Main Aquifer Research Articles

Hydrogeophysical investigation for the aquifers in part of Ilorin, Central Nigeria: Implication on groundwater prospect

Hydrogeophysical study involving the use of Vertical Electrical Sounding (VES) was carried out in part of the basement complex rocks of Ilorin, central Nigeria, with the aim of determining its geoelectric parameters and groundwater potential. A total of thirty (30) VES were carried out using Schlumberger electrode configuration, with half electrode separation (AB/2) varying from 1m to 100m. Information on the subsurface lithologies, overburden thickness and aquiferous layers were obtained from the different VES locations in the study area. From the quantitative interpretations of the data collected, using the method of curve matching with the Orellana-Mooney master curves and 1-D forward modeling with WinResist 1.0 version software, three to five lithologic units were identified in the study. These include: the topsoil, sandy/lateritic clay/laterite, the weathered basement, the fractured basement and the fresh bedrock which are predominantly of the ‘KH’ curve type (30%), followed by ‘H’ type (26.7%), other type curves include ‘QH’ (16.7%), ‘HKH’, ‘HA’ and ‘A’ (6.7% each) and KQ and KQH (3.3% each). The weathered layer and the fractured basement constitute the main aquifer units. The aquifers are of generally low resistivity values (mostly below 100 Ω-m). The depths to dry bedrock at the chosen VES locations vary from 2.7 to 62.7 m with a mean value of 13.02 m in the study area. The geoelectrical interpretations of data obtained in these areas have permitted the delineation of the study area into low and moderate groundwater potential zones. This study is expected to assist in future planning for groundwater resources.
 Keywords: Hydrogeophysical, Basement Complex, Groundwater, Electrical Soundings, Weathered, Fractured

Fault zone hydrogeology in arid environments: The origin of cold springs in the Wadi Araba Basin, Egypt

AbstractThe role of faults in controlling groundwater flow in the Sahara and most of the hyper‐arid deserts is poorly understood due to scarcity of hydrological data. The Wadi Araba Basin (WAB), in the Eastern Sahara, is highly affected by folds and faults associated with Senonian tectonics and Paleogene rifting. Using the WAB as a test site, satellite imagery, aeromagnetic maps, field observations, isotopic and geochemical data were examined to unravel the structural control on groundwater flow dynamics in the Sahara. Analysis of satellite imagery indicated that springs occur along structurally controlled scarps. Isotopic data suggested that cold springs in the WAB showed a striking similarity with the Sinai Nubian aquifer system (NAS) water and the thermal springs along the Gulf of Suez (e.g., δ18O = −8.01‰ to −5.24‰ and δD = −53.09‰ to −31.12‰) demonstrating similar recharge sources. The findings advocated that cold springs in the WAB represent a natural discharge from a previously undefined aquifer in the Eastern Desert of Egypt rather than infiltrated precipitation over the plateaus surrounding the WAB or through hydrologic windows from deep crystalline basement flow. A complex role of the geological structures was inferred including: (1) channelling of the groundwater flow along low‐angle faults, (2) compartmentalization of the groundwater flow upslope from high‐angle faults, and (3) reduction of the depth to the main aquifer in a breached anticline setting, which resulted in cold spring discharge temperatures (13–22°C). Our findings emphasize on the complex role of faults and folds in controlling groundwater flow, which should be taken into consideration in future examination of aquifer response to climate variability in the Sahara and similar deserts worldwide.

