Fractured Basement Research Articles

Assessment of groundwater potential using vertical electric sounding technique at Faculty of Medicine and Engineering, Federal University Dutsin-ma Katsina State, Nigeria

Geophysical exploration is used to locate boundaries between different elements of the subsoil as these procedures depend on variations in the gravitational, magnetic, electrical, radioactive or elastic properties of the subsurface. Electrical resistivity method was employed to investigate the groundwater potential of the Faculty of Medicine and Engineering at permanent site of Federal University Dutsin-ma, Katsina State. The study was carried out using ABEM SAS 300 Terrameter, Schlumberger electrodes configurations were used to acquire 9 Vertical Electrical Soundings (VES) soundings. The VES data obtained were interpreted using Winresist computer software which reveal five (5) geoelectric layers, namely; the topsoil, laterite, weathered basement, fractured basement and fresh basement. The weathered and fractured layers constitute the aquiferous zone in all the stations. The results of the interpreted VES data showed that the resistivity of the topsoil varies from 17.1 to 109.8 Ωm with an average value of 137.7 Ωm. The thickness of the weathered basement varied from 1.7 to 7.9 m with an average value of 4.67 m, while depth to this layer varies from 4.6 to 13.8 m with an average value of 10.6 m. The thickness of the fractured basement varied from 3.0 to 15.6 m with an average value of 8.01 m, while depth to this layer varies from 6.3 to 33.7 m with an average value of 18.85 m. The depth to aquifer ranges from 17 to 69 m, the resistivity of the aquifer unit ranges between 35 and 830 Ωm. Based on the results, the potential VES points for groundwater exploitation in the study area includes VES 02, 03 and 05 which indicates low to moderate resistivity at greater depth and are therefore recommended for borehole establishment.

Effect of Down-Hole Lithological Variation on Water Bearing Capacity of Some Boreholes in Ilorin, Nigeria

"Effect of Down-Hole Lithological Variation on Water Bearing Capacity of Some Boreholes in Ilorin, Nigeria. The paper attempts to explain the effect of downhole lithological variation on water bearing capacity of some boreholes in Ilorin Nigeria. Specifically, the study examined the lithological characteristics of the boreholes, assessed the variability in weathered overburden and analyzed the inter-relationships between lithology, hydrology and topography of the boreholes. Data used were extracted from twenty (20) borehole logs collected from the archive of Lower Niger Basin Development Authority in Ilorin. Information extracted from the borehole logs are: the number of lithological units intersected by each of the borehole and their depths, the nature of geological materials making up the lithological units and their moisture conditions. Information on coordinates and topographic heights of the boreholes are not given on the logs and those were collected from the field personally by the researcher using handheld GPS (Garmin GPS Channel 76 Model). The collected data were analyzed using descriptive statistics. Results reveal nine downhole lithological units with loamy and lateritic soil making up the first layer of lithology in 95% of the boreholes. Thickness of the top soil and the saprolite overlying the bedrock, has mean values of 4.2m and 11.3m respectively. Depth to water in the borehole ranged between 24.7 and 140m and with a mean value of 55.9m. Three (3) of the boreholes have two lenses of aquifer while the remaining seventeen (17) have one aquifer lens each. The three (3) boreholes with two aquifer lenses have their minor aquifers located within the saprolite. The main aquifer in most (65%) of the boreholes is located within the fractured basement while the remaining (35%) boreholes have their main aquifer located in the weathered basement. Correlation analysis revealed topographic elevation as one of the drivers of hydrology in the study area. Keywords: lithology, groundwater, saprolite, basement, topography. "

Laboratory Measurements of Zeta Potential in Fractured Lewisian Gneiss: Implications for the Characterization of Flow in Fractured Crystalline Bedrock

