Conference Abstracts

All Abstracts were presented at the Groundwater Conferences

Displaying 701 - 750 of 795 results

Title	Presenter Name	Presenter Surname	Area	Conference year Sort descending	Keywords
Risk-corrected contaminant detection probability of monitoring well networks for flow towards pumping wells in heterogeneous aquifers	T	Sarris	New Zealand	2023	Contaminant transport, Dispersion, Groundwater Contamination, Heterogeneity, monitoring networks, Risk corrected detection rate
Abstract A groundwater monitoring network surrounding a pumping well (such as a public water supply) allows for early contaminant detection and mitigation where possible contaminant source locations are often unknown. This numerical study investigates how the contaminant detection probability of a hypothetical sentinel-well monitoring network consisting of one to four monitoring wells is affected by aquifer spatial heterogeneity and dispersion characteristics, where the contaminant source location is randomized. This is achieved through a stochastic framework using a Monte Carlo approach. A single production well is considered, resulting in converging non-uniform flow close to the well. Optimal network arrangements are obtained by maximizing a weighted risk function that considers true and false positive detection rates, sampling frequency, early detection, and contaminant travel time uncertainty. Aquifer dispersivity is found to be the dominant parameter for the quantification of network performance. For the range of parameters considered, a single monitoring well screening the full aquifer thickness is expected to correctly and timely identify at least 12% of all incidents resulting in contaminants reaching the production well. Irrespective of network size and sampling frequency, more dispersive transport conditions result in higher detection rates. Increasing aquifer heterogeneity and decreasing spatial continuity also lead to higher detection rates, though these effects are diminished for networks of 3 or more wells. Earlier detection, critical for remedial action and supply safety, comes with a significant cost in terms of detection rate and should be carefully considered when a monitoring network is being designed.
Identifying water sources of Verlorenvlei using stable isotopes and hydrochemistry	Angela	Welham	Elands Bay	2023	Groundwater, rainwater, semi-arid, stable isotope, surface water, Verlorenvlei, Water chemistry, wetland
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
Variable-scale conceptual framework for shallow groundwater systems in the low-relief, water-limited Canadian Boreal Plains	K	Hokanson	Canada	2023	Groundwater-surface water interactions, long-term study, recharge, spatiotemporal scales, subsurface connectivity
Abstract Case studies illustrate a conceptual framework for shallow groundwater flow systems’ temporal and spatial variability with groundwater-surface water interactions in the Boreal Plains of Canada. The framework was developed using a twenty-year hydrometric dataset (e.g., climatological and streamflow data, hydraulic heads, vertical hydraulic head gradients, geochemical and isotopic signatures). The region is characterized by low-relief glacial landscapes, with a mosaic of forestlands and peatlands, and a subhumid climate, resulting in spatially heterogeneous storage and transmission properties, variable recharge and evapotranspiration potentials, and highly complex patterns of water movement. Two primary spatiotemporal scales were examined to create a holistic, variable-scale conceptual model of groundwater movement: the large scale (e.g., glacial landforms, regional topography, decadal climate cycles) and the small scale (e.g., individual landcover, local hummocks, annual moisture deficits). Water table behaviour, evapotranspiration rates, and runoff were controlled by a hierarchy of interactions between hydrological processes occurring at different spatiotemporal scales; however, the specific order of controls depends on the hydrogeological setting. The case studies, supported by empirical and numerical modelling, demonstrate that smaller-scale heterogeneities in geology and recharge can dominate over topographic controls, particularly in areas with high conductivity or hummocky terrain, where the climate, geology, and topographic relief are similar. Many hydrogeological studies rely on surface topography as a first‐order control; however, with field observations and modelling, this conceptual framework demonstrates the need to consider the potential dominance of subsurface characteristics and processes, plus climate, especially in landscapes with low recharge and low relief.
Tracing an arenitic aquifer by DNA-labelled nano particles	Alessandro	Gargini	Italy	2023	nanotechnology; DNA-labelled nano particles; arenite; groundwater; tracer test; Northern Apennines
Abstract The results of a full field application of a DNA-based nano tracer in an arenitic aquifer are presented along with the comparison with the breakthrough of a classical tracer injected in parallel. DNA is encapsulated into amorphous silica spheres (nanoparticles), protecting the molecule from chemical and physical stresses. The main advantages of using DNA with classical tracers, like ionic or fluorescent, are the lower detection concentration and the chance to perform multi-tracer tests with many distinct signatures of injection. To the authors’ best knowledge, this is the first tracing adopting nano-particles on full field conditions in a sedimentary fractured aquifer. Preliminary tests in the lab were performed adopting either deionized water or groundwater collected at the experimental site: a set of nanoparticles at a known concentration was dissolved by adding a buffered fluoride solution, and DNA was then quantified by qPCR reaction (SYBR green). The hydrogeological setting is represented by a Miocenic marine arenitic aquifer (Pantano formation) outcropping extensively in Northern Apennines (Italy) and the main groundwater reservoir for public water supply through the uptake of many perennial springs. The main purpose of the tracing was to verify the transmissive capacity of fractures with high aperture (15-20 cm) identified by optical and acoustic televiewers inside an 80 m deep borehole. The injection was performed inside the borehole, and the tracer’s recovery was between 5-15 m, both in the uptake points of two perennial springs and in another borehole drilled nearby.
A methodology for uncertainty quantification of dewatering volumes under the context of open-cast mining	C	Rivera Villarreyes		2023	FEFLOW, Groundwater Modelling, mining, PEST, PESTPP
Abstract Groundwater modelling at the mine sites involves assumptions from the geological model, mining stages, parametrization, and fractures, among others. Modelling work mainly focuses on calibrating against historical measurements before operations (pre-mining) or afterwards (transient calibration). Calibration is carried out mainly with gradient-based algorithms. However, the majorlimitation is the number of model runs, since the number of parameters can easily reach hundreds or more. PEST has become the common tool for parameter estimation. The Jacobin calculation required for the Levenberg Marquardt algorithm requires several model runs. This, a limited factor for the calibration and, subsequently, uncertainty quantification. The next generation of PEST, named PESTPP, is gained popularity in the groundwater community. The great advantage of PESTPP,, compared to the classical PEST, is its new module, Iterative Ensemble Smoother (IES). PESTPP-IES covers both parameter estimation and uncertainty quantification in one goal. Its empirical formulation of the Jacobian matrix reduces the number of runs; thus, the numerical bottleneck can be significantly reduced. PESTPP-IES has been extensively tested in an open-pit mine at the geological complex conditions in the Peruvian Andes. The work involves the task of model simplification, e.g., from a regional model to a detailed local pit model, calibration and uncertainty quantification of pit dewatering volumes. Detailed model was kept calibrated based on hydraulic-head measurements, and dewatering volumes were predicted. All these consider transient changes in the mining plan within the same FEFLOW model. Results validate the methodology and practicability in mining applications.
Using passive sampling to identify trends in aquatic pesticide pollution in the Western Cape, South Africa	Emma	Davies	Western Cape, South Africa	2023	Imidacloprid, passive water sampling, pesticide, South Africa, surface water, Sustainable Development Goal
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.
