Vertical Electrical Sounding Data Research Articles

APPLICATION OF ELECTRICAL RESISTIVITY METHOD FOR SAFETY EVALUATION OF ASEJIRE DAM IBADAN, SOUTHWESTERN NIGERIA

Dam construction provides economic importance to the environs through, water supply and flood control. Post-construction investigation is however necessary for maintenance stability to avoid irreversible environmental changes. In view of this, horizontal resistivity profiling and vertical electrical sounding (VES) were conducted along the embankments and the downstream of Asejire dam to determine its integrity. The methods used were horizontal resistivity profiling and vertical electrical soundings conducted along the embankments and the downstream. Thirty-one VES and Dipole-Dipole Profiling were occupied along the embankments and downstream using Resistivity meter at 20 m intervals for both the VES and Dipole-Dipole. The Dipole-Dipole data were inverted into 2-D Resistivity Images using DIPPRO™ 4.0 Inversion Software while the VES data were quantitatively interpreted using the partial curve matching technique and Winresist 1.0 Version Software. Results of dipole-dipole image and geo-electric section identified three geo-electric layers; comprising topsoil presumably clayey sand and laterites with resistivity and thickness between 59-760m and 0.7-5.2m respectively. The second layer is weathered layer attributed with clay/clayey sand having resistivity and thickness 18-766m and 3.1-36.7 m. The third layer suspected to be fresh bedrock with resistivity range 121-3672m and 18-766 m thick. The Dipole-Dipole results displayed resistivity less than 500m in the first layer with structural evidence of discontinuous observables, but the underlying sequences displayed no indicative of structural weakness. This significant features play a major role in seepage processes from the dam, therefore lithological composition obtained from these results shows the dam has a good integrity.

ASSESSMENT OF SUBSOIL CORROSIVITY USING GEOELECTRIC LAYER PARAMETERS AT ILERE COMMUNITY NEAR AKURE, SOUTHWESTERN NIGERIA

ASSESSMENT OF SUBSOIL CORROSIVITY USING GEOELECTRIC LAYER PARAMETERS AT ILERE COMMUNITY NEAR AKURE, SOUTHWESTERN NIGERIA

Spatial analysis of leachate penetration at Lemna dumpsite, Calabar: Implications for sustainable waste management in Cross River State

This study rigorously investigated the spatial analysis of leachate penetration at Lemna dumpsite, located in Calabar, Cross River State, Nigeria. Purposeful soil sampling, performed at specific intervals (5 m, 25 m, and 50 m) along the Electrical Resistivity profile line within the dumpsite, was augmented by water sample collection from five boreholes near Lemna dumpsite. Utilizing Electrical Resistivity Tomography (ERT) and Vertical Electric Sounding (VES) survey techniques, resistivity data were systematically gathered to comprehensively analyze the Leachate Penetration in the Lemna dumpsite. Laboratory analysis of soil and borehole water quality focused on Benzene, Toluene, Ethylbenzene, and Xylene (BTEX), with paired sample t-tests applied for statistical scrutiny. Analyzing the ERT and VES data employed sophisticated techniques embedded in Resistivity Two Dimension Invasion software and Advanced Geosciences Incorporation Earth Imager software. Substantial disparities (p < 0.05) emerged in the paired sample t-tests for BTEX in soil compared to National Environmental Standard Regulation and Enforcement Agency (NESREA) limits. Similarly, BTEX in borehole water displayed significant differences (p < 0.05) when compared to World Health Organization (WHO) standards, raising alarming concerns about the safety and portability of groundwater in the area. The examination of dumpsite leachate penetration revealed a resistivity anomaly of 8.01 Ωm and an inverse depth of 12.4 m, underscoring profound environmental implications and necessitating immediate remediation efforts. Additionally, Vulnerability and Aquifer Protective Capacity Index (VES) results, with a rating of <0.1, indicated severely compromised aquifer protective capacity, emphasizing the vulnerability of groundwater resources to further contamination. Our study advocates for strategic management, remediation, and monitoring measures to prevent contamination and safeguard water quality in the region.

