In the 1980s, due to the concentration of pumping wells in the central area, a cone of depression emerged, causing the flow directions to converge towards the centre of the cone, forming a zone of influence (ZOI) of approximately 30 km². All 20 geotechnical events recorded between 1940 and 2020 have occurred in high or considerable-risk zones where limestone outcrops or is mantled in association with the ZOI. For future scenarios, if the current global well pumping rate (Q = 144,675 m³/d) from 2020 remains constant until 2100, the high and considerable geotechnical risk zones will continue to expand. A 40% decrease in the global rate (Q = 85,200 m³/d) is necessary to achieve a sustainable state, defined by reduced and stabilized risk zones.

Abstract

Groundwater is a hidden resource, so as part of making it more visible, geophysical methods can be very useful in inferring the delineation of aquifers and/or more productive zones to target in fractured rock environments. The most commonly used techniques to assist groundwater studies or exploration are still resistivity profiles or sections known as ERT or electrical resistivity tomography and vertical electrical soundings or VES. One of the limiting factors with this technique is the scale of what surveys can be conducted, resulting in, at best, some kilometers per day. The Hydrogeophysics group of Aarhus University have developed the towed transient electromagnetic (tTEM) system as a cost-efficient tool for characterizing regional hydrological systems to depths of up to 70 m as an alternative to these more traditional methods - which is highly productive in that collection of 40- to-80-line kilometers of data per day is feasible. The system is based on the transient electromagnetic (TEM) method, which involves using a transmitter and receiver coil to measure the electrical resistivity of the subsurface. The hydrological value in electrical resistivity images stems from the ability to delineate different hydrogeological units based on their contrasting electrical properties. Consequently, 3D electrical resistivity images can infer the subsurface hydrogeology and enhance the success of installing productive boreholes. This work presents case studies from several African countries (e.g., South Africa, Zimbabwe, Ethiopia, Senegal, and Togo). It demonstrates how the tTEM method can identify reliable drinking water sources in these countries.

Abstract

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

Abstract

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

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

Abstract

 Predicting and quantifying the hydrogeological interference of big underground works is a complex effort. This is due to the considerable uncertainty in estimating the key geomechanical and hydrogeological parameters affecting the area of potential interference of the projects. Moreover, the pattern of involved groundwater flow systems is hardly identified, either in natural or disturbed conditions. Base tunnels through mountain ridges are particularly complex in their interactions with groundwater. Several approaches and tools have been published to predict the magnitude and distribution of water inflows inside tunnels and their impact on many receptors (springs, rivers, lakes, wells, groundwater-dependent ecosystems). The research, co-funded by Italferr Spa (Italian railway national company for tunnel design), deals with calibrating and validating these methods based on huge datasets. Main engineering companies provided data from completed base tunnel projects. In particular, in this study, the Drawdown Hazard Index (DHI) method has been calibrated with a dataset of a 15 km long sector of the Gotthard base tunnel drilled through a crystalline geological setting. The calibration involved only the Potential Inflow (PI) parameter to verify the matching between the probability of inflow and the actual output of the excavation, according to the available data in the preliminary stage of the project. An alternative tool based on a machine-learning approach was then applied to the same dataset, and a comparison was presented.

Abstract

Various electrical potential difference-audio magnetotelluric (EPD-AMT) geophysical equipment is now available in the market for groundwater exploration, and the Groundwater Detector is one of them. Due to their low cost, deeper penetration, and real-time measurement, the technology has been widely received in many developing and underdeveloped countries. However, research to understand the application of the EPD-AMT surface geophysics approach in groundwater exploration is very limited. This research gap needs urgent attention to promote the technology’s meaningful and wider application. The lack of published case studies to demonstrate the capabilities of the EPD-AMT approach is a limiting factor to its application.

Research on different hydrogeological settings is paramount as part of the efforts to improve the practical understanding of the application of the EPD-AMT geophysical approach in groundwater exploration. This study shares field experience from applying the EPD-AMT Groundwater Detector geophysical technique to explore groundwater in dolomite, granite, and Karoo sandstone hardrock aquifers in Southern Africa.