Balancing qualitative and quantitative issues of the groundwater extraction at the drinking water production site of Velm (Central Belgium)	S	Van den Broeck	Belgium	2023	Belgium, Drinking water, Drought, Pollution, sustainability, time series analysis
Abstract Recent findings allow a better insight into the interaction between two aquifers and their vulnerabilities at the groundwater extraction site of Velm, which produces drinking water for around 55,000 households. The shallow aquifer that is exploited is situated in the Formation of Hannut. This aquifer is vulnerable to pollution, especially from the agricultural lands close to the extraction site and is sensitive to natural recharge. In this case, the groundwater is captured in a basin via a naturally occurring spring flow. The second aquifer is situated in the Cretaceous at 50 to 100 m below the surface and is pumped by four wells. The drinking water quality is guaranteed by mixing and treating these two waters. To optimize the central decalcification and the pollution risks, the production volume in the deep aquifer was increased from 2017 to 2021 at the expense of the shallow aquifer. This led to a decrease in the available volumes of the shallow aquifer, which indicated a leakage from the shallow to the deeper aquifer, which was unexpected. Groundwater modelling and time series analysis have been used to assess the impact of the increased production volumes and the longer dry periods. Based on this data, a maximum production volume of 1,000,000 m3 /year is considered best for the cretaceous aquifer. With this extraction rate in the Cretaceous, it is possible to supply sufficient drinking water and limit the impact on the Formation of Hannut.
Distribution, Formation Conditions and Genesis of High-Quality Groundwater Containing Metasilicate in Zhaojue County, Southwest China	Shengzhang	Zou	Southwest China	2023	Groundwater; H2 SiO3 ; distribution; formation condition; Zhaojue County; Southwest China
Abstract The drinking water health issues have been considered due to improved living standards in recent years. Finding and developing high-quality groundwater with high-level minerals has become key to improving human health. The hydrochemical test data of 66 springs in Zhaojue County were analyzed using various methods, and the spatial distributions of H2 SiO3 -rich groundwater, hydrogeochemical characteristics, formation conditions and genesis were revealed. The main results including: 1) the groundwater with H2 SiO3 (≥25mg / L) was identified as the low salinity and alkaline water, which distributed in the six areas with the basement rocks of basalt,with a distribution area of about 79 square kilometers. The H2 SiO3 concentration was generally 25.74~46.04 mg/L; the low mineralization characterized the H2 SiO3 -rich groundwater of study area while the main hydrochemical types of groundwater are HCO3 - Ca·Mg, HCO3 -Ca, and HCO3 -Na; the Pearson correlation coefficient between the content of H2 SiO3 in groundwater and the content of pH is relatively high, indicating that the level of H2 SiO3 in groundwater in the study area is significantly affected by the pH value of the solution; the H2 SiO3 -rich groundwater was influenced by the water-rock interactions, the distribution range and solubility of silicate minerals ,the development of surrounding rock fissures, and water conservation and recharge conditions in the county, among which the water-rock interactions play a critical role. The results can provide a basis for the development of mineral water industry and the construction of urban and rural high-quality water sources in Zhaojue County.
Basin Water Balance modelling with the aim to make transboundary groundwater flow visible	M	Hunt	Estonia	2023	EUWaterres, Modflow6, transboundary aquifers, surface water groundwater interactions, water balance modelling
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.
Development and calibration of tools for preliminary quantification of the Hydrogeological Interference Risk of tunnels in different geological settings	E	Pugliese	Italy, Switzerland	2023	Hydrogeological Risk, potential inflow, tunnel, Machine learning
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.
Application of the multi-method approach to assess river aquifer interaction in Upper Berg catchment, Western Cape, South Africa	A	Umunezero	South Africa	2023	aseflow, EWR, Groundwater contribution, background condition, filtering base-flow separation method, hydrological cross-section
Abstract To better understand the role of groundwater contribution to baseflow and EWR in groundwater protection and allocation, groundwater contribution must be quantified. Groundwater contribution to baseflow remains a challenge. Baseflow values have been widely used as groundwater contribution to surface water, which overestimates or underestimates the role of groundwater in the ecological ecosystem sustainability. To achieve the aim of the study, which was to estimate groundwater contribution to baseflow in a perennial river system at a catchment scale of the Upper Berg catchment, three objectives were taken into consideration: 1) To describe the hydrogeology of river morphology for groundwater-surface water interaction, 2) To estimate groundwater contribution to baseflow 3) To demonstrate the use of the background condition in setting resource quality objectives. Baseflow separation method using the Lynne & Hollick and Chapman algorithms, mass balance equation using EC as the tracer, field observation, and hydrochemical analysis methods were used to determine groundwater contribution to baseflow. Based on the hydrogeological cross-section presented, the fractures and faults of the peninsula geological formation dominating the study area predicted groundwater contribution to baseflow, which was confirmed by the calculations. The mass balance equation showed that 2,397 % of the 7.9 % baseflow index calculated at G1H076 and 19,093% of the 7.2% baseflow index calculated at G1H077 was groundwater. The background condition of the Upper Berg catchment was determined to be pristine with clean water.
Understanding the pattern of spatial and temporal variations of groundwater levels using long-term monitoring data	P	Fuku	South Africa	2023	Groundwater decline, Hydrological stresses, long-term monitoring data
Abstract Monitoring regional groundwater levels provides crucial information for quantifying groundwater depletion and assessing environmental impacts. Temporal variation of groundwater levels is the response of the groundwater system to natural and artificial stresses in terms of groundwater recharge and discharge. The complexity and extent of the variation rest on the nature and storage properties of the aquifer system. High groundwater levels are usually found in the recharge zones and low in the discharge zones, resulting in groundwater flow from recharge areas to discharge areas. Continuous decline of groundwater levels has been observed in some of the monitoring boreholes within the National Monitoring Network. Groundwater level decline has been caused either by over-exploitation or reduction of groundwater recharge. Generally, the pattern of spatial and temporal variations of groundwater levels is the consequence of incorporating climatic, hydrological, geological, ecological, topographical, and anthropogenic factors. Therefore, understanding the pattern of spatial and temporal variations in groundwater levels requires a combined approach. A combination approach of National long-term groundwater level monitoring data, Hydrological stresses, Anthropogenic interferences, and characteristics of the groundwater system was used to understand the continuous decline of groundwater levels in selected monitoring stations across the country.
Pock Marks as a Nature-based solution for enhancing water availability in African marginal drylands?	D	Kibirige	South Africa	2023	Pockmarks, Groundwater, nature-based solutions
Abstract Nearly 1.9 billion people live in marginal environments, including drylands, semiarid, arid, and hyperarid environments. Obscure but ubiquitous circular pockmark depressions dot these lands. These circular depressions can range from a few meters to kilometers, and the depth of these depressions varies from a few centimeters to over 10 m. However, the genesis of the circles has been investigated among scientists for many years because of their obscure nature. Some researchers believe that termites cause fairy circles, while others believe they are caused by plants competing for water and nutrients. This study documented the Africa-wide prevalence and extent of the pockmarks for the first time, and it further classified the pockmarks according to their genesis and hydrological roles. We further investigated their relevance in serving as nature-based solutions to overcome water scarcity in dryland regions. So far, field evidence in Ethiopia and Somalia showed that these features potentially have water security significance in a) organizing surface water flows over arid/semi-arid landscapes, b) serving as the site of temporary surface water storage, and c) serving as the site of focused groundwater recharge into the underlying aquifers. This presentation will highlight the spatial prevalence, extent, and genesis model of the pockmarks across the drylands in Africa (South Africa, Namibia, Somalia, Ethiopia, Kenya, Chad, Senegal, Mali, Niger, etc.).
