Vertical Electrical Sounding Interpretation Research Articles

Interpretation of vertical electrical soundings by means of ISM, PHT and C-N, case of a ditch in Al-Sharquieh phosphate mine in Syria

The main objective of this paper is basically to calibrate and compare the different geoelectrical results obtained by the three interpretative techniques of the inverse slope method (ISM), Pichgin and Habibuleav (PHT) and concentration-number (C-N) fractal modeling with the well lithology of an existing known ditch in the Al-Sharquieh phosphate mine in Syria. Those interpretative techniques are applied herein to interpret the vertical electrical soundings (VES) points measured along a parallel profile to the ditch. ISM reveals the presence of four to five geoelectrical layers in the study region. The PHT allows the determination of the tectonic subsurface features of the study region, by analyzing the non homogeneity points and their distributions along a given geoelectrical profile. The fractal C-N modeling provides the different apparent resistivity ranges dominating in the study region. Good agreements are obtained between the direct observed field lithological descriptions of both wall sides of this ditch, and the results obtained by those three interpretative geoelectrical techniques. The high radioactive readings exceeding four hundred count per second (cps) are due to the presence of secondary uranium accompanied with fractures, cracks and joints. The secondary uranium occurrences accompanied by phosphate deposits are found in the study area in the fractured zones, as determined by the geoelectrical PHT technique. The three mentioned geoelectrical methodologies are therefore used as indirect techniques for delineating the radioactive zones related to uranium prospecting. It is a successful application of the joint use of those three techniques, that could be applied in mining to delimit the subsurface geological structure. The reliability and efficacy of (ISM), (PHT), and (C-N) fractal modeling techniques are consequently well confirmed, and it is therefore recommended to use and apply them for characterizing and describing similar lithological phosphatic sequences, and for several shallow mining, environmental and civil engineering applications.

Exploration of Ground Water Potential of Federal University of Technology, Owerri and Its Environs Using Resistivity Survey

The research focused on evaluating the groundwater potential in the vicinity of Federal University of Technology Owerri (FUTO) using a resistivity survey method. The investigation involved the utilization of eleven Schlumberger vertical electrical soundings (VES). The data collection was conducted using an ABEM Terrameter SAS4000 and then processed with IPI2Win Software, which relies on the conventional theory of curve matching. This process aimed to determine the depth, quality, and subsurface formations of the groundwater. The VES interpretation results revealed the presence of 3-5 geoelectric layers above the aquiferous layers. Various curve types were identified in the study area, including monotonically ascending (AA), bowed-ascending (HA), bowl-bell (HK), and ascending-bell (AK) curves. The majority of the field curves were found to be of the A-shaped type, signifying specific aquifer characteristics. The study indicated that the depth to the water table is relatively shallow in the Ihiagwa area, with an average depth of 7.26 meters. In contrast, the aquifer's depth is deeper around Avu, Nekede, and Eziobodo areas, with a mean depth of 32.33 meters. Obinze had very deep aquifers, with an average depth of 57.75 meters. Furthermore, the study established a relationship between aquifer characteristics and geoelectric parameters, allowing for the estimation of hydraulic conductivity and transmissivity values at all the sounding locations, even in areas lacking boreholes. These hydraulic characteristics showed that the aquifer had protective capacities ranging from 0.036 to 0.509 mhos, transmissivity values ranging from 11856.32 to 28661.28 m2/day, and hydraulic conductivity ranging from 13.47 to 1009.2 m/day. These values suggested that the aquifer materials are highly permeable, facilitating fluid movement within the aquifer. This research demonstrated the effectiveness of surface geophysics in estimating aquifer hydraulic characteristics, particularly in situations where pumping test data are unavailable. It also highlighted the vulnerability of the aquifer to surface contaminants. The findings are expected to be valuable for the long-term planning of groundwater exploitation projects in the study area.