Salinity distribution in agricultural land by geophysical, hydrochemical and geostatistical approaches: a pilot area located in Qelabshowah–Belqas, East Nile Delta region, Egypt

The study area is situated in the Qelabshowah–Belqas region, known for its Quaternary deposits. This research aims to demonstrate the two-dimensional (2D) variation of subsurface layers and salinity distribution using geoelectrical data, hydrochemical analysis, and geostatistical analysis. DC resistivity measurements were taken at fifteen vertical electrical sounding (VES) survey points using a Schlumberger array (AB/2 = 100 m) along three profiles. In addition, an electrical resistivity tomography (ERT) survey was conducted with a dipole–dipole array across one profile. Seven surface water samples were collected in the area. From the 1D and 2D inversion of VES and ERT data sets, three-to-four geoelectric layers were identified, including unconsolidated surface deposits, saturated clayey sand, saturated sand, and a salt-rich layer. The 2D inversion of VES data revealed an ancient salt-rich layer deposited in swampy conditions over a conductive wet sand layer along profile one due to salt mineral infiltration and dissolution. The 2D inversion of ERT data showed accurate lateral geometric accuracy compared to the 2D inversion of VES data, highlighting geological features, such as caves in the second layer and a buried water canal on the ground surface. Surface water samples showed high salinity levels with sodium hazards, indicating an Na–Cl composition. Geoelectric and hydrochemical data sets were geostatistically analyzed using spherical variogram supported ordinary Kriging interpolation. The analysis indicated weak to moderate spatial dependency for true resistivity parameters, while sodium content (SC) and permeability index (PI) showed strong spatial correlation. The 2D spatial distribution resistivity maps based on the 1D inversion of VES data displayed a general decrease in resistivity with depth, likely due to clay minerals or moist soil in the second layer and saline irrigation water infiltration in the third layer. The 2D spatial distribution of SC and PI showed a high concentration zone, posing a potential risk to agricultural crops regardless of soil permeability. It is recommended to use these maps when cultivating plants that can tolerate high sodium levels during the reclamation process.

Modeling and interpretation of electrical resistivity data in anisotropic media using a generalized regression neural network: A case study on the Lokbatan mud volcano, Azerbaijan

This study explores the electrical anisotropy effects in a vertical electrical sounding dataset acquired from the Lokbatan mud volcano in Azerbaijan. Vertical electrical sounding is a fundamental geophysical technique for mapping subsurface resistivity distributions; however, electrical anisotropy is a factor often ignored, can significantly influence field measurements, especially with respect to layer thicknesses. This study investigates electrical anisotropy effects on vertical electrical sounding data using generalized regression neural networks for estimating parameters of layered subsurface. Schlumberger electrode arrays were employed for these purposes with a 22-sounding dataset. In general, a classical approach for estimating electrical anisotropy coefficient fails. Vertical and horizontal resistivity values cannot be estimated using vertical electrical sounding data. Thus, generalized regression neural networks are considered. The generalized regression neural networks for appraising parameters of electrical anisotropy can be used with keeping vertical resistivity higher than horizontal resistivity in each layer as an assumption. Further, the proposed method applied how the surrounding clay-rich geological material and layered structure influence electrical properties of the Lokbatan mud volcano in Azerbaijan. As a conclusion, without considering electrical anisotropy makes interpretation erroneous especially with respect to layer thicknesses.

Groundwater Study Using Vertical Electrical Sounding (VES) Data Based on Resistivity and Porosity of Rocks in Kampung Melayu, Bengkulu City

