Conference Abstracts

All Abstracts were presented at the Groundwater Conferences

Displaying 101 - 150 of 795 results

Title	Presenter Name	Presenter Surname	Area	Conference year Sort ascending	Keywords
Application of Nanofiltration Membrane for Removal of VOCs and Heavy Metals in Groundwater, Ratchaburi, Thailand	Chunintorn	Chamathong	Ratchaburi, Thailand	2023	Heavy metals, Nanofiltration membrane, VOCs
Abstract he Namphu and Rangbua subdistricts in Ratchaburi province, in western Thailand, are affected by groundwater contamination. According to site characterization results, the aquifer has been contaminated with volatile organic compounds and heavy metals since 2014. Membrane filtration technology is an alternative method for treating groundwater to produce safe drinking water for household use. Nanofiltration membrane is a relatively recent development in membrane technology with characteristics that fall between ultrafiltration and reverse osmosis (RO). This study aimed to determine the hydrochemistry of contaminated groundwater and examine the efficiency of nanofiltration membranes for removing pollutants in groundwater and the potential implementation of the membrane. The membrane module used in this study is cylindrical in shape of 101.6 cm long and 6.4 cm in diameter, and the membrane surface charge is negative with monovalent rejection (NaCl) of 85-95%. The filtration experiments were conducted at a pressure of 0.4-0.6 MPa, which yielded flow rates of approximately 2 L/min. To examine the nanofiltration membrane efficiency, groundwater samples were extracted from four monitoring wells and were used as feed water. According to laboratory results, the nanofiltration maximum removal efficiencies for 1,2-dichloroethylene, vinyl chloride, benzene, nickel, and manganese were 97, 99, 98, 99, and 99%, respectively. However, the treatment efficiency depends on several factors, including pretreatment requirements, influent water quality and the lifespan of the membrane. Further research should be conducted to determine the maximum concentration of VOCs and heavy metals in the feed water before applying this treatment method to a large scale.
Characterisation of the Lower Berg River Aquifer System, Western Cape, South Africa	A	Parker	South Africa	2023	Lower Berg River, aquifer, Discharge, Geophysics, Groundwater, Isotopes, recharge, Tritium
Abstract The Lower Berg River Aquifer System, situated in the Western Cape province of South Africa, is important to the towns that overlay it, as they rely on the aquifer for water supply, which supplements industrial development and residential growth. This aquifer system is important because surface water resources in the area are finite and fully allocated. Despite studies on the Lower Berg River Aquifer System since 1976, knowledge of the geological layers, recharge and discharge areas, and groundwater flow paths remain limited. This study aimed to provide greater insight and understanding of the aquifer to assist in better management. Investigations included a Time Domain Electromagnetic airborne geophysical survey, the assessment of groundwater levels, infiltration tests, hydrochemical analyses, and stable and radioactive isotope analyses. These methods allowed for the identification of the aquifer’s layers and extent, determination of water quality in different parts of the aquifer, delineation of flow paths through the saturated and unsaturated zones, identification of inter-aquifer flow, as well as different modes of recharge.
Source protection zone delineation: Numerical insights on the effect of heterogeneity	T	Sarris	New Zealand	2023	Drinking water, Flow and transport modelling, Heterogeneity, Source protection zone delineation, Transition probability
Abstract Source protection area delineation has evolved over the last decades from fixed radius, analytical and numerical methods which do not consider uncertainty to more complex stochastic numerical approaches where uncertainties are often considered in a Monte Carlo framework. The representation of aquifer heterogeneity in these studies is typically based on a geostatistical representation of hydraulic properties. This presentation compares results from complex stochastic flow and transport simulations, simple homogeneous models, and existing analytical expressions. As a case study, we use the existing drinking supply wells in West Melton located Canterbury’s Selwyn District in New Zealand. Monte Carlo realisations are parameterised in MODFLOW6 so that the prior knowledge of the aquifer’s effective, large scale flow characteristics is honoured. Homogenous simulations are based on the same grid, using the aquifer’s effective properties to parameterise the numerical flow model. In both cases, conservative transport of pathogens is undertaken using Modpath7, using both forward and backward particle tracking. The numerical results are compared with analytical expressions from the international literature. Our results suggest that aquifer heterogeneity needs to be explicitly addressed in all cases. Homogeneous simulations almost certainly underestimate contamination risk and produce unrealistically small source protection areas. Parameterisation of the stochastic heterogeneous realisations also affects the size and extent of the source protection area, suggesting that these need to be carefully considered for practical applications.
A Review of potential and actual groundwater recharge: Insights and implications to groundwater use	N	Tuswa	Bellville, South Africa	2023	Groundwater allocation, capture principle, semi-arid region, water resource management
Abstract Recharge is one of the most significant parameters in determining the sustainability volume of groundwater that can be abstracted from an aquifer system. This paper provides an updated overview and understanding of potential and actual groundwater recharge and its implications for informing decision-makers on efficiently managing groundwater resources. The paper argues that the issue of potential and actual recharge has not been adequately addressed in many groundwater recharge studies, and if not properly addressed, this may lead to erroneous interpretation and poor implementation of groundwater resource allocations. Groundwater recharge has been estimated using various methods, revised and improved over the last decade. However, despite numerous recharge methods, many studies still fail to distinguish that some assess potential recharge while others estimate actual recharge. The application of multiple recharge methods usually provides a wide range of recharge rates, which should be interpreted in relation to the type of recharge they represent; as a result, the wide range of recharge findings from different methods does not necessarily imply that any of them are erroneous. A precise distinction should, therefore, be made between the potential amount of water available for recharge from the vadose zone and the actual recharge reaching the water table. This study cautions groundwater practitioners against using “potential recharge values” to allocate groundwater resources to users. The results of this paper may be useful in developing sustainable groundwater resource management plans for water managers.
Assessment of groundwater potential of the Kalahari aquifers in Kavango East and West regions, Namibia	Anna	David	Namibia	2023	groundwater potential, Kalahari aquifers, recharge, water-balance
Abstract The Kavango West and East regions are situated in a semi-arid area northeast of Namibia and bounded by the perennial Okavango River on the northern border. Groundwater in the area is the main source of water supply for the inhabitants living further from the river. In addition, most bulk water users along the river have boreholes for their water supply. With a semi-arid climate, drought in the regions is common and inflicts devastating effects on local communities. More drought relief boreholes are being drilled to sustain communities, increasing the dependency of the inhabitants on groundwater. The complexity of the behaviour and nature of the groundwater in the regions is poorly understood, and there are no strategies to manage these aquifers properly. As a result, an attempt was made to better understand the groundwater potential by examining several hydrogeological factors involved. A basic water-balance approach was used in determining the groundwater potential of the middle and lower Kalahari aquifers. The total resource potential for the entire region is estimated at 144 447.16 x 106 m3 /a, demonstrating great resource potential with significant storage space. The greatest potential is shown in the middle Kalahari aquifers, comprising about 94% of the total resource. Groundwater recharge, as one of the hydrogeological factors, was determined using the chloride mass balance method, giving an average of 6.03 mm/a for the entire study area. If utilized sustainably, the Kalahari aquifers can sustain most communities within the two regions, especially those further from the Okavango River.