Abstract

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

Abstract

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

Groundwater is a vital freshwater source, and its role in meeting water demands will become pivotal under future climate change and population growth. However, groundwater supply to meet this demand is at risk as aquifers can be rapidly contaminated, and the cost of aquifer rehabilitation and/or sourcing alternative water supplies can be high. The development of groundwater protection schemes is required to ensure long-term protection of groundwater quality and sustainable groundwater supply. A groundwater protection scheme is a practical and proactive means to maintain groundwater quality and forms an additional methodology for groundwater resource management/protection. There are no legislative guidelines on establishing groundwater protection schemes in water-scarce South Africa, despite groundwater being used extensively. Three groundwater protection schemes were designed and implemented to protect abstraction from a fractured aquifer in an undeveloped natural mountain catchment and two primary aquifers within different urban settings. The approach incorporated protection zone delineation (comprising four zones), aquifer vulnerability mapping/ ranking using the DRASTIC method (with the primary and fractured aquifer systems having varying vulnerabilities), and identification of potentially contaminating activities (which also vary significantly between the urban areas overlying the two primary aquifers, and the generally undeveloped natural mountain catchment fractured aquifer is situated within). Additionally, a protection response was established to determine monitoring frequencies. Practical insights into the design and implementation of these three groundwater protection schemes can serve as a model for implementation in other African aquifer systems.

Abstract

Shallow groundwater dynamics play a crucial role in wetland ecosystems and are key to climate change resilience. Therefore, conserving and restoring wetland areas requires excellent knowledge of groundwater flow dynamics, which are often rapidly changing following extreme weather events and anthropogenic impacts such as groundwater extraction. Traditional methods to estimate groundwater flow require extensive modelling or rely on point measurements, missing the effect of crucial short-term events and impeding quick actions to conserve the wetlands’ ecohydrological status. Here, we present a newly developed sensor that can measure real-time groundwater flow velocity and direction. The sensor probe consists of two bidirectional flow sensors that are superimposed. It is installed in a dedicated pre-pack filter and can measure a broad range of groundwater flow velocities from 0.5 cm/ day to 2000 cm/day. With an IoT (Internet of Things) system, sensor data is wirelessly transmitted and visualized in real-time on an online dashboard. In addition, we show a selection of results from a case study in the Biebrza National Park (Poland) and a nature reserve in Damme (Belgium). In both ecosystems, we could capture changes in groundwater flow velocity and direction resulting from precipitation and evapotranspiration events. As such, we are confident that our sensors provide new insights into rapidly changing groundwater dynamics and will become an invaluable tool in ecohydrological studies worldwide, ultimately leading to more integrated management strategies to protect and conserve remaining wetlands.

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

Aquifer test analysis is complex, and in many regards, the interpretation resembles an art more than a science. Under the best circumstances, aquifer test analysis is still plagued by ambiguity and uncertainty, compounded by the general lack of information on the subsurface. An approach which has seen widespread adoption in other fields that need to classify time series data is machine learning. A Python script that generates numerical groundwater flow models by interfacing directly with the modelling software produces training data for deep learning. Production yielded 3,220 models of aquifer tests with varying hydrogeological conditions, including fracture, no-flow and recharge boundary geometries. Post-processing exports the model results, and the Bourdet derivative is plotted and labelled for image classification. The image classifier is constructed as a simple three-layer convolutional neural network, with ReLU as the activation function and stochastic gradient descent as the optimizer. The dataset provided sufficient examples for the model to obtain over 99% accuracy in identifying the complexities present inside the numerical model. The classification of groundproofing data illustrates the model’s effectiveness while supporting synthetically prepared data using modern groundwater modelling software.

Abstract

Coal Ash Beneficiation is a government imperative for South Africa, and Eskom generates approximately 34 million tons of coal ash annually from their 14 pulverised coal fuel plants. It is estimated that there are approximately 6,000 abandoned coal mines in South Africa, of which 2,322 are classified as high risk, contributing to subsidence and the generation of acidic mine drainage. It is envisaged that coal ash could offer a support medium for the mines and neutralise the acidic mine water due to its alkaline nature. The Department of Fisheries, Forestry and the Environment has supported the initiative but has requested a means of modelling possible contamination due to placing the coal ash in these environments. To this end, laboratory trials were completed to generate the initial model and a controlled pilot site was established to validate the model’s accuracy. This trial evaluated stabilised and unstabilised coal ash as a means of acid water management. The laboratory trials showed that the ash could neutralise the pH of the mine water from approximately 2 to 7; this was sustained for the test period. In addition, sulphate and iron were significantly reduced in the treated water. The laboratory and site work results will be detailed in this presentation.