This research aims to identify groundwater based on the value of resistivity and porosity of rocks, which are important parameters in the management of groundwater resources and Development Planning in the region. This groundwater research using Vertical Electrical Sounding (VES) data based on the value of resistivity and porosity of rocks was carried out by measuring resistivity using the (VES) method at 20 sounding points located in Kampung Melayu District, Bengkulu City. The VES method is one of the approaches in the geoelectric method to determine the lithological characteristics of subsurface rocks. Resistivity Data obtained were then inverted and analyzed and interpreted to obtain lithology of subsurface rocks and groundwater level distribution in Kampung Melayu, Bengkulu City. The results showed the presence of groundwater based on low resistivity anomaly values with a range of values from 5 to 30 meters in the West and 10 to 50 meters in the East, with resistivity values ranging between 5 Ω.m up to 45 Ω.m. This research is expected to make a significant contribution to the management of groundwater resources in the District of Kampung Melayu, Bengkulu City and can be the basis for development planning in the area. In addition, it is hoped that the results of this research can be a reference for further research in the field of hydrogeology and groundwater modeling. Keywords: Aquifer; geoelectricity; groundwater; porosity; resistivity

Assessment of water shortage in underground aquifer in Abuja during dry season

Water shortage is a complex issue with severe implications for human well-being, agriculture, and ecosystems. Climate change, population growth, and inadequate water management practices contribute to this global problem. This study is to identify the causes of ground water scarcity and determine groundwater potential zones in the Abuja community. The research area's borehole coordinates, Landsat 8 satellite imagery, AsterDEM 30m resolution DEM data, and vertical electrical sounding (VES) data were all used to do this. Unsupervised classification of Landsat imagery was used to create a layer of land use and cover, image filtering techniques were used to improve the visualization of lineament extraction, and density analysis was used to quantify lineament density. AsterDEM data was subjected to surface analysis to acquire elevation data, while VES data were interpolated to produce spatial distributions of the resistivity and thickness parameters. To identify groundwater potential zones, multiple criterion analysis using the analytical hierarchical process (AHP) was utilized to reclassify variables such as land use, elevation, lineament density, resistivity, and thickness. To create the zones, these characteristics were weighted and layered. According to the findings, resistivity levels varied from 6.25 m to 676 m, and the geologic ground structure's thickness ranged from 0.27 m to 92.37 m. Elevation varied from 41 meters to 720 meters, while lineament density ranged from 0 to 0.04. 74% of the land was categorized as vegetated, 21% as built up, 2.7% as water bodies, and 2.3% as rock formations. Within Abuja, zones of groundwater potential were identified as being very low (5%), low (26.7%), marginally high (26.3%), moderately high (28.5%), and very high (13.4%)

Groundwater Characterization Studies Using Electric Resistivity Survey (ERS) in Kirana Hills, District Chiniot, Pakistan

This study demonstrates an application of resistivity surveys to understand local hydrological conditionsand basement configuration in Kirana Hills region of District Chiniot. Schlumberger configuration has been applied toacquire vertical electrical sounding (VES) data. The apparent resistivity curves were calibrated with theoretical curvesto compute true resistivity and depth of different layers. Maps of true resistivity at various depths were generated tostudy the lateral resistivity variation in the area. VES sounding data were compared with available lithological columnsto establish relationship of lithology and resistivity. Resistivity values are laterally variable due to lithology and qualityof water. Very low resistivity values were observed within alluvial sediments close to the Kirana Hills due to presenceof high Total Dissolved Solids in water. Resistivity value layers in unconsolidated sediments increases in the southernand western parts of the area where relatively better quality of groundwater occurs. In the northern and eastern parts ofthe study area very high resistivity (greater than 100 Ωm) is recorded at depth greater than 40m that indicates hard rockbasement. The resistivity survey in the area is useful to differentiate zones of low and high Total Dissolved Solidsgroundwater and also determine the zones where subsurface basement is shallow. Therefore, resistivity survey inKirana Hill regions is helpful in solving hydrological issues of the study area.