Sampling procedures for PFAS and pharmaceuticals –Recommendations vs. reality	A	Kuczyńska	Poland	2023	emerging contaminants, groundwater monitoring, sampling protocols
Abstract PFAS and pharmaceuticals in groundwater are two of many synthetic compounds currently under the attention of many researchers and environmental administration in Europe, especially in light of the revision of the EU Groundwater Directive 2006/118/EU. The two types of substances were first included in the voluntary groundwater watch list and were first formally regulated at the EU scale. This regulation implies that they will be obligatory to be monitored within national monitoring programmes for groundwater body status assessment procedures across the EU. While there is no doubt about the need to regulate the presence of these substances in groundwater, sampling procedures and QC/QA protocols may be challenging to implement as no official guidelines exist. Although scientific literature allows us to define protocols usually based on precautionary principle, these may be too difficult and expensive to implement at the national scale monitoring. This article describes a work that the Polish Geological Institute – National Research Institute undertook to define an optimal sampling process for PFAS and pharmaceuticals in groundwater. Experimentally tested factors included cleaning pumps between sampling sites, the need for using protective suits during sampling and the influence of ambient air on sample quality. Results showed that sampling protocols for PFAS and pharmaceuticals do not need to be modified concerning current protocols as these seem to be sufficient to protect groundwater samples from unintentional cross-contamination.
Groundwater potential and lateral connectivity of the Limpopo sand river system mitigating water scarcity and salinity in semi-arid Mozambique	P	Saveca	Mozambique	2023	Limpopo, aquifer connectivity, groundwater potential, salinity mitigation, sand river, semi-arid regions
Abstract In this study, we assess the potential of large riverbed aquifers in semi-arid Africa, known as sand rivers, to mitigate water scarcity and salinity for multiple-use water supply through a case study of the Limpopo River in Mozambique. Such sand river systems are widespread and still heavily underused at a regional scale, particularly in Mozambique, with the riparian vegetation currently being the primary user, though only consuming a minor fraction of available water. At a local scale, we performed geoelectrical surveys, water level measurements (in river and groundwater), as well as field physicochemical measurements and hydrochemical and isotopic sampling at 38 locations in the river channel, margins and up to 6 km away from the river, over five years. Results show that these shallow systems can be up to a kilometer wide and 15 m thick and, at some locations, can extend laterally beyond the river channel, below thin layers of clay and silt. Large areas of the sand river channel carry runoff yearly, providing optimal conditions for rapid recharge into the coarse sands with a high storage capacity. Connectivity between the river margin and channel is clearly shown at the local scale, even though sand pockets located further away appear isolated (revealed by geophysics), isotopically different and more brackish. Recharge, evapotranspiration and mixing processes are confirmed through hydrogeochemical modelling. The proven connectivity is highly relevant as groundwater is abstracted locally, promoting socio-economic development in water-scarce regions.
he complexity and importance of the intermediate vadose zone - Local-scale, Pore-scale, and Discrete Scale	Matthys A	Dippenaar	South Africa	2023	adhesion, saturated zone, capillarity, cohesion, fracture flow, moisture content
Abstract The intermediate vadose zone underlies the plant root zone and comprises soil and rock. Different soils have different hydraulic and mechanical properties, and the vertical and spatial distributions are variable at a small scale. In South Africa, except for the Cenozoic and Quaternary deserts and coastal deposits, rock forms most of the vadose zone, and the rock fractures exacerbate the complexity. The vadose zone is observed at a small scale and dictates what happens in large scale, as adhesion to mineral surfaces happens first, and cohesion between water molecules is next. The original consideration of the intermediate vadose zone was a black box approach measuring what goes in from the surface and what goes out as groundwater recharge, not accounting for the movement of the vast majority of the freshwater supplied through precipitation. That doesn’t address the preferential flow, velocity, and pore water changes in the medium. Soil science addresses the soil or plant root zone very well. This zone governs the vertical movement of water and controls the ecosystems and biodiversity. However, all evapotranspiration disappears below this zone, and capillarity and gravity both move water into and through the intermediate vadose zone. Movement is no longer solely vertical and will be affected by soil types, intergranular porosity in soil and rock, changing water content, and secondary fractures with different properties in rock. This presentation will cover concepts and advances in this field, emphasising how and why water moves in the intermediate vadose zone.
What decision-making information can be obtained from chemical data on a large-scale? A case study in Kunene and Omusati regions in Namibia	L	Gourcy	Namibia	2023	Kunene, Namibia, Omusati, chemical processes, Groundwater Quality, major dissolved elements
Abstract Since the end of the 1970’s, the Ministry of Agriculture, Water and Land Reform (MAWLR), through the development of the groundwater database (GROWAS II), gathered a great number of data on groundwater quality. In an ongoing study (MAWLR-MEFT-AFD-BRGM, 2023), an opportunity was presented to compile chemical data for groundwater in the two most north-western regions of Namibia, Kunene and Omusati, to elaborate and support decision-making with the available information. A selection of 3256 data presenting a good ionic balance (± 10%) was selected from a large dataset, using metadata from previous BGR projects and the Geological Survey of Namibia at a 1:250,000 scale as supporting information. During the assessment of chemical data, it was depicted that most of the good quality water for human consumption and irrigation is located in the carbonated sedimentary formations at the southeastern part of Kunene and a great part of the northern part of the Kunene region. With more detailed data treatment, it allowed for confirming a natural origin for high fluoride concentration linked to granite, gneiss, old volcanic rocks and high sulphate concentration due to evaporates (gypscrete) in the eastern part of Omusati. In contrast, high nitrate concentrations were found in various lithologies across the two regions confirming local anthropogenic contamination. These results were compared to information obtained through the few published works of local studies to evaluate the accuracy of this large-scale assessment of chemical data.
The connectedness of transboundary groundwater researchers: from network analysis to network-building	A	Fernald		2023	network analysis, network-of-networks, transboundary groundwater
Abstract The Transboundary Groundwater Resilience (TGR) Network-of-Networks project brings together researchers from multiple countries to address the challenges of groundwater scarcity and continuing depletion. Improving groundwater resilience through international research collaborations and engaging professionals from hydrology, social science, data science, and related fields is a crucial strategy enabling better decision-making at the transboundary level. As a component of the underlying data infrastructure, the TGR project applies visual analytics and graph-theoretical approaches to explore the international academic network of transboundary groundwater research. This enables the identification of research clusters around specific topic areas within transboundary groundwater research, understanding how the network evolved over the years, and finding partners with matching or complementary research interests. Novel online software for analysing co-authorship networks, built on the online SuAVE (Survey Analysis via Visual Exploration, suave.sdsc.edu) visual analytics platform, will be demonstrated. The application uses OpenAlex, a new open-access bibliographic data source, to extract publications that mention transboundary aquifers or transboundary groundwater and automatically tag them with groundwater-specific keywords and names of studied aquifers. The analytics platform includes a series of data views and maps to help the user view the entire academic landscape of transboundary groundwater research, compute network fragmentation characteristics, focus on individual clusters or authors, view individual researchers’ profiles and publications, and determine their centrality and network role using betweenness, eigenvector centrality, key player fragmentation, and other network measures. This information helps guide the project’s data-driven international networking, making it more comprehensive and efficient.
Potential land use changes and wildfires effects over the spatiotemporal distribution of groundwater recharge at a regional scale: RAPReHS indicator accounting for SDG-13 in Bolivia	Monica Ximena	Guzmán Rojo	Bolivia	2023	Climate change, groundwater recharge, SDG
Abstract Having knowledge of spatiotemporal groundwater recharge is crucial for optimizing regional water management practices. However, the lack of consistent ground hydrometeorological data at regional and global scales has led to the use of alternative proxies and indicators to estimate impacts on groundwater recharge, enabling effective management of future water resources. This study explores the impact of land use changes and wildfires on groundwater recharge at a regional scale in Bolivia, using an alternative indicator to estimate variations in groundwater recharge rates. Based on a study by de Freitas L. in 2021, the methodology developed the annual groundwater recharge reduction rate (RAPReHS) utilizing remotely sensed data from the FLDAS and TERRACLIMATE datasets. The RAPReHS employs a simplified version of the water balance equation, estimating direct vertical groundwater recharge by considering the difference between precipitation, evapotranspiration, and runoff. The methodology was upscaled to improve data processing and analysis efficiency using an open-source cloud-computing platform (Google Earth Engine) over a 20-year period. The first results reveal a strong correlation between decreasing groundwater recharge rates and natural vegetation in the eastern region. By utilizing the RAPReHS index, forest preservation strategies can be prioritized. This study is in the framework of SDG 13 (Climate Action), which aims to mitigate the impacts of climate change on the environment and society. By exploring the impact of land use changes and wildfires on groundwater recharge at a regional scale in Bolivia, this research contributes to the inclusion of groundwater in policy guidelines for sustainable water management
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.
