Earth Science

An integrated approach involving Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES), and Very Low Frequency Electromagnetic (VLF-EM) methods has been used to map the concentration and pathway of leachates plumes beneath Laka dump site in Ogbomoso Southwestern Nigeria. In-situ analysis, specifically, Electrical Conductivity (EC) and Total Dissolved Solids (TDS) were also carried out on water samples collected from hand dug wells, bore holes and stream around the area. The objectives of the study were to describe the physical/hydrogeological conditions in relation to the extent of the zone of contaminated groundwater in the aquifer. The subsurface ERT image obtained on the dump site indicated that the leachate plumes were probably near-surface at the western end and eastward at depth between 1.3m and 4.0m at horizontal distance between 40m and 44m. This is as corroborated by two high conductivity peaks on the conductivity map obtained from the VLF-EM measurements.

This study has been able to demarcate the subsurface geologic units based on the lithologic characters. The subsurface geology of Lagos Main land is made up of complex lithologies of an alternating sequence of clay and sand deposits. The borehole lithologic correlation shows that the subsurface geologic sequence is composed of alternations of sand, clay, lenses of clayey sand and sandy clay. All the boreholes correlated were located within the Ikeja, Lagos State. The borehole depths vary from 119 m to 127 m and the sand and clay though variable show lateral continuity across the section. Four major fresh water sand aquifer layers were delineated within the upper 127 m of the subsurface sequence. The first aquifer layers were located at depth ranging from 61 m to 71 m below the ground level and thickness of 10 m with the resistivity varying from Original Research Article Ilugbo et al.; AJOGER, 2(3): 1-13, 2019; Article no.AJOGER.51709 2 190 Ωm to 320 Ωm. The second aquifer layers were located at depth ranging from 79 m to 87 m below the ground level and thickness of 8 m with the resistivity varying from 500 Ωm to 700 Ωm. The third aquifer layers were located at depth ranging from 85 m to 92 m below the ground level and thickness of 7 m with the resistivity varying from 300 Ωm to 590 Ωm while the fourth aquifer layers were located at depth ranging from 82 m to 89 m below the ground level. It has a thickness of 7 m with the resistivity varying from 300 Ωm to 610 Ωm. The aquifers were very heterogeneous as indicated by wide range of aquifer characteristics. Due to the occurrence of the sand formations in the study area, the aquifer level is between the depths of 61 m to 92 m. Hence, if there is a need for industrial purpose the aquifer should be tapped at the depth between 61 m to 89 m, and also screened for water supply. Relatively higher resistivity indicates significant formation fluid.

An application of Electrical Resistivity and hydrochemistry investigation involving Vertical Electrical Sounding (VES) and water quality analysis was conducted around Okun Ilashe Island area of Lagos state, southwestern Nigeria where there have been reported cases of groundwater contamination. The hydrochemical analysis was performed on five water samples in the area; two Original Research Article Alabi et al.; JGEESI, 23(4): 1-15, 2019; Article no.JGEESI.53214 2 from boreholes and others from hand dug wells. Present study investigation showed that the groundwater had been contaminated by hydrocarbon arising from pipeline leakages in the studied area. The hydrocarbon contaminated plumes are specially characterized by relatively high resistivity values (> 800 Ω-m) and were delineated to a depth of about 12 m. Hydrochemical results showed that three of the sampled water have higher total dissolved solids (TDS) (>400 ppm) in compared to the remaining water samples. The major ions identified includes Na + , K + , Cl, Mg2 + , Ca2 + and NO 3-. Total Dissolved Solid (TDS) and Electrical Conductivity (EC) showed values not in agreement with WHO standards values. Ten (10) Vertical Electrical Sounding (VES) stations were occupied along four traverse lines trending E-W direction. The vertical electrical sounding results indicate maximum of four subsurface layers; Top soil, hydrocarbon contaminated sand, clay/clayey sand and sand/sandy clay. The contaminant plume has migrated to a significant depth of 12 m thus posing an inherent danger to the inhabitant of the area.

An application of Electrical Resistivity and hydrochemistry investigation involving Vertical Electrical Sounding (VES) and water quality analysis was conducted around Okun Ilashe Island area of Lagos state, southwestern Nigeria where there have been reported cases of groundwater contamination. The hydrochemical analysis was performed on five water samples in the area; two from boreholes and others from hand dug wells. Present study investigation showed that the groundwater had been contaminated by hydrocarbon arising from pipeline leakages in the studied area. The hydrocarbon contaminated plumes are specially characterized by relatively high resistivity values (> 800 Ω-m) and were delineated to a depth of about 12 m. Hydrochemical results showed that three of the sampled water have higher total dissolved solids (TDS) (>400 ppm) in compared to the remaining water samples. The major ions identified includes Na+, K+, Cl, Mg2+, Ca2+ and NO3-. Total Dissolved Solid (TDS) and Electr...

An integrated approach involving Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES), and Very Low Frequency Electromagnetic (VLF-EM) methods has been used to map the concentration and pathway of leachates plumes beneath Laka dump site in Ogbomoso Southwestern Nigeria. In-situ analysis, specifically, Electrical Conductivity (EC) and Total Dissolved Solids (TDS) were also carried out on water samples collected from hand dug wells, bore holes and stream around the area. The objectives of the study were to describe the physical/hydrogeological conditions in relation to the extent of the zone of contaminated groundwater in the aquifer. The subsurface ERT image obtained on the dump site indicated that the leachate plumes were probably near-surface at the western end and eastward at depth between 1.3m and 4.0m at horizontal distance between 40m and 44m. This is as corroborated by two high conductivity peaks on the conductivity map obtained from the VLF-EM measurements. Whereas, low resistivity values observed on the ERT image obtained at the control site were more gradational and not associated with the leachate plumes but rather indicate clayey material. The apparent resistivity curves obtained from the interpretation of VES data revealed 4-layer HA-type earth models for dump and control site comprising top soil, clayey intermediate conductive layer, clayey sand saprolite zone and fresh bedrock. The results of in-situ measurements indicated the electrical conductivity ranged from 0.52 mS/m to 0.94 mS/m for water samples from borehole; 0.90 mS/m to 4.67 mS/m for water samples from hand dug wells and highest in the surface water along the dump site with a value of 5.06 mS/m. The total dissolved solid ranged from 1240 ppm to 3350 ppm for water samples from hand dug wells; 980 ppm to 1380 ppm for water samples from bore holes and highest in the

Integrated investigations involving remote sensing and geology have been conducted with the aim of modeling groundwater potential zones within Akure metropolis, Ondo State, Southwestern Nigeria. Groundwater potential zones were delineated with the help of remote sensing and geology. Land sat imageries were used for land use/land cover mapping and lineament analysis for groundwater prospecting. Radar Digital Elevation Model was used for drainage network extraction, slope and geomorphological analysis. All the thematic maps were generated and analyzed in terms of hydrogeological importance and reclassified for integration using ArcGIS 10.5 software. The slope, landuse/landcover, drainage density, lineament density, geomorphology and geological maps generated were integrated with overlay weighted in ArcGIS environment. Suitable ranking and weighting factors were decided based on their capability to store groundwater. This procedure is repeated for all the other layers and resultant lay...