Vertical Electrical Sounding Stations Research Articles

Mapping of Aquifer Characteristics and Reservoir Protective Capacity Variation in Obafemi-Owode Local Government Area, Ogun State South-West Nigeria

Variation of Aquifer potential characteristics and its impacts on the groundwater subsurface protection of the aquiferous zone using electrical resistivity method was carried out at Obafemi-Owode Local Government Area, Ogun State South-West Nigeria with the principal purpose of assessing and rating aquifer protective capacity of the overburden units in the area. Twenty seven (27) vertical electrical sounding (VES) were conducted using Schlumberger configuration with the maximum electrode spacing of 100m at each point using Allied OMHEGA Resistivity meter. The data were interpreted using partial curve matching techniques and computer iteration program using WINRESIST. Parameters such as aquifer resistivity, aquifer thickness, overburden thickness, bedrock resistivity, reflection coefficient and longitudinal unit conductance were calculated and used for evaluating the groundwater yields and vulnerability of the aquiferous zone to contaminant seepages. The range of reflection coefficient is found to be between 0.02 and 0.98 while that of the protective capacity is between 0.00135 and 0.510. Groundwater potentials of the area were categorized as being high (overburden thickness 13m and reflection coefficient less than 0.8); medium (overburden thickness 13m and with reflection coefficient 0.8) and low (overburden thickness < 13m and reflection coefficient. Also, the study area shows a very poor, poor, and moderate protective capacity rating. Seven (7) VES stations have very poor protective capacity, eighteen (18) VES stations shows poor protective capacity and only two (2) VES stations shows a moderate protective capacity rating. Since the illustration the longitudinal conductance revealed the impermeability of the confining layers which is generally ˂ 1.0 Siemens; values ˃1.0 Siemens which indicates zones in which the confined aquifer is subject to protection by the overlying formation materials; these revelations in the study area were possible indications that the groundwater quality status may have been impaired which necessitated the urgent need for the groundwater to be randomly...

Resistivity Prospecting for Groundwater Potential at the Proposed Ibrahim Badamasi Babangida University Teaching Hospital, Lapai, Niger State

Resistivity methods have been increasingly used for aquifer characterisation due to their high level of effectiveness. In this study, electrical resistivity survey was carried out at the Proposed Ibrahim Badamasi Babangida University Teaching Hospital Lapai Niger State Nigeria in order to study the groundwater potential with a view of determining the depth to the bedrock and thickness of the overburden protective capacity. Vertical Electrical Sounding (VES) using Schlumberger array was used to occupy thirty (30) VES stations using ABEM Terrameter (SAS 300) for the acquisition of apparent resistivity data. The field data obtained was analysed using computer software (IPI2win) which gave the secondary geoelectric parameters of depth, layer thickness and layer resistivities. The results revealed heterogeneous nature of the subsurface geological sequence comprising top soil (clayey-sandy and sandy-lateritic), weathered layer, partly weathered (fractured basement) and fresh basement. The resistivity value for the topsoil layer varied from 20Ωm to 600Ωm with thickness ranging from 0.5 to 7.2 m. The weathered basement had resistivity values ranging from 15Ωm to 593Ωm while the thicknesses varied between 2.75 and 33.04m. The fractured basement had resistivity values ranging from 201Ωm to 835Ωm and thicknesses having values between 11 and 20.4m. The fresh basement (bedrock) had resistivity values ranging from 1161Ωm to 3115Ωm with infinite depth. The depth from the earth’s surface to the bedrock surface varied between 2.5 to 47.75m. The VES 10, 11 and 19 had very good overburden protective capacity and can serve as good sites for borehole drilling.

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.