Despite the broad range of interest and possible applications, the controls on the electric surface charge and the zeta potential of gneiss at conditions relevant to naturally fractured systems remain unreported. There are no published zeta potential measurements conducted in such systems at equilibrium, hence, the effects of composition, concentration and pressure remain unknown. This study reports zeta potential values for the first time measured in a fractured Lewisian gneiss sample saturated with NaCl solutions of various concentrations, artificial seawater and artificial groundwater solutions under equilibrium conditions at confining pressures of 4 MPa and 7 MPa. The constituent minerals of the sample were identified using X-ray diffraction and linked to the concentration and composition dependence of the zeta potential. The results reported in this study demonstrate that the zeta potential remained negative for all tested solutions and concentrations. However, the values of the zeta potential of our Lewisian gneiss sample were found to be unique and dissimilar to pure minerals such as quartz, calcite, mica or feldspar. Moreover, the measured zeta potentials were smaller in magnitude in the experiments with artificial complex solutions compared with those measured with NaCl, thus suggesting that divalent ions (Ca2+, Mg2+ and SO42−) acted as potential determining ions. The zeta potential was also found to be independent of salinity in the NaCl experiments, which is unusual for most reported data. We also investigated the impact of fracture aperture on the electrokinetic response and found that surface electrical conductivity remained negligibly small across the range of the tested confining pressures. Our novel results are an essential first step for interpreting field self-potential (SP) signals and facilitate a way forward for characterization of water flow through fractured basement aquifers.

Deep groundwater recharge mechanism in the sedimentary and crystalline terrains of Sri Lanka: A study based on environmental isotope and chemical signatures

Springs discharge groundwater that travels along flow paths of different spatial and time domains. In many instances, it is difficult to describe its involved groundwater movement, availability as well as geochemical evolution due to its hidden nature. The present study has assessed the deep groundwater in the form of thermal and non-thermal springs in the Palavi and Vanathavillu basins of sedimentary terrain as well as the Southern, Eastern, and Eastern-North Central lowlands of the crystalline terrain of Sri Lanka, using isotope and geochemical approaches. The results revealed that cation exchange in the sedimentary aquifers, whereas rock-water interaction in hard rock and fairly deep aquifers, are the important factors that control the groundwater chemistry. Artesian wells in the sedimentary terrain are mainly recharged by meteoric water, moving through fractured basement rocks at elevations from 100 to 200m above sea level, and have a long residence time. Despite its proximity to the West coast, the data acquired do not indicate that there is seawater mixing. Mixing of percolated water through an unconsolidated geological matrix appears to promote an increase in the salinity of groundwater. Non-mixed, non-evaporated, and young groundwater with a recharge elevation of more than 1000 m above mean sea level can be found in the Southern lowlands of the crystalline terrain. In the Eastern North Central lowlands, groundwater is lowland originated, fast replanished and significantly mixed with evaporated surface water. Thermal waters do not contain tritium and therefore are older than 50 years and have deeply percolated. Artesian water in the Eastern region is high altitude originated and intensely rock-water interacted. Some hot springs in the same area emerging through weathered overburden have water significantly mixed with recent precipitation. Thermal springs that emerge through quartzite bedrock have a non-mixed, non-evaporated, and less rock-water interacted nature. Both thermal and non-thermal water with artesian conditions have clearly indicated that they originate from a common recharge source but with different flow paths, penetration depths, and travel distances, resulting in different chemical characteristics. Non-thermal springs are recharged by recent precipitation and have percolated only to shallow depths.

GEOTECHNICAL INVESTIGATION OF THE PROPOSED IFE DAM SITE AT KAJOLA VILLAGE, ILE-IFE, SOUTHWESTERN NIGERIA

Geological and geophysical investigations were conducted to assess the competence and structural integrity of the foundation site of the proposed Ife-dam at Kajola Village, Ile-Ife, Southwestern Nigeria. Geological investigation along the two (2) proposed dam axes revealed that the overburden material is loose to dense with angular shearing resistance (ɸ) of 27o to 41o. The soils are predominantly elastic silts; cohesive with considerable strength and stability. Geophysical investigation involving the Schlumberger Vertical Electrical Sounding delineated four (4) lithologies namely: topsoil with resistivity of 69 – 558 Ωm and thickness between 1.5 and 4.0 m; weathered sandy layer with resistivity from 123 – 586 Ωm and thickness between 6.5 and 20.4 m; partially weathered/ fractured basement with resistivity from 60 – 220 Ωm and thickness between 6.5 and 14.0 m; and the fresh basement rock with resistivity from 1337 – 10683 Ωm. There are indications of fractures at a depth of 32 m beneath Axis B extending to Axis A at a depth of 35 m. The subsurface materials are suitable to host a dam. Axis B is more appropriate for the dam axis, although the fracture zone should be factored into the design of the dam to prevent water seepage.