Abstract

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

Abstract

Hermanus was originally supplied from springs and groundwater until the De Bos Dam was built in the 1950s. Due to increasing water demand, the municipality commenced wellfield development in 2002. The first wellfield comprised 3 boreholes, of which one borehole was later decommissioned due to reduced yield. Three additional boreholes were drilled recently to ensure abstraction capacity within the licence limits. A second wellfield was developed in the Hemel-en-Aarde Valley north of Hermanus. To ensure the sustainable management of the shared resource and minimise environmental impacts, a monitoring committee was established with all relevant roleplayers, other users, civil society, environmental groups and various commenting and regulatory authorities. A comprehensive monitoring network was established to assist with the scheme’s management and ensure that environmental impacts are minimized. The long-term monitoring (up to 20 years) shows that the groundwater abstraction from the Gateway Wellfield does not impact the environment and other users or increase the risk of saline intrusion. Identified impacts have been mitigated with the assistance of the monitoring committee. The municipality aims to provide at least half of the town’s water demand from groundwater and establish conjunctive use operation between surface water from the De Bos Dam and groundwater from these wellfields. The wellfields ensured sufficient water for the municipality when De Bos Dam’s water levels declined significantly during the Western Cape droughts in 2011 and 2017. The presentation will provide examples of the long-term monitoring records and trends.

Abstract

Groundwater quantity and quality of shallow aquifers have deteriorated in recent years due to rapid development that has created an increased demand for drinking water, which is increasingly being fulfilled by groundwater abstraction. The study evaluates the hydrogeological framework of the Quaternary aquifer of the Kabul basin, Afghanistan, and the impact of urbanization on the groundwater resources around the Kabul city plain. Time series of Landsat satellite LCLU images indicate that the urban area increased by 40% between 2000 and 2020, while the agricultural area decreased by 32% and bare land decreased from about 67% to 52% during this period. The assumed groundwater overdraft 2019 was 301.4×103 m3 /day, while the recharge was 153.4×103 m3 /day, meaning a negative balance of about 54 million cubic meters (MCM) this year. Due to the long-term decline of water levels at 80 90 cm/year, and locally (Khairkhana, Dasht-e-Barchi) 30-50m during 2005-2019, a considerable groundwater drawdown is shown. Groundwater quality, on the other hand, reveals that chloride concentrations and salinity increased throughout the aquifer between 2005 and 2020. The nitrate concentration decreased in most Kabul Plain places over the period. In conclusion, the quantity and quality situation of urban groundwater in Kabul is worrying; urgent scientific and sustainable solutions and measures should be considered to manage this situation.

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

Underground coal gasification (UCG) is a high-temperature mining method that gasifies coal in situ to produce a synthetic gas that can be used as feedstock for industrial purposes. Coal conversion leads to mineral transformation in the gasifier, which ultimately interacts with the rebounding groundwater post-gasification. This poses a groundwater contamination risk, the biggest environmental risk from a UCG geo reactor. There is currently no model for UCG operators and regulators to assess the total risk of groundwater contamination from UCG operations. This study collates literature on groundwater contamination from UCG operations and presents a workable but comprehensive groundwater risk assessment model for a spent UCG chamber. The model follows the source-pathway-receptor arrangement where groundwater contamination sources are identified as ash, char, roof and floor. All possible pathways are assessed for hydraulic connections with the spent geo-reactor via acceptable geochemical tests, including stable isotopes, hydrochemistry and stratification analysis. Finally, the receptor aquifers (e.g. shallow aquifers) are monitored periodically to determine if contamination has occurred.