Estimation of the variability of sand deposits in chosen communities in parts of Niger delta, Southern-Nigeria using geophysical techniques

Fine and coarse typical sand are among the most vital raw materials in building construction. A lot of drilling has been done without appropriate subsurface information resulting to a waste of resources and time. Geophysical methods give information on subsurface lithologies to locate areas with huge success. Thus, a geophysical investigation of subsurface deposits was carried out in this research to ascertain the quantity of fine/Coarse sand or areas with viable fine/Coarse sand utilizing Schlumberger configuration, Dipole–Dipole (2D) and well logging in parts of Okpe and Ughelli North LGA of Delta State, Nigeria, before extraction (dredging) for the benefit of exploitation and development. This was done by assessing the geo-electric formation of fine/coarse sand in the studied areas concerning their depths and thicknesses. Seven Vertical Electrical Sounding (VES) were obtained with the application of Schlumberger array, seven 2D and three well logging to estimate the viability of sand deposits in the study areas. These techniques have the efficacy of detecting near-bed formation with vital resolution. The data obtained from the field were illustrated by partial curve matching coupled with computer iteration using the WIN RESIST and Dipro Software to obtain sounding curves which revealed four to six layers. The layers consist of topsoil, lateritic clay and clayey sand, fine sand deposit, medium to coarse grain sand and coarse sand. For Agbarho, thicknesses of fine/coarse sand in the VES stations ranges from 18.0 to 55.6 m with resistivity varying from 223.7 to 572.9 Ωm, Osubi Fine/Coarse sand thickness ranges from 13.5 to 59.9 m with resistivity values within 211.9–891.0 Ωm and Oha town locations have fine/coarse sand thickness varied from 46.6 to 83.7 m with resistivity interval computed between 145.9 Ω-m and 466.4 Ω-m. Thus, the best VES stations that are more viable for sand mining are VES 1, 5 and 7 which contain relatively huge viable sand deposits in the study areas to a depth above 80 m.

GROUNDWATER POTENTIAL ASSESSMENT OF PART OF KAZAURE, NIGERIA USING ERDAS IMAGINE, PCI GEOMATICA, ARCMAP AND EXPERT CHOICE SOFTWARE

The possibility of utilizing groundwater as a source of water supply for public use is always attractive This research was focused to evaluate the groundwater potential of Kazaure area, Nigeria. The methodology adopted were mainly primary data in which six different thematic maps were integrated to generate the groundwater potential model (GWPM. It was produced by Weighted Linear Combination (WLC) where each class individual’s weight was multiplied by the map scores. In the research, Erdas Imagine 9.2, PCI Geomatica 10.0, ArcMap 9.3 and Expert Choice 10.0 in a GIS environment were used. Vertical electrical sounding (VES) was conducted using Ohmega resistivity meter with Schlumberger configuration. IP12win software was used in plotting the curves which revealed the resistivity, layers and thickness of the VES stations. Geological mapping was carried out using topographical map on a scale of 1:50,000Measurement of the depth to groundwater table in hand dug wells was carried out using dip meter. Water samples were collected and analyzed. Atomic Absorption Spectrometry (AAS) and X-Ray Fluorescence (XRF) were used in the analysis of water quality at the Multi-user laboratory, Chemistry Department, Ahmadu Bello University Zaria, Nigeria.

Characteristics of soils for civil engineering foundations in part of North Central Nigeria, using electrical resistivity method

A geophysical investigation was carried out using Vertical Electrical Sounding (VES) in part of North Central Nigeria to evaluate the subsoil thickness, competence, and corrosivity for civil engineering foundations. A total of 60 VES stations were covered within the study area using the Schlumberger configuration array with half current electrode separation (AB/2) varying from 1m to a maximum of 100m while the half potential electrode spacing (MN/2) varied by 0.3 m to a maximum of 5m. The analysis of data was done using IP2win and Surfer 12 softwares. The first layer has resistivity values between 4.728 Ωm to 4210 Ωm and varied in thickness between 0.15 m to 1.42 m, the second layer has resistivity values between 24.7Ωm to 355000 Ωm and varied in thickness between 0.0355 m to 8.983 m while the third layer has resistivity values ranging between 8.361 Ωm to151,608 Ωm and varied in thickness between 1.05 m to 34.2 m, the fourth layer which is the last of the geoelectric layers has resistivity values between 27.95 m to 77000 m. The subsoil within the study area is composed of clay, sandy clay, clayey sand, sand, and laterite. From the qualitative interpretation of the Isoresistivity and Isopach maps, the Southwestern, Southeastern and Northwestern parts of the study area are moderately corrosive to extremely corrosive subsoil with resistivity values ranging between 4.728 Ωm and 50.48 Ωm. The third layer consists of an incompetent low resistivity soft material that underlain the entire study area except at the central region which is essentially noncorrosive and highly competent. VES curves interpretations revealed the thickness and depths of the geoelectric layers within the study area. The results of this research could enable civil engineers to ascertain the requisite depth of soil evacuation for the sustainability of structures within the study area.