Integrated groundwater exploration in basement complex terrain for sustainable regional water supply in Abuja, Nigeria

This study integrates geophysical and geological analyses to identify potential areas for regional water supply in newly developed sites and regions lacking coverage from the lower Usuma Dam. Covering an expanse of approximately 5200 km2, high-resolution aeromagnetic data were collected, analyzed, and interpreted alongside thirty-five (35) vertical electrical sounding (VES) data points, utilizing the Schlumberger array with current electrode separations (AB/2) ranging from 100 to 140 m and potential spacing MN/2 varying from 0.25 to 5m. The aeromagnetic data, reduced to the equator, reveal anomalies characterized by variations in magnetic susceptibility, indicative of changes in rock composition. Total magnetic field intensity ranges from 435.7 nT to 568.3 nT, with variations attributed to the presence of diamagnetic materials, specifically magnetite and quartzite in basement rocks. Residual data, ranging from −92 to 41.4 nT and high residual values correspond to granite gneiss and coarse porphyritic biotite hornblende granite. First vertical derivative results expose lineaments with lengths ranging from 894.4m to 11.627 km, supported by tilt derivative lineaments of 1.131–11.400 km these delineate potential zones for urban and regional groundwater supply, emphasizing the role of lineaments and faults in controlling structural geometry for groundwater flow. Geological mapping affirms high fracturing with conjugate faults in the area. Interpreted VES curves identify 65.7% as H-type, 22.9% as KH, and 5.7% as QH curves, with HK- and A-type curves at 2.9%. Overburden thickness varies from 6 to 44 m at specific VES points. Iso-resistivity maps exhibit high resistivity values (6000 to 9000 Ωm) due to geological outcrops, while low resistivity values result from a partially or highly fractured basement. Recommendations include drilling 31 VES points for regional water supply in Abuja's urban area, offering a diversified water source and reducing dependence on potentially vulnerable surface water supplies.

Inversion of Vertical Electrical Sounding Data by Using General Regression Neural Network

Düşey elektrik sondajı (DES) verilerinin ters çözümü doğrusal olmayan bir problem olması nedeniyle zor bir işlemdir. Bu çalışmada, genelleştirilmiş regresyon sinir ağlarının özdirenç problemine uygulanabilirliği araştırılmıştır. Genelleştirilmiş regresyon sinir ağları (GRNN) ile düşey elektrik sondajı verilerinin ters çözümü test edilmiştir. Sinir ağı düz çözüm ile oluşturulan yapay verilerle eğitilmiştir. Ağ hem eğitim seti içinde bulunmayan diğer yapay veriler ile hem de arazi verisi ile test edilmiştir. Ayrıca GRNN parametresi olan yayılım parametresi de farklı değerler kullanılarak karşılaştırılmıştır. En düşük hata oranını veren yayılım parametresi kullanılmıştır. Yapay veriler 3 tabakalı modellerdir. Arazi verisi ise 4 tabakalı olarak değerlendirilmiştir. GRNN çıktısı yapay verilerde 3 tabakalı model için 3 özdirenç ve 2 tabaka kalınlığı olmak üzere 5 parametredir. Arazi verisinde ise 4 tabakalı bir model için 4 özdirenç ve 3 tabaka kalınlığı olmak üzere 7 parametredir. GRNN ile ters çözüm sonuçları çok düşük hata oranları ile başarılı olmuştur. DES verilerinin kalınlık ve özdirenç kestirimleri için GRNN yöntemi performansı yüksek bir oranda başarılı olmuştur.

Modeling of geophysical derived parameters for groundwater potential zonation using GIS-based multi-criteria conceptual model