Abstract

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

Abstract

Monitoring deep (~100 – 200 m) fresh-saline water interface is a challenge because of the low spatial density of deep boreholes. In this project, Vertical Electrical Soundings measurements were used to evaluate changes in the depth of the interface over various decades. Water quality monitoring is a well-known application of geo-electrical measurements but generally applies to the relatively shallow subsurface. In this case study, the saline groundwater interface is around 120 -200 m deep, and the time interval between the measurements is several tens of years. Several locations showing good-quality existing VES-measurements acquired in the last century were selected to see whether repeat measurements could be performed. The number of locations where a repeat measurement could be performed was limited due to the construction of new neighbourhoods and greenhouse complexes. When interpreting the measurements for the change in the depth of the fresh-salt interface, it is assumed that the transition from fresh to saline groundwater occurs over a small depth range and that the electrical conductivity of the fresh water above this interface has not changed. However, it turned out that the ion concentration of the groundwater in the layers above the fresh-saline interface had increased sharply at almost all locations. This complicated the approach, but still, useful results could be obtained. Based on the measurements, it can be said that the fresh-saline water interface has shifted downwards at 3 locations, and hardly any change has occurred at 5 locations.

Abstract

The intermediate vadose zone underlies the plant root zone and comprises soil and rock. Different soils have different hydraulic and mechanical properties, and the vertical and spatial distributions are variable at a small scale. In South Africa, except for the Cenozoic and Quaternary deserts and coastal deposits, rock forms most of the vadose zone, and the rock fractures exacerbate the complexity. The vadose zone is observed at a small scale and dictates what happens in large scale, as adhesion to mineral surfaces happens first, and cohesion between water molecules is next. The original consideration of the intermediate vadose zone was a black box approach measuring what goes in from the surface and what goes out as groundwater recharge, not accounting for the movement of the vast majority of the freshwater supplied through precipitation. That doesn’t address the preferential flow, velocity, and pore water changes in the medium. Soil science addresses the soil or plant root zone very well. This zone governs the vertical movement of water and controls the ecosystems and biodiversity. However, all evapotranspiration disappears below this zone, and capillarity and gravity both move water into and through the intermediate vadose zone. Movement is no longer solely vertical and will be affected by soil types, intergranular porosity in soil and rock, changing water content, and secondary fractures with different properties in rock. This presentation will cover concepts and advances in this field, emphasising how and why water moves in the intermediate vadose zone.

Abstract

The Guarani Aquifer System (SAG) is the main public water supply source in Bauru City (Brazil). It mostly consists of sandstones and is a confined unit of fossil waters (~600 thousand years); therefore, it is a non-renewable and finite resource. SAG is overlaid by the Bauru Aquifer System (SAB), predominantly consisting of sandstones, siltstones, and mudstones, and is essential for private water supply in the municipality. In recent decades, constant drops in water levels in SAG and increases in contaminant loads in SAB have been observed in production wells, generating the need to understand the geometry of those aquifer systems.

This work presents the preliminary results of the analysis and review of hydrogeological and geophysical data from 59 deep wells and 3D geological modelling using Leapfrog Works® to represent a conceptual model of the study area. SAG has a thickness of up to 356 m in the wells and is represented, from bottom to top, by Teresina, Piramboia, and Botucatu formations. In the north and northeast regions, SAG is covered by a layer of basalts from the Serra Geral Aquifer System (SASG) with a thickness of up to 190 m. The thickness of SASG is variable (or even null) due to the action of important faults with vertical displacements that created structural windows in the region. SAB covers the Araçatuba (basal portion), Adamantina (144 m), and Marília (65 m) formations. The lower contact of SAB is made with SASG or SAG (central region). Project funded by FAPESP (2020/15434-0).

Abstract

Per and Polyfluoroalkyl substances (PFAS) are ubiquitous on our planet and in aquifers. Understanding PFAS transport in aquifers is critical but can be highly uncertain due to unknown or variable source conditions, hydrophobic sorption to solid organic aquifer matter, ionic sorption on mineral surfaces, changing regulatory requirements, and unprecedentedly low drinking water standards. Thus, a PFAS toolkit has been developed to enable decision makers to collect the hydrogeologic data necessary to understand and better predict PFAS transport in aquifers for the purpose of managing water resources. This toolkit has been tested at a significant alluvial aquifer system in the western United States, which provides water for 50,000 people. Here, the toolkit has provided decision makers with the data necessary to optimize water pumping, treatment and distribution systems. The toolkit describes (1) the design and implementation of a sentinel well network to measure and track PFAS concentrations in the alluvial aquifer over time in response to variable pumping conditions, (2) data collection used to empirically derive input parameters for groundwater fate and transport models, which include the collection of paired aquifer matrix and groundwater samples, to measure PFAS distribution coefficients (Kds) and modified borehole dilution tests to measure groundwater flux (Darcy Velocity) and (3) the use of data collection techniques to reduce cross contamination, including PFAS-free, disposable bailers and a triple-rinse decontamination procedure for reusable equipment. The PRAS transport toolkit has the potential to assist decision makers responsible for managing PFAS contaminated aquifers.