Hydrological Evaluation of the Groundwater Potential in the Fractured Karoo Aquifer Using Magnetic and Electrical Resistivity Methods: Case Study of the Balfour Formation, Alice, South Africa

The study is aimed at evaluating the groundwater accumulations present in Alice using magnetic and electrical resistivity measurements to examine the trends of structural elements and characterize the groundwater resource for borehole drilling. The magnetic maps show a low magnetic linear structure moving northwest to southeast direction, which may be caused by fractures. The linear high intensities were probably caused by dolerite dykes, while dolerite sills caused broader high-intensity areas. The depth slices show that the near-surface magnetic structures are visible to a depth of about 19 m, and the deep-seated structures are found at a depth of about 31 m, possibly deeper. Twenty-five vertical electrical soundings (VES) of the Schlumberger array were measured with AB/2 varying between 1.5 m and 250 m across the study area. The VES interpretation showed four geoelectric layers composed of HK and HA curve types. The geoelectric layer’s thicknesses are (1) topsoil from 0.4 to 1.8 m, (2) weathered layer from 0.8 to 17.5 m, and (3) weathered/fractured layer from 9.9 to 143.9 m; the third layer could be the productive water-bearing zones, and (4) bedrock layer has an infinite thickness. The layers have resistivity values of 20-5752 Ωm, 3-51 Ωm, 136-352 Ωm, and 44-60428 Ωm, respectively. A correlation of the VES with the borehole log indicated a well-matched result. The magnetic and electrical resistivity surveys provided a detailed subsurface structure and helped identify possible fractures that could act as a passage for groundwater.

Vertical Electrical Sounding (VES) Technique to Map Potential Aquifers of the Guigou Plain (Middle Atlas, Morocco): Hydrogeological Implications

Vertical electrical sounding (VES) as a geoelectrical method has proven its effectiveness throughout the history of groundwater geophysical investigation. In this sense, VES was carried out 47 in the study area with the aim of determining the geometry and limits of Quaternary basaltic aquifer formations and, above all, the location of electrical discontinuities in the area located in the north of Morocco, between the center of Almis Guigou and the city of Timahdite. This area is experiencing an overexploitation of the groundwater due to excessive pumping and the development of intensive agriculture activities, resulting in a continuous decrease in piezometric levels. The processing of the diagrams by WINSEV software showed the presence of an electrically resistant surface level, attributed to basaltic formations, of the Quaternary age, whose thicknesses reach at least 150 m to the SW of the area. This level is superimposed on a moderately conductive horizon which, according to local geology, corresponds to Pliocene marl and limestone alternations. The correlation of VES interpretation models allowed us to elaborate thematic maps and geoelectrical sections which illustrate the vertical and lateral extension of the basaltic reservoir as well as its thickness, which decreases in general from the south-west to the north-east; however, the main electrical discontinuities also correspond to faults and fractures, and they show a NE–SW direction sub-parallel to the major accidents of the Middle Atlas. A prospectivity map of the local aquifer was generated, coinciding with regional fault lines and confirmed by the alignment of very good flowing water boreholes. This geophysical study by electrical sounding shed light on the geometry and extension of the aquifer and opened avenues to draw further conclusions on its physical and hydrodynamic characteristics, as well as to optimize the future siting of groundwater exploitation boreholes through the elaboration of the local aquifer prospectivity map.

Geo-electrical investigation of ground water potential using vertical electrical sounding

Groundwater potential assessment using the vertical electrical sounding (VES) technique was carried out at Ekiti state Southwestern, Nigeria with a view to solving the problem of incessant failure of groundwater boreholes in the study area. A total of 10 VES were carried-out using Schlumberger electrode configuration. The data was interpreted quantitatively using the partial curve matching and computer iteration techniques to generate the first order geoelectric parameters. The borehole lithological log was used to constrain the conventional VES interpretation. The VES results aided by the borehole lithological log reveal four distinct subsurface geologic layers which correspond to Top soil, Lateritic clayey sand, Sand, Sandstone and Consolidated sandstone. The analysis shows that sands at the upper layer within the depth of 2.3 - 76.2 m are unsaturated while sands at depth not less than 100 m in some sampling points are saturated and denote the aquifer units in the study area. Boreholes/deep wells could be cited at these points at depth interval 80 - 100 m. This study has provided an insight to the subsurface condition of the aquifer systems and delineated areas for probable groundwater development in Ekiti State.