Evaluation of sedimentary aquifer in tehsil Zehri area using VES technique, Balochistan Pakistan

A geophysical resistivity survey was conducted in Zehri tehsil in the district of Khuzdar for the metering of subsurface hydrogeological properties of aquifers. The Schlumberger electrode arrangement was employed with the vertical electrical sounding (VES) method for subsurface exploration. Two profile lines were designated for the survey. The distance between the two profile lines was about 1500 ​m and each profile contained four VES stations. The results of profile one show the aquifers were encountered in fractured limestone of the Jamburo Formation of Paleocene age at an average depth of 127 ​m, with an average resistivity of 39.7 ​Ωm, and the average aquifer thickness was 54.025 ​m. The result of profile two shows the aquifers were encountered only in VES four in the sandstone lithology of the Ziddi Formation with a resistivity of 79.9 ​Ωm, at a depth of 120 ​m with, and a thickness of 40 ​m. There was no aquifer encountered in the remaining all VES. The main lithology of these VES is thick impervious compacted limestone, shale, and clay of Jurassic age from the Ziddi Formation. The current tube wells were also rapidly depleting in the study area. The main factor behind the decline of aquifers in the study area is an uncontrolled installation of tube wells and continuous pumping of tube wells for agricultural purposes badly puts stress on aquifers and directly deteriorates the quality and quantity of groundwater.

Exploring the Geological Formation and Sub-Surface Lithology Modelling of Hadejia, Jigawa State Nigeria

This research aims to explore the geological formation and sub-surface lithology modelling of Hadejia, Jigawa State using the VES (vertical electrical sounding) method. The VES method is a geophysical technique that measures the electrical resistivity of the subsurface, which is related to the lithology of the rock units. The study area is located in the north-western part of Nigeria, on latitudes 12025’23.73‘‘N and longitudes 10°04’06.74‘‘E, and is characterized by a chad formation geological setting with a variety of rock units, including sandstones, shales, and limestone. The research was conducted using a total of 50 VES stations, which were distributed over the study area in a grid pattern. The data collected from the VES stations were analyzed using the IPI2WIN software. The results were used to create a subsurface electrical resistivity model, which was then used to infer the lithology units present in the subsurface. The results showed that the study area is characterized by a complex subsurface structure, with several rock units present, including sandstones, silt, and clay. The subsurface electrical resistivity model revealed that the sandstone units are located at shallow depths, while the silt units are found at deeper depths. The clay is present at intermediate depths and is interbedded with sandstones and clay. The results provide valuable information for hydro-geological and mineral exploration in the area.

Geoelectrical Characterization of Coastal Aquifers in Agbado-Ijaye, Lagos, Southwestern Nigeria; Implications for Groundwater Resources Sustainability

Water is a natural resource; its availability depends on climatic and geological conditions, and it is invariably controlled by human activities. Agbado-Ijaye lies within a coastal area, where local communities have been facing incessant water shortages, especially during the dry season. This study investigated the groundwater-bearing geological unit(s) using hydrogeophysical techniques in the coastal environment. The electrical resistivity technique, involving vertical electrical sounding (VES) and two-dimensional (2D) electrical resistivity imaging via Wenner array electrode configuration, was used to characterize the geoelectric distribution. Twenty VES stations were investigated and current electrodes (AB/2 m) spacing expanded from 1–200 m; four 2D electrical resistivity imaging traverses having a length of 200 m each and interelectrode spacing of 10 m (level 1) to 60 m (level 6) was adopted. Four geoelectric units were delineated, namely: topsoil (15–251 Ωm), clayey (28–100 Ωm), clayey sand (125–190 Ωm) and sandy (205–876 Ωm) with thicknesses ranging from 0.7–1.3 m, 4.1–19.0 m, 2.6–15.6 m and undefined depth, respectively. The 2D imaging sections also detected similar geoelectric layers, corroborating the VES-derived sections. The inverted sections delineated two different aquifers: the shallower low-yield aquifer comprising sandy clay/clayey sand units with a maximum depth of about 5.5 m. This layer is adjudged to be the continental plain sand of the Benin Formation. The deeper high-yield aquifer with a maximum depth of 30.4 m is a beach sand unit that belongs to the Tertiary Alluvium of the Dahomey Basin. The study showed that hydrogeophysical investigation is vital in exploring, developing, and managing coastal groundwater resources.