Groundwater models for water resources assessment at regional, local and site scales	V	Price	England	2023	England, Groundwater/surface-water relations, numerical modelling, scale, water-resources Management
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.
Assessing aquifer vulnerability using tritium and machine learning in Africa’s western Sahel	Joel	Podgorski	Switzerland	2023	Groundwater, groundwater mapping, groundwater recharge, Groundwater Vulnerability, Isotopes, Machine learning, Tritium
Abstract Understanding the sensitivity of groundwater resources to surface pollution and changing climatic conditions is essential to ensure its quality and sustainable use. However, it can be difficult to predict the vulnerability of groundwater where no contamination has taken place or where data are limited. This is particularly true in the western Sahel of Africa, which has a rapidly growing population and increasing water demands. To investigate aquifer vulnerability in the Sahel, we have used over 1200 measurements of tritium (3H) in groundwater with random forest modelling to create an aquifer vulnerability map of the region. In addition, more detailed vulnerability maps were made separately of the areas around Senegal (low vulnerability), Burkina Faso (high vulnerability) and Lake Chad (mixed vulnerability). Model results indicate that areas with greater aridity, precipitation seasonality, permeability, and a deeper water table are generally less vulnerable to surface pollution or near-term climate change. Although well depth could not be used to create an aquifer vulnerability map due to being point data, its inclusion improves model performance only slightly as the influence of water table depth appears to be captured by the other spatially continuous variables.
Winter irrigation as climate change adaptation strategy in northern Italy	Luca	Alberti	Italy	2023	Adaptation strategies, Climate change, Integrated Water Resources Management, Irrigation, Managed aquifer recharge, flow modelling
Abstract In 2021-23, northern Italy suffered a severe drought due to the absence of rainfall, which strongly affected the pre-alpine lake levels, affecting energy production, agriculture and sustainable river flows. This led to harsh consequences on agriculture, which in the Lombardy region almost completely relied on flooding irrigation methods using water from lakes through Ticino and Adda rivers. As part of the INTERREG Central- Europe project “MAURICE”, which focuses on Integrated Water Resources Management, the winter irrigation practice is proposed as a climate change adaptation strategy. The main project idea is to store surface water in aquifers in periods of exceedance (autumn/winter) using the very dense channels irrigation network as a “natural” infiltration system. The underground storage would increase the groundwater levels, bringing two main advantages during the spring/summer seasons: a good flow rate at plain springs and, in periods of water scarcity, the possibility to extract groundwater for agricultural purposes. Relying on the slow groundwater velocity (about 350 m/y), this practice keeps water stored in the subsoil just below the irrigated areas where the water is needed. In the early project stage, a basin-scale numerical model is presented to test the potentiality of such practice. A specified water volume was distributed on the crop fields during the winter period, and the effects of such managed recharge were evaluated, also considering the possible problems deriving from the groundwater levels increase. The model demonstrates the adaptation measure feasibility, which will be tested at a field scale in a Pilot Area.
Defining the Goldilocks Zone for Aquifer Thermal Energy Storage versus Unidirectional Ground Source Heat Pumps using Groundwater Flow and Heat Transport Modelling	H	Williams	Spain	2023	Aquifer Thermal Energy Storage, Ground Source Heat Pump, Urban Groundwater
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.
Groundwater porosities and effective porosities: definitions, physical relevance, and scale issues	Alain	Dassargues	Belgium	2023	REV, drainage effective porosity, effective porosity, porosity, scale issue, transport effective Porosity
Abstract Porosity describes the ratio between the volume of pores, cracks, and fissures and the total volume of a studied geological medium. This notion implies a volume averaging of the medium characteristics using the concept of Representative Elementary Volume (REV). Small volumes can contain only pores, while larger volumes typically contain both pores and fissures. Porosity can be highly scale-dependent, and different porosity values can be measured for the same geological formation. Furthermore, groundwater in the pores and cracks can be partly immobile or mobile. So, the porosity actively involved in groundwater flow can be discussed. A ‘mobile water porosity’ can be defined, but this remains highly dependent on the existing pressure conditions in the geological medium. In unconfined conditions, the term ‘effective porosity’ usually corresponds to the drainage porosity corresponding to the specific yield or storage coefficient. When dealing with solute transport and remediation of contaminated sites, another ‘effective porosity’ is needed to describe the advection velocity of the contaminant. This ‘mobile water porosity’ acting in solute transport processes typically takes lower values than drainage’s ‘effective porosity’. Scale issues must also be expected, as shown by field and lab tracer tests. The term ‘Darcy velocity’ will be banished herein because it induces much confusion. For clarity, we propose to distinguish ‘drainage effective porosity’ and ‘transport effective porosity’. The physical meaning of both terms is discussed, and examples of supporting observations are presented for illustration and discussion.
Groundwater trend analysis at an active underground coal gasification plant	L	Mokhahlane	Johannesburg, South Africa	2023	underground coal gasification, gasifier, groundwater risk assessment model, spent georeactor
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.
Basin-scale transfer of nitrate pollution from groundwater to surface water in an intensively irrigated system	M	Rotirot	Italy	2023	Cl/Br ratio, Irrigation return flow, Po Plain, boron, dilution, stable isotopes
Abstract Basin-scale studies addressing the transfer of pollutants among groundwater and surface water bodies are essential to support local authorities in the sustainable management of freshwater resources. This work revealed that, in the hydro-system of the Oglio River basin (Northern Italy), nitrate pollution in groundwater, originated by overfertilization, is transferred downstream to surface water bodies via outflow through lowland springs and baseflow to gaining rivers. Downstream groundwater is unaffected due to reducing conditions that facilitate denitrification. It follows that efficient measures to reduce nitrate pollution in surface water bodies should not be applied solely to rivers/streams but, instead, they should include the upstream groundwater body. The work aimed at understanding nitrate pollution dynamics in an intensively irrigated hydro-system, focusing on the role played by the complex interaction among irrigation water, surface water and groundwater. The study relied on nitrate concentration, Cl/Br ratio, stable isotopic composition of water, nitrate and boron in groundwater, river, lake, spring, and rainwater samples. Results highlighted a well-defined spatial distribution of nitrate concentrations in groundwater, mainly driven by irrigation practices: (1) where groundwater-fed irrigation is done, return flow promotes high nitrate concentrations (>50 mg/L) due to groundwater recirculation; (2) where intensive surface-water-irrigation is practised, fed by low-nitrate river water, return flow generates lower nitrate concentrations (<50 mg/L) due to dilution. This work highlighted the importance of a holistic approach jointly investigating surface water, groundwater, and irrigation water when nitrate pollution is examined at a basin scale.