This study modeled geophysical derived parameters and multi-critically synthesized their themes based on geospatial and analytical hierarchy processes (AHP) approaches for groundwater potentiality prediction mapping. These methodologies were investigated in a typical hard rock geologic terrain, southwestern, Nigeria. Considering the spatially acquired 96 vertical electrical sounding (VES) data in the area, geoelectric sections revealing five subsurface layers including the topsoil, laterite, weathered layer, fractured basement and fresh basement rock were produced mindful of the 2-D resistivity structure subsurface imaging data interpreted results. The correlative results of the 2-D resistivity structure images and VES data interpretation results delineated major low resistivity vertical discontinuity typical of fractured zones characterized with width range of 25–40 m, while the depth vary from about 40 to > 60 m. Themes of groundwater potential conditioning factors (GPCFs), namely: regolith, bedrock relief, hydraulic head, coefficient of anisotropy, aquifer resistivity and aquifer thickness were prepared from the re-analyzed hydrogeological and geophysical data. The produced themes were appropriately weighted in the context of AHP data mining technique. The groundwater potential prediction index (GPPI) mathematical modeling equation for the area was established via applying the weight linear average algorithm involving the AHP weightage results. The synthesized results of the applied GPPI model equation on the GPCFs’ hydrogeologic themes give GPPI values in the range 1.59–3.65 for the study area. The geospatial modeling of the GPPI estimated values result produced groundwater potential prediction index map for the area. The produced GPPI model map zoned the area into low (1.59–2.30), medium (2.30–2.61), medium–high (2.61–3.02) and high (3.02–3.65) groundwater potential classes. The area analysis of the GPPI map indicates that more than 70% of the study area has ‘low to medium groundwater potential. The GPPI map result verification using reacting operating characteristics technique results gave 86% and 81% success and prediction rates, respectively. The findings of this study are useful to water managers and decision-makers for locating appropriate positions of new productive wells in the study area and other areas with similar geologic settings.

Investigation of petrophysical and hydrogeological parameters of the transboundary Nubian Aquifer system using geophysical methods

The recent research aims to investigate the petrophysical and hydrogeological parameters of the Nubian aquifer system (NAS) in Northern Khartoum State, Sudan, using integrated geophysical methods, including surface electrical resistivity and geophysical well-logging. The Nubian aquifer is a transboundary regional aquifer that covers vast areas in Sudan, Egypt, Libya and Chad. The well-logs, including self-potential (SP), natural gamma ray (GR), and long normal resistivity (RS), are integrated with Vertical Electrical Sounding (VES) measurements to delineate the hydrostratigraphical units. As a result, two aquifers are detected. An upper aquifer comprises coarse sand with an average thickness of 50 m and a lower aquifer of sandstone with more than 200 m thickness. For a thorough evaluation of the aquifers, in the first stage, the petrophysical and hydrogeological parameters, including formation factor, total and effective porosity, shale volume, hydraulic conductivity, and transmissivity, are measured solely from geophysical well-logs. In the second step, the results of geophysical well logs are combined with VES and pumping test data to detect the spatial variation of the measured parameters over the study area. As a result, the hydraulic conductivity of the Nubian aquifers ranged from 1.9 to 7.8 m/day, while the transmissivity varied between 120 and 733 m2/day. These results indicated that the potentiality of the Nubian formation is high; however, in some regions, due to the sediment heterogeneity, the aquifers have intermediate to high potential. According to the obtained results, it can be concluded that the Nubian Aquifer in Khartoum state is ideal for groundwater development. This research discovered that geophysical approaches can be used to characterize moderately heterogeneous groundwater systems by comparing the Nubian aquifer with similar aquifer systems that have similar hydrogeological settings. This study emphasized the application of universal principles in extrapolating hydraulic parameters in hydrogeophysical surveys. This approach aims to reduce the costs and efforts associated with traditional hydrogeological approaches.

Stability and uncertainty assessment of geoelectrical resistivity model parameters: a new hybrid metaheuristic algorithm and posterior probability density function approach

Abstract. Estimating a reliable subsurface resistivity structure using conventional techniques is challenging due to the nonlinear nature of the inverse problems. The performance of the inversion techniques can be pretty ambiguous based on the optimal error, although traditional methods have proven to be quite effective. In this work, the impacts of the constraints accessible from a borehole are examined for further assessment and to enhance algorithm effectivity. The vPSOGWO strategy is a new approach that is based on a model search space without any prior information, and it describes the hybridization of particle swarm optimization (PSO) with the Grey Wolf Optimizer (GWO). To understand the efficiency and novelty of the algorithm, it has been validated on two different kinds of synthetic resistivity data with various sets of noise and, subsequently, applied to three field datasets of different geological terrains. The analyzed results suggest that the subsurface resistivity model shows considerable uncertainty. Thus, it is superior to examine the histograms and posterior probability density functions (PDFs) of such solutions to exemplify the global solution. A PDF with a 68.27 % confidence interval (CI) selects a region with a higher probability. Therefore, the inverted models are used to estimate the mean global solution and the most negligible uncertainties, where the mean global solution represents the best solution. Our vPSOGWO-inverted outcomes have been proven to be more accurate than classic PSO, GWO, and state-of-the-art variants of classic approaches. As a result, this novel method plays a vital role in vertical electrical sounding (VES) data inversion.

