Hydrogeological Conceptual Model Research Articles

Contributions to the conceptual hydrogeological model of the Quequén Grande River Basin at its southwestern limit

La Cuenca del Río Quequén Grande es una de las más extensas y productivas del sudeste bonaerense. Sus nacientes se encuentran ubicadas en las serranías de Tandilia, que constituyen el área de recarga preferencial del acuífero Pampeano en la región. Este acuífero, somero y de tipo libre, presenta injerencia sobre cursos de agua de carácter efluente. En su límite suroccidental, su morfología se presenta fuertemente asimétrica y destaca la presencia de numerosos humedales. Este fenómeno es asociado a rocas paleozoicas que afloran saltuariamente y constituyen lo que se ha considerado como el basamento hidrogeológico del acuífero Pampeano. Desde el punto de vista geoquímico, en esta zona se diferencian dos tipos de laguna relacionados con su contenido en cloruros, pudiendo relacionarse el grupo de alto contenido en este anión con flujos regionales ascendentes. El objetivo del presente trabajo consiste en aportar nueva información al modelo hidrogeológico conceptual que se tiene para la zona mediante el análisis de captaciones de agua superficial y subterránea. El mapa piezométrico reveló dos direcciones preferenciales en el flujo subterráneo. En el análisis fisicoquímico se observó que la mayoría de las muestras de agua subterránea presenta una composición bicarbonatada sódico-magnésica. Por otro lado, las muestras de agua obtenidas de lagunas presentaron una composición bicarbonatada sódica, distinguiéndose un grupo principal con mayor contenido en cloruros. La correlación entre las desviaciones isotópicas de ambos tipos de muestras sugiere la presencia de recarga de algunas lagunas procedente de las zonas de recarga regional en el sistema serrano de Tandilia.

Recharge área maps from precipitation isoscapes. Case study: Aburrá Valley, Colombia

The environmental isotopes are a tool for interpreting the hydrological processes related to underground environments. These are used for the validation of hydrogeological models, in terms of recharge, transit and discharge zones, as well as the identification of groundwater interactions with other water bodies and groundwater residence time in the hydrogeological units. The determination of the recharge processes have usually been validated from knowledge about the stable isotopes present in the water molecule (18O and 2H). At the regional level, this evaluation has been addressed through the construction of isoscapes combined with an understanding of the hydrological characteristics present in the study area and knowledge of conceptual hydrogeological models. The objective of this study is to apply a scheme for the analysis of potential groundwater recharge zones, from 18O and 2H spatial variability in precipitation, baseflow and groundwater, using spatial modelling tools. Based on a preliminary work done for the Antioquia department, a strategic area was chosen in which the results are more forceful and have greater implications in groundwater management: the Aburrá Valley-Colombia.

Distribution maps of stable isotopes in the Pampean aquifer in the Southeast of Buenos Aires province (Argentina)

The relatively recently developed isotopic maps (isoscapes) are used to visualize large-scale and spatiotemporal distributions of stable isotope ratios in various environmental matrices or reservoirs such as rainfall, tap water, oceans, rocks, plants and animals. In this context the International Atomic Energy Agency (IAEA) financed the project “Groundwater recharge processes inferred from isoscapes in the Buenos Aires Province, Argentina”. In the development of this research project, groundwater isoscapes in the southeast of Buenos Aires province were carried out, considering 787 groundwater sampling sites. In the generation of these maps, geostatistical techniques have been used in order to establish patterns of spatial self-correlation. The models obtained were tested using leave-one-out cross-validation. The results obtained are being integrated into the conceptual hydrogeological model of the region, generating tools that contribute to the management of surface and ground water resources. Additionally, it is expected that the results of this study will serve as an input in different research areas that use water traceability to study different environmental processes in the region.

