Vertical Electrical Sounding Results Research Articles

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

Geophysical and geotechnical investigations of the site of a collapsed two-storey building in Modomo, Ile-Ife, Southwestern Nigeria

Geophysical and the geotechnical methods were used to study the site of a collapsed two-storey building in orderto determine the sequence and competence of the subsurface layers and determine the cause of the collapse of the building. The geophysical method employed the electrical resistivity method involving one dimensional (1D) Vertical Electrical Sounding (VES) and the two dimensional (2D) imaging techniques. Three VES stations were occupied using Schlumberger electrode configuration. 2D imaging data were acquired along four traverses using dipole-dipole electrode configuration. The geotechnical method involved Cone Penetration Test (CPT). CPT data was acquired at two points with the aid of 2.5 ton Dutch CPT machine. The results showed four subsurface layers based on the 1D VES results and 2D imaging results namely: topsoil, weathered layer, fractured basement rock and fresh basement rock. The topsoil resistivity varied from 116 Ωm to 191 Ωm and has thickness of about 1.5 m. It was classified as moderately competent. The second layer is weathered rock with resistivity varying between 92 Ωm and 327 Ωm and of about 8 m to 13 m thickness. This layer is also moderately competent. The third layer is fractured basement rock. It underlies the weathered rock and have resistivity varying from 391 Ωm to 405 Ωm. Its thickness varied from about 2 m to 20 m. This layer is competent. The fourth layer is the fresh basement rock having resistivity varying from 1365 Ωm to 12348 Ωm and is highly competent. The subsurface materials in the area are competent and can sustain the foundation of the building. Hence, the study concluded that the building collapse did not result from incompetent subsurface materials. Factors other than incompetent subsoil material that is human factors are believed to be responsible. This study has demonstrated the effectiveness of geophysical and geotechnical investigations in determining the competence of subsurface materials at engineering sites.

Multi-Criteria Analysis Method for Aquifer Vulnerability Investigation Using Godt Method at Idi-Ayunre, Ibadan, Southwestern Nigeria

Geophysical investigation involving Vertical Electrical Sounding (VES) Schlumberger array was carried out across Idi-Ayunre, Ibadan, a typical basement complex area having a rock composition of migmatite-gneiss, quartzite, and biotite-hornblende. A total of forty (40) vertical electrical sounding data were acquired with maximum current electrode separation of 100m using resistivity meter and its accessories. The aim of the study was to evaluate the aquifer vulnerability of the study area to contamination. The VES results were both qualitatively and quantitatively interpreted using partial curve matching and were further subjected to computer iteration using WINRESIST. The longitudinal conductance, thickness of layer overlying aquifer and hydraulic conductivity were generated and synthesized to produce the vulnerability map. A GODT multi-criteria model which is an acronym of Groundwater occurrence, Overburden thickness, Depth and Topography developed from the hydrogeologic parameters were evaluated alongside the longitudinal conductance values to determine the aquifer vulnerability of the area and to classify the study area accordingly. The curve type obtained are H and HA. The interpretation revealed three to four geoelectric layers: the topsoil (18.9-178.9Ωm), clayey (9.0-70.6Ωm), fractured basement (31.9-43.1Ωm) and fresh basement (1131-2916Ωm). The longitudinal unit conductance ranges from 0.032-0.93mhos. And from the GODT model derivations, the study area shows 92.5% of high vulnerability rating, 2.5% of low-moderate and 5% of moderate rating; areas with high rating are prone to contamination than areas with low-moderate and moderate rating. Hence, zones of high vulnerability may be not be encouraged for groundwater exploitation and, if need be, constant water quality assessment should be carried out before consumption.