Well integrity assessment using fibre optic active distributed temperature sensing	M	Brown	Canada	2023	Active Distributed Temperature Sensing, fibre optic, multilevel monitoring well, well integrity
Abstract Groundwater quality and groundwater sample representativeness depend on the integrity of the water supply and monitoring wells. Well-integrity issues can occur by improper placement of grout seals behind the protective casing and/or by improper backfilling processes between ports. Multi-level monitoring systems are becoming common in the industry, providing depth-discrete groundwater samples and hydraulic head data from a single borehole. However, isolation between the monitoring intervals can be challenging when backfilled methods are used. No independent verification method exists to confirm seal placement for isolating monitoring intervals in such multi-level wells. A new approach using a hybrid fibre optic cable for adding heat, referred to as Active Distributed Temperature Sensing (A-DTS), is deployed in the annular space of a backfilled multi-level well. This new method is used to quantify the position of bentonite used as seals and sand packs that define the monitoring interval lengths and to identify issues associated with backfilling. A-DTS data from three boreholes with back-filled multilevel systems to 85 mbgs in a dolostone aquifer in Guelph, Ontario, Canada, demonstrates clear boundaries between backfill materials. In one interval, a deviation in the thermal data suggests a bridge in the bentonite seal, and this interval coincides with challenges in the backfilling from the field notes. The proposed method verifies well completion details, is repeatable and provides an efficient and effective way to assess well integrity impacting measurement uncertainty in a range of well types.
Integrated Modelling of the Hydrological Dynamics of the Semi-arid Hout-Sand Catchment, South Africa	E	Bjerre	South Africa	2023	drylands, conceptual flow model, integrated dynamic hydrological modelling, water resources, assessment and management
Abstract The interaction between dryland hydrological fluxes and the high spatial and seasonal climate variability is inherently complex. Groundwater recharge is episodic, and rivers are ephemeral. When flow occurs in the river network, water is lost through the riverbed, giving rise to focused recharge, which could be a significant part of total recharge. We have used the integrated and physically based MIKE SHE modelling system to analyze the hydrological processes and fluxes in the 7,715 km2 Hout-Sand catchment in the South African part of the Limpopo River Basin. The discharge hydrograph measured at the outlet station is highly episodic, with a small baseline flow component superimposed by high flow events in response to intense rainfall. Likewise, the groundwater hydrographs from the area are characterized by rapid increases in groundwater levels in response to high rainfall events with recurrence intervals of several years. Due to the scarcity of basic measurements and information, we used data products from satellite platforms to supplement the information on rainfall, evapotranspiration, soil moisture, land use and irrigated areas. We applied MIKE SHE to test different conceptual flow models of the catchment by calibrating the different models against direct measurements of river discharge and groundwater levels and indirect estimates of evapotranspiration and soil moisture from satellite products. By analyzing the simulated model dynamics and the resulting values for the calibration parameters, we identified the most plausible conceptual model, which then forms the basis for water resources assessment and management recommendations for the Hout-Sand catchment.
Using derivative plot analysis for diagnosing boundary conditions and flow regimes, Heuningnes, Cape Agulhas, South Africa	Abongile	Xaza	South Africa	2023	Flow regimes, boundary conditions, flow dynamics
Abstract This study focused on improving the understanding of flow regimes and boundary conditions in complex aquifer systems with unusual behavioural responses to pumping tests. In addition, the purpose was to provide a novel analysis of the hydrogeological properties of aquifers to deduce inferences about the general expected aquifer types to inform new practices for managing groundwater. In this paper, we report that using derivative analysis to improve understanding of complexities in aquifer flow systems is difficult and rarely used in groundwater hydraulics research work. Thus, we argue that if derivatives are not considered in the characterizing flow regime. The heterogeneity of aquifers, boundary conditions and flow regimes of such aquifers cannot be assessed for groundwater availability, and the decision to allocate such water for use can be impaired. A comprehensive database was accessed to obtain pumping tests and geological data sets. The sequential analysis approach alongside derivative analysis was used to systematically perform a flow dimension analysis in which straight segments on drawdown-log derivative time series were interpreted as successive, specific, and independent flow regimes. The complexity of using derivatives analyses was confirmed. The complexity of hydraulic signatures was observed by pointing out n sequential signals and noninteger n values frequently observed in the database. We suggest detailed research on groundwater flow systems using tracer methods like isotopes and numeric models must be considered, especially in multilayered aquifer systems such as the Heuningnes catchment.
How groundwater temperature is affected by climate change: a systematic review and meta-analysis	Elena	Egidio	Italy	2023	Climate change, Groundwater, groundwater temperature, review, temperature
Abstract Groundwater (GW) is a target of climate change (CC), and the effects become progressively more evident in recent years. Many studies reported the effects on GW quantity, but of extreme interest is also the assessment of qualitative impacts, especially on GW temperature (GWT), because of the consequences they could have. This study aims to systematically review the published papers dealing with CC and GWT, to determine the impacts of CC on GWT, and to highlight possible consequences. Scopus and Web of Science databases were consulted, obtaining 144 papers. However, only 45 studies were considered for this review after a screening concerning eliminating duplicate papers, a first selection based on title and abstract, and an analysis of topic compatibility through examination of the full texts. The analysed scientific production from all five continents covers 1995-2023 and was published in 29 journals. As a result of the review, GWT variations due to CC emerged as of global interest and have attracted attention, especially over the past two decades, with a multidisciplinary approach. A general increase in GWTs is noted as a primary effect of CC (especially in urban areas); furthermore, the implications of the temperature increase for contaminants and groundwater-dependent ecosystems were analysed, and various industrial applications for this increase (e.g. geothermy) are evaluated. It’s evident from the review that GWT is vulnerable to CC, and the consequences can be serious and worthy of further investigation.
Micro pore-pressure sensor (MEMs) and analysis technologies – towards a future of multi-scale groundwater monitoring	W	Timms	Australia	2023	multi-scale, pore pressure, sensors, analysis
Abstract Micro-electro-mechanical system (MEMs) technologies coupled with Python data analysis can provide in-situ, multiple-point monitoring of pore pressure at discrete and local scales for engineering projects. MEMs sensors are tiny, robust, inexpensive, and can provide wireless sensing measurements in many electrical and geomechanical engineering applications. We demonstrate the development of MEMs pressure sensors for pore pressure monitoring in open boreholes and grouted in piezometers. MEMs sensors with a 60 m hydraulic head range and centimetre vertical resolution were subject to stability and drawdown tests in open boreholes and in various sand and grouts (permeability 10-8 to 10-2 m/s). The resulting accuracy and precision of the MEMs sensors, with optimal calibration models, were similar to conventional pore pressure sensors. We also demonstrate a framework for estimating in-situ hydrogeological properties for analysis from vented pore pressure sensors. This framework method included Python code analysis of hourly pore pressure data at the millimetre vertical resolution, which was combined with barometric data and modelled earth tides for each borehole. Results for pore pressure analysis in confined boreholes (>50 m depth) included specific storage, horizontal hydraulic conductivity and geomechanical properties. Future improvements in the vertical resolution of MEMs pore pressure sensors and combined these two technologies will enable groundwater monitoring at multiple scales. This could include the deployment of numerous MEMs, at sub-meter discrete scale in boreholes and evaluating local site scale variations in pore pressure responses to recharge, groundwater pumping and excavations in complex sub-surface geological conditions.