Abstract

The 16th Lum Nam Jone reservoir is located in Chachoengsao Province, Thailand. Since 2019, water has become highly acidic with a pH of 2.5-3.5 and contaminated by heavy metals. The groundwater plume is associated with high concentrations of Iron (60 – 3,327 mg/L), Manganese (38 – 803 mg/L), Copper (5 –500 mg/L), Zinc (11 –340 mg/L), and high Total Dissolved Solids (2,600 –23,000 mg/L). The hydrogeochemical assessment confirmed that the contamination is related to the molybdenum ore processing plant located upgradient. The industrial wastewater was illegally discharged underground and flowed to the reservoir due to a hydraulic gradient. The main objective of this research is to evaluate the efficiency of different reactive materials for In-situ remediation using a permeable reactive barrier (PRB). The experiment column setup showed that marl has the highest efficiency in elevating pH by 3.6 units. The Fe, Cu, and Zn removal rates by crushed shells were 100, 98, and 60%, respectively. The Fe, Cu, and Zn removal rates by limestone were 100, 73, and 32%, respectively. The Fe, Cu, and Zn removal rates by marl were 100, 100, and 48%, respectively. Regarding the laboratory-scale experiment, the pilot PRB was installed upstream of the reservoir. The PRB was filled with marl at the bottom, overlain by limestone, and then covered with the uppermost rice straw layer. The pH increased by 2.6 units inside PRB (from pH 3.1 to 5.7). A reduction of about 50% in Fe, 85% in Cu, and 50% in Zn had been achieved.

Abstract

The Ordovician aquifer of the Izhora deposit is widely used for drinking by the population of St. Petersburg and its suburbs. Carbonate Ordovician rocks are intensively karstified. The water is fresh (0,5-0,8 g/l), bicarbonate-calcium on the predominant ions, pH 7.6; calcium content is 50-80 mg/l, magnesium content is 30-60 mg/l and the total hardness is 7,6-8,0 mg-equ./l. Western, northern and northeastern boundaries of the Izhora deposit go along the Baltic Klint, which is evident on the relief. Its southern boundary is along the zone of the dip of Ordovician limestone beneath the Devonian sandstone. The territory of the Izhora plateau belongs to the areas of intensive economic activity. Often, objects of human economic activity are located near drinking water intakes. Almost all sites are marked by excess sanitary norms of chemical elements. Pollution of groundwater in the Ordovician aquifer has been identified in some areas. Priority substances have been identified for assessing the quality of groundwater: total hardness, Fe, Mn, Ba, and B. According to hydrochemical modelling data, Ordovician groundwater is saturated with calcite over most territory. There are many springs of underground water along the Baltic Klint, for example, near the village of Lopukhinka, Duderhof springs and others. The springs waters have natural radioactivity (due to the contact of groundwater with dictyonema shales), which makes their use hazardous to human health.

Abstract

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

Abstract

The aquifers in the Chao Phraya River basin region were abundant in groundwater. Lately, the groundwater level has been declining due to agricultural activities. While in the wet season, these areas frequently suffered from flooding due to lower elevation than their surroundings. The Managed Aquifer Recharge (MAR) methods were applied to ease problems by constructing artificial recharge wells which can detain stormwater runoff and let it gradually infiltrate into the aquifer directly. For decades, the Department of Groundwater Resources started the MAR project to alleviate groundwater depletion and flooding over specific areas. However, most of the projects in the past lacked follow-up results and evaluation. Thus, later projects attempted to study recharge processes to evaluate the volume of recharged water through structures and calculate the infiltration rate through filter layers within the structures.