SOFTWARE FOR INTERPRETING THE RESULTS OF VERTICAL ELECTRICAL SOUNDING IN THE FORM OF A THREE-LAYER GEOELECTRIC STRUCTURE

By monitoring the state of the grounding system, electrical engineering personnel must independently solve the problem of interpreting the results of vertical electrical sounding (VES) of the soil using their own knowledge and practical experience. During the interpretation, outdated palettes or expensive software complexes are used, which allow analyzing only two-layer soils. This leads to a large number of errors and inaccuracies in the assessment of the state of the grounding system and worsens their operation. In this regard, a program was developed for the interpretation of the results of the VES in the form of a three-layer geoelectrical structure. The program is implemented in the Delphi programming language and contains two parts: computational and graphic. The computational part of the program uses point source current, Hooke-Jives, equivalence and reliability theory methods to optimize the determination of geoelectric model parameters. The graphical part allows the user to visualize the obtained results and perform their analysis. To confirm the reliability of the developed program, a comparison of the results of the experimental measurement of the resistance of the grounding arrangmants with the results of the calculation using the program was made for 65 substations with a voltage class of 35 kV of one of the regional energy companies of Ukraine. The obtained results showed that the program gives reliable results and can improve the quality of monitoring the condition of grounding systems, and accordingly increase the reliability and safety of operation of electrical stations and substations.

Subsurface Integrity Assessments of a Proposed Plaza Building at Oniru Lekki, Lagos, South-western Nigeria, Using Geoelectrical and Geotechnical Methods of Investigations

Subsurface integrity assessment for building foundation using geophysical and geotechnical methods was carried out at Oniru, Eti- Osa, Lagos State. A total of twenty-five Vertical Electrical Sounding (VES), five 2-D Resistivity Imaging Survey traverses and two borings with Standard Penetration Test (SPT) were carried out at the study site. The acquired data were processed quantitatively using partial curve matching and computer iteration technique to generate the geoelectric sections, the 2-D model and the SPT logs. The VES results revealed five to six geologic units corresponding to topsoil, clayey sand, sandy clay, clay/peat, and sand while the 2-D resistivity structure corresponds with the VES result. The borehole log reveals sand layers having an N-value of 22-30 which is indicative of medium-dense, brown (medium to fine) sand with occasional gravels from depth 1.50 - 7.50m. The borehole log information correlates well with the VES/2-D result. For the sand layer which connotes dense, grey (medium to fine) sand with occasional gravels from a depth 7.50 – 15.75m with N-value ranging from 26–30m. The study analysis shows that the proposed building could be placed on the dense sand at depth 7.50 – 15.75m, this, however, should depend on the proposed load, length, and breadth of the proposed building. This study has provided useful information about the subsurface condition for engineering structure and zone suitable for the proposed foundation.

3D geophysical mapping of the subsurface to support urban water planning: a case study from Simawa, Nigeria

ABSTRACT Simawa town, Ogun state, lacks the required water infrastructure for rapid urban development. This study seeks to use the geoelectric method – taking into account the geology and hydrogeology of the study area – to determine the groundwater potential of the town. Fifteen Vertical Electrical Sounding (VES) stations were spread across the town to characterise the subsurface layers. Interpretation of the VES data yielded five geoelectric layers. A lithology log from a prior borehole was used as a geologic control to confirm the validity of the VES results. The five geoelectric layers correspond to the topsoil (layer 1), Akinbo clay (layer 2), Akinbo shale (Layer 3), Ewekoro limestone (Layer 4), and Abeokuta sandstone (layer 5). The Abeokuta sandstone represents the main aquifer unit, a confined aquifer that can serve as a suitable source of potable water. Boreholes drilled in Simawa town should target the confined sandstone aquifer at a minimum depth of 80 m.

Potentiometric and Bedrock Map Drawn from Vertical Electrical Soundings (VESs) and Considerations on the Investigation Depth

The article presents considerations on the depths achieved by Vertical Electrical Soundings (VES) as a function of electrode distances, and also on their quantitative interpretation. Besides the distances among electrodes, the effective achieved depths will depend on the resistivity distributions. At the request of environmental agencies, resistivity geophysical surveys were carried out in an area designed to the implementation of a residential complex which, would have to present a site hydrogeological study, including a potentiometric map among other requirements to be met. For the referred map elaboration, 18 VES were carried out in order to determine the depth of the water level at these points. In addition to this information, the works provided another additional data: the determination of the bedrock depth. Based on VES results, the potentiometric map and the bedrock depth map were elaborated in the study area. The cost reduction with the use of this indirect technique is significantly lower when compared to the costs of mechanical soundings, besides the reduction of the execution time.