The impact of storage and hydrogeological conditions on the design and recovery performance of small-scale urban ASR systems	Niels	Hartog	The Netherlands	2023	Urban Groundwater, Managed aquifer recharge, Aquifer Storage and Recovery, MAR, ASR
Abstract Aquifer storage and recovery (ASR) can play a vital role in sustaining water availability to cope with increasing weather extremes. In urban areas, ASR systems may provide flooding risk mitigation and support urban greenery. However, such systems are often relatively small and therefore, their recovery performance depends more strongly on site-specific storage conditions such as dispersion and displacement by ambient groundwater flow. In this study, we evaluated the impact of these factors by adapting and developing analytical solutions and numerical modelling, with recently established Urban ASR systems as a reference for a wide range of realistic field conditions. We validated the accuracy and usefulness of the analytical solutions for performance anticipation. Results showed that a simple, analytically derived formula describing dispersion losses solely based on the dispersion coefficient (α) and the hydraulic radius of the injected volume (Rh) provided a very good match for all conditions tested where α/Rh<0.2. An expansion of the formula to include the development of recovery efficiency with subsequent cycles (i) was also derived and in keeping with simulation results. Also, displacement losses were found to be significant at groundwater flow velocities that are typically considered negligible, particularly as displacement and dispersion losses disproportionally enforced each other. For specific conditions where the displacement losses are dominant, using a downgradient abstraction well, effectively resulting in an ASTR system, might be beneficial to increase recovery efficiencies despite increased construction costs and design uncertainty.
Delineating wellhead protection areas and aquifer vulnerability in the Cape Flats, South Africa	Brynn	Hunink	South Africa	2023	Aquifer vulnerability mapping, groundwater sustainability, Resource protection, Source protection, Wellhead protection areas
Abstract Prevention of threats to the quality and quantity of groundwater supply is critical to ensure its sustainability. Several African studies have shown that contamination of aquifers is primarily caused by improper placement of land-based human activities. Therefore, adequate preventative measures are required to safeguard the water quality of African aquifers to avoid long-term deterioration. Spatially explicit, 3D numerical groundwater modelling is a common methodology to assess contaminant transport. However, model development is time-consuming and complex. Contrastingly, DRASTIC-L is a 2D, GIS-based aquifer vulnerability mapping technique. The method is simple to apply, but analyses are qualitative and subjective. The study aims to compare both methods and to combine their strengths using GIS overlay. Overall, aquifer vulnerability was determined using the DRASTIC-L method, while wellhead protection areas were delineated using steady-state numerical modelling. This study focuses on the Cape Flats area due to its rapid development and growing municipal water supply supplementation needs. DRASTIC-L mapping revealed that aquifers in the Cape Flats are highly vulnerable to contamination due to the region’s unconfined hydrogeological properties, shallow water table and high-risk land use types. Moreover, groundwater vulnerability mapping combined with the delineation of wellhead protection areas allows for reduced uncertainty in the contamination potential of delineated groundwater protection zones. As a result, this study highlights the need for overall resource protection of the Cape Flats aquifers and provides insights into mapping out potential source protection areas of existing water supply wells.
The pharmaceutical compounds diversity at two river bank filtration sites located in Warta River valley (Poland)	Krzysztof	Dragon	Poland	2023	pharmaceuticals compounds; river bank filtration sites
Abstract Emerging contaminants (e.g. pharmaceuticals or pesticides) are increasingly detected in aquatic environments. The most apparent contamination source of river water pollution by pharmaceuticals is sewage treatment plant stations that discharge treated sewage effluent to the rivers. The river bank filtration systems (RBF) can effectively remove these contaminants. The two RBF sites were examined for pharmaceuticals: Śrem and Gorzów waterworks. The water samples for pharmaceuticals investigation were taken from the river and four continuously pumped wells at each site. Two wells near the river were chosen at each site (40-50 m) and two at a greater distance from the river (70 m in Śrem and 110 m in Gorzów). A visible increase in pharmaceutical concentrations was observed along the river. The sum of pharmaceuticals concentration is 8151 ng/l in Śrem (upstream), while in Gorzów (downstream) concentration is 9142 ng/l. A very big differentiation in pharmaceutical occurrence was observed. In Śrem, the sum of pharmaceuticals concentration is between 657 and 3290 ng/l, while in Gorzów, despite the higher concentrations of pharmaceuticals in the river, these substances were detected only in one well located at a close distance from the river (two substances at a concentration of 92 ng/l). The research proves a very big differentiation of pharmaceutical concentration even on sites located at similar hydrogeological conditions and demonstrates the necessity of its monitoring, especially in groundwater strongly influenced by river water contamination (like at RBF sites). This work has received funding from the National Science Centre Poland (grant no. 2021/41/B/ST10/00094).
Radical evolution of the Geneva transboundary aquifer agreement: an example for the sustainability of TBA governance?	Gabriel	de los Cobos	Switzerland	2023	Geneva aquifer, MAR, Climate change, Governance, transboundary aquifer agreement
Abstract The Geneva aquifer is internationally recognized for its transboundary resource management agreement between Switzerland and France, described as the first groundwater management agreement in the world. Signed in 1978 and renewed in 2008, this agreement on managing a shared underground resource has long been an example for establishing other agreements worldwide, particularly by UNESCO and its hydrological program via the TBA commission of the IAH. Like many countries worldwide, Switzerland and France experienced a critical summer of 2022 concerning the use of water resources, both surface and underground. The system applied in the cross-border agreement for using the aquifer involves French participation in the costs of managing aquifer recharge (MAR), depending on the total pumping. It shows that the French part, having consumed more water to compensate for the extreme drought of 2022, has seen its bills increase considerably. Development plans show that the population of Greater Geneva will increase considerably by 2030-2040, requiring significant medium-term water availability (30% additional water). Therefore, the French institutions’ political leaders have formally asked the authorities of the canton of Geneva to review the conditions linked to the quotas and calculation methods included in the 2008 agreement. A new agreement could be a real example of positive cross-border coordination for decision-makers finding themselves in a blocked or even conflicting situation due to differences in managing a shared resource revived by the effects of climate change.
A mixing analysis to explore the distribution and behaviour of contaminants of emerging concern and regulated organic pollutants in the hydrogeological media. Case study: the endorheic catchment of the Fuente de Piedra Lagoon (Southern Spain)	M	Llamas	Southern Spain	2023	emerging contaminants, Groundwater, mixing model
Abstract An end-member mixing analysis has been conducted for the hydrogeological system of the endorheic catchment of the Fuente de Piedra lagoon (Malaga, Southern Spain). Three end-members have been considered because of the three main groundwater types related to the different kinds of aquifers found in the catchment. The model’s objective is to help understand the distribution of the organic contaminants (including contaminants of emerging concern [CECs]) detected in groundwater samples from the catchment. Results suggest that some contaminants can be related to long groundwater residence time fluxes, where contaminant attenuation can be limited due to low oxygen levels and microbial activity. The three main aquifer types are: (i) unconfined carbonate aquifers with low mineralized water corresponding to two mountain ranges with no human activities over theirs surface; (ii) an unconfined porous aquifer formed by Quaternary and Miocene deposits, exposed to pollution from anthropogenic activities (agriculture and urban sources); and (iii) a karstic-type aquifer formed by blocks of limestones and dolostones confined by a clayey, marly and evaporite matrix from Upper Triassic. The groundwater monitoring campaign for the analysis of organic contaminants was carried out in March 2018. Target organic contaminants included pharmaceuticals, personal care products, polyaromatic hydrocarbons, pesticides, flame retardants and plasticizers. For the mixing model, a dataset was built with the hydrochemistry and isotopic results (δ2 H, δ18O) from the monitoring campaign conducted in March 2018 and from campaigns carried out in previous years and retrieved from the literature.