The IWAVE Project in Latin America in support of SDG 6: secure water for all in a sustainable way

The IWAVE methodology of the International Atomic Energy Agency (IAEA) to improve water availability and sustainability through comprehensive assessments of national water resources proposes to strengthen national capacities to collect, manage and interpret hydrological data and the use of advanced tools and techniques to improve the management of water resources. The IAEA carried out in Latin America the Project ARCAL RLA 7018 (2014-2017) “Improvement of knowledge of groundwater resources to contribute to its protection, integrated management and governance” using IWAVE. Based on the favourable results, the IAEA launched the second phase of IWAVE in the region, Project RLA 7024 (2018-2021) “Integration of isotope hydrology in national assessments of water resources”. The main results include: a) knowledge for decision-makers on the importance of sound hydrological information to improve the management of water resources; b) the establishment of isotope monitoring networks and the use of isotopic tools to improve conceptual hydrogeological models; c) the development of scenarios of climate change and their impact on water resources; d) new national hydrological databases; and e) the development/implementation of National Water agendas. Both projects have linked hydrological data with decision-making in support of the sustainable development goal (SDG) 6 “Safe water for all in a sustainable way”, in particular with SDG 6.5, which focuses on integrated water resource management.

The role of superficial geology in controlling groundwater recharge in the weathered crystalline basement of semi-arid Tanzania

Study regionLittle Kinyasungwe River Catchment, central semi-arid Tanzania. Study focusThe structure and hydraulic properties of superficial geology can play a crucial role in controlling groundwater recharge in drylands. However, the pathways by which groundwater recharge occurs and their sensitivity to environmental change remain poorly resolved. Geophysical surveys using Electrical Resistivity Tomography (ERT) were conducted in the study region and used to delineate shallow subsurface stratigraphy in conjunction with borehole logs. Based on these results, a series of local-scale conceptual hydrogeological models was produced and collated to generate a 3D conceptual model of groundwater recharge to the wellfield. New hydrological insights for the regionWe propose that configurations of superficial geology control groundwater recharge in dryland settings as follows: 1) superficial sand deposits act as collectors and stores that slowly feed recharge into zones of active faulting; 2) these fault zones provide permeable pathways enabling greater recharge to occur; 3) ‘windows’ within layers of smectitic clay that underlie ephemeral streams may provide pathways for focused recharge via transmission losses; and 4) overbank flooding during high intensity precipitation events increases the probability of activating such permeable pathways. These conceptual models provide a physical basis to improve numerical models of groundwater recharge in drylands, and a conceptual framework to evaluate strategies (e.g., Managed Aquifer Recharge) to artificially enhance the availability of groundwater resources in these regions.

Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain)

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m3/day.

First conceptual hydrogeological model of two intermountain Andean basins based on isotopes and hydrochemistry

ABSTRACT Mountains arid environments are vulnerable under climate change scenarios. Variations in the recharge sources and the rising temperature can affect the water availability, threaten the socio-productive systems on local and regional scales. In this sense, two hydrological systems were studied in the Andes Range, Argentina, by hydrochemical and isotope techniques, with the purpose to understand the origin of water, the groundwater recharge, and to conceptualize the groundwater flow system. In the two sampling periods (winter and summer seasons) most of the waters were characterized by low mineralization and a HCO3-Ca type. The isotopic composition showed wide ranges of variation consistent with the altitudinal differences existing in the study systems. However, no significant isotope changes were observed between the samples collected in winter and summer periods. Therefore, little influence of liquid precipitation is inferred in the recharge source of both hydrological systems. This means that the western sector of the valley, where the ice bodies and permafrost are located, is the main recharge area for groundwater of both basins. This confirms the former hypothesis used for the hydrogeochemical conceptual model proposed, and highlights the importance of protecting these environments to ensure the provision of water in arid lands.

NECoM (Numerically Enhanced COnceptual Modelling) of two small Maltese Aquifers: Mizieb and Pwales

Two small Maltese aquifers, Mizieb and Pwales, were numerically analyzed to test the existing hydrogeological conceptual model and suggest optimized groundwater monitoring strategies in support of the forthcoming monitoring network coordinated by the Government of Malta through the Energy and Water Agency. The model will undergo further revision of the concepts on which it is based as soon as new data is available, considering the conceptual and numerical model development as parallel activities, rather than as sequential. The model structure and parameter estimation made use of qualitative information and data acquired by archive research; during model calibration information/assumptions were introduced as “prior information” while the available measurements were introduced as classical “observations” with proper associated weight. The information content of both qualitative and quantitative data could be assimilated along the calibration process, highlighting the uncertainties and open questions that remain because of data insufficiency.