Netherlands National Groundwater reserves: 3D mapping and development of management policies as part of a multilevel strategy to secure water supply for disasters and the far future.	G	Nijsten	The Netherlands	2023	3-D mapping, Multi-layer governance, National fresh-salt groundwater model, Water supply strategies
Abstract The Netherlands produces about 2/3 of drinking water from groundwater. Although there is seemingly abundant groundwater, the resource needs to be carefully managed and used wisely to safeguard the resource for future generations and in case of disasters whilst also preventing negative impacts from groundwater extraction on other sectors such as nature. Provincial governments are responsible for the protection of existing groundwater abstractions for water supply against pollution. To secure groundwater resources for the future, two additional policy levels have been introduced: Provincial governments have been made responsible for mapping and protecting Additional Strategic Reserves. These allow for additional groundwater abstractions to meet growing demands in coming decades (horizon 2040/2050). The National Government is responsible for mapping and protecting the National Groundwater Reserves (NGRs) as a third level of resource protection. NGRs serve multiple goals: to protect natural groundwater capital for future generations, to provide reserves for large-scale disasters affecting water supply and to provide reserves for possible use as structural water supply in the far future (horizon 2100 and beyond). NGRs are being delineated in 3D using detailed existing geological models and the Netherlands’ national (fresh-saline) hydrological model. The dynamics of the groundwater system are analysed through scenario analyses. Reserves for potential structural use are selected such that negative impacts on nature are prevented if future abstractions are to be realised. The policies being developed must balance interests of water supply against other sectoral interests such as the green-energy transition with increased use of geothermal energy and aquifer-thermal-energy-storage.
Water allocation and economic analysis for developing groundwater resources	P	Tungkidwanichakul	Thailand	2023	Epanet, WUSMO, groundwater management
Abstract Thailand has been grappling with a water scarcity problem every year, leading to insufficient water supply for consumption in many areas. To tackle this issue, groundwater is developed from large sources, making water allocation and economic analysis essential for measuring investments in water supply projects. This research study analyzes the water allocation for consumption and irrigation, including the water sent to hospitals, in two areas, Si Somdet & Roi Et Province and Nong Fai. The study uses the WUSMO program to analyze irrigation water and the EPANET program to analyze the entire water allocation system. The expected results include the appropriate allocation of water for maximum benefit, considering both delivery time and the amount of water to ensure adequate delivery. The study provides a guideline for effective and sustainable water allocation and management, including appropriate and sufficient water costs for managing the water distribution system in both areas. The results show that a water rate of 19 baht per cubic meter in Si Somdet & Roi Et Province results in a B/C value of 1.04 and an EIRR of 6.48%, while a water tariff of 15 baht per cubic meter in Nong Fai results in a B/C of 1.01 and an EIRR of 6.16%. The study highlights the importance of regular analysis of water allocation and cost-effectiveness of projects to ensure sustainable and efficient water management for the people.
Data-Driven approach to groundwater level prediction for improving water resource management: the Brenta aquifer system case study (Veneto, Italy)	Linda	Franceschi	Italy	2023	Foothill aquifer system, Climate change, groundwater management, predictive models
Abstract In the context of climate change, this work aims to model the piezometric levels of the foothill aquifer located in the middle-high Brenta river plain (Veneto, Italy) to support managing a groundwater system that provides drinking water for most of the Veneto Region. Using a Data-Driven approach, predictive Multiple Linear Regression Models were developed for the piezometric level at different wells, and scenarios of groundwater level evolution were achieved under dry periods. Results highlighted the high sensitivity of the aquifer to climate extremes, as well as the need to plan actions for mitigating the effects on such a strategic water supply system. Groundwater hosted in the foothill aquifer represents an important resource. However, these systems are highly sensitive to the variation of Meteo-climatic regimes. At the same time, the exploitations can lead to excessive groundwater drawdown and consequent threats of water scarcity. The Data-Driven approach adopted using long time series of meteorological, hydrometric and piezometric data can represent a valid example in these terms. The groundwater level evolution has been well-reproduced by these models. The equations describing models show the close dependence of groundwater from the Brenta River and the high sensitivity of the aquifer to meteo-climate regimes. Given this sensitivity, the forecast of groundwater level evolution under a dry period, similar to 2022, was performed. Results point out a progressive drawdown of groundwater level. These predictive models can be useful for local authorities to maintain these levels over specific critical values.
Electromagnetic measurements in the Netherlands using an All Terrain Vehicle to rapidly characterize groundwater salinity and clay distribution in 3D	Jan	Gunnink	Netherlands	2023	3d-mapping, clay distribution, groundwater salinity
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.
Hydrogeochemical and temporal nitrate variation in an unconfined urban aquifer in a tropical area in Brazil	D	Lookin	Brazil	2023	Bauru Aquifer System, Hydrogeochemistry, Nitrate, Urban Area
Abstract The Bauru Aquifer System (BAS) is a significant source of water supply in the urban area of Bauru city. Over the last decades, BAS has been widely affected by human activities. This study evaluates the nitrate plume in groundwater from 1999 to 2021 and how it relates to urbanization. The methods used were analysis of the data of 602 wells, survey of the sewer network and urbanization, and reassessment of nitrate concentration data. The seasonal analysis of 267 groundwater samples allowed the identification of concentrations up to 15.1 mg/L N-NO3 - mainly from the area’s central region, where the medium to high-density urban occupation dates back to 1910. Otherwise, the sewage system was installed before 1976. The reactions controlling the nitrogen species are oxidation of dissolved organic carbon, dissolution of carbonates, mineralization, and nitrification. Wells, with a nitrate-increasing trend, occur mainly in the central and northern regions, settled from 1910 to 1980-1990, when no legislation required the installation of the sewage network before urbanization. In turn, wells with stable or decreasing nitrate concentrations occupy the southwestern areas. Over the years, the concentrations of these wells have shown erratic behaviour, possibly caused by the wastewater that leaks from the sewer network. The bivariate statistical analysis confirms a high positive correlation between nitrate, sanitation age, and urban occupation density, which could serve as a basis for the solution of sustainable groundwater use in the region. Project supported by FAPESP (2020/15434-0) and IPA/SEMIL (SIMA.088890/2022-02).
Evaluation of the impact of artificial recharge of groundwater by river replenishment in the North China Plain using a numerical model	Qichen	Hao	China	2023	artificial recharge, groundwater management, river water replenishment, the North China Plain
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.
Springs of the Otavi Mountainland. Could they teach us something significant?	B	van Wyk	Namibia	2023	karst, Namibia, Otavi Mountainland, springs, conceptual model, groundwater flow
Abstract The work presented in this paper incorporates spring data for further conceptualizing the hydrogeology of northern Namibia’s so-called “Karst Area”, an area around the towns of Tsumeb, Otavi and Grootfontein. Also called the Otavi Mountainland, it can be described as a mountainous highland of parallel, east-west trending elongated valleys and ranges shaped by the underlying folded units of carbonate rocks of the Damara Supergroup. The karst aquifers are a supplementary source to the central areas of the country during drought. Most of these 35 springs are often found near hilltop crests or high up on the mountain flanks rather than lower down at the valley floors. If flows are generated locally as gravity or contact overflow springs, studying them would not add much to conceptualizing the regional groundwater flow. Fundamental insights are provided if flows arise due to hydraulic pressure from deeper down. As artesian boreholes do not occur as a rule in the Karst Area, artesian springs might indicate the presence of deeper aquifers out of reach at normal drilling depth. One such hypothesis is that the bottom of the dolomitic synclines, structurally weaker at the fold axis, had been subjected to deep-seated karstification. The work presented here investigates that possibility and argues for and against it. In addition, established concepts of groundwater flow mechanisms for the area have been revisited. A conclusion has not yet been reached, but the balance of the arguments is presented.
Use of krypton-81 to constrain the reliability of carbon-14 in estimating groundwater ages	S	Lu	China	2023	groundwater dating, krypton-81 isotope, radiocarbon
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.