Integrated Geophysical Assessment of Groundwater Potential in Southwestern Saudi Arabia

Saudi Arabia is seeking fresh groundwater resources to face the increase in anthropogenic activities. The groundwater storage variations and occurrence were investigated and the surface and subsurface structures influencing the groundwater resources in the research area were defined using a combined study of Gravity Recovery and Climate Experiment, aeromagnetic data, and electrical resistivity data with other relevant datasets. Results are: The groundwater storage fluctuation is calculated at −0.34 ± 0.01 mm/yr during the period 04/2002-12/2021. The area is receiving an average annual rainfall rate of 117.6 mm during the period 2002 to 2019. Three structural trends, defined in the directions of NS, NNW, and NNE are cutting the sedimentary cover and the basement rocks. The sedimentary cover ranges from 0 to 1.2 km thick. Vertical electrical sounding results indicate three main geoelectric layers: the surface geoelectrical layer of higher resistivity values (428-9626 Ω. m) is made up of unconsolidated Quaternary sediments; the water-bearing layer of saturated sands with a resistivity range between 5.1 and 153 Ω. m and with depths vary from 1 to 94 m, and highly fractured basement rocks with resistivity values ranging from 813 to 6030 Ω. m. The integrated results are useful in providing a comprehensive image of the study area’s surface and subsurface structures, as well as groundwater potential in the southwestern part of Saudi Arabia. Our integrated approach provides a reproducible model for assessing groundwater potential in arid and semiarid areas.

Potentiometric map based on integrated piezometer data with geophysical results, Manaus-AM / Mapa potenciométrico a partir de dados de piezômetros integrados com resultados de geofísica em Manaus-AM

The research carried out consisted of a field survey upstream of the Lago Amazônico area and close to the Ecological Effluent Treatment Station (ETEE) of the National Institute for Research in the Amazon - INPA. The objective of the study was to detect possible impacts on the quality of groundwater due to the ETEE and the waters of Lago do Bosque da Ciência, which requires knowledge of the direction of groundwater flow at the site. The geophysical resistivity method, through the technique of vertical electrical sounding with the Schlumberger arrangement, was applied with the purpose of defining the depth of the top of the saturated zone in the study area as well as detecting possible impacts of the effluents of the treatment plant in subsurface. The resistivity method, through measurements by equipment placed on the surface, determines the electrical resistivity of the materials and their subsurface contrasts at different depths. In the area, three piezometers were installed, which enabled the calibration of the interpretation of the results of vertical electrical sounding. The survey of geophysical data provided a volume of information about the subsurface situation of the layout, lithological content and the depth of the water level of the subsurface layers through the seven vertical electrical surveys carried out around the INPA Lake and close to the ETEE. The results of the interpretation of the vertical electrical sounding and water level depth measurements in the piezometers were integrated to produce a potentiometric map to understand the hydrogeological behavior from the point of view of underground flow. The electrical resistivity values, relatively high in the study area, attribute a predominantly sandy lithological constitution, a result that is consolidated with the lithological description of the piezometers. The top of the saturated layer around the lake is deeper compared to the lake, causing its waters to seep into the aquifer. This is because the lake is artificial, constantly receiving water to maintain its level. The potentiometric map indicates a practically radial flow direction, with a slight inclination towards the north. The electrical surveys carried out near the treatment plant showed lower resistivity values, which may be related to the influence of effluents in the subsurface. The study was carried out with resources provided for in Law No. 8,387 and in accordance with Article 21 of Decree 10,521 / 2020 - INPA / SAMSUNG Partnership.