Assessment of Paleocene to lower Oligocene formations and basement to estimate the potential hydrocarbon reservoirs using seismic inversion: a case study in the Upper Assam Shelf, India

The upper Assam shelf is a self-slope basin in north-east India, filled with nearly 7 km of sedimentary rocks of tertiary period with the granite basement and various oil fields along the border of the Naga thrust. The major producing fields are structural and strati-structural. The study area is placed in between the Mikir hills and Naga thrust. The objective of the study is to identify potential hydrocarbon reservoir zones in the geologically complex south upper of the Assam shelf using estimates of acoustic impedance and porosity derived by 3D post-stack seismic inversion. Well data, such as sonic velocity and density logs, from two wells (namely, KA and TE) are used in the inversion and validation of results. Inversion results are used to build a geological model in the form of acoustic impedance from which we derive 3D porosity cube which are used for hydrocarbon potential in the Paleocene to lower Oligocene sands, and the Precambrian basement. Although the amplitude maps provide an indication of potential reservoirs, the extent of these zones are much better identified in the inverted impedance maps and the corresponding estimated high-porosity zones. The analysis predicted the potential reservoir rocks in the Sylhet, Kopili and Barail formations, in which the Sylhet and Kopili appear to have good potential zones. Near the vicinity of the Naga thrust belt, the proximity of potential reservoir is predicted in the Kopili, Sylhet formation and in the fractured basement, respectively.

The deformation history of southern England, and its implications for ground engineering in the London Basin

Structures in the basement beneath the London Basin affect the geology of relevance to geotechnical engineering within London. Unfortunately, the basement beneath London is covered by Cretaceous and Tertiary sediments. It is cut by major faults linked to the compressive phases of the Hercynian and Alpine orogenies and to the regional extension that occurred during the Mesozoic between these compressive events. Evidence is presented that movement on basement fractures beneath London played a major role in the distribution and deformation of sediments within the Basin, causing local folding and faulting significant to engineering works. Basement rocks are exposed in SW England, where the type and orientation of these fractures (faults and joints) can be examined in outcrop. This study, complemented by seismic sections in the southern UK, allows the architecture of this fault network within the basement to be determined. Understanding the fracture system in the basement provides a basis for (1) interpreting the lateral facies variations of sediments in the Basin and hence provides a means for predicting from a ground investigation the likely presence, activity or influence on site of such structures at depth and (2) understanding the extent of local, steeply inclined and subhorizontal planar zones of shearing when encountered on site. Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin

Five Decades Of Petroleum Exploration And Discovery In The Malay Basin (1968-2018) And Remaining Potential

Since the first oil discovery in the Malay Basin in 1969, more than 700 exploratory wells have been drilled. To date, there are more than 181 oil and gas discoveries, about half of which are currently in production and about a dozen are already in their secondary or tertiary recovery stages. In 2014 it was estimated that a total of over 14.8 billion barrels of oil equivalent (bboe) of recoverable hydrocarbon resource have been discovered in the basin, contributing to approximately 40% of the total hydrocarbon resources of Malaysia. By the end of the first decade of exploration in 1979, all the major basin-centre anticlinal structures had been tested. This play type contributed 60% of the total discovered resource in the basin. By 1981 this most prolific play type had been practically exhausted, as all the giant fields (those with recoverable resource > 0.5 bboe) had been found. As “creaming” of the basin-centre anticlinal play continued into the early 1980s, exploration efforts gradually shifted to the newly discovered western margin play types, particularly in the Western Hinge Fault Zone, Tenggol Arch and the adjacent Penyu Basin. There was a “lull” period from 1985 to about 1990, due to the global oil crisis, after which exploration was rejuvenated through significant discoveries in several play types on the northeastern ramp margin. This followed a successful drilling campaign that lasted until around 1997 and contributed an additional ~1 bboe of recoverable resources over a seven-year period. Since then, most of the incremental resource addition came from the highly gas-charged play in northern region that comes under the Malaysia-Thai Joint Development Area (JDA) and on the northeastern ramp margin, which includes the Commercial Arrangement Area (CAA) between Malaysia and Vietnam. Individually, however, the hydrocarbon volumes in these later discoveries were relatively small compared to the earlier discovered play types. Subsequently, new play types were pursued, including stratigraphic channels, deeper reservoirs beneath existing fields, high pressure/high temperature (HPHT) reservoirs, overpressured and tight reservoirs, and fractured basement reservoirs. All had some measure of success but none were able to volumetrically match the discoveries made decades earlier. As of end of 2018, over 2100 exploration and development wells had been drilled in the entire basin. Based on the creaming curve, since around 1990 and into the fifth decade of exploration, the incremental resource addition has been increasing steadily at an average rate of ca. 120 MMboe per year. The data indicate that the expected average discovery size would be less than 25 MMboe, and that at least 5 wells need to be drilled per year to sustain the same rate of resource addition. If no new plays are explored and no significant discoveries made, resource addition is expected to plateau beyond 2020. The basin needs a new stimulus, and more importantly, new exploration play concepts to sustain exploration business.