Aquifer hydraulic parameters estimation based on hydrogeophysical methods in West Nile Delta, Egypt

Water scarcity is becoming a major constraint not only to the reclamation and cultivation of new areas, but also to the irrigation of already reclaimed areas, which could lead to global desertification. Groundwater exploration is one of the solutions to overcome the water resource shortage crisis in Egypt, especially after the building of the Ethiopian Renaissance Dam and its effects with unfavorable consequences for the water supply. The West Nile Delta region (WND) has been chosen by the Egyptian government in the past 30 years to develop several agricultural programs that rely mainly on groundwater for different aquifers. Vertical Electrical Sounding (VES) is the main method for determining the depths to groundwater, aquifer thicknesses, salinity and possibly hydrophysical parameters (transverse resistance and average transverse resistivity). The hydraulic parameters of aquifer and their important role in estimating the safe yields from production wells are essential for agriculture water management. To estimate of main aquifer parameters using geoelectric measurements, which are of great importance in selecting the suitable wells locations and in maintaining the sustainable management of groundwater, hydrogeological data are collected for 32 drilled wells and the Schlumberger array was used to implement 22 VES at specific sites in the study area. Some VES are performed alongside the already drilled wells that have lithology and pumping test data and others are carried out in well-free places especially in the northern and southern parts. Using the partial-curve matching technique, 22 VES data are interpreted to obtain the different geoelectric parameters (e.g., transverse resistance and average transverse resistivity). The constructed relationships between transmissivity—transverse resistance, hydraulic conductivity—average transverse resistivity, and salinity—average transverse resistivity showed well correlation between these parameters, where R2 equal 0.86, 0.7 and 0.8, respectively. Based on these relationships and the data of 22 VES, the predicted values of transmissivity range between 396.4 and 8830.7 m2/day, hydraulic conductivity range from 107.6 to 7.6 m/day and the TDS vary from 413.2 to 1991.6 mg/l. These results showed that VES is a useful method for exploring the groundwater aquifer and predicting its hydraulic parameters (for example, transmissivity and hydraulic conductivity) and salinity, which can be used as a primary data for drilling groundwater wells and further agricultural irrigation in the West Nile Delta, Egypt.

Battling Water Limits to Growth: Lessons from Water Trends in the Central Plateau of Iran.

The Zayandeh-Rud River Basin in the central plateau of Iran continues to grapple with water shortages due to a water-intensive development path made possible by a primarily supply-oriented water management approach to battle the water limits to growth. Despite inter-basin water transfers and increasing groundwater supply, recurring water shortages and associated tensions among stakeholders underscore key weaknesses in the current water management paradigm. There was an alarming trend of groundwater depletion in the basin's four main aquifers in the 1993-2016 period as indicated by the results of the Mann-Kendall3 (MK3) test and Innovative Trend Analysis (ITA) of groundwater volume. The basin's water resources declined by more than 6 BCM in 2016 compared to 2005 based on the equivalent water height (EWH) derived from monthly data (2002-2016) from the GRACE. The extensive groundwater depletion is an unequivocal evidence of reduced water availability in the face of growing basin-wide demand, necessitating water saving in all water use sectors. Implementing an integrated water resources management plan that accounts for evolving water supply priorities, growing demand and scarcity, and institutional changes is an urgent step to alleviate the growing tensions and preempt future water insecurity problems that are bound to occur if demand management approaches are delayed.

Hydrogeochemistry and isotope compositions of multi-layered aquifer systems in the Recife Metropolitan Region, Pernambuco (NE Brazil): An integrated approach using multivariate statistical analyses