Integrated geophysical methods and techniques for studying the perennial springs in Ikanje- Share, Kwara State, Nigeria

An integrated magnetic, self-potential (S.P.) and electrical resistivity survey involving magnetic profiling and 1D Vertical Electrical Sounding (VES) electrical imaging techniques were carried out in the transition environment between the Nupe Basin and Southwestern Nigeria Basement Complex at Ikanje-Share in Kwara State, Nigeria. The Ikanje-Share perennial springs started gaining a lot of attention after many travelers and tertiary institutions in Nigeria made it a good choice for their fieldwork exercise. The surveys were done in order to delineate the subsurface layers, determine the geoelectrical characteristics and identify geological structures (e.g., faults and fractures) that are responsible for the perennial spring formation. The magnetic profiling was used as reconnaissance technique to identify lineament features that are favourable to groundwater accumulation and transmission. Some magnetic lineaments were qualitatively inferred from some profiles in the study area. The fault locations coincide with inflection points in S.P. curves and occur as horizontal and consistent planes of discontinuities at depths of approximately 1.25, 4.25, 8.75, 13.15 and 21.25 m, respectively. The VES interpretation results indicated four to five major geologic units, which include: the topsoil/clay/lateritic layer, the lateritic layer, the weathered basement, the weathered/fractured basement and the fresh bedrock. The weathered and fractured basements constitute the main aquifer units and the overburden thickness varies from 5.0 to 16.8 m. The study has shown the usefulness of integrated geophysical methods and techniques in subsurface structural and groundwater development study over the perennial springs in the transition environment between the Nupe Basin and the Southwestern Nigeria Basement complex.

Vertical electrical sounding data inversion using continuous ant colony optimization algorithm: A case study from Hassi R'Mel, Algeria

ABSTRACTAmong the existing geophysical methods, the vertical electrical sounding remains a fast and economical way to detect groundwater resources. However, the interpretation of the vertical electrical sounding data often suffers from non‐uniqueness due to the ill‐posed nature of the inverse problem. In recent years, metaheuristic algorithms have been successfully used for solving ill‐conditioned and ill‐posed problems. This work presents a scheme that uses the continuous ant colony optimization (ACOR) technique to invert vertical electrical sounding data. The ACOR is a global search algorithm that explores and finds the globally optimal solution over a search space by mimicking the behaviour of biological ants. The development of this algorithm was due to the requirement to interpret a set of vertical electrical sounding collected at the region of Hassi R'Mel (Algerian Sahara). The area has a particular geological/geoelectrical structure, which renders the interpretation of vertical electrical sounding challenging as standard inversion approaches tend to fail to recover a reliable resistivity model. The ACOR algorithm was initially tested with synthetic data from models simulating the geological/hydrogeological structure of the studied area. The results verified the robustness and stability of the ACOR algorithm even in the presence of a high level of noise. Furthermore, the tests indicated that the ACOR algorithm performed better when compared to other inversion techniques for this particular geoelectrical structure. Five vertical electrical sounding profiles using a Schlumberger array collected in the region of Hassi R'Mel were inverted using the ACOR algorithm. The models confirmed the presence of the two central aquifer systems and showed the geometry of the aquifer with the most favourable conditions for water accumulations.

Electrical Resistivity and Geotechnical Attributes and The Dynamics of Foundation Vulnerability

This research evaluates the significance of geotechnical and Electrical Resistivity methods in studying structural integrity as fundamental factors that may account for failure in a typical sedimentary environment of Ukpenu Primary School, Ekpoma, Edo State, Nigeria. Two methods were used in this study such as the Electrical Resistivity approach involving the use of Lateral Horizontal Profiling (LHP), 2D Electrical Resistivity Tomography (ERT), and Vertical Electrical Sounding (VES) techniques. While geotechnical method involved the collection of soil samples from the study locations for the characterization of the soil properties that are very vital to foundation studies. Nine VES were carried out using Schlumberger array with current electrode spacing varying from 1 to 40 m, with 2-D ERT using Dipole-Dipole electrode array with inter-station separation of 5 m and an expansion factor varied from 1 to 5 while LHP involve Wenner array with an electrode spacing of 5 m interval and was used to determine the vulnerability factors for the building sustainability. The VES interpretation results were used to determine the second-order parameters for the determination of vulnerability. The results obtained from the two methods review that both are very fundamental to foundation dynamics. However, electrical attributes were found to give better information in terms of depth, lateral extent, layer stratification, and nature of materials which make it an indispensable tool over geotechnical attributes whose depth of investigation is up to a maximum of 5 m which poses great limitation in the evaluation of structural integrity, against stress, and strain occasion by geodynamic activities that often result into fracture, crack, highly weathered formation that usually goes beyond the shallow depth of investigation. Therefore, it can be stated that resistivity attributes account for 90% of the major contributing factors that affect foundation vulnerability.