Geoelectrical Investigation of Groundwater Potential at Proposed Staff Quarters of FCE Technical, Gusau, Zamfara State, Nigeria

Geoelectric investigation was carried out at proposed staff quarters of FCE, Technical Gusau, located along Gusau – Zaria highway, Zamfara State, Nigeria with the aim of delineating the groundwater potentials. The study area lies in the Basement Complex region of Northern Nigeria and it is situated on Latitude 12o819.64”N to 12o08’24.65’’N and longitude 06o43’28.65’’E to 06o43’37.25’’E with an area coverage of 500 m by 500 m. Vertical Electrical Sounding (VES) technique was employed using Schlumberger array pattern. A total of thirty-six (36) VES points were sounded on Six (6) grided profiles(A-F) separated by 100 m apart with inter VES spacing of 100 m, The VES results depict two distinct curve types namely; H-type and A-type. The results also reveal three distinct geoelectric layers: the top layer, weathered/fractured layer and fresh basement. The top layer has resistivity, depth and thickness range of 10.4 – 158.8 Ωm, 0.4 – 3.6 m and 0.4 – 3.6 m respectively. The second layer has ranges of: resistivity, 6.3 – 525.3 Ωm; depth, 1.4 – 20.8 m, and thickness, 1.0 – 20.4 m. The third layer has resistivity values range of 278.6 – 2726.5 Ωm, its depth and thickness are not defined (to infinity). Seven VES stations (A3, A4, B4, C3, E2, F2 and F5) were delineated for groundwater potential having weathered/fractured resistivity varying between 37.4 and 121.1 Ωm. Depths range were found from 7.9 – 20.8 m and thickness varying between 6.6 and 20.4 m. The results of the study implies that the area has a good groundwater potentials.

Groundwater Potential Detection Possibility in Southern Ondo State, Nigeria

A new simple and quick geophysical method for groundwater exploration of the coastal plains sands and alluvial deposits of parts of Ondo State, Nigeria has been developed. A geophysical evaluation using Electrical Resistivity method for groundwater exploration at the study area was carried out which involved the utilization of Vertical Electrical Sounding (VES) technique with schlumberger array system. About eight (8) points of vertical electrical sounding (VES) survey using ABEM tetrameter (SAS 300) was tabulated in a table which shows the resistivity, the thicknesses and the number of layers for each VES station. The field results were plotted, the curve types and lithologic layers were revealed. The plots showed type-Q, type-K, type-A and type-H curve merging while VES-3 did not reveal any type of curve. This was because of that point understudy being homogenously deposited and non-horizontally layered. Some of the VES points have horizontal layers not more than two for example, VES-1 and VES-3 whiles others have a maximum of four layers within them. The resistivity of the basement within the area ranges from 163.1 ohm-m to 9113.4 ohm-m with an average resistivity of 2627.76 ohm-m. In terms of geological structures and aquifer potential, VES-7 and VES-8 showed to possess characteristically a good geological structures and aquifers for groundwater potentials.

