Geophysical Site Investigation Of The Federal College Of Education Zaria Nigeria

A comprehensive geophysical survey was carried out over the premises of theFederal College of Education, Zaria, with a view to investigating the depth to basement,depth to and thickness of aquifer, depth to and thickness of the weathered basement as wellas the subsurface structural systems such as the fractures and faults. The D.C. Resistivityand VLF methods were employed to accomplish the study. The conventional verticalElectrical Sounding (VES) using Schlumberger array was carried out at 40 stations, 8 ofwhich were Radial stations with 4 profiles per station. So a total of 64 profiles weresounded. VLF data were taken from all the VES stations as well. ABM Terrameter (SAS300P) was used to collect resistivity data while EM/6 VLF equipment was used to collectthe VLF data. Results from the interpretation of the data collected suggest 3 layers in mostparts of the area studied. However, there are cases of 2 layers. The resistivity value for thefirst layer (topsoil) varies from 30 to 300 ohm-meters with thickness ranging between 3.5and 14 m. The second layer (weathered basement) has resistivity values of 84 to 480 ohmmetersand thickness of between 9 and 36.5 meters. Its depth varies from 5 to 14 meters.The third layer appeared to be the bedrock with the resistivity value as much as 3000 ohmmetersin some locations. Towards the eastern part of the study area, the fresh bedrockrecords the greatest depth of about 40.1 m. The depth of aquifer ranges from 1.5 to 4.0meters while its thickness ranges from 5 to 14 m. Further, the geologic sections derived inthis work together with the aquifer plots suggest that weathered basement in the area doesnot entirely represent a promising aquifer for the fact that in some cases, aquifers occurredboth in the topsoil and in the weathered basement while it disappeared in some areas ofweathered basement. Radial sounding plots revealed the existence of anisotropics, trendingNE-SW, NVV-SE and E - W directions. The VLF interpretations similarly indicated the presence of vertical contact or fractures zones which is more pronounced towards thewestern part of the survey area. The highest conductivity in the area occurs towards thewest as can be seen from VLF plots. There is hence a strong water-bearing potential withinthe subsurface rocks in this part of the study area.

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