Application of vertical electrical sounding resistivity technique to explore groundwater in the Errachidia basin, Morocco

The resistivity technique involving Vertical Electrical Sounding (VES) was carried out North of Ain Al Atti area, in Zaouia Jdida locality, with the aim of delineating zones not contaminated by the extension of the salinity and determining the potentiality of the existing aquifers. The measurements of apparent resistivity were collected using MolisanaApparecchiatureElettroniche (MAE) advanced geophysics instruments and were taken in twenty two VES points, along four profiles oriented N-S. The VES profiles were implanted using the Schlumberger configuration. VES Interpretation results shows that the potential aquifer horizon consists of the infracenomanian sand. The isopach map shows that the thickness of this geological formation varies between 20 m and 170 m. The sand layer is more thick (>80 m) along the profiles P3 and P4, with a maximum of about 170 m at 2P4 and 3P4 VES points. The isohypse map indicates that the sand formation is shallow (<10 m) in the East, and the depth of the roof of the infracenomanian sand increases gradually towards the West of the prospect area (>30 m). The transverse resistance (Tr) map shows that the identified aquifer has high values of Tr (Tr > 50000 Ω m2) in the western part, corresponding to zones with relatively high thickness and may have high transmissivity. The longitudinal conductance anomaly (Sl > 0.6 Ω-1) indicates that the area delimited by 1P2, 4P2, 1P4 and 3P4 VES points may have an important underground hydraulic potential. The interpretation of the acquired data also shows the presence of small depressions that could be implicated in the storage of the infracenomanian groundwater. Furthermore, the resistivity results reveal the presence of electrical discontinuities interpreted as faults and fracture zones. These could be the preferential axes of the groundwater circulation.

New Semi Quantitative Approach for Interpreting Vertical Electrical Sounding (VES) Measurements by Using Fractal Modeling Technique, Case Study from Khanasser Valley, Northern Syria

Fractal modeling technique, with adapting the concentration-number (C-N) model and the threshold break points concept is newly proposed to interpret vertical electrical sounding (VES) measurements distributed along a given profile. New semi quantitative approach is consequently proposed to rapidly differentiate between different apparent resistivity populations, where 2D semi quantitative interpretation and a primary geological analysis could be constructed. The new technique is practiced and tested on a case study taken from Khanasser Valley, Northern Syria, where different selected profiles (LP1, LP2, LP3, and TP5) are interpreted. The availability and the feasibility of the proposed approached are confirmed and approved through the different comparisons between the multi fractal established cross sections and the traditional 1D VES interpretation models. It is recommended to routinely use this new proposed fractal approach in the geoelectrical researches for interpreting VES measurements distributed along a given profile.

Integrated geophysical investigation of groundwater potential and bedrock structure in Precambrian basement rocks of Ife, southwest Nigeria

Telluric profiling (TP) and vertical electrical sounding (VES) techniques were employed for subsurface geophysical investigation at a new development site in Ife, southwest Nigeria. The study was carried out to provide geological data to assist in identifying locations of high potentials for good groundwater resource development and map suitable locations for infrastructural development in the area. Interpreted results of the two techniques (2-D profile map and geoelectric sections) are in good agreement, TP technique probes far deeper depth into the subsurface than VES technique. 2-D cross-section maps generated from TP data reveals zones of weathered/fractured bedrock delineated up to a depth of about 20 m in most locations with the exception of few locations showing outcrops close to the surface. TP cross-section also depict the presence of fault zones at the latter segment of the second traverse. Geoelectric sections generated from VES analysis and interpretation revealed a maximum of four subsurface strata which are topsoil (71–371 Ωm), weathered layer (22–94 Ωm), fractured/intensely fractured bedrock (453–496 Ωm and 122–311 Ωm respectively) and fresh bedrock (533–1088 Ωm). Weathered layer composed of clayey material originating from underlying schist rock occurred at depth below 5 m mainly along the first two traverses with thickness in the range 1.44–5.17 m. These clayey zones are unsuitable for groundwater abstraction. This medium is a less permeable bed of aquitard, with permeability not sufficient to allow the completion of production wells. Fractured zone is prevalent across all the traverses at varying thicknesses (3.65–12.2 m) and at depth range of 2.38–5.82 m. The regions with fractured zone are delineated at several spots for groundwater resource development and areas underlain by competent fresh bedrock at considerable depth identified for future infrastructural development in the study location.