Geology and Correlative Analysis of Borehole Logs with Geo-electric Sections of Some Parts of Ibadan, Southwestern Nigeria

The property of rocks varies from one geological location to another or even disappears laterally, and these properties are important factors in determining groundwater quantity. This makes this research work focused on the correlative analysis of lithologies and borehole logs with geo-electric sections in the basement terrain of Ibadan, southwestern Nigeria, using Borehole logging and geophysical electrical method. Twenty-two vertical electrical sounding stations and borehole Logsare acquired within the study area with a maximum Schlumberger electrode separation of 100m. The data are interpreted qualitatively and quantitatively by partial curve matching and computer iteration to obtain the first-order geo-electric model parameters. The results of the geo-electric investigation reveal some lithological Layers such as topsoil, clay, weathered laterite basement, and fresh basement. At the same time, those from boreholes include topsoil, loamy soil, friable brown soil, clayey-sand, sandy-clay, laterite weathered basement/saprolite, and Fresh Basement. Electrical resistivity and borehole logs correlation revealed: poor, poor-moderate and moderate-perfect correlations based on a comparison between the number of lithological layers encountered from both vertical electrical sounding derived lithology and those from borehole and depth of occurrence. The depth of water struck grouped into three 0 - 45 m, 45 - 70 m, and 50 - 100 m to bring out the most favourable depth of aquifer potential while three yields categories 0.5-2 lt/s; 2 - 4lt/s and 4 -12 lt/s are observed with the above depth classification respectively. Good yielding fractures increase with depth in the quartzite regions but decrease with depth in both gneisses and the schist rock bodies. The correlations between geo-electric sections and borehole logs have shown that the geoelectric section obtained from the vertical electric section cannot totally be substituted for borehole logging but can serve as alternative means of classifying the sub-surface lithologies in the absence of borehole logging.

Groundwater aquifer assessment using hydrogeophysical investigations: the case of western Al Ain Sokhna area, Gulf of Suez, Eastern Desert, Egypt

This study aims to assess the groundwater aquifer and defined the quality of water in the Gulf of Suez region. Hydrochemical and electrical resistivity techniques have been used for evaluating an aquifer, including its extension and quality, in the western Al Ain Sokhna area, Gulf of Suez. This study collected 16 groundwater samples from wells tapping the upper Miocene aquifer. Laboratory tests, including the estimation of electrical conductivity (E.C.), pH, total dissolved solids (TDS) and major ions such as Ca2+, Mg2+, Na+, K+, CO3 2–, HCO3 3–, SO4 2– and Cl–, were conducted. Most water samples belonged to the category of permissible water (TDS 500–1500 ppm) which represented 62.5% and brackish water which represented 37.5%. A total of 47 vertical electrical sounding stations were measured using the Schlumberger array of AB/2 up to 1500 m to detect the subsurface geologic section and delineate water-bearing layers. The results of geoelectrical interpretation illustrated that the subsurface section has five geoelectrical layers. The third layer represents the freshwater aquifer, and the fourth layer represents the brackish water aquifer. The upper Miocene aquifer represents the first aquifer with fresh groundwater of resistivities ranging from 14.7 to 100 Ω.m and thickness ranging between 28.4 and 86 m.

Mapping of aquifer hydraulic properties in Ogbeje and Umeghe in Abraka, Delta State Nigeria: insights from geophysical and hydrogeological methods

Vertical Electrical Sounding (VES), Pumping test, well logging and grain size analysis were conducted with the aim of studying the subsurface geophysical formation in order to determine aquifer characteristics such as hydraulic conductivity, transmissivity and other parameters for groundwater exploration purposes around Ogbeje and Umeghe, Abraka Delta State. Nine (9) VES stations were occupied and the results obtained from the computer iterations suggest 4 to 5 geoelectric layers. The aquiferous layers wwerefound at a depth ranging from 20.0 m – 38.3 m with resistivity ranging from 2200 ?m to 8500 ?m and thickness varying between 6.7 and 20.0 m. The VES study reveals the possibility of having a maximum drill depth the o water table of about 38 m. The results obtained from the pumping test and well logginwereas used to estimate the transmissivity value of T = 0.0722 m2/min, storativity S = 0.00063, specific capacity of the well = 0.39 m2/min and hydraulic conductivity, K= 8.5 m/day while the result from the grain size analysis gave hydraulic conductivity as Kmin= 12.96 m/d to Kmax = 26.96 m/d respectively. Thus, these results indicate that the aquifer is capable of proda ucing sufficient amount of water for both domestic and industrial purposes for the people in the area. 