The Paraíba and Pernambuco basins are part of the Northeast Brazilian rift system, which contains a series of Cretaceous terrestrial to marine sediments covered by Neogene-Quaternary deposits. Their main aquifers (i.e. Barreiras, Beberibe, Cabo, Quaternary and, Fractured) constitute multi-layered aquifer systems and are the main strategical source of drinking water for the Recife Metropolitan Region. In this research, 323 physical-chemical samples along with 25 isotopic groundwater analyses were used to characterize the main hydrochemical processes controlling groundwater's chemistry and to identify recharge sources. Graphical, ionic ratios and multivariate statistical methods were used to achieve these goals. The correlation matrix was used to evaluate significant associations between 11 geochemical parameters. Principal Component Analysis was employed and a two-factor model is suggested explaining 72.54% of the total variation within the dataset. PC1 is the major contributor to groundwater mineralization and is assigned to ‘natural’ processes (e.g. rock weathering, ion exchange, etc.), and PC2 is related to ‘anthropogenic’ processes (e.g. nitrate contamination). Hierarchical cluster analysis was employed and partitioned the water samples into 28 distinct hydrochemical water clusters (B1–B4, Barreiras; BE1–BE6, Beberibe; C1–C6, Cabo; Q1–Q7, Quaternary; and F1–F5, Fractured). The majority of the cluster samples have Na+–Cl− to Na+–HCO3− water type, including the low salinity groundwater, which in a first approximation could be spatially tied to the recharge zones, and intermediate ones probably related to transition zones. Na+–Cl−to mixed–Cl− water type is typical for high salinity groundwater that more probably results from mixing with infiltrating highly mineralized water. The groundwaters' major ion compositions are primarily controlled by the following interactions: (1) mixing of Pleistocene marine transgression with meteoric Holocene infiltrating water, besides atmospheric deposition; (2) water–rock interactions from silicate rock-forming minerals; (3) ion-exchange reactions; and (4) input from animal/human wastewater. The analyzed groundwater samples showed isotopic signature ranging from −1.98 to +0.36‰ and −2.0 to +7.0‰ for δ18O and δ2H respectively, which is similar to precipitation. These isotopic depleted signatures suggest that most of the deep groundwater was likely recharged from colder epochs and/or from a selection of winter infiltrating precipitation through time.

Regional groundwater flow and karst evolution\u2013theoretical approach and example from Switzerland

In regional scale aquifers in the Rhine Valley and Tabular Jura east of Basel (Switzerland), the groundwater circulation was investigated using regional-scale geological and hydraulic 3D models. The main aquifers in the area comprise the Quaternary aquifer of unconsolidated gravel deposits along the River Rhine and its tributaries, as well as the regional scale karst aquifer within the Upper Muschelkalk. Land subsidence, a process likely associated with salt solution mining, indicates further subordinate groundwater bearing segments and complex groundwater interactions along fault zones. In the aquifer systems we investigated, regional-scale groundwater circulation was simulated and visualized in relation to the geological settings. Lithostratigraphic units and fault structures were parameterized and analyzed, including the sensitivity of hydraulic properties and boundaries. Scenario calculations were used to investigate the sensitivity that the aquifer systems had to hydraulic parameter changes during Quaternary aggradation and degradation in the main valley. Those calculations were also done for base-level changes in the Rivers Rhine and Birs. For this purpose, this study considered probable historic base-levels before river regulation occurred, and before river dams and power plants were constructed. We also focused on scenarios considering increased groundwater recharge rates, e.g. due to exceptional long-lasting precipitation, or heavy rainfall events in the catchment area. Our results indicate that increased groundwater recharge rates in the catchment areas during such events (or periods) are associated with orders of magnitude increases of regional inflow into the Upper Muschelkalk karst aquifer. Furthermore, the groundwater fluctuations and groundwater saturated regions within the karst aquifer shift to places where high densities of sinkholes are documented. When the surface water base-levels adapt to probable historic levels, it leads to increased hydraulic gradients (i.e. local lowering of the groundwater level by up to 7 m). Those increased gradients are associated with increased groundwater flow within some aquifer regions that are particularly prone to karst development.

Integration of Magnetic Data and Geo-Spatial Analysis for Characterising Aquiferious Yields in New Estate, Covenant University, Ota, Ogun State