Modeling of groundwater yield by the electrical method case of the Triassic sandstone aquifer (Tataouine South-Eastern Tunisia)

Abstract The method of electrical resistivity has proven very effective in the evaluation of groundwater. This specialized technique uses Dar-Zarrouk (D-Z) parameters in the estimation of longitudinal unit conductance, transverse unit resistance, and longitudinal resistivity to examine the groundwater level, to distinguish the fresh, brackish, and saline water interface, and to assess the storage capacity of groundwater in the Triassic sandstone aquifer system in the Tataouine region (South-Eastern Tunisia). In this context, 23 vertical electrical soundings (VESs) were carried out in the Tataouine region using the Schlumberger configuration with a current electrode with a maximum spacing of the current electrodes (AB) of 500–600 m. The results indicate that the study area consists of three types of aquifers: (i) silt/clay saline water (&amp;lt;20 Ωm), (ii) a mixture of sand and clay freshwater (20–40 Ωm), and (iii) sand freshwater (40–200 Ωm). These sand freshwater aquifers are characterized by low longitudinal unit conductance (0–2.8 S), high values of transverse unit resistance (more than 9,000 Ωm2), and longitudinal resistivity (more than 35 Ωm) and are mainly concentrated in the north, south, and south-west regions of the study area. It should also be noted that the coefficient of anisotropy (λ) overlaps and does not clearly differentiate the characteristics of the aquifers of fresh, brackish, and saline water. An interpretation of VESs can also determine the storage capacity of groundwater by determining yield index values. Groundwater supply for the entire study area was classified as low yield, with a percentage of 13% and a maximum of 31% of the study area and 56% of moderate yield. Lastly, the real data from the drilling confirm all these results presented previously. The findings suggest that D-Z parameters are useful for making a distinction of various aquifer zones.

Linear geological structure, traverse orientation and structure resolution and characterisation using 1D and 2D resistivity images

ABSTRACT This paper presents results of previous investigations involving 1D and 2D resistivity imaging of linear geological structures with varying traverse orientations relative to the structure azimuth with a view to determining the effect of such variation on the resolution of the structures. It observed that the orientation of 2D traverse relative to a fault azimuth significantly determines the resolution of the structure while the alignment of 1D vertical electrical sounding (VES) relative to the structure azimuth defines the form of the VES curve and leads to inconsistency in resistivity and thickness estimates and overall depth estimates at deep depth. 2D structures were best resolved with 2D resistivity images when the traverses were established normal (in-line) to the structure azimuth. Structures delineated by in-line 2D images are corroborated by in-line VES interpretation models and confirmed by drillers’ logs, whereas the resolution of such structure is impaired on parallel (cross-line) 2D resistivity images/maps with distorted and disjointed image of the investigated fault at deep depth. For two orthogonal VES alignments (in-line and cross-line) to the azimuth of an investigated fault, deviations in layer resistivity values were generally ˂17% while thickness/depth estimates deviated by as much as 30–78%, at deep depth.

