Main Aquifer Research Articles

Neutralisation of Acid Rock Drainage by Youngest Toba Tuff Leachate Revealed by Hydrogeochemistry

ABSTRACTThe Youngest Toba Tuff (YTT) supervolcanic eruption occurred 75000 years ago, and resulted in distinctive ash fall deposition in different locations encompassing marine, estuarine, lacustrine, and fluvial sedimentary basins. Of the different sedimentary basins, the YTT crypto‐tephra horizon preserved in the South Kerala Sedimentary Basin (SKSB) of the western coast of India is hosted by a paleo‐estuarine carbonaceous clay layer. Along the eastern margin of SKSB, confined aquifers hosting highly acidic groundwater is associated with this YTT ash and associated organic matter (OM)‐rich carbonaceous clay layer, creating worse acid rock drainage (ARD), which eventually gets neutralised during summer, signalled by the crystallisation of halotrichite. Hydrogeological investigation gave insights on some of the unique geochemical processes, which facilitated the neutralisation of ARD. The main aquifers in the area include laterite and clayey‐sand, which is separated by this impervious layer hosting YTT ash. Wells tapping the clayey‐sand aquifer, beneath this layer, is affected by the ARD condition due to the interaction with pyrite, manifested as low pH of groundwater (3.7). Simultaneously, leaching from YTT ash, which constitutes 11.91% of Al2O3, facilitates Al content to reach groundwater in high concentration (2879.97 ppb). During dry season, when the surface of YTT‐hosting OM‐rich carbonaceous clay layer is exposed, the leached Al interacts with the acid derived from the YTT‐hosting OM‐rich carbonaceous clay layer and results in the precipitation of halotrichite. The two processes, one resulting in ARD condition and the other as formation of halotrichite, occur in succession. Thus, the crystallisation of halotrichite signals the neutralisation of water as well as heralding the potability of water.

Impacts of groundwater flow on borehole heat exchangers: Lessons learned from Estonia

The production of geothermal energy relies on subsurface properties. In low-enthalpy geothermal regimes, thermal energy extracted with a borehole heat exchanger (BHE) is the subsurface heat conducted from the rock and grout to the BHE fluid. Estonian geology provides a good opportunity to investigate how groundwater flow impacts BHE heat production. The hundreds of metres thick sedimentary rock sequence holds four main aquifers. We modelled single BHEs with lengths of 400 m, 500 m and 1000 m and a BHE field of ten 400-m wells at three sites across Estonia. Then, we parametrized different hydraulic conditions to compare how the groundwater flow velocity impacts the thermal energy yield of the systems.Our results indicate that if groundwater flow increases above 0.03 m/day, it increases the total energy yield from 3 % to 20 %. Thermogeological parameters, such as subsurface temperature and thermal conductivity, affect the thermal energy yield of the wells more than the modelled groundwater flow. Our study provides an estimate of the thermal energy yield from different BHE types and the detailed sensitivity analysis. We conclude that geothermal energy is a significant renewable energy resource for Estonia and areas with similar geology and climate.

Climate variability impact on groundwater quality in Small Island Developing States: Mauritius Island as a case study

This study investigates the impact of climate variability on groundwater quality in Mauritius. This is achieved by analyzing the physical and chemical water quality of the five main aquifers over eleven years. Temporal variations in water quality properties were compared to the Standardised Precipitation Index (SPI), Dry Spells, the Standardised Evapotranspiration Index (SPEI), and other climate variables to gain insights into how precipitation controls groundwater quality. The results reveal that the SPI and the SPEI correlate minimally with water quality indicators. Sulphate is the only water quality indicator that showed correlations above 0.4 in aquifers 2 and 3 against a 12-month SPI. Sulphate, alongside chloride, showed what is termed ”notable correlation,” a concept defined in this paper to accommodate correlations that fall above 0.3 when assessed against global climate modes ENSO and AAO, respectively. These results signify that sulphate is the most sensitive water quality indicator to water quantity changes, notwithstanding the modesty of the correlations. Heavy storms occurring during cyclones impact groundwater quality with respect to conductivity, TDS, salinity, and nitrate, although this could not be statistically tested given the lack of water quality indicators collected on the days surrounding the storm. Therefore, the conclusion is made based on one storm event. The study revealed that individual correlations between climate indices and water quality variables are present but weak. However, the long-term trend in water quality is visible.

