Bangura presented a dissertation submitted to the Department of Geology, Faculty of Pure and Applied Sciences, Fourah Bay College, University of Sierra Leone, in partial fulfillment of the requirement for the award of Bachelor of Science degree with Honors in Geology in 2019.The purpose of this study was to determine the groundwater potential of the Freetown Complex and the Granite Greenstone Terrain in Sierra Leone. The geology of the Granite Greenstone Terrain constitutes medium- to coarse-grained granite which is typical of the older Achaean formation.
Grey and pink granites are exposed in most parts of the area. These rocks have less porosity. The Freetown Complex on the other hand is younger (Jurassic to Triassic) and therefore has limited fractures and thin weathered layers (Overburden) with varying thicknesses. Though several parameters are used to identify the groundwater prospects of an area, this research was narrowed to evaluate the groundwater potential through Geophysical survey (Electrical
resistivity). Vertical electrical sounding (VES) were carried out in the locations mentioned above to understand the geology and also to verify the extent of weathering, fractures and other features like joints, dykes etc. and the geological and hydrogeological parameters were analysed.
Four locations were dealt with; Saint Ambrose School and Lebanese School for the Freetown Complex and Makalie town and Makeni Government Hospital for the Granite Greenstone Terrain. The field data obtained have been analyzed using computer software (Zondip) which gives an automatic interpretation of the apparent resistivity. The VES results revealed heterogeneous nature of the subsurface geological sequence. Geological and Topographic maps were prepared using coordinates during the data collection. Influencing factors of groundwater potential of the area were considered in detail.
Borehole logs were used to clearly explain the vertical variation in formation properties; (i.e. the extent of weathered layers, fractures in bed rock and unaltered crystalline basement rocks). Borehole diagrams were also utilized which clearly account for the variation in thicknesses of weathered zones between the Granite Greenstone Terrain and the Basic Complex. Pumping tests data were also attached to some of the existing data collected to determine the yield of wells to validate the groundwater potential zones and compare the sustainability rate of those boreholes.
[Note: Mr. Barunga might have benefited during his investigations from the UNESCO report Groundwater in Hard Rocks (here).]
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