Groundwater Dependent Ecosystems or wetland dependent groundwater systems: A case study	N	Vermaak	South Africa	2023	Wetlands; groundwater-dependent ecosystems; recharge; groundwater surface water interaction
Abstract The interaction between groundwater and wetlands is poorly understood, even though it has been the topic of many research projects, like the study done at the Langebaan Lagoon. This interaction is complex as it lies at the intersection between groundwater and surface water, but each situation is unique, with different conditions regulating the interaction. Wetlands can be the source of water that recharges groundwater systems on the one hand, while the other is dependent on the groundwater systems. This interaction became part of the project looking at how to implement Managed Aquifer Recharge for Saldanha Bay Local Municipality without having a negative impact on the groundwater-dependent ecosystems, such as the springs and wetlands in the area. Ten wetlands were identified on the Langebaan Road Aquifer Unit, and a monitoring programme was developed. The purpose of the monitoring was to determine the status of the wetlands as a baseline before the implementation of managed aquifer recharge and to determine the level of groundwater dependence. The latter was done by hydrochemical analysis of rainwater, groundwater and water from the wetlands and stable isotope analysis. The ability of the wetlands to act as a recharge point to the groundwater system will be investigated through column experiments and lithostratigraphic analysis of soil columns taken at the wetlands. Groundwater levels will also be plotted as contour lines to determine the intersection of the water table with the wetlands in the area.
Global potential groundwater recharge in response to climate variability and teleconnection	C	Moeck	Norway	2023	climate variability, global, groundwater recharge, teleconnections, unsaturated zone
Abstract Periodic climate variability, such as that caused by climate teleconnections, can significantly impact groundwater, and the ability to predict groundwater variability in space and time is critical for effective water resource management. However, the relationship between climate variability on a global scale and groundwater recharge and levels remains poorly understood due to incomplete groundwater records and anthropogenic impacts. Moreover, the nonlinear relationship between subsurface properties and surface infiltration makes it difficult to understand climate variability’s influence on groundwater resources systematically. This study presents a global assessment of the impact of climate teleconnections on groundwater recharge and groundwater levels using an analytical solution derived from the Richards equation. The propagation of climate variability through the unsaturated zone by considering global-scale climate variability consistent with climate teleconnections such as the Pacific-North American Oscillation (PNA) and the El Niño/Southern Oscillation (ENSO) is evaluated, and it is shown when and where climate teleconnections are expected to affect groundwater levels. The results demonstrate the dampening effect of surface infiltration variability with depth in the vadose zone. Guidance for predicting long-term groundwater levels and highlighting the importance of climate teleconnections in groundwater management is provided. The obtained insights into the spatial and temporal variability of groundwater recharge and groundwater levels due to climate variability can contribute to sustainable water resource management.
Formation of the groundwater chemical composition in the Quaternary aquifer of the coastal valley (North Sinai, Egypt)	Natalia	Vinograd	Egypt	2023	Quaternary sediments, Sinai Peninsula, fresh water, Groundwater, groundwater–rock system, mineral water, physicochemical equilibrium
Abstract The research aims to reveal possible ways of formation of the chemical composition of mineral and fresh groundwater in Quaternary sediments of the coastal plain of Northern Sinai. Statistical assessment of the distribution of various hydrochemical indicators of mineral and fresh groundwater has been carried out according to the following data samples: 1) the general population for all Quaternary deposits (164 wells); 2) the central zone (74 wells); the eastern zone (25 wells); the western zone (65 wells). The following variables were assessed: total dissolved solids (TDS) (in ppm), concentrations of major components (in epm and % epm), pH value and the depth of the sampled well (ds) (in meters). The physicochemical equilibria between the groundwater and rock–forming carbonate and sulfate minerals were calculated using the PHREEQC software. Saturation indices (SI) for groundwater of three zones in relation to various rock-forming minerals were analyzed. Correlation relationships were obtained for TDS, major components and some genetic coefficients ((Requ=(Na++K+)/ (Ca2++Mg2+); Na+/Cl-; SO4 2-/Cl-; Ca2+/SO4 2-). It was concluded that the groundwater chemical composition is defined by infiltration recharge and/or intrusion of Mediterranean seawater. Most likely, during short-term flood periods, the infiltration into aquifers significantly exceeds the evaporation. Despite the relatively high evaporation rate, the degree of groundwater metamorphization is below the saturation level in relation to sulfates and carbonates. The research is of great practical importance for assessing freshwater resources to provide potable water supply
Learning from complexity: Multi-stakeholder water resources management in the island of Santa Cruz, Galápagos (Ecuador)	Viviana	Re	Italy	2023	socio-hydrogeology, sustainability, technical cooperation, transdisciplinarity
Abstract The Galápagos Archipelago (Ecuador), traditionally considered a living museum and a showcase of evolution, is increasingly subject to anthropogenic pressures affecting the local population who has to deal with the challenges of accessing safe and sustainable water resources. Over the years, numerous national and international projects have attempted to assess the impact of human activities on both the water quality and quantity in the islands. However, the complexity of the stakeholders’ structure (i.e., multiple agents with competing interests and overlapping functions) and the numerous international institutions and agencies temporarily working in the islands make information sharing and coordination particularly challenging. A comprehensive assessment of water quality data (physico-chemical parameters, major elements, trace elements and coliforms) collected since 1985 in the Santa Cruz Island revealed the need to optimise monitoring efforts to fill knowledge gaps and better target decision-making processes. Results from a participatory approach involving all stakeholders dealing with water resources highlighted the gaps and potentials of water resources management in complex environments. Particularly, it demonstrated the criticalities related to data acquisition, sustainability of the monitoring plan and translation of scientific outcomes into common ground policies for water protection. Shared procedures for data collection, sample analysis, evaluation and data assessment by an open-access geodatabase were proposed and implemented for the first time as a prototype to improve accountability and outreach towards civil society and water users. The results reveal the high potential of a well-structured and effective joint monitoring approach within a complex, multi-stakeholder framework.
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.
Groundwater flow paths dictate terrestrial carbon inputs into a groundwater-dominated stream	Y	Xie	China	2023	Groundwater discharge; groundwater flowpaths; dissolved carbon; environmental tracers
Abstract Groundwater discharge is crucial for transporting terrestrial carbon into streams and rivers, but the effects of groundwater flow paths on terrestrial carbon inputs are poorly understood. Here, we investigated environmental tracers (EC, Cl-, 2H, 18O, 220Rn, and 222Rn) and carbon concentrations in riparian groundwater, streambed groundwater, and stream water over six groundwater-stream monitoring sites. Significantly high 220Rn and 222Rn activities in the stream and endmember analysis results of the environmental tracers reveal that vertical groundwater discharge from the streambed (VGD) and lateral groundwater discharge from the riparian zone (LGD) is of equal importance for the stream. We quantified VGD by modelling the detailed 222Rn and Cl- profiles at the streambed and then combined differential flow gauging to estimate LGD. VGD (2.9 ± 1.4 m2 d-1) prevailed in relatively wide and shallow channels, while LGD (2.6 ± 2.6 m2 d-1) dominated narrow and deep channels. Carbon measurements indicate that LGD had the highest CO2, CH4, DIC, and DOC, while VGD had relatively higher CO2 but lower CH4, DIC, and DOC than stream water. Our findings suggest that LGD is the primary carbon source for the stream, while VGD mainly dilutes the stream (except CO2). Finally, we observed that groundwater discharge and temperature overrode metabolism in controlling stream carbon dynamics, implying the importance of groundwater discharge for understanding stream carbon cycling. Overall, this study identified the impacts of groundwater flow paths on carbon exchanges between terrestrial and stream ecosystems.