GEOPHYSICAL EVALUATION OF SUBSURFACE PROTECTIVE CAPACITY AND GROUNDWATER PROSPECT IN A TYPICAL SEDIMENTARY ZONE, EASTERN DAHOMEY BASIN USING ELECTRICAL RESISTIVITY TECHNIQUE

Subsurface protective capacity evaluation is important in groundwater prospecting. With the aid of Dar-Zarrouk parameters which show direct relationship with contaminants infiltration time and transmissivity, joint interpretation of vertical electrical sounding (VES) and 2-D resistivity imaging were employed to evaluate overburden protective capacity and groundwater potentials at Mowe in Obafemi-Owode LGA, southwest Nigeria. Total longitudinal conductance S, total transverse resistance T, longitudinal resistivity ρL and transverse resistivity ρT were computed. Sand/clayey sand was delineated at 70% of the area either as confined aquifers (78%) or unconfined aquifers (22%). S values in 87% of locations has moderate protective rating (0.2071 – 0.5630), one location has good protective rating (0.7736), others have weak protective ratings (0.1053 – 0.1814). The entire area is characterized by low overburden thickness H (7.9 – 25.6 m), which agrees with a correlation coefficient of 0.58 between S and H. T values is in the range 235 – 2046 Ωm2 with high values indicating high transmissivity zones, suggesting high probability of pollutant contamination of aquifer, also agreeing with moderate correlation coefficient of 0.69 between T and H. The study area was grouped into three regions on the cross plot of T versus S: low S and high T – poor protection and high contaminant transmission; moderate/good S and low T – good protection with low contaminants transmission; moderate/low S and low T – weak protective capacity and poor transmissivity. Excellent correlation (0.99) exists between ρL and ρT, with ρT slightly higher than ρL, and low ρL signifying the presence of conductive clayey materials in the overburden.

Geological and structural characterizations of a basaltic environment by vertical electrical soundings and multifractal modeling techniques in Deir El-Adas Area, Yarmouk Basin, Syria

Concentration-number (C-N) fractal modeling technique is adapted and newly proposed to interpret vertical electrical sounding (VES) measurements. This proposed technique is practiced herein on a case study taken from Deir El-Adas, Southern Syria, where four VES geoelectrical profiles (Pro-1, Pro-2, Pro-3, and Pro-4) are interpreted. The general targeting concept of this technique is to use the threshold break points determined by the use of C-N log–log plots to indicate the passage from geoelectrical layer to another one. Different apparent resistivity population ranges are accordingly well determined for the treated geoelectrical data. Those apparent resistivity ranges are consequently used to establish 2D and 3D semi quantitative interpretations of the studied geoelectrical profiles for different fixed spacings AB/2. The established geoelectrical sections clarified the subsurface geological structures and contributed in distinguishing and classifying lateral and vertical different type of basaltic features in the study area. The fractal C-N model can be therefore used to calibrate the ID traditional inversion VES interpretation, particularly in basaltic environments, characterized by sharp and rapid resistivity variations. This calibration is one of the advantages of this fractal technique. This technique is therefore recommended to be applied in other similar basaltic environments.

Delineation of Near-Surface Structural Features Suitable for Groundwater Accommodation Using 1-D and 2-D Resistivity Methods in Igarra, Akoko-Edo, Southwestern Nigeria

Electrical resistivity methods using dipole-dipole and Schlumberger configurations of Vertical Electrical Sounding (VES) were carried out to evaluate the near-surface structural and lithological features suitable for groundwater development in parts of Igarra, Southwestern Nigeria. Two profiles with lengths of greater than 350m were carried out. A total of fifteen sounding locations along the profile lines were occupied. Dipole-dipole data were interpreted using DiprofWin software while interpretation of the VES data followed two stages of qualitative and quantitative data interpretation using Resist software. Dipole-dipole interpretation results indicate the occurrence of local fractures while VES interpretation results reveal the typical basement rock profile ranging from topsoil, lateritic sand, weathered front, fractured to fresh basement. The significant variations in terms of persistence and thicknesses of these basement vertical rock profiles were revealed by the geoelectrical correlation panels, which indicate typical basement inhomogeneities over short distances. The local structural domains, the weathered front (where thick) and the fractured basement are demonstrably potential sources of groundwater, at least for domestic and small scale enterprises in this part of Igarra. &#x0D; Keywords: 2-D Pseudosection, Dipole-dipole, Fracture Basement, Vertical Electrical Sounding

Mapping the Groundwater Potentiality of West Qena Area, Egypt, Using Integrated Remote Sensing and Hydro-Geophysical Techniques