Groundwater-dependent ecosystem dynamics in transboundary aquifer settings - a case study in the Tuli-Karoo aquifer	Kwazikwakhe	Majola	South Africa	2023	Groundwater-Dependent Ecosystem, Interactions, Transboundary aquifer
Abstract Knowledge of the nature and extent of groundwater-dependent ecosystems (GDE) at an aquifer scale enables incorporating ecological water requirements in integrated groundwater resource management activities, including transboundary aquifer cases (TBA). This way, sustainable groundwater management and functional ecosystem services can be achieved. Therefore, understanding groundwater- ecosystems-surface water interactions is crucial for assessing resources’ resilience or susceptibility towards certain impacts. Unfortunately, this subject is widely under-researched with fragmented information, especially in southern Africa. This study was thus initiated to understand groundwater processes controlling the maintenance of Tuli-Karoo TBA (Botswana, South Africa, Zimbabwe) GDEs towards developing a model that can be utilised in impact assessments, especially in climate change. The employed approach included stable isotope analysis (mainly 2 H and 18O) for groundwater, streams, springs, rainwater, vegetation, and soil; spatial imagery and GIS classification (incl. NDVI, NDRE, NDWI); and plant moisture stress techniques. Identified GDEs in the study area (characterized by intergranular alluvium aquifer underlain by the Karoo sandstone of intergranular and fractured secondary aquifer type) are riparian vegetation, floodplain and depression wetlands, and springs. Precipitation recharged alluvium aquifer’s contribution to Limpopo River baseflow is negligible as the discharge is mainly through springs and evapotranspiration. Monitoring data scarcity and skewed availability among sharing countries hamper research and its output applicability to TBA’s entirety. Therefore, data generation, exchange, and joint databases development are crucial for sustainable comanagement of groundwater and supported ecosystems and science-based decision-making.
The use of Coal Combustion Residues for the stabilisation of mines and the treatment of mine drainage	Kelley	Reynolds-Clausen	South Africa	2023	CCP, coal combustion residue, coal ash, mine backfilling
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.
A new Danish groundwater mapping and modelling concept for targeted agricultural N-regulation	Birgitte	Hansen	Denmark	2023	Groundwater, denitrification, modelling, nitrogen, regulation, surface waters
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.
Regional Scale Groundwater Monitoring Status Reporting: A mapping series within the Vanrhynsdorp aquifer system	Ashton	van Niekerk	South Africa	2023	Aquifer scale, groundwater availability, Groundwater Quality, spatial-temporal, trend analysis
Abstract A mapping series was generated using the Vanrhynsdorp aquifer system to illustrate an improved standardization groundwater monitoring status reporting, that includes a progressive conceptual site model linked with spatial and temporal groundwater monitoring network assessment on an aquifer scale. The report consists of 4 segments: Base map provides a conceptual site model of a groundwater resource unit (GRU) delineating an area of 1456 km2 representing the geology and geological structures that make up the Vanrhynsdorp aquifer system. The Groundwater Availability Map illustrated over a long-term trend analysis, the measured water levels indicate an 83% decreasing trend over an average period of 21.83 years, the water levels have declined by an average linear progression of 11.54 m (ranging 0.48-35.76 m) or 0.64 m per year, which equates to an estimated decline in storage of 218 Tm3 - 21 Mm3 within the GRU. The Groundwater EC map illustrated over the long-term analysis of an average period 24 years the average EC ranged between 57 - 791 mS/m, with certain areas tracking at a constant increasing trend beyond 1200 mS/m. The Groundwater Quality Characterization map provides EC contours and spatial Stiff diagram plots. The Stiff diagrams illustrate three aquifer water types namely, Na-Cl (Table Mountain Group Sandstones), Na-Cl with high SO4 concentration (Blouport and Aties Formation) and Na-Cl-HCO3 (Widouw Formation). These four segments of information products inform Resource Quality Objectives and the need for surveillance monitoring in conjunction with annual compliance monitoring and enforcement groundwater use audits.
Groundwater resource assessment and delineation of resource unit for the Komati catchment within the Inkomati Usuthu Management Catchment area – Mpumalanga Province, South Africa	Collen	Monokofala	South Africa	2023	Catchment scale integrated surface water and groundwater studies
Abstract The recent uncertainties in rainfall patterns have resulted in shortages in the availability of water resources, posing significant risk to the sustainability of all living organisms, livelihoods and economic prosperity. The fact that hidden groundwater resources in semi-arid regions present a challenge to understanding and managing the resources. Various groundwater studies have been undertaken; however, the quantification is generally over-simplified due to a limited understanding of the groundwater flow regime and consideration being mostly given to water supply. Thus, the data is often not comprehensive enough and generally limited in determining how much groundwater is available to supply rural areas. The Komati catchment area is dominated by coal mining in the upper reaches and irrigation and agriculture in the lower reaches, with human settlements competing for these water resources. Five significant dams in the Komati catchment are constructed to deal with the increasing water demand for commercial agriculture in the region. However, given uncertain weather patterns, the water mix approach is imperative. This study focused on understanding the groundwater potential, characterised the aquifer system, delineated the groundwater resource units, quantified baseflow and calculated the groundwater balance that can be used as a guide for the groundwater management protocol for the catchment area. The box model approach (surface-groundwater interaction) was used to characterize the groundwater regime and understand the spatial distribution of the aquifer types, water quality and significant aquifers of interest to protect this important resource.
Multiple-tool approach of combining microbial markers with artificial and natural tracers to specify the origin of faecal contamination on karst groundwater catchment scale	M	Sinreich	Switzerland	2023	Karst spring, MST, Catchment, faecal indicators, toolbox, tracers
Abstract Diverse tools exist to study the transfer of contamination from its source to groundwater and related springs. A backward approach, i.e. sampling spring water to determine the origin of contamination, is more complex and requires multiple information. Microbial source tracking (MST) using host-specific markers is one of the tools, which, however, has shown to be insufficient as a stand-alone method, particularly in karst groundwater catchments. A karst spring in the Swiss Jura Mountains was studied concerning the occurrence and correlation of a set of faecal indicators, including classical parameters and bacteroidal markers. Sporadic monitoring proved the impact on spring water quality, mainly during high water stages. Additional event-focused sampling evidenced a more detailed and divergent pattern of individual indicators. A multiple-tool approach, complementing faecal indicator monitoring with artificial tracer experiments and measuring natural tracers, could specify the origin of ruminant and human faecal contaminations. Natural tracers allowed for distinguishing between water components from the saturated zone, the soil/epikarst storage, or freshly infiltrated rainwater. Additionally, the breakthrough of injected dye tracers and their remobilization during subsequent recharge events were correlated with the occurrence of faecal markers. The findings hypothesize that human faecal contamination is related to septic tanks overflowing at moderate rainfall intensities. Linkage with vulnerability assessment and land-use information can finally better locate the potential point sources. Such a toolbox provides useful basics for groundwater protection and catchment management and insight into general processes governing the fate and transport of faecal contaminants in karst environments.