Fractured carbonate aquifers of Sibillini Mts. (Central Italy)

ABSTRACT The aim of the present map is to illustrate a detailed pre-earthquake hydrogeological conceptual model of the Sibillini Mts. This area was struck by a prolonged seismic sequence of up to Mw 6.5 in 2016. Geological, tectonic, and hydrogeological data were collected from the literature before 2016, subsequently standardized and re-interpretated with the aim of presenting a hydrogeological map (1:50,000 scale) of the Sibillini Mts. carbonate system (Central Italy). The map is supported by 11 hydrogeological both cross and longitudinal sections, which show the underground spatial relationship between aquifers, aquicludes, and tectonic elements. This Map provides a model of comparison for the new hydrogeological conditions emerging from the post-seismic research.

Combining continuous monitoring and High-Precision altitude measurements in forensic groundwater surveys: a case study of chlorinated solvent pollution in an urban context

This paper describes a forensic investigation of groundwater in an urban context in Italy. The present case study was conducted to detect the hydraulic flow path between a sportfishing pond and a nearby industrial plant’s contaminated groundwater site. The investigation was performed to evaluate the potential for diffusion of contaminants through groundwater flow into a fishing pond located downstream from a chemical factory. High-precision altitude measurements of monitoring stations combined with continuous water level monitoring were crucial to understand the groundwater flow dynamics and define the hydrogeological conceptual model. The study verified that the fishing pond, dug in low-permeability volcanic rock, was not hydraulically connected to the groundwater flow. The presence of contaminants in the pond may be related to the periodic topping-up activity performed using water from an existing well. The identified groundwater flow paths were consistent with the possible contaminant migration from the chemical factory to the water well near the fishing pond.

Hydrochemical and Isotopic Characterization of the Waters of the Manglaralto River Basin (Ecuador) to Contribute to the Management of the Coastal Aquifer

Coastal aquifers are strategic and fundamental in the development of touristic areas. The coastal aquifer within the Manglaralto River Basin in Ecuador is essential, as it is the only source of water supply for a large part of the northern part of the Santa Elena province. It is a semi-arid region where high volumes of water are pumped from the aquifer, causing a significant drawdown of groundwater levels, thus affecting the water quality. This work aims to characterize the characteristics of groundwater in the coastal aquifer using hydrochemistry and stable isotopes to propose a hydrogeological conceptual model. The methodology for determining the chemical and isotopic characteristics of groundwater follows the following scheme: (i) studies of ionic concentrations using the Piper diagram, (ii) assessment of the origin of salinity through the Cl/Br ratio, the presence of seawater intrusion through the Hydrochemical Facies Evolution Diagram HFE-D, (iii) characterization of precipitation events using stable isotopes (18O and 2H), and, (iv) development of a hydrogeological conceptual model of the study area. The results indicate that in the basin there are mixing processes of the existing water in the aquifer with recharge water, direct cation exchange processes in the freshening process during recharge, and evaporation in the unsaturated zone. A conceptual model of the flow system in the basin is built, based on the mentioned processes. The main conclusions are: seawater intrusion is present in the areas of the wells located closest to the coast, urban activity through septic tanks is affecting the quality of the aquifer, and rainfall is highly relevant in the different hydrochemical and isotopic processes that operate in the basin.

Deciphering groundwater flow-paths in fault-controlled semiarid mountain front zones (Central Chile)

The Mountain-Block Recharge (MBR), also referred to as the hidden recharge, consists of groundwater inflows from the mountain block into adjacent alluvial aquifers. This is a significant recharge process in arid environments, but frequently discarded since it is imperceptible from the ground surface. In fault-controlled Mountain Front Zones (MFZs), the hydrogeological limit between the mountain-block and adjacent alluvial basins is complex and, consequently, the groundwater flow-paths reflect that setting. To cope with the typical low density of boreholes in MFZs hindering a proper assessment of MBR, a combined geoelectrical-gravity approach was proposed to decipher groundwater flow-paths in fault-controlled MFZs. The study took place in the semiarid Western Andean Front separating the Central Depression from the Principal Cordillera at the Aconcagua Basin (Central Chile). Our results, corroborated by field observations and compared with worldwide literature, indicate that: (i) The limit between the two domains consists of N-S-oriented faults with clay-rich core (several tens of meters width low electrical-resistivity subvertical bands) that impede the diffuse MBR. The “hidden recharge” along the Western Andean Front occurs through (ii) focused MBR processes by (ii.a) open and discrete basement faults (mass defect and springs) oblique to the MFZ that cross-cut the N-S-oriented faults, and (ii.b) high-hydraulic transmissivity alluvial corridors in canyons. Alluvial corridors host narrow unconfined mountain aquifers, which are recharged by indirect infiltration along ephemeral streams and focused inflows from oblique basement faults. This study also revealed seepage from irrigation canals highlighting their key role in the recharge of alluvial aquifers in the Central Depression. The proposed combined geophysical approach successfully incorporated (hydro)geological features and geophysical forward/inverse modelling into a robust hydrogeological conceptual model to decipher groundwater flow-paths in fault-controlled MFZs, even in the absence of direct observation points.