Fractured basement imaging using random-space-shift reverse time migration: A vertical seismic profile survey in the Bohai Bay Basin, China

Fractured basements are not only potential reservoirs for hydrocarbon resources, but they also provide significant storage space for carbon dioxide ([Formula: see text]) sequestration and radioactive waste disposal. However, fractured basements are challenging for seismic imaging methods due to the complexities in their fault and fracture networks, strong heterogeneity, highly variable structural dip, and strong impedance contrasts between the basement rocks and the surrounding sediments. We present a field case in which a walkaway vertical seismic profiling (VSP) survey was conducted at a fractured basement play located in the Bohai Bay Basin, China, to improve the resolution compared with a preexisting surface seismic profile. Using the advanced random-space-shift (RSS) reverse time migration (RTM), we obtain a high-resolution image with a clear delineation of the highly faulted dipping basement. From numerical and field examples, we find that the application of the RSS-RTM improves the final image by mitigating unavoidable errors in the migration velocity model, which would otherwise result in an unfocused image using the conventional RTM approach. In addition, we determine the importance of proper wavefield separation using 3C recordings, which is the key to ensuring the quality of the final image. With an optimized VSP imaging workflow, we provide an enhanced image for the fractured basement to support the geologic interpretations and development decisions.

AQUIFER VULNERABILITY EVALUATION IN SOUTHWESTERN NIGERIA FROM AHP-GODT MODEL USING GEO-ELECTRICAL DERIVED PARAMETERS

<em>The study aimed to determine the exposure levels of the subsurface aquiferous layers, owing to the alarming rate of contamination of the groundwater within 8.150 <sup>0</sup>N - 8.156 <sup>0</sup>N and 4.244 <sup>0</sup>E - 4.248 <sup>0</sup>E. Thus, aquifers' overlying layers, resistivity, and thickness anomalies were determined to generate an aquifer vulnerability map. A multi-criteria decision method of estimated Groundwater confinement, Overlying strata, Depth to Aquifer, and Topography index approach was implemented. Schlumberger's Vertical Electrical Sounding technique was implemented to acquire 30 Vertical Electrical Sounding points under a maximum half-current electrode separation (AB/2) of 65 m. IP2Win geophysical software packages were used to analyze the varying layer resistivity, depth, thickness, and also the sounding curves of the study area. The 2D model revealed a maximum of four geo-electric layers. The layers' resistivity and thickness ranges are clayey silt topsoil (52.5-1104 Ωm; 0.5-9.59 m), weathered layer (10.3-804 Ωm; 0.6-12.1 m), fractured basement (5.5-50832 Ωm; 6.7-18.1 m) and fresh basement (8.3-27348 Ωm; infinity m). On the Groundwater Overlying Strata Depth to Aquifer and Topography model scale, the area is generally characterized by the moderate vulnerability. Implying here is that aquifers have a moderate protective capacity in which the overlying strata above the aquifer are mostly impermeable layers (clay and silt) of high thickness and low porosity.</em>

Geophysical Characterization of Subsurface Layers and Soil Competency of Naraguta Campus, University of Jos-Nigeria

The utilization of geophysical methods can increase the effectiveness of civil engineering works since it can provide the information which the conventional civil engineering method was hard to determine due to the concern of money, time and quality. One of such geophysical methods is the Electrical resistivity using the Schlumberger array which was employed in this study. The study identified three lithological units of top lateritic soil, weathered / fractured basement and the fresh basement. The thickness of the top lateritic soil ranges from 0-4m, the weathered/ fractured basement has an average thickness in the range of 3.0-25 m while the fresh basement thickness ranges from 25 m to infinity. The resistivity values of the sub-surface layers range from 11.40 Ωm to 5896.7 Ωm with most of the lithological units rated competent to highly competent. This study serves as basis for further engineering investigation for the design and construction of proposed buildings and has shown the relevancy of the application of geophysics to civil engineering works. Keywords: Competence, Resistivity, Schlumberger, Sub-surface layers, VES DOI: 10.7176/JEES/11-10-03 Publication date: October 31 st 2021