Understanding informal institutions’ role in groundwater management – Lessons from borderland communities	Kevin	Pietersen	Africa	2023	groundwater governance, informal institutions, transboundary aquifers
Abstract Across Africa, given the pressing challenges of climate change and widespread water, food and livelihood insecurity and poverty, there is an ever-increasing expanding role for groundwater in resilience building, especially in borderland communities. This situation is being investigated in several projects and geographies. This paper’s groundwater management analysis was based on literature reviews, key informant interviews (KIIs), and focus group discussions (FGDs) in selected case study areas throughout sub-Saharan Africa. The KIIs included representatives of water management institutions, community leaders, international development partners, the private sector and non-governmental organisations (NGOs) involved in the use or management of groundwater. The FGDs occurred in borderland communities in Ethiopia, Kenya, and Somalia (with these three countries sharing borders) and Mozambique, South Africa and Zimbabwe (with these three also sharing borders). The findings show that informal institutions such as clan, tribal or ethnic affiliations dictate access to natural resources such as groundwater in borderlands. These same Institutions also play a significant role in conflict resolution in the borderland areas. In addition, informal institutions play an essential role in groundwater management and should also be recognised – in engagements and formal water policies and legislation. Formal organisations, institutions and government structures should strengthen their focus on ensuring that discussions and decisions include informal role players. Further developing and enforcing conventions, land-use plans, and bylaws governing access to and use of groundwater should ensure engagement and co-creation of solutions towards effective water resource management.
Groundwater overuse and water quality challenges in a large metropolitan catchment	B	Karthikeyan	India	2023	Managed aquifer recharge, megacity, persistent organic pollutants, urban catchment
Abstract Conjunctive use of surface water and groundwater plays a pivotal role in sustainably managing water resources. An increase in population, especially in the cities, increases the demand for water supply. Additional infrastructure to meet the needs and treatment techniques to remove the pollutants should be updated from time to time. Closing the urban water cycle by recycling and reusing treated sewage in the water sector can significantly reduce excessive groundwater extraction. However, this method is being implemented in only a few cities in developed countries. In the closed urban water cycle, treated sewage is discharged to rivers or other surface water bodies and used for managed aquifer recharge (MAR). Bank filtration, soil aquifer treatment and infiltration ponds are available MAR methods that augment the groundwater resources and remove pollutants during the natural infiltration process. These cost-effective natural treatment methods serve as a pre-treatment technique before public water supply to remove turbidity, algal toxins, bulk dissolved organic carbon and pathogenic microorganisms. The successful performance of these treatment methods depends on the need and feasibility for MAR, suitable hydrogeological conditions, sub-surface storage capacity of the aquifers, availability of suitable areas for MAR, type of MAR, source of recharge water, quality criteria, assessing the past, present and future climatic conditions. Case studies on groundwater resources management and water quality assessment, including for organic micropollutants from a large urban catchment in India, are presented.
Showcasing a global-scale, 3D coastal groundwater salinity model	J	King	The Netherlands	2023	coastal aquifers, global modelling, groundwater salinity, paleo-reconstruction, parallel. SEAWAT, sea level rise
Abstract Being extensively available and of high quality, groundwater is the primary source of freshwater in coastal regions globally. However, due to anthropogenic and natural drivers, groundwater salinisation is a growing threat to this resource’s long- and short-term viability. The causes and timescales of aquifer salinisation are complex and difficult to quantify, information essential for suitably timed mitigation strategies. One way to inform these strategies and develop storylines of future freshwater (un)availability is through 3D groundwater salinity modelling. These models can predict current groundwater distributions and quantitatively assess the impacts of a projected increase in groundwater extraction rates and sea-level rise. Until recently, detailed 3D models on this scale have been largely unattainable due to computational burdens and a shortage of in-situ data. Fortunately, recent developments in code parallelization, reproducible modelling techniques, and access to high-performance computing (e.g., via parallel SEAWAT) have made this feasible. Machine learning and data mining developments have also allowed an unprecedented opportunity to constrain and calibrate those models. With this in mind, we present our progress towards global 3D salinity modelling by showcasing a regional-scale model in the Mediterranean Sea area. This test case uses newly developed, automated geological and salinity interpolation methods to create initial conditions while implemented in a parallelized version of SEAWAT. The modelling outcomes highlight the potential of supra-regional scale modelling in the context of global (planetary) processes and localised anthropogenic effects.
Validation of algorithms for estimating changes in groundwater storage from GRACE gravity satellite data for Poland	Tetyana	Solovey	Poland	2023	GRACE, groundwater storage assessment, validation
Abstract The development of satellite technologies creates more and more opportunities to build modern tools for monitoring the state of groundwater. The use of the GRACE satellites to monitor GWS changes has become widespread, but the degree of accuracy with which remote sensing data can estimate these changes is unclear. In this study, we quantified changes in the GWS in Poland from 2009 to 2022 using GRACE observations, in-situ data, and GLDAS. Long-term trends and seasonality were calculated and analysed for each time series. The correlation analysis between GRACE TWS, GWS obtained from GRACE and GLDAS, and GWS in situ was performed using linear regression. Pearson and Spearman’s methods show that GRACE performance is good in the region of shallow (up to 3 m) presence of thick (above 5 m) unconfined porous aquifers; however, performance is worse in a region with multiple aquifer systems, including fissured and karst aquifers. In addition, an unrepresentative groundwater GRACE signal is obtained in regions with surface water storage, such as the Baltic Sea area. It was also found that there is very high consistency between the GRACE observations and wells water level changes, while the GWS series obtained from GRACE and GLDAS do not provide adequate compatibility. According to the GRACE data, the results suggest that evapotranspiration and the hydrodynamic system have the greatest impact on the sensitivity of the GWS estimation. The results are important for better processing the GRACE data to obtain a representative signal for the GWS assessment.
Building evidence through hydrogeological survey and monitoring for the conjunctive development and management of water resources in Kunzila catchment area – Amhara Region, Ethiopia	Daniela	Benedicto van Dalen	Ethiopia	2023	catchment management, Conjunctive use, groundwater monitoring, participatory landscape Approach
Abstract Deploying a participatory approach for surveying the complex geohydrological system and defining the status of the groundwater resources in the Kunzila catchment area has crucial importance towards conjunctive use of its water and land resources for sustainable economic growth, social well-being, and environmental protection. Several initiatives are being undertaken to pilot the ‘Integrated Landscape Management and WASH’ project in this community to implement evidence-based approaches. A comprehensive hydrogeological study has been carried out to understand the hydrogeological system, propose ecosystem restoration measures, identify suitable locations for drilling boreholes and design a groundwater and surface water monitoring network. The first results pointed out the central area of the catchment as holding the best potential for groundwater abstraction, a productive Late Quaternary basalt aquifer. As this area is in use by private floriculture farms, several other borehole locations were sited to meet the domestic and livelihood demand across the watershed. In addition to the drinking water supply goals, the project proposed catchment intervention for soil and water conservation based on the Landscape Approach and 3R measures implementation - Retain, Recharge, Reuse. Such measures include but were not limited to riparian vegetation restoration, terracing and contour bunds, agroforestry, controlled grazing, etc. A telemetric monitoring network has been designed and installed to support the conjunctive management of shallow and deep groundwater water resources, streams and Lake Tana, together with a functional dashboard for data registrations and sharing. The monitoring program gauges the impact of groundwater abstraction and the quality parameters.