Integrated Resistivity, Index, and Strength Characteristics of Subgrade Soils: Implication for Highway Pavement Failure Studies in North-Central Nigeria

Integrated geophysical and geotechnical studies have been carried out to determine the geological cause(s) of the failure of sections of Ajaokuta – Anyigba Highway, North-central Nigeria. Forty-eight (48) Vertical Electrical Soundings (VES) were conducted on failed and stable sections of the highway. Also, twenty-one (21) subgrade soil samples close to VES stations from the unstable and stable sections of the highway were subjected to laboratory geotechnical analyses which include grain size distribution, Atterberg limits, compaction (Optimum Moisture Content, OMC, and Maximum Dry Density, MDD) and California bearing ratio (CBR) at soaked and unsoaked states following American Society for Testing and Material (ASTM) standards as appropriate. The geophysical results show that low resistivity (10–100 Ohms-m) inferred as clay/silt of low competence characterizes the subgrade soils of the unstable segment. While higher resistivity (148–272 Ohms-m) interpreted as sandy-clay/silt with moderate competence was obtained for the subgrade soils of the stable segment. Results of Geotechnical tests show that the subgrade soils of the unstable segment have geotechnical properties that generally fall below required standard specifications. Strong correlations of R = 0.86, 0.9, and –0.88 were obtained between CBR and sand, resistivity, and the amounts of fines, while a fairly strong correlation of R = –0.67 was obtained for the plasticity index. The high level of correlation implies that CBR can be predicted from geophysical data and other geotechnical parameters. The study has revealed that the advanced weathering of the underlying Mica-Schist to clayey/silty subgrades with unsuitable geophysical and geotechnical properties is a major contributor to the instability of the highway. Keywords: Atterberg limit; CBR; Grain size distribution; Resistivity; Subgrade soil.

ASSESSMENT OF PROBABLE FOUNDATION PROBLEMS USING GEOPHYSICAL AND REMOTELY SENSED DATA IN A TYPICAL BASEMENT COMPLEX, SOUTHWESTERN NIGERIA.

This research work asses the problems of building foundation within Sagari Estate, Akure, Southwestern Nigeria, using remotely sensed data and geophysical methods. The slope, lineament, hill, and contour map were generated using terrain analysis in ArcGIS 10.5 environment. Electrical Resistivity (ER) and Very Low Frequency (EM-VLF) Electromagnetic methods were used in this study. The ER method involves the use of Vertical Electrical Sounding (VES) with Schlumberger configuration. The initial geoelectric parameters obtained from the fifty three (53) VES station points interpretation (layer resistivities and thicknesses) were used to generate geoelectric maps. The variation of strata and physical strength information within the investigated area were determined from the integrated results of the three methods. Results revealed that substantial portion of the areas studied is relatively unsuitable for high rise civil engineering foundations. However, it was showed that the northern and southern parts of the investigated area were more suitable for foundations. The dominant presence of lineaments, steep slopes , fractures, streams, and thick clayey topsoil as well as weathered layers within the western, eastern, and the central portions reveals susceptibility to subsidence if adequate structural supports mitigate the effect of the persistent foundation failure are not provided.

GEOPHYSICAL INVESTIGATION FOR POST-FOUNDATION ASSESSMENT WITHIN EKITI STATE UNIVERSITY, ADO EKITI, SOUTHWESTERN NIGERIA

This study has evaluated the post-construction subsoil integrity of a distressed building in Ado-Ekiti, Southwestern Nigeria, to decipher the in-situ lithology and structural disposition. Four traverses of 100 m length were established in approximately E-W direction with an inter-station spacing of 10 m. Two Geophysical methods were deployed including the ground magnetic method using Proton Precession Magnetometer and Electrical Resistivity method utilizing 2D Electrical Imaging and Vertical Electrical Sounding (VES) techniques. Twelve (20) VES station points were acquired within the investigated area using Schlumberger configuration which gave relevant information on layer stratification and geoelectric parameters. The obtained results from the VES showed four geo-electric layers comprises topsoil, clayey layer, weathered layer, fractured bedrock, and fresh basement. Low apparent resistivity was delineated from the 2D imaging exhibiting unfit materials at distance between 50 to 75 m and 80 to 100m. The magnetic results showed a series of bedrock ridges and depressions. The integration of results revealed that the majority of the study areas are unsuitable except for central parts which indicate appreciable competence and stability.

