VLF-EM and VES: an application to groundwater exploration in a Precambrian basement terrain SW Nigeria

Adebowale Obasanmi Adelusi, Michael A. Ayuk, John Stephen Kayode

Abstract


In a hard rock environment with surface or near surface expression of outcrops, the use of VES only becomes difficult due to its associated problems and limitations. However, the use of VLF-EM becomes imperative in mapping basement structures relevant to groundwater development. A total of 2100 VLF-EM data plus selected VES points were covered over 7 traverses with length varying from 3000 to 4500 m. The VLF-EM result mapped basement structures relevant in groundwater development. This is further studied using VES. Results of the investigation indicate that a HKH sounding curve is obtained with a maximum of five subsurface layers comprising: the top soil, clay/sandy clay unit, the fresh basement, fractured basement and the basement bedrock. The fractured basement layer constitutes the main aquifer unit with thickness of 20-25 m. The layer resistivity and thickness ranges are 60-100 ohm-m; 40-80 ohm-m, 1600-2100 ohm-m, 250-420 ohm-m, and 2200-7500 ohm-m; and 0.3-1.2 m, 1.9-2.5 m, 16.5-22.5 m and 22-30 m for the five layers respectively. The geoelectric results compared favorably well with drilling information to above 90%. The yield of the well is 2 L/s with good recharge capability.


Keywords


Electromagnetic (VLF-EM); Hard rock environment; Groundwater development; Layer resistivity; Bed thickness mappingss mapping

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References


DOI: https://doi.org/10.4401/ag-6291
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X