Development of a Hydrogeological Conceptual Model of the Varaždin Alluvial Aquifer

The Varaždin aquifer represents the main source of water for public supply, agricultural, and industrial purposes in the Varaždin County in NW Croatia. In the last decades, this area has experienced contamination of groundwater with nitrates. This study describes the conceptualization of the Varaždin aquifer for the purpose of developing numerical model of groundwater flow and nitrate transport. Within the study, three important elements are defined: aquifer geometry, recharge from precipitation, and other boundary conditions. 3D aquifer model revealed that Varaždin aquifer consist of three layers: upper aquifer, semipermeable interlayer, and lower aquifer. The Wetspass-M model was used for the assessment of spatial and temporal distribution of water balance components for the period 2008–2017. Results of the model indicate that the average annual precipitation is distributed as 34% groundwater recharge, 21% surface runoff, and 45% actual evapotranspiration. The maps of equipotential lines show the behavior of the aquifer system and define boundary conditions, i.e., recharge and discharge areas of the aquifer: an inflow boundary from Drava River and accumulation lake Varaždin on the northwest and north, no flow boundary on the west and south, and an outflow boundary on the east.

Hydrogeological controls on the flow regime of an ephemeral temperate stream flowing across an alluvial fan

Alluvial fans often support ephemeral streams whose flow regimes and sediment dynamics are strongly controlled by fan sedimentary characteristics and interactions with shallow groundwater aquifers. The hydrogeology of such fans has most often been documented for large fans located within arid climate zones. This research focuses on a small (0.075 km2) alluvial fan situated in a temperate, high rainfall climate (the Lake District, North West England). An ephemeral stream flowing across this alluvial fan plays a key role in supplying water and sediment to the River Ehen, which is the focus of a habitat restoration initiative. This study combines high spatial resolution, near surface geophysics and outcrop data with hydrological data to characterise the hydrogeological properties of the alluvial fan. A conceptual hydrogeological model was developed to understand the hydrology across the alluvial fan and how that affects water and sediment supply to the River Ehen. The alluvial fan is composed predominantly of permeable debris flow deposits and numerous palaeochannels which may provide preferential groundwater flow paths. During streamflows, partial to full stream-aquifer connectivity occurs, especially in the distal fan where groundwater discharges back into the stream. Streamflows occur when the fan apex infiltration rate/capacity threshold of approx. 60 l/s−1 is exceeded, typically following rainfall events >9–11 mm. Understanding interactions between ephemeral streams and their underlying aquifers enables better predictions of the timing and magnitude of future flows, and in-turn, their likely impacts on the water courses into which they discharge.

Fresh groundwater lens dynamics of a small bedrock island in the tropics, Northern Australia