Geotechnical soil mapping from electrical and mechanical properties: Case study of the Bafoussam urban area, west Cameroon

Preliminary work in civil engineering works often involves the investigation of soil support in order to secure or predict project safety. The objective of this work is to purpose an urban geotechnical soil map combining physical and mechanical behaviour of the soil and its electrical properties. Field work with auger corer allowed collection of samples for analysis. The results of the Atterberg limits and particle size analysis enabled classification of those soils according to HRB as silty or clayey gravels and sands (class A-2-7) and clayey soils (A-7-5). The Casagrande Plasticity Diagram classifies them as At and Lt (very plastic clays and silts) and the GTR classifies them as sandy and gravelly soils with fines (B6) and fine clay soils (A2 and A3). These classifications show that the study area is mainly covered by sandy-clay, lateritic clay and lateritic gravelly soils. The iso-resistivity maps and resistivity sections made from the results of vertical electrical soundings, allow the identification of three ranges of resistivity: a low resistivity less than 300 Ώ.m, a medium resistivity range between 300 and 500 Ώ.m and a high resistivity greater than 500 Ώ.m. These ranges of resistivity correspond to the different formation disparities that make up the subsurface. Associated penetrograms show these soils are very resistive in the cuirass subsurface zones with very compact formations with permissible stress values between 2.5 and 5.2 bars. At greater depths, these values are moderate in the clayey sands with stresses between 0.8 and 3 bars and low in the clays and lateritic soils (˂1 bar). The application of determination coefficient (R2) and Spearman correlation (rs) between permissible stress and true resistivity gives values of 0.79 and 0.74 respectively. There is a good qualitative and quantitative correlation between these two parameters in the study area. The superimposition and comparison of the different results with the geological formations enables development of a geotechnical soil map. This map enables us to understand the lithological and mechanical heterogeneity of the soils during the construction of structures in the urban perimeter of Bafoussam.

GEOTECHNICAL AND GEOPHYSICAL EVALUATION OF SUBSOILS IN IKATE AREA, SOUTHWESTERN NIGERIA: IMPLICATIONS ON FOUNDATION INTEGRITY AND CORROSIVITY

Geophysical and geotechnical methods remain one of the most effective approaches for the evaluation of subsoil properties prior to engineering construction. This is important in the delineation of soil sequence and estimation of soil parameters necessary for ensuring sufficient supports for structures. This study therefore presents the results of subsoil integrity and corrosivity probability evaluation using Vertical Electrical Sounding (VES) and Standard Penetration (SPT) in Ikate Area, Lagos, Nigeria. Data were acquired in eight (8) VES positions using Pasi terameter deploying the Schlumberger array system along four traverses while SPT-N values were obtained at every 1.5m within six (6) boreholes drilled to 30.0m depth in the study area. The combined results of VES and SPT delineate four to five geologic units corresponding to topsoil, different shades of clays, peat, sandy/clayey sand and sand. The low resistivity values of the clayey, peaty, and sandy layers especially along traverse four was used to rate them as highly or extremely susceptible to corrosion. The presence of highly compressible organic clay and peat in the second layer precludes the adoption of shallow foundation in the medium dense sandy layer that made up the topsoil (0.0 – 2.50m). Foundation analysis carried out with N-values shows that pile installed within the clayed sand/sand clay and sand layers encountered between 12.0 – 27.m with diameter range of 300 – 600mm could mobilize ultimate and allowable loads ranges of [702.9 – 5012.4KN] and [234.3 – 1670.8KN]. The correlations of resistivity with N-values returned high to weak positive linear relationships suggesting that resistivity values may not be effective in estimation of the strength and stiffness of subsoil. Conclusively, the study demonstrated the complimentary role of both VES and SPT as an effective geoengineering characterization tool.

Method of integro-differential equations for interpreting the results of vertical electrical sounding of the soil