This study was conducted to understand the possible causes of abortive boreholes along the New Estate in Covenant University. The conceptual model predicted the two groundwater characteristics of weathered and the unweathered zones. The V-shape curve revealed two groundwater anomalies with high and low curves. The peak anomaly indicates the higher resistivity, presumed to be the geological structures of unsaturated features in the area. The sink V-shape curve indicate an anomaly with groundwater features, presenting low resistivity values attributed to be water bearing formation that will be viable for groundwater potential. The Iso-resistivity contour map identified possible groundwater features. The first Iso-resistivity column is a region of aquitard with a semipervious in nature that could transmit water in a slower rate. The second groundwater feature in column 2 is a perch aquifer that could enhance the main aquifer due to interconnectivity and pore pressure of downward-upward migration in confined hydrogeological aquifer setting. Column 3 depicts a complete impermeable feature of aquifuge or aquiclude of subsurface structure with rich in clay sediments or stratum of sediments found at the depth range of 30 m to 270 m. The forth groundwater column indicates a promising water bearing formation, probably sandy in nature with a depth range of 210 to 300 m and thickness of about 90 m. The spatial analysis identified the two locations along the survey areas to be suitable for productive boreholes as well as the trending of the groundwater in the area to be Northwestern Southeast direction. Consequently, the model could be a guide to organize site data, understand site processes and screen for applicability of drilling. These multiple methods of geophysical, spatial analysis and conceptual model could be used a tool for mapping hydrocarbon bearing formation.

Distribution of Groundwater Arsenic in Uruguay Using Hybrid Machine Learning and Expert System Approaches

Groundwater arsenic in Uruguay is an important environmental hazard, hence, predicting its distribution is important to inform stakeholders. Furthermore, occurrences in Uruguay are known to variably show dependence on depth and geology, arguably reflecting different processes controlling groundwater arsenic concentrations. Here, we present the distribution of groundwater arsenic in Uruguay modelled by a variety of machine learning, basic expert systems, and hybrid approaches. A pure random forest approach, using 26 potential predictor variables, gave rise to a groundwater arsenic distribution model with a very high degree of accuracy (AUC = 0.92), which is consistent with known high groundwater arsenic hazard areas. These areas are mainly in southwest Uruguay, including the Paysandú, Río Negro, Soriano, Colonia, Flores, San José, Florida, Montevideo, and Canelones departments, where the Mercedes, Cuaternario Oeste, Raigón, and Cretácico main aquifers occur. A hybrid approach separating the country into sedimentary and crystalline aquifer domains resulted in slight material improvement in a high arsenic hazard distribution. However, a further hybrid approach separately modelling shallow (<50 m) and deep aquifers (>50 m) resulted in the identification of more high hazard areas in Flores, Durazno, and the northwest corner of Florida departments in shallow aquifers than the pure model. Both hybrid models considering depth (AUC = 0.95) and geology (AUC = 0.97) produced improved accuracy. Hybrid machine learning models with expert selection of important environmental parameters may sometimes be a better choice than pure machine learning models, particularly where there are incomplete datasets, but perhaps, counterintuitively, this is not always the case.

Assessing Stream-Aquifer Connectivity in a Coastal California Watershed

We report the results of field and laboratory investigations of stream-aquifer interactions in a watershed along the California coast to assess the impact of groundwater pumping for irrigation on stream flows. The methods used include subsurface sediment sampling using direct-push drilling, laboratory permeability and particle size analyses of sediment, piezometer installation and instrumentation, stream discharge and stage monitoring, pumping tests for aquifer characterization, resistivity surveys, and long-term passive monitoring of stream stage and groundwater levels. Spectral analysis of long-term water level data was used to assess correlation between stream and groundwater level time series data. The investigations revealed the presence of a thin low permeability silt-clay aquitard unit between the main aquifer and the stream. This suggested a three layer conceptual model of the subsurface comprising unconfined and confined aquifers separated by an aquitard layer. This was broadly confirmed by resistivity surveys and pumping tests, the latter of which indicated the occurrence of leakage across the aquitard. The aquitard was determined to be 2–3 orders of magnitude less permeable than the aquifer, which is indicative of weak stream-aquifer connectivity and was confirmed by spectral analysis of stream-aquifer water level time series. The results illustrate the importance of site-specific investigations and suggest that even in systems where the stream is not in direct hydraulic contact with the producing aquifer, long-term stream depletion can occur due to leakage across low permeability units. This has implications for management of stream flows, groundwater abstraction, and water resources management during prolonged periods of drought.