Delineation of Aquiferous Zones in Some Parts of Umuahia and Uzuakoli Environs Using Vertical Electical Sounding Data

A delineation of aquiferous zones in some parts of Umuahia and Uzuakoli environs was carried out using Vertical Electrical Sounding (VES). A total of fourteen (14) VES data were acquired at different locations. Cross sections of the VES data were interpreted and correlated along profiles. The results showed that sands constitute the aquifer units while clay and shale made up the aquiclude. Aquifer units occur at shallow depths in some places such as Ibeku, Umule, Ohuhu, at 9m to 30m with thickness range of 9 m to 50m while some places such as Isingwu, Nkpa, Amachara, Ubakala, Lohum, Etitulo Bende areas have deep aquifer units with the depth to the top of aquifer ranging from 40m to 115m and the aquifer thickness ranges from 17m to 102m.The degree of the relationship of the aquifer parameters were investigated using some statistical analysis in which the coefficient of correlation between depth and resistivity is 0.6; From the analysis, it has been ascertained that there exist shallow and deep aquifer systems within the Ameki Formation and the depth to the top of these aquifers are in range of 40 m to 115m. The deep aquifer systems except the shallow units are confined. Recommended total drill depth (TDD) to guide a successful water borehole prospecting in the area should be 140m in the North, 180m in the south and west flank of the study area.

Delineating of Groundwater Aquifer Potential Using Vertical Electrical Sounding (VES) Methods in Giriloyo, Wukirsari Village, Imogiri District, Bantul Regency, Special Region of Yogyakarta

The geophysical investigation in Giriloyo, Wukirsari Village, has defined the groundwater potential zones. The research region underwent a geophysical examination utilizing the electrical resistance method, which comprised the vertical electrical sounding (VES) technique and the Schlumberger array system. The study area is surrounded by common rock types such as lava, tuff, agglomerate, and alluvial. In the study region, five lines were explored. Data for subsurface resistivity were gathered with an Oyo McOhm type 2115. IPI2win, a piece of computer software that analyzes data and automatically interprets apparent resistivity, was used to examine the data. The VES data showed the varied nature of the subsurface geological sequence. The geoelectrical cross-sections along the profile of (VES 2-3-4-1) show an aquifer, which stretches from the southeast towards the northwest part of the basin. Tuff is seen to have formed shallow aquifers due to the top weathered part at VES-2 and 3, while Quartz chlorite calcite (VES-4) and Plagioclases (VES-1) are devoid of shallow aquifers. The higher-elevation lithological areas recharge the low-elevation aquifer zones. At VES 2 and 3, relatively low resistivity values (&lt; about 100 Ωm) have been observed. A field observation at these locations reveals that these lithologies are highly fractured with a weathering profile of up to 10 m. Thus, these are the sites where groundwater potential zones can be marked (figure 4). The high resistivity (about 3162 Ωm regions is observed extending at the VES-4; this may be due to the least weathered Quartz chlorite calcite at high elevation. VES-1 is also located on the plagioclase and shows a slight resistivity zone, which could be considered a groundwater recharge zone. This profile shows the high possibility of groundwater potential due to the zone of lineaments.

