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Application of VLF-EM response and geoelectrical sounding in groundwater investigation around an active dumpsite
(Application of VLF-EM response and geoelectrical sounding in groundwater investigation around an active dumpsite, 2024) Adeniji, A. A.; Ajani, O. O.; Adagunodo, T. A.
An integrated geophysical method combining very low frequency electromagnetic (VLF-EM) and vertical electrical sounding (VES) methods were carried out around Adaland, Southwestern Nigeria, located within latitude 70 54' 0" and longitude 40 43' 0", with a view to investigate the possible impact of dumpsite on groundwater.This is the major study in the environment to offer extensive evidence regarding the suitability of obtaining quality groundwater. In this research, eight VLF-EM and twelve VES data sets were generated, which were then used to estimate the linear structure, bedrock formation, subsurface geological characteristics, and identification of leachate pathways. The VLF-EM data were analyzed by employing Karous_Hjelt and Microsoft Excel, while the VES data were investigated using the WinRESIST software. TheVLF-EM results confirmed the presence of conductive zones, which might be due to fracture, fault and contact zones or weathered basements. The lithological units acquired from the electrical resistivity results revealed four geoelectrical layers such as topsoil, weathered-based, fractured basement and fresh basement. However, the identified weathered layers and fractured basements from the geoelectrical sections and the corresponding Karous and Hjelt (K-H) pseudo sectionresults around the dumpsite, constitute the main passages for the possible impact of the open dumpsite on groundwater quality, since leachates from the dumpsite could slowly percolate downwards from the topsoil to the water table. Therefore, the impact of the dumpsite on the groundwater is caused by the inadequate clay materials, near-surface features such as fractures/faults, and lateral in-homogeneity. Thus, integrating both methods has been recommended in site characterization for accessing quality groundwater around a dumpsite environment.
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NS23C-03 Geophysical Imaging for Assessing Restored Wetlands' Soil Properties, Infiltration Rates, and Potential Surface Groundwater Interaction
(AGU24, 2024) Aizebeokhai, Ahzegbobor P.; LaPoint, Hannah N.; Doro, Kennedy O.
Efforts to reduce nutrient loading into Lake Erie include restoring old farm fields within Northwestern Ohio to wetlands. With a history of intensive farming, these fields are characterized by legacy nutrients, altered soil structure and drainage tiles. Inadequate knowledge of soil properties distribution, drainage tile locations and potential surface groundwater interaction at the sites limits restoration projects' effectiveness. This study combined a rapid geophysical site characterization framework with in-situ soil cores and hydraulic tests to assess variations in soil properties and hydraulic processes. We used a 250MHz PulseEkko ground penetrating radar (GPR) system and an EM38-MK2 conductivity meter to acquire GPR and electromagnetic imaging (EMI) measurements at selected wetlands with the equipment towed behind a utility terrain vehicle to allow extensive spatial coverage. Electrical resistivity (ER) data were acquired along transects using a Supersting R8 resistivity meter with an 84-electrode switch box. The ER measurement was done using a dipole-dipole array with 1m electrode spacing. Co-located soil cores were collected along the transects for laboratory soil moisture content, organic matter and texture measurements. In contrast, in-situ measurement of soil-saturated hydraulic conductivity was done using a SATURO infiltrometer. The apparent electrical conductivity (ECa) and ER distribution show comparable subsurface structures and parameter zones, and ECa correlates strongly with soil moisture, organic matter and silt contents (R2 >0.7; p-value <0.002). The ECa also notably correlates with the soil saturated hydraulic conductivity (R2 = 0.85), indicating the possibility of using EMI to rapidly characterize potential water retention zones (low Ksat) in restored wetlands. The spatial distribution of geophysical parameters depends linearly on soil properties distribution. This geophysical-soil-property relation, developed through a rapid site characterization framework, allows for improved soil sampling and monitoring plans. This study shows the effective application of EMI, GPR, and ER for pre- and post restoration characterization of old farm fields with legacy nutrients and drainage tiles that contribute to nutrient loading into Lake Erie.
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Hydrogeophysical Investigations for Groundwater Resources Sustainability in Parts of the Eastern Dahomey Basin, Nigeria
(ImprintCRC Press, 2024) Oyeyemi, Kehinde D.; Aizebeokhai, Ahzegbobor P.; Okon, Emmanuel E.; Oladunjoye, Michael A.