The paper is devoted to the problem of determining the geoelectric structure of the soil within the procedure of testing the grounding arrangements of existing power plants and substations to the required depth in conditions of dense development. To solve the problem, it was proposed to use the Schlumbergers method , which has a greater sounding depth compared to the Wenner electrode array. The purpose of the work is to develop a mathematical model for interpreting the results of soil sounding by the Schlumberger method in the form of a four-layer geoelectric structure. Methodology. To construct a mathematical model, it is proposed to use the solution of a particular problem about the field of a point current source, which, like the observation point, is located in the first layer of a four-layer soil. Based on this expressions, a system of linear algebraic equations of the 7-th order with respect to the unknown coefficients ai and bi was compiled. On the basis of its analytical solution, an expression for the potential of the electric field was obtained for conducting VES (the point current source and the observation point are located only on the soil surface). Results. Comparison of the results of soil sounding by the Schlumberger installation and the interpretation of its results for the same points shows a sufficient degree of approximation: the maximum relative error does not exceed 9.7 % (for the second point), and the average relative error is 3.6 %. Originality. Based on the obtained expression, a test version of the program was implemented in Visual Basic for Applications to interpret the results of VES by the Schlumberger method. To check the obtained expressions, the interpretation of the VES results was carried out on the territory of a 150 kV substation of one of the mining and processing plants in the city of Kriviy Rih. Practical significance. The developed mathematical model will make it possible to increase the sounding depth, and, consequently, the accuracy of determining the standardized parameters of the grounding arrangements of power stations and substations.

Mapping Of Groundwater Zones Using Vertical Electrical Sounding (VES): A Case Study of Malwah Distributary

In the last two decades, the water requirements for agriculture sector have increased due to high food demand, changes in the cropping pattern, and the increase of evapotranspiration rate due to the climate change. The irrigation water demands are not completely fulfilled by the available surface water, which resulted an increased use of the groundwater in Pakistan. It is essential that before applying the groundwater to agriculture land, its quality should be assessed. In this study, groundwater quality and quantum have been investigated through Vertical Electrical Sounding (VES) for the command area of Malwah distributary, district Shaheed Benazirabad. Total 23 sites were selected in a grid of 3km-by-3km area for the VES survey using Terrameter up to 100-meter depth. The VES results are interpreted in terms of the resistivity and corresponding thickness of various underground zones using IX1D software. The results indicated fresh groundwater up to maximum of 50 m depth, covers 75.65 km2 i.e., 21% of the total command area of 359.94 km2. However, the freshwater is accessible up to 100 m depth near the Indus River. The study suggests that the tubewells should be installed up to 50-meter depth, where the maximum quantity of fresh groundwater is available.

Vertical Electrical Sounding Exploration of Groundwater in Kertajati, Majalengka, West Java, Indonesia

DOI:10.17014/ijog.8.3.359-369Continuously increasing population and progressive infrastructural development in the region of Kertajati International Airport, Indonesia, emphasize the need to develop a sustainable water supply network. Airport facilities require sufficient water resources, which can be obtained from surface water and groundwater. Groundwater exploration can provide necessary information for assessing water resources. The purpose of this study is to analyze the configuration of aquifers in the studied area. A Schlumberger array was used to carry out twelve vertical electrical soundings (VES) with AB/2 electrode spacing ranging from 1.5 m to 150 m. IPI2win software was used to qualitatively interpret the VES results and it suggested the presence of three distinct lithological units interpreted as clay, alluvial sand, and a Lower Quaternary formation. In general, resistivity values in the studied area can be divided into five resistivity categories: very low resistivity with values ranging from 1 Ωm to 10 Ωm, low resistivity with values ranging from 10 Ωm to 50 Ωm, medium resistivity with values ranging from 50 Ωm to 100 Ωm, high resistivity with values ranging from 100 Ωm to 200 Ωm, and very high resistivity with values > 200 Ωm. The geo-electric interpretation revealed three geo-electric layers: topsoil (1 - 144 Ω m), sand (1 - 298 Ω m), and clay (1 - 82 Ω m). Aquifers in the studied area are lithologically composed of sand. Clay is the dominant lithology in the studied area, so the presence of aquifers in this area is very limited, and thus the supply of groundwater is also limited. The exploitation of groundwater must be limited and controlled to maintain the sustainability of groundwater in the studied area.