How alluvial storage controls surface water – groundwater interactions in dryland intermittent and ephemeral streams: A case study from semi-arid Australia	M	Zarate	Australia	2023	Groundwater, groundwater recharge, drylands, ephemeral streams, focused recharge, intermittent, semi-arid, streamflow, surface water, water balance
Abstract Water balance partitioning within dryland intermittent and ephemeral streams controls water availability to riparian ecosystems, the magnitude of peak storm discharge and groundwater replenishment. Poorly understood is how superficial geology can play a role in governing the spatiotemporal complexity in flow processes. We combine a new and unusually rich set of integrated surface water and groundwater observations from a catchment in semi-arid Australia with targeted geophysical characterisation of the subsurface to elucidate how configurations of superficial geology surrounding the stream control the variability in streamflow and groundwater responses. We show how periods of stable stream stage consistently follow episodic streamflow peaks before subsequent rapid recession and channel drying. The duration of the stable phases increases in duration downstream to a maximum of 44±3 days before reducing abruptly further downstream. The remarkable consistency in the flow duration of the stable flow periods, regardless of the size of the preceding streamflow peak, suggests a geological control. By integrating the surface water, groundwater and geological investigations, we developed a conceptual model that proposes two primary controls on this behaviour which influence the partitioning of runoff: (1) variations in the permeability contrast between recent channel alluvium and surrounding deposits, (2) the longitudinal variations in the volume of the recent channel alluvial storage. We hypothesise optimal combinations of these controls can create a ‘Goldilocks zone’ that maximises riparian water availability and potential for groundwater recharge in certain landscape settings and that these controls likely exist as a continuum in many dryland catchments globally.
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.
Time scale connection of groundwater with adjacent spheres	M	Taniguchi	Japan	2023	Anthropocene, Kumamoto, adjacent spheres, social revolution, time scale
Abstract Groundwater is connected with the earth’s interior, atmosphere, ocean sphere, and human sphere. Fluid, heat, and dissolved materials are crossed over the boundaries of adjacent spheres with different time scales in dynamics. These different time scales include event scales such as earthquakes and Tsunami, seasonal scales such as precipitation seasonality, a decade or longer scales such as climate change, and human scales such as groundwater pumping, land cover/use changes, and social revolutions such as industrialization, green revolution, urbanization, and globalization in Anthropocene. This study shows two examples of groundwater connected with different time scales. The first is thermal signals preserved in groundwater by earthquake, climate change, and anthropogenic impacts with different time scales. Thermal signals in groundwater from the Kumamoto earthquake in 2016 revealed evidence of fluid flow from the earth interior and Aso mountain. The thermal signal in groundwater in Kumamoto also showed the impacts of global warming and urbanization, as well as changes in precipitation and land use. The second example is the connectivity between residence time of groundwater and groundwater consumption in social revolutions such as industrialization and urbanization in the Anthropocene, as well as World War II as an example of groundwater for emergency situations.
Experiments of the artificial-recharge rate of sand and gravel aquifer through shallow recharge wells in the Chao Phraya River basin region	Kwankwai	Daranond	Thailand	2023	MAR, Managed aquifer recharge, clogging, recharge rate
Abstract The aquifers in the Chao Phraya River basin region were abundant in groundwater. Lately, the groundwater level has been declining due to agricultural activities. While in the wet season, these areas frequently suffered from flooding due to lower elevation than their surroundings. The Managed Aquifer Recharge (MAR) methods were applied to ease problems by constructing artificial recharge wells which can detain stormwater runoff and let it gradually infiltrate into the aquifer directly. For decades, the Department of Groundwater Resources started the MAR project to alleviate groundwater depletion and flooding over specific areas. However, most of the projects in the past lacked follow-up results and evaluation. Thus, later projects attempted to study recharge processes to evaluate the volume of recharged water through structures and calculate the infiltration rate through filter layers within the structures. Recently, the field experiments of artificial groundwater recharge were conducted as 8-hour and 20-day experiments with shallow recharge wells in the Chao Phraya River basin regions. These two types of experiments provided similar results. The average recharge rates of 8-hour and 20-day experiments are 2.22 m3/hr and 2.57 m3/hr, respectively. Recharge rates of each well were independently distinct depending on sedimentation characteristics, aquifer thickness, and volume of dry voids. During the test, the recharge well continuously encountered the problem of sediment clogging due to using untreated water from neighbouring streams and ponds. This clogging issue needed to be treated regularly to maintain the efficiency of the recharge well.
A non-anthropocentric perspective on groundwater quality and a proposed system for groundwater quality classification and regulation	Carin	Bosman	KZN	2023	Groundwater Quality, groundwater quality classification system, regulation, water quality standards
Abstract In many countries, groundwater quality is measured against drinking water limit values or standards. While that makes sense from a water supply perspective, it is not a scientifically correct yardstick to use to classify groundwater resources or even to determine whether groundwater has been “polluted”. Using this incorrect anthropocentric yardstick has led in some cases to legal action against industries, with significant liability implications, whilst the industry’s activities did not at all influence the quality of the groundwater but were reflecting the conditions under which the lithology of the aquifer was deposited. A case study in KZN demonstrating this will be discussed. We are, therefore, in a situation where regulatory decisions regarding groundwater quality and the regulation of the potential impact of human activities on groundwater systems are unfair, not scientifically credible, and not legitimate. This situation hampers the effective management and regulation of groundwater use and the prevention of detrimental impacts on groundwater, even saline groundwater systems. This paper argues that it is necessary to develop a groundwater quality classification system that will categorise aquifers based on their natural quality, not just from the perspective of their usefulness as a potable supply source but would recognise the important role that aquifers with more saline natural qualities play in maintaining ecosystems that require such salinity for its survival. It concludes by considering international approaches and proposing aspects to consider in developing such a system for groundwater regulation.
Making the Invisible Visible: Do Aquifers Have Agency?	Adrian	Healy	Wales	2023	agency, Groundwater, more-than-human, social, socio-hydrogeology
Abstract In the social sciences, there has been a ‘posthuman’ turn, which seeks to emphasise the role of non-human agents as co-determining social behaviours. In adopting a ‘more-than-human’ approach, the academy seeks to avoid claims of human exceptionalism and extend the social to other entities. In this paper, we explore the extent to which the more-than-human approach might be applied to groundwater and aquifers and the implications that this may have for groundwater science. The role of groundwater in complex adaptive socio-ecological systems at different scales is increasingly well-documented. Access to groundwater resources positively influences societal welfare and economic development opportunities, particularly in areas where surface waters are scarce. The potential adverse effects of human activities on the quantity or quality of groundwaters are also widely reported. Adopting a ‘properties’ approach, traditional social science perspectives typically describe aquifers as structuring the agency of human actors. To what extent might aquifers also have agency, exhibited in their capacity to act and exert power? Drawing on insights from 5 cities across sub-Saharan Africa, we argue for the agency of aquifers in light of their capacity to evoke change and response in human societies. In doing so, we draw on the concept of the more-than-human to argue for a more conscious consideration of the interaction between the human and non-human water worlds whilst acknowledging the critical role played by researchers in shaping these interactions.