Hydro-Geoelectrical Study for Groundwater Potential of Lassa And Environs, North Eastern Nigeria

Twenty-two Vertical Electrical Sounding (VES) were carried out to evaluate groundwater potential and aquifer protective capacity of the overburden units using Schlumberger configuration. It was observed that H-curve is the dominant curve type in the study area. The Geo-electro stratigraphic section revealed that the geologic sequence beneath the study area is composed of topsoil, highly weather basement, partly fractured basement and fresh basement. The first layer has an average thickness and resistivity of 1 m and 130 Ωm, respectively. The second layer has an average thickness of 14 m and an average resistivity of 53 Ωm. The third layer is partly fracture basement with an average resistivity of 747 Ωm while at some VES point represents fresh basement. The highly weathered basement and partly fracture basement layer make up the water bearing formation of the area. Dar-Zarrouk parameter revealed that the area under study has protective capacity range from weak to good capacity of the overburden material. Areas that are classified as poor and weak are indicative areas are thus vulnerable to infiltration of leachate and other surface contaminations. The groundwater potential of the area ranges from low to moderate potential; the moderate zone constitutes 86% while the low potential constitutes 14% of the study area. The transverse resistance within the study area ranges from 119.6 to 6983.7 ohms-m2 with an average value of 1024.59 ohms-m2. Hydraulic conductivity values determined from geoelectrical technique range from 3.05 to 38.04 m/day with an average value of 14.86 m/day.

On the Origin of Orphan Tremors and Intraplate Seismicity in Western Africa

On September 5–7, 2018, a series of tremors were reported in Nigeria’s capital city, Abuja. These events followed a growing list of tremors felt in the stable intraplate region, where earthquakes are not expected. Here, we review available seismological, geological, and geodetic data that may shed light on the origin of these tremors. First, we investigate the seismic records for parent location of the orphan tremors using a technique suitable when a single-seismic station is available such as the Western Africa region, which has a sparse seismic network. We find no evidence of the reported tremors within the seismic record of Western Africa. Next, we consider the possibility of a local amplification of earthquakes from regional tectonics, reactivation of local basement fractures by far-field tectonic stresses, post-rift crustal relaxation, landward continuation of oceanic fracture zones, or induced earthquakes triggered by groundwater extraction. Our assessments pose important implications for understanding Western Africa’s intraplate seismicity and its potential connection to tectonic inheritance, active regional tectonics, and anthropogenic stress perturbation.

Geophysical Investigation as an Aid to Understanding Complex Geological Terrain: A Case of Yikpata Transition Zone in Share, North-Central Nigeria

A geophysical method of investigation has been deployed in order to give a quick overview of the nature and the rapidly changing subsurface lithologies that characterized Yikpata, Share, Kwara State, Nigeria. A total of nine (9) vertical electrical soundings (VES), using Schlumberger Array uniformly divided into three groups: basement, basement/sedimentary boundary and sedimentary terrain, and horizontal profiling (HP) using Wenner Array were deployed for this study. The study revealed variation in the subsurface resistivity, thus depicting changes in lithology/rock types along this basement-sedimentary contact zone. The interpretation revealed that the Basement Complex terrain consists of 3-4 geoelectric layers: the topsoil, the weathered, weathered/fractured basement and the fractured basement. Depths beyond ≥ 12 m where the fractured basement occurs can be target for groundwater exploration and structurally controlled mineralization. The resistivity values around the Basement/Sedimentary unconformity zone shows about 3 – 4 geoelectric layers. The resistivity values show remarkable characteristics of the basement and the sedimentary terrains and also reflect the rapidly changing subsurface geology in the area. In the sedimentary terrain, 4 geoelectric layers were delineated: Top soil, clayey sand, sandy clay and clay. Geoelectric sections reveal the variation in the subsurface lithology laterally and vertically. The study has shown that the resistivity method can be an aid to understand complex geologic environments with rapidly changing subsurface geology. Also, the knowledge of the geology of an area is very important in order to make sensible geophysical interpretation. Keywords: Basement complex; Electrical resistivity, Geoelectric; Vertical electrical sounding.