Delineation of shallow groundwater potential zones using integrated hydrogeophysical and topographic analyses, western Saudi Arabia

Groundwater potentiality mapping is currently receiving more attention, particularly in arid regions, where natural freshwater resources are limited and scarce and instead costly unconventional methods such as seawater desalination are widely used to satisfy water demands. Water demand in Makkah city is considered a vital task, which receives millions of visitors every year for religious purposes. The present study evaluates the potential zones of groundwater in the southwest Makkah city applying hydrogeophysical modeling approach that integrates geoelectrical resistivity in form of vertical electrical sounding (VES), ground-penetrating radar (GPR), and topographic analyses. VES results indicate five main geoelectric layers: (1) dry wadi-fill deposits with a true resistivity varying from 73 to 650 Ohm.m and average thickness of 3.14 m, (2) partially saturated sands with a resistivity range between 19 and 43 Ohm.m and average thickness of 13 m, (3) water-bearing layer of saturated sands with a resistivity range between 55 and 110 Ohm.m, and average thickness of 52 m, (4) highly fractured diorite rocks with resistivity values ranging from 750 to 1450 Ohm.m and average thickness of 1.5 m, and (5) fresh diorite basement rocks with a resistivity of more than 4000 Ohm.m. Results of GPR profiles support the gained results of the VES technique, and together they are confirmed by the wells data. The integrated results suggest a structural control on the groundwater accumulation and call for a detailed mapping of alluvium-covered faults to provide a high-resolution mapping of groundwater occurrences and ensure environmental sustainability in southwest Makkah city.

Integrated vertical electrical sounding and hydrogeological approach for detailed groundwater pathways investigation: Gökpınar Dam Lake, Denizli, Turkey

Understanding the hydrodynamic systems in the dam lake surroundings is of great importance to protect the lakes feeding zones and maintain their water level. In this study, a combination of hydrogeological and geophysical surveying processes was carried out in order to distinguish the Gökpınar dam lake's recharge ways. The Gökpınar dam lake area is characterized by a very complicated hydrogeological system causing difficulty at distinguishing the groundwater flow pathways feeding the lake. Therefore, a detailed vertical electrical sounding survey was performed in accordance with the Shlumberger array in the surroundings of the Gökpınar dam lake. Results obtained from the resistivity measurements were processed using a partial curve matching technique then inverted in order to build 2D and 3D resistivity models which in their turn were corelated with the geology of the study area. In addition to the geoelectrical measurements 44 boreholes were drilled in order to confirm the vertical electrical sounding results. Data collected from these boreholes were also used for the plotting process of the water table contour map in the study area which highly correlated with the resistivity contour maps. Resistivity data evaluation led to the differentiation between water bearing and dry zones. Results showed that the Gökpınar dam lake is fed by several groundwater flows, deriving from South-West, North-West, and South-Eastern parts of the study area. These flows are generally more important near the surface than they are deeper toward the impermeable bedrock.

Delineating saline and fresh water aquifers in Tuticorin of southern India by using geophysical techniques

Geo-electrical survey was conducted in a highly industrialized area to delineate the freshwater and saline water aquifers. A total of 30 vertical electrical soundings (VES) were made along the coastal aquifers of Tuticorin, which covers both sedimentary formation and crystalline rocks. By using VES data, GIS was used to create spatial maps for resistivity and thickness at various depths. The results show that Q and H were the dominant curve types in the study area. Q type curves indicate saline water by decreasing resistivity values with respect to depths. In H type curves, low resistivity saline water aquifer was sandwiched between high resistivity topsoil and hard rock at the deeper horizon. The geophysical indicators such as Dar-Zarrouk parameters were calculated using the VES results. The Longitudinal unit conductance (S) values ranged between 0.075 and 7500 S. The transverse unit resistance (T) of the study area varied from 16.06 to 5909.25 Ωm2. The anisotropy (λ) values ranged from 1.00 to 55. Interpretation of data reveals that the saline water intrusion and industrial impact on shallow aquifers were observed in the coastal region of the study area. Few pockets of the freshwater aquifer were also noted in deeper horizons. Since the quality of groundwater was deteriorating, proper management plans will be needed to save this fragile coastal aquifer.