Developing and testing a Groundwater Mapping methodology to increase drilling success rates for sustainable drinking water boreholes in African Arid and Semi-Arid Lands – the case study of Cunene Province, Angola	Daniela	Benedicto van Dalen	Angola	2023	Analytic Hierarchy Process, WASH program, groundwater mapping, remote sensing
Abstract In recent years, practical applications of vector and raster multi-layers overlay analysis to enhance outcomes of conventional hydrogeological methods for allocation of productive boreholes have been applied in arid and semi-arid lands and is currently being tested in Ethiopia, Kenya, Somalia and Angola in cooperation with UNICEF. Advanced Remote Sensing (RS) and Geographic Information Systems (GIS) techniques combined with traditional geological, hydrogeological and geophysical methods are being used for improved access to sustainable drinking water supply boreholes in the scope of a WASH program. Identifying suitable areas with a good potential for sustainable groundwater resources exploitation mainly depends on a) consistent/reliable aquifer recharge and b) favourable hydrogeological conditions for groundwater abstraction. Multi-layer analyses and attribution of layer scores to the hydrogeological information layers – aquifer recharge, aquifer class, lineaments, slope, land cover, and presence of streams – combine into a qualitative Groundwater Suitability Map, using pairwise comparison (weights) to determine their relative importance with the Analytic Hierarchy Process (AHP). Additionally, traditional field methods enhance the quality of outputs and delineate Target Areas for detailed investigations: validation of hydrogeological conceptual models, hydrogeological assessment, groundwater sampling and finally, geophysical methods. Downscaling the remote sensed information of the groundwater suitability map with field verifications is required to recommend borehole drilling sites. The engagement of stakeholders is vital for the data collection and validation of the weighting criteria analyses (AHP method), as well as for the cooperation on the ground, validation of the Target Areas selection and implementation.
Enhancing resilience to hydrological extremes in the Limpopo River Basin: a collaborative modelling approach	S	Mustafa	Limpopo	2023	opo River Basin, climate resilience, collaborative modelling approach, hydrological extremes and stakeholders workshops
Abstract The Limpopo River Basin (LRB) is highly vulnerable to recurrent floods and droughts, significantly threatening its water and food security. Sustainable groundwater management is necessary to improve resilience. Scientists and stakeholders must collaborate to evaluate management scenarios that can identify sustainable practices. A transboundary basin-scale management instrument was developed using a multisector collaborative modelling approach to identify the role of groundwater in building resilience. The approach used an integrated hydro(geo)logical model, co-created through stakeholder workshops. The model assessed management scenarios identified during a series of local, national and transboundary stakeholders workshops, focusing on improving groundwater storage during wet periods for use during dry periods in a context of population growth and increasing groundwater reliance across the basin. Management scenarios: (1) increasing groundwater abstraction; (2) deforestation; (3) afforestation; and (4) managed aquifer recharge (MAR) using injection wells capturing excess water from major dams, rainwater harvesting through local ponds/ wells, and small water reservoirs. Analysis of scenario outputs suggested that local groundwater storage techniques, especially water harvesting and storage through small-scale water well recharge, were the most effective strategy in reducing the risk and impact of floods and drought at the basin scale. Upscaling this strategy can significantly increase groundwater levels across the basin, supporting increasing groundwater reliance. The study showed that the multisector collaborative modelling approach effectively co-creates management strategies and identifies appropriate and inclusive strategies to improve resilience in data-limiting conditions. The proposed modelling outcomes are useful in making informed decisions regarding water management and transboundary cooperation in the LRB.
Groundwater for people and the environment: A globally threatened resource	H	Loaiciga		2023	Groundwater, groundwater sustainability, overdraft, population growth, recharge, safe yield
Abstract Groundwater is an essential source of water worldwide. The increased reliance on groundwater has caused the mining of many aquifers, a situation compounded by climate change, rising surface-air temperature, declining precipitation, and reduced groundwater recharge in many regions. The global annual intensity of groundwater use rose from 128 to 155 m3 per capita between 1950 (when the world population was 2.5 billion people) and 2021 (when the population was 7.9 billion people) and is herein projected to rise to 178 m3 per capita by 2050 as the world’s population is projected to increase (to 9.7 billion people by 2050) throughout the rest of the 21st century and beyond. This study projects a global annual groundwater depletion of 1,008 km3 by 2050, representing a 256% rise from the estimated 2010 depletion. This projection is most likely a lower bound of the actual groundwater depletion that would be realized considering environmental flows, historical trends of global economic growth, and climate-change impacts, thus being a harbinger of rising environmental degradation (e.g., land subsidence, seawater intrusion, streamflow reduction, aridification). Measures to achieve groundwater sustainability are herein identified.
Numerical groundwater modelling of the Windhoek Aquifer (Namibia) for wellfield management	Jannie	Weitz	South Africa	2023	MODFLOW, Windhoek Aquifer, numerical groundwater modelling
Abstract The City of Windhoek in Namibia has developed wellfields and a managed aquifer recharge scheme within the fractured Windhoek Aquifer to ensure a sustainable potable water supply to the city during drought. A three-dimensional numerical groundwater model of the aquifer was developed using the finite-difference code MODFLOW to determine the potential impacts of varying pump inlet depth elevations and varying production borehole abstraction rates for optimal wellfield and aquifer management. The initial steady-state numerical model was calibrated to September 2011 groundwater levels, representing the best approximation of “aquifer full” conditions (following a good rainfall period and best available data). The subsequent transient numerical model was calibrated against groundwater level fluctuations from September 2011 to August 2019, the period after steady-state calibration for which data was available (and during which monitored groundwater abstraction occurred). The calibrated transient model was used to run various predictive scenarios related to increased emergency groundwater abstraction and estimate potential impacts on the Windhoek Aquifer. These predictive scenarios assessed groundwater level drawdown and recovery, aquifer storage potential, and potential abstraction rates under different pump elevations. Model results indicated a sharp initial groundwater level drop followed by a gradual decrease as groundwater levels approached the 100 m saturated depth mark. Pumping elevations were subsequently updated with recommended abstraction rates and volumes for the entire Windhoek Aquifer. The numerical groundwater model, in association with extensive groundwater monitoring, will be used to assess/manage the long-term sustainable and optimal utilisation of the Windhoek Aquifer.
Protecting groundwater resources in an era of geological carbon sequestration: A fractional stochastic model to predict pressure buildup due to CO2 injection into a saline aquife	H	Mbah	National	2023	Carbon Capture and Storage, CCS, CCS fractional operator, geological heterogeneity., injectivity, pressure buildup, saline aquifer
Abstract Carbon Capture and Storage (CCS) in deep saline aquifers is a viable option for Green House Gas (GHG) mitigation. However, industrial-scale scenarios may induce large-scale reservoir pressurization and displacement of native fluids. Especially in closed systems, the pressure buildup can quickly elevate beyond the reservoir fracture threshold and potentially fracture/ reactivate existing faults on the cap rock. This can create pathways, which could act as conduits for focused leakage of brine and/or CO2 up-dip and mobilization of trace elements into capture zones of freshwater wells. Careful pressure management can ensure the reservoir’s hydraulic integrity. This can theoretically be achieved through simulation with appropriate mathematical tools. This research aims to quantify pressure buildup at a CO2 injection well by applying fractional derivatives to the pressure diffusivity Differential Equation (PDE). A numerical solution has been developed to (1) predict and assess the consequence of pressure buildup within the storage formation on groundwater flow in shallow aquifers and (2) assess the impact of pressure-mobilized contaminants (CO2 , brine and/or trace elements) on the quality of usable groundwater, if there is a leakage. The efficiency of each derivative is shown to depend on the type of reservoir heterogeneity. The Caputo derivative captured the long tail dependence characteristic of fracture flow, while the ABC derivative was able to model the cross-over from matric into the fracture flow. The numerical tools presented here are useful for successful risk assessments during geo-sequestration in basins with freshwater aquifers.