The integrated use of remote sensing imagery and hydro-geophysical field surveys is a well-established approach to map the hydrogeological framework, and thus explore and evaluate the groundwater potentiality of desert lands, where groundwater is considered as the main source of freshwater. This study uses such integrated approach to map the groundwater potentiality of the desert alluvial floodplain of the Nile Valley west of Qena, Egypt, as alternative water source to the River Nile. Typically ground gradient, faults and their stress field, lateral variation of rock permeability, drainage patterns, watersheds, rainfall, lithology, and soil types are the main factors believed to affect the groundwater recharge and storage from the infiltration of present-time and paleo-runoff. Following this generally accepted approach, different remote sensing data sets (SRTM DEM, Landsat-8, ALOS/PALSAR-1, Sentinel-1, and TRMM) as well as auxiliary maps (geological and soil maps) were used to identify and map these factors and prepare thematic maps portraying the different influences they exert on the groundwater recharge. These thematic maps were overlaid and integrated using weights in a GIS framework to generate the groundwater potentiality map which categorizes the different recharge capabilities into five zones. Moreover, the aeromagnetic data were processed to map the deep-seated structures and estimate the depth to basement rocks that may control the groundwater occurrence. In addition, the vertical electrical sounding (VES) measurements were applied and calibrated with the available borehole data to delineate the subsurface geological and hydrogeological setting as well as the groundwater aquifers. Different geoelectric cross-sections and hydro-geophysical maps were constructed using the borehole information and VES interpretation results to show the lateral extension of the different lithological units, groundwater-bearing zones, water table, and the saturated thickness of the aquifer. The GIS model and geophysical results show that the southwest part of Nag’a Hammadi-El-Ghoneimia stretch has very high recharge and storage potentiality and is characterized by the presence of two groundwater-bearing zones. The shallow groundwater aquifer is located at a depth of 30 m with a saturation thickness of more than 43 m. However, there are NW–SE faults crossing the study area and most likely serve as recharge conduits by connecting the shallow aquifer with the deeper ones. Such aquifers connection has been confirmed by investigating the chemical and isotopic composition of their groundwater.

Modeling of Subsurface Integrity Using Dar-Zarrouk Parameters: A Case Study of Ikekogbe UBE Primary School, Ekpoma, Edo State, Nigeria

In this present study area, most building failures often start with minor/major cracks which widen over time, and it is often followed by post construction remedial measures which fail after sometime, thereby leading to total collapse and sinking of such buildings. The research was carried out in order to be able to unravel the causes of major cracks along the side of a major class room block at Ikekogbe, UBE Primary School, Ekpoma, Edo State, Nigeria in less than five (5) years after it was constructed. The cracks were visible both at the front and at the back of the building along the same axis and almost at this same distance as it was at the front of the building. The investigation involved Electrical Resistivity method using three techniques; Vertical Electrical Sounding (VES), 2-D Electrical Resistivity Tomography (ERT) and Horizontal Profiling (HP). The traverses were established along E-W directions and Eight (8) VES were carried out using Schlumberger array with current electrode spacing varying from 1 to 40 m, with 2-D ERT using Dipole-Dipole electrode array with inter-station separation of 5 m and an expansion factor that varied from 1 to 5 and HP using Wenner array with an electrode spacing of 5 m interval. The VES interpretation results were used to determine the second order parameters for modeling of subsurface integrity/competence. The 2 D imaging (Dipole-Dipole) gave information on the subsurface characteristic and the Wenner profile was characterised by low resistivity at the region of 30 to 45 m considered as the weak zone. Correlating the results with subsurface integrity model along traverses one and three, there was a high degree of correlation as this region coincides with the very low/low integrity/competence with the foundation of the classroom overlying this layers. The research revealed that the problem of structural failures/crack noticed along the building walls and axis was not as a result of human problem alone but mainly the existence of very low/low integrity/competence layers which contributed greatly to the cracks observed on the classroom block. These results reveal that the three Electrical resistivity techniques used for this study are complimentary to each other.