A hydrogeophysical conceptual model in the exploration of the "Las Sierras" aquifer: Case of Subwatershed III, southeast sector of Lake Managua, Nicaragua

This study proposes a hydrogeophysical conceptual model in a region southeast of Sub-basin III, which is part of the "Las Sierras" aquifer. The methodology employed combines geological data obtained from wells with geo-electric profiles, thus allowing a more precise representation of an underground valley hitherto unknown, primarily related to the materials of the Middle Las Sierras Group (TQps-M), identified as the main aquifer in the area. The delineation of hydrogeological units was carried out considering geological and geophysical conditions, providing valuable information to understand the distribution and behavior of groundwater in the region. The precise identification and delineation of hydrogeological units enable better management of groundwater resources in the region. This more detailed knowledge enables more effective strategies for the preservation and sustainability of local aquifers.

Three-dimensional model and environmental fragility in the Guarani Aquifer system, SE-Brazil

The Guarani Aquifer System (GAS) is a vast transboundary continental sedimentary basin in southern South America, encompassing sedimentary rocks and basalt flows across Uruguay, Paraguay, Argentina, and Brazil. It serves as a crucial water resource for urban supply and irrigation. This study aims to propose geophysical, geometric, and fragility models of the GAS in a critical exploitation area, utilizing geological data, geophysical logs, geomorphometry, and information from tubular wells. The models define distinct geophysical ranges for each formation and identify contacts between sedimentary and basaltic rocks. Integration of horizontal and vertical spatial distributions of geophysical and geological data forms a 3D model, revealing basaltic flows and intrusions distribution in fragile areas between formations, and potentially connecting aquifer layers. Natural fragility zones, characterized by high fracture densities, are observed in the central-east region, while outcrop and recharge areas of the main aquifer hydrofacies are found in the north. The 3D model highlights similarities between the topography of the Botucatu Formation (KJb – eolian sandstones) and the potentiometry of GAS at local scales, and overexploitation zones in Ribeirão Preto's city center. The assessment prioritizes areas at risk and conservation strategies for sedimentary aquifers, emphasizing interactions between surface and groundwater and addressing issues of overexploitation, identifying high-impact risks on GAS hydrodynamics and water quality.

Mapping and assessment of groundwater pollution risks in the main aquifer of the Mostaganem plateau (Northwest Algeria): utilizing the novel vulnerability index and decision tree model.

Water plays a pivotal role in socio-economic development in Algeria. However, the overexploitations of groundwater resources, water scarcity, and the proliferation of pollution sources (including industrial and urban effluents, untreated landfills, and chemical fertilizers, etc.) have resulted in substantial groundwater contamination. Preserving water irrigation quality has thus become a primary priority, capturing the attention of both scientists and local authorities. The current study introduces an innovative method to mapping contamination risks, integrating vulnerability assessments, land use patterns (as a sources of pollution), and groundwater overexploitation (represented by the waterhole density) through the implementation of a decision tree model. The resulting risk map illustrates the probability of contamination occurrence in the substantial aquifer on the plateau of Mostaganem. An agricultural region characterized by the intensive nutrients and pesticides use, the significant presence of septic tanks, widespread illegal dumping, and a technical landfill not compliant with environmental standards. The critical situation in the region is exacerbated by excessive groundwater pumping surpassing the aquifer's natural replenishment capacity (with 115 boreholes and 6345 operational wells), especially in a semi-arid climate featuring limited water resources and frequent drought. Vulnerability was evaluated using the DRFTID method, a derivative of the DRASTIC model, considering parameters such as depth to groundwater, recharge, fracture density, slope, nature of the unsaturated zone, and the drainage density. All these parameters are combined with analyses of inter-parameter relationship effects. The results show a spatial distribution into three risk levels (low, medium, and high), with 31.5% designated as high risk, and 56% as medium risk. The validation of this mapping relies on the assessment of physicochemical analyses in samples collected between 2010 and 2020. The results indicate elevated groundwater contamination levels in samples. Chloride exceeded acceptable levels by 100%, nitrate by 71%, calcium by 50%, and sodium by 42%. These elevated concentrations impact electrical conductivity, resulting in highly mineralized water attributed to anthropogenic agricultural pollution and septic tank discharges. High-risk zones align with areas exhibiting elevated nitrate and chloride concentrations. This model, deemed satisfactory, significantly enhances the sustainable management of water resources and irrigated land across various areas. In the long term, it would be beneficial to refine "vulnerability and risk" models by integrating detailed data on land use, groundwater exploitation, and hydrogeological and hydrochemical characteristics. This approach could improve vulnerability accuracy and pollution risk maps, particularly through detailed local data availability. It is also crucial that public authorities support these initiatives by adapting them to local geographical and climatic specificities on a regional and national scale. Finally, these studies have the potential to foster sustainable development at different geographical levels.