Hydrogeophysical investigation at El Moghra Area, North Western Desert, Egypt

El Moghra area, in the western desert of Egypt, is an important part of the national reclamation project (1.5 million acres—6.07 × 109 m2), which depends on the groundwater of El Moghra Formation (MF), the main aquifer in this area. Moghra Oasis and its surroundings are characterized by vast areas of good soil, which are favorable for agricultural development. In this respect, ambitious plans and successful programs are urgently required. Thirty-one vertical electrical sounding stations (VES’s) were measured in El Moghra. The results of quantitative interpretation of such stations and well logging data indicate that the subsurface stratigraphy of the investigated area consists of six geo-electrical units where the main aquifer is represented by the fourth and sixth units intercalated with a clay unit (fifth unit). Thirteen boreholes of depth reaching 200 m are drilled in the study area. The hydrochemical analyses for collected samples indicate that the salinity of the groundwater in the Moghra area increases with depth. The result of the pumping test for boreholes indicates that the efficiency of the wells is ranging from 65 to 96% of the average value of 84.5%. The aquifer has transmissivity which represents a highly potential aquifer.

Vulnerability Evaluation of Groundwater of N’Djamena City: Contribution of the Parametric Methods GOD and SI

The purpose of this work is to study the vulnerability of the Quaternary aquifer that lies beneath the N’Djamena city Chad. The subsoil of N’Djamena city Chad is made up of a multilayered aquifer in which there are two main aquifers located respectively at a depth of about 10 and 60 m, between the two there is an intermediate aquifer at about 30 m depth. It is this latter water table, generally captured by human-powered pumps, that is the subject of this study. Because of anarchic garbage dumping, wastewater discharge, latrines scattered throughout the city, chemical fertilizers and herbicides used on the banks of Chari River and its tributary the Logone for market gardening, the quality of the water in this aquifer is highly threatened. Moreover, it has been noting that the sources of pollution are constantly increasing in conjunction with the growth of the population, so the knowledge and protection of groundwater are necessary. We have therefore carried out a study of intrinsic vulnerability using two mapping methods (GOD and SI), as mapping is recognized as an effective tool for decision support in the case of safeguarding water resources. The results obtained by the GOD method show that 38% of the study area is covered by high vulnerability, 29% by moderate vulnerability, 21% by low vulnerability and 21% by the very low vulnerability. With the SI method, 54% of the study area is covering by low vulnerability and 46% by the low and moderate vulnerability. The coincidence rate of low nitrate values in groundwater with areas of very low and low vulnerability is 91% and 76% for the GOD and SI methods, respectively. Although these observations validated the different maps obtained, the SI approach seems to be the most adequate for vulnerability tracing in our study area.

Characteristics of groundwater in Northeast Qinghai-Tibet Plateau and its response to climate change and human activities: A case study of Delingha, Qaidam Basin

Delingha is located in the northeast margin of Qaidam Basin. Bayin River alluvial proluvial fan is the main aquifer of Delingha, in which groundwater generally flows from north to south. The hydrochemistry results showed that two different hydrochemical evolution paths formed along southeast and southwest directions, respectively. Cl-Na type groundwater was formed in front of Gahai Lake, and SO4·HCO3-Na·Ca type groundwater was formed in front of Keluke Lake. The results of deuterium (D) and 18O revealed that the groundwater mainly originated from the continuous accumulation of precipitation during geological history under cold and humid climate conditions. In addition, results of 14C indicated that the groundwater age was more than 1140 years, implying relatively poor renewal capability of regional groundwater. Moreover, our numerical modeling results showed that the regional groundwater level will continue to rise under the warm and humid climate conditions.© 2021 China Geology Editorial Office.