Geophysics and remote sensing applications for groundwater exploration in fractured basement: A case study from Abha area, Saudi Arabia

Groundwater can be the only salvation in arid or semi-arid mountainous areas, especially for those covered by basement rocks. The fractured groundwater aquifers are characterized by a lack of extension in all directions and the distribution of the main fractured and shear zones. An integrated approach of satellite remote sensing and geophysical techniques was used to investigate groundwater occurrence in the fractured aquifers of the mountainous area north of Abha city. A digital elevation model (DEM) was used to extract the streamlines and determine the eastward direction of the surface water flow. The average annual precipitation over the study area shows a positive increase trend estimated at 156 mm yr-1 based on Tropical rainfall measuring mission (TRMM) data during the 2002–2018 period. Seven vertical electrical soundings (VES) using Schlumberger array and twelve time-domain electromagnetic soundings (TEM) using an induction loop with size 50 by 50 m were conducted to detect accumulated groundwater in irregular shape pockets within the fractured basement rocks of the area. VES's and TEM indicate the occurrence of water saturation zones at depths varying from 45 to 60 m. The thickness of the saturated zone exceeds 100 m in some parts, extending toward the northeast-southwest direction parallel to the fractures and faults. The integrated approach provides a reliable study to better understand the groundwater occurrence in fractured basement aquifers.

Hydrocarbon Columns of Oil and Gas Fields in the South Sumatra Basin

The South Sumatra Basin is a prolific basin with a long history of oil and gas exploration that started in early 1900s. It is located in the southern part of Sumatra Island, Indonesia, where more than 300 oil and gas fields have been discovered. The basin contains multiple hydrocarbon reservoir horizons, from Pre-tertiary Basement to Miocene age. The kitchen areas also have various depths, with different levels of maturity. This petroleum system variation is reflected by the field size distribution and the heights of the hydrocarbon columns.Many authors have discussed the petroleum system of this basin and they are useful for providing regional geological perspectives. The oil and gas fields in South Sumatra are usually discussed independently by the operators. Different seismic vintages, density and quality make seismic correlations across the basin challenging. Apart from that, the data restriction is another hurdle in making correlation of the fields. Therefore, statistical studies of the fields and play level understanding become challenging.This study utilizes the Indonesian Petroleum Association Atlas of South Sumatra oil and gas fields, which was published in 1990. Several new fields, especially in fractured basement reservoirs, were added, based on recent publications. Additional information from the IHSE fields database was used to support the study. These data allow a statistical study on hydrocarbon column heights in the South Sumatra Basin. The result of this study could explain more about the charge and seal elements in the basin.

Investigation of Groundwater Potential Using Electromagnetic Method at a Basement Complex Area of University of Abuja, Gwagwalada

The Very Low Frequency Electromagnetic Method (VLF-EM) was used in view of detecting fractured or weathered zones within the University of Abuja Staff Quarters, Gwagwalada, Federal Capital Territory. The VLF -EM data measured along seventeen profiles of 400m at inter profile distance of 25m and interstation separation of 10m were done using the Scintrex ENVI Instrument. The VLF-EM survey revealed features significant to groundwater potential as conductive zones in the Fraser Filter maps and current density pseudosections. Three distinct zones were delineated based on the current density distribution. The fresh basement terrain corresponds to the highly resistive zone with current density value less than -20. The intermediate zone has current density value range of -20 to 25 typical of rocks and soil component which are slightly resistive to slightly conductive and corresponds to the partially saturated units. The third zone is highly conductive with current density value greater than 30 which includes the saturated weathered or fractured basement, fault zones, clay units and saturated sandy units within the study area. The north eastern, north western (profiles 1-8) and some parts of the southern region (profiles 16 and 17) of the study area show higher conductive zones than the central parts of the study area. This survey has helped in detecting sites that are suitable for groundwater exploration by identifying water bearing fractures and weathered zones in the study area. The areas with high conductivity response are areas with conductive overburden material such as clayey soil, saturated soil, water filled fractures and faults or weathered zone within the basement.