The paradox of success: Water resources closure in Axarquia (southern Spain)

Axarquia is a semi-arid region in southern Spain that in the past 25 years has experienced significant population growth, along with an economic boom driven by an increasing influx of tourists to Costa del Sol and the expansion of irrigated export-oriented subtropical crops. The combination of these factors has led to a chronic structural scarcity condition that has been intensified by the occurrence of a long and extreme drought. As a result, its only reservoir has reached historically low levels and the piezometric levels in its main aquifer have decreased significantly, suggesting that groundwater reserves are being overexploited. The water crisis is impacting citizens (urban supply), farmers (losses of yields and crops), and the environment (decreasing water reserves). The authorities have responded through supply-side measures such as incorporating reclaimed wastewater in the system and planning the deployment of desalination infrastructure in the region, but demand control and proper governance are required to guarantee sustainability. Consequently, in this case study we apply the European Environment Agency's DPSIR (driving forces, pressures, state, impact, and response model of intervention) framework to understand the basin closure process in Axarquia and assess the main actions that have been undertaken by public and private sector stakeholders to address the challenges faced by the region. Our results provide a valuable reference case to support the analysis of similar closure events, the early identification of potential crisis conditions, and the design of potential solutions in water scarce regions in the European Union, the Mediterranean, and elsewhere.

Review: Andesitic aquifers—hydrogeological conceptual models and insights relevant to applied hydrogeology

Research on the hydrogeology of andesitic volcanic aquifers in subduction areas is reviewed. Andesitic aquifers are of high interest in volcanic arc islands and subduction zones, where they constitute a strategic water resource. This review gathers a compilation of worldwide results and case studies to propose a generic hydrogeological conceptual model (GHCM). It is based on the geological conceptual model splitting the volcanic edifice, from upstream to downstream, into central, proximal, medial and distal zones. In this geological structure, the GHCM identifies where the main aquifer types (fractured lava, pyroclastic flows, and the volcano-sedimentary basins downstream) and the typical aquitards (lahars, fine pyroclastic falls and surges, indurated pyroclastic flow, and weathered rocks) are structured and organized. To integrate the evolution of volcanoes and some specific volcanic activities, a specific GHCM for old andesitic volcanoes or andesitic shield volcanoes is detailed. The paper also describes how the GHCM results are of use to hydrogeologists in terms of scale (from the lithological units to the regional scale), to effectively site water wells, and to sustainably manage groundwater resources in such aquifers. Among these various scales, the volcanic “flank continuum” is presented as the most adapted to support groundwater resources management. Several ways to improve this GHCM are suggested, notably to better consider the geological complexity of these aquifers.

Developing a 3D hydrostratigraphical model of the emerged part of the Pelotas Basin along the northern coast of Rio Grande do Sul state, Brazil