Hydrochemistry of Umm Er Radhuma Groundwater

Umm Er Radhuma Aquifer (UER) is the most important groundwater aquifer in Saudi Arabia, extending over 1.6 M·km2 in the eastern part of the Arabian Peninsula, forming the main aquifer throughout the Rub’ Al-Khali (RAK). Groundwater salinity increased from west to east, reaching more than 27,000 mg/L near the border with the United Arab Emirates, where a Na+-Ca2+Clˉ- water type dominated. Gibbs diagrams indicated that the dissolution/precipitation of carbonates and evaporation/precipitation of minerals, especially anhydrite, gypsum, and halite account for the solutes and salinity in groundwater. Most of the samples plot above the 1:1 line of (Ca2+ + Mg2+) against , indicating other sources of Ca2+ and Mg2+ in the groundwater along with dolomite and calcium carbonate minerals. Phreeqc model indicated that the main clay minerals are kaolinite and gibbsite which had major effect on the cation exchange process as indicated by the Chloro-Alkaline index (CAI), where most of groundwater samples had values greater than zero which indicated the occurrence of reverse ion exchange between the groundwater and its host aquifer. The water type Na+-Ca2+Clˉ-dominated in the eastern part of the aquifer as the anaerobic conditions prevailed and the reduction of sulphate took place.

Recognition Method of Mine Water Sources Based on Factor Analysis

Taking Jiaozuo mining area as the research background, according to the survey of water samples among the main water-filled aquifers of the mine and water gushing sources due to the exploitation of the No.21 coal seams in Shanxi group, six kinds of water chemical composition were selected as the sample indexes, including Cl-, SO42-, HCO3-, Na++K+, Ca2+, Mg2+, based on the data of groundwater chemical composition, and a principal component analysis was applied to establish the mathematical model by the method of factor analysis. A piper diagram was used to intuitively conduct the synthetical analyses for the general chemical characteristics and water quality types of the water samples. At the same time, via the comparative analysis between the water properties of water exits and that of the main aquifers in the Jiaozuo mining area, discrimination of the hybridization of the multiple water gushing sources due to coal mining was done. Moreover, by dint of the SPSS factor analysis, the water chemical proxies were carried on dimensionality reduction from the six kinds of water chemical composition to the three major factors, which replaced the original variables to participate in the data modeling. The results of the study showed that the combination of the piper diagram and the factor analysis modeling could effectively identify the water gushing sources owing to exploiting the No.21 coal seams of the Shanxi group in the Jiaozuo mining area and rank on the basis of the contributions of each aquifer to the amounts of water bursting in the mine, solving the problems of information superposition and correlations consisted in the identification of water gushing sources, which provides a theoretical basis for the prevention and cure of the mine water disasters.

Hydrogeophysical Characterization of the Coastal Aquifer System in the Northeast Gulf of Aqaba (Saudi Arabia): An Investigation in the Context of Groundwater Resources Management

El Waheidi, M.M.; Ghrefat, H.; Qaysi, S.; Batayneh, A.T.; Russo, G.; Jallouli, C.; Badhris, O.; Maeshi, T.; Elawadhi, E.A., and Bahkali, I., 2021. Hydrogeophysical characterization of the coastal aquifer system in the northeast Gulf of Aqaba (Saudi Arabia): An investigation in the context of groundwater resources management. Journal of Coastal Research, 37(1), 41–51. Coconut Creek (Florida), ISSN 0749-0208.A hydrogeophysical investigation has been conducted along the NE part of the Gulf of Aqaba coast that covered a total area of about 40 km2. The area represents a vital part of the ambitious national project NEOM that is a major outcome of the Saudi Arabia's strategic Vision 2030. The research aimed to provide decision makers with the characteristics of the main aquifer in the area in terms of its lateral and vertical extensions and quality of groundwater. To achieve the set objectives, an integrated methodology has been applied that is based on using electrical resistivity tomography (ERT) method and hydrochemical analysis of groundwater samples from the coastal aquifer collected via six shallow water wells. A total of 17 ERT profiles have been conducted; each has a maximum length of 350 m with a distance from the coast in the range 300–800 m. The derived two-dimensional and quasi-three-dimensional resistivity models successfully mapped the lateral and vertical extensions of the aquifer, determined the depth to the saturated zone, and provided the bulk resistivity of the aquifer. A basement uplift has been detected, indicating that the coastal aquifer is separated into northern and southern zones. The results related to the quality of groundwater were supported by the chemical analysis of the groundwater samples, which showed high concentrations of TDS and Cl–; this indicates a probable partial mixing of the groundwater with seawater. Water-quality index showed that the groundwater is unsuitable for drinking purposes, whereas it is classified as partially adequate for irrigation.