Geoelectrical Exploration of Groundwater by Using Vertical Electrical Sounding Technique at Wadi Morra, South Sinai, Egypt

Wadi Morra area is one of the most important areas targeted by the government for sustainable development. This development depends mainly on groundwater occurrences. This research aims to explore groundwater in this region, which depends on groundwater for its needs. To achieve this aim, the geoelectrical resistivity method was used, represented by Schlumberger Vertical Electrical Soundings (VESs). Seventeen VESs have been carried out with a maximum half current electrode spacing (AB/2) of 700m. The measured VESs are interpreted qualitatively and quantitatively to construct a geoelectrical model. To detect the water-bearing layers and their extensions, three geoelectric cross-sections in addition to a one-panel diagram were constructed using all the available data. Also, both true resistivity and isopach contour maps of waterbearing layers were created based on these data. The interpretation results indicate that there are five geoelectric layers (A, B, C, D, and E), two of them (C and D) are water-bearing layers. The first water-bearing layer is layer C, which represents the Nubian sandstone aquifer, and the second layer is layer D, which represents the fractured basement aquifer. These two aquifers were observed along the northern part of the Saint Catherine - Nuweiba road that dissects the Wadi Morra basin, while it is absent at the southern part of this road. It is due to the presence of a few faults. According to groundwater occurrences, the study area was divided into two zones. The first zone is zone (A) where the groundwater is present, either in the Nubian sandstone aquifer or in the fractured basement aquifer and the second zone is zone (B) where there is no groundwater at all due to the presence of basement rocks at a few depths. This research also recommends that the best places for drilling productive wells be at zone A.

Evaluation of groundwater potential using aquifer characteristics on parts of Boki Area, South- Eastern Nigeria

Vertical Electrical Sounding (VES) and pumping test (constant discharge and recovery test) was carried out in parts of Boki Local Government Area to evaluate the groundwater potential, using aquifer characteristics of the study area. Sixteen (16) VES point was employed for this study using the Schlumberger array, with a maximum spread of 400- 600m. The stimulated result from the field data shows 3-5 layers resistivity model with the following curve types A, AK, KH, KHA, QH, QHA and QHK. The geoelectric properties include resistivity of the various layers ranging from 33.58 - 2.29 x 105Ώm, thickness from 0.2 - 50.2m, depth to basement varies from 2.99 - 74.60m across the study area. The litho logs show a top layer comprising of laterite, gravel/gravelly sand and intercalations of siltstones, the layers underneath are made-up of clay, weathered basement containing migmatites and gneisses, fractured and unfractured basement are made up of granitic and metamorphic rocks. The weathered and fractured layers constitute the aquiferous layers in the study area. Hydraulic parameters show transmissivity (T) range of 4.1x 10-5 - 1.92 x 10-1 m 2/day, specific capacity (SC) ranges from 2.09-21.42m2 /day, hydraulic conductivity (K) varies from 2.6 x 10-5 - 3.0 x10-3m/day and mean static water level (SWL) of 7.39m. Iso resistivity map of saprolite, fractured basement map, isopach map and the transmissivity map show that the studied area falls within the low-moderate groundwater potential zone.

GEOPHYSICAL INVESTIGATION OF GROUNDWATER CONTAMINATION USING DC RESISTIVITY TECHNIQUE AT THE MALE HOSTEL OF ISA KAITA COLLEGE OF EDUCATION DUTSIN-MA, KATSINA STATE, NIGERIA

A geophysical investigation involving Vertical Electrical Sounding (VES) using the Schlumberger array was carried out at the Isa Kaita College of Education specifically at the Male Hostel. The aim of the investigation is to explore the groundwater contamination of the area with the objectives: to determine the depth to basement of the study area, to determine the aquifer thickness, to determine the depth to aquifer, to determine the conductivity of the aquifer and to determine the thickness of topsoil and its variation in resistivity. A total of four (4) vertical electrical soundings were carried out using Schlumberger configuration. Terrameter signal averaging system (SAS) model 300 was the instrument used. The survey area is dominated by mainly four layers, namely: Topsoil, Weathered basement, fractured basement. The value of VES 03 and VES 04 have high electrical conductivities which likely shows they are contaminated, The topsoil resistivity along the profile ranges from approximately 1 to 154, The depth to basement (basement topography) Varies from 4.94 m to 7.59 m, The thickness of aquifer range from 1 m to 6.8 m. Therefore VES 02 has high Potential for groundwater because it has retaining capacity and good aquifer thickness and is therefore recommended for borehole establishment. It is recommended that the management of Isa Kaita College of Education should provide a concrete dumping site to avoid leaching of waste in ground thereby contaminating the groundwater.