Integrated assessment of groundwater potential zones for deep groundwater exploration in hard rock aquifers using GIS and geophysical techniques: A case study of Huai Krachao, Kanchanaburi, western Thailand	Vanachawan	Hunyek	Thailand	2023	Deep groundwater exploration; Hard rock aquifer; groundwater potential zones; Analytical Hierarchy Process; weighted overlay analysis; spring
Abstract Groundwater is an important freshwater supply that has a significant role in the economy. However, water is increasingly becoming scarce in several regions. Huai Krachao Subdistrict in Kanchanaburi Province is an example of an area that has been experiencing a severe drought for decades due to the impacts of climate change. This study was conducted to delineate the groundwater potential zones in hard-rock terrains using geographic information system (GIS) techniques. The study aims to explore deep groundwater resources in challenging areas and propose alternative methods supporting traditional groundwater exploration. This finding revealed that the groundwater potential zones were classified into high, moderate, and low potential zones based on the groundwater potential index (GWPI), integrated using the Weighted Index Overlay Analysis. The computed weights from the Analytical Hierarchy Process were acceptable and consistent. The high potential zones mainly occur in the Silurian-Devonian metamorphic rocks. The GIS-based analytical results were later prepared for detailed field investigation, including collecting well information and conducting the 2-dimensional geophysical survey. To prove the GWPI map, 9 groundwater wells were drilled in the high potential zones. Consequently, well yields obtained from the pumping-test analysis ranged from 24-40 m3 / hr, some of which are springs rich in dissolved minerals. Accordingly, a significant amount of water could meet the water demand, supplying about 1 million m3 /year. Under these circumstances, discovering new groundwater resources can support roughly 5,000 people and agricultural lands no less than 480 hectares (4.8 km2 ).
Water Quality of Cape Town Aquifers – The WWQA African Use Case	K	Riemann	South Africa	2023	WWQA, Water quality, Awareness
Abstract Globally, rivers, lakes and groundwater face complex anthropogenic water quality alterations posing risks to human health, food security and ecosystems. The World Water Quality Alliance (WWQA) forms an open, global consortium, pooling expertise on water quality science and technology innovation and providing a participatory platform for water quality assessments and co-designing tailored and demand-driven services. It addresses priority topics relevant to water governance, scalable water solutions and emerging issues in water management. The African Use Cases provided an initial testbed that puts the quality of surface water and groundwater into the context of the local 2030 Agenda and its multiple linkages across the Sustainable Development Goals. Central to the initial Africa Use Cases was the integration of in-situ, remote sensing-based earth observation and modelling data to derive the best possible current state of water quality (baseline). Of the three African Use Cases, “Cape Town’s Major Aquifer Systems” focused mainly on groundwater quality in an urban environment. One of the success factors for the Cape Town Aquifer Use Case was the ability of the team to integrate the three different data types of the triangle approach on a sub-catchment scale. This required understanding the complex surface and groundwater systems and their interaction (flow paths and fluxes) in the urban environment. A robust stakeholder engagement process and the introduction of transformative art also drove the success of the Cape Town Use Case. The outcomes of this process will be presented and discussed in this presentation.
An assessment of hydrogeophysics application for groundwater resource assessment in Kalahari sands aquifers and crystalline basement aquifers with case studies from Namibia and South Africa	I	Muchingami	South Africa, Namibia	2023	Crystalline basement, Hydrogeophysics, Kalahari sand aquifer, groundwater assessment, groundwater controls
Abstract Integrated geophysical methods can be useful tools in mapping the subsurface characteristics likely to control groundwater occurrence and hence are useful in identifying potential drill targets in different aquifer formations in Southern Africa. This study applied hydrogeophysical methods (natural, electrical, and electromagnetic) to identify potential groundwater-bearing targets within the Kalahari sand aquifers in Namibia and the crystalline basement aquifer system in Namibia and South Africa. The results suggest that hydrogeophysical assessments in Kalahari sandstone aquifers could clearly show that the system exhibits a well-defined layered aquifer formation likely recharged from surface water. On the other hand, crystalline basement formations could be combined with geological observations and used to identify groundwater controls like lineaments and depths to fractured zones. The magnetic method, horizontal and vertical frequency domain electromagnetic geophysical methods presented herein managed to delineate the main dykes and lineament features associated with groundwater occurrence in typical crystalline basement aquifers, while the natural magneto telluric investigations managed to delineate the deep and shallow aquifer formation in Kalahari sandstone aquifer formation. The study also advocates for integrating geophysical methods with local and regional geology for groundwater evaluation to provide a more detailed approach to resource assessment in some of the vulnerable aquifer systems in Southern Africa. Results from this study are useful for technical groundwater management and promoting the utilization of groundwater as a climate-resilient strategy in Southern Africa.
Development of Table Mountain Group aquifer wellfields and monitoring networks for the City of Cape Town (Western Cape, South Africa)	Dylan	Blake	Western Cape, South Africa	2023	Critical Zone, Table Mountain Group aquifers, environmental monitoring, wellfield development, “no-regrets” approach
Abstract The City of Cape Town (CCT) initiated its “New Water Programme” in 2017 (during the major 2015-2018 “Day Zero” drought) to diversify its bulk water supply, thereby improving longterm water security and resilience against future droughts. This includes bulk groundwater abstraction from the major fractured Peninsula and Nardouw Aquifers of the Table Mountain Group (TMG) in the mountain catchments east of the CCT. The TMG aquifers are essential in sustaining groundwater-dependent ecosystems associated with the Cape Floral Kingdom – a global biodiversity (but also extinction) hotspot with exceptional endemic diversity. A strong geoethical, “no-regrets” approach is therefore required to develop TMG wellfield schemes for the CCT (and other towns/cities in the Western/Eastern Cape) to reduce the risk of any negative ecological and environmental impacts while still enhancing the drought resilience of the city, providing water for future urban growth, and meeting Sustainable Development Goals 6 and 11. To this extent, the CCT has developed an extensive regional (and local, in terms of Steenbras Wellfield) environmental monitoring network, incorporating a range of in-situ and remote sensing-based measurements across the Earth’s “Critical Zone” – this includes current groundwater, surface water, ecological, soil and meteorological monitoring stations, and future seismo-geodetic monitoring. An ongoing ambition is to include this CCT TMG monitoring network into the “Greater Cape Town Landscape”, which is currently in development as one of six national South African landscapes under the “Expanded Freshwater and Terrestrial Environmental Observation Network” (EFTEON) platform being hosted by the South African Environmental Observation Network.
Mitigating climate change with managed aquifer recharge: 5 Case Studies	D	Hohne	South Africa	2023	Climate change; drought; MAR; nature-based solution; case studies
Abstract In the past decade, Southern Africa has experienced periods of extreme drought. This was especially true in the western Karoo in South Africa. Continuous drought and limited rainfall led to declining aquifer water levels that curtailed sustainable water supply for towns and livestock. The western Karoo is almost completely dependent on groundwater. Managed aquifer recharge (MAR) is being used to reduce the effects of droughts and mitigate climate change impacts. A good understanding of the geology and the behaviour of the aquifers is needed for implementing various MAR designs, including nature-based solutions, which are used to recharge aquifers with limited rainfall. This paper discusses 5 active MAR case studies in the Western Karoo. Here, site-specific MAR methods that use small rainfall events deliver reasonable results, whereas the implemented MAR options keep most aquifers functional. Observations at the MAR sites also showed improved water quality and less bacterial clogging. This improves the environment around the managed aquifer recharge sites. The MAR methods and designs discussed in this paper can be used on a larger scale for a town or a smaller scale for a farm. Maintenance costs are low, which makes these options cost-effective for less wealthy areas.