Geophysical surveys including geoelectrical resistivity and time-domain induced polarization (IP) techniques have been conducted in Ota in Eastern Dahomey Basin. Thirty vertical electrical sounding (VES) profilings were conducted using a Schlumberger array with an AB/2 range of 180–240 m. Two profiles of 2D electrical resistivity imaging and IP surveys were conducted with Wenner array configuration. The delineated geoelectric layers are topsoil (lateritic clay), clayey sand, sandy clay, sand, and shale or clay units. Two aquifers were delineated in the area with the upper aquifer being a fine-to-medium sand and the lower aquifer of a poorly medium-to-coarse sand unit. The aquifer resistivity ranges are 347.4–411.4 https://www.w3.org/1998/Math/MathML" display="inline"> Ω m https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west 1.amazonaws.com/9781003454908/c35032d3-f666-459f-b1ca a1b405d5a7b1/content/C025_equ_0001.tif"/> and 104.5–143.3 https://www.w3.org/1998/Math/MathML" display="inline"> Ω m https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west 1.amazonaws.com/9781003454908/c35032d3-f666-459f-b1ca a1b405d5a7b1/content/C025_equ_0001.tif"/> for the upper and lower aquifer, respectively. The hydraulic parameters of both aquifers were estimated using established mathematical relations. The upper aquifer has porosity, hydraulic conductivity, and transmissivity ranges of 19.1% 21.8%, 10.8 × 10−2 (m/s)–17.0 × 10−2 (m/s), and 1.49–2.4 (m2/s), while the lower aquifer unit has porosity, hydraulic conductivity, and transmissivity values of 43%–55%, 248 × 10−2–782 × 10−2 (m/s), and 34.72–101.66 (m2/s). High hydraulic parameters in the two aquifers are important for sustainable groundwater development, ensuring efficient use and protection of this vital resource. Their significance extends to promoting regional economic growth by supporting agriculture, industries, and tourism. Mapping faults in the area highlights the need for hydrogeological modeling to discern their impact on aquifer parameters, vital for precise resource management, and predicting potential effects on availability and quality.
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INVESTIGATION OF LEACHATE INFILTRATION ON GROUNDWATER USING GEO RESISTIVITY AND NATURAL ELECTRIC FIELD METHOD AROUND OJOOU-OLAYANJU’S DUMPSITE, ADA, SOUTHWESTERN NIGERIA
(Nigerian Journal of Technology (NIJOTECH) Vol. 43, No. 1,, 2024) Adeniji, A. A.; Ajani, O. O.; Adagunodo. T. A.; Kolawole, T.
The investigation of groundwater within the dumpsite environment is highly important in geophysical study. This is because the extent of interaction between the aquiferous medium and the contaminated zone could pose a serious threat to the end users especially humans when consumed. This research aimed at investigating leachate infiltration and its potential influence on groundwater at Ojoou Olayanju's Dumpsite using combining geo-resistivity and natural electric field (NEF) methods. In this study, five dipole-dipole and five NEF measurements were obtained using the Omega resistivity meters and PQWT-150 equipment respectively. The dipole-dipole method was deployed to obtain a 2D near-surface pseudo-section, and the NEF method was used to obtain the frequency curve and profile maps of electric potential difference. The dipole dipole results revealed the lateral variation in the resistivity along the traverses, suggesting that the materials within this near-surface are heterogeneous, and the closely spaced contours' varying gradients indicate fracture, which would facilitate potential leachate filtration. The NEF results revealed curves, and a subsurface image with respect to depth and profile distance. The points of convergence signals on the frequency model correspond to a medium with low resistivity on the profile map. The conductive medium is seen as being saturated with leachate, which suggests that very large portion of the study area around the dumpsite has been contaminated by leachate. Conclusively, it was revealed that leachate filtration is evidence especially at the topsoil and due to the presence of fractured zones, the groundwater quality is at risk of contamination by continuous filtration of leachate.
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Delineation of structural lineaments of Shaki West Southwestern Nigeria using high resolution aeromagnetic data
(Journal of the Nigerian Society of Physical Sciences, 2025) Adedokun, O. M.; Oladejo, O. P.; Alao, K. N.; Adeniyi, E. O.; Otobrise, H.; Suleman, K. O.; Adagunodo, T. A.; Adedokun, O.; Sunmonu, L. A.
Aminor earthquake, known as earth tremor, often occurs in areas prone to seismic activity. However, there is a notable gap in knowledge about earth tremors, with little documentation conducted before 1987, but a series of notable events between 1990 and 2000 prompted researchers to delve deeper into the study of earth tremors in Nigeria. Therefore, this study is aimed at delineating the structural lineaments of Shaki West Southwestern Nigeria using High Resolution Aeromagnetic Data (HRAD) to identify the underlying basement geology and define the structural framework of the study area. The study area’s aeromagnetic data of Shaki (Sheet 199) underwent processing and interpretation using Oasis Montaj software to assess basement configuration and structural integrity. The data were further enhanced using the Total Horizontal Derivative (THDR) in order to determine the orientations of the lineaments in the study area. The orientations of the lineaments obtained from THDR map revealed that the Pan African orogeny constitutes 52%; Kibaran orogeny constitutes 31%, while Liberian orogeny constitutes 17% lineaments in the study area. The upward continuation maps suggest the presence of faults at the depth range of 2.0-2.25 km. The overall depth to magnetic sources of the area is relatively shallow compared to sedimentary basement area. Based on orientation of faults on magnetic fault map obtained from the superposition of the lineaments extracted from THDR map on the geological map of the study area, three distinct set of sinistral /dextral faults were recognized in Shaki west local government area which includes: E-W, NE-SW and NW-SE fault trend. This suggests that NE-SW and NE-SE fault-set could be responsible for the tremor experienced in Shaki west southwestern, Nigeria. It is concluded that the study area is not immune from experiencing occurrences of tremors from time to time