Fresh groundwater lens dynamics and transition zone geometries on small tropical islands have been investigated in a wide range of geological environments. However, the understanding of multi-aquifer fractured bedrock systems and how they respond to episodic wet season rainfall recharge is still limited. This study used a comprehensive suite of isotopic tracers, hydrogeological and near-surface geophysical methods to characterise the multi-layer aquifer system on Milingimbi, a small bedrock island located in the tropics of the Arafura Sea, Northern Australia. Near-surface geophysics was used to determine the subsurface structure of the aquifer, including the spatial extent and thickness of the fresh groundwater lens and the shape of the transition zone. Pore water chloride profiles, hydrochemistry, and δ18O and δ2H data supported the geophysics results. The lens was found to be 40 m thick on average, with an up to 70 m thick transition zone underneath. Water level time series data over 4 years showed that there was a strong tidal signal observed in the groundwater wells screened in the deeper aquifer and that the aquifer system showed a dynamic response to the wet season rainfall. Time series chloride and δ18O and δ2H rainfall and production bore data suggest that there was a freshening (i.e. lower salinity input) of the lens as a result of recharge during the wet season, which occurs up to 6 months after the event. Groundwater residence time indicators showed that the mean residence time in the lens was at least 25 years and the rate of recharge to the system was up to 200 mm y−1. The comprehensive data set, which is rather unique in its wide range of methods that were applied, resulted in a hydrogeological conceptual model of the multi-layer bedrock aquifer system of the island that also provides insight into the fresh groundwater lens and the transition zone geometry of similar island aquifer systems.

Multiproxy approach to urban geology of the historical center of Naples, Italy

The complex urban geology of the historic center of Naples is characterized by the emplacement of products from two adjoining volcanic areas that were reworked by alluvial and coastal processes. To expand the geologic knowledge of this densely populated area, multidisciplinary research was carried out on the recently drilled San Marcellino borehole, as part of a larger borehole collection project. Critical revision of 290 previously drilled sequences, and a complete set of tephrostratigraphic, sedimentologic, and paleoecologic data obtained on the San Marcellino stratigraphy, informed a hydrogeological conceptual model of water circulation and paleoenvironmental reconstruction of the city historic center. Both before and after the Neapolitan Yellow Tuff eruption, ca. 15 ka, the landscape was characterized by a marine to transitional paleoenvironment. This signifies a good balance between sea-level rise and volcaniclastic inputs, consisting of both primary and remobilized deposits in an area that is also subject to bradyseismic oscillations. Amongst the primary pyroclastic deposits, the products of an explosive event from Campi Flegrei about 16 ka, with an eastward-directed sustained-column phase, were recognized. Collectively, the multidisciplinary data obtained in this study favor the presence of a double-aquifer conceptual model, characterized by a volcanic and a marine-sedimentary aquifer.

Hydrogeological compartmentalization and connection of the Guarani (GAS) and Serra Geral (SGAS) aquifer systems from a multiscale perspective: a case study in southern Brazil

The Guarani (GAS) and Serra Geral (SGAS) aquifer systems are the main groundwater sources in southern Brazil. We investigated the crucial relationship between the primary, intergranular pore system in the GAS and the secondary pore system associated with fractures in the SGAS in order to understand better the compartmentalization and connection, water storage, and productivity of both aquifers. Data from 375 wells that produce from both aquifers was used to evaluate the hydrodynamic characteristics of the GAS-SGAS contact. The integration of data using remote sensing, structural data, and thin section analysis support interpretations about the compartmentalization and potential connection of the aquifers. Fault zones trending NW, EW, and NNE demarcate six structural blocks in which the GAS-SGAS contact varies more than 400 m in elevation. Thin section analysis of sandstone texture and composition allowed us to determine the relationship between the type of porosity and cement type and content. The surface demarcating the Guarani-Serra Geral contact is highly productive in 93% of the wells that reach both aquifers. The integration of our results allowed us to propose a conceptual hydrogeological model for the GAS and SGAS aquifers in the study area.

Understanding and conceptualization of the hydrogeology and groundwater flow dynamics of the Nyando River Basin in Western Kenya

Study regionThe Nyando River basin in western Kenya. It is part of the Lake Victoria basin. Study focusAs a first step towards numerical modeling, complementary datasets from different periods have been used to develop a conceptual hydrogeological model for this geologically complex basin. The study focused on characterizing the physical and process structures. Data from geological reports and geo-electrical survey reports were used to establish aquifer extents. Timeline comparison and interpolation of groundwater levels and hydrochemical data analysis were used to define groundwater flow characteristics. New hydrological insights for the regionA highland and a Kano Plains groundwater system exist and are separated by the faults at the Nandi and Kendu escarpments. The groundwater divide between Nyando and Nyamasaria Rivers flowing through the Kano Plains is indistinct, suggesting that their lowland groundwater system is the same. Kano Plains has a shallow and deep groundwater system, both occurring in highly heterogeneous and aquifers; the bedrock here occurs at >250 m below ground level. Generally, the groundwater flow is topography driven towards Lake Victoria, but it is not clear whether it discharges here. Rainfall has minimal effect on long-term groundwater variability. Because groundwater levels do not change significantly over time, steady-state groundwater flow occurs in the plains.