Recently, the field experiments of artificial groundwater recharge were conducted as 8-hour and 20-day experiments with shallow recharge wells in the Chao Phraya River basin regions. These two types of experiments provided similar results. The average recharge rates of 8-hour and 20-day experiments are 2.22 m3/hr and 2.57 m3/hr, respectively. Recharge rates of each well were independently distinct depending on sedimentation characteristics, aquifer thickness, and volume of dry voids. During the test, the recharge well continuously encountered the problem of sediment clogging due to using untreated water from neighbouring streams and ponds. This clogging issue needed to be treated regularly to maintain the efficiency of the recharge well.

Abstract

Faced with climate change and population growth, Dutch drinking water company Dunea is looking for additional water resources to secure the drinking water supply for the coastal city of The Hague. One of the options is to enhance the existing managed aquifer recharge (MAR) system in the coastal dunes by extracting brackish groundwater. Extracting brackish groundwater provides an additional drinking water source, can protect existing production wells from salinization, and can effectively stabilise or even grow the freshwater reserves in the coastal dunes, according to numerical groundwater modelling. To test this concept in the field, a three-year pilot commenced in January 2022 at Dunea’s primary drinking water production site, Scheveningen. Brackish groundwater is extracted at a rate of 50 m3 /h with multiple well screens placed in a single borehole within the brackish transition zone (85-105 meters below sea level). The extracted groundwater is desalinated by reverse osmosis, whilst the flow rate and quality of extracted groundwater are continuously monitored. The hydraulic effects and the dynamic interfaces between fresh, brackish and saline groundwater are monitored with a dense network of piezometers, hydraulic head loggers and geo-electrical measurement techniques. At the IAH conference, the monitoring results of the pilot will be presented. Based on the results of the field pilot and additional numerical modelling, the feasibility of upscaling and replicating the concept of brackish groundwater extraction to optimize MAR and increase the availability of fresh groundwater in coastal areas is reflected.

Abstract

In this study, we assess the potential of large riverbed aquifers in semi-arid Africa, known as sand rivers, to mitigate water scarcity and salinity for multiple-use water supply through a case study of the Limpopo River in Mozambique. Such sand river systems are widespread and still heavily underused at a regional scale, particularly in Mozambique, with the riparian vegetation currently being the primary user, though only consuming a minor fraction of available water. At a local scale, we performed geoelectrical surveys, water level measurements (in river and groundwater), as well as field physicochemical measurements and hydrochemical and isotopic sampling at 38 locations in the river channel, margins and up to 6 km away from the river, over five years. Results show that these shallow systems can be up to a kilometer wide and 15 m thick and, at some locations, can extend laterally beyond the river channel, below thin layers of clay and silt. Large areas of the sand river channel carry runoff yearly, providing optimal conditions for rapid recharge into the coarse sands with a high storage capacity. Connectivity between the river margin and channel is clearly shown at the local scale, even though sand pockets located further away appear isolated (revealed by geophysics), isotopically different and more brackish. Recharge, evapotranspiration and mixing processes are confirmed through hydrogeochemical modelling. The proven connectivity is highly relevant as groundwater is abstracted locally, promoting socio-economic development in water-scarce regions.

Abstract

Since the end of the 1970’s, the Ministry of Agriculture, Water and Land Reform (MAWLR), through the development of the groundwater database (GROWAS II), gathered a great number of data on groundwater quality. In an ongoing study (MAWLR-MEFT-AFD-BRGM, 2023), an opportunity was presented to compile chemical data for groundwater in the two most north-western regions of Namibia, Kunene and Omusati, to elaborate and support decision-making with the available information. A selection of 3256 data presenting a good ionic balance (± 10%) was selected from a large dataset, using metadata from previous BGR projects and the Geological Survey of Namibia at a 1:250,000 scale as supporting information. During the assessment of chemical data, it was depicted that most of the good quality water for human consumption and irrigation is located in the carbonated sedimentary formations at the southeastern part of Kunene and a great part of the northern part of the Kunene region. With more detailed data treatment, it allowed for confirming a natural origin for high fluoride concentration linked to granite, gneiss, old volcanic rocks and high sulphate concentration due to evaporates (gypscrete) in the eastern part of Omusati. In contrast, high nitrate concentrations were found in various lithologies across the two regions confirming local anthropogenic contamination. These results were compared to information obtained through the few published works of local studies to evaluate the accuracy of this large-scale assessment of chemical data.