Groundwater potentiality mapping: A case study in Baba and Sidri watersheds, South Sinai, Egypt

Groundwater potential zone (GWPZ) mapping is a multi-parameters approach that can assess the groundwater potentiality in mountainous terrain and coastal areas. This approach utilizes the geomorphology, lithology, rainfall, structure lineaments density, drainage density and slope which are the major effective factors controlling the groundwater potentiality. Primarily, these factors are prepared in the form of thematic layers using GIS technique, and then assigned different weights for these thematic layers using Analytical Hierarchy Process (AHP) technique to explore the GWPZ. This GWPZ is generated by the linear weighted sequence of all the prepared thematic layers. The moderate GWPZ (41.8%) sites are located in the main Wadi channels and alluvial fan at western portion; whereas, the high GWPZ (29.8%) concentrates in Homaier depression at the eastern region. Vertical electrical soundings (VES) and time-domain electromagnetic soundings (TEM) measurements have been achieved at high GWPZ to estimate depth and thickness of both saturated and unsaturated areas with water. This geophysical investigation has been done to confirm and support the effectiveness of applied factors of GWPZ mapping. The findings of these measurements are validated by standardizing the measured electrical resistivity values with the sequential layering layout and data records for five wells drilled at the locations of the geophysical soundings. VES and TEM data show the existence of moderately thick adjacent aquifers, covered with a dry area of different thicknesses (18–50 m). The aquifer units with thickness ranging from 43 to 71 m has resistivity values of 22–50 Ω m which is an indicator of freshwater content.

Application of frequency selection and geoelectrical sounding methods for mapping of leachate’s pathways in an active dumpsite

Contamination of surrounding environments is one of the threats to the proper maintenance of municipal waste sites in developing nations. This study integrates natural electromagnetic (EM) field and geoelectrical sounding methods to assess the leachate’s pathways in the near-surface layers and groundwater system in and around an active dumpsite. Five natural EM traverses were obtained in varying orientations using PQWT-TC 150 model. Fifteen vertical electrical sounding (VES) data points were randomly occupied using SAS 4000 ABEM resistivity meter. The two techniques revealed some intercalations of conductive and resistive media in the study area. The conductive media are composed of mixtures of leachates into clay and groundwater units, thereby creating zones of very low electrical potential differences from the surface to a depth beyond 30 m. A zone of leachate-aquifer’s interphase exists between the third layer and the fourth layer. The directions of the fluid flow are in the S–N and SE–NW trends, which could be linked to the fault towards the northwestern part of the study area. The fluid dynamics, however, justified the reason for the thick conductive materials being mapped at the northwestern and northern parts of the study area.

Multi-Criteria Evaluation (MCE) of Groundwater Prospect and Vulnerability Index Mapping from Second-Order Geo-Electric Indices: A Case Study of Coastal Environments

Exploration, management, and conservation of groundwater resources are critical stages toward potable water supply, driven by an expanding populace and the threat of a new norm posed by the distinctive coronavirus (COVID-19) pandemic. An in-depth assessment of the potential of groundwater reserves and susceptibility, using a multi-criteria evaluation, is required to aid in the planning of exploration programs for groundwater well location. Thirty (30) vertical electrical soundings (VES) were collected in Okerenkoko, Warri-Southwest, Delta State, to assess groundwater potential and vulnerability indicators. The VES data were used to obtain the first-order geoelectric variables, which were further exploited to calculate the geo-hydraulic parameters (hydraulic conductivity and transmissivity) and the vulnerability indices of the aquifer. For aquifer vulnerability appraisal, the AVI (aquifer vulnerability index), GOD (groundwater occurrence, overlying lithology, and depth to the aquifer), and GLSI (geoelectric layer susceptibility index) models were used. The groundwater characteristics in the area were evaluated using the aquifer resistivity, thickness, transmissivity and coefficient of anisotropy values of the aquifer layers defined from VES 1-30. The results show that aquifer layers with low resistivity favor more saturation due to immense porosity and therefore have greater groundwater potential than aquifers with high resistivity. The geoelectric structures defined by VES 1, 2 and 4 were consistent in their groundwater potential and yield judging from the multi-criteria assessments. The estimation of AVI, GOD, and GLSI models for aquifer threat assessment was facilitated by the multi-criteria evaluation of vulnerability indices utilizing hydro-geophysical parameters and index-based approaches. The models depend on the symbiotic effects of geologic array and thickness as the basis for the magnitude of conservation imparted to any particular aquifer involved. The AVI model map depicts that most of the VES locations were rated high (C between 1 and 2) to extremely high (C &lt; 1), indicating that the aquifers at these locations are vulnerable to pollution. However, the extent of vulnerability observed in the GOD model is less than in the AVI model, as GOD accords much more inclination to the inherent properties of geologic entities. The GOD model map categorized the vulnerability index ratings in the area as negligible (0.0-0.1), low (0.1-0.3) and moderate (0.3-0.5), with most VES locations ranked low to moderate, which indicates that these locations are susceptible to vulnerability. In the GLSI model, individual overlying layer thicknesses were prioritized. The GLSI model map shows that the vulnerability index ratings in the area are ranked as moderate (2.00-2.99), high (3.00-3.99) and extremely high (≥ 4.00) with most of the VES locations ranked moderate to high with the exception of VES 27, which ranked extremely high in both AVI and GLSI indices. By correlating the results of vulnerability index valuation for the AVI, GOD and GLSI models, more correlation was observed between the AVI and GLSI models. These findings validate the adoption of a multi-criteria evaluation methodology for groundwater potential and aquifer vulnerability studies and are strongly recommended as practical criteria for locating subsurface aquifers and their protective measures for groundwater prospect development planning and management.