The coastal plain of Rio Grande do Sul state, in Brazil, is highly vulnerable to expected changes in sea level, while having an increasing population and consequently increasing water demands. Adequate management is essential to restrain contamination, depletion and salinization of the region’s aquifers considering current and future challenges, but geologic knowledge is essential to guide groundwater sustainable practices. To contribute to this discussion, this work integrated existing geological data from the northern coast of Rio Grande do Sul state to create a three-dimensional representation of the main hydrostratigraphical units of the region and its relation to the basement rocks, expanding the current knowledge of the coastal aquifer system. A review of existing data was carried out, consisting of 307 borehole logs from 13 municipalities inside the area of interest, as well as 19 vertical electrical soundings and 37 logs from oil and coal exploratory drillings, that resulted in 315 input points for the model. This work builds up on the conceptual model previously developed for the area, that defined four hydrostratigraphical units for the region, and was able to constrain the geometries of the main aquifers (unit 1 and 3) and aquitards (unit 2 and 4) and their relation to the basement rocks, showing them to be more heterogeneous in thicknesses and extent than previously thought. In addition, this work was able to model what could be a fifth hydrostratigraphical unit, that strongly differs from the other four and could be an indication of the alluvial fans previously described in the literature.

Unraveling aquifer dynamics: Time series evaluation for informed groundwater management

Optimizing groundwater monitoring networks is essential for the sustainable management of this critical resource, which is vulnerable to both anthropogenic and natural changes. Focusing on the Hashtgerd aquifer in Iran, this research aims to enhance the efficiency of groundwater level monitoring systems by integrating statistical methods, artificial intelligence (AI), and hydrogeological studies. The study's core objective is to pinpoint and comprehend the factors that cause certain observation wells to become isolated from the main aquifer body, leading to parts of the aquifer being cut off from the central hydrogeological system. Employing clustering techniques on data from 29 observation wells, based on parameters like groundwater level (GWL), groundwater level change (GWLC), groundwater depth (GWD), air temperature (AT), distance (D), ground level (GL), and temperature (T) through Hierarchical Cluster Analysis (HCA), the research categorizes the groundwater information into four distinct groups. Significantly, Cluster 4 encompasses wells with similar characteristics. The analysis reveals that two wells, categorized in Clusters 1 and 2, exhibit unique behaviors, likely due to their connection to local karstic aquifers, as corroborated by geological evidence. Cluster 3's separation is determined through geophysical investigations, identifying confined conditions near specific wells, notably Wells 4 and 8. AI techniques further distinguish differences in meteorological influences and water discharges among the clusters, noting minimal weather impact on Clusters 1 and 2, considerable shallow groundwater influence on Cluster 3, and a pronounced effect of groundwater discharge on Cluster 4. This nuanced identification of aquifer segments disconnected from the main system underscores the need to refine monitoring networks for accurate assessment of groundwater resources. By leveraging a detailed analysis of aquifer complexities through state-of-the-art methodologies, the study guides towards informed, sustainable groundwater management strategies.

Hydrogeological Assessment of the Aquifers in Shwan Sub-Basin, Kirkuk, Iraq

Groundwater is considered one of the main sources of providing water for agricultural, domestic, and industrial activities within the Kirkuk province. The current article aims to assess the groundwater impound and estimate the hydraulic properties of the main aquifers within the Shwan sub-basin. Pumping test was conducted in 6 water wells with the aid of the principal observation wells drilled in the Bai-Hassan formation and Quaternary deposit. Based on the sketches of the drilling wells and according to the results of the hydraulic characteristics the aquifer types lie under the confined to semi-confined conditions. The saturation thickness varies between 35–82 m. The values of hydraulic conductivity ranged between 12–28 m/d the Transitivity is in the range of 570 m2/d–1032 m2/day, and the storage coefficient ranged between 3 x 10-4 – 9 x 10-4. The flow net map was created by measuring the depths of the groundwater from 55 wells drilled inside the area of interest. The depths to the water table range from 7.5 –108 m below the ground surface and the static water level varies from 235–750 m a.s.l. The groundwater flow map shows that the water in the area heads mainly from the eastern towards the western direction, then drains to the Lesser Zab River.

Groundwater investigation in the Dumoga area, north Sulawesi province, Indonesia

Dumoga is one of the areas in North Sulawesi Province, Indonesia, designated as an agriculture and food crop area. Groundwater is one of the sources of raw water and irrigation in this area. Therefore, it needs detailed information about the quantity and quality to support groundwater exploitation and management for sustainable use of groundwater resources. This study investigates the groundwater resource potential and quality, which has not been previously studied. The research methods used geological observation, springs mapping, geoelectrical survey, measurement of groundwater level, and physicochemical, including temperature, pH, total dissolved solids (TDS), and electrical conductivity (EC). The result shows that the Dumoga area has a high potential for groundwater resources, with sand and clayey sand as the main aquifers. Groundwater flows from around the research area to Dumoga River in the middle. Even though it has a high potential for groundwater resources, not all groundwater is recommended for irrigation water because of the quality, especially from the southwestern and eastern Dumoga areas.