Groundwater flow modelling for an assessment of abstraction and climate change impacts on groundwater resources—an example from the Wadi Araba Basin (Jordan)

The Wadi Araba Basin is a desert area in which finding water represents a real challenge. One potential source for the abstraction of groundwater is a sandstone aquifer which is partly covered by alluvial sediments distributed along the Wadi Araba Valley. The study analyses the impacts of abstraction and climate changes on groundwater quantity. It also aims to define a safe yield for the groundwater resources and to locate new wellfields in hydrogeological areas that will minimize high drawdown. Numerical modelling (MODFLOW NWT version) was applied in order to develop a regional groundwater flow model for the Wadi Araba Basin. The modelling area covers 6268 km2 (the Wadi Araba Basin on the Jordanian side). The cell sizes in horizontal directions are 500 m, and there are four layers in a vertical direction represented by the main aquifers and aquitards of the hydrogeological system (alluvial aquifer, A7/B2 carbonate aquifer, A1-A6 marly aquitard and Kb/Ram sandstone aquifer). Results of the modelling show that renewable groundwater resources stand at around 20 million cubic meters per year (MCM/year). According to the most pessimistic predictive scenario, the water table might decrease by 60 m by 2050, with the most optimistic scenario putting that figure at 24 m. Five new wellfield locations are proposed (four in the central part and one in the northern part of the Wadi Araba Valley). According to the model, the opening of new wellfields in these optimal locations, and the closing of some old wells where relatively large drawdowns were recorded, revealed that a more sustainable abstraction of groundwater could be achieved.

Evaluating the groundwater potential of coastal aquifer using geoelectrical resistivity survey and porosity estimation: A case in Ota, SW Nigeria

Geoelectrical resistivity sounding surveys was carried out at two locations (A and B) in the new CanaanCity residential estate of Canaan land Ota, Ogun state in order to locate possible targets for groundwater explorations. A total of twelve (12) vertical electrical soundings were conducted using the Schlumberger array configuration. The interpretations of the VES curves revealed five to six geoelectrical layers at location A which comprises VES1-7. The geoelectric units consist of the topsoil, sandy clay, lateritic clay, confining bed (clayey sand), and main aquifer (sand). The top of the aquifer in this part of the study area is between 40 m and 83.5 m. Likewise, a total of five to seven layers of geoelectrical units were delineated at the location B portion of the study site (VES 8–12) similar to location A with an addition of the shale unit that was interpreted to be that of the Akimbo Formation of the Dahomey Basin. The depth to the top of the productive aquifer within location B is in the range of 40–112.4 m. The delineated basal shale layer is impermeable, serving as the base seal rock for the confined aquifer system. The estimated porosity values range from 28% to 74%, indicating that the highly porous aquifer system in the area is the coastal plain sands mixed with the alluvium sand of the Benin Formation of Dahomey Basin. The study revealed the complexity of the productive aquifer system in the area and its undulating topography.

Contribution of the resistivity method to the determination of the fault zone and the hydro-geophysical characteristics of the aquifer system in Tataouine (Southern Tunisia).