Direct Detection of Groundwater Accumulation Zones in Saprock Aquifers in Tectono-Thermal Environments

Some vertical electrical sounding (VES) data from tectono-thermal environments usually plot anomalously on a VES curve, thereby distorting the curve trend at the points of their occurrence. These datasets usually plot noisily in the form of a sudden rise and drop in electrical resistivity values. They constitute abnormal datasets that are usually deleted to recover trends and consequently develop confidence in both the datasets and the modelling and interpretational processes. This study was conducted to assess their origin and consequently gain an understanding of their contributions to groundwater accumulation and transmission in saprock aquifers. The results, supported by co-located drilling and pumping test data, show that these datasets are indicators of subsurface conditions where high-resistivity unconformal structures directly overlie saturated (low-resistivity) porous media, provided that the resistivity of the first breakout point is less than those from subsequent points. Remote sensing data reveal that these types of curves are common in hard rock and metasedimentary environments. Borehole groundwater yields can also be assessed qualitatively from the number and trend of breakoff points. The integrity of the breakoff points must be affirmed by using more sensitive equipment for data acquisition and repeating the measuring process using different potential electrode separations and—where possible—VES profile orientation.

Evaluation of geophysical parameters for groundwater productivity in the Commune of Jesse, Delta State Nigeria

&#x0D; Aquifer geohydraulic properties in Jesse were studied by the application of vertical electrical sounding (VES) and pumping test. The VES data was collected using ABEM SAS 1000 Terrameter and results processed using manual matching of curves and computer iteration, and interpreted in the forms of geologic models and geoelectric layers. The aquiferous unit was found at a depth of 5.30 m to 30.30 m with a range of resistivity from 87.30 Ω-m to 1945.40 Ω-m. Dar-Zarrouk parameters estimation and results of borehole pumping test produced the aquifer hydraulic parameters. The hydraulic conductivity values range from8.171 - 8.279 m/day, transmissivity from 43.8770 - 517.7480 m2/day, and formation factor from 0.369 - 8.501. These results are indications of a prolific and high yielding aquifer capable of withstanding long duration of pumping. Results of groundwater electrical conductivity and total dissolved solids ranged from 11.65 - 198.80 μs/cm, and 29.40 - 35.40 mg/dm3 respectively, signifying very moderate mineralization of the groundwater. The average electrical conductivity of 68.04 μS /cm and total dissolved solids of 32.58 mg/L were lesser than the acceptable limits of the Nigerian Standard for Drinking Water Quality (NSDWQ) of 1000 μS/cm and 500 mg/L respectively. This study affirmed that the aquifer in Jesse is suitable for groundwater exploitation for local and regional purposes.