ome Trans-disciplinary Legal Options to Ensure the Protection of South Africa’s Utilisable Groundwater Resources	Carin	Bosman	South Africa	2023	Groundwater governance; water law; protection; land use activities; hydrogeology; aquifer protection zones
Abstract South Africa faces serious water scarcity challenges not only because it is a semi-arid country but also due to climate change. One of the most significant effects of climate change is an increase in temperature, which inevitably increases evaporation. Increased evaporation directly reduces the availability of surface water resources. Groundwater is less susceptible than surface water resources to evaporation and thus offers resilience against the impacts of climate change. Many South African cities, communities, and farmers depend on groundwater for domestic or other socio-economic purposes. This implies that groundwater resources which are currently or potentially utilisable should be identified, and suitable legal measures should be implemented to protect these resources from potential risks of harm or damage posed by anthropogenic activity. First, This article evaluates the effectiveness of the country’s existing regulatory framework to effectively protect South Africa’s groundwater resources and finds that the framework can be improved significantly. Secondly, it explores regulatory opportunities within the existing legal framework to strengthen South Africa’s groundwater governance regime, including using land use planning instruments to facilitate the implementation of groundwater protection zones
Combined Use of Environmental and Artificial Tracers to Characterise the Vadose Zone	Yazeed	van Wyk	South Africa	2023	vadose zone, contaminant transport processes, environmental and artificial tracers
Abstract Water and contaminant transport processes in the vadose zone through preferential flow paths can be understood using environmental and artificial tracer methods. Further improvement in tracer techniques can be achieved by applying numerical modelling techniques of both water and solute transport, accounting for additional information on water movement and the matric potential of the vadose zone. The vadose zone is often ignored as a key component linking the land surface to the groundwater table, even though it acts as a filter that removes or stores potential contaminants. The water transit time between the surface and the groundwater table is frequently investigated using artificial tracers that normally show conservative behaviour. The main advantage is that the input function can be clearly defined, even though artificial tracers can generally only be applied over a relatively small area. The research is expected to provide insight into the selection and use of environmental and artificial tracers as markers for detecting and understanding the contaminant transport processes and pathways of contaminants in altered vadose zone environments (open-pit quarry). The impact is improved characterisation of the pathways, transport and migration processes of contaminants, and residence times, leading to the development of appropriate conceptual and numerical models of vadose zone flow processes that consider various contaminant sources. The principal aim is, therefore, to systematically examine the transport mechanisms and associated pathways of different environmental and artificial tracers in an open-pit quarry.
Benefits and costs of managed aquifer recharge: An integrated water governance solution	Andrew	Ross	Australia	2023	Managed aquifer recharge; aquifer storage; water infrastructure; cost-benefit analysis; levelized cost; benefit-cost ratio
Abstract Managed Aquifer Recharge (MAR) provides an integrated water governance solution that improves water security for communities and farmers by storing water in aquifers and managing groundwater extractions to ensure water supplies are available during droughts. Quantitative analysis of levelised costs and benefit-cost ratios (BCRs) of 21 MAR schemes from 15 countries and qualitative assessment of additional social and environmental benefits demonstrates the benefits of MAR compared to water supply alternatives. Cost-benefit analysis provides a systematic method for comparing alternative water infrastructure options. Levelised cost is a widely accepted method of comparing MAR with alternative water infrastructure solutions when market valuations of water are unavailable. The benefits of MAR can be estimated by the cost of the cheapest alternative source of supply or the production value using water recovered from aquifer storage. MAR schemes recharging aquifers with natural water using infiltration basins or riverbank filtration are relatively cheap with high BCRs. Schemes using recycled water and/or requiring wells with substantial drilling infrastructure and or water treatment are more expensive while offering positive BCRs. Most MAR schemes have positive or neutral effects on aquifer conditions, water levels, water quality, and environmental flows. Energy requirements are competitive with alternative sources of supply. This analysis demonstrates strong returns to investment in the reported MAR schemes. MAR provides valuable social and environmental benefits and contributes to sustaining groundwater resources where extraction is managed.
Planning for increased water security and preventing salinisation in coastal areas of the Netherlands: A study on the suitability for managed aquifer recharge and extraction of brackish water, including quantification of potential extractable volumes	I	de Groot-Wallast	The Netherlands	2023	Aquifer Storage and Recovery, Managed aquifer recharge, aquifer salinisation, brackish water extraction, suitability maps, Water supply
Abstract Year-round water security is at risk as socio-economic developments lead to increasing water demands, while climate change affects water availability through higher-intensity rainfall and prolonged periods of drought. Coastal zones and deltas with often high population densities experience additional risks of salinisation and land subsidence. These developments ask for creative solutions to secure sustainable and year-round access to fresh water. The subsurface provides storage capacity to actively infiltrate freshwater, bridging the time-gap between demand and supply. Combining infiltration with extraction and desalination of brackish water prevents the salinisation of aquifers whilst providing an additional water source. We call this COASTAR. A Dutch research consortium with partners like water companies and water boards develops COASTAR. Among COASTAR results are suitability maps for Aquifer Storage and Recovery (ASR) and Brackish Water Extraction (BWE) in the coastal zone of the Netherlands. The maps are based on geohydrological factors. A quick-scan analysis was also performed to quantify the nation-wide potential extractable ASR and BWE volumes. COASTAR develops case study models and local scale pilots on ASR and BWE. For two water supply regions, an analysis has been made to geographically match development in water demand with suitability for ASR and BWE as a step in the search for strategic locations to develop ASR and BWE. The suitability maps provide guidance for initiatives’ development and practical experiences from pilot projects; this provides important information for further upscaling of COASTAR approaches.
Evaluating Karst Drywells for Urban Stormwater Management and Aquifer Recharge	Yonatan	Ganot	Israel	2023	Drywell, karst, MAR, RQD, unsaturated zone
Abstract Drywells are extremely useful for coping with excess surface water in areas where drainage and diversion of storm flows are limited, facilitating stormwater infiltration and groundwater recharge. Drywells have been used for stormwater management in locations that receive high precipitation volumes, naturally or due to climate change; however, to date, they have not been developed in urban areas overlying karst landscapes. To test the performance of karst drywells, we constructed a pilot system for collecting, filtering, and recharging urban stormwater through drywells in karst rock. The study site is in the Judaean Mountains, an urban residential area in Jerusalem, Israel. The infiltration capacity of the drywells was evaluated using continuous and graduated water injection tests, and its effective hydraulic conductivity (K) was estimated. Drywells’ infiltration capacity was up to 22 m3 /hour (the maximum discharge delivered by a nearby fire hydrant), while monitored water levels in the drywells were relatively stable. Calculated hydraulic conductivities were in the range of K=0.1-100 m/ day, and generally, K was inversely proportional to the rock quality designation (RQD) index (obtained from rock cores during the drilling of the drywells). The pilot system performance was tested in the recent winter: during 9 days with a total rainfall of 295 mm, a cumulative volume of 45 m3 was recharged through the drywell, with a maximum discharge of 13 m3 / hour. High-conductivity karst drywells and adequate pre-treatment filtration can be valuable techniques for urban flood mitigation and stormwater recharge.
Per and Polyfluoroalkyl Substances (PFAS) Groundwater Toolkit	Fern	Beetle-Moorcrof	western United States	2023	PFAS, fate and transport, Groundwater, sampling
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.