Assessing the hydrogeology of springs, Heuningnes catchment, South Africa	Paula	Finini	Bellville, South Africa	2023	Spring yield, conceptual model, confirmatory analysis, volumetric analysis
Abstract Springs are examples of groundwater discharges. This paper reports on findings from cold springs groundwater discharges that have served as important water sources for sustaining domestic and agricultural supply. This study assessed the hydrogeology of springs to inform practical measures for the protection, utilization, and governance of such discharges. The research assessed the hydrogeology of springs in terms of conditions in the subsurface responsible for occurrences of springs spatially and their flow paths to the surface. Spring locations were mapped and validated for spatiotemporal assessment. The study examined the flow dynamics and hydrogeochemistry of spring discharges. In-situ and laboratory measurements of spring discharges were carried out using standard methods. Results showed that shallow and deep circulating systems of springs existed in the study area, being controlled by lithology and faults. All springs had fresh water of Na-Cl type, and rock-water interaction was the dominant geochemical process that influenced spring water chemistry. Radon-222 analysis showed high values detected in spring waters that confirmed recent groundwater seepage on the surface. The drum-and-stopwatch technique was used to estimate yield from spring discharges because it’s only effective and reliable for yields of less than 2 l/s. Results suggest that some springs were locally recharged with some regionally recharged. Based on results from estimated yield and quality, it was concluded that spring waters had low discharges. A comprehensive assessment of spring discharges should be conducted to generate large datasets to inform practical measures for protection, utilization, and governance.
Literature review on methodologies used to assess surface water and groundwater interaction	Aashna	Bissoon	South Africa	2023	Groundwater, case studies, methodologies, surface water, sustainable
Abstract A major surface water–groundwater interaction difficulty is the complex nature of groundwater resources due to heterogenic aquifer parameters. Wholistic research is needed to inform the conceptual understanding of hydrological processes occurring at surface and groundwater interfaces and their interactions at watershed scales. Sustainable water resource use and protection depend on integrated management solutions involving cross-disciplinary studies and integrated hydrological modelling. Choosing appropriate methods such as spatial and temporal scales, measurable indicators, differences in software parameters, and limitations in application often results in uncertainties. The study aims to conduct a comparative literature analysis, integrating case studies focusing on surface water–groundwater interaction. Literature reviews from case studies focus on several factors, including soils and vegetation studies, hydrochemical signatures, hydrodynamics of the main stem channels, desktop land use assessments, surface water quality profiling, conceptual hydrogeological modelling and numerical modelling in support of understanding surface water – groundwater interaction and highlight the challenges of methods used to indicate baseflow transition. This paper considers the methodologies demonstrated in the literature and their use in numerical modelling to obtain measurable indicators related to the two hydrological disciplines comprising (i) the surface water component and (ii) the groundwater component. These outcomes should be used to inform the potential future impacts on water quality from activities such as mining, irrigation, and industrial development. Water management protocols related to integrated surface water and groundwater studies for the future are critical in ensuring sustainable water management methods on a catchment scale.
Improving groundwater dynamics: A key factor for successful tidal marsh restoration.	N	Van Putte	Belgium	2023	HYDRUS, groundwater dynamics, macroporosity, tidal marsh restoration, water quality improvement
Abstract Along estuaries and coasts, tidal wetlands are increasingly restored on formerly embanked agricultural land to regain the ecosystem services provided by tidal marshes. One of these ecosystem services is the contribution to estuarine water quality improvement, mediated by tidally induced shallow groundwater dynamics from and to tidal creeks. However, in restored tidal marshes, these groundwater dynamics are often limited by compacted subsoil resulting from the former agricultural land use in these areas. Where the soil is compacted, we found a significant reduction of micro- and macroporosity and hydraulic conductivity. To quantify the effect of soil compaction on groundwater dynamics, we set up a numerical model for variably saturated groundwater flow and transport in a marsh and creek cross-section, which was parametrized with lab and field measurements. Simulated results were in good agreement with in situ measured groundwater levels. Where a compacted subsoil is present (at 60 cm depth), 6 times less groundwater and solutes seep out of the marsh soil each tide, compared to a reference situation without a compact layer. Increasing the creek density (e.g., through creek excavation) and increasing the soil porosity (e.g., by organic soil amendments) resulted in a significant increase in soil aeration depth and groundwater and solute transport. As such, these design measures are advised to optimize the contribution to water quality in future tidal marsh restoration projects.
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.
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.
Governing groundwater in city regions: Water metabolism and actor networks in the cases of Cape Town and Nelson Mandela Bay	A	Taylor	Cape Town	2023	actor networks, drought risk, multi-level governance, urban metabolism
Abstract Groundwater is increasingly being exploited in South African cities as a drought crisis response, yet there is poorly coordinated regulation of increasing urban users and usage and fragmented management of aquifers. Designing interventions and innovations that ensure sustainable management of these resources requires systems thinking, where the city is understood as an integrated, interdependent set of actors and flows of water. This paper presents a study that applied and integrated an urban water metabolism (UWM) analysis with a governance network analysis for two major South African cities facing severe drought risk, Cape Town and Nelson Mandela Bay. ‘Learning Laboratories’ in each city brought together stakeholders from various groundwater-related domains to build a shared understanding of how groundwater fits into the larger system and how various actors shape urban groundwater flows and the health of local aquifers. The UWM quantified all hydrological and anthropogenic flows into and out of each city (or urban system) to conduct an integrated mass balance. How this mass balance changes under varying climate change scenarios and land use was used as a focal point of stakeholder discussions. The governance network analysis highlighted that many state and non-state actors have a stake in shaping the quantity and quality of urban groundwater, such as regulators, service providers, water users, knowledge providers, investors in infrastructure, and emergency responders.
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.
Integrated Modeling to Simulate Groundwater and Surface Water Interaction in the Letaba River Catchment, Limpopo Province, South Africa	Masilo	Mohale	South Africa	2023	Catchment., Groundwater, HydroGeoSphere, interaction, surface water
Abstract The current study investigates the spatial patterns and temporal dynamics of the groundwater and surface water interactions for integrated water resource management practices. This follows the results of the groundwater flow conceptual and numerical models developed for the Middle Letaba sub-catchment, indicating that groundwater and surface water interactions play a fundamental role in determining the hydrological water balance. The study area is an example of a fully allocated surface water resource in the northeastern part of South Africa, extensively developed for domestic use and agricultural farming. As a result of the semi-arid nature of the climate, limited surface water resources and increasing water demand, the situation has contributed to groundwater as the only dependable source of water supply for various uses. However, in the last few decades, periodic water level measurements in several boreholes indicated a continuous drop in the piezometric surface over time. This study utilised HydroGeoSphere to simulate water flow processes in a fully integrated and physically based model. The results of the steady-state groundwater flow simulation indicated that recharge from the rainfall and river leakages are the most important components of the inflows that control the availability of groundwater. Water resources management scenarios suggest a continuous decline in water level, which strongly influences the groundwater flow dynamics and future availability of fresh water. Regular monitoring and management of groundwater level and abstraction are required to avoid overexploitation and possible groundwater contamination due to the strong interaction between surface water and groundwater.
Study on the Relationship between Water Quality and Wetland Plant Community in Huixian Karst Wetland	L	Shen		2023	Huixian Karst Wetland, Water quality, Wetland Plant Community
Abstract Huixian Karst National Wetland Park is the most typical karst wetland in the middle and low latitudes of the world and has become an internationally important wetland. The relationship between water quality and aquatic organisms in Huixian Wetland is a hot research topic in wetland ecology. This article focuses on the relationship between the current water quality situation in Guilin Huixian Karst Wetland and the growth of wetland plants. Sixteen sampling points are set up in the wetland to monitor and analyze water quality in wet, normal, and dry seasons. The Kriging index interpolation method is used to obtain a comprehensive water quality interpolation map in the survey area during normal water periods and in combination with the wetland plant survey sample data and the landscape status. A comprehensive analysis of the relationship between wetland plant growth and water quality. The results show that the centre of Huixian Wetland receives recharge from surrounding groundwater, which is greatly affected by the surrounding water quality. The comprehensive water quality is relatively good in the dry season, relatively poor in the normal season, and the worst in the wet season. Agricultural production, non-point source pollution, rural domestic sewage, and human interference affect wetland water quality, which directly affects the structure and function of plant communities and the ecological service function of wetlands.