Assessment of hydraulic connectivity among shallow and deep aquifers and surface water of Central Gujarat: An isotopic approach

The primary objective of this study is to identify the surface water - groundwater interaction and interaction among groundwater at different depths using stable isotopes (δ18O and δ2H). The Fence diagram of the study area describes the subsurface geology where the main aquifer system includes both confined and unconfined in the VRB area and is complex multi-layered with different sources of recharge. The flow pattern of groundwater is generally from the highland of north-east to low-lying south-west of VRB and is indicated by the piezometric surface map of pre-monsoon, and post monsoon, 2016. The δ2H (‰ VSMOW) and δ18O (‰ VSMOW) values do not show any symmetric distribution among them. The values for shallow groundwater ranges between −23.0‰ and 1.9‰, and −3.2‰–2.3‰, respectively with a mean value for δ18O and δ2H are −1.26‰ and −11.194‰ respectively. The depth wise interpretation revealed that the locations Virpur and Nana Pura show connectivity. Therefore, deep and shallow aquifers are contaminated due to this connectivity. The plots of d-excess vs. electrical conductivity, d-excess vs δ18O and electrical conductivity vs. δ18O indicate that most of the groundwaters are primarily influenced by evaporation process, high mineral dissolution and enrichment of δ18O. The plot of δ18O vs. nitrate indicate the anthropogenic influences like agricultural activities in this region. The SI values of calcite and dolomite indicates oversaturated condition along with dissolution of these minerals in the aquifer matrix.

Tropical dry forests, water, biodiversity and the challenges of climate change in Nicaragua.

The Tropical Dry Forests of Nicaragua located mainly in the Pacific and Central-North zones play an essential role in maintaining resources such as water and the special biodiversity of this vulnerable ecosystem now under pressure from land-use changes and climate change These resources are essential to the well-being of the population as the main aquifers of the country are located in this area along with ecosystem services of this now heavily fragmented forest ecosystem. The ongoing influence of climate change along with land-use changes have caused the growth of arid zones in all of Central America. These on-going land use changes are lowering the resilience to the present and future climate change. Individual efforts to sustainable management of the forests are mentioned but it is nonetheless urgent to introduce wider and more intensive sustainable forestry and watershed management under a well-planned strategy based on findings of scientific research. The importance of the interrelationship between water and forests in the management of sustainable forest ecosystems will be stressed.

HYDRODYNAMIC MODEL OF SOLOTVYN ROCK SALT DEPOSIT

Rock salt development brings risks of harmful impact on water resources, in particular the Tysa River, posing a threat of cross-border spread of saline pollution on the border between Ukraine and Romania (Solotvyn rock salt deposit, Transcarpathia, western Ukraine). The impact of technogenic load (underground mining of rock salt) within the deposit led to deformation of the structure and nature of water exchange, intensification of suffusion and karst processes, ground surface deformations, catastrophic inflows of groundwater into mines, and, as a result, to the cessation of development of this deposit in 2010. However, the suspension of salt mining did not stop the development of the above-mentioned hazardous geological processes caused by both natural and man-made factors. In order to justify measures for prevention pollution of the Tysa River basin, a hydrogeological model of the Solotvyna rock salt deposit and surrounding areas was created, which allowed to predict the direction and flow rate of fresh and saline groundwater. The model was developed using new data on the geological structure and hydrogeological conditions of the study area (groundwater monitoring data). The modernised hydrodynamic model includes five layers (main aquifers and confining layers). As a result of modelling, maps of the velocity vectors and head contours for two aquifers (Quaternary and Tortonian) were obtained. Based on the results of solving a number of inverse problems, the functional correspondence of the model to natural and anthropogenic conditions was proved. According to the preliminary calculations of the actual groundwater filtration velocity and the path lines of the inert pollutant spreading, it was found that the time of its migration from the salt contour to the Tysa River is approximately 2–3 years. The developed groundwater flow model will be used to substantiate the network of hydrological and hydrogeological observation points in order to optimise the monitoring of water pollution processes.