Using a multi-disciplinary approach to characterize groundwater systems in arid and semi-arid environments: The case of Biskra and Batna regions (NE Algeria)

This study presents a multi-disciplinary approach for the hydrogeological assessment and characterization of water resources in typical arid and semi-arid areas with high anthropogenic pressure, and where environmental conditions and political context prevent extensive field surveys. The use of a three-dimensional (3D) hydrogeological conceptual model, integrating hydrochemical and multi-isotope data, is proposed for the Batna and Biskra area (NE Algeria).Geological data were assembled in 3D geological software, from which a 3D hydrogeological conceptual model was constructed, which included the delineation of groundwater flow directions. The isotopic characterization, including deuterium and oxygen isotopic composition of water (δ2H and δ18O), and tritium (3H), provided information regarding recharge sources, flow pathways and residence times of groundwaters. Hydrochemical parameters, measured on the same samples, supported the interpretation of isotope data. All data were processed in a geographic information system (GIS) environment. The effectiveness of this approach was tested on a complex system of aquifers with high hydrogeological heterogeneity. Results show the important role the tectonic setting of an area can play in the hydrogeology and hydrochemistry of its principal groundwater systems. The fault network in the study region connects different aquifers, resulting in the mixing of groundwaters. The region most influenced by geological structures is the southern part of the study area, close to Biskra city. In fact, besides a limited contribution of recharge from rain and surface water derived from flood events, the recharge of the Cenozoic aquifers seems to proceed from the ascension of deeper Cretaceous groundwaters through the fault network, as indicated by temperature, bulk chemistry and in particular δ2H, δ18O and 3H results. In contrast, results suggest that the recharge of the low mineralized Maastrichtian waters is primarily influenced by local precipitation and runoff in the mountainous northern part of the study area. Tritium content, low salinity, and bulk chemistry all suggest such waters to be a mix of pre-bomb (deeper flow-lines within the aquifer) and recent water, with no contribution from the deepest Continental Intercalaire groundwaters.The proposed approach reduces ambiguity about the studied aquifer systems, greatly improves the conceptual understanding of their behaviour, and could provide insights into the vulnerability of the aquifers to different anthropogenic pollution phenomena. The methodology used appears to be a valid tool that could be applied to other geographical areas, to inform the design and implementation of efficient management strategies aimed at improving the quality and availability of water resources. Moreover, three-dimensional modelling methods are becoming increasingly applied to different aspects of groundwater management, to obtain a detailed picture of subsurface conditions.

Three-dimensional hydrostratigraphical modelling supporting the evaluation of fluoride enrichment in groundwater: Lakes basin (Central Ethiopia)

Study regionThe Lakes Basin is located in the Main Ethiopian Rift. It covers the northern part of the rift valley basin, the Upper Awash River basin, and some sub-basins from the Omo River basin. Due to the presence of high fluoride (F−) content, natural contamination of groundwater has long been recognized as a water-related health issue in the area. Study focusA multidisciplinary research effort, including geological, hydrogeological, hydro-chemical, and geophysical investigations, was adopted to understand the 3D hydrogeological conceptual model and to evaluate F− enrichment in groundwater. New hydrological insights for the regionThe 3D hydrogeological conceptual model shows a complex hydrogeological environment and a clear hydraulic interconnection between different aquifers. The geological setting has deeply influenced the geometry of the aquifers, recharge and discharge areas, and F− enrichment in groundwater. Two hydrogeological units, namely sedimentary and volcanic multi-aquifers, were identified. The analyses of groundwater circulation, flow paths, and distribution of F- concentrations in each aquifer were conducted. In groundwater, the concentration of fluoride varies from 0.1 to 68.9 mg L−1; in surface water, it ranges from 0.6 to 244.2 mg L−1. Fluoride concentration of 62 % of the water samples analyzed exceeded the 1.5 mg L−1 WHO threshold for fluoride concentration in drinking water. The proposed methodological approach has been demonstrated to be a powerful tool that could be applied in other similar areas.