Effect of structure and lithological heterogeneity on the correlation coefficient between the electric\u2013hydraulic parameters of the aquifer, Eastern Desert, Egypt

Discovering, studying and determining the hydrogeoelectrical properties of the aquifer at the new area by using resistivity sounding parameters are difficult and need high accuracy in measurements and interpretation. The hydrogeological settings of the area of northwest Al Hurghada town are not studied on large scale by using the surface geophysical measurements before this study. So, for this aim, 24 vertical electrical soundings (VESs) were measured and interpreted. Discovering of groundwater aquifer along the main wadi called Wadi Om Dehas especially to the Far East, adds to determine the main lithology, shaly sandstone, sandstone and sandstone to limestone, of the aquifer and the complicated structural setting at form of inferred faults by using VESs curves, were the main tenets at this study for studying their effects on the correlation coefficient (R2) between the electric and hydraulic parameters of the aquifer. Accordingly, the two suggested locations were chosen for drilling and their results were as expected from VESs interpretation. The interpretation results using the true resistivity values assisted in delineating the complicated facies, heterogeneity of aquifer rock units and in expecting the flow direction of groundwater along the area. The relationship between the resistivity with transverse resistance and longitudinal conductance was carried out and assisted strongly in separating aquifer rock units. The heterogeneity and water salinity at different directions affected the strong relationship between the resistivity and transverse resistance where in case of shaly sandstone and sandstone it was weak but strong in case of sandstone to limestone. The hydraulic conductivity of aquifer was calculated using the transverse resistance. The transverse resistance was used in calculating the transmissivity and concluded that there is complicating and changing in its values from depth to others and from location to other due to the effect of structure and heterogeneity. This confirmed that the geological and hydrogeological settings of the area are more complicated. So, according to the relationship between the hydraulic conductivity (Kh) and resistivity (ρt), it can be said that it is strongly controlled by the nature of the aquifer rock units either heterogeneous or homogeneous. Accordingly, it can only use the last creating empirical equation in calculating the expected transmissivity values of the recorded water-bearing sandstone to limestone rocks at this area with taking into account the calculated value of R2 between both depending on the statistical analysis.

Integrated Geophysical and Hydro-chemical Investigations of Impact of the Ijemikin Waste Dump Site in Akure, Southwestern Nigeria, on Groundwater Quality.

Background.Improper waste disposal can negatively impact the ecosystem and constitutes a major human health risk.Objectives.The present study evaluated the environmental impact on groundwater quality of an open-air waste dump in Akure, southwestern Nigeria, using an integrated geophysical survey and hydro-chemical analysis of water samples.Methods.The geophysical survey involved three dipole-dipole 2-D imaging profiles and seven vertical electrical soundings (VES) along three traverses. The dipole-dipole data were inverted using the Dipro for Windows software, while the VES data were quantitatively interpreted using partial curve matching and computer assisted 1-D forward modeling with the WINResist software. The VES interpretation results were used to generate geoelectric sections. For the hydro-chemical analysis, samples were taken from five hand-dug wells at various distances from the dumpsite. The samples were analyzed for temperature, pH, conductivity, total dissolved solids (TDS), and some major elements (calcium ion (Ca2+), magnesium ion (Mg2+), chloride ion (Cl−), nitrate (NO3−), sulfate (SO42−)) whose concentration values were compared with World Health Organization (WHO) and Nigerian Industrial Standard (NIS) standards for assessment of groundwater quality.Results.The VES curves revealed three distinct geoelectric/geologic layers with thicknesses and resistivities in the range of 0.7 - 2.0 m and 31 - 55 Ωm for topsoil, 6.2 - 14.6 m and 13 - 114 Ωm for the weathered layer, and a fresh basement with resistivity values ranging from 344 - ∞ Ωm.In the hydro-chemical analysis, pH values ranged between 7.57 - 7.8, electrical conductivity ranged from 884 - 1510 μS/cm, and TDS ranged between 588 - 1008 mg/l. Concentration values of Ca2+ and Mg2+ ranged between 78 - 132 mg/l and 1.8 - 19 mg/l, respectively.Conclusions.The results from the combined electrical resistivity methods showed relatively low resistivity values at the topsoil and weathered layers and the hydro-chemical assessment of water samples indicated that the topsoil and groundwater within the dumpsite may have been polluted by leachate.Competing Interests.The authors declare no competing financial interests.