The Groundwater Balance Assessment in Holy Karbala, Central Iraq

Karbala is located in central Iraq, which is bounded by latitudes (32° 50' 15" - 32° 10' 15") and longitudes (43° 09' 41"– 44° 18' 56"), the area under study covers an area of 4,987 km2. It is a part of unstable shelf of the sedimentary plain zone and Al-Salman zone of the stable shelf, so it is a flat area, which gradually declines from the southwest towards the northeast. The geological formations which are exposed in the study area, having a range between middle Miocene and Pleistocene – Recent deposits. Two main aquifers were distinguished in the area, confined and unconfined one. Depending on the karbala meteorological station information (rainfall, temperature and humidity) from 1980 - 2019 utilizing Thornthwait formela's, the water overflow was accounted, appearing the renewed water store for the unconfined system, equalized to 111.0 *106 m3/year whereas the calculated constant volume of water for both systems was found to be equivalent to a total of 13.84 * 109 m3 However, after calculating the difference between the total water that in-coming the area (including, income subsurface runoff, recharge, fluctuation in monitoring wells and out-coming (including, discharge of pumping wells, outflow wells drainage, spring drainage, outcome subsurface runoff), the amount of change in the storage is found to be (+32.573 * 109 m3). The amount of positive change indicates the presence of excess water which can be added to both systems. The direction of the groundwater movements for the two main systems are highly matched between them as well as its similarity with the topographic surface.

Effect of leakage on confined non-darcian aquifer considering storage in semipervious layers

A set of analytical solutions have been presented for non-Darcian flow to a well in a leaky confined aquifer system considering leakage from the storage of semipervious layers/adjacent aquifer lying above and below the main aquifer. Flow in the main aquifer has been assumed to be non-Darcian and horizontal, whereas flow in the semipervious layers is assumed to be Darcian and vertical. The Izbash equation has been employed to describe the non-Darcian flow. Six general cases have been considered with/without wellbore storage and different adjacent aquifer conditions. Analytical solutions under unsteady and steady-state conditions have been obtained in the Laplace domain. Talbot method has been utilized for numerical inversion Laplace domain solution to the actual solution domain. The obtained analytical solutions clearly quantifies the effect of storage.

Hydrogeological characterization of the Silala River catchment

AbstractThis article reviews hydrogeological studies carried out between 2016 and 2018 in the Silala River basin, a catchment shared by Chile and Bolivia. These were conducted in the context of the Case Concerning the Status and Use of the Waters of the Silala River, submitted to the International Court of Justice in 2016, and contributed to multidisciplinary science to demonstrate that this system is an international watercourse. In 2016, the hydrogeological understanding of the Silala River basin was poor. The studies reviewed here filled many knowledge gaps, providing a solid hydrogeological baseline, and establishing new monitoring infrastructure to collect relevant aquifer data. The most important hydrogeological units were identified as the fluvial deposits, alluvial deposits, and the Cabana ignimbrite. The latter is highly heterogeneous, weathered and fractured, and exhibits a high permeability. It is the most important unit in terms of productivity, and is the major regional aquifer providing spring flows to Bolivian wetlands and groundwater flow across the international border. The studies provided a preliminary understanding of the main aquifers in Chile and their properties, which underpinned the development of a robust hydrogeological conceptual model of the system, reviewed elsewhere in this special issue. Subsequent refinements are also summarized. This work confirmed that both surface water and groundwater flows from Bolivia to Chile, and thus confirms the status of the Silala River as an international watercourse and provided the basis for a basin‐scale groundwater numerical model, used to investigate the impact of wetland channelization on surface water/groundwater partitioning.This article is categorized under: Science of Water > Hydrological Processes

Integration of Geological, Geochemical Modelling and Hydrodynamic Condition for Understanding the Geometry and Flow Pattern of the Aquifer System, Southern Nyírség–Hajdúság, Hungary