Geophysical Investigation of Groundwater Potentials of the Nanka Sand in Obosi and Its Environs, Anambra State Nigeria

Geophysical investigation for Groundwater which entails the use of vertical electrical sounding (VES) methods was carried out in parts of the Idemili area of Anambra State, Nigeria. Geologically the study area falls within the Nanka Sand, belonging to the Ameki Group in the Tertiary Niger Delta Basin. The investigation intends amongst others to assess the groundwater potential of the area, find out the existence of possible aquifer(s) within the area, and estimate the possible depth of a borehole. 15 VES stations were established at the site using Ohmega System Tetrameter and Schlumberger electrode configuration with current electrode spacing (AB/2) of 350 meters. The geologic parameters, such as the number of geo-electric layers, the thickness of the geo-electric units, and their resistivities were interpreted from the VES curves. A qualitative assessment of the curves shows that a model with 5 layers would sufficiently model the field curves. The thickness value ranged from 0.1 to 86 m, the resistivity ranged from 258 to 13,258 Ωm, and the depth ranged between 1.2 and 109 m. Quantitative interpretation of field curves involved inversion with appropriate parameters using Zond Res1D software.

Application of Electrical Resistivity Method to Site Characterisation for Construction Purposes at Institute of Agriculture Research and Training Moor Plantation Ibadan

This research was carried out within Institute of Agriculture Research and Training Moor Plantation Ibadan, Southwestern Nigeria, with the aim to ascertain suitability of the proposed site for building construction and usage. The geophysical investigation involved three electrical resistivity techniques; Vertical Electrical Sounding (VES) using the Schlumberger configuration, 2D ERT and 2-D electrical imaging using Dipole-dipole electrode configuration. Two traverses were established E–W direction cutting across geologic strike with a distance of 80 m and of varying inter-traverse spacing. Eight (8) VES stations were occupied covering the entire study area for layer stratification and geoelectric parameters. The results were qualitatively and quantitatively interpreted and are presented as sounding curves and geoelectric sections. The 2-D imaging gave information on the subsurface characteristic in the area with generally low apparent resistivity indicating low competence material. The results obtained from the VES delineate three geoelectric units which comprise of the topsoil, weathered layer and fresh basement. The results from the VES were used to determine the second order parameters. The entire results correlate well with one another showing that all the techniques used were complemented. This study has further justified the need for geophysical site investigation as pre-condition before any construction to avoid problems of differential settlement. In determining of foundation material, topography elevation, clay content and the depth of weak zones should be put into consideration, since the depth of the weak zone is appreciably high.

Detection of Trace Metal Contamination Around a Dumpsite in Iyara Area Warri Nigeria Using Geoelectrical and Geochemical Methods

Trace metal concentration in soils of Iyara area of Warri, Delta State was studied using geophysical and geochemical techniques. Eight vertical electrical sounding (VES) using SAS 1000 Terrameter with maximum current electrode spread of 150 m in the Schlumberger configuration was carried out. The geoelectric layers obtained are topsoil, clay, sand and fine-medium grained sand. The fine to medium grained sand of the third and fourth layers mainly constitute the aquifer with a depth ranging from 4.8 - 11.0 m. Soil samples were collected at three of the VES stations covering the dumpsite and stations away from the dumpsite. The trace metal content was higher than the maximum allowable levels in soils as specified by the World Health Organisation (WHO) and Department of Petroleum Resources of Nigeria (DPR) except for Pb with undetected concentration in VES 3, Mn with 135 mg/kg in VES 1 and undetected in VES 3 and VES 7. The Multiple pollution index, Enrichment factor, and Non-carcinogenic hazard decreases with increasing distance from the dumpsite. The soil around the dumpsite has been impacted and the results of this study will serve as background information for soil studies and groundwater development in the area.