Southern Tunisia aquifer's systems including Tataouine region has suffered since long time by over-exploitation resulting in a subsequent drop of the piezometric level. Consequently, the overexploitation of these layers poses various problems in term of quality and quantity. Therefore, to better recognize these hydraulic potentialities and evaluate their extensions in this region, a geophysical survey, using the electrical resistivity method was carried out to determine the structure, the configuration of these aquifer systems and to investigate the subsurface layering and evaluation of the aquifer characteristics. Applying the schlumberger array, a total of 335 Vertical Electrical Soundings were conducted along 4 profiles, using a maximum current electrode separation ranging between 500 and 600 m. Qualitatively and quantitively interpretation were both obtained and represents the outcomes from the study field. The qualitative interpretation is based on isoapparent resistivity maps, and the geoelectrical pseudosection analysis. It shows that Tataouine Basin is formed by alternating conductive and resistant anomalies related to the lateral and vertical variation of lithology in the study area. As well, quantitative interpretation using calibration, electrostratigrafic sections and isopach maps shows a clay-sandstone series of the Triasssic, Bathonian and Cretaceous. Theses series, with average low resistivity values, and low percentage of clay present some porosity and constitute the main aquifer unit in the study area. In addition, the carbonate unit shows in certain zone a sight fracking and high resistivity values composed of the aquifers such as; Triassic dolomite, Krachoua limestone, and marl-limestone of upper Jurassic. Furthermore, most of these aquifer units are communicating with each other through the tectonic discontinuities.

An appraisal of natural fluorine contamination of paleogroundwater in Tozeur oases, southern Tunisia, with emphasis on the anthropogenic impact

In southern Tunisia, environmental threat related to fluorine contamination of the “Complex Terminal (CT)" main aquifer paleogroundwater in one of the most important and strongly vulnerable oases was assessed. Emphasis was placed to hydrogeological and hydrochemical processes controlling the occurrence and the transfer of fluorine to paleogroundwater. It has been demonstrated that the fluorine is released from the Carbonate fluorapatite (CFA) deposit underlying the contaminated aquifer. The liberation of F− is ensured by its exchange with hydroxyl and/or by the CFA dissolution through the passage of hot waters ascending from the deep “Continental Intercalaire (CI)" aquifer. The transfer of F-rich waters to the CT aquifer is occurred mainly through deep faults, aquitard windows and through leakage behind casing. This transfer is due to the potentiometric contrast between the two superimposed aquifers, which is enhanced by anthropogenic processes i.e. the overpumping of the CT groundwater and the CI wellbore integrity failure.

Drainage feasibility of a Carboniferous thin-layer limestone aquifer based on a dewatering test: Luxi coal mine, China

Mine water damage is one of the main disasters threatening mine safety during production. The key to mine water hazard prevention and control is determining the main aquifer characteristics that threaten the mine and the hydraulic connections between aquifers and water diversion channels and proposing appropriate preventive measures. This paper focuses on the 16104 working face of the lower coal group in the Luxi coal mine of Shandong Province. The main water-filled aquifer that threatens the no. 16 coal mine is the Carboniferous no. 14 limestone thin-karst aquifer. Before adopting hydrophobic pressure-lowering measures, it is necessary to determine the water yield characteristics of the no. 14 limestone aquifer, the strength of recharging, and the hydraulic connection with the Ordovician limestone aquifer and to analyze and evaluate the feasibility of dredging. First, various geophysical exploration methods were utilized to comprehensively identify the anomalous water yield areas of the aquifer, which were verified by drilling methods. By combining these results with drilling and geophysical results, appropriate drainage and observation holes were selected. Second, a special water discharge stage and sequence were designed to carry out water discharge testing. By analyzing the change of water discharge and water pressure in dewatering test and the change of conventional ion concentration in water samples, the hydrogeological parameters were obtained, the hydrogeological situation was ascertained and the hydraulic connection with the Ordovician limestone aquifer was determined. The drainage time required for the aquifer to attain a safe water pressure and the amount of hydrophobicity were calculated. Through combination with the obtained hydrogeological parameters, the feasibility of depressurization was analyzed. The results show that the water yield property of the no. 14 limestone aquifer is not high, but the connectivity is good. There is a hydraulic connection between the no. 14 and the Ordovician limestone aquifers, but the connection is weak. The no. 14 limestone aquifer of the entire working surface was drained at a rate of 240 m3/h, indicating that the aquifer has good depressurization properties.