Geological heterogeneity impacts groundwater flow patterns, necessitating a detailed hydrogeological framework for conceptualization process of aquifer systems. This research developed a new conceptual model of detailed geologic geometry by integrating 133 well-logs, 366 hydrodynamic data and 118 water samples. As new results, systematic 3D log correlation detected four distinct hydrostratigraphic units in the Southern Nyírség–Hajdúság Groundwater Body (East Hungary). The primary aquifer was identified as an incised valley 10–13 km wide and a NE–SW strike. Logan’s approach estimated the average hydraulic conductivity of the Incised Valley Unit (IVU) at 11 m/d, higher than the other three aquifers (3.2 m/d to 4.6 m/d). The average specific capacity of wells screening the IVU is 315.6 m3/d/m, in contrast with the remaining aquifers ranging from 31.6 m3/d/m to 92 m3/d/m. Pressure–depth profiles, dynamic pressure increment and hydraulic head maps revealed recharge–discharge zones and hydraulic windows between hydrostratigraphic units. The elongated pattern on the hydraulic head map at the depth of the IVU showed the existence of a preferential path along its axis within the mapped borders of the IVU. Hydrochemical analysis revealed Ca-Mg-HCO3 water type within the primary aquifer and Na-HCO3 water type in the laterally connected aquifer. The saturation index values indicated a transition from undersaturated to supersaturated state inside the main aquifer for calcite and dolomite minerals. The correlation matrix and PCA results demonstrated that the carbonate weathering process is the main factor controlling the groundwater chemistry. This integrated approach holds significance for future applications of the regional conceptual model in water management planning, sustainable aquifer development and contaminant transport modelling. It provides essential contributions to informed decision-making and the formulation of effective strategies, ensuring the long-term availability and utilization of groundwater resources.

Hydrogeophysical Investigation in Parts of the Eastern Dahomey Basin, Southwestern Nigeria: Implications for Sustainable Groundwater Resources Development and Management

Geoelectrical resistivity measurements were conducted in five locations within the eastern portion of the Dahomey basin for the purpose of subsurface evaluation and detecting saturated zones. The locations are Covenant University (L1), Bells University (L2), Oju-Ore-Ilogbo Road (L3), Obasanjo-Ijagba Road (L4), and Iyana Iyesi (L5). The study was carried out to avert the common challenges of drilling low-yield groundwater boreholes in the area. A total of 30 Vertical Electrical Soundings (VES) and five two-dimensional Electrical Resistivity Tomography (ERT) data sets have been acquired along the study areas. The geoelectrical resistivity results were integrated with the borehole logs to generate the spatial distribution of the subsurface lithologies in the area. The delineated subsurface lithologies include the topsoil (lateritic clay), clayey sand, sandy clay, fine silty sand, coarse sand, and shale/clay units. The fine silty sand and coarse sand units were identified as the two main aquifer units within the area. The depths to the upper aquifer unit in the area include 31.7–96.7 m, 38.5–94.0 m, 30.7–57.5 m, 39.1–63.4 m, and 46.9–57.5 m for locations L1, L2, L3, L4, and L5, respectively. At the same time, the depths to the lower aquifer unit in the area include 43.4–112.7 m, 52.2–108.0 m, 44.2–72.5 m, 53.7–78.5 m, and 63.5–72.9 m for locations L1, L2, L3, L4, and L5, respectively. The estimated hydraulic parameters for both aquifers show they are highly productive with mean porosity, mean hydraulic conductivity, and mean transmissivity of 20–22%, 12.4–17.0 × 10−2 m/s, 1.56–2.18 m2/s for the upper aquifer, and 48–50%, 371–478 × 10−2 m/s, 50.00–62.14 m2/s for the lower aquifer. By focusing on these aquifer systems during exploration, sustainable groundwater resources can be secured, providing relief to homeowners within the study area who might otherwise face the frustration of drilling unproductive and low-yield boreholes. However, it is crucial to consider the presence of sub-vertical faults in the study area, as these faults can significantly impact groundwater development and management. These sub-vertical structural faults may lead to changes in the permeability, hydraulic conductivity, and transmissivity of the delineated aquifers, affecting their productivity across the divide and ultimately influencing the overall water availability in the area. Careful consideration of these geological factors is essential for effective aquifer management and sustainable groundwater utilisation.