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

The identification of hydrogeological boundaries and the assessment of groundwater’s quantitative and qualitative status are necessary for delineating groundwater bodies, according to the European Guidelines. In this context, this study tries to verify the current delineation of groundwater bodies (GWBs) through hydrogeochemical methods and multicriteria statistical analyses. The areas of interest are three GWBs located in the northern part of Campania Region (Southern Italy): the Volturno Plain, a coastal plain constituted of fluvial, pyroclastic and marine sediments; the Plain of Naples, an innermost plain of fluvial and pyroclastic sediments and the Phlegrean Fields, an active volcanic area with a series of monogenic volcanic edifices. Hydrogeochemical methods (i.e., classical and modified Piper Diagram) and multivariate statistical analyses (i.e., factor analysis, FA) were performed to differentiate among the main hydrochemical processes occurring in the area. FA allowed the handling many geochemical and physical parameters measured in groundwater samples collected at about 200 sampling points in the decade of the 2010s. Results reveal five hydrogeochemical processes variably influencing the chemical characteristics of the three GWBs: salinization, carbonate rocks dissolution, natural or anthropogenic inputs, redox conditions, and volcanic product contribution. Hydrogeochemical methods and FA allow the identification of areas characterised by one or more hydrogeochemical processes, mostly reflecting known processes and highlighting the influence of groundwater flow paths on water chemistry. According to the current delineation of the three GWBs, some processes are peculiar to one GWB, but others are in common between two or more GWBs.

Abstract

he Danakil Depression of the Afar Rift forms part of the north/south-trending Ethiopia-Eritrean arm of the East African Rift System, whereas the western margin of the depression forms part of an active plate boundary between the western Nubian and eastern Danakil tectonic blocks. Dallol (within the Danakil Depression) currently holds the record for the highest average temperature for an inhabited place on Earth, with annual average temperatures of ~35-36°C. The isolated area was initially explored geologically in the late 1960s, with recent geological and hydrogeological interest in its northeast Ethiopian portion due to easier access, geo-tourism and potash-ore exploration. Potash mining is proposed via solution-extraction techniques, requiring large volumes of water in one of the driest hyper-arid regions. Various hydrogeological investigations were therefore conducted between 2014 and 2016 as part of a feasibility and water resource study towards developing a water resource estimate for the region and proposed mining operations. Alluvial fans on the west side of the rift basin form a major, regional primary aquifer – fan boreholes have yields of 50 litres per second, although groundwater is highly saline (up to 3-5 times the salinity of seawater) and can reach temperatures of 50°C. Groundwater yields of hundreds of millions of cubic metres per annum are potentially available from the saline alluvial fan primary aquifers for potash solution mining. In contrast, groundwater from karstic limestone aquifers could provide a freshwater resource to settlements within the Lelegheddi River basin and the Danakil.

Abstract

Micro-electro-mechanical system (MEMs) technologies coupled with Python data analysis can provide in-situ, multiple-point monitoring of pore pressure at discrete and local scales for engineering projects. MEMs sensors are tiny, robust, inexpensive, and can provide wireless sensing measurements in many electrical and geomechanical engineering applications. We demonstrate the development of MEMs pressure sensors for pore pressure monitoring in open boreholes and grouted in piezometers. MEMs sensors with a 60 m hydraulic head range and centimetre vertical resolution were subject to stability and drawdown tests in open boreholes and in various sand and grouts (permeability 10-8 to 10-2 m/s). The resulting accuracy and precision of the MEMs sensors, with optimal calibration models, were similar to conventional pore pressure sensors. We also demonstrate a framework for estimating in-situ hydrogeological properties for analysis from vented pore pressure sensors. This framework method included Python code analysis of hourly pore pressure data at the millimetre vertical resolution, which was combined with barometric data and modelled earth tides for each borehole. Results for pore pressure analysis in confined boreholes (>50 m depth) included specific storage, horizontal hydraulic conductivity and geomechanical properties. Future improvements in the vertical resolution of MEMs pore pressure sensors and combined these two technologies will enable groundwater monitoring at multiple scales. This could include the deployment of numerous MEMs, at sub-meter discrete scale in boreholes and evaluating local site scale variations in pore pressure responses to recharge, groundwater pumping and excavations in complex sub-surface geological conditions.