Evaluating the Earth Subsurface for Civil Engineering Site Characterization in Agege, Southwest Nigeria Using Integrated Geoelectrical and Multichannel Analysis of Surface Wave (MASW)

A geophysical investigation involving 1D Vertical Electrical Sounding (VES), 2D Electrical Resistivity Imaging (2D ERI) and Multichannel Analysis of Surface Wave (MASW) has been carried out at Agege, Lagos, Nigeria with a view to delineating the subsurface stratigraphy and locate some competent strata/stratum for founding civil engineering structures. Six (6) 200 m long traverses were established within the study area. Along these traverses, 2D ERI were carried out adopting Wenner electrode configuration. Vertical Electrical Sounding (VES) adopting Schlumberger electrode array were carried out at selected points along profiles 1, 2 and 3 to determine the lithological sequence at depth. MASW data also were acquired along traverses 1, 2 and 3. The data were processed and the result yielded interpretable 2D resistivity structure and geoelectrical parameters (layer resistivity, thicknesses and depth) from the VES. The interpreted VES results were used to generate geoelectric section while the MASW resulted in 2D velocity sections. Three subsoils including topsoil, clay and clayey sand/sand were delineated beneath the study area. The resistivity and thickness range of the layers are; topsoil (34.0-54.6 ohm-m, 0.9 – 1.7 m), clay (10.3 – 17.7 ohm-m, 8.9 – 12.3 m) and clayey sand/sand (48.9 – 323 ohm-m) while the S-wave velocity range for the subsoil falls between 40 – 500 m/sec.

Mapping of groundwater potential using integrated geophysical techniques at forestry research institute of Nigeria, Ibadan, South Western Nigeria

Water is an essential commodity for life survival on Earth. Groundwater exists below the surface in the soil pores, fractures within rocks, fissures, and other weak geological features or zones. The aim of this research was to delineate groundwater potential within the Forest Research Institute of Nigeria (FRIN) and hence determining the possible areas suitable for siting borehole for sustainable potable water supply. Four electromagnetic traverses were carried out and ten vertical electrical sounding (VES) points were identified for detailed probing using the Schlumberger configuration. Wenner array survey was also carried out along two traverses. The VES data collected was processed using curve matching and Computer software called Winresist while Wenner array was processed using RES2DINV. The results from the interpretation of the four (4) EM profiles revealed low conductivity zone with a value ranging from 4.6 to 19.7 mS m.-1 The results of VES give a maximum of four subsurface geoelectrical layers with five curve types, which are K, Q, AK, HK, and KH. The weathered basement has a resistivity value ranging from143.8 to 450 Ωm and depth to basement ranging between 13.9 m and 39.4 m. The interpretation of the ten VES points obtained suggested that three VES points (VES 2, 5, and 7) are suitable for borehole drilling. The results of the 2D resistivity value ranges from 17.5 to 747 Ωm with a varying depth between 3.25 and 15.9 m. The results of the integrated geophysical survey techniques have proven to be an effective method for groundwater delineation in the study area.
 Keywords: Aquifer, Borehole, Electromagnetic, Geoelectric, and Groundwater

Optimizing Groundwater Aquifers Potential in The Development of Irrigation Wells for Agriculture Using Geo-Electrical Method

The identification of shallow groundwater aquifers is demanded to sustain the balance of utilization in agriculture and anticipate frictions that can occur due to the overlapping usage of groundwater resources. This study is aimed to identify the potential of groundwater resources based on the thickness and depth of the groundwater aquifer. Geoelectric resistivity methods have done with vertical electrical sounding (VES) and horizontal profiling techniques (2D mapping). The VES data acquisition was carried out with a Schlumberger array while 2D mapping by alpha Wenner array. Inversion results of vertical electrical sounding (VES) show that groundwater resistivity values in sedimentary rocks ranged from 1 to 100 ?m and in igneous rocks between 0.5 - 150 ?m. The results of 2D Resistivity Mapping also show that shallow aquifer depth ranged from 1 to 5 m with a thickness ranged from 15 m to more than 70 m. Meanwhile, bedrock depth ranged from 20 to 150 m with a pattern deeper to the west. Furthermore, the potential of groundwater aquifers in the development of irrigation wells for agriculture should be carried out in the western part of the study area.
 
 Keywords: Groundwater, Shallow Aquifer, Rock Resistivity, Irrigation Well, Geo-Electrical Sounding.